A Chinese team has tested an engine for hypersonic flight – powered by explosions

Researchers in southwest China say their air-breathing engine – driven by the explosions of cheap hydrocarbon fuel – achieved stable operation during a simulated test flight at hypersonic speed.

This approach can wreck an engine because the explosions release a huge amount of energy in a sudden, uncontrollable way.

But the team at the China Aerodynamics Research and Development Centre in Mianyang, Sichuan province say their rotating detonation engine could power a plane or missile at five times the speed of sound or faster by producing thousands of explosions per second.

These mini-explosions occur in a narrow gap between two metal cylinders filled with the vapour of ethylene or kerosene. Shock waves caused by the explosions travel through the circular space in a spiral pattern, producing a powerful thrust as they leave the engine.

When the engine’s operation stabilised during the recent test flight “it produced a faintly blue, transparent flame”, said lead author Wang Chao, in a paper published in the peer-reviewed Chinese-language Journal of Experiments in Fluid Mechanics.

Computer modelling in previous studies has shown that a rotating detonation engine can achieve fuel efficiency 50 per cent higher than that of a jet engine, where fuel burns under full control but much more slowly.

Many prototype detonation engines have been built in recent decades – mostly by the military – but for most the operation has been unstable.

The ones that have worked all used hydrogen as fuel. But to store liquid hydrogen, a large fuel tank with a complex cooling facility is needed, meaning it is not suitable for most military purposes.