Pratt & Whitney Rocketdyne has tested a dual-mode ramjet/scramjet combustor at Mach numbers from 2.5 to 6.0, possibly the widest range yet demonstrated for this high-speed propulsion system.
"This is a very big step towards the practical application [of scramjet propulsion] to missiles and aircraft," says Mike McKeon, manager of hypersonics and advanced programmes.
The sub-scale combustor for a hydrocarbon-fuelled dual-mode ramjet was tested at the United Technologies Research Center under contract to Lockheed Martin for the Falcon Combined-cycle Engine Technology (FaCET) programme.
Funded under the US Defense Advanced Research Projects Agency's Falcon programme, FaCET is developing technology for a turbine/scramjet combined-cycle engine to power the proposed HTV-3X hypersonic test vehicle.
"The ability to operate down to the Mach 2.5 range is extremely important for FaCET," says programme manager Bob Grabowksi. "It allows us to turn the ramjet on sooner, then transition to scramjet at Mach 5 and above."
Typically the turbine would accelerate the vehicle to M4, but the ability to start the ramjet at M2.5 means "we don't have to push as far with the turbine. Pushing a turbine to M4 is tough the temperatures get pretty high," he says.
Instead of the two-dimensional, or rectangular, flowpath of PWR's SJX61 scramjet powering Boeing's X-51A hypersonic demonstrator, the PWR9220 dual-mode ramjet has a three-dimensional shape to match the Lockheed-designed inward-turning inlet. This feeds both the Rolls-Royce Liberty Works turbine engine and dual-mode ramjet.
UTRC completed 250 direct-connect runs of the combustor. PWR is building a larger-scale engine to be coupled with the inward-turning inlet for freejet testing in mid-2008 in Arnold Engineering Development Center's altitude facility.
Conceptual design of the HTV-3X is under way at Lockheed's Skunk Works, leading to a DARPA decision by the end of 2008 whether to proceed with building and testing of the unmanned demonstrator.