US2560898A - Fuel composition - Google Patents

Description

Patented July 17, 1951 UNITED STATES PATENT E.

FUEL COMPOSITION Walter A, Schulze and John E. Malian, Bartlesville, kla., assignors to Phillips Petroleum Jompany, a corporation of Delaware 1 This invention relates to an improved motor fuel composition for use in high output aircraft engines. More-specificall it relates to an aviation fuel conforming to rigid specifications of antiknock rating, vapor pressure and distillation characteristics, and having, in addition, combustion characteristics which provide superior power output overa broad range of fuel-air ratios and particularly over the range classified as rich mixtures. "It relates further to a method of operating an aviation gasoline engine requiring a fuel having an octane number of at least about 90. r This application is. a continuation-in-part of our copending U. S. application Serial No. 660,- 6222, filed April 9, 1946.

High octane number aviation fuels are manu- Drawing. Application July 24, 1950,

Serial No. 175,650

as a source of volatility to adjust the vapor pressure of the blend, and to produce desirable distillation characteristics, especially in the initial portion of the distillation curve.

Since the synthetic isoparaifln blending stocks are ordinarily available in somewhat smaller volume than base stocks prepared from naturally occurring distillates, blending formulas which re-' quire minimum volumes of such synthetic stocks are preferred. Assuming that isopentane is plentiful and used to the maximum extent possible within vapor pressure and front-end volatility limits, it then remains to select and prepare other components commonly termed base-stocks of both factured and blended according to specifications so strict that the selection of suitable components is limited in many cases to high purity synthetic blending stocks and naturally occurring base stocks which'are segregated with such precision as to approximate the purity of the synthetic hydrocarbons. Such fuels must have high 'octane number ratings and this in turn means that the components must have high octane number ratings and/or excellent response to the addition of antidetonants. Further, the unsaturation of the components must be exceedingly low in order that the fuels be substantially free of gum and of susceptibility to gum formation. These qualifications together with rigid require! ments for vapor pressure, end point, and distillation characteristics, sharply limit the choice of fuel components to the relatively low-boiling, predominantly paraflinic hydrocarbons, say of 5 to 9 carbon atoms, and preferably to the higher octane number branched-chain or isoparaflins.

In the manufacture of aviation fuels of to octane number or of those fuels having antiknock ratings beyond the conventional octane scale, the

procedure usually includes the manufacture of synthetic isoparafllns as one blending component. For example, processes, such as selective polymerization, thermal or catalytic alkylation, or the like ,;may be utilized to prepare concentrates of isooctanes together with usually much smaller amounts of higher and lower homologues. Thermal alkylation may DION-106 such stocks as ne'- ohexane, which are highly desirable blending stocks. As a second component, base stocks comprising isohexanes, isoheptanes, isooctanes, etc., may in many instances be prepared by precise fractionation schemes from crude oil and/or. natural gasolines.

A third component, which is ordinarily considered separately, is isopentane, which can be prepared in substantially pure form by fractionation of hydrocarbon mixtures containing it. This last named material is ordinarily the lowest boiling stock included in aviation fuels, and it functions high octane number and low vapor pressure.

These characteristics are most conveniently obtained by segregation of isoparaflins, such as the isohexanes, etc., as being more valuable than a full boiling range naphtha, unless the naphtha is deficient in normal (low octane number) paraffins or has unusually high octane number as a result of its content of naphthene hydrocarbons.

The net result of the above'described blending procedure is the production of fuels of suitable distillation characteristics, vapor pressure, gum stability, and octane number rating comprising largely'isoparaflins of 5 to about 8 or 9 carbon atoms, substantially free of C4 hydrocarbons, and preferably containing only minor amounts of C5 .to C9 normal parafllns. The content of naphthenes is often small, since these compounds are usually present in only small quantities or in primary importance and the development. of fuels which will meet these severe requirements under all conditions is an essential military requirement.

It is also obvious that fuels which meet rigid military requirementswill be of great value in the development of commercial aviation. The pres:

ent invention, therefore, provides a novel fuelcomposition as well as mode of operating aviation engines requiring high octane fuels, particularly of 100 octane or higher. In the practice of this invention, as described herein, a gasoline essen-' tially comprising a mixture of. isoparafiin hydrocarbons having 5-9 carbonatoms permolecule,

containing TEL, usually at least about 3 inlrp'er gallon, together with aminor proportion of the aoeaeae I used by the art, and as referred to herein. describes the power output of aviation engines under rich mixture conditions, such, for example, as would be obtained by substantially increasing the fuel concentration in an air-fuel mixture at the intake of an aviation engine. This performance is usually defined in terms related to a standard 100 octane number reference fuel, the relative improvement being stated in ml. of tetraethyl lead.

