EPA-420-S-91-100
Docket Number: A-87-11
Document Number: 76) 1V-A
Summary of Changed Circumstances
Control of Air Pollution From New Motor Vehicles and New Motor
Vehicle Engines; Refueling Emission Regulations for Gasoline-
Fueled Light-Duty Vehicles and Trucks and Heavy-Duty Vehicles
August 1991
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Sources
Office of Air and Radiation
U.S. Environmental Protection Agency
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On August 19, 1987 EPA published in the Federal Register a
Notice of Proposed Rulemaking (NPRM) for the control of vehicle
refueling emissions (52 FR 31162). This document provides a
summary of relevant changed circumstances since the NPRM was
published. Section I details the changed circumstances and Section
II provides a discussion of the impact of these changed
circumstances on the proposed action.
The changed circumstances discussed in this document arise
from three sources. First, the 1990 Clean Air Act Amendments
(CAAA) include changes to the provisions related to onboard and
Stage II controls. Second, technology developments and several
recent/pending regulatory actions have potential effects on EPA's
analyses related to onboard controls. Third, comments received
following issuance of the NPRM indicate that changes may be
appropriate for several aspects of the proposal.
I. Changed Circumstances
This section discusses the changed circumstances since
issuance of the NPRM. The first portion discusses proposed or
final regulatory actions and technology improvements. These
include fuel volatility control requirements, the requirements for
improved evaporative emissions control, and vapor control
technology improvements. The second portion addresses changes due
specifically to enactment of the 1990 CAAA, including onboard
applicability, the level of the emission standard, and
implementation leadtime. The third portion discusses test
procedure changes which may be appropriate, based on comments
received on the NPRM and the proposed changes in evaporative
emission test procedures.
A. Fuel Volatility Regulation
The regulation of gasoline fuel volatility was proposed at the
same time as the August 1987 onboard proposal. However, because
the specific requirements for volatility control had not been
finalized at that time, EPA's onboard analysis assumed that onboard
designs would be based on a fuel volatility of 11.5 psi Reid vapor
pressure (RVP). EPA has since promulgated a final rule requiring
that, beginning in 1992, fuel volatility be limited to a maximum of
9.0 psi RVP in the summer months, when control of ozone-producing
emissions (including refueling vapors) is most critical (55 FR
23658, June 11, 1990). Fuel volatility of 7.8 psi RVP is called
for in some southern nonattainment areas. The volatility
specification for certification test fuel will remain at 9.0 psi
RVP, thus ensuring that in-use fuel volatility will not exceed
design basis fuel volatility in the critical control months.
These controls affect several areas of the analysis which
accompanied the onboard control proposal. The most significant
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effect is a decrease in the amount of refueling emissions
generated. Although there is some variation among vehicles, there
will typically be a decrease of about 11 percent in the amount of
emissions to be controlled, thus reducing the air quality benefit
of refueling controls somewhat. However, for onboard systems, this
also allows a reduction in canister size from that estimated in the
NPRM analysis. Purge requirements will also be eased somewhat.
Because smaller canisters are less expensive and easier to package,
it would be reasonable to expect that overall costs would be lower.
B. Improved Evaporative Emissions Control
Section 202 (k) of the amended Clean Air Act requires EPA to
promulgate regulations to improve the control of evaporative
emissions from gasoline-fueled motor vehicles. These regulations
must ensure emissions control during vehicle operation and over at
least 2 days of nonuse. Even before the CAAA were finalized, EPA
had proposed changes to the evaporative test procedure as part of
the original proposal to control in-use fuel volatility (52 FR
31274, August 19, 1987). This was supplemented by an additional
notice on January 19, 1990 (55 FR 1914). A public workshop was
held on December 19, 1990 (55 FR 49914, December 3, 1990). The
Agency plans to finalize the improved evaporative rulemaking this
year.
Although improved evaporative system designs will ultimately
depend on the test procedure requirements and the control
strategies elected by the manufacturers, it is expected that
canister sizes would need to be increased to handle increased vapor
loads, and that the purge system would need to be upgraded to
transport greater amounts of vapor to the engine. Manufacturers
would also need to ensure that these greater amounts of vapor do
not increase exhaust emissions above the standards.
