Flame spread rates of fuel droplet arrays with different volatilities in microgravity

The influence of fuel volatility on flame spread behavior was studied. Flame spread experiments were done with fuel droplet arrays in microgravity. It took about 1 sec from the start of droplet generation to the ignition of the first droplet of the array. When a high volatility fuel was used, the pre-vaporization of fuel during the droplet array generation process affected droplet array combustion. n-Octane, n-decane, and n-hexadecane for fuel were used. A case where the droplet spacing S/d₀ (non-dimensional inter-droplet distance) was relatively small was considered. The droplet heating time accounted for most of the flame spread time. The heating time for lower volatility fuel until the vaporization becomes active was longer. In the case where the droplet spacing S/d₀ was relatively large, a flammable mixture layer should be formed around the next unburned droplet so that the flame could spread over the next droplet. When the droplet spacing S/d₀ was relatively large, thermal conduction time and heating time for the next droplet should account for most of the flame spread time. The heating time for lower volatility fuel until the formation of a flammable-mixture layer around the droplet was larger. Therefore, the flame spread rate of the lower volatility fuels was smaller for all S/d₀. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).