IC 9462 

INFORMATION CIRCULAR/2002 

Review of Technology Available

to theUndergroundMining Industry


for Control of Diesel Emissions

Department of Health and Human Services

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 
Information Circular 9462 

Review of Technology Available

to the Underground Mining Industry

for Control of Diesel Emissions 

By George H. Schnakenberg, Jr., Ph.D., 

and Aleksandar D. Bugarski, Ph.D 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
 Public Health Service
 

Centers for Disease Control and Prevention
 

National Institute for Occupational Safety and Health
 

Pittsburgh Research Laboratory
 

Pittsburgh, PA
 

August 2002 
ORDERING INFORMATION 

Copies of National Institute for Occupational Safety and Health (NIOSH)
 

documents and information
 

about occupational safety and health are available from
 

NIOSH–Publications Dissemination
 

4676 Columbia Parkway
 

Cincinnati, OH 45226-1998

 FAX: 513-533-8573

 Telephone: 1-800-35-NIOSH 

(1-800-356-4674)

 E-mail: pubstaft@cdc.gov

 Web site: www.cdc.gov/niosh 

This document is the public domain and may be freely copied or reprinted. 

Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH. 

DHHS (NIOSH) Publication No. 2002-154 
i 

CONTENTS 

Page 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
 

Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 
 

1 Introduction ............................................................................ 4 
 

1.1 Health concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 
 

1.2 Diesel exhaust composition ........................................................... 4 
 

1.3 Occupational exposure .............................................................. 6 
 

1.4 Selected regulatory limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 
 

1.5 Diesel particle concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 
 

1.6 Document purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 
 

1.7 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 
 

2 Control technologies ..................................................................... 9 
 

2.1 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 
 

2.2 Engine design and selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 2.2.1 Lower DPM emission engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 2.2.2 Engine derating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 
 

2.3 Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

 2.3.1 Commercial fuel and the effects of sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

 2.3.2 Alternative fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

 2.3.3 Fuel additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

2.4 Aftertreatment technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 2.4.1 Diesel oxidation catalytic converters (DOCCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 2.4.2 Diesel particulate filters (DPFs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

 2.4.3 DOCC and DPF combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

 2.4.4 Disposable diesel exhaust filter (DDEF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 
 

3 Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 
 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 
 

Appendix A.—Low-PI MSHA-approved engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 

ILLUSTRATIONS

 1. Monolithic catalyst substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

 2. Catalyst washcoat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

 3. Example of a ceramic monolith filter element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

 4. Gas flow in a monolith, wall-flow filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

 5. Knitted microfiber filter (deep-bed filter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

 6. Example of a particulate filter system using fiber media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
 

TABLES

 1. Typical occupational DPM exposure levels ................................................... 6

 2. Exposure limits for DPM ................................................................. 7

 3. Isuzu-Deutz engine comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

 4. Derated Isuzu engine comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

 5. Minimum temperature for continuous regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

 6. Performance of the available control technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 
 

A-1. List of MSHA-approved engines (as of December 2001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 
ii 

ABBREVIATIONS USED IN THIS REPORT 

ACGIH American Conference of Governmental Industrial Hygienists 

CARB California Air Resources Board 

CDPF catalyzed diesel particulate filter 

CFR Code of Federal Regulations 

CONCAWE Oil Companies’ European Organisation for Environment, Health and Safety 

CRT Continuously Regenerating Trap 

DDEF disposable diesel exhaust filter 

DECSE Diesel Emission Control–Sulfur Effects Program 

DEEP Diesel Emissions Evaluation Program 

DETR Department of the Environment, Transport and the Regions (U.K.) 

DOC diesel oxidation catalyst 

DOCC diesel oxidation catalytic converter 

DPF diesel particulate filter 

DPM diesel particulate matter 

DST Dry System Technology 

EC elemental carbon 

EGR exhaust gas recirculation 

ELPI electrical low-pressure impactor 

EMA Engine Manufacturers’ Association 

EPA Environmental Protection Agency 

FBC fuel-borne catalyst 

F-T Fisher-Tropsch 

FTP Federal test procedure 

HC hydrocarbon(s) 

ISO International Organization for Standardization 

LS low-sulfur 

MECA Manufacturers of Emission Controls Association 

MOUDI Micro-orifice uniform-deposit impactor 

MSHA Mine Safety and Health Administration 

NIOSH National Institute for Occupational Safety and Health 

OC organic carbon 

OEM original equipment manufacturer 

OICA Organisation Internationale des Constructeurs d’Automobiles 

PAH polynuclear aromatic hydrocarbons 

PAS photoelectric aerosol sensor 

PDEAS personal diesel exhaust aerosol sampler 

PI (MSHA) particulate index 

PM particulate matter 

PRL Pittsburgh Research Laboratory (of NIOSH) 

RCD respirable combustible dust 

SAE Society of Automotive Engineers 

SMMT Society of Motor Manufacturers and Traders Ltd. (U.K.) 
iii 

SMPS scanning mobility particle sizer 

SOF soluble organic fraction (of DPM) 

SOL solid fraction (of DPM) 

SSPD Sasol slurry phase distillate 

TC total carbon 

TLV® threshold limit value (ACGIH) 

TPM total particulate matter 

ULSF ultralow sulfur fuel (<50 ppm of sulfur by weight) 

VERT Verminderung der Emissionen von Realmaschinen im Tunnelbau 

GLOSSARY 

category A	 MSHA designation for engines certified for use inby 

category B	 MSHA designation for engines certified for use in outby areas or metal and nonmetal 

mines 

inby	 refers to areas of a coal mine that are ventilated by air that are downstream from the 

point of coal extraction and thus may contain methane; electrical and diesel 

equipment in this area must be “permissible” and certified as such by MSHA 

outby	 refers to areas of a coal mine that are ventilated by air that has not yet passed the 

point of coal extraction; either “permissible” or “nonpermissible” diesel equipment 

can be used here 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

bpd	 barrel(s) per day 

cfm	 cubic foot (feet) per minute 

gal	 gallon(s) 

g/bhp-hr	 gram(s) per brake horsepower-hour 

g/hr	 gram(s) per hour 

hp	 horsepower 

hr	 hour(s) 

μg/m3	 microgram(s) per cubic meter (mass concentration) 

μm	 micrometer(s) (10-6 meter) 

mbar	 millibar(s) (which equals 0.1 kilopascal or about 0.7500617 mm mercury, 

0.01450284 pounds per square inch pressure) 

mg/m3	 milligram(s) per cubic meter (mass concentration) = 1,000 μg/m3 

min	 minute(s) 

nm	 nanometer(s) (10-9 meter) 

ppm	 part(s) per million 

rpm	 revolution(s) per minutes 

vol %	 volume percent 
REVIEW OF TECHNOLOGY AVAILABLE TO THE UNDERGROUND
 

MINING INDUSTRY FOR CONTROL OF DIESEL EMISSIONS
 

By George H. Schnakenberg, Jr., Ph.D.,1

1

Research physicist.
 

 and Aleksandar D. Bugarski, Ph.D.2 

2

Senior associate fellow.
 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
 

ABSTRACT 

This report reviews the performance and applicability of technology for the control of 

emissions from diesel-powered equipment used in underground coal and metal/nonmetal mines. 

The methods discussed include Mine Safety and Health Administration-approved low-emission 

engines, engine derating, fuels, fuel additives, diesel oxidation catalysts, and diesel particulate 

filters. The potential of each of these technologies is examined individually and in combination. 

The performance estimates are derived from the published literature and presented in narrative and 

tabular form. The purpose of this report is to help the mining industry select the most appropriate 

method to reduce underground exposures of miners to diesel exhaust in the context of the recently 

developed diesel regulations. It is important to note that the control technologies discussed in this 

report have received limited evaluation in underground mines. Additional research is ongoing, and 

some engineering design changes may need to be implemented before all of these diesel emission 

control technologies can be safely and successfully used in underground mines. 
2 

EXECUTIVE SUMMARY 

This report presents the potentials and limitations of control technology for reducing exhaust 

tailpipe emissions from diesel-powered equipment used in underground mining. It does not discuss 

ventilation, enclosed cabs, or personal protection (respirators), but only commercially available 

products that reduce the particulate matter (PM) and harmful gases from the exhaust pipe of dieselpowered equipment. While the current operational conditions for diesel equipment commonly 

provide adequate ventilation to control the harmful gases, these same conditions result in levels of 

worker exposure to diesel particulate matter (DPM) that are significantly higher than those of any 

other occupation and significantly higher than the new U.S. and current European standards. 

Because of a historical concern over the health effects from long-term exposure to DPM and the 

recent promulgation of two DPM rules by the Mine Safety and Health Administration (MSHA), 

the focus has been on solutions that reduce PM rather than the toxic exhaust gases. However, 

as we show, the existing technology can provide significant reductions to both. 

The control technology found to be appropriate for discussion falls into the following six 

general categories: MSHA-approved engines with low emissions, derated engines, fuels, 

fuel additives, diesel oxidation catalytic converters (DOCCs), and diesel particulate filters (DPFs). 

Using low-emission, MSHA-approved engines is a viable option that can result in a 

significant reduction of PM emissions and, in some cases, a reduction of toxic gas emissions. This 

option can be demonstrated using the Isuzu C240 (QD60), a very popular engine for outby 

applications in coal mines. The direct substitution of the Isuzu C240 with a Deutz F4L1011 would 

result in a 64% reduction of emitted DPM based on the MSHA particulate index (PI) for each 

engine. 

It is possible, and sometimes practiced, to limit the maximum fueling rate of a particular 

engine to less than its rated maximum specifically to reduce emissions. This practice is called 

derating. Relatively minor reductions in rated power may result in significant reductions in 

PM emissions. For example, by reducing the maximum deliverable horsepower of the Isuzu C240 

from 56 to 52, DPM emissions are reduced by 62% (from 9.35 to 4.25 g/hr). 

The use of commercially available alternative fuels—e.g., biodiesel and synthetic diesel— 

and water-fuel emulsions can result in lower gaseous and PM emissions. The sulfur content of the 

fuel becomes a concern when considering the application of oxidation catalysts to the point that the 

use of ultralow sulfur fuel (ULSF) is highly recommended. Fuel additives, developed as combustion 

enhancers and smoke reducers, can contain metal compounds. These additives create additional 

emissions of metallic ash with possible adverse health effects and thus are not recommended. 

However, some additives, notably fuel-borne catalysts (FBCs), are specifically formulated to lower 

the exhaust temperatures necessary to burn off the soot collected by particle filters. When used with 

a particle filter, the FBCs pose no additional health hazard, since the filter effectively prevents 

emissions of the catalyst metals. 

Diesel oxidation catalysts can significantly reduce both carbon monoxide (CO) and 

hydrocarbons (HC) (the source of the “diesel” odor). They also reduce the organic fraction of PM. 

However, oxidation catalysts greatly enhance sulfate formation from the sulfur present in the fuel 

and thereby add another toxic component to the exhaust emissions. Diesel exhaust also contains 

nitrogen oxides, NOx (NO + NO2); catalysts tend to convert some of the nitric oxide (NO) to a more 

toxic form, nitrogen dioxide (NO2), which can be of concern depending on the amount of NO 
3 

converted and the ability of the prevailing environment to dilute or adsorb (on mine surfaces) 

the NO2. 

DPFs are extremely effective at removing PM (primarily carbon soot and adsorbed HC) from 

engine exhausts. In addition, the DPFs can be catalyzed to provide good reductions of CO and HC. 

However, the DPM that is collected by the particle filter needs to be removed. The preferred 

approach is to use the high exhaust temperatures to burn off the collected soot during engine 

operation—that is, to cause spontaneous or autoregeneration. As a general rule, the engine should 

operate at medium to high loads for at least 20% to 25% of the time to ensure sufficient temperature 

for regeneration. Catalysts are used to lower regeneration temperatures, and their use ensures 

regeneration under a wide range of applications. Alternatively, filters with integral heaters that are 

connected to an air and electrical supply managed by an off-board system have been shown to be 

viable for application in which conditions do not favor autoregeneration. For low-horsepower, lightduty applications, a system that performs an on-board regeneration in 10 min is available. As a final 

alternative, a DPM-loaded filter can be exchanged for a clean filter that was regenerated in a simple 

electric kiln designed for the purpose. 

Combinations of these technologies provide better reductions of both the gaseous and 

particulate exhaust components. In particular, the systems combining catalytic oxidation and 

filtration offer the highest reductions of DPM and gases, except for NO2. This combination produces 

the best results when used with ULSF. 

NIOSH considers the combination of a low-PM-emitting engine (possibly derated), a form 

of oxidation catalyst, and a DPF, when operated within an effective maintenance program, to be the 

best available technology for reducing hazardous diesel emissions for applications in underground 

mines. It would be necessary to add the measurement of tailpipe DPM (by methods yet to be 

selected) to the accepted practice of monthly tailpipe gas checks to ensure that the DPF is 

performing as expected. 

The area of diesel emissions control technology is changing rapidly. The information 

presented is current as of December 2001. The best source for monitoring this changing field is the 

World Wide Web. The Web sites to consult include www.cdc.gov/niosh/mining, www.msha.gov/ 

S&HINFO/DIESEL.HTM, and www.deep.org for mining specific information; and 

www.DieselNet.com and arbis.arb.ca.gov/toxics/diesel/ss/summary_2.htm for developments in 

particulate emissions control for automotive, highway, and off-highway equipment. The authors of 

this document may also be contacted. 
4 

1 Introduction 

1.1 Health Concerns 

Continual expansion of the use of diesel engines in the mining industry and the uncertainties 

associated with the long-term effects of exhaust emissions on miners’ health have recently focused 

attention on risk assessments of diesel engine exhaust. The issue of DPM has raised a host of health 

and environmental concerns and has gained considerable attention of researchers and various 

regulatory agencies. 

The concerns about the health effects of DPM exposure have resulted in the issuing of 

regulations by MSHA governing the emission rates for diesel equipment used in U.S. coal mines 

[66 Fed. Reg.3

3

Federal Register. See Fed. Reg. in references. 

 5526 (2001)] and environmental compliance levels for DPM in U.S. metal and 

nonmetal mines [66 Fed. Reg. 5706 (2001)]. Other countries have also adopted regulations that 

limit environmental levels of DPM [DieselNet 2001]. It is clear from the documentation supporting 

the MSHA regulations that miners (and other workers in confined spaces) are the most highly 

exposed of any occupation. 

1.2 Diesel Exhaust Composition 

The complexity of the chemical and physical composition of diesel exhaust emissions makes 

the assessment of health risk from exposure to diesel engine exhaust a daunting task. Although the 

major portion of diesel exhaust contains nitrogen, oxygen, water, and the asphyxiant carbon dioxide 

(CO2), it also contains recognized noxious, toxic, and potentially harmful substances: particulate 

matter (PM) or soot; organic compounds such as lubricating oil and unburned or partially burned 

HC, which are primarily the source of the unpleasant odor associated with burning diesel fuel; 

oxides of nitrogen (NO and NO2, collectively known as NOx); CO; and sulfur oxides. Inorganic 

constituents of diesel exhaust, such as metals, acids, and salts, are also among the chemical 

constituents hypothesized to be toxic. 

MSHA regulations at 30 CFR 7 define DPM as “any material collected on a specified filter 

medium after diluting exhaust gases with clean, filtered air at a temperature of #125 °F (52 °C), 

as measured at a point immediately upstream of the primary filter. This material is primarily carbon, 

condensed HC, sulfates, and associated water.” This pragmatic definition provides engine testing 

facilities with a tool for assessing PM emissions simply by measuring the weight (mass) gain of the 

filter, i.e., by gravimetric analysis. In practice, physical and chemical processes governing the 

formation and transformation of the DPM before and after collection make accurate interpretation 

of DPM emissions and their health impact a complex issue. For example, despite the varying 

chemical composition of the DPM, the masses obtained are all considered “equivalent” whether they 

are organic condensates, solid carbon particles, sulfates plus water, or metallic ash from lubrication 

oils. Using the gravimetric determination of DPM may be useful for comparing engine emissions 

under nearly identical set of operating conditions, fuels, and measurement methods. However, it is 

flawed when used to compare the performance of some control technologies and equally inadequate 

in providing an assessment of health impact. Adding to the complexity is that the prescribed MSHA 

testing to determine PM emissions is performed over a set of eight steady-state engine operating 

conditions, which does not therefore include acceleration transients (a major source of PM) and may 
5 

not be representative of the actual engine operating conditions. According to Kittelson [1998], 

typical particle composition of a heavy-duty diesel engine tested under a heavy-duty transient cycle 

breaks down as follows: carbon, 41%; unburned fuel, 7%; unburned oil, 25%; sulfate and water, 

14%; and ash and other components, 13%. 

The structure and chemical composition of DPM is a function of numerous parameters; 

the major ones are fuel composition, engine design, engine operating conditions, and the exhaust 

aftertreatment process. The composition of exhaust particles also depends on where and how they 

are collected or measured. In addition, the composition of DPM might be significantly altered (and 

thus different from that measured in the laboratory) when the exhaust is released in the mine setting. 

