INDUSTRY

For 15 years, Cyrus Madnia and his team at the State University of New York at Buffalo have used NCSA resources to build direct numerical simulation codes that model complex combustion systems. Simulations like these can be used to show how to alter a flame's characteristics to create more or less heat and less pollution. Characteristics of flame-wall interaction. The snapshots show vorticity (white line contours) and heat-release rate (color contours) during the interaction. Image courtesy of Cyrus Madnia, State University of New York at Buffalo. Their work currently focuses on nonpremixed flame-wall interaction in which the fluctuation of the temperature and other features of the combustion chamber influence the behavior of the flame and vice-versa. This process thus influences how much and what kind of hydrocarbons are left unburned. It is of great practical importance in designing both diesel and liquid-fuel rocket engines. Recently, using NCSA's TeraGrid cluster called Mercury, the team modeled methane combustion using detailed reaction mechanism with 35 species and 217 elementary reactions steps. Various flame-wall interaction parameters like strain rates, flame power, flame-wall distance, and wall-heat flux were studied and compared with the established results for premixed flame wall interaction studies. Results showed nondimensional quenching distance (Peclet number) for nonpremixed flames was less than that for premixed flames. In the presence of a thermal boundary layer at the wall, the flame chemistry is mainly governed by water reactions that contribute approximately 95 percent of the total heat release rate at the wall. The concentration of unburned hydrocarbons at the wall, in presence of a thermal boundary layer, was found to be higher than when in the absence of a thermal boundary layer. The team also explored ignition dynamics and subsequent flame evolution of hydrogen-enriched methane mixtures. A detailed reaction mechanism and two augmented, reduced mechanisms (11-step and 12-step) were considered. Among other things, the team found that the 11-step model predicts well the ignition delay time. At later times, however, the fuel-rich side of the flame predicted by this reduced mechanism exhibits differences from the detailed model.