Emissions During and Real-world Frequency of Heavy-duty Diesel

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Emissions During and Real-world Frequency of Heavy-duty Diesel Particulate Filter Regeneration Chris Ruehl, Jeremy D. Smith, Yilin Ma, Jennifer Erin Shields, Mark Burnitzki, Wayne Sobieralski, Robert Ianni, Donald J. Chernich, M.-C. Oliver Chang, John Francis Collins, Seungju Yoon, David Quiros, Shaohua Hu, and Harry Dwyer Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b05633 • Publication Date (Web): 19 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

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Environmental Science & Technology

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Emissions during and Real-world Frequency of

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Heavy-duty Diesel Particulate Filter Regeneration

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Chris Ruehl*, Jeremy D. Smith, Yilin Ma, Jennifer Erin Shields, Mark Burnitzki, Wayne

4

Sobieralski, Robert Ianni, Donald J. Chernich, M.-C. Oliver Chang, John Francis Collins,

5

Seungju Yoon, David Quiros, Shaohua Hu & Harry Dwyer

6

California Air Resources Board

7

1001 I St.

8

Sacramento, CA 95812

9

ACS Paragon Plus Environment

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ABSTRACT: Recent tightening of particulate matter (PM) emission standards for heavy-duty

11

engines has spurred the widespread adoption of diesel particulate filters (DPF), which need to be

12

regenerated periodically to remove trapped PM. The total impact of DPFs therefore depends not

13

only on their filtering efficiency during normal operation, but also on the emissions during and

14

the frequency of regeneration events. We performed active (parked and driving) and passive

15

regenerations on two heavy-duty diesel vehicles (HDDVs), and report the chemical composition

16

of emissions during these events, as well as the efficiency with which trapped PM is converted to

17

gas-phase products. We also collected activity data from 85 HDDVs to determine how often

18

regeneration occurs during real-world operation. PM emitted during regeneration ranged from

19

0.2 to 16.3 g, and the average time and distance between real-world active regenerations was

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28.0 hours and 599 miles. These results indicate that regeneration of real-world DPFs does not

21

substantially offset the reduction of PM by DPFs during normal operation. The broad ranges of

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regeneration frequency per truck (3 – 100 hours and 23 – 4078 miles) underscore the challenges

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in designing engines and associated aftertreatment that reduce emissions for all real-world duty

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cycles.

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INTRODUCTION

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Heavy-Duty Vehicles (HDVs) used 18% of all transportation energy in the United States in

27

2012, and this contribution is projected to grow to 28% by 2040.1,2 Although Phase 2 U.S. EPA

28

standards for medium- and heavy-duty vehicles emissions project that their energy use will

29

decrease 22% by 2040 relative to 2016 (Phase 1) standards, diesel consumption is projected to

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decrease by only 18%.1 It is all but certain that HDVs will remain a major contributor of diesel

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combustion emissions over the coming decades.


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Many diesel emissions (or the secondary products formed when they react after emission) have

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been linked to adverse human health effects. These include gas-phase pollutants such as ozone

34

and NOx. Ambient particulate matter (PM) concentrations, however, have consistently shown the

35

highest correlations with human health endpoints.3-5 Other diesel-specific epidemiological work

36

has implicated PM from this source as a cause of disease, typically lung cancer.6,7 As a result of

37

this and much other work, diesel PM has been declared a toxic air contaminant by the State of

38

California,8 and diesel exhaust a carcinogen by the International Agency of Research on Cancer.9

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In response to human health concerns, PM emissions standards for heavy-duty engines in the

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United States have been tightened considerably, from 600 to 10 mg/bhp-hr between 1987 and

41

2007. Current standards effectively require the use of diesel particulate filters (DPFs) to trap PM

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emitted by heavy-duty engines. Under normal operation, DPFs remove more than 95% of

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engine-out PM, allowing such low standards to be met,10 but PM trapped in the DPF needs to be

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removed periodically before it impedes the exhaust flow. Emissions associated with this

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“regeneration” of the filter may strongly impact total HDDV emissions. While certification of

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the associated engines takes into account both the frequency of and the emissions associated with

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DPF regeneration during engine dynamometer testing, much less work has been done to

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characterize these variables in real-world operation. Furthermore, work is needed to characterize

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the efficiency with which the regeneration process converts trapped carbonaceous PM into CO2

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and other gases, and to characterize the chemical composition of regeneration emissions.

