Patent Description:
Evaporation of gasoline fuel from motor vehicle fuel systems is a major potential source of hydrocarbon air pollution. Such emissions can be controlled by the canister systems that employ activated carbon to adsorb the fuel vapor emitted from the fuel systems. Under certain modes of engine operation, the adsorbed fuel vapor is periodically removed from the activated carbon by purging the canister systems with ambient air to desorb the fuel vapor from the activated carbon. The regenerated carbon is then ready to adsorb additional fuel vapor.

An increase in environmental concerns has continued to drive strict regulations of the hydrocarbon emissions from motor vehicles even when the vehicles are not operating. When a vehicle is parked in a warm environment during the daytime heating (i.e., diurnal heating), the temperature in the fuel tank increases resulting in an increased vapor pressure in the fuel tank. Normally, to prevent the leaking of the fuel vapor from the vehicle into the atmosphere, the fuel tank is vented through a conduit to a canister containing suitable fuel adsorbent materials that can temporarily adsorb the fuel vapor. The fuel vapor from the fuel tank enters the canister through a fuel vapor inlet of the canister and diffuses into the adsorbent volume where it is adsorbed in temporary storage before being released to the atmosphere through a vent port of the canister. Once the engine is turned on, ambient air is drawn into the canister system through the vent port of the canister. The purge air flows through the adsorbent volume inside the canister and desorbs the fuel vapor adsorbed on the adsorbent volume before entering the internal combustion engine through a fuel vapor purge conduit. The purge air does not desorb the entire fuel vapor adsorbed on the adsorbent volume, resulting in a residue hydrocarbon ("heel") that may be emitted to the atmosphere. In addition, that heel in local equilibrium with the gas phase also permits fuel vapors from the fuel tank to migrate through the canister system as emissions. Such emissions typically occur when a vehicle has been parked and subjected to diurnal temperature changes over a period of several days, commonly called "diurnal breathing losses. " The California Low Emission Vehicle Regulation makes it desirable for these diurnal breathing loss (DBL) emissions from the canister system to be below <NUM> ("PZEV") for a number of vehicles beginning with the <NUM> model year and below <NUM>, typically below <NUM>, ("LEV-II") for a larger number of vehicles beginning with the <NUM> model year. Now the California Low Emission Vehicle Regulation (LEV-III) requires canister DBL emissions not to exceed <NUM> as per the Bleed Emissions Test Procedure (BETP) as written in the California Evaporative Emissions Standards and Test Procedures for <NUM> and Subsequent Model Motor Vehicles, March <NUM>, <NUM>.

Several approaches have been reported to reduce the diurnal breathing loss (DBL) emissions. One approach is to significantly increase the volume of purge gas to enhance desorption of the residue hydrocarbon heel from the adsorbent volume. This approach, however, has the drawback of complicating management of the fuel/air mixture to the engine during purge step and tends to adversely affect tailpipe emissions.

Another approach is to design the canister to have a relatively low cross-sectional area on the vent-side of the canister, either by the redesign of existing canister dimensions or by the installation of a supplemental vent-side canister of appropriate dimensions. This approach reduces the residual hydrocarbon heel by increasing the intensity of purge air. One drawback of such approach is that the relatively low cross-sectional area imparts an excessive flow restriction to the canister.

Another approach for increasing the purge efficiency is to heat the purge air, or a portion of the adsorbent volume having adsorbed fuel vapor, or both. However, this approach increases the complexity of control system management and poses some safety concerns. See <CIT> and<CIT>.

Another approach is to route the fuel vapor through an initial adsorbent volume and then at least one subsequent adsorbent volume prior to venting to the atmosphere, wherein the initial adsorbent volume has a higher adsorption capacity than the subsequent adsorbent volume.

The regulations on diurnal breathing loss (DBL) emissions continue to drive new developments for improved evaporative emission control systems, especially when the level of purge air is low. Furthermore, the diurnal breathing loss (DBL) emissions may be more severe for a hybrid vehicle that includes both an internal combustion engine and an electric motor. In such hybrid vehicles, the internal combustion engine is turned off nearly half of the time during vehicle operation. Since the adsorbed fuel vapor on the adsorbents is purged only when the internal combustion engine is on, the adsorbents in the canister of a hybrid vehicle is purged with fresh air less than half of the time compared to conventional vehicles. A hybrid vehicle generates nearly the same amount of evaporative fuel vapor as the conventional vehicles. The lower purge frequency of the hybrid vehicle can be insufficient to clean the residue hydrocarbon heel from the adsorbents in the canister, resulting in high diurnal breathing loss (DBL) emissions.

Accordingly, it is desirable to have an evaporative emission control system with low diurnal breathing loss (DBL) emissions even when a low level of purge air is used, or when the adsorbents in the canister are purged less frequently such as in the case of hybrid vehicles, or both. Though a passive approach has been greatly desired, existing passive approaches still leave DBL emissions at levels that are many times greater than the <NUM> LEV-III requirement when only a fraction of the historically available purge is now available.

In one aspect of the present invention, there is provided an evaporative emission control system according to claim <NUM>.

The present disclosure now will be described more fully hereinafter, but not all embodiments of the disclosure are shown While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the claims. In addition, many modifications may be made to adapt a particular structure or material to the teachings of the disclosure without departing from the essential scope thereof.

The drawings accompanying the application are for illustrative purposes only. They are not intended to limit the embodiments of the present application. Additionally, the drawings are not drawn to scale. Elements common between figures may retain the same numerical designation.

The evaporative emission control canister system includes one or more canisters. The evaporative emission control canister system comprises an initial fuel-side adsorbent volume having an effective incremental adsorption capacity at <NUM> of greater than <NUM> grams n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane; and more than one vent-side adsorbent volumes downstream of the fuel-side adsorbent volume, where at least one vent-side adsorbent volume has an effective incremental adsorption capacity at <NUM> of less than <NUM> grams n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol % n-butane, an effective butane working capacity (BWC) of less than <NUM>/dL, and a g-total BWC of between <NUM> grams and <NUM> grams. The evaporative emission control canister system desirably has a two-day diurnal breathing loss (DBL) emissions of no more than <NUM> at no more than about <NUM> liters of purge applied after the <NUM>/hr butane loading step.

<FIG> show non-limiting examples of an evaporative emission control canister system not according to the claims wherein an initial adsorbent volume and subsequent adsorbent volume(s) are located within a single canister. <FIG> show non-limiting examples of the embodiments of the evaporative emission control canister system that includes more than one canister, wherein an initial adsorbent volume and at least one subsequent adsorbent volume are located in separate canisters that are connected to permit sequential contact by fuel vapor.

