Chinese team says hypersonic engine can hit Mach 9 on low-cost jet fuel

The device travels at nine times the speed of sound without the expense or explosion risk of burning hydrogen, according to paper
Researchers in China say ground experiments at Beijing’s JF-12 shock tunnel were successful

Science

Stephen Chenin Beijing

Published: 8:00pm, 18 Nov 2022

Why you can trust SCMP

Researchers in China say they have developed the world’s first hypersonic detonation wave engine capable of powering flight at nine times the speed of sound using low-cost jet fuel.

Several successful ground experiments for the oblique detonation engine, which generates thrust through a burst of explosions, were carried out at the JF-12 hypersonic shock tunnel in Beijing earlier this year, according to the researchers.

The team led by Liu Yunfeng, a senior engineer with the Institute of Mechanics, Chinese Academy of Sciences, revealed technical details of the kerosene-powered engine in a paper published in the peer-reviewed Journal of Experiments in Fluid Mechanics on November 11.

“No test results for [hypersonic detonation engines using] aviation kerosene have been made public before,” they wrote.

Chinese scientists tested their hypersonic detonation wave engine in the JF-12 shock tunnel in Beijing. Photo: Institute of Mechanics, Chinese Academy of Sciences

A detonation engine can run more efficiently and powerfully than other hypersonic engines such as the scramjet. The detonation wave triggers a series of explosions, which happen almost instantly and release considerably more energy than conventional combustion does with the same amount of fuel, especially at speeds over Mach 8.

Scientists around the world have built detonation engines, but they mostly use hydrogen as fuel, which comes with a high price tag and risk of explosions.

Liu’s engine uses RP-3, a jet fuel commonly found in Chinese airports.

“Aviation kerosene is the fuel of choice for air-breathing engines due to its high energy density and ease of storage and transport,” he said.

02:18

Japan Airlines could be first in Asia flying new Boom Overture supersonic passenger jet

The idea of using jet fuel to power hypersonic flight has been around for decades, but the difficulty of igniting the kerosene in extremely hot and fast air has posed a challenge for scientists.

“It is not easy to detonate,” Liu said.

Kerosene burns more slowly than hydrogen, so kerosene-powered engines typically require a longer detonation chamber to retain the fuel-air mixture for a longer period of time.

Computer models estimated that the detonation chamber of a kerosene-fuelled engine would need to be 10 times longer than one that uses hydrogen.

The extra length would be impossible for most hypersonic planes, where every millimetre counts, according to the team.

The Chinese team’s engine burns aviation kerosene, generating a series of explosions within milliseconds of ignition. Photo: Institute of Mechanics, Chinese Academy of Sciences

But the Chinese scientists found that a simple modification – adding a thumbnail-size bump to the surface of the engine’s air inlet – could make the ignition of kerosene easier while keeping the chamber’s size small.

When fresh air arrives at the narrow mouth of the engine’s wedge-shaped inlet, fast-moving air molecules are compressed and heated.

The hot air then mixes with tiny droplets of kerosene, which break apart to form even smaller molecules.

As the mixture of air and fuel hits the bump on the otherwise smooth surface of the inlet, shock waves are produced.

The results of the test run, conducted under various conditions in the JF-12 tunnel, suggest that these bump-induced shock waves could not only ignite the kerosene but help confine the explosions to a small space, generating a steady supply of thrust.

00:52

China’s DF-26 ballistic missile drill sends ‘clear message’ to the U.S.

China has developed several hypersonic missiles, including the DF-17 and YJ-21, capable of hitting a building or moving warship fast enough to evade most air defence systems.

The Chinese government plans to find civilian applications for hypersonic technology by building a fleet of aircraft that can transport passengers anywhere on the planet within an hour or two.

Meanwhile, defence contractor Lockheed Martin plans to conduct the first flight of the SR-72, an unmanned hypersonic spy plane known as “Son of Blackbird”, by 2025.

Hypersonic aircraft must be capabale of making routine long-distance flights under extreme conditions. Reducing construction and operational costs remains a major challenge, according to scientists and engineers involved in developing the technology.