The effects of water emulsified fuel on diesel particulate matter

concentrations in underground mines

J.D. Noll, S.E. Mischler, L.D. Patts, G.H. Schnakenberg, Jr., A.D. Bugarski, & R.J. Timko

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 Lab,

Pittsburgh, PA, USA

G. Love

Carmeuse North America, Maysville, KY, USA

ABSTRACT: In this study, we evaluated the ambient diesel particulate matter (DPM) concentrations (at the

intakes and exhausts of the mine) as the entire vehicle fleet of a stone mine switched from using 35% biodiesel

to using a water emulsified fuel (PuriNOx). Elemental carbon (EC) was reduced by 45% when a PuriNOx blend

containing 10% water replaced 35% biodiesel and by 57% when a PuriNOx blend containing 20% water was

used. Other factors such as engine duty cycle and production changes could potentially cause some day-to-day EC

fluctuations, and no direct comparison to commonly used diesel fuels (No. 1 or No. 2) was achieved. Therefore,

a second study was performed in a controlled “isolated zone” environment of a metal mine, comparing PuriNOx

to No. 1 diesel fuel in a load haul dump vehicle. The EC fraction of the DPM was reduced by about 71% when the

PuriNOx blend containing 10% water was used and by about 85% when the PuriNOx blend containing 20% water

was employed. This study did not determine how the water emulsified fuel would affect the engine or power.

1 INTRODUCTION

Long-term exposure to diesel exhaust has become a

concern because diesel emissions are believed to be a

possible carcinogen by several organizations (IARC

1989, NIOSH 1988, EPA 2002). In addition, acute

overexposure to diesel exhaust has been linked to deleterious health effects such as eye and nose irritation,

headaches, nausea, and asthma (Kahn & Orris 1988,

Rundell et al. 1996, Wade 1993). Measurements have

shown that underground miners can be exposed to over

100 times the typical environmental concentrations of

diesel exhaust and over 10 times the concentrations

measured in other work environments where diesel

engines are common (Cantrell & Watts 1997, Nauss

1998, Haney 1992).

In the United States, the Mine Safety and Health

Administration (MSHA) has promulgated rules for

regulating miners’ exposure to diesel particulate matter (DPM) in underground metal/non-metal (MSHA

2001). In metal/non-metal mines, the MSHA rule

limits personal exposure to DPM, measured by collecting air samples on quartz fiber filters and analyzing

the filters for elemental carbon (EC) or total carbon

(TC) (summation of organic carbon (OC) and EC)

by NIOSH Method 5040. For the interim rule, miner

exposure is limited to an average of 308μg/m3 EC for

an entire shift (MSHA 2005). Due to this regulation,

many types of control technologies are being investigated to reduce the DPM emitted from diesel-powered

underground mining equipment.

Water-emulsified fuel is one such control technology being tried by the industry. The water in the fuel

is believed (1) to reduce the combustion temperature

which reduces the nitrogen dioxide (NO2) production

and (2) to alter combustion to inhibit soot formation.

Water emulsified fuels have been tried on several

different types of vehicles, such as buses, fire trucks,

tractors, etc. and mixed results were achieved (Rideout

1999, Rosenblatt 2000, Rosentblatt & Ainslie 1999,

Howes 2000, EPA 2002, Matthews 2002, Matthews

et al. 2002). For example, in a study done by Environmental Canada, a 24% total DPM reduction was

observed in an International 4600 flatbed when the

diesel fuel, used by the City of Houston, was replaced

with PuriNOx (a water emulsified fuel made by Lubrizol) (Howes 2000). In the same study, a 69% reduction

in total DPM was observed when PuriNOx was used

in a John Deere road sweeper.

Common problems observed when using PuriNOx

were power loss and increased fuel consumption

159
(Rideout 1999, Rosenblatt 2000, Rosentblatt &Ainslie

1999, Howes 2000, EPA 2002, Matthews 2002,

Matthews et al. 2002). In some cases, PuriNOx

affected the performance of the vehicle so much that it

prevented its use, but in other cases PuriNOx was successfully used for years (Matthews et al. 2002). Due

to the variation in these results, each type of engine

with the duty cycles being used needs to be tested

to determine the effects on the emission by the water

emulsified fuels for that type of vehicle and use.

