MXPA98000443A - Additives and compositions of combusti oil - Google Patents

Abstract

The present invention relates to fuel oil compositions containing specific mixtures of unsaturated monocarboxylic acids, show improved lubricity properties

Description

ADDITIVES AND COMPOSITIONS OF COMBUSTIBLE OIL This invention relates to additives to improve the lubricity of fuel oils, such as diesel fuel oil. The diesel fuel oil compositions, which include the additives, exhibit better lubricity and reduced engine wear. Concern for the environment has resulted in movements to significantly reduce the harmful components of emissions when burning fuel oils, particularly in engines such as diesel engines. Attempts have been made, for example, to minimize sulfur dioxide emissions. As a consequence, attempts are being made to minimize the sulfur content of the fuel oils. For example, although the fuel oil diesel typical in the past containing l weight percent or more of sulfur (expressed as elemental sulfur) it is now considered advisable to reduce the level, preferably to 0.05 weight percent, and conveniently to less than 0.01 weight percent, particularly less than 0.001 weight percent. The additional refining of fuel oils, necessary to achieve these low sulfur levels, often results in reductions in the level of polar components. In addition, refinery processes can reduce the level of polynuclear aromatic compounds present in these fuel oils. Reducing the level of one or more of the sulfur, polynuclear aromatic, or polar components of the diesel fuel oil can reduce the oil's ability to lubricate the engine's injection system, so that, for example, the pump Fuel injection of the engine fails relatively early in the life of an engine. Failure can occur in fuel injection systems, such as high-pressure rotary dispensers, in-line pumps, and injectors. The problem of poor lubricity in diesel fuel oils is likely to be exacerbated by future engine developments that aim to further reduce emissions, which will have more lubricity requirements than current engines. For example, it is anticipated that the advent of the high pressure unit injectors will increase the lubricity requirement of the fuel oil. In a similar way, poor lubricity can lead to wear problems in other mechanical devices which, for lubrication, depend on the natural lubricity of the fuel oil. Lubricity additives for fuel oils have been described in the art. International Publication Number WO 94/17160 describes an additive comprising an ester of a carboxylic acid and an alcohol, wherein the acid has from 2 to 50 carbon atoms, and the alcohol has one or more carbon atoms. The glycerol monooleate is specifically disclosed as an example. Although mixtures are contemplated in general, specific mixtures of esters are not disclosed. Patent United States Number US-A-3 273 981 discloses a lubricity additive being a mixture of A + B wherein A is a polybasic acid, or an ester of polybasic acid made by the reaction of the acid with monohydric alcohols of 1 to 5 carbon atoms; while B is a partial ester of a polyhydric alcohol and a fatty acid, for example glyceryl monooleate, sorbitan monooleate, or pentaerythritol monooleate. The mixture finds application in jet fuels. However, in certain circumstances, it has been unexpectedly discovered that these prior art esters promote blockage of fuel filters, particularly fine mesh filters typically present in diesel vehicle fuel lines. This problem of blocking the filter can result in insufficient fuel flow, a damaged engine operation, and it can be noticed especially at low temperatures. In addition, it was unexpectedly discovered that fuels containing the preferred ester (Additive D) described in International Publication Number WO 94/17160, show a loss of lubricity perance following a period of cold storage and filtration. The loss of perance can be noticed even in the absence of severe filter blocking problems. This loss in perance itself represents a significant problem, because, under field conditions, a stored fuel oil typically undergoes temperature cycling, and must still be capable of imparting effective lubrication to the mechanical devices downstream of the fuel line filters. In a diesel vehicle fuel system, example, diesel fuel must first flow through a fine-grained filter be reaching the fuel injection system, including the injection pump. The lower perance of lubricity after this filtration point, there, exposes the injection system to greater wear. There, there is a need better lubricity additives, which demonstrate a better possibility of filtration, and which, in fuel oils, do not show a loss in perance after filtration, followed by periods of storage at a cold temperature. .

These problems are. they have now surprisingly solved by additives comprising specific mixtures of certain esters. British Patent Number GB-A-1, 505, 302 describes combinations of esters, including, for example, glycerol monoesters and glycerol diesters as diesel fuel additives, it being described that the combinations lead to advantages, including less wear and tear of the equipment. fuel injection, piston rings, and cylinder linings. British Patent Number GB-A-1, 505, 302, however, is concerned with overcoming the operational disadvantages of corrosion and wear by the acid combustion products, the residues of the combustion chamber and of the exhaust system. The document reports that these drawbacks are due to incomplete combustion under certain operating conditions. Typical diesel fuels available at the date of the document contained, for example, 0.5 to 1 weight percent sulfur, as elemental sulfur, based on the weight of the fuel. U.S. Patent No. US-A-3, 287, 273 discloses lubricity additives which are reaction products of a dicarboxylic acid and an oil-insoluble glycol. The acid is typically predominantly a dimer of unsaturated fatty acids such as linoleic or oleic acid, although there may also be minor proportions of monomeric acid present. Only the alkane diols or the oxa-alkane diols are specifically suggested as the glycol reactant. Accordingly, in a first aspect, the invention provides a fuel oil composition comprising a higher proportion of a middle distillate fuel oil having a sulfur content of 0.2 weight percent or less, and a smaller proportion of an additive. of lubricity comprising: (a) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol, and (b) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol having at least three hydroxy groups, the esters being (a) and (b) different. In a second aspect, the invention provides the use of the additive defined in the first aspect, to improve the lubricity of a medium distillate fuel oil. In a third aspect, the invention provides the use of the fuel composition of the first aspect, in a combustion apparatus for reducing the rate of wear in the fuel supply system of the apparatus. Another embodiment of this invention is a method for reducing the wear rate in the fuel supply system of a combustion apparatus employing an average distillate fuel oil having a sulfur content of 0.2 weight percent or less, which comprises adding to this fuel, in an amount effective to reduce the wear index, a minor proportion of a lubricity additive comprising a mixture of two different esters prepared respectively from an unsaturated monocarboxylic acid and a polyhydric alcohol, and an acid unsaturated monocarboxylic acid and a polyhydric alcohol having at least three hydroxy groups. The mixture of esters (a) and (b) can provide unexpectedly improved lubricity performance, when compared to the individual performance of component (a) or (b). In addition, the mixture of (a) and (b) shows a better filtration possibility, and maintains good lubricity performance after cold storage followed by filtration. The invention will now be described in greater detail. The composition of Combustible Oil (first aspect of the invention). (i) The Additive The term "polyhydric alcohol" is used to describe a compound having more than one hydroxy group. It is preferred that (a) is the ester of a polyhydric alcohol having at least three hydroxy groups.

