Difference between the petrol engine and diesel engine

The temperature at the end of the compression
is less for the petrol engine.
 Thus a spark plug is needed for the  compression. In case of the diesel engine the  temperature at the end of the compression is  above the self-ignition temperature of the fuel.
 Hence the fuel ignited is allowed to enter the
cylinder due to the high temperature.
 No spark plug is required for the diesel
engine.
 For the separate entry of the fuel after the  compression stroke, a nozzle is provided for  the diesel engines.
 In case of the petrol engine they do not have
the nozzle.
 In petrol engine the air and the fuel, are mix  inside a carburetor before entering the engine  cylinder. In diesel engine there is no mixing  of air and fuel before suction stroke. Hence  diesel engine does not have a carburetor.

 Heat addition must take place at the constant  volume for petrol engine. It takes place at the  constant pressure for diesel engine
 For the same compression ratio, the efficiency  of a petrol engine is higher than that of the  diesel engine. This is theoretical.
 In an actual practice the compression ratio of  a diesel engine is 1.5 times to 2 times more  than that of a petrol engine.
 Hence the diesel engine efficiency is much
higher.
 Under some conditions the air fuel ratio for  the petrol engine must be 16 and for the diesel  engine case the ratio of the air fuel mixture  must be 25 to 35.