Patent Publication Number: US-2022228077-A1

Title: Production method of spark-ignition engine fuel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-006887 filed on Jan. 20, 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a production method of spark-ignition engine fuel, configured to produce fuel for a spark-ignition engine. 
     Description of the Related Art 
     Conventionally known high-octane gasolines use catalytic reformed gasoline as a high-octane base material (for example, see Japanese Unexamined Patent Application Publication No. 2007-246744 (JP2007-246744A)). The high-octane gasoline described in JP 2007-246744 A contains a gasoline base material derived from a catalytic reformed gasoline obtained by subjecting a naphtha fraction to catalytic reforming treatment. 
     However, in order to obtain the high-octane gasoline described in JP 2007-246744 A, it is necessary to further input energy to the naphtha fraction for catalytic reforming treatment; therefore, it is difficult to lower the carbon emission (carbon intensity) per unit energy of the resultant fuel. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is a production method of spark-ignition engine fuel, configured to produce fuel for a spark-ignition engine, including: mixing light naphtha with cyclopentane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, and advantages of the present invention will become clearer from the following description of embodiments in relation to the attached drawings, in which: 
         FIG. 1  is a diagram for explaining an example of renewable fuel produced using renewable energy; 
         FIG. 2  is a diagram illustrating exemplary octane numbers of mixed fuels prepared by adding cyclopentane to standard fuel; 
         FIG. 3  is a diagram illustrating characteristics of octane bonus with respect to mixing proportion of cyclopentane and octane number of standard fuel; 
         FIG. 4  is a diagram illustrating characteristics of octane number (actual measured value) of mixed fuel with respect to mixing proportion of cyclopentane and octane number of standard fuel; 
         FIG. 5  is a diagram illustrating an exemplary result of combustion test on mixed fuel; 
         FIG. 6  is a diagram illustrating characteristics of ignition delay time of mixed fuel with respect to mixing proportion of cyclopentane and octane number of standard fuel; 
         FIG. 7  is a diagram for explaining an exemplary suitable range of the mixing proportion of cyclopentane for adding cyclopentane to FT light naphtha to produce reformed gasoline; 
         FIG. 8  is a diagram for explaining another exemplary suitable range of the mixing proportion of cyclopentane for adding cyclopentane to FT light naphtha to produce reformed gasoline; 
         FIG. 9  is a diagram for explaining another exemplary suitable range of the mixing proportion of cyclopentane for adding cyclopentane to FT light naphtha to produce reformed gasoline; 
         FIG. 10  is a diagram for explaining effect of adding cyclopentane to paraffinic hydrocarbons; 
         FIG. 11  is a diagram for explaining chemical reaction in which typical paraffinic hydrocarbons burn; 
         FIG. 12  is a diagram for explaining chemical reaction in which cyclopentane burns; and 
         FIG. 13  is a diagram illustrating breakdown of OH radicals consumed and generated in combustion process of each mixed fuel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention will be explained with reference to  FIGS. 1 to 13 . A production method of spark-ignition engine fuel according to an embodiment of the present invention involves producing reformed gasoline with an octane number applicable to a spark-ignition engine by reforming light naphtha with a low octane number. 
     The average global temperature is maintained in a warm range suitable for organisms by greenhouse gases in the atmosphere. Specifically, part of the heat radiated from the ground surface heated by sunlight to outer space is absorbed by greenhouse gases and re-radiated to the ground surface, whereby the atmosphere is maintained in a warm state. Increasing concentrations of greenhouse gases in the atmosphere cause a rise in average global temperature (global warming). 
     Carbon dioxide is a greenhouse gas that greatly contributes to global warming, and its concentration in the atmosphere depends on the balance between carbon fixed on or in the ground in the form of plants or fossil fuels and carbon present in the atmosphere in the form of carbon dioxide. For example, carbon dioxide in the atmosphere is absorbed through photosynthesis in the growth process of plants, causing a decrease in the concentration of carbon dioxide in the atmosphere. Carbon dioxide is also released into the atmosphere through combustion of fossil fuels, causing an increase in the concentration of carbon dioxide in the atmosphere. In order to mitigate global warming, it is necessary to replace fossil fuels with renewable energy sources such as sunlight, wind power, and biomass to reduce carbon emissions. 
