Internal Combustion Engines
Diesel engine can work on very lean air fuel ratio of the order of 30: 1. A petrol engine can also work on such a lean ratio provided

It is properly designed
Best quality fuel is used
Flywheel size is proper
Cannot work as it is impossible

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Internal Combustion Engines
In a four stroke cycle diesel engine, the exhaust valve

Opens at 30° before bottom dead centre and closes at 10° after top dead centre
Opens at bottom dead centre and closes at top dead centre
May open and close anywhere
Opens at 30° after bottom dead centre and closes at 10° before top dead centre

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