Air Force Research Lab, DARPA and NASA Rotating Detonating Engine Research
There have been published papers by the Air Force Research Lab and NASA on rotating detonation engines having 10% or more efficiency gains. A rotating detonation engine (RDE) uses a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. Computational simulations and experimental results have shown that the RDE has potential in transport and other applications. Rotating Detonation engines have been studied for decades and there is lot of research showing that if they can work they could boost efficiency up to about 25%. There have been thousands of ground test firings and computational simulation. Venus Aerospace is first to fly rotating detonation engiines
Venus Aerospace has partnered with NASA on nozzle design optimization using CFD simulations and partnered with DARPA. NASA-supported testing of advanced nozzle designs for their RDRE has been completed and the best designs have been integrated into flight-ready engines. Venus Aerospace has applied CFD and conducted real engine testing demonstrating their RDRE’s performance, detailed CFD studies and comprehensive wind tunnel test results by Venus Aerospace do not seem to be publicly published in full technical detail yet. Venus has a partnership with NASA Marshall to reach the longest sustained tests of a rotating detonation rocket engine (RDRE). Any detailed performance data from partnerships (e.g., with DARPA, NASA, or the USAF) appears to be proprietary or restricted, as is common in defense and hypersonic development.
Venus Aerospace co-founder and CTO, Andrew Duggleby, has a background in CFD (having previously founded a CFD-focused aerospace startup), and Venus has collaborated with NASA on RDRE nozzle optimization via SBIR grants..
In detonative combustion, the flame front expands at supersonic speed. It is theoretically up to 25% more efficient than conventional deflagrative combustion potentially enabling increased fuel efficiency.
The basic concept of an RDE is a detonation wave that travels around a circular channel (annulus). Fuel and oxidizer are injected into the channel, normally through small holes or slits. A detonation is initiated in the fuel/oxidizer mixture by some form of igniter. After the engine is started, the detonation is self-sustaining. One detonation ignites the fuel/oxidizer mixture, which releases the energy necessary to sustain the detonation. The combustion products expand out of the channel and are pushed out of the channel by the incoming fuel and oxidizer.
DARPA is working with RTX on Gambit, researching the application of rotating detonation engines for supersonic air-launched standoff missiles. DARPA is also working with Venus Aerospace which successfully tested its RDRE engine in March 2024.
NASA Rotating Detonation Fluid Dynamic Study
Daniel Paxson at the Glenn Research Center used simulations in computational fluid dynamics (CFD) to assess the RDE’s detonation frame of reference and compare performance with the PDE. He found that an RDE can perform at least on the same level as a PDE. Furthermore, he found that RDE performance can be directly compared to the PDE as their performance was essentially the same.
A parametric optimization study is performed on the nozzle of a laboratory rotating detonation rocket engine (RDRE) using a three-dimensional computational fluid dynamic simulation. The primary optimization objective is maximum nozzle thrust. The basic nozzle configuration is a shrouded, truncated plug. The fluid in the RDRE chamber leading to the nozzle is choked at its exit so that its cyclic behavior is unaffected by any changes to the nozzle design. Optimization is performed for a single operating point. Parameters varied are the overall nozzle area expansion ratio and the fraction of the expansion area that is provided by the shroud. These two parameters indirectly affect the angle of the plug nozzle cone, and the bluff body area associated with its truncation. Nozzle thrust is evaluated as the difference between the thrust of the RDRE chamber-plus-nozzle combination and that of the chamber alone. The nozzle produces approximately 20% of the total engine thrust. The baseline nozzle is found to perform well, yielding 58.1% of the thrust calculated for a notional ideal RDRE nozzle which can instantaneously change shape to allow isentropic expansion of every fluid element. Optimization improves the performance, bringing the nozzle thrust to 70.0% of the notional ideal, and total engine thrust (chamber-plus-nozzle) to 94% of the ideal.
