Lubricating oil composition for ammonia-fueled internal combustion engine

Abstract

A lubricating oil composition for an ammonia-fueled internal combustion engine, said lubricating oil composition containing: at least one lubricating oil base oil selected from the group consisting of mineral base oils and synthetic base oils; and an anti-wear agent that is at least one substance selected from the group consisting of zinc aryl dithiophosphates having an aryl group and zinc dialkyldithiophosphates having at least one group selected from the group consisting of alkyl groups having 1-7 carbon atoms, the elemental phosphorous equivalent content of the anti-wear agent based on the total mass of the lubricating oil composition being 100-3000 ppm by mass.

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 achieve a high level of wear resistance while highly preventing gel formation 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 at least one lubricating oil base oil selected from the group consisting of mineral oil-based base oils and synthetic base oils, and at least one anti-wear agent selected from the group consisting of zinc dialkyldithiophosphate having at least one alkyl group having 1 to 7 carbon atoms, and zinc aryldithiophosphate having an aryl group, and having 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, it is possible to achieve a high level of wear resistance while highly preventing gel formation during use, thus completing the present invention.

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

[0012] [1] A lubricating oil composition for an ammonia fuel internal combustion engine, comprising: at least one lubricating oil base oil selected from the group consisting of mineral oil base oils and synthetic base oils; and at least one anti-wear agent selected from the group consisting of zinc dialkyldithiophosphate having at least one alkyl group having 1 to 7 carbon atoms, and zinc aryldithiophosphate having an aryl group, wherein the phosphorus content 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.

[0013] [2] The lubricating oil composition according to [1], wherein the zinc aryldithiophosphate is zinc diaryldithiophosphate.

[0014] [3] The lubricating oil composition according to [1] or [2], further comprising a metal-based detergent.

[0015] [4] The lubricating oil composition according to any one of [1] to [3], further comprising an ashless dispersant.

[0016] According to the present invention, it is possible to provide a lubricating oil composition for an ammonia-fueled internal combustion engine that can achieve a high level of wear resistance while highly preventing the formation of gel during use.

[0017] 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.

[0018] The lubricating oil composition for an ammonia-fueled internal combustion engine of the present invention contains at least one lubricating oil base oil selected from the group consisting of mineral oil-based base oils and synthetic base oils, and at least one anti-wear agent selected from the group consisting of zinc dialkyldithiophosphate having at least one alkyl group having 1 to 7 carbon atoms, and zinc aryldithiophosphate having an aryl group, wherein the phosphorus content 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.

[0019] 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).

[0020] 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.

[0021] 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 addition, when 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.

[0022] <Lubricating Oil Base Oil> The lubricating oil composition of the present invention contains, as an essential component, at least one lubricating oil base oil selected from the group consisting of mineral oil-based base oils and synthetic base oils. Thus, in the present invention, mineral oil-based base oils, synthetic base oils, or a mixture thereof are used as lubricating oil base oils.

[0023] 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.

[0024] 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).

[0025] 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.

[0026] 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).

[0027] 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.

[0028] 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.

[0029] Furthermore, suitable synthetic base oils include hydrocarbon-based synthetic oils and ester-based base oils. 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 (hereinafter sometimes referred to as "API group V base oils"; such base oils include ester-based base oils as one type), or mixed base oils obtained by combining these.

[0030] 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.

[0031] Furthermore, suitable API group V base oils for use as the aforementioned synthetic base oils include, for example, ester-based base oils such as monoesters (e.g., butyl stearate, octyl laurate, 2-ethylhexyl oleate, etc.); diesters (e.g., ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.); polyesters (e.g., trimellitic acid esters, etc.); and polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate, etc.). Other examples of the aforementioned API group V base oils include aromatic synthetic base oils such as alkylbenzenes, alkylnaphthalenes, dialkyldiphenyl ethers, and polyphenyl ethers. Of these API base oil classification group V base oils, the ester-based base oils mentioned above are more preferred from the viewpoint of ease of availability.

[0032] Examples of such synthetic base oils include poly-α-olefins and their hydrogenates, isobutene oligomers and their hydrogenates, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, bis-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, bis-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene glycols, dialkyldiphenyl ethers, polyphenyl ethers, and mixtures thereof.

