Who makes it
Jet Engine Simulator is an independent project by Muhammad Obair Ata. The engine model, the game and this website are original work. Questions, bug reports and ideas are welcome at jetenginesim@gmail.com.
It is a game. Its engines are simplified so they run smoothly in a browser and are fun to handle, and nothing in it is engineering, safety or maintenance advice.
The model in one paragraph
Each engine is a zero-dimensional model: instead of simulating the airflow in three dimensions, it follows the average pressure, temperature and flow of the gas at each station from inlet to nozzle (the stations are shown on how a jet engine works). Every frame it finds the steady operating point that matches the compressor to the turbine, works out the thrust from the gas leaving the nozzle, and then lets the rotor speed up or slow down according to the turbine's spare power and the rotor's inertia. It is the same Brayton cycle that textbooks use, with components that behave like real ones.
What it calculates
- Atmosphere. The International Standard Atmosphere for the chosen altitude and temperature offset, and the ram pressure and temperature from the flight Mach number.
- Compressor. Pressure ratio, airflow and efficiency follow the rotor's corrected speed. Efficiency falls away from the design point, and pushing too close to the limit causes a surge.
- Matching. The compressor's operating point is found where the turbine's choked inlet guide vanes pass exactly the flow the compressor delivers, plus the fuel.
- Combustor. Fuel energy raises the gas temperature, with a combustion efficiency of 98 % and a pressure loss of a few percent.
- Turbine. The gas expands through the turbine with a set efficiency; its power drives the compressor (and the fan or propeller) through a shaft with 99 % mechanical efficiency.
- Afterburner and nozzle. Extra fuel can be burned behind the turbine. The nozzle is treated as choked or unchoked as the pressure demands, and the thrust is the jet momentum plus pressure thrust, minus the ram drag of the incoming air.
- Fan and propeller. A second airstream whose flow and pressure ratio follow the rotor speed. Turboprops use a free turbine and propeller pitch positions, like gears.
- Transients. Rotor inertia, starter torque, light-off, hot and hung starts, flameouts and relights, and damage that builds up from over-temperature and over-speed.
Ramjets and scramjets
The ramjet and scramjet have their own steady-flow model in a wind tunnel at a fixed test altitude (15 km for ramjets, 25 km for scramjets). Inlet pressure recovery depends on the number of shocks; the terminal shock, spillage and unstart follow from whether the inlet can supply the pressure the nozzle throat needs; the scramjet combustor is limited by thermal choking (the Rayleigh limit); and the wall temperature comes from stagnation heating and combustion, cooled by the fuel.
Constants
| Quantity | Value |
|---|---|
| Gas constant of air, R | 287.05 J/kg·K |
| Air: cp, γ | 1005 J/kg·K, 1.4 |
| Hot gas: cp, γ | 1150 J/kg·K, 1.333 |
| Kerosene heating value | 43 MJ/kg |
| Hydrogen heating value (scramjet) | 120 MJ/kg |
| Combustion efficiency | 98 % |
| Mechanical (shaft) efficiency | 99 % |
| Hot-section temperature limits | 1150 K steel · 1350 K nickel · 1500 K single crystal · 1650 K ceramic |
The standard dyno test
To compare engines fairly, the dyno runs the same schedule on every turbine engine: sea level, standard day, FADEC on. It starts the engine cold, settles at idle, snaps to full power and holds until the thrust is steady, holds 70 % power for the fuel reading, lights the afterburner if there is one, and returns to idle. Spool-up is the time from the snap to 95 % of full thrust. Ramjets and scramjets run the equivalent test in the wind tunnel at Mach 3 and Mach 6. The engine pages quote these numbers, worked out by the same code the game runs.
How close to reality is it?
The trends are right: more pressure ratio and turbine temperature give more thrust per kilogram of air, bypass air saves fuel, hot starts and surges happen for the reasons they happen in real engines, and ramjets unstart when they get too much fuel. The magnitudes are in a realistic range: on the dyno the Training turbojet burns about 0.88 lb of fuel per pound of thrust per hour and the Airliner turbofan about 0.39, roughly where real turbojets and high-bypass turbofans sit at those conditions.
It is not a prediction of any real engine. The main simplifications:
- One spool. Real turbofans have two or three shafts turning at different speeds.
- Generic component behaviour instead of measured compressor and turbine maps.
- No humidity, icing, Reynolds-number or installation effects, and constant gas properties in each part of the engine.
- Simplified fan, propeller and afterburner models, tuned to be stable and readable at game speed.
- Damage and wear are game mechanics, not life calculations.
For textbook numbers you can check by hand, use the Brayton cycle calculator and the jet thrust calculator; they use the standard equations and show them on the page.