Letter to Greg O. Scherer and Dean Schoppe
United States Environmental Protection Agency
Office of Mobile Sources
October 29, 1997
Greg O. Scherer, Manager
Fuels Technology and Product Section
Southwest Research Institute (SwRI)
Dean Schoppe, Manager
Fuels Testing
EG&G-AR
Dear Mr. Scherer and Mr. Schoppe:
I am writing in response to your letter dated March 6, 1997,
in which you recommended that the Environmental Protection Agency
(EPA) apply revised test equipment qualification criteria in
evaluating the suitability of intake valve deposit (IVD) control
tests conducted to comply with the requirements of EPA's
certification program for gasoline deposit control (detergent)
additives (61 FR 35309, July 5, 1996). This response also
considers the additional data presented in a letter from Mr.
Schoppe dated September 24, 1997, on temperature corrections for
Stoddard solvent flow data. Specifically, you recommended that
revised pressure valve and fuel injector flow rate specifications
be substituted for those found in the American Society for
Standards and Materials (ASTM) D 5500-94 procedure entitled,
"Standard Test Method for Vehicle Evaluation of Unleaded
Automotive Spark-Ignition Engine Fuel for Intake Valve Deposit
Formation", which is specified for detergent certification
purposes at 40 CFR 80.165. You also requested that EPA
temporarily waive compliance with the injector flow pattern
specification in the ASTM D 5500-94 procedure until ASTM resolves
issues related to its application when injector flow rate is
tested with Stoddard Solvent rather than isooctane.
A detailed discussion of these procedural items is attached.
The order in which they are addressed follows that in your
letter. Until such time as EPA amends the IVD test procedure
through a rulemaking or issues additional guidance, this letter
may be used by the regulated community as a guide regarding EPA's
position on the suitability of the changes recommended in your
letter to the ASTM D 5500-94 procedure. As we discussed, this
letter will be released to the general public to serve as an
announcement to regulated parties. Thank you for your efforts in
maintaining the soundness of the ASTM D 5500 procedure. Please
contact me if you have additional concerns.
Sincerely,
Jeffrey Herzog
Mechanical Engineer
Fuels and Energy Division
Enclosures
Environmental Protection Agency Position on Suggested Changes to
the ASTM D-5500-94 Test Procedure Specified for Use Under the
Detergent Certification Program
Item 1:
Subject Requirement:
Section 8.7.1.1 of the ASTM D 5500-94 procedure states that
the coolant system integrity must be checked to conform to the
following specifications:
Pressure valve opens at ...... 90 to 110 kPa (13 to 16 psig)
Vacuum valve opens at ........ 90 to 110 kPa (13 to 16 psig)
Issue:
You stated that the specification for the pressure valve is
adequate and meaningful, but that it is not possible for the
vacuum valve to meet the specification listed. You also stated
that a reasonable specification for the vacuum valve would be as
follows:
Vacuum valve opens at 5.06 to 10.13 kPa (1.5 to 3.0 in Hg)
You recommended that this specification should apply to all
(past, present, and future) ASTM D 5500-94 tests conducted.
In a phone conversation on June 23, 1997, Mr. Schoppe
related that the replacement specifications suggested in your
letter resulted from a review of considerable data from tests run
at SwRI and EG&G which showed that the suggested specifications
would ensure proper functioning of the vacuum valve. Mr. Schoppe
also stated that the suggested specification will be balloted by
ASTM in the future for inclusion in a revised ASTM D 5500
procedure.
EPA Response:
It is clear that the vacuum valve specifications in section
8.7.1.1 of the ASTM D 5500-94 procedure are not meaningful since
these specifications bracket normal ambient air pressure. EPA
believes that the vacuum valve specifications recommended in your
letter are based on the best data currently available, and are
likely be adopted by ASTM in a revised ASTM D 5500 procedure.
Therefore, EPA will apply the suggested vacuum valve
specification of 5.06 to 10.13 kPa (1.5 to 3.0 in Hg) to all IVD
tests performed to support certification under the gasoline
detergent program (pursuant to 40 CFR 80.165) in place of the
vacuum valve specifications in section 8.7.1.1 of the ASTM D
5500-94 procedure. Based on a review of additional data which
might become available or the approval by ASTM of a different
specification, the Agency might consider adoption of a different
vacuum valve specification in the future.
