In-situ measurements of combustion systems are challenging due to high temperatures, rapidly varying spatial properties, and limited physical and optical access. In biomass combustion these challenges are further exacerbated by heterogeneous fuels, transient processes, and instrument fouling from soot and ash production. I will discuss an emerging diagnostic tool, based on dual frequency comb spectroscopy (DCS), for non-intrusive quantification of biomass combustion. These measurements are used to create controlled datasets for developing and validating reduced order chemical kinetic models.
DCS is an emerging broadband, high-resolution method of absorption spectroscopy that can simultaneously probe thousands of absorption features from many molecules, enabling accurate measurements of multiple species in transient high-temperature environments. We implement a near infrared dual-comb spectrometer to measure watervapor emissions and gas temperatures of the pyrolysis and flaming combustion of Douglas fir. The data is combined with mass-loss history and surface temperature measurements to quantify the pyrolysis and combustion across a range of moisture contents. While these experiments demonstrate the promise of DCS in biomass combustion experiments, the number of measured chemical species is limited by the weaker nearinfrared absorption features accessible by the DCS at laboratory scale path lengths. Recently the development of mid-infrared DCS technology has enabled measurements in an optimal wavelength region for multispecies detection of carbon based species. In collaboration with NIST Boulder, we demonstrate mid-infrared DCS of pyrolyzing wildfire-relevant fuels to quantify in-situ concentrations of eleven molecules and gas temperature, to characterize the thermal decomposition of six different species of wood.
Current work focuses on leveraging the laboratory scale DCS measurements for application to fire spread measurements in a combustion wind tunnel at the University of Colorado, as well as deploying the DCS system for field based measurements of controlled burns.