Effects of Diesel Exhaust Aftertreatment Devices On
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exposure to particulate matter and gaseous emissions from Effects of Diesel Exhaust diesel-powered equipment a major challenge. Techniques Aftertreatment Devices on for reducing worker exposure typically involve one or more of the following methods; improvements in mine ventilation, Concentrations and Size Distribution the curtailment of DPM and toxic gaseous emissions through improved engine maintenance, exhaust aftertreatment tech of Aerosols in Underground Mine Air nologies, and the use of alternative fuels. Diesel particulate filter (DPF) systems are recognized as an effective technology for removing DPM from the exhaust of diesel-powered equipment (2-4). Diesel exhaust filtration ALEKSANDAR D. BUGARSKI,* systems with disposable filter elements (DFEs) have been GEORGE H. SCHNAKENBERG, JR.,† extensively used to control DPM emissions from permissible JON A. HUMMER, EMANUELE CAUDA, heavy-duty diesel-powered coal mining equipment since the SAMUEL J. JANISKO, AND early 1990s (5). Various models of DPFs and DFEs are LARRY D. PATTS currently accepted by the U.S. Mine Safety and Health U.S. Department of Health and Human Services, Public Administration (MSHA) for controlling DPM emissions from Health Service, Centers for Disease Control and Prevention, underground coal mining equipment (6-9). Although a National Institute for Occupational Safety and Health, limited number of underground mining vehicles in operation Pittsburgh Research Laboratory, 626 Cochrans Mill Road, are currently retrofitted with DPF and DFE systems it can be Pittsburgh, Pennsylvania 15236 expected that this number will increase with advancements in engine, DPF and DFE technologies. The findings of laboratory (10) and field studies (3, 4, 11) indicate that the introduction of various diesel exhaust aftertreatment technologies dramatically changes the physi Three types of uncatalyzed diesel particulate filter (DPF) cal and chemical properties of diesel aerosols and potentially systems, three types of high-temperature disposable filter changes their associated health effects. Growing evidence elements (DFEs), and one diesel oxidation catalytic converter suggests that particle number, surface area, size, or perhaps (DOC) were evaluated in underground mine conditions for their some associated structural properties may affect nanoparticle toxicity, when compared with larger respirable particles of effects on the concentrations and size distributions of diesel the same composition (12). aerosols. Those effects were compared with the effects of a This paper summarizes the results of a study conducted standard muffler. The experimental work was conducted directly to evaluate the effects that several types of DPFs, DFEs, and in an underground environment using a unique diesel laboratory a DOC have on the concentration and size distribution of developed in an underground experimental mine. The DPF diesel aerosols in an underground mine. Previous studies on systems reduced total mass of aerosols in the mine air size-resolved characterization of diesel aerosols have typically approximately 10-fold for light-load and 20-fold or more for high- been performed in well-controlled and ideal laboratory load test conditions. The DFEs offered similar reductions in environments (13-16), on roads (11, 16), and in tunnels aerosol mass concentrations. The efficiency of the new DFEs (17, 18). Since the size and concentration of diesel aerosol significantly increased with accumulation of operating time and semivolatile materials emitted by diesel engines have been shown to be strongly influenced by a number of complex and buildup of diesel particulate matter in the porous structure processes (19), the National Institute for Occupational Safety of the filter elements. A single laundering process did not and Health (NIOSH) chose to assess the aforementioned exhibit substantial effects on performance of the filter element. effects in an underground mine setting. In order to achieve The effectiveness of DPFs and DFEs in removing aerosols by this goal, while still preserving relative precision, a unique number was strongly influenced by engine operating mode. The diesel laboratory was developed in a nonoperational lime concentrations of nucleation mode aerosols in the mine air stone mine; the NIOSH Lake Lynn Experimental Mine were found to be substantially higher for both DPFs and DFEs (LLEM), near Fairchance, PA (20). Although the measure when the engine was operated at high-load modes than at low- ments were taken underground, the findings should also be load modes. The effects of the DOC on mass and number applicable to other occupational settings where workers are concentrations of aerosols in mine air were relatively minor performing their duties in proximity to diesel-powered equipment. when compared to those of the DPF and DFE systems. Introduction Experimental Section In recent years, health issues associated with exposure to diesel