P.1 

OAR Box 1856 

Prepped by Keeia Richards 

Document Number: 

7DII-A-08 

Docket Number: 

A-87-11 

Printed 11/24/2008 12:41:50 PM Sheet 71 of 82 
fi-mi F/^ V'/TM i-fi-ot 

P.2 

Summary and Analysis of Comments on the 

Recommended Practice for the 

Measurement of Refueling Emissions 

March, 1987 

Standards Development and Support Branch 

Emission Control Technology Division 

Office of Mobile Sources 

Office of Air and Radiation 

U. S. Environmental Protection Agency 
P.3 

Summary and Analysis of Comments on the 

Recommended Practice for the 

Measurement of Refueling Emissions 

I. Introduction 

As a result of concerns about the emissions which occur 

when gasoline vapors are displaced from fuel tanks during the 

refueling of motor vehicles, EPA has been examining the need 

for the control of these refueling emissions and the methods to 

do so. One such method involves the collection on the vehicle 

of the displaced hydrocarbons and the measurement of the 

effectiveness of the refueling vapor control system. This type 

of control is referred to as onboard control of refueling 

emissions. On August 22, 1985, EPA transmitted to interested 

parties two technical reports concerned with the measurement of 

refueling emissions. One report, "Refueling Emissions from 

Uncontrolled Vehicles,"[1] detailed EPA's baseline emissions 

measurements of refueling emissions and the second report, 

"Draft Recommended Test Procedure for the Measurement of 

Refueling Emissions", [2] presented a test procedure for the 

determination of the effectiveness of onboard control of 

refueling emissions. These reports were accompanied by a draft 

recommended practice, "Subpart C - Refueling Emissions Test 

Procedure."[3] 

Recipients of the reports and draft test procedure were 

requested to review and provide comments on EPA's recommended 

test procedure, including comments on the test parameters and 

the test equipment. As a result of on-going EPA analyses of 

the test procedure issues and the comments provided by the 

reviewers, EPA revised the test procedure. On April 10, 1986 

EPA convened a technical meeting to present and discuss the 

revised refueling test procedures. In addition to the oral 

comments provided during the meeting, EPA requested that the 

participants provide written comments on the revised test 

procedure. Comments on both the original and revised test 

procedures were received from the following organizations: 

American Petroleum Institute (API) 

California Air Resources Board (CARB) 

Chrysler Corporation 

Ford -Motor Company 

General Motors Corporation (GM) 

Motor Vehicle Manufacturers Association (MVMA) 

Nissan Research and Development,•Inc. 

Radian Corporation 

Toyota Motor Corporation 

-2-
P.4 

This document presents a summary of the comments on the 

recommended refueling test procedure, EPA's analysis of the 

issues raised by the commenters, and the resulting changes made 

to the recommended test procedure. 

The remainder of this document is subdivided into two 

major sections. Section II presents the summary and analysis 

of test procedure issues. The comments received on a particular 

issue are first identified and then followed by EPA's analysis 

and response. Section II is subdivided into six subsections. 

These subsections address: test parameters, fuel tank heating, 

facility requirements, canister loading, preconditioning, and 

miscellaneous issues. The final section, Section III, is an 

overall description of the test procedure which has been 

developed as a result of the comments and EPA's analysis of the 

comments. The Appendix following Section III describes the 

canister testing program carried out in support of the analyses 

in this document. 

II. Summary and Analysis of the Comments 

A. Primary Parameters Affecting Refueling Emissions 

In the draft recommended procedure, five key parameters 

affecting refueling emissions were identified. These 

parameters were: dispensed fuel temperature, differential 

temperature between dispensed fuel temperature and fuel tank 

liquid temperature, fuel volatility, fuel dispensing rate, and 

fuel level prior to refueling. The values for these key 

parameters directly affect refueling emissions and were chosen 

with the goal of insuring emissions control for most all 

expected in-use conditions. To do this, the values of each 

parameter were chosen at approximately the 90th percentile 

point from distributions of in-use survey data. Test parameter 

values as originally proposed in the draft recommended 

procedure are listed in Table 1. Revisions have been made to 

three of the five test values for the parameters as a result of 

comments received and further EPA analyses. While the reasons 

for these changes are discussed in the remainder of this 

section and subsequent sub-sections, the revised values are 

listed here in Table 2 for ease of comparison. 

1. Temperature Specifications for Dispensed Fuel and 

Liquid Fuel In The Vehicle Tank 

In commenting on the stringency of the refueling test 

parameters, a number of motor vehicle manufacturers took the 

position that the values were overly stringent. The 

manufacturers stated that the selection of the 90th percentile 

of both the dispensed fuel temperature and the tank temperature 

would result in greater than the 90th percentile of refueling 

events being represented by the test procedure. According to 

these manufacturers, the test values selected in the draft test 

procedure would represent approximately the 99th percentile of 

refueling events. 

-3-
Table 1 

Draft Recommended Procedure, 

Critical Test Parameters 

Parameter 

1. Dispensed Temperature, TD 

2. Temperature Differential,AT 

3.Volatility, RVP 

4. Dispensing Rate 

i 5.Fuel Level 

i 

Meaning 

Temperature of dispensed fuel 

Tank temperature minus 

dispensed fuel temperature 

Test fuel volatility 

expressed in Reid 

Vapor Pressure 

Flow rate of fuel as it is 

dispensed 

Level of fuel in vehicle 

prior to refueling. 

Percent of capacity 

to nearest 0.1 U.S. gal 

Value 

88 + 2°F 

+2 to +5 °F 

11.5 + 0.5 psi 

8-10 gal/min 

10% 
Table 2 

Revised Critical Test Parameters 

i 

Ul 

I 

Parameter 

1. Dispensed Temperature, TD 

2.Tank temperature TT 

3.Volatility, RVP 

4. Dispensing Rate 

5.Fuel Level 

Meaning 

Temperature of dispensed fuel 

Soak area temperature 

Test fuel volatility expressed 

in Reid Vapor Pressure 

Flow rate of fuel as it 

is dispensed 

Level of fuel in vehicle 

prior to refueling. 

Percent of capacity to 

nearest 0.1 U.S. gal 

Value 

81-84°F 

80 + 3°F 

In range of 8 to ' 

11.5 psi (Final 

determination to 

be made on 

results of 

Volatility Study) 

Refueling 

measurement: 

9.8 + 0.3 

gal/min. 

Canister loading: 

3-4 gal/min. 

10% 
P.7 

The commenters are correct in their basic contention that 

the selection of the 90th percentile for the dispensed fuel 

temperature and fuel tank temperature will result in the 

combined percentile . being higher the individual percentiles. 

EPA disagrees, however, with the assertion that the test values 

would represent the 99th percentile of refueling events. First 

of all, the parameters are not fully independent variables, 

making it difficult to assess the combined probability of 

occurrence o~f extreme values. Second, both parameters do not 

have to be at their 90th percentile values to generate high 

emissions. As the value of one of the parameters rises beyond 

that point, the other can fall correspondingly below its 90 

percent value and still produce overall high emissions. 

Therefore, to analyze the total effect of these parameters on 

refueling emissions, EPA went back to the basic field survey 

data and constructed an estimated emission rate distribution 

from the fuel and tank temperature data. 

The dispensed temperature and AT data used in this 

distribution were taken from a 1975 gasoline temperature survey 

conducted for the American Petroleum Institute (API) by the 

Radian Corporation, the same data that was used in the draft 

recommended procedure report.[4] The temperatures are from the 

four ozone-prone regions in the country (shown in Figure 1) for 

the critical months of May through September. The fuel 

volatility was assumed to equal the ASTM upper limit. 

Refueling emission rates were calculated from the survey data 

using the following emission factor equation developed by EPA 

from refueling test data from uncontrolled vehicles:[1] 

Emissions (g/gal) = -5.909 -0.0949(AT) +0.0884(TD) +0.485(RVP) 

The distribution of the estimated refueling emission rates is 

presented in Figure 2. Assuming the individual 90th percentile 

temperatures, TD=88°F, AT=+2°F, and the fuel RVP=11.5, the 

resulting emission factor is 7.26 g/gal. As can be seen from 

Figure 2, this value (7.26 g/gal) represents approximately the 

93rd percentile of the calculated distribution for summer 

refueling events. 

Radian Corporation performed a similar analysis in a 

report submitted to EPA at the April 10 workshop.[5] Radian's 

analysis, which included consideration of relative refueling 

amounts, indicated that the specified test parameters require 

systems that control over 99 percent of the refueling cases 

during ozone-prone seasons. While not disagreeing with 

Radian's basic approach, EPA believes that there are other 

factors which must be considered in an overall stringency 

evaluation. Perhaps chief among these factors is the assumed 

driving pattern used to evaluate system purge. As will be seen 

later in the discussions of canister preconditioning, EPA has 

used a driving sequence of three trips per day as the basis for 

system evaluation. This pattern allows a fairly generous 

amount of canister purge and represents typical conditions 

-6-
P.8 

O O 

0) Ul 

3 
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01 

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Figur e 2 

SUMMER REFUELING EMISSION FACTOR DISTRIBUTION 

FOR SELECTED CITIES * 

MIDPOINT 

0. 

.20000 

.40000 

.60000 

.80000 

1 .0000 

1 .2000 

1 .4000 

1.6000 

1.8000 

2.0000 

2.2000 

2.4000 

2.6000 

2.B000 

3.0000 

3.2000 

3.4000 

:i. fiooo 

3.B000 

• 4 .110110 

4:2000 

4.4 000 

4.6O00 

4.8000 

5.0000 

5.2000 

5.4000 

5.6000 

5.8000 

6.0000 

6.2000 

6.4000 

6.6000 

6.8000 

7.0000 

7.2000 

7.4000 

7.6000 

7.8000 

8.0000 

8.2000 

8.4000 

B.6000 

B.HOOO 

9.0000 

MISSING 

TOTAL 

COUNT 

0 

0 

0 

1 

1 

0 

4 

5 

8 

1 1 

13 

10 

19 

26 

35 

37 

41 

56 

65 

108 

134 

1 16 

107 

129 

128 

139 

151 

159 

139 

1 10 

124 

90 

76 

55 

62 

72 

67 

70 

40 

31 

16 

8 

5 

4 

1 

0 

528 

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RVP = ASTM Maximum allowable for the months involved, 

co 
P.10 

rather than an upper limit. Its use has the effect of lowering 

the overall stringency of the test procedure from that 

represented by the fuel parameters. 

A second stringency consideration is the fact that, as 

described in the technical report accompanying the original 

draft procedure[2], the temperature data used represented 

smoothed average values. Thus, for example, the dispensed fuel 

temperatures were five day averages, and did not contain the 

highs that daily values would give. Nor did they represent the 

daily maximun values, which the report indicated would 

typically be 4 to 7°F above the average. 

Another factor described in the original report which has 

not been directly included in the procedure is the effect of 

fuel weathering on refueling emissions. The presence of 

weathered residual fuel in the fuel tank at the time of 

refueling, rather than unweathered fuel as used in the test 

procedure, would be expected to increase refueling emissions by 

perhaps 0.5 g/gal. EPA's decision not to use weathered fuel in 

the tank at this time is another factor reducing the overall 

stringency level of the refueling test. It would be possible 

to use weathered fuel and make some adjustment in the 

temperature parameters, but this change would have no 

beneficial effect on the test and would add the complexity of 

having to handle two different test fuels. 

Given all these factors, the precise overall stringency of 

the test procedure is difficult to determine. EPA believes 

that it is sufficient to insure control at nearly all expected 

conditions, as was its original goal. The chief impact of more 

demanding test parameters is to increase required canister 

sizes to hold the increased amounts of generated vapors. This 

result is not undesireable, so long as no other system changes 

are required which might markedly increase the marginal cost of 

compliance. If this were the case, then more detailed analysis 

of test condition stringency might be justified to determine 

whether some relaxation might be appropriate. 

2. Fuel Volatility 

The draft recommended procedure specified that the test 

fuel have an RVP of 11.5 psi. This volatility represents the 

RVP of summer commercial fuel as used in current EPA emission 

factors test programs, as well as being the ASTM class C 

volatility upper limit for summer months in the ozone prone 

areas of the country. MVMA, in its comments, advocated that 

the fuel used in the refueling test procedure have the same RVP 

as that of EPA's current certification test fuel, i.e., 9 psi. 

MVMA understood and agreed with the Agency's desire to 

eliminate the present discrepancy between summer commercial 

fuel volatility and the current certification fuel volatility. 

MVMA's solution is, however, to limit commercial summer fuel to 

-9-
P.11 

9.0 RVP as opposed to specifying that the refueling test fuel 

volatility equal present commercial fuel volatility, as the 

recommended test procedure specified. 

The issue of test fuel versus commercial fuel volatility 

is currently being examined by the Agency and EPA is studying 

fuel volatility to establish the best overall approach to 

dealing with this issue. Whatever the resolution of that 

process, EPA intends ' to adopt those results for refueling 

testing as well. The draft procedure used 11.5 RVP simply 

because it approximated the current in-use situation. That 

choice was not intended to represent resolution of the RVP 

issue. The procedure should more properly be viewed as 

potentially using a fuel with volatility anywhere in the range 

of possible options being considered by EPA at this time, i.e., 

anywhere from 8 to 11.5 psi. 

An additional volatility concern was raised by Nissan. In 

its comments, Nissan expressed concern about variations in the 

RVP of test fuels and questioned how it can be controlled. 

This concern, i.e., the need to limit the weathering of test 

fuel in the fuel cart so as to minimize test variability, is 

shared by EPA. The revised procedure contains the requirement 

for the collection of a fuel sample and measurement of the RVP 

immediately prior to the measurement of refueling emissions. 

EPA recognizes that this is a worst case requirement with 

respect to its effects on test facility and personnel 

resources. EPA is open to all suggestions on equipment design 

or test data on the rate of fuel weathering in the fuel cart 

which would allow less frequent measurement of the RVP of the 

test fuel. 

3. Fuel Dispensing Rate 

The final area of comments with respect to the test 

parameters concerned the recommended value for the fuel 

dispensing rate. In the draft recommended procedure, the 

specified range of 8 to 10 gallons per minute (gpm) was 

identified as covering the majority of the refueling events 

while minimizing nuisance shutoff of the fuel nozzle. Several 

commenters took issue with this range for a variety of 

reasons. API stated that some vehicles can not be fueled at a 

rate as high as 8 to 10 gpm and that premature nozzle shut off 

at high fueling rates is associated with some filler neck 

designs. MVMA commented that spit-back is highly probable at a 

fueling rate of 10 gpm when the tank approaches the 95 percent 

full level, especially with a liquid seal. MVMA stated that 

CARB limits fueling to the 90 percent tank level at a fueling 

rate of 10 gpm, applicable with the 1987 model year. MVMA also 

stated that the specified fueling rate range of 8 to 10 gpm is 

too broad and recommended a fueling rate specification of 

9.0+_0.2 gallons/minute to improve test repeatability and 

test-to-test and lab.-to-lab. correlation. 

-10-
p.i; 

EPA agrees that the occurrence of nuisance shutoffs and 

fuel spillage may be a function of filler neck design when 

vehicles are fueled at high flow rates. However, it is EPA's 

belief that .the design of a refueling control system which is 

capable of controlling premature nozzle shutoff and avoiding 

spit-back at expected in-use fuel dispensing rates is the 

responsibility of the motor vehicle manufacturers. Lacking 

spit-back control, fuel spillage from this source could be a 

major source of refueling emissions. Thus, a fuel filler 

system that prevents spit-back at the upper limit of the 

dispensing rate is integral to the effective control of 

refueling emissions. 

At the same time, EPA recognizes the fact that, given 

vehicles designed to operate at current maximum values, 

gasoline marketing pressures would be expected to lead to 

increased in-use despensing rates in the future. In order to 

prevent such a situation, it is likely that some control, 

voluntary or otherwise, would be required over in-use 

dispensing rates. 

EPA believes that a maximum dispensed fuel rate of 10 gpm 

is reasonable based upon current in-use conditions. The draft 

procedure reported that most refuelings take place at 10 gpm or 

less; also CARB has already specified 10 gpm for testing to 

demonstrate compliance with its refueling control program. 

Thus, 10 gpm will continue to be used as the approximate 

maximum flow rate. 

Turning to the question of variability in test results 

between tests and/or between laboratories with respect to the 

rate at which fuel is dispensed, EPA believes that some 

variability in results can be attributable to this factor; i.e. 

fuel dispensing rate. EPA also believes that, in a refueling 

emissions test, the upper limit of the dispensing rate is 

normally the important criteria. In selecting a tolerance band 

for the fuel dispensing rate to address the test variability 

concern, EPA also recognized the need for the use of a value 

which would be achievable at a relatively low cost. EPA 

believes that a tolerance band of approximately 3 percent at a 

flow rate of approximately 10 gpm, i.e. + 0.3 gpm, will 

achieve both objectives. Combining the selected tolerance band 

with the objective of holding the lower limit close to 10 gpm 

with a minimal exceedance of 10 gpm at the upper limit resulted 

in the flow rate specification of 9.8 +_ 0.3 gpm. Testing 

conducted at EPA will normally dispense fuel as close to 10 gpm 

without exceeding the 10.1 gpm limit as possible, since this 

value would be expected to be the most difficult test condition. 

B. - Fuel Tank Heating 

Heating of the fuel in the fuel tank was required in the 

draft recommended procedure to bring the liquid fuel and fuel 

vapors into equilibrium at the required test temperature. The 

test procedure included a method for heating the fuel tank 

-11-
P.13 

using a single heat blanket which allowed, the fuel vapor and 

liquid fuel to reach an equilibrium condition before testing. 

Concerns raised in the comments covered a wide range of areas. 

These concerns are summarized below. 

In its comments, MVMA stated that the fuel tank 

configuration greatly influences the ability to heat the fuel 

and to achiej/e the 3°F vapor to liquid temperature difference 

required in the procedure. MVMA questioned the feasibility of 

the recommended procedure to achieve the required heating on a 

variety of tank configurations. MVMA requested that EPA 

demonstrate the feasibility of the procedure on several tank 

configurations. Data submitted by Ford showed an inability to 

achieve the required vapor temperature with a single heating 

blanket on a Mercury Lynx. 

The question of how temperature measurements on in-use 

vehicles (use of an external thermocouple was proposed in the 

draft procedure) were to be made with plastic fuel tanks was 

also raised by MVMA. Another aspect of the fuel temperature 

measurement issue which was raised by commenters was the 

capability to read the true fuel temperature when heating a 

nearly empty fuel tank. The thermocouple would have to be very 

close to the heat blanket when the 10 percent fuel volume was 

being heated and MVMA stated that thermocouple readings could, 

as a result, be influenced by the heat blanket. 

Comments on the subject of fuel tank heating also 

identified test-to-test variability as a concern. Toyota 

stated that the initial boiling point of 11.5 RVP fuel is under 

88°F and that this fuel property, in combination with the 

specified temperatures of the fuel tank and of the fuel 

dispensing system, would result in high vapor losses and 

resultant test to test variability. Specifying a heating rate 

was recommended as a means of limiting the rate of boiling of 

the fuel and to avoid variability in test results caused by 

variability in the heating rate. 

Concerns about the fuel tank heating procedure and 

temperature measurement requirements such as those expressed by 

the motor vehicle manufacturers were shared by EPA. As a 

result of its experience, EPA set out to revise the tank and 

dispensed fuel temperatures in an effort to eliminate the need 

for external tank heating and tank fuel temperature measurement. 

• Using the emission factor equation given earlier, 

alternative dispensed fuel and tank temperatures can be defined 

which would yield approximately the same emission conditions as 

the test parameters otherwise selected on the basis of test 

stringency. The approach used was to select a fuel tank 

temperature equal to ambient laboratory conditions (thus 

eliminating the need for tank heating) and to determine a 

dispensed fuel temperature yielding the same emission rate as 

•12-
P.14 

did the initial test conditions. Temperatures developed from 

the equation were 80°F + 2°F for the fuel tank temperature 

(80°F was selected because it is the temperature maintained in 

the EPA's Motor Vehicle Emission Laboratory vehicle soak area), 

83°F + 2°F for the dispensed fuel temperature and the 

requirement that the temperature of the dispensed fuel be 1° to 

3°F higher than the soak area temperature. These temperatures 

resulted in _a mean refueling emissions value of 7.29 g/gal 

which compared very favorably to the value of 7.26 g/gal for 

the original test conditions. The 80°F fuel tank temperature 

can be readily achieved without the need to heat or measure the 

temperature of the fuel in the vehicle tank through the process 

of soaking the vehicle at the required temperature for a 

pre-specified soak period. EPA chose a soak period of six 

hours as sufficient to accomplish this task. 

Following the April 10, 1986 meeting,, manufacturers 

provided comments on the revised temperature specifications. 

