Assessment of Light Duty Vehicle
Evaporative Emission Control Technology
by
Eric Ellsworth
Environmental Protection
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Standards Development and Support Branch
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Assessment of Light Duty Vehicle
Evaporative Emission Control Technology
by
Eric Ellsworth
Notice
Technical support reports for regulatory action do not
necessarily represent the final EPA decision on regulatory
issues. They are intended to present a technical analysis of
an issue and conclusions and/or recommendations resulting
from the assumptions and constraints of that analysis. Agency
policy constraints or data received subsequent to the date
of release of this report may alter the conclusions reached.
Readers are cautioned to seek the latest analysis from EPA
before using the information containing herein.
Environmental Protection Agency
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Emission Control Technology Division
Standards Development and Support Branch
July 1975
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Table of Contents
Pages
I. Introduction. ...,.....,..,,....«.. j_
II. Leakage . . , ,..,..,.. i
III. Fuel Tanks. . ...,., «..».. 2
IV. Air Induction System 3
V. Storage Canister, , .,......,. 5
VI. Fuel, ..,.,,,.,........,.,,..,. 6
Vir. Control System. ,,,.,,,»,,,,.,,..,,, 7
VIII. Conclusion. ..,.,,..,.,,.,......,. 8
Appendix A, .,,,.,..,. , ........... 9
References for Evaporative Losses ........... 13
Figures ....,..,,.,,..........,, 14
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I. Introduction; The current federal test procedure for evaporative
emissions measurement for light duty vehicles, the canister method, is
expected to soon be replaced with a revised test procedure which involves
the use of a SHED (Sealed Housing for Evaporative Determination) to col-
lect the evaporative emissions rather than the currently used activated
carbon canister. The SHED test procedure was first proposed by the
Department of Health, Education and Welfare in 1967 and later evaluated
by General Motors, (Findings of GM*s early evaluations were reported in
SAE papers, numbers 680125 and 690502). This revised test procedure will
have a major impact on the measured effectiveness of evaporative emission
controls in use today on light duty vehicles, While the data available
using the SHED test procedure (Fig. 1) (3) generally indicate excessive
evaporative emissions, even from "controlled" vehicles, recent results
indicate that there are a limited number of production vehicle types with
evaporative control systems capable of passing the six gram standard which
California has proposed for 1977 (Fig. 2). Most current devices in use
consist of a storage canister used for the storage of evaporated hydrocarbons,
and associated tubing which connect the major sources of evaporative emis-
sions with the storage canister. (See Appendix A for a detailed review of
the types of evaporative control systems currently being used by
the automotive industry.) This report is an assessment of current control
technology and is not intended to represent the technical limits of evapora-
tive emission control. The report first addresses the basic sources of
evaporative emissions, then discusses the influence of fuel composition, and
finally addresses evaporative emission control from a total control system
standpoint,
IT. Leakage; Leakage of fuel system components occurs because of the
deterioration of those components through abuse, poor material selection
or improper manufacturing of components. The Department of Transportation
has recently (effective September 1, 1975) introduced Federal Motor Vehicle
Safety Standard (FMVSS) 301, for 1976 model year, which requires a vehicle's
fuel system to maintain its integrity through a 30 mph crash and subsequent
roll oyer_._ Compliance with this safety standard should result in an improve-
ment to the integrity of fuel system components and their interfaces, so
leakage may cease to be a significant source of evaporative emissions.
Abuse to the fuel system centers around the gas cap and its mating
sealing surface on the filler neck. This is indicated in the EPA sur-
veillance data gathered in the FY 73 program from Los Angeles and Denver.
From random samples totaling 40 vehicles approximately five percent of
the vehicles tested had leaks and these leaks were all at the gas cap.
During recent SHED testing at the EPA Motor Vehicle Emission Laboratory one
vehicle in the 6 vehicle test fleet had a gas cap failure. In attempting
to repair the vehicle, several gas caps had to be purchased'in order to find
one which did not leak. An inspection of the gas caps revealed a variance
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in distance from the locking lugs to the gasket. Caps displaying the
greater distances were the ones which leaked because sufficient loads
were not .applied to the gasket to maintain a leak free joint. Variance
from_cap to__cap_.could be the result of poor quality control at the
manufacturing plant or improper tolerances as a result of the design.
