阅读说明：本技术 润滑油组合物 (Lubricating oil composition ) 是由 J·D·帕拉佐托 M·J·布朗 于 2018-06-05 设计创作，主要内容包括：公开了一种具有增强的沉积物控制能力的润滑油组合物,其用于在持续的高负载条件下运行的发动机,例如天然气发动机和低速或中速柴油发动机。所述组合物包括(a)第一基础油组分,选自第I类基础油、第II类基础油、第III类基础油或它们的组合,在100℃下的运动粘度均为8.5至15mm<Sup>2</Sup>/s；和(b)第二基础油组分,选自第I类基础油、第II类基础油、第III类基础油或它们的组合,在100℃下的运动粘度均为4.0至小于8.5mm<Sup>2</Sup>/s；其中所述第一基础油组分与所述第二基础油组分的重量比为1:10至1：1.15。(Disclosed is a sediment with enhancedA lubricating oil composition for controlling the ability to operate under sustained high load conditions in engines such as natural gas engines and low or medium speed diesel engines. The composition includes (a) a first base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm 2 S; and (b) a second base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm 2 S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.)

1. A natural gas engine lubricating oil composition comprising:

(a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and

(b) a second base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²/s；

Wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

2. a low or medium speed diesel engine lubricating oil composition comprising:

(a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and

(b) a second base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²/s；

Wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

3. the lubricating oil composition of any of claims 1 or 2, wherein the weight ratio of the first base oil component to the second base oil component is 1: 5-1: 1.15.

4. the lubricating oil composition of any one of claims 1 or 2, which is an SAE 20, SAE30, SAE 40, SAE50 or SAE 60 viscosity grade engine oil.

5. The lubricating oil composition of any one of claims 1 or 2, which is a 15W-x, 20W-x, or 25W-x SAE viscosity grade engine oil, wherein x is 30, 40, 50, or 60.

6. The lubricating oil composition of claim 2, wherein the medium speed diesel engine lubricating oil composition is substantially free of zinc.

7. The lubricating oil composition of claim 1, wherein the lubricating oil composition is used to lubricate a natural gas engine selected from a stationary natural gas engine, a stationary biogas engine, a stationary landfill gas engine, a stationary unconventional natural gas engine, or a dual fuel engine.

8. The lubricating oil composition according to claim 2, wherein the lubricating oil composition is used for lubricating a low-speed diesel engine, and the low-speed diesel engine is a marine crosshead diesel engine.

9. The lubricating oil composition of claim 2, wherein the lubricating oil composition is used to lubricate a medium speed diesel engine selected from a locomotive diesel engine, a marine trunk piston diesel engine, or a land-based fixed power diesel engine.

10. The lubricating oil composition according to any one of claims 1 or 2, further comprising from 1 to 20 wt.%, based on the total weight of the composition, of a polyisobutylene having a kinematic viscosity at 100 ℃ of 200-5000mm²/s。

11. The lubricating oil composition of any one of claims 1 or 2, further comprising at least one additive selected from the group consisting of antioxidants, antiwear agents, metal detergents, dispersants, friction modifiers, corrosion inhibitors, demulsifiers, viscosity modifiers, pour point depressants, foam inhibitors, and mixtures thereof.

12. A method of controlling deposit formation in a mechanical component of an internal combustion engine selected from a natural gas engine, a low speed diesel engine or a medium speed diesel engine, said method comprising operating said internal combustion engine with a lubricating oil composition comprising:

(a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and

(b) a second base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

13. the method of claim 12, wherein the mechanical component is a piston, piston ring, cylinder liner, cylinder, cam, tappet, lifter, gear, valve guide, or bearing comprising journal, roller, taper, needle, or ball bearing.

14. The method of claim 12, wherein the mechanical component comprises steel.

15. The method of claim 12, wherein the internal combustion engine is operated at a load with a brake mean effective pressure greater than 20bar (2.0 MPa).

Technical Field

The present disclosure relates to lubricants for use in engines operating under sustained high load conditions, such as natural gas fueled engines and low or medium speed diesel fueled engines, and to methods for enhancing the deposit control capability of lubricants used in such engines, particularly those equipped with steel pistons.

