Shock tube/laser absorption studies of the decomposition of methyl formate

Abstract

Reaction rate coefficients for the major high-temperature methyl formate (MF, CH3OCHO) decomposition pathways, MF→CH3OH+CO (1), MF→CH2O+CH2O (2), and MF→CH4+CO2 (3), were directly measured in a shock tube using laser absorption of CO (4.6μm), CH2O (306nm) and CH4 (3.4μm). Experimental conditions ranged from 1202 to 1607K and 1.36 to 1.72atm, with mixtures varying in initial fuel concentration from 0.1% to 3% MF diluted in argon. The decomposition rate coefficients were determined by monitoring the formation rate of each target species immediately behind the reflected shock waves and modeling the species time-histories with a detailed kinetic mechanism [12]. The three measured rate coefficients can be well-described using two-parameter Arrhenius expressions over the temperature range in the present study: k1=1.1×1013exp(−29556/T, K)s−1, k2=2.6×1012exp(−32052/T, K)s−1, and k3=4.4×1011exp(−29 078/T, K)s−1, all thought to be near their high-pressure limits. Uncertainties in the k1, k2 and k3 measurements were estimated to be ±25%, ±35%, and ±40%, respectively. We believe that these are the first direct high-temperature rate measurements for MF decomposition and all are in excellent agreement with the Dooley et al. [12] mechanism. In addition, by also monitoring methanol (CH3OH) and MF concentration histories using a tunable CO2 gas laser operating at 9.67 and 9.23μm, respectively, all the major oxygen-carrying molecules were quantitatively detected in the reaction system. An oxygen balance analysis during MF decomposition shows that the multi-wavelength laser absorption strategy used in this study was able to track more than 97% of the initial oxygen atoms in the fuel.