[0033] Thus, the lubricating oil base oil according to the present invention may be a mineral oil-based base oil, a synthetic base oil, or a mixture thereof. For example, API Group I base oils, API Group II base oils, API Group III base oils, API Group IV base oils, API Group V base oils, or mixtures thereof can be suitably used. Among such lubricating oil base oils, from the viewpoint of the difficulty in dissolving ammonia and the ability to obtain a lubricating oil composition more suitable for applications such as internal combustion engines and hydraulic fluids for fuel pumps, hydrocarbon base oils that are API Group I base oils, API Group II base oils, API Group III base oils, API Group IV base oils, API Group V base oils, ester base oils that are API Group V base oils, or mixtures thereof are more preferable.

[0034] Furthermore, among the lubricating oil base oils, mineral oil-based base oils are preferred from the viewpoint of being a base oil in which ammonia is less soluble.

[0035] The kinematic viscosity of the lubricating oil base oil (whole base oil) at 100°C is 2.0 mm². ２ / s or more 100mm ２ / s or less (more preferably 3.0 mm) ２ / s or more 75mm ２ / s or less, more preferably 4.0 mm ２ / s or more 50mm ２ / s or less, particularly preferably 6.0 mm２ 40 mm or more and 100 mm or less per second ２ Preferably, it is (40 mm or more and 100 mm or less per second). 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 wear resistance. 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.

[0036] 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 the ammonia fuel internal combustion engine, it is 2 mm ２ or more and 15 mm ２ or less per second (more preferably 4 mm ２ or more and 12 mm ２ or less per second). When the composition is used as trunk piston engine oil (TPEO), it is 4 mm ２ or more and 18 mm ２ or less per second (more preferably 5 mm ２ or more and 16.3 mm ２ or less per second). Further, when the composition is used as cylinder oil, it is 12.5 mm ２ or more and 50 mm ２ or less per second (more preferably 16.3 mm ２ or more and 21.9 mm ２ or less per second). [[ID=三十二]]

[0037] Further, the kinematic viscosity at 40°C of the lubricating base oil (total base oil) is 5.0 mm ２ or more and 1500 mm ２ or less per second (more preferably 10 mm ２ or more and 1400 mm ２ or less per second, more preferably 20 mm ２ or more and 400 mm ２ or less per second, particularly preferably 30 mm ２ or more and 500 mm ２ or less per second). By setting the kinematic viscosity at 40°C to be not less than the lower limit, a higher effect can be obtained in terms of wear resistance. Also, by setting the kinematic viscosity at 40°C to be not more than the upper limit, a higher effect can be obtained in terms of energy saving.

[0038] 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 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 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.

[0039] 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).

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] <Anti-wear agent> The lubricating oil composition of the present invention contains an "anti-wear agent". Such an anti-wear agent is at least one selected from the group consisting of zinc dialkyldithiophosphate having at least one alkyl group selected from alkyl groups having 1 to 7 carbon atoms (more preferably, at least one alkyl group selected from the group consisting of primary alkyl groups having 1 to 7 carbon atoms and secondary alkyl groups having 1 to 7 carbon atoms); and zinc aryldithiophosphate having an aryl group; and the anti-wear agent must satisfy the condition that the phosphorus content, 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. Thus, in the present invention, the above-mentioned specific zinc dialkyldithiophosphate, the above-mentioned zinc aryldithiophosphate, or a mixture thereof is used as an anti-wear agent.

[0045] Such zinc dialkyldithiophosphate must have at least one alkyl group selected from those having 1 to 7 carbon atoms. The alkyl group having 1 to 7 carbon atoms in zinc dialkyldithiophosphate may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group.

[0046] Examples of such zinc dialkyldithiophosphates include the following formula (1):

[0047]

[0048] [In formula (1), R ａ , R ｂ , R ｃ and R ｄ Each of these is an alkyl group independently. However, R ａ , R ｂ , R ｃ and R ｄ The condition that at least one of them is an alkyl group having 1 to 7 carbon atoms is satisfied. Compounds represented by [ ] can be suitably used.

[0049] The zinc dialkyldithiophosphate according to the present invention must have at least one alkyl group selected from those having 1 to 7 carbon atoms. In other words, the zinc dialkyldithiophosphate according to the present invention has four alkyl groups in one molecule of the compound (in the case of formula (1) above, R ａ , R ｂ , R ｃ and R ｄ At least one of the four alkyl groups represented by must be an alkyl group having 1 to 7 carbon atoms. By using "zinc dialkyldithiophosphate" as an anti-wear agent according to the present invention, which contains an alkyl group having 1 to 7 carbon atoms, it is possible to achieve excellent anti-wear properties while highly preventing gel formation when used in a composition. Among such alkyl groups having 1 to 7 carbon atoms, those having 2 to 7 carbon atoms (more preferably 3 to 7 carbon atoms) are more preferable. By keeping the number of carbon atoms within the above range, an even higher effect can be obtained in terms of balancing anti-wear properties and anti-oxidation properties.

