5.1 5 BASICS OF ENGINE TECHNOLOGY 1BASICS OF ENGINE TECHNOLOGY 5.1History of thermal engines x First diesel engine Common Rail commercial vehicle diesel engine BASIC PRINCIPLES Thermal engine A thermal engine transforms the chemical energy bound in fuel into thermal and then into mechanical energy. The first functioning thermal engines were piston steam engines. They were built in 1814 in Sterkrade and achieved efficiency rates (ratio of the energy output to applied energy ➜ page 1.7) of η = 13 %. Later, plants in Augsburg and Nuremberg follo- wed with pioneering developments. Very quickly, MAN established a worldwide re- putation with the construction of steam engines. However, due to the heavy weight and enormous size, these steam engine were unsuitable for installation in vehicles. They could only be found in ships. EXAMPLE Spark-ignition engine The first improvements in efficiency were achieved by Gottlieb Daimler and Wilhelm Maybach in 1885 with a fast-running pe- trol engine. This engine was fitted on the first motorcycle in the world; it was air- cooled and generated a power output of 0.5 hp (0.37 kW). The efficiency was η = 15 %. Diesel engine After a detour in the form of an ammonia steam engine, which turned out to be use- less, Rudolph Diesel developed the engi- ne that bears his name in a machine fac- tory in Augsburg. The diesel engine was the first engine in which the energy conversion was initiated by blowing fuel by means of a compressor into highly compressed air. After four ye- ars of development time, the diesel engine was ready for production in 1897. The first model had one cylinder and was water-cooled. It generated 20 bar at a ro- tational speed of 172 rpm and achieved an efficiency of η = 26.2 %. The first diesel engine used as a drive unit in a factory was a two-cylinder power unit with 60 hp at 800 rpm. Its stroke was 460 mm, its diameter 300 mm. It only became possible to implement the original idea – to inject highly compressed fuel into the cylinder – in 1923, i.e 10 years after Diesel's death, through the develop- ment of the injection pump. Developments at MAN In the Motorenwerken Augsburg-Nurem- berg (MAN engine plants), a large number of technical processes were developed and implemented subsequently in the area of engine and commercial vehicle en- gineering. Some of the most significant are: First commercial vehicle with direct fuel injection 1924 (➜ page 5.32) Spherical combustion chamber 1937 (➜ page 5.32) Supercharged vehicle diesel engine 1951 (➜ page 5.34) Charge-air cooling 1979 (➜ page 5.38) First commercial vehicle engine with Common Rail injection of the second generation 2004 (➜ page 5.54)
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5.1
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First diesel engine Common Rail commercial vehicle diesel engine
BASIC PRINCIPLES
Thermal engineA thermal engine transforms the chemical energy bound in fuel into thermal and then into mechanical energy.
The first functioning thermal engines were piston steam engines. They were built in 1814 in Sterkrade and achieved efficiency rates (ratio of the energy output to applied energy ➜ page 1.7) of η = 13 %. Later, plants in Augsburg and Nuremberg follo-wed with pioneering developments. Very quickly, MAN established a worldwide re-putation with the construction of steam engines.
However, due to the heavy weight and enormous size, these steam engine were unsuitable for installation in vehicles. They could only be found in ships.
EXAMPLE
Spark-ignition engineThe first improvements in efficiency were achieved by Gottlieb Daimler and Wilhelm Maybach in 1885 with a fast-running pe-trol engine. This engine was fitted on the first motorcycle in the world; it was air-cooled and generated a power output of 0.5 hp (0.37 kW). The efficiency was η = 15 %.
Diesel engineAfter a detour in the form of an ammonia steam engine, which turned out to be use-less, Rudolph Diesel developed the engi-ne that bears his name in a machine fac-tory in Augsburg.
The diesel engine was the first engine in which the energy conversion was initiated by blowing fuel by means of a compressor into highly compressed air. After four ye-ars of development time, the diesel engine was ready for production in 1897.
The first model had one cylinder and was water-cooled. It generated 20 bar at a ro-tational speed of 172 rpm and achieved an efficiency of η = 26.2 %.
The first diesel engine used as a drive unit in a factory was a two-cylinder power unit with 60 hp at 800 rpm. Its stroke was 460 mm, its diameter 300 mm.
It only became possible to implement the original idea – to inject highly compressed fuel into the cylinder – in 1923, i.e 10 years
after Diesel's death, through the develop-ment of the injection pump.
Developments at MANIn the Motorenwerken Augsburg-Nurem-berg (MAN engine plants), a large number of technical processes were developed and implemented subsequently in the area of engine and commercial vehicle en-gineering. Some of the most significant are:
First commercial vehicle with direct fuel injection 1924 (➜ page 5.32)
Spherical combustion chamber 1937 (➜ page 5.32)
Supercharged vehicle diesel engine 1951 (➜ page 5.34)
Charge-air cooling 1979 (➜ page 5.38)
First commercial vehicle engine with Common Rail injection of the second generation 2004 (➜ page 5.54)
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Compression and expansion
T2 = T1T1
p1
p2
V2
V1
= p1
p3
V3
V1
=
p2 = p1p1
V1
V2
T1
T2
=
T3 = T1
V3 = 1 lT3 = 1173 KV2 = 0.5 l
T2 = 580 KV1 = 0.25 lT1 = 293 K
p3 = p1
V1
V3
T1
T3
=
V3 = 0.25 lp3 = 4 bar
V2 = 0.5 lp2 = 2 bar
V1 = 1 lp1 = 1 bar
LEGENDp1 Pressure source state 1p2 Pressure finish state 2p3 Pressure finish state 3T1 Temperature source state 1T2 Temperature finish state 2T3 Temperature finish state 3V1 Volume source state 1V2 Volume finish state 2V3 Volume finish state 3
BASIC PRINCIPLES
Combustion engineThe combustion engine is a thermal engi-ne. It transforms the chemical energy bound in fuel into mechanical energy. This is then available in the form of a rotational movement on a shaft (on reciprocating engines on the crankshaft).
The energy is converted according to va-rious function principles. Distinctions are made between:
Piston engines
Turbines
In the case of piston engines, combustion is not continuous, rather only during cer-tain combustion cycles according to the oscillating piston movement. In turbines, combustion takes place continuous du-ring rotation.
The combustion engines used in vehicle construction are almost exclusively reci-procating engines. On these engines, the up and down motion of the pistons is con-verted via the crankshaft drive into a rota-ting drive motion (➜ page 5.13).
Besides reciprocating engines, there are other types of combustion engine; these will only be mentioned briefly here as ex-amples.
FUNCTION
Reciprocating engineAir or a fuel-air mixture, compressed in a closed container, heats up: pressure and temperature increase (➜ Fig.). The physi-cal basis for this is the general gas equati-on (➜ page 1.13).
The combustion is initiated by injecting the fuel (diesel engine) or by an ignition spark (spark-ignition engine).
The amount of heat released during com-bustion leads to a sudden increase in temperature and pressure. The associa-ted volume change drives the piston downwards, thus converting it into me-chanical energy.
The crankshaft creates a rotational move-ment from the downward movement of the piston. The torque of this rotational movement is available to drive a vehicle or any other machine.
EXAMPLE
Stirling engineSo-called Stirling engines with a separate cold/warm chamber principle are current-ly only operated in vehicle research. The advantages of quiet running without com-bustion noise and very low pollutant emis-sions are cancelled out by the complex design and high manufacturing costs.
Rotary piston engineThe best-known rotary piston engine is the Wankel engine. However, due to the high oil and fuel consumption, it has not found its way into commercial vehicle en-gineering.
Gas turbineThe gas turbine is not yet suitable for the very dynamic driving sequences in the field of motor vehicles and as a drive sys-tem is still in the testing phase. The high fuel consumption is the main argument against its use in commercial vehicles.
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Displacement and compression volume
TDC
BDC
d
s
Vc
Vh
TDC
BDC
=V V
V
+ε c
c
h
LEGENDTDC Top dead centreBDC Bottom dead centred Bores Strokeε Compression ratio (➜ page 5.4)Vc Compression volumeVh Displacement
BASIC PRINCIPLES
BoreThe bore d is the diameter of the cylinder. The corresponding cross-section area is indicated by A.
StrokeThe stroke s is the path of the piston from the top to bottom dead centre.
DisplacementThe displacement Vh is the term for the vo-lume of the cylinder between the top dead centre (TDC) and the bottom dead centre (BDC) of the piston surface during the up-ward and downward movement.
The displacement of all cylinders (number: z) is referred to as the total displacement VH. In data sheets and technical docu-ments, only the term displacement is used.
Stroke-bore ratioThe stroke-bore ratio is the ratio of stroke to bore. If the stroke s of the piston is gre-ater than the bore of the cylinder, this is referred to as a long-stroke engine (s/d > 1); the other way around, is a short-stroke engine (s/d < 1). In diesel engines, the stroke is usually greater than the bore.
FUNCTION
Calculating the boreThe bore d results from the cross-section area A of the cylinder:
Calculating the displacementThe displacement Vh of a cylinder is the product of the piston or cylinder surface area A and the piston stroke s:
According to the number of cylinders z, the total displacement VH results from:
EXAMPLE
For a sample engine MAN D2876, the specifications are given according to the definitions stated in the data sheet. Mis-sing data can be calculated.
Cross-section area (cylinder):
A = 0.785 ⋅ (128 mm)2 = 12,861.4 mm2
Bore:
Piston stroke:
s = 166 mm
Displacement (6 cylinders):
Vh = 0.785 ⋅ (128 mm)2 ⋅ 166 mm = 2.135 l
VH = 2.135 l ⋅ 6 = 12.8 l
Stroke-bore ratio:
The stroke-bore ratio is greater than 1; this is a long-stroke engine.
d A0.785
=
4A =
π2d⋅ = 2d0.785 ⋅
2d0.785 ⋅ s⋅Vh =A s⋅=
z⋅VH Vh=
d 12,861.4 mm2
0.785= = 128 mm
166 mm128 mm
= = 1.29sd
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Compression ratio
1234567891011121314151617
1234567891011121314151617
1234567891011121314151617
TDC
BDC
TDC
BDC
TDC
BDC
1 2
1 3
ε = 17 : 1
ε = 17 : 1
V1 = Vh
V2 = Vc V3 = Vc
LEGENDε Compression ratioVc Compression volumeVh Displacement1 Starting point:
V1 = 2.135 lp1 = 1 barT1 = 20 °C
2 Finishing point; Compression heat is not taken into account:V2 = 0.125 lp2 = 17 barT2 = 20 °C
3 Finishing point; Compression heat taken into account:V3 = 0.125 lp3 = 43.6 barT3 = 700 °C
BASIC PRINCIPLES
Compression volumeThe space remaining above the piston crown when the top dead centre is rea-ched is called the compression volume Vc. It is limited at the moment of ignition by the piston and is also referred to as the com-bustion space.
Compression ratioThe compression ratio ε (epsilon) specifies how strongly the fuel-air mixture is com-pressed in the cylinder.
Air ratioThe composition of the fuel-air mixture is defined by the air ratio.
The air ratio λ (lambda) is the ratio of ap-plied air mass to theoretically required air mass. The mixture can be rich (λ <1) or lean (λ >1). This means that either too little or too much air is provided for the com-bustion. The theoretically required air mass depends on the fuel composition. For the complete combustion of 1 kg of petrol, for example, 14.8 kg of air is re-quired.
FUNCTION
Calculating the compressionCompression ε is the ratio of the volume of the cylinder to the compression volume. The volume of the cylinder is the total of displacement Vh and compression volume Vc (➜ Fig.).
For the compression ratio ε, the following calculation formula applied:
Derived from this:
EXAMPLE
For the sample engine MAN D2876, toge-ther with the already calculated displace-ment of a cylinder
Vh = 2.135 l (➜ page 5.3),
the following compression volume results:
The compression ratio results from:
This value is rounded up or down in the data sheet as:
ε = 17 : 1
As a general principle in diesel engines, the compression ratio is greater than in spark-ignition engines (➜ page 5.5). The reason for this lie in the higher compressi-on final temperature requires for self-igni-tion on engine start. On engines with glow plugs, the compression ratio can be lowe-red.
=V V
V
+ε c
c
h
=1−
VV εc
h
= =117 −
2.135 l0.133 lVc
= =+
ε2.135 l 2.268 l
0.133 l 0.133 l=
17.05
1
0.133 l
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Criterion Spark-ignition engine (naturally aspirated)
Diesel engine (turbo) for pas-senger cars
Diesel engine (turbo) for trucks
Service life 4000–6000 h 4000–6000 h 20,000–30,000 h
Full-load proportion 5–10 % 5–10 % 30 %
Power output per litre 50–110 hp/l (250 hp/l) 35–60 hp/l 25–45 hp/l (120 hp/l)
Rated speed 5500–8000 rpm (18,000 rpm) 4000–5000 rpm 1800–2600 rpm (3000 rpm)
Mean pressure 8–13 bar up to 17 bar 12–24 bar
Brake power 10–15 % 10–20 % 60–100 %
Ignition pressure 70 bar 120–150 bar 140–200 bar (280 bar)
Charging pressure – up to 2.0 bar up to 2.7 bar (4.5 bar)
Output-to-weight ratio 0.5–1.5 kg/hp (0.15 kg/hp) 1.0–2.0 kg/hp 2.0–4.0 kg/hp (0.7 kg/hp)
Efficiency ≈ 35 % ≈ 46 % ≈ 46 %
(values in parentheses for Formula 1 engine)
(values in parentheses for race truck)
Comparison of spark-ignition and diesel engines
BASIC PRINCIPLES
Diesel and spark-ignition enginesDiesel engines are subjected to more me-chanical and thermal stress compared to spark-ignition engines due to the high compression pressure (➜ table). For this reason, they have to be designed to be sturdier than spark-ignition engine. Due to the higher engine weight and greater di-mensions, diesel engines were for a long time used exclusively in commercial ve-hicles.
The high compression means that diesel engines achieve better utilisation of heat than spark-ignition engines and thus have higher thermal efficiency. Compared to the spark-ignition engine, they also fea-ture lower pollutant emission levels. The specific fuel consumption is lower.
The generally higher performance of spark-ignition engines must be achieved at the expense of higher fuel consumption and higher engine speeds. Diesel engines provide their rated power even at relatively low engine speeds and develop high le-vels of torque. The torque increase (➜ page 1.10) of charged diesel engines with charge-air cooling is up to 40 %. Charged spark-ignition engines achieve a maxi-mum of 35 %.
FUNCTION
Diesel processIn the diesel engine, air is drawn in, highly compressed in the combustion chamber, and thus heated. In line with the required power, fuel is injected into the highly com-pressed air. The fuel-air mixture only forms in the combustion chamber (interior mixture formation).
Depending on the required power, more or less diesel fuel is injected into the com-bustion chamber: the air ratio of the mix-ture that is created is controlled by chan-ging the fuel mass. As this changes the quality of the mixture, this is referred to as qualitative control.
The diesel engine requires a highly inflam-mable fuel with a low boiling point that self-ignites when injected into the highly compressed, hot air. This is why diesel engines are also referred to as self-ignition engines.
When the fuel is injected, a heterogene-ous fuel-air mixture is created.
Spark-ignition processIn the spark-ignition engine, a fuel-air mix-ture is created by injecting the fuel into the intake pipe or in front of the valves (injec-tion engine). In the case of carburettor en-gines, a carburettor provides the mixture formation. In both cases, the mixture is created outside the combustion chamber (exterior mixture formation). The only ex-
ceptions are the direct injection principles for spark-ignition engines that are current-ly being developed by numerous engine manufacturers.
Different performance requirements lead to changes in the amount of mixture taken in. The spark-ignition engine therefore has quantitative control.
The mixture is compressed in the com-pression stroke. As its temperature after compression is below its self-ignition threshold, the combustion must be trigge-red by timed ignition sparks from a spark plug. This is referred to as applied ignition.
At the ignition point, the fuel is vaporised, forming a homogeneous mixture with the air.
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Four-stroke principle for the spark-ignition engine
1 2 3 4
LEGEND1 Induction stroke2 Compression stroke3 Combustion stroke4 Exhaust stroke
BASIC PRINCIPLES
Four-stroke spark-ignition engineThe work process on the four-stroke spark-ignition engine is characterised by:
Applied ignition
Exterior mixture formation
Quantitative control
Homogeneous mixture
The mixture formation used to be achie-ved by means of a carburettor. However, closed-loop-controlled catalytic conver-ters require fuel injection systems that are able to precisely meter the fuel.
The spark-ignition engine is regulated by adjusting the throttle valve, i.e. changing the amount of mixture taken in (quantitati-ve regulation). The fuel injection system measures corresponding fuel volume for the air.
One working cycle on the four-stroke spark-ignition engine consists of four stro-kes (four piston movements), correspon-ding to two crankshaft revolutions (➜ Fig.).
FUNCTION
Combustion process (four-stroke spark-ignition engine)One working cycle of the combustion pro-cess on the four-stroke spark-ignition en-gine consists of four strokes (four piston movements), corresponding to two crankshaft revolutions (➜ Fig.).
1st stroke – induction stroke
The downward movement of the piston during the induction stroke creates a par-tial vacuum in the cylinder, which means that prepared, ignitable mixture is sucked through the open intake valve into the cy-linder.
2nd stroke – compression stroke
With the intake and exhaust valves closed, the mixture that has flowed in is compressed by the upward movement of the piston to the 8th to 12th part of its ori-ginal volume (➜ page 5.4) and thus hea-ted to 400 to 500 °C (compression stro-ke). The self-ignition temperature of the mixture is not reached by the compressi-on. The combustion must therefore be in-itiated by switching an ignition spark bet-ween the electrodes of the spark plug shortly before the top dead centre (TDC) is reached.
3rd stroke – combustion stroke
During the 3rd stroke, combustion of the compressed mixture takes place. The in-take and exhaust valve are closed. The
rise in pressure due to the combustion moves the piston downwards and it ap-plies work (combustion stroke) to the crankshaft.
4th stroke – exhaust stroke
With the exhaust valve open, the exhaust gases are emitted by the upward move-ment of the piston (exhaust stroke). For emission, the piston must overcome a back pressure of approx. 0.2 bar. For this reason, the upward movement of the pis-ton is supported by flywheel masses on the crankshaft (➜ page 5.14). Before the next downward movement of the piston, the intake valve opens and the cylinder is charged with fresh mixture: the next wor-king cycle starts.
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Four-stroke principle for the diesel engine
1 2 3 4
LEGEND1 Induction stroke2 Compression stroke3 Combustion stroke4 Exhaust stroke
BASIC PRINCIPLES
Four-stroke diesel engineThe work process on the conventional four-stroke diesel engine is characterised by:
Self-ignition
Interior mixture formation
Qualitative control
Heterogeneous mixture
The diesel engine is regulated by chan-ging the amount of fuel injected into the combustion chamber.
The change in the injected fuel volume changes the composition of the fuel-air mixture (qualitative control) and the engine provides the corresponding power out-put.
FUNCTION
Combustion process (four-stroke die-sel engine)As in the case of the four-stroke spark-ig-nition engine, the working cycle of the combustion process on the four-stroke diesel engine consists of four strokes (four piston movements), corresponding to two crankshaft revolutions (➜ Fig.).
1st stroke – induction stroke
During the downward movement of the piston, a suction effect is created in the cylinder, which means that clean air flows through the open intake valve into the cy-linder chamber. Here, the air absorbs heat from the valves, the piston and the cylin-der wall.
To enable smoke-free and combustion that is as complete as possible, the diesel engine always works with excess air (➜ page 5.4). When the piston has reached the bottom dead centre, the intake valve closes.