In their comments, they expressed strong support for the 

concept of selecting a fuel tank temperature equal to ambient 

laboratory conditions. However, a number of manufacturers 

commented that the +2°F soak area tolerance was too 

restrictive. GM reported that maintaining tight control of 

room ambient temperature in its larger laboratories can be very 

difficult. EPA's main concern in designating the +_ 2°F 

tolerance was to limit adverse impacts on test variability. In 

response to the comments, EPA performed additional analyses on 

the effects of test temperature tolerances on refueling 

emissions variability. The conclusion reached is that 

expansion of the soak area temperature tolerance band can be 

accommodated if accompanied by an adjustment in the dispensed 

fuel tolerance band to retain approximate equivalency in the 

refueling emissions tolerance band attributable to test 

variability in these temperatures. As a result, the fuel tank 

temperature is specified as 80°+3°F and the dispensed fuel 

temperature is specified as 81° to 84°F. EPA believes that 

maintaining the reduced dispensed fuel .tolerance band will not 

be excessively burdensome. Under this approach, the dispensed 

fuel would only need to be heated to 81° - 84°F, which would 

substantially reduce any problems with respect to the boiling 

point of the fuel in the fuel cart and the associated changes 

in the fuel RVP. EPA believes that., the use of these 

temperature specifications will alleviate the concerns 

expressed by the manufacturers without any reduction in the 

required control of refueling emissions. 

C. Facility Requirements 

The recommended refueling test procedure requires the use 

of a sealed housing for evaporative determination (SHED), 

similar to what is now used for evaporative emissions testing 

with minor alterations to accommodate fuel dispensing. The 

SHED is required for the actual refueling test and for loading 

-13-
P.U 

of the canister to breakthrough. Comments on the facility 

requirements of the test procedure addressed: 1) the use of a 

SHED to determine canister loading to breakthrough; 2) the 

impact of the test on facility requirements; and 3) the 

location of the refueling hose and nozzle. 

1. SHED Use for Breakthrough Determination 

Commenters suggested the use of procedures other than a 

SHED to determine canister loading to breakthrough. It was 

pointed out that some contract laboratories which measure 

exhaust emissions do not have SHED equipment and would, 

therefore, be unable to perform refueling tests because of the 

lack of a SHED. The facility requirement impact (as discussed 

below) was also a concern for those facilities with SHEDs. A 

procedure involving repeated refuelings to load the canister 

without the need for a SHED was suggested as an alternative. 

In addition to comments recommending the elimination of 

the use of a SHED when loading the canister, comments were made 

recommending changes to the SHED loading procedure itself. 

MVMA stated that the procedure should be written so as to 

prevent the continued forcing of vapors through a canister 

which is loaded to breakthrough. MVMA believes that the 

procedure as proposed would load the canisters past 

breakthrough, and as a solution recommended using a reduced 

fueling rate, e.g., 3 gallons/minute, during canister loading 

to breakthrough. MVMA also recommended that the sample pick-up 

point for detecting breakthrough be close to the canister 

rather than remotely mounted in the SHED as specified in the 

recommended procedure. MVMA believes that reducing the 

response time for breakthrough detection will prevent continued 

forcing of vapors through a canister already loaded to 

breakthrough. 

Responding first to the basic issue of needing a SHED to 

detect breakthrough, EPA agrees that a canister loading 

approach which would not require the use of a SHED to determine 

canister breakthrough is desirable so as to simplify testing 

and reduce resource requirements. Use of the SHED was proposed 

by EPA so as to address the following concerns associated with 

the use of a sample pick-up located at the canister. First, 

that a small transient puff of vapor from the canister, prior 

to breakthrough, could be interpreted as breakthrough and 

thereby result in incomplete loading of the canister. Second, 

that relatively small air currents around the vehicle, as could 

occur in a large room, could dissipate breakthrough vapors and 

lead to delayed detection of breakthrough. 

A small quantity of data recently collected by EPA using 

current evaporative emissions canisters suggests that small 

premature puffs of vapor may not be a significant concern. 

There is, however, no way of telling whether this data is 

-14-
P.16 

applicable to the larger and possibly reconfigured canisters 

which are anticipated for use with onboard refueling systems. 

There is also no information on the effects of air currents 

around the vehicle on breakthrough detection. EPA continues to 

believe, therefore, that the SHED needs to be used in 

determining canister breakthrough loading. At the same time, 

the Agency would welcome the submission of further data on this 

area which might lead to a non-SHED based approach. 

MVMA's concern with the SHED procedure is that 

breakthrough will occur significantly before detection because 

of the sample pick-up location. As a result of the detection 

delay, MVMA is concerned that a fueling rate of 10 g/min will 

cause a significant amount of additional vapor to be 

transmitted to the canister beyond the actual breakthrough 

point. EPA agrees that detection lag will result in some 

degree of canister loading beyond breakthrough and that the 

degree of loading beyond breakthrough will depend on the 

refueling rate. However, since the objective of the canister 

loading procedure is to achieve loadings to at. least 

breakthrough, this fact of itself is not troubling. What is of 

concern is the increased amount of variability in breakthrough 

measurements at high fuel flow rates. For this reason, some 

reduction in the fueling rate would be acceptable provided 

loading to a_t least breakthrough was achieved. Testing 

conducted by EPA at a fueling rate of 3 to 4 gallons per minute 

has shown that repeatable loading conditions should result. The 

fueling flow rate during the canister loading procedure will, 

therefore, be specified as 3-4 gallons/minute. 

2. Testing Capacity 

Commenting on the impact of the test on facility 

requirements, Toyota stated that adoption of the recommended 

refueling test procedure would result in either a significant 

reduction in the testing capacity of existing facilities or 

would require significant facility expansion to retain present 

testing capacity. The costs related to the modification and/or 

construction of expanded test facilities was a significant 

issue to a number of commenters. 

EPA recognizes that incorporation of % the refueling test 

procedure, or for that matter any other new testing 

requirement, into the existing emissions testing procedure will 

impact test facilities to some extent. EPA, like the 

manufacturers, is desirous of holding to a minimum the impact 

of the procedure on facility requirements. EPA is making every 

effort to minimize the impact whenever possible in developing 

the test procedure. In fact, the revised procedure, which will 

be described further below, has a much lower facility impact 

than did the previous draft. All comments on how the impact on 

facility requirements can be further minimized are encouraged 

and welcomed. 

15-
P.17 

In the area of costs, EPA recognizes that some 

expenditures will be necessary to expand test facilities to 

accommodate the demands of incorporating the refueling test 

procedure. However,- it appears that, as a part of overall 

cost, these impacts will be relatively small. For example, 

values used by the Motor Vehicle Manufacturers Association, 

when viewed as a cost per production vehicle, represent only 

approximately 30 cents per vehicle. Even these values would be 

expected to decline in the face of the procedural revisions 

being described in this document. 

3. Refueling Hose Location 

The draft procedure specified that the fuel dispensing 

hose and nozzle be located inside the SHED. One commenter 

questioned whether non-permeable fuel hoses would be required; 

fuel hose permeability, nozzle leakage, and nozzle-to-fuel hose 

joint leakage may cause a SHED contamination problem. 

During SHED background and retention validation tests 

conducted at EPA's Motor Vehicle Emission Laboratory, 

contamination problems were experienced as a result of the 

location of the fuel dispensing hose and nozzle inside the 

SHED. This problem was resolved by moving the hose and nozzle 

outside of the SHED and providing access to the vehicle's fill 

neck by a boot so that only the nozzle tip enters the SHED. 

The specific criteria developed for the boot are: that the 

aperture through which the nozzle tip passes seals against the 

tip when the nozzle is inserted and closes to form a vapor 

tight seal when the nozzle is not in place; that the boot be 

flexible and relatively long so as to avoid the need for 

precise locating of the vehicle in the SHED; and the boot be 

large enough to facilitate free passage of the nozzle through 

the boot and full operation of the nozzle inside of the boot. 

Location of the nozzle and fuel hose outside of the SHED has 

solved the contamination problems. The procedure has been 

modified to require the use of equipment for refueling with the 

refueling hose and nozzle located outside the SHED. 

D. Requirement for Loading Canister to Breakthrough 

Commenting on the requirement for canister loading, two 

commenters took issue with the need to fully load the canister 

to breakthrough. MVMA and Toyota stated that forced loading of 

the canister to breakthrough is not representative of in-use 

vehicle operation and should, therefore, not be part of the 

test procedure. These comments also claimed that loading of 

the canister in this manner will have a negative impact on 

exhaust emissions, on fuel economy and on driveability. MVMA 

stated that full canister loading followed by one prep LA-4 

will significantly add to the difficulty of complying with 

exhaust emissions standards and in meeting fuel economy 

objectives and will result in the collection of exhaust 

-16-
P.18 

emissions and fuel economy values under non-representative 

operating conditions. MVMA also believes that full loading of 

the canister removes any incentive to provide a safety margin 

in canister, sizing because excessive hydrocarbons have to be 

processed during purging and this will cause driveability 

problems. One commenter pointed out that the proposed 

procedure did not require loading to breakthrough of the 

evaporative canisters in non-integrated onboard systems. 

EPA believes that loading canisters to breakthrough is an 

important requirement of the procedure so as to demonstrate 

that the system will adequately purge the canister from a fully 

loaded condition. The need to demonstrate this capability in 

the test procedure stems from the wide variations which exist 

in the method of operation of in-use vehicles. Since the 

degree to which a canister is purged prior to refueling is 

dependent on vehicle operations preceding refueling, it is 

reasonable to expect that wide variations in the degree of 

canister purge can also exist in in-use vehicles. Vehicles 

used infrequently and in short trip operations will experience 

reduced canister purging while accumulating hot soak emissions 

after each trip and repeated diurnal loadings because of 

infrequent operation. As a result, these in-use vehicles can 

be expected to experience forced loading of the canister to 

breakthrough or saturation. Forced canister loading to 

breakthrough in the test procedure is, therefore, not 

unrepresentative of an event which can occur on an in-use 

vehicle. Data available to EPA indicate that the canister 

system does not undergo permanent adverse effects by being 

highly loaded and quickly recovers its capacity when vehicle 

operating conditions provide additional purge. Loading of a 

canister to breakthrough results in a readily achievable and 

repeatable canister loading condition. Retention of the 

loading to breakthrough requirement in the procedure thus 

provides a useful, readily identifiable point for beginning 

testing. 

It is important to note that loading the canister to 

breakthrough is regarded by EPA as a minimum loading condition 

before testing. If, because of its in-use operating factors, a 

vehicle comes in for testing loaded beyond breakthrough, it 

will be tested as received. If systems are properly designed, 

such occurrences should be rare; but if systems are not 

properly designed and frequently operate beyond the 

breakthrough point, then this is a consequence of the design 

and the systems still ought to be tested in that condition. 

Although some of the commenters felt that loading the 

canister to breakthrough would have an adverse impact on 

driveability, exhaust emissions, and fuel economy, and 

therefore should not be included in the test procedure, EPA 

does not agree. First, since canister loading to breakthrough 

-17-
P.19 

will occur on in-use vehicles, manufacturers will have to 

accommodate this condition in their system designs regardless 

of test requirements. Manufacturers will have to design their 

systems to operate satisfactorily with respect to both canister 

purge and driveability because of in-use -considerations. As 

for exhaust interactions, EPA has always expected that 

evaporative systems should be able to begin the evaporative 

test procedure from a loaded condition and expects to introduce 

this requirement apart from any onboard actions. The presence 

of an onboard canister could increase the amount of purge 

vapors under loaded conditions, but not to an unmanageable 

degree. As for fuel economy, EPA agrees that impacts on fuel 

economy measurements should be avoided. The simplest option 

would be to allow those manufacturers who believe that loading 

the canister to breakthrough will have a negative impact on 

fuel economy to omit the canister loading step for the fuel 

economy test. If this approach were unsatisfactory, then a 

CAFE adjustment might have to be considered. 

One revision was made to the canister loading procedure as 

a result of the comment which pointed out that there was no 

loading procedure for the evaporative canister in 

non-integrated systems. Omission of this step in the procedure 

was an oversight since, the intent of the procedure was to 

include a loading step for the evaporative canister in 

non-integrated systems. A step will, therefore, be added to 

the procedure requiring the loading to breakthrough of the 

evaporative canister in non-integrated systems prior to the 

vehicle preconditioning. As with refueling canisters, this 

step will require the use of the SHED to determine the 

breakthrough point. 

E. Vehicle (Canister) Conditioning for Performance of 

Refueling Emissions Control Test 

Background 

The test sequence proposed for refueling emissions added 

two new tests designed to check the capacity and purge 

capability of the refueling control system, respectively. Both 

of these tests depended upon canister preconditioning steps for 

their proper functioning. . ... 

The refueling capacity test was designed to ensure that 

the overall vapor control capacity of the canister was 

sufficient for a complete fill-up, i.e. from 10 percent of tank 

volume to at least 95 percent of tank volume. Certification 

test vehicles were expected to arrive at the test site with 

canisters purged to a level commensurate with a nearly empty 

tank. Prior to testing, the fuel tank would be drained and 

filled to 10 percent of capacity with test fuel. Since in-use 

vehicles could arrive in any condition, preconditioning by 50 

miles of driving using test fuel on either the durability 

-18-
driving schedule or equivalent urban driving was proposed. 

Following the 50 miles of driving, the fuel tank would be 

drained and fueled to 10 percent of capacity. Following this 

preconditioning, the actual refueling test would then be 

performed to verify that the refueling system indeed had 

adequate capacity to handle essentially a full refueling. 

The second, or purge, test began with a drive-down 

sequence on "the dynamometer, consisting of sequential Urban 

Dynamometer Driving Schedules (UDDS or LA-4), alternating with 

one hour hot soaks. This sequence was intended to use fuel and 

allow refueling canister purge, in order to subsequently 

perform a partial refueling with an amount of fuel large enough 

to adequately test the system's purge capability. To do this, 

the UDDS soak sequence would be repeated until approximately 30 

percent of the tank fuel capacity had been used. A refueling 

test would then be conducted as with the capacity test, except 

that the refueling amount would approximately correspond to the 

amount of fuel consumed in the drive-down. The purpose of this 

stage was to demonstrate that the refueling control system had 

adequate purge capacity to purge accumulated refueling vapors. 

Comments 

Since the condition of the refueling canister prior to any 

refueling test is very important, it is not surprising that 

considerable comment was directed at the various conditioning 

steps in the draft procedure. Commenters generally believed 

that the 50 mile drive for in-use vehicles was inadequate, and 

they opposed the use of a conditioning procedure for in-use 

vehicles different from that used on certification vehicles. 

Commenters also expressed concerns with respect to the 

capability of the 30 percent drive down to prove the purge 

capability of the system. 

Commenters suggested several alternative procedures for 

conditioning of the canisters prior to performance of the 

refueling capacity test. For certification vehicles MVMA 

suggested actual* vehicle driving while Toyota suggested 

starting with a full fuel tank and driving either 14 hours on 

the durability mileage accumulation procedure or 80 hours of 

UDDS/hot soak operation. The American .Petroleum Institute 

(API) suggested the use of a 50 mile drive for certification 

vehicles as had been proposed for in-use vehicles. 

"Actual", while not defined, seemed to imply operation of 

the vehicle either on a test track or on the road using an 

operating schedule which would reflect actual consumer 

driving patterns. 

-19-
P.21 

For capacity testing of in-use vehicles, both MVMA and 

Toyota suggested driving out the fuel contained in the fuel 

tank at the time that the vehicle entered the test program. 

MVMA suggested driving 75 miles for each 1/4 tank volume 

contained in the fuel tank. Toyota suggested driving the 

vehicle until 10 percent fuel volume remained in the tank. 

Commenters also questioned the 30 percent drive-down 

associated with the canister purge test. They suggested that 

actually driving out a whole tankful of fuel might be the only 

reliable way to verify proper system purge characteristics. 

EPA itself had indicated concern with respect to the adequacy 

of the 30 percent drive-down because of the non-linear nature 

of canister purging with time. The draft procedure contained 

EPA's suggestion that a full drive-down might be required. 

In order to effectively respond to all the concerns over 

canister preconditioning which have been raised, EPA has 

undertaken an extended analysis of canister purge 

characteristics and vehicle operating patterns. From this 

analysis the Agency has derived a revised approach to 

preconditioning and testing refueling control canisters. This 

approach is greatly simplified compared to the draft procedure, 

and provides a more accurate way to assess the ability of 

refueling control systems to perform properly in actual use. 

The results of EPA's analysis are presented in the following 

sections. 

Analysis 

1. Canister HC Purge Characteristics 

To develop an understanding of how canisters purge, EPA 

performed a series of tests on evaporative emission control 

canisters. Some of the canisters had been in use (aged) on 

durability data vehicles and were furnished by Chrysler, Ford, 

GM and Nissan while others were new units purchased from 

dealers. One relatively large canister, constructed by EPA, 

was also tested. The details of the testing and the test 

results are shown in the Appendix. The overall results are 

summarized below. 

Two basic steps were used in testing the desorption 

characteristics of carbon canisters. The first involved 

loading the canister to an appropriate level with refueling 

vapors. The second was to draw air over the carbon bed to 

purge it of its hydrocarbon load. Purge curves were developed 

by monitoring the change in hydrocarbon load as a function of 

the volume of purge air pulled over the carbon bed. 

The key results of the testing are shown in Figure 3. 

Shown are characteristic purge curves for the various canisters 

-20-
I 

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15 

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REPRESENTATIVE CURVES 

Normqlized by Canister Volume 

10 20 

Purge Volume (cubic feet/liter) 

FIGURE 3 

• My 

,• Ha 
P.23 

expressed as the weight of hydrocarbons removed from the 

canister versus the volume of air drawn through the canister. 

The test results have been normalized to a canister volume of 

one liter to provide a standardized basis for comparisons. 

In reviewing the results of this testing, EPA decided that 

the results of the tests on the Chrysler canister should not be 

used for subsequent analysis. This canister showed , a 

substantially lower storage capacity than the other canisters, 

for reasons which were never identified. In any event, a 

canister with such a small storage capacity per unit volume of 

charcoal would not be expected to be a reasonable choice for 

use in refueling control systems. To characterize the range of 

characteristics exhibited by the other three canisters, EPA has 

used the Nissan and Ford curves in its analysis. At this time, 

EPA does not know how representative of all canister designs 

these results are, nor how much improvement in canister 

performance could be gained by attempts to optimize charcoal 

performance. However, these questions are not critical in 

relation to the primary goal of describing general system 

characteristics and designing appropriate test techniques. 

2. Vehicle Operation 

Evaluation of in-use vehicle operational patterns 

important to an onboard refueling test program requires 

consideration of typical daily events which contribute to the 

loading and unloading of the canister. Hydrocarbon vapors 

generated during evaporative diurnals and hot soaks along with 

vehicle refuelings constitute canister loading events. Vehicle 

drive events cause canister unloading. 

On the basis of typical driving patterns, in-use vehicles 

are employed under widely varying conditions. As a result of 

this variability in daily operational trips, the loading, at 

any selected time, of a HC vapor control canister, whether it 

be a refueling control canister or an evaporative control 

canister, will also vary. At one extreme is the condition of 

multiple days wherein the vehicle is not driven at all. Under 

this non-driven condition, the canister will experience 

repeated daily diurnal loadings of HC vapor and will eventually 

reach a fully loaded (saturated) condition; i.e., the 

canister's capacity to adsorb and retain HC will be reached. 

At the other -extreme in the range of daily operational 

characteristics is continuous long trip operation. Under these 

conditions, the canister will undergo continuous purging and 

the amount of HC stored in the canister would approach zero. 

Between these limits lie a wide variety of daily vehicle 

usage patterns. Typically, vehicle usage patterns might 

-22-
include two employment related trips per day and one or more 

trips for other purposes. Under multiple vehicle trip per day 

operations, the canister will undergo purging while the vehicle 

is being driven and loading due to hot soaks and the daily 

diurnal while the vehicle is parked. To analyze overall system 

performance, EPA constructed a simple model of canister 

behavior. Using the canister purge curves described above, the 

model was abj.e to track canister performance for both Ford and 

Nissan type canisters. 

In the model, each daily trip is considered to be 

equivalent to one LA-4; i.e., 7.5 miles of vehicle operation. 

The purge rate is expressed as the volume of purge air, in 

cubic feet, per LA-4. The reference information stored in the 

model is the characteristic canister purge curve for one liter 

Ford and Nissan canisters. The input variables employed are 

desired canister size and type, purge air volume per LA-4, 

uncontrolled hot soak and diurnal loadings in grams, and the 

number of trips per day. The outputs from the model are 

tabulations of the running tally of the canister purges and 

loadings relative to miles driven plus other parameters which 

can be derived from these figures (e.g., amount of HC purged 

per mile). Running losses, if any, are treated as going 

directly to the engine and not impacting loading or purging of 

the canister. This assumption is not appropriate for all 

current evaporative control system designs, but EPA believes 

that such designs will not be found on future systems because 

of their adverse impact on canister purge. In addition, 

diurnal loadings are treated as a constant, neglecting the fact 

that, for example, immediately following a refueling, the fuel 

tank would be full and essentially no diurnal emissions would 

be generated. This means that the results from the model are 

representative of conditions after part of the fuel has 

actually been used up and not to be interpreted as the full 

time history of events beginning with a full tank. 