The diameter of diesel particles ranges from 5 nm (1 nm = 1×10-9 m) to 1 μm (1 μm = 

1×10-6 m), depending on engine design and operating conditions. Two distinct size modes 

characterize PM distribution: the agglomeration mode and the nucleation mode. Particles in the 

agglomeration mode (50 nm to 1 μm) contribute to the majority of the DPM mass. The chemical 

composition of agglomeration-mode particles are mainly a carbonaceous core and adsorbed organic 

compounds. The nucleation mode contains the majority of the particle number, but does not 

contribute significantly to the total particulate matter (TPM) mass. Particles in the nucleation mode 

have been found to be composed mostly of volatile or semivolatile organic compounds, sulfur 

compounds, and trace elements. 

Hydrocarbons, one of the major organic pollutants in diesel exhaust, are emitted as gaseous 

and PM-bound compounds. The phase (gas, condensed liquid, or solid) of HC in diesel exhaust 

depends on their molecular weight, temperature, and concentration and is expressed as a partition 

coefficient, which is the ratio of the mass of compound in the particulate phase to the mass of 

compound in the vapor phase. Higher molecular weight and some intermediate molecular weight 

compounds known as soluble organic fraction (SOF) are adsorbed on the PM. Common particulatebound compounds are linear- and branched-chain HC with 14 to 35 carbon atoms; polynuclear 

aromatic hydrocarbons (PAHs); alkylated benzenes; nitro-PAH; and a variety of polar, oxygenated 

PAH derivatives. These compounds are of particular concern because several of them have been 

associated with carcinogenicity and mutagenicity, as reported in various laboratory studies. Some 

of the vapor phase compounds that could potentially affect human health include formaldehyde, 

methanol, acrolein, benzene, 1,3-butadiene, and low-molecular-weight PAHs and their oxygenated 

and nitrated derivatives. 

Several methods are in use for determining occupational exposures to the components of 

diesel exhaust. Direct-reading instrument and chemical methods (stain tubes) are used to determine 

the gas concentrations of CO2, CO, NO, and NO2. Field determination of the organic vapor fraction 

is not normally performed. The determination of workplace concentrations of exhaust PM is a more 

complex undertaking. There is no consensus on exactly what is to be measured (total or elemental 

carbon, combustible carbon) or the analytical method (thermo-optical, coulometric, gravimetric) for 

determining workplace DPM concentrations. A synopsis of these methods is presented in the 

MSHA “Diesel Toolbox” [MSHA 1997]. Gravimetric-based methods that determine the amount 

of respirable combustible dust (RCD) [Maskery 1978; Gangal et al. 1990; Gangal and Dainty 1993] 

or that determine the amount of submicron particulate collected on a filter are inadequate at 

moderately low workplace concentrations because so little mass is collected that weighing error 

becomes significant. Methods based on determining the amount of elemental carbon (EC) present, 

such as the coulometric method [ZH 1/120.44 (1995)] adopted in Europe and the NIOSH Method 

5040 [NIOSH 1999], are much more sensitive to DPM. These methods exploit the established 
6 

unique and reasonably strong correlations between EC and DPM [NIOSH 1999]. In coal mines, 

because of the presence of both organic and EC in the coal mine dust, a submicron impactor 

[Cantrell et al. 1993] can be used to separate the larger dust particles from the diesel combustion 

particles for EC analysis. A direct-reading instrument, such as the Ecochem PAS 2000 photoelectric 

aerosol sensor (PAS), is available and can be used for noncompliance measurement of workplace 

or tailpipe (with dilution) carbon particle concentration. The state-of-the-art aerosol instrumentation 

used for measurement of mass (MOUDI, ELPI, etc.) and number (SMPS) concentrations is too 

costly, complex, and cumbersome for routine monitoring of PM underground. 

1.3 Occupational Exposure 

Table 1 shows the occupational exposures to DPM of miners and of those in other 

occupations. 

Table 1.—Typical occupational DPM exposure levels 

Occupational group Exposure level, mg/m3 

(1 mg/m3 = 1,000 μg/m3) 

Underground miners, coal, no aftertreatment1 0.9 - 2.1 

Underground miners, coal, disposable diesel exhaust filter1 0.1 - 0.2 

Underground miners, coal, wire mesh filter1 1.2 

Underground miners, metal/nonmetal, no aftertreatment1 0.3 - 1.6 

Surface miners1 <0.2 

Urban fire station2 0.1 - 0.48 

Forklift operators, dock workers, railroad workers2 0.02 - 0.10 

Truck drivers2 0.004 - 0.006 1

Haney et al. [1997]. 

2

DieselNet [1999b]. 

1.4 Selected Regulatory Limits 

Table 2 provides some regulatory limits for occupational exposures to DPM. 
7 

Table 2.—Exposure limits for DPM [DieselNet (2001)] 

Country or organization Value, mg/m3 DPM Measurand 

Current Limits: 

U.S.: MSHA metal/nonmetal 

underground mines [66 Fed. 

Reg. 5706 (2001)] 

July 19, 2002: 0.4 

January 19, 2006: 0.16 

Total carbon (EC + OC) 

as determined by 

NIOSH Method 5040 

U.S.: MSHA underground 

coal mines [66 Fed. Reg. 

5526 (2001)] 

Emissions rates set for 

various classes of equipment, 

e.g., heavy duty equipment: 

2.5 g/hr 

Total DPM measured in 

accordance with ISO 8178 

procedures [30 CFR4

4

Code of Federal Regulations. See CFR in references. 

7 

(1996)] 

Germany: General 

occupational environment 

0.1 EC, coulometric 

Germany: Underground 

metal and nonmetal mining 

and construction sites 

0.3 EC, coulometric 

Canada: Underground, metal 

and nonmetal mining 

1.5 RCD 

Switzerland [Majewski 1999] 0.1 EC, coulometric 

Proposed Limits: 

ACGIH [1995] 0.15 Particles <1 μm in size 

ACGIH (1998) 0.05 Total carbon in particles 

<1 μm in size 

ACGIH (2001) 0.02 (EC = 40% of DPM) EC particles <1 μm in size 

“In its 2001 Notice of Intended Changes, the ACGIH proposed a TLV of 0.02 mg/m3 for diesel exhaust particulates 

measured as elemental carbon (EC), with proposed carcinogenicity classification A2 - “Suspected Human Carcinogen.” 

This EC-based TLV is practically equivalent to the previously proposed TLV of 0.05 mg/m3

, presumably as total diesel 

particulate matter (EC fraction typically constitutes about 40% of the total diesel particulate mass).” (Source: 

www.DieselNet.com.) 

In January 2001, MSHA promulgated two new rules regulating the exposure of underground 

miners to DPM. The metal rule [66 Fed. Reg. 5706 and 35518 (2001)] requires underground metal 

and nonmetal mine operators to comply by July 19, 2002, with the interim DPM concentration of 

400 μg/m3

 measured as total carbon using NIOSH Analytical Method 5040 [NIOSH 1999]. On 

January 19, 2006, the compliance level DPM concentration limit will be 160 μg/m3

 measured as 

total carbon. 

The underground coal rule [66 Fed. Reg. 5526 and 27864 (2001)] controls the exposure of 

the miners by limiting the emission rate from newly introduced and existing diesel-powered 
8 

equipment. MSHA found that due to the absence of an accurate method for sampling DPM in 

underground coal mines, a performance rule, similar to that promulgated for metal and nonmetal 

mines, is not feasible. Additionally, in-place coal regulations [30 CFR 75.325(f) and (g) (1996)] 

specify ventilation air quantities for each piece of equipment, allowing reasonably precise estimation 

of the resulting DPM concentration from the engine emissions. Engine emission rates are calculated 

using the emission rate determined through MSHA engine certification [30 CFR 7 (1996)] and the 

reduction provided by the application of emission control technology, namely, particle filters. On 

its Web site, MSHA provides a list of filters and their accepted filtration performance for this 

purpose [MSHA 2001a]. Should alternative emission controls be used, the emission rates of the 

engine and control system would have to be determined using the MSHA engine certification 

procedures [30 CFR 7 (1996)]. Only systems verified as meeting the 2.5 g/hr (permissible or heavyduty) or 5 g/hr limits (outby light-duty) would be accepted. 

The coal rule contains a complex timetable of equipment type and emission rates. Suffice 

it to state that all heavy-duty equipment must eventually meet a DPM emission rate of #2.5 g/hr. 

Newly introduced light-duty equipment must either use an engine approved by the Environmental 

Protection Agency (EPA) or emit <5 g/hr of DPM. Existing light-duty equipment is exempt from 

the rule. The MSHA Web site lists MSHA-approved engines and their emission rates [MSHA 

2001b]. 

Both rules leave the choice of controls up to the mine operators. The metal and nonmetal 

rule allows a wider choice of control technology, since it uses an environmental standard to measure 

compliance. The choices of control technology for coal are much more limited, if for no other 

reason than economic: any system that does not use a device with an MSHA-accepted PM reduction 

factor must undergo expensive testing. Also, for coal mines, only a limited number of engines and 

associated power packages are available that are suitable for use in gassy areas of the mines. 

1.5 Diesel Particle Concerns 

Current PM emissions legislation is based on ambient mass concentrations, mg/m3

. None 

of these regulations contain a reference to either the size or the number concentration of the 

particles. Further, the prescribed gravimetric analysis of PM is nonspecific with respect to chemical 

composition and aerosol properties and, thus, delivers no toxicologically relevant information. 

Additionally, known DPM size distributions indicate the presence of very fine particles that, when 

inhaled, are eventually trapped in the slowly cleared alveolar regions of the human lungs. The 

health implications of these ultrafine particles is currently unknown and is the subject of much 

speculation and research. The MSHA DPM rule for metal and nonmetal mines [66 Fed. Reg. 5706 

and 35518 (2001)] uses total carbon as measured by NIOSH Method 5040 [NIOSH 1999] as a 

compliance measurement. This method, however, accounts for neither particle size nor inorganic 

continuants such as sulfates and transitional metals. 

The effects of inorganic constituents of DPM on mortality and morbidity have been the 

subject of numerous epidemiological and toxicological studies [Mauderly et al. 1995] and should 

not be underestimated. The transition metals can cause the production of hydroxyl radicals, which 

are considered to be toxic products. Residual lubrication oil ash is also toxic to cells and lungs. 

Finally, a wide range of inorganic and organic sulfur and nitrogen compounds have irritating, 

cytotoxic, and mutagenic properties. Animal studies [Schlesinger 1995] indicate that nitrates, 
9 

sulfates, and sulfuric acid particles impair pulmonary functions such as mucociliary clearance and 

airway resistance. 

1.6 Document Purpose 

The purpose of this document is to provide an overview and review of practical, available 

technology that can be used to reduce gaseous and particle emissions from new or older dieselpowered equipment in underground mines. Upon reading this document, it is hoped that the 

decision-makers in labor, industry, and government will be able to learn which control alternatives 

are available and proven, to what extent each is able to reduce toxic gases or harmful PM from diesel 

exhaust, the caveats and conditions of use for each, the effects of combining technologies, and the 

estimated costs. Armed with this knowledge, it is additionally hoped that the same entities will be 

able to recognize the most effective technologically feasible controls for reducing miners’ exposure 

to diesel emissions in underground mines. 

1.7 Scope 

This document presents the performance and limitations of control technology designed to 

reduce diesel exhaust emissions from the tailpipe. It does not discuss ventilation, enclosed cabs, 

personal protection (respirators), or measurement technology, but only proven commercially 

available technology that reduces the PM and toxic gases from the exhaust of diesel-powered 

equipment. 

The technology discussed is applicable to most, if not all, diesel equipment used in 

underground coal or metal/nonmetal mines. Additional design and engineering efforts must be made 

to adapt some of the technology for use in areas (inby) of coal mines that require precautions against 

methane ignition or hot surface temperatures. 

This document does not address maintenance or proper application of diesel engines. It is 

expected that the industry has or will shortly institute across-the-board maintenance procedures that, 

at a minimum, follow MSHA guidelines and the engine or vehicle manufacturer’s prescribed 

maintenance procedures. Additionally, engines, when operated at altitudes >1,000 ft, need to be 

properly derated, and then the torque converter of the vehicle needs to be matched to the derated 

engine to avoid excessive emissions from lugging down the engine and to allow the engine to attain 

the optimum engine speed for maximum power transfer to the drive train. 

The control technology found to be appropriate for discussion falls into the following general 

categories: low-emission engines, derated engines, fuels, fuel additives, DOCCs, and DPFs. 

Combinations of these technologies are possible and are also discussed. 

2 Control Technologies 

Mine ventilation has traditionally been the primary means for controlling workplace 

concentrations of diesel emissions in underground mines. With the continual increase in the number 

of diesel equipment units deployed in underground mines and the rising concerns about adverse 

health effects of diesel emissions, increasing the ventilation rate as the sole means to control 

exposures becomes an inadequate and expensive approach. Concerns with engine efficiency and 

the general environmental impact of diesels on urban air quality have driven research to reduce 
10 

emissions at the source, resulting in much lower-emitting (particularly NOx and PM) diesel engines 

and practical aftertreatment and other emission reduction technologies. Although some of the 

aftertreatment technology was originally developed for use in underground mines and tunnels, the 

present drive for research results from the need to address on-highway diesels. (The latest 

information on worldwide regulations can be found on at www.DieselNet.com/standards.html; 

the current EPA rules can be found at www.epa.gov/otaq/diesel.htm.) The underground mining 

industry can benefit greatly from the advances in technology and the economies of scale of the onhighway truck and bus market. This document provides a brief review of the most effective 

technologies developed for curtailment of diesel emissions, including the toxic gases and PM. These 

technologies include engine design, engine derating, fuel formulations, fuel additives, DOCCs, and 

DPFs. 

Evaluation of the performance of emission control technology in underground mine settings 

is difficult because of the intrinsically transient operation of machinery with the pronounced 

variations in numerous parameters, such as daily workload and ventilation rates. Therefore, only 

a very limited amount of accurate data exist on the emission reduction performance of the 

technologies in underground mine conditions. Nonetheless, the examination herein of the body of 

literature representing laboratory tests and the knowledge of the scientific and engineering principles 

of the technology provide an adequate foundation for estimating the effects of the application of this 

technology to reduce diesel emissions in the underground mine operations. This analysis also 

provides sufficient data to support decisions on the technical feasability of control technology 

alternatives. However, the limited field performance data available point to the need to perform 

more field evaluations on appropriately selected technology. 

2.1 Maintenance 

Over the relatively short history of the use of diesels in underground mining, the need for 

good maintenance has always been recognized. This recognition has not always generated the 

adoption and disciplined implementation of the best maintenance practices being applied to every 

diesel engine or vehicle in operation in underground mines. Nevertheless, it is extremely important 

to realize that the very first step on the path to reducing worker exposures is to implement an 

effective diesel vehicle/engine maintenance protocol and apply it to every diesel unit that operates 

underground. The early work in this area was performed by the U.S. Bureau of Mines [Waytulonis 

1987]. The University of Minnesota’s Center for Diesel Research [Spears 1997] developed 

procedures for using tailpipe gas measurements as a diagnostic for engine maintenance. 

A comprehensive study on the relationship between diesel engine maintenance and tailpipe 

emissions was recently completed by McGinn [2000] under a research effort by the Diesel 

Emissions Evaluation Program (DEEP). McGinn has developed a maintenance auditing procedure 

[McGinn et al. 2000] and guidelines [McGinn 1999], which were recently implemented in a hardrock mine with demonstrable results. The guidelines and training of the mine personnel involved 

participation by mine management, machine operators, mechanics, and most importantly the engine 

and vehicle manufacturers’ service (not sales) representatives. Dramatic reductions in exhaust PM 

and CO emissions were observed in some cases where good maintenance practice was applied. 

These documents can be found at www.deep.org/research.html. 
11 

There are several important reasons to provide the best possible engine maintenance when 

considering or implementing control technology. The first reason is that the lowest emissions 

resulting from the application of any control technology are obtained when starting with the lowest 

possible engine-out emissions. The second reason is that ventilation requirements and PM emission 

rates determined through MSHA’s engine certification process were obtained using a properly tuned, 

well-maintained (new) engine. It is important that the engines in the field have emission 

characteristics no worse than those of the certified engine so that calculations that use the MSHA 

ventilation and PM emission rates to ensure safe levels of toxic gases, to estimate workplace diesel 

particulate levels, or to compare particulate emission rates among engines are valid. In addition, 

excessive emissions from poorly maintained engines may jeopardize performance of aftertreatment 

technologies. For example, excessive emissions of the ash caused by burning crankcase oil might 

result in clogging and premature failure of the DPF. 

In sum, although maintenance is not strictly an “add-on” hardware control technology, 

the very first step in applying control technology to reduce workplace exposures to diesel exhaust 

is to implement an effective maintenance program and closely monitor its effectiveness. 

