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

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.

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, e-mail, 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

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, e-mail, 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

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.

Stages of Combustion in S.I.Engines BDC Compression TDC 0 180 360 Crank angle (deg) Pressure Compression a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines BDC Compression TDC 0 180 360 Crank angle (deg) Pressure Compression a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines BDC Compression TDC 0 180 360 Crank angle (deg) Pressure Compression a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines BDC Compression TDC 0 180 360 Crank angle (deg) Pressure b Compression a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines 0 180 360 Crank angle (deg) Pressure c Combustion b Compression spark a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines 0 180 360 Crank angle (deg) Pressure c Combustion Expansion b Compression spark a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines 0 180 360 Crank angle (deg) Pressure c Combustion Expansion b Compression spark a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines 0 180 360 Crank angle (deg) Pressure c Combustion Expansion b Compression spark d a Theoretical pressure crank angle (p-) diagram

Stages of Combustion in S.I.Engines BDC Compression TDC Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar)

Stages of Combustion in S.I.Engines BDC Compression TDC Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) Compression

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) Spark A Compression and combustion

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) Spark B Combustion A Compression Motoring and combustion TDC

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) C Expansion Spark B Combustion A Compression Motoring TDC

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) C Expansion D Spark B Combustion A Compression Motoring TDC

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) C Expansion D Spark B Combustion A Compression Motoring TDC

pressure crank angle (p-) diagram Motoring curve BDC Compression TDC pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar)

pressure crank angle (p-) diagram Motoring curve BDC Compression TDC pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) Compression

pressure crank angle (p-) diagram Motoring curve pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) TDC BDC Compression Compression

pressure crank angle (p-) diagram Motoring curve pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) TDC BDC Compression Compression

pressure crank angle (p-) diagram Motoring curve pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) TDC BDC Compression Expansion Expansion

pressure crank angle (p-) diagram Motoring curve pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) TDC BDC Expansion Compression Expansion

pressure crank angle (p-) diagram Motoring curve pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 30 20 10 Pressure (bar) TDC BDC Expansion Compression Expansion

Stages of Combustion in S.I.Engines Actual pressure crank angle (p-) diagram Crank angle (deg) 100 80 60 40 20 8 0 20 40 60 80 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

Stages A to B B to C C to D

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

Flame front propagation 0 20 40 60 80 100 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

Flame front propagation 0 20 40 60 80 100 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

Flame front propagation 0 20 40 60 80 100 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

Factors influencing the flame speed Turbulence Fuel-air ratio Temperature and pressure Compression ratio Engine output Engine speed Engine size 60 100 140 180 220 Lean Equivalence ratio 0.006 0.004 0.002 0.000 Time in seconds Stoichiometric mixture A Rich

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 120 80 40 TDC 40 80 120 Crank angle (deg) Illustrations of various Combustion rates

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 120 80 40 TDC 40 80 120 Crank angle (deg) Illustrations of various Combustion rates

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 120 80 40 TDC 40 80 120 Crank angle (deg) Illustrations of various Combustion rates

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 120 80 40 TDC 40 80 120 Crank angle (deg) Illustrations of various Combustion rates