US3067019A - Thermally stable combustion gas turbine fuels - Google Patents

Description

3,07,19 Patented Dec. 4, ram

Delaware No Drawing. Filed June 6, 1960, Ser. No. 33,935 4 Claims. (Cl. 44-62) This invention relates to thermally stable aviation turbine fuels. More particularly, the invention relates to aviation turbine fuel compositions that contain small amounts of a combination of N,N'-di(ortho-hydroxyarylmethylidene)alkylenepolyamines and certain oilsoluble copolymers of higher alkyl esters of acrylic or methacrylic acid and salts of oil-soluble aliphatic monoamines and acrylic or methacrylic acid, and that have a reduced tendency to form solid deposits at very high service temperatures.

Aviation turbine fuel is presently employed as a cooling medium, or heat sink, in combustion gas turbine powered aircraft to remove heat from lubricating oil that has absorbed heat developed in the engine by the compression of combustion air, by fuel combustion, and by friction of moving parts. As a result the fuel is subjected to service temperatures of the order of 300 to 400 F. for relatively substantial time intervals. In addition, aviation turbine fuel is subjected to even higher temperatures, of the order of 500 F., for short periods of time in the area of the nozzles or orifices from which the fuel is introduced into the combustion chamber of the engine. As a result, certain components of the fuel tend to undergo decomposition due to polymerization, oxidation, and thermal decomposition, and to form solid or semi-solid degradation products that clog the fuel orifices and thereby interfere with proper combustion of the fuel. Ordinary stabilizing agents, antioxidants and the like, of the kind that are employed to stabilize the fuels during storage have been found inadequate to inhibit deterioration of the fuels at the high service temperatures encountered in aviation turbine engines.

The use of copolymers of higher alkyl esters of acrylic or methacrylic acid and salts of oil-soluble monoamines and acrylic or methacrylic acid has been proposed to improve the thermal stability of aviation turbine fuels. Although these materials are excellent inhibitors of deposits in the fuel nozzle and combustion zone inlet area, when used alone they are not entirely satisfactory as thermal stabilizers in aviation turbine fuels of poor thermal stability, because they do not inhibit deposits due to thermal degradation in the fuel line or heatexchange section of the fuel supply system.

it has now been found that the tendency of aviation turbine fuels to form deposits in the fuel inlet area of the combustion zone and in the heat-exchange section of the fuel upply system of an aviation turbine engine can be substantially reduced by incorporation in the fuel of a small amount of a combination of (A) an N,N- di(ortho hydroxyarylmethylidene) alkylenepolyamine that contains 2 to 3 amino groups and Whose alkylene groups contain 2 to 6 carbon atoms each, and (B) an oil-soluble copolymer of (i) a monomeric alkyl ester of an acid selected from the group consisting of acrylic and methacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric salt of substantially equivalent proportions of an acid selected from the aforesaid group and an amine having as at least one N-substituent a monovalent aliphatic hydrocarbon radical containing 8 to 18 carbon atoms, and

