Study on two-stage ignition of two interactive droplets in flame spread over n-decane droplets in microgravity

Abstract

Microgravity experiments on flame spread over droplet arrays were conducted using ndecane as the fuel at 0.3 and 0.4 MPa. This study focused on the cool-flame appearance and two-stage ignition during flame spread over fuel droplets. Previous studies have reported that when a single droplet is inserted into a high-temperature, high-pressure furnace, two-stage ignition occurs in which a hot flame appears after a cool flame. In addition, we have reported that the cool flame appears in the flame spread over fuel droplets, but two-stage ignition was not observed. Therefore, this study further investigated whether two-stage ignition could occur in flame spread over some combinations of n-decane droplets in microgravity. Droplets were tethered at intersections of 14-micron SiC fibers. The flame spread was observed by an infrared camera, and the appearance of a cool flame was identified using the Thin Filament Pyrometry (TFP) method for the SiC fibers tethering the droplets. The results show that twostage ignition occurs around two interactive droplets during flame spread at 0.4 MPa. After a cool flame appears, a rapid temperature rise occurs between the two droplets, leading to the appearance of a hot flame.