C. Technology Improvements
The technology analysis provided in the proposal projected
that most onboard control systems would be integrated with the
evaporative emissions control system, so that the implementation of
onboard controls was considered incremental to current evaporative
emissions control requirements.
Onboard system concept development and prototype testing since
the proposal was issued have indicated that even further design
simplifications are possible. Basic components of a simplified
design are presented in an EPA memorandum, dated December 22, 1988
(available in Public Docket No. A-89-18, item II-B-6), and in a
number of other technical and briefing documents in Public Docket
No. A-87-11. As is discussed in these technical documents and
briefings, EPA has developed and tested a simplified onboard system
in a bench configuration and has installed a version of this system
in a late model passenger car. The prototype system met EPA's
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proposed refueling emission standard and performed satisfactorily
in limited in-use testing.
D. Applicability of the Standard
1. Vehicle Classes Regulated
The August, 1987 proposal covers gasoline-fueled light-duty
vehicles (LDVs), light-duty trucks (LDTs), and heavy-duty vehicles
(HDVs). The Clean Air Act, Section 202(a)(6), as amended in 1990,
directs EPA to "promulgate standards under this section requiring
that new light-duty vehicles manufactured beginning in the fourth
model year after the model year in which the standards are
promulgated and thereafter shall be equipped with [onboard]
systems." Light-duty vehicles are explicitly included, but no
specific language dealing with other vehicle classes is provided.
Section 223 of the amendments defines light-duty vehicles as having
the Code of Federal Regulations definition in effect at the time of
enactment of the amendments (see 40 CFR 86.082-2).
The report of the joint House/Senate conference on the 1990
CAAA contains no legislative history specifically dealing with
onboard controls, although it does point out that Title II
provisions (which include the paragraph requiring onboard controls)
are generally based on the House bill, H.R. 3030 (House Report No.
101-952, 101st Congress, 2nd Session, 336). The report of the
House Committee on Energy and Commerce on H.R. 3030, dated May 17,
1990 (House Report No. 101-490, 101st Congress, 2nd Session, 303),
contains wording similar to that of the final 1990 CAAA on onboard
controls, applying the requirement to "new light-duty motor
vehicles". The report goes on to say that "the standards required
to be promulgated under this paragraph are to apply to all new
passenger cars and all light-duty trucks," implying that the term
"light-duty motor vehicles" was intended to include LDVs and LDTs.
The Chafee-Baucus Statement of Senate Managers is described by
its authors as "our best effort to provide the agency and the
courts with the guidance that they will need in the course of
implementing and interpreting this complex act" (136 Congressional
Record, S16933, daily ed., October 27, 1990). In it they describe
the Conference agreement to essentially adopt the House provision
for onboard controls, specifically characterizing the House
provision as applying "to all new passenger vehicles and light-duty
trucks."
The legislative history discussed above suggests that Congress
may have intended that LDTs be included within the scope of the
onboard requirements. In addition, Congress did not preclude
imposition of onboard controls based on other statutory
authorities. Thus, onboard controls could be required for LDTs and
HDVs based on the Clean Air Act's general authority provision,
Section 202(a)(1), which states: "The Administrator shall by
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regulation prescribe (and from time to time revise) in accordance
with the provisions of this section, standards applicable to the
emission of any air pollution from any class or classes of new
motor vehicles or new motor vehicle engines, which in his judgment
cause or contribute to, air pollution which may reasonably be
anticipated to endanger public health or welfare."
It is estimated that LDTs contribute about one-third of
current total refueling emissions. Exempting LDTs from onboard
control requirements would reduce the benefit of the program
correspondingly, mitigated perhaps temporarily by the presence of
Stage II controls in some non-attainment areas. Furthermore,
because many of these vehicles are very similar to LDVs in terms of
design, hardware, and usage, controls would be similar. This is
reflected in the fact that these vehicle classes are treated
together in other provisions of the 1990 CAAA. The incremental
cost of onboard controls per light-duty truck is estimated in the
EPA memorandum on cost (referenced in Section I.C of this document)
to be slightly higher than that of a typical LDV. This is more
than offset, however, by fuel recovery credits.
