FIELD OF THE INVENTION  
       [0001]     The present invention relates to fuels, particularly ethanol fuels, which contain gasoline and which comply with the ASTM D 5798 and which are suitable for use in California.  
       BACKGROUND OF THE INVENTION  
       [0002]     Environmental and energy independence concerns have stimulated the development of alternative transportation fuels, such as alcohol fuels, for use in automobiles. Alcohol fuels include methanol and ethanol. Alcohol in the form of ethanol is combined in various percentages with gasoline to produce one type of alternative fuel. Ethanol in the form of E85 (i.e., 85 vol % ethanol and 15 vol % gasoline) is an example of a type of alcohol mixed with gasoline to produce an alternative fuel.  
         [0003]     There has been increased interest in E85 by the State of California and other states. E85 fuel formulations must be in compliance with applicable regulations, which in California would include meeting the vapor pressure minimum limits set forth in ASTM D 5798. Specification D 5798 has three volatility classes (1, 2, and 3) with minimum vapor pressures of 5.5, 7.0, and 9.5 psi which are assigned based on the expected minimum ambient temperature where they will be marketed. California requires Class 1 in the summertime, Class 2 in the spring and fall (and some areas during winter), and Class 3 is required in some areas in November, December, and January.  
         [0004]     Minimum vapor pressures are specified to ensure good cold starting and warm-up drivability. Simply blending commercially available gasoline meeting local volatility requirements with ethanol does not result in a fuel that meets the minimum vapor pressure limits of ASTM D 5798. Thus, there is a need for an E85 fuel formulation that meets the ASTM D 5798 specifications and a method for producing the E85 fuel.  
       SUMMARY OF THE INVENTION  
       [0005]     Among other things, the present invention provides, an E85 fuel composition comprising ethanol, gasoline and isopentane present in amounts so that the fuel meets the applicable minimum vapor pressure limits of ASTM D 5798. The present invention also provides a method for producing an E85 fuel composition by adding a sufficient quantity of isopentane to ethanol or a mixture of ethanol and gasoline which has a vapor pressure lower than an applicable minimum vapor pressure limit of ASTM D 5798 to produce an E85 fuel having a vapor pressure that complies with the applicable minimum vapor pressure limits of ASTM D 5798. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a bar graph showing the effect of gasoline vapor pressure on the vapor pressure of the finished E85 blend.  
         [0007]      FIG. 2  is a graph showing the effect of base fuel vapor pressure and isopentane content on the vapor pressure of the finished E85 blend.  
         [0008]      FIG. 3  is a graph showing the correlation between predicted and actual vapor pressures. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The diagrams and discussion refer generally to ethanol and specifically to an ethanol fuel in the form of E85 (i.e., 85% ethanol and 15% gasoline) as a type of alcohol mixed with gasoline to produce an alternative fuel. This is not intended as a limitation however, as it should be apparent to one skilled in the art that the present invention would equally apply to other alternative fuels and other combinations of ethanol and gasoline, such as E70.  
         [0010]     The term E85 as used herein is not limited to a fuel having 85% ethanol. As discussed below, ASTM D 5798 provides for variations in ethanol concentration. One example is E70 containing 70% ethanol for the wintertime. The term E85 as used herein is intended to include any and all such variations.  
         [0011]     The present invention is based on the findings as described herein that blending commercially available gasoline meeting local volatility requirements with ethanol does not result in a fuel that meets the minimum vapor pressure limits of ASTM D 5798. The present invention involves the inclusion of at least an amount of isopentane, or other high volatility gasoline components such as n-pentane and butanes, in ethanol or an ethanol-gasoline mixture that is sufficient to increase the vapor pressure of the ethanol or ethanol-gasoline mixture to meet the minimum vapor pressure limits of ASTM D 5798.  
         [0012]     A vapor pressure program investigating the blending of E85 (a nominal blend of 85 vol % denatured ethanol and 15 vol % gasoline) was undertaken to determine if using commercial gasoline meeting local volatility specifications would result in E85 meeting the requirements of ASTM D 5798 Specification for Fuel Ethanol (Ed75-Ed85) for Automotive Spark-ignition Engines.  
         [0013]     Three commercial gasolines were used: CARBOB (California Reformulated Gasoline Blendstock for Oxygenate Blending) regular gasoline with 5.7 psi vapor pressure, a premium gasoline with 8.7 psi vapor pressure, and a winter grade gasoline with 12.2 psi vapor pressure.  
         [0014]     Each of the three commercial gasolines was blended at 15 vol % with denatured ethanol to make E85. One-third and two-thirds of each of the gasoline portions were replace by isopentane resulting in six more blends. Another blend was made using 15 vol % of isopentane (no gasoline). Finally, for winter blending D 5798 allows up to 30 vol % gasoline. So, a 30 vol % blend was made using the 12.2 psi gasoline. The compositions of the blends are shown in Table 1 
                                                                                         TABLE 1                           E-85 VAPOR PRESSURE TEST PROGRAM BLENDS                mL of Blending Stock                Blend               8.7   12.2   DVPE       Number   Ethanol   Isopentane   CARBOB   psi VP   psi VP   psi                    1   1000   0   0   0   0   2.41       2   0   0   1000   0   0   5.67       3   0   0   0   1000   0   8.66       4   0   0   0   0   1000   12.18       5   850   0   150   0   0   4.44       6   850   50   100   0   0   6.45       7   850   100   50   0   0   8.51       8   850   150   0   0   0   10.85       9   850   0   0   150   0   4.73       10   850   50   0   100   0   6.63       11   850   100   0   50   0   8.51       12   850   0   0   0   150   6.32       13   850   50   0   0   100   7.86       14   850   100   0   0   50   9.12       15   700   0   0   0   300   8.26                  
 
