Flame Characterization and Flashback Studies of Hydrogen-Enriched Low-Swirl Flames Using High-Speed OH-PLIF

This paper reports the flashback mechanism observed in hydrogen-enriched flames stabilized in a low-swirl burner (LSB) at atmospheric temperature and pressure. The fundamentals of hydrogen-rich stable flames and spatiotemporal information of flashback phenomena were observed experimentally using a high-repetition-rate nanosecond (ns)-duration hydroxyl planar laser-induced fluorescence (OH-PLIF) diagnostic. Testing was conducted for methane and hydrogen ([Formula: see text], by mole) blends in an optically accessible LSB premixer with measured swirl numbers varying from 0.43 to 0.49. The flashback propensity showed dependence on liftoff length, which was dependent on premixer velocity ([Formula: see text]), hydrogen content ([Formula: see text]), and equivalence ratio ([Formula: see text]) at constant temperature and pressure. High-speed OH-PLIF images revealed that lifted flames were first observed at low [Formula: see text] conditions, which were changed to an M-shaped flame attached to the burner rim with an increase in [Formula: see text]. A further increase in [Formula: see text] triggered the flame flashback into the premixer. Flame [Formula: see text] at flashback ([Formula: see text]) showed an expected linearly increasing trend with increasing [Formula: see text] and decreasing [Formula: see text], and the conclusions drawn aligned well with detailed liftoff length investigations. The [Formula: see text] increased with increasing perforated plate hole diameter and increasing swirler vane angle. The vane angle had little effect on flashback tendency at high premixer velocity.