Combustion characteristics of nonuniform methane-air mixtures in the duct

Abstract

In this study, an experimental duct was divided into two sections (ducts A and B) and filled with methane-air mixtures at various equivalence ratios. The combustion characteristics of non-uniformly distributed methane-air mixtures were studied experimentally, and the effect of ignition position on them was analyzed. The results showed that the a change in the equivalence ratio in duct A had a more visible effect on flame propagation. As the ignition position moved toward the open end, rapidly oscillating pseudo-flat structures and distorted tulip structures were observed in the right flame, and the bimodal pressure waveform was transformed into a unimodal waveform. While the propagation of the LFF (i.e., the flame front that propagated to the left open end) is the main reason for the pressure increase, the RFF (i.e., the flame front that propagated to the right closed end) also exerted a certain influence on the second peak. The stretching effect of the LFF and the Rayleigh-Taylor instability jointly cause oscillations in the RFF. We also observed that the maximum flame propagation velocity and peak overpressure varied in a consistent manner, both increasing first and then decreasing as the ignition position approaches the open end.