       FIG. 1  is a diagram for explaining an example of a renewable fuel produced using renewable energy through Fischer-Tropsch (FT) synthesis. As illustrated in  FIG. 1 , renewable power is generated through solar power generation, wind power generation, or the like from renewable energy such as solar energy or wind energy, and water is electrolyzed by renewable power into renewable hydrogen. Further, FT synthesis is performed using renewable hydrogen and carbon dioxide recovered from gas emissions from factories and the like to generate FT crude oil. 
     FT crude oil is fractionated according to the range of boiling points and separated into FT diesel, jet fuel, and FT light naphtha. Among them, FT diesel and jet fuel can be directly used as a fuel for diesel engines and a fuel for jet engines, respectively. On the other hand, FT light naphtha, which is mainly composed of chain saturated hydrocarbons (paraffinic hydrocarbons) having about four to six carbon atoms, has a research octane number of as low as about sixty to seventy. Therefore, the direct use of FT light naphtha as a fuel for spark-ignition gasoline engines may lead to impaired engine combustion performance. 
     In this regard, the inventors have found that adding (mixing) cyclopentane to paraffinic hydrocarbons results in an increased octane number that is higher than expected from the octane numbers of and the mixing ratio between the two. Therefore, the present embodiment describes a production method of spark-ignition engine fuel, specifically, a method for producing reformed gasoline with an octane number applicable to a spark-ignition engine by reforming FT light naphtha through the addition of cyclopentane. 
       FIG. 2  is a diagram illustrating exemplary octane numbers of mixed fuels prepared by adding cyclopentane (octane number: one hundred and three point two) to a standard fuel (octane number (research octane number RON): sixty-five) at various mixing proportions x (volume percent in a standard state). The standard fuel is prepared by mixing isooctane (octane number: one hundred) and n-heptane (octane number: zero), both of which are paraffinic hydrocarbons, at an appropriate mixing ratio. Note that the octane number of cyclopentane used in the present embodiment is an experimental value measured in a test conforming to JIS standards. As indicated by the broken line in  FIG. 2 , the calculated value RONc of the octane number of mixed fuel calculated with Formula (i) below based on the mixing ratio between the standard fuel and cyclopentane linearly increases as a function of the mixing proportion x of cyclopentane. 
         RONc =65(100 −x )/100+103.2 x/ 100 
     On the other hand, as indicated by the plot and solid line in  FIG. 2 , the actual measured value RONa of the octane number of mixed fuel was higher than the calculated value RONc regardless of the mixing proportion x of cyclopentane, and reached a maximum at the mixing proportion x of fifty volume percent. Similar patterns were seen in standard fuels with different octane numbers. These results suggest that there is some kind of interaction between paraffinic hydrocarbons and cyclopentane. Hereinafter, the difference ΔRON between the actual measured value RONa and the calculated value RONc of octane number is referred to as an “octane bonus”. 
     As described above, the octane bonus ΔRON associated with the addition of cyclopentane to paraffinic hydrocarbons is maximized when the mixing proportion x of cyclopentane is fifty volume percent. Therefore, in the case of adding cyclopentane to FT light naphtha to produce reformed gasoline, the mixing proportion x of cyclopentane is preferably fifty volume percent or less, from the viewpoint of effective utilization of FT light naphtha. 
       FIG. 3  is a diagram illustrating the characteristics of the octane bonus ΔRON with respect to the mixing proportion x of cyclopentane and the octane number of standard fuel. As illustrated in  FIG. 3 , the octane bonus ΔRON shows a maximum when the mixing proportion x of cyclopentane is fifty volume percent, regardless of the octane number of standard fuel. The maximum of the octane bonus ΔRON increases as the octane number of standard fuel decreases. In the octane number range of sixty to seventy equivalent to FT light naphtha, it is possible to obtain the octane bonus ΔRON of fifteen or more by adjusting the mixing proportion x of cyclopentane. In the case of adding cyclopentane to FT light naphtha to produce reformed gasoline, it is preferable to determine the mixing proportion x of cyclopentane ensuring that the octane bonus ΔRON is a predetermined value (for example, fifteen) or more, from the viewpoint of full utilization of the effect of cyclopentane addition. 