For the underground mining industry, Environment

Canada showed some preliminary success in using

PuriNOx. In an underground salt mine, Rosenblatt and

Ainslie, from Environment Canada, reported a 46%

reduction in DPM by mass when a PuriNOx blend

replaced No. 2 diesel fuel in a front-end loader operating under a normal cycle (Rosenblatt 2000). This

study does not give the effects on elemental carbon by

the water emulsified fuel and was performed only on

one vehicle. Therefore, in order to obtain additional

information on the effects of PuriNOx on DPM from

metal/nonmetal underground mining vehicles, we conducted two studies evaluating the effects of PuriNOx

on DPM generated by diesel-powered underground

mining equipment.

One study looked at the effect that PuriNOx had on

DPM concentrations in a limestone mine. The limestone mine used a 35% biodiesel blend to reduce DPM

exposure. The 35% biodiesel gave about a 30% reduction in EC and TC from DPM when compared to No. 2

diesel (Gerbec & Fields, 2003, Bugarski et al. 2003).

The mine management had decided to switch from

35% biodiesel to PuriNOx blends. To evaluate this

change, samples of EC and TC were obtained at the

intakes and exhausts of the mine for three days when

35% biodiesel was used and again for three days when

warm weather and cold weather blends of PuriNOx

were being used. In this study, other factors such as

engine duty cycle and production changes could potentially cause some day-to-day EC fluctuations. Three

days of data were averaged in an attempt to minimize

any effects that these factors would have on EC reduction. Nevertheless, these factors could not be totally

accounted for. PuriNOx was also only compared to

35% biodiesel, and no direct comparison to commonly

used diesel fuels (No. 1 or No. 2) was achieved.

Therefore, another study was conducted to confirm

the results in the field by comparing PuriNOx to No. 1

diesel in a controlled environment. A loader was operated in an isolated zone (a long, sealed, entry supplied

with fresh air). The isolated zone provided a controlled

environment where the only source of DPM was the

piece of equipment being investigated. The loader was

operated over a duty cycle based on that used during

actual mining. Downwind of the operating path of the

vehicle, ambient EC, TC, and DPM mass measurements were obtained when No. 1 diesel fuel was used

in the loader (baseline case) and then when a PuriNOx

blend was used.

2 METHODS

2.1 Fuels

No. 1 Diesel: Cenex, Columbus, MT

Biodiesel: A 35% blend of Bio G-3000 biodiesel

from Griffin Industries, produced from recycled

restaurant grease with No. 2 diesel fuel. This fuel was

used as the baseline.

Cold weather PuriNOx blend: 10% Water, 2.15%

Lubrizol Emulsifier Additive, 2.15% Methanol, and

85.7% No. 2 diesel fuel.

Warm weather PuriNOx blend: 20% water, 3%

Lubrizol Emulsifier Additive, and 77% No. 2 diesel

fuel.

Sulfur content and other properties of the fuels can

be found in publications by Bugarski et al. (2003,

2005).

2.2 Sampling and analytical methods

2.2.1 EC-TC sampling train

The EC-TC sampling train used for DPM sampling

was identical to the one used by MSHA for DPM compliance monitoring (MSHA 2001). It consisted of a

flow-controlled MSA Elf Model pump (Mine Safety

Appliances Company, Pittsburgh, PA), a 10-mm DorrOliver cyclone, and an SKC DPM cassette (SKC, Inc.,

Eighty Four, PA). The SKC DPM cassette contained a

single-stage impactor and two 37 mm diameter tissue

quartz filters, mounted in series.The pumps were operated at 1.7 lpm. The flow rate for each of the sampling

pumps was measured and recorded at the beginning

and end of each day using a Gilibrator II bubble flow

meter (Sensidyne, Inc., Clearwater, FL). If the measured flow rates deviated more than 5% from 1.7 lpm,

the pumps were recalibrated.

Exposed SKC DPM cassettes were taken to NIOSH

Pittsburgh Research Laboratory (PRL) and analyzed in

the laboratory for EC andTC content using the NIOSH

Method 5040.