2.2 Engine Design and Selection 

Over the last decade or so, major improvements have been made in engine design that have 

resulted in substantially lower emission rates of DPM. Additionally, lower engine emissions can 

be obtained by limiting the maximum fueling rate to an engine, resulting in a lower power output 

but substantial reduction in DPM emissions and some fuel savings. 

2.2.1 Lower DPM Emission Engines 

The major efforts in reducing PM emissions from diesel engines have been directed toward 

optimizing the combustion and fuel injection systems and minimizing the lube oil consumption of 

the engine. The successful engineering techniques for these purposes are high compression, air 

intercooling of turbocharged engines, center positioning of the injector nozzle, increased number 

of the nozzle perforations, very high injection pressure, suppression of the air swirl, and a shallow 

piston bowl. These techniques have resulted in significant reductions of PM mass emitted from the 

engine. Mayer [1997] found that modern engines emit 10% of the total particulate mass emitted by 

engines designed 15 to 20 years ago. Unfortunately, these new low-emission engines were found 

to emit more ultrafine particles at all load points than the older engine of the same family [Bagley 

et al. 1993; Baumgard and Johnson 1996; Mayer 1997]. Mayer et al. [1999] concluded that engine 

designers presently do not have a strategy for effectively curtailing the emission of these 

nanoparticles. It is yet to be confirmed that this increase in nanoparticles, which was observed under 

laboratory test conditions, actually manifests itself in actual mine settings. Nevertheless, tests of 

DPFs using several different filter media confirm that filters are very effective in “trapping” the 

nanoparticles [Mayer et al. 1999; Czerwinski et al. 1998]. 

Although a variety of engineering technologies have resulted in engines with greatly reduced 

emissions, mine operators are presently limited in their choice of diesel engines. After 

November 24, 1999, only engines listed by MSHA [MSHA 2001b] as approved can be used in coal 

mines [30 CFR 75.1907 (1996)]. After March 20, 2001, all diesel engines introduced into metal and 

nonmetal mines must be MSHA- or EPA-approved [30 CFR 57.5067 (2001)]. Furthermore, they 
12 

must be set to operate at the conditions under which the approval was granted. Thus, with the 

exception of derating for altitude, there is little or no room for altering engines, let alone changing 

the design. Furthermore, the MSHA requirement that all engines in use in coal mines must have 

current approval may be the reason that many engines of older design appear along with the newer 

engines on the MSHA list. 

The engine selection limitation is exacerbated for the permissible areas in coal mines. Only 

six engines are approved, and these are of much older design. These engines have very high 

PM emission rates. In some cases, a reduction of 95% in PM is needed to bring the emission rate 

down to 2.5 g/hr required by the coal rule. As this review will reveal, a 95% reduction in total DPM 

challenges the capabilities of the contemporary control technology. The limited selection has also 

resulted in engine applications that underutilize the engine, wasting fuel, and unnecessarily 

increasing DPM concentrations in the workplace. On the other hand, some applications require 

more horsepower than these engines can provide, especially when they are derated for altitude. 

Clearly, there is a need for cleaner permissible engines. Because of the significant expense of 

certifying an engine for permissible applications and the minuscule market size, there is little 

incentive for engine manufacturers to provide new permissible engines to the coal industry. 

In its 1996 revision to diesel engine approval procedures [30 CFR 7 (1996)], MSHA 

recognized the concerns over diesel particulate emissions and recognized that newer engines can 

emit DPM at a much lower rate. Therefore, MSHA provided a means, the PI, for conveying this 

lower PM emission to the mining industry. The PI is the amount of air needed to dilute the engineproduced DPM to 1 mg/m3

. It is calculated from a weighted-average PM obtained over the 

ISO 8178 C1, eight-mode, steady-state test described in 30 CFR 7. A lower PI characterizes an 

engine with a lower PM emission. Unfortunately, but unavoidable, the MSHA test procedures do 

not account for the fact that a significant portion of real-life PM emissions occurs during engine 

transients (accelerations) or for the significant variation in duty cycles across applications. 

The PI and the ventilation rate are the keys for selecting a low-emission engine for 

underground mine applications. With the understanding that a given application requires an engine 

with a certain power, rated speed, and physical size, one can examine the MSHA approval list sorted 

by horsepower (see the appendix to this report) and pick an engine with the lowest PI that closely 

matches the engine power and rated speed required for the application. Next, one can check the 

ventilation rate required by that engine and determine whether that rate is acceptable. (Some of the 

low-PI engines require exceptionally high gaseous ventilation rates that may pose limitations on 

their use if ventilation is critical). Mine operators should consider these factors when purchasing 

new equipment or a replacement engine. Likewise, equipment suppliers should try to design their 

equipment for low-emission engines and offer it as an option in their equipment lines. 

A close look at the tabulated nameplate ventilation rates and particulate indices for the 

category B (nonpermissible or outby) engines approved by MSHA reveals significant differences 

in the emissions, especially in engines of low horsepower. Table 3 shows the differences between 

the Isuzu C240(QD60) engine and a comparable Deutz F4L1011 engine. 
13 

Table 3.—Isuzu-Deutz engine comparison 

Engine Rating 

hp @ rpm 

MSHA name 

plate 

ventilation 

rate, cfm 

MSHA PI, 

cfm 

MSHA 

approval 

Approximate 

cost 

Isuzu C240 

(QD60) 56.0 @ 3,000 2,500 5,500 7E-B038-0 $4,000 

Deutz 

F4L1011 56.3 @ 3,000 3,000 2,000 7E-B060-0 $6,000 

In MSHA approval tests, the Deutz F4L1011 engine emits, on average, approximately 64% 

less DPM than the Isuzu C240 engine. Assuming that the prevailing ventilation rate is already 

>3,000 cfm and remains unchanged, switching to the Deutz engine will reduce the contributions to 

the workplace DPM concentrations from that vehicle by almost two-thirds. If the ventilation rate 

must be increased from 2,500 to 3,000 cfm to accommodate the Deutz, then by virtue of this 

increased ventilation rate, the contribution of the Deutz to the workplace DPM concentration is 70% 

less than that of the Isuzu. 

The example involving the Isuzu and Deutz is not unique; numerous low-PI engines over 

100 hp are also available for substitution. Table A-1 in the appendix of this report lists MSHAapproved engines. In this table, the engines with exceptionally low PIs have been identified. 

Significant workplace reductions, primarily in metal and nonmetal mines, can be achieved by 

replacing any existing engine having a high PI with a current MSHA-approved engine with a low PI. 

It is noteworthy that DPM reductions attainable by selecting clean engines or derating 

engines can be quite substantial. EPA-certified engines emit one-tenth the DPM than those of 

10 years ago. There remains a question (which NIOSH hopes to investigate) about the alleged 

increase in nanoparticle number from low-PI engines [Bagley et al. 1993; Baumgard and Johnson 

1996; Mayer 1997]. Health professionals are concerned and uncertain about the effect of 

nanoparticles on worker health. 

Lastly, for optimum results regardless of the choice made, the engine-out (before any 

aftertreatment if it is used) emissions of DPM and toxic gases must be kept to the minimum by 

diligent application of proper maintenance. 

2.2.2 Engine derating 

Substantial reductions in PM emission rates can result from lowering of the maximum 

fueling rate of an engine. It is possible that many of the engines certified by MSHA are certified at 

or very near their maximum power where PM emissions are quite high. There is no restriction by 

MSHA on reducing the maximum power delivered by lowering the maximum fuel setting, i.e., 

derating. It is not unheard of that some mines choose to derate their engines to reduce DPM and CO 

emissions, reduce tire slippage and wear, and save on fuel costs. The MSHA list provides some 

insight into the effects of derating an engine on PM emissions. 
14 

Table 4 shows the effects of derating on gaseous and DPM emissions from an Isuzu 

C240MA engine. The DPM emission rate can be reduced by 55% (calculated from the MSHA PI) 

with only a 7% reduction in power. If each engine is operated at the nameplate ventilation rate, the 

resulting DPM concentration is reduced by 62%. 

Table 4.—Derated Isuzu engine comparison 

Engine Rating 

hp @ rpm 

MSHA name 

plate ventilation 

rate, cfm 

MSHA PI, 

cfm 

MSHA 

approval 

Isuzu C240MA 56.0 @ 3,000 2,500 5,500 7E-B085-0 

Isuzu C240MA 52.0 @ 3,000 3,000 2,500 7E-B086-0 

The comprehensive list of MSHA-approved engines provided on pages 5667-5668 of the 

coal rule [66 Fed. Reg. 5526 (2001)] have the Isuzu QD100-306 engine listed at 66 hp with a PI of 

10,000 cfm and at 70 hp with a PI of 50,000 under the same approval number. Therefore, the 

reduction of 4 hp by limiting the fueling rate results in an 80% reduction in the DPM emission rate 

for this engine. 

These two examples may be anomalies. PM emission rates for certified engines at powers 

lower than that of the certification testing may be obtained from the engine manufacturer. If the loss 

of power would not affect the performance of the equipment for a particular application, it is 

certainly advisable to check with the engine manufacturer on the emission reductions to be gained 

by derating the engine. If the derating is substantial, it is also advisable to check with the equipment 

or torque converter manufacturer to determine whether another converter should be used to obtain 

an optimum power match to the derated engine. The proper procedures are explained by 

Forbush [2001]. 

2.3 Fuels 

In parallel to the development of the cleaner diesel engine technologies, much attention has 

been given to the defining of future diesel fuel quality requirements. Extensive research in this field 

[Baranescu 1988; Cowley et al. 1993; Xiaobin et al. 1996] has shown that properties such as sulfur 

content, fuel density, cetane number, oxygen, and aromatic content are the physical and chemical 

properties that most significantly influence particulate and gaseous emissions. Research by 

Den Ouden et al. [1994] showed that the contribution from fuel properties other than sulfur to heavyduty diesel emissions is comparatively small and can be characterized by a combination of cetane 

number and density. Fuel sulfur forms both sulfur dioxide (gas) and sulfates (solids at room 

temperature). A comprehensive summary discussion and table are presented in the “Diesel Fuels” 

section of the Technology Guide of the DieselNet Web site [DieselNet 1998d]. 
15 

2.3.1 Commercial Fuel and the Effects of Sulfur 

The mechanism for sulfate formation is as follows: during fuel combustion, the sulfur 

oxidizes to produce sulfur dioxide (SO2), a fraction (<5%) of which can be further oxidized to sulfur 

trioxide, SO3, which combines with water to form a sulfuric acid aerosol [Heywood 1988]. Studies 

with low-sulfur fuel revealed that the number of relatively large particles (>0.040 μm) remains 

unaffected when fuel with low sulfur content is used. In contrast, low sulfur content is found to 

reduce the concentration of nanoparticles (<0.040 μm) by several orders of magnitude, revealing that 

most particles of this size are sulfur-related. Certain aftertreatment technologies such as diesel 

oxidation catalysts (DOC) and catalyzed diesel particulate filters (CDPF) can exacerbate the 

conversion of SO2 to SO3 and thus should be used with ULSFs (<50 ppm) to minimize sulfate 

particulate formation and poisoning of the catalyst. 

Sulfur content in current low-sulfur diesel fuel (Federal LS No. 2 diesel fuel, which is the 

U.S. on-highway truck fuel) is on average 340 ppm (maximum of 500 ppm) by weight and, most 

likely, will be reduced further in the future. The sulfur content of diesel fuel currently used in 

California (CARB diesel) averages 120 ppm S. A recent economic study sponsored by the Engine 

Manufacturers Association (EMA) concluded that the incremental cost to reduce sulfur level in 

diesel fuel from the current 500 ppm to <50 ppm would be on average about 5 to 7 cents/gal [EMA 

1999]. The Manufacturers of Emission Controls Association (MECA) reported that reducing the 

level of sulfur in diesel fuel would allow the introduction in the United States of several promising 

control technologies that reduce emissions of NOx and PM [MECA 1999b]. In December 1999, 

ARCO announced plans to offer a cleaner burning diesel fuel to help reduce soot emissions from 

urban municipal fleets in southern California. The ARCO fuel will have a maximum sulfur content 

of 15 ppm. The price of the ARCO fuel is expected to be approximately 5 to 7 cents/gal more than 

that of the CARB diesel fuel (120 ppm S). On December 21, 2000, EPA announced that refiners 

will be required to start producing diesel fuel for highway use with 15 ppm sulfur or less by June 

1, 2006, with availability at retail stations by September 1, 2006. 

Klein et al. [1998] studied the effects of fuel sulfur content on the PM emissions from diesel 

passenger cars equipped with oxidation catalysts. The engines were tested at steady-state 

conditions. Klein et al. found that with low-sulfur fuel and low exhaust temperature, the PM 

reduction was linked to a shift in particulate size distribution toward smaller sizes. For low-sulfur 

fuel and high exhaust temperature, the particulate mass emission rate increased with the use of an 

oxidation catalyst. This trend was attributed to SO3 production and a shift in particulate size 

distribution toward larger sizes. For high-sulfur fuel and low exhaust temperature, PM emissions 

had the same trend as that for low-sulfur fuel and low exhaust temperature. For high-sulfur fuel and 

high exhaust temperature, PM emissions showed the same trend as that for low-sulfur fuel and high 

exhaust temperature. Significantly, Carder [1999] found that reducing fuel sulfur from 0.3% (3,000 

ppm) to 0.04% (400 ppm) resulted in a 22% reduction of DPM mass emission in an MWM D916-6 

engine operated over the ISO 8178 cycle. 

The Diesel Emissions Control–Sulfur Effects (DECSE) Program, a joint government/industry 

research effort, evaluated the impact of diesel fuel sulfur level on the emission control systems such 

as NOx absorber catalyst, DPF, lean-NOx catalyst, and DOC [DECSE 2001]. A study [DECSE 

1999] on the effects of diesel sulfur level on DOC performed on the Cummins ISM 370 engine 

showed that, at high exhaust temperatures (518 °C, OICA Mode 2), the engine-out PM emissions 

are largely independent of fuel sulfur level. PM emissions over heavy-duty FTP cycle varied 
16 

independently of fuel sulfur levels for both engine-out and catalyst-out emissions. At this condition, 

engine-out sulfate conversion was approximately 2%. A DOC with relatively low precious metal 

content (low activity) increased the sulfate conversion to 10%. Catalyst-out emissions showed a 

very strong sulfur effect: an increase in fuel sulfur from 3 to 350 ppm resulted in a 400% increase 

in PM emissions. 

A study [DECSE 2000] of the effects of diesel sulfur level on performance of a CDPF and 

a Continuously Regenerating Trap (CRT) using a Caterpillar 3126 engine showed that the engineout PM emissions increased approximately 30% when the fuel sulfur level was increased from 3 to 

350 ppm. Both DPFs reduced PM emissions by 95% over the OICA cycle with 3-ppm sulfur fuel. 

However, with 30-ppm sulfur fuel, the PM reduction efficiencies dropped to 74% and 72% for the 

CDPF and CRT, respectively. With the 150-ppm sulfur fuel, the postfilter PM emissions increased 

and efficiencies were 0 and 3%; with the 350-ppm sulfur fuel, the PM emissions increase was 122% 

and 155% for CDPF and CRT, respectively. The effects of fuel sulfur level on gas-phase emissions 

and fuel consumption were not significant. Analysis of the PM showed that the increases were 

attributable to the sulfur content. Nearly 40% to 60% of fuel sulfur was converted to sulfate PM, 

as measured over the 13-mode OICA cycle for both DPFs. 

As a part of DETR/SMMT/CONCAWE Particulate Research Programme, Andersson and 

Wedekind [2001] compared effects of diesel fuel sulfur content on DPM emissions. They compared 

diesel fuels with sulfur content of 500 ppm, 300 ppm, and 50 ppm with ultralow sulfur (<10 ppm) 

Swedish Class I diesel fuel. Ultralow sulfur showed a small, but significant reduction in particle 

mass and number compared to the other fuels tested. Effects of fuel sulfur were found to be greatest 

within the nucleation mode particles. 

In summary, the sulfur content of diesel fuel adversely affects diesel emissions by producing 

SO2 and sulfates. The use of oxidation catalysts further increases the production of sulfates, which, 

unfortunately, are not significantly trapped by particle filters, decreasing their effectiveness to 

reduce DPM mass and creating the potential for nanoparticle formation [Kittelson 1998]. The rate 

of sulfate production depends on catalyst formulation and exhaust (catalyst) temperature. Catalysts 

that are highly effective at converting CO and HC are also highly effective at SO2 conversion. It 

follows, therefore, that a less active catalyst produces fewer sulfates, but with the penalty of less 

reduction in CO and HC. At low exhaust temperatures (<225 °C), SO2 conversion to sulfates is 

minimal, but at higher temperatures (between 225 °C and 560 °C, peaking at 450 °C) conversion is 

substantial [DieselNet 1999a]. Since exhaust temperature is not a freely controllable parameter in 

the field, the production of sulfates and thus workplace concentrations vary greatly and are 

unpredictable. Additionally, sulfates poison catalysts. It is clear, therefore, that both SO2 and 

sulfates add to the toxic burden of the exhaust. For these reasons, it is advisable to know the sulfur 

content of the fuel and crankcase oil used and to strive to use those with the lowest sulfur content 

in underground mines. Use of lower sulfur fuels and oils results in lower exhaust toxicity from 

lower sulfate and permits the use of more active catalysts that are highly effective in reducing CO 

and HC. DOCC suppliers should take into account the sulfur content of the fuel used at their 

customers’ mines when providing DOCCs for their equipment. 

