The effects of mixture preburning on detonation wave propagation

Pressure gain combustion in the form of continuous detonations can provide a significant increase in the efficiency of a variety of propulsion and energy conversion devices. In this regard, rotating detonation en-gines (RDEs) that utilize an azimuthally-moving detonation wave in annular systems are increasingly seen as a viable approach to realizing pressure gain combustion. However, practical RDEs that employ non-premixed fuel and oxidizer injection need to minimize losses through a number of mechanisms, including turbulence-induced shock-front variations, incomplete fuel-air mixing, and premature deflagration. In this study, a canonical stratified detonation configuration is used to understand the impact of preburning on det-onation efficiency. It was found that heat release ahead of the detonation wave leads to weaker shock fronts, delayed combustion of partially-oxidized fuel-air mixture, and non-compact heat release. Furthermore, large variations in wave speeds were observed, which is consistent with wave behavior in full-scale RDEs. Peak pres-sures in the compression region or near triple points were considerably lower than the theoretically-predicted values for ideal detonations. Analysis of the detonation structure indicates that this deflagration process is parasitic in nature, reducing the detonation efficiency but also leading to heat release far behind the wave that cannot directly strengthen the shock wave. This parasitic combustion leads to commensal combustion (heat release far downstream of the wave), indicating that it is the root cause of combustion efficiency losses. (c) 2020 Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

Pressure gain combustion through continuous detonations, particularly in rotating detonation engines (RDEs), offers significant efficiency improvements in propulsion and energy conversion devices. However, non-premixed fuel injection in practical RDEs faces challenges such as turbulence-induced shock-front variations and incomplete fuel-air mixing. Preburning was found to weaken shock fronts and lead to delayed combustion of partially-oxidized fuel-air mixtures, contributing to combustion efficiency losses. This parasitic combustion process hinders detonation efficiency by diverting heat release away from the shock wave.