FUEL CYCLE IN DIESEL ENGINE
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.”
Roger Krieger, GM R&D Center
Diesel Fuel
If you have ever compared diesel fuel and gasoline,
you know that they are different.
They certainly smell different.
Diesel fuel is heavier and oilier.
Diesel fuel evaporates much more slowly than gasoline
-- its boiling point is actually higher than the boiling
point of water.
You will often hear diesel fuel referred to as "diesel oil"
because it is so oily.
Diesel fuel evaporates more slowly because it is
heavier.
It contains more carbon atoms in longer chains
than gasoline does (gasoline is typically C9H20,
while diesel fuel is typically C14H30).
It takes less refining to create diesel fuel, which is
why it is generally cheaper than gasoline.
DIESEL FUEL
Diesel fuel must meet an entirely different set of
standards than gasoline.
The fuel in a diesel engine is not ignited with a
spark, but is ignited by the heat generated by
high compression.
All diesel fuel must be clean, be able to flow at low
temperatures, and be of the proper cetane
rating.
Cleanliness.
Low-temperature fluidity.
Cetane number.
Diesel Fuel Characteristics
Cetane number
Measure of relative ease to initiate combustion
Higher number: easier to ignite
Octane number for gas: opposite
Higher number: less tendency to ignite
Cetane Number
Ignition quality measure
Affects: cold starting, warm-up, combustion roughness,
acceleration, and exhaust smoke density
Cetane number is based on the ignition characteristics of
two hydrocarbons:
Cetane - short delay period and ignites readily (100)
Alphamethylnaphthalene (AMN) - long delay period and poor
ignition quality (0)
It is the percentage by volume of normal cetane in a blend
with AMN
PC engines require a minimum cetane no. of 35
DI engines require a minimum cetane no. of 40
Cetane Number
High cetane number indicates good ignition quality
(short delay period)
Low cetane number indicates poor ignition quality
(long delay period)
PC engines require a minimum cetane # of 35
DI engines require a minimum cetane # of 40
Cetane improver additive can improve ignition quality
and reduce white smoke during start up
FUEL CYCLE
Fuel Injection In CI Engines
Cylinder Pressure
Diffusion Combustion smoke
Rapid Combustion knock
Delay Period
Fuel Injection In CI Engines
7% decrease in air density per
1000m altitude
Fuel injection system has to
compensate for air density to
minimize smoke output
Less air means less fuel required
FUEL FILTERS
The fuel filtration and water separation needs of
today's new generation
diesel fuel systems demand extremely high
efficiency, flexibility, multiple
functions and ease of use with no risk of fuel spills
or contaminated parts.
Stan dyne's patented Fuel Manager® range of
Available for light, medium and heavy duty
trucks; and agricultural,
industrial, construction and marine applications,
there is a Fuel Manager
The FM10 Series is designed for diesel engines
with a fuel flow rate up
to 50 US gallons/hr (190 liters/hr). Typical
engines range from 10 to 200 HP
The FM100 Series is designed for diesel engines
with a fuel flow rate up
to 80 US gallons/hr (300 liters/hr). Typical
engines range from 50 to 350 HP.
The FM1000 Series is designed for
diesel engines with a fuel flow rate
up to 180 US gallons/hr (680 liters/hr).
Typical engines range from 200 to
Types of filters
Fuel pump
 The ‘traditional’ style of injection pump is the inline pump. They have been used for many
 decades and are still commonly found on
agricultural and stationary diesels, and very
many older
 model diesel road vehicles still employ them,
including the Toyota Landcruiser 2H diesel.. They
 are typically capable of generating injection
nozzle pressures up to about 750 bar in light road
 vehicles – towards the lower end of the range
that is required these days.
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They have a separate pump plunger for each
cylinder of the engine, so a 4 cylinder engine
has a four plunger pump, a 6 cylinder engine
has a six plunger pump, etc. The pump is run at
half engine crankshaft speed and has a central
shaft with four/six etc. cam lobes attached. So,
each plunger is operated by it’s cam once every
two crankshaft revolutions, coinciding of course
with the power stroke of its engine cylinder.
Each plunger has a spiral groove or helix
machined on it’s side and cut through to the top
of the plunger. When operated, the plunger is
pushed up by its cam lobe. At a certain point
the spiral groove will line up with a spill port on
the side of the plunger cylinder and the rest of
the fuel is ‘spilled’.
 Because the groove is a spiral shape, the
point in the plunger stroke when it uncovers
the spill port
 will vary as the plunger is rotated a few
degrees either way. This adjusts the spill point
and hence,
the volume of its fuel charge to the engine 
cylinder.
