THE IMPORTANCE OF HEAT TRANSFER TO IC ENGINE DESIGN AND OPERATION

The ideal IC engine cycle comprises isentropic compression, combustion, isentropic expansion and gas exchange and does not include any form of heat transfer (Fig. 1). In contrast to other types of heat engines, heat transfer in the IC engine is neither necessary nor desirable. Heat transfer cannot be avoided in practical IC engine processes and, in fact, plays an important role in the conceptual and detail design of the engine. It leads to considerable thermal loading of the engine components and requires that some form of cooling be employed, which in turn leads to increased heat transfer. The development of new high temperature materials, mainly ceramics, raises the possibility of disposing with cooling altogether and building an adiabatic engine with zero heat loss. The cyclic nature of the IC engine process hinders efforts in this direction considerably, so that the ideal situation of an adiabatic engine is virtually unachievable. At best, a thermally insulated engine results where indeed no heat is lost through the walls, but where heat is stored within the insulating material during the combustion process only to be transfered back to the gas during the gas exchange phase.