Reassessing the 2-D velocity boundary effect on the determination of extinction stretch rate and laminar flame speed using the counterflow flame configuration

Abstract

This study delivered a reassessment of the two-dimensional (2-D) velocity boundary effect on the determination of the extinction stretch rate and the laminar flame speed using the counterflow flame configuration. Experimental and numerical results showed that the extinction stretch rate was sensitive to the burner exit stretch rate, the burner separation distance, and the impinged flow temperature, but the reference flame speed is insensitive to these boundary conditions. A semi-quantitative analysis demonstrated that the boundary condition affected the computed function of the reference flame speed with respect to the stretch rate and thereby influence the extrapolated laminar flame speed using the computationally assisted nonlinear extrapolation. The experimental results over a broad range of equivalence ratios confirmed that the non-uniform velocity boundary would result in a considerable error in the determination of the laminar flame speed for the mixture with the non-unity Lewis number. This problem can be solved by applying the true measured velocity boundary in the extrapolation curve computation. The present study suggested the consideration of the 2-D velocity boundary condition effect in the determination of the laminar flame speed and the extinction stretch rate using the counterflow configuration.