<FIG> illustrates one embodiment of the evaporative emission control canister system having an initial adsorbent volume and a subsequent adsorbent volume within a single canister. Canister system <NUM> includes a support screen <NUM>, a dividing wall <NUM>, a fuel vapor inlet <NUM> from a fuel tank, a vent port <NUM> opening to an atmosphere, a purge outlet <NUM> to an engine, an initial adsorbent volume <NUM>, and a subsequent adsorbent volume <NUM>.

When an engine is off, the fuel vapor from a fuel tank enters the canister system <NUM> through the fuel vapor inlet <NUM>. The fuel vapor diffuses into the initial adsorbent volume <NUM>, and then the subsequent adsorbent volume <NUM> before being released to the atmosphere through the vent port <NUM> of the canister system. Once the engine is turned on, ambient air is drawn into the canister system <NUM> through the vent port <NUM>. The purge air flows through the subsequent adsorbent volume <NUM> and then the initial adsorbent volume <NUM>, and desorbs the fuel vapor adsorbed on the adsorbent volumes <NUM>, <NUM> before entering an internal combustion engine through the purge outlet <NUM>.

The evaporative emission control canister system may include more than one subsequent adsorbent volume. By way of non-limiting example, the evaporative emission control canister system <NUM> may include an initial adsorbent volume <NUM> and three subsequent adsorbent volumes <NUM>, <NUM>, <NUM> within a single canister, as illustrated in <FIG>.

Additionally, the evaporative emission control canister system may include an empty volume within the canister. As used herein, the term "empty volume" refers to a volume not including any adsorbent. Such volume may comprise any non-adsorbent including, but not limited to, air gap, foam spacer, screen, or combinations thereof. In a non-limiting example shown in <FIG>, the evaporative emission control canister system <NUM> may include an initial adsorbent volume <NUM>; three subsequent adsorbent volumes <NUM>, <NUM>, <NUM> within a single canister; and an empty volume <NUM> between the subsequent adsorbent volumes <NUM> and <NUM>.

<FIG> shows an evaporative emission control canister system wherein the canister system includes more than one canister. As illustrated in <FIG>, the canister system <NUM> includes a main canister <NUM>, a support screen <NUM>, a dividing wall <NUM>, a fuel vapor inlet <NUM> from a fuel tank, a vent port <NUM> opening to an atmosphere, a purge outlet <NUM> to an engine, an initial adsorbent volume <NUM> in the main canister <NUM>, subsequent adsorbent volumes <NUM>, <NUM>, <NUM> in the main canister <NUM>, a supplemental canister <NUM> that includes a subsequent adsorbent volume <NUM>, and a conduit <NUM> connecting the main canister <NUM> to the supplemental canister <NUM>.

When the engine is off, the fuel vapor from a fuel tank enters the canister system <NUM> through the fuel vapor inlet <NUM> into the main canister <NUM>. The fuel vapor diffuses through the initial adsorbent volume <NUM> and then the subsequent adsorbent volumes (<NUM>, <NUM>, and <NUM>) in the main canister <NUM> before entering the supplemental canister <NUM> via the conduit <NUM>. The fuel vapor diffuses through the subsequent adsorbent volume <NUM> inside the supplemental canister <NUM> before being released to the atmosphere through the vent port <NUM> of the canister system. Once the engine is turned on, ambient air is drawn into the canister system <NUM> through the vent port <NUM>. The purge air flows through the subsequent adsorbent volume <NUM> in the supplemental canister <NUM>, the subsequent adsorbent volumes (<NUM>, <NUM>, <NUM>) in the main canister <NUM>, and then the initial adsorbent volume <NUM> in the main canister <NUM>, to desorb the fuel vapor adsorbed on the adsorbent volumes (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) before entering the internal combustion engine through the purge outlet <NUM>.

Similar to the main canister, the supplemental canister of the evaporative emission control canister system may include more than one subsequent adsorbent volume. By way of non-limiting example, the supplemental canister <NUM> of the evaporative emission control canister system <NUM> may include subsequent adsorbent volumes <NUM> and <NUM>, as illustrated in <FIG>.

Furthermore, the supplemental canister of the evaporative emission control canister system may include an empty volume between the subsequent adsorbent volumes. By way of non-limiting example, the supplemental canister <NUM> of the evaporative emission control canister system <NUM> may include subsequent adsorbent volumes (<NUM>, <NUM>, and <NUM>) and an empty volume <NUM> between the subsequent adsorbent volumes <NUM> and <NUM> as illustrated in <FIG>. In a non-limiting example shown in <FIG>, the supplemental canister <NUM> of the evaporative emission control canister system <NUM> may include subsequent adsorbent volumes (<NUM>, <NUM>, <NUM>), an empty volumes <NUM> between the subsequent adsorbent volumes <NUM> and <NUM>, and an empty volumes <NUM> between the subsequent adsorbent volumes <NUM> and <NUM>. As previously discussed, the term "empty volume" refers to a volume not including any adsorbent. Such volume may comprise any non-adsorbent including, but not limited to, air gap, foam spacer, screen, conduit, or combinations thereof.

Additionally, the evaporative emission control canister system may include an empty volume between the main canister and the supplemental canister.

When desired, the evaporative emission control canister system may include more than one supplemental canister. The evaporative emission control canister system may further include one or more empty volumes between the main canister and a first supplemental canister, between the supplement canisters, and/or at the end of the last supplemental canister. By way of non-limiting example, the evaporative emission control canister system may include a main canister, a first supplemental canister, a second supplemental canister, a third supplemental canister, an empty volume between the main canister and a first supplemental canister, an empty volume between the first and second supplemental canister, and an empty volume at the end of the third supplemental canister.

When desired, the total adsorbent volume (i.e., the sum of the initial adsorbent volume and the subsequent adsorbent volumes) may be the same as the volume of the evaporative emission control canister system. Alternatively, the total adsorbent volume may be less than the volume of the evaporative emission control canister system.

The term "adsorbent component" or "adsorbent volume," as used herein, refers to an adsorbent material or adsorbent containing material along vapor flow path, and may consist of a bed of particulate material, a monolith, honeycomb, sheet or other material.

