Investigation on chemiluminescence and structure characteristics in CH4/O2 diffusion flames

The chemiluminescence characteristics of the excited state radicals are significant for flame emission spectroscopy. In this paper, the spatial profiles of OH* and CH* radicals in laminar and turbulent CH4/O2 diffusion flames were obtained by the UV imaging system and the high-spatial-resolution line-scan hyperspectral camera. The OH* and CH* molar concentration were calculated through CFD numerical simulation. The results show the two-dimensional and radial OH* and CH* distribution features for methane diffusion flames, and OH* generates near the oxygen side whereas CH* generates near the fuel side of the flame front. In turbulent flames, with the increase of the equivalence ratio (denoted as [O/C]e), the OH* emission intensity decreases whereas the OH* molar concentration increases instead. Both CH* emission intensity and molar concentration increase with increasing [O/C]e. Moreover, the OH* emission intensity and flame structure under different velocities present different trends, and the trend of OH* peak emission intensity with [O/C]e can be used to characterize the flame flow state.