Item 2:
Subject Requirements:
Section 8.5.5.1 of the ASTM D 5500-94 procedure states that
the flow rate of fuel injectors must be tested at 310 +/- 1.4 kPa
(45 +/- 0.2 psi) using Stoddard solvent or isooctane. The
specification for flow testing using isooctane states that each
injector must have a flow rate (at 310 kPa, 15.6øC) which
conforms to the following:
isooctane 2.03 to 2.09 g/s (0.0716 to 0.0737 oz/s)
Section 8.5.5.1 further states that:
Flow rates shall be adjusted for test conditions of fluid
temperature and pressure.
Issue:
You stated that the fuel injector flow rate specifications
in section 8.5.5.1 of the ASTM D 5550-94 procedure were produced
by ASTM based on data from flow tests on the fuel injectors which
were available when the procedure was developed in 1993. Since
1993, you related that the manufacturer of the fuel injectors
specified for use in the ASTM D 5500-94 procedure changed their
manufacturing processes resulting in a slight alteration to
injector flow properties. Subsequently, ASTM developed flow rate
specifications which are more appropriate for injectors of
current manufacture. I understand that the flow rate
specifications recommended for adoption by EPA in your letter
were approved by ASTM ballot in June of 1996, and will be
included in a revised ASTM D 5500 procedure to be published by
ASTM in the future. The revised injector flow rate
specifications for flow testing conducted using isooctane are as
follows:
isooctane 1.94 to 2.06 g/s (0.0684 to 0.0727 oz/s)
You also stated that in association with the modified flow
specifications, ASTM plans to include the following clarification
of the procedural specifications regarding the conditions to
which the reported fuel injector flow rates must be adjusted:
Flow rates shall be corrected to 15.6øC (60øF).
EPA Response:
EPA agrees that the flow specifications recommended in your
letter are appropriate for fuel injectors of current manufacture.
However, it is inappropriate to apply the revised specifications
to all tests conducted using the ASTM D 5500-94 procedure
regardless of whether the injectors used were of earlier or more
recent manufacture. The recommended lower bound in the revised
fuel injector flow rate specifications is less than the lower
bound in the ASTM D 5500-94 procedure (1.94 vs 2.03 g/s).
Therefore, injectors of earlier manufacturer which would have
complied with the specification on the lowest acceptable flow
rate in the ASTM D 5500-94 procedure would also comply with the
revised specification. However, the upper bound in the revised
acceptable range of flow rates is less than the upper bound in
the ASTM D 5500-94 procedure (2.06 vs 2.09 g/s). Thus, some
injectors of earlier manufacturer that conformed to the flow
specifications in the ASTM D 5500-94 procedure would not conform
with the revised specifications. Consequently, if the revised
specifications were applied to tests conducted in the past as
suggested, some tests that have already been conducted using the
earlier-production injectors might be inappropriately judged to
be invalid for detergent certification purposes. Such an action
would be unfair, since these tests were conducted in good faith
using properly functioning fuel injectors which were in
conformity with the requirements applicable at the time. Since
some certifiers might currently be relying on tests conducted
with earlier-production injectors to substantiate compliance with
the requirements for detergent certification, invalidating these
tests could necessitate recertification in some case which could
result in significant financial hardship for these parties.
To ensure that both earlier and later fuel injector
production batches are properly evaluated for their suitability
for use in the ASTM D 5500 procedure, EPA believes that it would
be most appropriate to provide separate specifications for the
two fuel injector variants. Under this approach, the fuel
injector specifications in the ASTM D 5500-94 procedure would
apply to fuel injectors from earlier production batches, and the
revised specifications would apply to injectors from current
production batches. In a phone conversation on July 23, 1997,
Mr. Scherer related that BMW states that it is not possible to
differentiate by lot number or other means between injectors of
earlier manufacture which were used by ASTM to produce the flow
rate tolerances specified in the ASTM D 5500-94 procedure, and
those of current manufacture which were used by ASTM to produce
the revised flow rate specifications. Fuel injectors of both
earlier and current manufacture conform to the same part number
as specified in the annex to the ASTM D 5500 procedure (BMW part
number 13 14 1 179 232).
Since it is not possible to apply separate specifications
for earlier and current fuel injector production batches, EPA
believes that it is suitable to apply broadened acceptance
criteria which spans the allowed variability for both injector
production variants to tests in which mileage accumulation was
initiated prior to the date of this notification. Tests in which
mileage accumulation was begun after October 30, 1997, would be
required to comply with the specifications suggested in your
letter for injectors of current manufacture. Allowing increased
variability in the flow rates of injectors used in tests that
have already been conducted is necessary to prevent the potential
invalidation of tests which used injectors from earlier
production batches that conformed to the flow specifications
germane to these injectors.
