-------
3.4.5 Chevrolet Silverado Test Results
- Original FTTP Acquired for WA 1-08
-7/23/13 3XLA-92(8psiRVP)
8/5/13 US-06 +Cruise (SpsiRVP)
-- 3/27/13 FTTP (8 psi RVP)
- 8/27/13 3 X LA - 92 (8 psi RVP)
114.3
113.6
112.8
^^
Ln
2156
Time(s)
1
|-0.05
S
Original FTTP Acquired for WA 1-08
7/23/13 3 X LA-92 (8 psi RVP)
8/5/13 US - 06 + Cruise (Spsi RVP)
-8/27/13 FTTP (Spsi RVP)
- 5/27/13 3 X LA - 92 (8 psi RVP)
A^
LJ v
' /""'n
"f~ --- \ ' f™< ..... ' ' J**""^ .................. /^ .....
20 «
0 ,E
1S26 2156
Time (s)
^
7/23/13 3 X LA - 92 (8 psi RVP)
8/5/13 US-06 +Cruise (Spsi RVP)
8/27/13 FTTP (8 psi RVP)
8/27/13 3 X LA - 92 (8 psi RVP)
1S26 2156
Time (s)
13
-------
3.4.6 Observations and Conclusions
Fuel tank temperature profile is influenced by a number of factors, such as the following:
• road surface temperature (or heated mat / simulated road surface temperature)
• distance from road surface to tank
• spatial arrangement, including exposed area of fuel tank to heated road surface
• fuel tank material and associated heat transfer properties
• volume of fuel in tank
• rate of heat generation from in-tank fuel pump
• proximity of exhaust to fuel tank
• arrangement of associated heat shielding, and
• volume and speed of air flowing under tank (which influences convective
cooling)
Although many of these parameters are fixed based on the vehicle type, the volume and
speed of air flowing under the tank will vary based on the drive cycle (speed of vehicle) while
the road surface temperature can vary from test to test.
This study demonstrated the difficulties in replicating the generation of OEM fuel tank
temperature profiles through an in-lab simulation, in particular without knowledge of actual road
surface temperatures and wind conditions from the original on-road temp profile development
work. It's also possible that the OEM fuel tank temperature profiles were numerically modified
(smoothed) before use in evaporative certification testing.
Further complications such as limited laboratory control of the road surface mat
temperature and potential temperature gradients in the laboratory flow tunnel resulted in
additional deviations between fuel tank temperature profiles developed during this study and
those originally developed by the original vehicle manufacturers.
As described in Appendix B, the Toyota Corolla showed increased temperatures for the
more aggressive drive cycles, an effect unique to this vehicle. All other vehicles demonstrated a
decrease in the tank temperature for the more aggressive cycles, likely due to the increased air
flow (and thus convective cooling) at the underside of the fuel tank. Further investigation
revealed the exhaust heat shields for the Corolla had been removed during a prior study, resulting
in exhaust system radiation heating of the fuel tank. This likely caused the tank temperature
profiles from the more aggressive traces to show increases above the original certification
profile. After new heat shields were acquired and installed, testing showed very good agreement
14
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between this study's temperature profile and the original certification temperature profile.
Figure 3.4.3 shows a corresponding increase in fuel tank pressure (reduction in tank vacuum) due
to the purge being overwhelmed from the excessive heating.
The Chevrolet Silverado (and to a lesser extent the Toyota Corolla) exhibited steep
temperature rate increases near the beginning of temperature development tests. This was seen
on all the Silverado tests, but was primarily limited to one of the LA-92 tests for the Corolla.
Supplemental measurements of the flow tunnel ambient temperatures conducted by SGS-ETC
suggested this could be due to ambient temperature gradients at the start of the tests (prior to
adequate ambient air mixing), although it's not entirely clear why this occurred with these two
vehicles and not the other test vehicles.