Use of multiple engines in aircraft has often necessitated the overloading of a portion of the engines by reason of the fact that another portion of the engines may cease to operate during flight. At such times, it has been found to be very desirable to have a fuel which will give an increased power output over that normally-utilized under cruising conditions. Additional power output has also been found to be necessary for take off and high rate of climb of aircraft when operating at fuel-air ratios much higher than the lean mixture ratios ordinarily employed for cruising operation. By reason of the necessity for such increased power output, a new consideration for blending formulas has been introduced for the purpose of increasing the potential power output of finished fuels.

Isoparafllic fuel compositions generally are very satisfactory from the standpoint of most specifications when it is not necessary to utilize additional power over' that normally required under lean mixture ratios used under cruising conditions. Use of these iso'paraflinic fuels permits the production of larger volumes of finished fuel per volume of synthetic blending stocks than are possible with other blending formulas. It is thus ordinarily most advantageous to retain the iso paraflln blending formulas insofar as possible. This procedure requires that such special performance characteristics as lean and rich mixture ratings be obtained through the inclusion of minor proportions of substantially pure chemical additives. These additive compounds must be carefully-selectedso that the desired improvements are obtained with such small quantities that other fuel characteristics are not impaired and blend specifications are not infringed.

An object of this invention is to provide an improved fuel composition for use in aircraft engines whereby the effective operation and power output of the engines. are improved. Another object of the invention is to provide an improvement in the blending formula for preparing predominantly isoparafilnic aviation fuels whereby the potential power output thereof is greatly increased. Another object of the invention is to provide an isoparafllnic aviation fuel of at least 90 leaded aviation octane number rating containing a relatively minor proportion of an added compound providing greatly improved power output characteristics without undesirably aifecting the other characteristics of the fuel. Another object of the invention is to provide an isoparaffinic aviation fuel of about 100 aviation octane number rating or better containing a relatively minor proportion of an added compound providing greatly improved rich-mixture characteristics without undesirably affecting the other characteristics of the fuel. Another object of the invention is to provide a fuel having an improved performance value. Another object of'the invention is to provide an isoparafllnic aviation fuel having an improved lead response and enhanced blending value. Another object of the invention is to provide an improved method for operating aviation engines under conditions requiring increased power output by the addition to the isoparaflinic aviation fuel utilized therein of a minor proportion of a monomethyl or polymethyl substituted pyridine. Other and further objects will be apparent to those skilled in the art upon study of the accompanying disclosure.

4 We have now found that aviation fuels of the type described and comprising essentially parafat a \N/ are added, the a being'a radical selected from the group consisting of hydrogen and methyl radicals and at least one of the radicals being a methyl radical. The monomethylpyridines, better known as picolines, are very adaptable for use in such fuel. The methyl substituted pyridines described above are employed as substantially pure compounds or mixtures of these pure compounds since their efficiency is hi hly P cific and definitely superior to certain other nitrogen bases and the like which mightbe present in crude methylpyridine fractions. A further purpose served by the use of substantially pure compounds or mixtures thereof is the elimination of associated impurities which have deteriorative effects on the fuel and/or on aircraft fuel systems in which it is used.

The use of the above identified methyl substituted pyridines to improve fuel performance under all fuel-air ratios is wholly new and unexpected. While their presence in petroleum from certain fields has long been known, they have always been regarded as harmful to fuel performance. The complex and expensive operations to which petroleum is subjected in refining distillates have either deliberately or incidentally removed all traces of nitrogen bases from the resulting gasolines. Thus petroleum from certain California fields has been shown to contain small amounts of a wide variety of heterocyclic nitrogen bases including the above identified methyl substituted pyridines and a number of other pyridine derivatives. In cracked distillates from these California oils the pyridines are the only compounds which occur in appreciable amount and whose presence has been definitely established. Extraction and treating processes to which the cracked distillates are subjected remove these nitrogen compounds and they are not present in the finished products. The highly naphthenic gasolines produced from these petroleum stocks are in any event radically different from the synthetic isoparafllnic aviation fuels used in our process and the presence of mixed p p l 'i- Although the monomethylpyridines, i. e., pioolines, is the only methyl substituted pyridine group specifically named hereinbefore, it is obvious upon study of the structural formula 'of the methyl substituted pyridine that we include polymethyl substituted pyridines in the group of additives which can be employed in our fuel composition. Methylpyridines which are utilized in minor proportions in our specific aviation fuel compositions include those set forth below:

