  Smoldering combustion plays a key role in wildfires in forests, grasslands,
and peatlands due to its common occurrence in porous fuels like peat and duff.
As a consequence, understanding smoldering behavior in these fuels is crucial.
Such fuels are generally composed of cellulose, hemicellulose, and lignin. Here
we present an updated computational model for simulating smoldering combustion
in cellulose and hemicellulose mixtures. We used this model to examine changes
in smoldering propagation speed and peak temperatures with varying fuel
composition and density. For a given fuel composition, increases in density
decrease the propagation speed and increase mean peak temperature; for a given
density, increases in hemicellulose content increase both propagation speed and
peak temperature. We also examined the role of natural fuel expansion with the
addition of water. Without expansion, addition of moisture content reduces the
propagation speed primarily due to increasing (wet) fuel density. However, with
fuel expansion similar to that observed in peat, the propagation speed
increases due to the overall drop in fuel density. Finally, we studied the
influence of fuel composition on critical moisture content of ignition and
extinction: mixtures dominated by hemicellulose have 10% higher critical
moisture content due to the increase in peak temperature.
