Fuel with Static Air in a Jet engine

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SUMMARY

Jet engines require bleed air to initiate combustion, as fuel injection necessitates the engine to be running at a minimum speed to sustain the compression process. Injecting fuel with static air, when the engine is not operational, would fail to generate the necessary power to drive the compressor and associated systems. The combustion process relies on the expansion of hot gases produced by the combustion of fuel mixed with compressed air, which only occurs effectively above a specific RPM threshold.

PREREQUISITES
  • Understanding of jet engine mechanics and operation
  • Knowledge of combustion processes in aerospace engineering
  • Familiarity with the role of bleed air in jet engines
  • Basic principles of thermodynamics related to gas expansion
NEXT STEPS
  • Research the role of bleed air in starting jet engines
  • Study the thermodynamic principles of jet engine operation
  • Learn about the RPM thresholds for various jet engine models
  • Explore the implications of static air injection on combustion efficiency
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Aerospace engineers, aviation mechanics, students studying jet propulsion, and anyone interested in the operational principles of jet engines.

TheBusFlyer
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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!
 
Science news on Phys.org
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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