Automobile companies mostly use two types of engines in their cars and that is petrol and diesel engines, though EV is new in trend but still not high in demand, today also people go for petrol and diesel engines only because they are cheap than EVs, they are more reliable than EVs, and they have a long legacy. But how these engines work, how these engines are different from each other. Let’s find out, engines are the combination of the pistons, cylinders, spark plugs and how this mechanicals works, let’s see.
In today’s world, all engines work on 4 stroke principle, which gives instant and more power to the engines compare to its predecessor 2 stroke engine and how this 4 stroke engine works let’s see.
Here the engine takes 4 strokes to develops energy. In the first stroke of the petrol engine which is known as the intake stroke, the piston goes down and fills air and fuel mixture in the cylinder of the engine. The second stroke is also known as the compression stroke, where the piston goes upward and compresses the mixture of fuel and air. In the third stroke which is known as the fuel or combustion stroke, where the spark plug does the work and burn that mixture of air and fuel because of which the piston again goes down downward and through this third stroke engine gets the power and energy. In the fourth stroke which is known as fuel exhaust stroke, where again the piston goes upward and exhausts which generate after burning the mixture of air and fuel.
Here in diesel engine also there are four strokes but the working of this engine is different from petrol in the engine. In the first stroke of the diesel engine which is known as induction stroke, where the piston goes down and fills only air in the cylinder, here no fuel comes in the cylinder in the first stroke of the diesel engine. In the second stroke known as compression stroke which works the same as the petrol engine but here the piston only compresses the air and burns the air. In the third stroke known as the power stroke, here because the air is already burning, fuel comes in the cylinder and starts burning without any need of a spark plug. And the fourth stroke known as exhaust stroke works the same as the fourth stroke of the petrol engine in eliminating the gases from the engine.
So this is the major difference between petrol and diesel engine. The petrol engine uses a spark plug to get ignition because of which petrol engine is also known as SI (spark ignition) engines and the diesel engine uses the compression process to get ignition and because of which diesel engine is also known as CI (compression ignition) engine. The diesel engine also has a more compression ratio than the petrol engine. Now, what is that compression ratio. Let’s see.
What is this compression ratio?
Here in the picture above, the petrol engine has a compression ratio of 10:1, which means 10 unit of air and fuel compresses into 1 unit to heat the mixture and in a diesel engine the compression ratio is 18:1 which means 18 unit of air compresses into 1 unit which gives the more heat as compared to the petrol engine. Compression is much higher with a diesel engine (14:1 to 25:1) than a gasoline engine (8:1 to 12:1).
Because of this compression ratio, the diesel engines are more fuel-efficient, more you compress the air, more you get the efficient, larger compression ratio would give better fuel efficiency, that why diesel engine is 20 percent more fuel-efficient than petrol engine.