The results from a typical run of the computer model are 

shown in Figure 4. In this case, a simple pattern is 

illustrated consisting of a single daily drive followed by a 

hot soak and a diurnal. The model indicates that after only a 

few repetitions of this pattern, an equilibrium is reached 

between purging and loading. This equilibrium indicates the 

vapor storage capacity available for refueling control. Note 

that continuing to operate on this pattern produces no further 

progress toward the fully purged capacity of the canister. 

One of the key effects on system performance in this 

example is the daily driving pattern which is assumed. Figures 

5 through 7 illustrate the effect of using two, three or four 

assumed trips per day instead of one. As can be seen from 

-23-
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CANISTER PURGE VS CYCLIC OPERATION 

FIGURE H 

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CANISTER PURGE VS CYCLIC OPERATION 

FIGURE 5 

120 

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CANISTER PURGE VS CYCLIC OPERATION 

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120 

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90 

80 H 

70 

60 -

50 -

40 

30 

20 -

10 -

0 

CANISTER PURGE VS CYCLIC OPERATION 

FIJ3URE 7 

CANISTER : 4.3 L NISSAN 

HOT SOAK : 10 g 

DIURNAL : 22 q 

PURGE : 12 CU FT / LA- 4 

DAILY TRIPS : 4 

- T -

40 80 120 160 !00 

Miles Driven 

JN> 
these figures, vehicles operated on either a one or two trip 

per day cycle will possess lower refueling capacities than 

vehicles operated under a three or four trip per day cycle. On 

the other hand, it is the case for all of the driving patterns 

that the canister reaches an equilibrium condition after only a 

few repetitions of the daily operating pattern. These results, 

incidentally, have been derived for a Nissan type canister 

because the iJissan canister shows the greatest sensitivity to 

driving patterns and makes the clearest example. Ford type 

canisters respond to driving patterns, but to a lesser degree. 

Following initial evaluation of the effect of driving 

patterns, EPA chose to do its subsequent modeling based upon a 

three trip per day sequence. As will be seen below, this 

pattern has also been used in the test procedure 

preconditioning sequence development. Three trips per day 

closely resembles, the value of 3.05 trips per day in the EPA 

MOBILE3 model for determining the effects of mobile source 

emission standards on pollutant inventories. From the above 

modeling results, however, it is clear that this represents a 

less demanding requirement than that of a one or two trip per 

day sequence. The overall effect of this choice upon test 

procedure stringency has not been quantified. 

3. Effect of Purge Rate 

For a given vehicle, the other key operating variable 

which affects refueling system performance is the purge rate. 

The refueling model shows that, holding canister size constant, 

the equilibrium level (which represents the available refueling 

capacity) can be increased or decreased by changing the air 

purge rate. These effects are illustrated in Figures 8 and 9. 

The effect of increasing the purge air rate in the example 

used above by 50 percent is shown in Figure 8. The increase in 

purge air rate results in an increase in the amount of 

hydrocarbons which are purged from the canister at equilibrium; 

i.e., an increase in refueling capacity. Conversely, it is 

shown in Figure 9 that a 50 percent decrease in purge air rate 

results in a reduction in the hydrocarbon purge level at 

equilibrium; i.e., a reduction in refueling capacity. 

4. Canister Sizing . - . . 

Having developed a basic model of refueling system loading 

and purging, required canister sizing for refueling operations 

was analyzed. The required refueling vapor capacity for a 

given vehicle was determined using the uncontrolled emission 

factor equation developed in EPA's refueling emission baseline 

study (Refueling Emissions from Uncontrolled Vehicles; 

EPA-AA-SDSB-85-6). An entrainment factor of 20 percent (based 

upon early test results with a liquid seal system) and a safety 

margin of 10 percent were added to this basic rate to estimate 

overall required design capacity. 

-28-
P.30 

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P.32 

The required capacity was then related to the equilibrium 

level of the canister in the EPA model. More specifically, 

required canister size was determined based upon the 

requirement,, that the canister have the necessary refueling 

vapor capacity at the end of the first trip following the daily 

diurnal loading of the day wherein the canister first reached 

equilibrium. This means that, at equilibrium, the vehicle is 

expected to _be able to handle a full refueling after having 

experienced a daily diurnal and then driving one trip to the 

gas station. 

Because of the tradeoff between purge rate and effective 

canister capacity described above, equal canister equilibrium 

levels and, therefore, refueling capacity can be achieved from 

a relatively wide range of canister sizes and a corresponding 

range of purge air flow rates. Canister size, for equal 

refueling capacity, is inversely proportional to purge air flow 

rate. This relationship is shown in Figures 10 through 13 for 

four different vehicle types: a small car, an average car, a 

full-size dual-tank light-duty truck, and a typical heavy-duty 

gasoline truck. The specific characteristics assumed for each 

vehicle are given in Table 3. 

A couple of common characteristics are apparent from these 

figures. First, when the purge rate is relatively high the 

Ford type canisters generally require somewhat greater canister 

volume than do the Nissan type canisters. However, as the 

purge rate is decreased to the low end of the purge rates 

investigated, the Nissan type canisters tend to be larger than 

the Ford type. Second, the curves are fairly flat over a broad 

range of purge rates, followed by a rapid upturning in canister 

size at low purge rates. 

Since both diurnal and refueling loads, which are the 

dominant vapor sources, are proportional to fuel tank size, it 

is possible to normalize the results for all four vehicles and 

produce a single family of curves. Figure 14 shows the 

relationship between canister volume per gallon of fuel tank 

capacity and LA-4 purge rate per liter of canister volume. 

5. Refueling System Effects on Engine Operation 

Recognizing that both canister size -and purge air flow 

rate can vary widely, it is appropriate to investigate those 

factors which could establish boundaries on these parameters. 

Since a small canister is desirable from both a cost and a 

packaging perspective, designers can be expected to use the 

smallest canister possible. Since canister size decreases as 

purge air flow rate increases an investigation of potential 

upper limits for purge air flow rate is warranted. 

-31-
CANISTER SIZE VS PURGE AIR FLOW RATE 

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FORD Fl 

PURGE AIR (CU FT / LA-4) 

FORD CARB O NIS Fl NIS CARB 
CANISTER SIZE VS PURGE AIR FLOW RATE 

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CANISTER SIZE VS PURGE AIR FLOW RATE 

LIGHT DUTY TRUCK/DUAL TANKS FIGURE 12 

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CANISTER SIZE VS PURGE AIR FLOW RATE 

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200 

FORD Fl 

PURGE AIR (CU FT / LA-4) 

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P.37 

Table 3 

Vehicle Parameters Used in Canister Sizing Calculations 

Vehicle 

Type 

Small Car 

Small Car 

Average Car 

Average Car 

LDT (Dual tanks) 

LDT (Dual tanks) 

HDV 

HDV 

Fuel Delivery 

System 

Fuel Injection 

Carburetion 

Fuel Injection 

Carburetion 

Fuel Injection 

Carburetion 

Fuel Injection 

Carburetion 

Fuel Tank 

Volume (gal) 

8.2 

8.2 

13.0 

13.0 

38.0 

38.0 

50.0 

50.0 

Hot Soak 

Loadinq 

6 

9 

10 

15 

29 

43 

38 

57 

Diurnal 

(q) Loadinq (q) 

14 

14 

22 

22 

64 

64 

84 

84 

Required 

Refueling 

Capacity (q)* 

65 

65 

104 

104 

303 

303 

399 

399 

Refueling capacity required calculated from refueling 

emissions at test conditions (i.e. 7.15 gram/gallon) x 85 

percent of tank volume x 1.2 (to account for 20 percent 

entertainment with liquid seal) x 1.1 (to provide a 10 

percent safety margin). 

-36-
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1.8 

1.7 

1.6 

1.5 

1.4 

1.3 

1.2 

1.1 

1 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

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NORMALIZED VALUES FIGURE 14 

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P.39 

5.1 Basic Considerations 

Control of the power output from a gasoline engine is 

accomplished by limiting the amount of air available to the 

engine, by means of a throttle placed in the engine intake 

system. The fuel metering system is designed to provide fuel 

in proportion to the amount of air allowed to enter the 

engine. Throttling of the intake air supply causes a reduction 

in the pressure of the air (or air and fuel mixture) in the 

intake manifold downstream of the throttle. This reduced 

pressure in the intake manifold downstream of the throttle 

provides an essentially zero cost method for moving the air 

necessary for purging of stored hydrocarbons from a canister. 

Activation of the canister purge system however, provides an 

additional source of air and fuel to the engine. This air is 

not under the control of the driver of the vehicle and the HC 

vapor (fuel) entrained in the air is not under the control of 

the engine's fuel metering system. Purging of the hydrocarbons 

stored in a canister can, therefore, impact engine operation 

through perturbations in the amount of air available to the 

engine and in the ratio of fuel to air supplied to the engine. 

The purpose of this segment of the analysis is to develop 

an understanding of limits which may be applicable to canister 

purge air flow and to the fuel supplied by the canister if 

unacceptable negative impacts on engine operation are to be 

avoided. A stepwise presentation of the effects of activating 

the canister purge system will facilitate the desired analysis. 

5 .2 Purge Air 

As was stated previously, activation of the canister purge 

system will allow more air and a variable amount of additional 

fuel to reach the engine. The resulting effect on engine 

operation will depend on the range of control and rate of 

response of the engine's fuel metering system. If the range of 

control were to be exceeded, the anticipated result could be 

either a substantial loss in power or stalling of the engine. 

Power loss would be associated either with an extremely rich or 

lean but ignitable mixture. Stalling would be associated with 

either a richening or leaning of the mixture beyond the 

ignition limit. .. . 

If the range of control was not exceeded, the effects on 

engine operation would depend on the speed with which the fuel 

met-ering system could compensate for the perturbation caused by 

the air and fuel coming from the canister. If the response 

rate was very rapid the effect would be for a rapid increase in 

the engine's power output because both the air and the fuel 

available to the engine increased and increased approximately 

-38-
P.40 

in the correct relative ratio. As perceived by the driver, the 

effect would be for the vehicle to accelerate without a driver 

initiated action for acceleration. If the acceleration was 

small, it could go unnoticed by the driver. If, however, the 

acceleration was large, the driver could perceive the 

acceleration as a loss of control of the vehicle. 

One straightforward approach to a large induced purge 

change is to simply use a damper or slowly operating purge 

control valve. Such a valve, by introducing the change in air 

flow over a lengthened period, would allow for driver 

compensation as a part of the normal driving process. In this 

way, a fairly large change could be made with no perceptible 

impact. Even so, it is worth evaluating reasonable limits for 

the purge perturbation to determine if such a control strategy 

is even needed. 

On the assumption, then, that the vehicle could rapidly 

adjust to the sudden onset of purge, one limit for purge rate 

would be the maximum acceptable power perturbation it would 

produce. The size of this limit is estimated below (limits 

from the purge related fuel flow will be treated later). 

Since vehicles presently do not incorporate systems which 

could cause relatively large, non-driver induced, changes in 

the power level at which the engine is operating and consequent 

vehicle accelerations or decelerations, it was necessary that a 

surrogate be identified. Vehicle accelerations and 

decelerations associated with the disengagement and engagement 

of air-conditioning compressors were selected as a guide to 

driver acceptable performance perturbations attributable to 

power changes at the driving wheels. This information was used 

in estimating a driver acceptable limit for purge air induced 

increases in engine power. 

Figure 15 shows manufacturer supplied nominal values for 

the power required to drive air conditioning compressors on 

typical vehicles (values furnished by Honda are for city type 

operations and are, therefore, not expressed in terms of 

vehicle speed). Figures 16, 17, and 18 show nominal engine 

brake horsepower (BHP)* curves with and without air-conditioner 

Engine brake horsepower (useful external power) values 

were derived from typical chassis dynamometer power 

absorption curves with allowances for power losses at the 

tire to dyno interface, times allowances for drive axle 

and transmission efficiency plus allowances for the power 

requirements of the alternator, water pump, fan, air pump 

and power steering pump. 

-39-
I 

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Ul 

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9: 

D 

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a: 

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if) 

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5 

O 

O 

AIR COND COMPRESSOR POWER REQUIREMENT 

FIGURE 15 

8 

6 -

5 -

4 -

3 -

1 -

0 

A. 

B. 

C. 

D. 

E. 

F. 

Ford. Small Car; Direct Drive 

Ford. Average Car, LDT; Over Drive 

Ford. Average Car, LDT; Direct Drive 

GM. Large Car; Durability Loads 

Honda Accord; City Average 

Honda Civic; City Average 

0 

D A 

. + 

1 1 1 

20 40 

VEHICLE SPEED (MPH) 

B O C A D 

60 80 
ENGINE BHP VS VEHICLE SPEED 

i 

Q. 

I 

a. 

o_ 

u 

o 

a. 

u 

z 

o 

z 

Ul 

SMALL CAR FIGURE 16 

D VEH VEH 

VEHICLE SPEED (MPH) 

+ AUX O VEH + AUX + AC 

fe 
ENGINE BHP VS VEHICLE SPEED 

i 

I 

Q. 

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OQ 

v ^ 

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CL 

Ul 

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o 

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u 

AVERAGE CAR FIGURE 17 

VEH 

VEHICLE SPEED (MPH) 

VEH + AUX O VEH -t- AUX + AC 

.KS 
I 

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a. i 

a_ 

oc 

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ENGINE BHP VS VEHICLE SPEED 

LIGHT DUTY TRUCK FIGURE 18 

0 20 40 60 

D VEH + 

VEHICLE SPEED (MPH) 

VEH + AUX O VEH + AUX + AC 
P.45 

compressor loading for three sizes of vehicles (small car, 

average car and full-size light-duty truck). At any selected 

vehicle speed, the difference between the with and without 

air-conditioning compressor curves represents the incremental 

change in engine horsepower available to accelerate the vehicle 

when the compressor, disengages. Incremental increases in 

engine power available to propel the vehicle when the air 

conditioning, compressor turns off were extracted from Figures 

14, 15 and 16 at 20, 35 and 50 mph and are shown in Table 4 as 

percentages of the BHP required to operate the vehicle. 

The power consumption figures in Table 4 cannot be used 

directly to evaluate purge rates, because they are applicable 

to output power, while any purge perturbation will impact total 

engine power. Total, or indicated, power includes both output 

(brake) power and internal motoring power. However, at the 

relatively low output (brake) power levels involved in the data 

being used here, it appears reasonable to assume that losses 

within the engine could approximate the brake horsepower 

output. Using this approximation, the percentage change in 

total engine power for an average car when the compressor 

cycles off at 35 mph would be approximately one half of the 31 

percent change in brake power shown in Table 4, or about 15 

percent. Similarly, average percentage changes in total engine 

power for the three vehicle types are about 8, 15 and 17 

percent for LDTs, average cars and small cars respectively. 

For the two car sizes only, the average change is about 16 

percent and this value was selected as a representative upper 

limit for the impact of an increase in air flow attributable to 

canister purging. Since the incremental increase in total 

engine power is directly proportional to the incremental 

increase in air flow, the 16 percent value can be applied 

directly to the purge air flow rate. 

Conversion of the 16 percent of engine air flow value to a 

volume of air purged through the canister was derived from fuel 

economy values for the vehicles on the LA-4 employing the 

assumption that stoichiometic air/fuel ratio would be 

maintained throughout. The fuel economy values employed for a 

small car, an average car and a full-size LDT were 52, 25 and 

14.5 mpg respectively. A value of 7.5 mpg was assigned for a 

heavy-duty gasoline vehicle. The corresponding volumes of air 

used by the vehicles on an LA-4 are 178, 369 and 637 and 

1231 ft3. The canister purge air flow rates corresponding to 

16 percent of the engine total air consumption so calculated 

are 28, 59, 102 and 197 ft3 of air per LA-4 for a small car, 

an average car, a full-size light duty truck and a heavy-duty 

gasoline vehicle respectively. These values, rounded to 30, 

60, 100 and 200 ft3 of air per LA-4 were used as initial 

estimates of upper limits for canister purge air volumes for 

systems characterized by the sudden onset of purge flow. 

-44-
P.46 

Air 

As 

Vehicle 

Speed 

20 

35 

50 

Conditioner 

Percentages 

Air Condi 

Small Car 

43 

36 

25 

Table 4 

Compressor Power Requirements Expressed 

of Power Required To Power The Vehicle 

At Three Speeds 

tioner Compressor Power as Percent of 

Vehicle Motive Power 

Average Car Liqht Duty Truck 

40 24 

31 16 

20 10 

-45 -
P.47 

Referring back to Figures 10, 11, 12 and 13, these values 

can be seen to approximately correspond to the maximum purge 

rates evaluated. They occur in the region of the curves where 

there is little sensitivity of canister size to purge rate. 

They, therefore, do not appear to represent any serious 

constraint on system design or the tradeoff between purge rate 

and canister size. However, as noted at the onset, if it were 

desirable to_ operate at higher purge rates than these limits, 

the power perturbation should not present a serious limiting 

factor because of the ability to use such techniques as damped 

purge control valves. 

5.3 Canister Supplied Fuel 

To this point, the analysis has looked at only one of the 

two canister purge factors which can impact engine operation 

(i.e., the amount of air coming from the canister). The second 

factor, canister supplied hydrocarbons which become part of the 

total volume of fuel supplied to the engine, is evaluated 

here. This analysis is performed by first examining existing 

evaporative systems, followed by an extrapolation to onboard 

systems. 

5.3.1 Present Evaporative Control Systems 

Purging of hydrocarbons stored in evaporative emission 

canisters is presently being , performed without an excessively 

negative effect on engine operation. Test data reported by API 

(Test Protocol for Automotive Evaporative Emissions, API 

Publication No. 4393) shows a range for evaporative canister 

purge air rates from a low of approximately 3 ft3 per LA-4 up 

to approximately 11 ft3 per LA-4 for the six GM and Ford 

vehicles tested. Combining the purge rates for each vehicle 

with the purge curve for Ford type canisters provides an 

estimate of the maximum mass of hydrocarbon purged from a fully 

loaded evaporative canister during an LA-4 (the Ford type 

canister characteristic was selected because it exhibits the 

highest initial desorption rates). For the six vehicles tested 

by API, the measured volume of air purged per LA-4 and the 

estimated mass of hydrocarbon purged from the canister, 

starting with a loaded canister, is shown in Table 5. 

Using the fuel economy values measured for each vehicle 

and the assumption used previously that the air/fuel ratio is 

maintained at 14.7:1, the mass of fuel and volume of air 

consumed by each vehicle during an LA-4 were calculated. The 

measured volumes of air coming from the canister and the 

estimated maximum mass of hydrocarbon purged from the canister 

during an LA-4 were then expressed as percentages of air and 

fuel used.. These values are shown in Table 6. 

-46-
P.48 

Table 5 

Evaporative Canister Purge Rates and Corresponding HC 

Removal for Six Production Vehicles 

Test Vehicle 

1983 Malibu (carb) 

1983 Escort (carb) 

1981 Omega (carb) 

1983 Fairmont (carb) 

1984 Omega (FI) 

1984 Escort (FI) 

Measured Fuel 

Economy on 

LA-4 (mpg) 

17.5 

24.1 

21.8 

17.3 

23.4 

27.0 

the 

Measured 

Canister Purge 

Air per LA-4 (ft ) 

8.5 

6.5 

11.0 

7.5 

3.0 

10.0 

Estimated 

Maximum HC 

Purged per LA-4 (g)* 

27.0 

25.5 

28.0 

26.5 

21.5 

27.8 

Because the HC purge of a canister is very high when the 

canister is fully loaded and decreases as the canister 

loading decreases, maximum HC purged during a LA-4 drive 

occurs when the drive is initiated with a fully loaded 

canister. Depending on the level of HC stored in the 

canister at the start of an LA-4 drive, the HC purged 

would vary from this maximum down to almost zero for a 

drive which was initiated with a nearly empty canister. 

-47-
P.49 

Table 6 

Air and Fuel Coming From Evaporative Canister 

During an LA-4 for Six Production Vehicles 

Vehicle 

1983 Malibu 

1983 Escort 

1981 Omega 

1983 Fairmont 

1984 Omega 

1984 Escort 

Total Fuel 

us 

LA 

ed per 

-4 (g)* 

1217 

884 

997 

1231 

910 

789 

Total Air 

used per 

LA-4 (ft3)** 

528 

384 

424 

535 

395 

343 

Per 

Tot 

Can 

cent*** of 

al Fuel From 

ister per LA-4 

2.2 

2.9 

2.9 

5.0 

5.4 

3.5 

Percent Total 

Air From Canister 

per LA-4 

1.6 

1.7 

2.6 

1.4 

0.8 

2.9 

* Fuel used in grams = (7.5 miles) E (MPG) x (3785.4 

cc/gal) x (0.75 g/cc gasoline). 

** Total air used in ft = (grams fuel used) x (14.7) x 

(1/453.6 g/lb) x 13.4 ft3/lb.-

*** Assuming LA-4 operation starts with a canister loaded to 

breakthrough. 

