Simplification of the combustion mechanism of Jatropha biodiesel surrogate fuel and reaction path analysis

Abstract

The objectives of this study were to explore the evolution process of the chemical reaction pathways in the combustion of a biodiesel surrogate fuel and to reduce the calculation burden in the numerical simulation of this combustion process due to the complicated mechanism. A mixture of methyl decanoate, methyl 9-decanoate, and n-heptane was selected as the Jatropha biodiesel surrogate fuel. A simplified combustion mechanism of the biodiesel comprising 170 components and 737 reaction components was formed by systematically simplifying 3299 components and 10806 reaction mechanisms using a multistep directed relation graph method, path flux analysis, and sensitivity analysis. The simplified mechanism was compared with the detailed mechanism and experimental data to effectively verify the accuracy of the mechanism. The simplified mechanism could reproduce the detailed mechanism, and the results were in good agreement with the experimental data in terms of the ignition time of a methyl decanoate/air mixture in a shock tube, the concentrations of the components generated in the combustion process of the biodiesel in a jet stirred reactor, and the flame propagation speed of methyl decanoate and n-heptane/air mixture. The rate of production analysis method was used to explore the main reaction pathways and the evolution process of important intermediate components in the Jatropha biodiesel surrogate fuel generated at high and low temperatures. Methyl decanoate and methyl 9-decanoate formed hydrogen peroxide ketone and oxy groups mainly through dehydrogenation, oxygenation, and isomerization at low temperatures. The high-temperature stage mainly involved bond-breaking decomposition reactions, partial dehydrogenation, and isomerization reactions of low-temperature reaction products, resulting in the formation of small molecular products.