Difference Between Petrol and Diesel Engine


The engine is the heart of every vehicle. It pumps fuel into the machine just like a heart pumps blood into a human body. If the engine is dead, the vehicle cannot move a muscle and dies as well. So, to keep your vehicle fit and healthy, it’s important to know what goes on in the engine. Today we will talk about the two types of engine, petrol and diesel. The difference between the two and advantages and disadvantages of both engine types. Let’s get into it.

Petrol Engine vs Diesel Engine

Both petrol and diesel engines work on the four-stroke cycle. In the intake stroke, the fuel mixture is drawn into the cylinder and sprayed with petrol/diesel. In the compression stroke, the fuel is compressed and prepared for ignition. In the power stroke, the compressed fuel is ignited to create an explosion. In the exhaust stroke, the gasses produced from fuel ignition are let out of the engine. 

The first difference between the two engines lies in the type of fuel mixed with the air. In petrol engines, the air is sprayed and mixed with petrol. In diesel engines, the fuel mixture is air and diesel.

The second difference is in the compression cycle. Petrol engines use the Otto Cycle to compress the fuel. In the Otto cycle, air and petrol are mixed in the intake stroke, and the fuel mixture is then compressed in the compression stroke. Diesel engines work on the Diesel Cycle, in which engine only compresses the air and not the fuel mixture. In diesel engines, only air is drawn into the cylinder in the intake stroke. The same air is compressed in the compression stroke. Then, diesel is mixed with that compressed air in the power stroke. Long story short, in petrol engines, air and fuel are mixed pre-combustion, and, in diesel engines, air and fuel are mixed post-combustion.

The third difference is the combustion ratio. Petrol engines have a relatively low compression ratio, somewhere between 8:1 to 12:1. Diesel engines have a high compression ratio between 14:1 to 25:1.

The fourth difference is the source of ignition in the power stroke. In petrol engines, the fuel is ignited with an electric spark. In diesel engines, the fuel mixture goes through self-ignition. There is no spark plug involved in the ignition process. The fuel mixture undergoes ignition due to over-combustion. 

Petrol engines consume more fuel than diesel engines.

Petrol engines have less torque but more power delivery than diesel engines.

Diesel engines have bigger flywheels, so they weigh more than petrol engines.

Petrol engines have a low maintenance cost. Diesel engines are harder to maintain, not only because of the cost factor but also because of the unavailability of an expert mechanic.

Lighter vehicles such as motorcycles, scooters, and cars typically use petrol engines, whereas diesel engines are found in much heavier machinery such as tractors, trucks, and buses.

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Hope you find this guide helpful. Do you know more difference between petrol and diesel engines? Share with us in the comments. Find thousands of used petrol cars and diesel cars for sale in Pakistan.

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