-48-
P.50 

Because of the non-linear shape of the canister purge 

curve, the average percentage of total fuel supplied from the 

evaporative canister over an LA-4 does not represent the 

greatest percentage of fuel contributed by the canister. The 

largest fuel contribution occurs just after canister purging is 

initiated i.e., during the first mile or fraction of a mile 

following initiation of purging. To investigate the maximum* 

percentage o_f fuel contributed by the evaporative canister on 

current vehicles, the computer model was used to calculate the 

percentage of total fuel coming from the canister for each of 

the first five miles of LA-4 operation, based upon the average 

fuel consumption of the vehicle. The results from this 

analysis are shown in Table 7 for each of the six vehicles 

analyzed. 

As can be seen in Table 7 the percentage of total engine 

fuel supplied by the evaporative canisters starts at highs of 

between 6 and 16 percent for the first mile of vehicle 

operation and diminishes as the canister purges. The percent 

of fuel coming from the canister would reach zero when the 

canister is fully purged. The values of 6 to 16 percent of 

total engine fuel supplied by the evaporative canister can be 

used as representative values for fuel supplied by a canister 

which do not presently produce adverse effects on engine 

performance. 

* Because of the transient speed characteristic of the LA-4 

and, therefore, transient engine loading and corresponding 

transient air and fuel flow to the engine, the term 

maximum here means the maximum averaged over a part of the 

LA-4 and not a maximum which may occur during short term 

transients. A transient maximum would tend to occur when 

the air and fuel flow rates from the canister were high 

and the engine was working at a light load, e.g., in the 

transition period from a cruise to a deceleration but 

prior to a reduction in canister supplied air and fuel. 

Actual determination of such a maximum would require 

continuous measurements of both air and fuel flows from 

the canister and through the engine's primary air and fuel 

supply systems. For this analysis the use of mile by mile 

maximum values on the LA-4 are considered to be acceptably 

accurate values for comparisons between present 

evaporative control systems and onboard systems because 

the onboard systems are projected to operate relatively 

similarly to present evaporative systems. 

-49-
P.51 

Table 7 

Percent Total-Engine Fuel Coming From Evaporative 

Canisters During the First Five Miles of Purging 

Percent Total Fuel Purged from Canister for. 

each of the first five miles of the LA-4 

Vehicle 

1983 Malibu 

1983 Escort 

1981 Omega 

1983 Fairmont 

1984 Omega 

1984 Escort 

1st 

Mile 

10 

12 

14 

9 

6 

16 

2nd 

Mile 

3 

4 

3 

3 

4 

3 

3rd 

Mile 

1 

2 

2 

1 

3 

2 

4th 

Mile 

1 

1 

1 

1 

2 

1 

5th 

Mile 

1 

1 

1 

1 

1 

1 

-50-
P.52 

5.3.2 Onboard Control Canisters 

Having identified the first mile fuel contributions from 

current evaporative emission canisters, the previously sized 

onboard refueling canisters were similarly reanalyzed to 

determine their first mile fuel contributions. The results 

from this reanalysis are shown in Figures 19 through 22 as 

percent first mile fuel from the canister plotted against 

percent engine air coming from the canister. The largest 

values for percent first mile fuel (16 percent, Table 7) and 

percent air (2.9 percent, Table 6) from the canister for the 

vehicles reported in the API study are also shown to indicate 

present practice. 

As can be seen in Figures 19 through 22, first mile fuel 

contributions by onboard canisters at higher purge rates can 

substantially exceed current evaporative canister first mile 

fuel contributions. While there is presently no data to 

indicate the degree to which first mile fuel contributions 

could increase beyond present evaporative canister practice, it 

appears reasonable to assume that the largest values shown 

(e.g., 80 to 90 percent of engine full) could cause operational 

problems. Therefore, canister supplied fuel appears to be a 

bigger constraint than does purge air flow. 

Reproduced in Figures 23 through 26 are the canister size 

versus purge air flow rate tradeoff curves for fuel injected 

systems as previously presented as Figures 10 through 13, with 

information added to indicate the points on these curves 

corresponding to various percent first mile fuel values. 

Indicated are values of 15 percent (approximately current 

evaporative system practice), 25 percent and 35 percent. As 

can be seen from these figures, a first mile fuel constraint 

would limit the use of the smallest canister highest purge air 

flow systems. The actual impact of this constraint would 

depend on the degree to which the vehicle's fuel metering 

system could accommodate fuel supplied due to canister purging. 

One possible strategy for dealing with this matter comes 

from the basic canister purge characteristics. Referring back 

to Table 7, it can be seen that the percent of the engine fuel 

coming from the evaporative canister falls off quite rapidly 

after the first mile of operation. This trend is similar for 

onboard systems- (see Table 8). Thus, by modulation of the 

purge air flow rate to reduce the flow rate initially and 

increase it later in the trip the first mile fuel could be 

reduced and spread out more gradually over subsequent miles. 

-51-
cm 

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%•'FIRST MILE FUEL VS % TOTAL AIR 

FORD TYPE CANISTER FIGURE 19 

D SMALL CAR 

% TOTAL AIR FROM CANISTER 

+ AVG CAR LDT HDV 
% FIRST MILE FUEL VS % TOTAL AIR 

100 

90 -

D: 

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cm L. 

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80 -

70 -

60 -

50 -

40 -

30 -

20 -

10 -

FORD TYPE CANISTER FIGURE 20 

D SMALL CAR 

% TOTAL AIR FROM CANISTER 

+ AVG CAR O LOT HDV 
% FIRST MILE FUEL VS % TOTAL AIR 

100 

90 -

cm 

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80 -

70 -

60 -

50 -

40 -

30 -

20 -

10 

NISSAN TYPE CANISTER FIGURE 21 

D SMALL CAR 

% TOTAL AIR FROM CANISTER 

+ AVG CAR O LDT HDV 

Ul 

Ul 
%' FIRST MILE FUEL VS % TOTAL AIR 

cm 

UJ 

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100 

NISSAN TYPE CANISTER FIGURE 22 

D SMALL CAR 

% TOTAL AIR FROM CANISTER 

+ AVG CAR O LDT HDV 
% FIRST MILE FUEL FROM CANISTER SM CAR 

i 

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if) 

cm 

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3.5 

3.4 

3. J -

3.2 -

3.1 -

3 -

2.9 -

2.8 -

2.7 -

2.6 -

2.5 

2.4 H 

2.3 

2.2 -

2.1 -

2 -

1.9 

1.8 H 

1.7 

1.6 H 

1.5 

CANISTER SIZE VS PURGE AIR FIGURE 23 

~T" 

8 12 16 

T " 

20 28 

FD CAN NIS CAN 

PURGE AIR PER LA- 4 (CU FT) 

O % FUL FD A % FUL NIS 

TJ 

bi 
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% FIRST MILE FUEL FROM CANISTER AV CAR 

CANISTER SIZE VS PURGE AIR FIGURE 24 

8 -

7 -

6 -

5 -

4 -

3 -

0 

15% 

FD CAN NIS CAN 

r i 

20 

PURGE AIR PER LA-4 (CU FT) 

O % EUL FD 

40 

FORD 

3 5% NISSAN 

60 

__ % FUL NIS 
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if) 

cm 

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% FIRST MILE FUEL FROM CANISTER LDT 

CANISTER SIZE VS PURGE AJR FIGURE 25 

100 

FD CAN 

PURGE AIR PER LA-4 (CU FT) 

NIS CAN O % F.UL FD % FUL NIS 
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cm 

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50 -

40 -

30 

20 -

10 -

0 

% FIRST MILE FUEL FROM CANISTER HDV 

CANISTER SIZE VS PURGE AIR FIGURE 26 

200 

FD CAN 

PURGE AIR PER LA-4 (CU FT) 

NIS CAN O % FUL FD % FUL NIS 
P.61 

Vehicle 

Small Car 

(2.41; 9 ft3)N* 

1st 

Mile 

21 

2nd 

Mile 

16 

Table 8 

Percent Tot-al Engine Fuel Coming From Typical 

Onboard Canisters During the First 

Five Miles of Driving 

Percent Total Fuel Purged From Canister for 

Each of the First Five Miles of the LA-4 

3rd 4th 5th 

Mile Mile Mile 

12 8 7 

Small Car 40 28 17 9 5 

(2.651; 9 ft3)F 

Average Car 27 11 9 8 7 

(3.01; 30 ft3)N 

Average Car 23 17 15 10 7 

(4.61; 10 ft3)F 

LDT 14 13 12 11 10 

(201; 20 ft3)N 

LDT 26 24 21 20 15 

(151; 20 ft3)F 

HDGV 16 14 14 12 12 

(52.51; 50 ft3)N 

HDGV 31 28 21 21 19 

(32.31; 50 ft3)F 

* Size of canister in liters, purge air flow rate in 

ft3/LA-4, N = Nissan type, F = Ford type.. 

-60-
6. Summary 

Prior to proceeding with the section of the analysis which 

addresses test procedure revisions, it is appropriate to 

summarize the key findings of the analysis to this point as 

they relate to vehicle conditioning for refueling 

measurements. The analysis of canister and vehicle operational 

characteristics has shown: 

° That the level of hydrocarbon stored in the canister when 

the vehicle is operated under repetitive cyclic drive, hot 

soak and diurnal conditions reaches stabilization after at 

most a few days of operation. 

° That the canister stabilization level is highly dependent 

upon the operating pattern of the vehicle and on the 

amount of purge which occurs with each drive and the 

amount of loading which occurs with each hot soak and 

diurnal. 

° That, for continuous driving with no hot soak or diurnal 

emissions, the canister will be rapidly purged to a very 

low level. 

° That, for given hot soak and diurnal loadings, appropriate 

selection of canister size and purge air flow rate will 

provide adequate storage capacity for refueling vapors at 

the stabilized canister loading. 

° That a range of canister size and purge air flow rate 

choices are available for any given vehicle which should 

not adversely affect vehicle performance. 

° That while required canister size is inversely 

proportional to purge air flow rate, the relationship is 

not linear. 

7. Test Procedure Revision 

7.1 Evaluation of Preconditioning in Draft Procedure 

The preceding analysis has identified how ah onboard 

canister would be expected to purge and load during typical 

in-use operation and has provided a method for modeling this 

operation. A comparison of the effects on canister purging due 

either to the 50 mile continuous drive or the 30 percent 

drive-down steps proposed in the original draft procedure with 

a representative onboard canister performance curve is shown in 

Figure 27. As can be seen, both the 50 mile drive and the 30 

-61-
CANISTER PURGE - THREE DRIVE TYPES 

FIGURE 27 

I 

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l-O 

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l-~> 

2 

Q 

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O 

0_ 

0_ 

T 

O 

CD 

cm < 

o 

o G_ 

Q 

>-

I 

160 

150 

140 

130 

120 

110 

100 

90 

80 

70 

60 

50 

AC\ 

30 

20 

10 

0 

120 

THREE TRIPS 

MILES DRIVEN 

30 % TANK 50 MILE 
P.64 

percent drive-down purge the canister well beyond expected 

in-use levels. These procedures would, therefore, produce 

non-representative canister purges and would not be appropriate 

for canister conditioning prior to the measurement of refueling 

emissions. 

It is also apparent from the modeling work that canister 

purge and refueling capacity are not separable items, and that 

the approach used in the original draft procedure of evaluating 

each aspect with a separate test is inappropriate. The actual 

storage capacity which the vehicle will have available upon 

refueling is a function of the canister purge rate and the 

vehicle driving, pattern as well as of the canister size. 

Because of this, the performance of the entire refueling system 

can be evaluated with a single test which first preconditions 

the canister to a level near its equilibrium level and then 

performs the refueling operation. This greatly reduces the 

overall complexity of the refueling test and its resource 

impacts and also allows it to be separated from the testing for 

exhaust and evaporative emissions. The following section 

develops the preconditioning procedures needed for the revised 

test. 

7 .2 Revised Canister Conditioning 

Based upon the modeling which has been done, there are two 

options for simulating in-use performance. The first is a 

cyclic drive-down of alternating drives and soaks directly 

simulating a few "days" of vehicle operation to approximately 

establish the canister equilibrium level. The second is a 

short, continuous, drive-down to the equilibrium level with no 

soak periods. 

Reproduction in the laboratory of the cyclic in-use daily 

operating pattern would be accomplished by the repetitive 

performance of a simulated daily pattern consisting of three 

LA-4s, each separated by a one hour hot soak plus the 

performance of a diurnal heat build following the last hot 

soak. This "daily" canister conditioning sequence would 

constitute the basic building block for the construction of the 

canister conditioning phase of the onboard test procedure. 

Sequential repetitions of this basic sequence until the 

canister stabilization level was reached (or approximated, in 

the case of a canister system requiring an unusually long time 

to completely stabilize) would constitute the primary procedure 

whereby canisters would be conditioned prior to measurement of 

refueling emissions. 

There are several things to note about this approach. 

First, it should accurately simulate a realistic conditioning 

sequence. Of course, as noted in the earlier discussion of the 

-63-
P.65 

effects of driving patterns, in-use patterns of less than three 

trips, per day would purge less than would this procedure. 

However, there are compensating conditions of test condition 

stringency which act to offset this difficulty. Secondly, it 

appears that nearly all vehicles will reach equilibrium within 

three to five "days" of simulated operation. In fact, after 

only three "days", all vehicles appear to be within at most a 

few grams o_f equilibrium. Therefore, three simulated days 

should provide adequate canister conditioning. This, of 

course, means that conditioning can be performed with 

substantially fewer testing resources than the originally 

proposed 30 percent drive-down. Third, because of the rapid 

rate of purge when the canister is fully loaded, this 

conditioning sequence is relatively insensitive to the initial 

starting condition of the canister. The initial ' period of 

canister purging to a level near the equilibrium level occurs 

within the first dozen or so driving miles, so the total time 

to reach stabilization is not significantly affected by the 

initial loading on the canister. 

While greatly reducing resource impacts from the original 

draft procedure, multiple repetitions of the "daily" operating 

sequence will still be somewhat time and facility intensive. 

Remembering that continuous vehicle driving (i.e., no hot soaks 

or diurnals) will result in rapid purging of the canister, EPA 

investigated this approach as another alternative for canister 

conditioning. The computer model was used to determine the 

number of continuous LA-4 miles required to achieve canister 

purging equivalent to the cyclic drive stabilization level. 

The results of this evaluation, plotted as continuous LA-4 

miles versus purge air flow rate, are shown in Figures 28 

through 31 for the systems previously evaluated. 

As can be seen from these figures, the number of 

continuous LA-4 miles required to reach the canister 

stabilization level is under 20 miles in most cases, although 

it goes as high as 33 miles for heavy-duty vehicles with very 

low purge rates. Relative to the "daily" cyclic drive 

conditioning procedure, the continuous drive procedure would 

provide significant savings in both time and facilities. 

As envisioned for the test procedure, the continuous drive 

would operate as follows. Following canister loading, the 

vehicle would be driven continuously over repetitive LA-4 

cycles until the stabilized level was reached. In the case of 

a partial cycle needed to complete the required mileage, the 

vehicle would be stopped at the first idle point after reaching 

the desired mileage. The refueling test would then be 

performed. The number of miles to be driven would be based 

upon previous testing to establish equivalence with the cyclic 

-64-
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CONTINUOUS DRIVE MILES FOR PURGE 

FORD TYPE CANISTER Fl FIGURE 28 

D SMALL CAR 

PURGE AIR PER LA-4 (CU FT) 

+ AVG CAR O LDT 

140 

HDV 
I 

I 

> 

Q_ 

C. 

if) 

Ul 

CONTINUOUS DRIVE MILES FOR PURGE 

FORD TYPE CANISTER CARB. FIGURE 29 

SMALL CAR 

PURGE AIR PER LA- 4 (CU FT) 

+ AVG CAR O LDT 

140 

HDV 
I 

OS 

v l 

I 

z 

UJ 

> 

cm 

Q 

if) 

UJ 

CONTINUOUS DRIVE MILES FOR PURGE 

NISSAN TYPE CANISTER Fl FIGURE 30 

D SMALL CAR 

PURGE AIR PER LA-4 (CU FT) 

+ AVG CAR O LDT 

140 

HDV 
CONTINUOUS DRIVE MILES FOR PURGE 

C3S 

CX) 

I 

Z 

Ul 

> 

cm 

c . 

in 

UJ 

NISSAN TYPE CANISTER CARB. FIGURE 31 

SMALL CAR 

PURGE AIR PER LA- 4 (CU FT) 

+ AVG CAR O LDT HDV 
drive. Based, as it would be, upon the purge level developed 

by the cyclic drive, this test would not be a fully independent 

operation. Rather, it would be an abbreviated approach to 

obtaining the same results as the cyclic drive. It could be 

used by manufacturers in repeated testing of the same or 

substantially similar vehicles, and by EPA in all phases of its 

testing. 

The continuous drive will allow canister conditioning with 

a greatly abbreviated procedure. Because of this, it would 

likely serve as the principal approach used by EPA. 

Manufacturers, once they had initially conducted the cyclic 

test in order to develop the appropriate continuous drive 

mileage, would also be able to use the continuous drive cycle 

for subsequent repetitive work. The continuous drive procedure 

should give equivalent results to the cyclic drive. 

On the other hand, the continuous drive procedure has the 

limitation that it does not itself physically demonstrate that 

the control system has the ability to actually purge hot soak 

and diurnal loads. Thus, in spite of its advantages in terms 

of resource impacts, the continuous drive cannot be the only 

preconditioning sequence. However, so long as the cyclic 

drive-down is also retained, EPA would in all likelihood be 

able to use the continuous drive-down for the bulk of its 

testing. The longer cyclic procedure would be reserved for 

those cases when the Agency felt the need to fully demonstrate 

system performance via direct testing. Overall then, the 

revised refueling procedure will specify both preconditioning 

sequences with the requirement that any vehicle be able to pass 

the test regardless of which is used. 

7.3 Conditioning of Non-Integrated Control Systems 

Throughout the preceding analysis, the use of fully 

integrated refueling and evaporative emission controls has been 

assumed. That is, the analysis has presumed that the same 

canister is used to collect and store hot soak, diurnal and 

refueling emissions*. Since manufacturers may elect to use one 

canister dedicated to the collection and storage of refueling 

vapors alone and another canister for hot soak and diurnal 

emissions, conditioning of these canisters .will be addressed at 

this time. 

The preceding analysis is also applicable to systems 

wherein the refueling canister is used to collect either 

hot soak or diurnal emissions (i.e., partially integrated 

sytems). 

-69-
P.71 

Since the refueling canister in a non-integrated system 

may not experience hot soak or diurnal loadings, purging would 

be the same whether the vehicle was driven continuously or 

under cyclic conditions. Such a system would also not be 

expected to come to an equilibrium condition since each drive 

would continue the process of purging the canister to lower and 

lower levels. Thus, the only way to fully simulate conditions 

of a nearly .empty fuel tank would be to actually drive out the 

required amount of fuel, beginning with a loaded canister and a 

full fuel tank. Since the refueling emissions measurement is 

initiated from the 10 percent tank volume level and fueling is 

continued until the fuel level in the tank is at least 95 

percent of tank volume, the continuous drive duration for 

non-integrated systems would have to be the mileage 

corresponding to the consumption of fuel equal to 85 percent of 

fuel tank volume. 

A full drive-down for non-integrated systems would be a 

time and resource intensive process. In addition, given the 

non-linear nature of the purge process (refer to the canister 

purge curves given in Figure 3) most of the purge would 

actually be accomplished in the initial phases of the 

drive-down. An alternative procedure, therefore might be a 

partial drive-down of perhaps 30 to 40 percent of tank volume 

followed by a nearly full refueling. Since this procedure 

would not directly verify full system performance, it would 

have to remain as an optional test, similar to the short 

continuous drive for integrated systems. It might also be 

coupled with supporting test data or engineering analysis to 

demonstrate that satisfactory performance at the intermediate 

level would be expected to result in full performance on a full 

test. The potential use of this option has not yet been 

analyzed in detail to determine adequate drive miles and fill 

amounts. Such an analysis is planned for the future. 

F. Miscellaneous Issues 

In addition to the comments addressed above, comments were 

provided on several other areas of the recommended test 

procedure. These areas included the baseline refueling 

emission factor, provisions for retests, vehicle temperature 

prior to the refueling test, specifications for refueling 

nozzles, and numerous other minor comments.* 

The California Air Resources Board (CARB) took issue with 

the baseline refueling emission factor. CARB stated that data 

collected in California from refuelings of in-use vehicle at 

service stations showed refueling emission factors of 3.7 

g/gallon with 8.0 RVP summer fuel and 5.6 g/gallon with 12.0 

RVP winter fuel for an average of 4.5 g/gallon. CARB went on 

to state that a national refueling control program should be 

based on the California annual average value of 4.5 g/gallon 

-70-
P.72 

rather than the 5.9 g/gallon value used by EPA for 12.6 RVP 

summer refuelings. The purpose of this approach was to achieve 

a lower refueling emission standard under a fixed percent 

reduction approach. 

