Variations in gaseous and particulate emissions from flaming and smoldering combustion of Douglas fir and lodgepole pine under different fuel moisture conditions

Abstract

The effects of fuel moisture content (FMC) on emissions under both flaming and smoldering combustion conditions were studied for two different vegetative fuels, Douglas fir and lodgepole pine. A custom linear tube-heater apparatus was developed to produce steady-state emissions for two extreme FMC, recently live (FMC ∼ 50%) and fully dead and dry (FMC ∼ 3%). The concentrations of particulate matter and gaseous species measured using a TSI DustTrak and Fourier transform infrared spectroscopy (FTIR), respectively, showed a significant relationship with FMC for both flaming and smoldering combustion conditions. As expected, smoldering combustion showed larger production of CO, particulate matter, and unburned hydrocarbons when compared to flaming combustion. Unburnt hydrocarbons with higher emission factors produced during smoldering are CH4, C2H2, C2H6, C4H10, C4H8, C2H4, C3H6, CH2O2, C3H4O, CH2O, and CH3OH. This work also identified butane (C4H10) and hydrogen bromide (HBr) as gaseous species, which have not been commonly reported in literature. Acrolein (C3H4O) was also identified during combustion and it has previously reported only by ion detection method. These emissions were further investigated by performing a carbon balance of the carbon in the fuel vs. emitted carbon, and these were compared to literature values. Flaming-mode emission factors significantly correlated with FMC, while FMC had little influence on emission factors for smoldering combustion, when considering the dry mass of the burned fuel. These variations were not the same for each fuel species, suggesting that the type of fuel plays an important role in burning behavior and emissions, possibly due to the chemical makeup of moist and recently live fuels. The results were discussed and compared with previous measurements, where good agreement was observed. This study provides an important emissions dataset for modeling emissions from common wildland fuels under varying FMC and combustion conditions.Novelty and significanceThis research investigates the impact of fuel moisture content (FMC) on emissions during flaming and smoldering combustion of Douglas fir and lodgepole pine. A unique linear tube-heater apparatus was developed to maintain steady-state emissions for extreme FMC levels of recently live (FMC 50%) and fully dead/dry (FMC 3%). The study reveals a noteworthy correlation between FMC and concentrations of particulate matter and gaseous species. This finding provides valuable insights into combustion behavior. It also identifies butane (C4H10), acrolein (C3H4O), and hydrogen bromide (HBr), not commonly reported in literature. Additionally, the study highlights the varying influence of FMC on emission factors for flaming and smoldering combustion, indicating the pivotal role of fuel type in emissions. The dataset obtained serves as a valuable resource for modeling emissions from wildland fuels under diverse FMC and combustion conditions, advancing our understanding of fire behavior and environmental impacts.