MAIN CHARACTERISTICS OF AERONAUTIC RECIPROCATING ICE ENGINES Subject: Propulsion 02/04/2014 ·Authors: Igual Campos, Javier (832) Oliver del Pozo, Antonio (832) Olmos Milotich, Sergio (832) Palomar Toledano, Marta (832) Vidal Navarro, Daniel (831)
MAIN
CHARACTERISTICS OF AERONAUTIC
RECIPROCATING ICE ENGINES Subject: Propulsion
02/04/2014
·Authors:
Igual Campos, Javier (832) Oliver del Pozo, Antonio (832) Olmos Milotich, Sergio (832)
Palomar Toledano, Marta (832) Vidal Navarro, Daniel (831)
1
INDEX 1.- Historical approach………………………………………..……………2
2.- Evolution of ICE engines in aviation………………………………3
3.- ICE nowadays: geometrical and effective parameters……..4
4.- Comparison with no-aeronautical ICE……………………………6
5.- Bibliography……………………………………………………………….8
6.- Annex………………………………………………………………………..9
2
1. – Historical Approach Reciprocating ice engines have more than a century of history, and they
have experienced an evolution since then. The first reciprocating ice engine can be
dated back to the 18th century with the steam engine. However, the first ever
considered reciprocating ice engine was built up in 1876 thanks to Nicolaus Otto,
who also established the strategy for the development of future ice engines.
The main characteristic we can consider from any reciprocating ice engine is
that they are volumetric machines where the fluid is inside the chamber limited by
moving walls. When these walls move, the fluid modifies its volume. This is a
characteristic they all share with the steam engine.
They had always been considered as complex but functional machines that
were able to produce mechanic energy. Throughout the years, these engines were
better understood, and it was after the commercial production of petrol by the
middle of the 19th century when the improvements and innovations became
important. Then, by the end of this century, there were many different engines
used in several different applications.
In this 19th century we can remark some important scientists who
contributed to the improvement of reciprocating ice engines: Samuel Morey, who
developed the first engine with gasoline or steam without compression (1826);
William Barnet, who invented the first engine that worked with compression
(1838); Sadi Carnot, who released the thermodynamic theory of the thermal
engines (1824); Nikolaus Otto, who patented the first gas engine with 4S cycle and
compression, and he also was the first manufacturer and seller of a gas engine
(1863-1864); Karl Benz, who patented a 2S engine based on the technology of the
4S engine of Bean de Rochas (1879) and he also created his own 4S engine which
he implemented in his cars: first ever cars (1885); Herbert Akroyd Stuart, who
invented the semi-diesel engines that used a system of fuel ignition by pressure
(1891) and Nils Gustav Dalén, who proposed the first gas turbine (1897).
But it was in the 20th century when the use and improvements of the
reciprocating ice engines took place in the field of aviation. The WWI and WWII
meant a huge improvement for the reciprocating ice engines in aviation: it was
then when Robert Goddard launched the first rocket (1926), Frank White patented
the first reaction engine (1930) and Rolls-Royce patented the first aviation engine
with centrifugal compressor and two stages with intercooler and aftercooler (1942).
Figure: 4S
internal
combustion
engine.
3
2. - The evolution of ICE
engines in Aviation The evolution of ICE in aviation followed during a large period of time of
their development the needs of the military aviation of the time.
The use of ICE engines in aviation starts with the first engine powered flight
in 1903 by the Wright Brothers. They used a simple 4-stroke 4 cylinder inline
engine that was used in cars with a displacement of 1655 cc.
On the early days of aviation the type of engines that provided the greatest
amount of power were radial engines in comparison to inline, V, or other type of
engines which were not as developed. For example the Rolls-Royce Eagle V12
engine introduced in 1915 with a displacement of 20 300 cc could only provide 360
hp in its latest version of 1922 whilst at that time a 9 cylinder radial engine such as
the Pratt&Whitney R-1340 Wasp with a very similar displacement (20 000 cc) could
provide up to 600 hp.
So during WWI and before WWII radial engines were more used in aviation
as they were much more developed technologically so they could provide much
more power. Their main problem was the large frontal area they have and as a
consequence the great amount of drag they produced. The objective of engineers at
this time was to improve technologically inline engines as they were much better
aerodynamically. By 1936 we can see a great improvement with the Junkers Jumo
211 35 litre V12 capable of providing 1011 hp. However, radial engines were still
more powerful. For example the 1933 Wright R-1820 9 cylinder radial engine with a
smaller displacement of 30 litres could provide 1000 hp. We can see from the table
in our annex that from 1930 till the end of WWII there was an important tendency
to have supercharged engines capable of providing more power, something
essential for combat aircraft.
