GB2106106A - Acid-ester-containing compositions useful to reduce fuel consumption - Google Patents

Abstract

Fuel consumption is reduced in internal combustion engines by lubricating them with a lubricant containing certain alkyl or alkenyl esters of polycarboxylic acids. Acid-esters of formula R'(COOR<2>)m are novel, where R' is a C10-35 aliphatic hydrocarbon-based radical free of acetylenic unsaturation and having at least 8C atoms in straight-chain configuration, each R<2> is H or C2-18 alkenyl, at least one H and and least one alkenyl being present.

Description

SPECIFICATION Ester-containing compositions useful to reduce fuel consumption This invention relates to compositions and methods for improving the operation of internal combustion engines, specifically by reducing fuel consumption thereof. More particularly, the invention comprises lubricating compositions which may be used in such engines to decrease fuel consumption, a method of using lubricating compositions to accomplish this purpose, and novel lubricant additives useful to accomplish this purpose.The novel lubricant additives comprise at least one acidic ester having the formula R'(COOR2)m, (I) wherein: R' is an aliphatic hydrocarbon-based radical free from acetylenic unsaturation and containing from about 10 to about 35 carbon atoms, in which at least 8 carbon atoms are in straight-chain configuration; each R2 is independently hydrogen or an alkenyl radical contaning up to about 18 carbon atoms, at least one R2 being hydrogen and at least one being alkenyl; and m is an integer from 2 to 5.

In view of the petroleum shortages in recent years, the increasing cost of petroleum products and the desire for conservation of natural resources such as petroleum, fuel economy is an inportant factor in designing engines and materials for use therein. It is readily recognized that a situation under which fuel consumption is minimized is desirable, both because of the conservation factor and because such a situation is economical for the user of the engine.

As will be apparent, the novel features of this invention are the esters having formula I and the use of these and similar esters in lubricants to reduce fuel consumption. In formula I, R' is an aliphatic hydrocarbon-based radical free from acetylenic unsaturation and containing from about 10 to about 35 and preferably at least about 12 carbon atoms. As used herein, the term "aliphatic hydrocarbon-based radical" denotes an aliphatic radical having carbon atoms directly attached to the remainder of the molecule and havng predominantly hydrocarbon character within the context of this invention. Such radicals include the following: (1) Aliphatic hydrocarbon radicals; that is, divalent to pentavalent saturated aliphatic radicals corresponding to decyl, undecyl, dodecyl, tetradecyl, octadecyl, eicosyl, docosyl, tiracontanyl and the like, and corresponding olefinic radicals.

(2) Substituted aliphatic hydrocarbon radicals; that is, aliphatic radicals containing nonhydrocarbon substituents which, in the context of this invention, do not alter the predominantly hydrocarbon character of the radical. Those skilled in the art will be aware of suitable substituents; examples are hydroxy, alkoxy (especially lower alkoxy, the term "lower" denoting radicals having 7 carbon atoms or less), carbalkoxy (especially lower carbalkoxy), nitro, alkylsulfoxy and alkylsulfone.

(3) Hetero aliphatic radicals; that is, aliphatic radicals which, while predominantly hydrocarbon in character within the context of this invention, contain atoms other than carbon present in a chain otherwise composed of carbon atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, nitrogen, oxygen and sulfur.

In general, no more than about three substituents or hetero atoms, and preferably no more than one, will be present for each 10 carbon atoms in the aliphatic hydrocarbon-based radical.

At least 8 and preferably at least 10 carbon atoms in R' are in straight-chain configuration.

Subject to this limitation, R' may contain branching on any carbon atom in the chain as exemplified by pendant alkyl groups including methyl, ethyl, propyl, butyl and hexyl (all isomers being included).

A preferred class of acidic esters for use according to the present invention consists of those in which R' is

R3 is a substantially straight-chain alkyl or alkenyl radical containing from about 8 to about 30 and usually from about 12 to about 25 carbon atoms, and m is 2. In these compounds, each of the free valences in formula II is satisfied by a COOR2 moiety. Thus, the preferred compounds are acidic esters of substituted succinic acids. Any carbon atom of R3 may be attached to the succinic moiety, either directly or through a methylene group. The term ''substantially straightchain" means that the radical otherwise contains as substituents no more than about 2 methyl groups.

