Today the automobiles are available in diesel and petrol variants. Customers often feel confused regarding which vehicle to choose as they do not 
know the difference between the two. Here a little effort has been put up to bring the difference between a petrol engine and a diesel engine into focus.
All about petrol engine
Coming to the most basic difference, a petrol engine uses petrol as a fuel. Simple it may appear to you, but the type of fuel used affects a lot of engine design. The ignition temperature of petrol is somewhat higher, so a good temperature is required to ignite the fuel in the combustion chamber. A carburetor is required for the purpose. Carburetor is responsible for mixing of atomized fuel in form of a fine spray with the air. This mixture is sucked in during the suction stroke. The compression of the fuel during the compression stroke produces heat but it is not enough to ignite the fuel. Hence an ignition coil and a spark plug is required to ignite the fuel.
The compression ratio of fuel in the combustion chamber varies from 5:1 to 8:1. The compression pressure varies from 6 to 10 kg/cm2. The temperature rises over 260°C during compression. The thermal efficiency varies from 25 to 32%. The weight of the engine per horsepower produced is comparatively lower than the diesel counterpart of the engine and the operating costs are also high.
All about diesel engine
As in case of a petrol engine using petrol as fuel, a diesel engine uses diesel as fuel. Hence the designing of a diesel engine is done keeping in mind the fuel used. The ignition temperature of the diesel is comparatively lower than petrol. The temperature rise obtained due to compression of the air is enough to ignite the fuel. Hence ignition coils and spark plugs are not required in these type of engines. Also it has to be noted that unlike petrol engines, mixture of air and fuel is not sucked in during the suction stroke. Only air is sucked in during the suction stroke and the fuel is injected in atomized form with high pressure ranging from 120 to 200 kg/cm2 after the compression has taken place.
The compression ratio of the fuel is comparatively high and ranges from 14:1 to 22:1 and the pressure of the compression varies from35 to 45 kg/cm2. The temperature rises up to 500°C during the compression. The thermal efficiency of the system varies from 32 to 38%. The weight of the engine per horsepower is comparatively higher and the operating cost is also low.
The way a diesel engine and petrol engine are different from each other is clearly defined in the above paragraphs. Based on the information provided above, a customer will be able to make a wise choice regarding the choice of engine.