EPA does not agree with CARB's analysis. First, EPA does 

not believe that it can equate refueling emissions measured at 

service stations under unknown measurement conditions to 

emissions measured under controlled laboratory conditions such 

as are included in the draft procedure and described in EPA's 

report, "Refueling Emissions from Uncontrolled Vehicles." This 

report details EPA's baseline program to measure refueling 

emissions and EPA will continue to use the baseline refueling 

emission factor resulting from its baseline program. Second, 

the CARB comment appears to focus on achieving the lowest 

possible numerical emission standard associated with a 95 

percent reduction of baseline emissions. The EPA standard is 

not intended to be a simple percent reduction of the baseline 

refueling emissions. The refueling standard will be chosen to 

be a measurable and reasonable level as near to zero emissions 

as is possible. Thus, a change in the baseline emission level 

would not automatically result in a change in the standard. 

In commenting on the need for retests, MVMA stated that 

the recommended procedure did not provide a clearly 

identifiable route for the performance of a retest of one 

segment, e.g., tailpipe emissions measurement, of the overall 

procedure either because of a test void or a failure in one 

segment of the test. A clear line of demarcation between the 

refueling segment and other segments of the overall procedure 

was requested. 

The draft test procedure report discussed provisions to 

rerun tests if needed. For the refueling tests, there were 

several appropriate places identified where partial testing 

could be restarted to avoid having to rerun the entire sequence 

in case of a test void in one segment of the test. The revised 

refueling procedure is now completely separable from the 

exhaust and evaporative test procedures, providing the clear 

line of demarcation requested by MVMA. In the event that a 

retest of the evaporative or exhaust test were to be required, 

the retest would be initiated at the first.step in the vehicle 

preparation procedure with the requirement to re-load the 

canister(s) prior to the 40 percent fueling for the prep LA-4 

preceding the cold soak. 

A concern regarding the test vehicle's temperature prior 

to the refueling test was noted by Toyota. To preclude 

inclusion of evaporative emissions into the refueling emission 

measurement, Toyota recommended that the test vehicle be cooled 

to soak area temperature prior to performing the refueling 

emission measurement test. This is a valid point, and in 

-71-
response the procedure will be modified to include the 

stabilization of the vehicle temperature at the soak area 

temperature. This will be achieved by soaking the vehicle, 

following the preconditioning of the canister, for a minimum of 

6 hours and a maximum of 24 hours. 

Two commenters stated that a specification was needed for 

the accuracy, of the dispensed fuel meter. EPA agrees with 

these comments and is including a dispensed fuel meter accuracy 

specification in the revised procedure. 

In addition to comments about limiting the dispensed fuel 

flow rate reviewed earlier in Section II A, a number of 

manufacturers commented on the need to control refueling nozzle 

specifications. These applied to both in-use and test nozzles, 

in areas of the nozzle which could impact the effectiveness of 

onboard control. Examples of the areas of nozzle design which 

could be considered for standardization under a uniform 

specification focus on the nozzle spout and include length, 

angle of bend in the spout and its location along the length of 

the spout, and position of the automatic shut-off port. 

Presently there are no standardized specifications applicable 

to these areas of the nozzle. 

EPA is concerned about the impact that nozzle geometry may 

have on refueling emissions, but has little data at present 

with which to evaluate these claims. If it were true that 

nozzle geometry could substantially affect the performance of 

refueling systems, then a standardized design might be 

considered. If this were the case, such standardization would 

have to be applied both to test equipment and to in-use 

nozzles. Otherwise, refueling system performance would suffer 

in practice. 

Lacking detailed information, no decision can be made on 

this issue at present. The submission of test data 

demonstrating the degree of sensitivity involved would be 

especially useful. It would also be necessary to determine to 

what degree fill neck designs could be modified to accept 

greater nozzle variability. 

Finally, numerous minor comments were provided. Examples 

of these minor comments include recommendations for the 

expansion of the tolerance bands for the hot soak times and the 

driver trace during the canister conditioning drive to 

facilitate testing and to avoid unnecessary test voids. These 

types of comments are addressed by minor changes, where 

appropriate, in the test procedure. 

-72-
P.74 

III. Test Procedure Overview Summary 

A. Onboard Test Procedure 

The onboard refueling emission test procedure, resulting 

from the preceding reanalysis would consist of four basic 

steps. In the first step, the onboard canister would be loaded 

to at least .breakthrough. The second step in the procedure 

would be canister purging to the appropriate level by means of 

the applicable vehicle drive. The third step would be vehicle 

cool down to ambient temperature followed by the fourth step 

wherein the refueling emissions are measured. The details of 

the tasks performed within each of these steps are shown in 

Figure 32. 

Briefly, the execution of the procedure as shown in Figure 

32 would be as follows. In the canister loading to 

breakthrough step, the vehicle, in as-received condition, is 

brought into the laboratory and the fuel tank is drained. The 

vehicle is soaked for six hours in the laboratory to bring the 

temperature of the vehicle into equilibrium with the laboratory 

ambient temperature. Following temperature equilibration, the 

vehicle is moved into the SHED and fuel is added to the fuel 

tank until canister breakthrough is detected. In those cases 

where the canister loading is already at or beyond breakthrough 

in the as-received condition (such as might occur during 

testing of in-use vehicles), the analyzer response to 

hydrocarbons emanating from the canister would closely coincide 

with the initiation of fueling and little fuel would have to be 

added to the fuel tank for the purpose of loading the canister. 

Upon completion of the canister loading step of the 

procedure, the vehicle will enter into the canister purge 

step. In the canister purge step, the procedure which will be 

followed will depend, first, on whether the vehicle is equipped 

with an integrated or a non-integrated emission control system 

and second, if an integrated system is employed, whether the 

cyclic drive procedure or the continuous drive procedure has 

been selected. In Figure 32, the blocks headed "Integrated 

System Canister Purge, Cyclic Drive" and "Integrated System 

Canister Purge, Continuous Drive" are applicable to integrated 

systems and specify the details of the steps ih each of these 

purge procedures. The block headed "Non-integrated System 

Canister Purge, Continuous Drive" specifies the details of the 

purge procedure for non-integrated systems. 

In each of the purge procedures, the first steps are the 

same, i.e., to disconnect the canister vapor line to avoid 

disturbing the canister loading, to drain the fuel tank, to 

fuel with the specified volume of fuel (40 percent for 

-73-
£ 

Integrated System 

Canister Purge, Cyclic Drive 

a. Disconnect Vapor Line to Canister 

b. Drain Fuel Tank 

c. 40% Fueling 

d. Reconnect Vapor Linie to Canister 

e. Drive One LA-4 

f. One Hour Hot Soak 

g. Repeat (e) and (f) Twice 

h. Disconnect Vapor Line to Canister 

1. Drain Fuel Tank 

j. 40% Fueling 

k. Reconnect Vapor Line to Canister 

1. Heat Build (60° + 2°F Initial, 

24 + 1°F Rise) 

m. Repeat (e) Through (1) Twice 

n. Drive One LA-4 

i 

i 

Canister Loading to Breakthrough 

° Drain Fuel Tank 

° Soak Vehicle for 6 Hours 

° Fuel in SHED to Breakthrough 

I 

Integrated System 

Canister Purge, Continuous Drive 

a. Disconnect Vapor Line to Canister 

b. Drain Fuel Tank 

c. 40% Fueling 

d. Reconnect Vapor Line to Canister 

e. Drive Repeated LA-4s Until Mileage 

Accumulated = Mileage Required for 

Purge Equivalent to Cyclic Drive. 

Mileage Accumulation Stops at the 

First Idle Past the Mileage 

Requirement 

1 

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-4s Until 

85% of Tank Volume Is 

Consumed 

Vehicle Cool Down 

Disconnect Line to Canister 

Drain Fuel Tank 

10% Fueling 

Soak Vehicle 6 to 24 Hours 

I 

Refueling Emissions Measurement 

Reconnect Vapor Line to Canister 

Fuel to Automatic Nozzle Shut-off 

(85% Mimimun Fueling). Restart Fueling 

Following Any Premature Shut-offs Within 

15 Seconds) 

ONBOARD TEST PROCEDURE FLOW CHART FIGURE 32 
integrated systems and 95 percent for non-integrated systems) 

and finally to reconnect the canister vapor line. For 

non-integrated systems actual purging of the canister will 

consist of driving the vehicle, using repetitions of the LA-4 

cycle, until 85 percent of tank volume has been consumed. For 

integrated systems, actual purging of the canister will be 

performed either by a short continuous drive using repetitions 

of the LA-4 .until the canister is purged to the level equal to 

that achieved with the cyclic drive or by the cyclic drive 

procedure. In the cyclic drive procedure, the LA-4 is 

performed three times with each performance of the LA-4 being 

followed by a one hour hot soak. Following completion of the 

third LA-4/hot soak, the canister vapor line is disconnected, 

the fuel tank is drained and fueled to 40 percent with chilled 

fuel, the vapor line is reconnected and a diurnal heat build is 

performed. The three LA-4, three hot soaks and one diurnal 

heat build cycle is repeated twice and is followed by the 

performance of one LA-4. At this point, the canister purge 

drives have been completed and the vehicle enters the cool down 

step of the procedure. 

In the cool down step, the vapor line is disconnected to 

ensure that canister loading is not disturbed, the fuel tank is 

drained and fueled with 10 percent fuel and the vehicle is 

allowed to cool to laboratory temperature for 6 to 24 hours. 

Measurement of refueling emissions is the final step of 

the procedure and follows the cool down step. In the refueling 

emissions measurement step, the vapor line is reconnected and 

the vehicle is placed in the SHED. The SHED is sealed and an 

initial measurement of the hydrocarbon level in the SHED is 

made. The vehicle is fueled in the SHED with at least 85 

percent of the tank volume of fuel. The final hydrocarbon 

level in the SHED is measured. The 85 percent fueling and the 

final hydrocarbon measurement are the last two steps in the 

refueling test procedure. 

B. Associated Changes to Present Test Procedures 

Existing test procedures for the measurement of 

evaporative and exhaust emissions were developed prior to any 

consideration of onboard refueling controls. Since these 

procedures (evaporative and exhaust tests for LDVs and LDTs and 

evaporative tests for HDGVs) include two forty percent tank 

volume fuelings, changes to account for the effects of onboard 

controls are necessary to achieve continuity in the results of 

these tests. The necessary changes are the disconnecting of 

the fuel tank to canister vapor lines prior to each fuel tank 

drain and forty percent fueling event and the reconnecting of 

the lines following each forty percent fueling. These 

-75-
P.77 

disconnecting and reconnecting events will ensure that new and 

non-representative canister loadings are not incorporated into 

existing test procedures. Specifically, within the test 

procedure, disconnecting the vapor lines would occur first when 

the test vehicle enters a test program and residual fuel is to 

be drained and the first forty percent fueling is performed 

prior to the preconditioning drive and cold soak and second 

immediately .prior to the second fuel tank drain and fueling 

with chilled fuel in preparation for the heat build. 

In addition to the previously indicated changes three 

other changes to existing test procedures are proposed. The 

first of these changes is the addition of two steps at the 

start of all testing on vehicles undergoing evaporative and/or 

exhaust emissions testing. These two steps are a fuel tank 

drain and a six-hour vehicle temperature equilibration soak at 

a room temperature of between 68°F and 86°F. The second of 

these changes is the requirement that all canisters be loaded 

to at least breakthrough prior to the performance of the 

preconditioning drive for LDV and LDT evaporative and exhaust 

emissions tests and prior to the preconditioning drive for HDV 

evaporative emissions tests. The third change is the 

requirement that all applicable canisters be installed and 

operational during the performance of HDGE exhaust emission 

testing. Prior to being instated on the HDGE undergoing 

testing, the canisters are required to be loaded with 

hydrocarbons to a level equal to that existing at the end of 

the diurnal heat build in the HDGV evaporative emission test 

procedure; i.e. the loading resulting from a loading to 

breakthrough, followed by a vehicle preconditioning drive, 

followed by a vehicle cold soak and finally followed by a 

diurnal heat build.. 

-76-
P.78 

Appendix 

Evaluation of the Purge Response Characteristics 

of Activated Carbon Canisters 

-77-
P.79 

I. Introduction 

EPA is currently in the process of developing a procedure 

to test the performance of refueling emission control systems. 

Regardless of the specifics of the procedure, it must evaluate; 

1) the hydrocarbon storage capacity of the system and 2) the 

ability of the system to restore that capacity between 

refuelings. .Testing the hydrocarbon storage capacity of the 

system is relatively straightforward, but testing the ability 

of a system to restore that capacity is significantly more 

complex. 

The standard hydrocarbon storage medium used in today's 

evaporative emission control systems is activated carbon, and 

it appears likely that activated carbon would be used for 

refueling emission control as well. The Draft Recommended Test 

Procedure for the Measurement of Refueling Emissions published 

in July 1985 was developed with limited detailed information 

about the purge characteristics of activated carbon beds.[2] 

The test of purge capacity was developed around a general 

knowledge of the stripping characteristics of activated carbon 

beds, i.e. that for a given purge air flow, the rate at which 

hydrocarbons are stripped f.rom the carbon bed is high when the 

bed is heavily loaded with hydrocarbons and this rate decreases 

as the hydrocarbon load is reduced. Since its publication, the 

proposed procedure has been further analyzed. This analysis 

has lead EPA to the conclusion that the procedure as originally 

proposed would not adequately test control system purge 

capability. In order to develop a procedure which does 

evaluate the purge capability of the control system, a better 

understanding of the desorption characteristics of activated 

carbon was needed. The test program described in this appendix 

was undertaken for this purpose. 

The rate at which hydrocarbons are stripped from" an 

activated carbon canister is influenced by several variables. 

Some of these are associated with the canister design and 

include; 1) size, 2) shape, 3) carbon base (the material from 

which the carbon is produced) and 4) internal configuration 

(how the vapors are routed through the carbon bed). Other 

variables, such as purge air flow rate and purge temperature 

are related to the purge process. The main body of this test 

program addressed the canister-related variables by evaluating 

the purge characteristics of several canisters of different 

sizes, designs, etc. Although no attempt was made to isolate 

the impact that individual variables had on canister 

performance, the data were used to estimate the variability in 

purge response that could be expected among different 

canisters. In addition to the evaluation of the purge 

characteristics of several canister designs, the effects of 

temperature, purge air flow rate and canister aging on 

hydrocarbon stripping were also investigated to a limited 

extent. 

-78-
II. Test Procedure 

The basic objective of this test program was to evaluate 

the hydrocarbon desorption characteristics of various activated 

carbon canisters when loaded with refueling emissions. There 

were two basic steps used in testing the desorption 

characteristics of carbon canisters. The first step involved 

loading the .canisters to an appropriate level with the chosen 

hydrocarbons - in this case refueling vapors. The second step 

was to draw air over the carbon bed to purge it of its 

hydrocarbon load. During purging, the change in hydrocarbon 

load was measured as a function of the volume of purge air 

pulled over the carbon bed. Each of these steps is described 

in greater detail below. 

A. Canister Loadinq 

In order to evaluate the stripping characteristics of an 

activated carbon canister, the canister must first be loaded 

with hydrocarbons. Because adsorption and desorption are 

mechanical processes they are affected by the size of the 

molecules being adsorbed or desorbed. Therefore, the purge 

characteristics of a carbon bed can be affected by the type of 

hydrocarbons used to load the canister. Because the 

information gathered in this program is being used in the 

development of a procedure to test the performance of refueling 

emission control systems, canisters were loaded with refueling 

emissions. 

Refueling emissions were generated by dispensing fuel with 

a volatility of approximately 11.5 psi RVP into a fuel tank for 

a 1983 Cutlass Supreme. The fillneck for this fuel tank was 

modified so that a tight seal was formed between the fillneck 

and the fuel dispensing nozzle when the nozzle was inserted 

into the fillneck. The fuel sender unit for this tank was also 

modified by adding an orifice and nipple to which a s/8" 

vapor line could be attached. This vapor line routed the 

vapors displaced during the refueling event to the carbon 

canister. 

The performance of a canister during purge is also 

affected by the extent to which the canister is loaded. The 

more fully loaded the canister is, the higher the rate at which 

hydrocarbons will be removed by a given volume of purge air. 

Therefore, to compare the results of various tests, it is 

desirable to load all canisters to the same extent. This 

program was designed to evaluate the performance of activated 

carbon canisters over their normal range of hydrocarbon 

loading. Therefore, it seemed logical to load the canisters to 

approximately the "breakthrough" point. The breakthrough point 

is that point at which the canister can no longer adsorb all of 

the hydrocarbon being put into it, and some hydrocarbon passes 

through the canister. Although breakthrough is easy to define 

in theory, there are several methods of defining a practical 

measure of breakthrough, each of which could result in a 

-79-
P.81 

somewhat different canister load for a given canister. In this 

program, the breakthrough point was detected using a flame 

ionization detector from an exhaust gas analyzer. Initially, 

the analyzer probe was placed near the canister outlet and the 

hydrocarbon concentration of the gas leaving the canister was 

monitored during the loading process. When a sharp, persistent 

rise in hydrocarbon content was observed, canister loading was 

discontinued.. 

During the early stages of the test program, some 

variability was observed between canister loadings for tests 

performed on the same canister loaded to the same breakthrough 

point. It was hypothesized that this variability was due to 

the technique used to determine breakthrough, i.e. that because 

the FID pickup was located so near the canister outlet that 

intermittent "spikes" of HC coming through the canister prior 

to breakthrough might have been mistaken for breakthrough in 

some instances. In an attempt to get more repeatable canister 

loadings, the test procedure was changed somewhat. Instead of 

measuring a breakthrough point for each test on a canister, a 

breakthrough point was only measured for the first test on the 

given canister. For each subsequent test on that canister, the 

canister was loaded with the vapors displaced by dispensing the 

same number of gallons of fuel that were dispensed in the 

original test. 

Bl. Canister Purge 

Hydrocarbons can be stripped from a carbon bed by passing 

hydrocarbon-poor gas over the bed. In this program, purge was 

accomplished by using a vacuum source to pull air over the 

carbon bed. In the purge characterization portion of the test 

program, both the canister ambient and purge air temperatures 

were maintained at 95° F. Purge air flowrate was measured 

using a rotometer downstream from the canister. The rotometer 

read in standard cubic feet per minute and was monitored 

throughout the canister purge. • A valve was installed in the 

air supply line downstream from the rotometer and was adjusted 

throughout the purge process to maintain the desired purge air 

flowrate. Most of the testing was performed using a flowrate 

of approximately one cfm, although flowrates of one half and 

two cfm were used in the investigation of the effects of purge 

air flow rate on the rate of hydrocarbon removal. 

B2. Measurement of Canister Loading 

The performance of an activated carbon canister can be 

defined in terms of the change in canister loading as a 

function of the volume of purge air that is pulled through the 

canister. . Changes in canister loading were measured by 

weighing the canister before and after loading and at several 

points during the purge process. The difference in the 

•80-
canister mass between weighings is equal to the change in 

canister load. Because hydrocarbons are more easily stripped 

from the carbon bed when the bed is heavily loaded, data were 

collected more frequently during the initial portion of the 

purge process. Canisters were weighed at the following times*: 

0,1,2,3,4,5,7,9,11,13,15,20,25,35,50,70, and every twenty 

minutes.thereafter as needed. 

After completion of the test program a procedural error 

was discovered. Specifically, the time clock was not stopped 

when the canisters were disconnected from the purge line for 

weighing, the clock was allowed to continue running for the 

5-10 seconds that elapsed during each weighing. The 

consequence of this error is that slightly less purge air 

actually passed through the canisters than is represented in 

the data tables accompanying this report. Although this data 

recording practice skews the results, it should skew all the 

results in the same direction and approximately the same amount 

for tests in which the purge air flow rate is similar. To 

compare tests done at different flow rates, the data must be 

adjusted by shifting the data to account for the time lost 

during each canister weighing. 

The only time this issue becomes important in this program 

is in the evaluation of purge rate on stripping 

characteristics. One canister was purged at three different 

purge rates in order to compare the effect of purge rate on 

hydrocarbon stripping characteristics. A ten second gap in the 

purge at 2 cfm represents four times as much purge air as does 

a ten second gap in the purge at 1/2 cfm. In order to compare 

the results of tests done at different purge rates, the results 

were corrected by shifting each data point to account for the 

gaps in purge air flow corresponding to canister weighings. It 

was estimated that each weighing took approximately ten seconds 

and that the canister was first disconnected after 55 seconds 

of purge. The correction procedure is more throughly described 

in the discussion of the results of the tests dealing with 

purge rate. 

Because flowrate is constant, time elapsed between 

canister weighings is proportional to the amount of air 

passing through the canister in that time interval. 

