Observation of Structure of Spherical Flame Formed in Suspended Droplet Cloud by Spark Ignition : 2nd Report

Abstract

A droplet cloud of liquid fuel produced by an ultrasonic atomizer was ignited by a spark, and the ball of flame propagating outwards was observed in detail in order to elucidate the mechanism of flame propagation and the complicated group combustion behavior of spray flames. For this purpose, the instantaneous images of droplet clusters, OH-radical chemiluminescence and C₂-band flame luminosity were taken simultaneously, and the light emission signals in OH- and CH-bands, Mie-scattering signal from droplets, and the size and velocity of droplets were monitored simultaneously in time series. It was found that a nonluminous flame propagated ahead of the luminous flame, that droplets disappeared in the luminous flame zone due to their rapid evaporation, and that a number of small droplet clusters burned in the diffusion combustion mode associated with solid-body emissions inside a ball of flame.