By Dr. Mahesh Jadhav, SRF at AICRP IARI New Delhi

1. Dr. M. L. Jadhav
Farm Power and Equipment
ICAR-Central Institute of Agricultural
Engineering, Bhopal

2. Various Sources of Power and IC Engine
Various Sources of Power:
1. Human Power
2. Animal Power
3. Mechanical Power
4. Electrical Power
5. Other Sources of Power

3. Mechanical Power
 Broadly speaking, mechanical power includes stationary oil
engines, tractors, power tillers and self propelled combines.
 In modern days, almost all the tractors and power tillers are
operated by diesel engines.
 Diesel engines are used for operating irrigation pumps, flour mills,
oil ghanis, cotton gins, chaff cutter, sugarcane crusher, threshers,
winnowers etc.
 The thermal efficiency of diesel engine varies from 32 to 38 per
cent where as that of petrol engine varies from 25 to 32 per cent.

4. Mechanical Power
Advantages: Efficiency is high; not affected by weather; can run
at a stretch; requires less space and cheaper form of power.
Disadvantages: Initial capital investment is high; fuel is costly
and repairs and maintenance needs technical knowledge.

5. Engine
 Engine converts chemical energy of fuel into mechanical energy.
 Engines are of two types
 External combustion
 Internal combustion
 Internal combustion engines used for agricultural applications
range from those used for one-horsepower garden tools to the
hundreds of horsepower required for very large tractors.

6. Types of engines depending on Engine cycle
a. Four-stroke cycle:
i. Suction Stroke:
 The piston travels from TDC to BDC with the intake
valve open and exhaust valve closed.
 The downward motion of the piston increases the
volume in the combustion chamber which in turn
creates a vacuum.
 The resulting pressure differential through the intake
system from atmospheric pressure on the outside to
the vacuum on the inside causes air to be pushed into
the cylinder.
 As the air passes through the intake system, air (CI)
or air-fuel mixture (SI) is introduced into the cylinder
in the desired amount.

7. Types of engines depending on Engine cycle
a. Four-stroke cycle:
ii. Compression Stroke:
 At the end of suction stroke, when the piston reaches
BDC, the intake valve gets fully closed and the
piston travels upward back to TDC with both the
valves (inlet and outlet) closed.
 As the piston moves upward, it compresses the air
(CI) or air-fuel mixture (SI) raising both the pressure
and the temperature inside the cylinder.
 Near the end of the compression stroke, the
combustion is initiated by injecting fuel (CI) or with
the help of spark plug (SI).
 The combustion of occurs in a very short but finite
length of time with the piston near TDC.

8. Types of engines depending on Engine cycle
a. Four-stroke cycle:
iii. Power Stroke:
 Also known as the expansion stroke, As the piston
travels from TDC to BDC, cylinder volume is again
increased causing pressure and temperature drop.
 This is the stroke which produces the work output of
the engine cycle.
 Late in the power stroke, the exhaust valve is opened
and exhaust blow down occurs.
 The pressure and temperature in the cylinder are still
high relative to the surroundings at this point and a
pressure differential is created through the exhaust
system when the piston is near BDC.
 Opening the exhaust valve before the piston reaches
BDC, reduces the work obtained during the power
stroke but is required because of the finite time needed
for exhaust blow down.

9. Types of engines depending on Engine cycle
a. Four-stroke cycle:
iv. Exhaust Stroke:
 By the time the piston reaches BDC during the power
stroke, the cylinder is still full of exhaust gases.
 With the exhaust valve remaining open, the piston now
travels upward to make the gases move out of the
cylinder into the exhaust system, leaving only that
amount of exhaust gasses which are trapped in the
clearance volume when the piston reaches TDC.
 Near the end of exhaust stroke, the intake valve starts to
open, so that it is fully open by TDC to start the new
intake stroke in the next cycle.
 Near TDC exhaust valve starts to close and finally is
fully closed sometime at TDC.
 This period when both intake valve and exhaust valve
are open is called valve overlap.

10. Types of engines depending on Engine cycle
b. Two-stroke cycle:
 In these engines the complete cycle of suction, compression, power
and exhaust is performed with two strokes i.e. one revolution of the
crankshaft.
 In two stroke engines, the air fuel mixture is entered from the
carburettor through the inlet port at the bottom when the piston starts
moving upward.
 The air fuel mixture is compressed at the same time during the same
stroke, hence suction and compression are being performed
simultaneously.
 When the piston reaches just at TDC, the combustion takes place and
piston generates movement to the crankshaft.
 As the piston moves downward with power stroke, it compresses the
mixture in crankcase to move into cylinder through the transfer port
which pushes the out the burnt/exhaust gases to move out from the
exhaust port.

11. Types of engines depending on Engine cycle
b. Two-stroke cycle:
 And at the same time, new charge
(air fuel mixture) start entering
through the inlet port, this process
is also know as cross-flow
scavenging.
 In this way, all four strokes of
engine cycle are completed in the
two strokes (one upward and one
downward movement of piston)
only.

