Question

Explain, in thermodynamic terms what happens and how it is achieved to ensure that an engine can operate at high altitude for commercial aircraft since the highier they go the less air is present for the engines to work with. What changes, differences in design for engines, are required for aircraft that operate at higher altitudes?

Answer 1

Commercial aircraft operate at higher altitudes where less amount of air is present for engines to work. But still aircraft engine manages to get decent efficiency.

Primary reason for aircraft operates efficiently at higher altitude is because of the supercharging of aircraft engines. Supercharger is a compressor which increases pressure and density of supplied air to aircraft internal combustion engines. When Aircraft reaches a higher altitude air pressure, as well as air density, will reduce. Output of an engine will drop because of a reduction in mass flow rate of air. Supercharger is use to compress air at sea level or higher than sea level. At higher altitude, there will be reduction in aerodynamic drag and engine will still produce rated power. Aircraft which is supercharged can ever perform more efficiently than the rated performance. Altitude at which throttle is full open and aircraft engine producing rated power is Critical Altitude.