There are many different kinds of “internal combustion engines” out there, but all of them run on one simple idea: take a bit of fuel, mix it with a bit of air, and ‘combust’ it (set it on fire). What comes out is energy, which the engine converts into power. An engine in real life is not as simple or straight forward, but they all follow this basic idea. Fuel and air go in, and power comes out.
But what makes an internal combustion engine different from just setting fuel on fire? Well, let’s take a look at the basic petrol engine, the kind you find in most of the cars on the road. Inside your basic engine, there is a piston that moves up and down, intake valves for things to go in, and exhaust valves for things to go out.
The basic combustion process happens in 4 separate parts, starting with the piston at the top of the cylinder and the intake valve open. As the piston moves down, it acts like a vacuum cleaner: air and petrol are sucked into the engine through the intake valve, and this is called the “intake” part of the process.
As soon as the piston reaches the bottom, the intake valve closes and the piston begins to travel back up, squeezing the air and petrol as it moves upwards. The piston squeezes everything together very tightly, and this is known as “compression”. The tighter the petrol and air is squeezed, the more power the engine produces.
When the piston reaches the top again, a spark is used to set the air and petrol on fire. The squeezed mixture wants to explode and expand, and as it expands the piston is forced back down. This is called the “power” stage, and this is where the engine produces its power.
When the piston reaches the bottom, the exhaust valve opens. This final stage is known as the “exhaust” stage: when the piston moves upwards it pushes all the burned petrol out through the exhaust valve, and when the piston reaches the top the process starts all over again from the “intake” stage.
This process happens many, many times a second. Whether the engine uses petrol or diesel, pistons or a rotor, electronic fuel injection or a carburettor; all of these are called internal combustion engines because they ‘combust’ fuel and air to produce power.
