(12) United States Patent
`Reddy
`
`USOO6279548B1
`(10) Patent No.:
`US 6,279,548 B1
`(45) Date of Patent:
`Aug. 28, 2001
`
`(54) EVAPORATIVE EMISSION CONTROL
`CANISTER SYSTEM FOR REDUCING
`BREAKTHROUGH EMISSIONS
`
`(75) Inventor: Sam Raghuma Reddy, West
`Bloomfield, MI (US)
`(73) ASSignee: sity Motors Corporation, Detroit,
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`1/1995 Krohm ................................. 123/520
`5,377,644
`10/1995 Wakashiro et al. .................. 123/519
`5,456,236
`5,482,023 * 1/1996 Hunt et al. ........................... 123/520
`5,687,697
`11/1997 Ishikawa et al. .................... 123/520
`6,098,601 * 8/2000 Reddy .................................. 123/520
`* cited by examiner
`Primary Examiner Thomas N. Moulis
`(74) Attorney, Agent, or Firm-George A. Grove
`(57)
`ABSTRACT
`The effectiveness against Vapor breakthrough of an adsor
`bent material (e.g., activated carbon granules) containing
`canister in an evaporative fuel emission control System is
`(21) Appl. No.: 09/459,101
`greatly increased by employing a relatively Small Secondary
`volume of adsorbent downstream of the vapor vent of the
`(22) Filed:
`Dec. 13, 1999
`rimarv adsorbent volume and heating the Secondarv Vol
`7
`(51) Int. Cl." .............................. F02M 33/04; F02G 5/00 E. its, prior to commencing the Av of purge A
`(52) U.S. Cl. ..................
`123/520; 123/557; 123/519
`through the two adsorbent volumes to remove adsorbed fuel
`(58) Field of Search ..................................... 123/516, 518,
`and carry the purged fuel to the induction System of an
`123/519, 520, 549,557
`asSociated engine. The Secondary Volume is heated to a
`temperature enabling complete purging of hydrocarbons
`from it and, thus, to greatly increase the capacity of that
`Volume to prevent fuel vapor breakthrough during the Sub
`Sequent engine-off fuel vapor Storage cycle. The Secondary
`Volume may be contained in a common canister with the
`primary volume or in a secondary canister.
`14 Claims, 6 Drawing Sheets
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`St.
`
`4,778.495.
`4,864,103
`5,355,861
`
`3.E. El al - - - - - - - - - - - - - - - - - - - - - - - - 'i
`
`...,
`10/19ss bishop ..
`... 219/375
`9/1989 Bishop et al. ...
`10/1994 Arai ..................................... 123/519
`
`-68
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`98
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`100
`
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`54 , 2
`N
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`70
`
`I -
`D 82
`
`
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`50
`
`N
`
`N/ N
`
`-
`
`N
`
`
`
`INGEVITY SOUTH CAROLINA, LLC, EXHIBIT 2003
`BASF Corporation v. Ingevity South Carolina, LLC
`IPR2019-00202
`
`

`

`U.S. Patent
`
`Aug. 28, 2001
`
`Sheet 1 of 6
`
`US 6,279,548 B1
`
`
`
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`
`

`

`U.S. Patent
`U.S. Patent
`
`Aug.28, 2001
`Aug. 28, 2001
`
`Sheet 2 of 6
`Sheet 2 of 6
`
`US 6,279,548 B1
`6,279,548 B1
`US
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`

`

`U.S. Patent
`U.S. Patent
`
`Aug. 28, 2001
`Aug. 28, 2001
`
`Sheet 3 of 6
`Sheet 3 of 6
`
`US 6,279,548 B1
`US 6,279,548 B1
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`

