A numerical investigation of the influence of radiation and moisture content on pyrolysis and ignition of a leaf-like fuel element

Abstract

The effects of thermal radiation and moisture content on the pyrolysis and gas-phase ignition of a solid fuel element containing high moisture content were investigated using the coupled Gpyro3D/FDS models. The solid fuel has dimensions of a typical Arctostaphylos glandulosa leaf which is modeled as thin cellulose subjected to radiative heating on one side. We incorporated a five-step extended Broido-Shafizadeh reaction model for thermal degradation, moisture evaporation, and pyrolysis of cellulose in Gpyro3D. The solid-phase model was successfully validated against published data. Ignition of the modeled leaf-like fuel element at three initial moisture contents (5%, 40%, or 80%) exposed to a 1500 K radiant source was simulated. Lower moisture content resulted in earlier onset of pyrolysis and ignition resulting in higher solid and gas phase temperatures. Local moisture evaporation and temperature rise were observed in all three cases and a significant amount of moisture remained in the sample during ignition. The numerical results suggested that moisture content not only affected the process of pyrolysis, but also influenced the ignition and gas phase combustion of the solid fuel.