The document discusses diesel fuel injection systems and combustion in compression ignition engines. It covers the stages of combustion (ignition lag, rapid combustion, controlled combustion, after burning), factors that affect ignition delay and knocking, different combustion chamber designs (direct injection, indirect injection), fuel spray behavior, and the role of air motion within the cylinder. Turbocharging is introduced as a way to compress more air into the cylinder before fuel injection, enabling increased power output and efficiency.

1. COMPRESSION IGNITION ENGINES
Diesel Fuel Injection Systems - Stages of combustion – Knocking –
Factors affecting knock – Direct and Indirect injection systems –
Combustion chambers – Fuel Spray behaviour – Spray structure and
spray penetration – Air motion - Introduction to Turbocharging.

2. The main purpose of the fuel injection system is
to deliver fuel into the cylinders of an engine. In
order for the engine to effectively make use of
this fuel:
 Fuel must be injected at the proper time, that is, the
injection timing must be controlled and
 The correct amount of fuel must be delivered to meet
power requirement, that is, injection metering must
be controlled.

3. Many specialized concepts and terms are used to
describe the components and the operation of
diesel fuel injection systems.
 Nozzle
 Nozzle
 Injector commonly refers to the nozzle holder and
nozzle assembly holder or injector body
 Start of injection (SOI) or injection timing
 Start of delivery
 End of injection (EOI)
 Injected fuel quantity
 Injection duration

4.  Injection pattern
 Multiple injection event
 Low pressure side components—These components
serve to safely and reliably deliver fuel from the tank to
the fuel injection system. Low pressure side components
include the fuel tank, fuel supply pump and the fuel
filter.
 High pressure side components—Components that
create high pressures, meter and deliver the fuel to
the combustion chamber. They include the high
pressure pump the fuel injector and fuel injection
nozzle. Some systems may also include an accumulator.

5. Stages of combustion in CI
engine
In the Compression Ignition Engine, the combustion
process will be completed in the four stages in an actual
engine.
Ignition Lag
Rapid Combustion
Controlled Combustion
After Burning

7. Ignition Lag
 The time interval between the injection of the fuel
and the start of the self-ignition of the fuel is known
as ignition lag or Ignition delay.
 It is also referred to as the preparation phase
 The fuel does not ignite immediately upon the
injection of fuel into the combustion chamber.
 There will be a definitely a certain amount of period
will be delayed between the first droplet of the
fuel injected into the combustion chamber and
the time at which it starts the burning phase.

8.  There are two chances that can cause the ignition
delay. Physical delay and chemical delay.
 Physical delay due to the complete injection of fuel,
atomisation, vaporization and mixing of air and fuel
and raised to its self-ignition point.
 The chemical delay due to the burning slowly starts
and then accelerates until the complete ignition takes
place.

9. Rapid Combustion
 The period of rapid combustion also known as the
uncontrolled combustion.
 This rapid combustion will starts right After the
ignition delay period ends.
 During this period the heat release is maximum.
 The pressure released during this period depends
on the ignition delay period.
 If the ignition delay period is more, then the
pressure rise is more due to the more fuel will be
accumulated during the delay period.

10. Controlled Combustion
 The rapid combustion followed by the third stage
called the controlled combustion.
 During the rapid combustion, the cycle reaches its
maximum pressure and the temperature.
 Which means the fuel droplets injected into the
combustion chamber during the rapid combustion
stage will burn faster with reduced ignition delay as
soon as they find the necessary oxygen and any
further pressure rise is controlled by the injection

11.  At the point at where it reaches the maximum
cycle pressure the rapid combustion ends and
the controlled combustion starts.
 The period of the controlled combustion is
assumed to end at the maximum cycle
temperature.

12. After Burning
 The combustion process will not stop right
after the completion of the injection
process.
 The unburnt particles left in the combustion
particles will start burning as soon as they
get in contact with the oxygen.
 This process continued for a certain period
amount of time called the after burning.

13.  Knocking, in an internal-combustion engine, sharp
sounds caused by premature combustion of part of
the compressed air-fuel mixture in the cylinder.
 In a properly functioning engine, the charge burns with
the flame front progressing smoothly from the point of
ignition across the combustion chamber.
 However, at high compression ratios, depending on the
composition of the fuel, some of the charge may
spontaneously ignite ahead of the flame front and
burn in an uncontrolled manner, producing intense high-
frequency pressure waves.
 These pressure waves force parts of the engine to vibrate,
which produces an audible knock.

14. Causes of Knocking
1. Low Quality Fuel
2. Carbon Deposits in the Cylinder Wall, and
3. Advanced or Delayed Sparking
4. Improper fuel supply.