To reduce the impact of Inadequate quality control and tolerance
stack-ups (the sum of tolerances on mating parts) General Motors has
developed a new design gas cap which is used on many intermediate and
full size vehicles beginning in the 1975 model year. This cap has two
features which will improve its reliability. First, the gasket is made
of a low durometer (soft) material. This provides a better seal because
a soft material will conform to irregularities on the sealing surface
more readily. Second, the cap has a torque limiting function which pro-
tects the soft gasket from excessive loads, thus extending the life of the
gasket.
III. Fuel Tanks; The following equation is a mathematical simulation
of vapor losses from a fuel tank due to thermal expansion and vapor
pressure changes:
G P 454W ^520 "1 p"
[690-4Mjpa -
f(Pt - P) v"[ - f(Pt- - P)v"|
(4)
G = weight of hydrocarbons lost, g
W = condensed vapor density, Ib/gal
M = molecular weight of hydrocarbon, Ib/lb mol
p = vapor pressure of gasoline at T, psia
p" = average vapor pressure, psia, (p^ + P£) ^ 2
P = total pressure, psia
v = volume of vapor space,
T = vapor temperature, °F
1 = initial state
2 = final state
t = tank
a = atmosphere
By manipulation of total tank pressure, temperature, and vapor space
terms for the final state expression, a reduction in tank losses can be
achieved. When vapor space and temperature decrease* the amount of fuel
evaporated decreases. An increase in tank pressure will result in a de-
crease in evaporative emissions.
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To reduce fuel tank temperature, the exhaust system could be rerouted,
fuel tanks could be relocated, a heat shield could be placed between the
tank and the exhaust system, or the fuel tank could be insulated. The
last option only produces the desired effect in short driving cycles.
After an extended engine-on mode the Insulation may result in the genera-
tion of equal or greater quantities of fuel vapor than the non-insulated
fuel tank because the tank will cool off more slowly, thus maintaining
the driving force for a longer period of time,
A fuel tank with internal baffles would generate fewer emissions than
a conventional tank. These baffles should be placed perpendicular to
the natural convection currents in the tank. By breaking up the con-
vection currents a severe temperature gradient is established in the fuel
tank with warm fuel on the bottom, cool fuel and cool fuel vapors at the
top. The lower the vapor temperature, the smaller the evaporative losses
3),
The vapor space could be reduced by using a fuel tank with a bladder
which would contain the fuel (Fig.. 4), As a tank is emptied the bladder
would shrink and when it is filled the bladder would stretch to the maximum
size allowed by the tank. By stretching the bladder to accommodate
particular fuel fill; in essence, the fuel tank is always full. A full
tank has no vapor space and very little evaporative losses (Fig. 5) (5).
Vehicles with fuel return lines have higher evaporative losses from
the tank. As a result of the pumping process and exposure to engine
compartment and exhaust heat, the temperature of the fuel in the return
line is raised. When this hot fuel is injected into the tank, the temper-
ature increase and the agitation create excessive losses.
All the control technology for steel fuel tanks can be applied to
non-metallic tanks. Plastic fuel tanks are inherently insulated due
to the material's low thermal conductivity. It should be noted that
many plastics are porous and will allow gaseous hydrocarbons to escape.
With the proper selections of materials or the proper surface treatment
the porosity can be eliminated.
It is believed that the only fuel tank modification that has been
discussed above that may have an adverse effect on vehicle performance
is the elimination of fuel return lines. These lines are required on
vehicles that have hot start problems or fuel injection. Relocation
and rerouting can be most efficiently handled during a vehicle's styling
change or new model design,
IV. Air Indue t ion Sy s t em ; The air induction system containing the air
cleaner, carburetor and intake manifold is the next area that will be
discussed from the aspect of reducing its contribution to overall
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evaporative emissions. The air cleaner is being utilized as a storage
compartment for hydrocarbons emitted from the Internal vents of the
carburetor. The air cleaner is at best a poor storage compartment
because its design allows high flows with minimum restriction. In a test
run by the Air Resources Board of California a 1974 AMC Ambassador with
air cleaner storage averaged 12 grams loss per SHED test. When the
vehicle was modified by venting the carburetor bowl to the storage canis-
ter the losses were reduced to an average of 3,3 grams per test (3). The
air cleaner*s performance as an evaporative control device could be
improved by including a filter element which would adsorb the hydrocarbons
or restrict their flow out of the air cleaner. Internal baffling would
be another method by which the evaporative emissions could be retarded
from leaving the air cleaner (Fig, 6).