Examples of polyhydric alcohols that have at least three hydroxy groups, are those having from 3 to 10, preferably from 3 to 6, more preferably from 3 to 4 hydroxy groups, and having from 2 to 90, preferably from 2 to 30, more preferably from 2 to 12, and very preferably from 3 to 4 carbon atoms in the molecule. These alcohols may be aliphatic, saturated or unsaturated, and straight or branched chain, or cyclic derivatives thereof. Straight aliphatic straight chain alcohols are preferred. Conveniently, both (a) and (b) are trihydric alcohol esters, especially glycerol or trimethylolpropane. Other suitable polyhydric alcohols include pentaerythritol, sorbitol, mannitol, inositol, glucose, and fructose. The unsaturated monocarboxylic acids from which the esters are derived may have an alkenyl, cycloalkenyl, or aromatic hydrocarbyl group attached to the carboxylic acid group. The term "hydrocarbyl" means a group containing carbon and hydrogen, which may be straight or branched chain, and which is attached to the carboxylic acid group by a carbon-carbon bond. The hydrocarbyl group may be interrupted by one or more heteroatoms, such as 0, S, N, or P. It is preferred that (a) and (b) are both esters of alkenyl monocarboxylic acids, the alkenyl groups preferably having from 10 to 36 , for example from 10 to 22, more preferably from 18 to 22, and especially from 18 to 20 carbon atoms. The alkenyl group may be mono- or poly-unsaturated. It is preferred in a particular manner that (a) is an ester of a monounsaturated alkenyl monocarboxylic acid, and that (b) is an ester of a polyunsaturated alkenyl monocarboxylic acid. The polyunsaturated acid is preferably di- or tri-unsaturated. These acids can be derived from natural materials, for example plant or animal extracts. Especially preferred monounsaturated acids are oleic and elaidic acid. Particularly preferred polyunsaturated acids are linoleic and linolenic acid. It has been found that mixtures in which (a) is an ester of a monounsaturated acid, and (b) is an ester of a polyunsaturated acid, have an especially good lubricity performance, and exhibit a possibility of filtration and storage resistance in cold particularly good. The esters may be partial or complete esters, that is, some or all of the hydroxy groups of each polyhydric alcohol may be esterified. It is preferred that at least one of (a) or (b) is a partial ester, particularly a monoester. A particularly good performance is obtained where (a) and (b) are both partial esters, and particularly where both are monoesters. The esters can be prepared by methods well known in the art, for example by condensation reactions. If desired, the alcohols can be reacted with acid derivatives, such as anhydrides or acyl chlorides, in order to facilitate the reaction and improve yields. The esters (a) and (b) can be prepared separately, and then they can be mixed with each other, the mixture being presented either before the addition to the fuel, or as a result of the separate addition of (a) and (b) ) to the fuel at the same time or at different times. Alternatively, the mixture of esters can be prepared directly from a mixture of appropriate starting materials. It was discovered that the latter products (ie, mixtures of esters formed directly from the reaction of a mixture of starting materials) have a particularly good filtration possibility, and show a particularly good lubricity performance. In particular, commercially available mixtures of suitable acids can be reacted with a selected alcohol such as glycerol, to form a mixed ester product in accordance with this invention. Particularly preferred commercial acid mixtures are those comprising oleic and linoleic acids. In these mixtures, there may be a smaller proportion of other acids, or acid polymerization products, present, but this preference ratio should not exceed 15 percent, more preferably should not be more than 10 percent, and most preferably should not be greater than 5 percent by weight of the total acid mixture. In a similar manner, mixtures of esters can be prepared by the reaction of a single acid with a mixture of alcohols. A highly preferred ester mixture is that obtained by the reaction of a mixture of oleic and linoleic acids with glycerol, the mixture predominantly comprising: (a) glycerol monooleate, and (b) glycerol monolinoleate, preferably in proportions by weight about the same In addition to the esters (a) and (b), the lubricity additive may further comprise a minor proportion of other esters formed, for example, during the esterification of the acid mixtures previously described. (ii) The Fuel Oil The fuel oil can be a petroleum-based fuel oil, suitably an average distillate fuel oil, that is, a fuel oil obtained in the refining of a crude oil as the fraction between the lighter kerosene and the fraction from fuel to jet, and the fraction of heavy fuel oil. These distillate fuel oils generally boil above about 100 ° C. The fuel oil may comprise an atmospheric distillate or a vacuum distillate, or a disintegrated gas oil, or a mixture in any proportion of direct distillates and thermally and / or catalytically disintegrated. The most common oil-based fuel oils are kerosene, jet fuels, and preferably diesel fuel oils. The sulfur content of the fuel oil is 0.2 weight percent or less, preferably 0.05 weight percent or less, more preferably 0.01 weight percent or less, and most preferably 0.001 weight percent or less , based on the weight of the fuel oil. The technique describes methods for reducing the sulfur content of middle hydrocarbon distillate fuels, including these methods solvent extraction, sulfuric acid treatment, and hydrodesulfurization. Preferred fuel oils have a cetane number of at least 40, preferably greater than 45, and most preferably greater than 50. The fuel oil may have these cetane numbers before the addition of any cetane improver, or it may be raised the cetane number of the fuel by adding a cetane improver. More preferably, the cetane number of the fuel oil is at least 52. (iii) Treatment Speeds The concentration of the additive in the fuel oil can be, for example, in the range of 10 to 5,000 ppm of additive ( active ingredient) by weight by weight of the fuel oil, for example from 20 to 5,000 ppm, such as from 50 to 2,000 ppm (active ingredient) by weight per weight of the fuel, preferably from 75 to 300 ppm, and more preferably from 100 to 200 ppm. The relative proportions of (a) and (b) in weight within the fuel oil can be in the scale of 1:10 to 10: 1, preferably from 1: 4 to 4: 1, and most preferably from 1: 2 to 2: 1. The 1: 1 ratio is more preferred. The Use of the Additive (Second Aspect of the Invention) and the Method (fourth Aspect of the Invention). The preferred additives for the second and fourth aspects of the invention are those described hereinabove in relation to the first aspect. The fuel oil of the second and fourth aspects of the invention, preferably is that described hereinabove in relation to the first aspect.