The term "nominal volume," as used herein, refers to a sum of the volumes of the adsorbent components, and does not include the volumes of gaps, voids, ducts, conduits, tubing, plenum spaces or other volumes along lengths of the vapor flow path that are devoid of adsorbent material across the plane perpendicular to vapor flow path. For example, in <FIG> the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes <NUM> and <NUM>. For example, in <FIG> and <FIG>, the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes <NUM>, <NUM>, <NUM>, and <NUM>. In <FIG>, the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In <FIG>, the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In <FIG> and <FIG>, the total nominal volume of the canister system is the sum of the volumes of adsorbent volumes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The term "nominal volume apparent density," as used herein, is the mass of the representative adsorbent in the adsorbent volume divided by the nominal volume of adsorbent, where the length of the volume is defined as the in situ distance within the canister system between the perpendicular plane of the vapor flow path initially in contact with the adsorbent component and the perpendicular plan of the vapor flow path exiting the adsorbent component.

Non-limiting examples of how to calculate the nominal volume apparent density for various forms of adsorbents are described herein.

The standard method ASTM D <NUM> (hereinafter "the Standard Method") may be used to determine the nominal volume apparent density of particulate adsorbents, such as granular and pelletized adsorbents of the size and shape typically used for evaporative emission control for fuel systems. The Standard Method may be used to determine the apparent density of adsorbent volume, when it provides the same apparent density value as the ratio of the mass and the nominal volume of the adsorbent bed found in the canister system. The mass of the adsorbent by the Standard Method is of the representative adsorbent used in the incremental adsorption analysis, i.e., equivalently including or excluding inert binders, fillers, and structural components within the adsorbent volume depending on what representative material is analyzed as the adsorbent sample.

Furthermore, the nominal volume apparent density of adsorbent volume may be determined using an alternative apparent density method, as defined below. The alternative method may be applied to nominal adsorbent volumes that have apparent densities that are not comparably or suitably measured by the Standard Method. Additionally, the alternative apparent density method may be applied to particulate adsorbents in lieu of the Standard Method, due to its universal applicability. The alternative method may be applied to the adsorbent volume that may contain particulate adsorbents, non-particulate adsorbents, and adsorbents of any form augmented by spacers, voids, voidage additives within a volume or sequential similar adsorbent volumes for the effect of net reduced incremental volumetric capacity.

In the alternative apparent density method, the apparent density of adsorbent volume is obtained by dividing the mass of adsorbent by the volume of adsorbent, wherein:.

The apparent density of cylindrical honeycomb absorbents may be determined according to the procedure of Purification Cellutions, LLC (Waynesboro, GA) SOP <NUM> - <NUM>. The volume of adsorbent is a multiple of the cross-sectional area (A) and the length (h) of the adsorbent. The length (h) of the adsorbent is defined as the distance between the front plane of the adsorbent perpendicular to vapor or gas flow entering the adsorbent and the back plane of the adsorbent where the vapor or gas exits the adsorbent. The volume measurement is that of the nominal volume, which is also used for defining bed volume ratios for purge. In the case of a cylindrical honeycomb adsorbent of circular cross-section, the adsorbent cross-sectional area is determined by πd<NUM>/<NUM>, where d is the average diameter measured at four points on each end of the honeycomb. The nominal adsorbent volume and the nominal volume apparent density are calculated as follows: <MAT> <MAT> wherein "Part Mass" is the mass of the adsorbent for which a representative adsorbent sample was tested for adsorptive properties, including representative proportions of inert or adsorptive binders and fillers.

By way of non-limiting examples, <FIG> shows the boundary definitions for the nominal volume of a honeycomb adsorbent <NUM> having a cross-sectional area A. The vapor or gas flows through the honeycomb adsorbent <NUM> in the direction of D1 to D2. The vapor or gas enters the front plane (F) of the adsorbent <NUM>, flows through the length (h) of the adsorbent <NUM>, and exits back plane (B) of the adsorbent <NUM>. The nominal volume of a honeycomb adsorbent <NUM> equals to the cross-sectional area A x the length h. Similarly, <FIG> shows the boundary definitions for the nominal volume of foam adsorbent <NUM>.

For pleated and corrugated adsorbents, the nominal adsorbent volume includes all the void space created by the pleats and corrugations. The volume measurement is that of the nominal volume, which is also used for defining bed volume ratios for purge. The nominal volume and the apparent density of adsorbent are calculated as follows: <MAT> <MAT> wherein.

By way of non-limiting example, <FIG> shows the boundary definitions for the volume of a stacked corrugated sheet adsorbent monolith <NUM>. It is also within those skilled in the art to form such a monolith as an extruded honeycomb.

In the case of a pleated adsorbent, the adsorbent cross-sectional area is determined by L x W, where L is the distance from one edge of the adsorbent to the opposite edge of the adsorbent in direction X, and W is the distance from one edge of the adsorbent to the opposite edge of the adsorbent in direction Y.

By way of non-limiting examples, <FIG> shows the boundary definitions for the volume of a single pleat or corrugation <NUM>. <FIG> shows the boundary definitions for the volume of a pleated or corrugated sheet <NUM> with vapor flow path provided through the sheet by some form of permeability to gas flow. The face of the sheet is perpendicular to the vapor flow. In contrast, <FIG> shows the boundary definitions for the volume of a pleated or corrugated sheet <NUM> where its face is angled to gas flow. <FIG> shows the boundary definitions for the volume of an adsorbent volume <NUM> of parallel adsorbent sheets. <FIG> shows the boundary definitions for the volume of an adsorbent sleeve <NUM>.

The term "nominal incremental adsorption capacity," as used herein, refers to an adsorption capacity according to the following equation: <MAT> wherein.

The standard method ASTM D5228 may be used to determine the nominal volume butane working capacity (BWC) of the adsorbent volumes containing particulate granular and/or pelletized adsorbents.

A modified version of ASTM D5228 method may be used to determine the nominal volume butane working capacity (BWC) of the honeycomb, monolith, and/or sheet adsorbent volumes. The modified method may also be used for particulate adsorbents, where the particulate adsorbents include fillers, voids, structural components, or additives. Furthermore, the modified method may be used where the particulate adsorbents are not compatible with the standard method ASTM D5228, e.g., a representative adsorbent sample may not be readily placed as the <NUM> fill in the sample tube of the test.

