Engine coolant heat rejection affects the coolant temperatures in the top tank, at the radiator inlet and engine inlet. It usually has the highest value near rated power or at a higher speed.

Heat rejection methods Air Cooled: A process by which air passes over a coil or channel containing fluid. Heat is transferred from the coil directly to the air. Water Cooled: This process utilizes a spray system to pass water over coils or fill media to reject heat to the atmosphere through evaporation.

The ability to reject heat at a certain temperature is directly related to the heat density (amount of heat per unit area). Therefore, the density of the internal heat has to be lowered to the values at which the radiator can reject it without exceeding specified temperatures.

Part of the heat which is rejected by the engine is carried away by the exhaust gas and the remainder must pass through the metallic walls which surround the combustion chamber, that is, the pistons, the cylinder walls, the piston rings, in- jectors, spark plugs, and exhaust passages.