Experimental Study on Oh*, Ch*, and Co2* Chemiluminescence Diagnosis of Ch4/O2 Diffusion Flame with Co2-Diluted Fuel

Abstract

OH* and CH* chemiluminescence in hydrocarbon flames are often applied to characterize flame structure, equivalence ratio, strain rate, heat release rate, etc. In this study, chemiluminescence images of OH*, CH* and CO 2 * in the CH 4 /O 2 diffusion flame were obtained using a CCD camera imaging system. The effect of CO 2 dilution on flame structure, strain rate, and other flame characteristics of CH 4 /O 2 diffusion flame was discussed. The results show that the OH* reaction zone is disconnected from the axis when a certain threshold dilution level is reached, and the combustion conditions can be judged depending on it. The flame front characterized by OH* can be fitted as an arc, and the radius of the fitted circle can be used to characterize the degree of flame bending. The radius of the flame front increases with the dilution level. There are quantitative functions between the chemiluminescence peak intensity of OH* and CH* and the CO 2 dilution level. The CO 2 addition changes the reaction characteristics of the OH* and CH* reaction zones. The CO 2 * average intensity in the flame zone is better suited to characterize the dilution level than the CO 2 * peak intensity. CH*/CO 2 * can characterize the dilution level. Moreover, the strain rate of CO 2 -diluted laminar flame is defined. It is found that there is a linear relationship between the thickness of the OH* reaction zone and the square root of the strain rate.

Keywords: OH* chemiluminescence, CO2 dilution, diffusion flame