Lubricating oil composition for ammonia-fueled internal combustion engine

Abstract

A lubricating oil composition for an ammonia-fueled internal combustion engine, said composition comprising: a lubricant base oil that contains at least one selected from the group consisting of ester base oils, mineral base oils, and synthetic base oils other than said ester base oils, and that has an ester base oil content of 3-100 mass% relative to the total lubricant base oil amount; and an anti-wear agent that is a zinc dialkyldithiophosphate represented by a specific formula, the amount of which in terms of elemental phosphorus based on the total mass of the lubricating oil composition is 100-3000 mass ppm.

Description

Lubricating oil composition for ammonia-fueled internal combustion engines

[0001] The present invention relates to a lubricating oil composition for an ammonia-fueled internal combustion engine.

[0002] In recent years, reducing greenhouse gas (GHG) emissions to combat global warming has become a major challenge, and in the maritime sector in particular, the goal is to achieve net-zero GHG emissions by 2050 in both international and domestic shipping. To achieve this goal, it is considered essential to improve the fuel efficiency of internal combustion engines and to use low-carbon fuels, and the use of carbon-free fuels such as hydrogen and ammonia as fuel for internal combustion engines is being considered. Among these fuels for internal combustion engines, ammonia is expected to be a major decarbonization fuel, especially in the maritime sector where long-distance transport is the main focus, because its fuel density is higher than that of hydrogen.

[0003] In internal combustion engines that use ammonia as fuel, just as in conventional internal combustion engines that use hydrocarbons as fuel, it is necessary to use lubricating oil compositions to lubricate the sliding parts and fuel pumps, and the use of various lubricating oil compositions has been proposed.

[0004] For example, Japanese Patent Publication No. 2023-520938 (Patent Document 1) discloses an engine composition that is partially or completely fueled by bio-derived fuels, ethanol or methanol, ammonia, gaseous fuels, residual fuels, marine residual fuels, low-sulfur marine residual fuels, marine distillate fuels, low-sulfur marine distillate fuels, or high-sulfur fuels. Thus, Patent Document 1 exemplifies an ammonia-fueled engine as one of the various types of engines. Furthermore, in paragraph

[0054] , etc., Patent Document 1 exemplifies C8 primary dialkyldithiophosphate zinc (ZnDTP) as one of the wear-resistant additives that the lubricating oil composition may further contain.

[0005] Furthermore, Japanese Patent Publication No. 2024-056645 (Patent Document 2) discloses an invention relating to the use of metal alkanates such as zinc neodecanoate as additives in a lubricant composition having good wear resistance for application in large diesel engines, and paragraph

[0151] of that document discloses that the lubricant composition described in the document may be useful as a lubricant for hydrogen engines and ammonia engines, etc. Paragraph

[0139] of Patent Document 2 exemplifies zinc dialkyldithiophosphate as a useful wear-resistant agent.

[0006] Japanese Patent Publication No. 2023-520938, Japanese Patent Publication No. 2024-056645

[0007] The inventors investigated using conventional lubricating oil compositions used in general internal combustion engines for internal combustion engines that use ammonia as fuel. However, they found that when a lubricating oil composition containing zinc dialkyldithiophosphate, which is widely used as an anti-wear agent in the field of internal combustion engines and is considered particularly important in terms of availability and the balance between anti-wear properties and antioxidant properties, is used as a lubricating oil composition for an ammonia-fueled internal combustion engine, gel formation may occur in the system during use, leading to problems such as a decrease in the fluidity of the lubricating oil composition. Thus, the inventors found that simply applying lubricating oil compositions used in other engines is not necessarily sufficient to prevent gel formation in ammonia-fueled internal combustion engines.

[0008] In contrast, while Patent Documents 1 and 2 state that the lubricating oil compositions described in those documents can be used in engines that use ammonia as fuel, they do not mention the problems such as the formation of gel that may occur when a lubricating oil composition using zinc dialkyldithiophosphate, in which all alkyl groups in the compound are C8 alkyl groups, is used as an anti-wear agent in an internal combustion engine that uses ammonia as fuel. Nor do they consider any means to solve such problems.

[0009] The present invention aims to provide a lubricating oil composition for an ammonia-fueled internal combustion engine that can highly prevent the generation of gel during use.

[0010] As a result of diligent research to achieve the above objective, the present inventors have discovered that by providing a lubricating oil composition for ammonia-fueled internal combustion engines containing: a lubricating oil base oil comprising at least one selected from the group consisting of ester base oil, mineral oil base oil, and synthetic base oil other than the ester base oil, wherein the ester base oil content is 3% by mass or more and 100% by mass or less based on the total amount of the lubricating oil base oil; and an anti-wear agent which is zinc dialkyldithiophosphate represented by the following formula (1), wherein the phosphorus element content, on an equivalent basis based on the total mass of the lubricating oil composition, is 100 ppm by mass or more and 3000 ppm by mass or less; it is possible to highly prevent gel formation during use while utilizing zinc dialkyldithiophosphate having only C8 alkyl groups as alkyl groups, and thus have completed the present invention.

[0011] In other words, the present invention provides the following embodiments.

[0012] [1] A lubricating oil base oil comprising at least one selected from the group consisting of ester base oils, mineral oil base oils, and synthetic base oils other than ester base oils, wherein the content of the ester base oil is 3% by mass or more and 100% by mass or less based on the total amount of lubricating oil base oil, and the content of phosphorus element on a basis of the total mass of the lubricating oil composition is 100 ppm by mass or more and 3000 ppm by mass or less, as shown in the following formula (1):

[0013]

[0014] [In formula (1), R ａ , R ｂ , R ｃ and R ｄ Both represent an alkyl group having 8 carbon atoms. A lubricating oil composition for an ammonia fuel internal combustion engine comprising a wear-resistant agent which is zinc dialkyldithiophosphate represented by ] and .

[0015] [2] The lubricating oil composition according to [1], wherein all alkyl groups of the zinc dialkyldithiophosphate are primary alkyl groups.

[0016] [3] The lubricating oil composition according to [1] or [2], further comprising an ashless dispersant.

