Biodiesel combustion: Kinetics and thermochemistry of H-atom abstraction from methyl propionate by Ö (3P) and O2H radicals: ab initio study

Abstract

• Thermochemistry and kinetics of bimolecular decomposition of methyl propanoate ( MePr ) have been studied. • BMK, BB1K, M06-2X, MP2, CBS–QB3 calculations were used in this study. • Six channels have been discussed which are exothermic. • Rate constants for channels obtained by TST, TST/W, TST/Eck. • RRKM has been considered to evaluate pressure effects on a microcanonical basis. Thermochemistry and kinetics of hydrogen abstraction through the oxidation by Ö ( 3 P ) and O 2 H radicals from a biodiesel, methyl propionate ( MePr ), have been studied. Density functional theory (BMK, BBIK, M06-2X) and ab initio (MP2, CBS-QB3) calculations were applied. Conventional transition state theory (TST) was used to calculate rate constants for all the six bimolecular reaction channels of MePr over a wide temperature range from 700-1600 K at 1.0 atm. For an H-atom is involved in these reactions tunneling should be considered and was therefore included by incorporating the Wigner (W) and Eckart (Eck) tunneling correction in increments of 50 K at pressure 1.0 atm. Statistical Rice–Ramsperger–Kassel–Marcus (RRKM) tight theory has been also used in a pressure range of 1.00E-06 atm to the high-pressure limit. The rate coefficients are found to be strongly pressure-dependent at low pressure. Analysis of branching ratios for the reaction channels shows that the secondary H atoms abstractions within MePr should be dominating the fate of fuel at low temperatures, and the contributions of abstractions from the two methyl groups increase with temperature for all oxidizing radicals.