2nd stroke – compression stroke
With the intake and exhaust valves closed, the mixture that has flowed in is compressed by the upward movement of the piston to the 16th to 23rd part of its original volume. This raises the tempera-ture of the compressed air to 700 to 900 °C. The fuel is injected shortly before (ap-prox. 20 to 30° crank angle) the TDC (➜ page 5.14).
The injected droplets of fuel mix with the air, evaporate and self-ignite due to the high temperature. The time between the start of injection and ignition is referred to as ignition delay. With an ignition delay of more than 0.0010 to 0.0015 s, rapid com-bustion occurs, which can he heard as "diesel knock" of the engine.
3rd stroke – combustion stroke
The piston moves downwards as a result of the rise in pressure caused by the com-bustion and applies mechanical work (en-ergy) to the crankshaft.
4th stroke – exhaust stroke
After the exhaust valve opens due to the excess pressure, some of the exhaust ga-ses automatically flow into the in exhaust duct. The remaining residual exhaust ga-ses are pushed out by the piston.
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Two-stroke principle (spark-ignition engine with cross scavenging)
1-1 2-11-2 2-2
TDC
BDC
Ü A E
LEGEND1 Compression stroke:1-1 Transfer
+ scavenging1-2 Compression
+ Pre-induction (creates partial vacuum in the crankcase)
2 Combustion stroke:2-1 Induction (in the crankcase)
+ Ignition2-2 Precompression (in the crankcase)
+ ExhaustA Exhaust portE Intake portÜ Transfer ductBDC Bottom dead centreTDC Top dead centre
BASIC PRINCIPLES
Two-stroke engineThe two-stroke engine comes as a diesel or spark-ignition engine. Due to the poo-rer charging (losses due to the open gas exchange), the higher specific fuel and lu-bricating oil consumption and the higher heat load (due to the shorter gas ex-change time), two-stroke engines are not used in commercial vehicles.
Due to the lower weight and the simple design, the main area of application for two-stroke spark-ignition engines is in motorcycles.
Very large, stationary engines, as used e.g. in shipping, are often designed as two-stroke engines on account of the simple design and high performance den-sity. For example, the MAN K98MC as a two-stroke diesel engine in the 12-cylin-der version has a power output of 38,520 kW (93,120 hp) at an engine speed of 104 rpm. The cylinder bore of this engine is 98 cm; its stroke is 2.40 m.
FUNCTION
Combustion process (two-stroke en-gine)The two-stroke engine required two stro-kes for a working cycle or one crankshaft revolution (➜ Fig.).
1st stroke – compression stroke
The upward movement closes the transfer duct and exhaust port in the displacement space and the air (on a diesel engine) or fuel-air mixture (on a spark-ignition engi-ne) is compressed. Shortly before the TDC, fuel is injected and self-ignites (die-sel engine) or ignition is applied (spark-ig-nition engine).
In the case of the two-stroke spark-igniti-on engine (➜ Fig.), fresh mixture flows th-rough the intake port which has now been released by the lower edge of the piston into the crankcase (partial vacuum balan-cing).
2nd stroke – combustion stroke
The energy released during combustion moves the piston downwards. When the intake port is closed, this compresses the mixture in the crankcase.
As soon as the exhaust port is reopened in the displacement space, the exhaust gases are first of all expelled with excess pressure and, after release of the transfer duct, are additionally purged by the pre-compressed mixture (spark-ignition engi-ne) or charged fresh air (diesel engine).
Gas exchange techniqueSo that the air or mixture can be pressed into the cylinder to purge the exhaust gas, precompression takes place in the crank-case of the two-stroke spark-ignition en-gine. This is why two-stroke diesel engi-nes are supercharged.
Timing methodsPort timing or port and valve timing are used for the gas exchange in two-stroke engines. The gas exchange methods im-plemented here are cross scavenging, re-verse scavenging or uniflow scavenging.
In the case of port timing with cross sca-venging (➜ Fig.), charged air or the pre-compressed mixture flows across and th-rough cylinder and is routed upwards by the curved piston surface. For reverse scavenging, two transfer ducts are arran-ged on the same side as the exhaust port, which deflect (reverse) the air flow in the cylinder.
The more complex uniflow scavenging creates a swirl in the air flow in the cylin-der. In the case of port and valve timing, the charged air flow in at the bottom th-rough transfer ducts and presses the ex-haust gas out at the top through two to three exhaust valves.
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Engine block of the MAN D2066 CR
1 4
23
4 35
LEGEND1 Cylinder liner2 Cylinder block3 Crankcase4 Crankshaft bearing cover5 Crankcase skirt
BASIC PRINCIPLES
Engine blockThe engine block consists of the cylinder block and crankcase.
The cylinder block encloses the cylinder barrels and creates a coolant chamber that is oil-tight and/or watertight.
The crankcase holds the crankshaft. The-re are thrust bearings for the crankshaft in the upper section of the crankcase. The oil pan is bolted to the bottom of the crankcase.
The gas forces that arise during combus-tion are routed via the cylinder head and main bearing bolts into the engine block. The engine forces generated by the piston movement are transferred to the frame via the mounting points of the engine.
Ribbing in line with the requirements of the function and the adequately sized wall thicknesses of the engine block ensure in-herent stability and low noise emission.
FUNCTION
Cylinder blockThe engineering design of the cylinder block must ensure a precisely metered supply of coolant and forced circulation around the hot area and the cylinder li-ners. This is regarded as an important re-quirement for long, trouble-free operation of the entire engine.
CrankcaseThe crankcase is usually split at the height of the crankshaft bearings. Modern crank-cases have crankcase skirts that are drawn downwards far beyond the crankshaft bearings (➜ Fig.).
The crankcase is fitted with a venting line. This prevents a pressure difference bet-ween the crankcase and outside air. This crankcase breather protects the environ-ment by returning gases and oil spray to the combustion chamber.
EXAMPLE
In the case of water-cooled engines, the engine block is usually cast as one piece. For example, the crankcase of MAN engi-nes is cast in special cast iron together with the cylinder block in one piece (➜ Fig.).
On air-cooled engines, the crankcase is frequently made of light alloy and then bol-ted onto the cylinder block (usually made of cast iron) or the individual cylinders.
On commercial vehicles, the engine block is made of grey cast iron or, as is the case at MAN, of special cast iron for particular solidity and elasticity.
On the MAN D2066 CR engine, the crank-case is made as a cast part of high-quality GJV-450 vermicular cast iron. This high-tensile material enables considerable weight savings in that the wall thicknesses are reduced.
The main bearing covers on the D2066 CR are cracked. Cracking main bearing cover is an absolute innovation in the construction of commercial vehicle engi-nes. The operation is equivalent to that of cracking the conrod bearing covers (➜ page 5.12). The coarse contact surfaces means that transversal loads can be bet-ter absorbed. This results in lower wear and a longer service life.
5.10
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5.4.
1.2C
ylin
ders
and
cyl
inde
r lin
ers
x
Cylinder liners
BA1
2
34
LEGENDA Wet cylinder linerB Dry cylinder liner1 Collar2 Coolant3 Leakage4 Sealing rings
BASIC PRINCIPLES
CylindersThe cylinders in the cylinder block have the following tasks:
Piston guidance
Absorbing the compression pressure
Rapid transfer of the absorbed heat to the coolant
They also have to meet certain require-ments:
Adequate resistance to high combus-tion pressures and temperatures
High resistance to large and rapid temperature fluctuations
High wear resistance to friction on the cylinder faces
FUNCTION
Cylinder linerIn spark-ignition engines, the pistons usu-ally run in cylinder barrels cast at the same time. On large diesel engines in the field of commercial vehicles, liners made of resili-ent materials are used.
In cylinder blocks made of aluminium al-loys, cylinder liners made of centrifugal cast iron (high-quality, fine-grain cast iron) are inserted. Two types of cylinder liners are distinguished:
Wet cylinder liners
Dry cylinder liners.
The MAN engines of the D28 model series have wet cylinder liners made of highly re-silient special centrifugal cast iron. On D08 engines, with the exception of the most powerful variant, where dry cylinder liners are used, no liners are fitted.
Wet cylinder linerA wet cylinder liner has direct contact to the coolant and thus has very effective cooling.
At the top end, most cylinder liners have a collar to prevent the lines from slipping. Towards the crankcase, the liner is usually sealed by rubber rings to prevent coolant from entering the crankcase. Compared to dry cylinder liners, wet cylinder liners re-quire more space. The reason for this is that the housing structure is weakened by
the coolant ducts, and this has to be rein-forced elsewhere.
Dry cylinder linerA dry cylinder liner makes no contact with the coolant. The heat transfer therefore not as good as in the case of a wet cylin-der liner.
Dry cylinder liners are used, for example, if a cylinder can no longer be rebored after a number of repairs. However, they are also used in new engines. There are versi-ons with or without a collar.
5.11
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5.4.
2Cra
nksh
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rive
5.4.
2.1P
isto
nsx
Piston structure
1 2 3 5 64
HK
LS
D
L
LEGEND1 Piston ring zone2 Piston-pin boss3 Piston crown4 Combustion-chamber recess5 Piston top landD Piston diameterL Total lengthLS Body lengthHK Compression height
BASIC PRINCIPLES
PistonA piston has the following tasks in the en-ergy conversion in the combustion engi-ne:
Accommodating the combustion chamber
Moving seal of the combustion cham-ber against the crankcase
Absorbing the gas pressure and for-warding this via the conrod as rotary force (torque) to the crankshaft
Forwarding the heat released to the piston crown by the combustion gases to the cylinder wall and engine oil as quickly as possible
The timing of the gas exchange on two-stroke engine
A piston is divided into the following areas:
Piston crown
Piston ring zone
Piston body
Piston-pin boss
FUNCTION
Combustion chamberIn the case of direct-injection diesel engi-nes, the piston crowns have combustion-chamber recesses, which partially shift the compression volume into the pistons. The land located between the piston crown and the top ring groove is called the piston top land. The piston body with the piston rings guides the piston in the cylinder. The curve in the interior of the piston makes the piston crown rigid and favours heat dissipation. The piston-pin bosses engage the gudgeon pins to transfer the piston force to the conrod.
Piston rings are used to seal the combus-tion chamber against the crankcase and to guide the piston. Two upper rings nor-mally ensure gas sealing; at least one ad-ditional ring is an oil scraper ring that pre-vents too much oil from remaining and burning on the cylinder wall. With three piston rings, the middle ring is sometimes designed as a combined sealing and oil scraper ring.
Piston dimensionsThe compression height influences the compression ratio of the engine. An ade-quate body length prevents the piston from tilting on changing sides.
Materials for pistonsOn account of the high temperature (2000 °C) and high pressures (approx.
150 bar) in the combustion chamber, the piston must be made of special material. With their low density (ρ = 2.7 kg/dm3) and high thermal conductivity, aluminium al-loys are very suitable.
In order to minimise the running clearance of the piston in the cylinder, steel bands are cast on the piston. These improve the sealing and sound damping. On most MAN pistons, the area to accommodate the top piston ring is made of steel.
Forced oil coolingOn charged engines, the high thermal load means that pistons with forced oil cooling have to be used. Here, the under-side of the piston is continuously cooled by an oil jet from spraying nozzles in the crankcase.
5.12
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5.4.
2.2C
onro
d
x
Structure of the conrod
1
2
34
Cracked conrod big end
LEGEND1 Conrod small end2 Conrod shank3 Slanting split conrod big end4 Conrod bearing cover
BASIC PRINCIPLES
ConrodThe conrod connects the pistons and crankshaft. It transfers the upward and downward movement of the piston to the crankshaft, which converts this into a ro-tational movement.
A conrod must withstand high mechanical loads:
High pressure forces caused by the gas pressure on the piston crown
High accelerating forces due to conti-nuously changing piston speeds and changes on the direction of move-ment (inertia forces)
High bending forces caused by the pendulum movement around the axis of the conrod small end
Due to the high loads, the strength calcu-lations for dimensioning the conrod must include adequate safety factors.
FUNCTION
Structure of the conrodThe conrod consists of the conrod small end, conrod shank and conrod big end.
Conrod small end
The conrod small end serves to secure the piston with a pin. The gudgeon pins are inserted through the conrod small end. To ensure a long service life, bearing bushes are normally pressed in where there are very high loads.
Conrod shank
The conrod shank connects the conrod small end and big end. The cross-section of the conrod shank has the shape of a double T to ensure increased buckling strength.
Conrod big end
The conrod big end encloses the crank pin. So that the conrod big ends can be given a greater diameter to reduce the load and still fit in through the cylinder liner from above on assembly, the friction bea-ring between the crank pin and conrod big end is split at a slant (➜ Fig.).
The exact fit of this friction bearing is of particular significance. In modern produc-tion processes (sintered conrods), the be-aring is placed on the undivided conrod big end. Only after this is the conrod big end slit using a laser and cracked with a wedge. Due to the corresponding break profile, the conrod bearing cover is seated
with an exact fit on the conrod big end (➜ Fig.). Furthermore, high transversal forces can be absorbed. Even without a special "fit bolt", the friction bearing on the cra-cked conrod big end is completely even.
Materials for conrodsConrods are usually made of heat-treated steel and forged in a die.
In the case of heavy-duty MAN engines, lead-bronze bearing bushes with high wear resistance are used. However, envi-ronmental regulations mean that material development is moving towards unleaded bearing materials.
On racing engines, the conrods are made of titanium.
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Con
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EXAMPLE
1 Conrod small end2 Conrod shank3 Conrod big end
Conrod function
1
2
3
5.14
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2.3C
rank
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Crankshaft on the MAN D2066 CR
1
2
3
4
5
LEGEND1 Shaft journal2 Counterweight3 Crankshaft web4 Crank pin5 Torsional vibration damper
BASIC PRINCIPLES
Crankshaft driveThe crankshaft is set in rotation by the conrod and the upward and downward movement of the pistons. The torque cre-ated is transferred by the crankshaft main-ly to the clutch. Part of the torque is avai-lable to drive the valve timing, oil, water, injection or fuel pumps and the dynamo.
The pistons and conrod transfer accelera-tion and torsional forces to the crankshaft. These forces subject the crankshaft to twisting, flexion and torsional vibrations. The crankshaft is exposed to slight additi-onal wear at the bearing positions.
Crank angleThe rotation angle of the crankshaft is re-ferred to as the crank angle and specified in ° crank angle. This is an exact dimensi-on for the position of the piston and it also defines a certain time of the diesel or spark-ignition process (e.g. 20° crank angle before TDC in the compression stroke).
FUNCTION
CrankshaftThe crankshaft is mounted on the shaft journal in the crankcase. The conrods are secured to the crank pin. Shaft journals and crank pins are connected by the crankshaft webs. The crankshaft webs contain drilled holes through which the oil flows from the shaft journals to the crank pins.
Mass balanceCrankshafts including pistons must be dy-namically balanced. The required mass balance is achieved using counter-weights.
The flywheel is located on the output end of the crankshaft. It accommodates the clutch, helps the pistons to surmount the idle cycles and dead centres, thus ensu-ring greater running smoothness of the engine.
On MAN D08 engines, there are gear wheels (spur gears) on the opposite side to drive accessories. So-called torsional vibration dampers prevent the crankshaft from experiencing non-permitted swings in the angle of rotation that can lead to the crankshaft breaking.
On D28 engines, the spur gears are on the output end. At the front of the engine, a viscous torsional vibration damper ensu-res smooth running.
Materials for crankshaftsCrankshafts consist of heat-treated steel, nitride steel or cast iron with spheroidal graphite.
Steel crankshafts are forged in dies. The course of the grain achieved here results in high solidity. Crankshafts made of cast iron with spheroidal graphite have good vibration damping properties.
5.15
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5.4.
3Cyl
inde
r hea
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d cy
linde
r hea
d ga
sket
x
Cylinder heads on MAN engines
2
1
LEGEND1 Individual cylinder heads
on the MAN D2876 CR2 Continuous cylinder head
on the MAN D2066 CR
BASIC PRINCIPLES
Cylinder headOn a diesel engine, the cylinder head of the engine holds the injection nozzles and valves. It limits the combustion volume and contains part of the compression vo-lume. The cylinder head is attached to the cylinder block by means of cylinder head bolts. A cylinder head gasket is used as seal. This is tensioned between the cylin-der block and head.
Depending on the gas exchange techni-que, two basic designs of cylinder head are distinguished:
Contraflow cylinder head
Crossflow cylinder head
High-volume commercial vehicle diesel engines can have individual cylinder heads for each cylinder or continuous cy-linder heads (➜ Fig.). On engines with in-dividual cylinder heads, the camshaft is arranged at the bottom; in the case of continuous cylinder heads, the camshaft is usually located at the top. On the whole, the overhead camshaft enables valve ti-ming with lower elasticity.
FUNCTION
Contraflow cylinder headThe intake and exhaust ducts are located on the same side of the cylinder head. Short lines favour the charging operation.
However, for reasons of space this engi-neering design is a problem for large engi-nes. Moreover, the exhaust gases heat up the intake air, which has a negative effect on charging the engine (➜ page 5.38).
Crossflow cylinder headThe intake and exhaust ducts end in op-posite directions of the cylinder head. Free pipe guidance and easier sealing are the advantages of crossflow cylinder heads.
Cylinder head coolingThe cylinder head must absorb the com-pression pressure and is subjected to se-vere heat stress by the combustion gases. This is why it has to be well cooled.
Air-cooled cylinder heads are fitted with cooling fins to enlarge the cooling surface. Most passenger car and almost all com-mercial vehicle engines are liquid-cooled. The coolant flows from the cylinder block via ducts into the ducts of the cylinder head. The cylinder heads on liquid-cooled engines consist of aluminium alloys or cast iron.
Cylinder head gasketThe cylinder head gasket is located bet-ween the cylinder head and crankcase. It seals the combustion chamber gastight,
and seals the water and oil ducts against one another. This is why the contact sur-faces of the cylinder head and cylinder block have to be completely even.
The cylinder head gasket is exposed to fu-el, exhaust gas, engine oil and coolant. This exposes it to high temperature diffe-rences and it is also exposed to stress from strongly fluctuating surface pressure due to the high pressure difference. The cylinder head gasket must withstand the-se extremely different loads for long peri-ods of time without losing its sealing pro-perties. If the cylinder head gaskets are damaged or worn, compression losses lead to losses in engine performance. Wa-ter entering the engine oil circuit can da-mage the engine.
5.16
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5.4.
4Val
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ear
x
Types of valve timing
1 2 43 1 5 11
OHV OHC DOHC
LEGEND1 Camshaft2 Push rod3 Rocker arm 4 Finger rocker arm5 Bucket tappet
BASIC PRINCIPLES
Valve gearThe valve gear refers to the arrangement for control of the gas exchange in com-bustion engines. Valves are used to cont-rol the inflow of fresh air or outflow of ex-haust gases at certain times.
In the push rod control frequently used in commercial vehicle engines, the valve gear consists of (➜ Fig. page 5.16):
Camshaft
Tappet
Push rod
Rocker arm
Rocker arm shaft
Valve spring
Valve
In four-stroke engines, the camshaft rota-tes only half as fast as the crankshaft. The arrangement and shape of the cams de-termine when and for how long the intake and/or exhaust valves open.
FUNCTION
CamshaftThe cams of the camshaft press against the valve stem via tappets and tappet push rods by means of rocker arms. De-pending on the cam position, the valves are opened against the spring force of the valve springs.
The camshaft receives its drive from the crankshaft via gear wheels, roller chains, toothed belts or vertical drive shafts.
Camshaft on heavy commercial vehicle diesel engines are generally driven by gear wheels. In the case of diesel engines, fin-ger rocker arm or bucket tappet control systems are also used alongside push rod control (➜ Fig.).
Depending on the position of the cams-haft and activation of the valves, the engi-nes are designated as follows:
OHV engineA low camshaft controls hanging over-head valves.
