Modeling of Emissions in a Laboratory Swirl Combustor

A swirl-stabilized combustor utilizes recirculation zones for stabilizing the flame. The performance of such combustors could depend on the fuel used as the cracked fuel products may enter the recirculation-zones and alter their characteristics. A numerical study is conducted for understanding the effects of fuel variation on the combustion and unburned-hydrocarbon-emission characteristics of a laboratory swirl combustor. A time-dependent, detailed-chemistry CFD model UNICORN is used. Six binary fuel mixtures formulated with n-dodecane and n-heptane, m-xylene, iso-octane or hexadecane are considered. A semi-detailed chemical-kinetics model (CRECK-0810) involving 206 species and 5652 reactions for the combustion of these fuels is incorporated into UNICORN code. Calculations are performed for a fuel-lean condition, which represents cruise operation of an aircraft. Combustor flows simulated with different fuel mixtures yielded nearly the same flowfields and flame structures. Production of the intermediate cracked fuel species that are key for the final flame structure and emissions seems to be independent of the fuel used. This finding could greatly simplify the detailed chemical kinetics used for obtaining cracked products. As the cracked fuel species are completely consumed with in the flame zone, no emissions are observed at the combustor exit for the considered fuel-lean condition.