Alexandria University Faculty of Engineering Marine and Naval Architecture Department Modern Diesel Engines Presented to: Prof . Dr : Mosaad Mosleh By: Eng: Walaa Morgan Ebied Eng: Noha Hassan
Alexandria University
Faculty of Engineering
Marine and Naval Architecture Department
Modern Diesel Engines
Presented to:
Prof . Dr : Mosaad Mosleh
By:
Eng: Walaa Morgan Ebied
Eng: Noha Hassan
Modern Diesel Engines
The internal combustion engine (ICE) finds its place in the market with latest
design modifications in various components to improve efficiency, economy and
overall performance .However, one component has remained unchanged in the
internal combustion engine development i.e., the camshaft ,has been the primary
means of controlling the valve actuation and timing, and therefore, influencing the
overall performance of the vehicle. Camless technology is capturing the future of
internal combustion engines.
It has been known to man that if valves could be controlled independently in an
Internal Combustion Engine then there would be benefits like increased power,
reduced emissions and increased fuel economy. In the camless technology valve
motion is operated by valve actuators of electro-mechanical and electro-hydraulic
type.
The other type of modern diesel engines is dual fuel engines
Dual Fuel engine
What is Dual Fuel engine?
A dual fuel engine burns both diesel and natural gas at the same time.
It differs from a Bi-fuel engine in so much that a Bi-fuel engine will run on one type
of fuel or another, not two fuels simultaneously as is the case with dual fuel.
The four stroke cycle is maintained as with a standard diesel engine. The only
difference is that the gas is injected directly into the cylinder while the inlet valves
are open and the engine is drawing in air. As a result a homogonous mix of gas
and air is present when the inlet valves close.
Dual Fuel engine operation
The gas is mixed with air before compression starts, a gas pressure of about 5 bar
is sufficient. This gas pressure is in the same range as the gas pressures in steam
turbine installations. Close to top dead- centre a very small amount of MDO is
injected in order to trigger ignition. On pilot injection, a flame is created which
then ignites the main air/fuel mixture in the main combustion chamber. Ignition
timing is thus directly controlled via injection timing of the pilot fuel.
1.The Air and gas enter the cylinder
The Air and gas mixture is compressed
The piston begins to move back up the cylinder on
the compression stroke, prior to the piston
reaching TDC the reduced amount of diesel is injected.
2. Diesel Fuel is injected into the cylinder
As the piston reaches TDC a reduced amount of
diesel fuel is injected to be utilized as the source of ignition.
3. The air and gas mixture combusts as a Result of the diesel
injection
This reduced diesel injection is sufficient to act as the ignition
catalyst and thus, combustion of the air and gas mixture
together with the diesel takes place.
4. The burnt mixture exits the cylinder as normal on the
exhaust stroke
The exhaust stroke remains unchanged and the exhaust gases
exit the cylinder as normal.
Following main modifications are made in the diesel engines
considering the use of gas as fuel:
Gas admission to each cylinder by individual valves.
Charge air and exhaust manifolds equipped with pressure relief valves to
avoid any gas operation risks.
Common rail system for pilot fuel oil injection integrated in the cylinder
head. The pilot fuel quantity is controllable by the injection system.
Separate conventional fuel system for liquid fuel mode.
A specially designed DF engine management system for the whole
operating range.
The basic design difference between a conventional diesel engine and a
dual fuel engine lies in the fuel injection systems.
Features of Dual Fuel Engine:
Less operation cost
→ Main fuel : Natural Gas
Environmental friendly
→ Drastic reduction of NOx, SOx & CO2 emission
Stable operation
→ Pilot injection system
→ Operatable on either fuel of natural gas or diesel oil
Excellent dependability
→ Main component : Diesel engine
Clean combustion and Less maintenance cost
Effective utilization of existing assets
Diesel fuel oil injection:
The diesel fuel oil supply system on the engine is divided into two systems.
Pilot Fuel Injection System:
The pilot fuel is raised to the required by a pump unit incorporating duplex filters,
pressure regulator and engine driven radial piston type pump. The high pressure
pilot fuel is then distributed through a common rail pipe to the injection valve at
each cylinder. The pilot fuel injected at around 900 bars pressure and the timing
and duration are electronically controlled. The individually controlled solenoid
valve allows optimum timing and duration of pilot fuel injection into every
cylinder when the engine is running in gas mode.
Main Diesel Fuel Oil Injection System:
The main diesel oil fuel is fed to a normal camshaft driven injection pump by
which it is pumped at high pressure to a spring loaded injection valve of standard
design for a diesel engine. The larger needle of the twin-needle injection valve is
used in diesel engine mode and the smaller needle for pilot fuel oil when the
engine is running in gas mode. Main diesel engine is hydro mechanically
controlled.
Schematic Diagram for DF
CAMLESS ENGINES
-Cam is a rotating machine element which
gives reciprocating motion to the follower.
-The motion of the follower is pre-determined
and accordingly the Cam is designed.
-The cams are normally placed on a fixed
camshaft which is then geared to the crankshaft.
-Movement of inlet and exhaust valves of Conventional Four Stroke IC Engine with
the help of Cam.
Conventional Valve train
It is fixed to deliver only one specific cam timing. The cam lobes
have to be shaped such that when the valve travels up and down at the engines
maximum speed it should still be able to slow down and gently contact the valve
seat. The valves crashing down on their valve seats results in an engine that is real
noisy and has a short life expectancy. Having different cam profiles will result in
different engine characteristics. While high-rpm power and low rpm-torque can be
each optimised, acompromise is required to obtain the best of both in the same
engine. With Variable Valve Timing (VVT) technologies the compromise is getting
better and better -reasonable low down torque and high-speed power .
