Patent Application
20070125235
The present invention relates to adsorption of hydrocarbon vapors; more particularly, to carbon-containing canisters for adsorbing fuel vapors displaced from fuel tanks during diurnal temperature changes; and most particularly, to an improved evaporative emissions canister suitable for use in boats having fixed onboard fuel tanks.
Canisters for adsorptive control of fuel vapors are well known in the automotive arts. A typical automotive emissions control canister comprises a housing having an inlet and outlet and a chamber for holding a charge of activated carbon. The inlet is connected to the headspace in the vehicle's fuel tank and the outlet is vented to atmosphere. In addition, the canister has a purge tube located on the inlet end of the canister which is connected to a vacuum source on the engine. When the fuel vapor volume expands thermally in the tank, the displaced fuel vapors are adsorbed by the activated carbon bed. When the engine is operated, the engine vacuum is applied to the purge tube and air is drawn through the carbon bed, desorbing the adsorbed vapors and carrying the vapors into the engine's intake manifold.
At the present time, emissions control canisters are not used with inboard marine applications. When boats having fixed fuel tanks are subjected to diurnal temperature changes, the displaced vapors are passed undesirably into the atmosphere. It is believed that US Federal law will require for model year 2011 that vessels having fixed on-board fuel tanks have evaporative emission control.
Prior art automotive-type canisters are not readily adaptable to use in boats. Such canisters are bulky and typically have a U-shaped vapor path with inlets and outlets formed at the top. On a marine vessel, the tank vent outlet typically is located high on the vessel topsides just below the rail, to avoid taking in water during vessel use. Thus, a suitable marine-use canister would have a vapor inlet at the bottom, for direct vapor flow from the fuel tank, and an outlet at the top, for connection to the vapor through-hull fitting. Of course, canisters may be mounted horizontal as well.
Further, most small pleasure boats having onboard fuel tanks are formed by assembling a molded inner hull, containing the decking and vessel superstructure, to a molded outer hull containing the engine mounts and through-hulls. Typically, a dead space is formed between the inner hull and outer hull above the waterline. Such space is available and strategically ideal for mounting a marine emissions adsorption canister; in fact, prior art vent lines typically pass through this space. However, such a canister must have a relatively small diameter, preferably less than about 4 inches, to fit easily into this space.
Another disadvantage of trying to adapt an automotive canister to marine use is that such canisters are manufactured in expensive, complicated molds which are justified only because many identical canisters are required for an entire line of automobiles, whereas the total annual volume of boats is only about 550,000 manufactured by over 1200 boat builders producing many thousands of lines of boats, each of which has different dimensions for the between-hull space. Thus, prior art automotive canisters, which may number in design no more than a few dozen or so in any model year, are not readily adaptable to fit into the huge number of different spaces presented by the boat industry.
An additional disadvantage is that the carbon beds in prior art automotive canisters are vulnerable to contamination by water in a marine environment, reducing the effectiveness of adsorption.
A still further disadvantage is that prior art automotive canisters are significantly more complicated than will be required, at least initially, for marine fuel tanks. A marine emissions canister may be inserted into the prior art vapor exhaust flow path, and is regenerated passively by the inhalation of air into the fuel tank as the fuel tank cools down during the diurnal. Thus, a marine canister can be significantly simpler and less expensive than an automotive canister.
A prior art linear canister having an inlet at one end and an outlet at the other is disclosed in U.S. Pat. No. 6,537,355, the relevant disclosure of which is incorporated by reference herein. A carbon monolith is disposed within a two-part cylindrical shell and is insulated and suspended therein by resilient annular spacers which also prevent bypassing of fuel vapors.
The disclosed canister is intended for automotive uses and therefore suffers from most of the above-recited shortcomings although it is linear and relatively slim. However, the housing is formed by injection molding in expensive molds to provide integral features for joining the shell halves together. Thus, the overall length and capacity of the canister is not easily or economically changed to accommodate different between-hull spaces. Further, the carbon monolith, although extremely efficient in scavenging fuel vapors, is both expensive and delicate; hence the need for resilient, insulative spacers. Initial marine requirements can be met by significantly simpler, less expensive forms of activated carbon.
It is a principal object of the present invention to provide a simple emissions control canister meeting anticipated marine requirements.