[0050] Furthermore, the alkyl group having 1 to 7 carbon atoms (in the case of formula (1) above, R) of such zinc dialkyldithiophosphate may also be present. ａ , R ｂ , R ｃ and R ｄ As for the C1-C7 alkyl group used in at least one of the C1-C7 alkyl groups, a primary alkyl group or a secondary alkyl group is more preferred from the viewpoint of achieving a better balance between high levels of wear resistance and thermal stability. Thus, the wear-resistant agent according to the present invention is more preferably a zinc dialkyldithiophosphate having at least one alkyl group selected from the group consisting of primary alkyl groups and secondary alkyl groups.

[0051] Furthermore, the zinc dialkyldithiophosphate according to the present invention has four alkyl groups in one molecule of the compound (in the case of formula (1), R ａ , R ｂ , R ｃ and R ｄ At least one of the four alkyl groups represented by is a C1-C7 alkyl group (more preferably a C1-C7 primary alkyl group or a C1-C7 secondary alkyl group), and other alkyl groups other than C1-C7 alkyl groups may also be included. There are no particular limitations on such other alkyl groups, but C8-C30 (more preferably C8) alkyl groups can be cited as preferred. The C8-C30 (more preferably C8) alkyl group that may be included as such other alkyl groups may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, but from the viewpoint of having better low-temperature properties, a primary alkyl group or a secondary alkyl group is preferred.

[0052] Furthermore, the zinc dialkyldithiophosphate according to the present invention has four alkyl groups in one molecule (for example, in the case of formula (1), R ａ , R ｂ , R ｃ and R ｄZinc dialkyldithiophosphate (I) consists of a compound in which all of the alkyl groups are C1-C7 alkyl groups; Zinc dialkyldithiophosphate (II) consists of a compound in which three of the four alkyl groups in one molecule are C1-C7 alkyl groups and the remaining one is a C8-C30 (more preferably C8) alkyl group; Zinc dialkyldithiophosphate (III) consists of a compound in which two of the four alkyl groups in one molecule are C1-C7 alkyl groups and the remaining two are C8-C30 (more preferably C8) alkyl groups; Zinc dialkyldithiophosphate (III) consists of a compound in which one of the four alkyl groups in one molecule is a C1-C7 alkyl group Dialkyldithiophosphate zinc (IV), which consists of a compound having a lucyl group and the remaining three atoms being alkyl groups having 8 to 30 carbon atoms (more preferably 8 carbon atoms), can be cited as a suitable example. Among these, at least one selected from the group consisting of dialkyldithiophosphate zinc (I), dialkyldithiophosphate zinc (II), and dialkyldithiophosphate zinc (III) is more preferred from the viewpoint of improving the gel formation prevention effect when ammonia is mixed into the lubricating oil composition, and dialkyldithiophosphate zinc (I) and / or dialkyldithiophosphate zinc (II) is even more preferred. The alkyl groups having 1 to 7 carbon atoms in dialkyldithiophosphate zinc (I) to (IV) may be primary alkyl groups, secondary alkyl groups, or tertiary alkyl groups, but primary alkyl groups or secondary alkyl groups are more preferred. The C8 to C30 (more preferably C8) alkyl groups in the aforementioned zinc dialkyldithiophosphate (II) to (IV) may each be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, but it is more preferable that they be primary or secondary alkyl groups.

[0053] In the zinc dialkyldithiophosphate according to the present invention, it is preferable that the molar ratio of primary alkyl group, secondary alkyl group, and tertiary alkyl group (primary alkyl group: secondary alkyl group: tertiary alkyl group) satisfies any of the following conditions (A) to (D): [Condition (A)] 100:0:0 to 0:100:0 (more preferably 100:0:0 to 50:50:0); [Condition (B)] 100:0:0 to 0:0:100 (more preferably 100:0:0 to 50:0:50); [Condition (C)] 0:100:0 to 0:0:100 (more preferably 0:100:0 to 0:50:50); [Condition (D)] 100:0:0 to 40:30:30 (more preferably 100:0:0 to 50:40:10). Such a molar ratio may be the ratio of combinations of alkyl groups within one molecule of a compound if the zinc dialkyldithiophosphate consists of one compound, or, if the zinc dialkyldithiophosphate is a mixture of multiple compounds represented by the above formula (1) with different types of alkyl groups, it may be the ratio of all primary alkyl groups to all secondary alkyl groups to all tertiary alkyl groups in the mixture (for example, if it is a mixture of zinc dialkyldithiophosphate having only primary alkyl groups and zinc dialkyldithiophosphate having only secondary alkyl groups, the mixing ratio will be the aforementioned molar ratio).