The conventional venturi carburetor is the most prevalent device
for introducing fuel to achieve a combustible mixture. The internal
vents of a carburetor provide many sources for fuel vapor to escape.
Valves could be added which would close idle ports, off-idle ports, primary
and secondary metering circuits and acceleration pump nozzle when the
engine is off. This would force the fuel vapor through an external vent
and into a storage canister. Reducing the number of passages in the
carburetor by using a common passage would reduce the heated surface area
of the fuel. The addition of an external bowl vent (certain carburetors
in production have this feature) along with the reduction in number of
internal passages and valving for these passages should be considered as
a single system.
Carburetor losses can be lowered by lowering the temperature to which
the carburetor is exposed (Fig. 7) (6). This reduction can be achieved by
heat shielding, improved air flow through the engine compartment, and in-
sulating the carburetor body. Heat shielding and insulating will have
the same effects and drawbacks as discussed in the fuel tank section
of this report. Increased air flow has an indirect effect by increasing
heat dissipation,thus lowering peak operating temperatures and peak hot
soak temperatures. Engine-off hot soak temperatures could be reduced
by using a thermostatically-controlled electric fan to force air through
the engine compartment.
Reducing fuel bowl volume lowers evaporative losses (6). As the
quantity of fuel in the bowl decreases, the quantity of fuel which would
be distilled at peak bowl temperature is reduced, which in turn is a
reduction in overall carburetor losses (Fig. 8),
Plastic carburetor bodies are being used on a few late model vehicles.
These plastic bodies may present unique problems due to permeability
exhibited by some plastics and low thermal conductivity. If the proper
material or surface treatment is not used, fuel vapor will escape through
the walls of the carburetor body. The low thermal conductivity will tend
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to reduce peak carburetor bowl temperature which will reduce evaporative
emission (Fig« 7), but the bowl will cool down more slowly. If this
cool down time is long enough, the advantage gained by a lower bowl
temperature will be nullified.
Carburetor sealing may become a major constitutent of the deterior-
ation factor as all other sources are reduced and/or eliminated. As the
vehicle ages, gaskets and seals in the carburetor wOt..lose their resiliency
and shafts running through the body of the carburetor will become worn
causing loss of fuel vapor to the environment at these points.
Briefly looking at Intake manifolds, they could be designed to help
dissipate heat from the carburetor, and/or the-manifold could be used as
a storage chamber for hydrocarbons from the carburetor, thus reducing the
load on the storage canister (Fig. 9).
Manufacturers are now offering types of fuel injection, electronic
or mechanical, as options on certain models. This device may significantly
reduce hydrocarbon losses from the induction system. The only problems
that may need resolution are the requirement for a fuel return line, which
was discussed in the tank section, and injector design. Currently, the
injectors are on-off valves activated by an electronic or mechanical
signal. If these injectors allow fuel to seep-by due to wear or poor
design, the evaporation losses could be significant. However, the
potential for complete control of hot soak losses exists with fuel
injection systems.
Analytically, any modifications that are made to the venturi car-
buretors will require a major undertaking by the manufacturers. Changes
to fuel flow and metering can affect exhaust emissions and vehicle per-
formance. Other modifications mentioned, such as improved gasket life,
the addition of baffles to an air cleaner and improved heat dissipation,
will require less design and development because their impact on exhaust
emissions and vehicle performance may be insignificant.
