Flow divergence in the turbulent premixed flames

Abstract

In order to elucidate the flow divergence in the rich propane-air turbulent premixed flames, the flow fields of lean and rich propane-air and methane-air turbulent premixed flames of the identical conditions of laminar burning velocity and characteristic of turbulence have been closely examined by using a three-color six-beam LDV system. A bi-modal distribution, composed of both the low velocity mode and the high velocity mode, is obtained from gas velocity fluctuation within the turbulent flame brush. The low velocity mode is composed of velocity fluctuations of the unburnt mixture and the high velocity mode is composed of velocity fluctuations of the burnt gas. The reaction progress variable can be calculated from the bi-modal distribution of the radial component of the gas velocity. Distributions of the reaction progress variable clearly show that the rich propane flame is skinner and shorter than the lean propane flame, indicating that the turbulent burning velocity is larger in the rich propane flame. Comparing the burnt gas mode of the radial component of the gas velocity of the lean and rich propane-air and methane-air flames, the flow divergence is found to be remarkable in the rich propane flame. The cellular instability due to the preferential diffusion causes the turbulent burning velocity and/or the heat release to increase in the rich propane flame.