Abstract
The paper presents results of numerical and experimental investigation of mixture ignition and detonation onset in shock wave reflected from inside a wedge. Contrary to existing opinion of shock wave focusing being the mechanism for detonation onset in reflection from a wedge or cone, it was demonstrated that along with the main scenario there exists a transient one, under which focusing causes ignition and successive flame acceleration bringing to detonation onset far behind the reflected shock wave. Several different flow scenarios manifest in reflection of shock waves all being dependent on incident shock wave intensity: reflecting of shock wave with lagging behind combustion zone, formation of detonation wave in reflection and focusing, and intermediate transient regimes. Comparison of numerical and experimental results made it possible to validate the developed 3-D transient mathematical model of chemically reacting gas mixture flows incorporating hydrogen – air mixtures.
Highlights
Self-sustaining waves can propagate in meta-stable media; energy needed to support such waves is released by the wave itself
Control of detonation onset is necessary in perspective pulse detonation engines using hydrogen-air mixtures in the working cycle, which are under development
For smaller intensity of incident shock wave its focusing in reflection from a wedge does not bring to immediate formation of detonation wave but it could cause mixture ignition and flame propagation
Summary
Self-sustaining waves can propagate in meta-stable media; energy needed to support such waves is released by the wave itself. Processes of transition between those regimes are less studied up to now, in comparison with pure subsonic or supersonic modes. Control of detonation onset is necessary in perspective pulse detonation engines using hydrogen-air mixtures in the working cycle, which are under development now. In our studies we’ll use hydrogen fuel because, on one hand, it is a very perspective fuel making the engine exhaust much cleaner than that for hydrocarbon combustion [1,2], and on the other hand, chemical kinetics for hydrogen – air mixtures combustion are well developed [3,4,5,6,7,8]. The thermodynamic efficiency of Chapman – Jouguet detonation as compared with slow combustion modes is due to the minimal entropy of the exhaust jet [10]. The present investigation is focused on initiation of detonation within limited in size spatial structures by relatively weak initiators using advantage of shock waves focusing and energy cumulation
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