Exquadrum (United States)

View Video Presentation: https://doi.org/10.2514/6.2021-3671.vid Characteristic timescales relevant to rotating detonation rocket engines (RDREs) are described in this study. The existence of traveling detonations within an RDRE create a highly complex reacting flow field that involves processes taking place over a large range of timescales. Specifically, characteristic times associated with various combustion kinetics (i.e., detonation and deflagration), injection (e.g., flow reversal and recovery), flow (e.g., residence time) and acoustic modes are quantified using first principle analyses to elucidate further understanding into the relevant physics pertaining to RDREs. Three rocket relevant fuels are investigated, including methane CH_4, hydrogen H_2 and rocket grade kerosene RP-2 for equivalence ratios ranging from phi = 0.25 to 3 and chamber pressures from 5 to 100 atm. Chemical timescales associated with detonation typically range from 0.05-1000 ns for the induction and chemical reaction times; detonation-based chemical equilibrium however, spans a larger range from 0.001 to 300 ns depending on the flow condition and fuel. This has implications regarding maximizing detonative heat release, especially in the presence of pre-detonation deflagration (as in actual RDREs). Synthetic detonation wave structures are generated and input into a simplified injector model that describes the periodic choking/unchoking process that occurs for varying injector stiffness. This analysis shows that injection timescales typically range from 5 - 50 microseconds depending on injector stiffness; for high-strength detonations and low-stiffness injectors, target reactants flow rates may not be reached prior to the next wave arrival, not allowing appropriate time for reactant mixing. This partially explains the detonation velocity deficit present in RDREs. Finally, timescales tied to chamber geometry such as residence time are typically on the order of 0.1-10 ms, and acoustic resonance times are 10 to 1000 microseconds (able to couple to the injection recovery processes). Overall, this work serves as the foundation for extended characteristic time- and length scale studies that will help enhance the understanding of relevant physics to optimize future RDRE designs.