Chemiluminescence diagnosis of oxygen/fuel ratio in fuel-rich jet diffusion flames

Abstract

Equivalence ratio is one of key parameters associated with various flame characteristics such as flame structure and heat release rate. Chemiluminescence diagnosis of equivalence ratio has received extensive attention but not yet perfected, especially for fuel-rich diffusion flames. In this paper, the feasibility for evaluating molar equivalence ratio of oxygen to fuel in the fuel-rich conditions based on radical chemiluminescence diagnosis was explored. The sensitivity of the spontaneous luminescence intensity to the change of the nominal oxygen/fuel ratio in co-flow CH4-O2 jet diffusion flames was quantitatively studied. In addition, the two-dimensional distributions of the intensity ratios of CH* to CO2* and OH* to CH* were further analyzed, and local oxygen/fuel ratios were reconstructed. The results show that OH* chemiluminescence is more sensitive to changes in nominal oxygen/fuel ratio than CH* and CO2*. The sensitivity of CH* to oxygen/fuel ratio increases with the rise of CH4 flow rate, while the sensitivity of CO2* decreases. The reconstructed value of local oxygen/fuel ratio according to the two-dimensional intensity ratio of CH* to CO2* is underestimated, while based on the intensity ratio of OH* to CH* it is overestimated. Combined with these two intensity ratio distributions, the local oxygen/fuel ratio can be roughly determined.