Experimental study on OH∗, CH∗, C2∗ and CO2∗ chemiluminescence characteristics and flame structure of methane/hydrogen diffusion flames
Xinming Tian, Yan Gong, Qinghua Guo, Bin Wang, Guangsuo Yu
Abstract
The flame characteristics of CH 4 /H 2 diffusion flames have garnered extensive attention owing to the unique diffusion and combustion advantages of H 2 . However, chemiluminescence characterization for the multi-radical coupling of the CH 4 /H 2 combustion system is still incomplete, and therefore the application of spontaneous emission diagnosis is not well developed. In this work, two-dimensional distributions of OH∗, CH∗, C 2 ∗ and CO 2 ∗ chemiluminescence were obtained using 310 nm, 430 nm, 455 nm and 515 nm filters, and the chemiluminescence characteristics of CH 4 /H 2 diffusion flames were comprehensively investigated. The results showed a quantitative relationship between the chemiluminescence intensity and the H 2 volume ratio. There was a proportional relationship between CH∗ and C 2 ∗ chemiluminescence intensities and an inverse relationship between OH∗ and CO 2 ∗ chemiluminescence intensities, which suggested that the chemiluminescence reactions were highly coupled to each other. The relationship between the chemiluminescence intensity ratios and fuel composition was further explored. OH∗/C 2 ∗ and OH∗/CO 2 ∗ were more sensitive to changes in H 2 volume ratios. The correlation between the two-dimensional distribution of chemiluminescence and the flame structure was discussed in detail. The two-dimensional distributions of CH∗ and C 2 ∗ were good indicators of the blue zone on the fuel side (fuel-rich zone), and CO 2 ∗ was a good indicator of the blue zone on the oxidant side (stoichiometric zone). The mechanism by which H 2 influences the reactions of carbon-containing species within the CH 4 /H 2 combustion system was unveiled through chemiluminescence reaction analyses.