particulate matter (DPM) and other, primarily com A schematic of the laboratory layout is shown in Figure 1. bustion-generated, nano and ultrafine aerosols have received The D-drift is approximately 530 m (1750 ft) long,6m(20 substantial attention from the public, government agencies, ft) wide, and2m(7ft) high. The major components of the and in academia. Long-term exposure to combustion-related laboratory are an engine/dynamometer system, three sam fine particulate pollution is perceived as an important risk pling and measurement stations, and a ventilation measure factor for cardiopulmonary and lung cancer mortality (1). ment and control system. Extensive utilization of diesel-powered equipment by the The Isuzu C240, one of the most popular light-duty engines mining industry makes the reduction of underground miners’ in U.S. underground coal mines, was operated at four steady- state engine operating modes (Table 1). * Corresponding author phone: +1 412 386 5912; fax: +1 412 386 The modes were selected to cover a wide range of engine 4917; e-mail: [email protected]. operating parameters such as exhaust temperatures and † Now retired. emission rates. The average exhaust temperatures at the inlet FIGURE 1. NIOSH Diesel Laboratory in D-drift of LLEM (not to scale). maximum allowable pressure drop across the DPF systems TABLE 1. Test Modes for all engine modes and DPM loads was set to 14.9 kPa (60′′ H2O). Consequently, the DPF systems with a 25.4 × 30.5 cm engine speed torque power (10 × 12 in) Cordierite element and with a 2.75 m2 sintered mode description (rpm) (Nm) (kW) metal element were evaluated as single element units, while R50 rated speed 50% load 2950 55.6 17.2 the SiC DPF system was evaluated with two 14.4 × 25.4 cm R100 rated speed 100% load 2950 111.2 34.3 (5.66 × 10 in) elements mounted in parallel. A butterfly valve I50 intermediate speed 2100 69.1 14.9 was installed in the exhaust pipe between the engine and 50% load I100 intermediate speed 2100 136.9 30.6 DOC (or muffler) and was used during the DOC and muffler 100% load tests to generate pressure drops comparable to those observed for the corresponding DPF and DFE tests. Prior to the start of the first evaluation runs, the DPFs were “de and outlet of the tested DPFs, DFEs, DOC, and muffler greened” and fully regenerated using a CombiClean auto observed for test modes are summarized in Table 2. matic cleaning station from Engine Control Systems, New- Fresh air was supplied to the underground facility via a market, ON. ventilation shaft located in E-drift (Figure 1). A series 1000 Three types of high-temperature DFEs with synthetic model 23017-3450 Axivane fan (Joy Technologies Inc., filtration media were tested using a DFE system consisting Franklin, PA) and a subsonic Venturi meter (Primary Flow of a custom filter housing and an air-to-air heat exchanger Signal Inc., Tulsa, OK) were used to maintain and measure designed and built by Mac’s Mining Repair Service (Hun constant flow of fresh air through the drift throughout the tington, UT). The heat exchanger was installed between the tests. The measurements showed the average volumetric flow engine and the DFE housing to cool exhaust below 343 °C rate of 5.687 ( 0.047 m3/s (12050 ( 100 ft3/min). The very (650 F). The following DFEs were evaluated: low test-to-test variability in flow rate (0.86%) eliminated 1. Donaldson Company, Minneapolis, MN, model P604516 the need for normalization of the data with respect to it. (DFE-A); The average exhaust dilution ratios for R50, R100, I50, and 2. A Laundered DFE, identical to DFE-A, but laundered I100 engine operating modes were calculated to be 148, by Mac’s Mining Repair Service, Huntington, UT, following 149, 186, and 188, respectively. The average ambient standard protocols (LDFE-A); temperatures upstream of the engine were between 10.5 3. FST Systems Corporation, Price, UT, model FST-115-26 and 18.7 °C. The corresponding average ambient tem (DFE-B). peratures at the downstream measurement station ranged DFE-A and DFE-B meet MSHA criteria for permissible between 14.7 and 22.3 °C. and nonpermissible applications, and they are listed as 83 Exhaust Aftertreatment Technologies. Three types of DPF and 80% efficient, respectively, in the removal of total DPM systems (representative of that which is currently available (6). The laundering process is used by some coal operators to the underground mining industry) were evaluated in this to extend the life cycle of the high-temperature DFEs. The study: laundered version of DFE-A (LDFE-A) tested in this study 1. Catalytic Exhaust Products (CEP), Toronto, ON, model was laundered only once. 912-SXT with uncatalyzed Corning EX-80 Cordierite element Two brand new elements (DFE-A and DFE-B) and the (31 cell per cm2 and 0.3 mm wall thickness) (Cordierite DPF). laundered element (LDFE-A) were conditioned prior to the 2. DCL International Inc., Concord, ON, model Minex 4-mode tests through 13 and6hof operation at R50 mode, Sootfilter 5.66 × 10 with uncatalyzed Ibiden silicon carbide respectively.