`

`U.S. Patent
`
`Aug. 28, 2001
`
`Sheet 4 of 6
`
`US 6,279,548 B1
`
`40:60 BUTANE/AIR
`10 CU ft PURGE
`
`
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`USED CANISTER
`SATURATED WITH BUTANE
`THEN PURGED WITH 10 CU ft
`AIR (NOSOAKAFTER PURGE)
`
`
`
`GREEN CANISTER
`OO 10 20 30 40 50 60 70 80 90 100 110 120 130
`BUTANE LOAD, g
`
`FIG. 4
`
`

`

`U.S. Patent
`
`Aug. 28, 2001
`
`Sheet S of 6
`
`US 6,279,548 B1
`
`2
`
`9 M
`
`1111 1 .4 M
`
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`
`40
`
`50
`
`60
`
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`
`30
`BUTANE LOAD, g
`
`FIG. 5
`
`

`

`U.S. Patent
`
`Aug. 28, 2001
`
`Sheet 6 of 6
`
`US 6,279,548 B1
`
`3 DAY SOAKPRIOR TOLOAD
`40:60 BUTANE/AR LOAD
`
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`
`BASELNE 1850 CC
`CANSTER
`
`1850 CC CANSTER
`--
`2OOCC STAGE I
`CANISTER (NOTHEATED)
`
`05
`
`10
`
`20
`
`1850 CC CANISTER
`-- 200 CCHEATED
`STAGE I
`CANISTER
`50
`60
`
`40
`3O
`BUTANE LOAD, g
`
`7O
`
`FIG. 6
`
`

