An Experimental Study of Flame Spread and Burning in Arrays of Monosize Hydrocarbon Droplets

The combustion of two-dimensional arrays of falling n-heptane droplets was studied by black-and-white and colour schlieren photography which could clearly distinguish between evaporating and burning droplets. No individual droplet flames were seen in this work. The first ignited droplet trailed a wake flame and acted as a moving ignition source, producing downward flame spread rates which were the same as the fall velocity of this droplet and much higher than the upward flame spread rate through the vapour. All drops above the first ignited one burned in a collective cylindrical flame. Simple models of flame spread through the array were consistent with experimental trends.