Monomethylpyridine (picolines) 2-methyl 3-methyl 4-methyl Dimethylpyridine 2,3-dimethyl 2,4-dimethyl 2,5-dimethyl 2,6-dimethyl 3,4-dimethyl 3,5-dimethyl Trimethylpyridine 2,3,4-trimethy1 2,3,5-trimethyl 2,3,6-trimethyl' 2,4,5-trimethyl 2,4,6-trimethyl 3,4,5-trimethyl Tetramethylpyridine 2,3,4,5-tetramethyl 2,3,5,6-tetramethyl 2,4,5,6-tetramethy1 Pentamethylpyridine:

2,3,4,5,6-pentamethyl It has been shown that some nitrogen compounds of the aromatic amine group, represented by aniline as the most common member, do have properties as antidetonants when added to aviation fuels. In this respect, however, they are analogous to the high octane number paraflins, or aromatic compounds such as benzene which have high value as blending agents. The improvement effected in fuel performance when minor amounts of aniline are added is similar to the effect of the addition of tetraethyl lead. That is to say, the octane number rating in the usual test method AN-VV-F-746 and ASTM Aviation method D-614-48T shows an improvement. But as has been clearly pointed out in the preceding paragraph this effect is not equivalent to the improvement in rich mixture performance as determined in the supercharged engine test (AN-VV-F-748a) and ASTM Supercharge method D-909-48T.

Mixtures of the methyl substituted pyridines are also utilized in many instances with very satisfactory results and are specifically included as a part of our specific aviation fuel composition. We have found that 2-methyl, 3-methy1, and 4 methylpyridines can be utilized in our process and that mixtures of these materials in varying proportions are also useful in our fuel. We have also found that the addition to the fuel of a mixture of trimethylpyridines result in considerable improvement of the performance number of the finished fuel over that of the base fuel. Impure preparations which contain other nitrogen bases, and other than nitrogen compounds, where such compounds are detrimental to the rating of the fuel, or the fuel injection system of the engine, or adversely affect the properties of the fuel, such as its volatility characteristics, are what is meant to be excluded by the expression substantially pure.

While specific embodiments of the present invention may be involved in a great varietyof blending operations involving isoparafiinic blending and base stocks, one satisfactory procedure is outlined in the following operations. A fuel is prepared according to a blendingformula from isooctane, isopentane, and a naphtha comprising Cs and C": isoparaflins in proportions which produce 100 octane number with 4 ml. of tetraethyl lead per gallon. This formula is altered according to the present invention to include at least one of the methyl substituted pyridines described above by use of a predetermined volume per cent of a methyl substituted pyridine-isopentane mixture having a vapor pressure substantially equal to that of the finished fuel (usually 7 pounds Reid vapor pressure) The volume of the mixture used replaces a corresponding volume of isoparaffin base stack and synthetic blending stock with the blending proportions of the latter ordinarily being readjusted to produce the same aviation octane number rating as before.

The methyl substituted pyridines may be added alone to fuel blends, but it is often more convenient to employ the isopentanized mixture. The advantages lie in the maximum utilization of isopentane and less difficulty in blending to meet vapor pressure specifications. The amount of methyl substituted pyridine thus included in the finished fuel is further limited by the relatively high boiling points (above 264 F.) which restricts the volume permissible in the fuel having a maximum of per cent evaporated temperature as determined by the ASTM distillation procedure, of 275 F.

The methyl substituted pyridines may be derived from any suitable source, providing a relatively pure product as explained above is obtained.

In many cases, it is difficult to separate the above described methyl substituted pyridines-from complex mixture of alkyl pyridines and other types of nitrogen bases, cresols, etc., such as may result from coal coking operations. For this reason, one preferred source of monomethylpyridines for the present invention is the synthetic proces by which acetaldehyde and ammonia are reacted to produce picolines as disclosed in copendin application, Serial No. 567,780, filed December 11, 1944, by one of us and issued as Patent 2,523,580. The p'icolines which ma be produced in high yields are substantially free of undesirable impurities and are readily separated from unreacted ammonia and aldehyde.

