Describe the Air Fuel Ratio in CI Engine.

Describe the Air Fuel Ratio in CI Engine.
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Answer :

Air Fuel Ratio in CI Engine: Thermodynamic analysis of the engine cycles has clearly established that operating an engine with a leaner air-fuel ratio always gives a better thermal efficiency but the mean effective pressure and the power output reduce. The CI engine is always designed to operate with an excess air, of 15 to 40% depending upon the application. The power output curve for a typical CI engine operating at constant speed is shown in Fig. given below. The approximate region of A/F ratios in which visible black smoke occurs is indicated by the shaded area.

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Irrespective of load at any given speed, an approximately constant supply of air enters the cylinder. With change in load, the quantity of fuel injected is changed varying the air fuel ratio. The overall air fuel ratio thus varies from about 18:1 at full load to about 80:1 at no load. The diesel engine always designed to operate with an excess air of 15 to 40% depending upon the application.

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