Summary of "Light Heavy-Duty
Gasoline Vehicle Evaporative
Emissions Test Program"
United States
Environmental Protection
tl Agency
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Summary of "Light Heavy-Duty
Gasoline Vehicle Evaporative
Emissions Test Program"
This technical report does not necessarily represent final EPA decisions or
positions. It is intended to present technical analysis of issues using data
that are currently available. The purpose in the release of such reports is to
facilitate the exchange of technical information and to inform the public of
technical developments.
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
&EPA
United States
Environmental Protection
Agency
EPA-420-S-19-002
December 2019
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Table of Contents
1. Executive Summary 2
2. Test Program 3
2.1 Vehicles 3
2.2 Evaporative Emissions Testing 4
3. Emissions Results 4
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1. Execir
There has been significant progress in reducing evaporative emissions from gasoline-fueled
passenger cars and light-duty trucks. Due to the increasing market share of gasoline engines in heavy-
duty vehicles it is necessary that we evaluate the evaporative emissions from these vehicles' fuel
systems. Evaporative emissions from heavy-duty vehicles can be a significant contribution to the
vehicles overall hydrocarbon (HC) emissions, therefore controlling this source of emissions is important.
To evaluate the evaporative emission performance on current production heavy-duty gasoline
vehicles, two vehicles were tested over a full set of evaporative emissions tests at the SGS
Environmental Testing Center Laboratory in Aurora, Colorado, under contract with Eastern Research
Group. Complete sets of running loss, hot soak, three-day diurnal, onboard refueling vapor recovery
(ORVR) and static tests procedures were run on each vehicle. Pressures, temperatures and continuous
on-board diagnostic (OBD) purge data were recorded in addition to the measurement of the HC
emissions.
The primary finding of this study was that the HC evaporative emissions of both vehicles
appeared to be controlled during the running loss, hot soak SHED, three-day diurnal, and static tests.
These vehicles are not regulated for ORVR and therefore the tests resulted in high levels of HC
emissions. However, further analysis of the ORVR data indicates that these test results likely
underestimate the amount of emissions because of test procedure issues.
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2. Test Program
The US Environmental Protection Agency (EPA) conducted benchmark evaporative emissions
testing on two heavy-duty gasoline vehicles. The testing was conducted through a contractor, Eastern
Research Group (ERG) at the SGS Environmental Testing Center (SGS) Laboratory in Aurora,
Colorado. Testing objectives were to understand the current state of heavy-duty gasoline vehicle
evaporative emissions performance. The test program details and results are available in the contractor
report.1
2.1 Vehicles
Two heavy-duty trucks, as described in Table 1, were selected to represent a significant portion of
the heavy-duty gasoline fleet. They were recruited under contract, by Jacobs Technology, Inc. They
were in-use vehicles which were leased for the duration of the test program. The engines in both
vehicles were certified as heavy-duty gasoline engines (HDGE) and certified to evaporative emission
standards, as shown in Table 2. Neither vehicle was required to contain an onboard refueling vapor
recovery (ORVR) system because these vehicles are not subject to ORVR emission standards.
Table 1: Test Vehicle Characteristics
Vehicle
Model Year
Engine Size
Transmission
Approx. Odometer
GVWR
(liters)
(miles)
(lbs)
Ford E450
2016
6.8
Auto 6 speed
34,000
14,500
Izuzu NPR
2015
6.0
Auto 6 speed
52,000
14,500
Table 2: Evaporative and Exhaust Emissions Standards
Vehicle
Engine
Certification
Evaporative Emission
Standard (grams/test)
Canister
Working
Capacity (g)
Fuel Tank
Volume
(gal)
Canister
Capacity /
Tank Ratio
(g/gal)
2 Day
3 Day
Running
Loss
Ford E-450
HDGE
>14.0k GVWR
2.3
1.9
0.05
265
55
4.82
Isuzu NPR
HDGE
All Vehicles
2.3
1.9
0.05
150
30
5
1 Eastern Research Group and SGS, Aurora. "Light Heavy-Duty Gasoline Vehicle Evaporative Emissions Test Program,"
February 2019
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2.2 Evapoirat' issions Testing
A full set of evaporative emissions tests on the two vehicles were performed at SGS, Aurora under
contract with ERG. Running Loss, Hot Soak, Diurnal, ORVR and Static tests were performed with
duplicate tests in most cases. Commercial regular grade fuel from the Denver Metro area was used for
the study. The fuel was 85 octane and had a Reid Vapor Pressure of 8.5 psi on average. The box on
each vehicle was removed so that it could fit into the SHED. The vehicles were also modified to include
two type-J thermocouples in the fuel tank, one in the liquid and one in the vapor space, and fuel pressure
measurement ports. Further details of the testing can be found in the referenced report.
3. Emissions Results
3.1 Permeation Emissions
Permeation emissions occur during all operating modes. Specifically they are the hydrocarbon
(HC) emissions that escape through the micro-pores in pipes, fittings, fuel tanks and other vehicle
components. They differ from leaks since they occur on the molecular level and are not a mechanical or
material failure in a specific region. The first hour of the Static tests (Phase 1) is representative of
permeation emissions. Both vehicles performed as expected and did not show any issues with
permeation emissions, as shown in Table 3.