The Use of the Fuel Composition (Third Aspect of the Invention) Where the fuel oil is diesel fuel, the fuel oil composition of the first aspect of the invention finds application in diesel engines (compression-ignition) as a fuel that, in addition to providing good combustion properties, it reduces the wear rate in the fuel supply system, and particularly in the fuel injection pump. The use of fuel in this way prolongs the working life of the equipment, and reduces the need to replace expensive mechanical parts. The fuel oil composition of the first aspect of the invention similarly finds application in other fuel oil systems where the mechanical devices of the fuel supply system rely on the fuel oil for lubrication, and according to the same, are subject to to wear. Concentrates Concentrates comprising the additive mixed with a liquid vehicle (for example, as a solution or a dispersion), are suitable as a means for incorporating the additive into the fuel oil by volume, which incorporation can be done by methods known in this art. countryside. The concentrates may also contain other additives as required, and preferably contain from 3 to 75 weight percent, more preferably from 3 to 60 weight percent, and most preferably from 10 to 50 weight percent of the additives, preferably in oil solution. Examples of the liquid carrier are organic solvents, including hydrocarbon solvents, for example petroleum fractions such as naphtha, kerosene, diesel, and heater oil; aromatic hydrocarbons such as aromatic fractions, for example those sold under the trade name "SOLVESSO"; paraffinic hydrocarbons such as hexane and pentane and isoparaffins; and oxygenated solvents such as alcohols. The liquid vehicle, of course, must be selected considering its compatibility with the additive and with the fuel. The concentrates are added to the fuel oil by volume, in sufficient quantities to supply the treatment speed of the additive indicated hereinabove. The additives of the invention can be incorporated into the fuel oil by volume by other methods, such as those known in the art. If co-additives are required, fuel in volume can be incorporated into the oil at the same time as the additives of the invention, or at a different time. Co-additives The fuel composition of the first aspect of the invention may additionally comprise other lubricity-improving compounds known as co-additives, for example, mono- or polycarboxylic acids, such as dicarboxylic acids. These acids are preferably mixtures of polymerized unsaturated fatty acids, which mainly comprise dimeric acid and some trimeric acid, with minor proportions of monomer and / or higher polymers. Typical examples are dimer acids of oleic acid, linoleic acid, or mixtures thereof. Esters of these acids can also be used with monohydric or dihydric alcohols in combination with the mixture of esters (a) and (b), to give other improved additives. In a similar manner, lubricity co-additives of the ethoxylated amine type can be used. The fuel oil of the first aspect of the invention may also conveniently comprise one or more cold flow improvers of the fuel oil, as co-additives, such as one or more of: (i) unsaturated ethylene-ester copolymers, (ii) hydrocarbon polymers, (iii) sulfur-carboxy compound, (iv) polar compounds, (v) hydrocarbylated aromatics, (iv) vi) linear compounds, and (vii) toothed polymers, as defined hereinabove, (i) Ethylene-unsaturated ester copolymer Ethylene copolymer flow improvers, eg, ethylene-unsaturated ester copolymer flow improvers , have a polymethylene base structure divided into segments by hydrocarbyl side chains interrupted by one or more oxygen atoms and / or carbonyl groups. More especially, the copolymer can comprise an ethylene copolymer having, in addition to the units derived from ethylene, units of the formula: -CR5R6-CHR7- wherein R represents hydrogen or a methyl group; R5 represents a group -00CR8 or -COOR, wherein R ° represents hydrogen or a straight or branched chain alkyl group of 1 to 9 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms; and R represents hydrogen or a group -COOR8 or -OOCR8. These may comprise a copolymer of ethylene with an ethylenically unsaturated ester, or derivatives thereof. An example is a copolymer of ethylene with an ester of an unsaturated carboxylic acid such as ethylene acrylates (for example, ethylene 2-ethylhexylacrylate), but the ester is preferably one of an unsaturated alcohol with a saturated carboxylic acid, such as is described in British Patent Number GB-A-1, 263, 152. An ethylene-vinyl ester copolymer is convenient; A copolymer of ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene-vinyl hexanoate, ethylene-2-ethyl hexanoate, or ethylene-vinyl octanoate is preferred. Preferably, the copolymers contain from 1 to 25, such as less than 25, for example, from 1 to 20 molar percent of the vinyl ester, more preferably from 3 to 15 molar percent of vinyl ester. They may also be in the form of mixtures of two copolymers, such as those described in Patent Numbers US-A-3, 961, 916 and EP-A-113, 581. Preferably, the number average molecular weight, measured by The vapor phase osmometry of the copolymer is from 1,000 to 10,000, more preferably from 1,000 to 5,000. If desired, the copolymers can be derived from additional comonomers, for example they can be terpolymers or tetrapolymers or hi polymers, for example where the additional comonomer is isobutylene or diisobutylene, or another ester that gives rise to different units of the formula above, and wherein the aforementioned molar percentages of ester, are related to the total ester. Also, the copolymers can include small proportions of chain transfer agents and / or molecular weight modifiers (eg, acetaldehyde or propionaldehyde), which can be used in the polymerization process to make the copolymer. The copolymers can be made by direct polymerization of the comonomer. These copolymers can also be made by transesterification, or by hydrolysis and reesterification, of an unsaturated ethylene-ester copolymer, to give a different ethylene-unsaturated ester copolymer. For example, copolymers of ethylene-vinyl hexanoate and vinyl ethylene-octanoate can be made in this manner, for example, from an ethylene-vinyl acetate copolymer. For example, the copolymers can have 15 or less, preferably 10 or less, more preferably 6 or less, and most preferably 2 to 5 side branches terminated in methyl per 100 methylene groups, measured by nuclear magnetic resonance, which are different of methyl groups on a comonomer ester, and others different from terminal methyl groups. The copolymers can have a polydispersity of 1 to 6, preferably 2 to 4, the polydispersity being the ratio of the weight average molecular weight to the number average molecular weight, both measured by Gel Permeation Chromatography using polystyrene standards. (ii) Hydrocarbon Polymers of Linear Hydrocarbon Polymers These have one or more polymethylene base structures, optionally divided into segments by hydrocarbyl groups of short chain length, ie. of 5 or less carbon atoms. The examples are those represented by the following general formula: where T represents. H or R; U represents H, T or substituted or unsubstituted aryl, and R represents a hydrocarbyl group having up to 5 carbon atoms, and vw represents the molar proportions, being v within the scale of 1.0 to 0.0, and w being within the scale from 0.0 to 1.0. Preferably, R is a straight or branched chain alkyl group. These polymers can be made directly from ethylenically unsaturated monomers, or indirectly by hydrogenation of the polymer made from monomers such as isoprene and butadiene. Preferred hydrocarbon polymers are ethylene copolymers and at least one α-olefin. Examples of these olefins are propylene, 1-butene, isobutene, and 2,4,4-trimethylpent-2-ene. The copolymer can also comprise small amounts, for example up to 10 weight percent of other copolymerizable monomers, for example olefins other than α-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene-propylene copolymer. It is within the scope of the invention to include two or more different ethylene-α-olefin copolymers of this type. The number average molecular weight of the ethylene-α-olefin copolymer is less than 150,000, as measured by gel permeation chromatography (CPG) in relation to the polystyrene standards. For some applications, it is conveniently at least 60,000, and preferably at least 80,000. Functionally there is no upper limit, but mixing difficulties result when the viscosity is increased in molecular weights greater than about 150,000, and the preferred molecular weight is 60,000 and 80,000 to 120,000. For other applications, it is less than 30,000, preferably less than 15,000, such as less than 10,000 or less than 6,000. Conveniently, the copolymer has a molar ethylene content of between 50 and 85 percent. More conveniently, the ethylene content is within the range of 55 to 80 percent, and is preferably in the range of 55 to 75 percent; most preferably from 60 to 70 percent, and most preferably from 65 to 70 percent. Examples of the ethylene-or-olefin copolymers are ethylene-propylene copolymers with a molar ethylene content of 60 to 75 percent, and a number-average molecular weight in the range of 60,000 to 120,000, and especially preferred copolymers are ethylene-propylene copolymers with an ethylene content of 62 to 71 percent, and a molecular weight of 80,000 to 100,000. The copolymers can be prepared by any of the methods known in the art, for example using a Ziegler-type catalyst. Conveniently, the polymers are substantially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures, (iii) Sulfur-Carboxy Compounds Examples are those described in European Patent Number EP-A-0 , 261, 957, which describes the use of compounds of the general formula: A X - R1 \ C I B XY R2 where -Y-R2 is S03 (") (+) NR33R2, -S03 (~) (+) HNR32R2, -S03 (') (+) H2NR3R2, -S0 (") (+) H3NR2, -S02NR3R2 or -S03R2, and -X-R1 is -Y-R2 or -CONR3R', -CO2 (") (+) NR33RI , -C02 ^ (+) HNR32 I, -R4-COOR ,, -NR3COR ', -R40R', -R4OCOR1, -R4, R ', -N (COR3) Rl or Z (") (+) NR33RJ; Z ("> is S03W or -C02 (); R1 and R are alkyl, alkoxyalkyl, or polyalkoxyalkyl containing at least 10 carbon atoms in the main chain, R3 is hydrocarbyl and each R3 may be the same or different, and R it is absent or is alkylene of 1 to 5 carbon atoms, and in: C B- the carbon-carbon (CC) bond is: a) ethylenically saturated when A and B can be alkyl, alkenyl, or substituted hydrocarbyl groups, or b) is part of a cyclic structure that can be aromatic, polynuclear aromatic, or cycloaliphatic, and it is preferred that XR and YR among them contain at least three alkyl groups, alkoxyalkyl, or polyalkoxyalkyl. Multi-component additive systems can be used, and the proportions of the additives to be used will depend on the fuel to be treated. (iv) Polar Compounds These compounds comprise an oil-soluble polar nitrogen compound bearing one or more, preferably two or more hydrocarbyl substituted amino or imino substituents, the monovalent hydrocarbyl groups being, and containing from 8 to 40 carbon atoms. carbon, whose substituent or one or more of whose substituents, optionally are in the form of a cation derived therefrom. The oil-soluble polar nitrogen compound is ionic or non-ionic, and is capable of acting as a wax crystal growth modifier in fuels. Preferably, the hydrocarbyl group is linear or slightly linear, that is, it can have a hydrocarbyl branch of short length (of 1 to 4 carbon atoms). When the substituent is amino, it may carry more than one hydrocarbyl group, which may be the same or different. The term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule, and having a hydrocarbon or predominantly hydrocarbon character. Examples include the hydrocarbon groups, including the aromatic, and aromatic substituted by alicyclic, and aliphatic substituted by aromatic, and alicyclic groups. The aliphatic groups are conveniently saturated. These groups may contain substituents other than hydrocarbon, provided that their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halogen, hydroxy, nitro, cyano, alkoxy, and acyl. If the hydrocarbyl group is substituted, a single substituent (mono) is preferred. Examples of the substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also alternatively contain different carbon atoms in a chain or ring, otherwise composed of carbon atoms. Suitable heteroatoms include, for example, nitrogen, sulfur, and preferably oxygen. More especially, each amino or imino substituent is linked to a moiety by means of an intermediate linking group such as -CO-, -C0 ^, -S0 ^, or hydrocarbylene. Where the linking group is anionic, the substituent is part of a cationic group, such as in an amine salt group. When the polar nitrogen compound carries more than one amino or imino substituent, the linking groups for each substituent may be the same or different. Suitable amino substituents are primary, secondary, tertiary, or quaternary amino substituents of long chain alkyl of 12 to 40 carbon atoms, preferably 12 to 24 carbon atoms. Preferably, the amino substituent is a dialkylamino substituent, which, as indicated above, may be in the form of an amine salt thereof.; tertiary or quaternary amines can only form amine salts. These alkyl groups may be the same or different. Examples of the amino substituents include dodecylamine, tetradecylamino, cocoamino, and hydrogenated tallow amino. Examples of the secondary amino substituents include dioctadecylamino and methylbehenylamino.

