UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MICHIGAN 48105-2498

 

MEMORANDUM

SUBJECT: Presentation on Evaporative Emission System Leaks for a Fuel Tank Under 

Pressure

FROM: Glenn W. Passavant, Senior Mechanical Engineer

Assessment and Standards Division

TO: Docket Number EPA-HQ-OAR- 2011-0135

DATE: February 27, 2013

Background

As part of it Tier 3 NPRM, EPA is proposing to add a more stringent evaporative emission 

standard for hot soak plus diurnal emissions, a leak emission standard, and a more stringent 

leak monitoring and detection orifice diameter for Onboard Diagnostic (OBD) systems. These 

tools are all designed to help assure zero fuel evaporative emissions (“zero evap”) over the 

vehicle useful life.

Presentation

In developing these requirements we were provided information which compared fuel tank leak 

emission rates for a system under pressure such as occurs in some designs today and has the 

potential for increased application in the future with more typical designs which vent to the 

canister. The attached informations shows that when leaks of various orifice diameter are

implanted in a fuel/evaporative system, the leak rate to the atmosphere is significantly greater

from a pressurized system than for one which is vented to the canister. For example, compare 

the emission rate information on slides 46 and 52.

Discussion

EPA is providing this information for public consideration and review. The information in the 

attached charts seems to indicate that if OBD monitoring on a pressurized system indicated a

detectable fuel/evaporative system leak, the hot soak plus diurnal emissions to atmosphere 

would be greatly reduced if the tank valve was programmed to vent to the canister.

OFFICE OF

AIR AND RADIATION
Leak Impact on Sealed Fuel Tanks
PurposeTo determine the relationship between leak size sealed systems and compare that with an open s0.02” leak.

Conclusion: 

• Very small leaks (as small as 0.005”) in sealed sys

totally uncontrolled diurnal emissions.

• Leaks as small as 0.002” on a sealed system relea

times the allowable Tier II limit per day
Overview1. Baseline Testing2. Installed Leak Orifice Testing3. Open System with Leak Orifice Testing4. Next Steps5. Theoretical Emission Calculations
Baseline Testing

PURPOSE: Establish emissions for completely sealTest Procedure:

♦ Precondition Volt canister with 3-6 ORVR cycles♦ Use of a trap canister for fuel tank fill and initial te

stabilization (prior to mini-shed test)

♦ Fill Volt tank with 3.7 gallons (40% fill) of 9 RVP (♦ Condition Volt tank in chamber at 72 

°

F

♦ After fuel in Volt tank is 72 

°F, place Volt system 

♦ Run EPA profile of 72-96 

°

F

♦ Monitor emissions, tank pressure, chamber temp

Tests 9166, 9170, 9210, and 9214 run with modified tTests 9202 and 9206 run on non-modified Volt tank
Setup #1: Sealed Tank Baselin
65707580859095

100

9/4/2012

16:19

9/4/2012

18:43

9/4/2012

21:07

9/4/2012

23:31

9/5/2012 1:55 9/5/2012 4:19 9/5/2012 6:43 9/5/2012 9:07 

Temperature (F)

Baseline #1 (Test 9166) Tank Pressure and Chamber Temperature

3.3 psi pressure build at peak temperature
0

10002000300040005000

9/4/12 4:19

PM

9/4/12 6:43

PM

9/4/12 9:07

PM

9/4/12 11:31

PM

9/5/12 1:55

AM

9/5/12 4:19

AM

9/5/12 6:43

AM

9/5/12 9:07

AM

9

Emissions (mg)

EmissionsChamber Temperature

Baseline #1 (Test 9166) Emissions and Chamber Temperature

705 mg total emissions 

generated for sealed 

system—later found leak 

at temperature weld port
65707580859095

100

9/7/12 12:14

PM

9/7/12 3:07

PM

9/7/12 6:00

PM

9/7/12 8:52

PM

9/7/12 11:45

PM

9/8/12 2:38

AM

9/8/12 5:31

AM

Temperature (F)

Chamber Tank Pre

Baseline #2 (Test 9170) Tank Pressure and Chamber Temperature

3.5 psi pressure 

build at peak 

temperature 

(similar to 

Baseline #1 Test)
0

10002000300040005000

9/7/12 12:14

PM

9/7/12 3:07

PM

9/7/12 6:00

PM

9/7/12 8:52

PM

9/7/12 11:45

PM

9/8/12 2:38

AM

9/8/12 5:31

AM

Emissions (mg)

