Low Temperature n-Dodecane Droplet Combustion Experiments Aboard the International Space Station

Abstract

This paper presents data from large, isolated n-dodecane droplets burning in microgravity on the International Space Station, along with preliminary comparisons with numerical and analytic predictions indicating general agreement in trends. The tests involved were primarily in air (a few in reduced oxygen) at ambient pressures ranging from 0.50 to 5.0 atm. After ignition, the droplets burn with a hot flame that extinguishes when the radiant energy loss causes the flame temperature to drop below the hot-flame-required value. The total flame radiative loss at extinction is nearly independent of pressure, while the peak flame diameter prior to hot-flame extinction decreases with increasing pressure. The maximum hot-flame temperature, inferred from fiber-support radiative emisssions, decreases with increasing pressure, and the hot flames become dimmer with increasing pressure. At 1.0 atm and below there is a prolonged period of coolflame burning that ends with cool-flame extinction at a finite droplet size; the cool-flame-extinction droplet diameter increases and the cool-flame burning rate decreases with decreasing ambient pressure. Above 1.25 atm warm-flame burning and hot-flame re-ignitions become prevalent. At 5.0 atm, there is no abrupt hot-flame extinction with transition to a cool flame; the flame gradually gets dimmer, and the flame temperature decreases over a much longer time, the transition between hot-flame and warm-flame burning becoming almost undiscernible.