2. Objective of fuel injection system of CIEs
1. Meter the quantity of injected fuel according to engine load and speed for each cycle.
2. Distribute the metered fuel equally among different cylinders.
3. Inject the fuel at the correct time.
4. Inject the fuel at the correct rate.
5. Fulfil the spray pattern and atomization requirements.
6. Begin and end the injection sharply without dribbling or after-injection.
Requirements
1. Pumping element.
2. Metering element.
3. Metering control.
4. Distributing element.
5. Timing control.
6. Mixing control.
2
3. • Fuel is injected with a pressure ranging from 80 to 300 bars in mechanical injection
systems and up to 3000 bars in electronically controlled ones. Meanwhile the pressure
inside the combustion chamber ranges from 50 to 100 bars. These large pressure
differences are necessary for;
1. Fuel has to enter the combustion chamber at a sufficiently high velocity to achieve
good atomization (break fuel spray into small droplets). Thus, enables rapid fuel
evaporation and mixing.
2. Sweep the combustion chamber in the time available and fully utilize the air charge.
3
5. Main components of fuel injection system in CIEs
1. Fuel tank.
2. Coase (water separator), fine filter.
3. Primary / transfer/ low pressure /
supply / feed / pump.
4. Fuel pump.
5. Injectors.
6. Common rail (in some systems).
Important note
There are two types of fuel injection systems
1. Air injection system.
a) Fuel is forced into the cylinder by means of compressed air.
b) It has good mixing of fuel with the air with resultant higher mean effective
pressure.
c) It is able to utilize high viscosity (less expensive) fuels.
d) The system is obsolete due to the requirement of multistage air compressors.
2. Solid injection system. (focus of the present study) 5
6. 6
Inlet and return pipes
injector
Glow
plug
Main pump
Fuel tank
Primary pump
governor
Injection
timing
Filter
Filling
neck
Air breeze
Drain plug
dividers
Fuel return
Feed pipe
strainer
rheostat
casing
To primary
pump
7. Fuel tank
• Fuel tanks used today can be constructed from aluminum or alloy steel. Baffles are
welded into the tanks during construction. The baffle plates are designed with holes in
them to prevent the fuel from sloshing while the vehicle is moving. The fuel inlet and
return lines should be separated by a baffle in the tank and be at least 30 cm apart to
prevent warm return fuel from being sucked right back up by the fuel inlet line.
Both the inlet and return lines should be kept at least
2.5 cm above the bottom of the tank so sediment or
water is not drawn into the inlet.
• The fuel tank filler cap is constructed with both a pressure
relief valve and a vent valve. The vent valve is designed
to seal when fuel enters it due to overfilling, vehicles.
Gauges
• Most gauge systems include a sending unit in the fuel tank
and a fuel gauge on the instrument panel. The sending unit
is a sliding contact (rheostat) in the tank that moves back
and forth as the position of the float changes. The
resistance in the unit changes as the contact moves.
7
8. Fuel Return Line
• The fuel return line returns fuel to the tank and deposits it into the open space above the
fuel. This allows the air bubbles to be vented. It should also be
inserted to the tank at least 30 cm away from the fuel pickup
point so that the returned fuel will not be picked up before
the air is vented.
Fuel Filters
• Function: to prevent dust and abrasive particles from
entering the pump and injectors hence, minimizing the
wear and tear of the components.
• Diesel fuel filters must be capable of trapping, through a
porous material, extremely small contaminants (in microns).
Diesel fuel filter elements are classified into two
categories of construction, depth filters and surface filters.
Depth filters are made of woven cotton. The common
material used for these filters is cotton thread that is elastic
blended with supporting material. These filters are typically
used as a primary filter and are located between the fuel
tank and the transfer pump.
Surface filters are made of pleated paper made from cellulose fiber. The fiber is treated
with a phenolic resin that acts as a binder. The physical properties of the paper--porosity,
thickness, tinsel strength, basic weight, and micron rating--can be controlled during the
manufacturing process.
8
9. Water separators
• The purpose of a fuel filter is mainly to remove
foreign particles as well as water as it would affect
engine operation. In this case filter is considered
incapable of protecting the system. Hence, most
diesel engine fuel systems are equipped with fuel
filter/water separators for the main purpose of
trapping and holding water that may be mixed in
with the fuel.
