Nozzle effect on heat transfer and CO emission of impinging premixed flames

Experiments were carried out to investigate the heat transfer and CO emission characteristics of a pre-mixed LPG/air circular flame jet impinging upwards normal to a flat plate. The effects of nozzle diameter and nozzle arrangement on the heat transfer and CO emission under different fuel/air mixture flow rates (Q(mix)), equivalence ratios (phi) and normalized nozzle-to-plate distances (H/d) were examined. For the effect of nozzle diameter, burners of nozzle diameters of d = 7.9, 9 and 10 mm were used, and for the effect of nozzle arrangement, a twin-nozzle burner and a triple-nozzle burner, each with a cross-sectional area equal to that of the 9 mm diameter burner, were investigated under different normalized jet-to-jet spacing, S/d, of 3, Sand 7. The heat transfer rate and CO emission index (EICO) are enhanced significantly with the decrease in the nozzle diameter for the single-nozzle flames. For the twin- and triple-nozzle flames, when the other operational conditions including Q(mix), phi and H/d are invariant, the moderate S/d of 5 gives the highest heat transfer rate, whereas the EICO increases with increasing S/d. Comparison of the flames from all the burners shows that the highest heat transfer rate and EICO are obtained on the single-nozzle burner with the smallest nozzle diameter while the lowest heat transfer rate and EICO are obtained on the triple-nozzle burner with the smallest S/d. (C) 2010 Elsevier Ltd. All rights reserved.