Patent Application
20080308072
The present invention relates to a fuel system for an internal combustion engine and, Particularly, to the separation of hydrocarbons from air in the separation tube at the fuel tank; and, most particularly, to a membrane separation system for providing a cleaner stream of air back into the fuel filler pipe.
Evaporative emissions result from any one of several events which includes venting of fuel vapors from the fuel tank due to diurnal changes in ambient pressure and/or temperatures (known in the art as “diurnal” emissions), by refueling of the vehicle (known in the art as “refueling” emissions) or by vaporization of fuel by a hot engine and/or exhaust. Generally, the venting of fuel vapor from the fuel tank due to diurnal pressure and/or temperature (diurnal emission) and the escape of fuel vapor during refueling are responsible for a majority of the emissions.
Environmental regulations imposed on the automotive industry, by the environmental Protection Agency require that automotive vehicles such as gasoline powered passenger cars and trucks have on board hydrocarbon emissions controls to prevent or limit the amount of hydrocarbon pollutants expelled into the atmosphere. Such hydrocarbon pollutants are a major contributor to smog formations and contribute to the depletion of the ozone layer in our atmosphere. As a result of government mandates, automotive manufacturers are constantly being challenged to find better and more efficient ways to prevent or reduce the emissions of hydrocarbon fuel vapors and other pollutants into the atmosphere. One such way that emissions can be controlled is by canister systems that employ carbon, preferably activated carbon, to adsorb and hold the hydrocarbon vapors. Examples of evaporative emissions canisters are described in a number of U.S. patents and patent applications such as U.S. Pat. No. 4,203,401 to Kingsley et al.; U.S. Pat. No. 4,658,796 To Yoshida et al.; U.S. Pat. No. 4,683,862 to Fornuto et al.; U.S. Pat. No. 5,119,791 to Gifford, et al.; U.S. Pat. No. 5,408,977 to Cotton; U.S. Pat. No. 5,924,410 to Dumas et al.; U.S. Pat. No. 5,957,114 to Johnson et al; U.S. Pat. No. 6,136,075 to Bragg et al; U.S. Pat. No. 6,237,574 to Jamrog et al.; U.S. Pat. No. 6,540,815 to Hiltzik et al.; and RE 38,844 to Hiltzik et al, and U.S. Pat. Appln. Nos. Nos. 2005/0061301 to Meiller; 2005/0123458 to Meiller; and 2006/0065252 to Meiller.
The adsorbed hydrocarbon vapor is periodically desorbed from the carbon by drawing fresh air into the carbon bed to displace the hydrocarbon fuel vapor. The displaced fuel vapor is then passed to the engine where it is consumed. The renewed carbon can then adsorb additional hydrocarbon fuel vapor from the fuel system by withdrawing the air back out through the vent side of the canister. The amount of fuel vapor that can be contained in the canister is finite and dependent upon the amount of carbon in the canister and the capability of the carbon to adsorb the fuel vapor until it is finally desorbed and consumed by the engine during purge cycles. Some prior art canisters employ auxiliary canisters to increase the adsorbent material capacity. The use of additional canisters not only increase the complexity and cost of the evaporative emissions system, but also requires additional space considerations due to the limited space available in the region of the vehicle wherein a canister is installed.
Fuel emissions can be further controlled by recirculation of fuel vapors in the fuel tank. The recirculation of fuel vapor during refueling from a fuel nozzle is described in U.S. Pat. No. 6,945,290 to Benjey et al. During refueling operations, displaced air that is saturated with fuel vapor, moves toward the external entry (filler pipe) and on to the carbon canister. During refueling, the displaced air/fuel mixture from the tank is circulated back near the filler pipe where it is reintroduced to the fuel tank in the fuel stream.
In view of the ever increasing government regulations preventing the escape of hydrocarbons into the atmosphere and the increasing cost of hydrocarbon fuel, there is a constant need for improved fuel systems which not only provide reduced fuel vapor emissions to the atmosphere but also provides for a more efficient use of the fuel.
It has been found that hydrocarbon fuels can be more efficiently consumed and the emission of hydrocarbon fuel pollutants into the atmosphere during fueling of an automotive vehicle, during diurnal changes in the fuel system, and in the operation of such vehicle, can be substantially reduced or eliminated, by employing a recirculation tube to act as a closed loop vent from the fuel tank to the filler pipe, and integrally incorporating a membrane separation device into the recirculation tube. According to the present invention, the use of the membrane separation device provides effective separation of hydrocarbons from the air/fuel mixture at the fuel tank resulting in an air/fuel vapor effluent having a significantly reduced concentration of fuel vapor therein. A particular advantage of the present invention is that hydrocarbon emissions can be substantially eliminated while effectively reducing the size requirements of the emissions canister necessary to achieve the desired emissions level. The use of a smaller canister not only reduces manufacturing costs, but also permits significant flexibility in determining the most efficient configuration and location of the device in the emissions system.