[0054] Furthermore, in the zinc dialkyldithiophosphate according to the present invention, if it contains alkyl groups other than alkyl groups having 1 to 7 carbon atoms, the content ratio of other alkyl groups (for example, alkyl groups having 8 carbon atoms) to the total alkyl groups in the zinc dialkyldithiophosphate (if the zinc dialkyldithiophosphate consists of one compound, this refers to the four alkyl groups within one molecule of the compound; on the other hand, if the zinc dialkyldithiophosphate is a mixture of multiple compounds represented by the above formula (1) with different types of alkyl groups, this refers to all alkyl groups contained in the mixture) is preferably 75% or less, and preferably 25% to 50%, based on the number of alkyl groups. By keeping the content of such other alkyl groups below the above upper limit, an even higher effect in preventing gel formation when ammonia is mixed into the lubricating oil composition tends to be obtained.

[0055] Furthermore, the zinc aryldithiophosphate according to the present invention may be any zinc dithiophosphate having an aryl group. By using such zinc aryldithiophosphate as an abrasion resistant agent, it is possible to exhibit abrasion resistance while highly preventing gel formation when used in a composition. In addition, such zinc aryldithiophosphate can be expressed by the following formula (2):

[0056]

[0057] [In formula (2), R ｅ , R ｆ , R ｇ and R ｈ Each of these is independently an aryl group or an alkyl group. However, R ｅ , R ｆ , R ｇ and R ｈ The condition that at least one of them is an aryl group is satisfied. Compounds represented by ] can be preferably used.

[0058] The aryl group in the zinc aryldithiophosphate (when the zinc aryldithiophosphate is a compound represented by formula (2), R ｅ , R ｆ , R ｇ and R ｈThe aryl group that can be selected is not particularly limited, but one with 6 to 30 carbon atoms (more preferably 9 to 18) is preferred. By keeping the number of carbon atoms within the above range, a higher effect in terms of antioxidant properties and wear resistance can be obtained. Examples of aryl groups in zinc aryldithiophosphate include phenyl group, naphthyl group, anthryl group, phenanthryl group, biphenyl group, terphenyl group, etc. Among these aryl groups, naphthyl group, anthryl group, phenanthryl group, biphenyl group, and terphenyl group are preferred from the viewpoint of obtaining even better antioxidant properties and wear resistance, anthryl group, phenanthryl group, biphenyl group, and terphenyl group are more preferred, and biphenyl group and terphenyl group are particularly preferred.

[0059] As for groups other than the aryl group that the zinc aryldithiophosphate may contain, alkyl groups are a good example. A suitable alkyl group as such a group other than the aryl group is (if the zinc aryldithiophosphate is a compound represented by formula (2), then R in the formula) ｅ , R ｆ , R ｇ and R ｈ As for the alkyl group that can be selected, an alkyl group having 1 to 30 carbon atoms (more preferably 2 to 18, and even more preferably 4 to 12 carbon atoms) is preferred from the viewpoint of improving antioxidant properties and wear resistance. Furthermore, such alkyl groups may be primary alkyl groups, secondary alkyl groups, or tertiary alkyl groups.

[0060] Furthermore, as for the zinc aryldithiophosphate, from the viewpoint of preventing gel formation when ammonia is mixed into the lubricating oil composition, zinc diaryldithiophosphate (represented by formula (2) and R ｅ , R ｆ , R ｇ and R ｈ Compounds in which all are aryl groups are preferred. Furthermore, the zinc aryldithiophosphate is represented by formula (2) and R ｅ , R ｆ , R ｇ and R ｈZinc diaryldithiophosphate is more preferable, in which each of the groups is independently a phenyl group, a naphthyl group, anthryl group, a phenanthryl group, a biphenyl group, or a terphenyl group (more preferably a naphthyl group, anthryl group, a phenanthryl group, a biphenyl group, or a terphenyl group).

[0061] Furthermore, in the present invention, the phosphorus content of the anti-wear agent 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 the anti-wear agent within this range, it is possible to achieve a high level of wear resistance. Also, from the same viewpoint, it is preferable that the phosphorus content of the anti-wear agent 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) for the benefit of obtaining a higher effect. Note that, when the anti-wear agent is the only phosphorus-containing component in the composition, the "phosphorus content of the anti-wear agent based on the total mass of the lubricating oil composition" is synonymous with the phosphorus content in the lubricating oil composition, and therefore, the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116 is adopted.