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Regeneration involves heating the DPF to a high enough temperature that trapped PM

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(primarily soot) is oxidized. These regenerations can occur either while the HDDV is parked or

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while it is driving, and on-road regenerations can either be active, involving injection of fuel into

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the HDDV aftertreatment, or passive, relying on the heat associated with normal engine


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operation. It is not known, however, how the concentration and composition of emissions depend

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on the type of regeneration. To address this question, we performed active parked, passive road,

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and active road DPF regenerations for both a 2007 (w/DPF) and 2010 (w/DPF and Selective

58

Catalytic Reduction, or SCR) engine model year (MY) HDDV.

59

Active regeneration of the DPFs on these two HDDVs was examined previously,11-13 and the

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size distribution and total mass of the emitted PM was reported. These regenerations were

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characterized by two phases: an initial “soot combustion” phase that featured a wide range of

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particle diameters, some larger than 1 µm, and a subsequent “fuel combustion” regime that was

63

dominated by smaller particle with diameters ~ 30 nm. This previous work did not determine the

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composition of these emissions, however, and also did not quantify the mass lost from the DPF

65

during regeneration. This study extends the previous work that only evaluated emissions during

66

parked active DPF regenerations to also include driving regenerations (both active and passive)

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at vehicle speeds ~50 mph.

68

This work reports the composition of emissions during parked, active driving, and passive

69

driving DPF regenerations. We compare these emissions to the gravimetrically quantified PM

70

lost from the DPF during regeneration. Finally, we report the real-world frequency of DPF

71

regenerations from 85 HDDVs used in ten different vocations that are representative of on-road

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HDDV activity in the State of California.14 These results are used in combination with the

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dynamometer tests described above to estimate the real-world impact of DPF regenerations.

74 75

MATERIALS AND METHODS


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Two Class 8 Heavy-Duty Diesel Vehicles (HDDVs), one with a MY 2007 engine including an

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original equipment manufacturer (OEM) DPF and the other with a MY 2010 engine including

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an OEM DPF and (downstream of the DPF) an SCR to remove NOx, were tested on a heavy-duty

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chassis dynamometer (Burke E Porter) at the California Air Resources Board’s Depot Park

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Facility, located in Sacramento, CA. The aftertreatment systems on both HDDVs included a

81

diesel oxidation catalyst. The test fuel was Ultra Low Sulfur Diesel (ULSD), with a maximum

82

sulfur content of 15 ppm. HDDV properties are summarized in Table S1. Details on both the

83

DPF loading procedure and the DPF regenerations, both of which were conducted on the

84

dynamometer, can be found in the SI.

85

The instrumentation used to measure real-time emissions, as well as analyses conducted on PM

86

collected on filters, are also described in the SI. Briefly, we performed chemical analysis of both

87

gas-phase and particulate tailpipe emissions during active parked, active driving, and passive

88

driving DPF regenerations. We also gravimetrically quantified PM lost from the DPF during

89

regeneration to calculate the fraction of trapped PM oxidized to CO, CO2, and gas-phase total

90

hydrocarbons (THC).

91

The DPF was physically removed from the truck and weighed three times during each

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regeneration cycle, including before loading with engine-out PM, after loading but before

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regeneration, and after regeneration. This allows determination of DPF mass loading per mile

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driven and mass lost from the DPF during regeneration. After being removed from the vehicle,

95

both the inlet and outlet of DPF were sealed with aluminum foil to avoid contamination.

96

Gravimetric masses were recorded after an overnight soak, which allowed internal DPF

97

temperature to decrease to ambient levels. Masses were determined to the gram with a large

98

package balance with a resolution of 0.1 g (model LP34001P, Sartorius, Bohemia, NY). Masses


5


99

of the unloaded and loaded 2007 DPF ranged from 21.959 to 21.964 kg and 22.098 to 22.128 kg,

100

respectively. For the 2010 DPF, these ranges were 20.699 to 20.720 and 20.723 to 20.826 kg.