The refueling emissions contributed by HDVs are estimated to
be about 5 percent of the total. Although much smaller than that
of LDVs and LDTs, this is still a significant contribution when
viewed in the context of the very high efficiency achievable by,
and required for, onboard controls. In addition, many of the
smaller HDV designs, such as class lib and III trucks, are
essentially extrapolations of conventional LDTs and could use
similar control technology. Furthermore, fuel system designs for
other gasoline-fueled HDVs are similar to those of lighter
vehicles, and so the approaches taken to designing LDV and LDT
onboard systems could apply to these larger vehicles as well.
2. Fuel Type Considerations
The growing interest in the use of alternative fuels
necessitates clarification of which vehicle fuel types are meant to
be subject to onboard refueling vapor control requirements. The
language in the 1990 CAAA is not specific regarding fuel type and
so does not directly resolve this issue.
Although the 1987 proposal applied only to gasoline-fueled
vehicles, it may be appropriate to broaden any onboard requirement
to other fuel types. This would be consistent with EPA's past
approach of establishing a level playing field for all fuel types.
If such an approach were taken, any vehicles which use a fuel of
low enough volatility that they can meet the refueling emissions
performance standard without onboard control systems would, of
course, not be required to install such systems. In some cases, it
may be feasible to waive testing requirements if refueling
emissions are inherently low. Vehicles designed to operate on more
than one fuel type would need to meet the refueling emissions
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standard under the fuel composition conditions with the greatest
refueling emissions.
E. Emission Standard
The statutory changes also raise the issue of the
appropriateness of the 0.10 gram per gallon (g/gal) emission
standard originally proposed in the 1987 NPRM. The 1990 CAAA
require a minimum emission capture efficiency of 95 percent. As is
shown below, the proposed standard appears to satisfy that
requirement.
Using the refueling emission rate equation developed by EPA
and the limiting values of the applicable parameters specified in
EPA's refueling test procedure, the efficiency of the proposed
standard is shown below:
ER = 0.485 RVP + 0.884 TD - 0.0949 AT - 5.909
= 0.485 (9.0) + 0.884 (81) - 0.0949 (+2) - 5.909
=5.43 g/gal
where:
ER = the refueling emission rate in g/gal.
RVP = Reid Vapor Pressure in psi.
TD = Dispensed fuel Temperature in °F.
AT = (Tank Temperature - Dispensed fuel Temperature)
in °F.
The efficiency is therefore calculated to be:
1 - (0.10 * 5.43) = 0.98 or 98%.
In the August 1987 NPRM, certification useful life, recall
testing, and warranty periods were proposed to be the same for
onboard refueling controls as for other elements of the vehicle
emission control system (52 FR 31220, August 19, 1987). The
amendments to the Act require that, with respect only to LDVs and
LDTs up to 3,750 Ibs. loaded vehicle weight and 6,000 Ibs. gross
vehicle weight rating, "in the case of any requirement of [Section
202] which first becomes applicable after enactment... the [useful
life] period shall be ten years or 100,000 miles (or the
equivalent), whichever first occurs, with testing for purposes of
in-use compliance under section 207 up to (but not beyond) seven
years or 75,000 miles (or the equivalent), whichever first occurs,"
unless otherwise specified (Section 202(d) (1) ) . With respect to
all other vehicles and engines, the periods are presumed to be the
same as above unless the Administrator finds that longer periods
are appropriate. Warranty periods were shortened by the 1990
amendments to two years/24,000 miles (or the equivalent) for most
emission control components including onboard refueling systems
(Section 207(i)). One possible approach to implementing these
provisions would be to make only the changes to this rule required
to make it conform to the CAAA. Taking this approach would mean
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that, for heavier LDTs and HDVs, the requirements which existed
during the time of the NPRM would apply.
F. Implementation Leadtime
In its 1987 NPRM, EPA estimated, based on its past experience
with evaporative emission controls, that a minimum leadtime period
of two years would be required to design, develop, and adequately
test onboard refueling systems. EPA acknowledged that some
uncertainty existed in its estimate and discussed the possibility
of using a phase-in approach to reduce the certification burden and
provide manufacturers more time to address any model-specific
safety concerns. Responding to EPA's proposal, most manufacturers
indicated that a minimum of four years leadtime was necessary to
ensure safe implementation of onboard controls. Longer leadtime
was also recommended by the National Highway Traffic Safety
Administration (NHTSA), which stated that it is critical for
manufacturers to receive sufficient leadtime in order to minimize
safety risks.
