EP3956423B1 - Method for reducing and/or controlling abnormal gas combustion in a marine engine or a controlled-ignition engine - Google Patents

Description

The present invention is disclosed in and by the appended claims.

The present invention relates to the reduction and/or control of abnormal gas combustion in a marine engine or spark ignition engine.

The present invention relates to the use of one or more polymers in a lubricating composition to reduce and/or control the abnormal combustion of gas in a marine engine or a spark ignition engine.

The present invention also relates to a method for reducing and/or controlling the abnormal combustion of gas in a marine engine or a spark ignition engine.

The present invention also relates to the use of a lubricating composition to reduce and/or control the abnormal combustion of gas in a marine engine or a spark ignition engine.

The marine propulsion industry is working to increase the efficiency of gas-powered marine engines, which then find themselves operating in increasingly loaded operating conditions. However, the low rotation speed associated with high loads favors the appearance of abnormal combustion phenomena which could cause destruction of the engine. Pre-ignition, which is characterized by the self-ignition of the air-gas pre-mixture before the normal ignition command, leads to an abnormal increase in the pressure in the cylinder of the gas engine.

In general, the combustion of gas or more precisely of the air/gas mixture in a marine engine or in a spark-ignition engine is initiated by controlled ignition coming either from contact between an electric arc and the gas or from an injection liquid fuel pilot initiating a diffusion flame. Controlled ignition can be carried out directly in the combustion chamber of the marine engine or in a pre-combustion chamber of the marine engine adjacent to the combustion chamber thereof.

We speak of controlled gas combustion when it is initiated directly by controlled ignition. This controlled combustion is generally characterized by a controlled expansion of the flame front through the combustion chamber. Controlled combustion can also be called normal combustion.

With the intake air, droplets (or particles) of lubricating composition are carried into the combustion chamber. The air/gas mixture can self-ignite prematurely before controlled ignition, in particular by self-ignition of the lubricating composition found in the combustion chamber. We are then talking about an uncontrolled pre-ignition phenomenon. This uncontrolled pre-ignition phenomenon results in abnormal combustion of the gas characterized by an uncontrolled expansion of the flame front through the combustion chamber.

This abnormal combustion of the gas generates a sharp increase in temperature and pressure in the combustion chamber. It has been found that these abnormally high temperature and pressure conditions have a significant negative impact on the overall efficiency and performance of a marine engine or spark ignition engine and can go so far as to cause irreversible damage to the internal engine parts: cylinders, pistons, spark plugs and valves in the marine engine or spark ignition engine. WO 2018/202743 A1 describes the use of one or more soluble fatty amines in a lubricating composition to reduce and/or control abnormal gas combustion in a marine engine.

During its research, the Applicant highlighted that the abnormal combustion of the gas can, among other things, result from the self-ignition of droplets (or particles) of lubricating composition which are found in the combustion chamber during the gas compression cycle and/or gas combustion during operation of a marine engine or spark ignition engine.

It therefore appears interesting to limit the presence of said droplets (or particles) of lubricating composition in the combustion chamber, which will limit the aforementioned drawbacks.

“Abnormal combustion” means combustion of the gas in the combustion chamber initiated by uncontrolled pre-ignition. Abnormal combustion results in uncontrolled expansion of the flame front through the combustion chamber. Abnormal combustion also results in a pressure level in the combustion chamber higher than the nominal pressure of the combustion chamber by at least 10%, preferably at least 20%, more preferably at least 30%. combustion of gas in a marine engine or spark-ignition engine. Abnormal combustion is notably due to the self-ignition of droplets (or particles) of lubricating composition carried into the combustion chamber by the intake air.

“Nominal pressure” means the maximum pressure supported by the parts of an engine during controlled combustion of the gas in the combustion chamber. combustion without risk of damage to all or part of the internal parts of the engine, such as cylinders, pistons, spark plugs and valves.

“Gas” means a mixed mixture of gas and air. Within the meaning of the invention, the mixed mixture of gas and air is produced upstream of the combustion chamber or in the combustion chamber before ignition of the marine engine or the spark ignition engine. The step allowing the mixed mixture of gas and air to be obtained is called the pre-mixing step. For the purposes of the invention, the terms "gas" and "mixed mixture of gas and air" have equivalent meanings and can be used to replace one another.

We speak of “homogeneous gas combustion”, when the gas is pre-mixed with air. For the purposes of the invention, the terms “combustion of gas”, “combustion of the mixed mixture of gas and air”, “homogeneous combustion of gas” or “homogeneous combustion of the mixed mixture of gas and air” have equivalent meanings and can be used in place of one another.

The term “marine engine” means a two-stroke or four-stroke marine engine operating solely on gas, also called a pure gas engine, or operating on gas and fuel oil, also called a dual fuel engine. The engines according to the invention are in particular 2-stroke engines or 4-stroke engines in which the lubricant is not pre-mixed with the fuel before its admission.

By “spark ignition engine” we mean gasoline engines which can for example be two-stroke or four-stroke gasoline engines, pure gas engines and low pressure dual fuel gas engines. Typically, the spark ignition engines used in the present invention are Otto cycle engines, as opposed to Diesel cycle engines.

In the context of the present invention, “between xxx and yyy” means that the values xxx and yyy are included in the interval.

• un ou des monomère(s) (A), identiques ou différents, choisi(s) parmi des monomères (C6-C10)alkyl méthacrylate ;
• un ou des monomère(s) (B), identiques ou différents, choisi(s) parmi des monomères (C10-C18)alkyl méthacrylate, les monomères (B) étant différents des monomères (A),

dans une composition lubrifiante comprenant au moins une huile de base pour réduire et/ou contrôler la combustion anormale du gaz dans un moteur.The present invention relates to the use of a copolymer (C) comprising repeating units corresponding to alkyl methacrylate monomers, said monomers comprising at least:

• one or more monomer(s) (A), identical or different, chosen from (C6-C10)alkyl methacrylate monomers;
• one or more monomer(s) (B), identical or different, chosen from (C10-C18) alkyl methacrylate monomers, the monomers (B) being different from the monomers (A),

in a lubricating composition comprising at least one base oil for reducing and/or controlling abnormal gas combustion in an engine.

Advantageously, the use according to the invention makes it possible to limit the presence of droplets (or particles) of lubricating composition in the combustion chamber, thus allowing a reduction and/or control of the abnormal combustion of gas in an engine, said engine which may be a marine engine or a spark ignition engine.

Typically, monomers (A) are different from monomers (B). Thus, the copolymer (C) is obtained from at least one monomer (A) and at least one monomer (B).

Typically, if the copolymer (C) is obtained from two different monomers of the (C10) alkyl methacrylate type, then preferably, one of the two monomers will have a linear C10 alkyl chain (this will then be monomer B) and the other monomer will have a branched C10 alkyl chain (this will then be monomer A).

