Computational fluid dynamics modeling of the combustion and emissions characteristics in high-temperature catalytic micro-combustors

Abstract

The combustion and emissions characteristics of methane-air mixtures in catalytic micro-combustors were studied in high-temperature environment where both heterogeneous and homogeneous reactions can occur simultaneously. Special emphasis was placed on understanding the role of each reaction mechanism in determining the distribution of combustion products. Computational fluid dynamics simulations were performed under various operating conditions to clarify the mechanism responsible for the formation of pollutants during the catalytic combustion process. Comparisons were made between the results obtained for different reaction pathways. Distribution diagrams of the combustion products were constructed and design recommendations were made. It was shown that catalytic combustion can effectively reduce the emission of pollutants, even though the system is operated within the homogeneous flammability limits. There is a strong interplay between heterogeneous and homogeneous chemistry during the combustion process, and their individual contributions depend critically on the operating conditions. Heterogeneous chemistry can significantly inhibit homogeneous chemistry, thus reducing the formation of pollutants and improving the distribution of products. The distribution of products can also be controlled by adjusting the design parameters such as pressure, temperature, feed composition, and combustor dimension. Nitric oxide is the main nitrogen pollutant formed in small-scale combustion systems under lean-burn conditions.