By 1938 with the development of the Rolls Royce Merlin engine equipped in
the Supermarine Spitfire we can see that in line engines (V-12 in this case) were
now at their best capable of providing up to 3000 hp with a displacement of 27
litres. Rolls Royce V-12 Merlin engines were one of the most powerful and
sophisticated V-12 engines used in fighter airplanes. The P-51 Mustang, another
mythical airplane also equipped it.
Another type of engine which was very good aerodynamically due to its
short length and capable of providing a great amount of power due to the large
number of cylinders it could have in a reduced space was the H-engine. One of the
first H-engines to be equipped in an aircraft was the one equipped in the Hawker
Typhoon a more sophisticated evolution of the Supermarine Spitfire. It equipped a
24 Cylinder Napier Sabre VA H-engine with a displacement of 36 litres, capable of
providing 3040 hp. This engine became one of the most powerful inline piston
engines in the world. Their development was put aside with the introduction of jet
engines which made the focus of military engine development change direction
from piston engines to jet engines.
Since the end of WWII until today, the evolution of piston engines followed a
different direction as, as it has been previously mentioned, military development
started to focus on jet engines. It can be seen on the table in the annex that the
4
tendency of ICE engines in aircraft since WWII has been that of making smaller and
smaller engines as great amounts of power are not required from them any longer.
This type of engines are now only used in small passenger/leisure airplanes such as
the Cessna 172 which equips a 6-cylinder horizontally opposed piston Continental
O-300, with a displacement of 5 litres and a power output of 145 hp. As it can be
seen in the table the power range for this engines since the end of WWII is from
around 100hp till 400hp, much different from the power outputs we obtained from
the massive V-12 engines used in the war.
If we look at the tendency in the cooling system of the engines we can
observe that at first there was a mixed tendency to use liquid and air cooling. It can
be seen that the big engines capable of providing up to 3000 hp all had liquid
cooling as air refrigeration was not sufficient to dissipate the large amounts of heat
this engines generated. Finally engines nowadays in aviation, due to their small size
and improved technology are most air cooled. In addition we can see that most of
them are natural aspiration engines instead of supercharged engines.
Diesel engines weren’t too successful in aviation. The Packard DR-980 was
the first diesel compression ignition engine to be used in aviation in 1928. It was a
9-cylinder radial engine with a displacement of 16000 cc capable of providing
240hp, significantly less than the petrol engines of similar characteristics of the
time. Nowadays due to their better efficiency and advanced development thanks to
the automotive industry general aviation aircraft are starting to use more this kind
of engines.
3. - ICE nowadays: geometrical
and effective parameters We are not going to distinguish between the cooling system, as nowadays
liquid refrigeration is not used except for some particular applications, being the air
flow cooling the most common.
Regarding the classification between the intake pressures, we can observe
that in aviation, naturally aspired engines suffer a decrease in power as flight level
increases. This is due to the fact that the air density becomes lower with height and
therefore the cylinder air-filling coefficient will decrease as well. To solve this
drawback, supercharged engines make a previous compression of the air,
smoothing the effect of density decrease over the power.
As for the cylinder configuration, the most common one nowadays is the
horizontally-opposed, as it has proved to have better power-to-weight ratios than
the in-line one. The higher power-to-weight ratio is, however, obtained with the
radial configuration, but the frontal area of the engine is higher and makes it
unsuitable for aviation purposes.
Figure: 2S internal combustion engine
5
If we take some examples of actual engines, which are detailed in the
annex, and we stablish relations between geometrical and operational parameters,
we get to the following graphs:
This first one is relating the power per unit cylinder volume (or specific
power) to the total displacement volume. We can observe that the tendency of the
specific power is to decrease when increasing Vt. This means that bigger engines
will show lower specific power, and the way to improve it would be to use
supercharching or change to a 2T. In the graph we can observe a peak of 70 kW/L
which in fact corresponds to the only one diesel engine that has been taken, so it is
accomplished that CI engines have higher specific power than SI. As well, 2T
engines have higher specific power than 4T.
Model Configuration Power-to-Weight
Havilland Gipsy Major In-line 0,78 kW/kg
P&W R-2800 Radial 1,46 kW/kg
Lycoming O-540 Horizontally opposed 1,12 kW/kg
Jabiru 2200 Horizontally opposed 1,07 kW/kg
0 2 4 6 8 10 12 14
0,000
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
Power/Vt vs Vt
Total Displacement Volume (L)
Po
we
r/V
t (k
W/L
)
50 60 70 80 90 100 110 120 130 140
0
1000
2000
3000
4000
5000
6000
7000
8000
Rotational Engine Speed - Bore
Bore (mm)
Ro
tatio
na
l E
ng
ine
Sp
ee
d (
rpm
)
6
Now we have compared the rotational engine speed to the bore dymension,
obtaining that the first one decreases when increasing the second. This means that
engines become slower as their geometrical dymension increases.
