This presentation was prepared by Mechanical Engineering students during their Internal Combustion Course. Students belong to a very prestigious Engineering institute of Pakistan "University of Engineering and Technology Lahore"

1. *
Presented By:
Hamid Ali 2013-ME-326
Mehmood-Ul-Hassan 2013-ME-305
Ahsan Ali Hanif 2013-ME-327
Waseem Sarwar 2013-ME-344
Tahseen Kanwal 2013-ME-322
Presented To:
Dr. Shahid Imran
1

2. Contents:2
• Ideal cycles
• Fuel air cycle
• Factors in fuel air cycles
• Cycle comparisons
• Actual cycles
• Problem statement

3. Otto Cycle
1-2 isentropic compression
2-3 constant volume heat addition
3-4 isentropic expansion
4-1 constant volume heat rejection 3
4
2
1
v
v
v
v
r 1
1
1 
 k
rVconst c
th

4. Diesel Cycle
1-2 isentropic compression
2-3 constant pressure heat addition
3-4 isentropic expansion
4-1 constant volume heat rejection

5. Dual Cycle
1-2 isentropic compression
2-3 constant volume heat addition
3-4 constant pressure heat addition k= p3/p2
4-5 isentropic expansion
5-1 constant volume heat rejection

6. Fuel-air cycle analysis:6
 In the Fuel-Air Cycle, the engine processes are still modelled as ideal but the
properties of the working fluid (residual gas mixture before combustion, and
burned gases after combustion) are described accurately.
 The Fuel-Air cycle Assumptions :
a. No change in the fuel or air chemical composition before combustion.
b. The process is frictionless and adiabatic.
c. Charge is in chemical equilibrium after combustion.
d. Combustion process is instantaneous.
e. Fuel is completely vaporized and perfectly mixed with the air (for SI only).

7. Factors in fuel air cycle:7
I. Actual composition of cylinder gases
II. The variation of Specific heat
III.Dissociation Effect
IV.Variation of No. of moles

8. Composition of cylinder gas:8
 (Fuel +Air + Water vapour + residual gas)
 The fuel air ratio changes during the engine operation
 The amount of exhaust gases changes with speed and load on the engine.
 The effect of cylinder composition on the performance of the engine can easily
computed by means of suitable numerical techniques.

9. Composition of cylinder gas:9

10. All gases except mono-atomic gases, show an
increase in specific heat with temperature.
However between the temperature range 300 K – 1500
K the specific heat curve is nearly a straight line which
may be approximately expressed in form
Above 1500 K the specific heat increases is much more rapid
and may be expressed in the form
The variation of specific heat

11. The variation of specific heat

12. Dissociation

13. Variation of no. of moles
The number of molecules in the cylinder varies as the pressure and
temperature change
The number of molecule presented after combustion depend upon
I. Fuel-Air ratio
II.Pressure and temperature
The number of mole does a direct effect on the amount of work that the
cylinder gas impact on the piston .

14. Cycle comparisons:14
• Equal compression ratio and equal heat added

15. Cycle comparisons:15
• Equal compression ratio and equal heat rejected

16. Cycle comparisons:16
• Equal maximum pressure and equal heat added

17. Cycle comparisons:17
• Equal maximum pressure and maximum temperature

18. Air Standard
Cycle
Air Fuel
Cycle
Actual
Cycle
Corrected for
characteristics
of air-fuel
mixture
Corrected for
losses
Actual cycle:18

19. Factors affecting thermodynamic cycles:19
Heat transfer
Finite combustion time
Exhaust blowdown loss
Crevice effects and leakage
Friction loss

20. Heat transfer loss:20
• Losses which occur due to heat transfer through water jackets and
cylinder walls
• Loss occur in compression and expansion stroke
Finite Combustion time:
• Combustion process is actual cycles is not instantaneous but is
spread over time
• Combustion process spread over 30-40° crank revolutions

21. Exhaust Blowdown loss:21
• Loss which occur due to early opening of exhaust valve
• Best Compromise is 40-60° bBDC
Friction loss:
• Loss which occur due to friction between piston and chamber
walls
• Loss due to energy spent in operating auxiliary equipments

22. Crevice effects and leakage:22
• Leaking of gas flow through crevices/gaps between piston, piston rings
and cylinder walls
Leakage
Compression stroke Expansion stroke

23. The NOX emission from automobiles is a mixture of NO and NO2. At high
temperatures, the mixture is mostly NO, and at low temperatures, mostly NO2.
Consider a mixture with elemental composition of 1 mole of nitrogen atom and 2
moles of oxygen atoms at a fixed pressure of 1 atmosphere. Plot the equilibrium mole
fraction of NO as a function of temperature in the 600 to 1000 K range. (The actual
exhaust gas is not in equilibrium; therefore, the equilibrium value of NO is a lower
bound.) Note that at equilibrium above 1000 K, most of the gas is NO.
The equilibrium
constants from the
JANAF table are:
T(K)
Log10Kp for NO Log10Kp for NO2
600 -7.210 -6.111
700 -6.086 -5.714
800 -5.243 -5.417
900 -4.587 -5.185
1000 -4.062 -5.000
Problem statement:

24. 2N+ 3/2 O2 → NO+NO2
Kp = (PNo * PNO2)/(P2
N * P3/2
O2 )
Px= x∗Pt
𝒙 =
𝐍𝐨 𝐨𝐟 𝐦𝐨𝐥𝐞𝐬 𝐨𝐟 𝐚 𝐠𝐚𝐬 𝐢𝐧 𝒎𝒊𝒙𝒕𝒖𝒓𝒆
𝐭𝐨𝐭𝐚𝐥 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐦𝐨𝐥𝐞𝐬 𝐨𝐟 𝒎𝒊𝒙𝒕𝒖𝒓𝒆
Formulas:

25. 0
1
2
3
4
5
6
7
8
9
10
600 700 800 900 1000 1100
MoleFractionofNO
Temperature (k)
Temperature Vs Mole fraction of NO
Temperatur
e
Mole
fraction of
NO
600 0.02835
700 0.199
800 0.887
900 3.16
1000 9.344
Crevice effects and leakage:

26. 0
1
2
3
4
5
6
7
8
9
10
600 700 800 900 1000 1100
AxisTitle
Axis Title
Mole fraction of NO2
Temperature
Mole fraction
of NO2
600 9.34
700 3.16
800 0.97
900 0.2
1000 0.028
Crevice effects and leakage: