|MLA Citation:||Bloomfield, Louis A. "Question 1416"|
How Everything Works 18 Feb 2018. 18 Feb 2018 <http://howeverythingworks.org/print1.php?QNum=1416>.
But before fuel is injected into the engine's compressed air, there is a side duct that allows some of that compressed air to flow toward the passenger cabin. So the engine is providing the air you breathe during a flight.
There is one last interesting point about this compressed air: It is initially too hot to breathe. Even though air at 30,000 feet is extremely cold, the act of compressing it causes its temperature to rise substantially. This happens because compressing air takes energy and that energy must go somewhere in the end. It goes into the thermal energy of the air and raises the air's temperature. Thus the compressed air from the engines must be cooled by air conditioners before it goes into the passenger cabin.