[0017] [4] A lubricating oil composition according to any one of [1] to [3], further containing a metal-based detergent.

[0018] According to the present invention, it is possible to provide a lubricating oil composition for an ammonia-fueled internal combustion engine that can highly prevent the generation of gel during use.

[0019] The present invention will be described in detail below with reference to its preferred embodiments. In this specification, unless otherwise specified, the notation "X to Y" for numerical values ​​X and Y means "X or greater and Y or less". If a unit is attached only to the numerical value Y in such notation, that unit shall also apply to the numerical value X.

[0020] The lubricating oil composition for an ammonia-fueled internal combustion engine of the present invention comprises a lubricating oil base oil containing at least one selected from the group consisting of ester base oils, mineral oil base oils, and synthetic base oils other than ester base oils, wherein the content of the ester base oil is 3% by mass or more and 100% by mass or less based on the total amount of lubricating oil base oil, and a phosphorus element content of 100 ppm by mass or more and 3000 ppm by mass or less based on the total mass of the lubricating oil composition, as shown in the following formula (1):

[0021]

[0022] [In formula (1), R ａ , R ｂ , R ｃ and R ｄ Both represent an alkyl group having 8 carbon atoms. The abrasion-resistant agent is zinc dialkyldithiophosphate represented by ] and contains .

[0023] In this specification, "ammonia-fueled internal combustion engine" refers to any internal combustion engine that uses ammonia as fuel, and is not particularly limited; it can be any internal combustion engine that uses known ammonia fuel (such as a so-called ammonia-fueled engine).

[0024] Furthermore, in this specification, "for ammonia fuel internal combustion engines" means that the product is intended for use in ammonia fuel internal combustion engines, and its uses are not particularly limited. Examples include its use in the ammonia fuel pump of an ammonia fuel internal combustion engine, its system oil, its cylinder oil, and, if the ammonia fuel internal combustion engine is a trunk piston type engine, its use in the trunk piston engine. Thus, in this specification, "for ammonia fuel internal combustion engines" means that the product is intended for use in ammonia fuel internal combustion engines and can be used without particular limitations for the various mechanisms of an ammonia fuel internal combustion engine.

[0025] Furthermore, unless otherwise specified in this specification, the phosphorus content in the lubricating oil composition shall be the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116. In cases where an ashless dispersant is used in the lubricating oil composition, and a compound containing nitrogen (e.g., succinimide) is used as the ashless dispersant, the nitrogen content derived from the ashless dispersant in the lubricating oil composition (the nitrogen content of the ashless dispersant) shall be the value obtained by calculating based on the amount of ashless dispersant added and the nitrogen content (ratio: ratio of constituent elements) relative to the total amount of constituent elements of the ashless dispersant.

[0026] <Lubricating Oil Base Oil> The lubricating oil composition of the present invention contains "lubricating oil base oil" as an essential component. Such lubricating oil base oil contains at least one selected from the group consisting of ester base oil, mineral oil base oil, and synthetic base oil other than the ester base oil, and the content of the ester base oil is 3% by mass or more and 100% by mass or less based on the total amount of lubricating oil base oil.

[0027] Thus, the lubricating oil base oil according to the present invention only needs to contain 3% by mass or more of ester base oil as an essential component, and may consist solely of ester base oil, or it may be a mixed base oil consisting of ester base oil and other base oils (the mineral oil-based base oil, the synthetic base oil other than the ester base oil, or a mixture thereof).

[0028] Such ester base oils can be any known type used in the field of lubricants. Examples of such ester base oils include diester oils such as dibutyl sebacate, dioctyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl talate, and methyl acetyl cinolate; aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromelitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane veralgonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol veralgonate; carbonate ester oils; and complex ester oils, which are oligoesters of polyhydric alcohols and mixed fatty acids of dibasic and monobasic acids. Among these ester base oils, polyol ester oils and complex ester oils are preferred, and complex ester oils are more preferred, from the viewpoint of improving thermal stability, oxidative stability, and low-temperature fluidity. These ester base oils can be used individually or in combination of two or more.

[0029] Examples of the mineral oil-based base oils include paraffinic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and naphthenic base oils, which are obtained by refining a lubricating oil fraction obtained by atmospheric distillation and / or vacuum distillation of crude oil using one or more refining treatments selected from solvent delamination, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, solvent refining, hydrorefining, chemical washing, and clay treatment; and mixtures of two or more of these.

[0030] Furthermore, as the mineral oil-based base oil, examples include a base oil obtained by using any of the following (1) to (8) as a raw material oil, and refining the raw material oil and / or the lubricating oil fraction recovered from the raw material oil by a predetermined refining method to recover the lubricating oil fraction. (1) Distillate of paraffin-based crude oil and / or mixed-based crude oil by atmospheric distillation (2) Distillate (WVGO) of atmospheric distillation residue of paraffin-based crude oil and / or mixed-based crude oil by vacuum distillation (3) Wax obtained by the lubricating oil dewaxing process (slack wax, etc.), and / or synthetic wax obtained by the Fischer-Tropsch (FT) process, Gas-to-Liquid (GTL) process, etc. (FT wax, GTL wax, etc.) (4) Mild hydrocracking oil selected from the raw material oils (1) to (3), and / or mild hydrocracking oil of a mixture of two or more selected from the raw material oils (1) to (3) (5) Mixture of two or more selected from the raw material oils (1) to (4) (6) Deflaxed oil (DAO) of raw material oil (1), (2), (3), (4) or (5) (7) Mild hydrocracking treated oil (MHC) of raw material oil (6) (8) A mixture of two or more oils selected from raw material oils (1) to (7).

[0031] The following are preferred purification methods: hydrogenation purification such as hydrocracking and hydrogenation finishing; solvent purification such as furfural solvent extraction; dewaxing such as solvent dewaxing and contact dewaxing; clay purification using acid clay or activated clay; and chemical (acid or alkali) washing such as sulfuric acid washing and caustic soda washing. One of these purification methods may be performed alone, or two or more may be performed in combination. When combining two or more purification methods, the order is not particularly limited and can be selected as appropriate.