2.2.2 High-volume sampling procedure

When testing the efficiencies of control technologies in underground mines, the concentration of DPM

can be low. To collect enough material to be at and

above the limit of quantification for NIOSH Analytical Method 5040, one might have to sample for many

hours. When doing research in the field, one does not

always have this luxury. A high-volume (HV) sampling train was developed by Bugarski et al. (2003,

2005) to collect more material in less time. The HV

flow rate was achieved by merging flows from five

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classifiers, each consisting of a 10-mm Dorr-Oliver

cyclone followed by a U.S. Bureau of Mines (BOM)

single stage diesel impactor, into a single stream.

A flow rate of between 1.7–2.0 lpm was maintained

through each cyclone and impactor pair. At this sampling flow rate only particles with geometric mean

smaller then 0.8μm were deposited on the filters. All

five classifiers were attached to a symmetrical plenum

that distributed a total flow rate of between 8.5–10 lpm

uniformly among the five streams. Each of the classifier assemblies was connected to the plenum chamber

by a 3-foot long section of conductive tubing. The

outlet of the plenum was directly connected to a stainless steel 25 mm diameter filter holder containing a

stack of two 25 mm tissue quartz fiber filters (Tissuequartz 2500QAT, Pall Corporation, Ann Arbor, MI).

This design is described in detail in the Bugarski et al.

reports (2003).

2.3 Stone mine survey

After vehicles in a stone mine had used 35% biodiesel

for almost one year, we sampled EC, TC, and NO2

one shift per day for three days. Each vehicle was

equipped with a diesel oxidation catalyst. The fuel for

the entire fleet was then changed from 35% biodiesel

to the cold weather PuriNOx blend (supplied by Lubrizol). After running the new fuel for approximately one

month, we again took three days of measurements.

Following this evaluation the fuel was changed to the

warm weather PuriNOx blend and run for about one

month. Once again we sampled for one shift for three

consecutive days.

This limestone mine had one main intake entry

and two main exhaust entries. In the one main intake,

one EC-TC sampling train (described earlier) was set

up. The EC-TC sampling trains were chosen instead

of the high volume sampling since we did not have

electricity to run the high volume sampling and we

were sampling for a long enough period (about 8

hours) to collect enough material using the EC-TC

sampling train. Three EC-TC sampling trains were

placed in each of the two main exhaust entries. In the

exhaust entries, an ITX multi-gas monitor (Industrial

Scientific Corp., Oakdale, PA) measured NO2 and an

anemometer measured air velocities.

Most of the vehicles in the mine (about 61%) had

Caterpillar engines. A complete list of diesel engines

is found in the report by Gerbec and Fields (2003).

EC and TC were chosen as surrogates for DPM,

which consists of over 80% carbon (Heywood 1988,

Pierson 1983).We could not directly measure the DPM

since we believed that gravimetric or mass measurements of DPM on a filter would not be sensitive or

precise enough to obtain reliable data and that even

the small portions of dust that penetrate through the

impactor (about 4–10%) may cause interference to

mass measurements. As described later in this paper,

we believed that we could account for TC interferences (e.g. cigarette smoke, oil mist, and vapor-phase

OC) usually seen in underground mines. Unlike TC,

EC is DPM-selective and would allow us to monitor

DPM concentrations without being concerned about

interferences.

2.3.1 Ventilation normalization

Factors other than fuels can cause different day-to-day

DPM concentrations in a mine. These include ventilation changes, varying production, and different duty

cycles on engines. To best evaluate the effects from the

fuel change, we took measurements over three days

to minimize the variable in-mine conditions and normalized the EC and TC concentrations to average

ventilation rates to account for any ventilation changes.

The normalization calculation is described in a report

by Bugarski et al. (2003).

2.3.2 Interferences

There were no known interferences for the EC measurements. For OC from DPM there were possible

interferences from mineral dust, cigarette smoke, oil

mist, and vapor-phase OC.

The SKC DPM cassette was used for EC and OC

measurements. This device allows only particles less

than 0.8μm to collect on the filter, eliminating any

significant interference from airborne mineral dust.