Background

It is well known that internal combustion engines exert a great pressure on lubricating oil. The oil is required to provide good lubricity under all conditions, provide protection against wear and corrosion, maintain a consistent level of contamination, maintain relatively clean engine surfaces, resist thermal and/or oxidative damage and carry away excess engine heat.

While all engines exert such pressure on these lubricating oils, stationary diesel-fueled engines and stationary natural gas-fueled engines are particularly challenging to lubricate. For engines that typically operate continuously for days or weeks at near full load conditions (e.g., stationary natural gas engines) and in remote locations, there is typically little or no monitoring, and little or no opportunity to quickly respond to engine or oil failures, and the need for oil for such engines is of a continuous rather than transient nature. This situation is further exacerbated by the trend toward higher loads and longer oil change cycles.

In recent years, Original Equipment Manufacturers (OEMs) have been designing internal combustion engines to provide greater power density, i.e., produce higher power per unit of displacement. A recent development in engine design is to replace aluminum pistons with steel pistons to maintain piston strength when operating at higher pressures and temperatures.

Steel piston engines operating at high brake mean effective pressures (i.e., BMEP > 20bar) have shown a tendency to form excessive deposits on mechanical parts (e.g., pistons, piston rings, cylinder liners, etc.) resulting in reduced part life when lubricated using conventional lubricating oil additive packages formulated with the highest viscosity component of API-type base oils (e.g., heavy neutral base oils) to achieve desired oil life characteristics.

It has now surprisingly been found that partial replacement of heavy neutral base oils by lighter neutral base oils provides a lubricating oil composition which shows improved resistance to deposit formation in engines running under sustained high load conditions, in particular steel piston engines.

Summary of the invention

In one aspect, there is provided a natural gas engine lubricating oil composition comprising: (a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and (b) a second base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

in another aspect, there is provided a low or medium speed diesel engine lubricating oil composition comprising: (a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and (b) a second base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

in another aspect, there is provided a method of controlling deposit formation in an internal combustion engine selected from a natural gas engine, a low speed diesel engine or a medium speed diesel engine, comprising operating said internal combustion engine with said lubricating oil composition disclosed herein.

In another aspect, there is provided a use of a lubricating oil composition as described herein for the purpose of controlling deposit formation in an internal combustion engine selected from a natural gas engine, a low speed diesel engine or a medium speed diesel engine.

Detailed description of the invention

Term(s) for

By "major amount" is meant 50% or more by weight of the composition.

By "minor amount" is meant less than 50% by weight of the composition.

As used herein, the terms "base stock" and "base oil" are used synonymously and interchangeably.

By "dual fuel engine" is meant an engine that can be operated using a mixture of natural gas and diesel. The combination of natural gas and diesel may comprise at least 60% natural gas.

Unless otherwise indicated, all percentages reported are by weight of active ingredient (i.e., without regard to carrier or diluent oils)

All ASTM standards referred to herein are the latest versions up to the filing date of this application.

INDUSTRIAL APPLICABILITY

The lubricating oil compositions disclosed herein are used in natural gas engines, low speed diesel engines, or medium speed diesel engines. The engine may be a two-stroke engine, a three-stroke engine, a four-stroke engine, a five-stroke engine, or a six-stroke engine. The engine may also include any number of combustion chambers, pistons, and associated cylinders (e.g., 1-24). For example, in certain embodiments, the engine may be a large industrial reciprocating engine having 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16, 18, 20, 24 or more pistons reciprocating in cylinders. In certain embodiments, the piston may be an aluminum piston or a steel piston (e.g., steel or any of a variety of steel alloys, such as 42CrMo4V or 38MnVS 6).

The natural gas engine may be a stationary natural gas engine, a stationary biogas engine, a stationary landfill gas engine, a stationary unconventional natural gas engine, or a dual fuel engine.

Diesel engines can be generally classified as low-speed, medium-speed, or high-speed engines. Herein, a "low speed" diesel engine refers to a compression ignition internal combustion engine driven at less than 500 revolutions per minute (rpm), such as a marine crosshead diesel engine; "medium speed" diesel engine means a compression ignition internal combustion engine driven at a speed of 500 to 1800rpm, such as a locomotive diesel engine, a marine trunk piston diesel engine or a land-based fixed power (power) diesel engine; by "high speed" diesel engine is meant a compression ignition internal combustion engine, such as a diesel engine for road vehicles, driven at a speed of rotation above 1800 rpm.