The modified version of ASTM D5228 method is as follows. The adsorbent sample is oven-dried for a minimum of eight hours at <NUM>±<NUM>, and then placed in desiccators to cool down. The dry mass of the adsorbent sample is recorded. The mass of the empty testing assembly is determined before the adsorbent sample is assembled into a testing assembly. Then, the test assembly is installed into the a flow apparatus and loaded with n-butane gas for a minimum of <NUM> minutes (± <NUM>) at a butane flow rate of <NUM>/min at <NUM> and <NUM> atm pressure. The test assembly is then removed from the BWC test apparatus. The mass of the test assembly is measured and recorded to the nearest <NUM> grams. This n-butane loading step is repeated for successive <NUM> minutes flow intervals until constant mass is achieved. For example, the total butane load time for a <NUM> diameter x <NUM> long honeycomb (EXAMPLE <NUM> Adsorbent <NUM>) was <NUM> minutes. The test assembly may be a holder for a honeycomb or monolith part, for the cases where the nominal volume may be removed and tested intact. Alternatively, the nominal volume may need to be a section of the canister system, or a suitable reconstruction of the nominal volume with the contents appropriately oriented to the gas flows, as otherwise encountered in the canister system.

The test assembly is reinstalled to the test apparatus and purged with <NUM> liter/min air at <NUM> and <NUM> atm pressure for a set selected purge time (± <NUM>) according to the formula: Purge Time (min) = (<NUM> x Nominal Volume (cc))/(<NUM> (cc/min)).

The direction of the air purge flow in the BWC test is in the same direction as the purge flow to be applied in the canister system. After the purge step, the test assembly is removed from the BWC test apparatus. The mass of the test assembly is measured and recorded to the nearest <NUM> grams within <NUM> minutes of test completion.

The nominal volume butane working capacity (BWC) of the adsorbent sample was determined using the following equation: <MAT> wherein.

The effective volume of adsorbents takes into account the air gaps, voids and other volumes between the nominal volumes of adsorbents along the vapor flow path that lack adsorbent. Thus, the effective volumetric properties of adsorbent refer to the properties of the adsorbent that take into account air gaps, voids and other volumes between the nominal volumes of adsorbents that lack adsorbent along the vapor flow path.

The effective volume (Veff) for a given length of the vapor flow path is the sum of the nominal volumes of adsorbent (Vnom, i) present along that vapor path length plus adsorbent-free volumes along that vapor flow path (Vgap, i).

A volumetric adsorptive properties of an effective volume (Beff), such as incremental adsorption capacity (g/L), apparent density (g/mL) and BWC (g/dL), is the sum of each property of the individual nominal volumes to be considered as part of the effective volume (Bnom, i) multiplied by each individual nominal volume (Vnom, i), then divided by the total effective volume (Veff): <MAT>.

Thus, the term "effective incremental adsorption capacity" is the sum of each nominal incremental adsorption capacity multiplied by each individual nominal volume, and then divided by the total effective volume.

The term "effective butane working capacity (BWC)" is the sum of each BWC value multiplied by each individual nominal volume, and then divided by the total effective volume.

The term "effective apparent density" is the sum of each apparent density multiplied by each individual nominal volume, and then divided by the total effective volume
The term "g-total BWC of the effective volume" is the sum of the g-total BWC gram values of the nominal volumes within the effective volume.

As non-limiting examples of how to determine effective volume of adsorbents, <FIG> shows the effective volume for three adsorbent honeycomb nominal volumes connected in the flow path by gaps of equal cross-sectional areas, with the arrow in the direction of D1 to D2 indicating vapor flow into the effective volume, towards the canister system vent. <FIG> shows three adsorbent honeycomb nominal volumes connected by conduit sections of different cross-sectional areas compared with the honeycomb cross-sectional areas. In <FIG> and <FIG>, the honeycomb nominal volumes and the gaps appear symmetric. However, it is understood that the honeycomb nominal volumes and the gaps may have different dimensions.

In some embodiments, the volumetric adsorptive properties of the adsorbent volumes may be deceased along the vapor flow path. By way of non-limiting example, the volumetric incremental capacity and butane working capacity (BWC) of the adsorbent volumes may be decreased towards the vent direction of the canister system. The diminished volumetric adsorptive properties may be attained by modifying the properties of the separate sections of adsorbent, by varying the size of the gaps between adsorbent nominal volumes (<FIG>), by adjusting the dimensions of individual adsorbent nominal volumes, separately (<FIG> and <FIG>), or by a combination thereof (<FIG>). By way of non-limiting examples, as shown in <FIG> and <FIG>, the canister system (<NUM>, <NUM>) may include adsorbent volume sections "F," "M," and "B" along the flow path in the direction of D1 to D2. The effective butane working capacities (BWC) of the adsorbent volume sections may be decreased along the flow path in the direction of D1 to D2 (i.e., the effective BWC of the adsorbent volume section F > the effective BWC of the adsorbent volume section M > the effective BWC of the adsorbent volume section B). In some embodiments, the effective BWC of the adsorbent volume section M and/or section B may be less than <NUM>/dL, while the effective BWC of the canister system may be more than or equal to <NUM>/dl.

The disclosed evaporative emission control system may provide low diurnal breathing loss (DBL) emissions even under a low purge condition. The evaporative emission performance of the disclosed evaporative emission control system may be within the regulation limits defined by the California Bleed Emissions Test Procedure (BETP), which is <NUM> or less, even under a low purge condition.

The term "low purge," as used herein, refers to a purge level at or below <NUM> liters applied after the <NUM>/hr butane loading step (i.e., <NUM> bed volumes for a <NUM> liter adsorbent component system).

The evaporative emission control system may provide low diurnal breathing loss (DBL) emissions even when being purged at or below <NUM> liters applied after the <NUM>/hr butane loading step. In some embodiments, the evaporative emission control system may be purged at or below <NUM> liters applied after the <NUM>/hr butane loading step.

The evaporative emission control system may provide low diurnal breathing loss (DBL) emissions even when being purged at or below <NUM> BV (bed volumes based on a <NUM> liter nominal volume of the canister system) applied after the <NUM>/hr butane loading step. In some embodiments, the evaporative emission control system may be purged at or below <NUM> BV (based on a <NUM> liter nominal volume of the canister system) applied after the <NUM>/hr butane loading step.

In some embodiments, the evaporative emission control system may include a heat unit to further enhance the purge efficiency. By way of non-limiting example, the evaporative emission control system may include a heat unit for heating the purge air, at least one subsequent adsorbent volume, or both.