[0032] Particularly preferred examples of mineral oil-based base oils include the base oils described in (9) or (10) below, which are obtained by performing a predetermined treatment on a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil. (9) Hydrocracking of a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil, and dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the product or the lubricating oil fraction recovered from the product by distillation, etc., or distillation after such dewaxing treatment. (10) Hydroisomerized base oil obtained by hydroisomerizing a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil, and dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the product or the lubricating oil fraction recovered from the product by distillation, etc., or distillation after such dewaxing treatment (base oil produced via a catalytic dewaxing process is more preferred as the dewaxing process).

[0033] Furthermore, when obtaining the mineral oil-based base oil described in (9) or (10) above, a solvent refining treatment and / or a hydrogenation finishing treatment may be carried out at an appropriate stage as needed.

[0034] Furthermore, as the mineral oil base oil, you can use API Group I base oil (hereinafter referred to as "API Group I base oil" as it may be), Group II base oil (hereinafter referred to as "API Group II base oil" as it may be), or Group III base oil (hereinafter referred to as "API Group III base oil" as it may be), or a blended base oil obtained by combining these. Here, API Group I base oil is a mineral oil base oil having a sulfur content of more than 0.03% by mass and / or a saturation content of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API Group II base oil is a mineral oil base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. Furthermore, API Group III base oil is a mineral oil base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more. API Group I base oils are typically produced through a solvent refining process, while API Group II and Group III base oils are typically produced through a hydrocracking process. In this specification, viscosity index means viscosity index measured in accordance with JIS K 2283-2000. In this specification, "sulfur content in lubricating base oil" shall be measured in accordance with JIS K 2541-2003. In this specification, "saturation content in lubricating base oil" means value measured in accordance with ASTM D 2007-93.

[0035] Furthermore, while there are no particular limitations on synthetic base oils other than the ester base oil that can be contained in the lubricating oil base oil according to the present invention, hydrocarbon-based synthetic oils are particularly suitable. Examples of such synthetic base oils include API base oil classification group IV base oils (poly-α-olefin base oils, hereinafter sometimes referred to as "API group IV base oils"; such base oils (hydrocarbon-based synthetic oils) are suitable as hydrocarbon-based base oils), API base oil classification group V base oils other than ester base oils (hereinafter sometimes referred to as "API group V base oils"), or mixed base oils obtained by combining these.

[0036] Suitable API Group IV base oils that can be used as the aforementioned synthetic base oils include, for example, hydrocarbon base oils (hydrocarbon synthetic oils) consisting of α-olefin oligomers and co-oligomers having 2 to 32 carbon atoms (preferably 6 to 16 carbon atoms), such as ethylene-propylene copolymers, polybutene, 1-octene oligomers, and 1-decene oligomers, as well as their hydrogenation products.

[0037] Furthermore, examples of API Group V base oils other than ester base oils that can be suitably used as the aforementioned synthetic base oils include aromatic synthetic base oils such as alkylbenzene, alkylnaphthalene, dialkyldiphenyl ether, and polyphenyl ether.

[0038] In addition, suitable synthetic base oils other than ester base oils include, for example, poly-α-olefins and their hydrogenates, isobutene oligomers and their hydrogenates, isoparaffins, alkylbenzenes, alkylnaphthalenes, polyoxyalkylene glycols, dialkyldiphenyl ethers, polyphenyl ethers, and mixtures thereof.

[0039] Furthermore, when the lubricating oil base oil consists of a mixed base oil of an ester base oil and other base oils, among mineral oil-based base oils and synthetic base oils other than the ester base oil, mineral oil-based base oils and hydrocarbon base oils (more preferably API group IV base oils) are preferred as base oils to be combined with the ester base oil, from the viewpoint of being base oils in which ammonia is less soluble, and mineral oil-based base oils are particularly preferred.

[0040] Furthermore, from the viewpoint of the difficulty of ammonia solubility, hydrocarbon base oils of API Group I, API Group II, API Group III, API Group IV, API Group V, or mixed base oils thereof are preferred as base oils to be combined with such ester base oils.

[0041] In the present invention, the lubricating base oil needs to satisfy the condition that the content of the ester base oil is 3% by mass or more and 100% by mass or less based on the total amount of the lubricating base oil. By setting the content of such ester base oil to be not less than the lower limit, even if ammonia fuel is mixed during the use of the composition, the generation of gel can be highly prevented. In addition, by using a lubricating base oil that satisfies the condition that the content of the ester base oil is 3% by mass or more and 100% by mass or less in this way, the reason why the generation of gel can be highly prevented is not necessarily clear, but the inventors speculate that the anti-gel effect may be obtained due to the ester bonds present in the system. Further, the content of the ester base oil in the lubricating base oil is preferably 3% by mass or more and 50% by mass or less (more preferably 3% by mass or more and 30% by mass or less) based on the total amount of the lubricating base oil. When the content of such ester base oil is not more than the upper limit, higher effects can be obtained in terms of water resistance and corrosion inhibition compared to the case where the upper limit is exceeded.

[0042] The kinematic viscosity at 100 °C of the lubricating base oil (total base oil) is 2.0 mm ２ / s or more and 100 mm ２ / s or less (more preferably 3.0 mm ２ / s or more and 75 mm ２ / s or less, still more preferably 4.0 mm ２ [[ID= thirteen]] / s or more and 50 mm ２ / s or less, particularly preferably 6.0 mm ２ / s or more and 40 mm ２ / s or less). By setting the kinematic viscosity at 100 °C to be not less than the lower limit, a higher effect can be obtained in terms of anti-wear property. Also, by setting the kinematic viscosity at 100 °C to be not more than the upper limit, a higher effect can be obtained in terms of energy saving.

