Group Combustion and Detailed Flame Structure of Liquid Fuel Spray Under the Infulence of Eddies

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(1) A spray flame has inevitably a complicated structure due to grouping behavior of droplets and preferential flame propagation through the mixture of air and fuel vapor from droplets. In order to observe the detailed structure of spray flames, the light emissions in OH and CH bands, and the laser light scattered by droplets were monitored simultaneously and analyzed spectrally in the flame of a premixed spray stabilized by an annular hydrogen pilot flame. The diameter and velocity of droplets in the flame were also monitored using a phase Doppler anemometer (PDA). It was confirmed experimentally that the combustion reaction occurred first in the intercluster regions by the preferential flame propagation through the fuel vapor from droplets, and then, as the droplet number density of clusters decreased along the stream line, the combustion zone gradually moved into the clusters, and eventually dense small subclusters or single droplets burned in the diffusion combustion mode.(2) A circular rod was inserted in a spray flame stabilized by an annular hydrogen diffusion pilot flame to investigate the detailed structure of the spray flame under the influence of wake flow behind the rod. The light emissions in OH and CH bands, and the laser light scattered by droplets were monitored simultaneously and analyzed spectrally in the flame with and without the rod. The droplet velocity was also monitored using a laser Doppler velocimeter (LDV). It was confirmed experimentally that the inserted rod promoted the reduction of the length scale of droplet clusters and the flame propagation into the clusters with solid-body light emission. This result suggests that the combustion behavior of the clusters was influenced by the turbulent mixing and slip velocity between gas and droplets due to the wake flow behind the rod.