The adsorbents suitable for use in the adsorbent volumes may be derived from many different materials and in various forms. It may be a single component or a blend of different components. Furthermore, the adsorbent (either as a single component or a blend of different components) may include a volumetric diluent. Non-limiting examples of the volumetric diluents may include, but are not limited to, spacer, inert gap, foams, fibers, springs, or combinations thereof.

The adsorbent volumes comprise activated carbon. Furthermore, activated carbon may be produced using a variety of processes including, but are not limited to, chemical activation, thermal activation, or combinations thereof.

A variety of adsorbent forms may be used. Non-limiting examples of the adsorbent forms may include granular, pellet, spherical, honeycomb, monolith, pelletized cylindrical, particulate media of uniform shape, particulate media of nonuniform shape, structured media of extruded form, structured media of wound form, structured media of folded form, structured media of pleated form, structured media of corrugated form, structured media of poured form, structured media of bonded form, non-wovens, wovens, sheet, paper, foam, or combinations thereof. The adsorbent (either as a single component or a blend of different components) may include a volumetric diluent. Non-limiting examples of the volumetric diluents may include, but are not limited to, spacer, inert gap, foams, fibers, springs, or combinations thereof. Furthermore, the adsorbents may be extruded into special thin-walled cross-sectional shapes, such as hollow-cylinder, star, twisted spiral, asterisk, configured ribbons, or other shapes within the technical capabilities of the art. In shaping, inorganic and/or organic binders may be used.

The honeycomb adsorbents may be in any geometrical shape including, but are not limited to, round, cylindrical, or square. Furthermore, the cells of honeycomb adsorbents may be of any geometry. Honeycombs of uniform cross-sectional areas for the flow-through passages, such as square honeycombs with square cross-sectional cells or spiral wound honeycombs of corrugated form, may perform better than round honeycombs with square cross-sectional cells in a right angled matrix that provides adjacent passages with a range of cross-sectional areas and therefore passages that are not equivalently purged. Without being bound by any theory, it is believed that the more uniform cell cross-sectional areas across the honeycomb faces, the more uniform flow distribution within the part during both adsorption and purge cycles, and, therefore, lower DBL emissions from the canister system.

In some embodiments, the evaporative emission control system may further include one or more heat input unit(s) for heating one or more adsorbent volume(s) and/or one or more empty volume(s). The heat input units may include, but are not limited to, internal resistive elements, external resistive elements, or heat input units associated with the adsorbent. The heat input unit associated with the adsorbent may be an element separate from the adsorbent (i.e., non-contacted with adsorbents). Alternatively, the heat input unit associated with the adsorbent may be a substrate or layer on to which the adsorbent is attached, bonded, non-bonded, or in physical contact. The heat input unit associated with the adsorbent may be adsorbent directly heated electrically by having appropriate resistivity. The resistivity properties of the adsorbent may be modified by the addition of conductive or resistive additives and binders in the original preparation of the adsorbent and/or in the forming of the adsorbent into particulate or monolithic forms. The conductive component may be conductive adsorbents, conductive substrates, conductive additives and/or conductive binders. The conductive material may be added in adsorbent preparation, added in intermediate shaping process, and/or added in adsorbent shaping into final form. Any mode of heat input unit may be used. By way of non-limiting example, the heat input unit may include a heat transfer fluid, a heat exchanger, a heat conductive element, and positive temperature coefficient materials. The heat input unit may or may not be uniform along the heated fluid path length (i.e., provide different local intensities). Furthermore, the heat input unit may or may not be distributed for greater intensity and duration of heating at different points along the heated fluid path length.

<FIG> shows a simplified schematic drawing of the apparatus used for the determination of the butane adsorption capacity. This is known in the field as the McBain method. The apparatus <NUM> includes a sample pan <NUM> and a spring <NUM> inside a sample tube <NUM>, a rough vacuum pump <NUM>, a diffusion pump <NUM>, a stopcock <NUM>, metal/O-ring vacuum valves <NUM>-<NUM>, a butane cylinder <NUM>, a pressure readout unit <NUM>, and at least one conduit <NUM> connecting the components of the apparatus <NUM>.

The representative adsorbent component sample ("adsorbent sample") was oven-dried for more than <NUM> hours at <NUM> before loading onto the sample pan <NUM> attached to the spring <NUM> inside the sample tube <NUM>. Then, the sample tube <NUM> was installed into the apparatus <NUM>. The adsorbent sample shall include representative amounts of any inert binders, fillers and structural components present in the nominal volume of the adsorbent component when the Apparent Density value determination equivalently includes the mass of the inert binders, fillers, and structural components in its mass numerator. Conversely, the adsorbent sample shall exclude these inert binders, fillers, and structural components when the Apparent Density value equivalently excludes the mass of the inert binders, fillers, and structural components in its numerator. The universal concept is to accurately define the adsorptive properties for butane on a volume basis within the nominal volume.

A vacuum of less than <NUM> torr was applied to the sample tube, and the adsorbent sample was heated at <NUM> for <NUM> hour. The mass of the adsorbent sample was then determined by the extension amount of the spring using a cathetometer. After that, the sample tube was immersed in a temperature-controlled water bath at <NUM>. Air was pumped out of the sample tube until the pressure inside the sample tube was <NUM>-<NUM> torr. n-Butane was introduced into the sample tube until equilibrium was reached at a selected pressure. The tests were performed for two data sets of four selected equilibrium pressures each, taken about <NUM> torr and taken about <NUM> torr. The concentration of n-butane was based on the equilibrium pressure inside the sample tube. After each test at the selected equilibrium pressure, the mass of the adsorbent sample was measured based on the extension amount of the spring using cathetometer. The increased mass of the adsorbent sample was the amount of n-butane adsorbed by the adsorbent sample. The mass of n-butane absorbed (in gram) per the mass of the adsorbent sample (in gram) was determined for each test at different n-butane equilibrium pressures and plotted in a graph as a function of the concentration of n-butane (in %volume). A <NUM> vol% n-butane concentration (in volume) at one atmosphere is provided by the equilibrium pressure inside the sample tube of <NUM> torr. A <NUM> vol% n-butane concentration at one atmosphere is provided by the equilibrium pressure inside the sample tube of <NUM> torr. Because equilibration at precisely <NUM> torr and <NUM> torr may not be readily obtained, the mass of adsorbed n-butane per mass of the adsorbent sample at <NUM> vol% n-butane concentration and at <NUM> vol% n-butane concentration were interpolated from the graph using the data points collected about the target <NUM> and <NUM> torr pressures.