[0043] Further, when the kinematic viscosity at 100 °C of the lubricating base oil (total base oil) is used as the working oil or system oil for the mechanism equipped with an ammonia fuel internal combustion engine of the composition, it is 2 mm ２ / s or more and 15 mm ２ / s or less (more preferably 4 mm ２ / s or more and 12 mm ２It is preferable to have a ratio of 0 / s or less, and when the composition is used as trunk piston engine oil (TPEO), 4 mm ２ / s or more 18mm ２ / s or less (more preferably 5 mm) ２ / s or more 16.3mm ２ It is preferable to have a ratio of 0 / s or less, and furthermore, when the composition is used as cylinder oil, it should be 12.5 mm. ２ / s or more 50mm ２ / s or less (more preferably 16.3 mm) ２ / s or more 21.9mm ２ It is preferable to set it to / s or less.

[0044] Furthermore, the kinematic viscosity of the lubricating oil base oil (whole base oil) at 40°C is 5.0 mm². ２ / s or more 1500mm ２ / s or less (more preferably 10 mm) ２ / s or more 1400mm ２ / s or less, more preferably 20 mm ２ / s or more 400mm ２ / s or less, particularly preferably 30 mm ２ / s or more 500mm ２ It is preferable that the kinematic viscosity at 40°C is less than or equal to the lower limit. By setting the kinematic viscosity at 40°C to above the lower limit, an even greater effect in terms of wear resistance can be obtained. Furthermore, by setting the kinematic viscosity at 40°C to below the upper limit, an even greater effect in terms of energy saving can be obtained.

[0045] Furthermore, the kinematic viscosity of the lubricating oil base oil (whole base oil) at 40°C should be 5 mm when the composition is used as hydraulic fluid or system oil for mechanisms in an ammonia-fueled internal combustion engine. ２ / s or more 165mm ２ / s or less (more preferably 20 mm) ２ / s or more 117mm ２ It is preferable to have a ratio of 0 / s or less, and when the composition is used as trunk piston engine oil (TPEO), it should be 20 mm ２ / s or more 220mm ２ / s or less (more preferably 30 mm) ２ / s or more 190mm ２It is preferable to have a ratio of 0 / s or less, and furthermore, when the composition is used as cylinder oil, it should be 125 mm ２ / s or more 500mm ２ / s or less (more preferably 190 mm) ２ / s or more 295mm ２ It is preferable to set it to / s or less.

[0046] In this specification, "kinematic viscosity at 40°C" and "kinematic viscosity at 100°C" refer to the kinematic viscosity at each temperature (kinematic viscosity at 40°C or kinematic viscosity at 100°C), measured in accordance with JIS K 2283-2000 using an automatic viscometer (product name "CAV-2100", manufactured by Cannon Instruments).

[0047] The viscosity index of the lubricating oil base oil (whole base oil) is preferably 90 or higher, more preferably 95 or higher, even more preferably 100 or higher, particularly preferably 105 or higher, and most preferably 110 or higher, from the viewpoint of improving the viscosity-temperature characteristics of the composition, and further improving fuel efficiency and wear resistance. In this specification, "viscosity index" refers to the viscosity index measured using an automatic viscometer (product name "CAV-2100", manufactured by Cannon Instruments) as the measuring device, in accordance with JIS K 2283-2000.

[0048] The pour point of the lubricating oil base oil (whole base oil) is preferably -5°C or lower, more preferably -10°C or lower, even more preferably -12.5°C or lower, particularly preferably -15°C or lower, and most preferably -17.5°C or lower, from the viewpoint of the low-temperature fluidity of the entire lubricating oil composition. In this specification, "pour point" refers to the pour point measured in accordance with JIS K 2269-1987.

[0049] If the lubricating oil base oil (whole base oil) contains sulfur, it is preferable that the sulfur content be 2% by mass or less, and more preferably 1% by mass or less from the viewpoint of oxidation stability. In this specification, "sulfur content" in the base oil refers to the amount of sulfur measured in accordance with JIS K 2541-2003.

[0050] Furthermore, in the lubricating oil composition of the present invention, the content of the lubricating oil base oil (total base oil) is preferably 30% by mass or more and 99.5% by mass or less (more preferably 50% by mass or more and 99.5% by mass or less, and even more preferably 60% by mass or more and 99.5% by mass or less) based on the total mass of the lubricating oil composition.

[0051] <Anti-wear agent> The lubricating oil composition of the present invention contains an "anti-wear agent" as an essential component. The anti-wear agent according to the present invention has a phosphorus content of 100 ppm by mass or more and 3000 ppm by mass or less based on the total mass of the lubricating oil composition, and is defined by the following formula (1):

[0052]

[0053] [In formula (1), R ａ , R ｂ , R ｃ and R ｄ (R ａ ~R ｄ ) all represent an alkyl group having 8 carbon atoms. It is necessary that it be a zinc dialkyldithiophosphate represented by ] (hereinafter, the zinc dialkyldithiophosphate represented by formula (1) above may be simply referred to as "C8ZnDTP" in some cases). Such C8ZnDTP can be said to be a particularly important component from the viewpoint of balancing wear resistance and oxidation prevention among zinc dialkyldithiophosphates, which are widely used as wear-resistant agents.

[0054] In equation (1) such as this, R ａ ~R ｄ Each of these can be an alkyl group having 8 carbon atoms, and each alkyl group can be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group. In such a formula (1), R ａ ~R ｄ The four alkyl groups present are preferably either a primary alkyl group having 8 carbon atoms or a secondary alkyl group having 8 carbon atoms. Furthermore, as for C8ZnDTP, from the viewpoint of improving solubility, R in formula (1) ａ ~R ｄIt is preferable that at least one of the four alkyl groups present is a primary alkyl group having 8 carbon atoms, and it is particularly preferable that all four alkyl groups in formula (1) are primary alkyl groups having 8 carbon atoms. Thus, as a C8ZnDTP, it is particularly preferable that all of the alkyl groups present in the C8ZnDTP are primary alkyl groups.

[0055] The phosphorus content of such anti-wear agents, based on the total mass of the lubricating oil composition, must be between 100 ppm by mass and 3000 ppm by mass. By keeping the phosphorus content of such anti-wear agents within the above range, it is possible to achieve high abrasion resistance while highly preventing gel formation during use of the composition. Furthermore, from the same viewpoint, it is preferable that the phosphorus content of the anti-wear agents, based on the total mass of the lubricating oil composition, be between 300 ppm by mass and 2000 ppm by mass (more preferably between 400 ppm by mass and 1500 ppm by mass). Note that, when the only phosphorus-containing component in the composition is the anti-wear agent (C8ZnDTP), the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116 is adopted.

