all four stokes and indicated mean effective pressure is enclosed. Some FAQ are also included.

1. Internal
Combustion
Engine Efficiencies
Prof. (Dr.) M P Poonia
Director
NITTTR, Chandigarh

2. What is Engine?
Engine is a Machine which Converts Heat
Energy of Fuel into Mechanical Power

3. ENGINE TERMINOLOGY

4. Chemical
Energy Heat Energy Mech. Work

5. Electrical and Chemical
Energy is Concentrated in
a Small Space. The
Molecules or Particles that
Store these Forms of
Energy are Highly Ordered
and Compact.
High-Grade Energy

6. Low-Grade Energy
Molecules, in which energy is
stored more randomly than
the molecules of carbon in a
coal, classified as low-grade
energy. Heat is low-grade
energy.

7. Indicated Power

8. Engine Power
Indicated
Brake

9. Suction Stroke
TDC
BDC
S
1 2
VC VS
CR=(VC+VS)/VC

10. Compression
Stroke
TDC
BDC
S
1
3
2

11. Heat Addition
TDC
BDC
S
1
3
2
4

12. Power Stroke
TDC
BDC
S
1
3
4
5

13. Exhaust Stroke
TDC
BDC
S
1
3
4
5

14. Indicated Power (QH-QC)
BDCTDC
ɳth= (QH-QC)/QH

15. Indicated Power

16. Indicated Power
1
2
3
4
V
P

17. Thermal Efficiency vs CR
ɳth = 1 −
1
rɤ−1 Otto Cycle
ɳth
CR

18. Air-Standard Cycle
Assumptions
• Working fluid is air as ideal gas.
• No change in composition.
• Heat addition from an External
Source.
• No Suction and Exhaust Strokes
• All the processes are internally
reversible
• Specific heats are constant

19. P
V
pm
patm
Indicated Mean Effective
Pressure (bar)
VS

20. Actual P-V Diagram
PMEP

21. • L-2Brake mean effective
pressure Meaning.mp4

22. Indicated Power (IP)
IP=
𝑷 𝒎
×𝑳×𝑨×𝑵
𝟏𝟐𝟎
IP=
𝑷 𝒎
×𝑽𝑺×𝑵
𝟏𝟐𝟎
Where IP= Indicated Power, W
Pm= Mean Effective Pressure N/m2
L = Stroke Length , m
A = Piston Top Area , m2
N = Engine RPM

23. 1. Only 25% of the power produced by the burning
fuel is useful .
2. Now, Computers control every aspect of Car.
3. Even most improving effect, the valve timing.
4. The cam is the brains of an engine.
5. It tells the engine when to fire its spark , when
and how long to breathe in and out.
Engine Future

24. An engine is setup to run most efficiently at
one speed. Every other speed the engine has no
chance to run as efficiently . There are
companies that are now trying to make engines
with variable valve timing.
Engine Future

25. FAQ
• The ratio of the heat equivalent to one
kW hour to the heat in fuel per B.P. hour
is termed as brake thermal efficiency.
a)True
b) False

26. FAQ
• The ratio of the work obtained at the
crankshaft in a given time to the energy
supplied during the same time is called
a) Mechanical efficiency
b) Overall efficiency
c) Indicated thermal efficiency
d) Volumetric efficiency

27. FAQ
• The ratio of the brake power to the
indicated power is called
a) Mechanical efficiency
b) Overall efficiency
c) Indicated thermal efficiency
d) Volumetric efficiency

28. FAQ
• The ratio of the indicated thermal
efficiency to the air standard efficiency is
known as
a) Mechanical efficiency
b) Overall efficiency
c) Relative efficiency
d) Volumetric efficiency

29. FAQ
• The correct sequence of the decreasing order
of brake thermal efficiency
a) Four stroke C.I. , four stroke S.I. , two stroke
S.I. engine
b) Four stroke S.I. , four stroke C.I. , two stroke
S.I. engine
c) Four stroke C.I. , two stroke S.I. , four stroke
S.I. engine

30. FAQ
• The brake power of a diesel engine,
keeping other parameters constant, can
be increased by
a) Decreasing the density of intake air
b) Increasing the temperature of intake air
c) Increasing the pressure of intake air
d) Decreasing the pressure of intake air

31. Thanks