Computer drawing of the inside of a ramjet
 engine with the parts labeled.

For high supersonic or hypersonic flight, the ideal propulsion system is a ramjet. A ramjet uses the forward speed of the aircraft to compress the incoming air and, therefore, has fewer moving parts than a turbojet.

On this slide we show a computer drawing of a typical ramjet engine. In the computer drawing, we have cut out a portion of the engine to have a look inside. At the front of the engine, to the left, is the inlet, which brings outside air into the engine. At the exit of the inlet, the air is at a much higher pressure than free stream conditions. Fuel is injected and mixed for combustion just downstream of the inlet. The resulting flame is stabilized in the engine by the red flame holder ring. This part is very similar to an afterburner in a fighter jet engine. The hot exhaust then passes through the nozzle, which is shaped to accelerate the flow and produce thrust. The thrust equation for a ramjet is shown on a separate slide.

To analyze ramjet operation, engineers have adopted a numbering scheme for the various parts. The numbering scheme for the ramjet is identical to the turbine engine. But the ramjet has no compressor or turbine. Therefore, some of the numbered stages are omitted in a ramjet analysis.

You can study ramjet design and operation by using the EngineSim Applet. You can vary the performance of any of the engine parts and investigate the effects on thrust and fuel flow. On the applet, choose "Ramjet," and any engine part from the image in the upper left of the program.

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byTom Benson
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