as the other N-substituents members selected from the group consisting of hydrogen, aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms and alkylol groups containing 1 to 4 carbon atoms, said monomeric amine salt and said monomeric alkyl ester being copolymerized in a weight ratio in the range of about 0.03:1 to 1:1, preferably 0.05:1 to 0.75:1. Polymers prepared from the above-indicated ratios of monomers will usually be characterized by a nitrogen content in the range of about 0.03 to 3.5 percent by weight. We normally prefer to employ copolymers containing at least about 0.2 percent and preferably about 0.2 to 2 percent nitrogen, but copolymers having greater and lesser nitrogen content can be used. Specific examples of copolymers with which excellent results can be obtained are the 1:9 weight ratio copolymer of monomeric oxo-octylammonium methacrylate and lauryl methacrylate, the 1:9 weight ratio copolymers of monomeric di(oxo-octyl)ammonium methacrylate and monomeric lauryl methacrylate, the 3:7 weight ratio copolymer of monomeric di(oxo-octyl)ammonium methacrylate and monomeric lauryl methacrylate and the 1:9 weight ratio copolymer of monomeric di(oxo-octyl)hydroxyethylammonium methacrylate and monomeric lauryl methacrylate. Examples of other copolymers whose use is included by the invention are the 1:19 weight ratio copolymer of monomeric di(oxo-octyl)hydroxyethylammonium methacrylate and monomeric lauryl methacrylate and the 2:8 weight ratio copolymer of monomeric di(oxo-octyl)hydroxyethyl-ammonium methacrylate and monomeric lauryl methacrylate. Examples of still other copolymers the use of which is included by this invention are the 0.05:1, 01:1, 05:1, and 1:1 weight ratio copolymers of monomeric octylammonium, dioctylammonium, trioctylammonium, laurylammonium, octadecylammonium, octadecenylammonium acrylates and methacrylate and monomeric n-octyl, lauryl, oxo-octyl, 2-ethylhexyl, oxo-tridecyl and n-hexadecyl acrylates and methacrylates. Insofar as the ortho-hydroxyarylmethylidene-substituted alkylene-polyamine component of the combination is concerned, we prefer to employ those members whose ortho-hydroxyaryl substituents are either unsubstituted or substituted only with hydrocarbon substituents, but ortho-hydroxyarylmethylidene-substituted alkylenepolyamines that are substituted with other groups such as alkoxy, halo, cyano and carboxy can be used. An example of a particularly outstanding ortho-hydroxyarylmethylidene-substituted alkylenepolyamine for the purposes of this invention is N,N'-disalicylidene-1,2- propylenediamine. Examples of other N,N-di(orthohydroxyarylmethylidene) alkylenepolyamines are N,N'- di(2 hydroxy 6 methylbenzylidene) 2,3 butylenediamine, N,N' di(ortho hydroxynaphthylidene) 1,3- propylenediamine, N,N di(2 hydroxy 3 methoxy benzylidene) 3,4 diaminohexane, N,N di(2 hydroxy 5 chlorobenzylidene) 1,2 propylenediamine, N,N' di(2 hydroxy 3 cyanobenzylidene)ethylenediamine, N,N di(2 hydroxy 3 carboxybenzylidene)- ethylenediamine and N,N' disalicylidenediethylenetriamine. The N,N' di(o'rtho hydroxyarylmethylidene)- alkylenepolyarnines and the copolymers disclosed herein can be employed in varying proportions with respect to one another. It is generally preferred to add them to aviation turbine fuels in about equal proportions by weight, but other proportions can be used provided the compound present in the smaller amount is present in an amount corresponding to at least about 2.5 pounds per thousand barrels of fuel. In general, it is preferred to employ the respective compounds in Weight ratio in the range of about 1:4 to 4:1, but other Weight ratios, for example 1:10 to 10:1, can be used.

The exact mechanism by which the compounds disclosed herein function to improve the thermal stability of aviation turbine fuels has not been definitely established. Nevertheless, available experimental data clearly indicate that the respective classes of compounds dis closed herein coact with one another, as it has been found that deposits in both the heat exchange section of the fuel supply line and the fuel inlet orifices of the combustion chambers of aviation turbine engines are not inhibited by combinations of N,N-di(ortho-hydroxyarylmethylidene) alkylenepolyamines and other materials that alone are capable of inhibiting deposits in the fuel inlet orifices of the combustion chambers of aviation turbine engines.

The preparation of the copolymers and the N,N'- di(ortho-hydroxyarylmethylidene) alkylenepolyamines disclosed herein forms no part of this invention. Thus, the N ,N di(ortho hydroxyarylmethylidene)alkylenepolyamines can be prepared conveniently in known fashion by condensation of an aromatic aldehyde with an alkylenepolyamine in molar proportions of 2:1, respectively. By the same token, the copolymers disclosed herein can be prepared in any convenient way. For example, they can be prepared by reacting the desired monomers in weight ratios of about 0.03 to 1 part by weight of the substantially neutral ammonium acrylate or methacrylate, that is, the salt formed by reaction of substantially equimolar proportions of amine and acrylic or methacrylic acid, for each part by weight of the ester monomer, in the presence of a diluent, preferably a solvent, such as toluene, benzene, ethyl acetate or other solvents having similar chain transfer activity, at a temperature in the range of 75 C. to 150 0, preferably 25 C. to 150 C., in the presence of a few hundredths percent to 2 percent, preferably 0.2 to 1.0 percent, of a free radical catalyst such as benzoyl peroxide, lauroyl peroxide, or alpha, alpha-azodiisobutyronitrile, preferably in the substantial absence of oxygen, until the rate of formation of larger polymer molecules has declined substantially, usually after about 3 to 35 hours or longer, as determined by periodic sampling of the reaction mixture and observing the viscosity thereof.

