This invention relates to a new fuel comprising a hydrocarbon mixture being limited to hydrocarbons within the range^C6 to C10, to a method for producing this fuel, and to a method of operating an improved internal combustion engine using the fuel of the invention.
Present day automotive gasoline consists of a mixture of hydrocarbons which range from C4 to about C12. The lower molecular weight fraction, such as butane isomers, is more volatile and it has always been the practice to include substantial portions of these volatiles in the fuel to insure proper engine performance. This practice, however, is at best a compromise since the presence of the volatiles, on the one hand, causes an undue risk of explosion during storage and handling; and the inherent evaporative and emission losses contribute to Pollution; but, on the other hand, the volatiles have always been considered necessary for good cold engine starting. Thus, a certain amount of the volatiles have been incorporated in gasoline. The exact amount of the volatiles may vary according to the climate where it is sold. In fact, industry has set voluntary limits so that each area will have a motor fuel having sufficient volatility for the prevailing climate. High levels of volatile components assure satisfactory starting and warm-up at the lowest temperature expected, and low levels of volatile components protect against vapor-lock in high temperature climates.
Generally current gasolines exhibit high levels of volatiles measured in terms of Reid Vapor Pressure. Reid Vapor Pressure is the accepted measurement of gasoline volatility and it represents the vapor pressure at 100°F (37.78°C). Current fuels require a relatively high amount of volatile components which raises the Reid Vapor Pressure to undesirable levels. It is highly desirable to formulate a fuel which satisfies the volatility requirements without raising the Reid Vapor Pressure to the undesirable level found in the prior art fuels.
The use of these volatiles in prior art fuels is associated with several problems. One such problem is that because present day engines depend on the volatiles, the spontaneous loss of them in storage results in a fuel which is of inferior quality after a period of storage. Thus, because of varying storage times, the consumer can never be certain if the gas he is purchasing contains the required amount of volatiles at the time of purchase. Naturally, therefore, a fuel whose efficiency and dependability is less dependent on the presence of volatiles is more desirable.
Another problem arising out of the use of these volatiles is the evaporative loss of gasoline which can occur in the gas tank. Industry has been hard pressed to solve this problem for quite some time. While this problem has been recognized for some time, industry has always been reluctant to solve the problem by reducing the volatility of the gasoline because in doing so they would lose the benefits of the compromise i.e., engine performance). In fact, this point has been expressed in the publication titled Effects of Automotive Emission Requirements on Gasoline Requirements; Symposium, American Society for Testing and Materials; 1971. Here it is stated on page 111 that "Severe volatility reduction could produce other problems. A more effective method than volatility reduction can be seen to be the elimination of evaporative losses by some mechanical device". This invention, however, seeks to reduce volatility or Reid Vapor Pressure and still maintain a fuel which can perform well.
Present day gasoline also contains, in addition to the volatile light-weight and the intermediate-weight components, a heavy-weight component which, like the volatile component, is also associated with several disadvantages. For example, the gasoline of today, when used as a fuel in present day short stroke engines, results in incomplete combustion because there is insufficient tine or temperature to burn the heavy hydrocarbon components. This results in a certain amount of gasoline being wasted and this contributes to pollution. Conventional C4-C12 has too much energy in it for conventional internal combustion engines in that if combusted with enough air (stoichiometric or slightly above) it will burn too hot for the engine or it will produce high levels of nitrous oxides. Yet, in spite of these shortcomings, the heavy components are left in present day fuel because their presence is considered necessary to provide a fuel having suitable properties for automotive use.
The presence of these heavy components in conventional C4-C12 gasoline requires considerable front end priming with light components (C4 and/or C5) to achieve adequate front end volatility for starting engines equipped with standard carburetion systems. In addition, conventional C4-C12 gasoline which contains these heavy components (C11 and C12) cannot be easily gasified and maintained in the gaseous state without recondensing. Consequently, conventional C4-C12 gasoline has limited utility in a more efficient carburetion system of the type which requires gasification in the absence of air before mixing the gasified fuel with air for combustion. Therefore, in view of the shortcomings associated with the heavy weight hydrocarbons, especially C11 and C12, it would be highly desirable to formulate a fuel without these heavy components being present while also avoiding the problems associated with the absence of these components.