EmissioChambe

Baseline #2 (Test 9170) Emissions and Chamber Temperature

Baseline 

Tried to seal leak at 

temperature weld port 

but did not hold 
0

255075

100125150175200

10/2/12 3:07 PM 10/2/12 6:00 PM 10/2/12 8:52 PM 10/2/12 11:45

PM

10/3/12 2:38 AM 10/3/12 5:31 AM 10/3/12 8:24 AM 

Emissions (mg)

EmissionsChamber Temperature

Baseline #3 (Test 9202) Emissions and Chamber Temperature

Baseline Emissions = 24 mg

t
0

255075

100125150175200

10/5/12 4:33 PM 10/5/12 7:26 PM 10/5/12 10:19

PM

10/6/12 1:12 AM 10/6/12 4:04 AM 10/6/12 6:57 AM 10/6/12 9:50 AM 

Emissions (mg)

EmissionsChamber Temperature

Baseline #4 (Test 9206) Emissions and Chamber Temperature

Baseline Emissions = 30 mg

(similar to Baseline #3 results)

t
Summary: Baseline Testing Em

Baseline Emissions

0

100200300400500600700800

9166 9170 9202 9206 9

Tests

Emissions (mg) Tests performed with non- modified Volt tank

• Observed 179 to 710 mg total emissions from mod• Observed 24 to 30 mg total emissions from unmod

◦ Unmodified Volt tank was brand new and only “

Emissions could be from adhesives on the tank
Summary: Baseline Testing Tank P

• Theoretical Pressure Build for completely sealed system • Observed 3.3 to 3.9 psi build with modified tank (with kn

temperature transmitter weld port)

• Unable to record pressure with non-modified tank (tests 

Baseline Tank Pressures

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

9166 9170 9202 9206 9

Tests

Pressure (psi) Tests performed with non- modified Volt tank so NO PRESSURE DATA
Installed Leak Orifice Testing

PURPOSE: Determine impact of varying leak sizes on seTest Procedure:

♦ Precondition Volt canister with 3-6 ORVR cycles♦ Use of a trap canister for fuel tank fill and initial tempera

to mini-shed test)

♦ Fill Volt tank with 3.7 gallons (40% fill) of 9 RVP (62 kP♦ Condition Volt tank in chamber at 72 °F♦ After fuel in Volt tank is 72 °F, attach preconditioned V

system set up in #2 configuration

♦ Place Volt system in Mini-Shed♦ Monitor tank pressure and chamber temperature♦ Run 1 day diurnal with EPA profile of 72-96 °F♦ Monitor emissions

All leak tests run on modified Volt tank (see set-up #2)Leak orifice sizes range from 0.002” to 0.02” (max OBD II a
Setup #2: Sealed Tank with Lea
Setup #2: Sealed Tank with Lea

FTIV

Temperature 

Transmitter

Leak 

Orifice

Canist
65707580859095

100

9/10/12 2:24 PM 9/10/12 5:16 PM 9/10/12 8:09 PM 9/10/12 11:02

PM

9/11/12 1:55 AM 9/11/12 4:48 AM 9/11/12 7:40 AM 

Temperature (F)

ChamTank 

0.020” Leak (Test 9172) Chamber Temperature and Tank Pressure

No pressure 

build up in 

system with leak
0

2000400060008000

100001200014000160001800020000

9/10/12 2:24

PM

9/10/12 5:16

PM

9/10/12 8:09

PM

9/10/12

11:02 PM

9/11/12 1:55

AM

9/11/12 4:48

AM

9/11/12 7:40

AM

Emissions (mg)

EmissionsChamber Temperature

0.020” Leak (Test 9172) Emissions and Chamber Temperature

Emissions increase wgrams vs. baseline at 
-5

5

15253545556575

9/10/12 2:24

PM

9/10/12 5:16

PM

9/10/12 8:09

PM

9/10/12 11:02

PM

9/11/12 1:55

AM

9/11/12 4:48

AM

9/11/12 7:40

AM

9/

Emission Rate (mg/min)

Emissions SlopeChamber Temperature

0.020” Leak (Test 9172) Emissions Rate and Chamber Temperatu

Emissions Ra

Initially Elevat
65707580859095

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10/22/12

8:52 PM

10/22/12

11:45 PM

10/23/12

2:38 AM

10/23/12

5:31 AM

10/23/12

8:24 AM

10/23/12

11:16 AM

10/23/12

2:09 PM

Temperature (F)

Chamber TempeTank Pressure D

0.005” Leak (Test 9217) Chamber Temperature and Tank Pressure

Slight i

of pres

reduce
0

2000400060008000

100001200014000160001800020000

10/22/12

8:52 PM

10/22/12

11:45 PM

10/23/12

2:38 AM

10/23/12

5:31 AM

10/23/12

8:24 AM

10/23/12

11:16 AM

10/23/12

2:09 PM

Emissions (mg)