The lubricating oil compositions disclosed herein are useful for controlling deposits in engines operating under high continuous load conditions, for example Brake Mean Effective Pressure (BMEP) of at least 20bar (2.0MPa), for example at least 22bar (2.2MPa), at least 24bar (2.4MPa), at least 26bar (2.6MPa), 20 to 30bar (2.0 to 3.0MPa), 22 to 30bar (2.2 to 3.0MPa), 22 to 28bar (2.2 to 2.8MPa) or 24 to 30bar (2.4 to 3.0 MPa).

The lubricating oil compositions of the present invention can provide improved deposit control performance in any of a number of mechanical components of an engine. The mechanical component may be a piston, piston ring, cylinder liner, cylinder, cam, tappet, lifter, gear, valve guide, or bearing including journal, roller, taper, needle, or ball bearing. In certain aspects, the mechanical component comprises steel.

Base oil

Group I, II, III, IV, and V are broad categories of base oils developed and defined by the American Petroleum institute (API publication 1509-appendix E) to create lubricant base oil guidelines group I base oils contain less than 90% saturates and/or greater than 0.03% sulfur content, and have a viscosity index greater than or equal to 80 and less than 120 group II base oils contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur content, and have a viscosity index greater than or equal to 80 and less than 120 group III base oils contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur content, and have a viscosity index greater than or equal to 120 group IV base oils are poly α -olefins group V base oils include all other base oils not included in groups I, II, III, IV, Table 1 summarizes the properties of each of these five categories.

TABLE 1

⁽¹⁾Group I-III are mineral oil base oils

⁽²⁾ASTM D2007

⁽³⁾ASTM D2622, ASTM D3120, ASTM D4294 or ASTM D4927

⁽⁴⁾ASTM D2270

The lubricating oil compositions of the present disclosure are mixtures of at least two base oil components. The mixture of at least two base oil components comprises a minor amount of a first base oil component having a kinematic viscosity at 100 ℃ of 8.5 to 15.0mm²S (e.g. 9.0-14.0 mm)²Or 10.0-13.0mm²Or 10.0-12.0mm²(s) said first base oil component is selected from one or more of group I base oils, group II base oils and group III base oils; and a major amount of a second base oil component having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S (e.g. 4.5 to 8.0 mm)²S, 5.0 to 8.0mm²Or 5.0 to 7.5mm²S) of a second base oil component selected from one or more of group I base oils, group II base oils and group III base oils. In some aspects, the first base oil component can be selected from a group II base oil, a group III base oil, or a combination thereof. In some aspects, the second base oil component can be selected from a group II base oil, a group III base oil, or a combination thereof.

The high viscosity first base oil component may consist of a single base stock meeting the kinematic viscosity range or two or more base stocks both meeting the kinematic viscosity limits.

The low viscosity second base oil component may consist of a single base stock meeting the kinematic viscosity range or may consist of two or more base stocks that both meet the kinematic viscosity limits.

The weight ratio of the first base oil component to the second base oil component may be in the range of 1:10 to 1: 1.15 (e.g., 1:10 to 1: 6, 1: 8 to 1: 5, 1: 5 to 1: 1.15, 1: 6 to 1: 4, 1: 4 to 1: 2, 1: 3 to 1: 1.15, 1: 6 to 1: 2, or 1: 3 to 1: 1.15).

Lubricating oil composition

The lubricating oil compositions of the present disclosure may be identified by the Society of Automotive Engineers (SAE) viscosity standard for engine oils (i.e., the SAE J300 standard). Table 2 summarizes the SAE J300 viscosity grades.

TABLE 2

⁽¹⁾ASTM D5293

⁽²⁾ASTM D4684

⁽³⁾ASTM D445

⁽⁴⁾ASTM D4683, ASTM D4741, ASTM D5481 or CEC L-36-90

⁽⁵⁾For 0W-40,5W-40 and 10W-40 grades

⁽⁶⁾For 15W-40,20W-40,25W-40 and 40 grades

The lubricating oil composition of the present disclosure may be a single stage engine oil, such as an SAE 20, SAE30, SAE 40, SAE50, or SAE 60 viscosity grade engine oil.