2.3.2 Alternative fuels 

Reformulated and alternative diesel fuels recently received significant attention as a way of 

controlling emissions and providing energy independence. Fuels such as biodiesel and synthetic 
17 

diesel fuel obtained through Fisher-Tropsch (F-T) conversion are high-quality alternative fuels. 

These fuels can be used in neat form or blended with petroleum diesel fuel to make a cleaner diesel 

fuel. Fuel-water emulsions also promise reductions in the NOx and PM emissions. 

2.3.2.1 Fisher-Tropsch 

Fisher-Tropsch (F-T) conversion is a gas-to-liquid process used for synthesis of HC from 

CO and hydrogen. Historically, the process was used for producing synthetic diesel fuel from coal, 

natural gas, and biomass resources in countries where petroleum fuel stock was in short supply. The 

process has received attention recently because of its ability to convert natural gas resources to 

liquid fuels and chemicals. The synthetic diesel fuel produced by this process is of very high quality 

and has the potential to significantly reduce exhaust emissions. The F-T fuels have a high cetane 

number (up to 70), a low sulfur content (<10 ppm), and a low aromatic content (<3%). The benefits 

are most pronounced in reducing PM emissions [Schaberg et al. 1997; Mayer 1997; Norton 

et al.1999] owing in part to the almost complete absence of sulfur and its accompanying sulfate 

emissions. Absence of sulfur also enables the use of catalytic oxidation technologies without the 

concern over catalyst poisoning or PM emission penalties from the catalytic creation of sulfates. 

McMillian and Gautam [1998] concluded that F-T fuels provide a basis for reduction of NOx using 

higher exhaust gas recirculation (EGR) rates. However, the low efficiency of the F-T process 

currently makes this fuel expensive. Because the lubricity of F-T fuel is significantly lower than that 

of regular diesel, the addition of a lubricity improver is required. 

F-T fuel is not commercially available in the United States, but companies including Shell, 

Chevron, Exxon, and ARCO are working on developing production. F-T fuel is commercially 

available in the Republic of South Africa from companies such as Sasol and Mossgas. Syntroleum 

Corp. currently owns and operates a pilot plant in Tulsa, OK, where it has successfully demonstrated 

numerous elements and variations of the Syntroleum Process (an F-T process based on a proprietary 

catalyst developed by Syntroleum) since 1990. ARCO and Syntroleum are presently building a 

70-bpd demonstration plant at ARCO’s Cherry Point Refinery in Washington State. Syntroleum and 

Enron are planning to complete an 8,000- to 10,000-bpd specialty chemical plant late in 2001. 

Syntroleum is expecting to build a commercial-scale gas-to-liquid plant within the next 3 years. 

Recently, the performance of synthetic diesel fuels was examined by several researchers. 

Schaberg et al. [1997] examined diesel exhaust emissions using Sasol slurry phase distillate (SSPD) 

process fuel. It was found that the SSPD fuels produce significantly lower emissions than the diesel 

No. 2 and CARB fuels in all four regulated emission categories. When compared to the No. 2 diesel 

fuel, HC, CO, NOx, and PM emissions were reduced by 49%, 33%, 27%, and 21%, respectively. 

The exhaust emissions were lower owing to the very high quality of the synthetic diesel fuel used 

(cetane number >70, aromatic content <1%, sulfur content <10 ppm). The soluble organic fraction 

(organic carbon (OC)) of the integrated PM was found to be significantly lower when the cetane 

number was increased, but this benefit was offset by an increase in the insoluble (EC) portion of the 

TPM. Schaberg et al. [1997] also found a linear relationship between fuel sulfur and the sulfate 

portion of total particulate emissions. The influence of F-T fuel on the particle size of the PM was 

not examined. 

Mayer [1997] compared standard Swiss low-sulfur diesel fuel with a chemically pure 

paraffin fraction made by DEA-Mineralöl AG, Hamburg, Germany (negligible content of sulfur, 

nitrogen, and aromatics). Emission improvements with synthetic fuel were reported as 
18 

“disappointingly low.” Mayer concluded that the reformulation of diesel fuel cannot efficiently 

curtail the emission of ultrafine particles. 

More recently, Norton et al. [1999] examined regulated emissions from older model transit 

buses operated on an F-T fuel (produced by Mossgas of the Republic of South Africa) using West 

Virginia University’s transportable chassis dynamometer. Three buses without and three with 

catalytic converters were tested. Compared to their emissions when operating on No. 2 diesel fuel, 

buses without catalytic converters emitted 20% lower PM; buses with catalytic converters emitted 

31% lower PM when operating on neat Mossgas fuel. 

Bugarski [1999] tested an Isuzu C240 engine with diesel No. 2 and neat F-T fuel. It was 

found that when using the synthetic diesel instead of diesel No. 2 the mass of PM emitted decreased. 

However, the number of ultrafine particles, i.e., those particles that are thought to be deposited in 

the alveolar region of the lungs, unfortunately, increased. 

2.3.2.2 Biodiesel 

Biodiesel is defined as the monoalkyl esters of long-chain fatty acids derived from renewable 

lipid sources. Biodiesel is registered with the EPA as a pure fuel or as a fuel additive and is a legal 

fuel for commerce. Pure biodiesel has extremely low sulfur content (maximum 50 ppm) and no 

aromatic content. The cetane number of biodiesel is comparable to that of No. 2 diesel. Since 

biodiesel is oxygenated (esters contain oxygen), its combustion in diesel engines is more complete 

than that of petroleum fuels. 

The use of biodiesel instead of regular diesel fuel in a conventional diesel engine may result 

in a substantial reduction of unburned HC, CO, and PM. A slight increase in the NOx emissions 

(caused by a significant increase in NO2) was observed for neat biodiesel or biodiesel blends 

compared with regular diesel fuel [Sharp 1998]. Durbin et al. [2000] observed that 100% biodiesel 

and biodiesel blends produce slightly higher PM emissions from 1995 Ford 350 than the California 

330-ppm sulfur fuel. Durbin et al. also observed significant difference in the fuel effects on 

emissions for different vehicles. Absence of sulfur also enables the use of catalytic oxidation 

technologies without the concern over catalyst poisoning or PM emission penalties from the 

catalytic creation of sulfates. A U.S. Bureau of Mines study reported by Howell and Weber [1997] 

showed PM reductions of 50% when neat biodiesel was used instead of regular diesel fuel. The test, 

performed with biodiesel and biodiesel blends in underground mines, also resulted in noticeably less 

offensive exhaust odor. A study conducted for DEEP by the combined staff of NIOSH, University 

of Minnesota, Michigan Technological University, and ORTEC reported by Watts et al. [1998] and 

Bagley and Gratz [1998] in an isolated zone of an underground metal mine compared standard lowsulfur No. 2 diesel fuel with a blend of 55.6 vol % soy methyl ester and D2 fuel. The test vehicle 

was equipped with a DOC for both fuels. The observed reduction in DPM was approximately 20% 

when measured by RCD or NIOSH 5040 methods [Watts et al. 1998]. Bagley and Gratz [1998] 

reported a reduction in solid particle fraction (SOL) of 20% and a reduction of 75% in mutagenic 

activity. 

The synthetic diesel and biodiesel fuels can be used in existing engines and fuel injection 

systems without negatively impacting operating performance. Additionally, results of tests on 

Jet A-1 fuel conducted at Southwest Research Institute concluded that biodiesel shows significant 

lubricity improvement compared to diesel fuel [Howell and Weber 1997]. In general, biodiesel fuel 
19 

produces lower CO, HC, and carbon particles, but increased soluble OC, so that TPM mass may 

either decrease slightly or increase. 

McCormick et al. [2001] studied the impact of biodiesel chemical structure, specifically fatty 

acid chain length and a number of double bonds, on emissions of NOx and PM. Seven biodiesel 

fuels produced from real-world feedstocks and 14 produced from pure fatty acids were tested in a 

heavy-duty truck engine using the U.S. heavy-duty Federal test procedure. They found that NOx 

emissions increased with increasing fuel density or decreasing fuel cetane number of biodiesel fuel. 

For tested biodiesel fuels with density <0.89, PM emissions were found to be constant. McCormick 

et al. also concluded that PM emissions were impacted only when cetane number values were less 

than those of conventional diesel fuels today. PM reductions were found to be proportional to the 

fuel oxygen content for biodiesel fuels with cetane number greater than about 45 or density less than 

0.89. An increase in NOx emissions over petroleum diesel was evident, but they could not explain 

a mechanism that would cause it. 

Biodiesel over time will soften and degrade certain types of elastomers and natural rubber 

compounds. Therefore, precautions are needed when using high-percentage blends to ensure that 

the existing fueling system, primarily its fuel hoses and fuel pump seals, does not contain elastomer 

compounds incompatible with biodiesel. If a vehicle’s fuel system contains these materials, their 

replacement with biodiesel-compatible elastomers such as Viton B is recommended. The recent 

switch to low-sulfur diesel fuel has caused most original equipment manufacturers (OEM) to switch 

to components suitable for use with biodiesel, but users should contact their OEM for specific 

information. Fuel-injection equipment manufacturers have agreed that fuels containing up to 5% 

of biodiesel are compatible with existing equipment. 

Petkewich [2001] reported that the first two public filling stations offering biodiesel fuel in 

the United States were opened in San Francisco, CA, and Sparks, NV, in May 2001. As of 

November 19, 2001, the price of neat biodiesel is about $2.20. The “Biodiesel Fuel” section of the 

Technology Guide [DieselNet 2001] provides a comprehensive discussion of this subject. An 

extensive list of the published literature on biodiesel fuels is available on the EPA Web site [EPA 

2001] and on the Web site of the National Biodiesel Board [2001]. 

2.3.2.3 Fuel-Water Emulsions 

The potential for reducing diesel emissions by adding water to diesel fuel (fuel-water 

emulsions) has been extensively explored recently. Introducing water to the combustion chamber 

of diesel engines has the effect of reducing combustion temperature and thus reducing the 

production of NOx. Other effects are the reduction of PM and an increase in CO and HC emissions. 

Fuel-water emulsions have been reported to reduce both NOx and PM by 40% to 50% [DieselNet 

1998b; Langer and Daly 1999]. Langer and Daly [1999] also indicated that there was no fuel cost 

penalty. The additional CO and HC produced can be handled by a DOCC. Special blending 

technologies, usually involving additives, are required to keep the water and petroleum-based fuel 

oil together in a stable emulsion. On the negative side, fuel oil-water emulsions suffer from the 

potential for corrosion of engine parts, freezing, emulsion instability in storage, and reduced 

lubricity. Ongoing research is addressing these problems and is driven simply by the costeffectiveness of this technology. 

Several low-emission, diesel fuel-water blends and blending technologies are available on 

the market. For example, A-55, Inc., has developed a clean fuel composed of 20% to 30% water, 
20 

70% to 80% petroleum, and 0.5% of the A-55 additive. The A-55 fuel is injected as small droplets 

into the engine’s combustion chamber in the same way as traditional fuels. However, once inside 

the combustion chamber, the water in the A-55 fuel vaporizes, shattering the fuel droplets into much 

smaller droplets. This secondary atomization of the fuel results in more complete combustion, 

reducing particulate emissions that are the product of incomplete combustion. 

Lubrizol Corp., in conjunction with Caterpillar, Inc., developed the water emulsion fuel 

technology named “PuriNOx.” The fuel emulsion is applicable to direct-injection heavy-duty diesel 

engines. According to Lubrizol, the technology is compatible with existing engines and 

aftertreatment devices. The system requires a relatively elaborate fuel mixing plant and thus is well 

suited for larger mines with centrally fueled fleets. The manufacturers claim reductions in NOx 

emissions from diesel engines of up to 30% and reductions of PM emissions of up to 50%. Using 

emulsions results in a 10% to 15% loss in engine rated power observed with regular diesel fuel 

[Lubrizol 1999]. 

According to the manufacturers, the fuel-water emulsions should be similar to or lower in 

price than diesel fuels and can be used as ordinary fuel without any modifications whatsoever. 

2.3.3 Fuel Additives 

Metals (such as platinum (Pt), strontium (Sr), copper (Cu), and iron (Fe)) and the rare earths 

(such as cerium (Ce)), when added to diesel fuel in small concentrations, were found to be efficient 

at oxidizing the soot, thereby reducing visible smoke [Howard and Kausch 1980]. Test results also 

showed that fuel additives may decrease the solid PM in raw exhaust by 15% to 25% [Lepperhoff 

et al. 1995; Mayer et al. 1999]. More significantly, FBCs lower the regeneration temperatures of 

DPFs. Spontaneous regeneration of uncatalyzed filters without FBC occurs at 550 °C to 650 °C. 

Use of a catalytic coating on the filter element and an FBC significantly lowers regeneration 

temperatures. Also, the type and dosage level of the fuel-borne additive make a significant 

difference in regenerating temperatures. For instance, when a Ce-based FBC is used, continuous 

regeneration of the catalyzed filters occurs at exhaust gas temperatures >400 °C, while stochastic 

(balanced or equilibrium) regeneration occurs between 200 °C and 400 °C [Lepperhoff et al.1995; 

Bach et al. 1998]. Regeneration is unlikely to occur at temperatures <200 °C. Jelles et al. [1999] 

found that a Pt-Ce fuel additive supports continuous regeneration of a CDPF at temperatures 

>327 °C. 

Today, it is recognized that the primary reason for using an FBC in underground operations 

is to attain spontaneous regeneration of DPFs at the lowest possible exhaust temperature. Use of 

an FBC for this purpose is pervasive in the tunneling equipment equipped with DPFs in Europe 

[Schnakenberg 1999a]. When the FBC is used in combination with a DPF, there is no concern with 

the toxicity of the metallic ash (emitted as nanoparticles). Furthermore, as noted above, some FBCs, 

notably the Pt-Ce FBC, are effective at extremely low dosing levels. In fact, Duffy and Samarchi 

[1997] observed no significant increase in toxicity of the raw exhaust with the optimum dose level 

of 7 ppm Pt-Ce. Thus, with a DPF in place, the toxic potential of this FBC is insignificant. 

Dosage of the FBC is an important subject of optimization. It was found that regeneration 

quality is not further improved if a threshold dosage is exceeded [Burtsher et al. 1999]. Minimizing 

the FBC dosage is important in order to minimize costs, to lower the potential increase in exhaust 

toxicity owing to the emission of the FBC metallic ash in the form of nanoparticles, and to reduce 

ash buildup on the DPF. A typical dosing level for the Fe-based additive Satacen® is about 
21 

36 ppm Fe. The typical dosing of Octel Octimax 4800 is 20/5 ppm of Fe/Sr. Considerably less ash 

is produced by Pt-Ce because the dosing level is much lower (2-8 ppm, with the Pt usually 

<0.5 ppm). The accumulated ash will eventually (at >2,000 hr of operation with Satacen and 

proportionally longer for Pt-Ce) require cleaning the DPF. 

In addition to the minor problem of ash accumulation, a more serious concern related to the 

use of the fuel additives is the emission of the FBC metal oxide upon DPF malfunction and the 

unintentional use of fuel containing an FBC in a vehicle not equipped with a DPF. Periodic 

monitoring of DPF performance could prevent potential for extended exposures to FBC ash. It is 

important to ensure that fuel containing the FBC is used only by engines with DPFs. Furthermore, 

adding the FBC to the equipment fuel tank upon fill-up does not ensure proper dosage. On-board 

fuel-dosing systems are available on the market, but they are not yet perfected [Schnakenberg 

1999a]. For these reasons, it is necessary to use separate fuel storage and handling systems at this 

time. One system stores and dispenses fuel for vehicles without DPFs, the other stores and 

dispenses fuel to which an FBC has been added and is intended for use by vehicles with DPFs. This 

segregation of fuel is the only burden to the mine imposed by FBC use. When perfected, the 

on-board dosing systems would eliminate the need to segregate fuel supplies for DPF-equipped and 

non-DPF-equipped vehicles. 

The selection and formulation of the FBC is probably the domain of the fuel additive 

manufacturer and the DPF system supplier. Temperature-time profiles of the engine exhaust 

temperature, taken during full-shift operation of the vehicle intended to receive a DPF, are essential 

in selecting an FBC. Some of the FBC products on the market are: 

(1) EOLYS-DPX9® (Ce) by Rhodia (formerly Rhone-Poulenc, Inc.); 

(2) Platinum Plus® (Pt-Ce) by Clean Diesel Technology (a Ce-based additive supplied by 

Rhodia); 

(3) Ferrocene (Fe) by Aldrich; Satacene®, Sat Chemie Gmbh, now Octel, U.K.; 

(4) OS-96401(Cu) by Lubrizol; and 

(5) Octimax® OCI-4800, Fe-Sr; Octel America, Inc. 