101

The “efficiency” of PM elimination during DPF regeneration was calculated using the mass

102

PM emitted and either the mass lost from the DPF, or the fuel injected into the aftertreatment

103

during active regeneration. If the PM emitted during regeneration is assumed to arise entirely

104

from PM trapped in the DPF, it can be divided by the total mass lost from the DPF during

105

regeneration to determine the DPF filtering efficiency accounting for regeneration:

106

107

regen = 1 − PM emitted⁄DPF mass lost

(1)

DPF mass lost is the difference in DPF mass before and after regeneration, and thus regen is

108

the probability that PM trapped by the DPF will not be subsequently released as PM during

109

regeneration. In an alternate calculation, the PM emitted during regenerations was assumed to

110

arise entirely from fuel injected into the HDDV aftertreatment to raise the DPF temperature to

111

~500 °C during regeneration. The PM emitted was then divided by the total quantity of fuel

112

added to the aftertreatment to determine the aftertreatment combustion fraction (ACF):

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ACF = 1 − PM emitted⁄fuel injected into aftertreatment

(2)

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Fuel injected into the aftertreatment was determined from either SPN 3522 or 3481 (defined in

115

the SAE J1939 protocol) from the vehicle’s OBD system. We note that neither of these

116

assumptions is completely valid, as PM emitted during regeneration arises both from PM stored

117

in the DPF and that created by incomplete combustion of fuel injected into the aftertreatment

118

during regeneration. Also, because fuel is not injected into the aftertreatment during passive

119

regenerations, ACF was only determined for active regenerations.


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In addition to the characterization of emissions during individual DPF regeneration

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events, we analyzed activity data collected from a set of 85 heavy-duty diesel vehicles, each

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either Class 7 or Class 8, representing ten vocations. This data was collected with J1939 Mini

123

LoggersTM (HEM Data, Southfield, MI) which record both global positioning satellite (GPS)

124

coordinates and ECU parameters. Data was recorded at 1-second intervals, and all points with

125

engine RPM < 300 were discarded to ensure that only “engine-on” conditions were sampled. The

126

total engine-on time recorded was 26,526 hours, and the total distance travelled during recording

127

was 489,327 miles.

128

Table 1. ECU parameters used to identify active regenerations, in order of precedence. SPN name

SPN #

# HDDVs

Aftertreatment 1 Total Fuel 3522 Used

38

Aftertreatment 1 Fuel Rate

3481

6

Fuel 3480

1

Aftertreatment 1 Diesel 3721 Particulate Filter Time Since Last Active Regeneration

1

Aftertreatment Diesel 3700 Particulate Filter Active Regeneration Status

21

Aftertreatment Pressure 1

1

129 130

Several ECU fields were used to determine when an active DPF regeneration was occurring.

131

Table 1 lists these fields in order of precedence. For example, fields that reported the amount of

132

fuel injected into the DPF were considered the most reliable, and were used whenever they


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133

included reliable data. Also, the Wheel-Based Vehicle Speed (SPN #84) was used to determine

134

the total distance travelled between active regenerations. Of the 85 HDDVs, 71 recorded at least

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one DPF regeneration event as determined by at least one of the fields in Table 1. 67 HDDVs

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recorded at least two DPF regenerations, and could therefore be used to calculate regeneration

137

frequency.

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RESULTS AND DISCUSSION

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Figure 1. (a) Engine parameters and (b) emissions during a parked regeneration of the 2007

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HDDV DPF, performed on April 23, 2015.

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Figures 1 and 2 display time series of engine parameters and emissions during a typical parked

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and a typical driving regeneration, respectively. Analogous plots for all other regenerations can

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be found in Figures 4 and S2 – S9. Emissions of gas-phase species, including NOx and

145

hydrocarbons (HC), occurred primarily during the first few minutes of the regeneration, before

146

aftertreatment temperatures reached their maximum values. Particulate emissions were also

147

distinct during this early phase, having greater diameters (~60 nm) compared those later in the

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test with diameters of 30 nm or less.13,15


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149 150

Figure 2. (a) Engine parameters and (b) emissions during a driving regeneration of the 2010

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HDDV DPF, performed on August 26, 2015.