Exploratory testing conducted by SGS-ETC in order to determine the cause of differences
between the FTTP profiles developed for this study and those used for original vehicle
evaporative emissions certification testing did seem to indicate the original profiles could be
obtained by adjusting the road surface mat temperature set point. Since the OEM mat set point
was unknown in most cases, this would entail an iterative process in which the mat temperature
was adjusted based on its predicted effect in order to match the OEM FTTP profile. Based on
this testing, numerical strategies were developed to "normalize" drive trace temperatures to
match the OEM FTTP profiles. These strategies are described in Appendix B, and sample
calculations are provided electronically as Appendix C. However, the temperature profiles
provided for this study have not been normalized using any of these strategies. Future work
could be conducted to determine how best to apply adjustments to the profiles provided as part of
this study, although care must be taken to apply the data corrections only to deviations resulting
from systematic bias.
15
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4.0 References
1. CRC E-77 reports: Haskew, H., Liberty, T. (2008). Vehicle Evaporative Emission
Mechanisms: A Pilot study, CRC Project E-77; Haskew, H., Liberty, T. (2010),
Enhanced Evaporative Emission Vehicles (CRC E-77-2); Haskew, H., Liberty, T.
(2010), Evaporative Emissions from In-Use Vehicles: Test Fleet Expansion (CRC E-
77-2b); Haskew, H., Liberty, T. (2010), Study to Determine Evaporative Emission
Breakdown, Including Permeation Effects and Diurnal Emissions Using E20 Fuels on
Aging Enhanced Evaporative Emissions Certified Vehicles, CRC E-77-2c; DeFries,
T., Lindner, J., Kishan, S., Palacios, C. (2011), Investigation of Techniques for High
Evaporative Emissions Vehicle Detection: Denver Summer 2008 Pilot Study at Lipan
Street Station; DeFries, T., Palacios, C., Weatherby, M., Stanard, A., Kishan,
S.(2013) Estimated Summer Hot-Soak Distributions for Denver's Ken Caryl I/M
Station Fleet
2. DeFries, T., Lindner, J., Kishan, S., Palacios, C. (2011), Investigation of Techniques
for High Evaporative Emissions Vehicle Detection: Denver Summer 2008 Pilot Study
at Lipan Street Station; DeFries, T., Palacios, C., Weatherby, M., Stanard, A., Kishan,
S.(2013) Estimated Summer Hot-Soak Distributions for Denver's Ken Caryl I/M
Station Fleet.
3. Sabisch, M., Kishan, S, Stewart, J, Glinsky, G. (2014), Running Loss Testing with
Implanted Leaks.
4. Lindner, J., Sabisch, M., Glinsky, G, Steward, J., StDenis, M., Roeschen, J, (2012)
Multi-Day Diurnal Testing, Contract CP-C-06-080, WA 5-11.
5. Haskew, H., Liberty, T. (2010), Enhanced Evaporative Emission Vehicles (CRC E-
77-2); Haskew, H., Liberty, T. (2010), Evaporative Emissions from In-Use Vehicles:
Test Fleet Expansion (CRC E-77-2b); Haskew, H., Liberty, T. (2010), Study to
Determine Evaporative Emission Breakdown, Including Permeation Effects and
Diurnal Emissions Using E20 Fuels on Aging Enhanced Evaporative Emissions
Certified Vehicles, CRC E-77-2c.
16
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5.0 Index of Appendices
The following is a list of the appendices to be provided with this report. As noted below,
some appendices will be provided as separate electronic files.
Appendix A - Test Fuel Specifications
Appendix B - Issues Encountered and Solutions
Appendix C - Drive Trace Temperature Normalization Examples (electronic
appendix, *.xlsx format)
Appendix D - Descriptions of Study Data (the following files will be provided
electronically, by vehicle)
DAQ Recording (*.csv)
Ford DTF Data Recording (*.txt)
OBDII Data (*.csv)
Test Data (*.xlsx)
17
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Appendix A
Test Fuel Specifications
-------
Test fuel used for this study conformed to the following specifications:
Test Fuel Type
Test Fuel Specification Number
Fuel Description/ Application
RON
MON
Sulfur (ppm)
T10(°C/F)orE70(%v/v)
T50 ( °C/F) or E100 (%v/v)
T90 (°C/F) or El 50 (%v/v)
Vapor Pressure (kPa / psi)
Oxygenates (vol%) (e.g. ethanol,
methanol, MTBE, ETBE, etc.)
