Effects of CO and H2 addition on OH* chemiluminescence characteristics in laminar rich inverse diffusion flames

Optical diagnostic technique based on chemiluminescence emissions is a promising alternative flame monitoring method to indicate the combustion regime and related characteristic parameters. In this work, laminar rich inverse diffusion flames were numerically studied to elucidate the effects of CO and H-2 addition on OH* chemiluminescence characteristics. A jet flame simulation based on CFD was carried out to determine the effects of CO and H-2 addition on OH* chemiluminescence distribution, and a 1-D counterflow diffusion flame calculation by CHEMKIN-PRO was performed to analyze the effects of CO and H-2 addition on the formation characteristic of OH* chemiluminescence. The results show that OH* chemiluminescence is mainly concentrated at the central axis of the downstream region in inverse diffusion flames. With the increase of oxy-fuel equivalence ratio, the intensity of OH* chemiluminescence gradually decreases, and location of peak OH* intensity gradually moves from the downstream flame to the upstream. When the oxy-fuel equivalence ratio is fixed, the increase of the CO content in the fuel will reduce the H concentration in the flame, thereby reducing the concentration of OH* radicals. But the increase of the H-2 addition would only accelerate the burning velocity of the flame without having a significant impact on the concentration of OH* radicals. When the flow rates of fuel and oxygen are fixed, the distribution and formation characteristics of OH* chemiluminescence are affected by the synergetic impact of fuel component and oxy-fuel equivalence ratio. The effect of H-2 addition plays the most important role in the upstream of flame, and CO addition mainly affects the OH* radical production in the downstream region.