We were also concerned with vapor-phase OC

adsorbing onto the quartz filter and causing a positive bias to the particulate TC. To account for this, a

second filter was placed in tandem (in series) with the

primary filter. In theory, the second filter was exposed

to the same concentrations of vapor OC as the first

filter but does not collect any particulate. Thus, to correct for the adsorbed vapor-phase OC, results from the

second filter were subtracted from the first filter OC

values. In the literature, this is referred to as the tandem filter correction (Kirchstetter et al. 2001, Eatough

et al. 1995, Turpin & Huntzicker 1994).

Oil mist should not be a significant interference by

the time it arrives at the samplers in the exhaust entries.

When compared to DPM, any cigarette smoke should

be so diluted that interference should be minimal at the

sampling locations used in this study (Haney 2000).

2.4 Isolated zone study

An isolated zone was set up in a metal mine as

described in reports by Bugarski et al. (2003). In the

isolated zone, the only source of diesel exhaust was the

vehicle being tested. Air flowed in through one intake

entry and out through one return entry.

A 344 Load Haul Dump (LHD) with a Caterpillar

3126B DITA engine was run with No. 1 diesel fuel

using a duty cycle typical to this vehicle in production.

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This was the same duty cycle described in reports by

Bugarski et al. 2003 for an LHD.

Duplicate EC and TC samples were collected

upstream and triplicate samples were obtained downstream of the operating vehicle using high-volume

(HV) samplers described earlier and analyzed using

NIOSH Method 5040 (Birch 2003). HV samplers were

used in this case since we could only sample for about

two hours. Therefore, we were not sure if we could

collect enough material on the filter using the EC-TC

sampling trains. An ultra sonic anemometer was set up

to measure entry air velocities.

Duplicate DPM mass samples were collected using

a design similar to the HV sampler described below.

Instead of a quartz filter, a Teflon filter (Pall Corporation, East Hills, NY) was used. Instead of mass flow

controllers, critical orifices were used to control the air

flow rate. Prior to and after each test gravimetric samples were desiccated and equilibrated in a controlled

environment (72◦F and 50% relative humidity) before

weighing. Balance precision was better than 6μg.

No. 1 diesel fuel was replaced with a cold weather

PuriNOx blend and the test was repeated. The vehicle

was run for some time to allow the engine to consume

the old fuel before the actual test began. Following this

series, another evaluation was started using the warm

weather PuriNOx blend.

2.4.1 Interferences

In the isolated zone a BOM impactor was used for

EC, TC, and DPM mass measurements. This sampler

should eliminate any significant interference from

ambient airborne mineral dust in the mine. Samples

were taken in the intake entry, upwind of the isolated

zone, so that any analyte present in the incoming

air could be determined and subtracted from its

value measured downwind. Based on the experimental

design, in the isolated zone the only source of DPM

should be from the vehicle in this area.

Vapor-phase organic carbon (OC), generated from

engine exhaust but not considered to be part of DPM,

can adsorb onto the quartz filters and cause a positive bias of the particulate TC results in both upstream

and downstream samples.As previously described, OC

quantities on a secondary filter, located in tandem with

the primary filter, were subtracted from the OC values

to correct for the adsorption of vapor-phase OC.

Exposed filters were taken to NIOSH Pittsburgh

Research Laboratory (PRL) and analyzed in the laboratory for EC andTC content using the NIOSHMethod

5040.

2.5 Confidence limits

Each value for OC, EC, and TC was the average of

triplicate samples for the isolated zone study and the

average of three days of triplicate samples for the stone

mine study. The 95% confidence limits for the carbon analysis for both the isolated zone and stone mine

studies were calculated using the following equation

(Skoog 1986):

where t is the factor for the confidence interval dependent on the degrees of freedom, s is the standard

deviation, and N is the number of samples.

Since the DPM mass for the isolated zone study

was only done in duplicate, the above equation cannot be used to give a reliable confidence limit. In this

case, we calculated an accepted confidence limit for

gravimetric samples by using the standard deviation

obtained when hundreds of samples were weighed

using the same procedure and balance used in this

study. The 95% confidence limit for the DPM mass

measurements was then calculated using the following

equation (Skoog 1986):

where s is the standard deviation.