       FIG. 4  is a diagram illustrating the characteristics of the octane number (actual measured value) RONa of mixed fuel with respect to the mixing proportion x of cyclopentane and the octane number of standard fuel. As illustrated in  FIG. 4 , the octane number RONa of mixed fuel varies depending on the octane number of standard fuel and the mixing proportion x of cyclopentane. By setting a calibration curve (predetermined characteristic) based on such test results and determining the mixing proportion x of cyclopentane based on the calibration curve, it is possible to produce reformed gasoline with an appropriate octane number through the addition of cyclopentane to FT light naphtha. For example, reformed gasoline with an octane number in the range of eighty-eight to ninety-five equivalent to regular gasoline can be produced. 
       FIGS. 5 and 6  are diagrams illustrating exemplary results of combustion tests on mixed fuel by means of a rapid compression machine. In the combustion tests by means of a rapid compression machine, an air-fuel mixture was introduced at the theoretical air-fuel ratio into a vacuum combustion chamber and compressed to a predetermined compression ratio, and the period of time (ignition delay time) ti [millisecond] from reaching the predetermined compression ratio to starting self-ignition was measured. 
       FIG. 5  shows the characteristics of the maximum thermal efficiency [percent] with respect to the ignition delay time ti. As shown in  FIG. 5 , the maximum thermal efficiency remarkably decreased as the ignition delay time ti became shorter than ten milliseconds, whereas the maximum thermal efficiency was somewhat stabilized within the range in which the ignition delay time ti was ten milliseconds or more. Therefore, in the case of adding cyclopentane to FT light naphtha to produce reformed gasoline, it is preferable to determine the mixing proportion x of cyclopentane so that the ignition delay time ti is ten milliseconds or more, from the viewpoint of securing sufficient performance of the spark-ignition engine to which the reformed gasoline is applied. 
       FIG. 6  shows the characteristics of the ignition delay time ti with respect to the mixing proportion x of cyclopentane and the octane number of standard fuel. As shown in  FIG. 6 , as the mixing proportion x of cyclopentane increases, the ignition delay time ti becomes longer, and the mixing proportion x of cyclopentane that causes the ignition delay time ti to reach ten milliseconds decreases as the octane number of standard fuel increases. 
       FIGS. 7 to 9  are diagrams for explaining exemplary suitable ranges of the mixing proportion x of cyclopentane with respect to the octane number of FT light naphtha for adding cyclopentane to FT light naphtha to produce reformed gasoline. 
     The mixing proportion x of cyclopentane is preferably fifty volume percent or less, from the viewpoint of effective utilization of FT light naphtha ( FIGS. 2 and 3 ). In addition, from the viewpoint of securing sufficient performance of the spark-ignition engine to which the reformed gasoline is applied, it is preferable to determine the mixing proportion x of cyclopentane so that the ignition delay time ti is ten milliseconds or more ( FIGS. 5 and 6 ). Therefore, as depicted in  FIG. 7 , in the case of adding cyclopentane to FT light naphtha to produce reformed gasoline, it is preferable to determine the mixing proportion x of cyclopentane so that the mixing proportion x is fifty volume percent or less and so that the ignition delay time ti is ten milliseconds or more. 
     From the viewpoint of full utilization of the effect of cyclopentane addition, it is preferable to determine the mixing proportion x of cyclopentane ensuring that the octane bonus ΔRON is a predetermined value (for example, fifteen) or more ( FIG. 3 ). In addition, from the viewpoint of securing sufficient performance of the spark-ignition engine to which the reformed gasoline is applied, it is preferable to determine the mixing proportion x of cyclopentane so that the ignition delay time ti is ten milliseconds or more ( FIGS. 5 and 6 ). That is, as depicted in  FIG. 8 , it is preferable to determine the mixing proportion x of cyclopentane so that the ignition delay time ti is ten milliseconds or more while ensuring that the octane bonus ΔRON is a predetermined value (for example, fifteen) or more. 
