1. CIET,LAM,DEPARTMENT OF MECHANICAL ENGINEERING
Combustion
Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.
Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion.
Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.
CIET,LAM,DEPARTMENT OF MECHANICAL ENGINEERING

2. Introduction Definition of combustion Homogeneous mixture
Combustion is a chemical reaction in which certain elements of the fuel like hydrogen and carbon combine with oxygen liberating heat energy and causing an increase in temperature of the gases
Presence of combustible mixture and means of initiating the process are necessary
Homogeneous mixture
Heterogeneous mixture
In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience’s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners.

3. Combustion in S.I.Engines
Homogeneous mixture from carburetor
Piston at the end of compression stroke
Combustion initiated by spark plug
Burnt mixture
If you have several points, steps, or key ideas use multiple slides. Determine if your audience is to understand a new idea, learn a process, or receive greater depth to a familiar concept. Back up each point with adequate explanation. As appropriate, supplement your presentation with technical support data in hard copy or on disc, , or the Internet. Develop each point adequately to communicate with your audience.
Un burnt mixture
Flame front spreading over a combustible mixture with certain velocity
Flame propagation

4. Combustion in S.I.Engines
Flame propagation is caused by heat transfer and diffusion of burning fuel molecules from the combustion zone to the adjacent layers of un burnt mixture.
Burnt mixture
Un burnt mixture
Flame front is a narrow zone separating the fresh mixture from the combustion products
The velocity with which the flame front moves w.r.t. the unburned mixture in a direction normal to its surface is called the NORMAL FLAME VELOCITY
Flame propagation
Flame speed ≈ 40 cm/s, for =1
Max. Flame speed occurs at =1.1 to 1.2 ( slightly rich mixture)
If you have several points, steps, or key ideas use multiple slides. Determine if your audience is to understand a new idea, learn a process, or receive greater depth to a familiar concept. Back up each point with adequate explanation. As appropriate, supplement your presentation with technical support data in hard copy or on disc, , or the Internet. Develop each point adequately to communicate with your audience.
For Richer mixtures Flame extinguishes as with the speed drops.
Qloss from combustion = Qdue to combustion
Flame speed can be increased by introducing turbulence and proper air movement
The rate of chemical reaction determines the combustion characteristics

5. Combustion in C.I.Engines
Piston at the end of compression
Combustion starts in the zones where =1.1 to 1.2 corresponding to maximum rate of chemical reaction
Fuel injection
Determine the best close for your audience and your presentation. Close with a summary; offer options; recommend a strategy; suggest a plan; set a goal. Keep your focus throughout your presentation, and you will more likely achieve your purpose.
The rate of combustion is determined by the velocity of mutual diffusion of fuel vapors and air and the rate of chemical reaction is of minor importance
Self-ignition or spontaneous ignition of F-A mixture at high temperature developed due to higher compression ratios, is of primary importance in determining the combustion characteristics.

6. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Crank angle (deg)
Pressure
Compression a
Theoretical pressure crank angle (p-) diagram

7. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Crank angle (deg)
Pressure
Compression a
Theoretical pressure crank angle (p-) diagram

8. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Crank angle (deg)
Pressure
Compression a
Theoretical pressure crank angle (p-) diagram

9. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Crank angle (deg)
Pressure b
Compression a
Theoretical pressure crank angle (p-) diagram

10. Stages of Combustion in S.I.Engines
Crank angle (deg)
Pressure c
Combustion b
Compression
spark a
Theoretical pressure crank angle (p-) diagram

11. Stages of Combustion in S.I.Engines
Crank angle (deg)
Pressure c
Combustion
Expansion b
Compression
spark a
Theoretical pressure crank angle (p-) diagram

12. Stages of Combustion in S.I.Engines
Crank angle (deg)
Pressure c
Combustion
Expansion b
Compression
spark a
Theoretical pressure crank angle (p-) diagram

13. Stages of Combustion in S.I.Engines
Crank angle (deg)
Pressure c
Combustion
Expansion b
Compression
spark d a
Theoretical pressure crank angle (p-) diagram

14. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)

15. Stages of Combustion in S.I.Engines
BDC
Compression
TDC
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
Compression

16. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
Spark A
Compression
and combustion

17. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
Spark B
Combustion A
Compression
Motoring
and combustion
TDC

18. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar) C
Expansion
Spark B
Combustion A
Compression
Motoring
TDC

19. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar) C
Expansion D
Spark B
Combustion A
Compression
Motoring
TDC

20. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar) C
Expansion D
Spark B
Combustion A
Compression
Motoring
TDC

21. pressure crank angle (p-) diagram
Motoring curve
BDC
Compression
TDC
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)

22. pressure crank angle (p-) diagram
Motoring curve
BDC
Compression
TDC
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
Compression

23. pressure crank angle (p-) diagram
Motoring curve
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
TDC
BDC
Compression
Compression

24. pressure crank angle (p-) diagram
Motoring curve
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
TDC
BDC
Compression
Compression

25. pressure crank angle (p-) diagram
Motoring curve
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
TDC
BDC
Compression
Expansion
Expansion

26. pressure crank angle (p-) diagram
Motoring curve
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
TDC
BDC
Expansion
Compression
Expansion

27. pressure crank angle (p-) diagram
Motoring curve
pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
TDC
BDC
Expansion
Compression
Expansion

28. Stages of Combustion in S.I.Engines
Actual pressure crank angle (p-) diagram
Crank angle (deg) 30 20 10
Pressure (bar)
Spark A
TDC B D
Motoring
Compression
Combustion
Expansion I II
III
I Ignition lag
II Propagation of flame
III After burning

29. Stages
A to B
B to C
C to D

30. Flame front propagation
The factors which influence the flame front are
Reaction rate
The rate at which the flame eats its way into the unburned charge
Transposition rate
Due to the physical movement of the flame front relative to the cylinder wall
The result of the pressure differential between the burning gases and the unburnt gases in the combustion chamber
Turbulence

31. Flame front propagation
Time of flame travel across the chamber (%)
100 80 60 40 20
Distance of flame travel across the chamber (%) B A
Area I
Low transposition rate Low Turbulence
Low reaction rate

32. Flame front propagation
Time of flame travel across the chamber (%)
100 80 60 40 20
Distance of flame travel across the chamber (%) C
Area II
High transposition rate High Turbulence High reaction rate B A
Area I
Low transposition rate Low Turbulence
Low reaction rate

33. Flame front propagation
Time of flame travel across the chamber (%)
100 80 60 40 20
Distance of flame travel across the chamber (%)
Low transposition rate Low Turbulence Low reaction rate D
Area III C
Area II
High transposition rate High Turbulence High reaction rate B A
Area I
Low transposition rate Low Turbulence
Low reaction rate

34. Factors influencing the flame speed
Turbulence
Fuel-air ratio
Temperature and pressure
Compression ratio
Engine output
Engine speed
Engine size
Lean
Equivalence ratio
0.006
0.004
0.002
0.000
Time in seconds
Stoichiometric mixture A
Rich

35. Illustrations of various Combustion rates
Rate of Pressure rise
Peak pressure
Start of pressure rise
Rate of pressure rise
Indicated by the slope of the curves between start of pressure rise and the peak pressure 30 20 10
Pressure (bar)
Motoring curve
Compression
Power
TDC
Crank angle (deg)
Illustrations of various Combustion rates

36. Illustrations of various Combustion rates
Rate of Pressure rise
Peak pressure
Start of pressure rise
Rate of pressure rise
Indicated by the slope of the curves between start of pressure rise and the peak pressure 30 20 10
Pressure (bar)
Motoring curve
Compression
Power
TDC
Crank angle (deg)
Illustrations of various Combustion rates

37. Illustrations of various Combustion rates
Rate of Pressure rise
Peak pressure
Start of pressure rise
Rate of pressure rise
Indicated by the slope of the curves between start of pressure rise and the peak pressure 30 20 10
Pressure (bar)
Motoring curve
Compression
Power
TDC
Crank angle (deg)
Illustrations of various Combustion rates

38. Illustrations of various Combustion rates
Rate of Pressure rise
High rate-I
Peak pressure
Start of pressure rise
Normal rate-II
Rate of pressure rise
Indicated by the slope of the curves between start of pressure rise and the peak pressure 30 20 10
Low rate-III
Pressure (bar)
Motoring curve
Compression
Power
TDC
Crank angle (deg)
Illustrations of various Combustion rates