There may be mixtures of amino substituents present, such as those derived from naturally occurring amines. A preferred amino substituent is the secondary hydrogenated tallow amino substituent, the alkyl groups of which are derived from hydrogenated tallow fat, and typically are composed of normal alkyl groups of about 4 percent of 14 carbon atoms; percent of 16 carbon atoms, and 59 percent of 18 carbon atoms, by weight. Suitable imino substituents are long chain alkyl substituents of 12 to 40 carbon atoms, preferably 12 to 24 carbon atoms. This fraction can be monomeric (cyclic or non-cyclic) or polymeric. When it is non-cyclic, it can be obtained from a cyclic precursor such as an anhydride or a spirobislactone. The cyclic ring system may include homocyclic, heterocyclic, or melted polycyclic assemblies, or a system where two or more of these cyclic assemblies join with one another, and where the cyclic assemblies may be the same or different. Where there are two or more of these cyclic assemblies, the substituents may be in the same assemblies or in different assemblies, preferably in the same assembly. Preferably, each cyclic assembly is aromatic, more preferably a benzene ring. More preferably, the cyclic ring system is a single benzene ring, when it is preferred that the substituents are in the ortho or meta positions, whose benzene ring may also be optionally substituted. The ring atoms of the ring assembly or ring assemblies are preferably carbon atoms, but may include, for example, one or more ring N, S, or O atoms, in which case or instances, the compound is a heterocyclic compound. Examples of these polycyclic assemblies include: (a) condensed benzene structures, such as naphthalene, anthracene, phenanthrene, and pyrene; (b) condensed ring structures wherein none or all of the rings are benzene, such as azulene oxide, indene, hydroindene, fluorene, and diphenylene; (c) "end-capped" rings, such as diphenyl; (d) heterocyclic compounds such as quinoline, indole, 2: 3 dihydroindole, benzofuran, coumarin, isocoumarin, benzothiophene, carbazole, and thiodiphenylamine; (e) non-aromatic or partially saturated ring systems, such as decalin (ie, decahydronaphthalene), α-pinene, cardinne, and bornelene, and (f) three-dimensional structures such as norbornene, bicycloheptane (ie, norbornane), bicyclooctane, and bicyclooctene. Examples of the polar nitrogen compounds are described below: (I) an amine salt and / or an amide of a mono- or polycarboxylic acid, for example having 1 to 4 carboxylic acid groups. It can be done, for example, by reacting at least one molar ratio of a hydrocarbyl substituted amine with a molar ratio of the acid or its anhydride. When an amide is formed, the linking group is -CO-, and when an amine salt is formed, the linking group is -CO, (-) The fraction may be cyclic or non-cyclic. Examples of the cyclic fractions are those in which the acid is cyclohexane-1,2-dicarboxylic acid; cyclohexane-1,2-dicarboxylic acid; 1, 2-dicarboxylic acid cyclopentan; and naphthalenedicarboxylic acid. In general, these acids have from 5 to 13 carbon atoms in the cyclic fraction. Preferred of these cyclic acids are benzenedicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, and benzetracarboxylic acids such as pyromellitic acid, phthalic acid being particularly preferred. Patents Nos. US-A-4, 211, 534 and EP-A-272, 889 disclose polar nitrogen compounds containing these fractions. Examples of the non-cyclic fractions are those wherein the acid is a dicarboxylic acid substituted by long-chain alkyl or alkylene, such as succinic acid, as described, for example, in U.S. Patent No. US-A-4, 147, 520. Other examples of non-cyclic fractions are those wherein the acid is an acid containing nitrogen, such as ethylenediaminetetraacetic acid. Additional examples are the fractions obtained wherein a dialkyl spirobislactone is reacted with an amine. (II) European Patent Number EP-A-0, 261, 957 discloses polar nitrogen compounds according to the present disclosure, of the general formula X- R C B? - R where -Y-R2 is S03 (") (+) NR3R2, -S03 (") (+) HNR32R2, -S03 (") (+) H2NR3R2, -S03 (") (+) H3NR2, -S02NR3R2 or -S03R2; and -X-R1 is -Y-R2 or -CONR, -C02W (+ ^ NR33RI, -C02 (") (+) HNR32R ', -R4-COOR |, - NR3COR', -R ^ R1, -R ^ COR1, -R4, ^ 1, -N (COR3) R1 or zW (+) NR33Rl; -Z (_ is S03 (") or -C02 ("); R1 and R are alkyl, alkoxyalkyl, or polyalkoxyalkyl which contains less 10 carbon atoms in the main chain, R is hydrocarbyl and each R may be the same or different, and R is absent or is alkylene of 1 to 5 carbon atoms, and in: C I C B the carbon-carbon (CC) bond is: a) ethylenically saturated when A and B can be alkyl, alkenyl, or substituted hydrocarbyl groups, or b) is part of a cyclic structure that can be aromatic, polynuclear aromatic, or cycloaliphatic, and it is preferred that X-R1 and YR between them contain at least three alkyl, alkoxyalkyl, or polyalkoxyalkyl groups. Multi-component additive systems can be used, and the proportions of the additives to be used will depend on the fuel to be treated. (III) European Patent Number EP-A-0,316,108 discloses an amine or diamine salt of a) a sulfosuccinic acid, b) an ester or diester of a sulfosuccinic acid, c) an amide or a diamide of a sulfosuccinic acid, or d) an ester-amide of a sulfosuccinic acid. (IV) A chemical compound comprising or including a cyclic ring system, the compound carrying at least two substituents of the following general formula (I), on the ring system: -A-NR ^ 2 (I) wherein A is an aliphatic hydrocarbyl group which is optionally interrupted by one or more heteroatoms, and which is straight or branched chain, and R 1 and R 9 are the same or different, and each independently is a hydrocarbyl group containing from 9 to 40 atoms of carbon optionally interrupted by one or more heteroatoms, the substituents being the same or different, and the compound optionally being in the form of a salt thereof. Preferably, A has from 1 to 20 carbon atoms, and is preferably a methylene or polymethylene group. Each hydrocarbyl group constituting R 1 and R 9 in the invention (Formula 1) can be, for example, an alkyl or alkylene group, or a mono- or poly-alkoxyalkyl group. Preferably, each hydrocarbyl group is a straight chain alkyl group. The number of carbon atoms in each hydrocarbyl group is preferably 16 to 40, more preferably 16 to 24. Also, it is preferred that the cyclic system be substituted with only two substituents of the general formula (I), and that A be a methylene group. Examples of the salts of the chemical compounds are acetate and hydrochloride. The compounds can conveniently be made by reducing the corresponding amide, which can be done by the reaction of a secondary amine with an appropriate acid chloride. (V) A long chain primary or secondary amine condensate with a polymer containing carboxylic acid. Specific examples include polymers such as are described in Patent Numbers GB-A-2, 121, 807, FR-A-2, 592,387, and DE-A-3, 941, 561; and also esters of teleeric acid and alkanolamines such as are described in U.S. Patent No. US-A-4,639,256; and the reaction product of an amine containing a branched carboxylic acid ester, an epoxide, and a monocarboxylic acid polyester, such as is described in U.S. Patent No. US-A-4,631,071. European Patent Number EP-0,283,292 describes amide-containing polymers, and European Patent Number EP-0,343,981 describes polymers containing amine salt. It should be noted that the polar nitrogen compounds may contain other functionality, such as ester functionality. (v) Hydrocarbic Aromatics These materials are condensed comprising aromatic and hydrocarbyl parts. The aromatic part is conveniently an aromatic hydrocarbon which may be unsubstituted or substituted, for example, with substituents other than hydrocarbon. This aromatic hydrocarbon preferably contains a maximum of three substituent groups and / or three condensed rings, and is preferably naphthalene. The hydrocarbyl part is a part that contains hydrogen and carbon connected to the rest of the molecule by 1 carbon atom.