The amounts of the above described methyl substituted pyridines which are added to the fuel will obviously be dependent on the other fuel components and on the particular lean mixture and rich mixture octane ratings which are desired in the final blend. In most cases, the quantity of the methyl substituted pyridines will vary between about 1 and about 20 volume per cent of the blend with a somewhat narrower range of between 1 and 10 volume per cent preferred. The methyl substituted pyridines in substantially pure form are relatively expensive and hence are not ordinarily used to replace conventional blending ingredients.

The use of certain aromatic compounds, es pecially isopropylbenzene (cumene) and butylbenzene, to improve the rich-mixture performance of aviation fuels of the type described in this disclosure has been proposed. In copending applications Serial No. 436,714 and 436,715, filed March 28, 1942, issued as Patents 2,409,156 and 2,409,157, respectively, of which one of us is a co- 7 inventor. the use of 'cumene and of butylbenaene for this Purpose is described in detail. While these materials perform in a very satisfactory manner their use is limited by the available supply, and the discovery that a high degree of improved performance can be obtained by the use of methyl substituted pyridines constitutes a further advance in the art.

It is an advantage of the use of methyl substituted pyridines over these aromatic substances when used as components of aviation fuels that they result in much reduced swelling of and diffusion through rubber or rubber-like materials with which the fuel compositions are in contact. Such materials are customarily used as fuel tanks in military aviation, and the notoriously bad effect of aromatics thereon has been a serious detriment to the useof fuels containing them.

Test method AN-VV-F-746 as referred to herein is the method identified as Army-Navy Aeronautical Specification Fuel: Aircraft Engine- General Specification (Method for Knock-Test AN-WF-746), dated October 5, 1940. This method is utilized for determiningordinary aviation octane number ratings of aviation fuels. 'I'estmethod AN-VV-F-748a, as referred to herein is identified as Army-Navy Aeronautical Specification Fuel;- Aircraft Engine, General Specification (Method for Supercharged Knock- Test) AN-VV-F-748a dated June 17, 1942. The test method described therein is used for determining lean and rich mixture ratings of 100 octane number aviation fuels. In this latter specification (AN-VV-F-'748a) a lean mixture is shown to be about 0.06 pound of fuel per pound of air and a rich mixture at least about 0.09 pound of fuel per pound of air.

More recently, however, it has been shown that while this latter method (AN-VV-F-748a) can be used to give an excellent measure of the performance of fuels in rich mixtures, lean mixture ratings obtained in this supercharged engine test are erratic and unreliable. At the present time the aviation octane ratings obtained in the ordinary aircraft engine tests (AN-VV-F-746 and ASTM Aviation Method D-614-48T) which are carried out under lean mixture conditions, are considered a more reliable measure of lean mixture performance and the lean mixture ratings obtained in the supercharged test have fallen into disuse.

It has been found that it is generally not possible to add directly the rich mixture ratings of the components of an aviation fuel blend in their volumetric proportions and arrive at a correct value for the rating of the blend, or conversely,

8 These numbers are so assigned and tabulated that they may be used directly ith the volumetric percentage of the constituents to give the performance rating ofthe blend. Thus, a fuel of very poor performance, which is equivalent to a blend of 83.0 per cent fuel S in fuel M has a blending index number of 4. Pure isooctane has a blending index number-of 100, while a superior fuel whose performance is equal to that of isooctane with 6.0 cc. of lead added has a blendin index number of 162.

Products which are useful as rich mixture addi- I tives should have high blending index numbers, preferably above 150 when tested in unleaded fuels. It is also important, however, that the additive is not detrimental to the lead response of the fuel, and is particularly advantageous if the effect 'of lead on the additive is to increase its rich mixture blending index number, i. e., to make it more effective for the'purpose for which it is designed. I

' It isan advantage of the use of many of our methyl substituted pyridine additives that they display an excellent lead response. This advantage is particularly apparent inthe use. of our monomethylpyridine additives. Thus, when tested in an unleaded fuel, the rich mixture blending index numbers are usually found to be about 150 to 160, utilizing a base fuel having a lean mixture octane rating of 100, but when tested in the 'same fuel and at the same concentrations, blending index numbers of about 240 are obtained when 4.6 ml. tetraethyl lead per gallon is present.

