“Prototype flown in hypersonic wind tunnel simulating flight conditions at nine times the speed of sound
The ‘sodramjet’ engine could offer the biggest hope so far of commercial flight reaching hypersonic speed, the scientists say
Chinese scientists have built what they claim is a revolutionary plane engine for Mach 16 flight. An aircraft powered by the engine could reach anywhere in the world within two hours, they said.
The test flight of a prototype in a hypersonic wind tunnel in Beijing suggested unprecedented performance in terms of thrust, fuel efficiency and operational stability.
The engine could also serve “reusable trans-atmospheric planes [that will] take off horizontally from an airport runway, accelerate into orbit around the Earth, then re-enter into the atmosphere, and finally land at an airport,” said the scientists, led by Professor Jiang Zonglin of the Chinese Academy of Sciences’ Institute of Mechanics in a peer-reviewed paper published in the Chinese Journal of Aeronautics on Saturday.
The futuristic engine has a relatively simple design. It consists of three major components without any moving parts: a single-stage air inlet, hydrogen fuel injector and combustion chamber. The chamber’s mouth opens to the upper end of the air inlet.
“It is easily mistaken for a sliding board,” said a Beijing-based hypersonic flight researcher who was informed about though not involved in the study.
Jiang’s team put the engine in a powerful wind tunnel that simulated flight conditions at nine times the speed of sound.
As high speed wind hit the inlet, it generated shock waves with extremely high temperature and pressure. The shock waves met hydrogen fuel at the combustor and produced an explosion that pushed the engine forward. As the engine fired up, the mouth of the combustion chamber glowed like a Star Wars spaceship, according to video footage provided by the research team.
In theory, the air-breathing engine could take a flight up to 16 times the speed of sound, but the only wind tunnel on Earth capable of simulating such flight is still under construction in Beijing, according to the Beijing-based researcher.
Jiang and colleagues called it the “standing oblique detonation ramjet engine”, or sodramjet for short. They said the engine could offer the biggest hope so far of taking commercial flight to hypersonic speed, or five times the speed of sound. Existing hypersonic flight engines, known as scramjets, are too weak, too fuel-hungry and too unstable.
“Seventy years’ exploration in hypersonic propulsion indicates that the revolutionary concept is really in need for hypersonic air-breathing engine development. The sodramjet … can be a very promising choice,” their paper said.
The United States has often accused China of stealing its ideas, allegedly ranging from the lawnmower to the stealth fighter jet. The sodramjet was an American idea, too.
In the 1960s and 1970s, Nasa encountered a series of setbacks in its scramjet experiments. The scramjet engine had no moving parts and was predicted to perform better than ordinary jet engines at hypersonic speeds, but it often faltered during operation. One reason was that the shock waves generated by high-speed air could put out the flame in a puff.
An engineer named Richard Morrison came up with a radical solution. If the shock waves carried so much energy, he thought, why not use them as a lighter to detonate the fuel and keep the combustion alive and constant? He presented the idea in a 1980 paper that can be downloaded from Nasa’s website.
But the US government shifted the bulk of hypersonic research from Nasa to private companies such as Boeing and Lockheed Martin, and Morrison’s idea was largely if not completely forgotten by the American defence industry. The contractors put all their resources into scramjet design and continued to suffer setbacks that eventually caused them to trail other countries.
Russia and China have deployed various types of hypersonic weapons in recent years, whereas the US military was not expected to receive them until next year, even if everything goes to plan.
Jiang and colleagues said they were fed up with scramjets’ fatal design weakness. The scramjet could barely generate any thrust at the speed of Mach 7 or beyond. The fuel consumption was so high that no commercial aviation company could possibly foot the bill. And the pilots – not to mention passengers – could suffer heart attacks if they were required to restart the engine from time to time during a flight.
The team found Morrison’s idea intriguing, but the paper contained only a few rough sketches; no one has actually built such an engine. It would require extensive redesign, a special alloy that could withstand the high temperature and pressure, powerful wind tunnels and an enormous amount of investment that would likely lead to nothing.
It turned out that the sodramjet beat the scramjet by almost every measure. Turning the shock wave from their enemy to their friend helped them sustain and stabilise combustion at hypersonic speed. The faster the engine flew, the more efficiently the hydrogen fuel burned. The new engine was also much smaller and lighter than previous models.
A Shanghai-based researcher studying hypersonic aerodynamics said the experiment was probably conducted “a while ago”. China’s hypersonic programme is much shrouded in secrecy because of its potential for military application, and the studies published in academic journals have been vetted carefully, he said.
In September, China test-flew an unmanned space plane that possibly landed in a secret military airport in the Gobi Desert. Details of the engine used in the experiment remained classified.
Jiang and colleagues said the sodramjet could mark an advance similar to the first flights by the Wright brothers in 1903 and the first supersonic passenger flight by Concorde in 1969.
It is “the dream for human beings to fly faster, higher and further than ever”, they said.
But Dr Uzi Rubin, founder and first director of the Israel Missile Defence Organisation, who is an expert in hypersonic missiles, said the new design was very still “very experimental” and its advantages still remained uncertain.
“Even if promising … it will take about a generation for it to be used commercially,” he said. “I believe that hypersonic human flight is not imminent, if at all.””