Flashback propensity of gas mixtures
In this study, experimental measurements of flashback propensity of hydrogen (H2)-carbon monoxide (CO) mixtures, which are the primary constituents of syngas fuels, are described. The effects of H2 concentration, diluents and swirl on the flashback propensity of H2-CO flames are discussed. For boundary layer type flashback, the critical velocity gradient (gF) values of 5 to 95%, 15 to 85%, and 25 to 75% H2-CO mixtures somewhat agree with the scaling relation [special characters omitted] and yield an average c value of 0.038. At a lower SL 2/α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher S L2/α ratio. For a given Ubulk, the %F at which the combustion induced vortex breakdown (CIVB) flashback occurs decreases with the increase in H2 concentration in fuel mixtures. The more swirl, the more stabilized the recirculation zone and flame. For a given U bulk, the %F at which the CIVB flashback occurs increases with the increase of swirl number. The 6 vane swirler (swirl number S = 0.71) stabilized flame is more prone to CIVB flashback than the 12 vane swirler (swirl number S = 0.97) stabilized flame. The flashback of 25% H2 - 75% CO mixture with 12 vane swirler (swirl number S = 0.97) occurs at 14.4 to 15.2% fuel; on the other hand, the same composition with 6 vane swirler (swirl number S = 0.71) stabilized flame flashback occurs at the 11.2 to 12.8% fuel. The flashback map for actual syngas compositions derived from different source of coal is different due to the presence of diluents in the mixtures. Diluents play a vital role to map the flashback regimes for both the swirler stabilized flames. Lignite coal derived syngas compositions went up to 33 to 35% fuel at which the flashback occurs. The strong swirled flow produces a more stabilized reaction zone (OH concentration) just after the swirler. The 12 vane swirler (swirl number S = 0.97) produce a more OH concentration (1 through 4 sequence images) after the flow separation as compared to the 6 vane swirler (swirl number S = 0.71).
Dam, Bidhan Kumar, "Flashback propensity of gas mixtures" (2009). ETD Collection for University of Texas, El Paso. AAI1473858.