OHC engineAn overhead camshaft controls hanging valves via finger rocker arms.
DOHC engineTwo overhead camshafts each control a row of valves via bucket tappets.
Valve clearanceBalancing the different coefficients of ex-pansion of components requires a mini-
mum free travel of approx. 0.2 mm. This free travel is called valve clearance.
If the valve clearance is too great, the ope-ning times are too short: The charging of the cylinder and engine output fall; loud noise develops.
If the valve clearance is too small, the val-ves do not close completely. The conse-quences are compression losses, kick back of the ignition flame into the intake manifold, burning of the valves or even piston damage.
Materials for valvesValves are subjected to very high tempe-ratures and pressure and pulling on ope-ning and closing. For this reason, they consist of heat-resistant and scale-resis-tant materials.
In addition, there are devices that specifi-cally turn the valve every time it is actuated to minimise valve seat wear and maintain the seal.
5.17
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EXAMPLE
1 Camshaft2 Rocker arm for exhaust valves3 Rocker arm shaft4 Rocker arm for intake valves5 Intake valve plate
6 Valve spring7 Intake valves8 Piston9 Cylinder liner10 Exhaust valves
11 Exhaust valve plate with engine brake MAN EVB
12 Holder for MAN EVB13 Setting screw for MAN EVB
Valve gear with overhead camshaft (OHC engine)
12
11
10
136
5
7
8
9
1 2 3 4
5.18
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5.5E
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s5.
5.1O
verv
iew
x
BASIC PRINCIPLES
Cylinder arrangementDepending on the arrangement of the cy-linders, various designs of engines are distinguished. Together with the number of cylinders, they influence the running smoothness and torque characteristics of an engine. The designs used most fre-quently on commercial vehicles are:
In-line engine (R engine)
V engine
4-cylinder, 6-cylinder, 8-cylinder and 10-cylinder engines are mainly used in com-mercial vehicles. The first cylinder always lies opposite the output end. An engine that runs anticlockwise viewed from the output end is referred to as right-handed.
Underfloor engines are not a separate en-gine design. These are usually in-line engi-nes that are arranged horizontally for space reasons.
In-line engines (R engines)The cylinders are arranged in a line. In-line engines are usually built with a maximum of 6 cylinders. In-line engines with more than 6 cylinders make no sense due to their excessive overall length. The advan-tage of in-line engines compared to V en-gines and flat engines is the narrow de-sign.
V enginesThe arrangement of the cylinders has two levels. These are positioned in a V shape, often at a 90° angle to one another. Due to the shorter design, V engines for com-mercial vehicles with up to 12 cylinders are possible.
V engines are short and flat, but wide. Ac-cess to the accessories is not as good as with in-line engines.
Flat engines (B engines)The cylinders are positioned opposite one another. Flat engines are very short and flat, but this means they are also very wi-de.
The pistons move in opposite directions.
EXAMPLE
V V engine R In-line engine B Flat engine
Engine designs
1 Engine bearings 2 Engine 3 Gearbox
Engine mounting with in-line engine on the TGA
V
B
R
1 2 31
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2For
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omen
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x
Type Schema Free forcesof the 1st order
Free forcesof the 2nd order
Free momentsof the 1st order
Free momentsof the 2nd order
R4-cylinder4 offsets
0 4 ⋅ F2 0 0
R5-cylinder5 offsets
0 0 0.449 ⋅ F1 ⋅ a 4.98 ⋅ F2 ⋅ a
R6-cylinder6 offsets
0 0 0 0
V6-cylinder 90°3 offsets2 levels
0 0 1.732 ⋅ F1 ⋅ a 2.449 ⋅ F2 ⋅ a
V8-cylinder 90°4 offsets2 levels
0 0 3.162 ⋅ F1 ⋅ a 0
Free forces and moments on in-line and V engines
a
a
a
a
b
b
BASIC PRINCIPLES
Free forces and momentsDue to the inertia forces that occur in the engine, the engine block vibrates in its suspension. Free forces and moments arise, leading to increased wear in the be-arings of the engine and rough running characteristics in certain speed ranges.
The forces and moments that occurs and what effect they have depends on the crank arrangement (offset sequence), i.e. the engine design and number of cylin-ders.
Engine mountingTo separate the chassis from the vibra-tions that occur during engine operation, the engine-gearbox unit on the TGA is mounted on four rubber bearing elements (➜ Fig. page 5.18). The natural frequency of this elastic engine mounting is far below the vibration frequencies of the engine. This means that the mechanical vibrations of the engine are, for the most part, not transferred to the chassis.
With the four-point mounting of the TGA, it is easier to remove the gearbox than with systems that have additional moun-ting points on the gearbox.
FUNCTION
Calculating the forces and momentsThe free forces and moments can be cal-culated using the formulae listed in the ta-ble. The following applies to the oscillating inertia force F1 (1st order):
F1 = mo ⋅ r ⋅ ω2 ⋅ λ ⋅ cos α
And for the oscillating inertia force F2 (2nd order):
F2 = mo ⋅ r ⋅ ω2 ⋅ cos 2α
The calculation variables are:
mo Oscillating mass
r Crank radius
ω Angle speed
λ Stroke/conrod ratio
α Crank angle
In-line engines (R engines)In-line engines have the following vibration characteristics:
4-cylinder engine: free forces of the 2nd order; no free moments
5-cylinder engine: no free forces; free moments of the 1st and 2nd order
6-cylinder engine: no free forces; no free moments
To minimise the moments and forces that occur, balancer shafts are used on com-mercial vehicles.
MAN was the first commercial vehicle ma-nufacturer to equip its D0824 4-cylinder in-line engines with balancer shafts. On the D2865 MAN engine, the use of two balancer shafts leads to a reduction in the free moments of the 2nd order at 1500 rpm of around 95 %.
V enginesCommonly used commercial vehicle V en-gines have no free forces. The moments of the 1st and 2nd order that occur are very high and lead to severe vibrations in the engine block. These are only comple-tely balanced out on the 12-cylinder V en-gine.
5.20
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5.6E
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atio
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6.1G
ener
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x
Engine lubrication circuit
N
5
2
3
4
5
6
1
H
3
LEGENDH Main circuit
(main flow filter)N Partial-flow circuit
(partial-flow filter)1 Oil manometer 2 Lubrication points3 Oil pump4 Oil pan5 Pressure relief valve6 Overflow valve
BASIC PRINCIPLES
Engine lubricationThe main task of engine lubrication is to reduce the friction of components of the engine that slide against one another and thus to reduce wear. To ensure reliable operation of the drive unit, the engine lub-rication has other important tasks:
Cooling by means of heat dissipation via the lubricant (e.g. piston cooling)
Fine sealing of components that slide on one another (e.g. cylinder wall and piston rings)
Cleaning by removal of combustion residues that could otherwise lead to damaging deposits
Corrosion protection by means of a continuous oil film
Sound damping due to the vibration and sound insulation effect of the lub-ricating film
In today's commercial vehicles, only pres-sure circulation lubrication systems with high-performance engine oils are used.
FUNCTION
Lubrication systemThe following elements are components of the lubrication system:
Oil collector tank (oil pan)
Oil pump
Oil filter
Oil lines
Oil cooler
Pressure limiting valve (excess pres-sure or overflow valve)
Oil pressure and oil temperature measurement devices with corres-ponding displays
The most important lubrication points of the engine include the crankshaft bea-rings, conrod bearings, piston-pin bea-rings, tappets as well as the camshaft and rocker arms.
Pressure circulation lubricationThe oil pump draws in oil from the pan th-rough a filter and feeds it first of all through an oil filter and then to the individual lubri-cation points. After the oil has flowed th-rough the bearing and sliding points, the oil collects again in the oil pan. Some sli-ding points are supplied by spray or cen-trifugal oil.
Depending on the arrangement of the oil filter, a distinction is made between main and partial-flow circuits (➜ Fig.).
Oil manometerThe oil-pressure gauge in the dashboard shows the oil pressure determined by the oil manometer at all times. The oil pressu-re during idling with the machine at opera-ting temperature must not fall below a va-lue of approx. 0.5 bar.
High oil pressure does not necessarily mean good lubrication, as the oil pressure can also be high with clogged filters, lines or dirty and viscous oil. A pressure relief valve downstream of the oil pump pre-vents high pressures from damaging the lines and components.
5.21
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5.6.
2Oil
pum
p
x
External gear pump
1 2
Rotor pump
2
1
LEGEND1 Pressure chamber2 Inlet chamber
BASIC PRINCIPLES
Oil pumpAn oil pump creates pressure in the engi-ne oil circuit according to the displace-ment principle (➜ page 16.3). From the in-take side, the oil is usually fed by means of tooth gaps or geometric toothing towards the pressure side. As the moving parts run completely in oil, small leak oil flows are al-lowed from the pressure chamber to inlet chamber.
Gear pumpThe most frequently used type of oil pump is the gear pump. They are often driven by spur gears directly from the crankshaft gear. Regulating valves can relieve the load on the oil pump during a cold start (viscous oil).
Distinctions are made between:
External gear pumps
Internal gear pumps (crescent pumps)
Rotor pumps
FUNCTION
External gear pumpIn the case of the conventional gear pump, a gearwheel pair feeds the oil into the exterior tooth gaps on the edge of the housing from the intake side to the pres-sure side (➜ Fig.). The inlet and pressure chambers are sealed off from one another by the tooth interlacing.
Internal gear pump (crescent pump)A more modern design of gear pump is a crescent pump. Here, the driven external-ly toothed inner gear runs eccentrically in an internally toothed outer gear. The free space is separated by a crescent-shaped body into an inlet and a pressure cham-ber. The tooth gaps of both gear wheels feed the oil along the crescent body to the pressure side. This type, compared to the conventional gear pump, provides more even oil pressure with a greater delivery volume. The manufacture also provides cost benefits.
Rotor pumpA rotor pump is a displacement pump with an internally toothed exterior rotor and externally toothed interior rotor. The interior rotor has one tooth fewer than the exterior rotor and is connected to the drive shaft. The teeth of the interior rotor make contact with the exterior rotor and largely seal off the spaces that are created (➜ Fig.).
The rotational movement of the rotors continuously enlarges the pump cham-bers on the intake side; the pump draws in oil. On the pressure side, the chambers are reduced in size and the oil is pressed into the pressure line. The simultaneous displacement by a number of narrowing cells means the rotor pump can create high pressures. Rotor pumps also run very evenly.
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3Oil
filte
r
x
Replaceable-cartridge filter
5
4
1
2
3
LEGEND1 Sealing ring2 Filter cover3 Filter bowl4 Paper insert5 Filter element
BASIC PRINCIPLES
Oil filterOil filters are intended to remove mecha-nical contamination such as soot, rubbed-off metal particles and dust from the oil in order to maintain its lubrication quality for as long as possible. With adequate main-tenance, they ensure a long service life and functional capability of the engine.
Depending on the arrangement in the lub-rication circuit, a general distinction is made between the main and partial-flow filter (➜ page 5.20)
Main flow filterThe entire delivery volume is pressed th-rough the main flow filter and cleaned. Due to the risk of filter clogging, it is usu-ally fitted with a pressure relief valve and a bypass line.
Partial-flow filterOnly part of the delivered oil volume flows through the partial-flow filter. On each run, part of the oil remains uncleaned, but the smaller pores mean that the cleaning is more intensive. The overflow valve is nor required.
FUNCTION
Disk filterA disk filter is composed of ring-shaped steel lamina. The lamina package can be turned by means of a ratchet, e.g. by pressing the clutch pedal. Scrapers bet-ween the steel lamina remove the accu-mulated contamination up to a size of 0.1 mm. The dirt particles collect on the base of the filter.
Screen disk filterA screen disk filter has slightly better clea-ning properties than a disk filter. The filter screens consist of phosphor bronze, chromium-nickel steel or plastic fibre. The fineness of the filter is limited by the mesh width of the screen. The filter elements can be taken out of the filter housing and cleaned.
Replaceable-cartridge filterThe replaceable-cartridge filter is one of the most frequently used types of filter in commercial vehicles. Replaceable-cart-ridge filters are used in different forms as main and partial-flow filters. They can ea-sily be replaced by a completely new filter.
The filter element consists of fine lamina (star-shaped, folded, impregnated paper or special fibre material) and is often firmly attached to the housing.
Replaceable-cartridge filters are frequent-ly fine filters, removing particles of dirt up to a size of 0.001 mm. When used as the
main flow filter, a bypass valve is normally fitted for safety reasons; this is designed for 2 bar opening differential pressure in the filter.
At MAN, filter elements that can be incine-rated are used exclusively. Environmental-ly friendly disposal of these filter elements is possible without difficulty.
5.23
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5.6.
4Oil
cool
ing
x
BASIC PRINCIPLES
Oil coolerAlongside lubrication, a major function of the engine oil is cooling the engine. The oil must draw off the heat as quickly as pos-sible so that it does not heat up too much in the process. With excessive oil tempe-rature, the oil becomes thin and loses its lubrication properties. If the oil film breaks, severe damage to engine can occur.
Better cooling is achieved on engines th-rough the use of light alloy oil pans rein-forced with cooling fins.
To ensure optimised oil cooling, oil coo-lers (heat exchangers) are fitted in the en-gine oil circuit.
Both air-cooled and liquid-cooled oil coo-lers are used in commercial vehicles. On special vehicles, the engine oil is usually cooled by oil-air coolers. These coolers are arranged in front of the coolant radia-tor to ensure adequate cooling.
Air-cooled oil coolerEngine oil flows through the air-cooled oil cooler and the cooling air (headwind or blower air) flows around it. The cooling air absorbs the heat of the oil and conveys it to the environment (➜ Fig.).
Liquid-cooled oil coolerLiquid-cooled oil coolers are connected to the cooling circuit of the engine. The coolant flows around the oil flowing th-rough radiator, which conveys its heat in the process.
Important on liquid-cooled oil coolers is the reverse effect: with a cold engine, the coolant heats up faster than the oil and thus conveys heat to it. The oil thus rea-ches its operating temperature more quic-kly and can retain this without great fluctu-ations.
Oil moduleOn the MAN D2066 CR, the oil filter, oil cooler and blow-by oil separator are grou-ped into an assembly, the so-called oil module (➜ Fig.). The low number of single parts meant that an overall weight reduc-tion and simplification of assembly were achieved. The oil cooler is integrated in the engine cooling circuit.
EXAMPLE
1 Headwind 2 Uncooled engine oil 3 Air-cooled engine oil
Air-cooled oil cooler
1 Oil filter 2 Oil separator 3 Oil cooler
Oil module on the D2066 CR
1
2
3
3
1
2
5.24
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7.1G
ener
al
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Diagonal flow-through of the cylinder block
BASIC PRINCIPLES
Engine coolingThe materials for the engine components and the lubricating oil in the engine have only limited heat resistance. The heat transferred by the combustion process to the components of the engine must be conveyed to the ambient air. The engine must be cooled.
As a general principle, a distinction is made between air-cooled and water-cooled engines. Both methods, as well as the various coolant circuits and fan de-signs, are explained on the next few pa-ges.
The standard cooling system for commer-cial vehicles is the pump or forced circula-tion cooling (➜ page 5.26).
The throughflow for the cylinder block and cylinder head usually takes place based on the crossflow principle with diagonally arranged inlets and outlets (➜ Fig.).
FUNCTION
Heat transferThe heat in the oil and engine compon-ents is absorbed by the media (water or air) flowing around them and conveyed to the environment.
For a high cooling effect of the cooling system, it is important to optimise the heat transfer with high flow-through speeds of the coolant as well as maximum contact surfaces.
The used of large-surface light-alloy coo-lers favours heat transfer and ensures low weight of the entire cooling system.
EXAMPLE
The cooling means that between 25 % and 30 % of the possible usable energy of the fuel is lost. It is conveyed to the envi-ronment in the form of heat.
Good cooling enables:
Improved cylinder charging
Higher compression
Higher performance with lower fuel consumption
Even operating temperatures
5.25
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5.7.
2Air
cool
ing
x
Fan air cooling on the flat engine
1 2
4567
3
LEGEND1 Oil cooler2 Fan3 Thermostat4 Oil pan5 Oil filter6 Oil pump7 Overpressure valve
BASIC PRINCIPLES
Air coolingIn the case of air cooling, the heat to be dissipated is conveyed directly from the engine parts to the swirling ambient air.
The advantages of air cooling compared to water cooling are:
Simpler, lower-cost structure
Low weight
Higher operating reliability
Low maintenance
Fast reaching of operating tempera-ture
Higher operating temperature (higher than the boiling point of the coolant with comparable system pressure of water cooling)
However, air cooling also has disadvan-tages:
Greater fluctuations in the operating temperature
Greater piston clearances required and thus more susceptible to piston rocking
No sound damping due to the lack of water jacket
Higher power requirement of the fan
Poor interior heating
FUNCTION
Fan air coolingIn the case of fan air cooling, cooling air is taken in by a powerful fan and pressed th-rough ducts to the cylinders fitted with de-flectors. The fan is often located directly on the crankshaft. However, it can also be driven with a V-belt, hydrostatically or via gear wheels.
The air volume delivered is controlled via the speed. A thermostat automatically sets the required speed.
Fan air cooling achieves adequate cooling of clad engines.
Fan-air-cooled engines are used above all in passenger cars with flat engines (Por-sche, VW Beetle). They are hardly ever used in commercial vehicles.
Headwind coolingThe simplest type of air cooling is used al-most exclusively for motorcycles. In order to achieve the greatest possible efficiency during heat exchange, the cylinders, cylin-der head and frequently also the engine housing are fitted with cooling fins.
5.26
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oolin
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7.3.
1Gen
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x
Forced circulation cooling
54321
B
A
A6
B
LEGENDA Minor coolant circuit
(bypass circuit)B Major coolant circuit
(main flow circuit)1 Expansion tank2 Thermostat3 Thermoswitch and temperature sen-
sor4 Temperature gauge5 Heating6 Coolant pump
BASIC PRINCIPLES
Water coolingOn water-cooled engines, the cylinders and cylinder head are built with dual pa-nels. Water or coolant is located between the panels. The fan, radiator and water pump are the most important compon-ents of the water cooling system.
The advantages of water cooling are:
Even cooling
Low power requirement
Good sound damping
Comfortable interior heating of the vehicle is possible
However, water cooling also has disad-vantages:
High weight
High space requirement
Higher susceptibility to malfunctions (leaks, engine damage due to thermo-stat failure, frost damage)
FUNCTION
Thermal circulation coolingThermal circulation cooling (also thermosi-phon cooling) exploits the physical prin-ciple of warm fluids rising due to their low density. The heated coolant rises in the cooling jacket and flows through the cylin-der head to the radiator. Colder water from the radiator flows out.
As thermal circulation cooling uses no pump, coolant only circulates if the coo-ling system is completely full. The flow speed of the water is also low, which makes the heat transfer inadequate and uneven.
Forced circulation coolingIn the case of forced circulation cooling, the coolant is circulated by a pump. This means that the coolant flows at high speed, enabling rapid absorption of the excess heat and thus a low temperature difference between the entry and exit tem-peratures (5 to 7 °C). Thermal stresses in the engine can be minimised.
With the engine cold, the pump transports the coolant in the minor cooling circuit so that it does nor run through the radiator and the engine reaches its operating tem-perature as quickly as possible. With the engine at operating temperature (approx. 85 °C), the thermostat (➜ page 5.29) opens. The coolant then flows through the main flow circuit (major cooling circuit) and the excess heat is dissipated.
An expansion tank can be used to check the coolant level; coolant can be added if necessary. This is fitted with a venting me-chanism, thus preventing damage to the lines if the coolant level is too high.