The lubricating oil composition of the present invention may be a multigrade engine oil, for example an engine oil having an SAE viscosity grade of 15W-x, 20W-x or 25W-x, wherein x may be selected from 30, 40, 50 or 60.

To obtain a finished lubricating oil composition having a desired viscosity grade, a thickener may be added to the lubricating oil composition to increase its viscosity. Any suitable thickener may be used, such as Polyisobutylene (PIB). PIB isMaterials are available from a variety of manufacturers. The polyisobutenes are generally viscous oil-soluble liquids having a number-average molecular weight of from 800 to 5000, for example from 1000 to 2500, and a kinematic viscosity at 100 ℃ of from 200 to 5000mm²S (e.g. 200 to 1000 mm)²In s). The amount of PIB added to the lubricating oil composition is typically 1 to 20 wt.% (e.g., 2 to 15 wt.% or 4 to 12 wt.%) of the finished oil.

The lubricating oil composition may contain low levels of sulfated ash as determined according to ASTM D874. The sulfated ash content of the composition may be less than 1.0 wt.%, based on the total weight of the composition (e.g., less than 0.6 wt.% or even less than 0.15 wt.%).

In some embodiments, the lubricating oil composition may be substantially free of zinc.

In some embodiments, the lubricating oil composition may be substantially free of bright stock.

Other additives

The lubricating oil compositions of the present disclosure may comprise one or more performance additives that may impart or improve any desired property of the lubricating oil composition. Any additive known to those skilled in the art may be used in the lubricating oil compositions disclosed herein. Some suitable Additives have been described by r.m. mortier et al, "Chemistry and Technology of lubricants", 3 rd edition, Springer (2010) and l.r. rudnik, "Lubricant Additives: Chemistry and Applications, second edition, CRC press (2009).

Typically, when used, the concentration of each additive in the lubricating oil composition can be from 0.001 to 10 wt.% (e.g., from 0.01 to 5 wt.%, or from 0.05 to 2.5 wt.%) of the lubricating oil composition. Further, the total amount of additives in the lubricating oil composition can be in the range of 0.001 to 20 wt.% of the lubricating oil composition (e.g., 0.01 to 15 wt.% or 0.1 to 10 wt.%).

The lubricating oil compositions of the present invention may additionally comprise one or more other conventional lubricating oil performance additives including antioxidants, antiwear agents, metal detergents, dispersants, friction modifiers, corrosion inhibitors, demulsifiers, viscosity modifiers, pour point depressants, foam inhibitors and the like.

Antioxidant agent

Antioxidants prevent oxidative degradation of the base oil during use. This degradation may result in metal surface deposits, the presence of sludge, or an increase in the viscosity of the lubricant. Useful antioxidants include hindered phenols, aromatic amines, and sulfurized alkylphenols, as well as alkali metal and alkaline earth metal salts thereof.

The hindered phenol antioxidant may comprise sec-butyl and/or tert-butyl as a sterically hindering group. The phenolic group may be further substituted with a hydrocarbyl group and/or a bridging group attached to the second aromatic group. Examples of suitable hindered phenol antioxidants include 2, 6-di-tert-butylphenol, 4-methyl-2, 6-di-tert-butylphenol, 2' -methylenebis (6-tert-butyl-4-methylphenol), 4 ' -bis (2, 6-di-tert-butylphenol), and 4, 4 ' -methylenebis (2, 6-di-tert-butylphenol). The hindered phenolic antioxidant may be an ester or addition product derived from 2, 6-di-tert-butylphenol and an alkyl acrylate, wherein the alkyl group may contain from 1 to 18 carbon atoms.

Suitable aromatic amine antioxidants include diarylamines such as alkylated diphenylamines (e.g., dioctyldiphenylamine, dinonyldiphenylamine), phenyl- α -naphthalene, and alkylated phenyl- α -naphthalene.

Antiwear agent

The antiwear agent reduces wear of the metal parts. Examples of antiwear agents include phosphorus-containing antiwear/extreme pressure agents such as metal thiophosphates, phosphate esters and salts thereof, phosphorus-containing carboxylic acids, esters, ethers, and amides; and phosphites. The antiwear agent may be zinc dialkyldithiophosphate. Non-phosphorus-containing antiwear agents include borate esters (including borated epoxides), dithiocarbamate compounds, molybdenum-containing compounds, and sulfurized olefins.