• un ou des monomère(s) (A), identiques ou différents, choisi(s) parmi des monomères (C6-C9)alkyl méthacrylate et des monomères alkyl méthacrylate présentant une chaîne alkyle ramifiée en C10;
• un ou des monomère(s) (B), identiques ou différents, choisi(s) parmi des monomères (C11-C18)alkyl méthacrylate et des monomères alkyl méthacrylate présentant une chaîne alkyle linéaire en C10,

dans une composition lubrifiante comprenant au moins une huile de base pour réduire et/ou contrôler la combustion anormale du gaz dans un moteur typiquement par la limitation de la présence de gouttelettes (ou particules) de composition lubrifiante dans la chambre de combustion.According to a particular embodiment, the present invention relates to the use of a copolymer (C) comprising repeating units corresponding to alkyl methacrylate monomers, said monomers comprising at least:

• one or more monomer(s) (A), identical or different, chosen from (C6-C9)alkyl methacrylate monomers and alkyl methacrylate monomers having a branched C10 alkyl chain;
• one or more monomer(s) (B), identical or different, chosen from (C11-C18) alkyl methacrylate monomers and alkyl methacrylate monomers having a linear C10 alkyl chain,

in a lubricating composition comprising at least one base oil to reduce and/or control the abnormal combustion of gas in an engine typically by limiting the presence of droplets (or particles) of lubricating composition in the combustion chamber.

Preferably, the monomers (B) comprise at least one (C12)alkyl methacrylate.

The monomers (A) and (B) can be linear or branched.

Preferably, the copolymer (C) of the invention comprises at least two units derived from monomers: a monomer (A) and a monomer (B) which are different.

Preferably, the monomers (B) comprise 50 to 80% by weight of (C12) alkyl methacrylate relative to the total weight of the monomers (B), and preferably 55 to 70% by weight.

Advantageously, the monomers (B) further comprise at least one (C14) alkyl methacrylate. Preferably, the monomers (B) comprise 15 to 40% by weight of (C14) alkyl methacrylate relative to the total weight of the monomers (B), and preferably 20 to 30% by weight.

• 50 à 80% en poids de (C12)alkyle méthacrylate par rapport au poids total des monomères (B), et de préférence de 55 à 70% en poids et
• de 15 à 40% en poids de (C14)alkyle méthacrylate par rapport au poids total des monomères (B), et de préférence de 20 à 30% en poids.

Preferably, the monomers (B) comprise:

• 50 to 80% by weight of (C12)alkyl methacrylate relative to the total weight of the monomers (B), and preferably from 55 to 70% by weight and
• from 15 to 40% by weight of (C14)alkyl methacrylate relative to the total weight of the monomers (B), and preferably from 20 to 30% by weight.

The copolymer (C) according to the invention may also comprise repeating units corresponding to other monomers. Said other monomers may be chosen from (C1-C5)alkyl methacrylates, (C19-C24)alkyl methacrylates, crosslinking monomers, (C1-C24)alkyl acrylates, styrene, etc.

According to a particular embodiment of the invention, the copolymer is substantially free of monomers other than monomers (A) and monomers (B) defined in the present invention, in particular free of (C1-C5) alkyl methacrylates, including by example of methyl methacrylates. According to one embodiment, the copolymer used according to the invention is substantially free of methyl methacrylate. Methyl methacrylate type monomers reduce the solubility of the copolymer in oil, so that this type of monomer is typically used in small quantities or is typically absent from the copolymer according to the invention.

For the purposes of the present invention, and unless otherwise stipulated, the expression “copolymer substantially free of a monomer X” means that the copolymer comprises less than 3.0% by weight of said monomer by weight of said monomer X, preferably less than 0.5% by weight of said monomer X, relative to the total weight of the copolymer.

Preferably, the monomers (A) chosen from (C6-C10) alkyl methacrylate monomers and the monomers (B) chosen from (C10-C18) alkyl methacrylate monomers represent at least 75% by weight of the total weight of the monomers used. used in the copolymer (C), preferably at least 90%, more preferably at least 95%, preferably at least 97%, or better still at least 99% by weight, preferably at least 99.5% by weight.

Preferably, the weight ratio of monomers (B) and monomers (A) in the copolymer is between 99:1 and 10:90.

Advantageously, the monomers (A) comprise at least 50% by weight of (C8) alkyl methacrylate relative to the total weight of monomers (A), preferably at least 75%, more preferably at least 90% and even more preferably at least 99% by weight.

According to a preferred embodiment, the monomers (A) are branched monomers (i.e. where the alkyl part of the alkyl methacrylate is branched) such as for example 2-ethyl-hexyl methacrylate or isodecylmethacrylate.

Advantageously, the monomers (B) may comprise a mixture of at least one (C10) alkyl methacrylate, (C12) alkyl methacrylate, (C14) alkyl methacrylate, (C16) alkyl methacrylate, (C18) alkyl methacrylate, it being understood that the C10 alkyl methacrylate preferably has a linear alkyl chain.

• 0,1 à 2% en poids de (C10)alkyle méthacrylate par rapport au poids de monomères (B), présentant typiquement une chaîne alkyle linéaire en C10 ;
• 50 à 80% en poids de (C12)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 15 à 40% en poids de (C14)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 2 à 12% en poids de (C16)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 0,1 à 1% en poids de (C18)alkyle méthacrylate par rapport au poids de monomères (B).

More advantageously, the monomers (B) may comprise a mixture of at least:

• 0.1 to 2% by weight of (C10)alkyl methacrylate relative to the weight of monomers (B), typically having a linear C10 alkyl chain;
• 50 to 80% by weight of (C12)alkyl methacrylate relative to the weight of monomers (B);
• 15 to 40% by weight of (C14)alkyl methacrylate relative to the weight of monomers (B);
• 2 to 12% by weight of (C16)alkyl methacrylate relative to the weight of monomers (B);
• 0.1 to 1% by weight of (C18)alkyl methacrylate relative to the weight of monomers (B).

• 1 à 2% en poids de (C10)alkyle méthacrylate par rapport au poids de monomères (B), présentant typiquement une chaîne alkyle linéaire en C10 ;
• 55 à 70% en poids de (C12)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 20 à 30% en poids de (C14)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 4 à 10% en poids de (C16)alkyle méthacrylate par rapport au poids de monomères (B) ;
• 0,1 à 0,5% en poids de (C18)alkyle méthacrylate par rapport au poids de monomères (B).

Preferably, the monomers (B) comprise a mixture of at least:

• 1 to 2% by weight of (C10)alkyl methacrylate relative to the weight of monomers (B), typically having a linear C10 alkyl chain;
• 55 to 70% by weight of (C12)alkyl methacrylate relative to the weight of monomers (B);
• 20 to 30% by weight of (C14)alkyl methacrylate relative to the weight of monomers (B);
• 4 to 10% by weight of (C16)alkyl methacrylate relative to the weight of monomers (B);
• 0.1 to 0.5% by weight of (C18)alkyl methacrylate relative to the weight of monomers (B).