152 153 154

Table 2. DPF mass balance during each regeneration. Test Date

MY

Type

DPF mass PM emitteda losta

regen

Regeneration fuel

AF


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g

g

%

gal

2/25/2015 2007 parked

168.4

0.72

99.6

3/18/2015 2007 parked

137.1

0.98

99.3

2.62

99.99%

4/23/2015 2007 parked

136.5

5.40

96.0

2.87

99.93%

5/12/2015 2007 driving

100.9

1.87

98.1

0.61

99.89%

5/29/2015 2007 driving

141.9

4.08

97.1

0.83

99.82%

7/15/2015 2010 parked

120.3

2.61

97.8

2.33

99.96%

8/5/2015

2010 driving

93.6

16.33

82.6

2.06

99.71%

8/26/2015 2010 driving

87.0

9.44

89.2

1.22

99.72%

9/15/2015 2010 passive 24.4

0.16

99.4

N/A

N/A

99.99%

155 156

Active regeneration emissions are listed for each test in Table S2, and average values grouped

157

by chassis MY and type (parked or driving) are given in Table S3. Engine-out PM during DPF

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loading ranged from 130 to 550 mg/mile driven. This quantity was determined by gravimetric

159

analysis of the DPF before and after loading, and so it only includes the overwhelming majority

160

of PM trapped by the DPF. Most of this 87 to 168 g was removed from the DPF during

161

regeneration. The mass balance of each DPF during regeneration is presented in Table 2. Note

162

that the emissions from road regenerations includes those arising from driving the vehicle at 50

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mph, as well as active regeneration. Table 2 includes the efficiency of PM elimination in terms

164

of both DPF mass lost (regen ), which ranged from 82.6 to 99.6%, and fuel injected into the

165

aftertreatment (ACF ), which ranged from 99.71 to 99.99%. For seven out of nine tests, regen >

166

95% and ACF > 99.8%. The two exceptions were the two road regenerations of the 2010 HDDV.

167

For these two tests, regen was reduced to 83 – 89% and ACF was reduced to 99.7%.


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The carbon dioxide associated with the decrease in DPF mass was minor compared to that

169

generated by fuel combustion during regeneration, which ranged from 10 to 29 kg C. Other

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forms of emitted gas-phase carbon, including carbon monoxide and hydrocarbons, were also

171

minor (35 to 92 g and less than 5 g, respectively). Typically less than 5 g particulate matter was

172

emitted during each regeneration (Table S2), and it was dominated by ultrafine (D < 100nm)

173

sulfate. Again, the exceptions were the active road regenerations of the 2010 HDDV, which

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emitted 9-16 g PM. These events involved larger particles (40-50 nm) and increased black

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carbon emissions.15

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Gravimetric analysis of the DPF before and after each regeneration event (Table 2) allowed for

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both derivation of DPF inlet (i.e., engine-out) PM and of the overall ability of the DPF to

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eliminate particulate emissions (e.g., regen ). (Note that this definition of “engine-out” only

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includes PM that remains trapped in the DPF, and therefore does not include any PM that

180

evaporates from the DPF.) Engine-out PM was highest (491 – 548 mg/mi) for loading of the first

181

two DPF regenerations, in which dynamometer force and thus engine loading were kept low.

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Engine loading was subsequently increased, which caused a decrease in engine-out PM from

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~500 to ~250 mg/mile (Table S2). The much higher values for the first two tests demonstrate the

184

differences in HDDV engine-out PM with changing duty cycle, and suggest that differences in

185

these cycles will influence the frequency of, and perhaps the emissions associated with, DPF

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regenerations. Additionally, lower engine-out PM emissions ranging from 126 - 229 mg/mi were

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reported for the truck with a MY 2010 engine (161 mg/mi) compared to 238 - 265 the truck with

188

the MY 2007 engine under similar loading conditions (Table S2). This suggests that a physical

189

failure of the DPF on a MY 2007 engine would result in a greater emissions impact than an

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equivalent failure on a MY 2010 engine.


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During active regenerations, PM emissions were dominated by sulfate. During passive

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regenerations, much less PM was emitted, and it was dominated by organic matter (Fig. 3).

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Although a greater proportion of the passive emissions was organic, the absolute amount of

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organic carbon emitted was similar during active (0.03 to 0.38 g) and passive (0.05 to 0.17 g)

195

regenerations. PM emitted during active regenerations ranged from 0.72 to 16.3 g, and the

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portion of this gravimetric mass that was speciated ranged from 43 to 125% (average 70%). For

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the passive regenerations, gravimetric PM emitted ranged from 0.10 to 0.22 g, 33 – 126% of

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which was speciated (average 88%). Gravimetric mass that was not speciated could either be in

199

species that were not analyzed, or could have been lost from the filters before analysis. The ratio

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of detected sulfate-S (by ion chromatography) to detected sulfur (by x-ray fluorescence) was

201

47% (Fig. S10). This indicates that less than half of the sulfur emitted was in the form of water-

202

soluble sulfate, and the remaining non-sulfate sulfur could be responsible for much of the

203

“missing” gravimetric mass. Other material that could contribute to unspeciated mass include

204

organic oxygen, nitrogen, etc., as well as insoluble inorganic ions.


