Combustion and Flame 145 (2006) 245–258 www.elsevier.com/locate/combustflame Detailed analysis of the mass burning rate of stretched flames including preferential diffusion effects J.A.M. de Swart a,∗ , G.R.A. Groot a , J.A. van Oijen a , J.H.M. ten Thije Boonkkamp b , L.P.H. de Goey a a Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands b Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands Received 22 December 2004; received in revised form 16 August 2005; accepted 10 October 2005 Available online 29 November 2005 Abstract This study focuses on the effects of flame stretch on the mass burning rate, for flames with nonunit Lewis numbers. The extended flame stretch model of de Goey and ten Thije Boonkkamp [Combust. Flame 119 (1999) 253–271], which was derived for multiple-species transport and chemistry, is used as a starting point. This model is adjusted to be able to predict the mass burning rate at the inner reaction layer of the flame. The accuracy of the theory is analyzed step by step using numerical results incorporating detailed chemistry and multispecies transport models. The adjusted model proves to be an accurate predictor of the mass burning rate. Furthermore, it is shown that not only the lean species Lewis number plays a role but also a number of other Lewis numbers have a signifi- cant influence on preferential diffusion. Preferential diffusion for methane/air mixtures is more difficult to predict accurately than for ethane/air and propane/air mixtures. Different contributions to the total preferential diffusion effect in methane/air mixtures partly cancel, which corresponds to an effective Lewis number being close to one. For fuels with Lewis numbers further away from one, no cancelation takes place and the accuracy of the predicted mass burning rate increases. Results show that the extended theory forms the basis for the first quantitative model to predict mass burning rates of premixed, laminar, stretched flames with nonunit Lewis numbers.  2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Laminar premixed flames; Mass burning rate; Flame stretch; Preferential diffusion 1. Introduction It is well known that flame stretch is a very im- portant quantity in combustion science. Karlovitz et al. [1] and Markstein [2] were the first to recog- * Corresponding author. E-mail address: j.a.m.d.swart@tue.nl (J.A.M. de Swart). nize the effect of flame stretch on premixed flame structures and dynamics. Flame stretch has been stud- ied by many researchers since, such as Buckmaster [3,4], Matalon [5], Matalon and Matkowsky [6], and Chung and Law [7]. A rigorous mathematical analysis of stretched flames, using matched asymptotic expan- sions, was introduced by Matalon and Matkowsky [6]. An integral analysis of flame stretch was presented by Chung and Law [7]. It must be stressed that the global 0010-2180/$ – see front matter  2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.combustflame.2005.10.009