P.1 

OAR Box 1830 

Prepped by Ollie Stewart 

Document Number: 

184) IV-C-151 

Docket Number: 

A-87-11 

Printed 11/13/2008 7:21:01 AM Sheet 184 of 232 
g _ \ \ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

\^StZJ ANN ARBOR. MICHIGAN 48105 

N«^/ 

OFFICE OF 

AIR AND RADIATION 

JAN ! 7 I98Q 

Mr. James E. Pasek ^TJ 

Manager, Federal Activities . > ^ r>c\'^ 

General Motors Corporation ^.v0,y ;-y:.^ 

General Motors Technical Center ^'"" c-"'' 

30400 Mound Road 

Warren, Michigan 48090-9015 

Dear Mr. Pasek: 

In your communication of December 8, 1988 to John Anderson 

regarding the October 24, 1988 memorandum from myself thru J. 

Anderson to Docket A-87-11) you-5 commented on several issues 

related to EPA testing of two vehicles equipped by Exxon with 

onboard refueling vapor recovery systems. The purpose of this 

letter is to respond to your comments, and to provide 

additional information about the tests that were performed and 

the. results obtained from them. 

The first of your concerns related to canister 

preconditioning prior to the first test of each vehicle and 

between subsequent test sequences. In particular, you noted 

that no information was provided about canister preconditioning 

before the start of testing on each vehicle, and that an 

"arbitrary" driving schedule was applied to each vehicle 

between test sequences. As you noted, the draft Federal Test 

Procedure for vehicles equipped with onboard refueling vapor 

recovery systems does not contain any provision for canister 

preconditioning prior to the start of the proposed test 

procedure. In fact, the test procedure itself is specifically 

designed to condition the onboard canister to a known and 

repeatable loading, regardless of prior canister history. 

Therefore, provision for a canister preconditioning procedure 

in addition to that contained in the proposed test procedure is 

specifically omitted. It should be noted that the existing 

Federal Test Procedure applicable to vehicles equipped with 

current evaporative emissions control systems also omits the 

type of canister preconditioning step that you find lacking in 

the proposed test sequence, yet the current procedures have 

been proven to be both consistent and repeatable. 
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Although not explicitly provided for in the proposed test 

procedures, testing of the vehicles did include an on-road 

drive between each of the test sequences that were carried 

out. The purpose of these drives was to qualitatively evaluate 

driveability of the vehicles under conditions of a fully-loaded 

refueling canister, as well as to provide some purge to ensure 

that the refueling canister was not loaded beyond its 

breakthrough point at the start of the next test sequence. It 

is the intent of EPA that vehicles equipped with integrated 

onboard vapor recovery systems be capable of passing the 

proposed test procedure regardless of the canister loading or 

history at the start of the test. This intent is reflected in 

the test procedure, which provides for a quantity of 

hydrocarbons to be added to the canister during preconditioning 

that may vary depending on the initial canister load. 

The on-road drives performed between test sequences were 

non-specific in. the sense of not conforming to a rigid 

time/speed schedule, but all drives were highly similar in 

nature. Each drive consisted of a core route consisting of 

mostly rural and highway roads. Posted speed limits were 

followed, so that the driving schedule over the route was 

consistent from test to test. In some cases, this core route 

was supplemented by additional highway and city driving to 

further evaluate driveability under different conditions. I do 

not believe that the nature of these drives contributed in any 

way to test results being inconsistent or unrepeatable. 

Another concern raised in you letter was that EPA measured 

emissions were higher than the baseline or stock vehicle 

emissions reported by Exxon, and that this indicated that 

serious concern should be given to purge/exhaust interactions. 

The data also show, however, that emissions from the onboard 

vehicles measured by EPA are higher than those measured by 

Exxon under the same conditions, indicating a systematic offset 

between results obtained from the two laboratories. Even 

before accounting for this offset, emissions from the 

onboard-equipped vehicles, as measured by EPA, are not 

significantly higher than those from the stock vehicle, as 

measured by Exxon. When the apparent laboratory offset is 

considered, the conclusion that the data show cause for serious 

concern about canister purge/exhaust emissions interactions is 

even less credible. It should be noted that in all cases, even 

the apparently "higher" emissions measured by EPA are within 

current standards, indicating that any interactions that do 

exist are small enough to avoid serious concern. 

As stated in the text, the refueling emissions systems 

designed and fabricated by Exxon did not provide sufficient 

purge to pass the refueling test. The very fact that the stock 

evaporative control system does provide nearly all of the 
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required purge volume, however, indicates that "extensive 

development work" is not needed to upgrade performance of 

critical purge system components to the required level. 

Evaluation of the Exxon-designed onboard vapor recovery system 

revealed several design flaws, so that test failures can be 

attributed to deficiencies in implementation of the system, 

rather than to any intrinsic deficiency in the simplified 

refueling emissions control system design. EPA cannot agree 

with your conclusion that extensive development work is needed 

to achieve the desired level of performance. 

Findings of the EPA evaluation of the Exxon refueling 

emissions control system also revealed deficiencies that relate 

to problems encountered with liquid seal establishment and with 

fill quality. In particular, EPA found that the Exxon systems: 

1) did not include proper placement of the fill pipe outlet 

inside the fuel tank; 2) did not use the correct vent/rollover 

valve; 3) did not provide acceptable quality checks on 

modifications made to the. vent/rollover valves supplied with 

the vehicle. Each of these components are essential to proper 

functioning of an integrated onboard refueling emissions 

control system. It cannot be logically concluded that failures 

of systems that do not conform to designs known by EPA to 

perform properly indicate that the liquid seal system itself is 

not capable of effectively controlling refueling emissions. 

Finally, I acknowledge that during production testing of 

onboard-equipped vehicles, refueling canisters would in fact 

remain in their intended position. The experimental nature of 

the tests performed on the Buick vehicle, however, dictated 

that the canister not remaining its "normal" position so that 

canister weights could be obtained to aid in understanding the 

influence of the test procedure on system performance. I do 

not believe, nor do experimental data show, that placement of 

the refueling canister of the Buick vehicle significantly or 

adversely affected performance of the vehicle or the test 

results obtained from it. 

Several additional concerns were expressed in your 

communication, including the fact that the tests did not 

consider the effects of high temperatures and fuel 

volatilities, running losses, or high fuel delivery rates. The 

tests performed on the two Exxon vehicles were intended 

primarily to evaluate the proposed Federal Test Procedures as 

applicable to vehicles equipped with onboard refueling 

emissions control systems, and to provide an initial evaluation 

of the Exxon-designed systems. Evaluation of the effects 

mentioned above are clearly beyond the scope of the tests 

performed on the Exxon vehicles. 
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Thank you for your comments on results obtained from this 

test program. I hope that the items discussed above will 

clarify the procedures and results associated with these tests, 

and be of assistance to you in interpreting the significance of 

the test results. 

Sincerely 

Dr. David B. Bartus, Chemical Engineer 

Standards Development and Support Branch 

cc: D^pCffcet A^87:-ll?