Abstract:
Based on the experimental platform of diffusion flame, the two-dimensional OH* distribution in the methane/oxygen co-flow diffusion flames was obtained by a UV imaging system, and a Abel deconvolution algorithm was performed as well. According to the variation of the distribution characteristics of OH*, the effects of the contents of N
2 and CO
2 on the flame reaction zone and structural characteristics were investigated. Additionally, the differences in the flame reaction zone and structural characteristics between the N
2 diluted flame and the CO
2 diluted flame were further compared. The results show that the flame turns to be thinner with increase in the diluent content. The CO
2 diluted flame presents a narrower flame front than that of the N
2 diluted flame under the same conditions, and the OH* chemiluminescence intensity is significantly lower. When more dilution is added into oxidant, the position of the OH* peak intensity slightly move toward flame downstream, until the dilution content reaches a certain critical value. Afterwards, it suddenly moves to the region near the outlet of the nozzle and finally tends to a constant. The increase in the diluent content in the oxidant leads to the change of dominant reaction for the OH* formation, resulting in a displacement of the flame core reaction zone. With the increase in the diluent content, the axial height of the flame reaction zone does not increase continuously, in contrast, it starts to decrease upon increasing to a certain range. Compared with the N
2 diluted flame, the reaction mechanism transformation has more impacts on the axial height of the flame reaction zone in the CO
2 diluted flame.