Chemical kinetic modeling study of methyl esters oxidation: Improvement on the prediction of early CO2 formation

The early CO2 formation is a characteristic for the methyl esters group of biodiesel. A new reaction pathway was added to skeletal methyl esters mechanism for improving the prediction of early CO2 formation. The methyl decanoate, methyl 9-decenoate, methyl 5-decenoate and methyl stearate sub-mechanisms with added reaction pathway were optimized by adjusting reaction rate constants for more accurate prediction. Based on decoupling methodology, a new skeletal mechanism for methyl butanoate was constructed by integrating detailed H-2/CO/C-1 sub-mechanism, reduced C-2-C-3 sub-mechanism and methyl butanoate sub-mechanism. These improved mechanisms were validated well in a shock tube for ignition delay times and in a jet-stirred reactor for major species concentrations over wide operating conditions, respectively. When compared to available mechanism in the literature, the present mechanism has good improvement for the prediction of early CO2 formation. Moreover, the effect of newly added reactions on ignition delay times was analyzed by sensitivity analysis method. Added reaction of Fuel Radical = ME2J + Short Chain Hydrocarbon mainly causes the influence on ignition delay time at high temperature, and decrease the reactivity of oxidation of fuel radical. The reaction of OCHO + M < = > H + CO2 + M dominates the early CO2 formation, and makes less contribution to production of CO2 with higher temperature. The improved mechanisms, which consist of methyl esters from a relatively short to long carbon chain, have a good performance for the prediction of early CO2 formation.