15.9 SUPEFICHAHGING OF SPARK-IGNITION ENGINE
The purpose of supercharging is to increase the power output without much sacrifice of the
engine efficiency and fuel economy. As the supercharging is done by increasing the inlet pressure of the charge, the power output is theoretically increased, but from the practical point of view there are several limitations of this process. As the inlet pressure is increased, the charge density inside the cylinder increases. Due to the burning of these charges, more heat is developed inside in the engine cylinder and the cooling system may not carry away the extra amount of heat. This causes overheating of the cylinder walls which may get damaged. The high inlet pressure also increases the peak pressure. So to withstand this high pressure the engine cylinder must be of high strength. It is observed that before cooling or structural problems occur, knocking is heard from the engine cylinder. Knocking is highly undesirable, because this causes rapid loss of power and complete failure of the piston.