[0062] 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.

[0063] <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.

[0064] 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.).

[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 from the viewpoint of improving their cleaning ability, and are not particularly limited in this respect. 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, 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.

[0071] 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 having 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 dispersibility. 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.

[0072] 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.

[0073] Suitable succinimide compounds include succinimides having a hydrocarbon group (e.g., alkyl group, alkenyl group) with 40 to 400 carbon atoms. Polybutenyl succinimide and its derivatives are more preferred. Furthermore, such succinimide compounds are preferred to 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 succinimide compounds (boronated succinimide) are more preferred from the viewpoint of further improving corrosion resistance and oxidation stability. The succinimide compounds may be used individually or in combination of two or more.

[0074] 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 15% 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. Setting the content above the lower limit tends to yield even higher efficiency in terms of dispersibility of combustion residues and degraded materials, while setting it below the upper limit tends to yield even higher efficiency in terms of fuel consumption. The nitrogen content of such ashless dispersants (succinimide-based ashless dispersants) can be calculated based on the amount of ashless dispersant added and the nitrogen content (percentage) relative to the total amount of constituent elements of the ashless dispersant.

[0075] Further, the lubricating oil composition of the present invention preferably further contains an antioxidant among the other additives. As such an antioxidant, components known in the field of lubricating oil compositions can be appropriately used and are not particularly limited, and examples thereof include diphenylamine, naphthylamine, phenolic antioxidants, and the like. Further, the content of such an antioxidant is preferably 0.01% by mass or more and 3% by mass or less (more preferably 0.1% by mass or more and 2% by mass or less, still more preferably 0.2% by mass or more and 1% by mass or less) based on the total mass of the lubricating oil composition.

[0076] <Regarding preferable conditions for characteristics of the composition, etc.> The lubricating oil composition of the present invention has a kinematic viscosity at 40°C of 12.5 mm ２ / s or more and 750 mm ２ / s or less (more preferably 30 mm ２ / s or more and 750 mm ２ / s or less, still more preferably 35 mm ２ / s or more and 700 mm ２ / s or less, particularly preferably 40 mm ２ / s or more and 650 mm ２ / s or less). By setting the kinematic viscosity at 40°C of the composition to be below the above upper limit, it becomes possible to further improve fuel efficiency. Further, by setting the kinematic viscosity at 40°C of the composition to be above the above lower limit, it becomes possible to achieve a high oil film forming property and to achieve a higher reliability as a lubricant.

[0077] Further, when the kinematic viscosity at of the lubricating oil composition of the present invention at 40°C is used as the working oil or system oil of the mechanism provided in the ammonia fuel internal combustion engine, it 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), and when the composition is used as trunk piston engine oil (TPEO), it is 20 mm ２ / s or more and 220 mm ２ / s or less (more preferably 30 mm ２ / s or more and 190 mm 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 750mm ２ / s or less (more preferably 190 mm) ２ / s or more 295mm ２ It is preferable to set it to / s or less.

[0078] Furthermore, the lubricating oil composition of the present invention has a kinematic viscosity of 3.0 mm at 100°C. ２ / s or more 40.0mm ２ / s or less (more preferably 7.0 mm) ２ / s or more 40.0mm ２ / s or less, more preferably 8.0 mm ２ / s or more 35.0mm ２ / s or less, particularly preferably 9.3 mm ２ / s or more 30.0mm ２ It is preferable that the kinematic viscosity of the composition at 100°C is less than or equal to the upper limit. By setting the kinematic viscosity of the composition at 100°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 100°C to more than or equal to the lower limit, it is possible to achieve a high degree of oil film formation, thereby increasing its reliability as a lubricant.

[0079] The kinematic viscosity of the lubricating oil composition of the present invention at 100°C is 3 mm when the composition is used as a hydraulic fluid or system oil for a mechanism in an ammonia fuel internal combustion engine. ２ / s or more 15mm ２ / s or less (more preferably 4 mm) ２ / s or more 12mm 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), 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 40mm ２ / s or less (more preferably 16.3 mm) ２ / s or more 21.9mm２ It is preferable to set it to / s or less.

[0080] The lubricating oil composition of the present invention preferably has a viscosity index of 90 or higher (more preferably 95 or higher, and even more preferably 100 or higher). By setting the viscosity index of the composition to be above the lower limit, it is possible to achieve a higher level of fuel efficiency.

