1. Field of the Invention
The present invention relates to a device for trapping hydrocarbon from an internal combustion engine fuel system and more specifically, to trapping hydrocarbons which would normally be released from an internal combustion engine intake system when the engine is not operating.
2. Disclosure Information
As automotive tailpipe emission controls have become increasingly more stringent, the emission of hydrocarbons from non-tailpipe or non-fuel tank sources has increasingly come under regulation. For example, California Air Resources Board (CARB) regulations applicable to future models specify that automotive vehicles may emit no more that about 0.35 grams of hydrocarbon per day in terms of evaporative emissions. Of this total, fuel-base hydrocarbon may comprise only 0.054 gm. per day. Because the engine's fuel charging system has the job of combining fuel and air, the fuel charging system provides a source from which fuel can escape from the vehicle through the air intake system when the engine is not operating, or in another words, when the engine is shut down. Thus, any hydrocarbons emitted by the fuel injectors, intake manifold walls, cylinders, or positive crankcase ventilation system may leave the engine and enter the ambient through the air induction or air intake system. Thus, emission levels is high as 0.366 gm per day have been recorded from an engine air intake system alone. A fugitive hydrocarbon treatment module according to present invention provides an apparatus and method for significantly reducing fuel hydrocarbon emissions from sources within the engine.
The present module uses zeolite, which comprises crystalline silicon-aluminum oxide structures capable of forming a weak chemical bond with hydrocarbon molecules of the type typically found in motor gasolines and other engine-borne sources. Although zeolite has a lower overall adsorption capacity than some activated carbon materials, zeolite can produce a much stronger interaction with hydrocarbon molecules, which results in a greater efficiency for the zeolite to trap and prevent hydrocarbon from flowing out of an adsorber. Additionally, the zeolite provides advantages upon purging, whereby the zeolite material releases the trapped hydrocarbons in a much more controlled manner than would activated carbon materials. As a result, efficient operation of the engine is not compromised during purging of the trap.
Although U.S. Pat. No. 3,838,673 discloses the use of zeolite to trap vapor, it is noted that the system of the '673 patent will not prevent the emission of vapor emanating from the induction system apart from the carburetor. Similarly, U.S. Pat. No. 5,207,734 also uses zeolite to trap hydrocarbon vapor from the fuel tank and from the engine when the engine is operating, but cannot prevent the emission of hydrocarbon from the internal regions of the engine when the engine is not in operation.
A system and module according to the present invention solves the problems associated with the prior art by providing complete trapping of hydrocarbons when the engine is off, combined with excellent airflow capability and regeneration of the hydrocarbon adsorber during operation of the engine.
A fugitive hydrocarbon treatment module for controlling the emission of hydrocarbon from the air intake system of the engine includes a zeolite adsorber unit positioned in the air intake system such that all air flowing to the engine passes through the adsorber. The adsorber unit may comprise a monolithic substrate having a zeolite-containing washcoat. This may be a metallic substrate such as stainless steel or other ferrous material or non-ferrous material known to those skilled in the art and suggested by this disclosure. The monolithic substrate preferably has a cell density of approximately 25 cells per square inch of substrate surface area, but could contain 1 to 400 cells per inch. As another alternative, the substrate may comprise a cordierite substrate. In any event, the substrate is positioned in the air intake system such that all air flowing through the engine passes through the cells of the substrate both when the engine is operating and when the engine is shut down.
According to another aspect of the present invention, a method for controlling the emission of fugitive hydrocarbon from the air induction system and interior of an internal combustion engine includes the step of causing fugitive hydrocarbon backflowing from the engine air induction system when the engine is shut down to flow through, and be adsorbed upon, a zeolite containing adsorber, and thereafter causing all combustion air entering the engine when the engine is operating to flow through the adsorber so as to desorb and induct previously adsorbed hydrocarbon.
According to another aspect of present invention, a combination air meter and induction system hydrocarbon treatment module for an internal combustion engine includes a total flow hydrocarbon treatment module positioned in the air induction system such that all gases flowing to and from the engine through the air intake system are caused to flow through the hydrocarbon treatment module, and an airflow meter positioned between the hydrocarbon treatment module and the engine such that all air flowing to the engine is caused to flow through the flow meter. Preferably, a single housing contains the hydrocarbon treatment module and the airflow meter. According to yet another aspect of the present invention, a combination air meter and induction system hydrocarbon treatment module may include two monolithic substrates, each having a hydrocarbon adsorbing coating, and an airflow meter mounted between the monolithic substrates.