The preferred ester monomers from which the copolyrners disclosed herein are prepared can be represented by the general formula: CH2=CRCOOR where R is hydrogen or a methyl radical and R is a straight or branched chain alkyl group containing 12 to 18 car- .bon atoms, such as lauryl, oxo-tridecyl, n-hexadecyl, or

n-octadecy'l.

The preferred ammonium salt monomers from which the herein-described copolymers' are prepared can be represented by the general formula:

RI CH2=CRCOOH.NR

where R is as defined above,

RI 7 NR/I is a secondary or tertiary amine, R is an alkyl, alkenyl, or alkadienyl radical containing 8 to 18 carbon atoms, such as lauryl, myristyl, n-hexadecyl, n-octadecyl, noctade-cenyl, or n-octadecadienyl, R" is a member selected from the group consisting of aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms such as methyl, propyl, butyl, or any of those mentioned in the description of R, and preferably alkylol groups containing 1 to 4 carbon atoms, such as ethylol or propylol, and the R" is either hydrogen or a member such as R".

Neither the alkyl ester substituents of the ester monomers nor the N-substituents of the ammonium salt monomers need be pure; instead these substituents can comprise mixtures of radicals derived from commercially available materials. Forexample, the alkyl ester su-bstituents of the ester monomers can be derived from a mixture of synthetically produced, isomeric, branchedchain alcohols of the kind produced by the well-known oxo-synthesis process. Alternatively, the ester substituents can be derived from a mixture of fatty alcohols obtained from coconut oil fatty acids or tallow fatty acids or other acids derived from naturally occurring fats or oils. Similarly, the N-substituents of the nitrogenous monomer can comprise a mixture of alkyl, alkenyl, and/or alkadienyl groups derived from commercial materials such as coconut oil fatty acids, soya fatty acids, or tallow fatty acids. When the substituents referred to above are derived from natural fats and oils, the mixed radicals will comprise homologous mixtures of alkyl or alkyl and alkenyl, or alkyl, alkenyl, and alkadienyl radicals containing an even number of carbon atoms from 8 to 18. The ester substituents of the ester monomer and the N-substituents of the ammonium salt monomer can also be substituted, if desired, with nonhydrocarbon substituents, such as halogens, hydroxyl, sulfhydryl, carbonyl, amino, or the like that do not adversely affect the oil solubility or deposit-inhibiting characteristics of the salts.

The preferred copolymers of this invention are copolymers of the above-indicated preferred monomers in weight ratios in the range of about 0.05 to 0.75 part by weight of ammonium salt monomer to 1 part by weight ester monomer.

The average molecular weight of the copolymers disclosed herein will normally be greater than about 2,000, and is preferably greater than about 7,500, as determined by conventional methods. Usually the molecular weights of the copolymer will not exceed about 500,000, but the molecular weights can be greater. In fact, copolymers having molecular weights of any upper limit can be used, provided that the molecular weight is not so great as to render the copolymers insoluble in the liquid hydrocarbon fuel distillates.

The copolymers and the N,N-di(ortho-hydroxyaryl methylidene)alltylenepolyamines disclosed herein can be incorporated in aviation turbine fuels in any suitable manner. For example, they can be added singly or in combination, either as such, or in' diluted form to the aviation turbine fuels either promptly after distillation of the latter or after storage of the fuels. Alternatively, the addition agents disclosed herein can be added to aviation turbine fuels in admixture with other addition agents adapted to improve one or more characteristics of the fuels. For example, the addition agents disclosed herein can be added to the fuels in admixture with corrosion inhibitors, such as amine salts of organic orthophos phates, antioxidants such as 2,6-ditertiary-butyl-4-methylphenol, or 2,4-dimethyl-6-tertiary-butylphenol.

The addition agents disclosed herein can be employed in aviation turbine fuels in any proportions sufiicient to improve the thermal stability of the fuels. Normally a noticeable improvement in thermal stability will be obtained by the use of as little as 2.5 pounds of copolymer per thousand barrels of aviation turbine fuel and as little as 2.5 pounds of N,N-di(orthohydroxyarylmethylidene)- alkylenepolyamines per thousand barrels of the fuel, but it is usually desirable to employ at least 5 pounds per thousand barrels of fuel of the respective additives in order to obtain a substantial improvement in thermal stability. A major improvement will ordinarily be obtained by the use of proportions in the range of about 10 .to 20 pounds per thousand barrels of the respective addition agents and accordingly such proportions are preferred. Normally it is not necessary to exceed 20 pounds per thousand barrels. of fuel but in instances of aviation turbin'e'fuels having very poor thermal stability characteristics, or in instances'of relatively less effective members of the respective classes of addition agents disclosed herein, the agents can be employed in proportions of as much as 250 pounds or 'more per thousand barrels of fuel.

