Experimental study of high swirl natural gas-air flame characteristics in lean premixed combustion

In this paper, combustion parameters of natural gas-air high swirl flames are analyzed. Swirl number of the flow is 0.69 and equivalence ratio of the mixture varies from 0.4 to 0.8 (lean combustion). For high swirl flame, equivalence ratio limits are compared when the burner performs properly, for nominal power from 13 to 25kW. Bluff body temperature and concentration of important emissions like CO, NO and NO2 are then compared in mentioned equivalence ratio range and a nominal power of 21kW, using infrared thermometry and exhaust gas analyzing methods respectively. OH*, CH*, C2*, CO2* and H2O* species chemiluminescence are also compared using flame spectroscopy. In order to measure combustion zone temperature, an s-type thermocouple is placed in three different vertical distances from the burner edge and different radial distances from its axis. Flame spectroscopy results show that C2* intensity is much smaller than other species intensities, because of lean premixed combustion. Also according to OH* intensities, maximum heat release rate happens in equivalence ratio of 0.6. On the other hand, maximum bluff body temperature, about 750oK, occurs in equivalence ratio of 0.5, consequently, maximum NO emission (50.3ppm) and minimum CO emission (49ppm) are observed in this equivalence ratio.

Keywords:

High-Swirl Burner , Swirl Number , Bluff-body Temperature , Exhaust Gas Analysis , Chemiluminescence , Flame Image Processing