On the extrapolation of laminar flame speed and Markstein length from outwardly propagating spherical flames

Motivated by the relatively large discrepancies in laminar flame speeds and Markstein lengths measured by different researchers using the same constant-pressure spherical flame method, the effects of choice of extrapolation model and flame radius range on the uncertainty of experimental results are studied theoretically, numerically, and experimentally. Three models for extracting the laminar flame speed and Markstein length from the flame front trajectories of propagating spherical flames are investigated. The sensitivity of the extracted results to extrapolation model and flame radius range is shown to increase with the Lewis number. For mixtures with a large Lewis number, the extracted laminar flame speed and Markstein length depend strongly on the model and flame radius range used in extrapolation. The linear extrapolation of the stretched flame speed based on flame curvature instead of stretch rate improves the accuracy in extracted laminar flame speed and Markstein length and reduces the influence of flame radius range. The results of this study can be used directly in spherical flame experiments.