Substituted acids and their derivatives (e.g., anhydrides, acid halides, esters) of this type may be conveniently prepared by the reaction of maleic or fumaric acid or a derivative thereof, preferably maleic anhydride, with one or more olefins containing from about 8 to about 30 carbon atoms and having the required straight-chain character. Many of such olefins are available, either pure or in the form of commercial mixtures. The olefinic bonds therein may be in terminal or internal position and may thus be present as vinyl, vinylidene or internal olefinic groups. Many of such compounds contain predominantly vinly and vinylidene groups; such compounds may be represented by the formulas CH2 = CHR and CN2 = CR2 respectively where each R is independently an alkyl radical.

The reaction between the olefin or mixture of olefins and maleic anhydride or a similar acid or acid derivative is typically an "ene reaction", resulting in the formation of a new carbon-carbon single bond between the maleic or similar moeity and the olefin and the migration of the double bond in the olefin. The conditions of the ene reaction are well known to those skilled in the art and are not believed to require extensive discussion herein.

The alkenyl R2 radicals may contain up to about 18, usually up to about 12, carbon atoms.

Suitable radicals of this type include allyl, butenyl, hexenyl, octenyl, decenyl, dodecenyl and octadecenyl (all isomers being included). Especially preferred are the lower alkenyl radicals, more especially those containing from 2 to 4 carbon atoms.

The integer m is from 2 to 5 and is preferably 2. As previously noted, the novel esters of the invention are acidic esters, so at least one R2 value therein is hydrogen and at least one is alkenyl.

The especially preferred esters from the standpoint of the present invention are the abovedescribed substituted succinic acid esters in which one R2 is hydrogen and the other is an alkenyl radical containing from 1 to 4 carbon atoms, and is usually allyl.

The acidic esters useful in accordance with the present invention may be prepared by conventional methods, such as by the reaction of at least one suitable.polycarboxylic acid or derivative thereof with at least one unsaturated alcohol, the number of equivalents of alcohol being at least one less than the number of equivalents of acid or acid derivative. The substituted succinic anhydrides are the preferred acid-derived compounds, but a substituted succinic acid or acid halide may be used; in the latter case, it is necessary to hydrolyze any remaining acid halide groups to free acid groups.

The details of preparation of suitable esters are known to those skilled in the art and are not belived to require extensive discussion herein. However, the following examples of the preparation of such esters are illustrative. All parts and percentages are by weight unless otherwise indicated. All acid number determinations use phenolphthalein as an indicator.

Example 1 A mixture of 500 parts (3.74 equivalents) of dodecenylsuccinic anhydride and 109 parts (1.87 equivalent) of allyl alcohol is heated for 10 hours at 110 C., with stirring. Two additional portions of allyl alcohol, 2.5 and 6.5 parts respectively, are added and heating is continued for 4 hours. The reaction mixture is then vacuum stripped. The residue is the desired acidic allyl ester; it has an acid number of 173.6.

Example 2 To a reaction vessel containing 2254 parts (23 moles) of maleic anhydride is added 5700 parts (25 moles) of a commercial mixture of C15,8 predominantly straight-chain a-olefins. The mixture is heated under nitrogen at 209-214 C. for about 15 hours. Textile spirits, 1500 parts, is added and stirring is continued for one hour, after which the material is filtered through a filter aid material and vacuum stripped to remove volatiles. The residue from stripping is filtered again; the filtrate is the desired substituted succinic anhydride.

A mixture of 485 grams (2.94 equivalents) of the substituted succinic anhydride and 85.9 grams (1.47 equivalents) of allyl alcohol is heated for 9-1 /2 hours at 110 C., with stirring.

Toluene, 150 ml., is added and the mixture is azeotropically distilled to remove water. The toluene is then removed under vacuum and two additional portions of allyl alcohol, 10.6 and 10.1 grams respectively, are added as heating at about 110on. is continued for seven hours.