Inspections:

Gravity, API 32.5-57. Existent gum, mg./100 mi.

(max) 5-7. P otential gum, mg./100 ml.

(max) 4-14. Sulfur, percent (max) 0.050.4. M e r c a p t a n sulfur, percent (max.) 0.0010.005. Freezing point, F. (max) 75 to 40.

Thermal value, B.t.u./lb. (min) Aniline-gravity constant n- 18,30018,500. 4,500, usually 5,250. Aromatics, vol. percent (max.) 525. Olefins, vol. percent (max) 1-5.

The ability of the combinations of the copolymers and ortho-hydroxyarylmethylidene-substituted alkylenepolyamines disclosed herein to reduce formation of solid deposits in aviation turbine fuels at high service temperatures has been demonstrated by subjecting fuel compositions of the kind disclosed herein to the CFR Fuel Coker test procedure. This test procedure is described in detail in the Manual of ASTM Standards on Petroleurn Products and Lubricants for 1959, ASTM D1660 591. In accordance with this test method, aviation turbine fuels are subjected to fiow conditions and temperature stresses similar to those in jet aircraft engines. schematically, the test apparatus comprises a fuel system containing two heated sections: (1) a preheater section that simulates the hot fuel line sections of a jet engine as typified by an engine fuel-lubricating oil cooler and (2) a filter section which simulates the nozzle, or fuel inlet, area of the combustion zone of a jet engine where fuel degradation particles may be trapped. A precision sintered stainless steel filter is employed in the filter section to trap fuel degradation particles formed during the test. The extent of the build-up of fuel degradation particles in the filter section is indicated by the pressure diiterential across the test filter and is used as an index of the high temperature stability of the aviation turbine fuel. The extent of deposit formation in the preheater section is determined by inspection and is used as an index of the high temperature stability of the aviation turbine fuel in the hot fuel line section, or heat exchange section, of an aviation turbine engine. Preheater deposits are rated according to the following scale: 0=no visible deposits; 1=visible haze or dulling, but no visible color; 2=barely visible discoloration; 3=light tan to peacock stain; 4=heavier than 3. In carrying out the test, the temperature of the fuel at the outlet of the preheater section is maintained at 400 F. and the filter section temperature is maintained at 500 F. During the test, fuel is caused to flow through the test apparatus at the rate of six pounds per hour and the test duration is five hours.

The ortho-hydroxyarylmethylidens-substituted alkylenepolyamine employed in the tests was N,N'-disalicylidene- 1,2-propylenediarnine. The copolymer employed in the tests was a 1:9 weight ratio copolymer of di(oxo-octyl) ammonium methacrylate and lauryl methacrylate. The copolymer was prepared by adding 10.32 parts by weight glacial methacrylic acid to 30.0 parts by weight of di(oxooctyl)amine in 208.8 parts by Weight of toluene, with stirring. To the resulting clear solution was added, with stirring, 360.0 parts by weight of lauryl methacry-late and 2.0 parts by weight alpha,alpha-azodiisobutyronitrile. The reaction mixture was stirred and heated. A color change was observed to begin at about 68 C. The yellow color of the reaction mixture changed gradually to pink at about C. and then rapidly reverted to yellow, With evolution of heat. .The temperature was allowed to rise to a maximum of 120 C. before cooling was begun. Stirring with heating to maintain the reaction temperature at 65 to 76 C. was continued for about 4% hours. Solvent was removed at reduced pressure with heating, to produce the above-indicated copolymer having a nitrogen content of 0.51 percent by Weight, a total acid number of 17.23, a total base number of 11.80, a saponification number of 13.53, an intrinsic viscosity at 77 F. in toluene of 0.12 deciliter per gram and a molecular weight of 130,000 as determined by the shear method of F. Bueche and S. W. Harding, Journal of Polymer Science, vol. XXXII, pages 177-186 (1958), with application of an appropriate instrument calibration constant. The di(oxooctyl)amine employed in this example was prepared from oxo-octyl alcohol, a typical sample of which contained about 38 percent 4,5-dirnethylhexy-l alcohol, 30 percent 3,5-dimethylhexy1 alcohol, 10 percent S-methylheptyl alcohol, 19 percent 3,4-dimethylhexyl alcohol, and 3 percent 5,S-dimethylhexyl alcohol.