Generally, a fuel filter/water separator is used as
the primary filter.
The basic operation of water separators is:
1. The first stage of the fuel filter/water separator uses a pleated paper element to change
water particles into large enough droplets that will fall by gravity to a water sump at the
bottom of the filter.
2. The second stage is made of silicone-treated nylon that acts as a safety device to prevent
small particles of water that avoid the first stage from passing into the engine.
9
10. Fuel Injection Pumps
• Injection pump: to meter and pressurize the fuel for injection.
• Diesel engines are equipped with one of several distinct types of fuel injection systems:
individual pump system; multiple-plunger, inline pump system; unit injector system;
pressure-time injection system; distributor pump system; and common rail injection
system.
Individual Pump System
• The individual pump system is a small pump supplies fuel to one cylinder. The
individual plunger and pump barrel, contained in its own housing, are driven by the
engine’s cam shaft. This system is found on large-bore, slow-speed industrial or marine
diesel engines and on small air-cooled diesels; they are not used on high-speed diesels.
•
10
11. Basic solid injection systems in CIEs
11
Individual-pump system Distributor system Common-rail system
12. PE or PT (in-line) VE (Bosch rotary) 12
single/double acting
primary pump
For 40 to 100 kW/cylinder
maximum power
For less than 30 kW/cylinder
maximum power
Fuel primary/transfer pump: to supply fuel from
the main fuel tank to the injection system.
13. Multi-plunger, Inline Pump System
• In this type individual pumps are contained in a single
injection pump housing. The number of plungers is equal
to the number of cylinders on the engine.
• Plungers are operated by a pump camshaft.
• This system is used on many vehicle applications.
• The fuel is drawn in from the fuel tank by a feed pump,
sent through filters, and delivered to the injection pump at
a pressure. All pumps in the housing are subject to this
fuel. The fuel at each pump is metered, pressurized,
timed, and delivered through a high-pressure fuel line
to each injector nozzle in firing order sequence.
• The pressure-time injection system (PT system) got its
name from two primary factors that affect the amount of
fuel injected per combustion cycle. Pressure, P , pressure
of the fuel at the inlet of the injector. While T stands for
the time available for the fuel to flow into the injector
cup. The time is controlled by engine speed. The metering
time is inversely proportional to engine speed.
13
14. Individual fuel pump - continued
• The axial movement of the
plunger is through camshaft
E, its rotational movement
about its axis by means of
rack D.
• When the plunger is below
port A fuel fills the barrel.
• As the plunger rises, port A
is closed.
• Fuel will flow out through
port C if aligned with helix.
• When rack rotates the
plunger, port C is closed.
• Fuel flows past the delivery
(check) valve through orifice
B to the injector due to the
high pressure developed.
• Injection continues till the
helical indentation on the
plunger uncovers port C.
D
B
A
C
E
14
17. Unit injector
17
• Fuel is brought up to the injector by low pressure
pump, where at the proper time, a rocker arm
actuates the plunger and thus injects the fuel into the
cylinder. Each cylinder has a its own unit injector.
18. Unit fuel injector and its driving mechanism
This type is used in small one- and two-cylinder engines as well
as large-sized engines of more than 100 kW/ cylinder. Primary
pump supplies fuel to all unit injectors through a fuel feed line at
a pressure ranging from 3 to 5 bars.
The unit injector systems times, atomizes, meters, and generates
fuel pressure inside the injector body and supply it to the cylinder
that is mounted on. This system is compact and delivers a fuel
pressure that is higher than any other system.
This system uses a camshaft-operated rocker arm assembly or a
pushrod actuated assembly to operate the
injector plunger.
18
8
9
7
6
5
4
3
2
1
10
1- Spray tip. 2- Bushing.
3- Plunger. 4- Spill deflector.
5- Nut. 6- Retainer.
7- Pin. 8- Rack.
9- Gear. 10-Body.
19. Some types of injector
nozzles
Injector: to take the fuel from
the pump and distribute it in
the combustion chamber by
atomizing it into fine droplets.