Congress addressed leadtime for light-duty vehicles, mandating
an implementation schedule in the 1990 CAAA. The Amendments
require a three year phase-in (40,80,100 percent, applicable to
each manufacturer's sales volume) of onboard refueling controls on
new light-duty vehicles beginning in "the fourth model year after
the model year in which the standards are promulgated." Because it
is probable that most vehicle models would be in 1992 model year
production before the final rule is promulgated, an onboard phase-
in requirement could not become effective before the 1996 model
year.
G. Refueling Test Procedure
It is desirable that the onboard system test procedure provide
an accurate assessment of the control of refueling emissions while
minimizing the testing burden on both industry and government. The
ideas discussed below for modifying the proposed test procedure are
based on comments received on the NPRM and anticipated changes in
the evaporative test procedure. These alternative approaches, each
of which is discussed in further detail below, are as follows: 1)
vehicles which have the onboard system integrated with evaporative
control systems would use all or part of the Federal Test
Procedure1 (FTP) as the preconditioning cycle before a refueling
test; 2) abbreviated preconditioning options would be added for
non-integrated systems; 3) an abbreviated procedure for testing
seals and connections would be added; 4) a four gallon per minute
lower limit would be specified for the refueling dispensing rate.
1 The Federal Test Procedure (FTP) refers to the testing
sequence that includes the exhaust and evaporative emission systems
test procedures.
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1. Preconditioning Fully-Integrated and Partially-Integrated
Systems
The refueling test procedure proposed in the August 1987 NPRM
for fully-integrated and partially-integrated systems is a
separate, stand-alone sequence which would be performed
independently from the FTP sequence. It consists of a vehicle
preconditioning sequence followed by the actual refueling emissions
measurement test. A diagram of this proposed refueling test
procedure is provided in Figure 1.
A number of comments on the original onboard refueling control
proposal concerned the complexity of the test procedure. Although
the proposed procedure was itself the product of interaction
between EPA and manufacturers, it still appeared to represent a
significant increase in impact on testing resources. These
resource impacts were largely associated with the vehicle
preconditioning sequence, which involved loading the vapor storage
canister to at least the breakthrough point and then simulating
three days of normal vehicle driving. Commenters suggested that
EPA should develop a simplified approach to refueling testing in
order to reduce the test's resource impacts. In response to the
comments, the Agency undertook further study aimed at identifying
alternative methods for vehicle preconditioning which would be less
resource intensive.
One concept is to use the FTP for conditioning of integrated
refueling/evaporative emission control systems. Since, in the
future, the FTP will likely include initial canister breakthrough
loading and a combination of vehicle driving and canister loading
conditions, the test vehicle and fuel vapor emission control system
would be conditioned as they proceed through the FTP to the
refueling measurement test. Such an approach could eliminate the
need for a special vehicle preconditioning cycle altogether, thus
greatly simplifying the overall test procedure, except perhaps in
tests run solely for the purpose of assessing compliance with the
refueling emission standard.
This assessment is based on the FTP sequence proposed in the
evaporative emissions workshop notice (55 FR 49914, December 3,
1990); the workshop was held on December 19, 1990. Although
currently a proposal, it represents the best projection of the FTP
likely to be in use at the time the onboard system test procedure
is finalized. A diagram of the FTP proposed in the workshop is
shown in Figure 2. It may be necessary to modify this alternative
if the proposed FTP is substantially changed in the improved
evaporative emissions control rulemaking now underway.
