Modelling of flame spread over biomass fuel arrays with various inclined angles and spacings

Flame spread of combustible materials with discontinuous distribution is a typical heat and mass transfer process that contributes a lot to the thermal disaster of building fires and wildland fires. However, application models of flame spread over discrete fuels have not been well addressed. In this study, 54 groups of line arrays of birch rods, 5 mm in diameter and 55 mm long, were designed by varying nine spacings (S, 1-9 mm) and six slopes (theta, 15 degrees- 90 degrees). Under the combined effect of fuel spacing and slope, flame spread behaviors are categorized into continuous flame spread regime (regime I) and discrete flame spread regime (regime II). Under the two regimes, calculation models of incident heat flux are respectively determined, which can predict flame spread rate well. Moreover, flame spread rate and mass loss rate per unit area present a growing tendency with increasing spacing in regime I, but have a limited dependency in regime II. The prediction models of mass loss rate and flame spread rate are developed, which match the experimental results well. Furthermore, a correlation between dimen-sionless flame length and modified dimensionless heat release rate is proposed in the inclined configuration. In the vertical configuration, flame length presents a power-law dependency on the heat release rate per unit width with the exponent range of 1.202-1.838.