Why is a turbine engine more efficient at higher altitudes?

A turbine engine is more efficient at higher altitudes primarily due to the characteristics of colder air temperatures and their impact on engine performance. At higher altitudes, the ambient air temperature is typically lower, which allows for increased air density. This denser air contributes to improved combustion efficiency within the engine. Specifically, colder temperatures promote better thermal efficiency because they help maintain a favorable pressure ratio across the engine, allowing it to extract more energy from the fuel.

Additionally, the reduced temperature aids in the cooling of various engine components, enhancing overall performance and longevity. Moreover, at higher altitudes, the reduction in drag on the aircraft enables it to maintain higher speeds without a proportional increase in fuel consumption, further contributing to the overall efficiency of turbine engines.

The other factors listed do not contribute positively to the efficiency of turbine engines at altitude. Higher air density typically decreases as altitude increases, while humidity has a negligible effect on performance at altitude. Aircraft speed is generally optimized at higher altitudes, but reduced speed does not enhance efficiency in turbine engines.