the performance and combustion characteristics of petrol and diesel engines are discussed

1. Engine Performance
Prof. (Dr.) MP Poonia
Director, NITTTR
Chandigarh (India)

2. Purpose of an engine
Converts the heat of burning fuel into
useful energy
Let's take a look at how the engine was
invented.

3. When expressed as a percentage, the thermal
efficiency must be between 0% and 100%. Due to
inefficiencies such as friction, heat loss, and other
factors, thermal engines' efficiencies are typically
much less than 100%. For example, a typical gasoline
automobile engine operates at around 25% efficiency.
The largest diesel engine in the world peaks at 51.7%.

4. Otto’s practical internal combustion
engine is used to power automobiles,
motorcycles and motorboats. Also, the
Diesel engine is a form of internal
combustion engine, which employs a
four-stroke cycle that is similar to
Otto’s. Nikolaus August Otto died on
January 26, 1891.

5. Basic Terminology
•Bore & Stroke
•Engine Displacement
•Compression Ratio
•Power
•Torque

10. Stroke
•Distance
TDC-BDC
•Distance piston travels
up or down

11. Figure 3 : Engine Terminology

14. Cylinder Displacement
0.7854 x D2
x stroke
or
π x r2
x Stroke

15. 15
Compression Ratio
Area of cylinder at BDC
compared to
Area of cylinder at TDC
600 cm3
to 8 cm3
=
7:5 compression ratio

16. 16
Kinds of Horsepower
• Brake Horsepower
• Indicated Horsepower
• Frictional Horsepower
• Rated Horsepower
• Corrected Horsepower

17. 17
Corrected Horsepower
• corrected for elevation (sea level)
• corrected for temperature
• barometric pressure
• quality of fuel
• humidity

18. Efficiency
• In general, energy conversion efficiency is the ratio
between the useful output of a device and the input.
For thermal efficiency, the input, to the device is heat,
or the heat-content of a fuel that is consumed. The
desired output is mechanical work, or heat, or
possibly both. Because the input heat normally has a
real financial cost, a memorable, generic definition of
thermal efficiency is;

20. Mechanical Efficiency
Some of the power generated in the cylinder is used to
overcome engine friction and to pump gas into and out of
the engine.
The term friction power, , is used to describe collectively
these power losses, such that:
gi
f
gi
fgi
gi
b
m
W
W
W
WW
W
W
,,
,
,
1






−=
−
==η
.
The mechanical efficiency is defined as:
bgif WWW  −= ,

21. • The final parameter to be defined is the
volumetric efficiency of the engine; the
ratio of actual air flow to that of a perfect
engine is
• In general, it is quite easy to provide an
engine with extra fuel; therefore, the
power output of an engine will be limited
by the amount of air that is admitted to an
engine.

23. How about gasoline?
• Gasoline is a product obtained by refining
crude oil (petroleum) obtained from wells
drilled into the earth.
• The crude oil is treated in various ways to
produce gasoline
• Since gasoline is a mixture of carbon and
hydrogen atoms, it is termed a
hydrocarbon

24. Fuel Properties
Fuel Heating value,
QR (J/kg)
f at stoichiometric
Gasoline 43 x 106
0.0642
Methane 50 x 106
0.0550
Methanol 20 x 106
0.104
Ethanol 27 x 106
0.0915
Coal 34 x 106
0.0802
Paper 17 x 106
0.122
Fruit Loops 16 x 106
Probably about the same as paper
Hydrogen 120 x 106
0.0283
U235 fission 82,000,000 x 106
1

25. Fuel Requirements
• Gasoline is a mixture of hydrocarbons (with 4 to
approximately 12 carbon atoms) ,SIT 450 o
C
• Diesel fuel is a mixture of higher molar mass
hydrocarbons (typically 12 to 22 carbon atoms), SIT
200 o
C.
• Fuels for spark ignition engines should vaporize
readily and be resistant to self-ignition, as indicated
by a high octane rating.
• Fuels for compression ignition engines should self-
ignite readily, as indicated by a high cetane number.

26. Octane number
Standard measure of the anti-knock
properties (i.e. the performance) of a
motor or aviation fuel. The higher the
octane number, the more
compression the fuel can withstand
before detonating.