12. Types of engines depending on Engine cycle

13. Types of engines depending on method of ignition
a. Spark Ignition (SI):
 Spark plug is used in SI engines to
initiate the combustion process in each
cycle with the help of a high voltage
electrical discharge between two
electrodes.
 The air fuel mixture in the combustion
chamber is ignited by the plug.
 Earlier the torch holes were being used
to start combustion from external flame
and then with the technological
advancements electric spark plug
replaced these torch holes.

14. b. Compression Ignition (CI):
The combustion process in a CI engine
starts when the air-fuel mixture self-
ignites due to high temperature in the
combustion chamber caused by high
compression.
 Direct injection: Fuel injected into
main combustion chamber.
 Indirect injection: Fuel injected into
secondary combustion chamber.
Types of engines depending on method of ignition

15. Combustion Chamber Design
• If the fuel were injected directly into the combustion chamber, there
would be an unnecessarily long delay before ignition begins,
resulting in a very high initial pressure.
• High-speed diesel engines employ several methods to reduce the
ignition lag and improve the combustion.
• The open-chamber, or direct-injection,
combustion chamber generally employs a
concave piston head.
• Mixing of the fuel and air is often aided
by an induction-produced air swirl or by a
movement of air from the outer rim of the
piston toward the center of the piston
commonly known as "squish“.

16. • The pre-combustion chamber is sometimes a
part of the injection nozzle, or it may be part of
the cylinder head.
• The entire fuel charge is injected into the pre-
combustion chamber, which contains 25 to 40
percent of the clearance volume.
• Compared to the open combustion chamber, it
is claimed the advantages of the pre-combustion
chamber are
• lower fuel-injection pressure required and
• the ability to use a wider range of fuels.
• The disadvantage is a higher specific fuel
consumption (sfc).

17. • The swirl combustion chamber, which is
sometimes called a turbulence chamber, is
designed so that the burning fuel-air mixture is
caused to swirl, thereby improving the mixing
and subsequent combustion in the main
combustion chamber.
• The swirl chamber contains from 50 to 90
percent of the compressed volume when the
piston is on top dead-center.
• On the compression stroke, air enters the swirl
chamber in a circular motion.
• When combustion begins, a reversal of flow
occurs and the burning gases stream out of the
chamber into the cylinder.
• Turbulence in the chamber is directly related to
the speed of the engine, and therefore, ignition
delay decreases as the engine speed increases.

18. • The auxiliary chamber (also called air cell or
energy cell) is an open chamber with a small cell
that is remote from the injection nozzle.
• It can be located either in the top of the piston
(where it is called an air cell) or, more commonly,
directly across the cylinder from the injection
nozzle (then it is called an energy cell).
• The latter arrangement allows for easy removal for
servicing and cleaning.
• In operation, approximately 60 percent of the fuel from the injection
nozzle is directed into the auxiliary chamber, which contains about 10
percent of the clearance space.
• The blast from the fuel igniting in the auxiliary chamber will then be
directed against the remainder of the fuel being sprayed from the
nozzle. Thus, a fuel-air mixture is swept around the cylinder.
• The duration of combustion is longer for this type of chamber,
resulting in lower peak pressures at the expense of slightly higher fuel
consumption.

19. Combustion Chamber Design

20. Types of engines depending on Valve location
a. I head engine:
Valves in head (Overhead valve).
b. L head engine:
Valves in block (flat head), also called L Head engine.
c. T head engine:
Some historic engines with valves in block had the intake valve on
one side of the cylinder and the exhaust valve on the other side.
d. F head engine:
One valve in head (usually intake) and one in block, also called F
Head Engine; this is much less common.

21. Types of engines depending on Air Intake Process
a. Naturally Aspirated:
No intake air pressure boosts system.
b. Super charged:
Intake air pressure increased with the compressor driven off of the
engine crankshaft.
c. Turbo charged:
Intake air pressure increased with the turbine compressor driven by
the engine exhaust gases.
d. Crankcase compressed:
Two-stroke cycle engine which uses the crankcase as the intake air
compressor.
Limited development work has also been done on design and
construction of four-stroke cycle engines with crank case
compression.

22. Types of engines depending on Fuel used
a. Petrol/Gasoline engines
b. Diesel engines
c. Gas, Natural gas, Methane engines
d. Alcohol-Ethyl, Methyl engines
e. Dual fuel engines:
There are a number of engines that use a combination of two or more
fuels. Some,
Usually large, CI engines use a combination of natural gas and diesel
fuel.
These are attractive in developing third world countries because of
the high cost of the diesel fuel.
Combined gasoline alcohol fuels are becoming more common as an
alternative to straight gasoline automobile engine fuel.
f. Gasohol engines:
Common fuel consisting of 90% gasoline and 10% alcohol.

