Thus, all heat engines need cooling to operate.Ĭooling is also needed because high temperatures damage engine materials and lubricants and becomes even more important in hot climates. Some waste heat is essential: it guides heat through the engine, much as a water wheel works only if there is some exit velocity (energy) in the waste water to carry it away and make room for more water. Internal combustion engines remove waste heat through cool intake air, hot exhaust gasses, and explicit engine cooling.Įngines with higher efficiency have more energy leave as mechanical motion and less as waste heat. Engines are inefficient, so more heat energy enters the engine than comes out as mechanical power the difference is waste heat which must be removed. Heat engines generate mechanical power by extracting energy from heat flows, much as a water wheel extracts mechanical power from a flow of mass falling through a distance. Some sport motorcycles were cooled with both air and oil ( sprayed underneath the piston heads). Modern motorcycles are lighter than cars, and both cooling methods are common. Modern cars generally favor power over weight, and typically have water-cooled engines. Modern propeller-driven aircraft with internal-combustion engines are still largely air-cooled. Radial engines were popular until the end of World War II, until gas turbine engines largely replaced them. Rotary engines were popular on aircraft until the end of World War I, but had serious stability and efficiency problems. Rotary engines have a similar configuration, but the cylinders also continually rotate, creating an air flow even when the vehicle is stationary.Īircraft design more strongly favors lower weight and air-cooled designs. Radial engines allow air to flow around each cylinder directly, giving them an advantage for air cooling over straight engines, flat engines, and V engines. Higher-power engines generate more waste heat, but can move more weight, meaning they are generally water-cooled. Water has a higher heat capacity than air, and can thus move heat more quickly away from the engine, but a radiator and pumping system add weight, complexity, and cost. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator. Watercraft can use water directly from the surrounding environment to cool their engines. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. System which uses either air or liquid to remove the waste heat from an internal combustion engine
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