Development of Forced Cool-Flame Ignition and Detection Device for a Fuel Droplet

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.