Ignition behavior and the onset of quasi-detonation in methane-oxygen using different end wall reflectors

Abstract

The shock wave focusing technique is beneficial to the development of detonation-based engines, which can shorten the long run-up distance that is usually required for a detonation, reducing the weight of the detonation engine. In this work, we performed experiments using different end wall reflectors to facilitate the formation and intensity of the combustion wave in a stoichiometric methane-oxygen mixture diluted by argon. By changing shock wave intensity, the effects of the incident shock Mach number (Ma) on the ignition delay times in two reflectors are systematically investigated. The experimental results show that the conical reflector creates an abrupt pressure rise in the apex, resulting in a 64.5% rise in the acceleration of the reflected shock velocity compared with the planar reflector. The introduction of a conical reflector significantly shortens the ignition delay time by an order of magnitude and facilitates the amalgamation of the leading reflected shock wave and the subsequent combustion wave. The experimental results also illustrate that conical reflectors promote the formation of the second ignition. However, only a weak deflagration wave is formed in a planar reflector, and a strong deflagration wave and quasi-detonation wave are observed by using a conical reflector. Our observation sheds light on the mechanism of ignition modes induced by the shape of reflectors.