Difference Between Petrol and Diesel Engine - Working of Petrol & Diesel Engines

Petrol engines and diesel engines are the most commonly seen engines in the market. However, petrol engines and diesel engines differ in their working cycles. The petrol engine runs on the otto cycle while the diesel engine runs on the diesel cycle. There are many other differences between the petrol engine and the diesel engine, which will be explored in the next section. Before going into details about the differences between petrol engines and petrol engines, let us have a look at their working cycles.

Petrol engine

The first petrol engine was developed in Europe in 1876. The petrol engine is otherwise called the gasoline engine. Scooters, cars, and machines use petrol engines. A petrol engine is basically an internal combustion engine consisting of spark ignition.

Fuel and air in petrol engines are mixed before their compression. After fuel and air are compressed, ignition of fuel is carried out using an electric spark.

Working of petrol engines

Petrol engines work on the otto cycle. The process involved in the working of petrol engines is explained below.

The Otto cycle consists of 4 internally reversible processes.

1. Mixture of fuel and air - Fuel and air are mixed together in a cylinder.

2. Compression of the mixture - The mixture of fuel and air is compressed with the help of a crankshaft.

3. Power stroke - Ignition of fuel is carried out using an electric spark. The mixture forcibly pushes the piston downwards.

4. Exhaust stroke - Gases are released from the exhaust valves of the vehicle.

Diesel engine

A German developed the first diesel engine named Rudolf Diesel in 1893. In olden times, diesel engines were used to run trains. But now, diesel engines are also used in heavy vehicles and trucks. Similar to petrol engines, diesel engines are also internal combustion engines. Diesel engines work on diesel. In diesel engines, compression of air takes place first. When the air is compressed, it becomes hot. To this hot compressed air, diesel is added. In the presence of hot compressed air, diesel also attains the ignition temperature.

Working of diesel engines

Diesel engines work on the mechanism of the diesel cycle. The process involved in the working of diesel engines is explained below.

The diesel cycle also consists of 4 internally reversible processes.

1. Induction stroke - The piston of the diesel engine moves downwards. The downward movement of the piston helps in drawing air into the cylinder.

2. Compression stroke - The compression of air takes place. The piston moves back to its place, thereby compressing the air. Due to compression, air starts becoming hot.

3. Power stroke - Power stroke is a phase where diesel is added to the hot compressed air.

4. Exhaust stroke - Diesel attains the ignition temperature in the presence of hot compressed air. Smoke or gases are released from the exhaust valves of the vehicle.

Differences between the petrol engine and diesel engine

Now that we have understood the working principles of the petrol engine and diesel engine, let us explore the differences between the both.

Petrol engine	Diesel engine
The petrol engine works on the basis of the Otto cycle.	The diesel engine works on the basis of the diesel cycle.
In petrol engines, the mixture of fuel and air takes place first, followed by its compression.	In diesel engines, the compression of air takes place first, followed by the addition of diesel into the hot air.
Highly volatile fuels are suitable for petrol engines.	Low volatile fuels are suitable for diesel engines.
In petrol engines, the cause of ignition is the electric spark. An electric spark is used to ignite the fuel.	In diesel engines, the cause of ignition is the heat produced by the compression of air. The heat produces by air compression heats up the diesel, thereby resulting in the ignition.
The compression ratios of petrol engines are low. The approximate compression ratio in petrol engines ranges from 7 to 10.	The compression ratios of diesel engines are high. The approximate compression ratio in diesel engines ranges from 11 to 20.
The amount of fuel consumed is higher compared to diesel engines	The amount of diesel consumed is lower compared to petrol engines.
The noise produced by petrol engines is less.	The noise produced by diesel engines is comparatively high.
The running cost of petrol engines is high.	The running cost of diesel engines is low.
Petrol engines are widely used for light-duty applications.	Diesel engines are widely used for heavy-duty applications.
Examples: Scooters, cars, and machines.	Examples: Heavy vehicles and trucks.