In Beijing, a detonation engine was tested that reaches hypersonic speeds while using only normal kerosene. Beijing stresses the civilian benefits of the development, but a hypersonic bomber is far more likely than a passenger plane.
Chinese researchers report that they have developed a hypersonic engine that can reach nine times the speed of sound and runs on kerosene. The structure of the engine is completely different from that of a conventional jet engine with its compressor blades. It is an inclined detonation engine. The thrust is not generated by a continuous burning of the fuel, but by a wave of explosions. A detonation engine is said to work more efficiently and powerfully than other hypersonic engines such as the scramjet. The detonation wave consists of a series of explosions occurring at almost the same time. This releases significantly more energy than conventional combustion with the same amount of fuel.
Precisely ignite inert kerosene
The team, led by Liu Yunfeng, chief engineer at the Institute of Mechanics of the Chinese Academy of Sciences, published their findings in the Journal of Experiments in Fluid Mechanics. A demonstrator was already being tested at the beginning of the year in a special facility in Beijing. ‘To date, no test results for hypersonic detonation engines using aviation kerosene have been published,’ the researchers write. Detonation engines have been built before, but these mostly used hydrogen as fuel. Green hydrogen would be CO2-neutral, but the gas is difficult to tame and kerosene is available at every airport.
“Kerosene is the fuel of choice for air-breathing engines because of its high energy density and ease of storage and transportation,” said Liu Yunfeng. Until now, it has not been possible to precisely ignite the kerosene in the hot and extremely fast-moving air. Compared to hydrogen, kerosene reacts too slowly. A special shape of the inlet compresses and heats the incoming mixture of air and kerosene. A bump in the current then creates the shock waves. The JF-12 hypersonic tunnel test run showed that these waves ignite the kerosene, helping to confine the blast wave to a small space while generating steady thrust.
Military use likely
China has already put two military hypersonic missiles into service – the DF-17 and the YJ-21. However, this novel engine would be reusable. The government in Beijing always emphasizes the civil benefit of the development. With a Mach 9 engine, passengers could reach anywhere in the world within a few hours. It took less than an hour to get from Beijing to Mallorca. However, the estimated construction and operating costs are currently so high that widespread civilian application is still a long way off. Far more likely it should be possible to equip strategic hypersonic bombers with this technology