Rotating Detonation Rocket Engine Design and Analysis

What is a RDRE? 

• A RDRE or Rotating Detonation Rocket Engine is a constant volume combustion rocket engine utilizing supersonic combustion waves started upon ignition to generate thrust, similar to a typical rocket engine. What separates the standard rocket engine like a SpaceX Merlin and a RDRE is the constant pressure versus constant volume process. Constant pressure is actually near constant, with minor pressure loses of around 5% taking place during combustion, then expansion as the flow exits the nozzle. The constant volume process leads to high speed waves traveling radially with exhaust gas propagating axially. This different environment allows large positive pressure and temperature gradients to occur, also known as Pressure Gain Combustion. 

Why develop a RDRE?

• Pressure Gain Combustion offers the possibility to use the constrained gas expansion by heat release, leading to a rise in stagnation pressure, reaching the initial pressure. This allows for an increased work extraction in comparison to typical rocket engines, gas turbines, or other deflagration processes. Higher work extraction allows for higher ISP outputs relative to the fuel volume used, allowing for various system optimizations and tradeoffs like:

  • Less fuel needed for same ISP as a typical rocket engine

  • Same amount of fuel for an increased ISP

  • Reduction in mechanical complexity of standard rocket engines

  • Possibility of using sustainable or exotic propellant mixtures for in-space use with even higher power outputs.

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• Secondly, I sought out a challenge for my thesis that I am also deeply interested in. 

Project Stages and Development

The initial stage focuses on literature review across propellant choices, engine material choices, current/proposed RDRE designs, and research on propulsion in a vacuum. The combined engine-propellant mass and ISP are chosen to be the constraints, as my master's project in the STEP Cohort initially proposed to use the Star 48BV Solid Rocket Motor (SRM) for the kick stage. I am designing this RDRE to have a minimum equal impulse of 292.1 seconds, and a combined estimated engine-propellant mass of ~2300 kg. 

1. The propellants have been chosen, primarily focusing on the highest energetic combinations that can be analyzed. In-space propulsion allows for more powerful fuel mixtures to be investigated.  Fluorine gas in multiple combinations can generate large ISP values and we avoid the toxic products being generated in the atmosphere. 

2. The first models in progress are a 1-Dimension Chapman-Jouguet calculation and ZND detonation structure calculation. 

3. 2D models with alternating geometry and constrained injectors are next.

4. Validate the 2D model, then simulate different Fluorine reactant combinations and alternate propellant mixtures. 

5. Leverage OpenFOAM addons, C++, and potentially CFD software to begin developing a sliced 3D model, or if computationally possible, a full 3D rendering of the detonation reaction. 

What will be publicized for this project is TBD, as the topic is a hot topic in defense and research across the world at the moment.