Table 3: Static Test Results
Static Test Results HC Mass (g)
Static Test Results HC Mass
'g/hr)
Phase 1
Phase 2
Phase 3
Total
Phase 1
Phase 2
Phase 3
Total
Isuzu
0.032
0.017
0.028
0.078
0.032
0.034
0.056
0.039
Ford
0.013
0.008
0.010
0.031
0.013
0.016
0.020
0.0155
3.2 Vapor Venting Emissions
Vapor venting emissions are running loss, hot soak and diurnal emissions minus the constant
permeation. Both vehicles were reasonably controlled for in-use vehicles. The testing that was
performed differed from the certification test procedures so these tests only give us an estimation for
comparing to the standards. The running loss results for both trucks are shown in Table 4. The Ford
truck results for the 3-Day Diurnal test was just over half of the standard and the Isuzu was just over the
standard, as shown in Table 5. See the testing report for more details on the procedure and results.
Table 4: 3-Day Running Loss Results
72 Hour Variable Temperature Running Loss HC (g/mile)
Phase 1
Phase 2
Phase 3
WTD
Ford Test 3
0.0007
0.0002
0.0001
0.0010
Ford Test 4
0.0006
0.0003
0.0002
0.0011
Isuzu Test 1
0.0004
0.0001
0.0000
0.0002
Isuzu Test 2
0.0002
0.0001
0.0000
0.0003
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Table 5: 3-Day Diurnal Results
72-hour VT SHED HC Mass (g)
Day 1
Day 2
Day 3
Total
Ford Test 3
0.303
0.270
0.301
0.874
Ford Test 4
0.302
0.240
0.295
0.836
Isuzu Test 1
0.609
0.682
0.672
1.962
Isuzu Test 2
0.530
0.717
0.581
1.828
3.3 Onboard Refueling Vapor Recovery
These two trucks are not subject to an Onboard Refueling Vapor Recovery (ORVR) emissions
standard, therefore uncontrolled HC evaporative emissions were anticipated. The ORVR results for both
trucks are shown in Table 6. However, after the analysis of the data, we determined that the emissions
from the ORVR tests were lower than expected when compared to uncontrolled refueling emissions
levels from predictive models, such as MOVES. Non-ORVR refueling emissions in the MOVES model
are based on a Coordinating Research Council (CRC) study in the 1990's of 22 vehicles with
uncontrolled refueling emissions. We would have expected the uncontrolled refueling hydrocarbon
emissions to be approximately 3.34 grams per gallon based on the CRC study, which equates to
approximately 168 grams from the Ford and 90 grams from the Isuzu assuming a 90% fuel tank fill.
Table 6: ORVR Test Results
ORVR HC Results
Average g/gal
SHED grams
Ford Test 1
2.261
113.611
Ford Test 2
2.145
107.631
Isuzu Test 1
2.163
55.252
Isuzu Test 2
2.833
72.390
To investigate the discrepancy, a detailed investigation into the test procedure, equipment, and
analysis was conducted. No issues were found with the calibration data from any of the analyzers or
equipment used for this testing. Furthermore, no issues were found with the calculations or data analysis.
After discussions with evaporative testing experts it was determined that the application of the existing
EPA ORVR test procedures, which were designed for light-duty vehicles, may not have been
appropriate for the size of these vehicles and the fact that the SHED used in this testing is approximately
one third larger than typical SHEDs. The existing CFR requirements only require emission
measurement for one minute after the completion of the refueling event. As shown in Figure 1 and
Figure 2, the hydrocarbon emissions were still climbing at the end of the tests (one minute after
refueling ends). We believe additional measurement time is required for mixing and likely more fans
for circulation of the air in the SHED for the emissions to stabilize properly. It is not known how much
additional mixing time is necessary without additional testing, but it is likely that between one to three
additional minutes would be required based on extrapolation of the test results, as shown in Figure 3 and
Figure 4.
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100
80
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ro
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u
I
40
20
0
00:00 01:00 02:00 03:00 04:00 05:00 06:00
Time minutesiseconds
Refueling ends
Ford E-450 ORVR Test 8-28-2018
Mixing still occuring,
Grams of HC still
rising in SHED v
Figure 1: Ford E-450 ORVR Test
Izuzu NPR ORVR Test 8-15-2018
1 on
Refueling ends —
140
1 ?n
Mixing still occuring,
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£ 100
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60
40
20
Grams of HC still
rising in SHED
\ —
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^
00:00 01:00 02:00 03:00 04:00 05:00 06:00
Time minutes:seconds
Figure 2: Isuzu ORVR Test
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180
160
140
120
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; 80
60
40
20
0
0C
180
160
140
120
£ 100
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80
60
40
20
0
Ford - Estimated Additional Time Required for Mixing
Three additional
minutes \
Actual End of Test
2.26g/gal
Refueling ends (114grams)
One additional
minute
2.65 8/gal^'
Two additional
minutes
3.08g/gaL,
~ N
MOVES models
3.34 g/gal,
at 2.45 extra
minutes —L
(168 grams)
01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00
Time minutes:seconds
Figure 3: Projected Ford E-450 QRVR Results based on Extrapolation
Izuzu - Estimated Additional Time Required for Mixing
Refueling ends
MOVES models
3.34 g/gal,
at 25 extra
seconds
(85 grams)
One additional
minute
Actual End of Test
2.83 g/gal
(72 grams)
\
01:00 02:00 03:00 04:00 05:00
Time minutes:seconds
Figure 4: Projected Isuzu ORVR Results based on Extrapolation
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