[0081] Furthermore, the lubricating oil composition of the present invention preferably has a base number (perchloric acid method) of 0 mg KOH / g or more and 300 mg KOH / g or less (more preferably 5 mg KOH / g or more and 200 mg KOH / g or less, and even more preferably 7 mg KOH / g or more and 150 mg KOH / g or less). Setting the base number (perchloric acid method) above the lower limit tends to yield an even higher effect in terms of neutralization of acidic components, while setting it below the upper limit tends to yield an even higher effect in terms of suppressing piston deposits.

[0082] Furthermore, the method for producing the lubricating oil composition of the present invention is not particularly limited. For example, a method can be employed in which each component to be included is appropriately selected and mixed so as to satisfy the above conditions, thereby producing the lubricating oil composition of the present invention.

[0083] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0084] [Regarding the components used in each example] First, the components of the base oils, 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 (3), metal-based detergent (1) to (4), etc.).

[0085] [Lubricating oil base oil] ・Base oil (1): Mineral oil-based base oil [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% by mass, manufactured by ENEOS Corporation, product name: Super Oil M100] ・Base oil (2): mineral oil-based base oil [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] • Base oil (3): Mineral oil-based base oil [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].

[0086] [Abrasion-resistant agent] ・ZnDTP(1) [The compound represented by the above formula (1) (R in the formula) ａ ~R ｄ Each of these is an alkyl group that is either a primary alkyl group having 4 carbon atoms or a primary alkyl group having 5 carbon atoms, and R in the formula ａ ~R ｄ Compounds in which one or more of the elements are primary alkyl groups having 4 carbon atoms and the remaining one or more are primary alkyl groups having 5 carbon atoms (primary ZnDTP), manufactured by Lubrizol Japan Co., Ltd., trade name: LUBRIZOL 1395] ・ZnDTP (2) [Compounds represented by the above formula (1) (R in the formula) ａ ~R ｄ One of them is a primary alkyl group having 8 carbon atoms, and R in the formula ａ ~R ｄ One or two of the remaining three are primary alkyl groups having four carbon atoms, and R in the formula ａ ~R ｄ The remainder of (R in the formula) ａ ~R ｄCompounds in which one or two of the following are primary alkyl groups having 5 carbon atoms (primary ZnDTP), manufactured by Chevron Japan Co., Ltd., trade name: OLOA267] ・ZnDTP (3) [Compounds represented by the above formula (1) (R in the formula) ａ ~R ｄ Each of these is an alkyl group that is either a secondary alkyl group having 4 carbon atoms or a secondary alkyl group having 5 carbon atoms, and R in the formula ａ ~R ｄ Compounds in which one or more of the elements are secondary alkyl groups having 4 carbon atoms and the remaining one or more are secondary alkyl groups having 6 carbon atoms (secondary ZnDTP), manufactured by Chevron Japan Co., Ltd., product name: OLOA262] ・ZnDTP (4) [Compounds represented by the above formula (1) (R in the formula) ａ ~R ｄ Compounds in which both are secondary alkyl groups having 6 carbon atoms (secondary ZnDTP), manufactured by Lubrizol Japan Co., Ltd., trade name: LUBRIZOL677A] ・ZnDTP (5) [Compound represented by the above formula (1) (R in the formula] ａ ~R ｄ One of them is a secondary alkyl group having 4 carbon atoms, R ａ ~R ｄ One of them is a secondary alkyl group with 6 carbon atoms, R ａ ~R ｄ One of them is a primary alkyl group having 4 carbon atoms, R ａ ~R ｄ One of them is a compound having 5 carbon atoms as a primary alkyl group), manufactured by INFINIUM JAPAN Co., Ltd., product name: C9425] ・ZnDTP(6) [a compound represented by the above formula (2) (R in the formula ａ ~R ｄ Compound (arylZnDTP) in which all are aryl groups (terphenyl groups), manufactured by Chevron Japan Co., Ltd., product name: OLOA260.

[0087] [Comparative wear-resistant agent] ・Comparative ZnDTP [Zinc dialkyldithiophosphate in which all alkyl groups contained in the compound are primary alkyl groups having 8 carbon atoms (referring to formula (1) above, R in formula (1) ａ ~R ｄCompounds in which both are primary alkyl groups having 8 carbon atoms), manufactured by Chevron Japan Co., Ltd., product name: OLOA269RJ.

[0088] [Ashless Dispersant] ・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% by mass, boron content: 0.5% by mass]

[0089] [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].

[0090] (Examples 1-18 and Comparative Examples 1-13) Lubricating oil compositions were prepared by mixing the aforementioned components to obtain the compositions shown in Tables 1-2.

