A comparison of saturated and unsaturated C 4 fatty acid methyl esters in an opposed flow diffusion flame and a jet stirred reactor S.M. Sarathy a , S. Gaı ¨l a , S.A. Syed a , M.J. Thomson a, * , P. Dagaut b a Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ont., Canada b CNRS, Laboratoire de Combustion et Syste `mes Re ´actifs, 1C, Ave de la recherche scientifique, 45071 Orle ´ans cedex 2, France Abstract Biodiesel fuels, made up primarily of fatty acid methyl esters (FAME), are advantageous because they are renewable and generally have lower pollutant emissions. In order to study in detail the effect of the FAME molecular structure on the combustion chemistry, a saturated (i.e., methyl butanoate) and an unsaturated (i.e., methyl crotonate) C 4 FAME were oxidized in an opposed flow diffusion flame and a jet stirred reactor. Some consistent trends were seen in both experiments. Both fuels have similar reactivity. The experimental results show that methyl crotonate combustion produces much higher levels of C 2 H 2 , 1-C 3 H 4 , 1-C 4 H 8 , and 1,3-C 4 H 6 than methyl butanoate. The methyl butanoate combustion had higher levels of C 2 H 4 . In the opposed flow diffusion flames, the methyl crotonate also produced benzene while for meth- yl butanoate it was not detected. These species are relevant to soot formation. In addition, the experiments measured higher levels of 2-propenal, methanol, and acetaldehyde for methyl crotonate than for methyl butanoate. The reactions controlling these differences are discussed. Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Biodiesel; Methyl butanoate; Methyl crotonate; Opposed flow diffusion flame; Jet stirred reactor 1. Introduction Biodiesel fuels, made up primarily of fatty acid methyl esters (FAME), are advantageous because they are renewable and generally have lower pollutant emissions. Engine combustion studies [1] have shown that the biodiesel feed- stock has a significant effect on emissions. The results suggest that animal fat-based biodiesel fuels emit lower quantities of NO x , particulate matter (PM), and CO compared to soybean based fuels. No significant difference was noted in hydrocarbon emissions from the three source categories. Vegetable oils and animal fats tend to be mixtures of saturated and unsaturated FAME. However, soybean oil predominantly contains unsaturated fats (88%) while beef tal- low contains more saturated fats (54%) than unsaturated fats (46%) [2]. McCormick et al. [3] tested 21 bio-diesel fuels derived from feed stocks as well as pure fatty acids in a heavy-duty truck engine using the U.S. heavy- duty federal test procedure to understand the effect of biodiesel chemical structure, i.e., fatty acid chain length and number of double bonds, 1540-7489/$ - see front matter Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2006.07.019 * Corresponding author. Fax: +416 978 7753. E-mail address: thomson@mie.utoronto.ca (M.J. Thomson). Proceedings of the Combustion Institute xxx (2007) xxx–xxx www.elsevier.com/locate/proci Proceedings of the Combustion Institute Please cite this article as: S.M. Sarathy et al., A comparison of saturated and unsaturated ..., Proceed- ings of the Combustion Institute (2007), doi:10.1016/j.proci.2006.07.019. ARTICLE IN PRESS