V. Storage Canister; A canister containing activated carbon is the
primary storage device for the evaporative emission control system. Fuel vapors
that are exposed to the activated carbon bed are adsorbed on the
surface of the carbon. A secondary storage mechanism is residency. This
occurs when carbon particles in an area are saturated and fuel vapor
can no longer be adsorbed on the surface of the carbon. At this point,
hydrocarbons remain in a gaseous state in the spaces between carbon
particles. As the requirement for evaporative emission control increases,
the capacity of the carbon canister will have to increase. One of the
obvious ways to do this is to increase the quantity of activated carbon
in the canister. Another way ±a to use a more efficient adsorber, one
that will adsorb more grams of fuel vapor per gram of adsorbent.
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Storage canisters may also be emitters of hydrocarbons. Open bottom
canisters have ahhigh concentration cloud of hydrocarbons at the bottom
of the canister. This may be a result of heavier hydrocarbons drifting
through the carbon bed. This situation can be remedied by placing a
semipermeable membrane at the bottom of the carbon bed. The membrane
would retard the flow of hydrocarbons from the bottom of the canister
while allowing the fuel tank to breath and the canister to purge (Fig.
1QJ. Another solution would be to install a bottom on the canister
with, a vent tube that has its opening at the same level as the top
of the carbon bed (Fig. 11).
The emissions from a storage canister can be reduced, significantly
in some cases, by providing for an adequate purging of the storage
can,$ster during the engine^on modes of vehicle operation. This purging
of the storage canister . will remove the hydrocarbons from the canister's
carbon bed. If a storage canister experiences an inadequate purge it
may not have sufficient capacity to retain all the fuel vapors generated
after the engine is turned off. Inadequate purging may ?»#. a result of poor
evaporative emission control system design and/or poor malCn^na^TOi'' Poor.
maintenance of the storage canister filter, if so equipped will have a
detrimental effect on storage canister purge rate. As the filter becomes
clogged the air flow through that filter is reduced which in turn reduces
the storage canister's purge rate.
It is believed that modification to the storage canister will have
an indirect effect on vehicle exhaust emissions. Due to the increase in
fuel vapors trapped, the purge rate of the canister will also have to be
increased, which may cause HC and CO emissions to increase.
VI. Fuel; Gasoline is a mixture of various hydrocarbon compounds and
additives. By changing the biend of the gasoline, its characteristics
can be changed. Reid vapor pressure (RVP) .and initial boiling?polnt (IBP)
are~the two characteristics that have effects on evaporat ive~emissilortsT
As the RVP of a fuel decreases, the evaporative losses decrease (Fig.
12) (7). IBP has an inverse effect on evaporative losses. As the
IBP increases, the evaporative emissions decrease.
To achieve the change in Reid vapor pressures and initial boiling
point, the quantities of aromatics, paraffins,and olefins in the fuel will
have to be changed. A typical low volatility fuel with an RVP of 6.8
psi and an IBP of 102°F compared to an average summer grade fuel would
have a higher concentration of paraffins and olefins and a lower con-
centration of aromatics (7). This means a refinery may have to modify
its cracking, reforming and blending. Particular modification will de-
pend on the type of crude a refinery uses to produce gasoline. The
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effect of low volatility fuel on exhaust emissions is an increase in
CO and HC (Fig. 13, 14). The fuel change would reduce evaporative
losses on in-use vehicles significantly (Fig. 15).
VII. Control System; The evaporative emission control system which will
be used by the automotive industry will contain a mix of component
modifications (3). This mix will vary from manufacturer to manufacturer
depending on the particular characteristics of individual components
used by the manufacturers.
Examples of various systems which could be used in the control
of evaporative emissions and their estimated incremental costs (costs
over currently installed evaporative control systems) are listed below.
Any one of these systems would impact only a moderate cost increase
and would not require extensive lead times, i,e. could be available
for 1978 model year (3). System I utilizes heat shielding and a high
pressure fuel tank with a bladder to reduce the amount of fuel vapor
generated, thus reducing the~ Mason t of vapor which must be stored and
subsequently burned in the engine when the canister is purged. Systems
II and III allow for greater production of fuel vapor which in turn
requires more storage canister capacity. Also,,the.additional fuel vapor
which is purged from the storage canister and .burned- In the engine will
increase the burden on the engine's exhaust coirtrol system. System IV
depends on a fuel modification to reduce the amount of fuel evaporated.
