Ram Compression: Speed as a Compressor
At Mach 3, the kinetic energy of incoming air is enormous. When this air is decelerated in the inlet diffuser, its temperature rises from -57°C at 15 km altitude to over 350°C, and pressure increases by a factor of 36.7 — all without a single moving part. The simulation uses isentropic flow relations to compute these ram compression effects and shows how they scale dramatically with Mach number.
Supersonic Inlet Design
The inlet is the most critical ramjet component. It must efficiently capture and decelerate supersonic airflow while minimizing total pressure losses from shock waves. External compression inlets use oblique shocks on a cone or wedge, followed by a terminal normal shock. Mixed-compression inlets bring some compression inside the duct. Inlet efficiency directly determines engine performance.
Combustion at High Enthalpy
After compression, the air temperature may already exceed 500°C at Mach 3, limiting how much fuel energy can be added before materials fail. The combustor must maintain stable flame in a high-velocity airstream using flame holders — physical obstructions that create recirculation zones. Fuel injection must achieve rapid mixing and complete combustion in milliseconds.
The Scramjet Frontier
Above Mach 5, decelerating air to subsonic speeds produces temperatures exceeding 2000K — hot enough to dissociate air molecules, wasting energy. Scramjets solve this by burning fuel in a supersonic airstream, but supersonic combustion is extraordinarily difficult. The fuel must mix, ignite, and release energy in microseconds as it traverses the combustor at kilometers per second.