Two revolutionary aerospace technologies collide as GE Aerospace and Lockheed Martin team up to demonstrate a new liquid-fueled rotating-detonation ramjet (RDRJ) designed to close the "efficiency gap" in hypersonic flight with new tactical inlets.
Hypersonic flight may seem like the biggest shove to the envelope since the sound barrier was broken in 1947 and rotating detonation may look like a quantum leap in propulsion, but combining the two shows how far both of these have come in recent years. Today, it isn't simply a matter of using one to boost the other. The technology has matured to the point where engineers have to seriously consider factors such as efficiency.
Being able to fly at over five times the speed of sound has a tremendous potential in both military and civilian applications but the technology is still in need of improvement. One area of concern is the efficiency gap for hypersonic missiles that use ramjets for propulsion.
Ramjets are jet engines that effectively have no moving parts. Instead of using turbines to compress incoming air as it flows into the combustion chamber, it uses the forward motion of the engine to compress the air by way of its own inertia. Unfortunately, for the ramjet to work properly, it has to be traveling at Mach 3 to ignite. That means the missile or other vehicle needs a massive rocket booster if it's to reach ignition velocity.
GE and Lockheed Martin plan to get around this by accelerating the missile using a rotating detonation engine, which uses a supersonic wave of detonating fuel that runs about inside an open-ended cylinder as fuel and water is fed in. This produces a self-sustaining cycle that maintains pressure during combustion.
Such an engine is 25% more efficient than a conventional engine, allowing it to be much more compact and lighter. It can also operate at subsonic speeds and the design allows it to modify itself so it can act as a ramjet at supersonic speeds and a scramjet at hypersonic speeds, so smaller rocket boosters are needed. The simplicity of the design also raises the possibility of low-cost hypersonic missiles that can be mass produced at scale.
Lockheed Martin's contribution to the enterprise is its high-speed tactical inlet that is designed for a Dual-Mode Ramjet (DMRJ). It's this that allows the detonation engine to act as both a ramjet and a scramjet by tuning itself to the rotating detonation core. This also allows the engine to work at varying altitudes – a persistent problem with detonation engines. It's simple in description, but making it work requires some pretty dense computational fluid dynamics to manage the complex shockwave patterns.
"Following two years of internal investment, this demonstration is a testament to the power of collaboration, innovation and joint commitment to get affordable capability into the hands of war-fighters at the speed of relevance," said Randy Crites, vice president and general manager at Lockheed Martin Advanced Programs. "This compact ramjet applies Lockheed Martin’s expertise in ramjet inlets and offers extended range at extreme speeds. We’re committed to delivering a propulsion system that advances America’s hypersonic capability in an intensifying threat environment."
Source: Lockheed Martin
