Browsing by Author "Saylor, John R."

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    A Fog-and-Tube Scrubber for the Removal of Diesel Particulate Matter from Engine Exhaust
    Tabor, Joseph; Sarver, Emily A.; Saylor, John R. (Taiwan Association of Aerosol Research, 2021-12)
    Diesel particulate matter (DPM), the solid portion of diesel exhaust, has been linked to a range of deleterious health impacts. While a number of control strategies have been effective at reducing DPM in some environments, exposure risks are still high in others such as underground mines. In prior work, a novel scrubber treatment that used fog to remove DPM from engine exhaust was successfully prototyped in bench-scale laboratory experiments. Here, for the first time, the treatment concept was scaled up and field tested in a stone mine. An exhaust blower was used to pull fog, diesel exhaust, and mine air through a 30.5-meter long tube, enabling coagulation of DPM and fog drops resulting in their subsequent removal. Excluding one of the eleven tests, which appeared to be an outlier, the results showed that this fog-and-tube scrubber removed an average of 63% of particles (11.5-154 nm) as compared to 18% in the control case (without fog), yielding an average improvement of 45%. Computer simulations suggest that the observed particle removal is predominantly due to rapid thermal coagulation between the DPM and fog drops, followed by removal of the DPM-laden drops via inertial impaction with the tube walls.
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    A fogging scrubber to treat diesel exhaust: field testing and a mechanistic model
    Tabor, Joseph Edward (Virginia Tech, 2020-07-27)
    Diesel particulate matter (DPM) is comprised of two main fractions, organic carbon (OC) and elemental carbon (EC). DPM is the solid portion of diesel exhaust and particles are submicron in size typically ranging from 10 to 1000 nanometers. DPM is a known respirable hazard and occupational exposure can lead to negative health effects. These effects can range from irritation of the eyes, nose, and throat to more serious respirable and cardiovascular diseases. Due to the use of diesel powered equipment in confined airways, underground mine environments present an increased risk and underground mine works can be chronically overexposed. Current engineering controls used to mitigate DPM exposure include cleaner fuels, regular engine maintenance, ventilation controls, and enclosed cabs on vehicles. However even with these controls in place, workers can still be overexposed. The author's research group has previously tested the efficacy of a novel, fog-based scrubber treatment for removing DPM from the air, in a laboratory setting. It was found that the fog treatment improved DPM removal by approximately 45% by number density compared to the control trial (fog off). The previous work stated thermal coagulation between the fog drops and the DPM, followed by gravitational settling of the drops to be the likely mechanisms responsible for the DPM removal. The current work investigated the efficacy of the fog treatment on a larger scale in an underground mine environment, by using a fogging scrubber to treat the entire exhaust stream from a diesel vehicle. A total of 11 field tests were conducted. Based on measurements of nanoparticle number concentration at the inlet and outlet of the scrubber, the fog treatment in the current work showed an average improvement in total DPM removal of approximately 55% compared to the control (fog off) condition. It was found that the treatment more effectively removed smaller DPM sizes, removing an average of 84 to 89% of the DPM in the 11.5, 15.4, and 20.5 nanometer size bins and removing 24 to 30% of the DPM in the 88.6, 115.5, and 154 nanometer size bins. These observations are consistent with expectations since the rate of coagulation between the DPM and fog drops should be greater for smaller diameters. Further analysis of the DPM removal was aided by the development of a mechanistic model of the fogging scrubber. The model uses the inlet data from the experimental tests as input parameters, and it outputs the outlet concentration of DPM for comparison to the experimental outlet data. Results provided support for the notion that DPM removal relies on DPM-fog drop coagulation, and subsequent removal of the DPM-laden drops as opposed to DPM removal by diffusion or inertial impaction of DPM directly to the walls. The model results suggest that inertial impaction of these drops to the scrubber walls is likely much more important than gravitational settling. Moreover, the ribbed geometry of the tubing used for the scrubber apparatus tested here appears to greatly enhance inertial impaction (via enhancement of depositional velocity) versus smooth-walled tubing. This is consistent with previous research that shows particle deposition in tubes with internally ribbed or wavy structures is enhanced compared to deposition in tubes with smooth walls.
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    A Laboratory Investigation of Abatement of Airborne Diesel Particulate Matter Using Water Droplets
    Rojas Mendoza, Lucas (Virginia Tech, 2016-10-07)
    The term diesel particulate matter (DPM) is used to refer to the solid phase of diesel exhaust, which is mainly composed of elemental carbon and organic carbon. DPM is generally in the nano-size range (i.e., 10-1,000 nm). Occupational exposure is a health concern, with effects ranging from minor eye and respiratory system irritation to major cardiovascular and pulmonary diseases. Significant progress has been made in reducing DPM emissions by improving fuels, engines and after-treatment technologies. However, the mining industry, in particular, remains challenged to curb exposures in some operations where relatively many diesel engines are working in confined environments with relatively low airflow. Basic theory and a limited amount of prior research reported in the literature suggest that water sprays may be able to scavenge airborne DPM. The goals of the work presented in this thesis were to build an appropriate laboratory set up and to test the efficacy of micron-scale water (or fog) droplets to remove DPM from an air stream. The general experimental approach was to direct diesel exhaust through a chamber where fog drops are generated, and to measure DPM up- and down-stream of the treatment. Initially, fundamental experiments were conducted to explore the effect of the fog drops on the removal of (electrically neutralized) DPM from a dry exhaust stream. Compared to no treatment (i.e., control) and with the use of a diffusion dryer downstream of the fog treatment, the fog improved DPM removal by about 57% by mass and 45% by number density (versus no treatment). Without the use of the diffusion dryer, improvement in DPM removal was about 19% by mass. Analysis of the results suggests that a likely mechanism for the DPM removal in this experimental system is thermal coagulation between DPM and fog droplets, followed by gravitational settling and/or impaction of the droplets with system components. Further tests using raw exhaust (i.e., neither dried nor neutralized) having a higher DPM number density; shorter residence times; additional fogging devices; and no diffusion dryer downstream of the fog treatment were also carried out. These yielded an average overall improvement in DPM mass removal of about 45% attributed to the fog treatment (versus no treatment). The significant increase in DPM removal in these tests compared to the initial test (i.e., 19% removal by mass) cannot be fully explained by differences in residence time or DPM and fog droplet densities. Increased humidity in the system (due to the undried exhaust) may have allowed for a larger mean droplet size, and therefore might explain more rapid settling of DPM-laden droplets. Another possible contributing factor is ambient surface charge of the DPM, which might perhaps result in more efficient attachment between DPM and fog drops and/or increased deposition loses in the system.