Abstract
An ignition device that can induce a cool flame
around a hydrocarbon droplet and simultaneously detect the
ignition occurrence was developed for microgravity
experiments of cool-flame spread along a fuel droplet array.
The ignition system circuit was designed based on the principle
of a hot wire anemometer to ignite droplet without inducing
hot-flame ignition. The ignition wire senses the heat generated
by the cool flame and decreases the output power. Thus, one
can detect the cool-flame ignition by measuring the current
passing through the ignition wire. As a result of the preliminary
experiments at normal gravity, the cool-flame ignition of a fuel
droplet was successfully induced, and, from the histories of current passing through the ignition wire, the
cool-flame ignition, the two-stage ignition (cool flame to hot flame transition), and pure evaporation were
distinguished respectively. The cool-flame ignition delay time for various droplet diameters and fuels was
also measured. It was found that the tendency of the cool-flame ignition delay time to the initial droplet
diameter and fuel type is the same as that of the hot-flame ignition delay time in high temperature
environments.
