Numerical Investigation of Auto-Ignition Characteristics in Microstructured Catalytic Honeycomb Reactor for CH_4-Air and CH_4-H_2-Air Mixtures

摘要

Stable ranges of auto-ignition for the microcombustion of CH4 and CH4-H-2 mixtures are identified numerically in a platinum-coated microcatalytic honeycomb reactor. Steady and transient simulations under pseudo-auto-thermal conditions were performed to investigate the coupling phenomenon between combustion and heat transfer in such microburner using ANSYS 17.2 coupled with a detailed CHEMKIN reaction mechanism. The model was validated utilizing the available data in the literature on a similar microreactor, and the results showed good agreements. A certain amount of heat is furnished from outside at constant temperature from an external electric furnace to investigate the variations of localized self-ignition temperature while changing the flow rate and mixture strength. It was found that the ignition temperature for CH4-air mixtures is not affected by the mass flow rate. However, the ignition temperature of CH4-H-2 air mixtures decreases while increasing the flow rate. The effect of equivalence ratio was studied to demonstrate the variations of flammability limits of the present microreactor. The equivalence ratio required for auto-ignition of CH4-air mixtures was found to be in the range from 0.4 up to 0.85 at a flow rate of 9.5 g/s. The reaction front moved from upstream to downstream under transient conditions matching with the reported experimental behavior in the literature.