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Why do jets burn less fuel the higher they fly?

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2014-06-09 19:47:26
2014-06-09 19:47:26
The chemical energy in the fuel is a function of the mass of the fuel. Since a gallon of fuel expands or contracts with temperature, a gallon of cold fuel contains more energy than a gallon of warm fuel. The temperature gets colder the higher you go (up to the tropopause, that is) and consequently, more thrust is derived from each pound of fuel which translates to greater fuel efficiency.Jets travel faster because of less atmospheric friction upon the aircraft. The engines are more efficient because of the colder air. The engines work by heating the air and it then it expands and exits the engine. When the air is colder (it easily gets -40 degrees up there) and the fuel air mixture is burned, the air expands alot more than if warm air was entering the engine. On a warm day a jet will not perform nearly as well as on a cold day.
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