On January 25, 2023, NASA reported successfully testing its first full-scale rotating detonation rocket engine (RDRE). This engine produced 4,000 lbf (18 kN) of thrust. NASA has stated their intention to create a 10,000-pound-force (44 kN) thrust unit as the next research step. On December 20, 2023, a full-scale Rotating Detonation Rocket Engine combustor was reportedly fired for 251 seconds, achieving more than 5,800-pound-force (26 kN) of thrust. Test stand video captured at NASA’s Marshall Space Flight Center in Huntsville, Alabama, US, demonstrated ignition.
In May 2016, a team of researchers affiliated with the US Air Force developed a rotating detonation rocket engine operating with liquid oxygen and natural gas as propellants. Additional RDE testing was conducted at Purdue University, including a test article called “Detonation Rig for Optical, Non-intrusive Experimental measurements (DRONE)”, an “unwrapped” semi-bounded, linear detonation channel experiment. IN Space LLC, in a contract with the US Air Force, tested a 22,000 N (4,900 lbf) thrust rotating detonation rocket engine (RDRE) while testing with liquid oxygen and gaseous methane at Purdue University
Space travel requires high-powered, efficient rocket propulsion systems for controllable launch vehicles and safe planetary entry. Interplanetary travel will rely on energy-dense propellants to produce thrust via combustion as the heat generation process to convert chemical to thermal energy. In propulsion devices, combustion can occur through deflagration or detonation, each having vastly different characteristics. Deflagration is subsonic burning at effectively constant pressure and is the main means of thermal energy generation in modern rockets. Alternatively, detonation is a supersonic combustion-driven shock offering several advantages. Detonations entail compact heat release zones at elevated local pressure and temperature. Specifically, rotating detonation rocket engines (RDREs) use detonation as the primary means of energy conversion, producing more useful available work compared to equivalent deflagration-based devices; detonation-based combustion is poised to radically improve rocket performance compared to today’s constant pressure engines, producing up to 10% increased thrust. This new propulsion cycle will also reduce thruster size and/or weight, lower injection pressures, and are less susceptible to engine-damaging acoustic instabilities. Here we present a collective effort to benchmark performance and standardize operability of rotating detonation rocket engines to develop the RDRE technology readiness level towards a flight demonstration. Key detonation physics unique to RDREs, driving consistency and control of chamber dynamics across the engine operating envelope, are identified and addressed to drive down the variability and stochasticity observed in previous studies. This effort demonstrates an RDRE operating consistently across multiple facilities, validating this technology’s performance as the foundation of RDRE architecture for future aerospace applications.
Rotating detonation rocket engines offer the potential to revolutionize space missions and exploration. This new detonation-based propulsion engine will allow the delivery of larger payloads to space through a more efficient and compact launch system and extend in-space vehicle life, as this engine technology produces increased performance, uses lower injection pressures, and is less susceptible to acoustic instabilities. Rotating detonation waves, i.e., supersonic combustion-driven shocks, generate significant heat release at intense pressures and temperatures, allowing more useful available work to be extracted from combustion. As a foundational step to advancing detonation-based engine technology, a collective effort has been undertaken by four propulsion facilities to standardize operability and benchmark performance of rotating detonation rocket engines to revolutionize future rocket propulsion. By standardizing the rocket engine facilities, the same two- to three-wave stable operating modes are observed by each group for propellant flow rates ranging from 0.270 to 0.375 kg/s at a fixed equivalence ratio of 1.1. Within this flow regime, a mode transition is successfully captured between
= 0.300–0.325 kg/s, and is supported by RDRE wave stability theory. Agreement amongst the local operating mode produces consistent engine performance across the investigated flow conditions, ranging from F = 350–625 N and = 123–175 s for the data collected at the various propulsion facilities. To produce a cohesive validation set of experimental results for this canonical RDRE, measurement standards including flow metering, high-speed image capturing and performance measurements are developed, in addition to data reduction approaches including high-speed image processing and uncertainty quantification. By providing detailed understanding towards stabilizing these operating modes for RDREs under this collective effort, this work serves as a path towards future design optimization studies to bolster the unique benefits of a detonation-based propulsion cycle for future space missions.