The mixture is vacuum stripped. The residue is the desired acidic allyl ester; it has an acid number of 154 Example 3 A portion of the commercial a-olefin mixture of Example 2 is isomerized by heating at 180-195 C. for 10 hours in the presence of an acidic ion exchange resin. The isomerized mixture is reacted with maleic anhydride and the resulting substituted succinic anhydride is reacted with allyl alcohol. The procedures for these reactions are substantially those of Example 2 except that the azeotropic distillation step in the presence of toluene is omitted. The product is the desired acidic allyl ester; it has an acid number of 147.

Example 4 The procedure of Example 3 is repeated, using a commercial mixture of C1520 predominantly straight-chain a-olefins. A similar product having an acid number of 136.6 is obtained.

Example 5 Following substantially the procedure of Example 3, a commercial mixture of C16,8 predominantly straight-chain a-olefins is isomerized and the isomerized mixture is reacted with maleic anhydride. The resulting substituted succinic anhydride is converted to the acidic allyl ester, which has an acid number of 118.

Example 6 Following substantially the procedure of Example 2, a commercial mixture of C18 24 olefins, comprising predominantly vinyl and vinylidene group-containing a-olefins, is reacted with maleic anhydride. The resulting substituted succinic anhydride is reacted with allyl alcohol and the product is the desired acidic allyl ester, which has an acid number 111.

Examples 7-8 Following substantially the procedures of Examples 4 an 5, acidic allyl esters are prepared from substituted succinic anhydrides in which the substituents are derived respectively from a commercial mixture of C2428 a-olefins and an isomerized derivative thereof. The products have acid numbers of 79.7 and 87.6, respectively.

As previously indicated, the esters of this invention are useful as additives for lubricants, in which they function primarily to decrease fuel comsumption. They can be employed in a variety of lubricants based on diverse oils of lubricating viscosity, including natural and synthetic lubricanting oils and mixtures thereof. These lubricants include crankcase lubricating oils for spark-ignited and compression-ignited internal combustion engines, including automobile and truck engines, two-cycle engines, aviation piston engines, marine and railroad diesel engines, and the like. The esters can also be used in gas engines, stationary power engines and turbines and the like.Automatic transmission fluids, transaxle lubricants, gear lubricants, metal-working lubricants, hydraulic fluids and other lubricating oil and grease compositions can also benefit from the incorporation therein of the esters of this invention.

Natural oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils.

Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins [ e.g., polybutylenes, polypropylenes, propyleneisobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1decenes) ] ; alkylbenzenes [ e.g., dodecylbenzenes, tetradecylbenzenes, dinoylbenzenes, di(2ethylhexyl)benzenes]; polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenyls); and alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic lubricating oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyi-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polyethylene glycol having a molecular weight of 500-1000, diethyl ether of polypropylene glycol having a molecular weight of 1000-1500); and mono- and polycarboxylic esters thereon for example, the acetic acid esters, mixed C3-C8 fatty acid esters and C13 Oxo acid diester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, malonic acid) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-nhexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethyihexanoic acid.

Esters useful as synthetic oils also include those made from C5 to C,2 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxysiloxane oils and silicate oils comprise another useful class of synthetic lubricants; they include tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl) silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(ptert-butylphenyl) silicate, hexa-(4-methyl-2-pentoxy)disiloxane, poly(methyl)siloxanes and poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid esters of phosphoruscontaining acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

Unrefined, refined and rerefined oils can be used in the lubricants of the present invention.

Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations, a petroleum oil obtained directly from distillation or ester oil obtained directly from an esterification process and used without further treatment would be an unrefined oil. Refined oils are similar to the unrefined oils except they have been further treated in one or more purification steps to improve one or more properties. Many such purification techniques, such as distillation, solvent extraction, acid or base extraction, filtration and percolation are known to those skilled in the art. Rerefined oils are obtained by processes similar to those used to obtain refined oils applied to refined oils which have been already used in service.Such rerefined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for removal of spent additives and oil breakdown products.

