Hypersonic travel: A step closer to reality

Maryland, USA: A joint research effort between an ethnic Indian-owned, privately held, US company, Astrox Corp and the University of Maryland has solved a fuel injection problem that makes hypersonic travel over vast distances more realizable than ever before.

According to Ajay Kothari, president of College Park, Maryland-based Astrox Corp., the innovative research had solved a fuel-mixing problem for combustion at speeds of Mach 6 and above. The breakthrough could allow airplanes designed by Astrox to eventually travel above the Earth's atmosphere at speeds as fast as Mach 25, or 17,500 miles-per-hour.

Mechanical engineering department Professor Ashwani K Gupta, faculty member Kenneth Yu and graduate student Ram A Balar, at the University of Maryland successfully designed and tested a combustor for Astrox' hypersonic plane that uses an inward-turning scramjet engine.

The problem with hypersonic travel is that mechanical engines don't function properly at such speeds, because moving parts don't work at 3,500-7,500 miles-per-hour, or 5-10 times faster than the speed of sound.

Hypersonic jet engines use scramjets, which are rectangular, duct-like engines with no moving parts. In a scramjet, air enters the engine at hypersonic speeds and is compressed to supersonic speeds, after which it is mixed with fuel and ignited. The ignition forces air to leave the engine at a faster, and also at a higher pressure, than when it came in, which creates the required thrust.

However, a rectangular design also means that a large surface area comes into existence, which generates tremendous heat transfer. This, in turn, requires extra fuel to cool areas around the engine chamber. According Astrox president Kothari, not only are the large surface areas inefficient, but the extra fuel also adds significant volume and weight to the aircraft. This, he says, makes single-stage-to-orbit travel, utilizing a rectangular-shaped engine design, difficult.

Kothari's engine is shaped like a funnel, with air entering through a circular opening, increasing in pressure as it passes through, and exiting with more thrust and less heat than through a rectangular design. The unresolved challenge was to inject fuel more efficiently into the fast-moving air as it goes through the engine.

"Roughly speaking, you're looking at the air flow traveling 1,000 meters-per-second inside the combustor," said Yu in a statement. "The combustor is a meter long, so you have one millisecond for everything to happen - not just the fuel and air mixing - but the burning as well."

The challenge, for Maryland researchers was to mix the fuel with the air quickly, before combustion occurred, with the air traveling at high speeds. The team designed an injector resembling a small, aerodynamic wing, which enters the engine at an angle in the same direction the air is flowing. Fuel is injected at the wake where the air crosses the wing-shaped injector.

"You have to inject the fuel in the same direction as the air is traveling," said Gupta. "That's where the novelty comes in, as it gives you both high thrust and good mixing."

The new design was tested in the combustor at Mach 2, twice the speed of sound, in the university's supersonic wind tunnel.

According to Astrox's Kothari, the Maryland team solved "one peg of a whole puzzle (of supersonic travel), but it was a very large peg." Professor Gupta, who immigrated to England from Punjab, and then eventually to the US, plans to help Astrox test his design and the combustor in a small, model space plane.

"Hypersonic space planes could revolutionize the transportation industry, much like jet planes did for subsonic commercial aviation 50 years ago," Kothari, who founded the company in 1987, said recently. "Seemingly remote parts of the world would be nearly as accessible as a two-hour drive."

Astrox will deploy its vehicle design for military use at first, both as a stand-alone plane and as a weapons delivery system. The company has received $5 million in contracts from the US Air Force, Army, Navy, and National Aeronautics and Space Administration, including three Small Business Innovation Research grants to design hypersonic airplanes and rockets.

According to Kothari, he sees single-stage planes eventually taking off from airports and reducing 20-hour flights to as little as 1.5 hours.