Alternatively, Micromeritics (such as Micromeritics ASAP <NUM>) may be used for determining the incremental butane adsorption capacity instead of the McBain method.

The evaporative emission control systems of EXAMPLES <NUM>-<NUM> (identified below) were assembled with the selected amounts and types of adsorbents as shown in TABLES <NUM>-<NUM>.

Each example was uniformly preconditioned (aged) by repetitive cycling of gasoline vapor adsorption using certified TF-<NUM> fuel (<NUM> RVP, <NUM> vol % ethanol) and <NUM> nominal bed volumes of dry air purge at <NUM> LPM based on the main canister (e.g., <NUM> liters for a <NUM> main canister and <NUM> liters for a <NUM> main canister). The gasoline vapor load rate was <NUM>/hr and the hydrocarbon composition was <NUM> vol%, generated by heating two liters of gasoline to about <NUM> and bubbling air through at <NUM>/min. The two-liter aliquot of fuel was replaced automatically with fresh gasoline every two hours until <NUM> ppm breakthrough was detected by a FID (flame ionization detector). A minimum of <NUM> aging cycles were used on a virgin canister. The aging cycles were followed by a single butane adsorption/air purge step. This step was to load butane at <NUM>/hour at a <NUM> vol% concentration in air at one atm to <NUM> ppm breakthrough, soak for one hour, then purge with dry air for <NUM> minutes with a total purge volume attained by selecting the appropriate constant air purge rate for that period. The canister was then soaked with the ports sealed for <NUM> hour at <NUM>.

The DBL emissions were subsequently generated by attaching the tank port of the example to a fuel tank filled <NUM> vol% (based on its rated volume) with CARB Phase II fuel (<NUM> RVP, <NUM>% ethanol). Prior to attachment, the filled fuel tank had been stabilized at <NUM> for <NUM> hours while venting. The tank and the example were then temperature-cycled per CARB's two-day temperature profile, each day from <NUM> to <NUM> over <NUM> hours, then back down to <NUM> over <NUM> hours. Emission samples were collected from the example vent at <NUM> hours and <NUM> hours during the heat-up stage into Kynar bags. The Kynar bags were filled with nitrogen to a known total volume based on pressure and then evacuated into a FID to determine hydrocarbon concentration. The FID was calibrated with a <NUM> ppm butane standard. From the Kynar bag volume, the emissions concentration, and assuming an ideal gas, the mass of emissions (as butane) was calculated. For each day, the mass of emissions at <NUM> hours and <NUM> hours were added. Following CARB's protocol the day with the highest total emissions was reported as "<NUM>-day emissions. " In all cases, the highest emissions were on Day <NUM>. This procedure is generally described in <NPL>, and in <NPL> and <NPL> and <NPL>).

For EXAMPLES <NUM>-<NUM>, <NUM> and EXAMPLES <NUM>-<NUM>, a <NUM> fuel tank and a <NUM> liter main canister (TABLE <NUM>, Main Canister Type #<NUM>) was used as a main canister having fuel-source side volumes (i.e., an initial adsorbent volume) filled with <NUM> liters of NUCHAR® BAX <NUM> activated carbon adsorbent and a vent-side volume filled with <NUM> liters of NUCHAR® BAX LBE activated carbon adsorbent. The volumes were configured such that there was a <NUM> fuel-source side chamber and a <NUM> vent-side chamber, where the fuel-source chamber had a cross sectional area (CSA) that was <NUM> times the vent-side CSA. The BAX <NUM> activated carbon filled the fuel source chamber (similar to volumes <NUM> plus <NUM> in <FIG>) and <NUM> of the immediate downstream volume in the vent-side chamber (similar to volume <NUM> in <FIG>). The <NUM> of the BAX LBE activated carbon filled the remaining volume of the vent-side chamber (similar to volume <NUM> in <FIG>). NUCHAR® BAX <NUM> activated and NUCHAR® BAX LBE activated carbon are wood-based activated carbon products, commercially available from MeadWestvaco Corporation, having an incremental adsorption capacity at <NUM> of <NUM> grams n-butane/L and <NUM> grams n-butane/L respectively, between vapor concentration of <NUM> vol% and <NUM> vol% n-butane ("Nominal Incremental Capacity" in TABLE <NUM>). For the post-butane loading air purge step, each canister system in EXAMPLES <NUM>-<NUM>, <NUM> and EXAMPLES <NUM>-<NUM> was purged with <NUM> liters of purge air at a purge rate of <NUM> lpm. In terms of bed volume ratios of purge volume divided by the total nominal volume of the canister systems, the purge applied was between <NUM> and <NUM> bed volumes (BV).

For EXAMPLES <NUM>-<NUM> and <NUM>-<NUM>, a <NUM> fuel tank and a <NUM> liter main canister (TABLE <NUM>, Main Canister Type #<NUM>) was used as a main canister having fuel-source side volumes (i.e., an initial adsorbent volume) filled with <NUM> liters of NUCHAR® BAX <NUM> activated carbon adsorbent and a vent-side volume filled with <NUM> liters of NUCHAR® BAX LBE activated carbon adsorbent. The volumes were configured such that there was a <NUM> fuel-source side chamber and a <NUM> vent-side chamber, where the fuel-source chamber had a cross sectional area (CSA) that was <NUM> times the vent-side CSA. The BAX <NUM> activated carbon filled the fuel source chamber (similar to volumes <NUM> plus <NUM> in <FIG>) and <NUM> of the immediate downstream volume in the vent-side chamber (similar to volume <NUM> in <FIG>). The <NUM> of the BAX LBE activated carbon filled the remaining volume of the vent-side chamber (similar to volume <NUM> in <FIG>). NUCHAR® BAX <NUM> activated is a wood-based activated carbon product, commercially available from MeadWestvaco Corporation, having an incremental adsorption capacity at <NUM> of <NUM> grams n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane. During the post-butane loading air purge step, each canister system example was purged with either <NUM> or <NUM> liters of purge air at a purge rate of <NUM> or <NUM> lpm, respectively. In terms of bed volume ratios of purge volume divided by the total nominal volume of the canister systems, the purge applied was between <NUM> and <NUM> BV.