`

`1
`EVAPORATIVE EMISSION CONTROL
`CANISTER SYSTEM FOR REDUCING
`BREAKTHROUGH EMISSIONS
`
`TECHNICAL FIELD
`This invention pertains to evaporative fuel Vapor emis
`Sions from automotive vehicles. More Specifically, this
`invention pertains to an improved fuel vapor adsorption
`canister System and method of operation that reduces the
`breakthrough of fuel vapor to the atmosphere.
`BACKGROUND OF THE INVENTION
`Fuel evaporative emission control Systems have been in
`use on automotive vehicles for over 30 years. The gasoline
`fuel used in many internal combustion engines is quite
`volatile. The fuel typically consists of a hydrocarbon mix
`ture ranging from high volatility butane (C-4) to lower
`volatility C-8 to C-10 hydrocarbons. When a vehicle is
`parked in a warm environment during the daytime heating
`(i.e., diurnal heating), the temperature in the fuel tank
`increases. The return of hot fuel from the engine also heats
`the contents of the fuel tank. The vapor pressure of the
`heated gasoline increases and fuel vapor will flow from any
`opening in the fuel tank. Normally, to prevent fuel Vapor loSS
`into the atmosphere, the tank is vented through a conduit to
`a canister containing Suitable fuel adsorbent material. High
`Surface area activated carbon granules are widely used to
`temporarily adsorb the fuel vapor.
`The fuel vapor enters the canister through a top inlet of the
`canister and diffuses downwardly under its own pressure and
`gravity into the bed of carbon granules where it is adsorbed
`in temporary Storage. The total Volume of adsorbent is
`Specified So as to be Suitable to retain a quantity of fuel vapor
`expected to evaporate from the fuel tank during normal or
`representative usage of the vehicle.
`The canister is molded of a thermoplastic material and
`shaped So that ambient air can be drawn through the carbon
`granule bed during engine operation to purge adsorbed fuel
`from the Surfaces of the carbon particles and carry the
`removed fuel vapor into the air induction System of the
`vehicle. Typically, a partition is formed in the canister to
`lengthen the flow path of vapor and air through the Volume
`of carbon particles. Thus, the fuel vapor enters at one end of
`the flow path and escapes to the atmosphere at the opposite
`end, the vent end, if the quantity of fuel exceeds the
`adsorption capacity of the carbon volume. Ambient air,
`induced to flow through the activated carbon bed under
`engine intake vacuum, enters the canister at the "vent' end
`of the flow path. The air traverses the full length of the flow
`path and exits the canister with desorbed, i.e., purged fuel at
`the vapor inlet end of the carbon volume. Typically, neither
`the canister nor the purge air experience heating other than
`ambient heating.
`The described emission control system obviously works
`in a repeating cyclical mode. When the engine is not
`running, fuel vapor generated by diurnal heating, or the like,
`flows to the canister and is adsorbed up to the capacity of the
`adsorbent volume. The vehicle may remain idle for several
`days and fuel vapor will accumulate in the canister. The
`initial loading will be at the inlet end of the adsorbent
`volume but the fuel gradually becomes distributed along the
`entire adsorbent bed pathway. When the vehicle engine is
`Started and can accommodate a Secondary fuel-air mixture,
`a purge valve is opened and purge air is drawn through the
`adsorbent volume. Purging can continue as long as the
`engine is running and the air can cause the removal of a
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`US 6,279,548 B1
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`2