The Health Effects Institute (HEI) conducted a study [HEI 2001] on health risks associated 

with Ce-based additives and concluded that using Ce as an FBC with a particulate filter would result 

in a measurable increase in the ambient levels of cerium oxide in particles <0.5 m (perhaps up to 

several orders of magnitude greater than current levels) depending on the level of Ce actually used, 

the filter efficiency in trapping the particles, and the degree of penetration in the vehicle fleet. 

HEI found as result of short-term diesel engine tests that despite the high efficiency of filters in 

trapping PM (>90%), a small amount of Ce was emitted in the particulate phase of the exhaust. 

Ce mass relative to the total particle mass was found to be between 3% and 18% based on two tests 

using two different types of filters. Based on the limited data available, HEI found that toxicity of 

cerium oxide seems to be small and that cerium oxide might not be of concern when inhaled at the 

low levels. 

2.3.3.1 Review of the Published Research 

Lepperhoff et al. [1995] conducted a study on the performance of a Ce-based fuel additive 

(DPX6, Rhone-Poulenc) in relation to particulate trap (Corning EX-47) regeneration quality, 
22 

trap filtration efficiency, particle size distribution, and fate of the additive under steady-state engine 

operating conditions. Lepperhoff et al. found that a Ce FBC, when added at a dosage of 50 ppm of 

Ce by weight, reduced particulate emissions by roughly 20%. The DPM reduction mainly resulted 

from the reduction of the EC content, and the quantity of the volatile HC was unaffected. In 

addition, the tested fuel additive lowered the collected PM ignition temperature to 200 °C. When 

using the Ce fuel additive at the Ce dosage of 50 ppm by weight and the Corning EX-47 trap, 

DPM emissions were reduced by >90%. Ninety-seven percent of the Ce compounds were filtered 

by the trap. 

Jelles et al. [1999] examined the performance of different additives. The results of their 

testing are shown in table 5. 

Table 5.—Minimum temperature for continuous regeneration [Jelles et al. 1999] 

Additive Concentration, 

ppm wt. Filter Minimum temperature, °C 

None — EX-80 540 - 560 

None — Pt EX-80 420 - 430 

Ce 100 EX-80 430 

Pt-Ce 0.5 - 5 Pt EX-80 330 

Pt-Cu 0.5 - 5 Pt EX-80 350 

Pt-Fe 0.5 - 22 Pt EX-80 360 

NOTE: EX-80 designates the type of Corning monolith filter material; Pt EX-80 indicates that the substrate is catalyzed 

with Pt. 

The highest temperature observed during a regeneration of the filter was >900 °C. 

Mayer et al. [1999] found that the use of Cu-based fuel additives resulted in elevated dioxin 

and furane emissions. Therefore, Mayer et al. suggested that Cu additives should not be used in the 

fuel for underground machinery. The tests also showed that the use of Fe and Ce additives did not 

result in elevated dioxin and furane emissions. 

Burtsher et al. [1999] examined the effects of the use of Ce-based fuel additives on the 

emission of nanoparticles and the concentration of the additive in the exhaust. The measurements 

were made on the exhaust generated by a heavy-duty diesel engine (Liebherr 914T) and a small 

naturally aspirated Yamaha diesel engine. The Ce additive at concentrations of 20 and 100 ppm was 

found in the particulate phase of the exhaust. The measurements taken by the scanning mobility 

particle sizer (SMPS) showed that the concentrations of nanoparticles significantly increased with 

increases in the concentrations of the additive in the fuel. Chemical analysis showed that the small 

particles consisted only of the additive material. Since there is concern with human exposure to 

nanoparticles, Burtsher et al. concluded that diesel exhaust filters should be used to eliminate 

emission of additive-based nanoparticles. 

In sum, FBCs should be used mainly to enhance the regeneration performance of DPFs. 

Care should be taken to ensure that FBCs are added only to the fuel that will be used exclusively by 
23 

engines equipped with the DPFs. Filters successfully curtail emissions of the metallic ash resulting 

from the use of additives. It is equally important to avoid use of the regular fuel with filter-equipped 

engines. With regular fuel, the filter may fail to regenerate, consequently overloading the filter with 

soot and eventually causing the filter and engine to malfunction. The additional cost associated with 

the use of an additive is usually less than 10 cents/gal (4 to 7 cents/gal for Platinum Plus®, for 

example). MSHA requires [30 CFR 75.1901(c)(1996)] that any fuel additive used in underground 

coal mines be registered with the EPA in accordance with 40 CFR 79. According to the literature, 

most of the commercially available additives are EPA-approved; all except the Cu-based additives 

are acceptable for underground use. 

2.4 Aftertreatment Technologies 

2.4.1 Diesel Oxidation Catalytic Converters (DOCCs) 

The primary function of a DOC is to oxidize CO and HC to CO2 and water in an exhaust gas 

stream. The role of the catalyst is to increase the oxidation rate without itself being consumed in 

the process. The catalyst also substantially reduces the temperature needed for oxidation of the CO 

and HCs. Catalysts are characterized by their activity and selectivity. Both characteristics are 

influenced by temperature. DOCs reduce DPM emissions by oxidizing some of the less volatile HCs 

that contribute to the SOF of the PM mass or become bound to the soot particles by adsorption. On 

the other hand, DOCs have no effect on the solid core carbon particles (soot) that also make up 

DPM. The efficiency of a DOC can be reduced by catalyst poisoning or excessive accumulation of 

the DPM on the catalyst’s surfaces. A catalyst can be poisoned by fuel sulfur and compounds from 

lubrication oils. 

Some other gaseous components of diesel exhaust are not fully oxidized and thus are also 

candidates for oxidation by the DOC. NO and SO2 are of particular concern. Nitrogen and oxygen 

(air) spontaneously combine at high combustion temperatures to form mostly NO and a little NO2. 

SO2 is produced by oxidation of the sulfur in the fuel during combustion. Further oxidation of NO 

and SO2 takes place in the DOC at high exhaust temperatures to produce sulfate and NO2. The 

unfavorable gaseous phase reactions taking place in the DOC are NO 6 NO2 and SO2 6 SO3. These 

reactions increase the toxicity of the emitted exhaust. NO, with a TLV of 25 ppm and a 

toxicological behavior similar to that of CO, is converted to the acid gas NO2, which has a ceiling 

of 5 ppm and attacks the mucous membranes, increasing the likelihood of infection and causing 

long-term effects from constant irritation as well. The impact of an increase in NO2 emissions on 

local workplace concentrations depends on the distance from the tailpipe and whether there is a 

mechanism for adsorption of NO2 (such as the rock dust and wet walls in coal mines). SO2 is also 

converted to SO3, which further combines with water to form sulfuric acid aerosols. The TLV for 

sulfuric acid is 2.5 mg/m3

. It is important in the purchase of DOC to specify that it is for diesel use, 

the fuel sulfur level, and that NO conversion should be specified if not controlled. 

Performance of a DOC is a function of the fuel composition and exhaust temperature. When 

standard, low-sulfur, Federal diesel No. 2 fuel (D2) containing an average of 340 ppm by weight of 

sulfur is used, the exhaust exiting the DOC may contain elevated concentrations of sulfuric acid and 

sulfate aerosol. Researchers [Mayer 1997; Klein et al. 1998; Carder 1999] observed substantial 

increases in particulate mass and particle number in exhausts treated with DOCs. They noticed that, 

depending on the concentration of sulfur in the fuel and the exhaust temperature, DOCs may 
24 

enhance the emission of sulfate aerosols. The increase in PM mass and number was, however, more 

pronounced for those engine operating conditions that generate high temperature exhaust and thus 

provide favorable conditions for sulfate formation. Therefore, the sulfur content of diesel fuel is 

critical in the design and application of catalyst technology. The use of ULSFs (<50 ppm by weight) 

results in substantial reduction in sulfate formation and TPM emissions. The use of low-sulfur fuel 

also reduces the risk of poisoning a catalyst. Since a catalyst is more efficient at high temperatures, 

a DOCC needs to be positioned close to the engine. A heat retention blanket should be used in the 

case of longer exhaust runs to maintain exhaust temperature. 

The science of formulating exhaust catalysts involves numerous factors, including selection 

of metal or metal combinations, supporting structure, interactions with stabilizers and promoters, 

and heat treatments. Catalyst formulations are usually proprietary. DOCCs presently in use mostly 

appear as two forms of cellular monoliths [DieselNet 1998a] that have replaced the pelletized forms. 

Figures 1 and 2 illustrate the differences between ceramic monolith [DieselNet 1997a] and the 

metallic monolith [DieselNet 1997b] design. Both are characterized by a high substrate area-tovolume ratio. They are usually enclosed in a stainless steel container adapted to fit the exhaust 

system. The size of the DOCC needs to be optimized with respect to engine size. The volume of 

the DOCC should be approximately equal to engine displacement [MECA 1999a]. 

DOCCs are extensively used for on- and off-road applications. They are also used by 

underground mine operators as an emission control device to reduce odor, HC, and CO emissions 

from diesel equipment [McClure et al. 1988]. Mayer [1997] has suggested that the positive effects 

of using DOCCs are irrelevant to construction site diesel engines used in tunnels. Therefore, 

a DOCC should not be deployed for utility vehicle diesel engines in an underground environment 

because the negative effects far outweigh the benefits. However, if and when ULSF (<50 ppm by 

weight) or sulfur-free fuel is available and used, DOCs with formulations that minimize the 

formation of NO2 can be used to achieve significant reductions in CO and HCs (and thus DPM and 

odors). 

Catalyst substrates are designed to last the entire lifespan of the engine. The substrates can 

stand harsh operating conditions and offer good thermal durability. The major reason for DOCC 

failure is deactivation of the catalyst. Catalysts can be deactivated by high temperatures (>650 °C) 

and poisoned by lubricating oil additives (phosphorus, zinc, heavy metals) and fuel sulfur [DieselNet 

1998c]. Leaks of lubricating oil into the exhaust system are very detrimental to catalyst life. 

Heywood [1988] and the more current “Technology Guide” at www.DieselNet.com/tg.html provide 

good reviews of DOC and DOCC technology. 

Figure 1.—Monolithic catalyst substrates. Figure 2.—Catalyst washcoat. 

2.4.1.1 Review of Published Results 
25 

Because catalyst formulations can be varied to accommodate various objectives and fuel 

sulfur levels, the performances reported must be carefully scrutinized. Early studies such as 

McClure et al. [1988], which investigated the effectiveness of DOCCs used in an underground 

mine, found that although DOCCs are effective at reducing CO, HC, and odors when the exhaust 

temperature remains >250 °C, they increased NOx emissions slightly. Sulfate emissions were found 

to increase, but the fuel sulfur level was >1,000 ppm, whereas fuel sulfur levels for fuel currently 

available in the United States averages 350 ppm. 

Pataky et al. [1994] investigated the effects of a DOCC on regulated and unregulated 

emissions from a 1991 prototype Cummins L10-310 diesel engine fueled with 100 ppm by weight 

sulfur fuel. The DOCC with metallic substrate and Pt coating was supplied by the Degussa Corp. 

Pataky et al. reported that the DOCC had no significant effect on NOx and NO at any test mode. The 

DOCC reduced HC emissions by 60% to 70% and TPM by 27% to 54%, primarily as a result of a 

53% to 71% reduction of the SOF. The DOCC increased SO =

4 at the higher temperature modes, 

but had no effects at the lowest temperature mode. 

DOCCs were used in the DEEP biodiesel study [Watts et al. 1995; Bagley and Gratz 1998]. 

Tailpipe emissions under torque converter loading showed 98% to 99% reduction in CO, but an 

increase of NO2 by 185% with the standard low-sulfur D2 fuel and 233% with the 55.6% blend of 

biodiesel and the standard fuel. This study also included 1 day of running without a DOCC 

(compared to 4 days of testing each on the blend and straight D2). Without the DOCC, CO was 

significantly greater than CO with the DOCC; the NO2 was about one-third of the value with 

the DOCC. 

Carder [1999] reported that the tested DOCC reduced HC and CO by an average of 72% and 

93%, respectively, while NOx emissions were not significantly affected. Interestingly, the exhaust 

treated in the DOCC contained on average 66% higher DPM. The substantial increase in DPM 

emissions was attributed to sulfate formation. 

Six different DOC formulations were tested on a Detroit Diesel Series 60 engine by MECA 

[1999a]: two of low-activity, two of medium-activity, and two of high-activity. The fuel sulfur 

level was 368 ppm for the baseline. MECA researchers found that an optimized catalyst system can 

achieve emission reductions of >35% for PM and 70% for HC and CO. Gaseous emission 

reductions of HC and CO were found to be directly related to catalyst activity. The researchers 

found that DOCs are extremely effective at reducing PAHs and other HC emissions. They also 

found that a DOC can be used in conjunction with an FBC to offset increased PM emissions 

resulting from the use of EGR. 

In conclusion, DOCCs are formulated specifically for diesel engine use and to balance the 

beneficial reductions of CO and HC with the increase in NO2 and sulfates. Use of ULSFs allows 

catalyst formulations that are more effective in reducing CO and HC without the penalty of sulfate 

(counted as DPM mass) formation. Conversion of NO to NO2 may be an issue. 
 

26 

2.4.2 Diesel Particulate Filters (DPFs) 

DPFs were found to be technically feasible, controllable in the field, and a cost-effective 

technology for controlling DPM in European tunneling work [Mayer 1997] and Canadian 

underground metal mines [McGinn 2001a]. Two performance aspects of DPFs are crucial: 

the filtration efficiency of the system and the ability of the system to regenerate and provide longterm operation without diminishing the filtration efficiency of the filter and performance of the 

engine. The design and performance of DPF systems strongly depend on the vehicle/engine duty 

cycle, and the systems require optimization for specific applications. Vehicle/engine type and 

operating conditions must be recognized before the design and optimization process. 

2.4.2.1 Particulate Filter Design 

Filter Media 

Filters control DPM emissions by physically trapping soot particles in their structure. Major 

designs of particulate filters on the market are based on media such as porous cordierite and silicon 

carbide (SiC) wall-flow monoliths and on deep-bed fiber filters constructed from matted, woven, 

or knitted glass or ceramic fibers. Wire mesh, nonwoven SiC ceramic fiber, and sintered metal 

substrates are some of the alternative substrates still under scrutiny by researchers. Filter media can 

be catalyzed to enhance filtration efficiency and removal of some gaseous compounds and to lower 

the regeneration temperature. 

Wall-flow monoliths, namely the cordierite filters from Corning, Inc., and NGK Insulators 

Ltd., are the best known and have the longest history of use (since the early 1980s) among all 

available materials (figure 3). Exhaust flows through the porous ceramic walls (wall flow), and 

DPM is collected on the upstream side of the walls, as shown in figure 4. The surface of the 

upstream wall may also contain a catalytic washcoat to help lower the autoregeneration temperature. 

Corning’s EX-80 is currently the most popular wall-flow monolith material. Recently, Corning 

developed a new material (DuraTrap RC) with larger filtration areas and better thermal and 

mechanical properties [Corning, Inc. 2000]. 

Figure 3.—Example of a 

ceramic monolith filter element. 

Figure 4.—Gas flow in a monolith, wall-flow filter. (Photograph courtesy of Corning Incorporated.) 
 

27 

In recent years, SiC materials (Ibiden Co. Ltd., NGK, NoTox A/S) has been successfully 

established as a viable alternative to cordierite. SiC has lower thermal shock resistance, but its 

higher melting temperature makes it more durable over cordierite substrates during uncontrolled 

regeneration. SiC filters also have higher porosity than cordierite, which results in less back 

pressure. SiC filters are generally more expensive than equivalent filters made of cordierite. 

Fiber filters are classified as deep-bed or depth filters because the particles are trapped deep 

within and onto the filter fibers directly, as shown in figure 5. The filter material is supported 

between two long, narrow concentric cylindrical grids or mesh to form a thick-walled tube. The 

exhaust flows through the walls of the tube, and several of these tubes are assembled to form a filter 

(figure 6). The fiber surfaces of these filters may also be catalyzed. 

Mayer et al. [1995] found that the ceramic monolith surface filter and the deep-bed filter of 

knitted fibers have distinctively different properties. When evaluated on a gravimetric basis, both 

systems showed comparable efficiencies of around 90%. When evaluated on a particle-count basis, 

the efficiency of the surface filter was <70%, while that of the deep-bed filter was >90%. The 

efficiency of the surface filters was found to deteriorate for particles <100 nm, falling practically to 

zero for the 30-nm-diam particles. The efficiency of the surface filter increased with loading 

(formation of the filter cake), and there was a simultaneous progressive increase in back pressure. 

