An examination of fuel moisture, energy release and emissions during laboratory burning of live wildland fuels

Abstract

A series of small-scale laboratory fires were conducted to study the relationship between fuel type, moisture content, energy released and emissions during the combustion process of live wildland fuels. The experimental design sought to understand the effects that varying moisture content of different fire-promoting plant species had on the release of total energy, gaseous emissions (CO, CO2), particulate matter less than 2.5µm in diameter (PM2.5) and fire radiative energy (FRE). Instantaneous FRE, or fire radiative power (FRP), is an important parameter used in remote sensing to relate the emitted energy to the biomass fuel consumption. Currently, remote sensing techniques rely on empirically based linear relationships between emitted FRE and biomass consumed. However, this relationship is based on the assumption that all fuels emit the same amount of energy per unit mass, regardless of fuel conditions (type, moisture, packing, orientation, etc.). In this study, we revisited these assumptions under the influence of moisture content for species that are adapted to fire, containing volatile oils. Results show that, in terms of the total energy released, this assumption holds fairly well regardless of fuel type and moisture content. However, FRE was found to be slightly dependent on the fuel type and very dependent on the moisture content of the fuel. Most of this variation was attributed to changes in the behaviour of the combustion process for different fuels, similarly observed in emissions measurements. These results highlight a need to further examine the role of fuel moisture and combustion state when determining emissions from remotely sensed measurements.