The cost differentials indicated for the various systems are engineering
estimates of component cost changes at the assembly plant.
- Vehicle Modification -
System I Cost Differential
• Screw on gas cap similar to ones used by General + $ .25
Motors
• Steel fuel tank with a bladder and pressure setting
of 30 inches of water + 25.00
• Heat shielding between the exhaust pipe and the fuel tank 3.00
• Standard vapor-liquid separator
• Air cleaner with baffles + .50
• Carburetor with an external bowl vent and heat shielding + 1.00
• Closed bottom storage canister containing 700 gm of
activated carbon + .15
• Manifold purge system for the storage canister
TOTAL incremental cost impact per vehicle + 29.90
System II
1 Screw on gas cap similar to ones used by General Motors
with a pressure setting of 18 inches of water + $ .25
• Heat shielding between the exhaust pipe and fuel tank + 3.00
• Vapor-liquid separator with a smaller orifice to in-
crease tank pressure
• Carburetor with reduced bowl-capacity and external vent
attached to a storage canister + .50
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System II (cont.) Cost Differential
* Two closed bottom storage canisters containing 700
grams of activated carbon each + $ 3.00
• Manifold purge for both canisters .50
TOTAL incremental cost impact per vehicle + $ 7.25
System III
* Improved gas cap gasket + $ .05
• Heat shielding between the exhaust pipe and fuel tank 3.00
• Carburetor with reduced bowl capacity, external bowl vent,
and heat shielding +1.00
• One storage canister containing 1000 grams of activated
carbon and intergral purge value (similar to Vega) + .75
< Manifold purge
TOTAL incremental cost impact per vehicle + 4.80
System IV
• Improved gas cap gasket + $ .05
• Heat shielding between the exhaust pipe and fuel tank + 3.00
. Carburetor with reduced bowl capacity and external vent
attached to a storage canister + .50
. Closed bottom storage canister containing 700 grams of
activated carbon + ,15
•. Manifold purge system
TOTAL incremental cost impact per vehicle + $ 3.70
NOTE: System IV . requires the use of a low volatility
fuel, RVP no higher than 6,8 psi, in conjunction
with the vehicle modifications to achieve a re-
duced emission level,
VIII., Conclusion: Evidence indicates there exists "sufficient evaporative
control technology to control 90% of the generated evaporative emissions
from a vehicle, thus allowing vehicles to meet an emission,standard
of from two to six grams using the SHED procedure, by model year 1978.
It is reasonable to assume that the manufacturers will choose a system
similar to system II and that the resultant incremental cost will be
on the order of $7^per vehicle, with negligible operating and maintenance
costs. Prom figure J^,; the incremental emission reduction (from "controlled"
vehicles) to be expected is approximately 1.8 to 2.3 grams per mile. Using
$7 per vehicle and 2.0 grams per mile reduction, the cost effectiveness
of such control would be $32 per ton, as compared to $437 per ton in
going from federal 1975 light duty vehicle exhaust standard (1.5 g/mi)
to the statuatory level (.4 g/mi) or $2020 per ton for light duty vehicle
inspection/maintenance (8).
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Appendlx A
The following is an excerpt fron the Phase I Task I report by Exxon
from contract #68-03-2172.
CURRENT ATUOMOTIVE PRACTICE FOR CONTROL OF EVAPORATIVE EMISSIONS
In this section, the types of Evaporative Control Systems (ECS)
used by the automotive industry to control evaporative emissions are re-
viewed.
A. Carburetor Evaporative Emission Control
The two modes of carburetor losses are running losses and hot soak
losses. The running losses are controlled Internally in the carburetor
by venting from the carburetor bowl to the air Intake of the carburetor
via the balance tube, allowing carburetor running vapors to be burned
in the engine. This is the case both when the bowl is vented to the
carbon canister as well as when it is vented to the carburetor intake
because the pressure in the intake is lower than that in the canister
when the vehicle is running.
To control hot soak losses during engine shutdown, two basic systems
are used. The first is storage of the vapors in the induction system
during shutdown followed by eventual consumption in the engine after
start-up. The hydrocarbon vapors move from the bowl into the carburetor
intake through the balance tube and then into the carburetor throat
and air cleaner. Because hydrocarbons are denser than air, they dis-
place the air.