The filtration efficiency of knitted fiber filters was found to be highest in the new state, but 

deteriorated slightly with increased loading. 

The efficiency of a DPF in the removal of CO, HCs, and the OC fraction of DPM from the 

exhaust stream can be enhanced by adding an oxidation catalyst to the filter material. In addition, 

a catalyst lowers the ignition temperature for initiating the autoregeneration process. DPFs can be 

catalyzed by a washcoat or by deposition of catalytic material from an FBC. The formulation and 

quantity of a catalyst need to be designed and optimized for a particular application, specific to the 

exhaust temperature of the engine considered, the engine duty cycle, and the formulation of the fuel. 

Armed with these parameters, the DPF manufacturer can specify the appropriate catalyst technology 

or recommend other means to accomplish DPF regeneration. An excess of catalyst in a system may 

result in increased emissions of sulfates or NO2 and increased toxicity of the exhaust. An 

insufficient amount of catalyst in a system may result in reduced efficiency of the system and/or the 

inability of the system to regenerate under the duty cycle. Properly optimized amounts of a catalytic 

coating and FBC allow for the use of Federal diesel No. 2 fuel with its specified maximum of 

500-ppm sulfur. 

Figure 5.—Knitted microfiber filter 

(deep-bed filter). 

Figure 6.—Example of a particulate filter system 

using fiber media. 
28 

DPF size depends on the size of the engine, the engine-out DPM emissions level, and the 

regeneration technique used. When systems are not capable of autoregeneration, filters are 

significantly larger to accommodate soot collected during relatively long periods of operation 

without imposing excessive exhaust back pressures. 

Installations of a DPF system require instrumentation for monitoring the exhaust gas back 

pressure. A gauge indicating exhaust back pressure as well as a visual and audible alarm should be 

installed on the dashboard of a vehicle where the driver can observe it to ensure that the back 

pressure remains under limits recommended by the engine manufacturer (usually between 100 and 

200 mbar). Thus, the driver can take corrective action if the back pressure exceeds recommended 

limits. Postnikoff [1999] found that the back pressure gauge, more specifically the tube from the 

exhaust pipe to the gauge, is the weakest component of a DPF system. This tube may become 

clogged with soot during use and needs to be cleaned periodically using compressed air. 

Maintenance of an autoregenerating DPF consists of, at most, removing it from the vehicle 

and cleaning accumulated ash from it. The need for these actions can be detected by an increase in 

baseline back pressure. The need for cleaning usually occurs at 2,000 hr or more depending on the 

FBC dosing and amount of lubrication oil ash. This period can be extended by using lubrication oils 

with low ash content and, when needed, fuel catalysts that require low dose rates. Additional efforts 

are needed to support filters that require off-shift regeneration. In addition to routine (monthly) 

maintenance checks on vehicle emissions is the need to measure the exhaust DPM to verify 

performance. According to the experiences of manufacturers, researchers, and operators, DPF 

systems do not seem to cause any additional engine wear or otherwise affect vehicle maintenance. 

Approximately 1,600 knitted glass fiber DPFs manufactured by Oberland Mangold GmbH 

have been deployed on different diesel engines, mostly in tunneling and mining [Kahlert 1999]. The 

exhaust temperatures are high enough to cause the collected PM to be removed by oxidation 

sometimes with the assistance of an FBC. Some of the Oberland Mangold systems have achieved 

over 8,000 hr of operation without failure or loss of efficiency. Postnikoff [1999] reported that a 

typical service life for a ceramic DPF deployed on vehicles in Agrium, Inc., potash mines is 5 years 

under severe service. Significantly, the author also reported that a few of the Engelhard Corp. units 

(ceramic DPF) presently have 10 years of service. Early on, premature failures of the ceramic DPF 

also occurred and were attributed to extreme vibrations and shock or improper canning. 

Regeneration Methods for Particulate Filters 

The soot collected by DPFs needs to be removed to avoid excessive fuel penalty and damage 

to the engine and the filter. The removal of the soot, termed “regeneration,” is a rather complex 

process. Many process parameters must coincide to ensure regeneration that does not harm the 

filter. The governing parameters are exhaust gas temperature, exhaust gas back pressure, the 

remaining oxygen content in the exhaust gas, volumetric flow rate, etc. When the temperature in 

a DPF exceeds the required soot ignition temperature, the DPM burns and the back pressure 

decreases. 

Depending on the exhaust temperatures, DPF systems are designed to regenerate on-board 

the vehicle during on-shift use, or either on-board or off-board while the vehicle is off-shift. 

Regeneration must occur at intervals that are frequent enough to ensure that the filters do not 

become overloaded. The concept of on-board, on-shift regeneration was found to be superior to 

off-shift regeneration due to significantly lower operating costs. Most importantly, on-shift in-line 
29 

regeneration systems offer unrestricted vehicle operation during the regeneration process and are 

thus favored by vehicle/engine operators. 

The temperatures at which DPM burning occurs are generally higher than the exhaust 

temperatures commonly achieved by modern engines. Tests by Bach et al. [1998] showed that 

uncatalyzed filters spontaneously regenerate at 550 °C to 650 °C. However, the exhaust 

temperatures in most heavy-duty diesel applications do not exceed 450 °C. Modern turbocharged 

diesel engines at low loads run at even lower exhaust gas temperatures, very often <200 °C 

[Bach et al. 1998]. 

A number of techniques have been developed for active and passive on-board regeneration 

of filters during continuous operation of a vehicle. The passive approach requires that vehicles 

operate at high part-loads or at full loads for at least 20% to 25% of the time with idling periods 

minimized. The deployment of particulate filters relying on passive regeneration is not 

recommended if the engine/vehicle is operating exclusively at low to medium part-load. 

The active regeneration approach allows more flexibility regarding engine operating 

conditions, but requires a source of energy for the heaters. Thus, it is imperative when considering 

using a DPF to obtain a temperature-time profile of the exhaust temperature for the vehicle to be 

equipped with the DPF. Armed with the temperature profile, the DPF manufacturer can specify the 

appropriate catalyst technology or recommend other means to accomplish DPF regeneration. 

Field data indicate that mine vehicles, depending on the type of operation, spend a significant 

percentage of time at engine operating conditions that do not favor passive regeneration. Data 

obtained from the engine control management system of trucks at Noranda, Inc.’s Brunswick Mine 

[McGinn 2001b] show that those vehicles average over 30% of the time at low idle. 

During continuous regeneration, the average rate of PM mass accumulation and the average 

rate of removal are in balance. At low exhaust temperatures, mass accumulates until the rate of 

accumulation equals the rate of removal by burning and an equilibrium loading and back pressure 

are reached. At these conditions, the engine back pressure should remain within acceptable limits. 

If regeneration does not occur frequently enough, a DPF may become overloaded with DPM. 

Excessive accumulation of DPM may result in uncontrolled regeneration. During uncontrolled 

regeneration DPM burns too quickly; this results in extremely high temperatures and CO emissions. 

Regeneration can cause high thermal stresses in the filter, which leads to cracks in the material. In 

addition, at high regeneration temperatures, chemical reactions can occur when fuel additives are 

present. This might result in changing the crystal structure, strength, and filtration properties of the 

ceramic filter. 

Passive regeneration of a filter is promoted by use of catalytic coatings and/or FBCs. Base 

metals (Fe, Sr), precious metals (Pt), and rare earths (Ce) have roles in reducing the ignition 

temperature necessary for oxidation of the PM. To obtain continuous regeneration, a DPF needs to 

reach the regeneration temperature frequently during a vehicle/engine duty cycle. The dosage of 

the coating and FBC needs to be optimized with respect to vehicle/engine operating conditions and 

fuel type used. In experiments, unsuccessful coatings on filters were found to reduce particle 

collection efficiency and reduce aerodynamic regeneration effectiveness of DPFs [Larsen et al. 

1999]. Excess catalyst may also result in increased emissions of sulfuric acid [Carder 1999] and 

NO2. 

Some of the engines deployed in underground mines are not candidates for passive, catalytic, 

on-board regeneration. Postnikoff [1999] found that most of the medium-duty outby vehicles in the 

Agrium potash mines do not work hard enough to meet the minimum 350 °C required for 
30 

deployment of catalyzed ceramic DPFs. Active regeneration techniques are the only option for 

continuous on-board regeneration when an engine/vehicle operates exclusively or mostly at low to 

medium part-load and thus exhaust temperatures are too low for obtaining passive regeneration. In 

active regeneration methods, the exhaust gas, and thus the filter, is heated to the necessary oxidation 

temperature by an external energy source. Under such a system, the filter collects the particulate 

contained in the exhaust gas during the so-called loading phase. The particulate load is burned 

intermittently, during the regeneration phase, when the entire exhaust gas is heated up to a 

temperature level such that the accumulated PM will begin burning. 

Electric heaters (DCL, Engelhard, ECS, etc.) and diesel fuel burners (Deutz) are some 

of the most common techniques used for active regeneration. Diesel fuel burner technology is 

well established and safe for DPF regeneration and is primarily designed for city bus application. 

This technology is well established in Europe, but Deutz, so far, has not introduced this technology 

to the North American market. The regeneration process for such a system takes approximately 

10 min [Houben et al. 1994]. Required control and regulation instrumentation results in substantial 

initial costs. In addition, a moderate fuel penalty is associated with the fuel burner system. 

Necessary regeneration temperatures can also be obtained by heating the exhaust gas or the 

trap material by means of electrical heaters. Due to high energy requirements, electrical heating has 

mostly been used for stationary regeneration of DPFs. However, some engine and aftertreatment 

equipment manufacturers are developing alternative techniques for heating traps, such as microwave 

technology [Popuri et al. 1999]. These active trap regeneration systems are generally expensive and 

energy-intensive. Therefore, manufacturers are working on solving these issues that currently are 

substantially limiting the scope of the application of such systems. 

Passive and active technologies can be combined to enable trap regeneration to take place 

at low exhaust gas temperatures, which reduces demand for external energy and lowers the cost for 

the active components of the system. Bach et al. [1998] tested a particulate trap regeneration system 

that combined the advantages of an FBC (in this case Ce) and additional electric heating. Bach et al. 

found that trap regeneration can take place at low exhaust gas temperatures of about 270 °C. The 

consumption of electrical energy was significantly reduced due to the catalytic action of the additive. 

The alternative to on-board regeneration during operation is to perform either an on-board 

or off-board regeneration while the vehicle is off-shift. On-board regeneration is usually performed 

by means of electrical heaters integral to the DPF and an off-board control unit. Off-board 

regeneration requires removal of the DPF and replacing it with a regenerated unit. The soot-laden 

filter is placed in a kiln where it is heated under controlled conditions. Either of these two 

regeneration procedures must usually be performed after every shift; thus, a vehicle is immobilized 

during regeneration. Manufacturers are working on shortening the time necessary for the 

regeneration process. Unikat AB has developed a system that can be regenerated in as little as 

30 min [Unikat AB 1999]. According to the manufacturer, the off-board regeneration of the 

Engelhard SPX soot filter requires only 14 min [Engelhard Corp. 1999]. A DCL filtration system 

retrofitted to a load-haul-dump vehicle at Noranda’s Brunswick Mine uses an onboard electrical 

heating system as a backup system in cases when the filter does not passively regenerate. The filter 

system must be connected to the regeneration station for approximately 2 hr to achieve complete 

regeneration [McGinn 2001a]. An ECS Omega diesel particulate system installed on a light-duty 

tractor at INCO’s Stobie Mine required <10 min at the regeneration station after each shift 

[Nault 2001]. 
31 

All filters, whether passively or actively regenerated, must, after a certain number of hours 

in operation, be cleaned from the accumulated ash. The accumulated ash results in a gradual 

increase in exhaust back pressure of the regenerated filter. The exhaust back pressure should be 

regularly monitored, and the filter should be cleaned before back pressure jeopardizes engine or 

filter performance. The rate of ash accumulation is a function of several factors, including engine 

condition, primary oil consumption, formulation of oil and fuel, and use of fuel additives containing 

metals. Due to complexity and requirement for specialized equipment, this cleaning procedure is 

usually performed by the filter manufacturer. 

2.4.2.2 Review of Published Results 

Baz-Dresch et al. [1993] tested an uncatalyzed Corning EX-66 cordierite filter (the 

advertized collection efficiency of the uncatalyzed trap was 65% to 70%). Testing was conducted 

on a Caterpillar 3304 engine, designed for mining applications. The engine was tested under six of 

the ISO 8178 C1 eight-mode, steady-state operating conditions (I50, I75, I100, R50, R75, R100). 

The engine was fueled with low-sulfur fuel. Baz-Dresch et al. found that the regeneration 

temperature increased from 405 °C measured after 839 hr of operation to 450 °C measured after 

2,881 hr of operation. Gaseous and DPM emission measurements indicated deterioration of the 

filter medium over time. Below are the reduction efficiencies obtained after 839, 1,584, and 2,881 

operating hr; the ranges result from different behaviors at different engine modes (and exhaust 

temperatures): 

Reduction efficiencies 

Operating hours 

839 hr 1,584 hr 2,881 hr 

CO, ppm 21.3% to 64.8% 14.3% to 57.5% 2.9% to 42.1% 

HC, ppm 5.4% to 89.7% 23.1% to 76.5% 39.4% to 83.2% 

DPM (mg/m3

) 48.1% to 94.5% 41.2% to 81.9% 28.5% to 82.2% 

Baz-Dresch et al. [1993] speculated that damage to the DPF occurred because of mechanical 

shocks and vibration, cracking or melting of the ceramic due to uncontrolled regeneration, or a 

cracked substrate that resulted from high thermal gradients during repeated regeneration. 

The U.S. Bureau of Mines conducted a study to evaluate the performance of a CDPF alone 

and combined with a DOC at two metal mines (Q and T) and under laboratory conditions [Watts et 

al. 1995]. The tested DPF was a ceramic monolith. Three methods were used to measure DPM and 

respirable dust concentrations in the two mines: personal diesel exhaust aerosol sampler (PDEAS), 

micro-orifice uniform-deposit impactor (MOUDI), and RCD sampler. The mean DPM reduction 

efficiency per unit production for the DOC + CDPF system, installed on a Caterpillar 3306 engine, 

was 71 ± 29% for mine Q. The efficiency of the CDPF was estimated to be 72 ± 21% (PDEAS) or 

62 ± 25% (RCD) for mine T. 
32 

Mayer [1997] reported 80% to 85% efficiency for a DPF tested in a study by VERT 

(Verminderung der Emissionen von Realmaschinen im Tunnelbau). This efficiency was assessed 

on the basis of “pure” gravimetric PM evaluation. The particulate count reductions were reported 

to be >90%. The filtration efficiencies for soot were >90%, and the filtration rate for nanoparticles 

>99%. From extensive testing, Mayer concluded that the DPF using a monolithic element was very 

efficient at filtering large diesel exhaust particles. However, for this and other DPFs using different 

filtration media, massive breakthrough of the smallest sized diesel particles—the nanoparticles— 

was found. This was also observed in DPFs using sintered metal filters. However, for the DPF 

using the fiber element, the deep-bed filters, the efficiency increased with a decrease in particle size. 

Mayer concluded that catalyzed diesel particulate traps are extremely efficient and state-of-the-art. 

MECA [1999a] found that a DPF, when used with 54-ppm (instead of 368-ppm) sulfur fuel, 

reduced PM, HC, and CO emissions from a Detroit Diesel Corp. (DDC) Series 60 engine exercised 

over the U.S. heavy-duty transient FTP cycle by 70%, 94%, and 63%, respectively. When the DPF 

was used with FBCs, the PM emissions were reduced by 78%. MECA concluded that the PM 

emission levels of 0.005 g/bhp-hr were achievable by using a DPF with a zero-sulfur fuel. 

Larsen et al. [1999] tested three different types of particulate traps: a Corning EX-66 

cordierite substrate coated with a micromembrane by CeraMem Corp., an Ibiden SiC material, and 

an Ibiden SiC substrate coated with a ceramic micromembrane. All of the filters achieved >93% 

total filtration efficiencies (by mass); the regular SiC filter reached levels of 97%. For the small 

particles, the uncoated SiC trap performed the best; it reduced the DPM by a factor of 99%. 

Carder [1999] reported results of testing a Caterpillar 3306 engine retrofitted with a CDPF 

designed for that particular engine by Clean Air System. The overall weighted ISO 8178 eightmode average DPM reduction of the system was 72%. The average reductions in HC, CO, and CO2 

were 88%, 83%, and 21%, respectively. Oxides of nitrogen were not substantially reduced. 

The DETR/SMMT/CONCAWE Particulate Research Programme [Andersson and Wedekind 

2001] has investigated the effects of engine technologies and fuel specifications on regulated PM, 

particle number, mass, and size. The largest effects of a single technology on particles was observed 

with DPFs (oxidation catalyst followed by a DPF), where particle mass and number were reduced 

by several orders of magnitude. The exception was at high exhaust temperature conditions, where 

significant numbers of nucleation mode particles were emitted after the DPF. The filter reduced 

integrated particle mass emissions by about 90%. Filter effects dominated within the accumulation 

mode (particles sizes between 0.08 and 1 μm). 