In a preferred embodiment, the monomers (B) are linear and are chosen in particular from n-(C10)-alkyl methacrylate, n-(C11)-alkyl methacrylate, lauryl methacrylate (n-(C12)-alkyl methacrylate), n-(C13)-alkyl methacrylate, myristyl methacrylate (n-(C14)-alkyl methacrylate), n-(C15)-alkyl methacrylate, n-(C16)-alkyl methacrylate, n-(C17)-alkyl methacrylate, n -(C18)-alkyl methacrylate.

The ratios of the different monomers can be adapted by those skilled in the art according to the desired characteristics of the copolymer (C). For example, the weight ratio of monomer (B): monomer (A) can be 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5 or 99:1. In particular, the monomers may be present in a (C10-C18)alkyl methacrylate/(C8)alkyl methacrylate weight ratio of 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, or 99 :1.

Preferably, in the context of the invention, the alkyl group of the (C8)alkyl methacrylate is a linear or branched C8 alkyl. Preferably, the (C8)alkyl methacrylate is 2-ethylhexyl methacrylate.

According to a particularly preferred embodiment, the copolymer (C) is a copolymer of 2-ethylhexyl methacrylate and a mixture of monomers comprising (C10)alkyl methacrylate, (C12)alkyl methacrylate, (C14)alkyl methacrylate, (C16) )alkyl methacrylate and (C18)alkyl methacrylate.

According to another preferred embodiment, the copolymer (C) of the invention is a copolymer of a mixture of monomers comprising (C10) alkyl methacrylate, (C12) alkyl methacrylate, (C14) alkyl methacrylate, (C16) alkyl methacrylate and (C18)alkyl methacrylate and a (C8)alkyl methacrylate monomer, wherein the weight ratio of the monomer mixture to the (C8)alkyl methacrylate is from about 99:1 to about 10:90.

• de 5 à 30% de (C8)alkyle méthacrylate ;
• de 40 à 70% en poids de (C12)alkyle méthacrylate ;
• de 12 à 35% en poids de (C14)alkyle méthacrylate ;
• de 1 à 12% en poids de (C16)alkyle méthacrylate ;
• de 0,1 à 15%, de préférence de 0,5 à 10%, plus préférentiellement de 1 à 5%, en poids d'autres méthacrylates,

par rapport au poids total du mélange.According to another preferred embodiment, the copolymer (C) of the invention is a copolymer of a mixture of monomers comprising at least, or preferably consisting of, a (C8) alkyl methacrylate, a (C12) alkyl methacrylate, a (C14) alkyl methacrylate and a (C16) alkyl methacrylate, and are present in the mixture in a ratio by weight of:

• from 5 to 30% of (C8)alkyl methacrylate;
• from 40 to 70% by weight of (C12)alkyl methacrylate;
• from 12 to 35% by weight of (C14)alkyl methacrylate;
• from 1 to 12% by weight of (C16)alkyl methacrylate;
• from 0.1 to 15%, preferably from 0.5 to 10%, more preferably from 1 to 5%, by weight of other methacrylates,

relative to the total weight of the mixture.

Generally, the copolymers (C) according to the invention have a mean radius of gyration (Rg) measured by hydrodynamic chromatography coupled with the measurement of the diffusion of laser light typically in a tetrahydrofuran solvent (HCC-MALS, in English "Hydrodynamic Column"). Chromatography-Multi Angle Light Scattering") between approximately 100 and approximately 200 (nm) Rg, preferably between approximately 120 and approximately 190 (nm), preferably between approximately 130 and approximately 180, preferably between approximately 140 and approximately 170 (nm). nm) Rg.

The copolymer (C) of the invention can be synthesized by all conventional methods of vinyl addition polymerization, known to those skilled in the art, such as for example solution polymerization, precipitation polymerization, dispersion polymerization, including suspension and emulsion polymerization.

In one embodiment, the polymer is formed by suspension polymerization, in which monomers that are not water soluble or poorly water soluble are suspended as droplets in water. The suspended monomer droplets are maintained by mechanical agitation and addition of stabilizers. Polymeric surfactants such as cellulose ethers, poly(vinyl alcohol-co-vinyl acetate), poly(vinyl pyrrolidone) and alkali metal salts of polymer including (meth)acrylic acid and colloids (insoluble in water) inorganic powders such as tricalcium phosphate, hydroxyapatite, barium sulfate, kaolin, and magnesium silicates can be used as a stabilizer. Furthermore, small quantities of surfactants such as sodium dodecylbenzene sulfonate can be used in combination with one or more stabilizers. Polymerization is initiated using an oil-soluble initiator. Suitable initiators include peroxides such as benzoyl peroxide, peroxy esters such as tert-butylperoxy-2-ethylhexanoate, and azo compounds such as 2,2'-azobis(2-methylbutyronitrile). At the end of the polymerization, the solid polymer product can be separated from the reaction medium by filtration and washed with water, acid, base or solvent to remove unreacted monomers or free stabilizers.

In another embodiment, the polymer is formed by emulsion polymerization, one or more monomers are dispersed in an aqueous phase and the polymerization is initiated using a water-soluble initiator. The monomers are typically water insoluble or minimally water soluble, and a surfactant or soap is used to stabilize the monomer droplets in the aqueous phase. Polymerization takes place in swollen micelles and latex particles. Other ingredients that may be present in emulsion polymerization include phase transfer agents such as mercaptans (e.g. dodecyl mercaptan) to control molecular weight, electrolytes for pH control, and small amounts of organic solvent. , preferably a water-soluble organic solvent, including, but not limited to, acetone, 2-butanone, methanol, ethanol, and isopropanol, to adjust the polarity of the aqueous phase. Initiators that can be used include alkali metal or ammonium salts of persulfate such as ammonium persulfate, water-soluble azo compounds such as 2,2'-azobis(2-aminopropane)dihydrochloride, and redox systems such as Fe(ll) and cumene hydroperoxide, and tert-butyl hydroperoxide-Fe(II)-sodium ascorbate. Usable surfactants include in particular anionic surfactants such as fatty acid soaps (for example sodium or potassium stearate), sulfates and sulfonates (for example sodium dodecyl benzene sulfonate), sulfosuccinates (for example dioctyl sodium sulfosuccinate); non-ionic surfactants such as for example octylphenol ethoxylates and linear or branched alcohol ethoxylates; cationic surfactants such as cetyl trimethyl ammonium chloride; and amphoteric surfactants. Anionic surfactants and combinations of anionic surfactants and nonionic surfactants are most often used. Polymeric stabilizers such as poly(vinyl alcohol-co-vinyl acetate) can also be used as surfactants. The solid polymer product free from the aqueous medium can be obtained by different processes including destabilization/coagulation of the final emulsion followed by filtration, solvent precipitation of the polymer from the latex or atomization of the latex.

The polymer can be isolated by conventional methods known to those skilled in the art, such as for example solvent exchange, solvent evaporation, atomization and lyophilization.

