Fire behavior and heat fluxes for lab-scale burning of little bluestem grass

• The fire behavior of grass fuels using experiments and modeling results is presented.
• 27 intermediate-scale experiments with little bluestem grass were conducted.
• The burning characteristics of single plants and multiple plants were discussed.
• The computational tool, FDS/WFDS, was used to model the experiments.

This paper discusses the physics and fire behavior of grassland fuel using experimental and modeling results. Experimental characterization included intermediate-scale tests to determine the mass loss rates, heat release rates (HRRs), and flame heat fluxes of burning little bluestem (Schizachyrium scoparium) grass plants at various fuel moisture contents and external flow conditions. The experiments included single-plant tests, multiple-plant tests with no forced flow/wind, and multiple-plant tests in which a forced flow was directed over the plants to simulate wind. The burning characteristics of single plants and fire spread between multiple plants under various conditions are discussed. The computational tool, Wildland–Urban Interface Fire Dynamics Simulator (WFDS), was then used to model the experiments using both a prescribed HRR and the particle-based fuel element model (predicted HRR). Comparisons are made between the experimentally measured quantities and the results predicted by WFDS. The results of the WFDS simulations with a prescribed HRR are in good agreement with the measured heat fluxes for the multiple-plant tests with no wind. The results of the particle-based WFDS fuel element model are in good agreement with the experimentally measured mass loss rates and HRRs of the single-plant tests. The WFDS fuel element model effectively captures the different stages of burning of the little bluestem plant. For the prediction of heat fluxes in the wind tests, there are limitations in the use of the prescribed HRR model.