The coolant normally flows through the cylinder block and cylinder head using the crossflow principle with diagonally arran-ged inlets and outlets (➜ Fig. page 5.24).
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5.7.
3.2F
an
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Operating modes of a viscous clutch
A B
6 754321
89
10
LEGENDA Engine coldB Engine hot 1 Bimetal2 Operating pin3 Leaf-spring valve4 Close-tolerance washer5 Driving disk6 Fan hub7 Valve opening8 Work chamber9 Pump body10 Storage chamber
BASIC PRINCIPLES
FanFans supply all the engine parts to be cooled and above all the radiator through which the coolant flows with an adequate amount of air. On commercial vehicles, disengageable viscous fans are frequently used. Fans of this kind are very economi-cal, as they are only engaged if cooling output is required.
The advantages are:
Reduction in fuel consumption
Increase in usable propulsion power
Reduction in fan noise
Operating temperature is reached quickly
Almost constant operating tempera-ture
Normally, viscous fans are activated via a bimetal-controlled viscous fan clutch by the temperature of the air behind the radi-ator. On vehicles equipped with retarders (➜ page 7.26), MAN uses directly – and thus more quickly – activated viscous fan clutches. Activation is by means of com-pressed air via coolant temperature sen-sors on the engine.
FUNCTION
Viscous fanThe function of the viscous fan is based on force transmission via fluid in the vis-cous clutch. The transfer fluid is viscous silicone oil. The fan is driven by a V-belt connected to the crankshaft or by gear wheels. The gear ratio (➜ page 1.11) of the fan drive lies between 1:1.1 and 1:1.25.
When the engine is cold, the fan runs at 25 % of its drive speed. The cooling out-put is considerably reduced and the engi-ne operating temperature is reached quic-kly.
As the radiator temperature rises, the fan clutch is steplessly engaged until the ope-rating temperature has been reached. The fan only runs with 100 % output at 90 °C. The speed is then approximately 2500 rpm.
If the viscous clutch fails, there is the pos-sibility to use a screw or bolt to set up a ri-gid connection between the driving disk and fan hub. The fan then runs constantly at maximum speed.
Viscous clutchThe work chamber of the viscous clutch (➜ Fig.) contains only a small amount of silicone, which means that the torque is transferred from the driving disk to the fan hub with very high slip.
As the temperature rises, the bimetal strip curves and the operating pin opens the valve. Silicone flows from the storage chamber into the work chamber. The more silicone flows into the work cham-ber, the lower the slip between the hub and driving disk, the greater the force transmission and thus also the speed of the fan. The speed rises steplessly and so does the cooling output.
As the temperature falls, the bimetal strip cools down and the operating pin slowly closes the valve. The silicone flows via the pump body back into the storage cham-ber. The speed of the fan is reduced.
5.28
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5.7.
3.3R
adia
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x
Installation of the preassembled radiator-engine unit on the TGA
21
3
LEGEND1 Coolant expansion tank2 Intercooler3 Engine radiator
BASIC PRINCIPLES
RadiatorThe heat transfer between media of all ty-pes rises when the flow speed is increa-sed and the contact surfaces are enlar-ged. Radiators consist of a pipe or fin sys-tem to ensure the contact surfaces are as large as possible. The radiator is connec-ted to the cooling circuit via the thermos-tat. When the thermostat is open, the coolant flows through the radiator and cools down (major cooling circuit ➜ page 5.26).
As a general principle, radiators consist of an upper and lower radiator tank. The cooling grid is located between the radia-tor tanks. The water inlet is at the upper radiator tank; after flowing through the cooling grid, the coolant leaves the radia-tor through the lower radiator tank. Pure water is never used as coolant. Coolant is a mixture of water with the lowest possible lime content, antifreeze agents and additi-ves for corrosion protection and lubricati-on (➜ page 17.9).
FUNCTION
Water-pipe radiatorIn the case of water-pipe radiators, the ra-diator tanks are connected to thin-walled metal pipes. Thin copper or aluminium plates connect the metal pipes and enlar-ge the cooling surface (cooling fins).
Pipe radiators are regarded as particularly resilient. On heavy trucks and special ve-hicles, the radiator is often divided into in-dividually replaceable sectional core radi-ators.
Finned radiatorSoldering together thin strips of metal pla-te (lamina) made of copper or copper al-loys creates flat channels that the coolant flows through.
The cooling effect of the finned radiator is greater than that of a pipe radiator with the same dimensions, but its solidity is lower. The thin lamina can also clog more easily.
Crossflow radiatorTo further improve cooling output, finned radiator are often configured as crossflow radiators. The inlet and outlet for the coolant are located on the side of the ra-diator: the radiator tank is divided. The coolant then flows through the radiator in the upper area to the right and in the lower area to the left.
The high cooling effect is achieved in that the coolant runs through the cooling grid twice. In order to be able to accommoda-
te the coolant in the event of thermal ex-pansion, crossflow radiators are often equipped with expansion tanks.
The filling cap on the expansion tank of the radiator is fitted with an overpressure and negative pressure valve to be able to balance out the pressure change due to expansion of the coolant on heating up. At an excess pressure of approx. 0.3 bar, the valve opens to enable the coolant tempe-rature to rise to 108 °C. The negative pressure valve opens when the tempera-ture falls, preventing the radiator from ca-ving in.
5.29
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3.4W
ater
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osta
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Expansion-element thermostat
1 2
2A B
LEGENDA Minor coolant circuit
(bypass circuit)B Major coolant circuit
(main flow circuit)1 Metal box filled with expansion ele-
ment2 Valve plate
BASIC PRINCIPLES
Water pumpIn order to ensure optimised heat transfer, the coolant must flow as quickly as pos-sible through the cooling system. The wa-ter pump creates rapid circulation of the coolant in the closed cooling circuit. It is driven by a V-belt from the crankshaft. In most cases, rotary pumps are used.
ThermostatTo prevent temperature fluctuations whe-re possible, a thermostat is used in coolant-cooled engines. This has the im-portant task of keeping the engine at an operating temperature that is as constant as possible.
Depending on the engine temperature, the thermostat switches from the minor to the major cooling circuit and increases or decreases the amount of dissipated heat. In the area of commercial vehicles, expan-sion-element thermostats are used al-most exclusively nowadays.
FUNCTION
Rotary pumpIn the pump housing, an impeller wheel runs in a narrowing housing, placing the coolant under pressure. This places the fluid in circulation.
Coolant flows continuously from the radi-ator or thermostat (depending on the tem-perature of the coolant) towards the pump.
Expansion-element thermostatA wax-type expansion element is contai-ned in a metal box. A piston connected to the thermostat housing protrudes into the expansion element. Two valve plates are attached to the metal box. Depending on the position of the valve plates, the coolant flows through the main or partial-flow circuit.
EXAMPLE
If the temperature of the coolant rises to approx. 85 °C, the expansion element ex-pands to such a degree that the piston shifts and the valve opens one of the th-roughflow directions (➜ Fig.). The main flow circuit is then activated and the radi-ator is integrated in the coolant circuit (➜ Fig. page 5.26).
5.30
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5.8.
1Spa
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Multi point injection (MPI) on the spark-ignition engine
1 2 3
4
5
LEGEND1 Spark plug2 Intake valve (fuel-air mixture)3 Injection valve (fuel)4 Fuel5 Throttle valve
BASIC PRINCIPLES
Mixture formation on the spark-igniti-on engineMixture formation on the spark-ignition engine is composed of three essential steps:
Mixture metering, i.e. regulation of the amount of mixture and mixture com-position: The position of the throttle valve in the intake pipe determines the amount of mixture; the mixture com-position is regulated by the carburet-tor or fuel injection system, as the case may be. On a petrol engine, depending on requirements, the air ratio λ can be greater than or less than 1 (lean or rich mixture ➜ page 5.4).
Mixture preparation, i.e. mixing the fuel and air in the intake pipe: for the subsequent combustion, the fuel dro-plets must be transformed into fuel vapour.
Mixture transport and distribution: Depending on the method (central injection, multi point injection or car-burettor), the fuel-air mixture is trans-ported and distributed in the intake pipe or directly before the intake val-ves.
FUNCTION
CarburettorA fuel feed pump (usually a membrane pump) transports the fuel from the fuel tank to the carburettor. The fuel collects in the float chamber of the carburettor; the float keeps the fuel volume in the float chamber constant.
The driver uses the accelerator to change the position of the throttle valve and thus the amount of air fed and/or the power output of the engine. Depending on the air volume, the carburettor feeds the corres-ponding fuel volume via a nozzle system.
Narrowing the cross-section of the intake pipe increases the speed of the air flowing past. A partial vacuum that increases with the speed and the air flow draws in the corresponding fuel volume in via the main nozzle.
Depending on the intended use and ar-rangement, downdraught carburettors, horizontal carburettors and mixing cham-ber arrangements are distinguished.
Central fuel injection (CFI)In the case of central fuel injection (e.g. mono Jetronic), the injection nozzle is lo-cated in front of the throttle valve and in-jects the fuel into the intake air flow. The spray jet should, where possible, be shaped in such a way that wetting the walls is avoided and the fuel reaches pre-cisely the gap between the intake pipe
wall and the throttle valve. There, prepara-tion of the fuel can be optimised by the high pressure difference. The injection val-ve is activated in the cycle of the ignition pulses.
Multi point injectionMulti point injection systems such as K Jetronic work according to the principle of continuous injection and direct airflow measurement. The injection valves are lo-cated directly in front of the intake valves and they inject the fuel with approx. 3.8 bar excess pressure into the gap opening of the valve (➜ Fig.).
A fuel distributor forwards the fuel volume determined by the airflow sensor to the in-jection valves. Fuel injection systems are monitored and controlled electronically.
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Prechamber
1
2
3
Swirl chamber
43
LEGEND1 Prechamber2 Drilled holes3 Glow plug4 Prechamber outlet
BASIC PRINCIPLES
Mixture formation on the diesel engi-neThe mixture formation on the diesel engi-ne only takes place after compression (in-terior mixture formation ➜ page 5.4). The combustion in the diesel process always takes place with excess air (λ > 1).
Depending on the type of injection, the fol-lowing are distinguished:
Prechamber system
Direct injection principle (➜ page 5.32)
Prechamber systemOn the prechamber system, the combus-tion chamber is divided into a main cham-ber and a secondary combustion cham-ber (main chamber and prechamber).
Depending on the design of the precham-ber, this is referred to as a prechamber system or swirl chamber system.
With the engine cold, the compressed air cools on flowing into the prechamber. This means it has to be preheated by glow plugs prior to the engine start.
FUNCTION
Prechamber systemOn this system, the prechamber accounts for around one third of the compression volume. It is connected to the main cham-ber by drilled holes. On compression, the air is pressed through the drilled holes into the prechamber.
Shortly before TDC, the fuel is injected into the prechamber with a pressure of 90 to 300 bar. The higher temperature in the prechamber leads to a brief ignition delay and thus to a rapid start of combustion. The rise in pressure blows the content of the at high speed into the main combusti-on chamber, which leads to very good mi-xing and thus complete combustion.
Prechamber engines run very smoothly due to the slow combustion; they used to be fitted exclusively in passenger cars. However, on account of the higher fuel consumption, they have been replaced in passenger cars by direct injection engi-nes.
Swirl chamber systemThis system uses a spherical or disk-shaped secondary combustion chamber (swirl chamber).
The connection between the main cham-ber and prechamber is called the prechamber outlet. During the compressi-on stroke, the air entering the swirl cham-ber is swirled violently by the tangential
position of the prechamber outlet and the shape of the swirl chamber. The seconda-ry combustion chamber then contains ap-prox. 50 % of the air taken in.
The fuel in this air swirl is injected eccen-trically in relation to the swirl direction. The fuel evaporates rapidly and combusts with a slight ignition delay. The high pressure forces the burning mixture to flow into the main chamber, where the rest of the com-bustion takes place.
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Direct fuel injection Piston design on the D2066 CR
BASIC PRINCIPLES
Direct injection principleMost current commercial vehicle diesel engines work with the direct injection prin-ciple. With this system, the fuel is injected directly into the combustion chamber.
The special shape of the intake port in the cylinder head swirls the air that is taken in. In addition, the design of the piston sur-face intensifies the air movement at the end of the compression stroke. Injection with multihole nozzles evenly distributes the fuel in the combustion chamber. De-pending on the sequence of injection, a distinction is made between air-distribu-ting mixture formation (➜ quiescent injec-tion principle) and mixture formation with wall-applied film (➜ M principle).
Engines using the direct injection principle have loud combustion due to the relatively long ignition delay. However, they have low specific fuel consumption and good cold-start properties.
FUNCTION
Quiescent injection principleThe combustion chamber is shaped as a recess in the piston crown (➜ Fig.). To op-timise the cold-start properties and keep the heat losses at a low level, an attempt is made to keep the surface of the com-pression volume as small as possible (low heat emission).
The injection pressure is up to 2000 bar, which achieves good, mainly air-distribu-ting mixture formation. The injected fuel ignites in the hot air and combusts rapidly. The large volume of fuel prepared during the long ignition delay leads to intensive combustion with a high pressure increa-se: the engine runs hard; the thermal load on the engine components is high. Howe-ver, the pollutant emission level is very low because of the rapid and complete com-bustion.
Due to exhaust emission regulations and fuel consumption requirements, almost all commercial vehicle engines use the direct injection principle nowadays.
MAN uses multi-jet direct fuel injection for its current heavy-duty engines.
M principleThe M principle (middle-sphere principle ) was developed by MAN and used up to the end of the 1970s. This is a direct injec-tion principle with wall-applied film.
With this principle, there is a spherical combustion chamber in the middle of the piston. The intake port is shaped as a swirl duct. The fuel is injected directly onto the walls of the combustion chamber with very high pressure; it evaporates on the walls and is removed by the moving air. The layer-by-layer evaporation of the fuel and the continuous combustion of the mixture leads to a soft flow of combustion.
The M principle enables smooth and elas-tic running of the engine in every operating mode. The fuel consumption is relatively low, but higher than with multi-jet injec-tion.
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filte
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Dry air filter with cyclone-type pre-separator (MANN)
1
2
LEGEND1 Air inlet2 Air outlet
BASIC PRINCIPLES
Air filterAir filters have two important tasks:
Cleaning the intake air (without signifi-cantly obstructing the air flow)
Damping the loud intake noise
The average dust content of the air on sur-faced roads is 1 mg/m3. On unsurfaced roads and above all with construction site deployment, this can rise to 40 mg/m3. The amount of dust taken in with the air forms an abrasive mass with the lubrica-ting oil and leads to high wear of all com-ponents of the engine. The service life of the engine is reduced drastically.
In order to be able to meet legal require-ments, the air intake noise, which is parti-cularly loud on commercial vehicles, has to be dampened. For this reason, the air filter is usually designed as a resonator-type muffler (Helmholtz resonator ➜ page 5.62).
FUNCTION
Dry air filterThe dry air filter contains a filter insert (cartridge made of folded paper) which can be replaced without difficulty. Paper air filters have good separation properties in all load ranges.
To extend the service life, so-called cyclo-ne-type pre-separators are frequently fit-ted in the housing of the dry air filter. To-gether with guide vanes, they apply rotati-on to the air that enters, whereby a large portion of the dust that occurs is separa-ted off before it enters the paper insert.
Dry air filters are the type of air filter most frequently used in commercial vehicles. When filter elements are heavily soiled, the flow resistance rises: the mixture beco-mes leaner, fuel consumption rises, engi-ne output falls, and the engine emits soot.
This means that regular maintenance and timely replacement of soiled air filter in-serts are very important.
Oil bath air cleanerIn the case of the oil bath air cleaner, the air filter housing is filled with oil. The filter element made of metal mesh is located above the oil. The air flowing in flows th-rough the oil bath. Oil droplets to which the dust adheres are pulled along and de-posited in the metal mesh. From there, they drip back into the oil bath, where the dust collects.
Oil bath air cleaners are the traditional air filters for commercial vehicles. Due to their self-cleaning mechanism, oil bath air clea-ners have long service lives and are there-fore suitable for deployment in dusty air (construction site and export vehicles). However, checking the oil level and oil changes within the prescribed mainte-nance intervals are essential here, too.
5.34
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5.8.
4Eng
ine
supe
rcha
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g5.
8.4.
1Sup
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argi
ng p
rinci
ples
x
Function of exhaust turbocharging
4
4
1
2
3
5
LEGEND1 Intake air2 Turbocharging3 Precompressed combustion air4 Exhaust gas5 Bypass valve (wastegate)
BASIC PRINCIPLES
Engine superchargingOn a naturally aspirated engine, the air ta-ken into the cylinder is under ambient pressure. The density of the intake air de-pends on the temperature. Increasing this density increases the air throughput of the engine. This means that more oxygen is available for the combustion: more fuel can be burned and the output of the engi-ne increases. In the case of a superchar-ged engine, the air is compressed before it enters the cylinder.
The so-called supercharging rate indica-tes the rise in compression of a superch-arged engine in comparison with a natu-rally aspirated engine. It depends on the supercharging system used and in the diesel engine is limited by the maximum permitted peak pressures on compressi-on.
Alongside the increase in power output, the advantages of supercharged engines also include better utilisation of the energy bound in the fuel. Because of the techni-cal and economic benefits, the superchar-ged engine is today's standard for engine technology in commercial vehicles.
FUNCTION
Exhaust turbochargingThe exhaust turbocharger is the most commonly used supercharging device in commercial vehicles. It consists of two turbo machines. A turbine built into the ex-haust tract uses the pressure, heat and flow energy in the fast-flowing exhaust gas to drive the compressor fitted in the intake tract. The turbine and compressor are connected via a rigid shaft. The speeds of exhaust gas turbochargers can reach up to 130,000 rpm. That means su-personic speed for the turbine vanes.
The output of a turbocharger depends on the amount of exhaust gas (pressure and engine speed). For this reason, the turbine powers up with a delay during accelerati-on. The range in which no or only very low charging pressure is available is referred to as the turbocharger lag. To minimise the delay on starting up, smaller turbine that can accelerate more quickly are used.
So that the charging pressure cannot be-come too high, a bypass valve (wastega-te) routes part of the exhaust gas past the turbine directly into the exhaust pipe as of a specified charging pressure. The super-charging effect is reduced (➜ Fig.).
Mechanical superchargingIn the case of mechanical supercharging, the compressor is driven directly by the engine (via crankshaft and an intermediate
gear system). With mechanical superchar-ging – in contrast to the exhaust tur-bocharger – the compressor drive power reduces the useful engine power. This is why mechanically driven superchargers are frequently engageable/disengageab-le.
The most familiar designs of mechanical superchargers are roots superchargers (roots blower) and vane-type superchar-gers. These are highly efficient and build up the charging pressure immediately.
Pressure-wave superchargingA pressure-wave supercharger is also dri-ven by the engine (by the crankshaft). A special configuration of the cellular spaces of a cellular wheel achieves a rise in pres-sure in the fresh gas flow via the pressure waves of the exhaust gas flow.
The problem with the pressure-wave su-percharger is the high space and energy requirement.
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x
EXAMPLE
1 Exhaust inlet2 Exhaust outlet3 Turbine housing4 Turbine vane5 Air inlet6 Air outlet7 Compressor housing8 Compressor wheel9 Take-off of the charge-air pressure at
the compressor housing10 Membrane actuation for wastegate11 Wastegate valve
Exhaust turbocharger
Exhaust turbocharger on the MAN D2066 CR
4
3
2
5
1
9876
10
11
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xhau
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ith v
aria
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geom
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(VTG
sup
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arge
r)
x
VTG supercharger of the second generation
32
4
5
6
7
1
9 108
LEGEND1 Exhaust inlet2 Exhaust outlet3 Turbine housing4 Turbine vane5 Adjustable vane ring6 Control membrane for setting unit7 Air inlet8 Compressor wheel9 Compressor housing10 Air outlet
BASIC PRINCIPLES
Variable turbine geometryA disadvantage of the exhaust turbochar-ger with wastegate control is the so-called turbocharger lag, i.e. the range in which no or only low charging pressure is avai-lable.
