Abstract
A microgravity experiment to elucidate the
cool flame dynamics in a multi-droplet system was
conducted using the TEXUS-60 sounding rocket. The
cool flame position was successfully observed
through formaldehyde chemiluminescence. This
allowed the study of cool flame propagation speed
along n-decane droplet arrays, with droplet spacings
of 8 mm (nine droplets) and 16 mm (five droplets).
The spread speed was analyzed at an ambient
temperature of 570 K and a pressure of 0.1 MPa,
using air as the ambient gas. For both droplet
configurations, the cool flame occurred from nearly
the same position 4.7 s after the droplet was inserted
and settled at the combustion position. The cool
flame spread speeds decreased from around 250
mm/s to approximately 100 mm/s after the
spontaneous ignition, and then increased. The
maximum speed reached around 600 mm/s for the 16 mm droplet spacing case. Under these experimental
conditions, the results suggest that in the first stage the cool flame spread follows the premixed
propagation mode, while in the latter stage the acceleration may be driven by the sequential spontaneous
ignition.
