1. Mechanical Engineering
Thermodynamics
2nd year Petrol dept.
2011-2012
Lecture (8) Internal Combustion
Engines (ICE)
Lecturer : Dr. Esmail Bialy

3. Air and Fuel will expand due to combustion, pushing the
piston downwards.

4. If we connected the piston to a crank mechanism, we can
convert the reciprocating motion into rotation.

5. Air and fuel need intake
system to get into the
cylinder.

6. Combustion products
need exhaust system to be
pushed out the cylinder.

9. Intake valve is oppened.

10. The Intake valve is closed,
when the piston reached
the BDC ( Bottom dead
center).

11. Both valves are closed

12. Now ignition starts to
begin the heat addition
process.

14. Exhaust valve begins
opening.

16. Engine Volume.
Vcylinder= ¼π d2l.
Where,
d: cylinder diameter (bore)
L: cylinder length (stroke)
Vcylinders= ¼π d2l * z where, z: number of cylinders
V˚Stroke = ¼π d2l * z * N/60ζ
Where,
N: number of crank shaft revolutions per minute (rpm)
ζ: =2 for 4-stroke engines
= 1 for 2-stroke engines

17. Engine Performance Parameters.
a- Power:
1- Brake Power: the measured power output of the engine
BP= T * ω
Where,
T: Torque (N.m)
ω: radial speed (rad/s) and ω= 2πN/60
2- Indicated Power: is the theoretical power of a reciprocating
engine if it is completely frictionless in converting the expanding
gas energy (piston pressure × displacement) in the cylinders.
IP= BP + FP
3- Friction Power FP: increases proportionally with N2

18. Engine Performance Parameters.
b- Thermal efficiency:
1- Brake thermal efficiency:
ηb= BP/Q˚add
Where,
Q˚add: rate of heat added to engine per second due to fuel burning
2- Indicated thermal efficiency :
ηI= IP/Q˚add
Q˚add=m˚f * C.V
Where,
m˚f : consumed fuel flowrate (kg/s)
C.V: fuel heating value: heat released per each kg of completely
burned fuel (kJ/kg)

19. Engine Performance Parameters.
c- mean effective pressure:
1- Brake mean effective pressure:
Bmep= BP/ V˚Stroke
Where,
BP : brake power
V˚Stroke :engine cylinders volume
2- Indicated mean effective pressure :
Imep= IP/ V˚Stroke
Mean effective pressure: a valuable measure of an engine's capacity
to do work that is independent of engine displacement.

20. Engine Performance Parameters.
d- specific fuel consumption:
1- Brake specific fuel consumption:
Bsfc= m˚f /BP
Where,
BP : brake power
m˚f : consumed fuel flowrate (kg/s)
2- Indicated specific fuel consumption :
Isfc= m˚f /IP

21. Engine Performance Parameters.
e- Engine efficiencies:
1- Mechanical efficiency :
ηm= BP/IP
ηm= ηb/ηI
2- Volumetric efficiency :
V˚Stroke )actual = ηv ¼π d2l * z * N/60ζ

22. Brake power calculation:
BP=ηb*Q˚add Q˚add=m˚f * C.V
=ηb m˚f C.V F/A = m˚f / m˚a
=ηb m˚a F/A C.V m˚a= ρa V˚Stroke
=ηb ρa V˚Stroke F/A C.V
=ηb ηv ρa F/A C.V ¼π d2l * z * N/60ζ
BP=ηb ηv ρa F/A C.V ¼π d2l * z * N/60ζ

23. Example (6-3):
An eight-cylinder, four stroke diesel engine develops 900 kW
of brake power at 600 rpm. The cylinder size is 37 cm bore by 46
cm stroke and the engine uses 4.5 kg of fuel per minute. Upon
complete combustion, the fuel releases heat energy of 45 MJ/kg.
The indicated mean effective pressure is 660 kPa. Calculate the
indicated, brake and mechanical efficiencies.