-81-
III. Canisters 

Ideally, the results of this test program would provide a 

characterization of the performance of typical refueling 

emission control canisters that had been well aged on refueling 

vapors (i.e. they would previously have been subjected to 

multiple refueling vapor loadings and subsequent purges) and 

had been well maintained. Since vehicles do not presently have 

refueling control systems, refueling canisters were 

unavailable. However, evaporative emission control canisters, 

which perform essentially the same function, have been used for 

more than a decade. The question then became one of finding 

several canisters that could be expected to be in good 

condition - that is well maintained in use. One source of such 

canisters is the fleet of vehicles used by automobile 

manufacturers to gather emission control system durability and 

deterioration information - durability data vehicles. These 

vehicles are operated for 50,000 miles and are well maintained 

and serviced during this mileage accumulation. However, 

although the canisters on the durability vehicle were subjected 

to a great deal of mileage accumulation, the canisters were 

probably not as well aged as a typical in-use canister. 

Durability vehicles typically accumulate mileage while 

operating on the AMA driving cycle. This cycle consists of 

essentially continuous operation with infrequent stops. This 

kind of operation results in infrequent loading and more 

extensive purge than would normally occur. 

Although the durability canisters may not have been fully 

aged, they were the best canisters readily available for use. 

Three domestic automakers (Chrysler, Ford, and General Motors) 

and one foreign maker (Nissan) were contacted and asked to 

supply EPA with a canister from a durability data vehicle. All 

of these manufacturers obliged. 

A description of each of the canisters from the 

durability-data vehicles (durability canisters) is provided in 

Table Al. Most of the information provided in the table is 

self-explanatory, but one item deserves some further 

attention. That is the item labeled "Treatment after 50K 

Testing". As discussed above, these canisters were taken off 

of durability data vehicles that had accumulated 50,000 miles. 

Upon completion of durability mileage accumulation and testing, 

manufacturers typically store these vehicles in case the 

vehicles are needed for any further testing. It can be seen 

that at least three of the vehicles had been stored outside 

between the time they finished mileage accumulation and the 

time their canisters were removed. Also, one manufacturer ran 

the durability vehicle on the test track prior to removing the 

canister. The significance of this information is discussed in 

the analysis of the test results. 

-82-
I 

CO 

I 

Canister 

Size (ml) 

Activated 

Carbon Base 

Design 

Butane(l) 

Working 

Capacity(gm) 

Estimated 

Design(2) 

HC Working 

Capacity(gm) 

Approximate 

Observed HC 

Working 

Capacity(gm) 

Vehicle 

Type 

Canister 

Shape 

Open/closed 

Bottom 

Treatment 

After 50K 

Testing 

Chrysler 

1320 

Wood 

50 

30-35 

31 

S-Body 

(Caravan, 

Voyager) 

Ford 

925 

Coal 

50 

30-35 

33 

Taurus(3) 

Table Al 

Description of canisters 

GM 

850 

Wood 

35 

cylindrical Rectangular 

Closed 

No 

Information 

Available 

Closed 

Completed 50K Jan 85 

Stored outdoors on 

vehicle until 8/28/85 

Vents covered with 

tape when removed 

from vehicle. No 

special treatment 

after removal. 

20-25 

35 

J-Car 

(Sunbird) 

Cylindrical 

Open 

Completed 50K 7/19/85 

Stored outdoors on 

vehicle until 9/5/85 

4 hrs AMA mileage 

accumulation (92 miles) 

prior to canister 

removal and delivery 

Nissan 

1230 

Coconut 

57 

34-40 

57 

Maxima 

EPA 

5000 

Wood 

260 

160-180 

190 

Cylindrical 

Open(4) 

Completed 50K Jan 84 

Stored outdoors until 

10/85. No special 

treatment after 

removal 

Cylindrical 

Open 

1. These are "Design Working capacities" as given in CERT application. 

Those that specify, specify Butane W.C. 

2. 60-70% of "Design Butane Working Capacity" 

3. Vehicle representing a Taurus. 

4. Open bottom with a cover over bottom with a 5/8" opening for air to enter. 

oo 
Two other canisters were tested in addition to the 

durability canisters. One was a new 925 milliliter Ford 

canister of the same design as the Ford durability canister. 

The results of the tests on the new canister are used in 

comparison with results of the Ford durability canister to 

evaluate the effects of aging. The sixth canister evaluated in 

this program was a canister built by EPA for refueling tests. 

This canistejr was not actually tested as part of this test 

program, nor was the' purge procedure used identical to that 

used in testing the other canisters. It was, however, loaded 

with refueling vapors and purged at approximately 2 cfm. The 

canister is cylindrical with a volume of about five liters (h = 

16 cm, r = 10 cm) . The canister was loaded with Westvaco 

extruded activated carbon. Although this canister was not 

fully aged prior to the start of this program, it had been 

exposed to several refueling vapor loading/purge cycles as part 

of another project. The results of tests on this canister were 

used to compare results from a large canister to those from the 

smaller evap canisters. 

IV. Results 

The data obtained in the test program are presented in 

Tables A2-1 through A2-20. Within the tables, the data are 

organized by canister. For each test, information is presented 

on; 1) refueling conditions, 2) purge conditions, and 3) 

canister mass as a function of purge volume. For each test, 

the following information is presented: 

° TT i, fuel tank temperature prior to refueling (°F) 

° TTf, fuel tank temperature following refueling (°F) 

° TD , dispensed fuel temperature (°F) 

° Gallons of fuel dispensed (gallons) 

° TP, purge air temperature (°F) 

° f, purge air flowrate (cfm) 

° t, cumulative purge time elapsed prior to canister 

mass measurement 

° Canister mass 1) prior to loading with refueling 

vapors, 2) following HC loading, and 3) following 

each purge interval. 

° Cumulative decrease in canister mass at each purge 

interval. 

V. Analysis 

The main purpose of this test program was to compare the 

performance of activated carbon canisters of various designs 

under various conditions of purge temperature and flowrate. 

The primary information of interest was how readily the 

-84-
I 

00 

Ul 

TEST NUMBER 

FUEL TRNK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE <deg. F) 

PURGE AIR 

FLOW RATE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

TABLE A2-1 

CHRYSLER DURABILITY TESTS 

Cl 

72 

73 

73 

95 

1.0 

974. a 

C2 

70 

73 

73 

95 

1.0 

860 

Vo1ume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

110 

Canister 

(grams) 

893. 3 

878.6 

876.2 

875.4 

874.9 

874.5 

874.1 

873.7 

873.4 

873. 1 

872.8 

871.8 

870.9 

869. 1 

866.5 

863.6 

861.2 

860.0 

i_e i ghfc. Cumu1at i ve HC 

purged (grams) 

0.0 

14.7 

17.1 

17.9 

18.4 

18.8 

19.2 

19.6 

19.9 

20.2 

20.5 

21.5 

22.4 

24.2 

26.8 

29.7 

32.1 

33.3 

Canister 

(grams) 

879.8 

865.0 

862.0 

860.8 

860.2 

859.8 

859.6 

859.5 

859.4 

859.2 

859.1 

858.8 

858.5 

857.7 

856.7 

uei ght Cumulative HC 

purged (grams) 

0.0 

14.8 

17.8 

19.0 

19.6 

20.0 

20.2 

20.3 

20.4 

20.6 

20.7 

21.0 

21.3 

22.1 

23.1 
TRBLE R2-2 

CHRYSLER DURRBILITY TESTS 

l 

oo 

I 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) . 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW RATE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LORDING (gms) 

C3 

71 

65 

65 

10 

95 

1.0 

B60 

C4 

70 

65 

65 

10 

95 

1.0 

857.9 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

Canister weight 

(grams) 

889.0 

879:6 

875.3 

872.4 

870.2 

868.6 

866.1 

864.4 

863.3 

862.6 

861.9 

860.8 

860.0 

859.0 

858.1 

Cumulative HC 

purged (grams) 

0.0 

9.4 

13.7 

16.6 

18.8 

20.4 

22.9 

24.6 

25.7 

26.4 

27.1 

28.2 

29.0 

30.0 

30.9 

Canister 

(grams) 

886.6 

879.7 

875.1 

871.7 

869.6 

867.8 

865.4 

863.4 

862.4 

861.7 

861.0 

859.8 

859.1 

858.6 

857.7 

we i ghfc Cumulative HC 

purged (grams) 

0.0 

6.9 

11.5 

14.9 

17.0 

18.8 

21.2 

23.2 

24.2 

24.9 

25.6 

26.8 

27.5 

28.0 

28.9 

oo 
TRBLE R2-3 

FORD DURHBILITY TESTS 

oo 

I 

TEST NUMBER El 

FUEL TRNK TEMP. PRIOR TO 78 

REFUELING (deg. F ) 

FUEL TRNK TEMP. FOLLOWING 75 

REFUELING (deg. F ) 

DISPENSED FUEL 75 

TEMPERATURE (deg. F) 

GALLONS OF 8 

FUEL DISPENSED 

PURGE AIR 95 

TEMPERATURE (deg. F> 

PURGE AIR 0.5 

FLOW ROTE (cfm) 

CANISTER WEIGHT 699.1 

PRIOR TO LOADING (gms) 

E2 

75 

75 

75 

9 

95 

0.5 

694.3 

Volume of purge 

air (ftA3) 

0.0 

0.5 

1.0 

1.5 

2.0 

2.5 

3.5 

4.5 

5.5 

6.5 

7.5 

10.0 

12.5 

17.5 

25.0 

35.0 

45.0 

Canister 

(grams) 

725.1 

716'. 2 

713.4 

711.4 

709.9 

708.9 

707.6 

706.5 

705.6 

705.1 

704.5 

703.4 

702.4 

700.4 

698.4 

696.4 

694.5 

uie i ght Cumulative HC 

purged (grams) 

0.0 

8.9 

11.7 

13.7 

15.2 

16.2 

17.5 

18.6 

19.5 

20.0 

20.6 

21.7 

22.7 

24.7 

26.7 

28.7 

30.6 

Cansister weight Cumulative HC 

(grams) purged (grams) 

719.5 

707.1 

703.4 

701.1 

699.8 

698.5 

697.0 

696.0 

695.3 

694.7 

694.4 

693.8 

693.3 

692.1 

691. 2 

0 . 0 

12.4 

16.1 

18.4 

19.7 

21. 0 

22. 5 

23. 5 

24. 2 

24. 8 

25.1 

25. 7 

26. 2 

27. 4 

28. 3 
I RULE Rl'-4 

FORD DURHBILITY TESTS 

oo 

03 

I 

TEST NUMBER 

FUEL TRNK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING <deg. F) 

DISPENSED FUEL 

TEMPERRTURE (deg. F) 

GRLLONS OF 

FUEL DISPENSED 

PURGE RIR 

TEMPERRTURE (deg. F) 

PURGE RIR 

FLOW RRTE (cfm) 

CRNISTER WEIGHT 

PRIOR TO LORDING (gms) 

E3 

76 

75 

75 

95 

1-0 

691.2 

E4 

68 

73 

74 

95 

1.0 

686.3 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

Canister 

(grams) 

716.4 

702-.4 

698.6 

696.8 

695.5 

694.4 

693.0 

691.9 

691.4 

690.8 

690.5 

690.0 

689.5 

688.5 

687.2 

686.5 

uei ght Cumu1 atIve HC 

purged (grams) 

0.0 

14.0 

17.8 

19.6 

20.9 

22.0 

23.4 

24.5 

25.0 

25.6 

25.9 

26.4 

26.9 

27.9 

29.2 

29.9 

Cansister weight Cumulative HC 

(grams) 

715. 1 

701.4 

697.7 

695.5 

694.1 

692.9 

691.3 

690.0 

689.0 

688.5 

688.0 

686.7 

686.2 

685.3 

684.2 

683.1 

purged (grams) 

0.0 

13.7 

17.4 

19.6 

21.0 

22.2 

23.8 

25.1 

26. 1 

26.6 

27.1 

28.4 

28.9 

29.8 

30.9 

32.0 

00 

CD 
I 

cc 

T 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERRTURE (deg. F) 

GRLLONS OF 

FUEL DISPENSED 

PURGE RIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW RATE (cfm) 

CANISTER WEIGHT 

PRIOR TO LORDING (gms) 

TRBLE R2-5 

FORD DURABILITY TESTS 

E5 

69 

72 

74 

95 

683.1 

E6 

69 

72 

74 

8 

95 

678.2 

Volume of purge 

air (ftA3) 

0 

2 

4 

6 

8 

10 

14 

18 

22 

26 

30 

40 

50 

70 

100 

140 

Canister 

(grams) 

713.7 

695.0 

691.7 

689.5 

688. 1 

687.3 

685.9 

684.9 

684. 1 

683.7 

683. 1 

682.2 

681.6 

680.5 

679.6 

678.2 

weight Cum ulative HC 

purged (grams) 

0.0 

18.7 

22.0 

24.2 

25.6 

26.4 

27.8 

28.8 

29.6 

30.0 

30.6 

31.5 

32. 1 

33.2 

34.1 

35.5 

Cansister weight 

(grams) 

709.2 

689. 2 

686. 1 

684. 0 

683. 0 

682.2 

681. 0 

680. 1 

679. 2 

678.9 

678.7 

677. 8 

677.3 

676.7 

675. 9 

675.3 

Cumulativ e HC 

purged (grams ) 

0 . 0 

20. 0 

23.1 

25. 2 

26. 2 

27. 0 

28. 2 

29.1 

30.0 

30.3 

30.5 

31.4 

31.9 

32. 5 

33. 3 

33.9 

CO 

o 
TRBLE R2-6 

GM DURABILITY TESTS 

I 

s£> 

O 

I 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F). 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW RATE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

Bl 

69 

73 

73 

95 

1.0 

445. 1 

B2 

70 

73 

74 

8 

95 

1.0 

424.1 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

(grams) 

471.1 

459.8 

451.5 

449.4 

447.7 

447.0 

445.6 

444.6 

444.0 

443.2 

442.5 

441.2 

439.9 

437.5 

433.8 

429.5 

424.7 

weight Cumulative HC 

pur ged (grams) 

0.0 

15.3 

19.6 

21.7 

23.4 

24.1 

25.5 

26.5 

27.1 

27.9 

28.6 

29.9 

31.2 

33.6 

37.3 

41.6 

46.4 

Canister 

(grams) 

451.8 

438.4 

433.2 

431.1 

429.5 

428.7 

427.3 

426.2 

425.4 

424.6 

424.0 

422.6 

421.4 

419.7 

417.1 

415.0 

414.1 

weight Cumulative HC 

purged (grams) 

0.0 

13.4 

18.6 

20.7 

22.3 

23.1 

24.5 

25.6 

26.4 

27.2 

27.8 

29.2 

30.4 

32.1 

34.7 

36.8 

37.7 
TABLE A2-7 

GM DURABILITY TESTS 

I 

TEST NUMBER B3 

FUEL TANK TEMP. PRIOR TO 71 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 65 

REFUELING (deg. F) 

DISPENSED FUEL 65 

TEMPERATURE (deg. F) 

GALLONS OF 10 

FUEL DISPENSED 

PURGE AIR 95 

TEMPERATURE (deg. F) 

PURGE AIR 1.0 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 417.1 

PRIOR TO LOADING (gms) 

84 

70 

65 

65 

10 

95 

1.0 

417.2 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

(grams) 

456.1 

446'. 1 

442.3 

439.7 

437.5 

435.9 

433.4 

431.2 

429.7 

428.5 

427.4 

425.1 

423.6 

421.0 

418.9 

417.1 

weight Cumulative HC 

purged (grams) 

0.0 

10.0 

13.8 

16.4 

18.6 

20.2 

22.7 

24.9 

26.4 

27.6 

28.7 

31.0 

32.5 

35.1 

37.2 

39.0 

Can i ster 

(grams) 

450.2 

443.3 

439.1 

436.4 

434. 1 

432.3 

429.7 

428.0 

426.6 

425.5 

424.6 

422.9 

421.2 

419.3 

417.8 

416.6 

welght Cumulative HC 

purged (grams) 

0.0 

6.9 

11.1 

13.8 

16.1 

17.9 

20.5 

22.2 

23.6 

24.7 

25.6 

27.3 

29.0 

30.9 

32.4 

33.6 

CO 

N> 
TABLE R2-8 

GM DUPRBILITY TESTS 

I 

ro 

I 

TEST NUMBER B5 

FUEL TANK TEMP. PRIOR TO 72 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 65 

REFUELING (deg. F) 

DISPENSED FUEL 65 

TEMPERATURE (deg. F) 

GALLONS OF 10 

FUEL DISPENSED 

PURGE AIR 95 

TEMPERATURE (deg. F> 

PURGE AIR 1.0 

FLOW RATE (cfm.) 

CANISTER WEIGHT 416.8 

PRIOR TO LOADING (gms) 

B6 

73 

65 

65 

10 

95 

1.0 

417.6 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

(grams) 

443.8 

437.0 

433.9 

431.7 

430.0 

428.7 

426.9 

425.6 

424.6 

423.8 

423.2 

421.7 

420.6 

419. 1 

417.6 

weight Cumulative HC 

purged (grams) 

0.0 

6.8 

9.9 

12.1 

13.8 

15.1 

16.9 

18.2 

19.2 

20.0 

20.6 

22.1 

23.2 

24.7 

26.2 

Canister 

(grams) 

450.6 

442.6 

438.7 

435.6 

433.3 

432. 1 

429.3 

427.7 

426.5 

425.7 

425.0 

423.4 

421.9 

420.2 

418.5 

417.4 

weight Cumulative HC 

purged (grams) 

0.0 

8.0 

11.9 

15.0 

17.3 

18.5 

21.3 

22.9 

24.1 

24.9 

25.6 

27.2 

28.7 

30.4 

32. 1 

33.2 

(not used in average) 

CO 

CO 
TRBLE A2-9 

NISSAN DURABILITY TESTS 

I 

VD 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

Dl 

70 

65 

65 

25 

95 

1.0 

1103.9 

D2 

71 

67 

67 

15 

95 

1.0 

1100.2 

Volume of purge 

air (ftA3> 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

Canister 

(grams) 

1163.3 

1152.9 

1148.3 

1145.1 

1141.7 

1139.0 

1134.8 

1132.0 

1128.9 

1126.5 

1124.4 

1120.4 

1116.8 

1111.3 

1104.9 

1100.3 

weight Cumulative HC 

purged (grams) 

0.0 

10.4 

15.0 

18.2 

21.6 

24.3 

28.5 

31.3 

34.4 

36.8 

38.9 

42.9 

46.5 

52.0 

58.4 

63.0 

Canister 

(grams) 

1162.9 

1154.3 

1150.2 

1146.7 

1143.7 

1141.3 

1136.8 

1132.5 

1129.5 

1126.9 

1124.6 

1120.2 

1117.0 

1112.0 

1107.3 

1103.2 

weight Cumulative HC 

purged Cgrams) 

0.0 

8.6 

12.7 

16.2 

19.2 

21.6 

26. 1 

30.4 

33.4 

36.0 

38.3 

42.7 

45.9 

50.9 

55.6 

59.7 

CO 
TRBLE R2-10 

NISSHN DURHBILITY TESTS 

l 

VD 

I 

TEST NUMBER D3 

FUEL TANK TEMP. PRIOR TO 66 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 59 

REFUELING (deg. F) 

DISPENSED FUEL 5 3 

TEMPERATURE (deg. F ) 

GALLONS OF 16 

FUEL DISPENSED 

PURGE RIR 95 

TEMPERATURE (deg. F) 

PURGE AIR 1.0 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 1097.4 

PRIOR TO LOADING (gms) 

D4 

66 

59 

59 

16 

95 

1.0 

1094.1 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

(grams) 

1150.4 

1137.8 

1131.2 

1126.2 

1121.7 

1118.4 

1114.1 

1110.8 

1108.5 

1106.7 

1105.3 

1102.1 

1100.0 

1097.2 

1094.4 

weight Cumulative HC 

purged (grams) 

0.0 

12.6 

19.2 

24.2 

28.7 

32.0 

36.3 

39.6 

41.9 

43.7 

45. 1 

48.3 

50.4 

53.2 

56.0 

Canister 

(grams) 

1145.9 

1138.2 

1133.5 

1130.0 

1126.9 

1124.5 

1120.7 

1117.9 

1115.9 

1114.1 

1112.3 

1109.2 

1107.1 

1103.3 

1098.5 

1093.5 

1089.7 

we i ght Cumulative HC 

pur ged (grams) 

0.0 

7.7 

12.4 

15.9 

19.0 

21.4 

25.2 

28.0 

30.0 

31.8 

33.6 

36.7 

38.8 

42.6 

47.4 

52.4 

56.2 

CO 
I 

VO 

Ul 

I 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

Vo1ume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

D5 

64 

59 

59 

16 

95 

TABLE R2-11 

NISSAN DURABILITY TESTS 

D6 

65 

59 

58 

26 

95 

1 . 0 

1086.8 

Canister weight 

(grams) 

1127.4 

1120.2 

1115.8 

1112.8 

1110.3 

1108.4 

1104.9 

1102.5 

1101.1 

1099.6 

1098.0 

1095.4 

1093.8 

1091.1 

1088.1 

1085.1 

1082.7 

(not used in 

Cum ulative HC 

purged (grams) 

average) 

