Optical Measurement of Burning Droplet Clusters in a Premixed Spray.

Abstract

A spray flame has an inevitably 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, small dense subclusters or single droplets burned in the diffusion combustion mode.