`substantial portion of the stored fuel vapor. But a portion of
`the adsorbed hydrocarbons remain adsorbed on the carbon.
`That portion is called the “heel” and it significantly limits the
`capacity of the carbon to adsorb additional fuel.
`Environmental regulators are proposing lower limits on
`the amount of fuel vapor that can escape the evaporative
`emission System during a prescribed test of the System in a
`closed space called SHED (Sealed Housing for Evaporative
`Determination). For example, the California Air Resources
`Board (CARB) has proposed “near Zero” and “Zero” evapo
`rative emission Standards for automotive vehicles for year
`2004. The proposed Standards require near-Zero fuel vapor
`emissions from all the Sources: permeation losses through
`plastic fuel System parts, leaks through the fittings and
`joints, and canister breakthrough emissions. Reducing the
`emissions through the leaks involves the Selection of better
`Sealing joints and connectors or eliminating Some of joints,
`and reducing permeation losses involves the Selection of low
`permeability or no permeability materials, whereas reducing
`canister breakthrough emissions to near-Zero requires new
`technologies in the canister design. An object of this inven
`tion is to provide a canister System, and method of operating
`the System, that will limit canister breakthrough emissions to
`less than 0.02 grams fuel loSS per test.
`SUMMARY OF THE INVENTION
`In one aspect, this invention provides a method of increas
`ing the adsorption capacity of an evaporative emission
`control System by Selectively heating a Small portion of the
`adsorption material before air purging of the canister. Granu
`lar activated carbon is a preferred adsorbent material. The
`adsorbent portion that is heated is located at the purge air
`inlet region of the canister system. Generally, only about 1%
`to 5%, and preferably less than 3%, by volume of the total
`adsorbent is heated prior to purging. But that portion is
`heated to a temperature at which the normal flow of ambient
`purge air will remove substantially all of the adsorbed fuel,
`including the hydrocarbon heel, during a purge cycle. When
`high Surface area carbon granules are employed, the
`upstream Secondary carbon volume is preferably heated to
`about 350° F (177° C).
`A volume of carbon granules heated to 350 F. is readily
`Stripped of gasoline vapor with a flow of ambient air of
`suitable duration. No hydrocarbon heel remains in the
`heated Volume, and during the Subsequent vapor loading
`cycle, vapor breaking through the main carbon volume is
`readily adsorbed in the "green,” or hydrocarbon-free, Sec
`ondary volume.
`Preferably, the relatively small secondary volume of
`adsorbent is thus heated prior to each purge cycle. Heating
`may be initiated by the engine control computer module and
`accomplished using vehicle battery-powered, embedded
`electrical heating elements, or the like. When a temperature
`Sensor in the Secondary adsorbent Volume indicates that a
`Suitable purge temperature has been reached, the engine
`control computer causes the heater to be shut off and the
`purge valve to be opened. Engine induction System vacuum
`induces the flow of purge air from the engine compartment,
`through the Secondary and primary adsorbent volumes and
`into the operating engine. The air flow both Strips the Volume
`of hydrocarbons and cools the granules to restore their full
`adsorptive capacity before the next vapor load cycle.
`The secondary volume of adsorbent may be located in the
`canister adjacent the air purge inlet. In this embodiment, the
`Secondary Volume is closely adjacent the main adsorbent
`Volume and it may be preferable to provide Some thermal
`
`