• un ou des monomère(s) (A) choisis parmi les (C6-C10)alkyle méthacrylate;
• un ou des monomère(s) (B) choisis parmi les (C10-C18)alkyle méthacrylate;

peuvent être contrôlées en contrôlant les réactifs supplémentaires ajoutés au milieu réactionnel. Ces réactifs inclus, sans y être limité, des systèmes initiateurs et surfactant.The characteristics of the copolymer obtained by combination of alkyl methacrylate monomers, said alkyl methacrylate monomers comprising at least:

• one or more monomer(s) (A) chosen from (C6-C10) alkyl methacrylate;
• one or more monomer(s) (B) chosen from (C10-C18) alkyl methacrylate;

can be controlled by controlling additional reagents added to the reaction medium. These reagents include, but are not limited to, initiator and surfactant systems.

The nature and quantity of initiator systems used in the polymerization medium can influence the properties of the resulting polymer. An initiator system may be a single initiator compound (e.g. persulfate salt) or a mixture of two or more compounds (e.g. hydrogen peroxide and sodium ascorbate). In some examples, the initiator system may include an oxidant, a reductant and optionally a metal salt. The oxidant may be a persulfate, such as for example ammonium persulfate, or a peroxide such as for example hydrogen peroxide (H ₂ O ₂ ) or tert-butyl hydroperoxide (TBHP). The desired copolymer can be obtained, for example, when the polymerization medium comprises tert-butyl hydroperoxide in an amount of about 0.01 to about 0.06 weight percent based on the weight of all monomers in the mixture. In other examples, the mixture may include tert-butyl hydroperoxide in an amount of about 0.01 to about 0.03% by weight of the monomer mixture. In other examples, the mixture further comprises tert-butyl hydroperoxide in an amount of 0.013% by weight of the monomer mixture. Typical initiators of the copolymers of the invention include conventional redox initiators.

In one embodiment, the reductant of the redox initiator system may be ascorbic acid or one of its salts. For example, the polymerization mixture may include sodium ascorbate in an amount of about 0.04 to about 0.1% by weight of the monomer mixture. In other examples, sodium ascorbate may be present in an amount of about 0.08 to about 0.1% by weight of the monomer mixture. In other embodiments, the polymerization mixture comprises sodium ascorbate in an amount of about 0.098% by weight of the monomer mixture.

The initiator system may also include a metal salt. The metal can be any transition metal, such as, for example, iron. In one embodiment, the metal salt of the initiator system may be iron sulfate (FeSO ₄ ). In another embodiment, the metal salt is present in the polymerization mixture in an amount of about 0.0005 to about 0.1% by weight of the monomer mixture. In some examples, the metal salt is added to the polymerization mixture as a solution.

The copolymer can also be in the form of a mixture further comprising a surfactant. In one embodiment, the surfactant may include a sulfonate group. For example, the surfactant may include a dialkyl sulfosuccinate, such as example sodium salt of dioctyl sulfosuccinate. The surfactant can for example be Aerosol ^® OT.

The copolymer may be a random copolymer, a block copolymer or a mixture. In one embodiment, the copolymer is substantially a random copolymer (e.g. greater than 90, 95, 98, or 99% by weight). The copolymer may also be a partially random and partially block copolymer. In this case, the weight ratio of random copolymer to block copolymer is generally 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 or 10:90. The copolymer may also be a substantially block copolymer (e.g. greater than 90, 95, 98, or 99% by weight). In other examples, the copolymer (C) of the invention may comprise other monomers in addition to the monomers (A) chosen from (C6-C10) alkyl methacrylate, and the monomers (B) chosen from (C10 -C18)alkyl methacrylate. These additional monomers may be present in an amount of less than 25% by weight, preferably less than 10% by weight. In one embodiment, the additional monomers are present in an amount of about 0.5 to 10% by weight, or about 1 to 10% by weight, or about 1 to about 5% by weight, or about 5 to 10% by weight. In another embodiment, the monomers are present in an amount less than 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 or about 0.5% by weight. Additional monomers may include, for example, (C1-C5) alkyl methacrylates and (C19-C24) alkyl methacrylates, crosslinkable monomers, (C1-C24) alkyl acrylates, styrene, and other similar monomers.

The copolymer (C) can also be crosslinked. The copolymer can therefore comprise monomeric units which link one or more chains of the polymer backbone. In some examples, the copolymer contains cross-linked monomeric units present in an amount of up to about 5% by weight of the copolymer. According to another embodiment, the copolymer according to the invention is not crosslinked, and is substantially free of monomers which have a crosslinking agent function. According to other embodiments, the mixture of monomers to obtain the copolymer is substantially free of crosslinking agents.

For the purposes of the present invention, the expression "copolymer substantially free of crosslinking agents" means that the copolymer comprises less than 1.0% by weight, preferably less than 0.5% by weight, of monomeric units which bind one or more chains of the polymer backbone, relative to the total weight of the copolymer.

The crosslinked copolymer can be obtained by adding a crosslinking agent when the mixture of monomers comprises such a crosslinking agent. In one embodiment, the crosslinking agent is a diacrylate or dimethacrylate crosslinking agent, such as for example, 1,6-hexanediol dimethacrylate. The mixture may, for example, include a crosslinking agent in an amount up to about 0.005% by weight of the monomers in the mixture.

For example, a method for preparing copolymer (C) is described below. The method includes the polymerization of monomers (A) chosen from (C6-C10) alkyl methacrylate and of monomers (B) chosen from (C10-C18) alkyl methacrylate, advantageously the polymerization of a mixture of monomers comprising C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate and C18 alkyl methacrylate, and C8 alkyl methacrylate, wherein the weight ratio of monomers (B)/monomers (A) in the copolymer is about 99:1 to approximately 10:90 (e.g. 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40 , 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, 99:1).

The method includes: the combination of monomers (A) chosen from (C6-C10) alkyl methacrylate and monomers (B) chosen from (C10-C18) alkyl methacrylate, advantageously the combination of a mixture of monomers comprising C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate and C18 alkyl methacrylate, and C8 alkyl methacrylate in a weight ratio (mixture/C8 alkyl methacrylate) of approximately 10:90, 15:85, 20:80 , 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85 :15, 90:10, 95:5 or 99:1 and initiating the polymerization of the monomers to provide the copolymer.

For example, the monomer ratio and initiators, or initiator system, can be selected as described above. The method may include other compounds to provide a copolymer with the desired properties. For example, the method can also include a surfactant, such as for example Aerosol ^® OT, or a crosslinker, such as for example 1,6-hexanediol dimethacrylate.

The polymerization can be carried out in an aqueous medium or a mixture which includes an aqueous solvent and an organic solvent. For example, the polymerization medium may include a mixture of water and acetone. In one embodiment, the polymerization medium may require an organic solvent. It may be advantageous to include an organic solvent when (C10-C18) alkyl methacrylate monomers are used. Organic solvents which can be used for such a polymerization reaction are known and can be selected by those skilled in the art. Organic solvents which can be used include acetone, 2-butanone, methanol, ethanol and isopropanol.

The copolymer (C) is preferably used in an amount of 50 to 10,000 ppm by weight, preferably 100 to 1000 ppm by weight of active material, relative to the total weight of the lubricating composition.