The harsh environment makes deployment of filters on diesel-powered underground mining 

equipment a challenging task. So far, limited data are available in the literature on the performance 

of DPFs deployed on underground mining production equipment. One of the valuable sources of 

such data is the trap evaluation studies at Noranda’s Brunswick Mine and INCO’s Stobie Mine. 

These studies, sponsored by DEEP, have the evaluation of the different DPFs deployed on heavyand light-duty production vehicles as the long-term goal. The preliminary results of those studies 

were presented at the Mining Diesel Emissions Conference (MDEC 2001). 
33 

2.4.3 DOCC and DPF Combinations 

Systems incorporating a DOCC and DPF are commercially available; such systems have 

been tested by several researchers. The combined systems incorporating both a DOCC and DPF 

were designed to provide good reductions of gaseous and PM emissions. 

The CRT developed by HJS and Johnson Matthey is an example of such a system. The CRT 

system consists of an extremely active DOCC followed by a DPF. CO and HC are almost 

completely oxidized to CO2 and water. The catalyst was formulated so that it also oxidizes a 

substantial portion of the NO to NO2. The NO2 generated oxidizes the carbon in the particulate trap, 

thus performing regeneration at low exhaust temperatures. Trap regeneration occurs at temperatures 

between 200 °C and 450 °C, low enough to result in almost continuous regeneration. An advantage 

of continuous regeneration is that the local peak thermal stresses can be avoided. Unfortunately, 

substantial amounts of NO2 are not utilized and pass through the DPF (NO2 slip). Three key 

requirements for the system to perform properly are reasonable balance between NOx and particulate 

emissions, a duty cycle that regularly gives rise to exhaust gas temperatures >260 °C, and the use 

of ULSF. 

CRT systems have been successfully applied for curtailing DPM emissions from city buses. 

Czerwinski et al. [1998] tested an HJS-CRT system on a Liebherr D914T construction engine as part 

of the VERT suitability project. They reported very good filtration efficiency of the system at all 

test conditions and recommended the system to the users. The average reductions over the ISO 8178 

eight-mode test were about 85% for PM, 94% for CO, 39% for HC, and 21% for NOx. Despite 

decreases in NOx concentrations, the concentration of NO2 increased when the exhaust was treated 

in the CRT system. This increase in NO2 has caused a reluctance on the part of the manufacturer 

to offer systems for use in underground tunneling and mining operations. (This was, in fact, the 

reason given for their declining to bid on a DEEP DPF evaluation project [Schnakenberg 1999b]). 

2.4.3.1 Review of Published Results 

Czerwinski et al. [1998] tested a HJS-CRT system on a Liebherr D914T construction engine. 

The HJS-CRT system consists of a ceramic monolith oxidation catalyst in line with a ceramic 

monolith particulate trap. The engine was fueled by Swiss standard diesel fuel (sulfur 500 ppm, 

cetane number 48) and Greenenergy ULSF (sulfur 25 ppm, cetane number 50). The engine 

operating conditions were: rated speed, 100% load (R100); intermediate speed, 100% load (I100); 

R50, I50, I25, I10, as defined in ISO 8178 [30 CFR 7 (1996)]. The evaluation was performed on 

the basis of measurements taken by an SMPS, PAS, and ELPI and by gravimetric and coulometric 

(reports EC) analysis. The observed average filtration efficiency was 85%. The count of 

nanoparticulates was also reported to be reduced efficiently. The HJS-CRT system also reduced 

concentrations of CO, HC, and NOx by 93%, 35%, and 21%, respectively. An increase in NO2 

concentration of in the exhaust treated in the system was also reported. 

Kauffeldt and Schmidt-Ott [1998] tested a passenger car with a particulate trap and a truck 

powered by a diesel engine and equipped with an oxidation catalytic converter and a particulate trap. 

The type of filter medium, catalyst, and fuel used were not reported. Treatment of the passenger car 

exhaust gas in the particulate trap resulted in a large reduction of particulate mass and a significant 

increase in the number concentration of ultrafine particles. Small particles were found to be droplets 

of HC. 
34 

Carder [1999] tested a Rohmac-DCL system consisting of a monolith oxidation catalyst in 

line with a ceramic monolith particulate trap. The system was installed on an Isuzu C240 engine. 

The filtration system was designed for underground coal mine applications with the catalyst 

formulation selected to enhance regeneration. The formulation was not optimized for control of 

sulfate production. Diesel fuel sulfur content was 400 ppm (by weight). The weighted ISO 8178, 

eight-mode average DPM reduction for the system with the particulate trap placed downstream of 

the oxidation catalyst was reported to be 67.7%. The DPM reduction for the particulate trap with 

an oxidation catalyst installed upstream of it ranged from 40% to 99%, with an average of 78%. 

Therefore, the position of the trap and the DOC was found to have little effect on DPM emissions. 

The particulate trap with a downstream oxidation catalyst system also reduced HC and CO, 

on average, by 79% and 95%, respectively. The system with the catalyst upstream of the trap 

reduced HC and CO, on average, by 87% and 94%, respectively. 

The Rohmac-DCL system was also tested on a Lister-Petter LPU-2 engine using the same 

fuel as in the work described above [Carder 1999]. The reductions in PM emissions of the trapcatalyst system were reported as 80% over modes 6 and 7. The average reductions of HC, CO, and 

NOx were found to be 97%, 90%, and 28%, respectively. MECA [1999a] found that when a DPF 

was used with an upstream NO-to-NO2 catalyst and low-sulfur fuel (54 ppm), reductions in PM, HC, 

and CO emissions were 87%, 95%, and 93%, respectively. 

Hansen et al. [2001] tested an in-use bus engine retrofitted with CRT system over 

13 stationary modes (13-mode test) using 45 to 49 ppm of sulfur fuel. They found that sulfate, 

formed from sulfur in the fuel, is stored in the catalytic washcoat in the CRT filter’s precatalyst at 

temperatures <380 °C and released again at temperatures >380 °C. The overall PM reduction 

efficiency of the tested CRT system measured over 13 modes was 55%. The system had a PM 

reduction efficiency >80% at the exhaust temperatures <375 °C. Hansen et al. found that sulfate, 

formed from sulfur in the fuel, is stored in the washcoat in the CRT filter precatalyst at temperatures 

<380 °C and released again at temperatures >380 °C. The analysis showed that sulfate and water 

constitute almost the entire particulate mass when the filter was used. In popular terms, the CRT 

filter just replaces carbon particles with sulfate particles. Hansen et al. concluded that reducing the 

sulfur content in the fuel cannot completely solve sulfate storage, but can prolong the time needed 

for the washcoat to become saturated with sulfur. They also concluded that even if ULSF is used, 

sulfur from the lubrication oil is sufficient to saturate the precatalyst. This is because 1% sulfur in 

the lubrication oil, which is not an unusual amount, corresponds to about 10-ppm sulfur in the fuel 

at normal rates of oil consumption. 

2.4.4 Disposable Diesel Exhaust Filter (DDEF) 

Disposable diesel exhaust filter (DDEF) systems are widely accepted by the underground 

coal mining industry [Ambs et al. 1994]. The DDEF system usually consists of a heat exchanger, 

filter element, filter housing, flame arrester, complete water jacketing to keep surface temperatures 

below MSHA requirements, exhaust temperature and exhaust back pressure monitor, and engine 

shutoff system. Heat exchangers are used to reduce the exhaust temperature to below 150 °C 

(dry exchangers) or 185 °C (water scrubber), one of several requirements for diesel equipment used 

in inby areas of underground coal mines [30 CFR 7 (1966)]. The reduced exhaust temperatures 

enable the use of disposable paper filters ($35 and $145). The filter elements presently used have 

a service life of about one to three shifts and cost from $35 to $145 depending on the system. 
35 

Since the maximum surface temperature of all surfaces of the permissible diesel engine and 

the diesel power package is limited by regulations to 150 °C (302 °F) [30 CFR 7 (1996)], exhaust 

system components of such a package are usually water-jacketed. Some efforts are now being made 

to replace bulky water-jacket systems with high-tech insulation materials. 

Water scrubbers and dry-heat exchanger systems are the most commonly used systems for 

reducing exhaust temperature. The water scrubber has the dual purpose of cooling the exhaust and 

quenching flames and sparks at an acceptable engine back pressure. However, the water scrubber 

has high maintenance requirements due to the need for replenishing the water in the scrubber every 

few hours and the corrosion caused by the conversion of the SO2 in the water box to sulfuric acid. 

Dry scrubber systems use a heat exchanger to reduce exhaust temperatures at the filter face. 

This technology with an incorporated DOC has demonstrated the capability to reduce DPM by 97% 

compared to the engine output, when tested under the ISO 8178, eight-mode protocol in the 

laboratory [Paas 1999]. 

The major drawbacks of DDEF systems are high initial costs and large dimensions. 

However, these paper filter systems are currently the only filtration systems available for inby diesel 

equipment in underground coal mines. 

2.4.4.1 Review of Published Results 

Ambs et al. [1994] conducted a study on the performance of DDEFs. The study was done 

on a Jeffrey 4114 Ramcar powered by an MWM D916-6 engine and equipped with a DDEF system 

and waterbath exhaust conditioner (water scrubber). Field evaluation results showed that the DDEF 

reduced diesel exhaust aerosol concentrations in the mine ambient air from 70% to 90%. Ambs 

et al. found that the usable life of the filter ranged from 10 to 32 hr depending on factors such as 

mine altitude, engine type, and duty cycle. 

Carder [1999] tested a Caterpillar 3306 engine retrofitted with a Dry System Technology 

(DST) dry scrubber system. The tests showed an 82% reduction in the averaged ISO 8178 eightmode PM mass emission rate, but the reduction was rather low (8%) under rated speed/maximum 

load conditions. This indicated a low efficiency of the paper filter at high filter face temperatures, 

resulting from inability of the heat exchanger to cool the exhaust sufficiently. 

3 Conclusions and Recommendations 

Table 6 illustrates potential reductions in diesel emissions achievable by various control 

technologies that can be applied to curtail diesel emissions from underground equipment. Caution 

should be exercised when interpreting the emission numbers given in the examples. The numbers 

are based on published results from tests on similar technologies, but performed with different 

engines and under a variety of test conditions. The references for the data can be found in the text 

describing the particular technology applied. Where numerical data were not available, the 

performance evaluation is descriptive and not quantitative. 

Extrapolation of these estimates to other applications (engines and/or duty cycles) is not 

exact. They should be considered as indicative of possible results and not necessarily as 

quantitatively accurate. The complexity of the problem requires a system to be designed and 

optimized for a particular application. Thus, the actual field performance of the combinations of the 

engines and control technologies may differ significantly from the estimates given in the table. 
36 

Selection of a particular technology is based on recognizing all of the peculiarities and interactions 

of the application. The choice is complex, based on engine operating conditions, reduction 

performance, and capital and operational costs. Further, present health concerns and worker 

exposure data indicate the need to focus on the reduction of PM emissions when choosing the 

appropriate technology. However, at the same time, the opportunity to reduce toxic gases should 

not be neglected. Fortunately, several combinations of technologies result in reductions of both PM 

and gases. 

The use of a CDPF in combination with an FBC if needed for regeneration (DPF + FBC) 

seems to be the most effective aftertreatment technology for reductions of DPM and gaseous 

emissions from the diesel exhaust. The continuous regeneration of the DPF can be achieved for 

vehicles that operate at medium and high loads for at least 20% to 25% of the time. DPF + FBC 

combinations were reported to have efficiencies as high as 95% in the removal of DPM in both field 

and laboratory conditions. The use of ULSF is not mandatory in such systems, but can further 

reduce DPM mass emission and nanoparticle concentrations by eliminating sulfate formation. 

DPFs were proven to be effective in removing ultrafine and nano-sized particles from the 

exhaust. When this combination is used with a new low-PM emitting engine, the resulting DPM 

emissions are further reduced in proportion to the ratio of the PM emissions (MSHA PI indices) of 

the two engines. Literature indicates that the potential of this latter combination is a reduction of 

DPM by 97%, resulting in an additional 40% lower workplace DPM concentration over the system 

that provides a 95% reduction. This combination (low-PI engine + DPF + FBC) provides good 

reductions of gaseous emissions as well. 

If the reduction of gaseous emissions is the primary target, any combination of technologies 

using a DOCC is the most effective. The use of ULSF is recommended to prevent increases in the 

emission of sulfate particles. Substantial PM reductions (50%) can be obtained by the use of a water 

emulsion of the ULSF. Alternatively or in addition, replacement of the (older) engine with a lowemission engine can further reduce PM emissions up to 80%. The combination of a DOCC, waterfuel emulsions, and ULSF with or without low-emission engines is not well explored in the 

literature. The authors would welcome the opportunity to verify this promising option. 
37 

Table 6.—Performance of the available control technologies 

TECHNOLOGY 

TOTAL DPM TOXIC GASES COMMENTS 

SOL SOF SULFATE CO NO2 HC 

New lowemission engine 

Unknown Unknown Not affected Unknown Unknown Unknown See table of MSHA-approved 

engines listed in table A-1. Extra initial capital cost may pay off in the long run in lower operating costs owing to fuel efficiency. 

Possibly >60% reduction based on MSHA 

certification testing, depending on engine 

The MSHA ventilation rates indicate a reduction or 

increase in the gaseous emissions 

DOC + diesel No. 2 

No reductions Up to 80% 

reduction 

Possible 

significant 

increase, 

function of 

exhaust 

temperature 

Reductions 

from 70% to 

93% 

Slight 

increase, 

strong 

function of 

exhaust 

temperature and catalyst 

formulation 

Reductions 

from 60% to 

75% 

Diesel No. 2 has <500 ppm sulfur by weight, average 350 ppm. Sulfate generation has detrimental effects. Ultralow sulfur is recommended to prevent sulfate formation. DOCs are relatively inexpensive. Depends on SOF levels and fuel sulfur level one can expect either reduction or increase in total 

DPM. 

DOC + ULSFs 

No reductions Reduction up 

to 80% 

Insignificant 

presence 

Same as DOC 

above 

Same as DOC 

above 

Same as DOC 

above 

ULSFs are defined as those with <50 ppm sulfur per weight. Relatively low additional fuel costs make the technology viable. On-highway availability by mid-2006. 

Reduction up to 35% 

NOTE: The effects on DPM emissions are reported on a mass basis, not a number basis. “Unknown” means that the authors have not found specific data for that diesel 

exhaust component, usually the SOL and SOF of the DPM. However, in all cases, the total effect on DPM is known. 
38 

TECHNOLOGY 

TOTAL DPM TOXIC GASES COMMENTS 

SOL SOF SULFATE CO NO2 HC 

Biodiesel 

Unknown Reduction up 

to 48% 

Not present Reductions up 

to 40% 

Significant 

increase, NOx 

up to 12% 

Significant 

reductions 

Biodiesel is oxygenated fuel that provides more complete combustion, generating less unburned HC and more NOx and 

NO2. Significant reductions in 

PAHs observed. Available torque is reduced up to 7%. Higher fuel consumption up to 13%. Available, but $2.60/gal. 

Reduction up to 50% 

Synthetic diesel (Fisher-Tropsch) 

Unknown Unknown Not present Reductions up 

to 33% 

Unknown, 

reductions in 

NOx up to 

27% 

Reductions up 

to 49% 

Significant reductions in PAHs. Small effects on available torque and fuel consumption. Industry is working on establishing economical production facilities. 

Reduction up to 21% 

Water-fuel emulsions 

Unknown Unknown Unknown Increase Unknown, 

reductions in 

NOx up to 

30% 

Increase Simultaneously reduces PM and 

NOx. Emulsion stability in 

storage, freezing, corrosion, and lubricity are concerns. Available and priced comparably to regular diesel fuel. 

Reduction up to 50% 
39 

TECHNOLOGY 

TOTAL DPM TOXIC GASES COMMENTS 

SOL SOF SULFATE CO NO2 HC 

Fuel-borne catalyst (FBC) 

Reduced Increased Not affected Not affected Not affected, 

reductions in 

NOx up to 

15% 

Not affected Fuel economy might improve by 

4.5%. Primary role of the FBC in mining is to lower DPF regeneration temperature. Because of significant emission of the nanoparticles, the FBC should not be used without DPF. 

Reductions up to 25% 

Particulate filters (DPFs) 

Unknown Unknown Not affected Not 

significantly 

affected 

Not 

significantly 

affected 

Not 

significantly 

affected 

High exhaust temperature required for autoregeneration can be reduced by catalysts. Slight increase in fuel consumption. 

Reductions from 80% to 95% 

DOC + DPF 

Up to 95% Up to 80% Slight increase Reductions up 

to 93% 

Slight to 

significant 

increase, 

strong 

function of 

exhaust 

temperature and catalyst 

formulation 

Reductions up 

to 97% 

The best reductions of DPM with DOC occurs with use of ULSF. 

