Experimental, Computational, and Chemical Kinetic Analysis to Compare the Flame Structure of Methane-Air with Biogas–H2–Air

Abstract

This paper presents a numerical and experimental investigation of the laminar burning velocity and flame structure of methane, biogas, and hydrogen-enriched biogas. Experiments were performed on flat flame burners based on heat flux method, and numerical computations for the flame structure were conducted over the same burner using three-dimensional CFD simulations with DRM19 detailed chemistry. To get deeper insight of chemical reactions, sensitivity analysis of the studied mixtures was also conducted using ANSYS Chemkin-Pro® with GRI-Mech. 3.0 reaction mechanism. All experiments and numerical simulations were conducted at 1 atm and 298 K. The experimental results show that the laminar burning velocity of the methane-air mixture reduced by 47% when diluted with 50% carbon dioxide. On the other hand, 40% hydrogen addition in the biogas-air mixture (containing 30% methane + 30% carbon dioxide), enhanced the laminar burning velocity by 117% compared to pure biogas-air mixture at stoichiometry. The three-dimensional CFD computational results predicted a 580 K drop in temperature, 32% reduction in CH3 concentration, and 30% reduction in CO concentration for methane, when diluted with 50% carbon dioxide. Chemical kinetic analysis of methane-air, biogas-air, and 40% hydrogen-enriched biogas-air mixture predicted H + O2↔O + OH (R38) and H + CH3(+M)↔CH4(+M) (R52) to be most dominant reactions with positive and negative sensitivity coefficients, respectively. However, the dominance of these reactions were significantly higher in hydrogen-enriched biogas-air mixture compared to pure methane-air mixture due to the increased production of OH/H radicals in the reaction zone.