[0056] Furthermore, the content of the wear-resistant agent is preferably 0.1% by mass or more and 6% by mass or less (more preferably 0.1% by mass or more and 4% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less) based on the total mass of the lubricating oil composition. By keeping the content of the wear-resistant agent within the above range, it becomes possible to efficiently adjust the content of the wear-resistant agent in terms of phosphorus element to the above range.

[0057] <Regarding other additives> Furthermore, the lubricating oil composition of the present invention may contain the lubricating oil base oil and the anti-wear agent, and may appropriately contain other known additives used in the field of lubricating oil compositions, as long as they do not impair the effects of the present invention. As such other additives, for example, various additives described in International Publication No. 2013 / 147162, International Publication No. 2017 / 073748, Japanese Patent Publication No. 2018-177875, Japanese Patent Publication No. 2020-76004, International Publication No. 2020 / 095969, International Publication No. 2020 / 095970, Japanese Patent Publication No. 2022-158121, Japanese Patent Publication No. 2022-158124, Japanese Patent Publication No. 2022-090378, etc., can be appropriately used.

[0058] Other suitable additives include, but are not limited to, other known anti-wear agents other than the aforementioned anti-wear agents (zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate esters, phosphate ester compounds, molybdenum dithiocarbamate, etc.), ashless dispersants, metal-based detergents, antioxidants, metal deactivators, anti-emulsifiers, rust inhibitors, defoamers, friction modifiers such as dithiocarbamite (ZnDTC) and glycerol monooleate (GMO), and amine-based friction modifiers (oleylamine, oleylamine ethylene oxide adduct, oleylamide, etc.).

[0059] Furthermore, among the other additives mentioned above, the lubricating oil composition of the present invention preferably further contains an ashless dispersant from the viewpoint of improving the dispersibility of combustion residues and degraded products. Such an ashless dispersant is not particularly limited, and known ones can be used as appropriate. For example, succinic acid-based ashless dispersants can be suitably used as such an ashless dispersant. Suitable succinic acid-based ashless dispersants include, for example, alkyl succinic acid, alkenyl succinic acid and their ester compounds; succinimide compounds and their derivatives; and the like.

[0060] As such alkyl succinic acid, succinic acid having an alkyl group with 40 to 400 carbon atoms is preferred. As such alkenyl succinic acid, succinic acid having an alkenyl group with 40 to 400 carbon atoms is preferred. As such alkyl and alkenyl groups, branched alkyl or alkenyl groups (polyisobutenyl groups) derived from an isobutene oligomer called polyisobutylene are more preferred, and polybutenyl groups are particularly preferred. Furthermore, the alkyl or alkenyl groups of such succinimide are preferably weight-average molecular weights of 800 to 1500 (more preferably 950 to 1400). Among alkyl succinic acid and alkenyl succinic acid, polybutenyl succinic acid is particularly preferred from the viewpoint of improving the dispersibility of combustion residues and degraded products. Furthermore, the succinic acid ester compound may be any esterified alkyl succinic acid and / or alkenyl succinic acid. For example, compounds obtained by directly esterifying alkyl succinic acid and / or alkenyl succinic acid (those obtained by reacting with alcohol) or compounds obtained by esterifying the anhydride of alkyl succinic acid and / or alkenyl succinic acid can be used as appropriate.

[0061] Furthermore, the succinimide compound is not particularly limited, and known succinimides and their derivatives used as ashless dispersants (for example, succinimides disclosed in Japanese Patent Publication No. 2024-013504, Japanese Patent Publication No. 2022-158121, Japanese Patent Publication No. 2020-76004, etc.) can be used as appropriate.

[0062] Suitable succinimide compounds include succinimides having a hydrocarbon group with 40 to 400 carbon atoms (e.g., alkyl groups, alkenyl groups). More preferably, polybutenyl succinimides and their derivatives are used as such succinimide compounds. Furthermore, it is preferable that such succinimide compounds have a nitrogen atom content of 0.5 to 4.8% by mass (more preferably 1.0 to 3.0% by mass, and even more preferably 1.2 to 2.4% by mass). Among these succinimide compounds, boron-modified succinimides (boronated succinimides) are more preferable from the viewpoint of further improving corrosion resistance and oxidation stability.

[0063] Furthermore, while there are no particular limitations on such succinimide compounds, from the viewpoint of improving the dispersibility of combustion residues and degraded materials, those with a base number (perchloric acid method) of 10 mg KOH / g or more and 100 mg KOH / g or less (more preferably 20 mg KOH / g or more and 80 mg KOH / g or less) are preferred. The succinimide compounds may be used individually or in combination of two or more.

[0064] Furthermore, the content of such ashless dispersant is preferably 0.1% by mass or more and 25% by mass or less (more preferably 0.5% by mass or more and 20% by mass or less, and even more preferably 0.8% by mass or more and 14% by mass or less) based on the total mass of the lubricating oil composition. Moreover, if the ashless dispersant is a succinimide-based ashless dispersant, the nitrogen element content of such succinimide-based ashless dispersant is preferably 10 ppm by mass or more and 6000 ppm by mass or less (even more preferably 50 ppm by mass or more and 3000 ppm by mass or less) based on the total mass of the lubricating oil composition. The nitrogen element content of such ashless dispersant (succinimide-based ashless dispersant, etc.) can be determined by calculating based on the amount of ashless dispersant added and the nitrogen content (ratio) to the total amount of constituent elements of the ashless dispersant.

