What is the difference between Petrol and Diesel engine?

Petrol (gasoline) and diesel are the two primary fuels used in engines nowadays. Although both these fuels are derived from crude oil, their properties differ a lot. The engines working on Petrol (gasoline) have a different design and ignition system as compared to engines working on Diesel. In this article, we will discuss the major differences between Petrol and diesel engines.

Major differences between Petrol and Diesel engines

(If you are reading this article, it is expected that you know the basic working of four-stroke and two-stroke engines)

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1. In Petrol engines, the air-fuel mixture is supplied to the combustion chamber which is ignited using a spark plug. Petrol engines are therefore also known as Spark ignition engines. In diesel engines, the air is supplied to the combustion chamber. The air is compressed by the piston raising its temperature and pressure. Diesel is then injected using the fuel injector. The diesel ignites on coming in contact with the hot compressed air thereby producing a power stroke. Diesel engines are also known as compression ignition engines.

2. Petrol is a highly volatile fuel as compared with diesel. Diesel has lower volatility and lower self-ignition temperature. This is the reason why petrol engines use spark plug ignition and diesel engines use compression ignition.

3. Petrol engines are less noisy and are suitable for cars and motorcycles. Diesel engines are more noisy and are suitable for heavy-duty vehicles like trucks. Diesel engines produce more torque.

4. Compression ratio

The volume of the combustion chamber when the piston is at the Bottom Dead Centre (BDC) divided by the volume of the combustion chamber when the piston is at the Top Dead Centre (TDC) is the compression ratio. In other words, Clearance volume plus swept volume divided by clearance volume is the compression ratio. Petrol engines have lower compression ratios as compared with diesel engines. In Diesel engines, the stroke length is more.

5. Petrol engines have lower efficiencies. Fuel consumption is generally higher in petrol engines.

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