It may be saturated or unsaturated, and may be straight or branched, and may contain one or more heteroatoms, provided that they do not substantially affect the hydrocarbyl nature of that part. Preferably, the hydrocarbyl part is an alkyl part, which conveniently has more than 8 carbon atoms, (vi) Linear Compounds These compounds comprise a compound wherein at least one substantially linear alkyl group having from 10 to 30 carbon atoms. carbon, is connected by means of an optional linking group that can be branched to a non-polymeric residue, such as an organic waste, to provide at least one linear chain of atoms that includes the carbon atoms of those alkyl groups, and one or more non-terminal oxygen, sulfur, and / or nitrogen atoms. The linking group can be polymeric. "Substantially linear" means that the alkyl group is preferably straight chain, but straight chain alkyl groups having a small degree of branching can be used, such as in the form of a single branching of the methyl group. Preferably, the compound has at least two of these alkyl groups when the straight chain can include the carbon atoms of more than one of these alkyl groups. When the compound has at least three of these alkyl groups, there may be more than one of these linear chains, whose chains may overlap. The chain or the linear chains can provide part of the linking group between any two of these alkyl groups in the compound. The oxygen atom or atoms, if present, are preferably directly interposed between the carbon atoms of the chain, and may, for example, be provided in the linking group, if present, in the form of a mono- or polyoxyalkylene, preferably having this oxyalkylene group having 2 to 4 carbon atoms, the examples being oxyethylene and oxypropylene. As indicated, the chain or chains include carbon, oxygen, sulfur, and / or nitrogen atoms. The compound can be an ester, wherein the alkyl groups are connected to the rest of the compounds as groups-0-CO-normal alkyl, or -CO-0-normal alkyl, wherein the alkyl groups are derived from a acid, and the rest of the compound is derived from a polyhydric alcohol, and the alkyl groups are derived from an alcohol in the latter, and the remainder of the compound is derived from a polycarboxylic acid. Also, the compound can be an ether wherein the alkyl groups are connected with the remainder of the compound as -0-n-alkyl groups. The compound can be either an ester or an ether, or it can contain different ester groups.

