CAREER: Droplet Vaporization under Asymmetric Conditions: Implications for Combustion at Conventional and Reduced Scales

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The primary objective of this CAREER project is to assess the impact of asymmetrical convective and thermal conditions on the fuel-vapor distributions and ignition characteristics of vaporizing liquid-fuel droplets. The experimental methodology exposes monodisperse acetone droplet streams to thermally and convectively asymmetric flow conditions. Two separate flow reactors, a heated linear plug-flow reactor (LPFR) and a heated circular Couette-flow reactor (CCFR), provide thermally asymmetric (LPFR), convectively asymmetric (CCFR), and combined thermal/convective asymmetric (CCFR) environments for observation of vaporization of acetone droplets. An Nd-YAG laser sheet illuminates the vaporizing droplet streams, causing the acetone vapor to fluoresce. An intensified CCD camera captures the fluorescence images. Analysis of these images reveals the degree to which asymmetric thermofluid conditions induce nonuniform fuel-vapor distributions, which in turn can impact adversely droplet ignition, combustion, and pollutant formation. By comparing the effects of thermal, convective, and combined thermal/convective asymmetric conditions, individual and collective effects can be exposed, thus providing the basis for extending classical droplet vaporization theory to include nonuniform environments. A separate, concurrent numerical modeling effort is being developed to simulate observed anomalous vaporization behavior and to validate new vaporization models using parallel processing architectures and micro-scale transport formulations.As emission regulations become ever more restrictive for traditional combustion devices, environmental compliance may depend increasingly on understanding higher-order effects, such as asymmetric droplet vaporization phenomena. Further, asymmetric droplet vaporization phenomena may play a dominant role in combustion processes within miniature (~ 1 mm) combustors, an emerging technology being developed to provide power for portable electronics, remote sensors, and remotely piloted vehicles. Such miniature combustors require liquid fuels in order to allow the long refueling intervals needed to compete with electric batteries. However, miniaturization increases the size of liquid fuel droplets relative to the combustor dimensions and produces stronger and more prominent thermofluid property gradients within the combustor itself. Thus, successful miniaturization of combustors depends on identifying and understanding anomalous combustion phenomena that are nearly insignificant at conventional scales but which predominate at these reduced scales.The educational component of this CAREER project uses vertically integrated teams ("Engineering Collectives" or ECs) of high school, undergraduate, and graduate students to embark upon guided science and engineering discovery projects. High school students are recruited from the neighborhoods surrounding the IIT campus, which are predominantly African-American and Latino, thereby helping to broaden the participation of underrepresented groups in science and engineering and their representation on the IIT campus.