The problems associated with volatile and heavy-weight components are also outlined in "Le Pétrole, Raffinage et Génie Chimique, Tome I, p. 19-27 (1972)", where it is stated, that a fuel should contain hydrocarbons in the range from C4 to C10, and should have a Reid Vapor pressure of not more than 800 g/cm2 in winter and not more than 650 2/cm2 in summer. It is, however, not teached to completely eliminate heavy-weight hydrocarbons, but to reduce their content much, that a residue of not more than 3 % remains at 250°C. "Erdöl-Lexikon, 5th edition, p. 206", provides the information that paraffins having from 5 to 10 carbon atoms are present in fuel for Otto engines.
The use of conventional C4-C12 fuels in standard carbureted internal combustion engines requires that the volatility of the fuel be adjusted to achieve a Reid Vapor Pressure of at least 9 in the summer and 12 in the winter. If the Reid Vapor Pressure of conventional C4-C12 gasoline falls below the above limits, starting and running the engine is severely impaired. The fuels of the present invention will easily start and operate identical engines yet these fuels have a reduced Reid Vapor Pressure in comparison to the above-mention conventional C4-C12 gasoline. Thus the summer fuels of the present invention may have a Reid Vapor Pressure less than 9 and the winter fuels may have a Reid Vapor Pressure of less than 12. In particular, it is been discovered that the fuel of the present invention having a Reid Vapor Pressure as low as 6 in the summer and 9 in the winter will easily start and operate identical engines which require conventional fuels having a Reid Vapor Pressure of 9 in the summer and 12 in the winter. The Reid Vapor Pressures can be reduced even further by using the fuels of the present invention in combination with the improved carburetion system of the present invention.
The ideal combustion mixture for internal combustion engines consists of a fuel in the vapor or gaseous state thoroughly mixed with adequate air to support combustion. In this condition, fuel-rich pockets, which are responsible for detonation or "knock," are eliminated and carbon deposits responsible for preignition are minimized due to more complete combustion. Because detonation or preignition can damage or ruin an engine, current gasolines have octane boosters such as aromatics contained therein to reduce "knock" since current engines have fuel and air intake systems which produce droplets of fuel that contribute to fuel rich pockets in the combustion chambers of the engines. Slowing the burn with octane boosters lowers the combustion efficiency of the engine and increases the exhaust pollution. Therefore, it would be highly desirable to provide a fuel which avoids octane boosters, is rated at a lower octane value but which has highly desirable burning characteristics so that the fuel does not produce engine knock
Automotive and aviation gasolines have always had an ASTM average octane number (R+M/2) of 80 or higher; wherein R represents the research octane number and M represents the motor octane number. Current engines generally require an average octane number in excess of 85.
A primary object of this invention is to provide an improved fuel which facilitates the achievement of ideal combustion mixtures for internal combustion engines.
Another object of this invention is to provide a lower octane fuel and method of use so as to further improve the combustion efficiency of the fuel in an internal combustion engine.
A further object of this invention is to provide a method of operating an internal combustion engine whereby greater combustion efficiencies can be achieved in the engine.
It is an object of this invention to provide a fuel for automotive engines which minimizes the requirement for volatile components in the fuel without sacrificing adequate engine performance and which lowers the Reid Vapor Pressure while maintaining good front end volatility.
It is also an object of this invention to provide a fuel having a low Reid Vapor Pressure which combusts more efficiently than conventional gasoline of the type having a hydrocarbon range of C4-C12.
It is another object of this invention to provide a fuel which has greater tolerance for alcohol enrichment because of low Reid Vapor Pressure.