The lubricating composition of the invention may also comprise detergents, in particular detergents well known to those skilled in the art.

According to a particular embodiment of the invention, the detergents commonly used in the formulation of lubricating compositions are typically anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation is typically a metallic cation of an alkali or alkaline earth metal. The detergents are preferably chosen from alkali or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, as well as phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium. These metal salts may contain the metal in approximately stoichiometric quantities. In this case, we are talking about non-overbased or “neutral” detergents, although they also provide a certain basicity. These “neutral” detergents typically have a BN, measured according to ASTM D2896, less than 200 mg KOH/g, or less than 190, or even less than 180 mg KOH/g. This type of so-called neutral detergents can contribute in part to the BN of the lubricants according to the present invention. For example, neutral detergents of the carboxylate, sulfonate, salicylate, phenate, naphthenate type of alkali and alkaline earth metals, for example calcium, sodium, magnesium, barium, will be used. When the metal is in excess (in quantities greater than the stoichiometric quantity), we are dealing with so-called overbased detergents. Their BN is high, greater than 150 mg KOH/g, typically between 200 and 700 mg KOH/g, generally between 250 and 450 mg KOH/g. The excess metal providing the overbased character to the detergent is in the form of metal salts insoluble in oil, for example carbonate, hydroxide, oxalate, acetate, glutamate, preferably carbonate. In the same overbased detergent, the metals in these insoluble salts may be the same as those in oil-soluble detergents or may be different. They are preferably chosen from calcium, magnesium, sodium or barium. The overbased detergents are thus in the form of micelles composed of insoluble metal salts held in suspension in the lubricating composition by the detergents in the form of metal salts soluble in the oil. These micelles may contain one or more types of insoluble metal salts, stabilized by one or more types of detergents. Overbased detergents comprising a single type of detergent-soluble metal salt will generally be named after the nature of the hydrophobic chain of the latter detergent. Thus, they will be called carboxylate, phenate, salicylate, sulfonate, naphthenate type depending on whether this detergent is respectively a carboxylate, phenate, salicylate, sulfonate, or naphthenate. Overbased detergents will be called mixed type if the micelles include several types of detergents, different from each other by the nature of their hydrophobic chain. For use in the lubricating compositions according to the present invention, the oil-soluble metal salts will preferably be carboxylates, phenates, sulfonates, salicylates, and mixed phenate - sulfonate detergents and/or salicylates of calcium, magnesium, sodium or barium. The insoluble metal salts providing the overbased character are carbonates of alkali and alkaline earth metals, preferably calcium carbonate or magnesium carbonate. The overbased detergents used in the lubricating compositions according to the present invention will preferably be carboxylates, phenates, sulfonates, salicylates and mixed phenate - sulfonate - salicylate detergents, overbased on calcium carbonate or magnesium carbonate.
Preferably, the lubricating composition comprises from 4 to 30% by weight of detergents relative to the total weight of the lubricating composition, preferably from 5 to 25%, for example from 6 to 25%.

Preferably, the lubricating composition has a BN determined according to standard ASTM D-2896 less than or equal to 70 milligrams of potash per gram of lubricant, more preferably less than or equal to 60 milligrams.

Advantageously, the lubricating composition has a BN determined according to the ASTM D-2896 standard of between 3 and 50 milligrams of potash per gram of lubricant, preferably between 4 and 40 milligrams of potash per gram of lubricant.

According to a particular embodiment of the invention, the base oil included in the lubricating composition is chosen from oils of mineral, synthetic or vegetable origin as well as their mixtures.

Mineral or synthetic oils typically used in the application belong to one of the classes defined in the API classification as summarized in the table below. Table 1 Saturates content Sulfur content Viscosity index Group 1 Mineral oils <90% > 0.03% 80 ≤ VI < 120 Group 2 Hydrocracked oils ≥90% ≤ 0.03% 80 ≤ VI < 120 Group 3 Hydroisomerized oils > 90% ≤ 0.03% ≥120 Group 4 DTP Group 5 Other bases not included in bases groups 1 to 4

Group 1 mineral oils can be obtained by distillation of selected naphthenic or paraffinic crudes and then purification of these distillates by processes such as solvent extraction, solvent or catalytic dewaxing, hydrotreatment or hydrogenation.

Group 2 and 3 oils are obtained by more severe purification processes, for example a combination of hydrotreating, hydrocracking, hydrogenation and catalytic dewaxing.

Synthetic Group 4 and 5 base oils can be chosen from esters, silicones, glycols, polybutene, polyalphaolefins (PAO), alkylbenzene or alkylnaphthalene. The polyalphaolefins used as base oils are for example obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100°C is between 1.5 and 15 mm ² .s ^-1 according to ASTM D445. Their average molecular mass is generally between 250 and 3000 according to the ASTM D5296 standard.

The base oils can also be oils of natural origin, for example esters of alcohols and carboxylic acids, which can be obtained from natural resources such as sunflower oil, rapeseed oil, palm oil, soy etc.

These base oils can be used alone or in a mixture. Mineral oil can be combined with synthetic oil.

Cylinder oils for 2-stroke marine diesel engines typically have a viscosimetric grade SAE-40 to SAE-60, generally SAE-50 equivalent to a kinematic viscosity at 100°C of between 16.3 and 21.9 mm ² /s.

Grade 40 oils have a kinematic viscosity at 100°C of between 12.5 and 16.3 mm ² /s.

Grade 50 oils have a kinematic viscosity at 100°C of between 16.3 and 21.9 mm ² /s.

Grade 60 oils have a kinematic viscosity at 100°C of between 21.9 and 26.1 mm ² /s.

According to professional practice, cylinder oils for 2-stroke marine diesel engines can be formulated to have a kinematic viscosity at 100°C of between 18 and 21.5, preferably between 19 and 21.5 mm ² /s.

This viscosity can be obtained by mixing additives and base oils, for example containing Group 1 mineral bases such as Neutral Solvent bases (for example 500NS or 600 NS) and Brightstock and/or Group 2 mineral bases. Any other combination of mineral, synthetic or plant-based bases having, when mixed with the additives, a viscosity compatible with the SAE-50 grade can be used.

According to one embodiment, the lubricating composition comprises at least 40% by weight of base oil(s), preferably at least 50% by weight of base oil(s), more preferably at least 60% by weight of base oil(s), or even at least 70% by weight of base oil(s), relative to the total weight of the lubricating composition.

Typically, a classic formulation of cylinder lubricant for slow 2-stroke marine diesel engines is of grade SAE 40 to SAE 60, preferably SAE 50 (according to the SAE J300 classification) and comprises at least 50% by weight of one or more oils of lubricating base of mineral and/or synthetic origin, suitable for use in marine engines, for example, API class Group 1 and/or Group 2, that is to say obtained by distillation of selected crudes then purification of these distillates by processes such as solvent extraction, solvent or catalytic dewaxing, hydrotreatment or hydrogenation. For Group 1 base oils, their Viscosity Index (VI) is between 80 and 120; their sulfur content is greater than 0.03% and their saturated content less than 90%. For Group 2 base oils, their Viscosity Index (VI) is between 80 and 120; their sulfur content is less than or equal to 0.03% and their saturated content greater than or equal to 90%.

