Burning velocity and OH concentration in premixed combustion

Abstract

In the present paper, we have simulated laminar premixed flames in several types of flow configuration. The counter-flow flame, 1D flame in uniform flow, and 2D flame on a slot burner have been considered. The fuel is propane, and detailed chemistry has been used. We have obtained burning velocity in these flames to examine the response of peak OH concentration in flame zone to burning velocity (SL). In case of counter-flow flame, peak OH concentration is decreased at the larger stretch rate. At the same time, the burning velocity is decreased. The peak OH concentration of 1D flame in uniform flow is decreased at lower equivalence ratio, with smaller burning velocity. It is interesting to note that, for both flames as well as 2D flame, the same linear relationship is observed between two parameters of peak OH and SL. Thus, consistent with earlier findings of turbulent flames, peak OH concentration can be a good measure of burning velocity. In the experiments, we have estimated local burning velocity in turbulent combustion with a cyclone-jet combustor. The slot burner has been used for calibration. It is found that the peak OH concentration in the flame becomes smaller with an increase of turbulence. The local burning velocity is monotonically decreased at higher turbulence. In some cases, its value is almost zero, which could be local extinction. When the fuel is propane, Markstein number is positive for lean mixture. In that case, the burning velocity is decreased due to the stretch effect, which is well in accordance with the fact that the turbulence always suppresses the burning velocity in our measurements.