In this graph we can see how the efficiency of the aeronautical engines has
been changing along the years. It is increasingly distributed with some picks
belonging to the WWII and its previous years. This was calculated by using the
power per unit of displacement*velocity (rpm).
4. - Comparison with
no-aeronautical ICE ICE engines are not used only in the aeronautical industry, but they are very
important in other sectors where that kind of engine is the only one which is used,
such as the automotive industry.
In general, cars’ ICE have more power and can reach higher rotation speeds
than for aircrafts, although the torque is lower. The reason is that the compression
ratio is higher for the automotive’s ICE than for aeronauticals. Another difference is
that cars’ engines can work at higher temperatures due to their bigger cylinder
heads, while aircrafts cool the engine using the air flow generated by the propeller
which also has the function of engine’s refrigeration.
The ranges of some important functional parameters for SI and CI engines
and for different application fields are shown below:
0
2
4
6
8
10
12
14
16
18
20
1900 1950 2000 2050
BM
EP
Year
BMEP - Year
BMEP
Potencial (BMEP)
7
Ranges of imep:
SI cars → imep(max.) = [8, 14] bar
SI sport cars → imep(max.) = [8.5, 25] bar
SI automotive → imep(max.) = [6, 16] bar
CI 4T industrials → imep(max.) = [5.5, 23] bar
CI 2T low velocities → imep(max.) = [10, 15] bar
Ranges of ηe:
SI → ηe = [0.25, 0.3]
SI industrials → ηe = [0.35, 0.45]
CI → ηe = [0.3, 0.5]
Ranges of Sp at Pmax:
SI cars → Sp = [8, 16] m/s
SI sport cars → Sp = [15, 23] m/s
CI automotive → Sp = [9, 13] m/s
CI 4T industrials → Sp = [6, 11] m/s
CI 2T low velocities → Sp = [6, 7] m/s
Usual ranges of relative fuel/air ratio:
CI → φ = [0.04, 0.7]
SI automotive → φ = [0.9, 1.3]
SI industrial → φ = [0.6, 0.8]
The three first engines of the table are aircraft’s ICE that we have compared
with other internal combustion engines. As we can observe, the geometric
parameter represented by L/B is very similar except in the case of the CI engine of
a ship which is twice higher than for the others. The effective power over the total
volume is a bit lower than the one for the automotive industry but very higher than
the tractor’s or ship’s, just because in the last ones the volume they fill is not so
important. The highest effective power over the piston area is the one for aircrafts.
Finally, as we have said, the rotation speeds of the aircrafts’ ICE are lower than for
the automotive industry but they are higher than the ones for ships and industrial
CI:
8
L/B
imep (bar)
Pef/Vt (kW/l)
Pef/Ap (kW/cm²)
rpm (min¯¹)
Continental IO-240
A 0,9 10 24 0,93 2800
Lycoming R 680
E3A 1,0 12 24 2,29 2300
Pratt&Whitney R 2800 54
1,0 15 34 9,35 2700
SI automotive 4T (1000cc, 4 cyl.)
0,9 10 45 0,25 5800
SI automotive 4T
(2000cc) 0,9 10 50 0,30 5500
SI competition
(400 kW) 0,6 13 140 0,60 12000
CI automotive 4T Indirect injec.
1,1 11 30 0,22 4500
CI automotive 4T
Direct inject. (100 kW)
1,0 13 50 0,30 4500
CI automotive 4T (300 kW)
supercharged
1,1 17 25 0,35 2000
CI tractor 4T (75 kW)
1,2 7 14 0,15 2400
CI industrial 4T (10000 kW) supercharged
1,2 20 8 0,42 520
CI ship 2T (35000 kW) supercharged
2,2 13 2 0,42 70-200
5.- BIBLIOGRAPHY www.wikipedia.org
“Motores de combustión interna alternativos de uso aeronáutico” –
Belinda Joana Villanueva Comunidad – Unidad “Ticomán”
www5.uva.es/guía_docente/uploads/2012/389/51445/1/Documento.
http://www.repositoriodigital.ipn.mx/bitstream/handle/123456789/8
003/TESINA-TERM-001.pdf?sequence=1
9
6.- ANNEX Next annex contains data of 76 different engines used in aeronautics.
Since the grid is too big, it is distributed in groups two groups of 25
engines and one las group of 26; each group on each sheet of paper.
The data we have collected from each engine is (in order):
Name of the engine
Year when started operations
Manufacturer
Example of an airplane that is equipped with this engine
The type of ignition process and kind of fuel
The cylinder arrangement and the working cycle
Type of Cooling system
Type of Intake pressure
Value of the stroke
Value of the bore
Power (hp or kW)
Compression ratio
Displacement
Bibliography