To reduce this range, variable turbine ge-ometry has been developed. Adjustable turbine vanes at different engine speeds achieve a virtually constant charging pres-sure.
An enhancement is the VTG supercharger of the second generation. Instead of adju-stable vanes, this has a vane ring that can be shifted on a sliding piston to enable dif-ferent turbine outputs.
With the electrically supported turbochar-ger, the turbocharger lag is finally going to disappear.
FUNCTION
VTG superchargerThe exhaust turbocharger with variable turbine geometry (VTG supercharger) has adjustable turbine vanes that deliver a gre-ater air flow at lower engine speed and are thus able to create higher charging pres-sure than comparable exhaust turbochar-gers with wastegate control.
The advantage is that the range with insuf-ficient charging pressure, the so-called turbocharger lag, becomes smaller. A dis-advantage is that the VTG supercharger is almost twice as expensive as a wastegate supercharger.
VTG supercharger of the second ge-nerationA VTG supercharger of the second gene-ration has a vane ring instead of the sepa-rate adjustable turbine vanes; this vane ring is seated on a sliding piston as a pre-cision-cast part.
Depending on the desired charging pres-sure, the vane ring can be shifted in such a way that the larger or smaller vane sur-face also provides variable turbine output. The simpler mechanism and lower num-ber of parts enable lower costs.
Electrically supported turbochargerAs long as there is no adequate exhaust gas flow, an electric motor located coaxi-ally between the turbine and supercharger
accelerates the supercharger, creating the desired charging pressure.
The corresponding turbine geometry makes it possible to generate the maxi-mum charging pressure even at 1000 rpm.
An option is also support from an electric motor, both for the VTG supercharger and the wastegate supercharger.
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Turbocompound system
1
2
3
4
5
6
LEGEND1 Exhaust gas flow2 Power turbine3 Hydraulic clutch4 Mechanical gear system5 Intake point6 Exhaust gas turbocharger
BASIC PRINCIPLES
Compound systemThe deployment of a second turbine can further improve the turbocharging of a die-sel engine. Systems of this kind are refer-red to as compound systems. The best-known method is the turbocompound method.
With the compound method, the energy that remains in the exhaust gas after it has run through the exhaust turbocharger is also used. Part of this energy is converted into rotation energy in a second turbine, transferred to the crankshaft, and used as driving power for the engine.
In this way, up to 20 % of the energy in the exhaust gases can be recovered. Only with turbocompound engines (TC engi-nes) can levels of efficiency of up to 46 % be reached: The performance of an engi-ne is enhanced.
FUNCTION
Turbocompound systemIn the turbocompound system, an additi-onal exhaust gas turbine behind the tur-bocharger drives the crankshaft of the en-gine via a hydraulic clutch.
Due to the great speed differences, the rotation energy of the turbine cannot be transferred directly to the crankshaft. The stepless gear system, usually in the form of a hydraulic clutch, adapts the speed of the turbine to the engine speed.
The hydraulic clutch, the turbine and a mechanical gear system form the turbo-compound unit (➜ Fig.).
First of all, the high speed of the turbine is drastically reduced by a mechanical gear system.
Then, the hydraulic clutch balances out the speed difference between the turbine and crankshaft. At low speeds and low load (low exhaust gas energy), freewhee-ling means that the engine does not have to drive the turbine.
After the turbocompound unit, a gear dri-ve transfers the force to the crankshaft.
Due to the high engine speed, strong heat develops in the turbocompound unit. Adequate cooling is usually implemented in a separate oil circuit.
The efficiency of turbocompound engines can only be achieved at full load. In practice, however, TC engines mainly run
in the partial-load range and do not achie-ve the favourable consumption values of engines without turbocompound.
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Charge-air cooling
16
6
23
7
4
5
ϑ = 150 ˚C
ϑ = 50 ˚C
LEGEND1 Intake air2 Turbocharging3 Precompressed combustion air4 Charge-air cooler5 Cooled, precompressed combus-
tion air6 Exhaust gas7 Bypass valve (wastegate)
BASIC PRINCIPLES
Charge-air coolingOne problem with supercharged engines is that the intake air heats up due to the precompression. First of all, this happens due to transfer of the heat to the compres-sor from the turbine which has been hea-ted intensely by the hot exhaust gases. However, the main cause of the tempera-ture increase in the intake air is the pre-compression (➜ page 5.2). The tempera-ture increase causes the air to expand, thus reducing the density.
If the charge air is cooled, more air mole-cules - and thus more oxygen atoms - are obtained with the same pressure. Char-ging of the engine is improved.
Charge-air cooling also reduces the ther-mal load of the engine, the exhaust tem-perature and the NOX emissions. The spe-cific fuel consumption is also improved.
Engines with charge-air cooling are refer-red to internationally as intercooler engi-nes. In the meantime, exhaust turbochar-ging with charge-air cooling is standard equipment on commercial vehicles.
FUNCTION
Water-air coolingThe advantage of water-air cooling is mainly the free choice of installation posi-tion of the intercooler. The low temperatu-re that can be achieved, however, is that of the coolant in the cooling circuit.
Fitting an additional cooling circuit is to complex and costly and is seldom done.
Air-air coolingIn passenger cars and commercial vehic-les, cooling the charge air with air (head-wind) has become the system most com-monly used. This is referred to as air-air cooling.
Usually, the intercooler is arranged in front of the coolant radiator; this means that the charge air is also adequately cooled when the vehicle is moving slowly. However, the main radiator must be configured for hig-her output. Separate radiators are often operated with a blower.
EXAMPLE
The intake air is heated by the compressi-on to 0.8 bar excess pressure and heat transfer from the exhaust gas turbine to up to 150 °C.
On an intercooler engine, the air can be cooled down from 150 °C to 50 °C by an intercooler arranged in front of the radiator (➜ Fig.).
This cooling results in a possible enhance-ment of engine output of up to 30 %.
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Flame starting system
1
2
3456
LEGEND1 Intake pipe2 Indicator lamp3 Control unit4 Fuel feed line5 Solenoid valve6 Flame glow plug
BASIC PRINCIPLES
Starting aidsAs the self-ignition on diesel engines takes place by injection into the hot, com-pressed combustion air, special equip-ment is required to start the cold engine.
The compression heat that occurs on compression is not sufficient to ignite the injected fuel with a cold engine. In the case of prechamber engines (➜ page 5.31), glow plugs are required to preheat the compressed air in the prechamber. There are also preheating systems with glow plugs for diesel engines with direct fuel injection. However, they are only used in engines with a displacement of up to 1 litre per cylinder.
Larger diesel engines with direct fuel injec-tion, as are fitted in commercial vehicles, are usually equipped with flame starting system. On these systems, the intake air is already preheated in the intake mani-fold. The compression means that it rea-ches the necessary temperature in the cy-linder: the injected fuel can ignite.
FUNCTION
Preheating systemIn a preheating system, used above all in passenger car diesel engines, the glow-plug filament of the glow plug protrudes into the prechamber or combustion chamber of the cylinder. A glow plug is fit-ted in each cylinder. After pressing the preheating switch or turning the ignition key to the preheating position, the glow-plug filament of the glow plug starts the preheating. The air in the prechamber or in the combustion chamber is preheated. After the preheating display goes out, the driver can operate the starter; the injected fuel can ignite in the hot air.
Glow time control units regulate the pre-heating and post-heating time by means of temperature sensors. After-heating the glow plugs improves the way the engine runs and reduces the white-smoke emis-sion during the warm-up phase. On mo-dern preheating systems, preheating ti-mes of only 4 to 7 s are possible.
Flame starting systemA flame starting system consists of a con-trol unit, indicator lamp, temperature sen-sor, solenoid valve and flame glow plug.
The flame glow plug is located in the in-take manifold. It preheats the intake air jointly for all cylinders. After the ignition is switched on, the preheating time starts. Depending on the temperature, this lasts 20 to 30 seconds. A flashing indicator
lamp signals that the engine is ready to be started. The switching point is determined by a temperature sensor. When the starter is operated, the solenoid valve opens and releases fuel. The fuel ignites on the flame glow plug. The intake air flowing past is heated. The fuel injected into the prehea-ted air can then be ignited in the cylinder without difficulty (➜ Fig.).
Once the engine has started, the intake air is heated further within the so-called post-flame time until the coolant temperature is approx. 20 °C.
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Fuel system
5
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3 24
4
1
6
6
6
6
9
8
LEGEND1 Fuel tank2 Fuel intake line3 Fuel feed pump4 Fuel feed line
(low-pressure line)5 Fuel filter6 Fuel overflow line
(return line)7 Injection pump8 Fuel injection line
(high-pressure line)9 Injection nozzle
BASIC PRINCIPLES
Fuel systemThe fuel system of the diesel engine con-sists of:
Fuel tank
Fuel lines
Fuel feed pump
Fuel filter
The fuel is drawn in through the intake line from the tank by the fuel feed pump and pressed through a pre-filter and fine filter to the inlet chamber of the injection pump. A pump plunger then presses it to the in-jection nozzle, from where – finely ato-mised – it is injected into the combustion chamber.
As the fuel is being transported, air and vapour bubbles can form. If there is air in the fuel system, the pressure cannot build up in the injection line. The fuel system must be vented.
FUNCTION
Fuel tankFor weight reasons, the fuel tank on com-mercial vehicles is often made of alumini-um or plastic. It must be corrosion-resis-tant and airtight at double operating pres-sure. The legally prescribed minimum value is 0.3 bar excess pressure.
Baffle partitions are frequently fitted in lar-ger tanks to prevent the fuel from shifting around when cornering, braking and mo-ving off at low speed. The drain screw is located at the lowest position of the tank.
Fuel linesSteel pipes (high pressure) or plastic pipes (low pressure) are used as fuel lines on commercial vehicles with diesel engines.
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Fuel feed pump
BA
1
2
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45
67
8
9
1011
12
LEGENDA Intermediate strokeB Delivery and intake stroke1 Camshaft2 Eccentric drive3 Roller tappet4 Pressure pin5 Pressure chamber6 Plunger7 Intake chamber8 Pressure valve9 Feed (intake line)10 Pre-cleaner11 Suction valve12 Drain line (pressure line)
BASIC PRINCIPLES
Fuel feed pumpThe fuel feed pump transports the fuel from the fuel tank to the injection pump. Its task is to feed the fuel to the injection pump under pressure of around 1 to 2.5 bar.
In the case of the in-line injection pumps frequently used in commercial vehicles (➜ page 5.44), the fuel feed pump is a piston pump. It is flanged onto the injection pump and is usually equipped with a hand pump for venting the fuel system.
Distributor injection pumps (➜ page 5.50) have integrated feed pumps configured as vane pumps or separately arranged membrane pumps, as in the case of the MAN D08 engines.
FUNCTION
Piston pumpThe fuel feed pump configured as a piston pump uses a piston to deliver diesel fuel from the intake side (line to the intake pipe of the tank) to the pressure side (line to in-let chamber of the injection pump).
The fuel feed pump is driven by an eccen-tric shaft seated on the camshaft of the in-jection pump. The rotational movement of the camshaft means that the eccentric shaft shifts the piston inwards via the roller tappet and the pressure pin (➜ Fig.). The fuel is fed via the pressure valve to the pressure chamber. The suction valve re-mains closed. The spring-loaded pressure valve closes at the end of the stroke (inter-mediate stroke).
As the surface of the eccentric shaft moves back, the piston moves back due to the spring force. Part of the fuel is fed from the pressure chamber towards the injection pump. During a simultaneous delivery stroke, fuel is taken in from the fuel tank through the opened suction val-ve into the inlet chamber. The delivery stroke is at the same time the intake stro-ke. A prefilter is frequently built into the fuel line of the fuel pump.
If the pressure on the pressure side of the pump is too high, the piston spring can no longer press the piston back completely: the delivery stroke and delivery volume are reduced. Thus, the greater the pressure in
the delivery line, the less fuel is delivered. This is referred to as elastic delivery. This protects the lines against excess pressu-re.
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Fuel Service Centre (FSC) on the MAN D2066 CR
3
45
6
12
LEGEND1 Fuel filter housing2 Hand pump3 Fuel prefilter4 Low-pressure connections5 Fuel filter heating (optional)6 Main filter element
BASIC PRINCIPLES
Fuel filterTo optimise the function and service life of the diesel injection system, careful clea-ning of the diesel fuel is essential. The components of the injection pump and the injection nozzles themselves are made with an accuracy of a a few thousands of a millimetre. Fuel filters must filter out con-tamination of this size so as not to endan-ger the function principle of the fuel injec-tion system.
The consequences of low porosity due to contaminated filters are:
Unfavourable combustion
Poor starting
Low engine output
Rough idling
High fuel consumption
When the prescribed replacement inter-vals expire (approx. 30,000 km), the filter insert must be replaced.
FUNCTION
Filter insertThe main constituent of the fuel filter is the filter insert. It consists of special paper with a separation rate that depends on the porosity, paper weight and the type of fib-res used. Filters for distributor injection pumps must have a maximum pore size of 4 to 5 µm. On all other types of injection pump, 8 µm is sufficient.
Depending on the shape and arrange-ment of the filter elements in the filter hou-sing, star-shaped or wound inserts. Both types of filter can be equipped with water separators and filter heating. The filter he-ating prevents the filter from clogging by paraffin separation (➜ page 17.2).
Line filterLine filters are only used upstream of dis-tributor injection pumps. They frequently have a water collection chamber. The wa-ter in the fuel collects on the fouled side of the filter paper and separates on the clean side. The maximum permitted water level can be seen via a sensor on the filter base.
Box filterBox filters are intended for use upstream of in-line injection pumps. The replaceab-le-cartridge filter screwed onto the filter cover consists of a sheet metal housing with a built in paper filter insert.
The filter box has a number of feed bore holes for the unfiltered fuel and a drainage
bore hole for the filtered fuel. There diffe-rent versions of the filter cover, including one with integrated hand pump for ven-ting the fuel system, which makes restar-ting after the tank has been emptied or af-ter a fuel filter change easier.
Fuel Service Centre FSCModern MAN engines are supplied th-rough a Fuel Service Centre (FSC) instead of through conventional box filters.
The FSC combines the pre-cleaner, the manual supply pump and the main filter in one compact component, optionally with or without heating element. The heating element can also be retrofitted without dif-ficulty (➜ Fig.).
The filter element is made without metal parts and can be disposed of in an envi-ronmentally friendly manner. Compared to conventional box filters, there is 50 % more available filter surface. The prefilter can be washed.
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Fuel injection systems for diesel engines
BA C D
1 3
4 52 6 7
LEGENDA Distributor injection pump (alterna-
tively: in-line injection pump)B Common Rail systemC Unit injector systemD Unit pump system1 Injection pump with individual line to
each injection nozzle2 Injection nozzle3 Injection pump with shared high-
pressure line4 Shared high-pressure distributor
(Common Rail)5 Injector (injection nozzle with sole-
noid valve)6 Individual pump element and injec-
tion nozzle with solenoid valve7 Individual pump element with sole-
noid valve, high-pressure line and injection nozzle
BASIC PRINCIPLES
Fuel injectionIn a diesel engine, the fuel has to be injec-ted into the combustion chamber (➜ page 5.5). To achieve this, modern fuel injection systems create pressures of up to 2000 bar, and in future even higher pressures. The process requires an accuracy of the start of injection of approx. ±1° crank ang-le (➜ page 5.14). In addition, the fuel has to be metered are precisely as possible.
Important criteria for the injection process are:
Timing and duration of injection
Distribution in the combustion cham-ber
Timing of the combustion start
Fuel volume delivered per ° crank angle
Total fuel volume delivered
To be able to meet these criteria, it must be possible to determine the start of the fuel injection exactly. Fuel injection sys-tems for diesel engines have an injection adjustment function which either mecha-nically or electronically changes the start of delivery of the injection pump or the start of injection depending on the engine speed, load and engine temperature.
Another special feature of fuel injection systems for diesel engines is the engine speed limitation. With an unlimited air vo-lume, the engine speed of a diesel engine
depends only on the injected fuel volume. If this were unlimited, the engine speed of the unloaded diesel engine could rise until it self-destructed. This is why every fuel in-jection system has a governor for engine speed limitation that also ensures a stable idle speed.
Fuel injection systems on modern diesel enginesCurrently, the following fuel injection sys-tems are relevant to commercial vehicle diesel engines:
In-line injection pump
Distributor injection pump
Unit injector system
Unit pump system
Common Rail
The in-line injection pump (➜ page 5.44) is the "classical" diesel fuel injection system. A camshaft simultaneous actuates a num-ber of individual pump elements.
The fuel is delivered from each individual pump element through a separate pres-sure line of an injection nozzle on each cy-linder. There is an individual pump ele-ment for each cylinder on the in-line injec-tion pump.
The distributor injection pump (➜ page 5.50) also has separate pressure lines to all the injection nozzles, but only one joint pump element for all cylinders. This runs
the required number of delivery strokes for each crankshaft revolution of the engine. A distributor in the pump routes the fuel to each injection nozzle with each delivery stroke.
Some commercial vehicle manufacturers use the modular multi point injection sys-tems unit injector system or unit pump system (➜ page 5.52). Here, the solenoid-valve-controlled pump element forms a unit together with the injection nozzle, of which there is one for each cylinder.
Currently gaining in significance is the Common Rail injection system (➜ page 5.54), where the high pressure generation and injection process are completely se-parated. The injectors (injection nozzles with solenoid valves) of all cylinders are connected by high-pressure lines to a "Common Rail". The storage volume of the Common Rail (CR) always contain fuel with injection pressure, created by central high-pressure pump. The quick-acting solenoid valves of the injectors enable pre-injection, multiple injection and post-injections per combustion stroke.
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Mechanically controlled injection (schema with PE)
1
5
94
4
3
2
7
8
11
6
6
6
6
10
LEGEND1 Fuel tank2 Fuel intake line3 Fuel feed pump4 Fuel feed line
(low-pressure line)5 Fuel filter6 Fuel overflow line
(return line)7 Fuel injection line
(high-pressure line)8 Nozzle holder with injection nozzle9 Mechanically controlled
In-line injection pump (PE)10 Injection timing mechanism11 Speed governor
BASIC PRINCIPLES
In-line injection pump PEThe in-line injection pump PE has its own camshaft and an individual pump element for each injection nozzle. For each cylinder of the engine, the fuel is feed through a se-parate high-pressure line to each injection nozzle (➜ Fig.).
The camshaft of the PE, driven by the en-gine, regulates the injection operations in the individual injection nozzles. The stroke of the pump plunger is unchangeable. The feed volume is controlled by means of the timing edges (➜ page 5.46).
For lubrication of the moving pump parts, the in-line injection pump is connected to the lube oil circuit of the engine.
Mechanical injection controlDepending on the engine load, the para-meters for fuel injection into the combusti-on chamber of the diesel engine have to be adapted. With mechanical injection control, this function is handled by the go-vernor together with a mechanical injec-tion timing mechanism.
FUNCTION
Speed governorThe main task of the speed governor is to limit the final speed of the diesel engine. There are no fixed control rod settings at which the diesel engine keeps its idle speed constant. For this reason, the go-vernor must adapt the injected fuel volu-me when the engine speed changes. De-pending on the governing activity, distinc-tions are made between:
Maximum-speed governor
Idling maximum-speed governor
Variable-speed governor
Combination governor
By shifting the control rod of the injection pump, the governor changes the fuel vo-lume fed to the injection nozzles (➜ Fig. page 5.47).