EmissionsChamber Temperature

0.005” Leak (Test 9217) Emissions and Chamber Temperature

Total emiss

grams sim

0.005” and 
65707580859095

100

11/7/12 4:04

PM

11/7/12 6:57

PM

11/7/12 9:50

PM

11/8/12 12:43

AM

11/8/12 3:36

AM

11/8/12 6:28

AM

11/8/12 9:2

AM

Temperature (F)

ChambTank P

0.003” Leak (Test 9233) Chamber Temperature and Tank Pressure

Max Pressure: 

2.19 psi
0

2000400060008000

10000120001400016000180002000011/7/12 4:04 PM 11/7/12 6:57 PM 11/7/12 9:50 PM 11/8/12 12:43

AM

11/8/12 3:36 AM 11/8/12 6:28 AM 11/8/12 9:21 

Emissions (mg)

EmissionsChamber Temperature

0.003” Leak (Test 9233) Emissions and Chamber Temperature

Total emissio

grams + 1

canister we
65707580859095

100

12/4/12 1:55

PM

12/4/12 4:48

PM

12/4/12 7:40

PM

12/4/12

10:33 PM

12/5/12 1:26

AM

12/5/12 4:19

AM

12/5/12 7:12

AM

1

10

Temperature (F)

Chamber TTank Press

0.002” Leak (Test 9253) Chamber Temperature and Tank Pressure

Max Pressure = 

2.9 psi
0

2000400060008000

10000120001400016000180002000012/4/12 1:55 PM 12/4/12 4:48 PM 12/4/12 7:40 PM 12/4/12 10:33

PM

12/5/12 1:26 AM 12/5/12 4:19 AM 12/5/12 7:12 AM 

Emissions (mg)

EmissionsChamber Temperature

0.002” Leak (Test 9253) Emissions and Chamber Temperature

Total 

7
Summary: Leak Orifice Testing 

• Emissions observed for 0.005” & 0.02” orifices in range 

similar to tank open to atmosphere, with no environmen

• Per Wade Reddy equation, range of theoretical emissio

(RVP range of 9 – 10.5) is 16.7 to 28.4 grams

• Observed reduction in emissions as leak orifice size dec

still significant

NOTE: Weight gain by canister NOT included in these va

Leak Orifice Test Emissions

0

5000

10000150002000025000

0.02" 

9172 

0.02"

9176

0.005"

9179

0.005"

9217

0.003"

9233

0.003"

9238

0

Emissions (mg)
Summary: Leak Orifice Testing 

Leak Orifice Impact on Emissions

0

5000

10000150002000025000

0 10 20 30 

Data Points

Normalized Total Emissions (mg)

0.02" Test 91720.02" Test 91760.005" Test 91790.005" Test 92170.003" Test 92330.003" Test 92380.002" Test 92490.002" Test 9253
Summary: Leak Orifice Testing 

• Negligible pressure build with 

≥ 0.005” orifice, beh

system

• Pressure build 2 - 2.2 psi for 0.003” orifice tests an

Leak Orifice Test Tank Pressure

0

0.5

1

1.5

2

2.5

3

3.5

0.02" 

9172 

0.02"

9176

0.005"

9179

0.005"

9217

0.003"

9233

Pressure (psi)
Open System Testing with Leak Ori

PURPOSE: Determine total emissions released with conv

(ambient pressure) and leak orifice; Compare results to 

Test Procedure:

♦ Precondition Volt canister with 3-6 ORVR cycles♦ Use of a trap canister for fuel tank fill and initial tempera

to mini-shed test)

♦ Fill Volt tank with 3.7 gallons (40% fill) of 9 RVP (62 kP♦ Condition Volt tank in chamber at 72 °F♦ After fuel in Volt tank is 72 °F, attach preconditioned V

system set up in #3 configuration (NOTE: FTIV remov

♦ Place Volt system in Mini-Shed♦ Monitor tank pressure and chamber temperature♦ Run 1 day diurnal with EPA profile of 72-96 °F♦ Monitor emissions

All open system tests run on modified Volt tank (see set-up 
Setup #3A: Open Tank with L
65707580859095

100

10/26/12

1:12 PM

10/26/12

4:04 PM

10/26/12

6:57 PM

10/26/12

9:50 PM

10/27/12

12:43 AM

10/27/12

3:36 AM

10/27/12

6:28 AM

Temperature (F)

