CHEMICAL ENGINEERING TRANSACTIONS VOL. 37, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Eliseo Ranzi, Katharina Kohse- Höinghaus Copyright © 2014, AIDIC Servizi S.r.l., I SBN 978-88-95608-28-0; I SSN 2283-9216 Reduced Kinetic Model of Biodiesel Fuel Combustion Alessandro Stagni, Chiara Saggese, Mattia Bissoli, Alberto Cuoci, Alessio Frassoldati, Tiziano Faravelli, Eliseo Ranzi Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”, Politecnico di Milano, Milano, Italy alessandro.stagni@polimi.it In times where the attention on alternative energy sources is continuously increasing, the study of biofuels is taking a primary role, as a possible replacement, or integration, of traditional transportation fuels. Among them, biodiesel fuels are typically a complex mixture of large fatty acids, obtained through trans- esterification of soybean and rapeseed oils with methanol. In this background, the pyrolysis and combustion kinetics of methyl esters is essential for a proper understanding of the combustion behavior and pollutant formation from biodiesel fuels. From a modeling point of view, when studying the combustion of large methyl esters a reliable kinetic mechanism is required. Nevertheless, the main problems of these molecules lie in their length and lack of symmetry in their structure, which results in the huge size of the related detailed kinetic mechanisms (thousands of species) with a consequent significant computational load, even when dealing with 0D and 1D models. In order to maintain the applicability of the kinetic mechanism also in multidimensional models, it should be useful someway to reduce its dimensions. For this reason, a reduced kinetic scheme for methyl esters was developed and is presented in this work. It is the result of the coupling of two different techniques: (i) an upstream lumping of species and reactions, through which several species are grouped into a single pseudo-species according to proper rules; (ii) a successive further reduction of the kinetic mechanism through a novel technique, based on the analysis of the reacting system in the desired range of operating conditions. The reduced mechanism was validated through comparison with experimental data in a wide range of conditions using shock tube, laminar flame speeds and ideal reactors. A satisfactory agreement with both experimental data and the original scheme was observed. Additionally, thanks to its limited dimensions, the kinetic model could be applied on more complex, multidimensional models. As an instance, its performances on a multi-zone model of an HCCI (Homogeneous Charge Compression Ignition) engine are assessed: the obtained results show the great advantages of this mechanism, which can then be used in place of the original one without losing in accuracy, but with considerable savings in computational times. 1. Introduction The introduction of biodiesel fuels in a market currently dominated by fossil sources is one of the current research paths towards a higher exploitation of renewable energies. Indeed, they are obtained from the transesterification of vegetable oils or animal fats with methanol, which results in fatty acid methyl esters (FAME) with physicochemical properties very similar to traditional diesel fuels (Lin et al., 2011). From a chemical point of view, the transesterification process produces five major methyl esters: methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate. In the last decade, the deep experimental and modeling effort around them was crucial in understanding their kinetics of pyrolysis and oxidation, as well as in defining the reaction classes involved. In spite of this, when a detailed kinetic mechanism for methyl esters is built up, the geometrical asymmetry of the molecules becomes a serious disadvantage. The final number of species may reach the order of some thousands (Herbinet et al., 2008, Westbrook et al., 2011), thus restricting its field of applicability to the simplest 0D and 1D simulations. When a smaller mechanism for methyl esters is needed, e.g. for CFD applications, two strategies can be adopted (Lu and Law, 2009): chemical lumping and skeletal reduction. In this case, these techniques are of fundamental importance: indeed, the number of radicals and isomers increases with the size (and DOI: 10.3303/CET1437147 Please cite this article as: Stagni A., Saggese C., Bissoli M., Cuoci A., Frassoldati A., Faravelli T., Ranzi E., 2014, Reduced kinetic model of biodiesel fuel combustion, Chemical Engineering Transactions, 37, 877-882 DOI: 10.3303/CET1437147 877