Enlarged view of a pintle
nozzle.
Enlarged view of a multi-hole
nozzle.
The Ricardo - CAV Pintaux
nozzle.
19
20. Distributor
Fuel Pump
• The distributor pump systems are used on S- to M- sized
engines. These systems lack the capability to deliver high
volume fuel flow to heavy-duty, large displacement, high-speed
diesel engines like those used in trucks. These systems are
sometimes called rotary pump systems. Main advantages of this
type of pump lies in its small size, light weight, and low cost.
• This pump has only a single pumping element and the fuel is
distributed to each cylinder by means of a rotor.
• A central longitudinal passage in the rotor and two sets of
radial holes (each equal to the number of engine cylinders)
located at different heights.
• One set is connected to pump inlet via central passage whereas
the second set is connected to delivery lines leading to injectors
of the various cylinders.
• The fuel is drawn into the central rotor passage from the inlet
port when the pump plungers move away from each other.
• Wherever, the radial delivery passage in the rotor coincides
with the delivery port for any cylinder the fuel is delivered to
each cylinder in turn.
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26. Electronically Controlled Common-Rail Injection System
The common rail injection is the newest high-pressure direct injection fuel delivery system. An
advanced design fuel pump supplies fuel to a common rail that acts as a pressure accumulator.
The common rail delivers fuel to the individual injectors via short high-pressure fuel lines. The
system’s electronic control unit precisely controls both the rail pressure and the timing and
duration of the fuel injection. Injector nozzles are operated by rapid-fire solenoid valves or piezo-
electric triggered actuators.
Glow plug configurations
1.Terminal.
2.Insulator shin.
3.Housing (locking nut and thread).
4.Glow tube.
5.Element seal (filling powder).
6.Heater and control coil.
26
28. Reasons for diesel knock
As the ignition delay gets longer, the actual burning of the first few droplets is delayed
and accumulation of greater quantity of fuel vapor take place. When burning take place
under such conditions the rate of pressure rise increases and becomes very high
accompanied with and audio noise (knock).
1. Very high rate of fuel injection during the ignition delay period.
2. Very early injection timing.
3. High self ignition temperature (Low cetane number, e.g., high iso-octane number).
4. Low engine temperature (overcooling in cold weather—lack of thermostat in cooling
system).
5. Prolonged idling [resulted in low swirl (bad mixing– high ignition delay) and low
engine temperature].
6. Bad combustion chamber design (location of injector).
28
31. Effect of injection timing and rate of injection
on CIE knock.
31
1.Too early injection timing (knock).
2. Too late injection timing (loss of power).
3.Too high rate of injection (knock).
4. Too low rate if injection (loss of power).
Knock is defined as the rapid increase in the rate of
pressure rise (dp/dφ→∞) accompanied with metallic
audible noise (ping).
32. CIE smoke
1. BLACK SMOKE
Black exhaust smoke is caused by incomplete combustion because of a lack of
air or a fault in the injection system that could cause an excessive amount of fuel in
the cylinders. Items that should be checked include the following.
• Fuel specific gravity (API gravity).
• Injector balance test to locate faulty injectors using a scan tool.
• Proper operation of the engine coolant temperature (ECT) sensor.
• Proper operation of the fuel rail pressure (FRP) sensor.
• Restrictions in the intake or turbocharger.
• Engine oil usage.
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33. 2. WHITE SMOKE.
White exhaust smoke occurs most often during cold engine starts because the fuel
droplets (compare with water vapor condensation on SIEs) within smoke is usually
condensed. The most common causes of white exhaust smoke include:
• Inoperative glow plugs.
• Incorrect injector spray pattern.
• Low engine compression.
• Coolant leak into the combustion chamber.
• Cylinder misfire on a warm engine.
3. GRAY OR BLUE SMOKE.
Blue exhaust smoke is usually due to oil consumption caused by worn piston rings,
scored cylinder walls, or defective valve stem seals. Gray or blue smoke can also be
caused by a defective injector(s).
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34. Rate of discharge and
needle lift and rate of
discharge for
conventional and
common rail fuel
injection
34
Mean press peak press
Start of delivery
Start of
injection
Pilot injection
Main injection
Mean injection press= rail
press.