EXAMPLES <NUM>-<NUM> each included none, one, or two additional vent-side adsorbent volumes in-series. The first supplemental canister downstream along the vapor flow path from the main canister (if present) was noted as "Adsorbent <NUM>" and a second in-series supplemental canister (if present) downstream along the vapor flow path from Adsorbent <NUM> was noted as "Adsorbent <NUM>. " One type of additional vent-side adsorbent (similar to supplemental canister <NUM> in <FIG>) was described as "35x150," which was a <NUM> diameter x <NUM> long, <NUM> cells per square inch (cpsi) cylindrical carbon honeycomb. The accounting of the effective volume for the "35x150" adsorbent was the same boundaries as shown in <FIG>, that is, the effective volume was bounded by the vapor entrance and exit faces of the honeycomb, and equal to its nominal volume. The second type of additional vent-side adsorbent (similar to supplemental canister <NUM> in <FIG>) was described as "<NUM>-35x50," which was three <NUM> diameter x <NUM> long, <NUM> cpsi cylindrical carbon honeycombs, including two <NUM> diameter x <NUM> thick foam spacers. Each foam spacer created a <NUM> voidage gap between each sequential <NUM> long honeycomb length, similar to gaps <NUM> and <NUM> in <FIG>. The accounting of the effective volume was the same boundaries as shown in <FIG>, that is, the effective volume was bounded by the vapor entrance face of the first of the three honeycombs and exit faces of the third of the three honeycombs, and equal to the nominal volumes of the three honeycombs plus the volumes of the <NUM>-mm thick spacers. The nominal incremental adsorption capacity at <NUM> of n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane was shown as the "Nominal Incremental Capacity. " When based on the effective volume, the incremental adsorption capacity at <NUM> of n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane was shown as the "Effective Incremental Capacity. " The two-day DBL emissions were reported as the "<NUM>-day DBL Emissions" in units of mg. The reported results were often the average of several replicates of the BETP in order to verify findings.

The evaporative emission control canister system of EXAMPLES <NUM>-<NUM>, <NUM> and EXAMPLES <NUM>-<NUM> each included an initial adsorbent volume of BAX <NUM> activated carbon adsorbent having a nominal incremental adsorption capacity at <NUM> of <NUM> n-butane/L (i.e., more than <NUM>/L) between vapor concentration of <NUM> vol% and <NUM> vol% n-butane, and a subsequent adsorbent volume of BAX LBE activated carbon adsorbent having a nominal incremental adsorption capacity at <NUM> of <NUM>/L (less than <NUM>/L) between vapor concentration of <NUM> vol% and <NUM> vol% n-butane (less than <NUM>/L). This is main canister type #<NUM> in TABLE <NUM>.

EXAMPLE <NUM> was the evaporative emission control canister system disclosed in the <CIT>. As shown in TABLE <NUM>, the evaporative emission control canister system of EXAMPLE <NUM> provided a <NUM>-day DBL Emissions of <NUM> under a low purge condition of <NUM> bed volume (BV) of purge air after butane loading (i.e., <NUM> liters). These <NUM>-day DBL Emissions were more than an order of magnitude above the <NUM> regulation limit under the California Bleed Emissions Test Procedure (BETP). Thus, the <NUM> regulation limits under the California Bleed Emissions Test Procedure (BETP) could not be achieved by the evaporative emission control canister system disclosed in the <CIT>.

For EXAMPLE <NUM>, an additional vent-side adsorbent volume (Adsorbent <NUM>) was added to EXAMPLE <NUM> in the form of an activated carbon honeycomb ("35x150") having an effective incremental adsorption capacity at <NUM> of <NUM>/L (less than <NUM>/L) between vapor concentration of <NUM> vol% and <NUM> vol% n-butane (less than <NUM>/L), an effective BWC of <NUM>/dL and a g-total BWC of <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL Emissions for EXAMPLE <NUM> with a low purge level of <NUM> liters (applied after butane loading) was <NUM>, which was still above the <NUM> regulation limit under the California Bleed Emissions Test Procedure (BETP). Thus, at the purge level of <NUM> liters applied after butane loading, the evaporative emission control canister system of the <CIT> still could not satisfy the <NUM> regulation limit under BETP even when it was used in combination with the additional vent-side adsorbent volume (Adsorbent <NUM>).

For EXAMPLE <NUM>, a second additional vent-side adsorbent volume in the form of a activated carbon honeycomb (Adsorbent <NUM>) of the same type and properties as Adsorbent <NUM> ("35x150") was added to the canister system of EXAMPLE <NUM>. Surprisingly, as shown in TABLE <NUM>, there was only a marginal reduction in the <NUM>-day DBL emissions from the additional vent-side adsorbent volume in EXAMPLE <NUM>, to <NUM> and still above the <NUM> regulation limit under the California Bleed Emissions Test Procedure (BETP).

EXAMPLE <NUM> was a variation of EXAMPLE <NUM> in that the activated carbon honeycombs were each divided in to three <NUM> long section with narrow spacers in between. For EXAMPLE <NUM>, the spacers reduced the effective incremental capacities of Adsorbents <NUM> and <NUM> to <NUM>/L and reduced the effective BWC to <NUM>/dL, but, by definition, kept the g-total BWC the same, at <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions of EXAMPLE <NUM> remained high at <NUM> and were still above the <NUM> regulation limits under the California Bleed Emissions Test Procedure (BETP).

In EXAMPLE <NUM>, Adsorbent <NUM> was honeycombs divided into two <NUM> long sections with a narrow spacer in between. The effective incremental capacity was <NUM>/L and the effective BWC was <NUM>/dL. By definition, the g-total BWC was <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions of EXAMPLE <NUM> remained high at <NUM> and were still above the <NUM> regulation limits under the California Bleed Emissions Test Procedure (BETP).

For EXAMPLE <NUM>, Adsorbent <NUM> had an effective incremental capacity of <NUM>/L, an effective BWC of <NUM>/dL and a g-total BWC of <NUM>. For EXAMPLE <NUM>, Adsorbent <NUM> had an effective incremental capacity of <NUM>/L, an effective BWC of <NUM>/dL and a g-total BWC of <NUM>. As shown in TABLE <NUM>, with <NUM> liters of purge, the canister systems of EXAMPLES <NUM> and <NUM> provided the <NUM>-day DBL Emissions of <NUM>/dl and <NUM>/dl, respectively. Thus, the canister systems of EXAMPLES <NUM> and <NUM> had the <NUM>-day DBL Emissions well below the BETP requirement of less than <NUM> for low purge conditions of <NUM> liters (<NUM> BV).

The evaporative emission control canister system of EXAMPLES <NUM>, <NUM> and <NUM>-<NUM> were based on the main canister type #<NUM> in TABLE <NUM>.