Chamber TemTank Pressur

0.020” Leak w/o FTIV (Test 9Chamber Temperature and Tank Pressure

As expected, no 

pressure build up
0

500

1000150020002500300035004000

10/26/12

1:12 PM

10/26/12

4:04 PM

10/26/12

6:57 PM

10/26/12

9:50 PM

10/27/12

12:43 AM

10/27/12

3:36 AM

10/27/12

6:28 AM

Emissions (mg)

EmissionsChamber Temperature

0.020” Leak w/o FTIV (Test 9Emissions and Chamber Temperature

3.1 g emitted to Chamber

17.9 g to Canister

.01 g to Kynar Bag =

21.0 g Total
Setup Adjustment from 3A to 3

• Removed Kynar Bag attachment and opened cani

port to inside of Mini-SHED

• Noticed significant change in system behavior

♦ Majority of emissions flow through the canister vs

• Exact cause for different results is unknown
Setup #3B: Open Pressure TanLeak Orifice 
Setup #3B: Vented Pressure Tank wi

Canister Vent Open to 

Mini-SHED

Temperature 

Transmitter

Leak 

Orifice

Press

Indic

Can
65707580859095

100

1/4/13 4:19

PM

1/4/13 7:12

PM

1/4/13 10:04

PM

1/5/13 12:57

AM

1/5/13 3:50

AM

1/5/13 6:43

AM

1/5/13 9:36

AM

Temperature (F)

Chamber TTank Press

0.020” Leak w/o FTIV (Test 9Chamber Temperature and Tank Pressure

As expected, no 

pressure build 

observed 
0

500

100015002000250030003500

1/4/13 4:19

PM

1/4/13 7:12

PM

1/4/13 10:04

PM

1/5/13 12:57

AM

1/5/13 3:50

AM

1/5/13 6:43

AM

1/5/13 9:36

AM

Emissions (mg)

EmissionsChamber Temperature

0.020” Leak w/o FTIV (Test 9Emissions and Chamber Temperature

0.25 g emitted 

25.5 grams to 

25.7 g 
65707580859095

100

1/9/13 3:07

PM

1/9/13 6:00

PM

1/9/13 8:52

PM

1/9/13 11:45

PM

1/10/13 2:38

AM

1/10/13 5:31

AM

1/10/13 8:24

AM

Temperature (F)

Chamber TemTank Pressure 

0.005” Leak w/o FTIV (Test 9Chamber Temperature and Tank Pressure

No pressure 

build observed, 

same as 0.02” 

leak OPEN test 

results
0

500

100015002000250030003500

1/9/13 3:07

PM

1/9/13 6:00

PM

1/9/13 8:52

PM

1/9/13 11:45

PM

1/10/13 2:38

AM

1/10/13 5:31

AM

1/10/13 8:24

AM

Emissions (mg)

EmissionsChamber Temperature

0.005” Leak w/o FTIV (Test 9Emissions and Chamber Temperature

0.20 g emitted 

21.1 g to C

21.3 g 
Impact of Leaks on Open vs

System

Any leak size >0.002" (and likely smaller) in a sealed sys

will generate emissions higher than an open system wi

0.02" leak orifice, vented through the canister

05

10152025

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.013

0.014

0.015

0.016

Leak Orifice Size (in)

Day 1 Diurnal Emissions (g) Sealed System Open System Trendline Seal

Trendline Open 

Chevrolet Volt Fuel Tank

 9.3 gal capacity; EPA Temp Profile

9 RVP E-10 Fuel
Impact of Leaks on Open vs. Se

0.05.0

10.015.020.025.0

0.02 0.005 0.003 

Avg Day 1 Diurnal Emissions (g)
Appendix: Orifice Flow Calcula

Q = C * A (2 * P / 

ρ

)0.5

M = Q * 

ρ

Q = Volumetric Flow Rate m

3/s

C = Orifice CoefficientA = Area of orifice m

2

P = Pressure Paρ = Density kg/m

3

M = Mass Flow Rate kg/s

Ass

1. HC c

emittis thinsid

2. Orifi

is 0.7
Appendix: Orifice Flow Calcula0.003” Actual vs. Predicted Emissions

0

2000400060008000

1000012000140001600018000

0 100 200 300 400 500 600 7

Time (min)

Emissions (mgs)

0.003in Leak Actual0.003in Predicted
Appendix: Orifice Flow Calcula0.002” Actual vs. Predicted Emissions

0

2000400060008000

1000012000140001600018000

0 100 200 300 400 500 600 700 

Time (min)

Emissions (mgs)

0.002in Actual0.002in Predicted