Whereas the mechanical governor is con-trolled by centrifugal force via linkage on the control rod, an electromagnetic cont-rol mechanism is used for the electronic governor.
The position of the driving pedal is passed on by a sensor to the control mechanism. The pedal travel is converted by the cont-rol unit into a certain control rod travel, ta-king account of the engine speed ; the re-quired fuel volume is set. The governor thus sets the delivery volume.
Mechanical injection timing mecha-nismThe ignition delay, which becomes greater with increasing engine speed shifts the start of combustion to later and the power output of the diesel engine deteriorates. An injection timing mechanism is used to balance out this effect. It serves to control the time of injection and with increasing engine speed it advances the start of deli-very by turning the camshaft of the injec-tion pump in relation to the crankshaft.
The mechanical injection timing mecha-nism works with centrifugal weights. With increasing engine speed, the centrifugal weights move outwards and enable a small turn of the pump camshaft. With the maximum turn of the injection pump camshaft by 8°, the start of delivery of all individual pump elements and thus the start of injection in all cylinders of the engi-ne is advanced by 4° crank angle.
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EXAMPLE
1 Camshaft2 Roller tappet3 Tooth segment4 Control rod
5 Feed line connection6 Pump cylinder7 Control sleeve8 Pressure line connection
9 Pressure valve10 Oil level11 Pump plunger
First in-line injection pump PE made by Bosch
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Delivery principle of a PE individual pump element
4321
3
BDC
BA
98
5
6
7 10
C
11TDC
3
LEGENDA Intake strokeB Delivery strokeC Residual strokeBDC Bottom dead centreTDC Top dead centre1 Pump housing
of the in-line injection pump (PE)2 Pump cylinder
of the PE individual pump element3 Inlet chamber4 Feed bore hole5 Control bore hole6 Pump plunger
of the PE individual pump element7 High-pressure chamber8 Pressure valve9 High-pressure to injection nozzle10 Longitudinal groove11 Timing edge
FUNCTION
Individual pump elementThe in-line injection pump PE delivers die-sel fuel from the individual pump elements through separate pressure lines to the in-jection nozzles on the engine.
The plungers of the individual pump ele-ment can be rotated and fitted with high accuracy in pump cylinders. Depending on design, the pump cylinder contains one or two feed bore holes. The second feed bore hole is also referred to as the control bore hole. The holes connect the inlet chamber with the high-pressure chamber (➜ Fig.).
Fuel deliveryEach PE individual pump element delivers the fuel to one injection nozzle. The fuel delivery takes place in three phases (➜ Fig.):
Intake stroke: The pump plunger is located at the bottom. The feed bore holes are open. The diesel fuel flows from the inlet chamber (feed line from the fuel feed pump) into the high-pres-sure chamber of the pump cylinder.
Delivery stroke: After the pump plun-ger has closed the feed bore holes, the delivery stroke starts. In the course of the vertical motion, the pressure rises to such a degree that the pressure valve opens and the fuel is delivered to the injection nozzle.
Residual stroke: When the lower end of the timing edge in the pump plun-ger has reached the control bore hole in the pump cylinder, the delivery stroke ends. The fuel is pressed back through the longitudinal groove into the inlet chamber. Once the TDC is reached, the feed bore hole is reope-ned during the downward movement of the pump plunger. A partial vacuum is created and fuel is drawn in; a new cycle of fuel delivery starts.
Delivery-rate controlThe governor of a PE in-line injection pump moves the control rod and turns the pump plunger, setting the required delive-ry volume simultaneously in all PE indivi-dual pump elements.
The fuel flows, depending on the position of the pump plunger, via the vertical longi-tudinal groove along the slanted timing edges back into the inlet chamber (➜ Fig. page 5.47). The delivery volume can thus be steplessly controlled depending on the rotation angle of the pump plunger bet-ween zero and full load.
Pressure valvesDepending on the injection conditions, there are additional pressure valves seated between the high-pressure cham-ber of the PE individual pump element and the pressure line to the cylinder. They
ensure exact termination of the injection process and prevent fuel dribbling at the injection nozzle.
Fuel dribbling would deliver non-atomised fuel to the combustion chamber at the wrong time. Excessive smoke formation as well as poor combustion would be the consequence.
The most important, currently common pressure valve types are the constant-vo-lume relief valve and the constant-pressu-re valve. In both types, an additional throttle dampens the pressure wave that is partially reflected at the injection nozzle, this preventing renewed opening (fuel dribbling) of the injection nozzle.
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EXAMPLE
A Maximum deliveryB Partial deliveryC Zero delivery
Delivery-rate control for the in-line injection pump PE
A
B
C
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In-line control sleeve injection pump PE
FUNCTION
Control sleeve PEIn-line injection pumps PE also include the in-line control sleeve injection pump, on which the delivery volume and also the start of delivery can be can be changed as desired.
To do so, the mechanical injection timing mechanism has been replaced by a cont-rol sleeve on the pump plunger. The mo-ving control sleeve now contains the con-trol bore hole which was firmly arranged on the pump cylinder on conventional in-line injection pumps (➜ Fig. page 5.46).
When the shaft is turned, the articulated levers of the control sleeve adjusting shaft move all the sliders - and thus also the control bore holes of all individual pump elements - upwards or downwards simul-taneously (➜ Fig. page 5.49).
Depending on whether the control sleeve is positioned lower or higher, the piston closes the feed bore hole and thus starts the delivery stroke earlier or later. The end of the delivery stroke has been reached when the slanted timing edge in the piston reaches the control bore hole in the cont-rol sleeve and the fuel can flow back th-rough the hole in the piston.
Delivery-rate control is the same as for the conventional in-line injection pump. To achieve this, the pump plungers are tur-ned by moving the control rod, which changes the position of the machined ti-
ming edges relative to the control bore ho-le. On the in-line control sleeve injection pump, however, relatively low control forces are sufficient; these are created by a linear-effect control path operating ma-gnet (➜ Fig. page 5.49).
EDC for control sleeve PEWhen the accelerator pedal is pressed, EDC control unit is informed of a travel-dependent resistance value by means of a potentiometer. The electronic engine con-trol EDC uses this to calculate the re-quired current for the control rod opera-ting magnet. The changed current shifts the control rod against the spring force and influences the injection volume direct-ly. By means of a travel sensor, the control unit is continuously informed of the dis-tance travelled by the control rod and can thus continuously check the position (➜ Fig. page 5.58).
The sequence for control of the start of in-jection is the same as that via the control sleeve adjusting shaft.
EXAMPLE
In-line control sleeve injection pumps en-able very exact control of the start of injec-tion, this minimising consumption and pollutant emissions. They are used in light and heavy commercial vehicles up to a power output per cylinder of 70 kW. The maximum injection pressure is up to 1150 bar.
As series standard, MAN uses in-line con-trol sleeve injection pumps with EDC con-trol on the engine model series D2866 with 12 litres displacement.
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x
FUNCTION
A Intake strokeB Delivery strokeC Residual stroke1 Start of delivery operating magnet2 Control sleeve adjusting shaft3 Control path operating magnet
4 Control rod travel sensor (induc-tive)
5 Plug connection6 Speed sensor (inductive)7 Camshaft8 Control rod9 Control sleeve
10 Control bore hole11 Inlet chamber12 Control groove13 Pressure chamber14 Feed and return bore hole15 Pump plunger
Control of the control sleeve PE
5
9
8
7
910111213
14
15
A B C
1
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5.50
5.10
.2.3
Dis
trib
utor
inje
ctio
n pu
mp
x
Axial piston distributor injection pump VE
2
3
45
1
LEGEND1 Fuel inlet; vane-type supply pump
with pressure valve2 Mechanical speed governor3 Electromagnetic stop valve4 High-pressure pump with pump and
distributor plungers; distributor body with individual fuel lines to the injec-tion nozzles
5 Hydromechanically controlled injec-tion timing mechanism
FUNCTION
Axial piston distributor injection pump VEIn contrast to the in-line injection pump, the VE axial piston distributor injection pump has only one high pressure pump element with one pump plunger for all cy-linder. During a revolution of the crankshaft of the engine, the pump plun-ger runs as many strokes as there are in-jection nozzles (cylinders). Simultaneous rotational movement of the pump plunger during the stroke feeds the fuel to the va-rious outlets of the distributor and delivers it to each injection nozzle.
A mechanical speed governor that works as an all-speed, idling speed or maxi-mum-speed governor, is integrated in the housing of the VE.
The hydromechanically controlled injec-tion timing mechanism uses the speed-dependent delivery pressure (5 to 10 bar) of the integrated vane-type supply pump (➜ Fig.). This delivery pump pressure exerts force on a spring-loaded injection timing mechanism plunger which for ex-ample with increasing engine speed sets an earlier start of delivery (time of injec-tion).
Radial piston distributor injection pump VP44The VP44 radial piston distributor injection pump has an integrated control unit to control the injection volume via the high-
pressure solenoid valve and to set the op-timised time of injection with the injection timing mechanism cycle valve (➜ Fig. page 5.51). The pump control unit can communicate with the engine control (EDC) across a CAN data bus (➜ page 5.59).
The special feature of the VP44 is its high volume accuracy and dynamics, achieved using a rotation angle timing control of the high-pressure solenoid valve. The delivery output is provided by at least two radial pump plungers, enabling smaller forces and faster profiles on the cam ring.
EDC for distributor injection pumpThe electronic engine control EDC for dis-tributor injection pumps controls the feed-forward of the signal for the start of injec-tion and injection volume electrohydrauli-cally. Frequently, if required, feed-forward groups enable other control functions in addition to the standard control. These in-clude temperature-dependent fast idling, cold start with earlier start of delivery, and a great deal more.
EXAMPLE
The area of application of distributor injec-tion pump includes fast-running passen-ger car and commercial vehicle diesel en-gines up to a power output per cylinder of 25 kW. The injection pressure of the VE axial piston distributor injection pump VE is approximately 700 bar. Electronically controlled VEs achieve injection pressures of up to 1500 bar. The electronically con-trolled VP44 radial piston distributor injec-tion pump achieves injection pressures of up to 1950 bar.
MAN uses e.g. VP44 distributor injection pumps for engines of the model series D0836 with 6.9 litres displacement.
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EXAMPLE
1 Vane-type feed pump2 Sensor (rotation angle, time)3 Cam ring4 Radial pump piston5 Electronic control unit
6 Solenoid-valve needle7 High-pressure solenoid valve
(injection volume)8 Fuel outlet
(individual line to the injection nozzle)
9 Return-flow restriction10 Distributor body11 Distributor shaft12 Injection timing mechanism cycle
valve13 Injection timing mechanism
Radial piston distributor injection pump VP44
5
21
7
9
8
12 1113 10
6
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5.52
5.10
.2.4
Mul
ti po
int i
njec
tion
syst
ems
UIS
and
UP
Sx
Multi point injection systems UIS and UPS
5
2
1
3
4
6
21 3 4 6
A B
LEGENDA Unit injector system (UIS)B Unit pump system (UPS)1 Engine cylinder head2 Injection nozzle (injector)3 Solenoid valve4 Individual pump element5 High-pressure fuel line6 Camshaft
FUNCTION
Unit injector system UISThe unit injector system is also known by its abbreviation UIS. Unit injector systems are seated in the individual cylinders. They are driven by the engine camshaft via an additional injection cam.
The individual pump element and injection nozzle are grouped in one unit. Each UIS is equipped with a quick-action solenoid valve. An electronic control unit with cha-racteristic map control (EDC) activates this valve and thus determines the start of injection and duration of injection.
The great advantage of the UIS is that all high-pressure lines are eliminated. Nowa-days, pressures of up to 1800 bar can be generated in the unit located directly in the cylinder head; in future, over 2000 bar will be possible.
There are significantly higher injection pressures on the HPI system (High Pres-sure Injection) from Scania. Here, separa-tely arranged solenoid valves control the start of injection and duration of injection for each UIS via additional fuel pressure li-nes. As the solenoid valves are not activa-ted here with high pressure, rather with "controlling" fuel (18 bar), the injectors of the HPI system already work with pressu-res of approx. 2400 bar.
The high injection pressures and exact electronic control enable a significant re-duction in pollutant emissions. A require-
ment for this system, however, is an addi-tional cam drive with overhead camshaft, which in turn has a one-piece, continuous cylinder head as a condition (➜ page 5.15).
Unit pump system UPSThe unit pump system is also known by its abbreviation UPS. This system also has a separate injection module for each engine cylinder. A short high-pressure line con-nects each individual pump with the cor-responding nozzle (➜ Fig.).
The control system, drive system and ma-ximum pressure of the UPS correspond to those of the UIS. However, the spatial se-paration of the pump and injection ele-ment of the UPS provide greater space for the construction of the engine. The UPS can also be used on engines without an overhead camshaft and thus without a continuous cylinder head. However, an additional cam drive is also necessary he-re.
EXAMPLE
Possible areas of application for the unit injector system (UIS) and the unit pump system (UPS) are passenger car and commercial vehicle engines with a maxi-mum power output per cylinder of 70 kW and injection pressures up to 1800 bar.
The unit injector systems are used, for ex-ample, by Scania and Volvo for commer-cial vehicle engines with displacements between 9 and 16 litres.
Examples of the deployment of the unit pump system are the V6 and V8 engines with 11.9 or 15.9 litres of displacement in the heavy Mercedes-Benz series as well as the Mack engines with 12 litres dis-placement in the heavy Renault series.
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IS a
nd U
PSx
EXAMPLE
1 Injection nozzle2 Nozzle needle3 Nozzle spring4 High-pressure chamber5 Pump plunger6 Pump body
7 Return spring8 Control attachment for camshaft
rocker arm9 Solenoid valve10 Valve seat11 Fuel feed line
12 Fuel return duct if solenoid valve in resting position (return valve open)
13 Fuel injection duct if solenoid valve with switch impulse (return valve closed)
Unit injector systems in the Scania engine
9
4
3
1
5
6
7
8
2
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5.10
.2.5
Com
mon
Rai
l (C
R) i
njec
tion
syst
em
x
Selectable injection point on the systems Common Rail and UIS (UPS)
p[bar]
p[bar]
n [1/min]600 1800
n [1/min]600 1800
Common-Rail
UIS (UPS)2
1
LEGEND1 Free choice of operating point within
the marked area on the Common Rail system
2 Choice of operating point only along the line on the UIS (UPS) system
BASIC PRINCIPLES
Common Rail (CR) injection systemOn engines with a Common Rail system, the injection pressure builds up indepen-dently of the load and engine speed. The central high-pressure pump creates an accumulated volume with a potential of up to 1600 bar. This is available on a com-mon rail to each injection nozzle for finely atomised injection.
The time of injection and duration are spe-cified by the EDC control unit via electri-cally activated solenoid valves. These val-ves are seated directly on the injector. The essential feature of the CR system is thus the separation of pressure generation and injection. The independent injection of the Common Rail system is independent of the engine speed and engine load provi-des high injection pressures even at low engine speeds.
The increased mean injection pressure as well as the time of injection can be chosen freely within a wide range independently of the engine operating point. Multiple injec-tion with advanced, main and post-injec-tion is possible. In the case of cam-cont-rolled multi point injection systems (UIS, UPS ➜ page 5.52), this more or less free choice of injection parameters is not pos-sible (➜ Fig.).
FUNCTION
Central high-pressure pumpThe volume-controlled high-pressure pump delivers diesel fuel into the common rail until the desired fuel pressure (appro-ximately 1600 bar) has been reached.
Common railThe common rail contains a defined accu-mulated volume with the fuel pressure desired for the injection. It is connected via high-pressure fuel lines with all the so-lenoid-valve-controlled injection elements (injectors).
Injection element (injector)Each injection element of the Common Rail system is activated by a quick-action solenoid valve. When the solenoid valve is activated, the injection elements (injec-tors) can inject a defined amount of fuel into the combustion chambers of the en-gine from the accumulated volume (Com-mon Rail) which is continuously under high pressure.
Multiple electrical activation of the soleno-id valve enables multiple injection (up to 4 per ignition). This is the basis for a com-bustion process that achieves the best values with regard to exhaust emissions and acoustics.
EDC for Common Rail systemThe hydraulic components of the Com-mon Rail fuel injection system are monito-red by the engine-mounted control unit
EDC, the sensors of which continuously record data with regard to the engine or vehicle operation.
In this way, for example, the rail pressure sensor RPS, the control unit and the volu-me-controlled high-pressure pump form a control loop.
Other sensors such as the coolant tempe-rature sensor, charge-air temperature sensor or atmospheric pressure sensor help to adjust and optimise the engine to changing conditions.
Examples of the implementation of the CR fuel injection system are the MAN engines of the D0836 CR model series with 6.9 lit-res displacement and D2876 CR with 12.8 litres displacement as well as the 11.0-litre engines made by Renault.
On the MAN D2066 CR engine, the Com-mon Rail fuel injection system of the se-cond generation has already been used with the engine control unit EDC7.
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Com
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emx
EXAMPLE
1 Fuel tank2 Gear pump3 Fuel filter4 Central high-pressure pump5 Common Rail6 Pressure limiting valve PLV7 Injector8 Engine-mounted EDC control unit9 Metering unit10 Other actuators11 Rail pressure sensor RPS12 Speed sensor (crankshaft)13 Speed sensor (camshaft)14 Accelerator pedal sensor15 Other sensorsa Fuel intake lineb Fuel high-pressure linec Fuel overflow lined Electr. control cablee Electr. sensor cable
Schema of the Common Rail injection
1 Common Rail injector2 Cable set between injector and
engine control unit3 Common Rail
with pressure limiting valve andrail pressure sensor
4 Fuel Service Centre5 Common Rail pump
(low-pressure section)6 Common Rail pump
(high-pressure section)
Version of the Common Rail system on the MAN D2066 CR
611
8
ed
1
2
3
a
a
c
4
b
b
c
5
714
15
9
10
13
12
c
cb b b
bb
b
c
c
3
4
5
6
1
2
5.56
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5.10
.3In
ject
ion
proc
ess
x
Injection process for a hole-type nozzle
1
6
3
4
3
4
7
5
2
dD
FHFH
FD
Spray formation of a 6-hole nozzle
LEGEND1 Feed bore hole2 Pressure chamber3 Annular surface (exposed annular
surface)4 Seating area (conical seat)5 Nozzle body6 Nozzle needle7 Nozzle bore holes (holes)D Diameter of annular surfaced Diameter of seating area FD Pressure spring forceFH Lifting force
BASIC PRINCIPLES
Injection nozzlesThe injection nozzles inject fuel into the cy-linder. They have to inject the finely ato-mised fuel delivered under high pressure into the combustion chamber. They are mounted in the individual cylinders and connected to the injection pump by high-pressure lines.
The length and hole diameter as well as emission direction and hole shape of the injection nozzles influence the fuel prepa-ration and thus the performance, fuel con-sumption and pollutant emissions of the engine. A fundamental distinction is made between throttling-pintle and hole-type nozzles.
It is only possible to inject fuel through the nozzle if the fuel pressure level is adequa-te. In the case of in-line and distributor in-jection pumps, this takes place with every delivery stroke, creating a high-pressure impulse. On the unit injector, unit pump and Common Rail fuel injection systems, the high pressure created by the pump is only effective as long as the solenoid valve is activated.
FUNCTION
Injection processIf the injection nozzle has a nozzle holder with pressure spring, the fuel delivered by the pump plunger into the high-pressure line pressed on the spring-loaded nozzle needle of the injection nozzle. If the pres-sure on the nozzle needle and thus the force FH becomes greater than the pres-sure spring force, the nozzle needle opens the bore hole (bore holes in the case of multihole nozzles). The finely atomised fuel is injected into the hot combustion air, where it ignites immediately (➜ Fig.).