Examples include polyoxyalkylene esters, ethers, ester / ethers, and mixtures thereof, particularly those containing at least one, preferably at least two linear alkyl groups of 10 to 30 carbon atoms, and a polyoxyalkylene glycol group of a molecular weight of up to 5,000, preferably from 200 to 5,000, containing the alkylene group in this polyoxyalkylene glycol of 1 to 4 carbon atoms, as described in Patent Numbers EP-A-61,895 and US Pat. 4,491,455. The preferred esters, ethers, or ether / esters that can be used can comprise compounds wherein one or more groups (such as 2, 3, or 4 groups) of the formula -OR9 * 5J are bonded with a residue E, in where E can represent, for example, A (alkylene) q, where A represents C or N or is absent, q represents an integer from 1 to 4, and the alkylene group has from 1 to 4 carbon atoms, where A ( alkylene) q, for example, N (CH2CH2) 3; C (CH2); or (CH) 2; and R5 can be independently: (a) normal alkyl- (b) normal alkyl -C0- (c) normal alkyl-0C0- (CH2) n- (d) normal alkyl-0C0- (CH2) nCO- where n, example, from 1 to 34; the group being the linear alkyl group, and containing from 10 to 30 acarbon omos. For example, they may be represented by the formula R23OBOR24, each of R23 and R24 being defined as for R9 * JS above, and B representing the polyalkylene segment of the glycol, wherein the alkylene group has 1 to 4 carbon atoms , for example, a polyoxytrimethylene, polyoxyethylene, or polyoxytrimethylene fraction that is substantially linear; some degree of branching can be tolerated with the lower alkyl side chains (such as in polyoxypropylene glycol), but it is preferred that the glycol be substantially linear. Suitable glycols in general are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG), having a molecular weight of about 100 to 5,000, preferably about 200 to 2,000. The esters are preferred, and fatty acids containing from 10 to 30 carbon atoms are useful for reacting with the glycols, in order to form ester additives, preference being given to using fatty acid of 18 to 24 carbon atoms, especially behenic acid . Esters can also be prepared by esterification of polyethoxylated fatty acids or polyethoxylated alcohols. The polyoxyalkylene diesters, diethers, ether / esters and mixtures thereof are suitable as additives, the diesters being preferred when the petroleum-based component is a narrow boiling distillate, where smaller amounts of monoethers and monoethers may also be present. monoesters (which are often formed in the manufacturing process). It is important, for an active performance, that a greater amount of the dialkyl compound be present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol, or mixtures of polyethylene glycol / polypropylene glycol are preferred. Examples of other compounds in this general category are those described in Japanese Patent Publications Nos. 2-51477 and 3-34790, and in European Patents Nos. EP-A-117,108 and EP-A-326, 356, and cyclic esterified ethoxylates, such as are described in European Patent Number EP-A-356, 256. (vii) Toothed Polymers Toothed polymers are described in "Comb-Like Polymers. Structure and Properties ", NA Platé and VP Shibaev, J. Poly. Sci. Macromolecular Revisions., 8, pages 117 to 253 (1974) In general, toothed polymers consist of molecules where there are long chain branches, such as hydrocarbyl branches, optionally interrupted by one or more oxygen atoms and / or carbonyl groups, having from 6 to 30, such as from 10 to 30 carbon atoms, pendants from a polymer base structure, these branches being directly linked or Indirectly with the base structure Examples of the indirect link include linking by means of interposed atoms or groups, the linkage of which may include covalent and / or electrovalent bonding, such as in a salt In general, toothed polymers are distinguished by having a minimum molar ratio of units containing these long chain branches, conveniently, the toothed polymer is a homopolymer or copolymer that has when minus 25, and preferably at least 40, more preferably at least 50 mole percent. of the units having side chains containing at least 6, such as at least 8, and preferably at least 10 atoms, selected from, for example, carbon, nitrogen, and oxygen, in a linear chain, or in a chain containing a small amount of branching, such as a single methyl branching. As examples of the preferred toothed polymers, those containing units of the general formula may be mentioned: wherein D represents R1 1, COOR11, OCOR1 1, Rl2C00Rp or OR1 1; E represents H, D or R19, • G represents H or D; J represents H, R12, R12C00Rn, or a substituted or unsubstituted aryl, or a heterocyclic group; K represents H, COOR12, OCOR12, OR12, or COOH; L represents H, R12, COOR12, OCOR12 or substituted or unsubstituted aryl; R1 represents a hydrocarbyl group having 10 or more carbon atoms, and R represents a hydrocarbyl group which is divalent in group 1 COOR, and which is otherwise monovalent, and m and n represent molar proportions, being its sum of 1, and being finite, and being up to and including 1, and n being from zero to less than 1, preferably being within the range of 1.0 to 0.4, where n is from 0 to 0.6. R suitably represents a hydrocarbyl group with from 10 to 30 carbon atoms, preferably from 10 to 24, and more preferably from 10 to 18. Preferably, R is a linear or slightly branched alkyl group, and R 19 suitably represents a hydrocarbyl group with from 1 to 30 carbon atoms when it is monovalent, preferably with 6 or more, more preferably with 10 or more, preferably up to 24, and more preferably up to 18 carbon atoms.