According to a particular embodiment of the invention, the lubricating composition may further comprise one or more thickening additives whose role is to increase the viscosity of the composition, both hot and cold, or additives improving the index of viscosity (VI).

Preferably, these additives are most often polymers of low molecular weight, of the order of 2000 to 50,000 Dalton (Mn).

They can be chosen from PIB (around 2000 dalton), poly-Acrylate or Poly Methacrylates (around 30000 dalton), Olefin-copolymers, Olefin and Alpha Olefin copolymers, EPDM, Polybutenes , High molecular weight poly-Alphaolefins (viscosity 100°C > 150), Styrene-Olefin copolymers, hydrogenated or not.

According to a particular embodiment of the invention, the base oil(s) included in the lubricating composition according to the invention can be partially or totally substituted by these additives.

Therefore, the polymers used to partially or completely substitute one or more of the base oils are preferably the aforementioned thickeners of the PIB type (for example marketed under the name Indopol H2100).

According to a particular embodiment of the invention, the lubricating composition may also comprise at least one anti-wear additive.

Preferably, the anti-wear additive is zinc dithiophosphate or DTPZn. We also find in this category various phosphorus, sulfur, nitrogen, chlorine and boron compounds.

There is a wide variety of anti-wear additives, but the most used category is that of phospho-sulfur additives such as metal alkylthiophosphates, in particular Zinc alkylthiophosphates, and more specifically Zinc dialkyldithiophosphates or DTPZn.

Amine phosphates and polysulphides, particularly sulfur olefins, are also commonly used anti-wear additives.

We also usually encounter in lubricating compositions anti-wear and extreme pressure additives of the nitrogen and sulfur type, such as for example metallic dithiocarbamates, in particular molybdenum dithiocarbamate. Glycerol esters are also anti-wear additives. Examples include mono, di and trioleates, monopalmitates and monomyristates.

According to a particular embodiment of the invention, the lubricating composition may also comprise at least one dispersant.

Dispersants are well-known additives used in the formulation of lubricating compositions, particularly for application in the marine sector. Their primary role is to maintain in suspension the particles initially present or appearing in the lubricating composition during its use in the engine. They prevent their agglomeration by playing on steric hindrance. They may also have a synergistic effect on neutralization.

Dispersants used as lubricant additives typically contain a polar group, associated with a relatively long hydrocarbon chain, containing generally from 50 to 400 carbon atoms. The polar group typically contains at least one nitrogen, oxygen or phosphorus element.

Compounds derived from succinic acid are dispersants particularly used as lubrication additives. In particular, succinimides are used, obtained by condensation of succinic anhydrides and amines, succinic esters obtained by condensation of succinic anhydrides and alcohols or polyols.

These compounds can then be treated with various compounds including sulfur, oxygen, formaldehyde, carboxylic acids and compounds containing boron or zinc to produce, for example, borated succinimides or zinc-blocked succinimides.

Mannich bases, obtained by polycondensation of phenols substituted with alkyl groups, formaldehyde and primary or secondary amines, are also compounds used as dispersants in lubricants.

We could use a dispersant in the succinimide PIB family, for example borated or zinc-blocked.

According to a particular embodiment of the invention, the lubricating composition may further comprise all types of functional additives adapted to their use, for example anti-foam additives, which may for example be polar polymers such as polymethylsiloxanes, polyacrylates, anti-foam additives. oxidants and/or anti-rust agents, for example organometallic detergents or thiadiazoles. These are known to those skilled in the art.

According to the present invention, the compositions of the lubricants described refer to the compounds taken separately before mixing, it being understood that said compounds may or may not retain the same chemical form before and after mixing. Preferably, the lubricants according to the present invention obtained by mixing the compounds taken separately are not in the form of emulsion or microemulsion.

• les amines de formule (I) :
  
          R₁(NR₂)-R₃)_q-NR₄R₅,     (I)
  
  dans laquelle,
  • R₁ représente un groupement hydrocarboné saturé ou insaturé, linéaire ou ramifié, comprenant au moins 12 atomes de carbone, et optionnellement au moins un hétéroatome choisi parmi l'azote, le soufre ou l'oxygène,
  • R₂, R₄ ou R₅ représente indépendamment, un atome d'hydrogène ou un groupement hydrocarboné saturé ou insaturé, linéaire ou ramifié, et comprenant optionnellement au moins un hétéroatome choisi parmi l'azote, le soufre ou l'oxygène,
  • R₃ représente un groupement hydrocarboné saturé ou insaturé, linéaire ou ramifié, comprenant un ou plusieurs atome(s) de carbone, et comprenant optionnellement au moins un hétéroatome choisi parmi l'azote, le soufre ou l'oxygène, de préférence l'oxygène,
  • q est supérieur ou égal à 0, de préférence q est supérieur ou égal à 1, plus préférentiellement est un entier compris entre 1 et 10, encore plus préférentiellement entre 1 et 6, avantageusement est choisi parmi 1, 2 ou 3 ;
• un mélange de polyalkylamines grasses comprenant une ou plusieurs polyalkylamines de formules (III) et/ou (IV) :
  
  
  dans lesquelles
  • R, identique ou différent, représente un groupe alkyle, linéaire ou ramifié, comprenant de 8 à 22 atomes de carbone,
  • n et z, indépendamment l'un de l'autre, représentent 0, 1, 2 ou 3, et
  • quand z est supérieur à 0, o et p, indépendamment l'un de l'autre, représentent 0, 1 ,2 ou 3, ledit mélange comprenant au moins 3% en poids de composés ramifiés tels que au moins un de n ou z est supérieur ou égal à 1, ou de leurs dérivés, ou
• les mélanges d'amines grasses de formules (I), (III) et/ou (IV).

De telles amines grasses sont notamment décrites dans la demande internationaleWO2018202743.The lubricating compositions according to the invention may also comprise at least one fatty amine chosen from:

• the amines of formula (I):
  
  R ₁ (NR ₂ )-R ₃ ) _q -NR ₄ R ₅ , (I)
  
  in which,
  • R ₁ represents a saturated or unsaturated hydrocarbon group, linear or branched, comprising at least 12 carbon atoms, and optionally at least one heteroatom chosen from nitrogen, sulfur or oxygen,
  • R ₂ , R ₄ or R ₅ independently represents a hydrogen atom or a saturated or unsaturated, linear or branched hydrocarbon group, and optionally comprising at least one heteroatom chosen from nitrogen, sulfur or oxygen,
  • R ₃ represents a saturated or unsaturated hydrocarbon group, linear or branched, comprising one or more carbon atom(s), and optionally comprising at least one heteroatom chosen from nitrogen, sulfur or oxygen, preferably oxygen ,
  • q is greater than or equal to 0, preferably q is greater than or equal to 1, more preferably is an integer between 1 and 10, even more preferably between 1 and 6, advantageously is chosen from 1, 2 or 3;
• a mixture of fatty polyalkylamines comprising one or more polyalkylamines of formulas (III) and/or (IV):
  
  
  in which
  • R, identical or different, represents an alkyl group, linear or branched, comprising from 8 to 22 carbon atoms,
  • n and z, independently of each other, represent 0, 1, 2 or 3, and
  • when z is greater than 0, o and p, independently of each other, represent 0, 1, 2 or 3, said mixture comprising at least 3% by weight of branched compounds such that at least one of n or z is greater than or equal to 1, or their derivatives, or
• mixtures of fatty amines of formulas (I), (III) and/or (IV).

