Engineers at NASA Langley Research Center, Virginia are preparing to run a hypersonic scramjet demonstrator engine on heated hydrocarbon fuel, having completed ignition tests with gaseous ethylene.

The transition from ethylene to JP-7 represents a key milestone for the fuel-cooled scramjet, developed by Pratt & Whitney Rocketdyne to power the US Air Force Research Laboratory's Boeing X-51A hypersonic demonstrator. The X-51A engine is a flight-weight version of the hydrocarbon-fuelled scramjet developed under the USAF's HyTech programme.

The first test engine, the SJX61/1, is being evaluated in Langley's 2.5m (8ft)-wide high-temperature test facility, which has been upgraded to replicate Mach 5 conditions. "This is currently calibrated to Mach 4.6 and we're testing at this now," says facility manager Steve Harvin. "We've completed ignition tests with gaseous ethylene and are working on the transition to get the engine off ethylene and on to heated JP7. That's the tricky part."

Recently completed tests on the similarly fuelled GDE-2 ground demonstrator engine involved the same issues. "We had to purge out cold fuel from each system to prevent unstarts," says Harvin. The current test series will include runs at M5 and later M6.5. A refined SJX61/2 engine will be tested at M5 at Langley later this year. Testing will culminate in 2009 with a series of flights in which the 4.3m-long X-51A will be boosted by solid rocket to a scramjet ignition speed of M4.5, after which the actively fuel-cooled engine is expected to accelerate the vehicle to between M6.5 and M7.

Source: Flight International