Flashback propensity of syngas fuels

Abstract

This paper presents experimental measurements of the critical velocity gradient and flashback behavior of H 2–CO and H 2–CH 4 mixtures. Effects of H 2 concentration, external excitation, and swirl on the flashback behavior for flames of these fuel mixtures are discussed. For H 2 concentration burner and scaling studies the critical velocity gradient ( g F), defined as the ratio of the square of the laminar burning velocity to the thermal diffusivity of the mixture ( g F = S L 2 α ) , was used to quantify the flashback propensity of the flames. The critical velocity gradient of both H 2–CH 4 and H 2–CO flames changed nonlinearly with the increase in H 2 contents in the mixture. The critical velocity gradient ( g F) of 5–95% and 15–85% H 2–CO mixtures somewhat agreed with the scaling relation ( g F = c S L 2 α ) and yielded an average c value of 0.04. Similarly, values of a 25%H 2-75%CH 4 for different burner diameters were also fitted using the scaling relation yielding an average c value of 0.044. The g F values of 25–75% H 2–CO mixture showed non-linear variation with the S L 2 / α ratio (especially for S L 2 / α > 19 , 000 s - 1 ), and at a lower S L 2 / α ratios burner diameter had small effect on critical velocity gradient measurements. The opposite trend was observed for a 25–75% H 2–CH 4 mixture showing non-linear variation at a lower S L 2 / α ratios (for S L 2 / α > 5600 s - 1 ) and having less effect at higher S L 2 / α ratios. It was also determined that the effect of external excitation on the flashback propensity of H 2–CO flames with more than 5% H 2 was not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H 2–CO flames.