The second control system for hot soak losses uses both the in-
duction system and a charcoal canister to store vapors. A line from
the bowl to the canister diverts a portion of the vapors to this alter-
nate storage. Vapors stored in the carbon canister are ultimately purged
by a portion of engine combustion air which Is drawn through the canister
during operating modes.
B. Fuel Tank Evaporative Emission Control
In all cases, fuel tanks are "closed" systems (non-vented fill caps)
which are connected to a vapor storage system through a vapor-liquid
separator. The vapor-liquid separator reduces system load by returning
condensed and entrained liquid to the tank. Three types of vapor storage
techniques are used: (1) charcoal canister, (2) engine crankcase, and
(3) an auxiliary tank.
C. Charcoal Canisters
The majority of ECS's use a charcoal canister to store the hydro-
carbon vapors emitted from the fuel tank. In these system, all of the fuel
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tank vapors from both hot soak and running losses pass into the canister.
A few systems, however, use a control valve which allows running loss
vapors to bypass the charcoal bed and move directly to the engine, as
will be described later.
The charcoal canister system functions via an adsorption-regeneration
process. Hydrocarbon vapors are adsorbed on the surface of the activated
carbon for storage purposes. Later the vapors are desorbed from the
surface by passing a portion of engine combustion air through the
charcoal bed. This regeneration, or purging process, is necessary to
restore the capacity of the bed for further hydrocarbon storage.
There are several types of carbon canisters in use. They may be
classified by the method of introducing purge air to the bed and by
the technique for the handling of running vapors. In most cases, purge
air enters the bed through the open bottom of the canister as illustrated
in Figure 3* A replaceable filter is used to prevent dust contamination.
A second type of canister in use has a sealed bottom with an air inlet on
top. In many canisters, running vapors as well as hot soak emissions
pass into the carbon bed. In others, a purge valve is used which allows
running vapors to bypass the carbon bed.
D. Purge Systems
There are three general types of purge systems for regeneration
of carbon beds. These systems can purge to: (1) the air cleaner,
(2) the carburetor, and (3) the Positive Crankcase Ventilation valve
(PCV). Units purging to the air cleaner generally utilize the pressure
drop through the air cleaner and inlet system to draw purge air through
the canister. One system utilizes the velocity of the air in the air
cleaner snorkel to pull air through the carbon bed. Purging to the
carburetor is the most popular technique. A part at the idle position
is most often used so that at idle the purge rate will be very low but
will increase as the throttle is opened. The third type of purge is to
the PCV system. With this system, a purge valve is used which permits
only tank running vapors to reach the engine at idle. As the throttle
is opened from idle, engine vacuum opens the purge valve on the canister
so that both tank running vapors and stored vapors in the bed are drawn
into the engine via the purge air stream.
E. Summary of Techniques for Evaporative Emission Control
-Induction system only
^^
1. Carburetor Bowl Emissions Tot
Both induction system
and charcoal bed canister
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2. Fuel Tank Emissions Tot
3. Carbon Canister:
-11-
Charcoal bed
Auxiliary Tank
Engine crankcase
.Open or closed bottom
All vapors enter the bed
•Running vapors bypass bed
IV.
4. Purges To>
5. Other
CLASSIFICATION OF SYSTEMS
Evaporative Control Systems have been divided into two general
categories: (1) those using a charcoal canister, and (2) those using
a system other than a charcoal canister for storage of fuel tank vapors.
Over 98% of the 1973-1975 vehicle population utilize a charcoal canister.
These systems have been further typed according to carburetor storage and
type of canister purge. This is shown in Figure 5. Systems not using a
charcoal canister may use the engine crankcase or a small auxiliary tank
for storage.
A further subdivision is by the-style of canister. A description
of the charcoal canisters used by each U.S. manufacturer is given in
Table 1.
V. SURVEY OF ECS's IN USE
A cross section of about 120 vehicles from the 1973-1975 car
population has been used in this survey of evaporative control systems
in current use. In addition to describing the ECS, the fuel system com-
ponents which affect their function such as proximity of fuel tank to a
tank have also been surveyed. This survey covered all families of engines
from each U.S. manufacturer and the leading foreign-manufactured cars.
