Search for: All records

Wildfires are increasing in size, frequency, and intensity, releasing increased amounts of contaminants, including magnetic particles, into the surrounding environment. The aim of this paper is to develop a sensing method for the detection and quantification of magnetic particles (MPs) in fire ash and fire runoff using a compact Time-Domain Nuclear Magnetic Resonance (TD-NMR) system. The system is made up of custom NMR electronics with a compact and rugged permanent magnet array designed to enable future deployment as an in situ sensor. A signal-to-noise ratio of 25 dB was measured for a single scan, and sufficient data can be acquired in one minute. A linear relationship with an R 2 value of 0.9699 was established between transverse relaxation rates and MP concentrations in ash samples. This was validated by testing known dilutions of pure magnetite particles and showing that they fit within the same linear curve. The developed approach was then applied to detect MPs in surface water, where changes in the relaxation rates as high as 400% were observed before and after a wildfire event. MPs were removed from the surface water using a magnetic particle separator to confirm that observed changes were solely due to the presence of MPs. The compact NMR system can be used as a simple and rapid approach to track and quantify the concentrations of magnetic particles released from fire ashes and also from other sources such as discharges from coal ash and other combustion ashes. 

Liquid transportation fuels are composed of a wide range of molecular structures and weights, therefore exhibiting a relatively large distillation temperature range. When fuel chemical properties change along with the distillation temperature curve, preferential vaporization effects could play a role in near-limit combustion behaviors. The objective of this study is to experimentally evaluate the role of preferential vaporization on flame flashback behaviors. A unique spray burner is developed to control the extent of fuel spray vaporization by adjusting flow rates and/or the spray injection location from the burner exit. Spray characteristics are comprehensively determined using Phase Doppler Particle Analyzer. Two binary component mixtures are formulated (n-octane/iso-cetane and iso-octane/n-hexadecane) to exhibit common combustion behaviors in the fully vaporized condition but have considerably different preferential vaporization characteristics. Identical flashback behaviors of two mixtures are observed for fully pre-vaporized conditions by setting the burner temperature at 700 K, including both propagation- and ignition-driven flashback behaviors. Partially vaporized conditions are investigated at two global equivalence ratios (1.0 and 1.4) by setting the burner temperature at 450 K. The flashback behaviors for both global equivalence ratio conditions are found to be affected by the preferential vaporization characteristics represented by laminar flame speeds of the vaporized fuel mixture composition. The relative significance of local flow perturbation induced by instantaneous fuel droplet evaporation near the flame surface has been also investigated by analyzing planar laser-induced fluorescence images, as well as considering the changes of Markstein length with the extent of fuel vaporization. Finally, the relative contributions of local laminar flame speed representing local fuel vapor deposit, local flow perturbation, and preferential vaporization are evaluated through feature sensitivity analyses.