China tests a hypersonic afterburner, doubling thrust at Mach 6

Chinese scientists have unveiled a propulsion breakthrough that could redefine the future of hypersonic flight. Led by Yang Qingchun, an associate professor with Beihang University in Beijing, the research team has developed an innovative secondary combustion technique that nearly doubles the thrust of a scramjet engine by injecting magnesium powder into the exhaust gases from conventional jet fuel combustion. Tested under conditions simulating Mach 6 flight at 30km altitude, this unprecedented afterburner promises to strengthen China’s lead in hypersonic technology, offering faster speeds, greater manoeuvrability and extended range for next-generation weapons and aircraft. Traditional scramjets face limitations at extreme speeds – the energy output of the kerosene fuel plateaus and ignition during low-speed take-off becomes erratic. So, Yang’s team turned to magnesium, a metal known for its violent reactivity. Their solution exploited a simple yet radical concept: they could harness the residual water vapour and carbon dioxide from the burned kerosene as oxidisers to ignite magnesium particles. “Magnesium doesn’t need atmospheric oxygen,” Yang and his colleagues wrote in a paper published in peer-reviewed journal Acta Aeronautica et Astronautica Sinica last month. The magnesium particles react explosively with the waste gases already inside the engine, releasing energy that was once thrown away, according to the researchers. In ground tests using commercial RP-3 jet fuel, injecting magnesium at 13 per cent of the exhaust mass boosted thrust by 86.6 per cent, with combustion efficiency reaching 65.1 per cent. The engine’s specific thrust – a measure of force per airflow – surged from 613 Newton-seconds per kilogram to 1,126 Newton-seconds per kilogram, a leap engineers attribute to magnesium’s rapid exothermic reaction, primarily with water vapour. At Mach 6, kerosene burns to near exhaustion, leaving scorching gases of 1,800 kelvin (1,527 degrees Celsius) rich in water and carbon dioxide. Magnesium powder, injected via a central strut, ignites upon contact, releasing heat two to three times faster than kerosene alone, according to the study. Unlike traditional afterburners requiring fresh air, magnesium thrives on “waste” gases. Water vapour drives the reaction – burning twice as fast as with carbon dioxide – to form magnesium oxide crystals and hydrogen, further boosting thrust. Liquid kerosene first cools engine walls via regenerative cooling, while magnesium, added downstream, combusts in a supersonic “firestorm” stabilised by twin cavities and optimised flow paths, the researchers said. This design also allows the hypersonic aircraft to use every drop of jet fuel as a coolant to reduce the temperature on its surface, achieving efficiency unmatched by other designs. But the technology is not without hurdles. Supersonic turbulence risks uneven dispersion. At 5 per cent magnesium, thrust gains plummeted to 18.7 per cent due to poor particle penetration, Yang’s team found. Also, sharp magnesium oxide crystals, while heat-resistant, threaten engine longevity. This would require erosion-resistant materials to prevent the damage caused by these microscopic “blades”. Small differences in design parameters, such as resistance distance ratio – powder path vs engine length – can also affect the engine efficiency significantly, according to the team. The breakthrough arrives as global powers race to master hypersonic technology. The US military has said it is planning to deploy its first hypersonic weapon in September, more than three years later than originally planned, while China has been pushing hypersonic air-breathing engine technology to Mach 10 and beyond. Yang’s team claims that its design could slash launch weights or extend ranges for missiles and hypersonic aircraft. But some questions remain. While the team achieved stable powder injection using a nitrogen carrier gas, scaling the system for variable-speed flight poses challenges. Supersonic mixing of liquid and solid fuel elements, for instance, is as difficult as threading a needle in a hurricane. Solving this would require more extensive testing in various flight conditions. The researchers said they aimed to refine particle blending and test nano-sized magnesium for higher efficiency.

China tests a hypersonic afterburner, doubling thrust at Mach 6

Researchers have developed an innovative secondary combustion technique to help China win the global hypersonic race