Preferably, R 19, when monovalent, is a linear or slightly branched alkyl group. When R 12 is divalent, it is preferably a methylene or ethylene group. "slightly branched" means that it has a single methyl branching. The toothed polymer may contain units derived from other monomers, if desired or required, examples being CO, vinyl acetate, and ethylene. It is within the scope of the invention to include two or more different toothed copolymers. For example, the toothed polymers may be copolymers of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, for example an α-olefin or unsaturated ester, for example vinyl acetate, as described in European Patent Number EP-A- 214, 786. It is preferred, but not essential, that equimolar amounts of the comonomers are used, although molar proportions on the scale of 2 to 2 are adequate. Examples of olefins that can be copolymerized with, for example, maleic anhydride, include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and styrene. Other examples of toothed polymers include methacrylates and acrylates. The copolymer can be esterified by any suitable technique, and although it is preferred, it is not essential that the maleic anhydride or the fumaric acid is at least 50 percent esterified. Examples of the alcohols that can be used include n-decan-1-ol, n-dodecan-1-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and n-octadecan-1-ol . The alcohols should also include up to one methyl branch per chain, for example, 1-methylpentadecan-1-ol, 2-methyltridecan-1-ol, as described in European Patent Number EP-A-213,879. it can be a mixture of normal and simple branched methyl alcohols. It is preferred to use pure alcohols instead of mixtures of alcohols, such as may be commercially available.; if mixtures are used, the number of carbon atoms in the alkyl group is taken as the average number of carbon atoms in the alkyl groups of the mixture of alcohols; if alcohols containing a branching at positions 1 or 2 are used, the number of carbon atoms in the alkyl group is taken with the number in segment of the straight chain base structure of the alkyl group of the alcohol. The toothed polymers can be especially polymers and copolymers of fumarate or itaconate such as, for example, those described in European Patent Applications Nos. 153,176; 153,177; 156,577; and 225,688; and in International Publication WO 91/16407. Toothed polymers fumarate Particularly preferred are copolymers of alkyl fumarates and vinyl acetate, wherein the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms, or wherein the alkyl groups are a mixture of alkyl groups of 14 carbon atoms / 16 carbon atoms, made, for example, by copolymerization in solution of an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or with the mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used as it is, it is conveniently a mixture of 1: 1 by weight of normal alcohols of 14 carbon atoms and of 16 carbon atoms. Furthermore, mixtures of the 14 carbon atom with the mixed ester of 14 carbon atoms / 16 carbon atoms can be conveniently used. In these mixtures, the ratio of 14 carbon atoms to 14 carbon atoms / 16 carbon atoms, conveniently is in the scale of 1: 1 to 4: 1, preferably 2: 1 to 7: 2, and most preferably about 3: 1, by weight. Particularly preferred fumarate toothed polymers, for example, can have a number average molecular weight on the scale of 1000 to 100,000, preferably 1000 to 50,000, as measured by Steam Phase Osmometry (OFV). Other polymers suitable serrations are polymers and copolymers of .alpha.-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid, as described in European Patent No. EP-A-282, 342; mixtures of two or more toothed polymers can be used according to the invention, and, as indicated above, this use may be convenient. Other examples of toothed polymers are hydrocarbon polymers such as copolymers of ethylene and at least one a-olefin, preferably having the a-olefin at most 20 carbon atoms, examples being n-octene-1, isooctene-1 , n-decene-1, and n-dodecene-1, n-tetradecene-1, and n-hexadecene-1 (for example, as described in International Publication Number WO 9319106). Preferably, the number average molecular weight measured by Gel Permeation Chromatography against polystyrene standards of this copolymer is, for example, up to 30,000, or up to 40,000. The hydrocarbon copolymers can be prepared by methods known in the art, for example using a Ziegler-type catalyst. These hydrocarbon polymers, for example, can have an isotacticity of 75 percent or greater. Some of the cold flow improver coadditives described hereinabove may provide synergistic improvements to lubricity performance when combined with a mixture of esters (a) and (b) Other co-additives that can be used are those known in the art, for example detergents, antioxidants, corrosion inhibitors, de-aebulizers, de-emulsifiers, metal deactivators, antifoaming agents, combustion improvers such as cetane improvers, co-solvents, package compatibilizers, reoperants, and metal-based additives such as metal combustion improvers. Evaluation of the Benefits of the Different Aspects of the Invention It is believed that the mixture of esters (a) and (b) can form at least partial layers of a lubricating composition on certain metal surfaces. This means that the formed layer is not necessarily complete on the contact surface. The formation of these layers and the extent of their coverage of a contact surface can be demonstrated, for example, by measuring the electrical contact resistance or electrical capacitance. One test that can be used to demonstrate one or more of a reduction in wear, a reduction in friction, or an increase in electrical contact resistance in accordance with this invention, is the High Frequency Reciprocating Rigging test (or "ARAF"), described in the CEC PF 06-T-94 or ISO / TC22 / SC7 / WG6 / N188 standard test methods. The degree to which an additive composition causes blockage of the fuel oil line filters can be measured using a known leakage test. For example, a method for measuring the possibility of filtration of fuel oil compositions is described in the Petroleum Institute Standard designated "IP 387/190" and entitled "Determination of the tendency to block the oil filter. of gas and distilled diesel fuels ". In summary, a sample of the fuel oil composition to be tested is passed at a constant flow rate through a glass fiber filter medium; the pressure drop across the filter is monitored, and the volume of fuel oil passing through the filter medium is measured within a prescribed pressure drop. The tendency to block the filter of a fuel composition can be described as the pressure drop across the filter medium for 300 milliliters of fuel to pass at a rate of 20 milliliters / minute. The aforementioned Standard should be referenced for more information. In the evaluation of the additive composition of the present invention, this method was adapted by conducting the measurements at different temperatures lower than that specified in the Standard, to simulate cold storage conditions, which occur in the field. The invention is further illustrated with reference to the following Examples. Example 1 The following materials and methods were used. Fuel Oil A "Class I" diesel fuel oil having the characteristics shown below: Sulfur: 4.5 ppm w / w Cetane number: 51.6 CFPP (Auto): -36 ° C Distillation: 50% evaporation 237.1 ° C Point of Final Boiling 294.l ° C Residue (% by volume) 1.2 Additives Additives A, B, C, and D were added to diesel fuel oil in the amounts recorded in Table 1, and the possibility of filtering each one of the fuel compositions according to the IP 387/90 test, at the temperatures shown in Table 1. In each case, after a complete mixing, the sample fuel composition was cooled to the required temperature in one unit of refrigeration, and stored at that temperature for the aforementioned period of time, before undergoing the filtration test.