Metal detergent

Typical detergents are anionic materials comprising a long chain hydrophobic portion of the molecule and an anionic or oleophobic hydrophilic portion of the smaller molecule. The anionic portion of the detergent is typically derived from an organic acid, such as sulfuric acid, carboxylic acid, phosphorous acid, phenol, or mixtures thereof. The counterion is typically an alkaline earth or alkali metal.

In some embodiments, the lubricating oil compositions provided herein comprise at least a neutral or overbased metal detergent as an additive or additive component. In certain embodiments, the metal detergent in the lubricating oil composition acts as a neutralizer for acidic products in the oil. In certain embodiments, the metal detergent prevents the formation of deposits on engine surfaces. Detergents may have other functions, such as antioxidant properties, depending on the nature of the acid used. In certain aspects, the lubricating oil composition comprises a metal detergent comprising an overbased detergent or a mixture of neutral and overbased detergents. The term "overbased" is intended to define an additive having a metal content in excess of the stoichiometric requirements for the particular metal and the particular organic acid used. The excess metal is present in the form of particles of an inorganic base (e.g. hydroxide or carbonate) surrounded by a shell of a metal salt. The shell layer serves to maintain the dispersion of the particles in the liquid oleaginous vehicle. The amount of excess metal is typically expressed as the ratio of the total equivalents of excess metal to the equivalents of organic acid, and is typically in the range of 0.1 to 30.

Some examples of suitable metal detergents include sulfurized or unsulfurized alkyl or alkenyl phenates, alkyl or alkenyl aromatic sulfonates, borated sulfonates, sulfurized or unsulfurized metal salts of polyhydroxy alkyl or alkenyl aromatic compounds, alkyl or alkenyl hydroxyaromatic sulfonates, sulfurized or unsulfurized alkyl or alkenyl naphthenates, metal salts of alkanoic acids, metal salts of alkyl or alkenyl polyacids, and chemical and physical mixtures thereof. Other examples of suitable metal detergents include metal sulfonates, phenates, salicylates, phosphonates, thiophosphonates, and combinations thereof. The metal may be any metal suitable for making sulfonate, phenate, salicylate, or phosphonate detergents. Non-limiting examples of suitable metals include alkali metals, and transition metals. In some embodiments, the metal is Ca, Mg, Ba, K, Na, Li, or the like. Exemplary metal detergents that may be used in the lubricating oil composition include overbased calcium phenates.

Ashless dispersants

Dispersants are additives whose primary function is to keep solid and liquid contaminants in suspension, thereby passivating them and reducing engine deposits while reducing sludge deposition. For example, dispersants suspend oil-insoluble materials produced by oxidation during lubricant use, thus preventing sludge from flocculating and settling or depositing on metal components of the engine.

Dispersants are typically "ashless," non-metallic organic materials that form substantially no ash on combustion, as opposed to metals and thus ash-forming materials. They comprise a long hydrocarbon chain with a polar head, the polarity being derived from at least one of nitrogen, oxygen or phosphorus atoms. Hydrocarbons are, for example, lipophilic groups having 40 to 500 carbon atoms, which impart oil solubility. Thus, ashless dispersants may comprise an oil soluble polymer backbone.

A preferred class of olefin polymers consists of polybutenes, in particular Polyisobutylene (PIB) or poly-n-butene, which may be polymerized, for example, by C₄Polymerization of refinery streams.

Dispersants include, for example, derivatives of long chain hydrocarbon-substituted carboxylic acids, examples being derivatives of high molecular weight hydrocarbyl-substituted succinic acids. The dispersant group of note is comprised of hydrocarbon-substituted succinimides, for example, made by reacting the above acids (or derivatives) with a nitrogen-containing compound, preferably a polyalkylene polyamine, such as a polyethylene polyamine. A typical commercially available polyisobutylene-based succinimide dispersant comprises a polyisobutylene polymer with a number average molecular weight of 900 to 2500, functionalized with maleic anhydride, and derivatized with a polyamine with a molecular weight of 100 to 350.

Other suitable dispersants include succinate and ester-amide, mannich bases, polyisobutylene succinic acid (PIBSA), and other related components.

