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Lecture 3 10/03/2012
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Diesel engine applications
To derive mobile power generator (up to 10 kW/cylinder)
Cars and light commercial vehicles ( up to 50 kW/cylinder)
Construction industry and agricultural machinery (up to 50 kW/cylinder)
Heavy trucks and tractor vehicles (up to 80 kW/cylinder)
Fixed installations such as emergency power generator (up to 160 kW/cylinder)
Railway locomotives and ships (up to 1000 kW/cylinder)
Diesel History
The Diesel Engine
“.... an internal combustion engine in
which air is compressed to a temperature
sufficiently high to ignite fuel injected
into the cylinder where the combustion
actuates a piston.”
Typical DI Chambers
Heavy duty - 4-valve,
central injector, low swirl,
wide shallow bowl Light duty - 4-valves, central
vertical injector, high swirl,
deep narrow bowl
Spray Outline
Diesel Combustion
Fuel sprayed in cylinder near TDC
Atomization, vaporization & mixing delay ignition
Ignition occurs wherever conditions right (1000 F)
Combustion rate controlled by injection
characteristics (injection rate, spray angle,
injection pressure, nozzle size and shape),
chamber shape, mixture motion, & turbulence
Glow plug may be used to aid cold starting
Power output controlled only by amount of fuel
injected
MAXIMUM SPECIFIC POWER & BMEP
COMPARISONGASOLINE vs DIESEL
0
5
10
15
20
25
30
35
40
45
50
0 1000 2000 3000 4000 5000 6000 7000
SPEED, r/min
PO
WE
R,
kW
/L &
BM
EP
, b
ar
BMEP-GAS
POWER-GAS
POWER-DIESEL
BMEP-DIESEL
COMPARISON OF FUEL CONSUMPTIONDIESEL & GASOLINE @ 2500 r/min
BSFC vs BMEP
150
200
250
300
350
400
450
500
550
600
0 2 4 6 8 10 12 14 16
BMEP, bar
BS
FC
, g
/kW
h
Gasoline
DI-Diesel
Compression Ratio
The diesel engine compresses at a very high ration of 14:1 to 25:1.
The higher the compression ratio, the more power is generated.
The main limiting factor to compression ratio is based on the knock limits of the fuel.
Knock is the term used to describe the auto ignition that occurs when a fuel ignites because the pressure in the cylinder is such that combustion occurs.
The knock limit of the fuel is determined by the point at which the engine begins to shake.
The higher the knock limit, the higher the compression ratio, the more power is generated
Dr. Walid Abdelghaffar
DIESEL ENGINES
Dr. Walid Abdelghaffar
A typical injector-pump-type automotive diesel fuel injection system
DIESEL ENGINES
A typical injector-pump-type automotive diesel fuel injection system.
Basic Parts Of A Diesel Fuel System
Injection nozzles
Injection pump
Filters
Transfer pump
Fuel tank
Dr. Walid Abdelghaffar
HOW AN ENGINE WORKS:
Dr. Walid Abdelghaffar
DIESEL ENGINES
The diesel engine requires compression ratios of 14:1 and higher.
Incoming air is compressed until its temperature reaches about 1,000°F (540°C).
This is called heat of compression.
As the piston reaches the top of its compression stroke, fuel is injected into the cylinder, where it is ignited by the hot air
Diesel combustion occurs when fuel is
injected into the hot, highly compressed
air in the cylinder.
DIESEL ENGINES Indirect and Direct Injection
In an indirect injection
(IDI) diesel engine, fuel is
injected into a small pre-
chamber, which is
connected to the cylinder by
a narrow opening.
The initial combustion takes
place in this pre chamber.
This has the effect of
slowing the rate of
combustion, which tends to
reduce noise.
Dr. Walid Abdelghaffar
An indirect injection diesel engine uses
a pre chamber and a glow plug.
DIESEL ENGINES Indirect and Direct Injection
Dr. Walid Abdelghaffar
direct injection diesel
engine injects the fuel
directly into the combustion
chamber. Many designs do
not use a glow plug.
ENGINE-DRIVEN VACUUM PUMP
Because a diesel engine is un throttled, it creates
very little vacuum in the intake manifold.
Several engine and vehicle components operate
using vacuum, such as the exhaust gas
recirculation (EGR) valve and the heating and
ventilation blend and air doors.
Most diesels used in cars and light trucks are
equipped with an engine-driven vacuum pump to
supply the vacuum for these components.
Dr. Walid Abdelghaffar
Durability
Diesel engines are also capable of running high miles
without major engine work.
Truck diesel engines can run 250,000 or even 500,000
miles without major engine work.
In 1978, Mercedes-Benz launched a “Great Diesel
Search” to find the highest mileage diesel in the United
States.
Robert O’Reilly drove his 1957 Mercedes-Benz 180D
1,184,000 miles, 750,000 on its original engine.
Another owner drove his 1968 Mercedes-Benz 220 D
912,000 miles, 902,000 miles on its original engine.
Efficiency One positive aspect of the diesel engine is that
they are thermally efficient.
The improved efficiency is caused by the
relatively high compression ratios
The diesel engine is 54% thermally efficient,
while gasoline engines are only 34%.
As a result of diesel engines thermally efficiency,
they are able to achieve better gas mileage
because they produce greater horsepower
output for fuel intake.