It is yet another object of this invention to provide a fuel which minimizes the priming needed to achieve adequate front end volatility for starting engines equipped with standard carburetion systems.
It is a further object of this invention to provide an improved fuel which has enhanced gasification characteristics in improved carburetion systems.
It is another object of this invention to provide an improved process for more completely combusting the fuel of this invention in an engine thus negating the need for fuel injection systems or catalytic converters.
These and other objects of the invention will become apparent to those skilled in the art from the following disclosure of the invention.
The objects of the present invention are achieved by the fuel claimed in claim 3, which can be produced by the method claimed in claim 1, and the method of operating an internal combustion engine claimed in claim 9. The respective dependent claims relate to preferred embodiments of the invention.
Subject matter of the present invention are the methods and the fuel as defined in the claims. In particular, the hydrocarbon mixture of the fuel of the present invention is limited to hydrocarbons within the range C6-C10. Where C4 and/or C5 hydrocarbons are additionally present in the fuel of the present invention, they are a priming agent, said priming agent being present in a minimum effective amount for raising the front end volatility of the fuel to a minimum level for cold engine starting with said minimum effective amount being less than that required for C4-C12 gasoline.
The present invention is based on the discovery that front-end priming of fuel is not necessary in gasifier type carburetors and that the heavier components in gasoline are not stable as gases in air using gasifier type carburetors. Therefore it was possible to develop a new fuel that has unique benefits not obtained in C4-C12 gasoline. In addition the new gasification method has distinct advantages over the prior art.
The invention relates to a fuel having an intermediate hydrocarbon range relative to conventional C4-C12 gasoline which contains C4, C5, C6, C7, C8, C10, C11 and C12 hydrocarbons. This fuel of the invention is made by removing the lighter volatile component as well as the heavier component from a conventional gasoline starting material. The resulting fuel is C6-C10; i.e. the hydrocarbons are limited to those in the range C6-C10. Also, it may be desirable to further remove the C10 component to form a C6-C9 fuel for improved winter performance in gasifier type carburetors.
Suitable starting material to produce the fuel of this invention is conventional gasoline having a range of C4-C12. Both the heavy and light components are removed by any of the known methods currently available such as heat fractionization or the use of heat and vacuum in the absence of air. Once removed, the heavy component may be "cracked" at the refinery to make more fuel and the volatile component, most of which is being wasted today, may be fully recovered at the refinery.
Although gasoline having a range of C4-C12 is mentioned as a useful starting material, it is not critical that the starting material be precisely in this range. Rather, it is the essence of this invention to produce a fuel of intermediate carbon range (i.e. C6-C10 or C6 to C9) relative to the given range C4-C12 that may be produced directly from refinery hydrocarbon streams.
It will be apparent, of course, that the C6-C10 and C6-C9 fuels of the invention cannot be used efficiently in conventional internal combustion engines without modification of the carburetion system. It has been found, however, that the fuel of this invention can be quickly volatilized in a heated chamber by heating to a temperature above the final boiling point of the fuel at one atmosphere pressure in the absence of air, and such apparatus can be readily installed in an automobile. The resulting vapor (produced as needed) will mix readily with air to form a homogenous mixture without formation of condensed droplets which can wet the wall in an internal combustion engine; will not be subject to liquid phase oxidation prior to ignition; and will ignite well in the gaseous form.
