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What's the difference between a scramjet and a ramjet engine? © iStock

What's the difference between a scramjet and a ramjet engine?

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These experimental engines both work in different ways to achieve supersonic speeds.

Asked by: Steve O'Brien, Bath


Both are types of experimental engine designed for speeds greater than that of sound, in the hypersonic realm. They are jet engines with no moving parts, relying on the enormous pressures created by supersonic airflow into the engine to ignite fuel without needing the compressors and turbines used in the turbofan engines found on conventional jet planes.

In a ramjet, the combustion chamber - where the air is mixed with fuel and ignited - only works at subsonic speeds. So the intake slows the air down, releasing some of its energy as a shock wave, but this reduces fuel efficiency. The scramjet is an innovation on the ramjet in which the combustion chamber is specially designed to operate with supersonic airflow. Scramjet is simply an acronym for 'supersonic combustion' ramjet.

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