GE Aerospace and Lockheed Martin recently announced that they have successfully jointly demonstrated a new liquid-fuel rotary detonation ramjet (RDRJ). They are trying to use this new propulsion system and tactical inlet design to fill the "gap" in the efficiency of current hypersonic flight and promote the development of hypersonic weapons in a more efficient and mass-produced direction.
The report pointed out that hypersonic flight is regarded as another major leap forward in promoting the flight envelope since humans broke the sound barrier in 1947, while rotational detonation technology is regarded as a "quantum leap" in the field of propulsion; now the combination of the two means that related technologies have moved from the early feasibility verification stage to the engineering optimization stage, and engineers have begun to put efficiency issues at the core. Being able to fly at more than 5 times the speed of sound has great potential in both the military and civilian fields. However, the existing technology still has many areas for improvement. Among them, the shortcomings in efficiency of hypersonic missiles propelled by ramjet engines are particularly prominent.
According to the article, a traditional ramjet engine is essentially a jet engine with almost no moving parts. It does not rely on turbomachinery to compress the intake air. Instead, it uses the dynamic pressure brought by its own high-speed forward motion to compress the air and send it into the combustion chamber. However, for such a ramjet engine to ignite normally, the flight speed usually needs to reach at least Mach 3, which means that the missile or aircraft must rely on a large and powerful rocket booster to accelerate it to the ignition speed in the initial stage.
To solve this problem, GE and Lockheed Martin plan to use a rotating detonation engine to accelerate the missile in the early stages of flight. By maintaining a fuel detonation wave propagating at supersonic speed in an open cylindrical channel, it circulates in an annular manner in the channel, while continuously injecting fuel and water to achieve a self-sustaining high-pressure combustion cycle. This structure can maintain pressure during the combustion process, rather than relying on subsonic flame surfaces like traditional combustion chambers, thereby significantly improving energy utilization efficiency.
According to reports, the efficiency of this type of rotating detonation engine can be increased by about 25% compared to conventional engines, which can significantly reduce the size and weight. More importantly, it can work under subsonic conditions, and can be adjusted through configuration and flow channels to act as a ramjet engine under supersonic conditions and switch to a scramjet under hypersonic conditions, thus significantly reducing the size of the required rocket booster. The simplification of the design means that hypersonic missiles with relatively simple structures, low costs, and mass production are expected to appear in the future.
Lockheed Martin's key contribution to this joint demonstration was its design of a high-speed tactical inlet for the dual-mode ramjet (DMRJ), which can be matched with a rotating detonation core to allow the engine to switch between ramjet and scramjet modes at different speed ranges. This air intake system also targets the long-term problem of poor adaptability of detonation engines at different altitudes. By tuning the coupling between the air intake and the detonation wave field, the engine can maintain operation in multi-altitude and multi-Mach number environments. However, it requires extremely complex computational fluid dynamics analysis to manage the highly complex shock wave structure.
Randy Kreitz, Lockheed Martin's vice president and general manager of advanced programs, said that after two years of internal investment, this demonstration demonstrated the power of collaboration, innovation and shared commitment to deliver affordable warfighting capabilities to the warfighter at the "speed of relevance." He said that this compact ramjet engine solution embodies Lockheed Martin’s expertise in ramjet inlet design and can provide longer range at extreme speeds. The company is committed to providing more advanced propulsion systems for U.S. hypersonic capabilities in the context of an increasingly fierce threat environment.
According to reports, this demonstration project uses the official release of Lockheed Martin as the source of information, showing that the US military is shifting from purely pursuing high speed in the field of hypersonic weapons to seeking a new balance between speed, range, cost and large-scale production capabilities. The combination of rotating detonation ramjet engines and new generation tactical inlets is regarded as one of the key routes to achieve this goal.