Since not all the C6-C10 and C6-C9 fuel can be used efficiently in a conventional internal combustion engine without modification of the carburetion system, the present invention also provides an improved fuel for use in cars having standard carburetion systems. In connection with this, it has been discovered that the above described C6-C10 and C6-C9 fuel can be used in an internal combustion engine having a standard carburetion system by priming the fuel with a minimum amount of C4,C5 or a mixture of C4 and C5 to produce a fuel having adequate front end volatility for starting cars equipped with standard carburetion systems. Since the fuel may be primed with C4 and/or C5 , then the permissible range of the primed fuel will be C4-C9 (winter) and C4-C10 (summer). In particular, it has been discovered that the amount of C4 or C5 priming necessary for achieving adequate front end volatility for starting engines equipped with a standard carburetion system is less than the amount required with conventional C4-C12 gasoline. Thus, this aspect of the invention provides an improved fuel for standard carbureted engines and this fuel advantageously contains less C4 or C5 than conventional C4-C12 gasoline while maintaining adequate front end volatility and reduced Reid Vapor Pressures. In other words, the C6-C10 and C6-C9 fuel requires less priming to achieve adequate front end volatility for starting engines equipped with standard carburetion systems than does normal C4-C12 automotive gasoline. This represents a unique and unexpected method of achieving lower Reid Vapor Pressure in automotive fuel while maintaining adequate-front end volatility since one would assume that lighter fuel (C4-C9 and C4-C10) would have higher Reid Vapor Pressure than heavier C4-C12 gasoline.
The amount of C4, C5 or mixture of C4 and C5 used to prime the C6-C10 or C6-C9 fuel is a minimum effective priming amount necessary to achieve adequate front end volatility for starting a car equipped with a standard carburetor, the priming amount being less than that required for C4-C12 gasoline.
The C6-C10 and C6-C9 fuel, primed with C4 and/or C5, can also be made by removing the heavy and light components from gasoline as described above for making C6-C10 and C6-C9 with the exception that a minimum effective priming amount of C4 and/or C5 is retained in the product to achieve adequate front end volatility for starting a car equipped with a standard carburetor, the priming amount being less than that required for C4-C12 gasoline.
It has also been discovered that adequate front end volatility for engines equipped with standard carburetion can be achieved by priming with additional C5 so that adequate front end volatility can be achieved without any C4 priming, the priming amount being less than that required for C4-C12 gasoline.
Prior art aviation gasoline having a carbon range of C4 to C9 would not require the removal of higher molecular weight constituents to be stable as a vapor or gas in ambient air but the use of such prior art fuels would require the lowering of the octane to increase the speed of burn, thus improving combustion efficiency and lowering the pollutants produced during combustion.
Since the temperature of intake air used in an engine can vary widely because of seasonable variations or altitudes, the amount of heavy molecules removed can vary, with molecules heavier than C10 being completely removed. Preheated intake air systems could utilize more of the energy contained in the dense heavier molecules but this would result in too much loss in volumetric efficiency caused by the preheating or preexpansion of the intake air.
The conversion of the fuels of this invention into vapors or gasses, homogenizing these vapors or gasses with intake air (ambient or heated) while maintaining gas or vapor stability and combusting this fuel mixture in an engine represents an improved method for achieving higher combustion efficiency while lowering the pollutants of combustion.
Figure 1 is a graph which illustrates the fuel efficiency of selected fuels in a 1500 c.c. Volkswagon engine at various engine speeds. The vertical axis shows the efficiency in term of lbs. of fuel/horsepower hour. The horizontal axis measures the engine speed. Figure 1 also illustrates the fuel efficiency of the C5-primed fuel of this invention combusted in an identical engine equipped with the improved carburetor of this invention.
In the manufacture of the fuel in accordance with the present invention, both the lighter volatile component and the heavier, slow-burning component are removed from gasoline in the C4-C12 range. The removal of the volatile component makes the resultant fuel have a slower rate of burning. By also removing the heavy slow-burning component, the resultant fuel is a C6-C10 or C6-C9 fuel having a burn rate comparable to or better than the starting stock gasoline (C4-C12) from which it was made.
The most abundant of the volatile components in conventional C4-C12 gasoline is butane and pentane. With regard to the removal of the volatile components it is primarily the butane and pentane which is removed from the C4-C12 gasoline in the practice of this invention. If the gasoline contains hydrocarbons lighter than butane, they are removed, too. The heavy, slow-burning component consists primarily of C11 and C12, each of which exists in numerous isomeric forms. These are removed and, if the starting stock gasoline contains hydrocarbons greater than C12, they are also removed. The light volatile components and the heavy, slow-burning components are removed according to conventional known methods.
