Evaporative Engine Cooling for Fuel Economy - 1983

Automotive engineers have recognized the fuel economy advantage of elevated coolant temperatures for many years. Evaporative engine cooling is a well established technology which maintains the engine coolant at its boiling temperature regardless of operating conditions. By assuring that the coolant entering the engine is at nearly the same temperature as that leaving the engine, overcooling is avoided. Excellent temperature uniformity is assured throughout the engine, permitting coolant temperatures to be raised without raising peak metal temperatures.

Evaporative cooling allows engine coolant to boil freely at atmospheric pressure, taking advantage of the inherently high heat transfer rates obtained with boiling and condensing. The benefits derived from evaporative cooling are faster warm-up, reduced friction, (which contribute toward fuel economy) greater engine durability, and safe, low pressure operation. This paper reviews the history, theory, and practice of vapor cooling in stationary and mobile powerplants.