0.0 

7.2 

11.6 

14.6 

17.1 

19.0 

22.5 

24.9 

26.3 

27.8 

29.4 

32.0 

33.6 

36.3 

39.3 

42.3 

44.7 

1.0 

1082.1 

Canister 

(grams) 

1146.4 

1138.4 

1133.6 

1129.4 

1126.6 

1124.4 

1120.2 

1117.3 

1114.9 

1113.0 

1111.1 

1107.9 

1105.4 

1101.2 

1096.6 

1090.8 

1086.4 

weight Cumulati 

pur ged ( 

0.0 

8.0 

12.8 

17.0 

19.8 

22.0 

26.2 

29.1 

31.5 

33.4 

35.3 

38.5 

41.0 

45.2 

49.8 

55.6 

60.0 

HC 

co 

0> 
TABLE A2-12 

NISSHN DURHBILITY TESTS 

l 

VD 

I 

TEST NUMBER D7 

FUEL TRNK TEMP. PRIOR TO 59 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 58 

REFUELING (deg. F) 

DISPENSED FUEL 58 

TEMPERATURE (deg. F) 

GALLONS OF 22.5 

FUEL DISPENSED 

PURGE AIR 95 

TEMPERATURE (deg. F) 

PURGE AIR 1.0 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 1059.1 

PRIOR TO LOADING 

D8 

66 

60 

60 

16 

115 

1.0 

1011.4 

air 

of purge 

t

A3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Can is teiCgrams) 

1119.1 

1114.7 

1112.0 

1109.8 

1107.6 

1105.9 

1102.6 

1099.9 

1098.2 

1096.6 

1095.3 

1092.0 

1089.2 

1084.7 

1079.3 

1073.0 

1068.5 

weight Cumulative HC 

purged (grams) 

0.0 

4.4 

7. 1 

9.3 

11.5 

13.2 

16.5 

19.2 

20.9 

22.5 

23.0 

27.1 

29.9 

34.4 

39.8 

46.1 

50.6 

Canister 

< grams) 

1061.5 

1058.3 

1056.7 

1055.3 

1054.0 

1052.8 

1051.0 

1049.7 

1048.7 

1048.0 

1047.3 

1046.3 

1045.5 

1044.0 

1042.5 

1040.6 

1038.8 

weight Cumulative HC 

purged (grams) 

0.0 

3.2 

4.8 

6.2 

7.5 

8.7 

10.5 

11.8 

12.8 

13.5 

14.2 

15.2 

16.0 

17.5 

19.0 

20.9 

22.7 

CO 
I 

VD 

-•J 

TEST NUMBER D9 

FUEL TANK TEMP. PRIOR TO 67 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 59 

REFUELING (deg. F) 

DISPENSED FUEL 59 

TEMPERATURE (deg. F) 

GALLONS OF 16 

FUEL DISPENSED 

PURGE AIR 115 

TEMPERATURE (deg. F) 

PURGE AIR 1.0 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 1038.8 

PRIOR TO LOADING 

I MOLE 02-13 

NISSHN DURABILITY TESTS 

Volume of purge 

air (ftA3> 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

<grams) 

1093.1 

1088.2 

1085.5 

1083.4 

1081.7 

1080.3 

1078.0 

1076.3 

1075.0 

1073.9 

1072.7 

1071.0 

1069.6 

1067.4 

1064.8 

1061.8 

1058.8 

weight Cumulative HC 

purged (grams) 

0.0 

4.9 

7.6 

9.7 

11.4 

12.8 

15.1 

16.8 

18.1 

19.2 

20.4 

22.1 

23.5 

25.7 

28.3 

31.3 

34.3 

CO 

00 
TRBLE n2-14 

NEW FORD TESTS 

I 

VD 

OO 

I 

TEST NUMBER 

FUEL TRNK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE RIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW ROTE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

A l 

75 

76 

76 

12 

95 

1.0 

587.9 

Canister 

(grams) 

635.8 

620.5 

616.5 

614.1 

612.1 

610.8 

608.8 

607.6 

606.4 

605.6 

604.9 

603. 1 

601.7 

599.4 

596.8 

594.4 

weight Cumu1at i ve HC 

purged (grams) 

0.0 

15.3 

19.3 

21.7 

23.7 

25.0 

27.0 

20.2 

29.4 

30.2 

30.9 

32.7 

34. 1 

36.4 

39.0 

41.4 

02 

69 

75 

75 

12 

95 

1.0 

Canister 

(grams) 

634.7 

619.5 

614.0 

612.1 

610.3 

609.2 

607.5 

606.5 

605.7 

605.0 

604.4 

602.9 

601.8 

599.7 

597.5 

595.6 

5 34.4 

594. 

we i ght 

7 

Cumulative HC 

purged (grams) 

0.0 

15.2 

19.9 

22.6 

24.4 

25.5 

27.2 

28.2 

29.0 

29.7 

30.3 

31.8 

32.9 

35.0 

37.2 

39. 1 

40.3 

CO 

CO 
TRBLE R2-15 

NEW FORD TESTS 

I 

v_5 

TEST NUMBER R3 

FUEL TANK TEMP. PRIOR TO 74 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 75 

REFUELING (deg. F) 

DISPENSED FUEL 75 

TEMPERRTURE (deg. F) 

GALLONS OF 10 

FUEL DISPENSED 

PURGE RIR 95 

TEMPERATURE (deg. F) 

PURGE RIR 1.0 

FLOW RATE (cfm.) 

CANISTER WEIGHT 594.4 

PRIOR TO LOADING <gms) 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister weight 

(grams) 

6 34.2 

617.4 

613.0 

610.4 

609.0 

608.0 

606.5 

605.3 

604.6 

603.9 

603.3 

602.0 

600. B 

599. 1 

597. 1 

595.8 

594.7 

Cumulative HC 

purged (grams) 

0.0 

16.8 

21.2 

23.8 

25.2 

26.2 

27.7 

28.9 

29.6 

30.3 

30.9 

32.2 

33.4 

35. 1 

37. 1 

38.4 

39.5 

R4 

75 

75 

75 

12 

95 

1.0 

595. I 

Canister 

(grams) 

630.8 

616.8 

614.0 

611.1 

609.9 

609.0 

607.9 

607.2 

606.6 

605.9 

605.4 

604.4 

603.3 

601.4 

599.7 

598.3 

597.3 

weight Cumulative HC 

pur ged (grams) 

0.0 

14.0 

16.8 

19.7 

20.9 

21.8 

22.9 

23.6 

24.2 

24.9 

25.4 

26.4 

27.5 

29.4 

31.1 

32.5 

33.5 
TABLE A2-16 

NEW FORD TESTS 

o 

o 

I 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F> 

PURGE AIR 

FLOW RATE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LOADING (gms) 

Volume of purge 

air (ftA3> 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

R5 

70 

74 

74 

10 

95 

1.0 

602.4 

Canister 

(grams) 

636.3 

622.0 

618.8 

616.6 

615.3 

614.3 

613.0 

612.2 

611.4 

610.7 

610.1 

608.8 

607.6 

606.1 

604.6 

603.3 

602.8 

ueight Cumulative HC 

purged (grams) 

0.0 

14.3 

17.5 

19.7 

21.0 

22.0 

23.3 

24.1 

24.9 

25.6 

26.2 

27.5 

28.7 

30.2 

31.7 

33.0 

33.5 

R6 

69 

74 

74 

10 

95 

1.0 

Canister 

(grams) 

640.8 

628.3 

622.0 

620.1 

616.2 

614.3 

612.8 

611.8 

610.7 

610.0 

609.3 

608.0 

606.8 

604.7 

602.7 

602. 

weight 

8 

Cumulative HC 

purged (grams) 

0.0 

12.5 

18.8 

20.7 

24.6 

26.5 

28.0 

29.0 

30.1 

30.8 

31.5 

32.8 

34.0 

36.1 

38.1 

"U 

N> 
TRBLE R2-17 

NEW FORD TESTS 

TEST NUMBER 

FUEL TRNK TEMP. PRIOR TO 

REFUELING Cdeg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING Cdeg. F> 

DISPENSED FUEL 

TENPERRTUPE (dog. F ) 

GRLLONS OF 

FUEL DISPENSED 

PURGE RIR 

TENPEPRTURE Cdeg. 

PURGE RIR 

FLOW RRTE (cf«.> 

F> 

CHNISTER WEIGHT 

PRIOR TO LORDING igots) 

o Volume of pwr 

«ir <ft~3> 

O 

1 

2 

3 

4 

5 

7 

9 

1 1 

1 3 

15 

20 

25 

35 

50 

?0 

90 

1 IO 

130 

ISO 

i?o 

ISO 

210 

ge Canister 

(grams) 

671.5 

660.0 

658.6 

657. 1 

65-4.3 

651. 7 

6-48.2 

646. O 

644.4 

6-42.8 

642. 1 

640.2 

638.8 

636.4 

633.8 

631.6 

629.9 

R7 

72 

64 

64 

13 

95 

1.0 

627.4 

R8 

71 

62 

62 

13 

115 

l.O 

628. 1 

Cumulative HC 

purged (grama) 

O.O 

11.5 

12.9 

14.4 

17.2 

19.8 

23.3 

25.5 

2 7. 1 

28.7 

29.4 

31.3 

32.7 

35. 1 

37.7 

39.9 

41.6 

Canister ueight 

(grams) 

665. 8 

662 . O 

659.-4 

657. 5 

656 . 1 

65*1-9 

653. 2 

651. 8 

650. 9 

650. 2 

649. 6 

648. 2 

647. 3 

646 . O 

644. 4 

643 . 1 

6-12. O 

640. 5 

639 . 1 

637. 9 

636. 6 

635. 6 

634 . 7 

Cumu1at i ve HC 

pur ged < gr ams) 

O.O 

3.8 

6.4 

8.3 

9.7 

10.9 

12.6 

14.O 

14.9 

15.6 

16.2 

17.6 

18.5 

19.8 

21.4 

22.7 

23.8 

25.3 

26.7 

27.9 

29.2 

30.2 

31. I 

TJ 

CO 
TR8LE R2-18 

NEW FORD TESTS 

o 

I 

TEST NUMBER 

FUEL TRNK TEMP. PRIOR TO 

REFUELING (deg. F) 

FUEL TRNK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE RIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW RATE (cfm.) 

CRNISTER WEIGHT 

PRIOR TO LOADING (gms) 

Volume of purge 

air (ftA3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

R9 

67 

61 

61 

13 

115 

1.0 

634.5 

RIO 

66 

61 

61 

13 

115 

1.0 

635.8 

Canister 

(grams) 

674.7 

665.0 

659.8 

657.5 

655.0 

653.7 

651.1 

649.5 

648.2 

647.2 

646.6 

645.0 

643.6 

641.9 

639.5 

637.8 

636.0 

weight Cumulative HC 

purged (grams) 

0.0 

9.7 

14.9 

17.2 

19.7 

21.0 

23.6 

25.2 

26.5 

27.5 

28.1 

29.7 

31.1 

32.8 

35.2 

36.9 

38.7 

Canister 

(grams) 

667.3 

659.5 

656.1 

653.6 

651.9 

650.7 

648.7 

647.3 

646.3 

645.6 

644.9 

643.6 

642.7 

641.0 

639.1 

638.0 

637.0 

ue i ght Cumulative HC 

purged (grams) 

0.0 

7.8 

11.2 

13.7 

15.4 

16.6 

18.6 

20.0 

21.0 

21.7 

22.4 

23.7 

24.6 

26.3 

28.2 

29.3 

30.3 

J> 
TABLE R2-19 

NEW FORD TESTS 

o 

co 

TEST NUMBER All 

FUEL TANK TEMP. PRIOR TO 71 

REFUELING (deg. F ) 

FUEL TRNK TEMP. FOLLOWING 61 

REFUELING (deg. F ) 

DISPENSED FUEL 61 

TEMPERATURE (deg. F ) 

GALLONS OF 13 

FUEL DISPENSED 

PURGE AIR 75 

TEMPERATURE (deg. F) 

PURGE AIR 1.0 

FLOW RATE (cfm.) 

CANISTER WEIGHT 636.5 

PRIOR TO LORDING (gms) 

R12 

67 

61 

61 

13 

75 

1.0 

643.4 

Volume of purge 

air (ft*3) 

0 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

Canister 

(grams) 

673.9 

668.3 

665.7 

663.7 

662.1 

661.0 

659.0 

657.8 

656.8 

656.0 

655.5 

653.6 

652.9 

650.9 

648.6 

645.9 

643.4 

hie i ght Cumulative HC 

purged (grams) 

0.0 

5.6 

8.2 

10.2 

11.8 

12.9 

14.9 

16.1 

17.1 

17.9 

18.4 

20.3 

21.0 

23.0 

25.3 

28.0 

30.5 

Canister 

(grams) 

678.2 

671.0 

667.2 

664.7 

663.0 

661.7 

659.5 

657.8 

656.9 

655.9 

655.1 

653.3 

651.8 

649.7 

646.8 

643.7 

ue i ght Cumulative HC 

purged (grains) 

0.0 

7.2 

11.0 

13.5 

15.2 

16.5 

18.7 

20.4 

21.3 

22.3 

23.1 

24.9 

26.4 

28.5 

31.4 

34.5 

CJ! 
TABLE R2-20 

NEW FORD TESTS 

o 

•tl 

TEST NUMBER 

FUEL TANK TEMP. PRIOR TO 

REFUELING (deg. F> 

FUEL TANK TEMP. FOLLOWING 

REFUELING (deg. F) 

DISPENSED FUEL 

TEMPERATURE (deg. F) 

GALLONS OF 

FUEL DISPENSED 

PURGE AIR 

TEMPERATURE (deg. F) 

PURGE AIR 

FLOW RATE (cfm.) 

CANISTER WEIGHT 

PRIOR TO LORDING Cgms) 

Volume of purge 

air (ftA3) 

O 

1 

2 

3 

4 

5 

7 

9 

11 

13 

15 

20 

25 

35 

50 

70 

90 

A13 

67 

61 

61 

13 

75 

1.0 

650.4 

R14 

69 

61 

61 

13 

75 

1.0 

643.4 

Canister 

(grams) 

681.4 

672.4 

668.3 

665.8 

663.8 

662.4 

660.4 

658.8 

658.0 

657.1 

656.7 

655.2 

654.3 

652.5 

650.4 

649.5 

ue i ght Cumulative HC 

purged (grams) 

0.0 

9.0 

13.1 

15.6 

17.6 

19.0 

21.0 

22.6 

23.4 

24.3 

24.7 

26.2 

27.1 

28.9 

31.0 

31.9 

Canister 

(grams) 

683.1 

676.1 

672.3 

670.3 

668.4 

667.3 

665.0 

663.7 

662.7 

661.9 

661.4 

660.1 

659.2 

656.8 

654.7 

652.6 

650.4 

ueight Cumulative HC 

purged (grams) 

0.0 

7.0 

10.8 

12.8 

14.7 

15.8 

18.1 

19.4 

20.4 

21.2 

21.7 

23.0 

23.9 

26.3 

28.4 

30.5 

32.7 

b> 
P.7 

canister releases hydrocarbon in response to a given volume of 

purge air when purged at a given flowrate and temperature. 

Because the amount of HC purged does not vary linearly with the 

purge air volume, canister performance should be compared over 

a continuum rather than at any given time during the purge 

sequence. The simplest way to do this is with a graphical 

representation of the results which were presented in the 

previous section. Throughout the rest of the data analysis, 

canisters are compared by comparing plots of cumulative HC 

purged from the canister (ordinate) versus the cumulative 

volume of purge air pulled through the canister prior to the 

given mass measurement (abscissa). The data points were 

connected with a smooth curve to approximate the performance of 

the canister at all times in the purge sequence. 

Because there is some variability in canister performance 

from one test to another the results from a series of tests on 

a given canister were averaged to find a "typical" purge curve 

for each series. The averages were found by finding the 

average amount of hydrocarbon purged from the canister at each 

data point. The average values were found and plotted, and a 

smooth curve drawn between the average values. Most of the 

analysis in this report is based on the average curves 

developed as described above. 

The remainder of the analysis of results is divided into 

five sections. The first section addresses some differences 

that were observed between the first test or tests performed on 

a given durability canister and later tests performed on the 

same canister. The next section touches on the effects of 

canister aging by evaluating the results from sequential tests 

on a new canister and by comparing results of tests performed 

an aged (durability) Ford canister of identical design. The 

effect of purge rate is then briefly discussed followed by a 

description of the results of the tests designed to evaluate 

the effect of temperature on purge rate. The next section 

describes the most substantial portion of the work in this test 

program. That is the development of a "representative" purge 

curve for each canister type examined in this program. The 

final section discusses the internal temperature of the 

refueling canister during the purge process. 

A. Initial Tests versus Average Curves 

As part of the analysis of the canister test results, the 

results from tests performed on individual canisters under 

similar conditions of purge were plotted individually on the 

same set of axes. When plotted . in this way, the results from 

three of the four durability canisters tested show a pattern in 

the test results. The pattern observed was that the shape of 

-105-
P.8 

the curve generated from the results of the first one or two 

tests on a given canister was markedly different from the shape 

of the curve generated in subsequent tests. In two of these 

three cases the canister working capacity appeared to improve 

after the first few tests, and in the third case the canister 

working capacity appeared to decrease after the first few 

cycles. 

The durability canisters supplied by Ford and Chrysler 

both showed a lower working capacity in the initial tests than 

in subsequent tests. Figure Al shows two curves generated from 

the results of the tests on the Chrysler durability canister. 

The curve labeled "Initial" was generated by averaging the data 

taken in the first and second tests on the canister. The curve 

labeled "Average" is the average of the other two tests 

performed on that canister. The results of the first two tests 

were nearly identical to each other as were the results of the 

third and fourth tests. An examination of Figure Al shows that 

the purge curve representing the initial tests is different 

from that representing later tests in terms of both working 

capacity (lower for initial tests) and shape. A similar 

pattern is seen in Figure A2. Figure A2 shows results of tests 

performed on the durability canister provided by Ford Motor 

Company. An examination of the plots shows a lower working 

capacity and a distinctly different pattern of purge response 

in the initial test as compared with later tests. 

Results of the tests performed on the durability canister 

supplied by General Motors are shown in Figure A3. As in the 

tests on the Ford and Chrysler durability canisters, there is a 

noticeable difference between the initial tests and later 

tests. In this case, however, the working capacity observed in 

the initial test on the canister is greater than the capacity 

observed in succeeding tests. 

The results of the initial tests on the durability 

canisters raised two questions: 1) Why did the initial test (or 

tests) on these durability canisters produce different results 

than subsequent tests? and 2) Why did the capacities of the 

Ford and Chrysler canisters apparently increase over the 

capacity observed in their initial tests, while the capacity of 

the General Motors canister appeared to decrease? One possible 

explanation of these results is described in the following 

paragraph. 

An increase in canister working capacity with time 

suggests that the canister is being purged somewhat more fully 

than it recently had been, and that some hard to remove 

hydrocarbons are being stripped from the carbon. Conversely, a 

decrease in canister working capacity suggests that the 

canister was initially fairly well stripped, but that 

-106-
FIGURE A- 1 

INITIAL CURVES VS. AVERAGE CURVE 

I 

h-07

1 

-

(SLU "O 

3 

Q. 

O 

I 

0> > 

o ITlU 

ZJ 

O 

30 

28 

26 

24 

22 

20 

18 

16 

14 

12 

10 

8 

Chrysler Durability 

AVERAGE 

INITIA L 

0 20 40 

Purge Volume (cubic ft) 

J

2 
FIGURE A-2 

INITIAL CURVE VS. AVERAGE CURVE 

< — . 

(T> 

E 

o> V - * 

•o 

a> 

o> t~ 

3 

Q_ 

U 

I I 

T > 

o 

3 

E 

3 

u 

32 

30 

28 

26 

24 

oo 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

Ford Durability 

0 20 40 

Purge Volume (cubic ft) 

o 
o 

VO 

I 

UO 

E 

o> 

x> 

a> 

01 

3 

CL 

O 

I 

> 

3 

E 

3 

o 

FIGURE A- 3 

INITIAL CURVE vs. AVERAGE CURVE 

GM Durability 

Purge Volume (cubic ft) 
load/purge cycles are increasing the canister "heel." 

Therefore, the difference in the results on the Ford and 

Chrysler canisters versus the General Motors canister could 

have been due to the condition of the canister prior to 

testing. The results suggest that the General Motors canister 

was fairly well purged and the Ford and Chrysler canisters had 

more of a residual load. This was exactly the case. Each of 

these durability canisters (Ford, Chrysler, G.M.) was taken off 

of a vehicle that had completed its durability testing months 

earlier. As can be seen in Table Al, the Ford and GM vehicles 

were stored outdoors between completion of durability testing 

and the time of canister removal. (Though no information was 

available, it is safe to assume that the Chrysler vehicle was 

treated similarly). During that time the canisters were 

subjected to multiple diurnals and could be expected to have 

been thoroughly saturated. The difference between the Ford and 

the General Motors canisters is that General Motors attempted 

to "stabilize" the canister prior to delivering it to EPA. In 

this case, stabilization was achieved by driving the vehicle 

for four hours of AMA mileage accumulation with the evap 

canister onboard. This type of operation probably purged the 

canister quite thoroughly, and led to the difference between 

the plots of the initial tests on these canisters. 