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r
Integrated System
T" egg
a. Disconnect Vapor Line to Canister
b. Drain fuel Tank
c. 40?. Fuel ing
d. Reconnect Vapor Line to Canister
e. Drive One LA 4
f. One Hour Hot Soak
g. Repeat (e) and (C) Twice
h. Disconnect Vapor Line to Canister
i. Drain Fuel Tank
j. 40% Fueling
k. Reconnect Vapor Line to Canister
1. Heat Uuild (60° 4 2°F Initial,
24 + 1°F Rise)
m. Repeat (e) Through (1) Twice
n. Drive One LA-4
Can Iste r_Load ing to Breakthrough
0 Drain Fuel Tank
0 Soak Vehicle for 6 Hours
0 Fuel in SHED to Breakthrough
Integrated System
ig r Purge, Coi»tinugus Dr^ve
a. Disconnect Vapor Line to Canister
b. Drain Fuel Tank
c. 403; Fueling
d. Reconnect Vapor Line to Canister
e. Drive Repeated LA-4a Until Mileage
Accumulated = Mileage Required for
Purge Equivalent to Cyclic Drive.
Mileage Accumulation Stops at the
First Idle Paat the Mileage
Requirement
Non-integrated System
Canister Purge, Continuous Drive
a. Disconnect Vapor Line to Canister
b. Drain Fuel Tank
c. 95% Fueling
d. Reconnect Vapor Line to Canister
e. Drive Repeated LA-43 Until
85% of Tank Volume Is
Consumed
Vehicle Cool Down
0 Disconnect Line to Canister
0 Drain Fuel Tank
0 10* Fueling
0 Soak Vehicle 6 to 24 Hours
I
Refuel ing Emissions Measurement
Reconnect Vapor Line to Canister
Fuel to Automatic Nozzle Shut-off
(B5* Mimimun Fueling). Restart Fueling
Following Any Premature Shut-offs Within
15 Secondn)
NPRM Onboard Test Procedure Flow Chart
Figure 1
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Proposed Federal Test Procedure
Fuel
9 RVP, 40% full
I
Preconditioning
LA-4
Purge & Load Canister
SHED or bench procedure
I
Refuel
Cold Soak
68-86° F
Exhaust Test
Fuel Temp Profile
Refuel
Refueling Emissions
Measurement Test
Two Heat Builds
2 hrs ea, fuel 72-96F
natural cool to 72° F
Diurnal Test
2 hours
fuel 72-96° F
Refuel
Running Loss Test
LA-4,2*NYCC,LA-4, 95F
SHED or point source
Hot Soak and
Permeation Loss Test
5 hours
ambient 95° F
Refueling Emissions
Measurement Test
Figure 2
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Refueling Test Procedure:
Integrated Systems
FTP* Through the
Exhaust Test
Disconnect Refueling Canister
Remove Fuel Filler Cap
Drain Fuel Tank
10% Fueling
Replace Fuel Filler Cap
Vehicle Temperature Stabilization (80 ± 3°F
for at least 6 hours)
Connect Refueling Canister
Remove Fuel Filler Cap
Place Vehicle in Shed
Refueling Emissions Measurement Test
Fuel to Automatic Nozzle Shut-off (85% Minimum Fueling : 81° - 84° F Fuel)
Restart Fueling Following Any Premature Shut-offs Within 15 Seconds
* The Federal Test Procedure (FTP) refers to the testing sequence that includes exhaust and evaporative
emission system test procedures
Figure 3
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For integrated systems, it may be appropriate for the test
procedure to adopt one of two options which would use the FTP to
condition the vehicle/canister for the refueling emissions
measurement test. The first option is shown in Figures 2 and 3 as
the sequence labeled option "1". Under this option, the refueling
emissions measurement test would be placed at the end of the FTP
and would be retained in the same form as that described in the
NPRM.
The basic premise for positioning the refueling test in this
way is that the vapor loads and purge requirements involved in the
evaporative emissions test are expected to be generally sufficient
to test the integrated system's purge capability and to prepare the
system for a refueling event. Therefore, a separate refueling
preconditioning would not be needed.
One possible issue concerning use of the FTP to condition
vehicles/canisters prior to the refueling test is the amount of
work that must be performed if the only objective is conducting the
refueling measurement test, such as might occur for recall
evaluation testing or if the refueling test were voided during
certification testing by, for example, the accidental spillage of
fuel during refueling. In such instances the entire FTP sequence
would have to be performed for the purpose of conditioning a
vehicle for a refueling test under Option 1. It may be useful to
consider alternative methods of determining if the vehicle
conditioning sequence can be further abbreviated, while maintaining
proper evaluation of the refueling emission control system.