It is also recognized that the heavy and light components do not exist as absolutes but rather, as points on a continuum with the most volatile being the lighter hydrocarbons, and a gradual reduction in volatility and burning tendency as the weight is increased. This gives rise to certain "border line" components near both ends of the continuum. It is inevitable that some of these will be removed with the heavier and the lighter components. In general, it is recognized that the border line weights are C6 and C10. According to this invention, a substantial quantity of volatile component, namely hydrocarbons up to 5 carbon atoms, is removed to effectively reduce the potential for explosion and minimize the loss of gasoline due to evaporation. Likewise, the heavy component, namely hydrocarbons having more than more than 10 carbon atoms, is also removed to raise the burn rate of the fuel and effect more complete combustion. Both of these components are removed and this fuel is used with an improvement in fuel combustion efficiency and engine performance.
This improvement is illustrated in Figure 1. It will be noted that Figure 1 shows a comparison which measures the efficiency of the fuel of the present invention primed with C5 versus the efficiency of conventional C4-C12 prior art fuels at various engine speeds. The fuel efficiency is measured in terms of Brake Specific Fuel Consumption (lbs. of fuel per horsepower hour). Lower Brake Specific Fuel Consumption values indicate better fuel efficiency.
The C6-C10 fuel of this invention may be used to run an engine equipped with the improved gasifier carburetor described herein. However, it is not necessary that volatile components be absent from the fuels used in the improved gasifier combustors since their presence in the fuel does not hinder the gasification process. Thus, some volatile C4 and/or C5 may be added to the C6-C10 fuel as a primer, the priming amount being less than that required for C4-C12 gasoline, so that the fuel can be used in a standard carbureted engine as well as an engine equipped with the improved gasifier carburetor. For this reason the comparison presented in Figure 1 utilized the C6-C10 fuel of the invention containing some C5 volatile component as a primer, the priming amount being less than that required for C4-C12 gasoline, so that the resulting C5-C10 fuel will run an engine equipped with an improved gasifier carburetor as well as a standard carbureted engine. The C5-C10 has a boiling point range of about 49°F-345°F (9.4 to 174°C).
In order to obtain the data shown in Figure 1, identical engines were used to compare conventional C4-C12 unleaded gasoline (line A) with the C6-C10 fuel of this invention, primed with C5 (line B). An identical engine was used to test the use of the C6-C10 fuel of this invention, primed with C5, in an improved carburetion system of the present invention (line C). It will be noted by comparing line A with line B that at all engine speeds, more pounds of fuel are required per horsepower hour for the C4-C12 gasoline than for the C6-C10 fuel of the present invention, primed with C5. Therefore, the C5-C10, primed with C5, is significantly more efficient when combusted in identical engines. It will also be noted from Figure 1 that an even greater efficiency is observed when the C6-C10 fuel primed with C5, is combusted in an identical engine equipped with the improved carburetion system of the present invention.
In a preferred embodiment of this invention, the C4-C12 gasoline is used as a starting ingredient from which the volatile C4 and C5 constituents and the heavy C11 and C12 components are removed. In the preferred embodiment the starting C4-C12 gasoline contains a mixture of each of the hydrocarbons (i.e., a mixture containing C4, C5, C6, C7, C8, C9, C10, C11 and C12). Consequently, the C6-C9 and C6-C10 fuel of the preferred embodiment will likewise contain the same intermediate hydrocarbons which are present in the starting gasoline. In other words, C6-C9 will contain, C6, C7, C8, and C9 and the C6-C10 fuel will contain, C6, C7, C8, C9 and C10 hydrocarbons.