Another aspect of the present invention is a method of reducing fuel consumption in an internal combustion engine which comprises lubricating said engine during operation with a lubricating composition comprising a major amount of a lubricating oil and a minor amount of at least one ester having the formula r"1(CO0R4)m, (ill) ,wherein R' and m are previously defined with respect to formula I and each R4 is independenty hydrogen or an alkyl or alkenyl radical containing up to about 12 carbon atoms, at least one R2 being alkyl or alkenyl. This genus of esters includes those of formula I and, in addition, the analogous neutral esters and alkanol esters.The neutral esters may be prepared by methods known to those spilled in the art, including methods analagous to those for the preparation of the acidic alkenyl esters wherein, however, at least 2 equivalents and often more of alcohol is used per equivalent of acid or acid derivative. Suitable esters (acidic and neutral) in this genus may also be prepared from alkanols such as methanol, ethanol, the propanols, butanols, hexanols, octanols, decanols, dodecanols and octadecanols (all isomers being included). Pre fer,ed are the alkanols haivng 1 to 4 carbon atoms, especially n-propanol. However, the esters for use in the method of this invention are usually those of formula 1, and especially those in which the R' radical has formula 11.

The following example illustrates the preparation of alkyl esters for use in the method of this invention.

Example 9 A substituted succinic anhydride essentially identical to that of Example 6 is similarly reacted with an equivalent amount of n-propyl alcohol. The product is the desired acidic n-propyl ester; it has an acid number of 126.

The amount of ester used in a lubricant for the purpose of this invention is generally sufficient to provide it with fuel consumption-decreasing properties. This amount will normally be about 0.05% to about 5.0 /0 by weight and preferably between about 0. 1% and about 2.0%.

The invention also contemplates the use of other additives in combination with the esters.

Such additives include, for example, detergents and dispersants of the ash-producing or ashless type, corrosion- and oxidation-inhibiting agents, pour point depressing agents, extreme pressure agents, color stabilizers and anti-foam agents.

The ash-producing detergents are exemplified by oil-soluble neutral and basic salts of alkali or alkaline earth metals with sulfonic acids, carboxylic acids, and organic phosphorus acids characterized by at least one direct carbon-to-phosphorus linkage including those prepared by the treatment of an olefin polymer (e.g., polyisobutene having a molecular weight of 1000) with a phosphorizing agent such as phosphorus trichloride, phosphorus heptasulfide, phosphorus pentasulfide, phosphorus trichloride and sulfur, white phosphorus and a sulfur halide, or phosphorothioic chloride. The most commonly used salts of such acids are those of sodium, potassium, lithium, calcium, magnesium, strontium and barium.

The term "basic salt" is used to designate metal salts wherein the metal is present in stoichiometrically larger amounts than the organic acid radical. The commonly employed methods for preparing the basic salts involve heating a mineral oil solution of an acid with a stoichiometric excess of a metal neutralizing agent such as the metal oxide, hydroxide, carbonate, bicarbonate, or sulfide at a temperature above 50 C and filtering the resulting mass.

The use of a "promoter" in the neutralization step to aid the incorporation of a large excess of metal likewise is known. Examples of compounds useful as the promoter include phenolic substances such as phenol, naphthol, alkylphenols, thiophenol, sulfurized alkylphenols, and condensation products of formaldehyde with phenolic substances; alcohols such as methanol, 2propanol, octyl alcohol, Cellosolve, Carbitol, ethylene glycol, stearyl alcohol and cyclohexyl alcohol; and amines such as aniline, phenylenediamine, phenothiazine, phenyl-fl-napthylamine and dodecylamine. A particularly effective method for preparing the basic salts comprises mixing an acid with an excess of a basic alkaline earth metal neutralizing agent and at least one alcohol promoter, and carbonating the mixture at an elevated temperature such as 60-200 C.

