The paper presents experimental measurements of flashback propensity of H2-CO mixtures (primary constituents of syngas fuels). Effects of H2 concentration, external excitation and swirl on the flashback propensity of H2-CO flames are discussed. The flashback behavior of H2-CO flames changes nonlinearly with the increase in H2 contents in the mixture. The critical velocity gradient (gF) values of 5%–95% and 15%–85% H2-CO mixtures somewhat agree with the scaling relation (gF = c(SL2/α)) and yield an average c value of 0.035. However, the gF values of 25%–75% H2-CO mixture show higher order variations with the SL2/α ratio (especially for SL2/α < 19,000 s−1). At a lower SL2/α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher SL2/α ratio. The effect of external excitation on the flashback propensity of H2-CO flames with more than 5% H2 is not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H2-CO flames.

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