Reductions up to 85% [Czerwinski et al. 1998] 
40 

TECHNOLOGY 

TOTAL DPM TOXIC GASES COMMENTS 

SOL SOF SULFATE CO NO2 HC 

CDPF 

Unknown Unknown Slight increase Reductions up 

to 63% 

Slight to 

significant 

increase 

Reductions up 

to 94% 

Depends on catalyst and temperatures, ignition temperatures around 450o C. 

Use of ULSF is recommended. Reductions up to 95% depending on sulfate 

CDPF + FBC 

Unknown Unknown Slight increase Reductions up 

to 63% 

Slight to 

significant 

increase 

Reductions up 

to 94% 

Ignition temperatures around 320o C. Fuel additive increases 

cost of fuel by up to 10 cents/gal. Reductions up to 95% depending on sulfate 

CDPF + ULSF + FBC 

Unknown Unknown Insignificant 

Presence 

Reductions up 

to 63% 

Slight to 

significant 

increase 

Reductions up 

to 94% 

Most effective retrofit technology. Ignition temperatures around 320o C. 

Fuel additive and lower sulfur increase cost of fuel by up to 20 cents/gal. 

Reductions up to 95% and no contribution from 

sulfates 

Low-emission engine + DOC + No. 2 diesel fuel (350 ppm S) 

Unknown Significant 

reductions 

Slight increase 

depending on 

DOC 

Significant 

reductions 

Slight to 

significant 

increase 

depending on 

DOC and 

engine 

Significant 

reductions 

Effective combination, yielding significant reductions in CO and HC (not NO2) and fairly good 

reductions in PM. However DOC produces some sulfates that diminish the PM reductions possible. 

Reductions up to 87% compared to old technology 

engine baseline 

(up to 80% from engine, 35% reduction from 

DOC, but diminished by sulfate content) 

Low-emission engine + DOC + ULSF 

Unknown Significant 

reductions 

Insignificant 

Presence 

Significant 

reductions 

Slight to 

significant 

increase 

Significant 

reductions 

Very effective combination, yielding significant reductions in CO and HC (not NO2) and 

fairly good reductions in PM. Reductions up to 87% compared to old technology engine baseline 

(up to 80% from engine, 35% from DOC + ULSF) 
41 

TECHNOLOGY 

TOTAL DPM TOXIC GASES COMMENTS 

SOL SOF SULFATE CO NO2 HC 

Low-emission engine + DOC + ULSF + water emulsion 

Unknown Significant 

reductions 

Insignificant 

presence 

Significant 

reductions 

Slight to 

significant 

increase 

Significant 

reductions 

Very effective combination yielding significant reductions in CO, HC, and NOx and good 

reductions in PM. Reductions up to 85% (estimate) 

Low-emission engine + CDPF + No. 2 diesel fuel (350 ppm S) + FBC 

Unknown Significant 

reductions 

Slight increase 

depending on 

DOC 

Moderate 

reductions 

Decrease 

reported, 

but increase 

possible 

Moderate 

reductions 

Excellent reduction in PM and good reduction in gaseous emissions. However, DOC produces some sulfates that diminish the PM reductions possible. 

Reductions up to 97%, but diminished by presence 

of sulfates 

Low-emission engine + CDPF + ULSF + FBC 

Unknown Significant 

reductions 

Insignificant 

presence 

Moderate 

reductions 

Decrease 

reported, 

but increase 

possible 

Moderate 

reductions 

The most effective combination results in excellent reduction in PM and good reduction in gaseous emissions. Reductions up to 97% 
42 

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48 

APPENDIX A.—LOW-PI MSHA-APPROVED ENGINES 

Table A-1 lists the MSHA-approved engines (as of January 2, 2001) for nonpermissible areas. 

Shaded entries indicate an engine with a significantly lower PI than those of comparable horsepower. 

Although in some cases an engine choice may not be physically possible, an engine with the lowest PI 

that meets the physical size and approximate horsepower for the application should be chosen. For 

example, one should consider the 28.2-hp Deutz F2L1011 (PI=1,000) over either the Lister-Petter, LPU3 

MKI (PI=7,000), LPU3 MKII (PI=4,500), or Deutz F2L1011F (PI=3,500). Similarly, the Deutz 

F4L1011 56.3 hp (PI=2,000) could replace the Isuzu C240 (PI=5,500). In the latter example, the 

tailpipe DPM is reduced by 64%. 

Table A-1.—List of MSHA-approved engines (as of December 2001) 

Approval 

No. Engine model hp @ rpm 

MSHA 

nameplate 

ventilation 

rate, cfm 

MSHA 

particulate 

index, cfm 

7E-B070-0 Farymann Diesel, 43F 14 @ 3,000 1,000 4,000 

7E-B042-0 Lister-Petter, LPU2 MKI1 17.5 @ 3,000 1,000 5,000 

7E-B053-0 Kubota, Model V1200 25.8 @ 3,000 1,000 1,500 

7E-B041-0 Lister-Petter, LPU3 MKI1 26.3 @ 3,000 1,500 7,000 

7E-B062-0 Deutz, F2L10111 28.2 @ 3,000 1,500 1,000 

7E-B044-0 Lister-Petter, LPU3 MKII 29 @ 3,000 1,500 4,500 

7E-B015-0 Deutz F2L 1011F 30 @ 3,000 2,000 3,500 

7E-B091-0 Deutz F2L1011F 30 @ 3,000 2,000 1,500 

7E-B074-0 Isuzu 3LD1MA 33.3 @ 3,000 2,000 3,500 

7E-B040-0 Lister-Petter, LPU4 MKI1 35 @ 3,000 2,000 9,500 

7E-B043-0 Lister-Petter, LPU4 MKII 38.6 @ 3,000 2,000 6,000 

7E-B026-0 Deutz, F3L912W (2.8L)1 40 @ 2,300 2,500 2,500 

7E-B076-0 Isuzu 4LC1MA 41 @ 3,000 2,000 4,500 

7E-B061-0 Deutz, F3L10111 41.6 @ 3,000 2,500 1,500 

7E-B033-0 Perkins, 104-19 42.5 @ 2,800 2,000 7,000 

7E-B014-0 Deutz F3L1011F 44 @ 3,000 2,500 5,000 

7E-B090-0 Deutz F3L1011F 44 @ 3,000 3,000 2,500 

7E-B054-0 Deutz, Model F3M1011F 46 @ 2,800 3,000 3,500 

7E-B031-0 Deutz, F3L912W (3.1L)2 47 @ 2,500 2,500 2,500 

7E-B071-0 Kubota Engine Corp., Model V2203-E 48.4 @ 2,800 2,500 2,000 

7E-B079-0 New Holland North America, 201, 3.3L NA 51 @ 2,200 4,500 8,500 

NOTE: Shaded entries indicate an engine with a significantly lower PI than those of comparable horsepower. 
49 

Approval 

No. Engine model hp @ rpm 

MSHA 

nameplate 

ventilation 

rate, cfm 

MSHA 

particulate 

index, cfm 

7E-B086-0 Isuzu C240MA 52 @ 3,000 3,000 2,500 

7E-B025-0 Deutz, F4L912W (3.8L)1 54 @ 2,300 3,000 3,500 

7E-B075-0 Isuzu 4LE1MA 54 @ 3,000 2,500 6,500 

7E-B085-0 Isuzu, C240MA 56 @ 3,000 2,500 5,500 

7E-B038-0 Isuzu, C240MA (QD60)1 56 @ 3,000 2,500 5,500 

7E-B060-0 Deutz, F4L10111 56.3 @ 3,000 3,000 2,000 

7E-B027-0 Perkins, 704-26 58 @ 2,600 2,000 8,000 

7E-B089-0 Deutz F4L1011F 59 @ 3,000 4,000 3,000 

7E-B013-0 Deutz F4L1011F 59 @ 3,000 3,500 6,500 

7E-B089-0 Deutz F4L1011F 59 @ 3,000 4,000 3,000 

7E-B077-0 Deutz BF3M1011F2 61 @ 2,800 5,500 5,500 

7E-B055-0 Deutz, Model F4M1011F 61 @ 2,800 3,500 4,500 

7E-B029-0 Deutz, F4L912W (4.1L)2 62 @ 2,500 3,000 3,500 

7E-B024-0 Deutz, F5L912W (4.7L)1 67 @ 2,300 4,000 4,500 

7E-B019-0 Deutz BF4L 1011F 74 @ 2,800 5,500 4,500 

7E-B030-0 Deutz, F5L912W (5.1L)2 76 @ 2,500 4,000 4,000 

7E-B006-0 Isuzu QD 100-3011,2 79 @ 2,800 5,000 8,500 

7E-B023-0 Deutz, F6L912W (5.6L)1 80 @ 2,300 4,500 5,000 

7E-B056-0 Deutz, BF4M1011F2 82 @ 2,800 5,500 5,500 

7E-B072-0 Detroit Diesel Series, Model DDC 

D704LTE 84 @ 2,600 6,500 7,000 

7E-B028-0 Deutz, F6L912W (6.1L)2 93 @ 2,500 4,500 5,000 

7E-B001-0 Deutz-MWM 916-61 94 @ 2,300 4,000 11,500 

7E-B004-0 Caterpillar 3304 PCNA1 100@ 2,200 5,000 15,000 

7E-B022-0 Perkins, 1004-40T2 108 @ 2,400 9,000 9,000 

7E-B064-0 Caterpillar, 3054 DIT2 108 @ 2,400 9,000 9,000 

7E-B011-0 Deutz BF4M1012C2 110 @ 2,500 6,500 4,000 

7E-B045-0 Isuzu, 4BGIT-MA 111 @ 2,400 7,000 13,000 

7E-B011-0 Deutz BF4M1012EC2 113 @ 2,500 6,500 4,000 

7E-B084-0 Cummins 4BTA3.9-C 116 @ 2,500 6,500 7,500 

7E-B088-0 Isuzu CBG1-MA1 116 @ 2,500 4,500 11,500 

7E-B020-0 Perkins, 1004-40TW 122 @ 2,300 10,000 7,500 

7E-B065-0 Caterpillar, 3054 DIT 122 @ 2,300 10,000 7,500 

7E-B073-0 Detroit Diesel Series, Model DDC 

D706LTE 123 @ 2,600 7,500 11,000 

7E-B059-0 Deutz, BF4M1013E 125 @ 2,300 11,500 4,500 

7E-B059-0 Deutz, BF4M1013 127 @ 2,300 11,500 4,500 
50 

Approval 

No. Engine model hp @ rpm 

MSHA 

nameplate 

ventilation 

rate, cfm 

MSHA 

particulate 

index, cfm 

7E-B046-0 Isuzu, 6BGI-MA 129 @ 2,500 6,000 16,000 

7E-B039-0 Isuzu, 6BD1MA (QD145)1 135 @ 2,800 9,000 12,000 

7E-B034-0 Deutz, F6L413FW 137 @ 2,300 8,000 7,000 

7E-B003-0 Caterpillar 3306 PCNA1 150 @ 2,200 7,500 23,000 

7E-B021-0 Perkins, 1006-60T 152 @ 2,200 13,000 12,000 

7E-B066-0 Caterpillar, 3056 DIT 152 @ 2,200 13,000 12,000 

7E-B008-0 Deutz BF4M1013C2 158 @ 2,300 8,500 7,500 

7E-B005-0 General Motors L57, 6.5L Hummer 160 @ 3,400 7,500 9,500 

7E-B052-1 Cummins Model B5.9,2

 without DOC 160 @ 2,500 11,500 5,000 

7E-B052-3 Cummins Model B5.9,2

 with DOC 160 @ 2,500 12,000 3,500 

7E-B052-2 Cummins Model B5.9,2

 without DOC 175 @ 2,500 11,500 5,000 

7E-B052-4 Cummins Model B5.9,2

 with DOC 175 @ 2,500 12,000 3,500 

7E-B052-5 Cummins Model B5.9,2

 with DOC 180 @ 2,500 12,000 3,500 

7E-B035-0 Deutz, F8L413FW 182 @ 2,300 10,500 9,500 

7E-B067-0 Navistar, A185, 

Model years 1988-1994 185 @ 3,300 8,500 15,000 

7E-B058-0 Deutz, BF6M1013E 189 @ 2,300 17,500 5,500 

7E-B058-0 Deutz, BF6M1013 194 @ 2,300 17,500 5,500 

7E-B016-0 General Motors, L65, 6.5L, TurboHummer 195 @ 3,400 9,500 24,000 

7E-B052-0 Cummins Model B5.92 215 @ 2,700 14,500 4,000 

7E-B052-6 Cummins, Model B5.9,2

 with DOC 215 @ 2,000 14,500 4,000 

7E-B068-0 Navistar, A215 and A225, Model years 

1994.5-1997 215 @ 3,000 18,000 11,000 

7E-B036-0 Deutz, F10L413FW 228 @ 2,300 13,500 12,000 

7E-B057-0 Deutz, BF6M1013EC 228 @ 2,300 16,000 8,500 

7E-B050-0 Detroit Diesel Series, 40 Model 

N063DH322 230 @ 2,200 12,500 4,500 

7E-B057-0 Deutz, BF6M1013C 233 @ 2,300 16,000 8,500 

7E-B051-0 Cummins, Model ISB-235 235 @ 2,700 10,000 6,000 

7E-B069-0 Navistar, A250, B235, and B250 250 @ 2,600 15,000 6,000 

7E-B080-0 Detroit Diesel Series 40, N063-DH32 

I-3082 250 @ 2,200 16,500 3,000 

7E-B007-0 Deutz BF6M1013C2 261 @ 2,300 12,000 19,000 

7E-B010-1 Caterpillar, 3306 DITA1,2 270 @ 2,200 15,000 6,000 

7E-B037-0 Deutz, F12L413FW 274 @ 2,300 16,000 14,000 

7E-B083-0 Daimler Chrysler 275 @ 2,200 11,000 7,000 
 

51 

Approval 

No. Engine model hp @ rpm 

MSHA 

nameplate 

ventilation 

rate, cfm 

MSHA 

particulate 

index, cfm 

7E-B078-0 Deutz BF6M1013FC-MVS 282 @ 2,300 17,000 4,000 

7E-B017-0 Caterpillar, 3306 ATAAC1 300 @ 2,200 11,500 12,000 

7E-B047-0 Detroit Diesel Series, 50 DDFC1,2 315 @ 2,100 16,000 5,000 

7E-B092-0 Detroit Diesel Series, 50 Model 

6043TK322 315 @ 2,100 21,000 7,000 

7E-B048-0 Detroit Diesel Series, 60 (11.1L)DDEC1,2 325 @ 2,100 18,000 5,500 

7E-B012-0 Caterpillar 3176 ATAAC2 335 @ 2,100 15,000 8,000 

7E-B002-0 Deutz BF6M1015C2 402 @ 2,100 18,500 17,500 

7E-B049-0 Detroit Diesel Series, 60 (12.7L)DDEC1,2 475 @ 2,100 28,000 8,500 

7E-B018-0 Caterpillar, 3406E ATAAC1,2 500 @ 2,100 24,000 12,500 

7E-B082-0 Caterpillar, 3408E DITA 510 @ 2,000 33,000 17,000 

7E-B009-0 Deutz BF8M1015C2 536 @ 2,100 24,000 18,000 

7E-B087-0 Detroit Diesel Series 60 14L DDEC IV 

Model 6063HK322 575 @ 3,000 28,000 12,000 

7E-B081-0 Cummins QSK19-C 650 @ 2,100 45,000 33,000 

7E-B032-0 Detroit Diesel, 8V-2,000TA DDEC 650 @ 2,100 45,000 10,000 

1

Engine was previously approved under Part 32.

2

Lower horsepower ratings have been approved. 

Because the PI increases with engine horsepower (just as the ventilation rate does), it is easier to compare 

engines by examining their rate of particulate production per engine horsepower—that is, by comparing the 

number obtained by dividing the PI by the rated horsepower of each engine chosen. For example, the 175-hp 

Cummins engine (7E-B052-4) has a PI/hp of 20 cfm/hp (3,500 cfm/175 hp). Using this as a benchmark, of the 

remaining 21 MSHA-approved engines rated between 200 and 650 hp, only 7 have a PI/hp <20 cfm/hp; 5 have 

a PI/hp between 21 and 30; 3 between 31 and 40; 2 between 41 and 50; and only 1 at 72.8 cfm/hp. The range 

of PI/hp for the engines listed above is 19.6 to 285.7 cfm/hp. 
Delivering on the Nation’s Promise:

Safety and health at work for all people
 

Through research and prevention
 

For information about occupational safety and health topics contact NIOSH at: 

1-800-35-NIOSH (1-800-356-4674) 

Fax: 513-533-8573 

E-mail: pubstaft@cdc.gov 

www.cdc.gov/niosh 

DHHS (NIOSH) Publication No. 2002-154