`

`3
`insulation between them. In a Second embodiment, the Small
`heated Volume is located in a Smaller, Secondary molded
`canister in the air inlet line with the vent valve.
`Other objects and advantages of the invention will
`become more apparent from a detailed description of pre
`ferred embodiments that follows. The description will refer
`to the drawings that are described in the next Section of this
`Specification.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic view of the evaporative fuel
`emissions control System of an automobile.
`FIG. 2 is a sectional view of a carbon granule filled
`canister in accordance with a first embodiment of the
`invention.
`FIG. 3 is a Sectional view of a Secondary carbon granule
`filled canister in accordance with a Second embodiment of
`the invention.
`FIG. 4 is a graph of breakthrough emissions, in grams, of
`butane verSuS butane load, in grams, for a green carbon
`canister and a used carbon canister.
`FIG. 5 is a graph using the same ordinates as FIG. 4 but
`illustrating the effect of increasing Soak periods on break
`through emissions.
`FIG. 6 is a graph using the same ordinates as FIG. 4 but
`comparing baseline canister performances with a canister
`utilizing the Subject invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`A typical evaporative fuel emissions control system 10 for
`an automotive vehicle is illustrated in FIG. 1. The illustra
`tion is Schematic and the components are not drawn to Scale.
`The System comprises an engine Schematically indicated
`at block 12. However, the engine would typically be a
`multi-cylinder, gasoline-powered, internal combustion
`engine. The operation of a modern fuel efficient, low exhaust
`and evaporative emissions engine is controlled using a
`Suitable programmed digital microprocessor or computer,
`indicated at block 14. The microprocessor is part of a control
`module that controls the operation of at least the engine and
`its emission controls (an engine control module, ECM) or
`the engine and transmission (a powertrain control module,
`PCM). Such control modules in various similar forms are
`used on millions of cars, Sport utility vehicles, trucks, and
`the like, today.
`When the engine is started, the control module, which is
`powered by the vehicle battery, not shown, Starts to receive
`Signals from many Sensors on the engine, transmission and
`emission control devices. Line 16 from the engine 12 to
`control module 14 schematically depicts the flow of Such
`Signals from the various Sensors on the engine. During
`engine operation, gasoline is delivered from a fuel tank 18
`by a fuel pump (not shown, but often located in the fuel tank)
`through a fuel line, not shown, to a fuel rail and fuel injectors
`that Supply fuel to each cylinder of the engine or to ports that
`Supply groups of cylinders. The timing of the operation of
`the fuel injectors and the amount of fuel injected per cylinder
`injection event is managed by the control module 14. The
`Subject emission control purge System is operated in har
`mony with engine operation to avoid upsetting the air-to
`fuel ratio in the engine.
`Since gasoline and other fuels are quite volatile, fuel tank
`18 is closed except for a vent line 20. Tank 18 is often made
`of blow molded, high density polyethylene provided with a
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`4
`suitable interior gasoline impermeable layer(s). The tank 18
`is provided with fill tube 22 with a gas cap 24 closing the gas
`fill end 26. The outlet end 28 of fill tube 22 is inside tank 18
`and is provided with a one-way valve 30 to prevent liquid
`fuel from Splashing out the fill tube 22.
`A Volume of gasoline 32 is indicated with upper Surface
`34. A float-type fuel level indicator 36 provides a fuel level
`signal through line 38 to the control module 14. Fuel tank
`preSSure Sensor 40 and temperature Sensor 42 provide their
`respective data through Signal transmitting lines 44 and 46,
`respectively, to controller 14. These Sensors are not neces
`Sarily present in all evaporative control Systems and Some
`times their functions may be combined. They are Sometimes
`used for diagnostic purposes.
`Fuel tank 18 is provided with a vent line 20 that leads
`through seal 48 from the top of the tank to a fuel vapor
`adsorption canister 50. Float valve 52 within the tank 18
`prevents liquid gasoline from entering vapor vent line 20.
`During heating of the fuel in the tank by liquid fuel returned
`from the hot engine (through fuel return line, not shown) or
`by ambient heating, hydrocarbon fuel vapor is generated
`from the gasoline. Vapor mixed with air flows under the
`vapor pressure through vent line 20 to the vapor inlet of
`canister 50 (see FIGS. 1 and 2). The vapor enters canister
`vapor inlet 54, flows past granule retainer element 56 and
`diffuses into primary volume 57 and 57" of adsorptive
`material 58.
`Canister 50 is typically molded of a suitable thermoplastic
`polymer Such as nylon. In this embodiment, canister 50
`comprises four side walls, defining an internal Volume of
`rectangular cross Section (two side walls 60 shown), with an
`integral top 62 and a vertical internal partition 64 that
`extends from top 62 and the non-shown front and rear Sides.
`Canister 50 includes a bottom closure 66 that is attached to
`the side walls. At the top of canister 50 is a vent opening 68
`that also serves as an inlet for the flow of air during the
`purging of adsorbed fuel vapor from the adsorbent material
`58. Also formed in the top 62 of the canister 50 is a purge
`outlet 70 through which a stream of purge air and purged
`fuel vapor can exit the canister.
`Connected to vent opening 68 is a vent line 72 (see FIG.
`1) and solenoid actuated vent valve 74. Vent valve 74 is
`normally open as shown, but upon actuation of battery
`powered Solenoid 76, stopper 78 is moved to cover vent
`opening 80. Solenoid 76 is actuated upon command of
`control module 14 through signal lead 79. The vent valve 74
`is usually only closed for diagnostic purposes.
`Purge outlet 70 is connected by purge line 82 through
`Solenoid actuated purge valve 84 to the engine 12. Purge
`valve 84 includes a battery powered solenoid 86 and stopper
`88 to close purge opening 90. Purge valve 84 is opened only
`by command of control module 14 through signal lead 91
`when the engine 12 is running and can accommodate the
`fuel-laden air stream drawn through canister 50.
`Referring again to FIG. 2, it will be appreciated that as an
`airfuel mixture flows from the fuel tank through vent line 20
`and through the inlet 54 into canister 50, fuel vapor will be
`absorbed onto the granules of adsorbent material 58 in the
`canister. Gradually, the granules of activated carbon or other
`Suitable adsorbent material will become laden with butane
`and heavier hydrocarbons, and the vapor will further settle
`into the portion of adsorbent material 58 on the left side
`volume 57" of partition 64. While partition 64 extends from
`the top 62 of the canister, it does not reach all the way to the
`bottom closure piece 66.
`Thus, there is a flow path from the granules 58 on the left
`side volume 57" of partition 64 up into the granules on the
`
`

