Experimental investigation on the effects of hydrogen addition on thermal characteristics of methane/air premixed flames

Abstract

This paper presented an experimental study on the measurements of premixed laminar methane/air flames with and without hydrogen addition. The premixed flames were stabilized on a McKenna flat fame burner at atmospheric pressure. The traveling thermocouple approach was used to measure the axial flame temperature profiles over ranges of equivalence ratios and hydrogen enriching ratios. The measured temperatures, corrected by considering radiation loss, were analyzed to estimate the rate of flame heat release, by solving the continuity equations of mass, energy, and species which were applied to a flat flame. Some of important flame properties, such as the peak temperature, the average temperature, the flame thickness, the thickness of reaction zone and combustion efficiency, were presented to characterize the effect of hydrogen enrichment on laminar flame propagation. It is shown that the presence of hydrogen in laminar flame can promote flame reaction to some extent. With an increase of hydrogen addition fraction in fuel, the peak rate of heat release and combustion efficiency show increases, while the average temperature gives decrease. The analysis of the heat release profiles suggested that hydrogen addition has significant effect on the early part of flame heat release profile. The flames enriched by hydrogen show linear approximations in the plots of the logarithmic heat release rate against the reciprocal of flame temperature. A modeling for one dimensional premixed laminar burner-stabilized flame had been implemented with GRI-Mech 3.0 detailed kinetic reaction mechanism, based on the measured temperature profiles of these premixed flames. And then an analysis on the heat release was performed for each reaction. It suggested that the reaction OH+H2⇔H+H2O gradually increases its contribution to the early heat release with the increase of hydrogen enrichment, which is due to the fact of hydrogen addition resulting in an increased concentration of radical H in flame. The promoted H formation accelerates the flame burning velocity, and then thins the thicknesses of flame and reaction zone to a great extent.