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.
Parajuli et al. (Sun,) studied this question.
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