Objective

The objective of this project is to understand both the evolution and chemical composition of gaseous and particulate products from a pyrolyzing wildland fuel through the flame and into the smoke plume via measurement and modeling. The research will be a large step toward predicting emissions based on fundamental physics and chemistry. Emissions at the base of the smoke plume above the flame are directly related to the reaction chemistry inside the flame and the pyrolysis of the wildland fuel, yet the composition and reaction chemistry inside flames of wildland fuels are not well understood. They have seldom, if ever, been measured, thus being effectively treated as a “black box”. To further the understanding and fill these knowledge gaps, the specific goals of this project are to 1) measure fires in longleaf pine (Pinus palustris) needle fuel beds to characterize the chemical composition of gases and particulates, including soot, within flames and in the plume at distances up to 15 m above the flame, and 2) develop improved models of flame and soot behavior drawing on advanced physics-based computational models to gain further insight into the key underlying processes. The work will improve the understanding of physical and chemical fire processes at the base of the plume (i.e., the flame) of a wildland fire and these results will be incorporated into existing physical modeling tools.

Technical Approach

The project will model processes and measure the chemical composition (gas and particulate) in a series of fires in longleaf pine needle fuel beds. Physics-based models (PBM) will include sub-models for advanced representation of primary pyrolysis, soot formation, fuel moisture evaporation, and secondary pyrolysis working within the framework of the Fire Dynamics Simulator by revising this software. PBM will identify data needed from the experiments, and sub-models will be validated against existing and new experimental data. Gases and particulate matter in a vertical transect from the pyrolyzing fuel through the flame and into the near-field smoke plume will be measured in laboratory fires. CO, CO2, H2 and C1-C6 hydrocarbon gases will be measured using canister samples processed offline using a gas chromatograph with flame ionization detector. Infrared spectroscopy will provide real-time measurement of multiple gases in the experiments using Fourier transform spectrometers. CO2, CH4, H2O, NH3 and N2O will be measured in real-time by near-infrared cavity ringdown spectroscopy (Picarro G2509). Particulate size, quantity, composition, and shape characteristics will be measured by a variety of instruments including a Single Particle Laser Ablation Time-of-Flight mass spectrometer. Data from prior experiments (outside the “black box”) will be integrated with the new data and analyzed using compositional data analysis techniques. Existing and new experimental data will be used to evaluate the physics-based modeling of the flame.

Benefits

This project will develop models and collect data for a key piece of the evolution of a wildland fuel into smoke—an area that has generally been overlooked in wildland fire research. The work will improve understanding of physical and chemical fire processes at the base of the smoke plume of prescribed fires. The modeling and measurements will be integrated with prior lab and field measurements collected by the research team (and funded by SERDP), thus extending the life of those data acquired at significant expense. This project will improve understanding of the “black box” which is important because the flame’s energy release and production of gases and solid particles provide both the energy necessary for development of a plume and the initial chemical composition of the plume. The experiments will also allow probing of soot/gas heterogeneous chemistry. Linking the lab results with existing field measurements potentially applies to 1.7 million hectares of publicly and privately-owned longleaf pine forests in the southern U.S. where prescribed fire is used.