[0091] In the "Composition" column of Tables 1 to 7 below, a blank space indicates that the component was not used. In the "Composition" column of Tables 1 to 7 below, "mass%" represents the mass-based content (mass%) 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% (mass%). In the "Composition" column of Tables 1 to 7, "Base number (perchloric acid method)" indicates the value obtained by measuring the composition in accordance with JIS K 2501:2003, item 9. Furthermore, in the "Composition" section of Tables 1 to 7, "Nitrogen content" represents the mass-based content of nitrogen in the ashless dispersant relative to the total amount of the lubricating oil composition (nitrogen-equivalent 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 7, since the only components containing phosphorus are the anti-wear agent and the comparative anti-wear agent, the "Phosphorus content" for each composition is synonymous with the phosphorus-equivalent content of the anti-wear agent. Furthermore, in the compositions shown in Tables 1 to 7, the only component containing the nitrogen element is the ashless dispersant (1).

[0092] <Evaluation Test of Lubricating Oil Compositions Obtained in Examples 1-18 and Comparative Examples 1-13> <Observation of the Appearance of the Composition After Ammonia Injection Test (Confirmation Test for 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) was performed in this manner, 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 1-2.

[0093] <High-Speed ​​Four-Ball Test> The wear resistance of each lubricating oil composition was evaluated by a high-speed four-ball test in accordance with ASTM D4172-94. The test conditions for the high-speed four-ball test were as follows: SUJ2 was used as the rigid ball, rotation speed 1800 rpm, load 294 N, test temperature (composition temperature) 80°C, and test time 30 minutes. The average value (unit: mm) of the wear mark diameter of the fixed ball was measured. The obtained average values ​​are shown in Tables 1 and 2 as wear mark diameter (unit: mm) (however, the wear resistance was not specifically evaluated for compositions in which gel formation occurred in the aforementioned test to confirm the presence or absence of gel formation). In this test, the smaller the wear mark diameter measured, the better the wear resistance, and in particular, if it is 0.7 mm or less, it can be evaluated as having a high level of wear resistance.

[0094]

[0095]

[0096] As is clear from the results shown in Tables 1 and 2, the lubricating oil compositions obtained in Examples 1 to 18, which contain a mineral oil-based base oil and an anti-wear agent consisting of a primary and / or secondary alkyl group having 1 to 7 carbon atoms (ZnDTP(1) to (5)) or an aryl zinc dithiophosphate having an aryl group (ZnDTP(6)), and in which the phosphorus content of the composition (concentration of phosphorus in the anti-wear agent) is 100 ppm by mass or more and 3000 ppm by mass or less relative to the total amount of the composition, all showed no gel formation after the ammonia injection test, and the wear mark diameter in the high-speed four-ball test was 0.45 mm or more and 0.59 mm or less, confirming that they possess a high level of excellent wear resistance. From these results, it was found that the lubricating oil compositions obtained in Examples 1 to 18 are suitable for use in lubricating internal combustion engines that use ammonia as fuel.

[0097] In contrast, the lubricating oil compositions obtained in Comparative Examples 1, 3, 5, 7, 9, and 11, in which the phosphorus content of the composition (converted phosphorus content of the anti-wear agent) was 50 ppm by mass (less than 100 ppm by mass) relative to the total amount of the composition, all showed a wear mark diameter of 1.2 mm in the high-speed four-ball test, indicating insufficient wear resistance. Furthermore, the lubricating oil compositions obtained in Comparative Examples 2, 4, 6, 8, 10, and 12, in which the phosphorus content of the composition (converted phosphorus content of the phosphorus-containing anti-wear agent) was 4000 ppm by mass (a value exceeding 3000 ppm by mass), all showed a wear mark diameter of 1.1 mm or more in the high-speed four-ball test, indicating insufficient wear resistance. It should be noted that in Comparative Examples 1 to 12, which utilized a specific phosphorus-containing anti-wear agent, no gel formation was observed after the ammonia injection test.

[0098] On the other hand, the lubricating oil composition obtained in Comparative Example 13, which used a comparative zinc dialkyldithiophosphate containing only a C8 alkyl group as a comparative anti-wear agent, was found to be unsuitable for lubrication of internal combustion engines that use ammonia as fuel, as gel formation was observed after the ammonia injection test.

