Most internal combustion engines are "air-cooled" or "liquid-cooled". Each principle has advantages and disadvantages, and particular applications may favor one over the other. For example, most cars and trucks use liquid-cooled engines, while most small airplane engines are air-cooled.
Most liquid-cooled engines use a mixture of water and other chemicals such as antifreeze and rust inhibitors. Some use no water at all, instead using a liquid with different properties, such as propylene glycol or the combination of propylene glycol and ethylene glycol. Although the term "liquid-cooled" is used here, most air-cooled engines also use some liquid oil cooling, and most liquid-cooled engines subsequently cool the hot liquid with air.
Conductive heat transfer is proportional to the temperature difference between materials. If an engine metal is at 300°C and the air is at 0°C, then there is a 300°C temperature difference for cooling. An air-cooled engine uses all of this difference.
In contrast, a liquid-cooled engine might dump heat from the engine to a liquid, heating the liquid to 150°C which is then cooled with 0°C air. Thus, in each step, the liquid-cooled engine has half the temperature difference and so may need as much as twice the cooling area.
Most liquid-cooled engines use a mixture of water and other chemicals such as antifreeze and rust inhibitors. Some use no water at all, instead using a liquid with different properties, such as propylene glycol or the combination of propylene glycol and ethylene glycol. Although the term "liquid-cooled" is used here, most air-cooled engines also use some liquid oil cooling, and most liquid-cooled engines subsequently cool the hot liquid with air.
Conductive heat transfer is proportional to the temperature difference between materials. If an engine metal is at 300°C and the air is at 0°C, then there is a 300°C temperature difference for cooling. An air-cooled engine uses all of this difference.
In contrast, a liquid-cooled engine might dump heat from the engine to a liquid, heating the liquid to 150°C which is then cooled with 0°C air. Thus, in each step, the liquid-cooled engine has half the temperature difference and so may need as much as twice the cooling area.
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