This excellent response to the addition of tetra- EXAMPLE I A 100 aviation octane number aviation .fuel was prepared according to blending formula A, given below, plus 4.6 ml. tetraethyl lead per gallon. The alkylate used was a cut from the prodnot of a commercial hydrogen fluoride alkylation -unit in which isobutane is alkylated with from the rating of the blend to determine the value of the additive. where the components differ widely in their rating, and results in part from the conventions used in expressing rich ratings. While rich ratings superior to the performance of isooctane are This is particularly true given in terms of the value of tetraethyl lead that must be added to reference fuel S (essentially pure isooctane) to reproduce the same engine performance, rich ratings inferior to isooctane butylenes to produce a mixture comprising largely isooctanes. This formula was then modified to permit the inclusion of ten volume per cent of each of the following additives (l) 2-picoline, (2) 3-picoline, and 3) 4-picoline. These three modified blends, noted below as B, C, and ,D conformed to fuel specifications and rated approximately aviation octane number with 4.6 ml. of tetraethyl lead per gallon.

Isoparaifin components (parts by volume) I h Additive, Formula Alk-ylate 8 Isohexane l0 pagtls by A 21.3 41. 0 22.6 15. 1 None. 13.. 21. 8 41. 0 22. 6 15. 1 2-picoline. O 21.3 41. 0 22. 6 l5. 1 3-picoline. D 21. 3 41. 0 22. 6 l5. 1 d-picoline.

. gine test AN-VV-F-748a.

were read from the standard tables correspond ing to these ratings. and the blending index method AN-VV-F-748a in the two series of blends were tabulated below.

numbers calculated for the additive from the known composition of the fuel. Octane numbers were also converted to performance number so that the improvement in performance number The blending index numbers, which represent the performance of the additive in the fuel blend, show the very markedly greater effect of the additive in the presence of the tetraethyl lead.

resulting from the addition of the picolines could Thus. while the increase in'blending index numbe obtained. her is 51 to 63 numbers in the unleaded fuel E.

Antiknock'lleting cal c eg ted, Performance Formula AN VV F 748& m ggge Number AN-VV-F-746 Index No. Imprmmm Rating Index ofAdditive ml. TE No.

100 0.54 115.2 116.8 100 1. 11 12s. 4 241. 2 12s. 4 11.6 100 1.12 121.4 231. 2 120.1 12. a mo 1. 14 121. s 241.2 121. c 11.1

since the rich mixture ratings in mi. of TEL of fuels B, C, and D are approximately twice that of fuel A and performance number improvement is quite good. v

The three picolines, when rated in blends with reference fuel A without addition of lead by the ordinary engine test (AN-VV-F-746) gave blending octane numbers of 93.0, 89.0, and 91.0 for 2, 3, and 4-picoline, respectively. These ratings in themselves gave no indication of the unexpectedly good rich mixture performance of the picolines. Likewise ratings in motor fuel base blends by the usual motor fuel test method (AS'IM-D357-43T) gave octane numbers of only about 72 to 83 for these nitrogen compounds.

EXAMPLEII The rich-mixture ratings of 2-methyl-, 3-methyl-, and 4-methylpyridines were determined in blends in an isoparaffinic fuel without the addition of tetraethyl lead, by the supercharged en- The fuel used designated below as fuel E comprised essentially isooctane, and rated 100 aviation octane number in the conventional aviation engine test procedure (AlN-VV-F-746) without lead. Rich mixture blending index numbers were calculated for the three heterocyclic nitrogen compounds.

The blends were then duplicated in the isoparaflinic aviation fuel of Example I which rated 100 aviation octane number (by method AN-W- F-746) when 4.6 ml. TEL per gallon were added. Rich mixture blending index numbers were thus obtained in the presence of lead in a fuel of addition of the same quantities of picolines to the leaded blend A, which in itself had a higher number, produced an increase of 122 to 132 units. Stated in another way, the increasedeifect of the addition in the presence of lead may be seen in thev case of 2-picoline for instance by comparing the blending index number of 151 obtained for this addition in unleaded fuel with the value of 247.2 obtained in the leaded base.

i As illustrations of the improved performance characteristics obtained by the addition of polymethyl substituted pyridines which have at least two methyl radicals attached to the pyridine structure, the following example is set forth.

EXAMPLE III between 329 F. and 349 F. These fuels were tested by ASTM Aviation'Method D-614-48T and ASTM Supercharge Method D-909-48T to determine the aviation octane number and supercharge rich octane number ratings; respectively. These octane numbers were converted'to performance numbers and the improvement in performance number resulting from the specific ad ditive of each fuel was determined. These data are tabulated below in order to determine the relative performance of the above identified methyl substituted pyridines as a comparison with pyridine. Performance numbers and performance number improvements were determined for suchpyridine with other similar base stocks G and H. By converting the octane numbers to performance numbers and determining theperformance number improvement with each spesimilar type. Results of the ratings obtained by cific additive, a ready comparison is obtained between the effect of the unsubstituted pyridine as compared with the methyl substituted pyridine described above. Although-the perforance number improvement of the fuel containing 2,6-dimethylpyridine and the fuel containin pyridine 12 said methyl substituted pyridine is at least one tetramethylpyridine.