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205 206

Figure 3. Chemical composition of PM emission during active and passive HDDV

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regenerations. Note the split y scale.

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The PM emitted during active regenerations ranged from 0.2 to 5.4 g, except for the active

209

driving regenerations of the 2010 DPF. During these two tests, 9.4 and 16.3 g PM were emitted.

210

Correspondingly, regen was over 97% for all tests except for these two with relatively high PM

211

emissions, when it was 90 and 82%. About half of the emitted gravimetric mass could be

212

accounted for by sulfate (Fig. 3), which ranged from 0.6 to 6.2 g per regeneration (Table S2).

213

The maximum sulfur content of the ULSD used in this study is 15 ppm. The amount of this fuel

214

used for active regenerations ranged from 0.61 to 2.87 gallons, with generally higher amounts for

215

driving regenerations. This corresponds to a maximum amount of sulfur in this fuel of 0.03 to

216

0.14 g. Because the sulfur emitted during regenerations is much higher than the amount in fuel

217

burnt during these events, it must derive from fuel and/or oil burned during DPF loading and


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stored in the aftertreatment,16-18 or from oil burned during the event. This sulfur is released only

219

when aftertreatment temperatures are high, or similar to typical regeneration temperatures. XRF

220

measurements suggested particulate sulfur in other forms, perhaps organosulfates, contributed to

221

emitted PM (Fig. S10). Recent work has highlighted the formation of organosulfates in

222

secondary organic aerosol formation from diesel fuel,19 and the results of this study suggest that

223

future work should also attempt identify these compounds in primary emissions from modern

224

HDDVs.

(a)

(b)

225 226

Figure 4. (a) Engine parameters and (b) emissions from a driving regeneration of the DPF from

227

the 2010 HDDV performed on August 5, 2015.


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PM emissions were much lower during passive regenerations of the 2010 DPF (Fig. 3). This

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PM had much lower sulfur fractions than all active regenerations. This most likely results from

230

the difference in aftertreatment temperature between passive and active events and/or the

231

differences in chemistry (unlike active regeneration, NO2 is the dominant oxidant during passive

232

regeneration). During passive events, the HDDV was driven at a constant speed of 50 mph, and

233

temperature throughout the aftertreatment plateaued at about 400°C (Figs. S7-S9). The

234

maximum aftertreatment temperature during active regenerations was about 100°C greater than

235

passive regenerations (Figs. 2, 4). The lower temperatures during passive regeneration could

236

have prevented stored sulfur from being oxidized and/or volatilized. This lower temperature did

237

not inhibit the effectiveness of the regeneration, however: regen was 99.4% during the one event

238

for which it was quantified, which is at the upper end of the range of regen observed for active

239

regenerations (Table 2). Given the fuel penalty associated with active regeneration, these results

240

demonstrate that passive regenerations are preferable to active regenerations of HDDV DPFs

241

from a fuel consumption perspective. While such passive regenerations are able to remove stored

242

carbonaceous material, however, they may not be able to remove stored sulfur as effectively. It is

243

also possible, however, that passive regenerations release sulfur as SO2 (i.e., without oxidizing it

244

to SO3). Because sulfur has the potential to poison catalysts,20 future work should focus on the

245

chemistry of the sulfur storage process and sulfur oxidation during both active and passive

246

regenerations.


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Figure 5. Chemical composition of size-segregated PM emitted during a passive regeneration,

249

followed by two forced regenerations, of the 2010 DPF.

250 251

Inorganic PM composition as a function of particle size was determined during one of the

252

regenerations of the DPF on the 2010 HDDV (Fig. 5). These samples were also dominated by

253

sulfate, which was distributed approximately equally between the nucleation mode (Dp ~ 30 nm

254

and below) and accumulation mode (Dp ~ 100 nm). Ammonium was also present in these

255

particles, although not in sufficient quantity to fully neutralize the sulfate - NH4+:SO42- ratios

256

ranged from 0.05 to 0.90 (Fig. 5), whereas an NH4+:SO42- ratio of 2 corresponds to full

257

neutralization. In general, the size-segregated samples that had the highest sulfate concentrations

258

were the least neutralized.