Ashless detergents and dispersants are so called despite the fact that, depending on its constitution, the dispersant may upon combustion yield a non-volatile material such as boric oxide or phosphorus pentoxide; however, it does not ordinarily contain metal and therefore does not yield a metal-containing ash on combustion. Many types are known in the art, and any of them are suitable for use in the lubricants of this invention. The following are illustrative: (1) Reaction products of carboxylic acids (or derivatives thereof) containing at least about 34 and preferably at least about 54 carbon atoms with nitrogen-containing compounds such as amine, organic hydroxy compounds such as phenols and alcohols, and/or basic inorganic materials. Examples of these "carboxylic dispersants" are described in many U.S. patents including 3,272,746; 3,381,022; and 4,234,435.

(2) Reaction products of relatively high molecular weight aliphatic or alicyclic halides with amines, preferably polyalkylene polyamines. These may be characterized as "amine dispersants" and examples thereof are described for example, in U.S. patents 3,275,554; 3,438,757; 3,454,555; and 3,565,804.

(3) Reaction products of alkyl phenols in which the alkyl group contains at least about 30 carbon atoms with aldehydes (especially formaldehyde) and amines (especially polyalkylene polyamines), which may be characterized as "Mannich dispersants". The materials described in U.S. patents 3,368,972; 3,413,347; and 3,980,569 are illustrative.

(4) Products obtained by post-treating the carboxylic, amine or Mannich dispersants with such reagents as urea, thiourea, carbon disulfide, aldehydes, ketones, carboxylic acids, hydrocarbonsubstituted succinic anhydrides, nitriles, epoxides, boron compounds, phosphorus compounds or the like. Exemplary material of this kind are described in a number of U.S. patents.

(5) Interpolymers of.oil-solubilizing monomers such as decyl methacrylate, vinyl decyl ether and high molecular weight olefins with monomers containing polar substituents, e.g., aminoalkyl acrylates or acrylamides and poly-(oxyethylene)-substituted acrylates. These may be charao terized as "polymeric dispersants" and examples thereof are disclosed in U.S. patents 3,329,658; 3,449,250; 3,519,565; 3,666,730; 3,687,849; and 3,702,300.

All of the above-noted patents are incorporated by reference herein for their disclosures of ashless dispersants.

Extreme presure agents and corrosion- and oxidation-inhibiting agents are exemplified by chloroinated aliphatic hydrocarbons such as chlorinated wax; organic sulfides and polysulfides such as benzyl disulfide, bis(chlorobenzyl)disulfide, dibutyl tetrasulfide, sulfurized methyl oleate, sulfurized alkylphenols, sulfurized dipentene, and sulfurized terpenes; phosphosulfurized hydrocarbons such as the reaction product of a phosphorus sulfide with turpentine or methyl oleate; phosphorus esters including principally dihydrocarbon and trihydrocarbon phosphites such as dibutyl phosphite, diphenyl phosphite, dicyclohexyl phosphite, pentylphenyl phosphite, dipentylphenyl phosphite, tridecyl phosphite, distearyl phosphite, dimethyl naphthyl phosphite, oleyi 4pentylphenyl phosphite, polypropylene (molecular weight 500-substituted phenyl phosphite and diisobutyl-substituted phenyl phosphite; metal thiocarbamates such as zinc dioctyldithiocarbam- ate and barium heptylphenyl dithiocarbamate;Group II metal phosphorodithioates such as zinc dicyclohexylphosphorodithioate, zinc dioctylphosphorodithioate, barium di(heptylphenyl)phosphorodithioate, cadmium dinonylphosphorodithioate, and the zinc salt of a phosphorodithioic acid produced by the reaction of phosphorus pentasulfide with an equimolar mixture of isopropyl alcohol and n-hexyl alcohol.

The esters of this invention can be added directly to the lubricant. Preferably, however, they are diluted with a substantially inert, normally liquid organic diluent such as mineral oil, naphtha, benzene, toluene or xylene, to form an additive concentrate. These concentrates usually contain from about 5% to about 50% by weight of the composition of this invention and may contain, in addition, one or more other additives known in the art or described hereinabove.

The following lubricating compositions are typical of those useful in the method of this invention. All amounts except those for mineral oil are exclusive of oil used as diluent. The presence of the above-described esters in these lubricants causes a reduction in fuel consumption when they are used in internal combustion engines.