The fuels of the present invention have an intermediate hydrocarbon range relative to conventional gasoline which has a hydrocarbon range of C4-C12. The conventional C4-C12 gasoline contains paraffinic hydrocarbons including C4, C5, C6, C7, C8, C9, C10, C11 and C12 paraffinic hydrocarbons. Thus removing the C4, C5, C11 and C12 paraffinic components of the C4-C12 fuel will result in a fuel which contains paraffinic hydrocarbons, including paraffinic C9 and C10 which were originally present in the C4-C12 paraffinic fuel from which the fuel of this invention is derived.
In one embodiment of the present invention the light and heavy components are removed from conventional C4-C12 gasoline to produce a fuel having a hydrocarbon range of C5-C10, with C5 being a priming agent as defined in claim 4. Such a fuel is identical to the C6-C10 fuel with the exception of the presence of the C5 priming component in the C5-C10 fuel. Thus the C5-C10 fuel will have a boiling point range of about 49°F-345°F (9.45 to 174°C).
Although the starting gasoline preferably contains the entire range of hydrocarbons from C4-C12 as described above, it is not absolutely essential that all of the intermediate hydrocarbons be present in the starting gasoline. However, it is critical that the C6-C9 fuel contains C9 hydrocarbon and the C6-C10 fuel contain C9 and C10 hydrocarbon.
The preferred C6-C10 fuel may be defined as the portion remaining when C4-C12 gasoline has removed therefrom lower weight volatile components (up to C5) to substantially reduce evaporative loss and explosion potential and higher weight components (C11 and higher) to raise the burn rate of the remaining hydrocarbons. The C6-C10 fuel which has these characteristics can be made by removing the volatile and heavy components so that the remaining hydrocarbon mixture will boil within a range of about 121°F-345°F (49.4 to 174°C) at one atmosphere. Such a boiling point range encompasses the boiling point of the lowest boiling C6 component and the highest boiling C10 component. Of course, it is possible that a small amount of C4, C5 , C11 and C12 may remain after the separation process due to imperfections of gasoline fractionation procedures.
Since the largest hydrocarbon in the C6-C10 fuel is C10, then the final boiling point of such a mixture will be 345°F (174°C). It has been discovered that hydrocarbons having boiling points above 350°F (177°C) must be substantially eliminated so that the fuel can be gasified in a heated chamber in the absence of air, and then mixed with ambient air (i.e., about 70°F or 21°C) without condensing to form droplets of heavy hydrocarbons which could wet the surfaces in an internal combustion engine. This property is an essential aspect of the C6-C10 fuel because the C6-C10 fuel is used in a modified carburetion system in which the fuel is gasified in a heated chamber and then mixed with air for immediate combustion in an automotive internal combustion engine. The absence of condensed droplets allows the fuel to burn much more efficiently than conventional C4-C12 gasoline and, consequently, reduces pollution and improves engine performance. By removing C11 and C12 components from the starting stock gasoline, the final boiling point will be 345°F (174°C) and, thus, the resulting fuel will have the desired gasification property.
The gasification system used for the C6-C10 fuel of the present invention requires heating the fuel to lower temperatures that would be required for the gasification of C4-C12 gasoline. When lower temperatures are attained, the volumetric efficiency of the air and gas mixture going into an engine is improved.
The fuel having hydrocarbons comprised of C6-C10 hydrocarbons will have lower Reid Vapor Pressure than conventional C4-C12 gasoline with functional Reid Vapor Pressures less than two. Nonetheless, the C6-C10 fuel will exhibit good ignition properties in the gaseous state when mixed with air. It will also provide excellent engine starting ability, will have reduced explosive potential and will burn more completely than C4-C12 gasoline. In addition, the C6-C10 fuel will burn cooler in the engine with the modified carburetor and consequently the use of such a fuel will result in less lubrication requirements for the engine.
