Spray flame structure in conventional and hot-diluted combustion regime

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A laboratory scale experimental setup was built to study ethanol pressure-swirl spray flames in a coflow of either air or hot-diluted oxidant. The latter case resembles conditions similar to those found in practical combustion systems of liquid fuels operating in MILD conditions.First, experiments have been performed to investigate the phenomena associated with the atomization process. High-speed visualizations show that in the presence of a hot-diluted coflow, an almost immediate disruption of the liquid jet takes place, indicating significant changes in the atomization mechanism, compared to the case with air coflow. Secondly, a comprehensive set of measurements was obtained by complementary single-point measurement techniques to reveal the gas and droplets flow fields as well as temperature fields. Measurements of droplet size and velocity components in the spray region were obtained by phase Doppler anemometry. Gas temperature was measured using coherent anti-Stokes Raman spectroscopy even in regions with droplet density as high as 105cm-3. It has been observed that in a reacting spray in air coflow, an inner and an outer flame-front are present. For a reacting spray with similar injection pressure in hot-diluted coflow, weakening of the inner flame-front is attributed to the fact that the gaseous mixture becomes increasingly rich towards the center region. Consequently, a significant reduction of occurrence of temperature samples above 2000K is observed throughout most of the spray region.