     The mixing proportion x of cyclopentane for adding cyclopentane to FT light naphtha to produce reformed gasoline can be determined according to the desired octane number of the reformed gasoline ( FIG. 4 ). For example, the mixing proportion x of cyclopentane can be determined based on a predetermined characteristic so that the octane number is within the range of eighty-eight to ninety-five equivalent to regular gasoline. In this case, the performance of the engine to which the reformed gasoline is applied is secured, but from the viewpoint of full utilization of the effect of addition, it is preferable to determine the mixing proportion x of cyclopentane ensuring that the octane bonus ΔRON is a predetermined value (for example, fifteen) or more ( FIG. 3 ). That is, as depicted in  FIG. 9 , it is preferable to determine the mixing proportion x of cyclopentane based on a predetermined characteristic so that the octane number RONa of mixed fuel is within a predetermined range while ensuring that the octane bonus ΔRON is a predetermined value (for example, fifteen) or more. 
       FIG. 10  is a diagram for explaining the effect of adding cyclopentane to paraffinic hydrocarbons, showing temporal changes in combustion temperature with different compositions of fuel. As shown in  FIG. 10 , there was a large difference in the time to reach low-temperature oxidation reaction accompanied by a rise in combustion temperature between the mixed fuel of fifty-percent isooctane and fifty-percent n-heptane (standard fuel) and the mixed fuel of fifty-percent cyclopentane and fifty-percent n-heptane. Low-temperature oxidation reaction is an exothermic reaction that is caused by a slow oxidation reaction of fuel molecules and proceeds in a chain-reaction fashion through generation and consumption of OH radicals. 
       FIG. 11  is a diagram for explaining a chemical reaction in which typical paraffinic hydrocarbons burn. A chemical reaction analysis showed that the chemical reaction in which typical paraffinic hydrocarbons (RH) burned generated nearly twice as many OH radicals as it consumed, in terms of chemical equivalents. Thus, in the combustion of typical paraffinic hydrocarbons, the amount of OH radicals generated is larger than the amount of OH radicals consumed, which facilitates a chain reaction in which low-temperature oxidation reaction rapidly proceeds. 
       FIG. 12  is a diagram for explaining a chemical reaction in which cyclopentane burns. The chemical reaction in which cyclopentane burned generated nearly zero point six five times as many OH radicals than it consumed. In addition, thirty-five percent of the product turned out to be stable cyclopentene, and the ratio of termination reaction in which radicals disappeared was confirmed to be high. Thus, in the combustion of cyclopentane, the amount of OH radicals generated is smaller than the amount of OH radicals consumed, which hinders a chain reaction and prevents low-temperature oxidation reaction from rapidly proceeding. 
       FIG. 13  is a diagram illustrating the results of a chemical reaction analysis for explaining a breakdown of OH radicals consumed and generated in the combustion process of each mixed fuel. As shown in  FIG. 13 , regarding the mixed fuel of fifty-percent isooctane and fifty-percent n-heptane, the combustion process of isooctane consumes and generates substantially equal amounts of OH radicals (forty-three percent and forty percent, respectively), and the combustion process of n-heptane consumes and generates substantially equal amounts of OH radicals (fifty-seven percent and sixty percent, respectively). Therefore, the rate of the low-temperature oxidation reaction of n-heptane is not changed by the coexistence of isooctane. 
     On the other hand, regarding the mixed fuel of fifty-percent cyclopentane and fifty-percent n-heptane, the combustion process of cyclopentane consumes more OH radicals (fifty-six percent) than it generates (thirty-eight percent), and the combustion process of n-heptane consumes fewer OH radicals (forty-four percent) than it generates (sixty-two percent). That is, when the low-temperature oxidation reaction of n-heptane and the low-temperature oxidation reaction of cyclopentane proceed in parallel, OH radicals generated in the combustion process of n-heptane are consumed in the combustion process of cyclopentane. Therefore, the low-temperature oxidation reaction of n-heptane is inhibited from proceeding by the coexistence of cyclopentane. 