`

`S
`right side volume 57" of partition 64. When vent valve 74 is
`open, the air-fuel mixture can ascend the adsorbent material
`to the right of partition 64 and gradually pass through a
`porous, thermal insulator Separator 92 into a Secondary
`volume 93 of adsorbent material 94. Embedded in this
`secondary volume 93 of adsorbent material is an electrical
`heating element 96. The secondary volume of adsorbent
`material 94 is held in a relatively small compartment
`between porous Separator 92 and a granule retainer element
`98. Once both the primary volume 57, 57" of adsorbent
`material 58 and the secondary volume 93 become saturated
`with vapor, then Vapor will accompany air exiting the
`canister at vent outlet 68 and pass through vent line 72 and
`through the open solenoid-actuated valve 74.
`The flow path of fuel-laden vapor entering the canister
`through inlet 54 is extended by partition 64 to include two
`vertical portions 57, 57" of the primary adsorbent material
`58 and a smaller volume 93 of adsorbent material 94.
`Although the Secondary Volume of adsorbent may be Some
`what larger, preferably it is less than 3% of the primary
`absorbent volume.
`Conversely, when the engine is operating and the control
`module 14 has opened purge valve 84 to permit air to be
`drawn past vent valve 74 through vent line 72 and into the
`Vent/purge inlet 68, the purge air is drawn through the
`extended path, i.e., through the Secondary adsorbent volume
`93 and the primary adsorbent volume 57, 57". The air
`stream laden with desorbed fuel vapor exits purge vent 70
`and is drawn through purge line 82, through purge Valve 84,
`into the induction System of the engine 12. It is realized that
`the temperature of the primary adsorbent volume 58 is that
`of the ambient temperature of the engine compartment, also
`taking into consideration any heat of adsorption or desorp
`tion of the fuel vapor. However, before the purge Solenoid 84
`is opened, a command is issued from the control module 14
`to actuate heating element 96 by battery (not shown) power
`until the secondary volume 93 is heated to a relatively high
`temperature at which Substantially all fuel vapor is desorbed
`by the ambient air Stream passing through the Secondary
`adsorbent volume. The temperature of the Secondary volume
`is controlled by the engine control module utilizing the
`temperature Sensor information from temperature Sensor
`100.
`A preferred adsorbent material is activated carbon gran
`ules. AS Stated, whereas the carbon granules in the primary
`volume of the canister 58 are not especially heated, the
`granules in the Secondary volume 93 are heated to a Suitable
`temperature such as 350 F., at which the ambient air strips
`substantially all fuel vapor from the secondary volume. At
`this temperature the Secondary volume is rapidly Stripped of
`fuel. Further air flow cools the secondary volume for effec
`tive high capacity adsorption during a Subsequent diurnal
`cycle.
`A Second Embodiment
`FIG.3 illustrates a second embodiment of the invention in
`which the secondary volume 193 of adsorbent carbon gran
`ules (for example) 194 are contained within a Stage II
`canister 191 located in the vent line 72 between a conven
`tional canister 150 and vent valve 74. Canister 150 is quite
`similar to the canister 50 depicted in FIG. 2 (and thus the
`common parts are identified by the same numbers) except
`that the Secondary volume of adsorbent is not contained
`within canister 150.
`Stage II canister 191 contains a relatively small volume of
`carbon granules, Suitably only about two to ten percent by
`Volume of the primary volume of granules in unheated
`canister 150. Canister 191 includes the secondary volume
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`