Injection
pressure
Injection
pressure
Needle lift for main
injection
Needle lift for main injection
Needle lift for pilot injection
Crank shaft angle, °CA, Φ TDC
Cylinder
pressure
Cylinder
pressure
Needle
lift
Needle
lift
Time Time
35. Cetane number (CN)
• The cetane number for diesel fuel is the opposite of the octane number for gasoline.
Cetane rating differs from the octane rating used in gasoline in that the higher the
number of the octane scale, the greater the fuel resistance to self ignition, which is
desirable property in gasoline engines with a high compression ratio.
• The cetane number is a measure of the ease with which the fuel can be ignited. The
higher the rating, the easier the engine will start and the smoother the combustion
process will be. Current diesel fuels named 1D and 2D diesel fuels have a cetane
rating between 40 and 50.
• The cetane rating of the fuel determines, to a great extent, its ability to start the engine at
low temperatures and to provide smooth warm-up and even combustion (1D or D#1).
High altitudes and low temperatures require the use of diesel fuel with an increased
cetane number. Low temperature starting is enhanced by high cetane fuel oil in the
proportion of 1.0°C lower starting temperature for each cetane number increase.
• If an engine runs in a fuel with too low cetane number, there will be diesel knock and
puffs of white smoke in cold weather. Ignition occurs only after the pressure and
temperature have been above certain limits for sufficient time, and fuels with high cetane
numbers are those that self-ignite easily (low SIT).
35
36. Cetane number - continued
• The cetane number of a fuel is defined as the volume percent of n-hexadecane in a
blend of n-hexadecane (cetane) (100) and α-methylnaphthalene
(alfamethylnathalene) (zero) that gives the same ignition delay period as the test
sample.
• For example, a fuel with a cetane number of 40 will perform the same
in the engine as a blend of 40% n-hexadecane and 60% α-methylnaphthalene.
• Another primary reference fuel is heptmethylnonane (15) beside cetane, but with
a different method of calculating CN.
• Cetane number is actually a measure of a fuel’s ignition
delay; the time period between the start of injection and start of combustion
(ignition) of the fuel. In a particular diesel engine, higher cetane fuels will have
shorter ignition delay periods than lower cetane fuels. Cetane numbers are only
used for the relatively light distillate diesel oils.
• CN testing is carried in a standard engine (CLR or CFR) with standard testing
procedure and measuring instruments (ASTM and SAE). Then, the cetane percent
is calculated and assigned to the fuel under test.
36
37. Governor
• A governor is a device that senses engine speed and load, and changes
fuel delivery accordingly. The type of governor used on a diesel engine
is dependent upon the application required.
Function
1. Regulate the amount of fuel delivered at idle to prevent it from stalling.
2. Cut off the fuel supply when the engine reaches its maximum rated speed.
3. Ensure that the amount of fuel injected is in accordance with variation in
load in constant speed engines for power generation and marine vessels.
Reason
The main reason is that a diesel engine operates with excess air under all
loads and speeds.
Location
As governor is directly related to the fuel system by regulating the speed,
hence it would be a part of this system. The governor acts through linkage to control the
fuel injection system to regulate the amount of fuel delivered to the cylinders. As a result,
the governor holds engine speed reasonably constant during fluctuations in load. 37
Governor
Mechanical
Pneumatic
Hydraulic
Servo-
mechanical
Electric
electronic
38. Term Definition
Maximum no-load
speed
The highest engine rpm obtainable when the throttle linkage is moved to
its maximum position with no load applied to the engine.
Maximum full-load
speed
Indicates the engine rpm at which a particular engine will produce its
maximum designed horsepower setting as stated by the manufacturer.
Idle or low-idle speed
Indicates the normal speed at which the engine will rotate with the
throttle linkage in the released or closed position.
Overrun
Expresses the action of the governor when the engine
exceeds its maximum governed speed.
Stability
Refers to the ability of the governor to maintain speed with either
constant or varying loads without hunting.