Parts by weight ingredient Lubricant A B C D E F Mineral oil 99.00 99.00 97.96 99.00 97.56 97.56 Product Example 1 1.00 - - - - Product Example 2 - 1.00 - - - Product Example 3 - - 1.00 - - Product Example 4 - - - 1.00 - Product Example 6 - - - - 1.00 Product Example 9 - - - - - 1.00 Reaction product of polybutenyl (mol. wt. 200) succinic anhydride with ethylene polyamine mixture - - 0.10 - 0.10 0.10 Reaction product of polybutenyl (mol. wt. 1000) succinic anhydride with pentzerythritol 6 ethylene polyamine mixture - - 0.13 - 0.13 0.13 Basic calcium petroleum sulfonate - - 0.05 - 0.05 0.05 Basic magnesium petroleum sulfonate - - 0.06 - 0.06 0.06 Zinc dialkylphosphorodithionte - - 0.11 - 0.11 0.11 Sulfurized alkylphenol - - 0.08 - 0.08 0.08 Sulfurized alkyl cyclohexenecarboxylate - - 0.02 - 0.07 0.02 Ethylene-propylene-diene terpolymer - - 0.75 - 0.75 0.75 Vinyl ether-dialkyl fumarate copolymer - - 0.14 - 0.14 0.14 Silicone anti-foam agent - - 0.011 - 0.001 0.001

Claims (16)

1. An acidic ester having the formula R1(COOR2)mg wherein: R1 is an aliphatic hydrocarbon-based radical free from acetylenic unsaturation and containing from about 10 to about 35 carbon atoms, in which at least 8 carbon atoms are in straight-chain configuration; each R2 is independently hydrogen or an alkenyl radical containing up to about 18 carbon atoms, at least one R2 being hydrogen and at least one being alkenyl; and m is an integer from 2 to 5.

2. An ester according to claim 1 wherein R' is

R3 is a substantially straight-chain alkyl or alkenyl radical containing from about 8 to about 30 carbon atoms, and m is 2.

3. An ester according to claim 2 wherein R2 contains up to about 12 carbon atoms and R3 contains from about 12 to about 25 carbon atoms.

4. An ester according to claim 3 wherein one R2 is an alkenyl radical containing from 2 to 4 carbon atoms.

5. An ester according to claim 4 wherein said R2 is an allyl radical.

6. An additive concentrate comprising a substantially inert, normally liquid organic diluent and from about 20% to about 90% by weight of an ester according to any of claims 1-5.

7. A lubricating composition comprising a major amount of a luricating oil and a minor amount of an ester according to any of claims 1-5.

8. A method of reducing fuel consumption in an internal combustion engine which comprises lubricating said engine during operation with a lubricating composition comprising a major amount of a lubricating oil and a minor amount of at least one ester having the formula R1(C0OR4)rn, wherein: R' is an aliphatic hydrocarbon-based radical free from acetylenic unsaturation and containing from about 10 to about 35 carbon atoms, in which at least 8 carbon atoms are in straight-chain configuration; each R4 is independently hydrogen or an alkyl or alkenyl radical containing up to about 18 carbon atoms, at least one R4 being alkyl or alkenyl; and m is an integer from 2 to 5.

9. A method according to claim 8 wherein R1 is

R3 is a substantially straight-chain Elkyl ou alkeaoyl medical containing from about 8 to atoms 30 carbon atoms, and m is 2.

10. A method according to claim 9 wherein R4 contains up to about 12 carbon atoms and R3 contains from about 12 to about 25 carbon atoms.

11. A method according to claim 10 wherein one R4 contains from 1 to 4 carbon atoms.

12. A method according to claim 1 1 wherein said R4 is alkenyl radical containing from 2 to 4 carbon atoms.

13. A method according to claim 12 wherein said R4 is an allyl radical.

14. A method according to claim 11 wherein said R4 is an alkyl radical.

15. A method according to claim 14 wherein said R4 is the n-propyl radical.

16. The invention in its several novel aspects.