`6
`193 of adsorbent granules 194 and heating element 194.
`Heating element 194 is tuned on by a suitable signal lead,
`not shown, from controller 14 (FIG. 1) prior to opening of
`purge vent 84 and the commencement of purge air flow. The
`granules are retained by porous retainers 197 and 198 that
`permit purge air flow through the canister 191 and vapor
`over from canister 150 into the secondary volume 193.
`Thus, air and fuel vapor overflow from canister 150 enters
`canister 191 and the fuel vapor is temporarily adsorbed. At
`a Suitable time following engine Startup, heater 196 is
`activated and the granules heated to about 350 F. using
`temperature sensor 200. After the purge solenoid 84 (FIG. 1)
`is opened, air flows through vent valve 74 in to the hot
`secondary volume to fully remove all adsorbed fuel vapor.
`Experimental
`The subject invention is better understood following a
`description of the mechanism of canister breakthrough emis
`Sions. Breakthrough emissions from a green or Virgin can
`ister are very low as shown by the data in FIG. 4. For
`comparison, the breakthrough emissions from a used can
`ister are also shown in FIG. 4.
`Each canister contained 1850 cubic centimeters of com
`mercial activated carbon granules Specified to have an
`adsorption working capacity of 15 grams of butane per 100
`cc granules (15BWC). The “green” canister contained
`unused carbon granules. The carbon granules in the “used
`canister had been Saturated with butane and then purged with
`a stream totaling ten cubic feet of ambient air. For
`convenience, a mixture of 40 parts by volume butane and 60
`parts by Volume air was used instead of gasoline vapor to
`load and evaluate the adsorption capacities of the canisters.
`Butane/air mixtures are commonly used in the canister
`Studies, and butane loading is also used in the CARB and
`Federal test procedures.
`The green canister was loaded with 40 g of butane from
`a 40:60 butane/air mixture to simulate the loading of a
`vehicle canister with gasoline vapor. The experiment was
`conducted in a closed container like the SHED test proce
`dure for evaluating automotive evaporative emission Sys
`tems. As the carbon was being loaded with butane from the
`Synthetic mixture, the atmosphere around the canister was
`tested with a flame analyzer to detect any escape or “break
`through” of butane.
`FIG. 4 records the cumulative weight of breakthrough
`emissions of butane, in grams, Versus the weight of butane
`being adsorbed by the respective carbon granule-filled can
`isters. It is seen that the green carbon canister lost only about
`0.001 g of butane while being loaded with about 40 grams
`of butane. In fact, there was no significant breakthrough of
`butane from the green canister until its loading reached
`about 109 grams of butane. At that point in the loading
`process, Substantially all of the butane entering the canister
`was escaping from its vent opening. In contrast, as FIG. 4
`shows, the “used’ canister permitted a significant amount of
`butane to break through from the beginning of the loading
`proceSS.
`The difference in performances of the green and used
`canisterS is explained as follows. After Several load/purge
`cycles, an adsorbent canister builds a residual hydrocarbon
`content, called a heel, and reaches a stable adsorption
`capacity which is lower than the adsorption capacity of a
`green canister. The residual hydrocarbon in the pores of the
`granules of activated carbon is difficult to remove by air
`purging and is, therefore, called "heel”. Breakthrough emis
`Sions from the used canister were higher than those from the
`green canister (FIG. 4) because of the hydrocarbon heel on
`the used carbon. Thus, the 40 g butane loading resulted in
`
`

