Calculator
| Compressor exit, T2 | 731 K (458 °C) |
|---|---|
| Compressor exit pressure, P2 | 2,027 kPa |
| Turbine exit, T4 | 724 K (450 °C) |
| Compressor work, wc | 445.4 kJ/kg |
| Turbine work, wt | 780.3 kJ/kg |
| Heat added, qin | 772.5 kJ/kg |
| Back work ratio, wc/wt | 57.1 % |
| Pressure ratio for most work (ideal cycle) | 17.9 |
How to use it
The calculator follows one kilogram of air around the cycle. State 1 is the compressor inlet, 2 the compressor exit, 3 the turbine inlet and 4 the turbine exit. The two numbers that matter most are the pressure ratio and the turbine inlet temperature; the component efficiencies turn the ideal cycle into a realistic one.
The equations
η = (wt − wc) / qin ηideal = 1 − 1 / PR(γ−1)/γWork, heat and thermal efficiency. For the ideal cycle the efficiency depends on the pressure ratio alone.
Worked example
With the default inputs (a standard day, pressure ratio 20, turbine inlet 1500 K, an 88 % compressor and a 90 % turbine), the compressor heats the air to about 731 K and takes 445 kJ for every kilogram. The turbine gives back 780 kJ, leaving 335 kJ/kg of net work from 773 kJ/kg of heat: a thermal efficiency of 43.3 %. The ideal cycle at the same pressure ratio would reach 57.5 %, and the compressor alone uses 57 % of the turbine's work, which is why component efficiency matters so much.
What the numbers show
- Pressure ratio raises efficiency, up to a point. With the default components, efficiency climbs from 30 % at a pressure ratio of 5 to about 45 % around 30, then levels off. Net work peaks earlier, near a pressure ratio of 10.
- A hotter turbine gives more work. Raising the turbine inlet temperature from 1150 K to 1650 K nearly triples the net work per kilogram (153 to 413 kJ/kg). More work per kilogram of air means a smaller, lighter engine for the same thrust.
- Materials set the limit. In the game, the hot section's material decides how hot the turbine may run: about 1150 K for steel, 1350 K for nickel superalloy, 1500 K for single-crystal blades and 1650 K for ceramic composite.
Assumptions and limits
This is the textbook "cold-air standard" cycle: air is a perfect gas with constant cp and γ, there are no pressure losses in the combustor or ducts, and the mass of the fuel is ignored. Real engines use hotter gas with a lower γ, lose a few percent of pressure in the combustor, and bleed air for cooling, so their numbers are somewhat lower. In a jet engine the net work does not leave as shaft power: it speeds up the exhaust, which the jet thrust calculator turns into thrust. The game's own engine model is more detailed; the About page explains how.