When the fuel pressure drops (residual stroke ➜ Fig. page 5.46), the spring force presses the nozzle needle downwards again; the surplus fuel flows back through the fuel overflow line into the fuel tank.
The nozzle needle must close without any leaks to prevent fuel dribbling. It also has to seal the fuel injection system against the hot exhaust gases which are under high pressure. In order to prevent exhaust gas blow-back when the injection nozzle is open, the pressure in the nozzle pressu-re chamber must always be higher than the compression pressure. Precise har-monisation between the injection pump, injection nozzle and pressure spring is therefore particularly important.
In the case of injection elements with a so-lenoid valve, an electronic control unit de-termines the opening and closing of the
injection nozzle, thus specifying the start of injection and duration of injection (➜ Fig. page 5.57).
Throttling-pintle nozzleThe throttling-pintle nozzle creates a coa-xial jet; the nozzle needle opens inwards. In the range of very small needle strokes, throttling-pintle nozzles have a very flat change in cross section.
Throttling-pintle nozzles are only used in diesel prechamber engines.
Hole-type nozzleThe spray holes or a hole-type nozzle are arranged at various angles and have to be geared to each combustion chamber.
In contrast to throttling-pintle nozzles, the cross-section of hole-type nozzle grows even with very small strokes immediate af-ter opening.
Hole-type nozzles are used above all in commercial vehicle diesel engines with di-rect fuel injection.
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FUNCTION
Common Rail injectorThe Common Rail system controls the in-jection process by means of an extremely fast solenoid valve in the injector. When there is electrical power flowing in the so-lenoid coil, the anchor of the solenoid val-ve with valve ball moves upwards and opens the drain restrictor. The fuel return with opened drain restrictor causes the pressure in the control chamber on the control plunger to fall and the nozzle needle opens.
When there is no current on the solenoid coil, the valve springs presses the anchor of the solenoid valve with valve ball down-wards again and closes the drain restric-tor. This increases the pressure in the control chamber and the nozzle needle is closed by the control plunger.
The opening and closing speed of the nozzle needle is determined by the feed restrictor in the control chamber of the in-jector. The exact injection volume results from the outflow cross section of the nozzle, the duration of opening of the so-lenoid valve and the fuel high pressure.
LEGEND1 Electrical connection2 Solenoid coil3 Feed restrictor4 Control chamber5 High-pressure sealing ring6 Fuel feed
from high-pressure distributor(Common Rail)
7 Injector body8 Nozzle spring9 Pressure element10 Nozzle needle11 Fuel return12 Control plunger13 Drain restrictor14 Valve ball15 Anchor of the solenoid coil16 Valve spring
Course of combustion pressureThe division of the injection volume into advanced and main injection ensures quieter combustion. A comparison of the course of combustion pressure with and without advanced injection shows the sig-nificantly more even rise in the course of pressure with advanced injection.
EXAMPLE
Injection process for Common Rail injector
A Course of combustion pressure without advanced injection
B Course of combustion pressure with advanced injection
Course of combustion pressure
8
7
9
10
1
2
3
5
6
412
1314
15
16
11
P[bar]
t [s]
pmax
B
A
5.58
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5.10
.4El
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inje
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n co
ntro
l ED
C
x
EDC system with in-line control sleeve injection pump
15
8
23
21
16 17 18 19 20 24 25
22
5
2
3
1
4
46
6
67
6
9 10 11 12 13
14
LEGENDItem 1 to 8 ➜ Fig. page 5.449 In-line control sleeve injection pump
(➜ page 5.48)10 Electric shut-off11 Fuel temperature sensor12 Control travel sensor13 Rack with linear magnet14 Speed sensor15 Coolant temperature sensor16 Accelerator pedal sensor17 Switch for clutch, brake, engine
brake18 Control panel19 Warning and diagnosis20 Driving speed sensor21 Engine control unit EDC22 Air temperature sensor23 Charge pressure sensor24 Battery25 Glow-start switch
BASIC PRINCIPLES
Electronic injection control EDCTo optimise control of the injection pro-cess, the mechanical control unit for elec-tronic injection control is replaced by an electronically controlled control mecha-nism. In the meantime, EDC (electronic diesel control) has become standard on many commercial vehicles. Depending on the version, this can be used to precisely control the injection volume (EDCM) or in-jection volume and start of injection (ED-CMS) of the injection pump.
This results in the following advantages:
Lower fuel consumption
Lower pollutant emissions
Optimised torque characteristics
Optimized performance
Besides the start of injection and delivery volume, the EDC system naturally also ensures idle control and full-load volume limitation. A starting volume limitation de-pendent on the charge pressure and a li-mitation of the maximum engine speed to prevent damage to the engine are also among the tasks of the EDC system.
FUNCTION
Components of the EDC systemAn EDC system is divided into the follo-wing components:
Sensors to pick up the operating con-ditions
Control unit to assess the operating conditions (comparison of input sig-nals with stored target values of start of injection and delivery volume depending on engine speed and tem-perature) and control of the control mechanisms
Control mechanisms to convert the electronic output signals of the control unit into mechanical impulses
EDC systems have safety and emergency functions that run in the event of malfunc-tions of the system. For example, if the en-gine temperature lies above the limit va-lue, the vehicle can still be driven with re-duced power output.
Regulating intervention on the EDC systemDepending on the system, the starting points of the regulating intervention differ.
In the case of EDC systems with in-line control sleeve injection pumps or distribu-tor injection pumps, the control elements are mounted at the point of pressure ge-neration, i.e. directly at the pump ele-ments, and influence the start of delivery and delivery volume.
Also in the case of the unit injector system or unit pump system, the control interven-es by means of a solenoid valve in the pump section of the injection unit and de-termines whether the high-pressure im-pulse is delivered to the injection nozzle or routed back to the fuel tank.
On the Common Rail system, on the other hand, pressure generation is disconnec-ted from the injection process. Here, the solenoid valve is mounted directly on the injector and it influences only the injection process itself.
5.59
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5.10
.5En
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man
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ith C
AN
bus
tech
nolo
gy
x
Function schema for EDC with CAN bus technology
888 888
T-CAN
M-CAN
FFR
EDCA
B
8
9
10C
11
12
13
14
76543211
LEGENDA Engine control unit EDCB Injection controlC Vehicle management computer 1 Speed sensor2 Needle movement sensor3 Charge pressure sensor4 Fuel temperature sensor5 Coolant temperature sensor6 Fuel pressure sensor7 Oil pressure sensor8 Engine brake9 Speed signal10 Brake signal11 Warning lamp in the display12 Steering column switch13 Electronic driving pedal14 Clutch position
BASIC PRINCIPLES
Engine managementCAN bus technology (CAN = Controller Area Network) is a serial bus system for data interchange specially conceived for use in vehicles. The CAN bus is divided into individual areas for the drive train (T-CAN), engine (M-CAN) and instrument unit (I-CAN) (➜ page 11.4).
On vehicles with a CAN electronics struc-ture, the EDC control unit works in a fra-mework with other electronic control and regulating systems. In the case of the TGA series from MAN, the control unit EDC and FFR (vehicle management computer) share the tasks of engine management.
The electronic engine management of the EDC control unit in combination with the vehicle management computer FFR en-ables a reduction in fuel consumption and pollutant emissions as well as optimisation of the torque characteristics and perfor-mance characteristics. The inquiry of en-gine-specific maps guarantees optimised engine and driving characteristics in every operating mode.
FUNCTION
EDC with CAN bus technologyThe M-CAN bus connection of the EDC control unit via the vehicle management computer FFR enables comprehensive data interchange between the connected systems (sensors, control units) without complex wiring harnesses. This means that a wide variety of information is avai-lable to the engine control unit across a single cable.
Integration with other electronic systems makes the vehicle more comfortable, more economical, more environmentally friendly and safer.
Combination of EDC with FFRStart, idling, engine output, soot emission and driving characteristics are decisively influenced by the injected fuel volume. Ac-cordingly, maps for start, idling, full load, smoke limitation and pump characteris-tics are programmed in the engine control unit EDC (Electronic Diesel Control).
The driver uses the driving pedal to ex-press the desired torque and/or engine speed. The vehicle management compu-ter FFR uses other input variables to cal-culate a specified torque for the EDC con-trol unit and provides this information via the CAN bus. The EDC control unit takes account of the stored maps and actual va-lues of the sensors to determine the injec-tion volume and time of injection and/or
the target value for the control rod position of the injection pump.
All recorded variables can be used as the basis for the diagnosis.
Power take-off controlPower units that are driven by a power take-off from the vehicle engine usually re-quire a defined drive speed. In the vehicle management computer FFR, a number of fixed working engine speeds can be pro-grammed with upper and lower limits, and these can be called up by the driver when a power take-off is engaged.
The vehicle management computer for-wards the engine speed request to the EDC control unit. The requested engine speed is also maintained under load up to each maximum power output. The EDC control unit automatically increases the in-jection volume.
5.60
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5.11
Exha
ust t
ract
5.11
.1E
xhau
st g
as c
ompo
sitio
n
5.11
.1.1
Eng
ine
conf
igur
atio
n x
Exhaust gas composition
Total exhaust gas
N2
CO2
CO
HC
NOx
O2
H2O
Pollutants
Particles
Particles
Soot
Hydrocarbondroplets
Water droplets
Ash, Salts, Rust0 0 0
0,3
20
40
60
80
100%
0,3%
0,05%
0,1
0,2
LEGENDExhaust gas components:– 66 % nitrogen N2
– 12 % carbon dioxide CO2
– 11 % water vapour H2O– 10 % oxygen O2
– <1 % inert gasesSubstance classified as pollutants:– 0.11 % nitrogen oxides NOx
– 0.09 % carbon monoxide CO– 0.06 % hydrocarbons HC– 0.05 % particles
BASIC PRINCIPLES
Exhaust gas compositionIn contrast to the spark-ignition engine, the diesel engine works with excess air. To burn 1 kg of diesel fuel, 14.5 kg of air is required. If the settings of the engine are optimised, this leads to only very little in-completely combusted pollutant compon-ents. The diagram shows the exhaust gas composition of a diesel engine at full load and maximum engine speed (➜ Fig.).
In order to remove the pollutants of the Euro exhaust gas standard for the most part from the exhaust gases and to com-ply with the pollutant limit values, the com-bustion process has to be optimised. This requires engine modifications and a spe-cial exhaust-gas aftertreatment for pol-lutant reduction.
FUNCTION
Combustion chamber designThe design of the combustion chamber in the diesel engine has a major influence on the mixture of air and fuel and thus on the exhaust emissions.
The higher the temperature during com-bustion, the higher the nitrogen-oxide content in the exhaust gases. This means that prechamber engines emit fewer nitro-gen oxides than engines with direct injec-tion. However, direct injection engines consume less fuel, which also leads to lo-wer carbon dioxide emissions.
The combustion temperature also rises with increasing temperature of the intake air. Cooling the charge air on superchar-ged engines (➜ page 5.38) reduces NOx formation.
Fuel injectionThe start of injection, course of injection and atomisation of the fuel also determine the composition of the exhaust gases.
Late injection reduces the NOx emission, but simultaneously increases the HC emission. A deviation of the start of injec-tion from the target value by 1° crank ang-le can increase the NOx or HC emission by 5 % or 15 %. Unburned fuel that enters the exhaust system results in a higher hy-drocarbon content in the exhaust gases.
Fine atomised fuel leads to optimised mi-xing of fuel and air and reduces the hydro-
carbon and soot or particle emission. High injection pressures and favourable geo-metry of the spray holes achieve fine ato-misation of the fuel.
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5.11
.1.2
Exha
ust-
gas
reci
rcul
atio
n
x
Cooled exhaust-gas recirculation on the MAN engine
5
6
4
2
1
3
LEGEND1 Exhaust gas take-off points2 EGR heat exchanger (radiator)3 Pressure peak valve4 EGR shut-off valve5 Intake tract6 Coolant connection
BASIC PRINCIPLES
Exhaust-gas recirculation EGRThe Euro 3 guidelines that came into force in October 2000 require a reduction in ni-trogen oxides (NOx) in the exhaust gas to less than 5 g/kWh. The technical measu-res to adhere to this value lead to higher fuel consumption.
To minimise the increased consumption, MAN Euro 3 engines have been equipped with a cooled exhaust-gas recirculation, EGR, since the Trucknology Generation was introduced.
With exhaust-gas recirculation, part of the exhaust gas is added to the air volume ta-ken in to further reduce the combustion temperature. This measure increases the specific heat of the intake air and reduces the oxygen content.
FUNCTION
Heat exchanger for exhaust-gas coo-lingExhaust gas is routed from two take-off points in front of the turbocharger through separate pipes into a heat exchanger con-nected to the cooling circuit.
The cooled exhaust gas is mixed with the air volume in the intake manifold via pres-sure peak valves that exploit the pulsing pressure of the exhaust gas flow. This re-duces the surplus oxygen of the charge air and increases its specific thermal capaci-ty.
Both influences lower the combustion temperature and thus lower the nitrogen-oxide formation in the exhaust gas. An ad-justment of the time of injection to retar-ded is not necessary, and excessive load on the engine oil due to combustion soot (interior EGR) is avoided.
EDC controlDepending on the engine operating mo-de, the EDC control unit regulates an elec-tropneumatic shut-off flap in the connec-ting pipe between the EGR heat ex-changer (radiator) and the intake manifold. This means that the exhaust-gas recircu-lation is deactivated during a cold start and in the engine braking mode.
Boundaries of engine modifications with EGRWith the current state of the art, the engi-ne modifications for pollutant reduction (➜ page 5.60) in conjunction with externally cooled exhaust-gas recirculation EGR are not yet adequate to comply with the Euro 4 limit values.
For this reason, various additional techni-ques for exhaust-gas aftertreatment are available on MAN vehicles depending on the planned area of application of the commercial vehicle (➜ page 5.63).
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.2So
und
dam
ping
x
Resonator-type and absorption-type mufflers
21
A
B
1 13
4
LEGENDA Resonator-type mufflerB Absorption-type muffler1 Chamber2 Perforation3 Pipe4 Absorbing material
BASIC PRINCIPLES
Exhaust systemIn view of the increasingly strict exhaust gas and noise protection regulations, the exhaust systems of modern commercial vehicles are becoming increasingly impor-tant. Their main tasks are:
Reducing the sound waves that arise during combustion
Safe removal of hot exhaust gases without their entering the interior
Unhindered removal of the exhaust gases without drops in performance
The exhaust system consists of pots and pipes. The pots contain the mufflers. In-most cases, main and auxiliary mufflers are combined. The muffler is the most im-portant component of the exhaust sys-tem. Depending on the function principle, a distinction is made between resonator-type and absorption-type mufflers.
FUNCTION
Resonator-type mufflerA resonator-type muffler consists of chambers of different lengths connected to one another (➜ Fig.). The different cross-sections and deflections lead to damping that is particularly effective for low frequencies. Linking the individual chambers creates resonators. These ensure the mutual elimination of sound waves (interference principle). The greater the number of chambers, the more effi-cient the damping.
Resonator-type mufflers lead to a rela-tively high exhaust counterpressure and are heavy. This means that the very effi-cient sound damping is negated by a rela-tively high power loss. They are frequently used as main mufflers.
Absorption-type mufflerThe absorption-type muffler has only one chamber, through which a perforated pipe runs. The chamber is filled with sound-ab-sorbing material. This absorption material consists of long-fibre, silicon-based mine-ral wool with an apparent density of 120 to 150 g/l.
The sound goes through the perforated pipe and penetrates the absorption mate-rial; the friction converts it into heat. The damping achieved depends on the mate-rial used, the apparent density, the length and the layer thickness of the chamber. The flow resistance of an absorption-type
muffler is lower compared to that of the resonator-type muffler. The absorption-type muffler is usually combined with a re-sonator-type muffler as a rear muffler.
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.3Ex
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t-gas
afte
rtrea
tmen
t5.
11.3
.1G
ener
alx
Possibilities for pollutant reduction in accordance with Euro limit values
0.5
PM[g/kWh]
NOX [g/kWh]
G
SS
Euro 1, 1993
Euro 2, 1996
Euro 3, 2000
0.4
0.3
0.2
0.1
0.02
0.15
02 3.5 4 5 6 7 8 9
Euro 52008
Euro 42005
LEGENDG Limit of pollutant reduction by
means of engine modificationsS Point reached for pollutant reduction
by means of engine modifications (proportion of particles and nitrogen oxides shifts on the limit line)
BASIC PRINCIPLES
Development opportunities for pol-lutant reductionThe increasingly strict Euro pollutant limit values ensure a reduction or limitation of the damaging effect of freight transport on human beings. It was possible to un-dershoot the Euro 3 limit values by optimi-sing or influencing the combustion pro-cess (➜ page 5.60). However, with regard to the even lower limit values of Euro 4 and 5, the limit of pollutant reduction pu-rely through engine modifications has been reached.
In particular, the conflicting objectives of reduced nitrogen oxides and reduced particle emissions makes engine develop-ment more difficult:
High combustion temperatures lead to low particle emissions and low fuel consumption; at the same time, however, the creation of nitrogen oxi-des is promoted. This relationship can be shown in a diagram (➜ Fig.). The achievable pollutant reduction (point S) shifts downwards on the limit line shown (fewer particles, but more nitrogen oxides).
A reduction in the combustion tempe-ratures reverses the effect: the achie-vable pollutant reduction (point S) shifts upwards on the limit line.
This circumstance limits the engine modi-fications on the path towards the nitrogen
oxide and particle limit values of Euro 4 and 5. Additional measures for the after-treatment of exhaust gases will be re-quired.
Technologies for Euro 4With the current state of the art, two solu-tions appear practicable for undershoo-ting the pollutant limit values of Euro 4:
1. Reduction in the nitrogen oxide va-lues by means of externally cooled exhaust-gas recirculation (EGR ➜ page 5.61) in conjunction with ex-haust-gas aftertreatment for reduc-tion of particle emissions (MAN PM catalytic converter system ➜ page 5.65). The advantages of this tech-nology are low weight, low costs and no recourse to additional use of space on the chassis.
2. Increase in the combustion tempera-ture and optimisation of the combus-tion process to reduce particle for-mation. Comprehensive exhaust-gas aftertreatment, in particular to reduce nitrogen oxides, using selec-tive catalytic reduction by means of carbamide (GD catalytic converter ➜ page 5.66). The advantages of this technology are higher efficiency and lower fuel consumption.
At MAN, both techniques are available to customers depending on the desired area
of vehicle deployment. Here, the focal point for vehicles with selective catalytic exhaust-gas aftertreatment will be more in long-distance transport.
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.3.2
Oxi
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onve
rter
x
Oxidation catalytic converter
LEGEND1 Muffler with
integrated diesel oxidation catalytic converter
2 Oxidation catalytic converter modu-les
BASIC PRINCIPLES
Exhaust-gas aftertreatmentCatalytic converters and particulate filters are used in the diesel engines of commer-cial vehicles to reduce unwanted exhaust gas components. In most cases, the follo-wing substances are involved:
Carbon monoxide (CO)
Hydrocarbons (HC)
Nitrogen oxides (NOx)
Soot particles (C)
In simplified terms, oxidation catalytic converters convert damaging exhaust gas components into non-damaging sub-stances by combining them with oxygen (O2). CO is converted into CO2 (carbon di-oxide) and HCs are converted into CO2 and H2O (water vapour). In order to work perfectly, they require low-sulphur diesel fuel with a maximum of 0.05 Vol. % sul-phur.
A combination of oxidation catalytic con-verter and particulate filter is the self-rege-nerating filter system CRT or CRTec (with electronic control).
