Comparison between a 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.
|1||A petrol engine draws a mixture of petrol and air during the suction stroke.||A diesel engine draws only air during the suction stroke.|
|2||The carburetor is installed in petrol engines to mix air and petrol in the required proportion and to supply it to the engine during the suction stroke.||The injector or atomizer is installed in diesel engines to inject the fuel at the end of the compression stroke.|
|3||The pressure at the end of the compression is about 10 bar.||The pressure at the end of the compression is about 35 bar.|
|4||The charge (i.e. petrol and air mixture) is ignited with the help of spark plug.||The fuel is injected in the form of a fine spray. The temperature of the compressed air is about 600° C at a pressure of about 35 bars.|
|5||A petrol engine has compression ratio approximately from 6 to 10.||A diesel engine has compression ratio approximately from 15 to 25.|
|6||The 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.|
|7||The thermal efficiency is up to about 26%.||The thermal efficiency is up to about 40%.|
|8||Overheating trouble is more in petrol engine due to low thermal efficiency.||Overheating trouble is less in diesel engine due to high thermal efficiency.|
|9||The starting of petrol engine is easy due to low compression ratio.||The starting of the diesel engine is slightly difficult due to higher compression ratio compared to a petrol engine.|
|10||As 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.|
|11||The running cost of petrol engine is high because of the higher cost of petrol fuel.||The running cost of the diesel engine is low because of the lower cost of diesel fuel.|
|12||The maintenance cost is less.||The maintenance cost is more.|
|13||Petrol engines are high-speed engines.||Diesel engines are relatively low-speed engines.|
|14||The petrol engines are are installed in light duty vehicles such as scooters, motorcycles, cars. These are also used in airplanes.||The diesel engines are are installed in heavy-duty vehicles such as buses, trucks, tractors, earth moving machines, etc.|
What is the compression ratio of the diesel engine?
Compression ratio of diesel engine would be in between 15 to 25.
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