Turbocharger: Description and Operation

The turbocharger is an exhaust driven device which compresses the air/fuel mixture that is used to increase engine power on a demand basis, allowing a smaller, more economical engine to be used.
A turbine in the exhaust gas flow is connected through a shaft to the impeller (compressor). During normal, steady operation, the turbine does not rotate with sufficient speed to boost pressure to compress the air/fuel mixture. As speed increases, the mixture is compressed, allowing the denser mixture to enter the combustion chambers and develop more engine power during the combustion cycle.
The intake manifold pressure (boost) is controlled by a wastegate valve which is used to bypass a portion of the exhaust gases around the turbine at a predetermined point in the cycle, limiting the boost pressure.