Turbocharger: Description and Operation

The turbocharger is used to increase power on a demand basis. As engine load increases and the throttle is opened, more air/fuel mixture is drawn into the combustion chambers. As this increased volume is burned, a larger volume of high energy exhaust gasses enters the engine exhaust system and is directed through the turbocharger turbine housing. Some of the exhaust gas energy is used to increase the speed of the turbine wheel which is connected to the compressor wheel. The increased speed of the compressor wheel compresses the air/fuel mixture and delivers it to the intake manifold. The high pressure in the intake manifold allows a denser charge to enter the combustion chambers, in turn developing more engine power during the combustion cycle. The intake manifold pressure (boost) is controlled to a maximum value by an exhaust gas bypass valve (wastegate). The wastegate allows a portion of the exhaust gas to bypass the turbine wheel, thereby not increasing turbine speed. The wastegate is operated by a spring-loaded diaphragm device sensing the pressure differential across the compressor. When intake manifold pressure reaches a predetermined value above ambient pressure, the wastegate begins to bypass the exhaust gas.