ramjet

Ramjet is a form of jet engine that produces thrust by accelerating air through a simple inlet, mixing it with fuel in a combustion chamber, and expanding the hot gases through a nozzle. Unlike turbojets or turbofans, a ramjet has no rotating compressor or turbine. It relies on the vehicle’s forward speed to compress incoming air, and it uses atmospheric oxygen for combustion, carrying only fuel.

Operation: The engine must be moving at substantial speed before it operates efficiently. The inlet compresses air to subsonic or mild supersonic speeds inside the combustor. Fuel is injected and burned, and the hot gases exit through a converging-diverging nozzle to produce thrust. Ramjets are most effective at high Mach numbers, typically around Mach 3 to 6, with some designs up to Mach 8. They are not self-starting and require an initial boost from another propulsion system to reach operating speed.

Advantages and limitations: Ramjets have a simple, robust structure and a high thrust-to-weight ratio at high speed due to the absence of a compressor and turbine. They operate efficiently using atmospheric oxygen, so they carry only fuel. However, they provide little or no thrust at low speed or when stationary, and performance depends strongly on flight speed and altitude. Inlet design and surge margins are critical to prevent flow instabilities.

Applications and history: The ramjet concept emerged in the early 20th century and saw practical use in missiles and research vehicles in the mid- to late 20th century. Today ramjets are primarily used in high-speed missiles, target drones, and experimental propulsion platforms, where sustained operation at hypersonic to high supersonic speeds is advantageous. They are often contrasted with scramjets, which operate with supersonic combustion but are more complex to build.