The performance of reaction mechanism in prediction of the characteristics of the diffusive-thermal oscillatory instability of methane–hydrogen–air burner-stabilized flames

Abstract

In this work the performance of various detailed reaction mechanisms of combustion of methane–hydrogen fuel mixtures is studied. The investigation is focused on the burner stabilized flame configuration and is undertaken for the normal pressure conditions, which is a starting point for the analysis of the combustion chemistry at elevated pressures met in rocket engine chambers. The study presents the experimental setup, computational approach and results of comparison, which allow us to access the properties of complex combustion systems in variety of dynamical regimes. The comparison of the predicted and measured characteristics of these regimes is used to test the performance of the reaction models. In particular, the critical behavior, e.g. for blow-up, onset of pulsations and quasi-steady flame front propagation and bifurcation between these regimes may be used to characterize and to study properties of combustion systems with mixed fuels. A neutral stability boundary for onset of pulsations is suggested to be used in this study. A method for automatic identification of the boundary is proposed and implemented with several detailed mechanisms. Although for pure methane the results look acceptable, they show gradual divergence with the increase of percentage of hydrogen addition. Significant quantitative differences between experiments and modeling with respects to frequencies of oscillations are reported even for 2:1 ratio of hydrogen to methane in the unburned mixture. The results of the work indicate that current reaction mechanisms need to be improved in order to gain the quantitative predictability of methane–hydrogen–air combustion at normal pressure before proceeding to the conditions fuel-oxygen high pressure combustion more relevant for rocket chamber.