How A Turbocharger Works
The principle of turbocharging
In order to explain how a turbocharger works we must first look at the four-stroke cycle:
The four stages of the cycle – commonly known as Suck, Squeeze, Bang and Blow – are as follows:
Suction (charge exchange stroke)
In a diesel or petrol injection engine, the piston moves down and air is drawn through the intake valve. In a carburettor petrol engine, the air is mixed with petrol.
Compression (power stroke)
As the piston moves back up, the air or petrol/air mixture is compressed.
Expansion (power stroke)
In the carburettor or injected petrol engine, the fuel/air mixture is
ignited by a spark plug; in the diesel engine, fuel is injected under high
pressure and the mixture ignites spontaneously. In either case, the
explosion drives the piston downwards.
Exhaust (charge exchange stroke)
The exhaust gas is expelled through the exhaust valve when the piston moves up.
In a turbocharged engine, the air is pre-compressed before being supplied to the cylinder during the suction stroke. Because it is at a higher pressure, a greater mass of air is held in the combustion chamber, which means that fuel is burned more efficiently. This increases the engine’s power output, giving more torque and a higher top speed compared to a normally aspirated engine of the same swept volume, and reduces emissions.
Some diesel engines can also be set up to accept more air but the same amount of fuel, which does not increase the power but results in cleaner exhaust gases.