 Vapor Pressure Testing 
 
         [0015]     The vapor pressure of the blends was determined by ASTM D 5191. The vapor pressure values reported were single determinations.  
         [0016]     The vapor pressure results for the blending stocks (Blends 1 through 4) and for the ethanol blends (Blends 4 through 15) are shown in Table 1.  
         [0017]     The effect on vapor pressure of adding the three commercial gasolines and isopentane at 15 vol % to denatured ethanol and on adding 30 vol % of the 12.2 psi gasoline are shown graphically in  FIG. 1 .  
         [0018]     The three ASTM D 5798 minimum vapor pressure class limits are plotted on  FIG. 1  and show that when commercial gasolines meeting the federal summertime vapor pressure limits of 7.8 and 9.0 psi maximum are blended with denatured ethanol, the resulting E85 blend will not meet the minimum vapor pressure limits. Using the winter gasoline which is not normally available in the summertime resulted in complying only with the summertime Class 1 minimum limit and not complying with the transition months and the wintertime limits of Class 2 or Class 3. Even adding 30 vol % of the 12.2 psi gasoline didn&#39;t result in E85 that complied with the wintertime specification. Isopentane alone at 15 vol % provided a vapor pressure of 10.85 psi which readily met the winter minimum limit.  
         [0019]     The effects of replacing portions (one-third and two thirds) of the 15 vol % gasoline with isopentane are shown graphically in  FIG. 2  for each of the three commercial gasolines.  
         [0020]     Replacing a part of the gasoline portions with isopentane increased the resulting vapor pressure of E85. For summer gasolines it took about 3 vol % isopentane of the 15 vol % total hydrocarbon portion to meet summer standards. It took about 6.5 vol % isopentane to meet Class 2 standards. For wintertime, it took about 11.5 vol % isopentane with the 12.2 psi gasoline and about 12.3 vol % isopentane with the two summertime gasolines to meet winter standards.  
         [0000]     Predicting Vapor Pressure  
         [0021]     There are two procedures for calculating the vapor pressure of blends. One is the linear method where the vol % of each blending component is multiplied by its measured vapor pressure, summed across all components, and divided by 100. A more accurate way is to use Blending Indexes in place of the measured vapor pressures. Both procedures were used to calculate the vapor pressure of the E85 blends and the results are shown in  FIG. 3 .  
         [0022]     For blending E85, the calculated vapor pressures by both methods are lower than the measured vapor pressure and the difference increases with increasing vapor pressure. The Blending Index approach is slightly better than the linear approach, but probably not sufficiently better to justify the use of the more complicated Blending Index method. Regression analyses were run using combinations of variables and the best practical equation using vapor pressure data is as follows: 
 
 E 85 Vapor Pressure=−1.699+2.025*Calculated  E 85  VP+ 0.133*Vol % 
 
 Isopentane, where the calculated E85 VP is determined using the linear method. 
 
 Water Tolerance 
 
         [0023]     Using isopentane to increase the vapor pressure of E85 resulted in an additional unexpected benefit, a significant increase in the water tolerance of the fuel.  
         [0024]     The water tolerance of the E85 made with 15 vol % CARBOB and the E85 made with 15 vol % isopentane was assessed. The basic test for water tolerance of fuel is ASTM D 1094. The test method was modified for use in the field to detect and roughly quantify the ethanol content of E10 (10 vol % ethanol blends) or of blends having lower ethanol concentrations.  
         [0025]     The basic procedure involves using a 100 mL graduated mixing cylinder. 100 mL of gasoline-ethanol blend is placed in the graduated cylinder and 10 mL of water is added. The graduate is shaken and time is allowed for the water or water/ethanol phase to settle to the bottom. The increase in the volume of the water/ethanol bottoms is used to determine how much ethanol is present.  
         [0026]     The situation is different for E85 in that water dissolves in the ethanol and forces the gasoline out of solution (phase separation). Since gasoline is less dense than ethanol or water it floats to the top when phase separation occurs. To keep the proportions the same and still be able to measure the amount of separated gasoline, a 250 mL graduated mixing cylinder was used for the E85 assessment.  
         [0027]     When 10 mL of water was added to 100 mL of E85 made from CARBOB and shaken, the water dissolved into the E85 and the mixture remained clear. Additional water was added. When 16 mL water had been added, the mixture became hazy. It took more than 8 hours and less than 24 hours for the lower phase to clear. At this point 2 mL of gasoline was floating on the top. A total of 20 mL of water produced 6 mL of phase separated gasoline and 30 mL of water resulted in 8 mL of gasoline separated from the E85. This finding shows that E85 is considerably more tolerant of water contact than E10 which separates when about 0.5 mL water is added.  
         [0028]     It was thought that with no aromatics present, the isopentane would separate faster than the commercial gasoline. This was not the case. No haze or separation appeared until 40 mL of water was added. At that point 13 mL of isopentane floated to the top and the fuel cleared of its haze quickly. Thus, the isopentane-based E85 is more tolerant of water than the commercial gasoline-based E85.  
         [0029]     There are numerous variations on the present invention which are possible in light of the teachings and supporting examples described herein. It is therefore understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described or exemplified herein.
An E85 fuel composition comprising ethanol, gasoline and isopentane present in amounts so that the fuel meets the applicable minimum vapor pressure limits of ASTM D 5798 is disclosed. A method for producing an E85 fuel composition comprising adding a sufficient quantity of isopentane to ethanol or a mixture of ethanol and gasoline which has a vapor pressure lower than an applicable minimum vapor pressure limit of ASTM D 5798 to produce an E85 fuel having a vapor pressure that complies with the applicable minimum vapor pressure limits of ASTM D 5798 is also disclosed.