In the particular tests reported below, the test fuel, hereinafter referred to as Aviation Turbine Fuel A, was a blend of straight run distillates having the following characteristics:

Gravity, API 43.3 Freezing point, F. 6O Sulfur, L, percent 0.058

Mercaptan sulfur, percent 0.001

Existent gum, mg./ 100 ml. Potential gum, rug/100 ml. 1.6 Aromatics, vol. percent 16-2 Olefins, vol. percent 1.5 Thermal value, B.t.u./lb. 18,576 Aniline gravity constant 6,343 Distillation Over point, F. 335 End point, F. 532 10% evap. at, F. 368 50% 418 486 518 Table I II III IV Make-Up, Percent by Vol.2

Aviation Turbine Fuel A 100 100 100 Stabilizer Added, Lb./1,000 Bbls. 1:9 Wt. Ratio Copolymer of Diisooctylammontum Methaerylate and Lauryl Metbacrylate 20 20 N N Disahoylidene 1,2

lropylene-diamine 20 20 Inspections:

Thermal Stability, CFR Fuel Ooker- Time to Reach a Pressure Drop of 10 In. Hg, Minutes 127 300 10 300 Time to Reach a Pressure Drop 0125 In. Hg, Minutes 163 300 15 300 AP at 300 Minutes, In. Hg 25. 0 3. 10 25 2. 40 Maximum Preheater Deposit Rating 3 4 0 0 Average Prehcater Deposit Rating 0.9 1. 5 0.0 0.0

From the results set forth in the preceding table, it is apparent that neither the copolymers nor the N,N'-di (ortho hydroxyarylmethylidcne) alkylenepolyarnines of the classes disclosed herein are capable of inhibiting deposit formation in both the hot fuel line section and the fuel nozzles of an aviation turbine engine. In fact, as shown by the foregoing data, although the copolymers are excellent inhibitors of filter deposits (fuel nozzle deposits), they tend to promote preheater deposits (hot fuel line deposits). Similarly, although the N,N-di(ortho-hydroxyarylmethylidene)alkylenepolyamines are excellent inhibitors of preheater deposits, they tend to promote filter deposits. As also shown by the foregoing data, when a combination of the materials is employed, each material modifies the undesirable characteristics of the other without diminishment of its Own desirable characteristics.

It will be understood that the invention is not limited to the particular copolymer and N,N'-di(ortho-hydroxyarylmethylidene) alkylenepolyamine set forth in the specific preceding embodiment, and that other materials disclosed herein can also be employed with good results. For example, there can be substituted for the copolymer in the foregoing specific embodiment, in proportions of, for example, 10 or 20 pounds per thousand barrels of fuel, the 0.05:1, 0.1:1, 0.521, and 1:1 weight ratio copolymers of monomeric octyl-ammoni.um, dioctylarnmonitun, trioctyl-amrnoni-um, lauryl-ammonium, octadecylammonium, octadecenylammonium acrylates and methacrylates and monomeric n-octyl, lauryl, oxo-octyl, Z-ethylhexyl, oxo-tridecyl and n-hexadecyl acr'ylates and methacrylatesi Similarly for the N,N-di(ortho-hydroxyarylmethylidene)alkylenepolyamine of the foregoing specific embodiment, there can be substituted in proportions of 10 or 20 pounds per thousand barrels of fuel any of N,N-di(2-hydroxy-6-methylbenzylidene)-2,3-butylenediamine, N,N'-di(ortho-hydroxynaphthylidene) 1,3-propylenediamine, N,N di(2-hydroxy 3 methoxybenzylidene) )-3,4-diaminohexane, N,N'-di(2-hydroxy-5-ch-lorobenzylidene) -1,2 propylenediamine, N,N-di(2-hydroxy- 3-cyanobenzylidene)ethylenediamine, N,N-di(2-hydroxy- 3-carboxybenzylidene)ethylenediamine, and N,N-disalicylidenediet-hylenetriamine.

