Comparison between Petrol and Diesel Engines

Petrol and Diesel engines
Comparison between petrol engine and diesel engine can be done in aspects like working, pressures, combustion, operating cycle, compression ratios, thermal efficiency, engine speeds, maintenance cost and running costs are listed below in tabular form.

S.no
Petrol Engines
Diesel Engines
1A petrol engine draws a mixture of petrol and air during suction stroke.A diesel engine draws only air during suction stroke.
2The carburetor is installed in petrol engines to mix air and petrol in the required proportion and to supply it to the engine during suction stroke.The injector or atomiser is installed in diesel engines to inject the fuel at the end of the compression stroke.
3The pressure at the end of the compression is about 10 bar.The pressure at end of the compression is about 35 bar.
4The charge (i.e. petrol and air mixture) is ignited with the help of spark plug.The fuel is injected in the form of fine spray. The temperature of the compressed air is about 600° C at a pressure of about 35 bar.
5A petrol engine has compression ratio approximately from 6 to 10.A diesel engine has compression ratio approximately from 15 to 25.
6The combustion of fuel takes place approximately at constant volume. In other words, it works on Otto cycle.The combustion of fuel takes place approximately at constant pressure. in other words, it works on Diesel cycle.
7The thermal efficiency is upto about 26%.The thermal efficiency is upto about 40%.
8Overheating trouble is more in petrol engine due to low thermal efficiency.Overheating trouble is less in diesel engine due to high thermal efficiency.
9The starting of petrol engine is easy due to low compression ratio.The starting of diesel engine is slightly difficult due to higher compression ratio compared to petrol engine.
10As the compression ratio is low, the petrol engines are cheaper and lighter in weight.As the compression ratio is high, the diesel engines are costlier and heavier in weight.
11The running cost of petrol engine is high because the higher cost of petrol fuel.The running cost of diesel engine is low because of lower cost of diesel fuel.
12The maintenance cost is less.The maintenance cost is more.
13Petrol engines are high speed engines.Diesel engines are relatively low speed engines.
14The petrol engines are generally are installed in light duty vehicles such as scooters, motorcycles, cars. These are also used in airplanes.The diesel engines are generally are installed in heavy duty vehicles such as buses, trucks, tractors, earth moving machines etc.
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All Comments

  • What is the compression ratio of the diesel engine?

    Bipin Apr 1, 2016 10:07 pm Reply

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