Main Differences of Gasoline and Diesel
The main difference between a gasoline engine and a diesel engine is that in a diesel engine, there is no spark plug to ignite the fuel.
Diesel fuel is injected into the cylinder, and it ignites spontaneously as the heat and pressure of the compression stroke cause the temperature inside the cylinder to increase.
The other major difference between the two types of engines is in the gas mileage.
As a result of diesel fuel having a higher energy density than gasoline, diesel engines get higher gas mileage.
Dr. Walid Abdelghaffar
Fuel supply system (low pressure stage)
Fuel Supply system (low-pressure stage)
The job of the fuel supply is to store the fuel required, to filter it and to supply it to the fuel-injection installation at a specific supply pressure under all operating conditions. For some applications, the fuel return is also cooled
1. Fuel tank
2. Preliminary filter
3. Control unit cooler
4. Pre-supply pump with non-return
valve
5. Fuel filter
6. Main pre-supply pump
7. Pressure control valve
8. Fuel distributor line
9. Fuel cooler
FUEL TANK AND LIFT PUMP
A fuel tank used on a vehicle equipped with a diesel engine differs from the one used with a gasoline engine in several ways, including:
A larger filler neck for diesel fuel.
No evaporative emission control devices or charcoal (carbon) canister.
The diesel fuel is drawn from the fuel tank by a lift pump and delivers the fuel to the injection pump.
Between the fuel tank and the lift pump is a water-fuel separator.
Water is heavier than diesel fuel and sinks to the bottom of the separator.
Fitted far the engine for no ignition in accidents
Should be corrosion resistance and leak-proof to a pressure equivalent to double the system pressure and at least 30 kPa
Should have Pressure relief vents or valves
Dr. Walid Abdelghaffar
DIESEL INJECTOR NOZZLES
Diesel injector nozzles are spring-loaded closed valves
that spray fuel directly into the combustion chamber or
pre combustion chamber.
Injector nozzles are threaded into the cylinder head, one
for each cylinder, and are replaceable as an assembly.
The top of the injector nozzle has many holes to deliver
an atomized spray of diesel fuel into the cylinder.
Parts of a diesel injector nozzle include:
Heat shield.
Injector body.
Diesel injector needle valve.
Injector pressure chamber.
Dr. Walid Abdelghaffar
DIESEL INJECTOR NOZZLE OPERATION
The electric solenoid
attached to the injector
nozzle is computer
controlled and opens to
allow fuel to flow into
the injector pressure
chamber
Dr. Walid Abdelghaffar
Typical computer-controlled diesel engine
fuel injectors
GLOW PLUGS
Glow plugs are always used in diesel engines
equipped with a pre-combustion chamber and may
be used in direct injection diesel engines to aid
starting.
A glow plug is a heating element that uses 12
volts from the battery and aids in the starting of a
cold engine.
As the temperature of the glow plug increases, the
resistance of the heating element inside increases,
thereby reducing the current in amperes needed
by the glow plugs.
Dr. Walid Abdelghaffar
Can be metal line or flexible
Fire resistant lines
Avoid contact with the moving parts
Leakage fuel should not collect or ignite
Far from the heating source
Should not gravity fed
Must not be routed through the passenger compartment
Fuel lines
Diesel fuel filter The job is to reduce the
contamination of the fuel by suspended particles
Must capable of accumulating a quantity of particles
Preliminary filter is a strainer type filter (300 m)
Main filter: easy-change, two in parallel
Water separator: water removed by a discrete separator after collection in an accumulation chamber.
Fuel preheating: using electrical heater, engine coolant, or recirculation fuel, to prevent clogging of the filter
Should give adequate supply of fuel to the high
pressure components:
1. Irrespective of operating state
2. With a minimum of noise
3. At the necessary pressure
4. Throughout the vehicle’s complete service life
Manual priming pumps
Prime and vent the system after changing the filter
Fuel pre-supply pump
Fuel-supply pump types
Electrical
fuel pump
Gear fuel
pump
Vane
type
pump
Tandem
pump
Distributor tube: in Unit injector system to ensure the same quantity to each injector.
Low-pressure control valve: installed in the fuel return of the UIS and UPS to ensure adequate operating pressure in the low pressure stages so that the pumps are always filled with fuel.
ECU Cooler:
In commercial vehicles for the ECU of the UIS and UPS. Fuel is used as a cooler and passed through cooling channels
Fuel cooler: fuel return from the high pressure pump should be cooled to avoid damage to the fuel tank and level sensor. Connection to the engine cooling system should not affect the fuel cooling.
How Is Engine Speed Controlled In A Diesel Engine?
Dr. Walid Abdelghaffar
The throttle control regulates only the amount of
fuel injected into the cylinder
The throttle control in a gasoline engine regulates
the amount of air/fuel mixture allowed into the
cylinder
How Are Diesel Engines Stopped?
Dr. Walid Abdelghaffar
By shutting off the fuel to the cylinders
by a manual control or solenoid switch
Gasoline engines are stopped by
cutting off the spark from the spark
plugs to the cylinders
High Pressure Systems 1. In-line fuel-
injection pumps
2. Distributor injection pumps
3. Common-rail (CR) system
4. Discrete cylinder systems
Unit injector system
Unit pump system