Disadvantages Of Conventional Valve train
Increased frictional losses
Cam profile is fixed
Noise
Overview Of Camless Engine
Mainly Five Sensors are present,which senses;
Speed of the engine.
Load on the engine.
Exhaust gas Sensor.
Valve position Sensor.
Current Sensor.
Sensors sense parameter & Send signals to (Electronic Control Unit ) ECU
ECU contains microprocessors with associated software
This ECU controls the actuators to work according to requirements
Microprocessors are present in ECU to issue signals and control the Actuators.
Actuators
It is electro_hydraulic camless valve train (ECV)
Uses elastic property of compressed hydraulic fluid which acts like a liquid spring ,
accelerates & decelerates the valves
Types of Camless Mechanisms
I. Electromechanical Poppet Valves.
II. Electromechanical Ball Valves.
III. Electrohydraulic Poppet Valves.
I. Electromechanical Poppet Valves
Early systems magnetic attraction/repulsion was used on an iron or ferromagnetic
armature
Varying Air Gaps which lead to high energy losses and High Seating Velocities
which made varying of the lift difficult.
It is replaced with a current-carrying armature coil. A magnetic field is generated by a magnetic field generator and is
directed across the fixed air gap.
The force generated on the armature coil drives the armature coil
linearly in the air gap in a direction parallel with the valve stem.
Depending on the direction of the current supplied to the armature coil,
the valve will be driven toward an open or closed position.
II. Electromechanical Ball Valves
An alternative to the conventional poppet valve for use in camless valve trains is
a ball valve. This type of electromechanical valve system consists of a ball through
which a passage passes. If the ball is rotated such that the passage lines up with
other openings in the valve assembly, gas can pass through it. Opening and closing
the valve is accomplished by electromagnets positioned around its exterior
Referring to the following figure
The valve housing (7) is shown in two pieces. Ball valve (8) has two rigidly attached
pivots (12). the ball valve needs only to rotate on its axis to achieve the desired
flow conditions, rather than be accelerated up and down in a linear fashion. A
partially open ball valve state may also be able to be used to create more
turbulence disc (10) is permanently attached and indexed to the ball
valve and contains permanent magnets around its perimeter. The electromagnets
(11) are situated on both sides of the ball valve (8) and they are fixed to the valve
housing. The electromagnets are controlled through the ECU. A crank trigger
sensor on the crankshaft provides information about the position of the pistons
both electromagnets so that they are of opposite polarity to the magnets in
the ball valve, rotating the ball valve to the closed position.The substitution of a
simple,efficient ball valve and valve housing arrangement in a four stroke
reciprocation piston engine eliminates all the independent moving parts in the
valve train. This may even be an improvement over the poppet valve camless
system.
III. Electro-hydraulic Poppet Valves
The engine poppet valves (22) and the valve springs (24) that are used to reset
them are shown. The poppet valves are driven by hydraulic actuators (26),
which are controlled by electrically operated electro-hydraulic valves (28)
supplying hydraulic fluid to the actuators via conduit (29). The preferred hydraulic
fluid is engine oil, supplied to the electro-hydraulic valves by the pressure rail (30).
An engine-driven hydraulic pump (32) supplies the oil pressure, receiving the oil
from the engine
oil sump (34). The pump output pressure is also limited by an unloader valve (36),
as controlled by an accumulator (38) connected to the oil pressure rail.
With this design the hydraulic pump could be periodically disconnected, such as
under braking, so that the valve train would run off the stored accumulator
hydraulic pressure. As is the trend with all modern engine systems, the camless
engine has an even greater reliance on sensors. The valve actuation and control
system typically needs a manifold pressure sensor, a manifold temperature
sensor, amass flow sensor, a coolant temperature sensor, a throttle position
sensor, an exhaust gas sensor, a high resolution engine position encoder, a
valve/ignition timing decoder controller, injection driver electronics, valve coil
driver electronics, ignition coil driver electronics, air idle speed control driver
electronics and power down control electronics. A valve developed by Sturman
Industries is said to be about six times faster than conventional hydraulic valves.
To achieve such speeds, it uses a tiny spool sandwiched between two electrical
coils. By passing current back and forth between the coils, a microprocessor-
based controller can quickly move the spool back and forth, thereby actuating the
engine valves in accordance.
Advantages of Camless Engines
Infinitely variable valve timing.
More torque is made available throughout the rev-range.
Increases durability and engine life.
Valve train weight which limits the rotational speed at which the engine can
operate is reduced.
Increases engine performance.
Decreases fuel consumption
Decreases harmful emissions
The efficiency of a camless engine would be 20% greater than a comparable
camshaft-operated engine.
Disadvantages of Camless Engines
1. Relatively high cost (cost of microprocessor & software control)
2. Power consumption (opening & clothing of valves require some power)
3. Noise and vibration
Questions
Q1) With the aid of a neat sketch Explain the Operation of the Dual
Fuel engine . page 3,4
Q2) Diesel engines can be modified and uses as Dual Fuel engines
what are these modifications? page 5
Q3) The diesel fuel oil supply system on the engine is divided into
two systems , Explain the two systems. Page 6
Q4) Draw Schematic Diagram for Dual fuel engine . page 7
Q5) There are three types of Camless Mechanisms , Define them,
and Explain briefly one type. page 10,11,12.13