Kinetic studies of methyl acetate pyrolysis and oxidation in a flow reactor and a low-pressure flat flame using molecular-beam mass spectrometry

The combustion chemistry of methyl acetate (MA) pyrolysis and oxidation was studied experimentally in an atmospheric flow reactor and a low-pressure flat flame using molecular-beam mass spectrometry (MBMS). Rate constants such as H-abstraction of MA by O, H, OH, CH₃, and HO₂ radicals as well as MA radical decomposition were computed by high-level ab initio and RRKM master equation calculations. A new methyl acetate kinetic model was developed and compared to the experimental data along with other existing models. Two-dimensional direct numerical simulations were conducted and the results were used to validate the zero-dimensional prediction in a flow reactor. The MA pyrolysis results in the flow-reactor experiments showed that MA decomposition to CH₃ + CH₃ + CO₂ and CH₃OH + CH₂CO are the dominant pathways, which is consistent with the theoretical prediction of the new model. In addition, a two-stage MA oxidation was observed between 800 K and 1050 K, suggesting the possible existence of low-temperature chemistry for MA oxidation. The low-pressure flame experiment at a rich condition suggested that MA has unique reaction pathways to form aldehydes, ketones, and acids. Comparison with previous kinetic models showed that the present model considerably improved the predictability of species-temperature histories in the flow reactor and successfully identifies the main reaction pathway of ketene and acetic acid in a low pressure flame for the first time.