Speed droop
Expresses the difference in the change in the governor rotating speed
which causes the output shaft of the governor to move from its full-open
throttle position to its full-closed position or vice versa.
Hunting
Is a repeated and sometimes rhythmic variation of speed due to over
control by the governor. Also called speed drift.
38
39. Mechanical governor
• When the two opposing forces are equal, or balanced, the speed of the engine remains constant.
These two forces are the centrifugal force of the rotating weights derived by the engine and the
tension spring/s connected to fuel system through mechanical linkage.
Advantages
1. They are inexpensive
2. They are satisfactory when it is not
necessary to maintain the same (exactly)
speed, regardless of load.
Disadvantages
1. Their power is relatively small unless they are excessively large.
2. They have large deadbands, since the speed measuring device must also furnish
the force to move the engine fuel control. Deadband of governor is the range of speed, only
after which the governor starts responding. Thus, it is inversely proportional to sensitivity.
There should be a limited percentage of deadband to avoid hunting of governor and for stable
operation
3. They have an unavoidable speed droop (speed droop is the decrease in engine speed as the
engine load is raised), and therefore cannot truly provide constant speed when this is needed.
39
40. Hydraulic Governors
• Hydraulic governors have more moving parts and are generally more
expensive than mechanical governors.
• Hydraulic governors can be used in many applications as:
1. They are more sensitive,
2. Have greater power to move the fuel control mechanism of the
engine, and
3. Can be timed for identical speed for all loads.
In hydraulic governors the power which moves the engine
throttle does not come from the speed-measuring device, but
instead comes from a hydraulic power piston, or servomotor.
This piston is acted upon by oil under the pressure of a pump.
With appropriate piston size and oil pressure, the power of the
governor at its output shaft (work capacity) can be made sufficient to operate the fuel-changing
mechanism of the largest engines.
Principle of operation
When the governor is operating at control speed or state of balance, the pilot valve closes the
port and there is no oil flow.
When the governor speed falls due to an increase in engine load, the flyweights move inward,
and the pilot valve moves down. This opens the port to the power piston and connects the oil
supply of oil under pressure. This oil pressure acts on the power piston, forcing it upward to
increase the fuel. The opposite occurs when the engine speed decreases. 40
41. Pneumatic Governor
• The amount of vacuum applied to
the diaphragm is controlled by the
accelerator pedal through the
position of the butterfly
valve in the venturi unit.
• A diaphragm is connected to the
fuel pump control rack.
• Position of the accelerator pedal
also determines the position of the
pump control rack and hence the
amount of fuel injected.
41
42. Fuel Injector
• Fuel injectors atomize the fuel into very fine droplets, and
increases the surface area of the fuel droplets resulting in
better mixing and subsequent combustion
• Atomization is done by forcing the fuel through a small
orifice under high pressure.
• The injector assembly consists of:
1. a needle valve,
2. a compression spring,
3. a nozzle, and
4. an injector body.
• Fuel supplied by the injection pump exerts sufficient force
against the spring to lift the nozzle valve.
• At the end of injection, the spring force pushes the nozzle
valve back on its seat.
• Small quantity of fuel is allowed to leak through the clearance
between nozzle valve and its guide for proper lubrication.
• Valve opening pressure is controlled by adjusting the screw
(spring tension).
42
screw
needle
43. Nozzle
• The nozzle should fulfill the following functions.
1.Atomization: It is important function since it is the first phase in obtaining proper
mixing of the fuel and air in the combustion chamber.
2.Distribution of fuel: Distribution of fuel to the required areas within the combustion
chamber. Factors affecting distribution are:
• Injection pressure:
• Density of air in the cylinder:
• Physical properties of fuel: The properties like self-ignition temperature, vapor
pressure, viscosity, etc .
3.Prevention of impingement on walls: Prevention of the fuel from impinging directly
on the walls of combustion chamber or piston. This is necessary because fuel striking
the walls, decomposes and produces carbon deposits. This causes smoky exhaust as
well as increase in fuel consumption.
4.Mixing: Mixing the fuel and air in case of nonturbulent type of combustion chamber
should be taken care of by the nozzle.
The common types of nozzles are; Pintle, Single hole, multi-hole, and pintaux.
43
