Development of a Global Mechanism for Oxy-Methane Combustion in a CO2 Environment

There has been some recent work on the global kinetic modeling of flames in oxy-fuel combustion for methane. The main challenge is that none of the mechanisms were developed to understand the time-scales of ignition. Here, a 3-step mechanism was developed for methane combustion in oxy-fuel environment. The mechanisms were simulated using a closed batch homogeneous batch reactor with constant pressure and compared to baseline simulations performed using a detailed mechanism. All simulations were performed for methane used a mixture of XCH4 = 0.05, XO2 = 0.10 and XCO2 = 0.85. Mechanisms were altered using the global mechanism equilibrium approach to ensure that the steady-state values matched the reference values and were further altered using an optimization scheme to match experimental data that was taken in a shock tube. Simulation results of methane, CO time-histories, and temperature profiles from the global mechanism were compared to those from the detailed mechanism. Ignition delay times were used to represent the time-scales of combustion. This was defined for current simulations as the time required for methane concentration to reach 5% of its initial value during combustion. Using this approach, the 3-step methane combustion mechanism showed excellent improvement in the ignition timing over a range of pressures (1 to 10 bar) and initial temperatures (1500 to 2000 K) for both lean and stoichiometric mixtures but fails to predict ignition delay times at 30 bar or the ignition delay times of fuel rich mixtures. Ongoing effort focuses on extending this new global mechanism to higher pressures and to syngas mixtures.