The aviation turbine fuel compositions of this invention can contain various other addition agents adapted to improve one or more properties of the fuel. For example, the fuel compositions of this invention can contain in addition to the addition agents disclosed herein, corrosion inhibitors, freezing point depressants, antioxidants, metal deactivators and the like.

Many modifications and variations of the invention as herein described will suggest themselves to those skilled in the art, and resort may be had to such modifications and variations without departing from the spirit and scope of the invention. Accordingly, only such limitations should be imposed as are indicated in the claims appended hereto.

We claim:

'1. A combustion gas turbine fuel composition comprising a major amount of a normally thermally unstable,

polymer of (i) a monomeric alkyl ester of an acid selected from the group consisting of acrylic and methacrylic acids Whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric salt formed from substantially equivalent proportions of an acid selected from the aforesaid group and an amine having as at least one N-substituent an aliphatic hydrocarbon radical containing 8 to 18 carbon atoms, and as the other N-substituents members selected from the group consisting of hydrogen, aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms and alkylol groups containing 1 to 4 carbon atoms; said monomeric amine salt and said monomeric alkyl ester being copolyrnerized in a weight ratio in the range of about 003:1 to 1:1, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

2. The fuel composition of claim 1 wheresaid small amount comprises about 2.5 to 250 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight gatlig with respect to each other of about 10:1 to about 3. The fuel composition of claim 1 Where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 4:1 to 1:4.

4. A combustion gas turbine fuel composition comprising a major amount of a normally thermally unstable, liquid hydrocarbon aviation turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of N,N-disalicylidene-1,2-propylenediamine, and an approximately 1:9 weight ratio copolyrner of di(oxo-octyl)ammoniurn methacrylate and lauryl methacrylate, said small amount comprisingS to 20 pounds of each member of said combination per thousand barrels of fuel.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,06%,019 December 4 1962 I Arthur Va Churchill et all It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 61 f read RI, 0

Signed and sealed this 11th day of June 19630 SEAL) Attestz' DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nm 3,06%019 December 4 1962 Arthur V. Churchill et al.

It is hereby certified that error appears in the above numbered patent req'liring correction and that the said Letters Patent should read as corrected below.

Column 3, line 61, for "R" read R Signed and sealed this 11th day of June 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

Claims (1)

1. A COMBUSTION GAS TURBINE FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A NORMALLY THERMALLY UNSTABLE, LIQUID HYDROCARBON AVIATION TURBINE FUEL AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE THERMAL STABILITY OF SAID FUEL OF A COMBINATION OF (A) AN N,N''-DI(ORTHOHYDROXYARYLMETHYLIDENE) ALKYLENEPOLYAMINE CONTAINING 2 TO 3 AMINO NITROGEN ATOMS AND WHOSE ALKYLENE GROUPS CONTAIN 2 TO 6 CARBON ATOMS EACH, AND (B) AN OIL-SOLUBLE COPOLYMER OF (I) A MONOMERIC ALKYL ESTER OF AN ACID SELECTED FROM THE GROUP CONSISTING OF ACRYLIC AND METHACRYLIC ACIDS WHOSE ALKYL ESTER SUBSTITUENT CONTAINS 8 TO 18 CARBON ATOMS, AND (II) A MONOMERIC SALT FORMED FROM SUBSTANTIALLY EQUIVALENT PROPORTIONS OF AN ACID SELECTED FROM THE AFORESAID GROUP AND AN AMINE HAVING AS AT LEAST ONE N-SUBSTITUENT AN ALIPHATIC HYDROCARBON RADICAL CONTAINING 8 TO 18 CARBON ATOMS, AND AS THE OTHER N-SUBSTITUENTS MEMBERS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALIPHATIC HYDROCARBON RADICALS CONTAINING 1 TO 18 CARBON ATOMS AND ALKYLOL GROUPS CONTAINING 1 TO 4 CARBON ATOMS; SAID MONOMERIC AMINE SALT AND SAID MONOMERIC ALKYL ESTER BEING COPOLYMERIZED IN A WEIGHT RATIO IN THE RANGE OF ABOUT 0.03:1 TO 1:1, SAID SMALL AMOUNT COMPRISING AT LEAST ABOUT 2.5 POUNDS OF EACH MEMBER OF SAID COMBINATION PER THOUSAND BARRELS OF FUEL.