Evaluation on Spontaneous Ignition Characteristics of Fuel Droplets Using Microgravity

Abstract

Normal- and microgravity experiments examined spontaneous ignition of isolated fuel droplets. Suspended fuel droplets of either n-dodecane or n-heptane is employed. A Michelson interferometer visualized cool and hot flames and discovered two-stage ignition process. According to the observation, induction times to cool flame and hot flame occurrences are determined. Significantly deformed vapor layer preceding ignition and elongated induction times under normal gravity conditions are found out in comparison with microgravity data. Influence of initial diameter, that is a measure of transport time scale, appeared only on the induction time to cool flame occurrence. These gravity and initial diameter effects on induction times clarified the roles of natural convection and the rela­tive importance of transport and chemical characteristics on the ignition process during each induction time.