Experimental study of the effects of low swirl injector blockage ratio on stability limits and combustion regimes of natural gas flame

In this study, the effect of a low swirl injector blockage ratio on the flame stability limits is investigated by using a low swirl burner. The blockage ratio is one of the main geometrical parameters of the low-swirl injector which has a significant impact on the stability of the flame. In order to investigate the influence of the blockage ratio of the central channel of low swirl injector on stability, nine swirler with distinct geometries were investigated. The results showed that with increasing the blockage ratio, the flame extinction limit was reduced so that increasing the blockage ratio from 43% to 76% reduced the extinction limit to about 25% and improved flame stability. It was also observed in this study that by increasing the equivalence ratio, the flame undergoes a transition process in which the flame proceeds from a stable lifted bowl shape to a vortex shape attached to the burner nozzle. The transition process can be divided into three different combustion regimes and in this study, these limits presented based on the equivalence ratio and the Reynolds number of the burner inlet. Evaluation of NOx pollutants of swirlers showed that Nox increased with increasing equivalence ratio and at equivalence ratios near stoichiometric values, the Nox level was about 20 ppm.