How a Jet Engine Works: Startup and Operation

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The intake of an aircraft jet engine. Photo Credit: Michael Henley

All jet engines work in a similar manner regardless of the modern modifications such as in the turboprops and the turbofans – the basic core engine remains the same. This fundamental core engine is often referred to as the “Basic Engine.”

How Does a Jet Airplane’s Engine Work? Startup Process Explained

The following events take place in sequence to enable a sustained combustion in jet aircraft engines:

  1. Prior to the introduction of the fuel/air mixture (Avgas or Avtur), ignition takes place.
  2. A stoichometric mixture of aviation fuel and air, efficient for the specific engine type, is introduced.
  3. Controlled combustion begins and is sustained via constant supply of the fuel/air mixture.

Jet engines incorporate pneumatic starters and electrical starters that crank the engine to a certain rpm (engine specific), and then allow the fuel/air mixture to enter the combustion chamber. After the accomplishment of a sustained combustion, the starter disengages itself to end the starting cycle.

The startup procedure in a jet’s engines ends as soon as the electrical or the pneumatic starter disengages. After that, the engine runs independent of the starter.

Post-Startup Phase: Engine Intake

A Qantas Airbus A380 powered by Rolls-Royce Trent 972s. Photo Credit: Jorge Láscar.

This phase of the engine operation is characterized by air entering the engine through its “Ram effect”. The inlet vanes are designed so as to maximize streamlined intake to the first stage of compressors.

Maintaining a streamlined flow is vital to engine operation. Turbulent air, formed by any intake damage, icing, or a foreign body entering the inlet duct, may cause the compressor to surge or stall.

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