Effects of the equivalence ratio on turbulent flame–shock interactions in a confined space

Abstract

In this work, the influences of the equivalence ratio on flame front propagation velocity, shock wave velocity and pressure oscillation as well as flame–shock interactions with different combustion phenomena were comprehensively studied experimentally in a newly designed constant volume combustion bomb (CVCB). And a hydrogen–air mixture was chosen as the test fuel. In the CVCB, an orifice plate was used to obtain flame acceleration and promote turbulent flame formation. High-speed Schlieren photography was employed to capture the turbulent flame front and shock wave in the present work. The evolution of the flame and shock wave together with influences of the equivalence ratio on the flame tip velocity, shock wave velocity and pressure oscillation were clearly presented. The results showed that, after the laminar flame passed through the orifice plate, wrinkled turbulent flame gradually formed, and the shock wave ahead of flame front could be seen at a certain condition. The shock wave formation and enhancement process induced by flame acceleration was clearly captured by the Schlieren photography. It was found that the mean turbulent flame tip velocity reached a maximum value at an equivalence ratio of 1.25. In addition, an increase in the initial ambient pressure resulted in an increase of the turbulent flame tip velocity. Forced by the flame–shock/acoustic interactions, the flame would reverse and the backward flame velocity was positively related to that of the forward flame. The forward shock wave showed little differences among different equivalence ratios, while the reflected shock decayed fastest for the fastest flame, and the turbulent flame was pushed back more apparently. And the effect of the equivalence ratio on the pressure oscillation caused by flame acceleration and flame–shock interactions in the end gas region of confined space was determined.