Additives
Lead (g/L)
General Purpose and other DV
WW XE-M4CX560-A
E10 GASOLINE, Worldwide Driveability Sign-off,
91 RON E10 Summer Nominal (0°C and above)
90-92
82-84
10 max
T10 = 50-60C(122- 140 F)
T50 = 90- 100 C (194- 212 F)
T90 = 160 - 170 C (320 - 338 F)
55 - 60 kPa (8.0 - 8.7 psi)
10+/- 0.2 %v/v Ethanol
Normal Commercial
0.0025 max
A-l
-------
Appendix B
Issues Encountered and Solutions
-------
This appendix provides a summary of issues that were encountered during this study and
a description of how each of those issues was addressed.
The study performed previously in Work Assignment 1-08, Running Loss Testing with
Implanted Leaks, demonstrated difficulties in collecting the OBD commanded evaporative purge
data stream. Only two of the vehicles from that study (which are the same as the vehicles in this
study, the 2009 Toyota Corolla and the 2010 Ford Focus PZEV) broadcasted the OBD
commanded evaporative purge. SGS-ETC measured and recorded the purge valve voltage to
determine the commanded purge signal for the remaining vehicles, using an Omega multichannel
portable data acquisition system (DAQ).
The Ford DTF did not have any viable means of measuring temperature data from the J-
Type thermocouples which had been previously installed in the vehicle's sending units for
vehicle fuel and fuel vapor temperature measurements, so SGS-ETC used the portable data
acquisition system previously described in order to measure temperatures of the fuel liquid and
vapor and also the ambient temperatures, in addition to the commanded evaporative purge.
Due to challenges with obtaining OBD data during Work Assignment 1-08, SGS-ETC
made stronger efforts to collect OBD data from all tests during this study. While SGS-ETC was
more successful in this endeavor than during Work Assignment 1-08, there are several instances
of missing data. This is most notable with the Corolla data, where OBD data is missing from
several tests. Since SGS-ETC expected to obtain the commanded evaporative purge from the
OBD datastream, purge voltage was not collected, so for these tests, no purge rate signal (voltage
or OBD) is available. Consequently, of the five tests performed on the Corolla, only two have
commanded evaporative purge.
The Caravan does not have commanded purge data available for the LA-92 trace. This
happened to be the first test performed using the DAQ system and it was not connected. This
test did not demonstrate any other problems so it was decided to accept this test despite missing
data.
Time alignment was handled by starting the DAQ recording as the test began. OBD data
and pressure data (as measured by the Ford DTF) were aligned using vehicle speed and
dynamometer roll speed, respectively.
During initial testing, the vehicle was moved into the wind tunnel while the wind tunnel
was heating up, before the SGS-ETC technical supervisor arrived on-site. This would cause the
liquid fuel temperature to fall below the 92 °F cutoff specified in 86.129-94(d)(4)(ii)(B), so test
B-l
-------
personnel would then wait until the fuel temperature reached 92 °F, plus an additional hour to
allow the fuel temperature to stabilize prior to the start of testing on that vehicle.
During the first day of testing (July 22, 2013), the SGS-ETC technical supervisor noticed
poor control of the thermal mat temperatures. The mat temperature was being controlled using a
simple step control method and the simulated air speed of the more aggressive trace was causing
large fluctuations in the mat temperature. Ford DTF improved the control by applying insulation
over the surface thermocouple. However, the mat temperatures continued to swing, so SGS-ETC
set the mat temperature to be greater than the minimum required 125 °F so that the temperature
swings would not cause the mat temperatures to fall beneath the minimum temperature specified
in the CFR.
