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A Chinese scramjet is reported to have run at maximum boost of 600 seconds, outdoing the American X-51A Waverider (pictured). Photo: Handout

Report of Chinese scramjet test a challenge to most-advanced missile defence systems

  • Engine built for China’s classified hypersonic strike weapon hits 600 seconds in ground test
  • A 10-minute scramjet boost to a weapon could give it a range of over 4,000km at top speed

A scramjet engine built for China’s hypersonic strike weapon can run at maximum boost for at least 10 minutes, the longest in the world.

In a ground test in Beijing, Dr Fan Xuejun and colleagues from the Institute of Mechanics fed extremely fast, super-hot air into the engine and took the burn to the maximum for 600 seconds, according to an article posted on the institute’s website last month.

Since 2013, the United States Air Force X-51A Waverider has held the duration record with a 210-second burn that pushed the plane to Mach 5. In 2016, an Indian test vehicle reached Mach 6 with the engine running for just five seconds.

The Chinese breakthrough was based on the “world’s first systematic investigation into the effect of hydrocarbon fuel state change on the performance and stability of supersonic combustion”, the article said.

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The Institute of Mechanics was founded by Dr Hsue-Shen Tsien, the founding father of China’s rocket programme and developer of some of the world’s earliest hypersonic flight models in the 1940s.

The Chinese Academy of Sciences has nominated Fan – a Princeton physics PhD who has worked on the scramjet programme since 2004 – for a national “innovator of the year” prize.

A scramjet is an air-breathing engine for flight that becomes operational at Mach 5 – five times the speed of sound – or above. Traditional jet engines can melt at hypervelocity. The scramjet has no moving parts, like a turbofan, but instead uses the forward motion of a plane to compress air and mix it with high-energy fuel to generate explosive thrust.

Unlike a ramjet, the air in the scramjet moves faster than sound even after compression.

Supersonic air stream could raise the temperature of the engine to over 4,000 degrees Celsius – twice that of ordinary jet engines – and if the heat built up, the scramjet could explode.

Fan and his colleagues dealt with this problem by directing fuel to the surface of the most heated components, such as the combustion chamber, the article said. With precise control, the fuel could absorb and dissipate the heat. The heat, in turn, would turn the fuel into a gas of carbon and hydrogen molecules eager to meet the oxygen in the compressed air, and burn.

Huang Yue, associate professor of aerospace engineering at Xiamen University, said 10 minutes for a single scramjet run was an impressive achievement.

“In many tests, it lasts only a few seconds,” he said.

The US Air Force Research Laboratory in Tennessee, for instance, spent nine months last year to accumulate 30 minutes of combustion time on a scramjet engine.

But whether a scramjet engine can maintain the performance at high speed flight remains a question.

Huang said that ground tests could not simulate all the elements of an actual flight at high altitude and some components that worked on the ground might become less reliable in the air.

The article did not say when the experiment was conducted or if the performance was in actual flight. But the engine had been applied in a classified hypersonic weapons programme, according to the institute.

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Hypersonic weapons can travel up to Mach 20, according to the US Defence Advanced Research Projects Agency.

A 10-minute scramjet boost to a weapon could give it a range of more than 4,000km (2,500 miles) at top speed. Even the most advanced missile defence system would struggle to intercept threats manoeuvring at such high speed.

The Beijing active cooling scramjet engine facility used for the test was a world leader, the institute said.

Military vehicles carrying DF-17 missiles take part in China’s National Day parade in Beijing. Photo: AFP

In a related development, the world’s most powerful wind tunnel is expected to be finished construction in China this year. The simulator facility dubbed JF22 is in Huairou, a mountainous district in northeast Beijing, and will host the development of a new generation of hypersonic weapons to Mach 20 or beyond.

Russia deployed Avangard, a nuclear-capable hypersonic glide vehicle that was reportedly capable of reaching a top speed of Mach 27 in December last year. It was two months after China showcased its DF-17 missile, a mid-range hypersonic weapon, at the national day parade.

The United States, though an early starter, has fallen behind China and Russia in the hypersonic race, according to the Pentagon. To catch up with China and Russia, the US defence department said in March that it had tested a prototype to validate the design of a hypersonic weapon that could be available for deployment by 2023.

“Delivering hypersonic weapons is one of the department’s highest technical research and engineering priorities,” the Pentagon said at the time.

Fan’s team has sought to commercialise the scramjet technology, according to the institute. They have established a company in Hefei, in southeastern Anhui province, with nearly 200 million yuan (US$28 million) investment by the government to produce engines for future space planes.

Current space flights are conducted almost exclusively by rocket engines. The scramjet could, in theory, reduce the cost of space travel to just a fraction of the present expense.

The Chinese team has also built a high-performance air purifier using the scramjet technology that can kill the viruses causing Covid-19 and other diseases in hospitals, government buildings, factories and schools with a scorching hot jet steam.
This article appeared in the South China Morning Post print edition as: Chinese engine breakthrough raises bar