It is a further object of the invention to simply, reliably, and inexpensively adsorb fuel vapor emissions from a fixed fuel tank on a marine vessel.
Briefly described, a canister assembly in accordance with the invention comprises a longitudinal housing, preferably cylindrical and preferably formed by extrusion of a polymer such as polypropylene, or nylon. Thus, there are no molding costs, fixed and variable, for the housing as in prior art injection molded automotive canisters. The housing may be extruded to any desired length or may be cut from generic extruded stock of indeterminate length. First and second end caps, which preferably are identical and have tubing connectors extending therefrom, are bonded to opposite ends of the housing, defining respectively inlet and outlet means. Preferably, the ends are identical and either end may be used as either the inlet or the outlet. Adsorptive material, preferably marine-grade, pelletized, activated carbon, is disposed loosely within the housing between first and second porous transverse slidable plates that are spring loaded axially against the interiors of the end caps to maintain the carbon pack tightly against the walls of the housing. Preferably, a mounting bracket is rotatably attached to each of the end caps such that opposite ends of the assembly may be attached to different surfaces of a vessel hull which may undergo relative movement, thus relieving stress which would otherwise be introduced into the assembly. Preferably, the assembly is wrapped in a fire retardant material.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring to
An amount of a vapor-adsorbent material 22 is disposed within housing 12 such that vapors entering housing 12 through one of tubing connectors 18,20 must pass through material 22 before reaching the other connector. Preferably, material 22 contains activated carbon, and most preferably, material 22 is in the form of marine grade carbon pellets which are readily handled with minimal carbon dust and which are treated to sustain lower moisture adsorption than other carbon grades commonly used for prior art automotive canisters.
An amount of carbon pellets may be loaded into the housing sufficient to fully fill the internal chamber; however, because shifting and settling are known to occur in pelletized materials, it is preferable to provide means for actively maintaining the carbon pellets in a compact bed with full contact against the inner walls of the housing. In a presently preferred embodiment, assembly 10 includes at least one porous plate 24 slidably disposed within housing 12 and substantially full-fitting therewithin against the walls of housing 12 between adsorbent 22 and one of end caps 14,16. A compression spring 26 is disposed between plate 24 and the adjacent end cap 14,16 to urge adsorbent material 22 into compression. Preferably a second plate 24a is similarly disposed adjacent the other end cap. Each of plates 24,24a may include a foam screen 25 adjacent adsorbent material 22.
Preferably, the outer surface 29 of assembly 10 is wrapped, at least in part, in a fire-resistant material 27, e.g., fiberglass cloth.
Referring now to
Brackets 48,50 include for suitably attaching the assembly to the hull of the vessel as readily known in the art. Brackets 48,50 each further include circular recess 62 for rotatably receiving circular ends 64 of end caps 14,16 such that, once brackets 48,50 are secured to the vessel hull, elongate housing 12 is trapped axially between the brackets but is permitted to rotate within the recesses. An important advantage of canister assembly 10 over the prior art is that it is relatively long and slim, making it readily adaptable to use in a wide range of boats having spaces 44 of varying dimensions. Preferably, the overall length of assembly 10 is at least three times the diameter of housing 12.
In use, vent line 32 defines a breather pipe for fuel tank 28 to accommodate volumetric changes in tank headspace 52. For example, when fuel 54 and headspace 52 are thermally heated, the vapor pressure of the fuel increases forcing vapor from the headspace 52 through vent line 32 where it is adsorbed in canister assembly 10 and prevented from reaching atmosphere 56. Conversely, as the fuel 54 and headspace 52 are thermally cooled, the vapor pressure decreases and air is drawn in through fitting 40 and sweeps adsorbed vapors from canister assembly 10 into fuel tank 28.
Another important advantage of assembly 10, not possessed by prior art injection molded canister assemblies, is that the length of housing and volume of adsorbent may be varied at will without requiring any tooling changes in manufacture. Because the housing is formed by continuous extrusion, preferably as a cylindrical pipe, the housing may be formed to any desired length. Indeed, the housing may be cut, the canister filled with carbon pellets, and the end caps bonded to the housing at the point of assembly into a vessel if so desired.
Another important advantage of a canister in accordance with the invention is that it may be used not only for marine purposes but also in various land-based applications, for example some automotive applications requiring only a simpler emissions control device wherein an inexpensive canister having an extruded plastic housing can suffice.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
