Comparison of Biodiesel Performance Based on HCCI Engine Simulation Using Detailed Mechanism with On-the-fly Reduction Shuliang Zhang, † Linda J. Broadbelt, ‡ Ioannis P. Androulakis, † and Marianthi G. Ierapetritou †, * † Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854 ‡ Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208 ABSTRACT: Biodiesel is a complex mixture of long-chain methyl esters. Accurate numerical study of biodiesel combustion requires detailed chemistry of large biodiesel surrogates representing realistic biodiesel fuels. However, the detailed kinetic mechanisms for large biodiesel surrogates involve large number of species and reactions, leading to extremely expensive or even infeasible computation when incorporated in engine CFD (computational fluid dynamics) calculations. In this study, the scheme of on-the-fly mechanism reduction incorporated with engine CFD code KIVA-3V is first extended to two large biodiesel surrogate mechanisms, namely methyl decanoate and methyl-9-decenoate. Detailed combustion and engine performance characterization for biodiesel fuels are enabled, and the computational intensity is significantly reduced with satisfactory accuracy. In the simulations, lower CO and NO emissions and lower engine power are observed for biodiesel surrogates. Combustion features such as early oxidation of ester groups are also well captured. This work provides the insight to study combustion and engine operation of complex fuels on the basis of detailed chemistry with efficient mechanism reduction technique. ■ INTRODUCTION Facing the burgeoning global energy demands and limited resource of fossil fuels in the world, biodiesel is becoming an important alternative fuel. 1-3 The production and consumption of biodiesel is quickly increasing. With an oxygenated molecular structure, biodiesel has the potential to reduce pollutant emissions. Also, biodiesel can be used with existing diesel engines without major changes. Most importantly, biodiesel is derived from various biorenewable feedstocks, making it promising as an ideal sustainable source of energy. Biodiesel is a complex mixture of monoalkyl esters of long-chain fatty acids derived from a variety of biorenewable sources, such as vegetable oils and animal fats. 4 The most commonly used biodiesel fuels, derived from soybean or rapeseed oil, are mainly composed of five methyl esters including methyl palmitate (C 17 H 34 O 2 ), methyl stearate (C 19 H 38 O 2 ), methyl oleate (C 19 H 36 O 2 ), methyl linoleate (C 19 H 34 O 2 ), and methyl linolenate (C 19 H 32 O 2 ). 5 These components have similar structures of a methyl ester group attached to a long saturate or unsaturated hydrocarbon chain. The oxygen content in bio- diesel could change the combustion features and also con- tribute to a lower heating value compared to conventional diesel. Also, different physical properties (such as viscosity and volatility) of biodiesel also lead to different fuel spray and mixing process. 6,7 Therefore, biodiesel combustion process has some different characteristics compared with the combustion of conventional diesel fuels. There are substantial efforts toward understanding the per- formance of biodiesel combustion. A large number of experi- mental studies have been focusing on the performance and emissions of biodiesel fuels working with existing diesel engines. 8 Some important characteristics of biodiesel and its combustion process have been investigated. In general, most studies reported lower engine power for biodiesel due to its lower heating value. However, the higher cetane number for biodiesel, that is, advanced ignition, could counterbalance the effect of low heating value and results in similar power in diesel engine. 9 In terms of emission characteristics, it is believed that biodiesel combustion generates less CO, hydrocarbon, and particulate emissions as a result of its oxygenated moiety. Also, for the NO x emissions, most studies reported increases for bio- diesel as a result of the advanced ignition. Lee et al. 9 reported that NO x emission of biodiesel blend increases about 20% compared to conventional diesel. However, different effects, such as similar or lower NO x emission, do exist under different engine conditions, as found in the study of Brakora et al. 10 Although extensive efforts have been made, uncertainties in the biodiesel combustion studies still remain since both physical properties and chemical kinetics affect the overall performance under diesel engine conditions. The combustion kinetics of biodiesel is still not fully understood because detailed informa- tion in the combustion process is not easy to capture through experiments. Therefore, computational study of biodiesel com- bustion is of great interest in order to better explore the underlying details of the biodiesel combustion process. To study the chemical kinetic characteristics of biodiesel, homogeneous charge compres- sion ignition (HCCI) engines are appropriate because the homo- geneous engine charge eliminates the effects of mixing related to fuel physical properties. 4 In HCCI engine simulations, detailed chemical kinetic models of biodiesel surrogates are required to represent the chemistry of biodiesel combustion. In the past few years, chemical kinetic models for various biodiesel surrogates have been developed 11 to facilitate computational study of biodiesel combustion. The first methyl ester kinetic model, proposed by Fisher et al., 12 is methyl butanoate (MB, C 5 H 10 O 2 ), which is Received: December 12, 2011 Revised: January 13, 2012 Published: January 16, 2012 Article pubs.acs.org/EF © 2012 American Chemical Society 976 dx.doi.org/10.1021/ef2019512 | Energy Fuels 2012, 26, 976-983