비정상 대향류 확산 화염의 소화 한계 확장에 대한 실험적 연구

Abstract

In this study, extinction limit extension of unsteady (CH₄+N₂)/air diffusion flames was investigated experimentally. A spatially locked flame in an opposing jet burner was perturbed by linear velocity variation, and time-dependent flame luminosity, transient maximum flame temperature and OH radical were measured over time with the high speed camera, Rayleigh scattering method and OH laser-induced fluorescence, respectively Unsteady flames survive at stram rates that are much higher than the extinction limit of steady flames, and unsteady extinction limits extend as the slope of the stram rate increases or the initial stram rate decreases We verified the validity of the equivalent stram rate concept by comparing the course of unsteady extinction process and steady extinction process, and it was found that the equivalent stram rate concept represents well the unsteady effect of a convective-diffusive zone. To investigate the reason of the unsteady extinction limit extension, we subtracted the time lag of the convective-diffusive zone by using the equivalent stram concept. Then the modified unsteady extinction limits become smaller than the original unsteady extinction limits, however, the modified unsteady extinction limits are still larger than the steady extinction limits. These results suggest that there exist the unsteady behavior of a diffusive-reactive zone near the extinction limit due to the chemical non-equilibrium states associated with unsteady flames.