At the beginning of testing, the air conditioning system in the Honda Accord was
inoperable. The temperature inside the vehicle exceeded 110 °F during the first test performed on
July 22, 2013 on this vehicle. This thermal extreme caused a problem with the data acquisition
system inside the car, resulting in the data having a severe noise issue. To correct this problem,
the vehicle was transported to SGS-ETC facilities in Jackson, MI, where the air conditioning
system was repaired. The original test was voided and later successfully repeated.
On August 5, 2013, a failure in the DTF wind tunnel resulted in wind speed not being
maintained for a portion of two of the US-06 tests performed on the Ford Focus and the Dodge
Caravan. SGS-ETC technical oversight elected to continue testing and performed a repeat of the
less aggressive 3 x LA-92 test cycle on the Accord to allow Ford DTF staff to make necessary
repairs to the wind tunnel. After repairs, two subsequent US-06 tests were successfully
completed on the Silverado and Corolla. The two tests on the Focus and Caravan were voided
and repeated the following night.
During the US-06 test conducted on August 5, 2013 the vent line on the Caravan was
clamped closed by one of the chain tie downs in the wind tunnel. This caused the amount of
vacuum on the system to increase well beyond the typical amount of vacuum. This test had
already been voided due to the previously-described wind tunnel malfunction. On subsequent
tests, as part of the test process SGS-ETC technical oversight verified that the vent line was not
pinched prior to test commencement.
The data acquisition computer crashed during the August 27, 2013 standard Fuel Tank
Temperature Profile (FTTP) testing on the Corolla. Since SGS-ETC was not able to recover data
from this experiment, this test was voided and repeated on September 24, 2012.
B-2
-------
The Chevrolet Silverado's brakes failed during the US-06 test on August 6, 2013, causing
a brief period of driver violations. The driver attempted to use the emergency brakes to slow the
vehicle during this period. This was discussed with EPA and ERG personnel and it was decided
that this was acceptable as the Silverado is an in-use vehicle.
Several vehicles, most notably the Silverado and the Corolla (prior to installing the heat
shield as later described in this section), displayed a very rapid increase in liquid fuel
temperature during the first ten minutes of testing, on occasion climbing as much as 10 °F during
this period of time. This behavior was rigorously investigated through several techniques. SGS-
ETC first performed a test in which the vehicle was parked in a shaded area and idled for at least
20 minutes. During this time, SGS-ETC measured the liquid fuel temperature to determine if the
rapid increase in liquid fuel temperature was being induced by the vehicle. The temperature
gains after 20 minutes were never greater than 5 °F. Results from additional data reviews
suggested this temperature increase was caused by the facility's wind tunnel air temperature. Air
temperature measurements collected in various locations by SGS-ETC showed the air
temperature dipped during the first minutes of testing and the following air temperature increase
coincided with the fuel temperature increase.
The Corolla showed greatly increased temperatures for the more aggressive cycles than
for the previously obtained tank temperature profile. This effect was unique to this vehicle. All
other vehicles demonstrated a decrease in the tank temperature for the newer cycles. During the
latter stages of the project, it was discovered that the Corolla was missing the original
manufacturer's fuel tank heat shield. A replacement shield was ordered and installed by SGS-
ETC. The FTTP test performed after installing the heat shield showed very good agreement
between the obtained temperature profile and the original certification temperature profile.
During the course of the study, the scope was expanded to include correlation testing to
verify the each vehicle manufacturer's original certification tank temperature profile. The
temperature profiles developed during this study using the FTTP drive trace did not match the
manufacturer's original FTTP temperature profiles. The tank temperature profiles developed at
the Ford DTF facility were consistently higher or lower than the OEM profiles. Additional
testing was performed on the Ford focus, increasing the mat temperature above the 125 °F set
point in an attempt to generate a matching temperature profile. This testing produced a good
match, with the final test performed on the Corolla (with the heat shield installed) obtaining a
superior match using the 125 °F mat temperature.