According to another aspect of the present invention, a combination throttle body, air meter, and induction system hydrocarbon module for an internal combustion engine includes the previously described total flow hydrocarbon treatment module and airflow meter, as well as a throttle body positioned between the airflow meter and the engine. All three components, that is the hydrocarbon treatment module, the airflow meter, and the throttle body may be contained within a single housing. It is an advantage of the present invention that use of a single housing for a hydrocarbon treatment module, for an airflow meter, and for a throttle body according to present invention will prevent air leakage associated with the assembling of numerous components, each requiring independent sealing means and hoses to connect them.
It is an advantage of the present invention that a hydrocarbon treatment module according to this invention is a completely passive device that needs no control valves or efficiency monitoring. This means that the ease of employing such a device in view of onboard diagnostic requirements (OBD) is greatly enhanced.
It is another advantage of the present invention that the present fugitive hydrocarbon treatment module is robust, which is particularly important in the automotive environment in which an engine may occasionally experience backfiring operation.
It is yet another advantage of the present invention that a system including a hydrocarbon treatment module according to this invention provides very little restriction to the flow of air into the engine and thus does not contribute to engine power loss.
Other advantages as well are objects and features of the present invention will become apparent to the reader of this specification.
Engine 20, having air intake plenum and manifold 28, is supplied with air that first passes through air cleaner 12, and then through fugitive hydrocarbon treatment module 14. Thereafter, the charge air passes through mass airflow sensor 16 and past throttle body 18 into intake manifold 28. From a position between mass airflow meter 16 and throttle body 18, a portion of the incoming airflow is diverted to engine crankcase 30 through hose 31. This diverted air then flows through crankcase 30 and into intake manifold 28 through positive crankcase ventilation (PCV) hose 32.
A plurality of fuel injectors (not shown) provides fuel to the engine. The injectors cooperate with manifold 28 to provide both fuel and air to the engine. However, when the engine is shutdown, fuel vapors may escape from intake manifold 28 and flow back past throttle body 18 and airflow sensor 16. Fuel reaching hydrocarbon treatment module 14 along with any crankcase borne hydrocarbons that backflow through hose 31 will ultimately reach substrate 22, which is shown with more particularity in
The inventors of the current fugitive hydrocarbon treatment module have determined that a zeolite based hydrocarbon trap produces excellent result because the flow rate out of the engine air intake system is quite low when the engine is not operating. Because the flow rate is very low, the hydrocarbon flowing through substrate 22 has a very high residence time. This permits adequate time for equilibrium to be established between the zeolite adsorbent and the gas phase adsorbate (i.e., hydrocarbon). As a result, high trapping efficiency is facilitated. Of equal importance however, is the fact that although the interaction between the hydrocarbon and zeolite is strong, the weak chemical bond resulting between the hydrocarbon and zeolite is easily broken once the engine is started because of the high concentration gradient that exists between the hydrocarbon trapped by the zeolite and the hydrocarbon free air flowing to the engine through the air intake system. As a result, the hydrocarbon treatment module is quickly purged of hydrocarbon and ready to accept more hydrocarbon upon the next engine shut down.
In a test, a fugitive hydrocarbon treatment module according to the present invention and having dimensions of approximately in 3 inches in length and 3 inches in diameter and comprising cordierite was coated with zeolite and placed in the induction system of a vehicle having a 2.3 liter 1-4 engine with port fuel injection. The hydrocarbon treatment module operated very effectively and caused about a 95% reduction in fugitive hydrocarbon emission from the engine's air intake system.
In another test, the same 2.3 L 1-4 engine was fitted with a hydrocarbon treatment module of the design shown in
In yet another test, the same 2.3 L 1-4 engine was fitted with a hydrocarbon treatment module of the design shown in
Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention. It is intended that the invention be limited only by the appended claims.
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Number | Date | Country | |
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