23. Types of engines depending on Type of cooling
a. Air cooled:
Circulating air is used to dissipate the heat from the fins on an
engine.
Mostly small engines are used with air cooled engines.
b. Liquid cooled, Water-cooled:
Water is made to flow through the water jackets provided along the
surface of cylinders or liners to absorb the heat.
Further the heated water is cooled with the help of radiator.

24. Terminology of IC engine
Bore: Bore is the diameter of the engine cylinder.
Stroke: It is the linear distance travelled by the piston from Top dead
centre (TDC) to Bottom dead centre (BDC).
Stroke-bore ratio: The ratio of length of stroke (L) and diameter of
bore (D) of the Cylinder is called Stroke-bore ratio (L/D). In
general, this ratio varies between 1 to 1.45 and for tractor engines,
this ratio is about 1.25.
Swept volume (Piston displacement): It is the volume (AxL)
displaced by one stroke of the piston where A is the cross sectional
area of piston and L is the length of stroke.
Displacement volume : It is the total swept volume of all the pistons
during power strokes occurring in a period of one minute.
Compression ratio: It is the ratio of the volume of the charge at the
beginning of the compression stroke to that at the end of
compression stroke. Compression ratio of diesel engine varies
from 14:1 to 20:1, petrol engine varies from 4:1 to 8:1.

25. SI Engine

26. CI Engine

27. Components of IC engine

28. Working Principle of an
IC Engine

29. Valve Mechanism

30. Valve Mechanism

31. Valve Timing Diagram

32. PV Diagram of Otto and
Diesel Cycle Engines

33. Assumptions of the Ideal Air-
Standard Otto Cycle
1. The piston has zero friction in the cylinder.
2. Air is used in the cylinder as the working fluid.
3. No heat transfer takes place through the engine walls.
4. The crank starts at the bottom of the stroke under conditions of P1
V1, and T1
5. Adiabatic compression occurs along AB and adiabatic expansion
occurs along CD.
6. Constant-volume addition of heat occurs along BC, and a
constant-volume rejection occurs along DA.
7. The working fluid (air) is treated as a perfect gas with constant
specific heats. All thermodynamic processes are assumed ideal.

34. Otto and Diesel Cycle Efficiency
1. Efficiency of an ideal Otto cycle increases as the compression
ratio increases.
2. It is independent of the heat liberated by the fuel.
1. Efficiency increases as the compression ratio V1/V2 increases.
2. Also as the fuel cutoff ratio V3/V2 is diminished.
3. Maximum efficiency will be obtained with high compression and
early fuel cutoff.
4. As the fuel cutoff approaches zero the efficiency of the diesel
cycle approaches that of the Otto cycle for the same compression
ratio.

35. Actual Cycle Efficiency
• The actual performance or efficiency considerably less than that
indicated by the ideal analysis.
• Because the assumptions made do not hold true for the actual cycle.
• The entire gas is not air, the specific heat is not constant, chemical
reaction does occur during the cycle.
• Heat is transmitted to the cylinder walls during the cycle, and
leakage past the rings and valves contributes to the loss.
• The intake stroke takes place at less than atmospheric pressure,
whereas the exhaust stroke takes place above atmospheric pressure.
• The combustion process is not an instantaneous process as assumed
for the ideal Otto cycle but takes place over a finite amount of time,
during which the piston is moving and heat is being lost to the
cylinder walls.
• Combustion will usually not be complete because of poor mixing or
an insufficient supply of oxygen.

36. Actual Cycle Efficiency
• The efficiency of an internal-
combustion engine is frequently given
by the indicated thermal efficiency
which is the ratio of the work
equivalent of the area on the actual
indicator diagram to the work
equivalent of the lower heat of
combustion of the fuel used (25-35%).
• The relative efficiency is defined as the
ratio of the indicated thermal efficiency
of an engine to the efficiency of the
ideal process upon which the design of
the engine is based, the ratio being a
measure of the perfection of design and
performance of the engine.

37. Cut section of Tractor
John Deere 3350 tractor cut engine

38. Engine Overhauling
Reasons of overhauling
• Engine seize
• Engine knocking
• Continuous decrease in engine oil level
• Significant decrease in fuel efficiency
• Continuous white or black smoke from exhaust
• Engine performance (Power output)
• Wear in main bearing

39. Engine Overhauling
• Cleaning of dirt and debris from parts of engine
• Inspection of parts for damage and replacement
• Repair of damaged parts
• Piston
• Piston rings
• Main bearings
• Intake and exhaust values
• Valve springs
• Cylinder liner
• Cylinder rebore
• All gaskets
• Connecting rod
• Camshaft bearing
• Oil seals
• Timing gears
• Oil filter

40. Engine Overhauling
demonstration
1 2 3

41. 1. https://youtu.be/DwuxPFYxRNM
2. https://youtu.be/dS-SpGnT3js
3. https://youtu.be/25UCs9kCMdE
4. https://youtu.be/UMiKmEm2ulU
Video Lectures for
Numerical Related to IC
Engine