 So that all engine cylinders receive the same
sized fuel charge, all of the plungers are rotated
 together. This is achieved by each plunger having
gear teeth machined to it’s circumference which
 are engaged by a common gear rack which runs
through the pump body. As the rack moves back
 and forth, all four (or six or more) plungers are
rotated together. The extremes of travel of the
 pump rack control the minimum and maximum
fuel charge quantities the pump is capable of
PRE SUPPLY PUMP
The electric fuel pump comprises of:
1.Electric Motor
2.Roller-Cell Pump
3.Non Return Valve
PRE SUPPLY PUMP
The roller cell is 
driven by an electric
motor.
Its rotor is mounted 
eccentrically and
provided with slots in
which movable rollers
are free to travel.
PRE SUPPLY PUMP
The rollers are forced
against the base plate
by rotation and by fuel
pressure .
The fuel is transported
to the outlet openings
on the pump’s
pressure side.
PRE SUPPLY PUMP
variants
Gear type fuel pump
The drive gear wheel
is driven by the
engine .
Delivery quantity is
directly proportional
to engine speed .
Shut off is by means
of an electromagnet..
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High- pressure pump
The pump plunger moves downwards ë
The inlet valve opens ë
The fuel is drawn in to the pumping element ë
chamber(suction stroke)
High- pressure pump
At BDC, the inlet valve closes ë
The fuel in the chamber can be compressed by the ë
upward moving plunger.
High- pressure accumulator
(Rail)
Store fuel
Prevent pressure fluctuations
High- pressure accumulator (Rail)
Rail is a forged-steel tube.
ID is approx.. 10mm
Length is between 280 and 600mm
The volume must be “ as small as possible, as
large as necessary”
Pressure-control valve (DRV)
Responsible for 
maintaining the
pressure in the
rail at a constant
level.
Fuel Injector
The injector on a diesel engine is its most complex
component and has been the subject of a great
deal of experimentation -- in any particular
engine it may be located in a variety of places.
The injector has to be able to withstand the
temperature and pressure inside the cylinder
and still deliver the fuel in a fine mist.
Getting the mist circulated in the cylinder so
that it is evenly distributed is also a problem,
so some diesel engines employ special
induction valves, pre-combustion chambers
or other devices to swirl the air in the
combustion chamber or otherwise improve
the ignition and combustion process.
CI Engine Combustion
Chambers
Two types: 
Indirect (divided 
chamber) injection - into
a pre-combustion
chamber
CI Engine Combustion
Chambers
Two types: 
Direct injection - into 
cylinder
Combustion Chamber
Comparison
Indirect 
Good 
Excellent mixing, turbulence characteristics 
Can burn lower quality fuel 
Lower injection pressure 
Less pronounced knock 
Combustion Chamber
Comparison
Indirect 
Bad 
Very high temperature/pressure in injection 
chamber
Higher emissions, especially NOx 
Harder to start - glow plugs 
Less efficient 
Combustion Chamber
Comparison
Direct 
Bad 
Pressure rise can be great, 
knock
High injection pressure, high 
quality fuel
Combustion Chamber
Comparison
Direct 
Good 
Lower specific fuel consumption - 
20%
Lower emissions 
Bigger valves, higher volumetric 
efficiency
Direct Injection
Air-fuel mixing important 
Controlled by: 
Use of swirl-inducing designs 
Intake port geometry 
Piston cap geometry 
Injection system design 
High pressure 
Many nozzle holes 
Positioning 
Bad: high-tech injection system
Good: Higher volumetric efficiency
DIESEL ENGINES
Indirect and Direct Injection
FIGURE 4-4 A direct injection diesel
engine injects the fuel directly into
the combustion chamber. Many
designs do not use a glow plug.
DIESEL ENGINES
Indirect and Direct Injection
In an indirect injection 
(abbreviated IDI) diesel
engine, fuel is injected
into a small prechamber,
which is connected to
the cylinder by a narrow
opening.
The initial combustion 
takes place in this
prechamber.
This has the effect of 
slowing the rate of
combustion, which tends
to reduce noise.
FIGURE 4-3 An indirect injection diesel engine uses
a prechamber and a glow plug.
DIESEL ENGINES
Diesel Fuel Ignition
Ignition occurs in a diesel engine by injecting 
fuel into the air charge, which has been
heated by compression to a temperature
greater than the ignition point of the fuel or
about 1,000°F (538°C).
Fuel Injection Systems
Electronic distributor pump
Electronic unit injector (EUI)
High-pressure common rail
Roger Krieger, GM R&D Center
Electronic Distributor Pump
Electronic Unit Injector (EUI)
Roger Krieger, GM R&D Center
High-Pressure Common Rail
Common Rail
Spill
Control
Valve
Injectors
Fuel Return
to Tank
ECU
High-Pressure Pump