THE OXIDATION OF METHANE AT ELEVATED PRESSURES - EXPERIMENTS AND MODELING

A detailed chemical kinetic model has been developed for methane oxida tion which is applicable over a wide range of operating conditions. A reaction mechanism, originally developed for high-temperature methane oxidation, was expanded and extended to include reactions pertinent to the lower temperature, elevated pressure conditions encountered in th e flow reactor experiments performed in the study. The resulting 207-r eaction, 40-species mechanism is capable of reproducing the experiment al species concentrations for each of the cases studied. The concentra tion profiles of reactant, intermediate, and product species, includin g CH4, CH2O, CH3OH H-2, C2H6, C2H4, CO, and CO2, were obtained in the High Pressure Optically Accessible Flow Reactor (HiPOAcFR) facility fo r temperatures ranging from 930 to 1000 K and pressures of 6 and 10 at m. Based on the model, no appreciable change in reaction pathway was o bserved over the pressure and temperature range studied, with HO2 prov iding the major route for CH3 oxidation. CH2O was found to be a vital intermediate for all of the CH4 oxidation paths. In addition, inclusio n of trace amounts of CH2O measured at the initial sampling location i nto the model initial conditions greatly reduced the predicted time to onset of fuel disappearance and enhanced the model agreement. This re sult is consistent with past engine studies which have found that CH2O is a significant pro-knock additive when added to a methane base fuel . The expanded reaction mechanism was also tested against shock-tube i gnition delay and laminar flame speed data and was found to be in good agreement with the relevant experimental data.