27. • The octane or cetane rating of a fuel is established byThe octane or cetane rating of a fuel is established by
comparing its ignition quality withcomparing its ignition quality with respect torespect to
reference fuels in CFR (Co-operative Fuel Research)reference fuels in CFR (Co-operative Fuel Research)
enginesengines
• RON is determined by running the fuel in a testRON is determined by running the fuel in a test
engine with a variable compression ratio underengine with a variable compression ratio under
controlled conditions, and comparing the results withcontrolled conditions, and comparing the results with
those for mixtures of iso-octane and n-heptane.those for mixtures of iso-octane and n-heptane.

28. Simple Combustion
Equilibrium
• A stoichiometric mixture contains the
exact amount of fuel and oxidizer such
that after combustion is completed, all the
fuel and oxidizer are consumed to form
products.

29. • Equivalence Ratio:
• Lambda is the ratio of the actual air-fuel ratio
to the stoichiometric air-fuel ratio defined as

30. Methods of Quantifying Fuel and Air
Content
of Combustible Mixtures
• If less air than the stoichiometric amount is
used, the mixture is described as fuel rich.
• If excess air is used, the mixture is described as
fuel lean.
• Fuel-Air Ratio (FAR): The fuel-air ratio, f, is
given by

31. Octane rating: The octane rating indicates
how well the gasoline will resist detonation
(burning too rapidly) in the cylinders.
The lower the octane rating the faster the
fuel burn
Slower burning fuel provides more even
combustion throughout the power stroke
of the piston.

32. Unleaded gasoline
All gasoline sold today is unleaded.
Unleaded gasoline contains no tetraethyl
lead.
Tetraethyl lead quickly destroys catalytic
converters.

33. Preparing the fuel
As you know,
gasoline burns
readily. However to
get the most power
from this fuel, and
in fact, to get it to
power an engine,
special treatment
is required.

34. If you were to place
a small amount
of gasoline in a
jar and drop a
match into it, it
would burn.
Such burning is fine
to produce heat
but it would not
give us the
explosive force
needed to
operate an
engine.

35. OXYGEN,
GOTTA HAVE IT
In order to burn, gasoline
must combine with oxygen
in the air.
For purposes of illustration
imagine that a gasoline
particle is square. It will burn
on all sides. However it will
still not burn quickly enough
to for use in an engine

36. To make the gasoline burn more rapidly, we
can break it up into smaller particles. Notice
that as you divide it into smaller particles, you
expose more surface area to the air.

37. Internal Combustion Engines
– Carnot cycle

38. The Ideal Air Standard Otto Cycle

39. Ignition and Combustion in Spark Ignition
and Diesel Engines
Spark ignition (SI) engines usually have
pre-mixed combustionCompression
ignition (CI) engines the combustion is
controlled primarily by diffusion.

40. December 20, 2014 I.C. Engines Laboratory Slide 40

41. Premixed vs. Non-premixed
Charge Engines
Flame front Fuel spray flame
Premixed charge
(gasoline)
Non-premixed charge
(Diesel)
Spark plug Fuel injector
Fuel + air mixture Air only

43. I.C. Engines Laboratory

45. December 20, 2014 I.C. Engines Laboratory Slide 45

46. December 20, 2014 I.C. Engines Laboratory Slide 46
Combustion
in SI engine

47. I.C. Engines Laboratory

48. Flames detected
between
Type of cycle
- 450
and TDC early burn cycle
TDC and 45° Fast burning cycles
450
and 900
slow burn cycles
90° and BDC Late burn cycles
BDC and TDC delayed burn cycles
Flames not detected misfires and partial burn
cycles
Good combustion
is almost entirely
made up of fast
burn cycles. poor
combustion
consists of a high
proportion of late
and delayed burn
cycles.
COMBUSTION QUALITY

49. EFFECT OF ENGINE VARIABLES ON
FLAME PROPAGATION
Fuel-air ratio :

50. December 20, 2014 I.C. Engines Laboratory Slide 50

51. December 20, 2014 I.C. Engines Laboratory Slide 51
Compression Ratio

52. December 20, 2014 I.C. Engines Laboratory Slide 52
P-t diagram of a normal cycle

53. December 20, 2014 I.C. Engines Laboratory Slide 53
p-t diagram of a knocking cycle

54. Pressure-Volume Graph 4-stroke SI engine
One power stroke for every two crank shaft revolutions
1 atm
Spark
TDC
Cylinder volume
BDC
P
Exhaust valve
opens
Intake valve
closes
EVC
IVO

55. • Otto cycle efficiency predicts an efficiency of
60% and the fuel-air cycle predicts an
efficiency of 47% for stoichiometric operation.
In reality, such an engine might have a full
throttle brake efficiency of 30%, and this
means 17 percentage points must be accounted

56. Diesel engines have a higher maximum
efficiency than spark ignition engines for
three reasons:
• 1. The compression ratio is higher.
• 2. During the initial part of compression,
only air is present.
• 3. The air-fuel mixture is always weak of
stoichiometric.

