Group Combustion Behavior of Premixed Spray Streams and Group Combustion Number.

Abstract

Spray flames inherently show complicated behaviors due to the group-forming character of droplets and the preferential flame propagation through the most favorable routes. In order to observe the detailed structure of spray flames, the light emission signals in OH- and CH-bands, the Mie scattering signals from droplets, and the size and velocity of droplets with a phase Doppler anemometer (PDA) were monitored simultaneously in a premixed spray flame stabilized by an annular hydrogen pilot flame. It was experimentally confirmed that the homogeneous premixed spray was divided into a number of droplet clusters due to the preferential flame propagation in the process of combustion, while there existed no droplet clusters in an approaching nonburning premixed spray flow. The group combustion number for each droplet cluster Gc was estimated from the present experimental data. It was found that the mean value of Gc fell within the range of the external and internal group combustion mode according to the definition of Chiu et al., and that the observed burning behavior of clusters corresponded well to their classification of group combustion mode.