Detailed Local Chemiluminescence Measurement (OH*, CH* and C-2*) and Nitrogen Oxides Emissions in Laminar Partially Premixed CH4/Air Flames

An experimental study was performed to investigate the effects of partially premixing, varying the equivalence ratios from 0.79 similar to infinity, on NOx emissions and chemiluminescence of excited OH*, CH*, and C-2* radicals in laminar partially premixed flames. the signal from the electronically excited state of OH*, CH*, and C-2* was detected through a band pass filter with a photo multiplier tube, which are processed to the intensity ratio (C-2*/CH*, C-2*/OH*, and CH*/OH*) to reveal the correlation with local equivalence ratio. And measurements of NOx emission were made to investigate the relationship between visible flame appearance, chemiluminescence, and EINOx. The results demonstrated that (1) the flames at Phi<1.59 exhibited classical double flame structure, at Phi 4.76, the flames exhibited diffusion flame structure, and the intermediate flames at 1.59<Phi<4.76 was a merged flame, (2) the OH* peak was located inside the CH* and C-2* radical for all measured conditions and the emission intensity ratio of C-2*/CH* and C-2*/OH* were identified as good marker for local equivalence ratio over a range of Phi=0.79 similar to 1.2 and CH*/OH* is 0.79<Phi<1.9. However, it was difficult to predict the equivalence ratio in partially premixed flames using this system for Phi>2.38, (3) the minimum NOx emission index (EINOx) is obtained for a equivalence ratio of 3.19 in the intermediate flames.