Flame spread over liquid fuel films on metallic substrates

New experimental studies of parametric dependences of the flame spread velocity and limits for liquid fuel films on metallic substrates confirmed the main features of the physical model proposed previously. For thermally thin layered systems "fuel-substrate," a steady-state regime of flame spread is possible, It is shown that the flame velocity depends on the effective thermal diffusivity of the layer system, and its value is determined mainly by the volumetric heat capacities of the components of the system and, to a lesser degree, by their thermal conductivities. The mechanism of flame spread includes a series of interrelated elementary processes: heat conduction over the substrate from the combustion zone to the preflame zone, heating and evaporation of the fuel by the substrate, formation of a combustible mixture, and heating of the metallic substrate by the combustion products. The flame edge is located at the liquid surface, where the temperature corresponds to the formation of a stoichiometric mixture under equilibrium conditions. The liquid fuel is completely evaporated from the substrate at temperatures below the boiling point.