EPA will apply the following fuel injector flow
specifications for flow testing conducted using isooctane in
evaluating the acceptability of IVD test data for detergent
certification purposes in place of the specifications in section
8.5.5.1 of the ASTM D 5500-94 procedure:
For tests in which vehicle mileage accumulation was
initiated on or prior to October 30, 1997, the following
specifications on injector flow rates will apply:
isooctane 1.94 to 2.09 g/s (0.0684 to 0.0737 oz/s)
For tests in which vehicle mileage accumulation was
initiated after October 30, 1997, the following
specifications on injector flow rates will apply:
isooctane 1.94 to 2.06 g/s (0.0684 to 0.0727 oz/s)
EPA agrees that the suggested revision to the specifications
on the conditions to which the reported fuel injector flow rates
must be adjusted resolves ambiguities present in the current ASTM
D 5500-94 procedure. In keeping with your suggested revision to
the procedure, EPA will continue to require that flow rates
reported pursuant to section 8.5.5.1 of the ASTM D 5500-94
procedure be adjusted to 15.6øC (60øF).
Potential Impacts of the Temporary Application of Broadened
Acceptance Criteria
The temporary application of broadened acceptance criteria
in evaluating the suitability of fuel injectors for certification
testing purposes necessitates an evaluation of the potential
introduction of test bias and associated impact on the emissions
control goals of the detergent program. The application of
broadened acceptance criteria will allow injectors from later
production batches that have a flow rate as high as 0.03 g/s
greater than that specified in the planned ASTM amendments to
procedure D 5500 to be judged acceptable in past tests. However,
EPA does not believe that this will result in the introduction of
significant test bias since the magnitude of the increase in the
upper limit of the allowable injector flow rates for later
production injectors is minimal and there are factors which
mitigate against such variation having a significant impact on
test results.
The application of broadened acceptance criteria will also
allow earlier production injectors that have flow rates as much
as 0.09 g/s lower than that specified in the ASTM D 5500-94
procedure to be judged acceptable for use. The magnitude of this
potential difference from appropriate flow specifications raises
somewhat more concern regarding potential test bias which might
be introduced. However, there are several factors to mitigate
this concern. Firstly, EPA believes that most injectors of
earlier manufacture were evaluated for use based on the criteria
in the ASTM D 5500-94 procedure, which were tailored to the
particular flow characteristics of these injectors. If earlier
production injectors did not conform to these specifications,
they would have been identified as unsuitable for use and
discarded. It was only after current-manufacture injectors were
identified as requiring different flow specifications and
appropriate specifications were developed by ASTM that industry
began applying the revised flow specifications. EPA believes
that it is unlikely that a significant number of earlier
production injectors continued in use after industry started
evaluating the acceptability of injectors based on the flow
specification developed for current production fuel injectors.
EPA's experience regarding the various test parameters which
influence the results of IVD testing indicates that injector flow
has a relatively small effect on test results within the
described range of variability, relative to the effect of other
testing parameters such as valve temperature (as evaluated by
engine coolant temperature). In addition, it is not possible to
definitively determine the directional effect that decreased (or
increased) fuel flow will have on IVD test results since the
important factors to consider have competing effects on test
severity. As discussed below, the overall effect that these
factors will have on IVD test results is dependent on the deposit
forming tendency of the base fuel, the efficacy of the additive
used, and unknowns regarding deposit formation processes relative
to these factors.
Flowing additional fuel over the intake valves tends to
provide more material to form deposits. However, increased fuel
flow also tends to decrease the temperature of the valves
slightly, thereby reducing the amount of deposits formed. EPA is
not aware of data to quantify the differential cooling effect.
However, it is reasonable to assume that this effect is very
small relative to the magnitude of the difference in injector
flow rates considered. The degree to which increased fuel flow
increases deposit test results due to the availability of more
material to build deposits varies according to the severity of
the base test fuel, with the potential impact probably being more
pronounced for more severe fuels. However, there are inadequate
data to quantify the magnitude of the potential increase in test
severity which results from increased fuel flow relative to
differences in test fuel deposit forming severity.
If the fuel is additized, flowing greater volumes over the
valves will not only bring more material from which to form
deposits, but will also increase an additive's deposit control
activity since more additive will flow over the valve.