[0065] Furthermore, among the other additives mentioned above, the lubricating oil composition of the present invention preferably further contains a metal-based detergent from the viewpoint of improving engine cleanliness. Such a metal-based detergent is not particularly limited, and known metal-based detergents such as alkali or alkaline earth metal alkyl salicylates, alkali or alkaline earth metal alkylbenzene sulfonates, and alkali or alkaline earth metal alkylphenates can be used as appropriate. Sodium or potassium is preferred as the alkali metal, and calcium or magnesium is preferred as the alkaline earth metal. In addition, the metal-based detergent may be over-basified with a carbonate (for example, alkali metal carbonates such as sodium carbonate or potassium carbonate, or alkaline earth metal carbonates such as calcium carbonate or magnesium carbonate), or it may be over-basified with a borate (for example, alkali metal borates such as sodium borate or potassium borate, or alkaline earth metal borates such as calcium borate or magnesium borate).

[0066] Furthermore, calcium sulfonate detergents, calcium salicylate detergents, and calcium phenate detergents are preferred as the metal-based detergents. These calcium sulfonate detergents, calcium salicylate detergents, and calcium phenate detergents may be neutral or overbasic, and are not particularly limited in terms of improving their cleaning properties. However, from the viewpoint of improving the neutralization of acidic components, they are preferably overbasicated with calcium carbonate. Thus, the metal-based detergents are preferably overbasic calcium sulfonate detergents, overbasic calcium salicylate detergents, and overbasic calcium phenate detergents. Herein, "overbasic" means that the base number (perchloric acid method) is 60 mg KOH / g or higher.

[0067] Furthermore, the base number (perchloric acid method) of such metal-based detergents can be appropriately determined according to the application of the lubricating oil composition and is not particularly limited, but is preferably 60 mg KOH / g or more and 1000 mg KOH / g or less, more preferably 100 mg KOH / g or more and 500 mg KOH / g or less, and even more preferably 150 mg KOH / g or more and 400 mg KOH / g or less. In this specification, "base number (perchloric acid method)" refers to the value measured according to JIS K 2501:2003, item 9. Such metal-based detergents may be used individually or in combination of two or more types.

[0068] Furthermore, the content of such metal-based detergents is preferably 0.1% by mass or more and 70% by mass or less (more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 40% by mass or less) based on the total mass of the lubricating oil composition. Moreover, when the metal-based detergent is a calcium sulfonate detergent, a calcium salicylate detergent, or a calcium phenate detergent, the content of such metal-based detergents in terms of calcium element is preferably 500 ppm by mass or more and 80,000 ppm by mass or less (even more preferably 1,000 ppm by mass or more and 75,000 ppm by mass or less) based on the total mass of the lubricating oil composition. Setting the content above the lower limit tends to yield an even higher effect in terms of improving the neutralization of acidic components, while setting it below the upper limit tends to yield an even higher effect in terms of suppressing piston deposits. Furthermore, this "calcium element content" refers to the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116.

[0069] Furthermore, when the lubricating oil composition is used as hydraulic fluid or system oil for a mechanism in an ammonia fuel internal combustion engine, it is preferable that the content of the metal-based detergent be 0.1% by mass or more and 20% by mass or less (more preferably 0.5% by mass or more and 15% by mass or less). When the composition is used as trunk piston engine oil (TPEO), it is preferable that the content of the metal-based detergent be 1% by mass or more and 35% by mass or less (more preferably 2% by mass or more and 30% by mass or less). Furthermore, when the composition is used as cylinder oil, it is preferable that the content of the metal-based detergent be 1% by mass or more and 70% by mass or less (more preferably 2% by mass or more and 60% by mass or less).

[0070] Furthermore, the lubricating oil composition of the present invention preferably further contains an antioxidant among the other additives mentioned above. Such an antioxidant can be any component known in the field of lubricating oil compositions, and is not particularly limited, but examples include diphenylamine, naphthylamine, and phenolic antioxidants. The content of such an antioxidant is preferably 0.01% to 3% by mass (more preferably 0.1% to 2% by mass, and even more preferably 0.2% to 1% by mass) based on the total mass of the lubricating oil composition.

[0071] <Regarding preferred conditions such as the properties of the composition> The lubricating oil composition of the present invention has a kinematic viscosity of 12.5 mm at 40°C. ２ / s or more 750mm ２ / s or less (more preferably 30 mm) ２ / s or more 750mm ２ / s or less, more preferably 35 mm ２ / s or more 700mm ２ / s or less, particularly preferably 40 mm ２ / s or more 650mm ２ It is preferable that the kinematic viscosity of the composition at 40°C is less than or equal to the upper limit. By setting the kinematic viscosity of the composition at 40°C to less than or equal to the upper limit, it is possible to further improve fuel efficiency. Furthermore, by setting the kinematic viscosity of the composition at 40°C to or greater than the lower limit, it is possible to achieve a high degree of oil film formation, thereby increasing its reliability as a lubricant.

[0072] Further, when the lubricating oil composition of the present invention is used as the operating oil or system oil of the mechanism provided in the ammonia-fuel internal combustion engine, the kinematic viscosity at 40 ° C. of the composition is 12.5 mm ２ / s or more and 165 mm ２ / s or less (more preferably 20 mm ２ / s or more and 117 mm ２ / s or less). Also, when the composition is used as trunk piston engine oil (TPEO), 20 mm ２ / s or more and 220 mm ２ / s or less (more preferably 30 mm ２ / s or more and 190 mm ２ / s or less). Further, when the composition is used as cylinder oil, 125 mm ２ / s or more and 750 mm ２ / s or less (more preferably 190 mm ２ / s or more and 295 mm ２ / s or less) is preferable.

[0073] Further, the lubricating oil composition of the present invention has a kinematic viscosity at 100 ° C. of 3.0 mm ２ / s or more and 40.0 mm ２ / s or less (more preferably 7.0 mm ２ / s or more and 40.0 mm ２ / s or less, more preferably 8.0 mm ２ / s or more and 35.0 mm ２ / s or less, particularly preferably 9.3 mm ２ / s or more and 30.0 mm ２ / s or less). By setting the kinematic viscosity at 100 ° C of the composition to be below the above upper limit, it becomes possible to further improve the fuel efficiency. Also, by setting the kinematic viscosity at 100 ° C of the composition to be above the above lower limit, it becomes possible to achieve a high oil film forming property and a higher reliability as a lubricant.

