DYNAMICS OF PREMIXED HYDROGEN-AIR FLAMES IN MICROCHANNELS WITH A WALL TEMPERATURE GRADIENT

Two-dimensional numerical investigations on flame dynamics in a microchannel have been carried out for premixed hydrogen-air mixtures with detailed chemistry. Detailed studies on the formation of flames with repetitive extinction and ignition (FREI) mode have been carried out for a 0.75-mm diameter tube with fixed conditions of flow velocity of 10 cm/s and Phi = 0.5-1.0 with wall temperature linearly varying from 300 K to 960 K. An unsteady flame propagation behavior similar to FREI has been observed to appear for a range of mixture equivalence ratios and channel diameters. FREI was observed to occur for 0.5 < Phi < 0.8 for 0.75-mm diameter channel and disappears for higher mixture equivalence ratios. The effect of tube diameter has also been analyzed for 10 cm/s inlet velocity of mixture at 300-1050 K wall temperature for diameters of 0.6 mm, 0.75 mm, and 1.0 mm. As the tube diameter increased, the frequency of the FREI process decreased, which hints to the contribution of disappearance of FREI phenomenon.