Modeling of the oxidation of methyl esters—Validation for methyl hexanoate, methyl heptanoate, and methyl decanoate in a jet-stirred reactor

Abstract

The modeling of the oxidation of methyl esters was investigated and the specific chemistry, which is due to the presence of the ester group in this class of molecules, is described. New reactions and rate parameters were defined and included in the software EXGAS for the automatic generation of kinetic mechanisms. Models generated with EXGAS were successfully validated against data from the literature (oxidation of methyl hexanoate and methyl heptanoate in a jet-stirred reactor) and a new set of experimental results for methyl decanoate. The oxidation of this last species was investigated in a jet-stirred reactor at temperatures from 500 to 1100 K, including the negative temperature coefficient region, under stoichiometric conditions, at a pressure of 1.06 bar and for a residence time of 1.5 s: more than 30 reaction products, including olefins, unsaturated esters, and cyclic ethers, were quantified and successfully simulated. Flow rate analysis showed that reactions pathways for the oxidation of methyl esters in the low-temperature range are similar to that of alkanes.

Experimental and modeling investigation of the low-temperature oxidation of n-heptane

“…Dagaut et al also verified that the macro-mixing was good and that the temperature of the gas phase was homogeneous using a thermocouple [43]. Since then this reactor has often been used for numerous gas phase kinetic studies of hydrocarbons and oxygenated compounds oxidation [16,[44][45][46].…”

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

“…The two distinct reaction regimes are shown very strongly in both the experimental and computational results, and the agreement between the experimental and computational results is excellent. The slightly greater amount of low temperature conversion of methyl palmitate than that of n-decane can be attributed primarily to the weakly bound H atoms at the '2' site adjacent to the methyl ester group in methyl palmitate [28][29][30]36,37], so the total rate of methyl palmitate consumption is slightly greater than that of n-decane. It is interesting to note that the 1-olefin concentrations are significantly higher than their corresponding 1-olefin methyl esters.…”

“…These studies have examined ignition and combustion of alkyl esters from methyl and ethyl hexanoate and methyl and ethyl heptanoate to methyl decanoate [24][25][26][27][28][29][30][31][32][33], followed closely by extensions to methyl stearate and rapeseed methyl ester [34][35][36][37].…”

“…The same general approach is used by Battin-Leclerc et al [27,28,[56][57][58] who use the EXGAS software to automatically generate new detailed chemical kinetic reaction mechanisms for other large hydrocarbon and other fuels, with similarly good results. Until high quality theoretical techniques become able to compute reaction rates of elementary reactions of large hydrocarbon species, this estimation technique will continue to be used extensively.…”

“…These modifications have been explored in detail in past kinetic studies of methyl ester fuels [25][26][27][28][29][30] and hydrocarbon fuels containing C=C double bonds [44][45][46], and the present mechanism combines both of these features as needed for each fuel component. In particular, internal abstraction of an H atom at an allylic site is assumed to have the same A factor as internal abstraction from a conventional site, but with a reduced activation energy due to the weaker C-H bond being broken.…”