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B Fuel with Static Air in a Jet engine

  1. May 11, 2017 #1
    Good evening,

    Today's planes' need bleed air to start. Above a certain speed, igniters fire up and we inject fuel inside the combustor chamber. Why do we need to have the engine running to inject fuel (around 20%N2)? Can we simply not inject fuel with static air (i.e. when engine is not running)? What would happen if I would do so?

    Thanks a lot!
  2. jcsd
  3. May 11, 2017 #2


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    Jet engines work by compressing the air then injecting fuel. The resulting hot gasses expand rushing out the back turning a turbine that's connected to the compressor at the front.

    This process only becomes self sustaining above a certain minimum speed (rpm). Below that speed the power generated isn't enough to run the compressor, fuel and oil pumps and shift the air that is going through the bypass.
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