Difference between Petrol Engine & Diesel Engine

Petrol Engine	Diesel Engine
i) A petrol engine draws a mixture of petrol and air during suction stroke.	i) A diesel engine draws only air during suction stroke.
ii) The carburetor is employed to mix air and petrol in the required proportion and to supply it to the engine during suction stroke.	ii) The injector or atomizer is employed to inject the fuel at the end of compression.
iii) The pressure at the end of compression is about 10 bar.	iii) The pressure at the end of compression is about 35 bar.
iv) The charge (i.e. petrol and air mixture) is ignited with the help of a spark plug.	iv) The fuel is injected in the form of fine spray. The temperature of the compressed air (about 600oC at a pressure of about 35 bar) is sufficiently high to ignite the fuel.
v) The combustion of fuel takes place approximately at constant volume. In other words, it works on Otto Cycle.	v) The combustion of fuel takes place approximately at constant pressure. In other words, it works on Diesel Cycle.
vi) A petrol engine has compression ratio approximately from 6 to10.	vi) A diesel engine has compression ratio approximately from 15 to 25.
vii) The starting is easy due to low compression ratio.	vii) The starting is little difficult due to high compression ratio.
viii) As the compression ratio is low, the petrol engines are lighter and cheaper.	viii) As the compression ratio is high, the diesel engines are heavier and costlier.
ix) The running cost of petrol engines is high because of the higher cost of petrol.	ix) The running cost of diesel engines is low because of the lower cost of diesel.
x) The maintenance cost is less.	x) The maintenance cost is more.
xi) The thermal efficiency is upto about 26%.	xi) The thermal efficiency is upto about 40%.
xii) These are high speed engines	xii) These are relatively low speed engines
xiii) The petrol engines are generally employed in light duty vehicles such as scooters, motorcycles, cars. These are also used in airplane.	xiii) The petrol engines are generally employed in heavy duty vehicles such as buses, trucks and  earth moving machines etc.