<P> The output power of an engine is dependent on the ability of intake (air--fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the cylinder head . To increase an engine's output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed, and, with the aid of an air flow bench, the radii of valve port turns and valve seat configuration can be modified to reduce resistance . This process is called porting, and it can be done by hand or with a CNC machine . </P> <P> An IC engine on an average is capable of converting just 30 - 40% of the supplied energy into mechanical work . A large part of the waste energy is in the form of heat that is released to the environment through coolant, fins etc . If we could somehow recover the waste heat we can improve the engine's performance . It has been found that even if 6% of the entirely wasted heat is recovered it can increase the engine efficiency greatly . </P> <P> Many methods have been devised in order to extract waste heat out of an engine exhaust and use it further to extract some useful work, decreasing the exhaust pollutants at the same time . Use of Rankine Cycle, Turbocharging and Thermo electric Generation can be very useful as a waste heat recovery system . </P> <P> Though waste heat recovery systems are being used frequently among all the devices but still some issues like their low efficiency at lower heat supply rates and high pumping losses remain a cause of concern for the researchers . </P>

Mode of operation of a four stroke diesel engine