Differences in the deposit control characteristics of different
additive types and in the efficacy of different detergent
packages relative to the base test fuel used will affect the
extent to which increased additive flow over the valve tends to
reduce IVD test results. Although it is not possible to
determine which of these competing mechanisms would predominate
in determining the overall effect on IVD test results of
increased fuel flow, EPA believes that given that the potential
effect of any of these mechanisms is small for the case
considered, the overall impact on test severity would be marginal
at most. Therefore, it appears reasonable to assume that the
potential impact of the additional variability in injector flow
within the range allowed would not result in significant test
bias.
The test validation criteria regarding the amount of fuel
consumed during the test in section 10.4.4 of the ASTM D 5500-94
procedure will also serve to limit the potential impact on test
results of increased variability in injector flow rate. Section
10.4.4 states that average fuel consumption must be between 10.2
km/L and 12.8 km/L (24 to 30 mpg) for the test duration for the
test to be valid. The potential impact on test results of
allowing broader injector acceptance criteria will also be of
limited duration, since tests initiated after October 30, 1997,
are required to comply with the flow rate specifications tailored
to the characteristics of current manufacture injectors. In
addition, since EPA expects that additive manufacturers will
retire additive certifications at a rate of 15% per year[1], the
potential impact on the emissions control goals of the detergent
program of certifications which might be based on tests that were
biased to a degree by increased variability in injector flow
would be of limited duration.
Considering these factors, EPA believes that the potential
impact on the emissions benefits of the detergent program of
applying the broadened injector flow criteria is negligible.
EPA might consider the adoption of a different flow rate
specification for flow testing conducted using isooctane based on
a review of additional data, if such data becomes available, or
the approval by ASTM of a different specification.
Item 3:
Subject Requirements:
The specification for flow testing fuel injectors using
Stoddard solvent in section 8.5.5.1 of the ASTM D 5500-94
procedure states that each fuel injector must have a flow rate
(at 310 kPa, 15.6 øC) which conforms to the following:
Stoddard solvent 2.30 to 2.36 g/s (0.0811 to 0.0832 oz/s)
Section 8.5.5.3 of the ASTM D 5500-94 procedure states
that the spray pattern of each injector must conform to specified
visual inspection criteria.
Issues:
You stated that at the time the ASTM D 5500-94 procedure was
finalized, data on appropriate fuel injector flow rates using
Stoddard solvent were not available. Consequently, a conversion
factor based on specific gravity was applied to the isooctane
flow testing specifications to produce the specifications for
flow testing using Stoddard solvent. It is now recognized that
this means of conversion does not take into account viscosity
differences between isooctane and Stoddard solvent, which will
affect the flow rate. You noted that since Stoddard solvent has
a higher viscosity, less Stoddard solvent will flow through a
given injector in comparison to isooctane.
Your letter dated March 4, 1997, included the results of a
program conducted at three different test laboratories which
compared flow rates on three sets of four injectors using
isooctane and Stoddard solvent. In a follow-up letter dated
September 24, 1997, Mr. Schoppe provided additional data to
correct the results of this interlaboratory data to 60øF, as
required in the ASTM D 5500 procedure. The temperature-corrected
results of the inter-laboratory study showed smaller differences
in flow rate using Stoddard solvent and isooctane than was
predicted by the specific-gravity conversion calculation which
formed the basis for the specifications for flow testing with
Stoddard solvent in section 8.5.5.1 of the ASTM D 5500-94
procedure.
Based on the temperature-corrected inter-laboratory test
data and other testing experience, you suggested that the
Stoddard solvent flow rate specifications be changed from the
specification in the ASTM D 5500-94 procedure to the following:
Stoddard solvent: 1.89 to 2.01 g/s (0.0667 to 0.0709 oz/s).
You stated that, the suggested specification should apply to
all (past, present, and future) ASTM D 5500-94 tests.
You also stated that due to the viscosity differences
between isooctane and Stoddard solvent, a proper fuel injector
spray pattern cannot be attained using Stoddard solvent. You
stated that it is intended that ASTM review the sections
pertaining to visual inspection of the fuel injectors and develop
a consensus on how to address the problem. Until ASTM makes such
a determination, you recommended that EPA not require the visual
evaluation of fuel injector spray pattern if the injectors are
flow tested with Stoddard solvent.