9. The fuel composition of claim 1 wherein said methyl substituted pyridine is pentamethylpyridine.

are about the same under supercharge conditions, 5 10. An aviation engine fuel having an imthe 2,6-dimethylpyridine containing fuel is much proved performance number when used in aviasuperior under aviation octane number condltion engines which consists essentially of isotions. These data are tabulated below. paraflinic hydrocarbons of 5 to 9 carbon atoms Aviation superman Performance gzgfi fg f}? 3%? Performance lsoparaf- 2,4-Di- 2,0-Di- Tri- E1- Nmber provement TEL in 101 Number provement iinic Base methyl methyl methyl 0 0.0 to 4.0 mLTEl'l 0.0 4.0 4.01111. TEL

Study of the data set forth in the above exper molecule having gasoline characteristics of amples will readily show that the improvement vapor pressure and distillation range, and from in performance number of the various fuels is 80 1 to per cent by volume of at least one subparticularly impressive by reason of the presstituted pyridine having the following structural ence of the methyl groups in the fuel additive. formula This improvement in the fuel by reason of the R presence of the methyl radical in the fuel additive is totally unexpected.

We claim: I 1. An improved fuel composition having gasoline characteristics which consists essentially of isoparafilnic hydrocarbons having between 5 and N a 9 carbon atom per molecule; and from 1 to wherein R is a: radical 581800611 from the group volume per cent of at least one substituted pyriconsisting of hydrogen and methyl radicals and dine having the structural formula at least two said radicals are methyl radicals, B said fuel having 2. Reid vapor pressure not a greater than about seven pounds, containing 46 tetraethyl lead, having a maximum 90 per cent 3-0 0-11 ASTM distillation procedure evaporated temperature of 275 F., and havin an octane rating of at least 90.

N 11. The fuel composition of claim 1 wherein wherein R is a radical selected from the group 50 said methyl substituted pyridine is 2,4-dimethconsisting of hydrogen and methyl radicals and ylpyridine. at least two of said radicals are methyl radicals. 12. The fuel composition of claim 1 wherein 2. The fuel composition of claim 1 wherein said methyl substituted pyridine is 2,6-dimethylsaid fuel composition has a maximum Reid vapor pyridine. pressure of seven pounds; and has a maximum 13. The fuel composition of claim 1 wherein 90 per cent ASTM distillation procedure evaposaid methyl substituted pyridine is 2,3,4,5-tetrarated temperature of 275 F. methylpyridine. 3. The fuel composition of claim 1 wherein the WALTER A. SCHULZE. methyl substituted pyridine content is between 1 JOHN E. MAHAN. and 10 volume per cent.

4. The fuel composition of claim 1 wherein the REFERENCES CITED methyl supstituted pyridine is at least one The following references are of record in the methylpyridine. I me or this patent.

5. The fuel composition of claim 4 wherein the trimethylpyridine is a mixture of trimethyl- UNITED STATES PATENTS pyridines. Number Name Date 6. The fuel composition of claim 5 wherein said 1,524,674 Sadtler Feb. 3, 1925 mixture of trimethylpyridines boils within the 2,401,983 Stanly et al. July 5, 1941 range of between 329 F. and 349 F. 2,406,667 Clarke Apr. 27, 1943 7. The fuel composition of claim 1 wherein said 7 2,407,716 Marschner Sept. 17, 1946 methyl substituted pyridine is at least one di- 2,407,717 Marschner Sept. 17, 1946 methylpyridine. 2,409,156 Schulze et a1. Oct. 8, 1946 8. The fuel composition of claim 1 wherein 2,409,157 Schulze Oct. 8, 1946

Claims (1)

1. AN IMPROVED FUEL COMPOSITION HAVING GASOLINE CHARACTERIZED WHICH CONSISTS ESSENTIALLY OF ISOPARAFFINIC HYDROCARBONS HAVING BETWEEN 5 AND 9 CARBON ATOMS PER MOLECULE; AND FROM 1 TO 20 VOLUME PER CENT OF AT LEAST ONE SUBSTITUTED PYRIDINE HAVING THE STRUCTURAL FORMULA