Another possible option is the placement of the refueling
emissions measurement test after the exhaust emissions measurement
test in the FTP. Labeled option "2" in Figures 2 and 3, this
testing option would provide a shorter preconditioning method for
integrated systems, and thus would provide a savings in time and
resources for those cases in which the only desired objective is
the refueling emissions measurement. In this approach, the
vehicle/canister would be preconditioned as in the proposed
evaporative procedure and the vehicle would be driven through the
driving cycles specified in the exhaust test (exhaust measurements
may or may not be required). The refueling emissions measurement
test would then be conducted.
To conduct the evaporative emissions tests under Option 2, the
entire FTP would need be performed separately. Alternatively, it
is possible to design a test procedure that allows re-entry into
the FTP sequence after completion of the refueling emissions
measurement test in order to complete the evaporative and running
loss portions of the test. Use of this approach would require that
additional purge be provided before continuing through the rest of
the FTP, because the refueling event would be expected to load the
canister to near its full capacity. Additional purge opportunity
could be provided by inserting another exhaust emissions driving
11
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cycle (without measurement), or some comparable driving sequence,
into the FTP after the refueling emissions test.
Another approach is to use Option 1 for normal certification
testing, but to retain Option 2 as a stand-alone, short test to be
used at the Administrator's discretion. This option would provide
maximum flexibility and reduce overall testing resource impacts for
both certification and in-use compliance testing.
2. Preconditioning Non-Integrated Systems
The second test procedure modification which may be
appropriate is, again, inspired by the desire to make the onboard
system test less resource-intensive. Under the August 1987 onboard
proposal, 85 percent of the fuel tank capacity must be consumed
during the preconditioning sequence for non-integrated systems. In
the modification being considered, the manufacturers would have the
option of using any integer number of continuously driven LA-4
driving cycles to sufficiently condition the canister (by the
manufacturer's definition) prior to the refueling test (Figure 4),
provided that 85 percent or less of the fuel tank capacity is
consumed. This modification would be expected to decrease the
amount of testing resources required without lessening the test
procedure's ability to evaluate the capacity to control refueling
emissions.
The use of this preconditioning sequence would be expected to
lead to similar canister size and purge requirements as the full
drivedown (85 percent) option because the manufacturers would still
be required to pass the refueling emission test. Consequently,
this revised test sequence might be desirable because it provides
the opportunity to reduce resource impacts for both the
manufacturers and EPA. It should be noted that the option given in
the original proposal to use test track/road purge in lieu of
vehicle dynamometer driving would be retained.
As a possible alternative method for EPA testing of non-
integrated systems, a vehicle would be fueled to automatic nozzle
shut-off, driven some integer number of LA-4 driving cycles, and
then subjected to the refueling emissions measurement test (Figure
4). This method differs from the above-described modification in
that the SHED refueling event would directly follow the driving,
with no intervening drain and fill to 10 percent, and in that it
would be conducted at EPA's discretion only. The basis for this
approach is the fact that partial refuelings are common in use and
so an onboard system should have adequate design margin to
accommodate partial refuelings. The number of LA-4s driven would
be at EPA's discretion on a per test basis.