B-3
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Based on results of this verification testing, EPA, ERG and SGS-ETC discussed whether
or not the LA-92/US-06 tank temperature profiles that were developed during this study should
be "normalized" to correct for the temperature discrepancies seen between this study's FTTP
profiles and the vehicle manufacturer's original FTTP profiles. This would help ensure the LA-
92/US-06 temperature profiles developed during this study are the same as if they had been
developed by vehicle manufacturers using this study's drive cycles (manufacturer-equivalent,
with all vehicle and test conditions equivalent to those at the manufacturer's test facility). Using
"normalized" temperature profiles would help ensure running loss evaporative emissions
measured using this study's LA-92/US-06 drive traces would not be biased by drive trace
temperature discrepancies (which were shown in work assignment 1-08 to have a large influence
on running loss emissions for vehicles with induced leaks).
Three different candidate strategies were developed for drive trace temperature
"normalization". The first strategy (Final Temperature Correction of Original FTTP Profile)
would scale the original (vehicle manufacturers') FTTP profile by the ratio of the final
temperatures of the original FTTP profile to the recorded FTTP profile multiplied by the final
drive trace temperature. This strategy is shown mathematically as follows:
rri S-\ L/> lyiflUl I \JI lyillUl ™ fAQOR^ Q ^ I I Q ^
' C.nTTfrtfr} \^) 7^ ^ M n «^.x ,,. r- ' I 7^ / * n «^.x ' ' Rprnrrlprf I T'OUo J "D I ~r " J
The second candidate strategy (Final Temperature Correction of the Recorded FTTP
Profile) would scale the recorded FTTP profile by the ratio of the final temperatures of the
original FTTP profile to the recorded FTTP profile multiplied by the final drive trace
temperature. This strategy is shown mathematically as follows:
m_ ^corded (0-95 /7>rrPor.fl.nai(4308)
TcorrectedW ~ ~ - ^ - ' - ^corded (4308) -
- 95 T
yD \l FTTPRecorded
The third candidate strategy (Continuous Correction) would provide a continuous
correction of the recorded temperature by an ongoing ratio of the temperatures of the original
FTTP profile to the recorded FTTP profile. This strategy is shown mathematically as follows:
_ rgna _
1 Corrected W T /••% L Recorded v"v
lFTTPRecorded\l)
Examples of each of these strategies are provided electronically (Appendix C). None of
the temperature profiles developed during this study have been corrected using any of these
strategies.
B-4
-------
Appendix C
Drive Trace Temperature Normalization Examples
(Note: This appendix will be provided electronically as a *.xlsx file)
-------
Appendix D
Study Data
(Note: Descriptions of the data to be provided electronically follow)
-------
Several files were obtained for each test performed during this study. These are
described below, and the files are provided electronically as appendices. The file naming
convention for these files is as follows:
[Date]_[Vehicle]_[Test Type]_[DAQ/DTF/OBD Data SetJ.csv
The date stamp is compressed into a six-digit number, the first two digits represent the
year, the following two digits represent the month, and the last two digits are the day.
Date Stamp:YYMMDD so 130723 becomes 7/23/2013
The Test Type identifier designates the trace tested during a particular test. The following
table coordinates the test type with the specific trace performed.
Table 3. Running Loss Testing Sequence
Test Type
FTTP
LA92
US06
Specific Trace
Standard Running Loss Trace
3 X LA-92
2 X US-06 + 70 mph Cruise + 2 X US-06
Duration (s)
4308
4308
4308
Average
Speed (mph)
14.4
24.6
57.1
Maximum
Speed (mph)
56.7
67.2
80.3
DAQ Recording (*.csv)
The DAQ recording is parsed into a csv. During experimentation additional instruments
were added and removed from the configuration as necessary. The data presented in the DAQ
files doesn't conform to a single standard output. There was some consideration as to adding a
MFM to measure purge flow, however this instrument was never connected as it might interfere
with proper purge behavior on the vehicle. The existence of such a channel within the data is
erroneous, and reflects that nothing was measured using this device. The dataset contains the
following measurements.