259 260

There are three general explanations for the relatively high PM emissions during road regenerations of the 2010 DPF. First, the added surface area associated with the SCR could allow


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261

for more storage of sulfur in the 2010 aftertreatment. However, much less PM (2.61 g) was

262

emitted during a parked regeneration of the 2010 DPF. Furthermore, carbonaceous emissions

263

were also elevated in the 2010 driving regenerations relative to other events (Fig. 3, Table S2).

264

Thus, while sulfur storage in the DPF may explain part of these anomalously high emissions,

265

there must be other major contributions. A second potential cause is incomplete combustion of

266

(carbonaceous) PM stored in the DPF, and a third is incomplete combustion of fuel injected into

267

the aftertreatment during regeneration. Either of both of these could contribute to the higher CO

268

emissions during road regenerations of the 2010 DPF (51 – 92g) relative to parked 2010 and all

269

2007 regenerations (5 – 35 g) (Table S2).

270

Gas-phase emissions during the beginning of regenerations events, when aftertreatment

271

temperatures increase sharply, provide insight into the relatively high PM emissions during

272

driving regenerations of the 2010 HDDV. As the first such test was initiated, a ~2 minute spike

273

in HC emissions was seen, similar to all other tests (Fig. 4). However several minutes later, HC

274

emission increased again, something generally not seen in the parked test or in either driving or

275

parked tests of the 2007 HDDV. NOx emissions were relatively low during this increase in HC

276

emissions, suggesting that either stored PM or fuel injected into the aftertreatment was not being

277

completely combusted. A similar pattern was seen during the second 2010 driving regeneration

278

(Fig. 2), although the HC emitted, as well as the PM, was lower. The overall pattern of increased

279

HC emissions at the beginning of a regeneration event, and increased particle number emissions

280

towards the end, was also observed recently for heavy-duty diesel trucks with similar

281

aftertreatment systems but certified to Japanese emissions standards.21

282 283

Nucleation mode particles have often been observed during active regeneration of DPFs, including those on light-duty vehicles22 and from heavy-duty engines.23 The median diameter of


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284

particulate emissions during active parked regenerations of the same 2007 and 2010 HDDVs

285

used in this study was below 30 nm during the later stages of these events.12 The promotion of

286

homogeneous particle nucleation by lowered particle surface area for competing heterogeneous

287

nucleation is also consistent with the inverse relationship between particle number and volume

288

observed during a series of consecutive DPF regenerations (Fig. S11, note that such repeated

289

regenerations are not expected to be representative of real-world use.Furthermore, the relatively

290

low ammonium to sulfate ratios observed in this study (Fig. 5) are consistent with observations

291

of gaseous sulfuric acid in DPF-equipped heavy-duty engine exhaust.24

292

Of the 71 on-road vocational HDDVs that logged at least one DPF regeneration, most were

293

actively regenerating between 1 and 3% of engine-on time (Fig. S12, based on SPN 3100). A

294

small number of HDDVs were actively regenerating their DPFs greater than 5% of the time their

295

engines were on. These HDDVs had lower DPF outlet temperatures during regeneration,

296

suggesting inhibited fuel injection into the aftertreatment (Fig. S13). However, removal of these

297

HDDVs did not significantly change the average frequency of DPF regeneration among the

298

entire fleet. On average, these HDDVs underwent active DPF regeneration every 28.0 ± 2.5

299

hours the engine was on, or every 599 ± 95 miles the truck traveled (all quoted uncertainties are

300

the standard error of the mean). Generally, HDDVs with higher average vehicle speeds (such as

301

line haul trucks) had longer time periods (Fig. S14) and distance travelled (Fig. S15) between

302

regenerations.

303

The observations of real-world regeneration frequency suggest that PM emitted during

304

regeneration will be comparable to or less than that emitted during “normal” (non-regenerating)

305

operation. A recent study of on-road heavy-duty truck emissions in CA found that HDDV PM

306

emissions ranged from 4 to 14 mg/mi.25 Given that the average distance travelled by the


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307

vocational HDDV fleet between regenerations was 599 miles, this would be equivalent to 2.4 –

308

8.4 g of emitted PM during regeneration events. The range of PM emitted during these

309

regeneration events was 0.7 to 16 g, suggesting that while PM emitted during regeneration can

310

be more variable, it is on average roughly equivalent to PM emitted during normal operation.

