Experimental investigation of chemiluminescence and NOx emission characteristics in a lean premixed dual-swirl flame

Temperature and radical concentration are the two most important factors affecting NOx emissions in the methane combustion, while chemiluminescence is from the radiative transition of excited radicals, related to the heat release closely. Accordingly, there must be an implicit link between NOx formation and chemiluminescence. Chemiluminescence and NOx emission characteristics under various equivalent ratios (phi) and swirl numbers (S) have been investigated in a lean premixed dual-swirl flame. The results show that phi and S have different effects on chemiluminescence intensities and flame structures, and the change trend of NOx emissions is the same as chemiluminescence intensities. More importantly, a linear relationship between chemiluminescence intensities and NOx emissions was proposed and tested, making it possible to monitor NOx emissions in combustion by the non-intrusive and cost-effective chemiluminescence technique.