Start Time: Time and date the data recording was initiated.
Elapsed Time: Measured in seconds since Start Time.
Purge Valve: Measured in voltage. When converting this to voltage, the minimum
voltage was assumed to correspond with a commanded purge of 0%, and the maximum voltage
was assumed to correspond with a commanded purge of 100%.
D-l
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Liquid Fuel Temperature: Measured in degrees Celsius, uses instrumentation installed for
WA 1-08 Running Loss Testing with Implanted Leaks.
Vapor Fuel Temperature: Measured in degrees Celsius, uses instrumentation installed for
WA 1-08 Running Loss Testing with Implanted Leaks.
Ambient Temperature/Ambient Top Temperature: Measured in degrees Celsius. A
thermocouple was installed on the roof of the vehicle to verify ambient temperature simulation.
Ambient Front Temperature: Measured in degrees Celsius. A thermocouple was installed
at the front of the vehicle extending downward so as to measure the temperature of the air before
it passes under the vehicle. This was done to check for thermal stratification.
Ford DTP Data Recording (*.txt)
This tab delimited file is produced by Ford DTP data recording systems. The file begins
with a row of header information containing the following data.
Vehicle: The test vehicle is identified.
Start Date: The date the test was performed.
Start Time: The time data recording began.
Operator: The technician responsible for controlling the wind tunnel during the test.
The file then produces several measurements of streaming data and test inputs. The
recording frequency for these data are 1 Hz. Only a few of these data were used in the post-
processing and quality analysis.
AID-Roll-Speed-F: Measured in miles per hour, this was used to align the individual data
files for front wheel drive vehicles.
AID-Roll-Speed-R: Measured in miles per hour, this was used to align the individual data
files for the one rear wheel drive vehicle, the Silverado.
AIRSPEED: Measured in miles per hour, this was checked against roll speed to verify
proper operation of the wind tunnel
D-2
-------
AIRHUMIDITY: Measured in percent relative humidity, this was checked to verify that
the wind tunnel temperature and humidity controls were operating properly.
AIRTEMP: Measured in degrees Fahrenheit, this was checked against the ambient
thermocouples installed on the vehicle and recorded using the DAQ.
MATS SUR: Measured in degrees Fahrenheit, this is the surface temperature of the
forward pavement simulation mat.
MAT4_SUR: Measured in degrees Fahrenheit, this is the surface temperature of the
middle pavement simulation mat.
MATS SUR: Measured in degrees Fahrenheit, this is the surface temperature of the rear
pavement simulation mat.
MAT6_SUR: Measured in degrees Fahrenheit, this is the surface temperature of the rear
pavement simulation mat used for the Silverado.
Fuel Vapor Pressure: Measured in inches of water, this is a measurement of positive
pressure on the fuel system.
OBD2 Data (*.csv)
OBDII data was collected using a HEM Data mini logger provided by the EPA during the
three driving portions (the FTP 72, the FTP 75, and the running loss test) of the test sequence.
The OBDII data collection system was problematic and didn't consistently record data for all
tests (as discussed above in the Issues Encountered and Solutions section). Data is stored in a
binary file that is processed using the HEM Data's DawnEdit software. The data available varies
for each vehicle as some vehicles use different communication standards and don't broadcast the
same types of data. The data description in below describes only the data that was used during
analysis. Also, per the discussion above in the Issues Encountered and Solutions section - OBDII
data is not available for all driving tests.
Time: When the drive cycle began
VIN: The vehicle identification number for the unit under test
Vehicle Speed: The vehicle speed measured in miles per hour
D-3
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Commanded Evaporative Purge: Measured in percent, this is how much purge was
commanded by the vehicle while the vehicle was in operation
Test Data.xlsx
The three data files are collated, and then added to a single Excel workbook containing
all test results and responsible for data visualization. Data from each vehicle is contained on a
single sheet for that particular vehicle.
D-4
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