3 RESULTS AND DISCUSSION

3.1 Stone mine study

Significant reductions were observed when a mine

used PuriNOx in its entire vehicle fleet. Table 1 shows

the average concentrations of EC and TC for the three

days of measurements at the two main exhausts of the

mine.

When the cold weather PuriNOx blend was used

instead of the 35% biodiesel, the average of the two

locations showed a 45% reduction in the EC from

DPM. There was no significant effect on the OC concentration, and the TC concentration was reduced by

about 36%.

Substituting the warm weather PuriNOx blend for

the 35% biodiesel, a 57% reduction in EC and a 43%

reduction in TC was observed. There was again no

significant effect on the OC concentration.

These emission reductions were observed when

using 35% biodiesel as a baseline fuel. The diminutions would most likely be higher if PuriNOx blends

were compared to No. 1 or No. 2 diesel fuel.

These numbers do have limitations. Other factors

such as engine duty cycle and production changes

could result in day-to-day EC fluctuations. Three days

of data were averaged in an attempt to minimize any

effect that these factors would have on EC reduction,

but nevertheless, these factors could not be totally

accounted for.

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Table 1. Reduction in DPM from PuriNOx compared to

35% biodiesel at Black River Mine.

∗ There was no significant (average concentration <5μg/m3)

EC or TC particulate collected on the intake samples.

The OC, EC, and TC concentrations were the concentrations measured after tandem filter correction without being

normalized for ventilation.The reductions are after being normalized for ventilation.

Confidence limits were calculated as described in methods

section.

0

1

1.4

1.8

2

01234567

35 % biodiesel

cold weather

PuriNOx

warm weather

PuriNOx

1.6

NO2 (ppm) 1.2

0.8

0.6

0.4

0.2

Figure 1. NO2 concentrations observed in Black River

Mine when each fuel was used. Each point represents the

concentration at a location for each day.

3.1.1 NO2 measurements

Figure 1 shows the daily NO2 concentrations at each

location and for each fuel. A reduction in NO2 was

observed.

3.1.2 Problems

A reduction in engine power was observed by operators with the use of PuriNOx fuels but did not seem

to affect the production during the days of the study.

However, this study was too short to determine how

much this power loss would affect the use of the vehicles. That would have to be determined after a longer

use of the fuel. It would also take a longer study to

Table 2. The reduction of DPM in the isolated zone study.

* There was no significant (<3μg/m3) EC or TC particulate

collected on the upstream samples. Therefore, they were not

subtracted from the data.

Confidence limits were calculated as described in methods

section.

determine how the fuel would affect the engines. An

odor was observed when the warm weather blend was

used.

3.2 Isolated zone study

Use of the cold weather PuriNOx reduced EC by

71% relative to No. 1 diesel fuel; the warm weather

formulation reduced EC by 86% (see Table 2).

The cold weather PuriNOx increased OC by 41%

(no DOC was used) but the warm weather PuriNOx

showed no significant change in OC. DPM mass was

reduced by 44% with the cold weather PuriNOx and

by 57% with the warm weather PuriNOx.

The ventilation did not change between tests. The

duty cycle was the same and the same number of

cycles were run for each test. Therefore, the effects

of PuriNOx fuels should be the only cause of DPM

reduction.

The operator and researchers did experience some

burning of the eyes when the PuriNOx blends were

used. This was not observed when running PuriNOx

blends at Black River stone mine. This may have been

because diesel oxidation catalysts were equipped on

all vehicles in the stone mine but were lacking on the

vehicle used in the isolated zone study. Some power

loss was observed but not enough to prevent the vehicle

from performing the duty cycle.

4 CONCLUSION

PuriNOx substantially reduced EC from DPM in two

studies. The OC concentration was either not affected

or increased (when no DOC was used). An odor and

burning of the eyes can occur, but might be mitigated

if DOCs (which probably should be used with PuriNOx) are also used on the vehicle. Power loss was

observed and may inhibit the use of a water emulsified

163
fuel on certain vehicles. These studies were too short

to determine how this fuel will affect the engine.

Disclaimer: Mention of a company name or product does not constitute endorsement by the Centers

for Disease Control and Prevention. The findings and

conclusions in this report are those of the authors and

do not necessarily represent the views of the National

Institute for Occupational Safety and Health.

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