`

`US 6,279,548 B1
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`15
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`35
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`40
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`25
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`7
`0.016 g of breakthrough emissions from the used canister
`compared to 0.001 g from the green canister.
`The heel is not distributed uniformly. There is less heel
`where the purge air enters the canister and more heel where
`the fuel tank vapor enters the canister. It can be observed that
`if a purged canister is allowed to Simply Stand for Some time
`before loading (called Soak or Soaking), the breakthrough
`emissions increase further as shown by the data in FIG. 5.
`During a Soak period, the hydrocarbon heel redistributes
`more uniformly over the volume or bed of carbon. This
`redistribution reduces the loading capacity of the carbon
`even more and increases breakthrough emissions as illus
`trated in FIG. 5.
`FIG. 5 records the SHED test data of a group of substan
`tially identical 1850 cc 15BWC canisters that had been
`loaded with butane from a 40:60butane/air mixture and then
`purged with a total of 10 cubic feet of air flow. The first
`canister was then immediately tested (no Soak period) during
`reloading with a 40:60 butane/air mixture. Subsequent can
`isters were tested in the Same way after increasing Soak
`periods of one, two, four and Six days, respectively. It is
`clearly Seen that the breakthrough emissions of butane
`increased from canisterS Subjected to a longer Soak periods.
`Although each of these canister performances meet 1999
`emission requirements, it is clear that they can release
`hydrocarbons after appreciable Soak periods.
`Similar results were obtained when the test was repeated
`by increasing the purge air Volume to 20 cu. ft. In real world
`and also in the CARB test, the purged canister experiences
`Some Soaks before loading; therefore, it is desirable to find
`ways to reduce the breakthrough emissions to near-Zero
`from a Soaked canister. By using a Small Secondary volume
`of adsorbent in Series with the primary volume of fuel vapor
`adsorbent, the breakthrough emissions can be reduced to
`near-Zero as demonstrated in the following experiment.
`Heated Stage II Canister
`Extrapolating on the very low breakthrough emissions
`from the green canister (FIG. 4), it has been found that
`near-Zero breakthrough emissions from a used canister can
`be realized if there is some activated carbon without any heel
`at the vapor exit (e.g., volume 93 in FIG. 2 or Stage II
`canister 191 in FIG.3). However, it is found that heel cannot
`be removed completely by purging with ambient air. The
`heel can be completely removed by heating the carbon and
`then purging with air. Experimental data had shown that if
`the carbon is heated to 350 F. and then purged with air, the
`heel is removed completely. Based on this observation, a
`heated Stage II canister was made as shown in FIG. 3.
`Experiments were conducted to prove the concept by using
`a 200 cc Stage II canister with 200 cc of activated carbon
`granules identical to those used in the above-described tests.
`The heel concentration in the Stage II canister was
`near-Zero after every heated purge as determined by the
`Stage II canister weight change. Effectiveness of Stage II
`canister in reducing the breakthrough emissions was mea
`55
`sured and the results are shown in FIG. 6. For comparison,
`a non-heated Stage II canister System is also included in
`FIG. 6. The results clearly show that the heated Stage II
`canister is very effective in reducing the canister break
`through emissions to very low levels.
`It is noted that in this early experiment the 200 cc volume
`of the Stage II canister was nearly ten percent of the total of
`the primary (1850 cc) and secondary volumes. It has been
`found that the volume of the Stage II canister or secondary
`volume can be smaller, less than 50 cc (or less than 2.5% to
`3% of the total of 1900 cc), for reducing breakthrough
`emissions in the SHED test. This, of course, means that the
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`45
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`50
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`60
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`65
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`8
`energy requirement for heating the Secondary volume of
`adsorbent can be reduced.
`At illustrated above, the secondary volume of adsorbent
`may be located in the same canister as the primary volume
`or it may be located in a separate heated canister upstream
`of the primary adsorbent volume with respect to purge air
`flow (or downstream of the flow path during vapor storage).
`The temperature sensors 100 (in FIG. 1) and 200 (in FIG.
`2) can be eliminated by using a heater (heater 96 in FIG. 2
`and heater 196 in FIG. 3) made of a self-regulating positive
`temperature coefficient material.
`While the invention has been described in terms of certain
`preferred embodiments, it is recognized that other could
`readily be made by one skilled in the art. Accordingly the
`scope of the invention is to be considered limited by the
`following claims.
`What is claimed is:
`1. An evaporative emissions control System for a vehicle,
`Said System comprising, in combination, a fuel tank for
`Storing a volatile fuel, an engine having an air induction
`System and adapted to consume Said fuel, a canister con
`taining a first volume of fuel Vapor adsorbent material for
`temporarily adsorbing and Storing fuel vapor from Said tank,
`a conduit for conducting fuel vapor from Said tank to a
`canister vapor inlet, a fuel vapor purge conduit from a
`canister purge outlet to Said induction System of Said engine,
`and a Vent/air inlet for venting Said canister and for admis
`Sion of air to Said canister during operation of Said engine
`induction System;
`Said canister defining an air flow path through said first
`Volume of adsorbent between a first region of Said
`canister at Said vent/air inlet and a Second region at Said
`purge outlet, and a vapor flow path from said vapor
`inlet toward Said vent/air inlet, Such that fuel vapor
`formed in Said tank flows through Said vapor inlet into
`said first volume of adsorbent where it is adsorbed and,
`during operation of Said engine induction System,
`ambient air flows in a path to and through Said vent/air
`inlet and along Said air flow path in Said canister
`through Said first Volume and Said purge ou