Such fatty amines are described in particular in international application WO2018202743.

Those skilled in the art will know how to adapt the quantity of functional additives according to the specific use of the lubricating composition.

According to a particular embodiment, the lubricating composition used in the invention comprises at least one additive chosen from detergents, dispersants, and their mixture.

According to a specific embodiment, the lubricating composition used in the invention comprises one or more detergents and one or more dispersants. According to this embodiment, if the lubricating composition is used in a marine engine, then the mass proportion of detergent(s) will preferably be greater than the mass proportion of dispersant(s) and if the lubricating composition is used in a marine engine. controlled ignition, then the mass proportion of detergent(s) will preferably be less than the mass proportion of dispersant(s).

The use of the copolymer (C) according to the invention in a lubricating composition makes it possible to reduce and/or control the entrainment of droplets (or particles) of lubricating composition with the intake air, thus limiting the presence of lubricating composition in the combustion chamber which reduces and/or controls abnormal combustion of gas in an engine, such as a marine engine or a spark ignition engine, particularly in a marine engine.

According to a particular embodiment of the invention, the engine is a marine engine, in particular a pure gas or dual fuel engine, two-stroke or four-stroke.

According to a particular embodiment of the invention, the use of the copolymer (C) according to the invention makes it possible to reduce and/or control the abnormal combustion of gas in an engine, preferably a marine engine, from the automobile -inflammation of the lubricating composition.

According to a particular embodiment of the invention, the use of the copolymer (C) according to the invention in a lubricating composition makes it possible to reduce and/or control the abnormal combustion of any type of gas, in particular gas having a number of low methane (NM), preferably a methane number less than 80, more preferably less than 60.

In general, it is known that the lower the methane number (NM) of the gas, the more accentuated the phenomenon of abnormal combustion of the gas.

The different embodiments, variants, preferences and advantages described above can be taken separately or in combination for the implementation of the first object of the invention.

Another object of the invention covers a method for reducing the quantity of lubricating composition in the combustion chamber of an engine, the method comprising the use of a copolymer (C) in said lubricating composition. The engine is as defined above, in particular it may be a marine engine or a spark-ignition engine, preferably the engine is a marine engine.

The copolymer (C) and the lubricating composition are as defined above.

The different embodiments, preferences, advantages, variants described for the first subject of the invention covering the use of the copolymer (C) in a lubricating composition to reduce and/or control the abnormal combustion of gas in an engine , apply separately or in combination to the other objects of the invention covering the process described above.

The present invention also relates to the use of the copolymer (C) or the lubricating composition according to the invention to reduce and/or control the abnormal combustion of gas in an engine, preferably a marine engine, in particular a pure gas marine engine. or dual fuel, two-stroke or four-stroke.

The present invention also relates to the use of the copolymer (C) or the lubricating composition according to the invention to reduce and/or control the abnormal combustion of gas in an engine, preferably a marine engine, resulting from self-ignition of the lubricating composition.

The use according to the invention relates to any type of gas, in particular gas having a low methane number (NM), preferably a methane number less than 80, more advantageously less than 60.

The present invention also relates to a method for reducing and/or controlling abnormal gas combustion in an engine comprising lubricating the engine with a lubricating composition according to the invention or a lubricating composition comprising at least one copolymer (C) according to the invention. The engine being as defined above, preferably, the engine is a marine engine, in particular of the pure gas or dual fuel type, two-stroke or four-stroke.

The present invention also relates to a method for reducing and/or controlling the abnormal combustion of gas in an engine resulting from the self-ignition of the lubricating composition comprising the lubrication of the engine with a lubricating composition according to the invention or a lubricating composition comprising at least one copolymer (C) according to the invention. The engine being as defined above, preferably, the engine is a marine engine, in particular of the pure gas or dual fuel type, two-stroke or four-stroke.

The methods according to the invention relate to any type of gas, in particular gas having a low methane number (NM), preferably a methane number less than 80, more advantageously less than 60.

The invention is illustrated by the following examples given without limitation.

There figure 1 translates the percentage of pre-ignition by the lubricant as a function of the intake temperature.

There figure 2 translates the frequency of abnormal combustion as a function of the intake temperature.

The test to measure the frequency of pre-ignitions of the gas mixture when using different lubricating compositions was carried out in a single-cylinder gas engine comprising a combustion chamber with a bore of 108 mm and a stroke of 115 mm respectively. with a compression ratio of 11.4, corresponding to a single-cylinder displacement of 1054 cm ³ .

The rotation speed of the single-cylinder gas engine is 1000 rpm. The operating point retained is equivalent to an Average Indicated Pressure of 23 bar, corresponding to a representative application of high engine load.
The single-cylinder gas engine has a spark plug ignition system with “open chamber” technology in order to be able to repeat the ignition command precisely on each engine combustion cycle. The single-cylinder gas engine also has a cylinder pressure sensor in order to measure the evolution of the pressure in the cylinder, determine the maximum cylinder pressure values at each engine cycle and calculate the energy release produced during the combustion cycle. Prior to the test to measure the abnormal combustion of a gas in the combustion chamber, a mixture is prepared consisting of gas having a methane number equivalent to 70% and air comprising nitrogen and oxygen with a excess air ratio (air/gas) of 1.6 compared to the stoichiometric ratio used for gas combustion. In order to see the effect of the lubricant on the phenomenon of abnormal combustion, the air/gas mixture is heated to a temperature of approximately 55°C then gradually increased, in particular up to a maximum temperature of 110°C, and admitted compressed to 3.6 bar in the single-cylinder gas engine.

The lubricating compositions according to the following Table 2 were tested. Table 2 Comparative example Example according to the invention Base oil (% by weight) 89.08 87.08 Copolymer composition (C) - 2% by weight of a base oil composition comprising 0.1% by weight of copolymer solids (C) Additives 10.92 10.92

The copolymer (C) is obtained according to the following protocol:
In a quadricol equipped with a stirrer, a condenser, a thermocouple and a nitrogen purge, 645.5 g of water and 8.7 g of Aerosol ^® OT are added. Agitation is set at 200 rpm (revolution per minute) and the nitrogen purge is started. To the reaction mixture are added 240 g of C10-C18 alkyl methacrylate, 60 g of 2-ethylhexyl methacrylate and 129.9 g of acetone. The reaction medium is heated to 43°C via a water bath set at 45°C. When the reaction medium has reached 43°C, 0.04 g of t-butyl hydroperoxide in 7.5 g of water are added. After 5 minutes, 0.29g of sodium ascorbate dissolved in 7.5g of water and 0.60g of a 0.25% solution of iron sulfate ion hexahydrate are added. The nitrogen purge is replaced by nitrogen inerting. The reaction continues for 5 hours, then the reaction mixture is allowed to cool to room temperature and isolated.

