When heavy fuel oil sprayed in droplets burns in water heating boilers, there are cases when the zones of incomplete combustion are present. The volatile compounds and tar contained in the droplets burn out there and the carbon starts to accumulate on the pipes of the screen. Combustion of a fuel droplet on a solid surface is less investigated than that of the droplet falling down in hot air. In this work, the burnout of a droplet of a heavy fuel oil has been measured on a hot surface whose temperature varies in the interval from 400 to 700 degrees C. Times of evaporation of volatile compounds and burnout of the resulting carbon residue were measured. Changes of the form of the carbon residue depending on the surface temperature were recorded. Ceramic, quartz and stainless steel surfaces were used. The effect of surface roughness was additionally examined. In the case of a droplet of the heavy fuel oil dropped on a hot surface, heat transfer into the droplet is very sudden. The surface wetting condition is important, as it determines evaporation and boiling. Another difference from a freely falling droplet is oxidation of the pure coke because the oxygen diffusion is possible only from one side of the space. (c) 2005 Elsevier Ltd. All rights reserved.