57. The Ideal Air Standard
Diesel Cycle

58. What is Diesel Fuel?
Various Petroleum Components:
• Paraffins
• Isoparaffins
• Napthenes
• Olefins
• Aromatic Hydrocarbons

59. Cetane Number
CN is a measurement of the combustion
quality of diesel fuel during compression
ignition.

60. Cetane Number
• Measures readiness of fuel to auto-ignite.
• High cetane means the fuel ignite quickly
• Most fuels have cetane numbers between 40
and 60.
• ASTM requires a minimum cetane number of
40
• Premium Diesel fuel typically has a cetane of
47

61. Cetane
Ignition Delay: The period that occurs
between the start of fuel injection and the
start of combustion; the higher the cetane
number, the shorter the ignition delay and
the better the quality of combustion.
Cetane

63. Low Cetane Impact
Poor Ignition Quality
Long ignition delay
Abnormal Combustion
Possible High Combustion Pressure
Increased Engine stress
Excessive Engine Knock
Smoke on Cold start

65. Direct Injection vs. Indirect Injection

68. Swirl :
• The orderly motion of the air particularly parallel to the axis
of the engine.
• Very much required for diesel engines.
Squish/Squash :
• The radial inward motion of the air-fuel mixture towards
(squish) and away from the axis of the engine (squash).
• Very much required for the diesel engines.
Turbulence :
• Random mixing of the burned and unburned gases

69. December 20, 2014 I.C. Engines Laboratory Slide 69
Effect of Fuel-Air Ratio on Power Output
of CI Engine

70. December 20, 2014 I.C. Engines Laboratory Slide 70
Stages of Combustion in CI Engines

71. December 20, 2014 I.C. Engines Laboratory Slide 71
Combustion Rate (CI)

72. December 20, 2014 I.C. Engines Laboratory Slide 72
Effect of varying the amount of fuel
injected on P-θ diagram

73. December 20, 2014 I.C. Engines Laboratory Slide 73
Effect of speed on ignition delay in a
diesel engine

74. December 20, 2014 I.C. Engines Laboratory Slide 74

75. December 20, 2014 I.C. Engines Laboratory Slide 75

76. December 20, 2014 I.C. Engines Laboratory Slide 76

80. December 20, 2014 I.C. Engines Laboratory Slide 80
CI Engine Combustion
Chambers
• Open Chamber or DI engine
• Divided Chamber or IDI engine

81. Diesel Ignition System
• Glow plug
• Glow plug relay
• Fusible Link
• Glow Plug Temp Sensor
• Heat Sink

82. Current Modern fuel injector design-
The fuel injection systems on the
John Deere Power Tech Plus engines
operate at 2,000 bar
Photos compliments of the National Alternative Fuel Training Consortium

83. In-Line Injection Pumps
• An injection pump with a
separate plunger for each
engine cylinder.
• Plunger is rotated by a rack to
determine metering helical
cuts on the pump plungers.
• The plungers are driven off a
camshaft, which usually
incorporates a centrifugal
controlled timing advance
mechanism.

84. A diesel fuel injection system
employing a common
pressure accumulator
The rail is fed by a high
pressure fuel delivery pump.
The injectors, are activated by
solenoid valves.
The solenoid valves and the
fuel pump are electronically
controlled.
Also known as CRD, Common
Rail Diesel Technology
Common Rail
Injection

85. • ic engines fdpIC Engines Videos
• Video not found

86. Common Rail Injection Vehicles

87. Advantages of DI Engines
 Fuels of poorer ignition quality can be used.
 Single-hole injection nozzles and moderate
injection pressures can be used and can
tolerate greater degrees of nozzle fouling.
 Higher fuel-air ratios can be used without
smoke.

88. Disadvantages of IDI
Engines
 More expensive cylinder construction.
 More difficult cold starting because of greater
heat loss through the throat.
 Poorer fuel economy due to greater heat
losses and pressure losses through the throat,
which result in lower thermal efficiency and
higher pumping loss.

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