1
25-024
Diesel Powertrains for Underground Mining Mobile Equipment
Aleksandar D. Bugarski
NIOSH PMRD
Dylan A. Ritter Jr.
NIOSH PMRD
ABSTRACT
The results of laboratory characterization of tailpipe emis-
sions for three “clean” engines that meet U.S. EPA Tier 4
final emissions standards were used to assess the viability
and effectiveness of repowering existing engines and pow-
ering new mobile equipment with those engines as a con-
trol strategy for reducing exposure of underground miners
to diesel aerosol and criteria gases. 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) combina-
tion of DOC and the full-flow wall flow monolith diesel
particulate filter (DPF), or (3) combination of DOC, die-
sel 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, prefer-
ably 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 concentra-
tions 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 substan-
tial secondary NO2 emissions that would limit the viability
of those engines for underground mining applications. It
appears that the catalyst formulations used in the exhaust
aftertreatment systems of the “clean” engines marketed to
the underground mining industry need to be formulated
to minimize the potential for generation of secondary NO2
emissions. The results indicate that the engines fitted with
viable SCR/ASC systems present a low-NO2 alternative. All
three “clean” engines were found to have low CO output.
Therefore, due to nuances associated with the use of diesel-
powered mobile equipment in underground mines, special
attention needs to be paid to the selection and potentially
optimization of “clean” engines for underground mining
applications.
Keywords: Diesel engines, underground mining, emis-
sions, diesel particulate matter, nitrogen dioxide
INTRODUCTION
In the case of underground mining operations, the sub-
stantial fraction of energy demand is associated with the
use of diesel-powered mobile equipment to load, trans-
port, and drill ore and transport materials and person-
nel (1,2,3,4,5,6,7,8,9). The diesel engines are ubiquitous
due to relatively high efficiency, reliability, and durability.
However, the extensive use of the diesel-powered under-
ground mining mobile equipment contributes substantially
to the exposure of underground miners to submicron aero-
sols, also known as diesel particulate matter (DPM), and
toxic gases including CO, NO, NO2, and hydrocarbons
(10). The long-term exposure to complex mixtures of sub-
micron aerosols and gas emitted by traditional diesel engines
was found to result in adverse pulmonary (11,12,13,14),
cardiovascular (15,16,17,18), and other health outcomes
(19,20,21). In 2012, based on the available evidence, the
International Agency for Research on Cancer (IARC)
declared diesel exhaust a Group 1 human carcinogen (22).
The use of diesel engines in underground mines is
regulated worldwide (23). In the United States, two inde-
pendent sets of regulations promulgated by the U.S. Mine
Safety and Health Administration (MSHA) standard-
ize the use of diesel equipment in (1) underground coal
mines (24), and in (2) underground metal/nonmetal (M/
NM) mines (25). The heavy-duty (HD) diesel power pack-
ages used in the inby areas (26) and the HD diesel engines
used in the outby areas of underground coal mines (27)
must be MSHA approved (24, 28). The light-duty (LD)
outby diesel engines used in coal mines should be MSHA
approved, or U.S. Environmental Protection Agency (EPA)
certified (29). The latter group must exceed the EPA Tier 2
25-024
Diesel Powertrains for Underground Mining Mobile Equipment
Aleksandar D. Bugarski
NIOSH PMRD
Dylan A. Ritter Jr.
NIOSH PMRD
ABSTRACT
The results of laboratory characterization of tailpipe emis-
sions for three “clean” engines that meet U.S. EPA Tier 4
final emissions standards were used to assess the viability
and effectiveness of repowering existing engines and pow-
ering new mobile equipment with those engines as a con-
trol strategy for reducing exposure of underground miners
to diesel aerosol and criteria gases. 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) combina-
tion of DOC and the full-flow wall flow monolith diesel
particulate filter (DPF), or (3) combination of DOC, die-
sel 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, prefer-
ably 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 concentra-
tions 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 substan-
tial secondary NO2 emissions that would limit the viability
of those engines for underground mining applications. It
appears that the catalyst formulations used in the exhaust
aftertreatment systems of the “clean” engines marketed to
the underground mining industry need to be formulated
to minimize the potential for generation of secondary NO2
emissions. The results indicate that the engines fitted with
viable SCR/ASC systems present a low-NO2 alternative. All
three “clean” engines were found to have low CO output.
Therefore, due to nuances associated with the use of diesel-
powered mobile equipment in underground mines, special
attention needs to be paid to the selection and potentially
optimization of “clean” engines for underground mining
applications.
Keywords: Diesel engines, underground mining, emis-
sions, diesel particulate matter, nitrogen dioxide
INTRODUCTION
In the case of underground mining operations, the sub-
stantial fraction of energy demand is associated with the
use of diesel-powered mobile equipment to load, trans-
port, and drill ore and transport materials and person-
nel (1,2,3,4,5,6,7,8,9). The diesel engines are ubiquitous
due to relatively high efficiency, reliability, and durability.
However, the extensive use of the diesel-powered under-
ground mining mobile equipment contributes substantially
to the exposure of underground miners to submicron aero-
sols, also known as diesel particulate matter (DPM), and
toxic gases including CO, NO, NO2, and hydrocarbons
(10). The long-term exposure to complex mixtures of sub-
micron aerosols and gas emitted by traditional diesel engines
was found to result in adverse pulmonary (11,12,13,14),
cardiovascular (15,16,17,18), and other health outcomes
(19,20,21). In 2012, based on the available evidence, the
International Agency for Research on Cancer (IARC)
declared diesel exhaust a Group 1 human carcinogen (22).
The use of diesel engines in underground mines is
regulated worldwide (23). In the United States, two inde-
pendent sets of regulations promulgated by the U.S. Mine
Safety and Health Administration (MSHA) standard-
ize the use of diesel equipment in (1) underground coal
mines (24), and in (2) underground metal/nonmetal (M/
NM) mines (25). The heavy-duty (HD) diesel power pack-
ages used in the inby areas (26) and the HD diesel engines
used in the outby areas of underground coal mines (27)
must be MSHA approved (24, 28). The light-duty (LD)
outby diesel engines used in coal mines should be MSHA
approved, or U.S. Environmental Protection Agency (EPA)
certified (29). The latter group must exceed the EPA Tier 2