Example 1. Experimental protocol for measuring the frequency of pre-ignition initiations by the lubricant before the ignition command of the single-cylinder gas engine and the frequency of abnormal combustion generated by the pre-ignition of the lubricant

In order to determine the effect of the lubricant on the abnormal combustion phenomenon, we measure on the single-cylinder gas engine the frequency of pre-ignition initiations due to the lubricant before the main ignition command of the engine as well as the frequency of pre-ignition by the lubricant generating an increase in cylinder pressure corresponding to abnormal combustion.

To determine the frequency of pre-ignition initiations due to the lubricant, the heat release law is measured for each combustion cycle. The ignition control is set repeatably at -4° crankshaft angle before top dead center. Thus, for each cycle, each increase in energy release beginning before -6° crankshaft angle is counted as an abnormal pre-ignition generated by the lubricant before the main ignition command of the engine. The test is started at an inlet temperature of the air-gas premix set at approximately 55°C. Throughout the test, the temperature is gradually increased until a pre-ignition event is observed. All of these abnormal events compared to all of the 15,000 combustion events recorded during the 30 minutes of each test gives the frequency of abnormal pre-ignition generated by the lubricant before the main ignition command of the engine.

To determine the frequency of pre-ignition by the lubricant generating an increase in cylinder pressure corresponding to abnormal combustion, the maximum pressure reached in the cylinder is measured for each cycle. The test is started at an inlet temperature of the air-gas premix set at approximately 55°C. Throughout the test, the temperature is gradually increased until a pre-ignition event is observed. The operating point of the single-cylinder gas engine is fixed, and generates a normal maximum cylinder pressure of 80 bar. In the event of abnormal combustion, it is considered that the maximum cylinder pressure of the combustion chamber must exceed the limit of 120 bar for the cycle to be counted as abnormal pre-ignition generated by the lubricant. All of these abnormal events compared to all of the 15,000 combustion events recorded during the 30 minutes of each test gives the frequency of abnormal pre-ignition generated by the lubricant.

This test makes it possible to highlight, among other things, the effect of the lubricant on the resistance to the phenomenon of pre-ignition of the air/gas mixture due to the self-ignition of the lubricant before the normal ignition command and the effect of the lubricant on the intensity of the maximum cylinder pressure peaks in the event of abnormal combustion, representing the energy released by the abnormal combustion.

The lubricating compositions according to Table 2 were tested.

The results shown in the figure 1 are generated from temperature conditions in which an abnormal combustion phenomenon is initiated and reflect the intensity of the abnormal combustion phenomenon.

The results shown in the figure 2 reflect the temperature conditions from which the abnormal combustion phenomenon appears and the frequencies of appearance of this phenomenon over a given cycle.

To the figure 1 the pre-ignition frequency is measured by the lubricating composition. It is observed that this percentage decreases for the composition according to the invention. Furthermore, we note that the pre-ignition by the lubricant starts at a higher temperature for the lubricating compositions according to the invention.

To the figure 2 , we measure the frequency of abnormal combustion as a function of the inlet temperature of the air-gas pre-mixture. It is observed that the frequency decreases for the composition according to the invention, that is to say that the frequency of pre-ignition initiations, also called abnormal combustion, starts at a higher temperature unlike the comparative composition.

Therefore, from the results of figures 1 And 2 , we observe that the compositions according to the invention make it possible both to limit the appearance of abnormal combustion phenomena and at the same time to limit its intensity, unlike the comparative composition.

Claims (10)

1. Use of a copolymer (C) comprising repeat units corresponding to alkyl methacrylate monomers, said monomers comprising at least:

   - one or more monomer(s) (A), the same or different, selected from among (C6-C10) alkyl methacrylate monomers;

   - one or more monomer(s) (B), the same or different, selected from among (C10-C18) alkyl methacrylate monomers, said monomers (B) differing from said monomers (A);

   in a lubricant composition comprising at least one base oil for reducing and/or controlling abnormal gas combustion in an engine, preferably a marine engine or controlled-ignition engine.
2. The use according to claim 1, wherein the copolymer (C) comprises repeat units corresponding to:

   - monomers (A), the same or different, selected from among (C6-C10) alkyl methacrylate monomers;

   - monomers (B), the same or different, selected from among (C10-C18) alkyl methacrylate monomers, said monomers (B) comprising at least one (C12) alkyl methacrylate monomer and/or at least one (C14) alkyl methacrylate monomer.
3. The use according to claim 1 or 2, wherein monomers (A) and monomers (B) represent at least 75 weight % of the total of monomers used to prepared copolymer (C), preferably they represent at least 90 %, more preferably at least 95 %, further preferably at least 97 %, better still at least 99 %, preferably at least 99.5 weight %.
4. The use according to any of claims 1 to 3, wherein the weight ratio of monomers (B) to monomers (A) is between about 99:1 and about 10:90.
5. The use according to any of claims 1 to 4, wherein monomers (A) are branched and are preferably 2-ethyl-hexyl methacrylate and/or monomers (B) are linear, preferably monomers (B) are a mixture of C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate, and C18 alkyl methacrylate.
6. The use according to any of claims 1 to 5, wherein copolymer (C) comprises units corresponding to C10 alkyl methacrylate, C12 alkyl methacrylate, C14 alkyl methacrylate, C16 alkyl methacrylate, C18 alkyl methacrylate, and C8 alkyl methacrylate monomers.
7. The use according to any of claims 1 to 6, wherein the lubricant composition comprises from 50 to 10000 ppm by weight of active material of copolymer (C) relative to the total weight of the composition.
8. The use according to any of the preceding claims, wherein the engine is a marine engine, preferably a pure gas or dual-fuel marine engine, two-stroke or four-stroke.
9. The use according to any of the preceding claims, for reducing the quantity of lubricant composition in the combustion chamber of the engine, preferably of the marine engine.
10. Use of a lubricant composition comprising:

    - at least one base oil;

    - at least one copolymer (C) such as defined in any of claims 1 to 7

    to:

    - reduce and/or control abnormal gas combustion in an engine, preferably in a marine engine or controlled-ignition engine, preferably to reduce and/or control abnormal gas combustion in an engine, preferably a marine engine, in particular a pure gas or dual-fuel engine, two stroke or four stroke; and/or

    - reduce the quantity of lubricant composition in the combustion chamber of an engine, preferably a marine engine or controlled-ignition engine, preferably a marine engine; and/or

    - reduce and/or control abnormal gas combustion resulting from auto-ignition of the lubricant composition in an engine, preferably a marine engine or controlled-ignition engine, preferably a marine engine and in particular a pure gas or dual-fuel engine, two stroke or four stroke.

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