wunder beta✈️ How Jet Engines Work
Follow air through a jet engine as compressors, combustors, turbines, and fans turn fuel energy into thrust.
What you’ll learn
- Air becomes thrustExplain how a gas-turbine core changes atmospheric air into thrust and how a turbofan divides the flow.Jet engines are open Brayton-cycle machines that compress air, add heat, recover shaft work, and accelerate exhaust. Turbofans add a fan and bypass path so much of the thrust comes from moving a large mass of air.
- The fan and inletDefine bypass ratio and connect fan size, air mass flow, efficiency, and mission tradeoffs.The inlet and fan condition and accelerate the incoming air, then split it between bypass and core paths. Bypass ratio is a mass-flow comparison whose useful value depends on aircraft speed, size, noise, and range.
- Compression and combustionDescribe how compressor stages prepare air and how the combustor adds controlled heat.Rotors and stators build pressure in stages, while the combustor burns fuel in a stable stream of compressed air. The resulting hot gas carries energy forward to the turbine and nozzle.
- Turbines, spools, and nozzlesTrace energy from hot gas through turbines, shafts, spools, and exhaust nozzles.Turbines extract enough work to drive compressors and fans, often through independently rotating spools. Nozzles then shape the remaining flow into directed exhaust, with engine designs choosing separate, mixed, or reversible paths.
- Why bypass ratio changes everythingExplain why high-bypass turbofans suit subsonic transport and why bypass ratio remains a design compromise.A high bypass ratio can move more air with a smaller velocity increase, improving the propulsion trade for airliners and often reducing exhaust noise. Fan size, speed, drag, weight, and mission requirements prevent one ratio from fitting every aircraft.
Questions this course answers
Put the core processes in the order air encounters them
The core first compresses air, then heats it, extracts work from its expansion, and finally accelerates the remaining flow through the nozzle.
Where does the main forward force of a jet engine come from?
The engine produces thrust by giving the exhaust flow rearward momentum; the reaction force acts forward on the engine and aircraft.
Match each flow term to its meaning
These terms distinguish the two air paths and define the comparison used to describe turbofan design.
A turbofan has a bypass ratio of 9. About how many times more air bypasses the core than enters it?
By definition, a bypass ratio of 9 means the bypass mass flow is about nine times the core mass flow.
In your own words, why does a combustor need compressed air?
The compressor prepares a dense, pressurized stream, allowing the combustor to add heat continuously before the gas expands through the turbine and nozzle.
What do stator vanes mainly do between compressor rotor rows?
Stators remove some swirl and convert velocity into pressure while setting the flow angle for the next rotating row.
Grounded in trusted sources
- NASA Glenn Research Center, Turbofan Engine, https://www.grc.nasa.gov/WWW/K-12/BGP/aturbf.html
- NASA, NASA's HyTEC to Help Jets Burn Less Fuel, https://www.nasa.gov/aeronautics/nasas-hytec-to-help-jets-burn-less-fuel/
- Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge, Chapter 7: Aircraft Systems, https://www.faa.gov/sites/faa.gov/files/pilot_handbook_1.pdf
- MIT OpenCourseWare, 16.50 Introduction to Propulsion Systems, Lecture 21: Turbofan Engines, https://ocw.mit.edu/courses/16-50-introduction-to-propulsion-systems-spring-2012/resources/mit16_50s12_lec21/
- Rolls-Royce, Trent: Delivering continuous improvement, https://www.rolls-royce.com/media/our-stories/discover/2024/trent-striving-for-continuous-improvement.aspx
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