Investigation on the improved lifted flame stabilization of methane/hydrogen mixtures with oxygen co-flow based on OH* chemiluminescence

Understanding the methane-hydrogen lifted flame behavior is significant for improving the stability and safety of practical combustion systems. In this study, the effects of the hydrogen addition ratios and oxygen-fuel ratio on the lifted flame stability, OH* chemiluminescence distribution, and lift-off height are investigated using spectral diagnostic techniques. The results show that the addition of hydrogen can enhance the stability of lifted flame. The flame exists in a single main reaction zone and the peak intensity decreases as the hydrogen addition ratio increases. The flame lift-off height decreases as the hydrogen addition ratio increases at low oxygen-fuel ratios, but there is an opposite trend at high oxygen-fuel ratios. In addition, a fitting line is obtained by considering the effect of co-flow to summarize the effect of jet velocity variation on flame lift-off height after hydrogen addition and the fitting correlation is well established.