In a phone conversation with Dean Schoppe on June 23, 1997,
Mr. Schoppe related that unless EPA waives this requirement,
parties who test injector flow rate with Stoddard solvent will be
forced to continue performing a separate evaluation of injector
spray pattern using isooctane, resulting in additional cost and
logistical difficulties.
EPA Response:
EPA agrees that the Stoddard solvent flow specifications in
the ASTM D 5500-94 procedure are unrepresentative and should be
replaced with the specifications suggested in your letter dated
September 24, 1997. Since the specifications in your letter are
based on temperature-corrected results from a matrix of inter-
laboratory test data, they are clearly more appropriate than
those in the ASTM D 5500-94 procedure which are based on a
methodology of extrapolation from isooctane flow specifications
that did not take into account the substantial effect of
differences in viscosity between isooctane and Stoddard solvent.
Application of the injector flow rate specifications for Stoddard
solvent in the ASTM D 5500-94 procedure would allow injectors
with inappropriately high flow rates to be used, and would
exclude from use injectors with flow rates in the appropriate
range, thereby effectively barring the use of Stoddard solvent
for flow testing. However, EPA believes that applying the
revised flow specifications to past tests is inappropriate since
this would potentially invalidate tests which met the
qualification criteria applicable at the time. Consequently, in
keeping with the discussion in the previous section, EPA believes
that the only workable approach in evaluating the validity of
past tests is to apply broadened injector flow specifications
which encompass both the specifications in the ASTM D 5500-94
procedure and those recommended in your letter.
In place of the specifications in section 8.5.5.1 of the
ASTM D 5500-94 procedure, EPA will apply the following fuel
injector flow specifications for flow testing conducted using
Stoddard solvent:
For tests in which vehicle mileage accumulation was
initiated on or prior to October 30, 1997, the following
specifications on injector flow rates will apply:
Stoddard solvent 1.89 to 2.36 g/s (0.0667 to 0.0832 oz/s)
For tests in which vehicle mileage accumulation was
initiated after October 30, 1997, the following
specifications on injector flow rates will apply:
Stoddard solvent 1.89 to 2.01 g/s (0.0667 to 0.0716 oz/s)
EPA cannot at this time waive compliance with the
requirement that the fuel injector flow pattern conform with the
specifications in the ASTM D 5500-94 procedure. ASTM determined
through an industry consensus process, and EPA continues to
believe, that a specification on injector flow pattern is useful
in limiting test variability. EPA does not believe that
requiring parties who evaluate flow rate using Stoddard solvent
to conduct an evaluation of flow pattern quality represents a
substantial hardship for these parties. A party who wishes to
conduct flow rate testing using Stoddard solvent can evaluate
flow pattern at their laboratory using isooctane or contract with
another laboratory to have the flow pattern evaluated using
isooctane. In addition, both injector flow rate and flow pattern
testing can be conducted using isooctane. All things considered,
EPA believes that it is appropriate to defer further
consideration of the issue until input from ASTM is available.
Potential Impact of the Temporary Application of Broadened
Acceptance Criteria
Specifying that tests conducted before the release of this
notification must comply with the combined range of acceptable
flow values discussed above will allow the use of IVD test data
which were collected using injectors that have a flow rate as
much as 0.33 g/s above the appropriate limit identified in your
letter. This magnitude of increased fuel injector flow outside
of the bounds of the appropriate limits raises somewhat more
concern regarding the potential impact on the representativeness
of IVD test results with respect to ensuring a proper level of
deposit control than that discussed in the previous section.
However, for many of the same reasons discussed in the section
above, EPA believes that the potential impact on the deposit
control goals of the program is marginal and would be short-term
in nature. In addition, EPA believes that little if any IVD
testing was conducted using Stoddard solvent to flow test
injectors until the development of the revised flow
specifications. Flow tests conducted using Stoddard solvent
immediately after the development of the ASTM D 5500-94 procedure
would have quickly shown that meeting the stated specification
was impractical. The specifications determined to be appropriate
through your inter-laboratory study are significantly different
and do not overlap those in the ASTM D 5500-94 procedure. Thus,
it is highly unlikely that lengthy and costly IVD testing would
have been undertaken using injectors flow tested with Stoddard
solvent until the appropriate flow specifications were available.
Also, it is EPA's understanding that the revised flow
specifications have been observed by laboratories which have used
Stoddard solvent to flow test injectors in conducting IVD tests
intended for detergent certification purposes.
___________________________
[1] Regulatory Impact Analysis for the Detergent Certification Program,
Docket A-91-77, Item V-B-01.
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