Conventional C4-C12 gasoline has high Reid Vapor Pressure and the Reid Vapor Pressure can be adjusted somewhat to provide summer or winter fuels. For example, the Reid Vapor Pressure can be increased by adding volatiles such as C4 to enhance the winter performance of the conventional gasoline. However, the present C6-C10 fuel of the invention requires lowering the Reid Vapor Pressure by removing the C4 and C5 components. Thus it would be expected that ability to formulate winter and summer fuels would be lost if the hydrocarbon range is limited to C6-C10 hydrocarbons. It is therefore surprising that the C6-C10 fuel can be formulated for winter use without additional C4 priming. It has been discovered that a winter fuel can be made in the same manner as the C6-C10 summer fuel with the exception being that the C10 component is additionally separated from the starting C4-C12 gasoline along with the C4, C5, C11 and C12 components to provide a fuel that when gasified will remain substantially a gas when mixed with colder air. Thus, the present invention also provides a winter fuel having hydrocarbons which consists of hydrocarbons in the range C6-C9. The C6-C9 winter fuel differs from the C6-C10 fuel only in the elimination of the C10 component which is left in the C6-C10 summer fuel. Consequently, the winter C6-C9 fuel has a final boiling point of 303°F (151°C) and a boiling range of about 121°F-303°F (49 to 151°C).
The C6-C9 fuel must contain the C9 hydrocarbon component and preferably should contain the remaining intermediate hydrocarbons which are C6, C7, and C8 since these are preferably present in the C4-C12 gasoline. The C6-C9 winter fuel is burned in an engine in the same manner described above with respect to the C6-C10 fuel and enjoys the same benefits described above with respect to the C6-C10 fuel.
The C6-C10 and C6-C9 fuel is gasified by heating in a chamber in the absence of air to a temperature above the final boiling point of the fuel. The C6-C10 and C6-C9 fuels are preferably heated to a temperature 350°F (177°C). Higher temperatures may be used but are not necessary. Conventional C4-C12 would require a temperature of about 75°F (24°C) higher to gasify and when mixed with air it would still have the problem of forming condensation droplets. Additionally, the higher temperature would lower the volumetric efficiency of the engine.
It has been emphasized that C9 and C10 must be present in the C6-C10 fuel and C9 must be present in the C6-C9 fuel because heavy molecular components have the highest energy density. Since these are the highest density components capable of being gasified and remaining a gas when mixed with air, it is important that they remain in the fuel for production of engine power.
It has also been discovered that the C6-C10 and the C6-C9 fuels can be adapted for use in engines having standard carburetion i.e., carburetors which do not require gasification in a heated chamber in the absence of air). In particular, it has been discovered that priming the C6-C9 and the C4-C10 fuel with a small amount of a volatile component, i.e. a priming agent, will result in the production of an improved fuel which may be used in automobiles equipped with standard carburetion. The priming agent may be C4, C5, or a mixture of C4 and C5. Consequently the primed fuel will have hydrocarbons which consists of hydrocarbons in the range C4-C10 (summer) and C4-C9 (winter). The C4-C9 and C4-C10 fuel is the same as the analogous C6-C9 and C6-C10 fuel except for the presence of a small amount of priming agent in both the C4-C9 and C4-C10 fuel, said small amount being the minimum effective amount for raising the front end volatility of the fuel to a minimum level for cold engine starting with said minimum effective amount being less than that required for C4-C12 gasoline.
In both the winter and summer fuel, the amount of priming agent is the minimum amount effective to raise the front end volatility so that the fuel can be used in cars equipped with standard carburetion. Thus the C4-C9 (primed with C6-C9) is particularly suitable for winter use and the C4-C10 (primed with C6-C10) is particularly suitable for summer use in cars equipped with standard carburetors. It is particularly significant and surprising that the amount of C4 or C5 in the C4-C9 (primed C6-C9) and C4-C10 (primed C6-C10) fuel is less than the amount of C4 or C5 in conventional C4-C12 gasoline without sacrificing any of the desirable properties of the gasoline. It is also surprising that the C4-C9 and C4-C10 fuels have adequate front end volatility yet are lower in Reid Vapor Pressure than conventional C4-C12 gasoline. It is believed that this is because removal of C11 and C12 from C4-C12 gasoline means that the remaining fuel will have a higher percentage of C4, C5, and C6 hydrocarbons. therefore much of the C4 and some of the C5 hydrocarbons can be removed from the C4-C10 and C4-C9 fuel to obtain a functionally equivalent front end volatility in comparison to the original C4-C12 gasoline. This reduces the Reid Vapor Pressure.