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Refueling Test Procedure:
Non-Integrated Systems
Canister Loading
Drain Fuel Tank
Soak Vehicle for at Least 6 Hours at 80° ± 3° F
Load Canister(s) to Breakthrough
(Identical to Evap Loading Technique)
Continuous Drive Canister Purge
Disconnect Vapor Line to Canister
Drain Fuel Tank
95% Fueling: 81° - 84° F Fuel
Reconnect Vapor Line to Canister
Drive the Number of LA-4s Specified by
Manufacturers (up to 85% of Fuel Tank)
Disconnect Vapor Line to Canister
Drain Fuel Tank
10% Fueling
Soak Vehicle for at Least 6 Hours at 80° ± 3° F
Reconnect Vapor Line to Canister
Remove Fuel Filler Cap
Place Vehicle in Shed
Refueling Emissions Measurement Test
> Fuel to Automatic Nozzle Shut-off
(85% Minimum Fueling : 81° - 84° F Fuel)
Restart Fueling Following Any Premature
Shut-offs Within 15 Seconds
Testing Option for EPA
Disconnect Vapor Line to Canister
Fuel to Automatic Nozzle Shut-off
(at Least 95% of Fuel Tank, 81-84 F Fuel)
Reconnect Vapor Line to Canister
Drive Integer Number of LA-4s Determined
by EPA
Remove Fuel Filler Cap
Place Vehicle in Shed
Refueling Emissions Measurement Test
Fuel to Automatic Nozzle Shut-off
(at least as much fuel as used during drive,
81 °-84° F Fuel)
Restart Fueling Following Any Premature
Shut-offs Within 15 Seconds
Figure 4
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P.16
The refueling emissions measurement test contains a provision
for fueling to automatic shut-off, and, because automatic shutoff
is commonly practiced in use (even for small partial fills such as
with rental car returns), it would appear reasonable to retain this
provision for this test as well. However, the automatic shutoff
mechanisms on fuel pumps are not designed to ensure that a measured
volume of fuel is in the vehicle fuel tank at shutoff. Therefore,
it is likely that the refueling measurement test would add somewhat
more or less fuel than was burned during the LA-4 driving cycles,
thus introducing uncertainty into the results. The effect of this
variability in nozzle shutoff on a test involving just a few LA-4
cycles of drivedown could be significant.
Concern about pumping too much fuel would tend to be mitigated
by the fact that the rate of hydrocarbon reduction during purge is
generally much higher when the canister is heavily loaded with
hydrocarbons (i.e. during the initial LA-4 cycles) than when the
hydrocarbon concentration in the canister has been reduced, thus
helping to ensure that the purge provided by initial drivedown of
a fully loaded canister will free up more than enough storage
capacity to accommodate the corresponding partial refueling vapor
load. EPA would welcome input from others on whether or not the
higher purge rates present at the start of a purge cycle would
adequately cover for nozzle shutoff uncertainties.
To avoid inaccurate test results caused by the pumping of too
little fuel, the test procedure would need to ensure that the
amount of fuel dispensed during the refueling measurement test is
at least as much as that burned during the LA-4 driving. To verify
this, some method of determining the amount of fuel consumed during
the driving sequence would need to be included, such as by
measuring exhaust emissions during some portion of the driving and
performing a carbon balance calculation, or by using the vehicle's
previously determined fuel economy rating. The amount of fuel
pumped during the refueling test would also need to be metered to
ensure that, if automatic pump shut-off were to occur before the
proper amount of fuel was displaced, refueling would be resumed
until sufficient fuel was pumped. EPA would welcome other
suggestions for dealing for pump shutoff variability.
One of the more attractive features of a non-integrated system
(fully separate refueling and evaporative systems) is that it
permits a lower purge rate than for an integrated system since the
purge of the refueling canister can be spread more evenly over the
driving associated with the fuel dispensed. This lower purge rate
is valuable since it allows for a reduction in the potential
effects of purge on exhaust emissions. Considering the
sophisticated purge strategies available with electronic controls,
there is some concern that, because of potential purge/exhaust
emission interactions, manufacturers could design a purge system
which operates at lower purge rates during the exhaust emission
test than during a subsequent portion of the preconditioning
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P.17
driving cycle. To avoid the possibility of adverse or
unrepresentative exhaust emission effects, it may be necessary to
include a requirement that, for vehicles using non-integrated
systems, the purge volume must be essentially the same for each LA-
4 driving cycle during the test.
Finally, it may be appropriate to apply the procedure for
loading canisters to breakthrough proposed in the evaporative
emissions revisions to the FTP (55 FR 49914, January 19, 1990) to
tests of non-integrated systems as well as integrated systems.
This would simplify testing procedures and reduce the need for
additional equipment. Any subsequent changes to the loading
procedure resulting from finalization of the improved evaporative
rule would be factored in as well.
3. Testing of Seals and Connections
Vapor emissions from a refueling emissions test can occur from
two sources: emissions vented from the canister and emissions that
escape from the fillpipe seal, vapor line connections, and other
leaks. The test procedures proposed in the NPRM and the options
described above test for both of these sources of emissions.
Although the purge/canister system capacity and operation would be
evaluated through the full preconditioning and refueling emissions
measurement sequence, there may be situations in which it is
desirable to only measure emissions arising from areas other than
the canister.