By installing the membrane in the recirculation tube, the membrane separates a substantial amount of the hydrocarbon fuel from air at the fuel tank and recirculates the hydrocarbon fuel to the fuel tank, thereby reducing the load on the canister system so that the overall evaporative emissions system can be optimized by allowing the use of smaller canisters which can be more efficiently configured and located in the emissions system.
The use of a separating membrane device as described herein allows the use of a larger diameter recirculation tube thereby allowing a larger volume of the air/fuel mixture to flow through the recirculation tube, thereby reducing the pressure inside the fuel tank leading to a lower flow rate through the carbon canister employed to adsorb the fuel vapors until they are purged and consumed in the internal combustion engine. The effective separation of hydrocarbons from air based on a membrane separator is achieved with an effective pressure drop across the membrane module. This can be achieved more effectively by having a gas compressor or a vacuum pump in the recirculation tube to create the desired pressure head. The improvement provided by the present invention is a much cleaner stream of air fed back into the filler pipe, a significantly more efficient reduction in the amount of fugitive emissions released to the atmosphere during fueling, and more smaller spatial requirements for the emissions canister which not only reduces material and labor costs, but allows greater flexibility with respect to the installation of such canisters.
The membrane useful in the present invention is characterized as a cellular fibular material having physical properties such as pore size, nominal flow path, membrane area and thickness favorable for the separation and trapping of fuel vapor molecules while allowing any air molecules present to flow freely therethrough. Membranes found to be effective in the present invention are available from Amersham Biosciences Membrane Separations Group, W. L. Gore & Associates.
In addition to the afore-mentioned physical properties necessary for the sufficient separation of fuel vapor molecules from fresh air molecules in the evaporative emissions system, there are other properties that affect mass transfer during gas separation through a membrane. Such additional properties include:
In accordance with the invention, a module containing the membrane is positioned in a recirculating tube, which provides a closed loop vent from the fuel tank to the fuel filler pipe. During refueling, the displaced air/fuel vapor mixture from the fuel tank is passed to the membrane module where the membrane effectively separates the fuel vapor from the air/fuel mixture. Typically, the membrane is effective to prevent substantially all of the fuel vapor from passing therethrough while allowing substantially all of the air molecules to pass therethrough. The membrane allows the fuel vapor to return to the fuel tank while the air, separated from the air/fuel mixture, is allowed to freely pass to the filler pipe and eventually to the canister where any residual fuel vapor remaining in the air is adsorbed until it is consumed by the internal combustion engine during a purge step. More typically, the membrane prevents greater than about 80% of the fuel vapor molecules from passing through the membrane while allowing greater than about 95% of the air molecules to pass therethrough. Most typically, the membrane prevents greater than about 95% of the fuel vapor molecules from passing through the membrane while allowing greater than about 99% of the air molecules to pass therethrough. As in conventional canisters, the air substantially free of any fuel vapor is expelled through the canister to the atmosphere.
In one aspect of the invention, a gas compressor is placed between the fuel tank and the membrane module. In this design, the compressor is attached at the inlet of the membrane module, where it creates sufficient pressure head to provide a more effective separation of hydrocarbons from air wherein the hydrocarbons are returned to the fuel tank, while the clean air molecules are allowed to pass through the membrane.
In another aspect of the invention, a vacuum pump is placed between the membrane module and the filler pipe. The vacuum pump creates a significant pressure differential across the membrane module to draw clean air, separated from the air/hydrocarbon mixture, across the membrane module and introduce it to the recirculation tube while the separated hydrocarbons prevented from passing across the membrane module, are returned to the fuel tank. While a typical configuration would be to employ either the gas compressor or the vacuum pump in carrying out the invention, it is within the scope of the present invention to utilize both devices.
Accordingly, it is a primary object of this invention to provide an improved evaporative emissions system, which incorporates a membrane module in the recirculation tube at the fuel tank to separate most of the hydrocarbon fuel vapor from an air/hydrocarbon fuel vapor mixture, and return the hydrocarbon fuel vapor back to the fuel tank while allowing the clean air having a significantly reduced amount of hydrocarbon fuel vapor to pass on to the canister where the residual hydrocarbon fuel vapor is separated from the air and adsorbed on a bed of adsorbent material until it is desorbed in a purge step and consumed by the engine.
It is another object of the invention to provide an evaporative emissions system that provides reduced fuel emissions to the atmosphere.
It is still another object of the invention to optimize the overall packaging of the evaporative emissions system by allowing the use of smaller canisters, which can be more efficiently configured and located in the emissions system.
It is yet another object of the invention to provide all of the above objects of the invention with reduced complexity and economic considerations.
These objects as well as other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, appended claims and accompanying drawings.
In accordance with the present invention, an effective separation system is employed for separating hydrocarbon fuel vapor molecules from air in an air/hydrocarbon fuel vapor mixture.
In one aspect of the invention, as illustrated in
In another aspect of the invention, as best illustrated in
While the present invention has been fully illustrated and described in detail, other designs, modifications and improvements will become apparent to those skilled in the art. Such designs, modifications and improvements are considered to be within the spirit of the present invention, the scope of which is determined only by the scope of the appended claims.