[0099] These results confirm that by using a wear-resistant agent consisting of dialkyldithiophosphate zinc having primary and / or secondary alkyl groups having 1 to 7 carbon atoms (ZnDTP(1) to (5)) or aryldithiophosphate zinc having an aryl group (ZnDTP(6)) in addition to a mineral oil-based base oil in a lubricating oil composition such that the phosphorus content relative to the total composition is 100 ppm by mass or more and 3000 ppm by mass or less, the resulting composition not only does not produce gel after ammonia injection tests, but also exhibits excellent wear resistance.

[0100] Furthermore, the anti-wear agents used in Tables 1 and 2 (ZnDTP (1) to (6)) all exhibited similarly high levels of excellent anti-wear properties when their phosphorus content, in terms of equivalent phosphorus, was between 100 ppm by mass and 3000 ppm by mass, regardless of their type. Therefore, it is clear that excellent anti-wear properties are exhibited when the phosphorus content derived from the anti-wear agent is within the aforementioned range.

[0101] (Examples 19-71 and Comparative Examples 14-34) Lubricating oil compositions were prepared by mixing the aforementioned components to obtain the compositions shown in Tables 3-7.

[0102] Furthermore, the lubricating oil compositions obtained in Examples 19-71 and Comparative Examples 14-34 were used to check for the presence or absence of gel formation in the lubricating oil compositions, using the same method as employed in the "Visual Observation of Compositions After Ammonia Injection Test (Confirmation Test for Presence or Absence of Gel Formation)" described above. The results are shown in Tables 3-7, respectively.

[0103]

[0104]

[0105]

[0106]

[0107]

[0108] As is clear from the results shown in Tables 1 to 7, in all lubricating oil compositions obtained in Examples 19 to 71, in which a wear-resistant agent consisting of a primary and / or secondary alkyl group having 1 to 7 carbon atoms (ZnDTP(1) to (5)) or an aryl zinc dithiophosphate having an aryl group (ZnDTP(6)) was used together with a mineral oil-based base oil, such that the phosphorus content in terms of elemental phosphorus relative to the total composition was between 100 ppm by mass and 3000 ppm by mass, it was confirmed that no gel was generated after the ammonia injection test. Furthermore, considering the results shown in Tables 1 to 2 together, it is clear that all lubricating oil compositions obtained in Examples 19 to 71, having the compositions shown in Tables 3 to 7, have excellent wear resistance because the phosphorus content of the phosphorus-containing wear-resistant agent is in the range of 100 ppm by mass and 3000 ppm by mass. Furthermore, although the lubricating oil compositions obtained in Examples 19 to 24 did not utilize metal-based detergents or ashless dispersants, no gel formation occurred after the ammonia injection test in these compositions. This indicates that the use of the wear-resistant agent described in the present invention can suppress gel formation.

[0109] On the other hand, the lubricating oil compositions obtained in Comparative Examples 14 to 34, which utilized zinc dialkyldithiophosphate (ZnDTP for comparison) having only a C8 alkyl group, all exhibited gel formation after the ammonia injection test.

[0110] Considering these results, it is clear that even if the composition differs in terms of the type and amount of base oil used, the type and amount of anti-wear agent used, the presence or absence of ashless dispersant, and the type and presence or absence of metal liquid detergent, by using an anti-wear agent consisting of dialkyldithiophosphate zinc having a primary alkyl group of 1 to 7 carbon atoms and / or a secondary alkyl group of 1 to 7 carbon atoms (ZnDTP(1) to (5)), or aryldithiophosphate zinc having an aryl group (ZnDTP(6)), such that the phosphorus content is between 100 ppm by mass and 3000 ppm by mass, the wear resistance of the lubricating oil composition can be made to a high level, and it is also possible to highly prevent the formation of gel in the lubricating oil composition when it is used under conditions in which it comes into contact with ammonia. From these results, it is clear that the lubricating oil composition of the present invention is useful as a component for lubricating the sliding parts of an ammonia-fueled internal combustion engine.

[0111] 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 gel formation during use while maintaining a high level of wear resistance. Therefore, the lubricating oil composition for ammonia-fueled internal combustion engines of the present invention is particularly excellent in preventing gel formation 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 composition for an ammonia-fueled internal combustion engine, comprising: at least one lubricating oil base oil selected from the group consisting of mineral oil-based base oils and synthetic base oils; and at least one anti-wear agent selected from the group consisting of zinc dialkyldithiophosphate having at least one alkyl group having 1 to 7 carbon atoms, and zinc aryldithiophosphate having an aryl group, wherein the phosphorus content, 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.

2. The lubricating oil composition according to claim 1, wherein the zinc aryldithiophosphate is zinc diaryldithiophosphate.

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

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

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