Expert: Ray Wilkinson - 1/2/2011

Question
I'm curious what the pressure is inside a jet engine that the compressors produce.  This is not the combustion chamber.  My understanding is the newer engines have higher pressures do to more compressors inside them so I would be mostly thinking of the newer engines.
thanks

Answer
Each stage of a gas-turbine compressor (consisting of a row of rotating blades plus a row of static or stator blades) can increase the pressure by a factor between about 1.15 and 1.6. Since a typical modern gas turbine contains a number of stages per spool, and two or three spools running at different speeds, a total pressure ratio of about 40:1 is achievable. Of course, the majority of the operating time is at around 35000 feet for a civil airliner, although the pressure ratio is the same at all altitudes. The flow from the final compressor stage usually passes through a diffuser before entering the combustor, and this diffuser slows down the air with a further increase in pressure. The air will then be travelling at a suitable speed for combustion to take place without the risk of flame-out (i.e. the speed at which the flame front can travel is at least equal to the speed of the incoming air.