All told, this group is representative of at least 99% of the vehicles in
the 1973-1975 car population. The results from this survey are shown
in Table 1.
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CHARCOAL CANISTERS ON u.s. CARS
Tube Designation
Manufacturer
General Motors
Chrysler
Ford
American Motors
No.
1
2
3
4
1
2
1
2
1
2
No. of Tubes
2
3
3
(purge valve)
4
(purge valve)
3
A
(purge valve)
2
2
2
3
Inlet
Tank
Tank
Carburetor Bowl
Tank
Tank
Carburetor Bowl
Tank
Carburetor Bowl
Tank
Carburetor Bowl
Tank
Tank
Tank
Tank
Outlet Other Reaarks
Purge
Purge
Purge . Vacuum for
Purge Valve
Purge Vacuum for
Purge Valve
Purge Carburetor Bowl
sometimes not used
(Same as GM-2)
Purge Vacuum for (Same as GM-A)
Purge Valve
Purge 500 gms
Purge 300 gms
Purge
Purge
Carburetor Bowl
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References for Evaporative Losses
1, Martens, S.W,; Thurston, R,W., "Measurement of Total Vehicle
Evaporative Emissions" SAE Transaction 680125, 1967.
2. Martens, S.Wt, "Evaporative Emissions Measurement with the
SHED - A Second Progress Report" SAE Transaction 690502, 1968,
3. Statements given before the Environmental Protection Agency
Waiver Hearing on the California 1977 Light Duty Evaporative
Emission Standards, May 28, 1975,
4, Wade, D.T., "Factors Influencing Vehicle Evaporative Emission",
SAE Transaction 670126, 1967.
5, Patterson, D,J, and Heneim, N,S.., "Emissions from Combustion
Engines and Their Control", Ann Arbor Science Publishers, 1972.
6, Koehl, W.J,, Jr., "Mathematical Models for Predictionof Fuel Tank
and Carburetor Evaporative Losses", SAE Transaction 690506, 1969.
7. Nelson, Edwin E., "Hydrocarbon Control for Los Angeles by Reducing
Gasoline Volatility", SAE Transaction 696087, 1969.
8. ''Examination of Interim Emission Control Strategies for Heavy
Duty Vehicles" prepared by Emission Control Technology Division
of the Office of Mobile Source Air Pollution Control May 30, 1975.
9. "Investigation and Assessment of Light Duty Vehicle Evaporative
Emission Sources and Control", Phase I Task I 68-03-2172,
10. "Study of the Interaction of Fuel Volatility and Automotive Design
as they Relate to Driveability", GPS 22-69-66.
11, California Air Resources Board, Los Angeles County A.P.C.D.,
Western Oil and Gas Association Modification Its Potential
as an Air Pollution Control Measure in Los Angeles County".
12. Muller, H,L.; Kay, R.E. and Wagner, T.O., "Determining the
Amount and Composition of Evaporatives Losses from Automotive
Fuel Systems", SAE Transaction 660407, 1966,
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Figure
SHED Results
Canister Result
Model
Year
57-69
70-71
72
73
78 (Calif)
Possible
Diurnal
(g/phase)
26
18
14
16
1 Cest)
,4 Cest)
Hot Soak
Cg/phase)
15
12
12
15
5 (est)
1.6 (est)
Total
Cg/test)
41
30
26
31
6 (std)
2 (std)
g/mi
equiv.
