Smoldering combustion in cellulose and hemicellulose mixtures: Examining the roles of density, fuel composition, oxygen concentration, and moisture content

TL;DR

This study presents a computational model to analyze smoldering combustion in cellulose and hemicellulose mixtures, revealing how fuel properties like density, composition, moisture, and expansion influence combustion behavior and ignition thresholds.

Contribution

The paper introduces an updated model for smoldering in cellulose-hemicellulose fuels, exploring effects of density, composition, moisture, and expansion on combustion dynamics.

Findings

Higher density decreases propagation speed and raises peak temperature.

Increased hemicellulose content boosts both propagation speed and peak temperature.

Fuel expansion with moisture can increase propagation speed despite added moisture.

Abstract

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.