Different combustion modes caused by flame-shock interactions in a confined chamber with a perforated plate

© 2017 The Combustion InstituteThe present work investigates the interaction of the turbulent flame and shock wave as well as the end-gas autoignition in a newly designed constant volume combustion chamber equipped with a perforated plate using a stoichiometric hydrogen-air mixture. Detailed high speed schlieren photography is used to track the turbulent flame fronts and shock waves which are generated by the laminar flame passing through the perforated plate. The different propagation speeds of the turbulent flames and shock waves can be obtained by controlling the initial pressures and the hole size of the perforated plate. In this work, three combustion modes were obtained clearly by experiment, depending on the interactions of the turbulent flame and shock wave, such as normal combustion, oscillating combustion and end-gas autoignition. The normal combustion is a weak turbulent flame propagation without an obvious shock wave in the confined chamber. The oscillating flame propagation is generated by the interaction of the reflected shock wave and flame front and this process can be clearly visualized in the present work. The end-gas autoignition is induced by the combined effect of the supersonic flame and the shock waves. The accelerating combustion in the confined chamber could produce the primary shock wave and the subsequent secondary shock wave is induced by the secondary flame occurring between the primary flame and primary shock wave. It is found that the secondary shock wave with speed of 780 m/s is faster than the primary one, which is the source of the end-gas autoignition. It is also observed that quasi-detonation wave produced by the end-gas autoignition can reach the speed of 1700 m/s. This wave is accompanied by a strong pressure oscillation which can explain the mechanism of engine knock.