The fuel of this invention may also contain any of the various additives presently in use or known to be useful in gasoline. In fact, because this invention produces a fuel having a low Reid Vapor Pressure, as compared to normal automotive gasoline, it is possible to add large amounts of alcohol such as ethanol to the fuel of this invention without raising the Reid Vapor Pressure above the current allowable limits. Alcohol addition to conventional gasoline is known to raise the Reid Vapor Pressure above the allowable limits. Additions of alcohol can be added to the fuels of this invention in an amount of 10-20 per cent by weight without exceeding current Reid Vapor Pressure standards.
It is also possible to add lubricants or anti-knock compounds to the fuel. For example, a suspension of fine synthetic upper end lubricants or small amounts of anti-knock compounds may be added the fuel of this invention.
It has also been surprisingly discovered that the fuels of this invention when gasified burn almost completely in the engine producing equivalent torques with less fuel and at temperatures which are lower than the temperatures achieved when combusting conventional fuels in engines equipped with standard carburetion systems. This is true at stoichiometric or slightly higher air-to-fuel ratios which would normally result in the development of excessive engine temperature. Therefore, combusting the fuel of this invention produces less nitrous oxide and allows some increase in compression or supercharging without damage to the engine and without environmental contamination.
The fuel of this invention is a C6-C10 hydrocarbon fuel and naturally exists in the liquid state at standard temperature and pressure. Thus the fuel can be shipped, stored and dispensed like conventional gasoline and requires no further processing for use.
It has also been discovered that the fuels of this invention burn cooler than conventional C4-C12 fuel. For this reason it may be advantageous to add an oxygen source to the fuel to obtain more complete combustion. The oxygen source raises the combustion temperature. However, due to the fact that the fuels of the present invention burn cooler than conventional C4-C12 gasoline, the elevated combustion temperature can be tolerated in automobile engines. Thus, an oxygenate compound may be added to the fuels of the present invention to raise combustion temperatures or to effect more complete combustion. Many suitable oxygen source may be used. Typical oxygen sources include oxygenated hydrocarbons such as 1, 2 butylene oxide.
C5-C10 fuel was made by removing the hydrocarbons lighter than C5 and the hydrocarbons heavier than C10 from a conventional C4-C12 gasoline. The C4-C12 gasoline which served as the starting ingredient contains C5, C6, C7, C8, C9, and C10 hydrocarbons in addition to the heavy and light hydrocarbons which were removed therefrom. The resulting C5-C10 fuel therefore contains C5, C6, C7, C8, C9, C10 hydrocarbons. The C5-C10 fuel had a Reid Vapor Pressure of 6. The fuel was used to start and run a standard carbureted Volkswagon engine. Measurements of fuel efficiency were taken and the results are shown in Table I, (line B). During the test it was noted that the standard carbureted engines started and ran easily even though the fuel had a Reid Vapor Pressure of only 6.
For the purpose of comparison, the C4-C12 gasoline described in example 1 was used to start and run a Volkswagon engine which was identical to the engine used for testing the C5-C10 fuel in example 1. The C4-C12 gasoline had a Reid Vapor Pressure of 10. The efficiency of the C4-C12 gasoline was measured and the results are shown in Figure 1 (line A).
The C5-C10 fuel used in example 1 was also tested in an engine identical to the engine used in example 1 with the exception that the engine used in example 3 was equipped with an improved carburetion system of the present invention. The fuel efficiency was measured and the results are shown in Table I (line C). During the test it was noted that the C5-C10 fuel easily started and ran the engine equipped with the improved carburetor even though the fuel had a Reid Vapor Pressure of only 6.