Therefore, it may be appropriate to add a test procedure
option, to be used at EPA's discretion only, in which the canister
would be thoroughly bench purged prior to conducting a refueling
emissions measurement test. The canister would then be reconnected
and the normal refueling emissions measurement test conducted. The
emissions would need to meet the refueling emission standard in
order to pass the test. The advantage of this type of test over a
complete test sequence is that the integrity of the seals and
connections can be determined with a modicum of effort in cases
where this determination is the only desired result.
4. Lower Limit on Refueling Dispensing Rate
In its proposal, EPA had specified a fuel dispensing rate of
approximately 10 gallons per minute (gal/min) for refueling tests.
An option was included, however, for EPA to test at lower flow
rates if desired. This was done to ensure that the Agency would
have the ability to adequately test systems which it believed might
lose control effectiveness at low flow rates. Based upon comments
received, it may be appropriate to specify a lower limit for such
testing. Since extremely low dispensing rates would not be
expected to occur in use, they would be unrepresentative.
Consequently, replacing the 10 gal/min proposed rate with a
dispensing rate range of 4-10 gal/min may be a reasonable solution.
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Nearly all in-use refuelings occur at a rate of 5 gal/min or
greater, and at least some fuel dispensing nozzles themselves fail
to operate properly if used at 3 gal/min.
II. Impact of Changed Circumstances on the Proposed Action
In addition to the impacts on the test procedure discussed in
Section I.G, the changed circumstances discussed in Section I of
this document have potential impacts on costs, benefits (emissions
reductions), and the resulting cost effectiveness of onboard
controls.
A revised cost analysis, addressing most of the changed
circumstances discussed in Section I of this document, is contained
in an EPA memorandum, dated December 22, 1988, available in Public
Docket No. A-89-18, item II-B-6. This analysis calculated onboard
control costs based on a design incremental to improved evaporative
controls, a simplified onboard system design concept, and 9.0 psi
RVP certification fuel. The resulting estimated cost increment was
lower than the NPRM estimate. An adjustment for the fuel recovery
credit provided by combustion of the collected vapors resulted in
a net average cost savings of a few dollars per vehicle. Since
there are Stage II vapor recovery systems in some areas of the
country now, and their use is expected to expand to a number of
other areas under the CAAA of 1990, it is worthwhile assessing the
affects of Stage II on EPA's cost analysis for an onboard equipped
vehicle. Based on current onboard and Stage II technologies,
refueling events in nonattainment areas in which both onboard and
Stage II systems are operative will result in the refueling vapors
being captured by the onboard system; thus the onboard fuel
recovery credit would be retained. Without this adjustment for the
fuel recovery credit it is expected that, instead of a small per
vehicle net cost savings, a positive average cost of a few dollars
per vehicle would result.
The changed circumstances discussed in Section I of this
document will produce a small net decrease in emissions reduction
benefits of onboard controls, compared to the benefits calculated
in the NPRM. The effect of volatility controls was accounted for
in the sensitivity analysis in Section V of the NPRM, yielding the
conclusion that the annual average gasoline refueling emission
factor is about 11 percent less for the case in which summertime
RVP is controlled in class C areas at 9.0 psi than the case in
which it is set at 11.5 psi. It is also possible that use of
reformulated gasoline in some nonattainment areas would cause a
slight reduction in benefits.
The implementation schedule for onboard controls would
obviously impact how quickly emissions reductions would begin to
occur. However, it is reasonable to expect that the full annual
benefit would eventually be attained as phase-in and fleet turnover
progresses. The installation of Stage II systems, required in some
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nonattainment areas by the 1990 CAAA, would also temporarily reduce
the emissions control benefit of onboard systems. However, because
the Act also calls for the retirement of the federally-mandated
Stage II control requirements once onboard controls are in
widespread use, the reduction in onboard control benefits would be
expected to be temporary. It should be noted that the onboard
control standards and their implementation schedule are intended to
apply to vehicles sold in all parts of the United States, even
where Stage II controls are (or will be) in place, such as in
California.
Because, as discussed above, the net cost of onboard refueling
emissions control is projected to be modest, the impact of changed
circumstances on calculated benefits does not alter the NPRM's
general conclusion regarding cost-effectiveness.
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