[0074] The kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention is 3 mm ２ / s or more and 15 mm ２ / s or less (more preferably 4 mm ２ / s or more and 12 mm ２ / s or less), and when the composition is used as trunk piston engine oil (TPEO), 4 mm ２ / s or more and 18 mm ２ / s or less (more preferably 5 mm ２ / s or more and 16.3 mm ２ / s or less), and further, when the composition is used as cylinder oil, 12.5 mm ２ / s or more and 40 mm ２ / s or less (more preferably 16.3 mm ２ / s or more and 21.9 mm ２ / s or less) is preferable.

[0075] The lubricating oil composition of the present invention preferably has a viscosity index of 90 or more (more preferably 95 or more, still more preferably 100 or more). By setting the viscosity index of the composition to be not less than the above lower limit value, it becomes possible to make the fuel efficiency more advanced.

[0076] Further, the lubricating oil composition of the present invention preferably has a base number (perchloric acid method) of 0 mgKOH / g or more and 300 mgKOH / g or less (more preferably 5 mgKOH / g or more and 200 mgKOH / g or less, still more preferably 7 mgKOH / g or more and 150 mgKOH / g or less). By setting such a base number (perchloric acid method) to be not less than the above lower limit, a higher effect tends to be obtained in terms of neutralization of acidic components, while by setting it to be not more than the above upper limit, a higher effect tends to be obtained in terms of suppression of piston deposits.

[0077] Further, the method for producing the lubricating oil composition of the present invention is not particularly limited. For example, a method of appropriately selecting and mixing each component to be contained so as to obtain the lubricating oil composition of the present invention (so as to satisfy the above conditions) can be adopted.

[0078] [[ID=3^2]] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0079] [Regarding the components used in each example] First, the components of the base oil, etc., used in each example and their abbreviations are shown below. In the table of examples shown below, each component will be expressed using the abbreviations listed below (base oil (1) to (4), ashless dispersant (1) to (4), etc.).

[0080] [Lubricating oil base oil] <Ester base oil> ・Ester base oil (1): Polyol ester oil [Ester of trimethylolpropane and fatty acid, kinematic viscosity at 40°C: 10.6 mm] ２ kinematic viscosity at 100°C ( / s): 3.0 mm² ２ / s, viscosity index: 146, manufactured by NOF Corporation, product name "Unistar (registered trademark) H-210R"] ・Ester base oil (2): Polyol ester oil [Ester of trimethylolpropane and fatty acid, kinematic viscosity at 40°C: 48.7 mm] ２ kinematic viscosity at 100°C (k / s): 9.8 mm² ２ / s, viscosity index: 192, manufactured by NOF Corporation, product name "Unistar (registered trademark) H-381R"] ・Ester base oil (3): Polyol ester oil [Ester of trimethylolpropane and fatty acid, kinematic viscosity at 40°C: 64.6 mm] ２ kinematic viscosity at 100°C (k / s): 12.3 mm² ２ / s, viscosity index: 191, manufactured by NOF Corporation, product name "Unistar (registered trademark) H-481R"] ・Ester base oil (4): Complex ester oil [Oligoester of polyol and mixed fatty acids of dicarboxylic acid such as adipic acid (or sebacic acid), which is a dibasic acid, and monocarboxylic acid, which is a monobasic acid, kinematic viscosity at 40°C: 77.4 mm] ２ kinematic viscosity at 100°C ( / s): 11.4 mm² ２ [ / s, viscosity index: 141, manufactured by NOF Corporation, product name "Unistar (registered trademark) C-3371A"].

[0081] <Mineral oil-based base oil> ・Mineral oil-based base oil (1): Hydrogenated refined base oil [API Group I base oil, kinematic viscosity at 40°C: 97.5 mm] ２ kinematic viscosity at 100°C (k / s): 10.9 mm² ２ / s, viscosity index: 96, sulfur content in base oil (sulfur content in base oil): 0.32 mass%, manufactured by ENEOS Corporation, product name "Super Oil M100"] ・Mineral oil-based base oil (2): Hydrogenated refined base oil [API Group I base oil, kinematic viscosity at 40°C: 110.6 mm] ２ kinematic viscosity at 100°C (k / s): 11.9 mm² ２ / s, viscosity index: 95, sulfur content in base oil (sulfur content in base oil): 0.58 mass%, manufactured by ExxonMobil, product name "AP / E CORE600"] ・Mineral oil-based base oil (3): Hydrogenated refined base oil [API Group I base oil, kinematic viscosity at 40°C: 155.6 mm] ２ kinematic viscosity at 100°C ( / s): 15.01 mm² ２ [Fluid: / s, Viscosity index: 96, Sulfur content in base oil: 0.80% by mass, Manufactured by ENEOS Corporation, Product name: "Super Oil K170"].

[0082] [Abrasion-resistant agent] ・Abrasion-resistant agent (1): Zinc dialkyldithiophosphate (C8ZnDTP) [represented by the above formula (1) and R in the formula] ａ ~R ｄ [A compound in which all are primary alkyl groups having 8 carbon atoms, manufactured by Chevron Japan Co., Ltd., product name: OLOA269RJ].

[0083] [Ashless Dispersants] ・Ashless Dispersant (1) [Boron-modified compound of polybutenyl succinimide, manufactured by Chevron Japan Co., Ltd., product name: OLOA5096, base number (perchloric acid method): 32 mg KOH / g, nitrogen element content: 1.5 mass%, boron content: 0.5 mass%] ・Ashless Dispersant (2) [Ester compound of alkenyl succinic acid: polybutenyl succinic acid half ester, manufactured by Nippon Lubrizol Co., Ltd., product name: LUBRIZOL936] ・Ashless Dispersant (3) [Alkenyl succinic acid: polybutenyl succinic acid, manufactured by Infinium Japan Co., Ltd., product name: Infinium M7045].

