Air Cooled Engines
Most modern internal combustion
engines are cooled by a closed circuit carrying liquid coolant through
channels in the engine block, where the coolant absorbs heat, to a heat
exchanger or radiator where the coolant releases heat into the air,
and so on, ad infinitum.
Thus, while they are ultimately cooled by air, because of the liquid-coolant
circuit they are known as water-cooled. In contrast, heat generated
by an air-cooled engine is released directly into the air. Typically
this is facilitated with metal fins covering the outside of the cylinders
which increase the surface area that air can act on.
It is worth noting that
in all combustion engines, a great percentage of the heat generated
(around 44%) escapes through the exhaust, not through either a liquid
cooling system nor through the metal fins of an air-cooled engine (12%).
About 8% of the heat energy finds its way into the oil, which although
primarily meant for lubrication, also plays a role in heat dissipation
via a cooler.
Many motorcycles use air-cooling
for the sake of reducing weight and complexity. Few current production
automobiles have air-cooled engines, but notable past models include
the Volkswagen Beetle and related models, Citroën 2CV, the Chevrolet
Corvair, the Porsche 911 and others.
Most aviation piston engines
are air-cooled, including most of the engines currently (2005) manufactured
by Lycoming and Continental and used by major manufacturers of light
aircraft Cirrus, Cessna and so on. Notable exceptions have included
the Allison V-1710 and Rolls-Royce series of (most well known, the Merlin
V-1650) liquid-cooled V12 engines which powered P-51 Mustangs, Avro
Lancasters, Hawker Hurricanes and Spitfires.
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