Aviation propulsion

Jet, turboprop and helicopter engines burning jet fuel or SAF.

Conversion and use · Transport systems · No. 114

• Conversion and use

Airlines will burn about 104 billion gallons of fuel in 2026, and less than 1% of it will be sustainable.

Chart: Illustration: Aviation propulsion

Where it comes from

Chart: Map of where it comes from

A turbofan squeezes air, burns fuel in it and uses the hot gas to spin a big front fan. The best cores now reach about 55% thermal efficiency at cruise, up from about 30% fifty years ago.

Three things to know

1. Fan bypass ratios have grown from about 2:1 to about 11:1 in seventy years, because pushing more air gently wastes less energy.
2. Fuel was 25.4% of airline costs in 2025, forecast to jump to 31.4% in 2026 after a jet fuel price spike.
3. An open-fan design under test has a bypass ratio of about 60:1 and targets about 20% better fuel use.

The journey

1. 1 Jet fuelKerosene or sustainable aviation fuel loaded
2. 2 CompressorSqueezes incoming air to high pressure
3. 3 CombustorFuel burns in the compressed air
4. 4 Turbine and fanHot gas spins turbines driving the fan
5. 5 ThrustAir pushed backwards moves passengers and cargo

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