Characteristics of gas phase-controlled flame spread over liquid fuels

Abstract

Comparative flame spread tests were conducted on the basis of a typical hydrocarbon fuel mixture (No. 3 jet fuel, RP-3) and a typical pure alcohol fuel (n-butanol), with the initial fuel temperature above the flashpoint of each fuel. Flame spread appearances, velocity of flame spread, and controlling mechanism of flame spread were discussed and achieved. Based on the experimental results, a flame spread model as well as a scaling analysis of velocity with non-dimensional temperature was established. Results show that the gas phase-controlled flame spread is separated into super-flash lean regime and super-flash stoichiometric regime at 64.9°C for RP-3 and 46.1°C for n-butanol. A blue precursor flame periodically appears in the super-flash lean regime with the velocity significantly larger than the yellow main flame speed, whereas both flames possess the same flame speed in the super-flash stoichiometric regime. Moreover, the value of the stoichiometric temperature of n-butanol is predicted as approximately 46.7°C based on the liquid evaporation theory, which agrees well with the experimental value of 46.1°C. Scaling analysis of gas phase-controlled flame spread indicates that the variation in velocity of flame spread Vf is directly proportional to 1T01/3(Tb-T0)2.