TABLE 1 Footer: '-' means not measured Additive A was prepared by esterifying a commercial mixture of oleic and linoleic acids with glycerol, to produce a mixed ester product predominant in: (a) glycerol monooleate, and (b) glycerol monolinoleate, in approximately equal proportions by weight, with minor amounts of di- and trioleate and glycerol linoleate also present. In addition, the acid mixture contained a smaller proportion of other acids, whose esters were not believed to represent more than about 6 weight percent of the mixed ester product. Additive B was prepared by the esterification of oleic acid with glycerol, to form a predominant product in glycerol monooleate (additive of International Publication Number WO 94/17160). Additive C was prepared by the esterification of linoleic acid with glycerol, par? form a predominant product in glycerol monolinoleate. Additive D was a 1: 1 molar mixture of additive B and additive C. In Table 1, the test results indicate the pressure drop on the filter at the end of each test, indicating the highest pressure drops a greater degree of partial blockage of the filter. Where the pressure drop became greater than 103.4 kPa (15 psi) during the 15-minute test, the test time at which this pressure was reached (103.4 kPa, i.e. 15 psi, corresponds to a severe blockage of the filter, and is considered for these purposes as a "failure" of the test). From the results of Table 1, it can be seen that Sample 2 (the fuel composition of the invention) showed a surprisingly improved filtration possibility on Sample 3 (comparative fuel composition containing additive D of International Publication Number WO 94/17160), both at 0 ° C and -10 ° C. In addition, although both examples exceeded 103.4 kPa in the test after one week at -10 ° C, Sample 2 had a better performance (it was exceeded just before the end of the 15 minute test in contrast to Sample 3, that exceeded this pressure drop almost immediately). In addition, the results at -5 ° C indicate that samples 2 and 5 (combustible compositions of the invention) showed an improved filtration possibility on Samples 3 and 4 (comparative), failing these two comparative examples in the test. Sample 2 containing Additive A (made by esterification of a mixture of starting acids), also showed surprisingly improved performance compared to Sample 5 containing Additive D (made by blending together the component esters ).

Example 2 A small aliquot was removed from each of the Samples of Example 1, stored at -5 ° C for 2 weeks, immediately before the filtration step described in Example 1, and the operation of ARAF at 60 ° was measured. C of each aliquot as an indication of lubricity performance "before filtration". Operation of ARAF at 60 ° C of each sample filtrate produced in Example 1 was also measured as an indication of lubricity performance "after filtration". The results are compared in the following Table 2. Table 2 The results in Table 2 indicate that samples 3 and 4 (comparatives) show a significantly poorer lubricity performance after filtration (ie, a larger wear mark), in contrast to samples 2 and 5 (compositions fuel of the invention), which maintained its lubricity performance. The untreated fuel (Sample 1) showed no changes, confirming that the differences in the results of the other samples are due to the additives present in these compositions. The differences in the diameter of the wear mark after the filtration indicate a significant technical improvement, and demonstrate the best lubricity properties provided by the blends of the esters (a) and (b), on the comparative additives.

Claims (12)

1. NOVELTY OF THE INVENTION Having described the foregoing invention, it is considered as a novelty, and therefore, property is claimed as contained in the following: CLAIMS 1. A combustible oil composition comprising a greater proportion of a combustible oil than middle distillate having a sulfur content of 0.2 percent by weight or less, and a minor proportion of a lubricity additive comprising: (a) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol, and (b) an ester of an unsaturated monocarboxylic acid and a polyhydric alcohol having at least three hydroxy groups, the esters (a) and (b) being different.
2. 2. The composition according to claim 1, characterized in that the fuel oil has a sulfur content of 0.01 weight percent or less.
3. 3. The composition as claimed in claim 1 or claim 2, characterized in that the fuel oil is a diesel fuel.
4. 4. The composition as claimed in any of the preceding claims, characterized in that (a) is an ester of a polyhydric alcohol having at least three hydroxy groups.
5. 5. The composition as claimed in any of the preceding claims, characterized in that (a) and (b) are esters of alkenyl monocarboxylic acids.
6. 6. The composition according to claim 5, characterized in that (a) is an ester of a monounsaturated alkenyl monocarboxylic acid, and (b) is an ester of a polyunsaturated alkenyl monocarboxylic acid.
7. The composition according to claim 6, characterized in that both acids have alkenyl groups of 10 to 36 carbon atoms.
8. The composition as claimed in any of claims 4 to 7, characterized in that (a) and (b) are both esters of trihydric alcohols, especially glycerol.
9. 9. The composition according to claim 8, characterized in that (a) and (b) both monoesters.
10. The composition according to claim 9, characterized in that (a) is a monoester of oleic acid and glycerol, and (b) is a monoester of linoleic acid and glycerol.
11. 11. The use of the additive according to claim 1 in any of the preceding claims, to improve the lubricity of medium distillate fuel oil.
12. 12. The use of the fuel oil composition according to claim 1 in any of claims 1 to 10, in a combustion apparatus, for reducing the rate of wear in the fuel supply system of said apparatus.