EXAMPLE <NUM> was the evaporative emission control canister system similar to those disclosed in the <CIT>. As shown in TABLE <NUM>, the evaporative emission control canister system of EXAMPLE <NUM> did not include any additional adsorbent volume on the vent side. EXAMPLE <NUM> provided <NUM>-day DBL Emissions of <NUM> under a low purge condition of <NUM> bed volume (BV) of purge air after butane loading (i.e., <NUM> liters), which was about nine time higher than the <NUM> regulation limit under the California Bleed Emissions Test Procedure (BETP). This confirmed that the evaporative emission control canister system similar to those disclosed in the <CIT> was not able to achieve the <NUM>-day DBL Emissions requirements under the BETP (i.e., less than <NUM>) when low purge was used.

In EXAMPLE <NUM>, a low volume of purge after butane loading <NUM> liters was applied, or <NUM> BV for the <NUM> nominal volume of the canister system that included an additional vent-side adsorbent volume of a "35x150" activated carbon honeycomb as Adsorbent <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions were high at <NUM> and above the <NUM> regulation limit under the California Bleed Emissions Test Procedure (BETP).

For EXAMPLE <NUM>, the purge applied was reduced to <NUM> liters, or <NUM> BV for the main canister type #<NUM> that included the same additional vent-side adsorbent volumes as EXAMPLE <NUM>. As shown in TABLE <NUM>, the <NUM>-Day DBL emissions were high at <NUM> and above the <NUM> regulation limits under the California Bleed Emissions Test Procedure (BETP).

The canister systems of EXAMPLES <NUM>, <NUM> and <NUM> each included an initial adsorbent volume of NUCHAR® BAX <NUM> activated carbon adsorbent having an incremental adsorption capacity at <NUM> of <NUM> n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane (i.e., more than <NUM>/L) as part of the main canister type #<NUM>, and at least one subsequent adsorbent volume ("Adsorbent <NUM>" in TABLE <NUM>) having an effective incremental adsorption capacity at <NUM> butane adsorption capacity of less than <NUM>/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane and a g-total BWC of between <NUM> and <NUM>.

Adsorbent <NUM> in EXAMPLE <NUM> had an effective incremental capacity of <NUM>/L, an effective BWC of <NUM>/dL (greater than <NUM>/dL) and a g-total BWC of <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions for EXAMPLE <NUM> under the low purge of <NUM> liters (i.e., <NUM> BV) were <NUM> and well above the BETP requirement of less than <NUM>.

In contrast, Adsorbent <NUM> in EXAMPLE <NUM> had an effective incremental capacity of <NUM>/L, an effective BWC of <NUM>/dL (less than <NUM>/dL) and a g-total BWC of <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions under the low purge of <NUM> liters, equal to <NUM> BV, were <NUM> and within the BETP requirement of less than <NUM>.

Likewise, Adsorbent <NUM> in EXAMPLE <NUM> had an effective incremental capacity of <NUM>/L, an effective BWC of <NUM>/dL (less than <NUM>/dL) and a g-total BWC of <NUM>. As shown in TABLE <NUM>, the <NUM>-day DBL emissions under the low purge of <NUM> liters, equal to <NUM> BV, were <NUM> and within the BETP requirement of less than <NUM>.

TABLE <NUM> and TABLE <NUM> summarized the conditions of the canister systems of EXAMPLES <NUM>-<NUM>, and their measured <NUM>-day DBL emissions. The canister systems of EXAMPLES <NUM>, <NUM>, <NUM> and <NUM> provided the <NUM>-day DBL emissions of less than <NUM>, as required under the California Bleed Emissions Test Procedure (BETP). The requirement not to exceed <NUM> for BETP under low purge was met by satisfying a window of adsorptive properties by a vent-side volume, where the window was an effective BWC of less than <NUM>/dL and a g-total BWC of between <NUM> and <NUM>. Thus, the means to achieve the BETP emissions requirement under low purge conditions was more than only a reduction in the working capacity or incremental capacity across the vapor flow path of the canister system and specifically of the vent-side adsorbent volume to a prescribed level, but to additionally have sufficient gram working capacity in that vent-side volume to restrain the emissions.

Claim 1:
An evaporative emission control system, comprising:
a fuel tank for storing fuel;
an engine having an air induction system and adapted to consume the fuel;
an evaporative emission control canister system (<NUM>), the canister system comprising:
a canister having a support screen (<NUM>) and a dividing wall (<NUM>);
a fuel vapor inlet conduit (<NUM>) connecting the evaporative emission control canister system to the fuel tank;
a fuel vapor purge conduit (<NUM>) connecting the evaporative emission control canister system to the air induction system of the engine; and
a vent conduit (<NUM>) for venting the evaporative emission control canister system and for admission of purge air to the evaporative emission control canister system,
wherein the canister comprises a fuel-side adsorbent volume (<NUM>) comprising activated carbon and having an effective incremental adsorption capacity at <NUM> of greater than <NUM> grams n-butane/L between vapor concentration of <NUM> vol% and <NUM> vol% n-butane, wherein the effective incremental adsorption capacity is measured as described in the description, and more than one vent-side adsorbent volumes (<NUM>, <NUM>, <NUM>) downstream of the fuel-side adsorbent volume (<NUM>) towards the vent conduit, the downstream vent-side adsorbent volumes (<NUM>, <NUM>, <NUM>) comprising activated carbon, and
wherein at least one vent-side adsorbent volume comprises activated carbon and has an effective incremental adsorption capacity at <NUM> of less than <NUM> grams n-butane/L between vapor concentration of <NUM> vol % and <NUM> vol % n-butane, an effective butane working capacity (BWC) of less than <NUM>/dL, and a g-total BWC of between <NUM> grams and <NUM> grams, wherein the effective BWC is measured as described in the description and the g-total BWC is measured as described in the description;
wherein the evaporative emission control canister system is defined by a fuel vapor flow path from the fuel vapor inlet conduit (<NUM>) to the fuel-side adsorbent volume (<NUM>) toward the more than one vent-side adsorbent volume (<NUM>, <NUM>, <NUM>) and the vent conduit (<NUM>), and by an air flow path from the vent conduit (<NUM>) to the more than one vent-side adsorbent volume (<NUM>, <NUM>, <NUM>) toward the fuel-side adsorbent volume (<NUM>) and the fuel vapor purge conduit (<NUM>).