Numerical and Experimental Study of Lean M-and V-Shaped Flames

Abstract

Numerical modeling results of M-and V-shaped methane/air flames with an equivalence ratio of 0.7 are presented and compared with experimental results in this paper. The numerical model uses a one-step chemistry model and a vorticity-streamfunction formulation for the flow field. The experimental results used to validate the model consist of flame shapes, stand-off distances, velocity profiles measured with Laser Doppler Velocimetry and critical transition and blowoff gradients. The flame shape and the stand-off distance of the M-shaped flame are reproduced well by the model. The values of the vertical velocity are. however, lower than the experimental values. The lower vertical velocities computed with the model are due to relatively small differences between the computed and the experimental flame shape. The shape of the V-shaped flame is also reproduced reasonably well by the model. The stand-off distance predicted by the model differs 0.8 mm from the experimental value. The vertical velocities predicted by the model are, as for the M-shaped flame, lower than the experimental values. This is also caused by flame shape differences. The small differences between the computed and experimental flame shapes is probably related with the absence of highly diffusive radicals in the one-step model. The model is also used to compute the critical transition (from M-to V-shaped flame) and blowoff (of the V-shaped flame) gradients. The values for the critical gradients predicted by the model differ no more than 10 % from the experimental values obtained with our burner.