Slide 1
The compressor raises air pressure before combustion
A turbojet’s compressor raises the pressure of incoming air before fuel is burned. That compression requires substantial shaft power.
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Compressing air also raises its temperature. The compressor is therefore part of a thermodynamic cycle, not merely a device that packs more oxygen into a smaller space.
Slide 2
Burning fuel adds energy to the flowing air
Fuel burns in the compressed airflow, increasing its thermal energy. A steady-flow combustor is designed to avoid a large loss of total pressure.
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The combustor must stabilize a flame while air continuously moves through it. Its internal flow arrangement differs from simply allowing the entire stream to rush through at the same speed.
Slide 3
The turbine extracts power to drive the compressor
Hot gas expands through a turbine that drives the compressor by a shaft. The turbine extracts some of the energy supplied by combustion.
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In a turbojet, enough useful energy remains after the turbine to accelerate the exhaust in the nozzle. Component matching determines whether this balance can be sustained.
Slide 4
The nozzle converts energy into exhaust speed
A nozzle allows the gas to expand and accelerate. The outgoing momentum and pressure conditions contribute to the engine’s thrust.
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The atmosphere does not act as a solid surface that the exhaust must push against. Thrust follows momentum exchange, although ambient pressure affects how the nozzle operates.
Slide 5
A turbofan also uses turbine power to drive a fan
A turbofan uses turbine power to drive a fan as well as the core compressor. Much of its thrust can come from air passing around the core.
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Moving more air with a smaller speed increase can improve propulsive efficiency at suitable flight conditions. This is why a large fan can matter as much as a very fast core exhaust.
Sources
- Turbojet Engine
NASA Glenn Research Center
- Nozzle Design
NASA Glenn Research Center
- How Gas Turbine Power Plants Work
US Department of Energy