Flame-Vortex Interaction Studies to Reduce Pollutants from Engines

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The goal of this work is to understand how flame stretch and flame curvature affect premixed flame properties. A laminar vortex will be created in an existing test apparatus and will be interacted with a laminar premixed flame. Vortex conditions first will be chosen to represent a single eddy in a turbulent flow to show how strain and flame curvature affect the local burning velocity, the creation of pockets of unburned CO pollutants, flame extinction, and deviations from the "laminar flamelet" profiles of temperature and OH concentration. Secondly, vortex conditions later will be chosen to represent the piston-generated vortex of an internal combustion engine and the vortex will be interacted with a centrally ignited flame kernel in order to understand kernel growth in a realistic strain field. Thirdly, the measurements will be used to assess and improve a recent full Navier-Stokes CFD simulation of the laminar flame-vortex interaction, which forms the "building block" of future models and can provide a useful submodel for existing statistical models. Operational diagnostics to be employed include Rayleigh scattering for temperature images and profiles, OH and NO fluorescence imaging, and PIV to image the two-dimensional strain field. This study should provide information useful to a number of other research efforts in the area of turbulent premixed flame structures. In particular, it should be of use in development of better simulations of flame-vortex interactions, leading to better understanding and modeling of critical processes affecting levels of production of carbon monoxide and oxides of nitrogen in devices such as internal combustion engines, in which flame-vortex interactions play a crucial role. This in turn will lead to definition of design strategies for reduction of levels of these pollutants produced by such engines, an important national need.