It should be pointed out here that the Nissan canister was 

also subjected to multiple diurnal loadings before delivery to 

EPA. There was, however, no significant difference between the 

plot of the initial canister tests and later tests. 

B. Canister Aging 

Canister aging refers to the process by which an activated 

carbon bed loses working capacity with repeated load/purge 

cycles until a stabilized level is reached. On a molecular 

level, aging is the process by which certain molecules are 

adsorbed onto the carbon bed in such a way that they are very 

difficult to remove. Although it might be possible to remove 

them with an extensive amount of purging, the effective working 

capacity of the carbon bed under normal, in-use purge modes is 

reduced. The aged condition appears to develop gradually over 

repetitive load/purge cycles. 

One of the secondary goals of this program was to evaluate 

the magnitude of the aging effect. Because of the extensive 

amount of testing that would be required, it was outside the 

scope of this project to age a new canister from its virgin 

state to its stabilized level. It is unlikely that aging could 

be observed after the limited number of cycles possible during 

this test program. Figure A4 shows the first six tests 

performed on the new Ford canister. Although the first five 

-110-
FIGUR

E A- 4 

i 

V 

tn 

t o> "O 

9> Oi i_ 

3 

o 

I 

> 

o 

3 

E 

3 

o 

40 35 30 25 20 15 10 

FORD DURABILITY 

AGING 

0 

0 20 40 

Purge Volume (cubic ft) 

Tl CJ 
P.14 

tests tend to show a decrease in capacity with time, the sixth 

test shows the second highest working capacity in the group. 

This suggests that the difference between tests is being masked 

by test-to-test variability and no trend in working capacity 

can be established from this data. 

Because of the time involved in aging a virgin canister, 

an alternative method of evaluating the effect of canister 

aging was needed. One logical approach was to perform a series 

of tests on a new canister (as outlined above) and to compare 

the results of these tests with the results of a series of 

tests done on an aged canister of identical design. Figure A5 

shows four plots. The two upper curves were generated from the 

results of the tests on the new canister. The top curve is the 

purge record from the initial test on the virgin canister. The 

next curve is an average of the six plots shown previously in 

Figure A4. The lower two curves in Figure A5 were generated 

from the results of the tests on the Ford durability canister. 

The lowest shows the results of the first test performed on the 

durability canister after it was received by EPA and the final 

plot (labeled "durability average") shows the average of all 

the tests performed on the durability canister. 

Figure A5 illustrates a few significant points. First, 

the original test on the virgin canister shows the highest 

working capacity of all the tests performed on the new and the 

durability canisters. Second, the average working capacity 

observed in the tests on the new canister is higher than the 

average working capacity of the durability canister. This 

suggests that some aging has taken place. Finally, the first 

test on the durability canister showed the lowest working 

capacity of all the tests, suggesting that the canister may 

have "aged" more than the average durability plot shows and 

that the repeated bench purge performed in this program has 

restored some capacity. Although the results of these tests 

are not a definitive measure of the effects of aging, the 

results do suggest that the durability canister has been aged 

to some extent. In this case, the durability canister appears 

to have lost about twenty percent of its original capacity. 

C. Purge Rate 

Another secondary goal of this test program was to 

evaluate the effect that the rate of purge air flow has on 

canister stripping characteristics. If the rate of hydrocarbon 

stripping is independent of purge air flow rate then the 

cumulative amount of hydrocarbon purged from the canister would 

be a constant function of the volume of purge gas passing 

through the canister. Traces of cumulative hydrocarbon purged 

versus volume of purge air pulled through the canister would be 

-112-
I 

LA 

t o> 

T> Q> Oi i~ 

3 CL 

O 

I d> _o 

3 

E 

3 

o 

40 35 30 ^ 5 

'.0 

1 0 

0 

FIGURE A- 5 

CANISTER AGINC 

New Ford vs. Ford Durability 

0 

>0 

40 

Purge Volume (cubic ft) 
P.16 

similar regardless of the purge air flowrate. However, because 

desorption is a mechanical process and the molecules in 

refueling vapors range widely in size, a dependence between 

purge air flow rate "and the rate of hydrocarbon removal could 

be possible. In this program, an attempt was made to determine 

whether the amount of HC stripped from an activated carbon 

canister is a constant function of the volume of purge gas 

pulled over the bed, independent of purge air flowrate. 

The effect of purge air flow rate on hydrocarbon stripping 

was investigated by performing three sets of purge tests on the 

Ford durability canister. Each set of tests was performed 

under identical conditions of purge, except that the purge air 

flowrate was different for each set of tests. The flowrates 

chosen were nominally 1/2, 1, and 2 cfm. Although these values 

may be somewhat high for current evaporative emission control 

system purge flowrates, it seems that flowrates of this 

magnitude may be necessary for some evap/refueling control 

systems. 

As noted in the discussion of the canister weighing 

procedures, the results of this series of tests had to be 

corrected to account for time spent weighing the canister. For 

each test, it was assumed that the canister was purged for 55 

seconds, and then the canister was disconnected and weighed. 

The weighing procedure was estimated to take approximately ten 

seconds. Therefore, ten seconds were substracted from the 

cumulative total for each canister weighing. Table A3 shows 

the corrected results of the tests used in the evaluation of 

the effect of purge rate on hydrocarbon stripping (tests El -

E6). Each column represents the average of the two tests done 

at the purge rate shown at the top of the column. 

The results of the tests designed to evaluate the effects 

of purge rate are plotted in Figure A6. Each curve represents 

the average of the tests done at one flowrate as marked on the 

figure. If the rate of hydrocarbon desorption were 

proportional to purge air flow rate, one would expect to see a 

pattern in the purge curves in Figure A6. Specifically, one 

would expect to see a steeper purge curve, and possibly a 

greater working capacity in the tests performed at the highest 

flowrate. An examination of Figure A6..shows that no such 

pattern is apparent. The curve generated from results of the 

tests performed using the lowest flowrate falls between the 

curves of the tests done using the higher flowrates. In 

addition, all of the tests are very similar and the differences 

between them are certainly within the range of test to test 

variability. Therefore, within the range of purge rates 

examined here, the amount of hydrocarbon stripped from the 

carbon bed is a function of the volume of purge air pulled over 

the carbon bed and • is basically independent of purge air 

flowrate. What will happen at higher purge rates is unclear. 

-114-
P.17 

TABLE A3 

CORRECTED AUERAGE PURGE HISTORIES 

FORD DURABILITY CANISTER 

Volume of Purge 

Air <ftA3) 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

15 

20 

25 

30 

35 

40 

50 

1.0 

0 

14.5 

18.2 

20.3 

21.7 

22.8 

23.6 

24.3 

24.8 

25.3 

25.7 

27.2 

27.6 

28.2 

28.6 

29.0 

29.4 

30.2 

Purge flir Flow Rate 

0.5 

0 

15.9 

19.5 

22.2 

23.6 

24.2 

25.0 

25.4 

25.6 

25.9 

26.1 

27.4 

27.8 

28.4 

29.0 

29.6 

30.1 

31.0 

2.0 

0 

17.0 

20.4 

21.8 

23.3 

24.6 

25.4 

26.0 

26.5 

26.9 

27.3 

29.0 

29.8 

30.4 

30.8 

31.2 

31.5 

32.3 

-115-
FIGUR

E A-6 

I-" 

<T> 

1 

.—-

E o> "O o> 

3 0. 

X tive 

o 

—_3 

r-Cun 

34 32 30 28 26 24 4 L X- 20 18 16 14 12 10 

8 

6 

4 

2 

0 

EFFECT OF PURGE RATE 

Ford Durability 

2 . 0 

1.0 

20 

Purge Volume (cubic ft) 

40 

T l CO 
P.19 

D. Temperature of Purge 

Canister temperature can effect both the loading and 

stripping of carbon beds. Increased temperature is equivalent 

to an increase in the kinetic energy of the molecules in the 

gas. An increase in the kinetic energy of air and hydrocarbons 

associated with a temperature increase in an activated carbon 

bed should eause a decrease in the amount of hydrocarbon 

adsorbed but should also aid the desorption process. This test 

program was focused on the process of purging hydrocarbons from 

a carbon bed, and therefore the temperature/loading 

interactions are not addressed. The effect of canister 

temperature on purge was tangentially investigated, however. 

Fourteen tests were performed on the new Ford canister. 

In the first six tests, both the canister ambient and purge air 

temperatures were maintained at 95°F. In the thirteenth and 

fourteenth tests, the canister ambient and purge air 

temperature were held at 75°. Figure A7 shows two plots; one 

representing the average of the results of the tests in which 

canisters were purged at 95°, the other representing the tests 

using a 75° purge. 

From the graph it appears that temperature has a distinct 

effect on purge. There are circumstances of the testing, 

however, which suggest that the results may be confounded. As 

mentioned above, the tests in which the canister was purged at 

95° were the first six tests done on the new canister. The 

tests in which the canister was purged at 75° were the 13th and 

14th tests performed on that canister. Although it is expected 

that extensive aging would not be observed after a limited 

number of cycles, any aging effects would bias the results of 

these tests toward the pattern observed in Figure A7. 

Although there is a possibility that the results of these tests 

may be somewhat confounded by aging effects, it appears that 

the increased purge temperature did have some effect on the 

amount of hydrocarbon that was stripped from the canister by a 

given volume of purge air. 

E. Representative Curves 

As was stated previously, the main . goal of this test 

program was to evaluate the purge response characteristics of 

several activated carbon canisters when loaded with refueling 

vapors. This was done by loading each canister to or near the 

breakthrough point with refueling vapors, and then pulling 

hydrocarbon-poor air over the activated carbon bed and 

monitoring the canister mass change as a function of purge air 

flow. The purge air flow rate and temperature of purge were 

generally held at 1.0 cfm and 95°F, respectively, during the 

-117-
FIGURE A-7 

EFFECTS OF TEMPERATURE 

75 deg vs. 95 deg 

i 

I-1 

OO 

I 

it> 

E 

Oi 

« — ' 

X> 

a> 

o> 

i_ 

3 

Q_ 

O 

I 

a> 

> 

3 

E 

3 

u 

Purge VOLUME (cubic ft) 
'.21 

canister purge sequences.* Average curves were then generated 

for each canister. The average curves for the four evap 

canisters from durability vehicles are shown in Figure A8. 

Figure A9 shows the- curve for the EPA canister, which was 

designed and built as a refueling canister and has a working 

capacity much larger than the evaporative canister capacities. 

The plots of the average curves are valuable in that some 

understanding of the differences in the purge response of the 

various canisters (as measured by the differences in the shapes 

of the various curves) can be gained. It is difficult to use 

the curves to fully evaluate the performance of the various 

canisters however, because some of the differences are simply 

due to the fact that the canisters are not all of one size. 

Although there are several variables other than size that may 

affect the performance of the canisters (carbon type, shape, 

and interior configuration, to mention a few), this program was 

not designed to investigate the effects of the differences in 

canister designs. The differences in the curves due only to 

differences in size can be effectively eliminated, however. 

The differences in canister sizes were eliminated by 

normalizing the average curves presented in Figures A8 and A9 

by canister volume. In scaling the canister curves, the 

characteristic shape of each curve was preserved, but the purge 

curves were scaled to represent the results expected for a one 

liter canister. The normalization was done by dividing the X 

and Y components of the points on the average curve by the 

canister volume (in liters). The use of this scaling technique 

implicitly assumes that a small canister designed exactly like 

a large canister (in terms of length to diameter ratio, 

interior configurations, carbon base, etc.) would demonstrate 

stripping characteristics (for equivalent amounts of activated 

carbon) identical to those of the large canister. For example, 

a half-sized canister purged half as much would release half 

the hydrocarbons that a full sized canister would. 

The volume-normalized purge curves are shown in Figure 

A10. The curves are labeled with the source (or supplier) of 

the canister as well as with the base material used in the 

production of the activated carbon. Several features of Figure 

A10 are worthy of discussion. The first thing that is 

noticeable in Figure A10 is that the curve generated from the 

Three purge rates were used in the tests on the Ford 

durability canister, but as discussed in the section on 

the effects of purge rate, this had little impact on the 

results. 

-119-
FIGURE A- 8 

DURABILITY CANISTERS 

AVERAGE CURVES 

i 

E o 

i 

E 

01 

•o 

a> 

o> 

3 

Q. 

O 

I 

a> 

> 

3 

E 

3 

o 

Purge Volume (cubic ft) 
FIGUR

E A-9 

1 21M -

(0 

E 

«

o * > TJ urge Q_ 

O 

I tive cs 

3 Cum 

170 

160 

150 

140 

130 

120 

110 

100 90 80 70 60 50 40 30 20 10 

0 

EPA CANISTER 

Average Curve 

^L. 

20 

40 

Purge Volume (cubic ft) 

CO 
FIGURE A-1 0 

a> 

I 

M 

to 

to 

I 

\ 

tn 

E 

o *—' 

a> 

Oi 

k_ 

3 

Q_ 

4> 

> 

•*-• 

O 

3 

t 

3 

o 

40 

35 

30 

25 

20 

15 

10 

REPRESENTATIVE CURVES 

Normalized by Canister Volume 

0 -j 

0 10 20 

Purge Volume (cubic feet/liter) 

30 
results of the tests on the Chrysler canister is isolated from 

the rest of the curves. An examination of the information on 

canisters presented in Table Al reveals nothing extraordinary 

about the Chrysler canister. The activated carbon used in this 

canister and the canister construction appear very similar to 

the material and construction of the other canisters tested in 

this program. Chrysler was unable to provide information on 

the history, of the canister, and there may have been some 

unusual treatment of the canister which lead to these 

unexpected results. Although no explanation for the 

performance of the Chrysler canister is apparent, it is clear 

that the results of the tests on this canister fall well 

outside of the range predicted by the tests of the other 

canisters. Because the results of the tests on the Chrysler 

canister cannot be explained by the information available to 

EPA, the curve for the Chrysler canister will not be included 

in any further analysis of the results. 

The main feature of interest in Figure A10 is that it 

shows the differences in the purge response characteristics of 

similarly sized canisters of several designs. The Nissan 

canister apparently releases hydrocarbons relatively grudgingly 

during the initial stages of purge, but shows a less drastic 

decay of hydrocarbon stripping as the purge process continues. 

The Ford canister lies' at the opposite end of the purge 

response spectrum. This canister type apparently gives little 

resistance to hydrocarbon removal during the initial stages of 

purge, but the hydrocarbon stripping rate drops quite rapidly 

thereafter. The other two curves (the G. M. and EPA curves) 

fall within these extremes. 

Also shown in Figure A10 is the type of carbon used in 

each of the canisters tested. Looking at the right side of 

Figure A10 it appears there might be a distinct purge curve for 

each carbon type. Upon examining the left side of the figure, 

however, it can be seen that the Ford (coal base) and EPA 

(wood) curves are almost identical through the early stages of 

purge. The Nissan curve is distinct throughout its purge 

history, however, and there may be some differences in the 

fundamental absorption/desorption characteristics of coconut 

based carbons. The comparison of purge curves by carbon type 

should not be emphasized, however, because there are several 

other variables in canister design that could not be separated 

from carbon type by this experimental design. 

F. . Canister Temperature During Purge 

The canister listed in Table Al under "EPA" was designed 

and built for refueling emission control tests. When this 

canister was loaded with activated carbon, a thermocouple was 

installed in the canister so that internal canister 

-123-
temperatures could be measured as needed. The thermocouple was 

used to monitor internal canister temperature during two of the 

purge sequences done on the refueling canister. 

The trace of canister temperature as a function of the 

volume of purge air pulled through the canister for one of 

these tests is shown in Figure All. As can be seen from the 

trace, the desorption process absorbs heat. The temperature of 

the canister drops from its peak (measured at 135°F immediately 

after loading) down to its lowpoint (70°F, 6°F below the 

ambient) in under 10 minutes. The canister temperature then 

climbs back to the ambient in about ten minutes and remains 

near the ambient throughout the remainder of the purge. 

This information is significant for two reasons. First, 

as hydrocarbon is stripped from the canister, the temperature 

of the canister falls rapidly. The decrease in temperature 

could tend to inhibit the removal of more hydrocarbons. 

Second, as noted above, the canister temperature can fall below 

the ambient during the purge and in certain situations the 

internal canister temperature could fall below the dewpoint 

resulting in condensation inside the canister. Although this 

situation would probably not arise with any regularity, 

condensation inside the canister could occasionally occur. 

G. Conclusions 

As stated in the introduction to this paper, this test 

program had one primary goal and several secondary goals. The 

primary goal of the program was to evaluate the purge response 

characteristics of several canisters of different designs. 

Part of this evaluation was the development of "purge curves" 

which could be used in the development of a procedure for 

evaluating the purge capability of onboard refueling emission 

control systems. The secondary goals of the program were to 

investigate the effects of aging, purge air flow rate and purge 

air temperature oh hydrocarbon stripping characteristics. In 

the course of gathering data to address the topics mentioned 

above, information was also obtained on internal canister 

temperatures during the purge process. Although this test 

program had a limited scope several useful conclusions can 

still be drawn from the data. 

The conclusions that can be drawn concerning the 

secondary goals of the program were stated as part of the 

analysis of results. The results of the tests to develop 

representative curves for the various canisters merit some 

further discussion, however. The remainder of this section 

describes the manner in which the representative curves can be 

-124-
FIGURE A-11 

1 40 

to 

I 

W 

•V 

T3 

UJ 

DC 

Z> 

I -

< 

QC 

UI 

CL 

2 

ui 

CANISTER TEMPERATURES 

DURING PURGE 

100 

TIME (min ) 
used in the development of a refueling test procedure, and some 

recommendations for improvements in the experimental design 

used in this program. 

A test procedure designed to evaluate the effectiveness of 

onboard control systems must test the ability of the system to 

provide capacity for the storage of refueling emissions. In 

the case of _a system that uses activated carbon as the storage 

medium (which is expected to be the case), this involves 

stripping hydrocarbons from the activated carbon bed by pulling 

hydrocarbon poor air across it. A basic understanding of the 

relationship between hydrocarbon stripping and purge air flow 

is needed in order to develop a procedure which adequately 

tests the purge capability of the control system. The main 

purpose of this test program was to develop a series of purge 

curves which could be used to represent the range of purge 

response patterns that could be expected of onboard control 

system canisters. 

The representative purge curves developed in this program 

are shown in Figure A10. These curves represent the expected 

performance of one liter canisters of the same design as those 

used in the test program. As discussed in the analysis of 

data, the curve for the Chrysler canister falls well outside of 

the range of curves generated from the data from the other 

canisters. Since there is no evidence to suggest that the 

Chrysler canister is radically different from the other 

canisters in terms of material or design, the curve generated 

for this canister is probably not representative of this 

canister's typical performance. 

The remaining curves fall within a relatively narrow band 

in Figure A10. Although the curves are closely grouped 

spatially, there are significant functional differences across 

the curves in that range. The curve representing the 

performance of the Ford canister rises quite sharply and shows 

a relatively clear breakpoint early in the purge process after 

which the curve flattens out. The curve generated from tests 

on the Nissan canister is less steep in the initial stages of 

purge and tends to break over more gradually. The curves for 

the Ford and Nissan canisters are the most dissimilar of those 

in Figure A10 (excluding the Chrysler curve). Because these 

curves are the most dissimilar, they can be used to represent 

the range of response patterns expected from activated carbon 

canisters. Therefore, these two curves were used in the 

analysis performed in the development of the refueling test 

procedure. 

-126-
P.29 

References 

1. "Refueling Emissions from Uncontrolled Vehicles," 

D. Rothman and R. Johnson, EPA-AA-SDSB-85-6, U.S. EPA, OAR, 

OMS, ECTD, July, 1985. 

2. "Draft Recommended Test Procedure for the 

Measurement _ of Refueling Emissions," L.D. Snapp, 

EPA-AA-SDSB-85-5, U.S. EPA, OAR, OMS, ECTD, July 1985. 

3. "Subpart C - Emission Regulations for 19XX and Later 

Model Year New or In-Use Light-Duty Vehicles and New or In-Use 

Light-Duty Trucks; Refueling Emissions Test Procedure," Draft, 

U.S. EPA, OAR, OMS, ECTD, July 1985. 

4. "Summary and Analysis of Data From Gasoline 

Temperature Survey Conducted by American Petroleum Institute," 

Radian Corporation, May 1976. 

5. "An Assessment of EPA's Certification Procedure for 

Onboard Refueling Emission Control Systems," Technical note 

prepared for American Petroleum Institute by Robert Kausmiez, 

Radian Corporation, February 19, 1986. 

6. "Fuel Volatility Trend," Final Report, Letter from 

Bruce B.Bykowski, Southwest Research Institute to Craig Harvey 

and Amy Brochu, U.S. EPA, September 28, 1984. 

-127-