15. Knocking in CI Engine

16. Knocking in SI and CI Engine

17. Normal Combustion
Under ideal conditions the common internal combustion engine burns
the fuel/air mixture in the cylinder in an orderly and controlled fashion.

18. Abnormal Combustion

19. Factors affecting Delay period

20. Factors affecting Delay period

21. Factors affecting Delay period

22. Factors affecting Delay period

23. Factors affecting Delay period

24. Reducing Knocking in SI and CI engine

25. The main reason of knocking in a CI engine is the ignition delay,
after the compression stroke has ended.
Following parameters will minimize knocking in CI
engines.
 Compression ratio: high
 Self ignition temp: low
 Delay period: less
 Inlet temp and pressure: high
 Combustion chamber temp: high
 RPM : low
 Engine size : small
 Cetane Rating: High

26. Combustion Chamber in CI engine
1. Direct Injection type
2. Indirect Injection type
1. Direct Injection Type.
• Shallow depth Chamber
• Hemispherical Chamber
• Cylindrical Chamber
• Toroidal Chamber

27. Direct Injection Type
Shallow depth Chamber Hemispherical Chamber

28. Direct Injection Type
Cylindrical Chamber Toroidal Chamber

29. 2. Indirect Injection Type.

30. Indirect Injection Type
1. Swirl Chamber

31. Indirect Injection Type
2. Precombustion Chamber

32. Indirect Injection Type
3. Air-Cell Combustion Chamber

33.  A significant difference between a
turbocharged diesel engine and a traditional
naturally aspirated gasoline engine is the air
entering a diesel engine is compressed
before the fuel is injected. This is where the
turbocharger is critical to the power output
and efficiency of the diesel engine.

34.  It is the job of the turbocharger to compress more
air flowing into the engine’s cylinder. When air is
compressed the oxygen molecules are packed
closer together. This increase in air means that
more fuel can be added for the same size naturally
aspirated engine. This then generates increased
mechanical power and overall efficiency
improvement of the combustion process.
Therefore, the engine size can be reduced for a
turbocharged engine leading to better packaging,
weight saving benefits and overall improved fuel
economy.

35. Turbo charging
1. Exhaust Turbo charging of Single cylinder engine.

36. Turbo charging
2. Exhaust Turbo charging of a V type engine.

38. Fuel Spray Behaviour

40. Spray Formation

41.  The spray characteristics of fuel mainly
depend on the fuel injection pressure,
density, viscosity, ambient pressure, and
temperature.
 Among these parameters, fuel injection
pressure significantly affects the spray
structure

44. Fuel Spray

49. AIR MOTION WITHIN THE CYLINDER
The air motion inside the cylinder greatly influences the performance of diesel
engines. It is one of the major factors that controls the fuel-air mixing in diesel engines. Air-
fuel mixing influences combustion, performance and emission level in the engine. The air
motion inside the cylinder mainly depends on manifold design, inlet and exhaust valve profile
and combustion chamber configuration. The initial in-cylinder intake flow pattern is set up by
the intake process, and then it is modified during the compression process. The shape of the
bowl in the piston and the intake system, control the turbulence level and air-fuel mixing of the
DI diesel engine. The variation of shape of intake system, shape of piston cavity, etc. lead to a
change in the flow field inside the engine.

50. EFFECTS OF AIR MOTION
• Atomizes the injected fuel into droplets of different sizes.
• Distributes the fuel droplets uniformly in the air charge.
• Mixes injected fuel droplets with the air mass.
• Assists combustion of fuel droplets.
• Peels off the combustion products from the surface of the burning drops as they are being
consumed.
• Supplies fresh air to the interior portion of the fuel drops and thereby ensures complete
combustion.
• Reduces delay period.
• Reduces after burning of the fuel.
• Better utilization of air contained in the cylinder.

51. TYPES OF AIR MOTION
The air motion in a diesel engine is generally caused by either by the intake port
during the suction stroke or by combustion chamber geometry during the
compression stroke. Three different elements of the air motion present during
intake to expansion strokes in a diesel engine cylinder have been classified as
1) Swirl
2) Squish
3) Turbulence

52. Swirl Motion
Swirl is defined as the organized rotation of the charge about the cylinder
axis. It is created by bringing the intake flow into the cylinder with an initial angular
momentum. Swirl is generated during the intake process in DI diesel engines by the
intake port and subsequently by combustion chamber geometry during the compression
stroke.

53. Squish Motion
The squish motion of air is brought about by a recess in the piston crown. At
the end of the compression stroke, the piston is brought to within a very small distance
from the cylinder head. This fact causes a flow of air from the periphery of the cylinder
to its center and into the recess in the piston crown.