[0084] [Metal-based cleaning agents] ・Metal-based cleaning agent (1) [Perbasic calcium salicylate, manufactured by Osca Chemical Co., Ltd., product name: OSCA463, base number (perchloric acid method): 170 mg KOH / g, calcium element content: 6.3% by mass] ・Metal-based cleaning agent (2) [Perbasic calcium salicylate, manufactured by Osca Chemical Co., Ltd., product name: OSCA438B, base number (perchloric acid method): 320 mg KOH / g, calcium element content: 11.4% by mass] ・Metal-based cleaning agent (3) [Perbasic calcium phenate, manufactured by Chevron Japan Co., Ltd., product name: OLOA219, base number (perchloric acid method): 250 mg KOH / g, calcium element content: 9.25% by mass] - Metal-based cleaning agent (4) [Perbasic calcium sulfonate, manufactured by Lubrizol Japan Co., Ltd., product name: Lubrizol 6446, base number (perchloric acid method): 400 mg KOH / g, calcium element content: 9.25% by mass].

[0085] (Examples 1-52 and Comparative Examples 1-22) Lubricating oil compositions were prepared by mixing the aforementioned components to obtain the compositions shown in Tables 1-5.

[0086] In Tables 1-5, a blank space in the "Composition" column indicates that the component was not used. Furthermore, in the "Composition" column of Tables 1-5, the "mass%" unit for each lubricating oil base oil represents the mass-based content (mass%) relative to the total amount of lubricating oil base oil, while the "in mass%" unit for additives represents the mass-based content (mass%) relative to the total amount of the lubricating oil composition. In each example and comparative example, the lubricating oil base oil and additives were used so that the total amount of lubricating oil base oil and additives was 100 mass% (in mass%). Also, in the "Composition" column of Tables 1-5, the "Base Number (Perchloric Acid Method)" indicates the value measured for the composition in accordance with JIS K 2501:2003-9. Furthermore, in the "Composition" section of Tables 1 to 5, "Nitrogen content" represents the mass-based content of nitrogen derived from the ashless dispersant relative to the total amount of the lubricating oil composition (nitrogen content of the ashless dispersant in the lubricating oil composition, unit: mass ppm), and "Phosphorus content" represents the mass-based content of phosphorus relative to the total amount of the lubricating oil composition (unit: mass ppm). The "Phosphorus content" is measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116, and the "Nitrogen content" is calculated based on the amount of ashless dispersant added and the nitrogen content (ratio) relative to the total amount of constituent elements of the ashless dispersant. In the compositions shown in Tables 1 to 5, the only component containing phosphorus is the anti-wear agent (C8ZnDTP), therefore, the "Phosphorus content" for each composition is synonymous with the phosphorus content of the anti-wear agent. In addition, in the compositions shown in Tables 1 to 5, the only component containing the nitrogen element is the ashless dispersant (1), "a boron-modified compound of polybutenyl succinimide."

[0087] <Evaluation Test of Lubricating Oil Compositions Obtained in Examples 1-52 and Comparative Examples 1-22> <Observation of the Appearance of the Composition After the Ammonia Injection Test (Confirmation Test for the Presence or Absence of Gel Formation)> 200 g of the lubricating oil composition was placed in a 500 mL four-necked flask, and the opening of a gas injection nozzle was placed in the composition. Then, ammonia gas was injected through the nozzle into the composition with the nozzle opening introduced into the liquid at room temperature (approximately 25°C) for 90 minutes. The amount of ammonia injected in this manner was 37 L per 200 g of lubricating oil composition over 90 minutes. After the ammonia injection test (ammonia injection test), the appearance of the lubricating oil composition was visually observed to confirm whether or not gel formation occurred in the lubricating oil composition. As a result of this appearance observation, lubricating oil compositions in which gel formation was confirmed after the ammonia injection test were evaluated as "present," and lubricating oil compositions in which gel formation was not confirmed were evaluated as "absent." The results are shown in Tables 1-5.

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] As is clear from the results shown in Tables 1 to 5, the lubricating oil compositions obtained in Examples 1 to 54, which contain a lubricating oil base oil in the range of 5% to 100% by mass of ester base oil and an anti-wear agent consisting of C8ZnDTP with a phosphorus element content of 100 ppm to 3000 ppm by mass, all showed no gel formation after the ammonia injection test, regardless of whether or not an ashless dispersant was used and its type, or whether or not a metal-based detergent was used and its type.

[0094] In contrast, in the lubricating oil compositions described in Comparative Examples 1 to 22, in which the lubricating oil base oil does not contain an ester base oil, it was confirmed that gel was generated after the ammonia injection test.

[0095] These results indicate that, in a lubricating oil composition containing a lubricating oil base oil and C8ZnDTP, using a lubricating oil base oil containing 3 to 100% by mass of ester base oil can effectively prevent gel formation even when ammonia fuel is mixed into the composition.

[0096] As described above, the present invention makes it possible to provide a lubricating oil composition for ammonia-fueled internal combustion engines that can highly prevent the generation of gel during use. Therefore, the lubricating oil composition for ammonia-fueled internal combustion engines of the present invention is particularly excellent in preventing the generation of gel when in contact with ammonia, and is therefore useful as a lubricating oil composition for lubricating various mechanisms of ammonia-fueled internal combustion engines, such as for ammonia fuel pumps, system oils, cylinder oils, and trunk piston engines.

Claims

1. A lubricating oil base oil comprising at least one selected from the group consisting of ester base oils, mineral oil base oils, and synthetic base oils other than ester base oils, wherein the content of the ester base oil is 3% by mass or more and 100% by mass or less based on the total amount of lubricating oil base oil, and the content of phosphorus element, calculated on a basis of the total mass of the lubricating oil composition, is 100 ppm by mass or more and 3000 ppm by mass or less, as shown in formula (1): [In formula (1), R ａ , R ｂ , R ｃ and R ｄ Both represent an alkyl group having 8 carbon atoms. A lubricating oil composition for an ammonia fuel internal combustion engine comprising a wear-resistant agent which is zinc dialkyldithiophosphate represented by ] and .

2. The lubricating oil composition according to claim 1, wherein all alkyl groups of the zinc dialkyldithiophosphate are primary alkyl groups.

3. The lubricating oil composition according to claim 1, further comprising an ashless dispersant.

4. The lubricating oil composition according to claim 1, further comprising a metal-based detergent.

Images