Draw P-ⱷ diagram showing stages of combustion in SI engine.

Draw P-ⱷ diagram showing stages of combustion in SI engine.
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Answer :

Stages of combustion in SI engines 

Stage I: Ignition Lag or Preparation Phase: The time elapsed between the fuel injection into the combustion chamber and starting of combustion. It is the growth and development of a semi propagating nucleus of flame. It is a chemical process which depends on-nature of fuel, temperature & pressure, proportion of exhaust gas, rate of burning and temperature. 

Stage II: Propagation of flame: It is a simple, pure and mechanical process. The starting point of the second stage is where first measurable rise of pressure can be seen on the indicator diagram. i.e. the point where the line of the combustion departs from the compression line. During second stage, the flame spreads throughout the combustion chamber. The second stage ends as maximum pressure (on indicator diagram) is reached. 

Stage III: After burning. End of second stage means completion of flame travel. But it does not result in complete heat release (burning of fuel). Even after the passage of flame, some chemical adjustments continue throughout the expansion stroke- near the walls and behind the turbulent flame front. The rate of combustion reduces due to surface of the flame front becoming smaller and reduction in turbulence. 

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