Abstract
Chemical kinetics mechanisms describing Fatty Acid Methyl Ester (FAME) biofuel combustion are quite extensive and cannot be implemented in Computational Fluid Dynamics simulations of real engine systems. Using the reduction methodology Ant Colony Reduction (ACR), skeletal reduction followed by optimization has been performed for the C-11 FAME biodiesel components methyl decanoate (MD), methyl 5-decenoate (MDe5), and methyl 9-decenoate (MDe9), and for the alkane n-decane. The aim of the present study was to produce small reduced mechanisms accurately describing ignition of the fuels over a wide range of conditions, and in addition to compare the size and composition of reduced mechanisms constructed from two parent mechanisms of different complexity. Reduction targets were ignition delay times over a wide range of equivalence ratios and pressures, for separate temperature ranges of 600–1100 K (LT) and 1100–1500 K (HT). One of the complex mechanisms was constructed to be simplified by a lumping approach and this one included MD and was also used to perform reduction for the alkane n-decane. The most detailed parent mechanism was used to create reduced mechanisms for all the three methyl esters. The lumped complex mechanisms resulted in more compact reduced mechanisms, 157 reactions for LT of MD, compared to 810 reactions for the more detailed mechanism. MD required the largest fuel breakdown subsets while the unsaturated methyl esters could be described by smaller subsets. All mechanisms had similar subsets for the smallest hydrocarbons and H/O chemistry, independent of the fuel and the choice of parent mechanism. The ACR approach for mechanism reduction created reduced mechanisms with high accuracy for all conditions included in the present study.
Highlights
Methyl esters are components of biodiesel used as a fuel in Compression Ignition (CI) engines, both in mixtures with fossil diesel and as a stand-alone fuel [1]
The parent mechanisms are referred to with the names CRECK and Herbinet, respectively, for the mechanisms developed by Saggesse et al [2] and Herbinet et al [13]
This work reveals some important characteristics of relevance for the development of reduced mechanisms
Summary
Methyl esters are components of biodiesel used as a fuel in Compression Ignition (CI) engines, both in mixtures with fossil diesel and as a stand-alone fuel [1]. Just like the fossil counterpart, biodiesel is composed of a wide range of hydrocarbon components with different carbon chain lengths, degree of saturation, and branching. Carbon chain length vary in the range 12 to 22, with the dominating components mostly having 16 or 18 carbon atoms and ranging from saturated to unsaturated with up to three double bonds [2]. Efficient and environmentally friendly use of methyl ester biodiesel as a replacement for fossil diesel require a thorough understanding of the combustion characteristics and pollutant formation. Comprehensive chemical kinetics mechanisms for biodiesel combustion have been produced by a research group at Lawrence Livermore National Lab (LLNL) and the CRECK group at Politecnico Fundamental studies in laboratory setups [3,4,5,6,7,8,9,10] are used to increase the detailed understanding of chemical and physical properties, often in combination with modeling.
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