A revised chemical kinetic mechanism for methanol combustion in sub and supercritical water

Abstract

A revised detailed chemical kinetic mechanism for the combustion of methanol in sub and supercritical water was developed, which is accurate across a wide range of thermodynamic states relevant to hydrothermal combustion. Development was accomplished by revising an existing mechanism for air dilute combustion of methanol at elevated pressures, to include a real gas model and reaction rate modifications relevant to hydrothermal combustion kinetics. Subsequent analysis using the revised mechanism revealed that trends in auto-ignition delay time and dominant reaction pathways are relatively invariant across sub and supercritical states, even near the critical point. While reaction pathways were consistent with previous findings, the addition of a formic acid pathway from formaldehyde to CO2 was found to be important. Analysis results also support a hypothesis that formation of the superoxide ion at higher pressure lower temperature conditions enhances the rate of self-termination of HO2, through the activation of an alternative pathway, HO2 + O2− + H2O = H2O2 + O2 + OH−.