Advanced Diesel Powertrains for Underground Mining Mobile Equipment

Strategies based on the repowering existing and powering new mobile equipment with contemporary diesel engines with substantially lower tailpipe and crankcase emissions are expected to play an important role in the efforts to curtail exposures of underground miners to criteria diesel pollutants. Laboratory characterization of tailpipe emissions for three "clean" engines that meet U.S. Environmental Protection Agency (EPA) Tier 4 final emissions standards were used to assess the viability and effectiveness of those strategies. The evaluated engines were representative of those that achieve the emission standards through implementation of various in-cylinder emissions control strategies, use of crankcase filtration, and use of three types of exhaust aftertreatment systems: (1) diesel oxidation catalytic converter (DOC), (2) combination of DOC and the full-flow wall flow monolith diesel particulate filter (DPF), or (3) combination of DOC, diesel exhaust fluid (DEF)-based selective catalytic reduction (SCR) system, and ammonia slip catalyst (ASC). The study showed that the highest reductions in concentrations of diesel aerosols in underground workings, in terms of both mass and number, could be achieved if the engines, preferably in all power classes, are fitted with viable DPF systems. The use of U.S. EPA Tier 4 final engines equipped with DOC and DOC/SCR/ASC systems could help operators to considerably reduce mass, but not number concentrations of aerosols. The emissions of two of the evaluated engines, one equipped with DOC and the other equipped with DOC/DPF systems, were characterized by substantial secondary NO₂ emissions that would limit the viability of those engines for underground mining applications. The catalyst formulations used in the exhaust aftertreatment systems of the diesel engines marketed to the underground mining industry need to be formulated to minimize the potential for generation of secondary NO₂ emissions. Engines fitted with viable SCR/ASC systems present a low-NO₂ alternative. All three of the evaluated advanced engines were found to have low CO output. Due to nuances associated with the use of diesel-powered mobile equipment in underground mines, the selection and potentially optimization of advanced engines for underground mining applications deserves special consideration.