Pulsed Detonation Engines in the Choked Flame Regime

When a combustible mixture in a pulsed detonation engine fails to undergo transition to detonation, the combustion wave consists of turbulent flame which eventually accelerates to a steady state supersonic velocity, referred to as the choked flame velocity. The present study aims to measure the engine performance of a PDE under choked flame conditions. Two sets of experiments were conducted; the first series measured thrust from the AFRL research PDE on a thrust stand. The mixtures used in this series were hydrogen-air mixtures of equivalence ratios varying between 0.7 and 1. The second series of experiments used propane-nitrous oxide-air mixtures, again varying the equivalence ratio such that the combustion wave varied between the detonation, choked flame, and subsonic flame regimes. To eliminate such effects as varying tube wall temperature and the stochastic nature of DDT, this was a series of single shot impulse measurements using a ballistic pendulum.