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It is difficult to make generalizations about air-cooled and liquid-cooled engines. Air-cooled diesel engines are chosen for reliability even in extreme heat, because air-cooling would be simpler and more effective at coping with the extremes of temperatures during the depths of winter and height of summer, than water cooling systems, and are ...
Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. Air-cooled designs are far simpler than their liquid-cooled counterparts, which require a separate radiator , coolant reservoir, piping and pumps.
Internal combustion engines are often cooled by circulating a liquid called engine coolant through the engine block and cylinder head where it is heated, then through a radiator where it loses heat to the atmosphere, and then returned to the engine. Engine coolant is usually water-based, but may also be oil.
Biermann, A.E. (1941). "The design of fins for air-cooled cylinders" (PDF). Report Nº 726.NACA.; P V Lamarque, "The design of cooling fins for Motorcycle Engines", Report of the Automobile Research Committee, Institution of Automobile Engineers Magazine, March 1943 issue, and also in "The Institution of Automobile Engineers Proceedings, Session 1942-1943, pp 99-134 and 309-312.
Engines that do not have a water cooling system cannot heat the cabin via a heater core; one alternative is to guide air around the (very hot) engine exhaust manifold and then into the vehicle's interior. Temperature control is achieved by mixing with unheated outside air. Air-cooled Volkswagen engines use this method.
But if the engine is a racing engine that is always producing huge amounts of heat, water or liquid cooling may be preferable. Air-cooled aviation engines may be subject to "shock cooling" when descending from cruising altitude prior to landing. During descent, very little power is needed, so the engine is throttled back and thereby develops ...
For passive heat transfer, a working fluid is a gas or liquid, usually called a coolant or heat transfer fluid, that primarily transfers heat into or out of a region of interest by conduction, convection, and/or forced convection (pumped liquid cooling, air cooling, etc.).
Many engineers did not understand the operating principles of the effect. A common mistake was the idea that the air-cooled radial engine would benefit most, because its fins ran hotter than the radiator of a liquid-cooled engine, with the mistake persisting even as late as 1949. [2]