FUNCTION
Oxidation catalytic converterThe maintenance-free oxidation catalytic converter developed by MAN consists of honeycomb-shaped modules with a large surface, integrated in the mufflers of the exhaust system (➜ Fig.).
As the exhaust gases flow through, the catalytic coating of the oxidation catalytic converter modules leads to chemical re-actions of the damaging exhaust gas components with oxygen. The proportion of unburned hydrocarbons and carbon monoxide in the exhaust gases can be re-duced by 80 % to 90 % in this way. The typical diesel exhaust smell is for the most part suppressed. Moreover, exhaust clou-ding and the emission of particles are re-duced by around 15 %. The NOx propor-tion is not reduced.
CRT filter systemThe letters CRT stand for Continuously Regenerating Trap, i.e. a continuously self-regenerating filter system. It is a com-bination of an oxidation catalytic converter and particulate filter.
The so-called passive regeneration leads to what is for the most part automatic re-moval of soot particles (C) from the filter element. To achieve this, the fact that car-bon (C) can be converted even at relatively low temperatures with nitrogen dioxide (NO2) is exploited. Here, the following fun-damental reaction runs:
2NO2 + C => CO2 + 2NO
In the ESC test program, which is the standard for the exhaust gas classification of the engine, the CRT achieves a reduc-tion in the particle emission of around 80 %; the proportions of carbon monoxide and unburned hydrocarbons are reduced by over 90 %.
At exhaust temperatures that are too low (depending on the operating conditions), the system can reach its function limit.
CRTec filter systemTo safeguard the functional capability, the operating temperature of the CRT must be kept within certain boundaries.
In the case of the CRTec (electronically controlled), an additional control loop has been implemented in the electronic engi-ne control. The interplay of the EGR shut-off valve (➜ page 5.61) and engine pres-sure flap means it able to provide the CRT filter with the required exhaust temperatu-re.
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FUNCTION
MAN PM catalytic converter systemThe PM catalytic converter system is a MAN in-house enhancement of the CRT filter system (➜ page 5.64). The designa-tion "PM-Kat" (PM catalytic converter) is a registered trade mark, protected for MAN. In comparison with the CRT filter system, the soot particle separator section of the MAN PM catalytic converter is configured as an open, non-clogging system.
The PM catalytic converter system re-quires no additional fitting space beyond the existing dimension of the muffler. It will be used at MAN together with the cooled external exhaust-gas recirculation (EGR ➜ page 5.61) as a technical solution to undershoot the Euro 4 limit values for mu-nicipal, freight distribution and local trans-port vehicles.
LEGENDV Pre-oxidation platinum catalytic con-
verterP Soot particle separator
EXAMPLE
Function schema of the MAN PM catalytic converter
Throughflow of the MAN PM catalytic converter
V
V
P
2NO + O2 2NO2
P
2NO2 + C CO2 + 2NO
VP
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Schema of the MAN GD catalytic converter
1 2
10
9
3
Oxidation catalytic converter
SCR catalytic converter
a
4 5
78
6b
c
LEGENDa Exhaust inletb Air supplyc Exhaust (cleaned exhaust gas)1 AdBlue tank2 Temperature sensor3 Fill level sensor4 Delivery module5 Air reservoir6 Air compressor7 Exhaust gas sensor (NOx sensor)8 Exhaust gas temperature sensor9 Metering module10 Control unitOxidation catalytic converter contains:1st stage: Oxidation catalystSCR catalytic converter contains:2nd stage: Carbamide catalyst3rd stage: Reducing catalyst4th stage: Ammonia blocking catalyst
BASIC PRINCIPLES
Selective catalytic reduction SCRTo reduce the NOx content of the exhaust gases from diesel engines, measures for engine configuration (➜ page 5.60), ex-haust-gas recirculation (➜ page 5.61) and in the near future the so-called controlled diesel catalytic converter are used. The SCR method (Selective Catalytic Reduc-tion) applied here has been tried and tes-ted in power station technology.
In contrast to the oxidation catalytic con-verter (➜ page 5.64), the catalytic reduc-tion draws the oxygen out of the dama-ging exhaust gas components to convert them into non-damaging substances. The method is called selective because the re-duction agent ammonia prefers (selec-tively) to react with the oxygen of the nitro-gen oxides.
The GD catalytic converter is an in-house MAN enhancement of the diesel catalytic converter. To obtain a more compact unit, the catalytic converter components are separated and minimised. Sulphur-free diesel fuel is necessary for its operation. The carbamide additionally required as an operating material is available under the designation AdBlue through the network of filling stations that are equipped accor-dingly. Series-standard deployment of the GD catalytic converter is planned for 2005.
FUNCTION
Controlled diesel catalytic converterThe controlled diesel catalytic converter for NOx reduction of the exhaust gases was developed from 1992 onwards by a consortium of the leading European com-mercial vehicle manufacturers, including MAN and Siemens.
The method of NOx reduction using am-monia in one catalytic converter is familiar from power station technology, where it is termed "NOx control". With pure ammo-nia, nitrogen oxide reduction rates of over 90 % are achieved.
However, as handling pure ammonia is hazardous, only harmless carbamide wa-ter is used in commercial vehicles; ammo-nia is only generated from this inside the catalytic converter. Using carbamide wa-ter achieves a reduction in the NOx con-tent in the exhaust gas of up to 60 %. The content of unburned hydrocarbons also falls due to conversion with the remaining oxygen in the exhaust gas. No additional emissions occur.
The concept of the diesel catalytic conver-ter has not been developed to series pro-duction maturity above all due to the poor level of particle reduction. Compliance with the EURO 4 standard would have been possible.
GD catalytic converterThe GD catalytic converter combines the oxidation catalytic converter (➜ page 5.64) and SCR catalytic converter with the corresponding carbamide supply (➜ Fig. below). Cleaning and NOx reduction of the exhaust gas runs in four stages:
1st stage: Oxidation catalytic converter
Reaction of CO, HC, NO and soot partic-les (C) with O2 to create CO2 (carbon dio-xide), H2O (water vapour) and NO2 (nitro-gen dioxide), which are required as star-ting products for the SCR catalytic converter (➜ Fig. page 5.67).
2nd stage: Carbamide catalyst
Formation of NH3 (ammonia) from the in-jected carbamide water.
3rd stage: Reducing catalyst
NOx reduction, i.e. for reaction of NH3 with NO and NO2 to create H2O and N2.
4th stage: Ammonia blocking catalyst
Oxidation of the surplus ammonia.
The GD catalytic converter will enable NOx reduction rates of over 80 %. It is intended to control the system using an NOx sen-sor. The GD catalytic converter and com-bination with a suitable engine can also comply with the particle limit values of the Euro 4 and Euro 5 exhaust gas standards without additional filters.
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FUNCTION
The oxidation catalytic converter con-tains:1st stage: Oxidation catalytic converterfor bonding with oxygen (O2)
soot particles (C),carbon monoxide (CO),hydrocarbons (HC),nitrogen monoxide (NO):2C + O2 => 2CO2
2CO + O2 => 2CO2
2HC + 3O2 => 2CO2 + 2H2O2NO + O2 => 2NO2
The SCR catalytic converter contains:2nd stage: Carbamide catalystfor creation of ammonia (NH3)
carbamide (NH2)2CO),water (H2O):(NH2)2CO => NH3 + HNCO(thermal decomposition at 250 – 450 °C)HNCO + H2O => NH3 + CO2
(hydrolysis)
3rd stage: Reducing catalystto draw off oxygen (O2)
nitrogen monoxide (NO),nitrogen dioxide (NO2),ammonia (NH3):NO + NO2 + 2NH3 => 2N2 + 3H2O
4th stage: Ammonia blocking catalystfor bonding with oxygen (O2)
ammonia (NH3):4NH3 + 3O2 => 2N2 + 6 H2OGD catalytic converter main products:CO2 (carbon dioxide – component of air)N2 (nitrogen – component of air)H2O (water vapour)Residual substances => compliance
with Euro 4 (and 5)
Exhaust-gas aftertreatment in the MAN GD catalytic converter
CO
CO
HC
HC NO
NO
O2
O2
O2
CO2
CO2
C
C
O2
O2
H2ONO2
22
2
22
3
2
2
2
NO
H2O
NH3NO2
N2 3
2
2
(250–450˚C)
CO2
O2
H2O
H2O
NH3
N2
N2
6
4 3
2
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Engi
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12.1
Par
amet
ers
x
Torque of the combustion engine
M = F · r
F
F
r
LEGENDF Pushing power of the pistonM Torquer Radius of the conrod movement
BASIC PRINCIPLES
Engine parametersIn the area of commercial vehicles, the economy of engines plays a decisive role.
The guiding principle is maximum benefit from minimum overhead. Powerful engi-nes that reduce the burden on the envi-ronment to a minimum with low dead weight and the lowest possible fuel con-sumption are in demand.
In order to be able to compare commer-cial vehicle engines, three main parame-ters are used:
Power output
Torque
Specific fuel consumption
The quality of the engine design is also characterised by the variables output-to-weight ratio and power output per litre.
FUNCTION
Engine outputThe power output of an engine is the me-chanical work (➜ page 1.6) it performs within a certain time. It is the product of the determined torque and corresponding engine speed:
The power output is the most important parameter of a combustion engine. It alo-ne determines the possible driving perfor-mance (acceleration and climbing capaci-ty) of a commercial vehicle.
Engine torqueOn a reciprocating engine, the pushing power of the piston is converted via the conrods by the crankshaft into torque (➜ Fig.). High torque in the lower engine speed range is important for good starting performance.
Powerful commercial vehicle engines fea-ture torque characteristics that are as even as possible across the entire rotatio-nal speed range of the engine (➜ page 1.10).
Specific fuel consumptionThe specific fuel consumption indicates how many grams of fuel are required to generate 1 kW of power in one hour.
To determine this, the throughput time of 100 ml fuel is measured at constant engi-ne speed and power output.
Output-to-weight ratioThe output-to-weight ratio of an engine [kg/kW (hp)] refers to the ratios of dead weight and maximum power output. The aim of modern engine design is to minimi-se the output-to-weight ratio.
The first diesel engine had an output-to-weight ratio of 250 kg/hp. A D2876 engine comes to 2.15 kg/hp. This means that it has been possible to reduce the output-to-weight ratio of diesel engines to around 1 % of the original value within 100 years.
Power output per litreThe power output per litre is specified in kW/l.
⎥⎦
⎤⎢⎣
⎡=
minNm
kW9550
nMP
⋅=
5.69
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Performance chart
MAND 2866 LF20
320
300
280
260
240
220
200
180
160
140
120
P
M
be
[kW]
g
kWh
1800
1700
1600
1500
1400
1300
220
210
200
190
180
800 1000 1200 1400 1600 1800 2000 n [1/min]
[Nm]
LEGENDbe Specific fuel consumptionM Engine torquen Engine speedP Engine power output
Note:The diagram uses an obsolete engine as an example.
BASIC PRINCIPLES
Engine performance chartThe characteristics of an engine are de-scribed by the course of the three most important parameters over the entire engi-ne/rotational speed range:
Torque
Power output
Specific fuel consumption
Measuring these variables at individual engine speeds as well as at full load and interpolating the measured values provi-des a continuous course over the entire rotational speed range of the engine. The-se engine characteristic curves enable the evaluation of the performance capability and economy of an engine.
If all three characteristic curves are ente-red in a diagram, a so-called performance chart is obtained.
FUNCTION
Course of torque and power outputWith increasing engine speed, power out-put rises. After surmounting losses due to friction and the greater heat losses at low engine speeds, the engine reaches its maximum torque with optimised charging of the cylinder. As the engine speed incre-ases further, the torque falls due to the ri-sing flow resistances and short valve ope-ning times.
The power output is the product of the torque and engine speed. As the drop in torque takes place more slowly than the increase in engine speed, there is initially another rise in the power output of the en-gine. Diesel engines usually reach their maximum power output at maximum en-gine speed.
Elastic rangeBetween the maximum power output and the maximum torque is the elastic range of the engine. Within this range, with decre-asing engine speed the power output is kept constant by rising torque (➜ page 1.10).
Full-load consumption curveThe specific fuel consumption be is speci-fied in g/kWh. It has to be multiplied by the determined power output to calculate the consumption achieved.
The full-load consumption curve shown in the engine performance chart only reflects
the circumstances at full load, i.e. with the driving pedal pressed down fully. This means it is unsuitable as an indicator of an economical driving style. The fuel-con-sumption map (➜ page 5.70) provides the right information.
The course of the full-load consumption curve in the performance chart can be ex-plained as follows:
in the low engine speed range, the poor mixture of the fuel particles with air leads to unfavourable specific fuel consumpti-on. At high engine speeds, the combusti-on is incomplete, and the fuel consumpti-on also increases. The charging and mi-xing are only optimised at one engine speed point.
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.3Fu
el-c
onsu
mpt
ion
map
x
Fuel-consumption map (engine characteristic chart)
800
PO
1000 1200 1400 1600 1800 2000
8002
4
6
8
10
12
14
16
18
20
200
400
600
800
1000
1200
1400
1600
1800
1000 1200 1400
25 kW50 kW
100 kW
205200195
1600 1800 2000
191 g/kWh
MAND 2866 LF20
n [1/min]
n [1/min]
pme
[bar]M
∆ P ∆ be
[Nm]
LEGENDM Engine torquen Engine speedpme Effective mean piston pressureMarks on curves:∆ b Consumption line distance: 5 g/kWh∆ P Power output line distance: 25 kWP0 Operating point (➜ EXAMPLE)
Note:The diagram uses an obsolete engine as an example.
BASIC PRINCIPLES
Fuel-consumption mapDue to the shape of the lines of the con-stants fuel consumption, the fuel-con-sumption map is also called a "shell chart". It specifies the relationship bet-ween specific fuel consumption, power output, torque and engine speed of a re-ciprocating engine. It is possible to deter-mine the above-mentioned values at eve-ry operating point of the engine.
Reducing the fuel consumption increases the economy of an engine directly and it is thus one of the main aims in the develop-ment of commercial vehicle engines. The consumption map can be used to check the constructive changes to an engine and analyse their effects.
FUNCTION
Partial-load consumption curvesThe fuel-consumption map is limited in an upward direction by the full-load con-sumption curve (➜ Fig.). The partial-load consumption curves are determined and included in the characteristic map. The li-nes of the constants fuel consumption are usually entered at an interval of 5 g/kWh. Furthermore, the consumption map con-tains the curves of constant power output.
The complete engine characteristic chart can be used to determine the operating points that are most favourable as regards consumption.
Looking at the consumption values along the 100 kW line (40 t truck-trailer unit on flat surface at 80 km/h), it can be seen that there is a favourable range between 1000 and 1200 rpm.
Above 1300 rpm, the specific consumpti-on exceeds the 200 g limit and at 1500 rpm it reaches the 205 g line.
The engine characteristic chart indicates the consumption characteristics of the en-gine. The actual consumption, however, cannot be calculated, as while the engine is running there is a continuous change in load (position of the driving pedal) in line with the traffic circumstances.
EXAMPLE
Nonetheless, we want to perform a purely theoretical calculation of the consumption for so-called stationary operation:
40 t truck-trailer unit on flat surface
No headwind
No acceleration
No deceleration
The engine in the example is the MAN D2866 LF20 engine:
The theoretical consumption bth with con-tinuous driving in the same operating point
P0 (be = 200 g/kWh, P = 100 kW)
is:
The value calculated in this way is the lo-west consumption value that can be achieved for a fully loaded 40 t truck-trailer unit.
0.835 kg/l
0.2 kg/kWh 20 kg/h
20 kg/h
⋅bth 100 kW=
bth= =
=
23.59 l/h
80 km/h23.59 l/h
bth=
bth=
= 0.299 l/km
29.99 l/100 km
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5.12
.4Po
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out
put m
easu
rem
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x
Torque measurement with water-flow retarder
1 2 3
4
5
r
F
LEGEND1 Rotor2 Water3 Housing4 Force indicator (dial gauge)5 Force gaugeF Forcer Lever
BASIC PRINCIPLES
Brake horsepowerIn order to be able to make statements about the quality of a commercial vehicle engine, the power output must be ascer-tained. The brake horsepower or net po-wer output is measured. This refers to the power output taken up at the crankshaft or gearbox.
The power dissipation of any gearbox placed in between must be added to the power output value determined.
Torque measurementSince 1988, uniform test conditions have been in force across Europe for power output and torque measurement in accor-dance with Directive 88/195 EEC. Here, all of the power units necessary for opera-tion of the engine must be driven, with the exception of the viscous fan.
Other test standards are ISO 1585 or SAE J 1349. Both standards specify the net power output values. In the case of the SAE gross standard, the measurement is run without air filter, intake muffler, fan and water pump. This results in values that are approx. 10 % above the values of the net measurement.
For all standards and the EEC Directive, the measurements must be made at an outdoor temperature of 25 °C and an air pressure of 1 bar. As the different test lo-cations make these conditions dependent
on the altitude and weather, the actual measured values are converted to the above-mentioned values using correction factors.
The engine to be tested is applied a load by a hydraulic retarder (frictional, water-flow or electric retarder). Multiplying the determined force with the length of the le-ver results in the torque. The correspon-ding power output can be determined by multiplying the torque by the correspon-ding engine speed.
FUNCTION
Water-flow retarderThe crankshaft of the engine drives the ro-tor (fitted with vanes) of the water-flow re-tarder. This rotates in a housing fitted with vanes (➜ Fig.).
The housing is filled with water. The torque is transferred by the water to the housing, which is mounted in pendulum bearings. A lever attached to the housing presses on a force gauge; a dial gauge in-dicates the force determined.
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5.72
5.12
.5En
ergy
bal
ance
of t
he d
iese
l eng
ine
x
Energy balance of a diesel naturally aspirated engine
100 %
1 2 3 4
28 %
25 %
7 %
40 %
LEGEND1 Overall efficiency (usable energy)2 Exhaust gas energy loss3 Thermal energy loss4 Frictional energy loss
BASIC PRINCIPLES
Overall efficiencyModern commercial vehicles engines convince above all with their economy. What percentage of the energy introdu-ced in the form of fuel is available at the crankshaft to drive the vehicle?
In order to be able to assess the economy of combustion engine, a level of efficiency is defined. It is calculated for the energy output and supplied energy. The efficien-cy (also overall efficiency) is a direct indi-cation of the benefit and efficiency of a combustion engine.
The losses that occur during the combus-tion process can be divided into three areas:
Exhaust gas energy loss
Thermal energy loss
Frictional loss
Exhaust gas energy lossOn leaving the cylinder, the high tempera-ture and flow speed mean that the ex-haust gases have high residual energy. On a non-supercharged diesel engine, this energy is lost without being used. Super-charging systems can reduce this by up to 30 % and it then accounts for approx. 28 % of the total supplied energy on modern diesel engines.
Thermal energy lossThermal energy loss arises above all at the walls of the combustion chamber due to cooling of the engine (➜ page 5.24). It is approximately 25 % of the supplied ener-gy.
Frictional energy lossFrictional energy loss occurs in the engine itself and in all of the power units driven by the engine such as the alternator, coolant pump, fan etc. It accounts for approx. 7 % of the supplied amount of energy.
EXAMPLE
The overall efficiency of a combustion en-gine is calculated as follows:
The energy provided by the fuel is, for ex-ample, 6000 KJ. The energy output of 4 KWh corresponds to thermal energy of 15,000 KJ (multiplied by 3600). This re-sults in the following efficiency:
The lost energy in this example is 60 %. Its approximate distribution to individual en-ergy losses is shown in the diagram (➜ Fig.).
Win
Wout=η
0.415000 kJ6000 kJ= = 40 %=η