     Thus, cyclopentane is advantageous not only because of its property of resistance to oxidation but also because when it is added (mixed) to paraffinic hydrocarbons, it consumes OH radicals generated in the combustion process to inhibit the low-temperature oxidation reaction of the mixed fuel as a whole from proceeding and slow down the combustion. 
     The present embodiment can achieve advantages and effects such as the following: 
     (1) The production method of spark-ignition engine fuel, configured to produce reformed gasoline for the spark-ignition engine, includes: mixing the light naphtha with the cyclopentane. Because the production of reformed gasoline with an octane number applicable to a spark-ignition engine is achieved by the addition of cyclopentane to light naphtha with a low octane number, it becomes possible to produce reformed gasoline with a low carbon intensity without any input of additional energy. 
     (2) The mixing proportion x of the cyclopentane is determined so that the ignition delay time ti of the reformed gasoline burning at a predetermined compression ratio, from a time point when the reformed gasoline is compressed up to the predetermined compression ratio until a time point when the reformed gasoline is self-ignited, is ten milliseconds or more. With this, it becomes possible to secure sufficient performance of the spark-ignition engine to which the reformed gasoline is applied. 
     (3) The mixing proportion x of the cyclopentane is fifty volume percent or less. By setting the mixing proportion x of cyclopentane to fifty volume percent or less at which the effect of cyclopentane addition due to the interaction between light naphtha and cyclopentane is maximized, it becomes possible to effectively utilize light naphtha. 
     (4) The mixing proportion x of the cyclopentane is determined so that the difference ΔRON between the calculated value RONc of the octane number of the reformed gasoline calculated based on the octane number of the light naphtha, the octane number of the cyclopentane, and the mixing ratio between the light naphtha and the cyclopentane and the actual measured value RONa of the octane number of the reformed gasoline is a predetermined value (for example, fifteen) or more. By determining the mixing proportion x of cyclopentane ensuring a sufficiently large effect of cyclopentane addition due to the interaction between light naphtha and cyclopentane, it becomes possible to fully utilize the effect of cyclopentane addition. 
     (5) The light naphtha is FT light naphtha obtained by Fischer-Tropsch synthesis. By utilizing FT light naphtha, it becomes possible to further lower the carbon intensity of the reformed gasoline. 
     (6) The mixing proportion x of the cyclopentane is determined based on the predetermined characteristic predetermined so that the octane number of the reformed gasoline is within a predetermined range, and is determined so that the difference ΔRON between the calculated value RONc of the octane number of the reformed gasoline calculated based on the octane number of the light naphtha, the octane number of the cyclopentane, and the mixing ratio between the light naphtha and the cyclopentane and the actual measured value RONa of the octane number of the reformed gasoline is the predetermined value (for example, fifteen) or more. 
     By determining the mixing proportion x of cyclopentane ensuring a sufficiently large effect of cyclopentane addition due to the interaction between light naphtha and cyclopentane, it becomes possible to fully utilize the effect of cyclopentane addition and efficiently produce high-octane reformed gasoline. In addition, by determining the mixing proportion x of cyclopentane based on a predetermined characteristic in consideration of the interaction between paraffinic hydrocarbons which are main components of light naphtha and cyclopentane, it becomes possible to produce reformed gasoline with an appropriate octane number. 
     (7) The predetermined range is predetermined based on the octane number of regular gasoline. In this case, the reformed gasoline can be suitably applied to a gasoline engine produced for use with regular gasoline. 
     In the above-described embodiment, cyclopentane is added to FT light naphtha, which is a renewable fuel, but cyclopentane may be added to a naphtha derived from fossil fuel. In addition, cyclopentane may be a renewable cyclopentane derived from renewable fuel. In this case, the carbon intensity of the reformed gasoline can be further reduced. 
     The above embodiment can be combined as desired with one or more of the above modifications. The modifications can also be combined with one another. 
     According to the present invention, it becomes possible to produce a fuel for a spark-ignition engine with a low carbon intensity. 
     Above, while the present invention has been described with reference to the preferred embodiments thereof, it will be understood, by those skilled in the art, that various changes and modifications may be made thereto without departing from the scope of the appended claims.