The turbocharger of an internal combustion engine consists of a turbine, and a compressor. Hot exhaust gases flow through the turbine to produce work and the work output from the turbine is used as the work input to the compressor. The pressure of ambient air is increased as it flows through the compressor before it enters the engine cylinders. Thus, the purpose of a turbocharger is to increase the pressure of the air so that more air gets into the cylinders. Consequently, more fuel can be burned and more power can be produced by the engine. In a turbocharger, exhaust gases enter the turbine at 400 degrees C and 120kPa at a rate 0.02 kg/s and leaves at 350 degrees C. Air enters the compressor at 50 degrees C and 100kPa and leaves at 130kPa at a rate of 0.018 kg/s. The compressor increases the air pressure with a side effect: It also increases the air temperature, which increases the gasoline engine to experience and engine knock. To avoid this, an aftercooler is placed after the compressor to cool the warm air by cold ambient air before it enters the engine cylinders. It is estimated the aftercooler must decrease the air temperature below 80 degrees C if knock is to be avoided. The cold ambient air enters the aftercooler at 30 degrees C and leaves at 40 degrees C. Disregard any frictional losses in the turbine and the compressor and treating the exhaust gases as air, determine (a) the temperature of the air at the compressor outlet and (b) the minimum volume flow rate of ambient air required to avoid knock.

Explanation:

The turbocharger of an internal combustion engine consists of a turbine, and a compressor. Hot exhaust gases flow through the turbine to produce work and the work output from the turbine is used as the work input to the compressor. The pressure of ambient air is increased as it flows through the compressor before it enters the engine cylinders. Thus, the purpose of a turbocharger is to increase the pressure of the air so that more air gets into the cylinders. Consequently, more fuel can be burned and more power can be produced by the engine. In a turbocharger, exhaust gases enter the turbine at 400 degrees C and 120kPa at a rate 0.02 kg/s and leaves at 350 degrees C. Air enters the compressor at 50 degrees C and 100kPa and leaves at 130kPa at a rate of 0.018 kg/s. The compressor increases the air pressure with a side effect: It also increases the air temperature, which increases the gasoline engine to experience and engine knock. To avoid this, an aftercooler is placed after the compressor to cool the warm air by cold ambient air before it enters the engine cylinders. It is estimated the aftercooler must decrease the air temperature below 80 degrees C if knock is to be avoided. The cold ambient air enters the aftercooler at 30 degrees C and leaves at 40 degrees C. Disregard any frictional losses in the turbine and the compressor and treating the exhaust gases as air, determine (a) the temperature of the air at the compressor outlet and (b) the minimum volume flow rate of ambient air required to avoid knock.