2. .8
2,1
2,0
2,5
.7 (est)
,23 (est)
Percent
Imp
0
25
28
11
75
92
Cert Std,
(g/test)
None
6
2
2
-
_
Ay g Loss
Os/test)
-
-
-
.5
-
_
-------
-15-
Figure 2
Vehicles passing 6 gram per test, proposed California SHED Standard
Vehicle No,
1975 Vega 140-2BBL
1975 Camaro 350-2BBL
1975 VW Beetle 97-FI
1972 Pontiac 2BBL
1972 Chevrolet
1974 Ambassador (modified)
1975 Coupe DeVille 500-FI
1975 Omega 260-2BBL
1975 Olds 350-4BBL
1975 Olds 455-4BBL
1975 Vega 140
1975 VW Sedan 1600-FI
1975 VW Rabbit
1975 VW Type 1
1975 Chry, Type SS22 360-2BBL
1975 Chry, Type VS29 360-HP
1975 Chry, Type VH23B18-2BBL
1975 Chry. Type RV41 318^2BBL
1975 Chry, Type DH41
of Test
3
3
3
1
1
2
2
2
22
16
7
1
NA
NA
9
1
1
1
1
Diurnal
.4
.5
1.0
.35
,15
1.1
,25
.49
2,85
1.27
.3
1,4
NA
NA
1.50
,28
,31
,62
1.71
Hot Soak
1.5
4.6
2,5
4.25
5.28
2,1
1.07
3.89
2,60
3.83
1,0
2.9
NA
NA
1,22
1,94
2.96
4,20
3.73
Total
1.9
5.1
3.5
4.6
5,43
3.2
1,32
4.38
5.45
5.10
1.3
4.3
4,3
5,0
2,72
2,22
3,27
4,82
5.44
*
*
*
3
3
3
3
3
3
3
3
3
3
3
3
3
3
.3
3
NA - not available
* - testing done at tfVEL
3 ^ reference 3
-------
-16-
Figure 3
Fuel Tank with Baffle
C - ^
Baffles-
V H
<
, >(
Fuel
f ^
]onvec.t±v£ Currents*
Heat
\
Tank without Baffle
J1
O
J
(^ A
f
1
V v
}
1
t
Convective Currents)
t
1
1
41
[5
}
Heat
Heat
Tailpipe
Tailpipe
Heat
Figure 4
Fuel Tank with Bladder
*r Pressure-vacuum vent
air space
Bladder Membrane
>
-------
rt
en
0)
co
(0
o
50
40
30
20
10
-17-
Figure 5
Losses vs Volume of Fuel
.25
.50
,75
Fraction Tank Filled
Reference
Full
Figure 6
Air Cleaner with Internal Baffles
"-Baffle
LBaffle
Carburetor
-------
-J.O-
25
8
I 20
CO
0)
CO
S 15
10
Figure 7
Losses vs Peak Bowl Temp
Bowl Vol=100cc
180 °F
160°F
140°F
10 20 30 40 50
Percent Evaporated at 160°F
Reference
50
40
M
60
o 30
0)
CO
CO
20
10
Figure 8
Losses vs Bowl Vol., cc
200
150
100
50
100 120 140 16Q 180 200
Peak Bowl Temp. °F
Reference
Figure 9
Intake Manifold Storage
Bowl Vent
External Bowl Vent — «•
Storage Canister Lirye_
r»d •>>
=f=
-*-.
Carburetor
^
-------
Figure 10
Carbon Canister with S6mipermeable Membrane
Carbon Bed
Semipermeable
Membrane
Screen-
•Foam Filter
-Fiberglass Filter
Figure 11
Storage Canister with Bottom
/oVo\
-/
Vent Pipe
-------
-20-
co
0
2
00
CO
0)
CO ;
0)
o
h-J 1
I'
1
W
100
80
60
40
20
! 700
650
S
0)
P.
£ 550
o
•H
(0
CO
450
Figure 12
Losses vs RVP
46
RVP psi
Reference
Figure 14
Effect of RVP on CO
CO
10
RVP-5.3
RVP-7.9
•RVP-10
20 ,45 70 95
Ambient Temperature °F
Reference ' '
en
cu
co
3
t-i
00
I
co
§
•rl
CO
co
I
r
co
OJ
co
co
O
rt
Q
80*
Figure 13
Effect of RVP on NOx & HC
— HC
-_ NOx
140
1201
100
80
60
40
20
RVP-5.3
•RVP-7.9
RVP-10
RVP-5.3
RVP-7.9
^-RVP-10
45 70 95
Ambient Temperature °F
(11)
Reference
Figure 15
Daily Losses vs RVP
"RVP-9.3
-6.0
60
70
80
90
100
Ambient Temperature °F
Reference ^ '
US. QOViRNMEffT PR1NTINQ OFFICE: 1978-850-618/11
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