Abstract:
Fuel tank system for a direct ethanol injection octane boosted gasoline engine. The system includes a gasoline engine and a main fuel tank that contains a mix of gasoline and gasoline E85. A smaller secondary tank is provided to contain ethanol or E85. An injector directly injects in a separately controlled fashion ethanol or E85 into a cylinder of the engine to boost octane. A control module controls the relative amounts of gasoline and ethanol used and structure is provided for fueling the main and secondary fuel tanks.

Description:
[0001]     This application claims priority to provisional application Ser. No. 60/780,981 filed Mar. 10, 2006, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a fuel tank system for a direct ethanol injection octane boosted gasoline engine.  
         [0003]     As described in U.S. patent application Ser. No. 10/991,774 filed on Nov. 18, 2004 and application Ser. No. 11/100,026 filed Apr. 6, 2005, on-demand octane boost using direct ethanol injection can be used to enable high fuel economy in two types of vehicle operation. The contents of these applications are incorporated herein by reference. In the first, the vehicle is essentially powered by gasoline (with a minimal amount of ethanol used for on-demand octane boost). In another mode of operation when the cost and availability of ethanol make its use attractive, the vehicle is powered by a flexible fuel mix of E85 and gasoline. In this case, the E85 can constitute up to 100% of the fuel. In contrast to the use of ethanol as a fuel that is blended with gasoline, the driver has the freedom to determine when and how much ethanol to use. As will be described below, the amount of ethanol or E85 required to be stored in a separate tank for on-demand octane boost is on the order of only 4 to 20 gallons per year when a vehicle is essentially powered by gasoline. The requirement is less when the vehicle is powered by a flexible fuel mixture of ethanol or E85 and gasoline. The ethanol can be added using either 1.0 to 2.5 gallon containers or by the use of a pump at the growing number of E85 fueling stations in the United States. This small amount of ethanol could be provided for 50 million vehicles using less than 1 billion gallons of ethanol per year which is about 25% of the present U.S. ethanol production. Thus, the required extension of the ethanol transportation fuel infrastructure is very modest. Moreover, with the substantial increase in E85 infrastructure as presently planned by the 2005 Energy Act, additional ethanol can be used as a substitute fuel in addition to its use as an on-demand octane boost agent.  
         [0004]     An object of the present invention is to minimize the inconvenience and cost of using a separate tank for the on-demand octane boost agent. Another object is a fuel management system designed so as to reduce the additional cost of flexible fuel operation.  
       SUMMARY OF THE INVENTION  
       [0005]     The fuel tank system according to the invention for a direct ethanol injection octane boosted gasoline engine includes a gasoline engine and a main fuel tank for gasoline or E85. A smaller, secondary tank (octane boost tank) is provided to store ethanol or E85. An injector is provided for direct, separately controlled injection of ethanol or E85 into a cylinder of the engine to boost octane. A control module controls the relative amounts of gasoline and ethanol used and means for fueling the main and secondary fuel tanks is provided. In one embodiment, the means for fueling includes a single spigot with dual lines. In another embodiment, a first fuel inlet fitting is provided that accepts a nozzle that dispenses gasoline or E85 and a second fuel inlet fitting is provided that accepts a nozzle that dispenses ethanol or E85. In yet another embodiment, the smaller secondary tank is fueled from a container or a pump. Suitable containers have volumes of 1.0 to 2.5 gallons. The system can further include a valve allowing both tanks to be filled from a single inlet fitting.  
         [0006]     In yet another embodiment, the control module reduces the amount of ethanol or E85 from the secondary tank injected into the engine when the main tank contains E85. In another embodiment, the means for refueling refuels the main and secondary tanks simultaneously from a single fuel spigot having a nozzle design allowing gasoline into the main tank and ethanol into the secondary tank. It is also preferred that the capacities of the main and secondary tanks can be reconfigured. Such a reconfiguring may be on the basis of a previous driving pattern with an operator override. It is preferred that the engine be operated at a substantially stoichiometric air/fuel ratio so that 3 way catalytic converters can be used. In yet another embodiment, engine pressure boost, torque or horsepower is decreased to reduce consumption of ethanol. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]      FIG. 1  is a block diagram illustrating an embodiment of the invention.  
         [0008]      FIG. 2  is a schematic illustration of an embodiment of the fueling system disclosed herein. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]     The fuel tank system disclosed herein uses a small separate fuel tank as a source of ethanol or E85 while the primary tank contains gasoline, E85, ethanol or a combination of these fuels.  FIGS. 1 and 2  illustrate the fueling arrangement for a primary gasoline tank  10  and a secondary ethanol tank  12 . The small separate ethanol tank  12  is referred to as the secondary tank or octane boost tank. As shown in  FIG. 2  there is one fuel inlet fitting  14  for E85 or ethanol and another fitting  16  for gasoline. The E85 fuel inlet fitting  14  is compatible with the pump nozzle that is currently used at E85 fueling stations. As shown in  FIG. 1  the two tanks  10  and  12  could be integrated together into one unit  18 . Delivery of gasoline and ethanol from the integrated unit  18  is under the control of a control module  20  for delivery to an engine  22  that powers a vehicle  24 .  
         [0010]     The octane boost tank  12  can be fueled from 1.0 or 2.5 gallon containers or by use of a pump. The refilling by containers can be carried out either by the driver or by a mechanic at the time of an oil change as part of routine servicing since the interval for ethanol refill could be on the order of three months or more.  