311

Therefore, if a properly functioning DPF removes 99% of engine-out PM during non-

312

regenerating operation, accounting for regeneration PM will lower this number at most to 98%.

313

The minor influence of regeneration PM on overall emissions is also reflected in the observation

314

that regeneration PM represents less than 0.3% of total PM stored in the DPF (Table 2).

315

As illustrated in Figure S14, the average time between regeneration events for the 67 HDDVs

316

for which this quantity could be derived ranged from 11,451 to 363,012 seconds. The FTP cycle

317

used during certification of HDD engines has a length of 1200 seconds. Thus the real-world

318

regeneration frequencies reported here suggest that active regenerations may occur, on average,

319

in anywhere between 10 and 300 FTP cycles, which is consistent with results from the Advanced

320

Collaborative Emission Study.26,27 There was even greater variability in the average road

321

distance traveled between regenerations (Fig. S15). This wide range in regeneration frequency,

322

seen even within specific vocations, demonstrates the adaptability required of advanced control

323

systems to effectively monitor and ensure the proper operation of the DPF. It also represents a

324

challenge for regulators attempting to select driving cycles representative of real-world HDDV

325

operation.

326

ASSOCIATED CONTENT

327

Supporting Information.

328

Description of DPF loading procedure


20

Page 21 of 29


329

Description of real-time instrumentation

330

Description of PM filter collection and analysis

331

Figure S1. Typical pattern of acceleration/deceleration used to load HDDV DPFs with PM.

332

Figure S2. (a) Engine parameters and (b) emissions from a parked regeneration of the DPF

333 334 335 336 337 338 339 340 341 342 343 344 345 346 347

from the 2007 HDDV performed on February 25, 2015. Figure S3. (a) Engine parameters and (b) emissions from a parked regeneration of the DPF from the 2007 HDDV performed on March 18, 2015. Figure S4. (a) Engine parameters and (b) emissions from a driving regeneration of the DPF from the 2007 HDDV performed on May 12, 2015. Figure S5. (a) Engine parameters and (b) emissions from a driving regeneration of the DPF from the 2007 HDDV performed on May 29, 2015. Figure S6. (a) Engine parameters and (b) emissions from a parked regeneration of the DPF from the 2010 HDDV performed on July 15, 2015. Figure S7. (a) Engine parameters and (b) emissions from a passive regeneration of the DPF from the 2010 HDDV performed on September 15, 2015. Figure S8. (a) Engine parameters and (b) emissions from a passive regeneration of the DPF from the 2010 HDDV performed on September 17, 2015. Figure S9. (a) Engine parameters and (b) emissions from a passive regeneration of the DPF from the 2010 HDDV performed on September 22, 2015.


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Page 22 of 29

348

Figure S10. Sulfur detected by IC (as sulfate) vs detected by XRF.

349

Figure S11. Results from four consecutive forced regenerations of the DPF on the 2007

350

HDDV. SMPS results are presented as (a) number size distributions, (b) total volume

351

concentration, and (c) total number concentration.

352 353 354 355 356 357 358 359

Figure S12. Histogram of the percentage of total running time that real-world vocational HDDVs underwent active DPF regeneration. Figure S13. Fraction of engine-on time in which active DPF regeneration was occurring vs. average DPF outlet temperature during regeneration. Figure S14. Average engine-on time between DPF regenerations, by HDDV vocation, model year (symbol), and OEM (color). Figure S15. Average distance travelled between DPF regenerations, by HDDV vocation, model year (symbol), and OEM (color).

360

Table S1. Heavy-Duty Diesel Vehicle Specifications.

361

Table S2. Summary of active regeneration tests, emissions, and DPF loading conditions.

362

Table S3. Emissions and DPF mass lost during active regenerations. This is the same data as in

363

Table S2, but grouped first by Model Year and then by type (parked or driving).

364


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365 366 367 368 369 370


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AUTHOR INFORMATION

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Corresponding Author

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*Chris R Ruehl

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Email: [email protected]

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Phone: (916) 323 - 1520

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ACKNOWLEDGMENT

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Page 28 of 29

The authors would like to thank William Robertson (CARB) for insightful comments on an

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earlier draft that improved the manuscript.

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TABLE OF CONTENTS (TOC) ART

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Page 29 Environmental of 29 Science & Technology

ACS Paragon Plus Environment MY 2007

MY 2010

Emissions During and Real-world Frequency of Heavy-duty Diesel

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