P.1 

OAR Box 1830 

Prepped by Ollie Stewart 

Document Number: 

235) IV-B-28 

Docket Number: 

A-87-11 

Printed 11/13/2008 9:00:23 AM Sheet 235 of 236 
P.2 

V 

J"**% 

w 

JAN 1 4 1994 

\ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

IN ARB©RTrTilTDHXG5RI«1 48105 

MEMORANDUM 

OFFICE OF 

AIR AND RADIATION 

SUBJECT: 

FROM: 

THRU: 

Determination of Flow Rate for Vapor Vent Line 

Leak in Onboard Vapor Recovery System 

Br 

Spe 

yan J. Manning, Mechanical Engineer 0. (V /VL \ 

ecial Regulatory Projects Branch ^V^ f j ' {AfMl^^<U 

TO: 

Glenn W. Passavant, Branch Chief 

Special Regulatory Projects Branch 

Docket No. A-87-11 

The purpose of this memo is to discuss the methodology used to 

determine the maximum leakage rate in the onboard vapor recovery 

vent line that could occur before the onboard diagnostic (OBD) 

system indicated a problem. A hole larger than 0.04 inches would 

be detected as a failure by the OBD system and would require repair; 

therefore, we determined the amount of vapor that could leak out of 

the vent line during a refueling without OBD detection. 

For this analysis, the leak-hole was assumed to be an orifice 

with a pressure difference across it. We assumed that the 0.5 inch 

diameter-vent line had a constant vapor flow rate of 12.5 gallons 

per minute through it and a pressure inside it of 10 inches of water 

(or 52 lb/ft2) greater than the ambient air (atmospheric pressure) . 

As mentioned above, the orifice was assumed to have a diameter of 

0.04 inches. The fluid in the vapor vent line was assumed to be a 

40 percent gasoline vapor and 60 percent air mixture. The density 

of the mixture was determined to be 0.115 lb/ft3 at a temperature 

of 80 degrees Fahrenheit. 

The leak rate was determined using an equation for the flow of 

fluids with constant density through an orifice: 

v0 = C0*[2g(Pi " P0)l/P] 1/2, 

where 

v0 ••= velocity through the orifice, 

C0 = orifice coefficient, 

g = gravitational acceleration, 

p L = pressure inside vent line, 

p0 = atmospheric pressure, 

p = density. 
P.3 

Since the Reynolds number at the orifice was greater than 20,000, 

we used a constant orifice coefficient of 0.61. The leak rate is 

shown below. 

v0 - 0.61 * [ ( 2 * (32.2 ft/s2) * ( 52 lb/ft2) ) / 0.115 lb/ft3]

1/2 

v0 = 104 ft/sec. 

The corresponding volumetric flow rate is 0.41 gal/min (flow rate 

= v0 * Orifice area). 

Furthermore, four grams of gasoline vapor is equivalent to 

one gallon of vapor. Thus, for a two-minute refueling (about 20 

gallons), 3 grams of gasoline vapor is projected to leak through 

a 0.04 inch diameter vent-line hole into the atmosphere. 

This calculated value is supported by testing performed by 

the American Petroleum Institute. In that testing they measured 

the mass of vapor pushed through a 0.05 inch orifice from the 

fuel tank during a refueling event. The attached letter from 

Exxon indicates that in all but one case, the emissions from the 

tank were 3 grams or less regardless of the RVP of the fuel. 

Thus, the vapor flow rate from a leak undetected by an OBD 

system would be 3 grams or less per refueling, depending on the 

amount of fuel dispensed. 

Attachment 
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SENT.BY:LINDEN, NJ ;12-14-93 ;10:21AM ; EXXON RES & ENG-PRD-+ 313 741 7816;# II 3 

E^pN RiStlARGH AND iNOINEIRING COMPANY 

P.O. BOX 51, LINDEN, NEW JERSEY 07036-O051 

PRODUCTS RESEARCH DIVISION 

CH. Martinez 

Dlrwtor 

Fuels RsMansh Uboratmy 

December 13, 1993 

Mr. G. Passavant 

EPA Motor Vehicle Emissions Laboratory 

2S6S Plymouth Rd. 

Ann Arbor, MI 481905 

Dear Glenn, 

I was able to retrieve the following data on the weight gain of the production evaporative 

canister during a refueling event (see attached sheet). The four vehicles are the four vehicles 

described in my SAE papers. The refueling conditions are those described in my SAE papers (i.e., 

not the same conditions for the dispensed and tank temperatures). The only modifications to the 

vehicles was the installation of thermocouples to measure tank vapor and liquid temperatures. 

Otherwise the vehicles were production vehicles. The events are not necessarily in order but are as 

I retrieved them from the boxes. 

The data indicates to me that the weight gain of the production evaporative canister for these 

four vehicles during a refijeling event are between 0 and 3 grams and very much vehicle dependent. 

If there are any questions, please call 

Sincerely, 

George Musser 

R = 93% 908 474 2335 12-14-93 11:30AM P002 #46 
P.5 

:LINDEN, NJ 

Date Vehicle 

Dec. 1987 Buick 

Apr. 1988 Ford 

Apr. 1985 Pontiac 

Apr- 1985 Dodge 

;12-14-93 ;10:22AM 

Te^t Fuel RVP 

psi 

9 

9 

9 

9 

9 

9 

12 

9 

9 

10.5 

12 

10.5 

12 

9 

9 

10.5 

12 

12 

9 

10.5 

12 

9 

12 

10.5 

12 

9 

10.5 

12 

9 

10.5 

10.5 

9 

12 

9 

12 

9 

12 

10.5 

; EXXON RES & ENG-PRLV 

- 2 -

Evaporative Canister 

Weight Gain 

grams 

2.3 

2.2 

2.0 

0.0 

1.0 

1.0 

3 

2 

2 

1 

0 

2 

3 

2 

2 

1 

2 

2 

1 

1 

3 

1 

J 

1 

1 

1 

0 

I 

1 

1 

1 

1 

1 

0 

1 

1 

1 

12 

313 741 7816;# 3/ 3 

R = 97% 908 474 2335 12-14-93 11:30AM P003 tt46