Evaluation of the equivalence ratio of the reacting mixture using intensity ratio of chemiluminescence 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 to 9.52, on OH∗, CH∗ and C2∗ in laminar partially premixed flames. The signals from the electronically excited states of OH∗, CH∗ and C2∗ were detected through interference filters using a photo multiplier tube, which were processed to the intensity ratios (C2∗/CH∗, C2∗/OH∗ and CH∗/OH∗) to determine a correlation with the local equivalence ratios. Furthermore, the consistency between the results of the tomographic reconstruction; Abel inversion technique, image with CCD (Couple Charged Detector) camera and the local radical intensity with PMT was investigated. The results demonstrated that (1) the flames at Φ ⩽ 1.36 exhibited classical double flame structure, at Φ ⩾ 4.76, the flames exhibited non-premixed-like flame structure and the intermediate flames at 1.36 < Φ < 4.76 merged, (2) the peak intensities of OH∗, CH∗ and C2∗ were maximal at Φ = 0.86, 0.91 and 1.06, (3) the intensity ratio of CH∗/OH∗ was nearly proportional to 1/Φ   for the 1 dimensional results with PMT, with a correlation coefficient of 0.99 at the equivalence ratios of 0.79–9.52. These results are in good agreement with those obtained from the two dimensional results with ICCD. However, it is difficult to predict the relationships between the equivalence ratios and intensity ratios of C2∗/CH∗ and C2∗/OH∗.