Experimental Study of the Darrieus-Landau instability on an inverted-'V' flame, and measurement of the Markstein number

We present an experimental study of the growth rate of the Darrieus-Landau instability on propane-air and on oxygen enriched propane-air flames using a two-dimensional inverted-"V" flame on a slot burner. We use a novel syste m of electrostatic deflection to produce an initial perturbation of control led wavelength and amplitude. The growth rate of this spatially growing per turbation is measured as a function of wavenumber, of equivalence ratio and of oxygen enrichment using high speed flame imaging. The results are analy zed using the Clavin-Garcia laminar flame stability theory (including tempe rature dependent diffusivities). The dependence of the growth rate on waven umber and flame speed is reasonably well represented by this theory. As a b y-product of this analysis, we obtain values of the Markstein number, which , for rich flames, are found to decrease with equivalence ratio and to incr ease with oxygen concentration.