         [0011]     The E85 fuel inlet fitting  14  can also accommodate E85 or ethanol that is added by containers in combination with a pour spout that could be screwed on to the container. Such a pour spout would be similar to the pour spout that is attached to present 2.5 gallon containers.  
         [0012]     The octane boost tank  12  is sized so that the refill interval can generally be as long as three or more months under normal driving conditions. For example, a total fuel tank with a capacity of 22 gallons might have a capacity of 6 gallons for the octane boost tank  12  and  16  gallons for the gasoline tank  10 . Because of the increased fuel efficiency from the on-demand direct injection octane boost, this 16 gallon gasoline tank configuration will not lead to any decrease in range relative to a conventional 20 gallon gasoline tank.  
         [0013]     Based upon the computational model described in the above identified pending applications, the required amount of ethanol or E85 to provide the on-demand octane boost for a 20% to 30% improvement in fuel economy is between 1 and 5 gallons for every 100 gallons of gasoline. The on-demand octane boost allows an increase in manifold pressure by a factor of 1.8 or more.  
         [0014]     By way of illustration, assuming an annual gasoline consumption rate of 400 gallons a year (12,000 miles per year at 25 miles per gallon), the ethanol or E85 consumption rate is between 4 and 20 gallons a year, corresponding to 0.3 to 1.7 gallons per month. A representative consumption rate could thus be 1 gallon per month under normal driving conditions. Therefore, the use of a 6 gallon tank would allow for an ethanol or E85 refill interval of three months or more. This is approximately the same time interval as that for an oil change.  
         [0015]     With E85 or ethanol comprising part, or even all of the fuel in the primary fuel tank  10 , the consumption of E85 or ethanol from the on-demand octane boost fuel tank  12  to prevent knock would be reduced. Hence the rate of use of E85 or ethanol from the on-demand octane boost tank  12  could be accordingly reduced and the refill interval for this tank can thus be extended.  
         [0016]     The amount of E85 or ethanol drawn from the secondary fuel tank  12  can also be reduced by the control module  20  that may be activated by a driver. In this case, turbocharging, torque and/or horsepower capability would be decreased in order to reduce the demand for E85 or ethanol needed to insure knock free operation. This “octane boost economy” mode can also increase the refuel time interval and/or reduce the amount of E85 or ethanol that would be needed to be added at any time to the octane boost tank  12  at the expense of decreased power.  
         [0017]     The control module  20  also controls, in one embodiment, the air/fuel mixture to provide substantially stoichiometric operation both during the time that the on-demand direct injection octane boost is used and when flexible fuel operation with ethanol or E85 in the primary tank  10  is employed. Stoichiometric operation makes it possible to use a three way catalytic converter which is highly effective in reducing emissions of pollutants in the engine  22  exhaust. Those skilled in the art will recognize that fuel injectors used for direct E85 or ethanol injection from the smaller tank  12  can also be used for injection of gasoline or E85 from the primary tank  10 .  
         [0018]     If the price and availability of E85 are such as to motivate greater use in a flexible fuel mode, the octane boost tank  12  and the primary fuel tank  10  can be simultaneously fueled. In this way the time interval for separate refueling of the octane boost tank  12  is additionally lengthened. This mode can be accomplished by opening a valve (not shown) which allows E85 to flow into the main tank  10  in addition to the octane boost tank  12 . The valve can be controlled by a switch activated by the driver.  
         [0019]     Another option for providing convenient pump refueling is to use a single spigot. In order to make it transparent to the driver, a single spigot with dual lines to the refueling station could be used to fill simultaneously both the main fuel tank  10  and the octane boost tank  12 . Such a system is similar to that proposed for diesel/SCR operation, but using gasoline/ethanol instead.  
         [0020]     It is preferred to use a single spigot that refuels both the main fuel tank  10  and the on-demand octane boosting tank  12  in which the vehicle  24  determines how much of each fuel is needed, and the refueling station adjusts the rate and amount of fuel that is introduced into the vehicle. In this case, the vehicle  24  automatically determines how much fuel and ethanol octane enhancement is available, and how much is needed, assuming a pattern of driving that could include an onboard expert system that analyzes previous driving patterns.  
         [0021]     The system disclosed herein can be arranged so that the onboard fuel management system reconfigures the fuel tank, adjusting the size of the respective tanks in order to provide the appropriate ratio of antiknock fuel to main fuel, with the refueling system just filling both tanks to capacity. This refueling can be achieved either with a single spigot with dual fuel dispensers, separated feeds, or a single feed with a valve to switch tank being refueled. This mode would be particularly useful for those engine designs and/or driving patterns that require substantial amounts of octane boosting agent.  
         [0022]     The most transparent adjustment of the tank configuration (ratio of the capacities of the main fuel tank  10  and the on-demand octane boost tank  12 ) occurs if the operation is done automatically by the fuel management control module  20 . However, the system can be most flexible if the operator can adjust the ratio, overriding the instructions from the control module  20  in order to best match future driving patterns (for example, before starting on a long trip with a highway driving pattern, or, conversely, after a long drive and readjusting to a city driving pattern).  
         [0023]     Those skilled in the art will recognize that the above discussion applies to methanol and M85 as well as ethanol and ethanol blends such as E85.  
         [0024]     It is recognized that modifications and variations will occur to those of ordinary skill in the art and it is intended that all such modifications and variations be included within the scope of the appended claims.