Succinic esters are formed by a condensation reaction between a hydrocarbon-substituted succinic anhydride and an alcohol or polyol. For example, the condensation product of a hydrocarbon-substituted succinic anhydride and pentaerythritol is a useful dispersant.

The succinate-amide is formed by a condensation reaction between a hydrocarbon-substituted succinic anhydride and an alkanolamine. For example, suitable alkanolamines include ethoxylated polyalkylpolyamines, propoxylated polyalkylpolyamines, and polyalkenyl polyamines, such as polyethylene polyamines. One example is propoxylated hexamethylenediamine.

Mannich bases are prepared from the reaction of an alkylphenol, formaldehyde and a polyalkylene polyamine. The alkylphenol may have a molecular weight in the range of 800 to 2500.

The nitrogen-containing dispersant may be post-treated by conventional methods to improve its performance by reaction with any of a variety of agents. Including boron compounds (e.g., boric acid) and cyclic carbonates (e.g., ethylene carbonate).

Friction modifiers

A friction modifier is any material or materials that can alter the coefficient of friction of a surface lubricated by any lubricant or fluid containing such a substance. Friction modifiers include alkoxylated fatty amines, borated fatty epoxides, fatty phosphites, fatty epoxides, fatty amines, borated alkoxylated fatty amines, metal salts of fatty acids, fatty acid amides, glycerol esters, borated glycerol esters, and fatty imidazolines. As used herein, the term "fat" refers to a hydrocarbon chain, typically a straight hydrocarbon chain, having from 10 to 22 carbon atoms.

Other known friction modifiers include oil-soluble organo-molybdenum compounds. Such organo-molybdenum friction modifiers also provide antioxidant and antiwear effects to the lubricating oil composition. Suitable oil-soluble organo-molybdenum compounds have a molybdenum-sulfur core. Mention may be made, as examples, of dithiocarbamates, dithiophosphates, dithiophosphinates, xanthates, thioxanthates, sulfides and mixtures thereof. The molybdenum compound may be binuclear or trinuclear.

Corrosion inhibitors

Corrosion inhibitors can protect lubricated metal surfaces from chemical attack by water or other contaminants. Suitable corrosion inhibitors include polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, thiadiazoles, and anionic alkyl sulfonic acids.

Viscosity improver

Viscosity modifiers provide lubricants with high and low temperature operability. These additives increase the viscosity of the oil composition at elevated temperatures, which increases the film thickness, while having a limited effect on the viscosity at low temperatures.

Suitable viscosity modifiers include high molecular weight hydrocarbons, polyesters, and viscosity index improver dispersants that function as both a viscosity index improver and a dispersant. Typical molecular weights of these polymers are from 1000 to 1,000,000 (e.g., 2000 to 500,000 or 25,000 to 100,000).

Examples of suitable viscosity modifiers are polymers and copolymers of methacrylates, butadienes, olefins or alkylated styrenes. Polyisobutylene is a commonly used viscosity modifier. Another suitable viscosity modifier is polymethacrylate (e.g., copolymers of alkyl methacrylates of various chain lengths), some of which may also be used as pour point depressants. Other suitable viscosity modifiers include copolymers of ethylene and propylene, hydrogenated block copolymers of styrene and isoprene, and polyacrylates (e.g., copolymers of various chain length acrylates). Specific examples include styrene-isoprene or styrene-butadiene based polymers having a molecular weight of 50,000 to 200,000.

Pour point depressant

Pour point depressants lower the minimum temperature at which the fluid will flow or can be poured. Suitable pour point depressants include fumaric acid C₈-C₁₈Dialkyl fumarate/vinyl acetate copolymers, polyalkylmethacrylates, and the like.

Foam inhibitor

Foam inhibitors hinder the formation of stable foams. Examples of suitable foam inhibitors include polysiloxanes, polyacrylates, and the like.

In one aspect, there is provided a natural gas engine lubricating oil composition comprising: (a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and (b) a second base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

in another aspect, there is provided a low or medium speed diesel engine lubricating oil composition comprising: (a) a first base oil component selected from group I base oils, group II base oils, group III base oils, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 8.5 to 15mm²S; and (b) a second base oil component selected from a group I base oil, a group II base oil, a group III base oil, or combinations thereof, each having a kinematic viscosity at 100 ℃ of from 4.0 to less than 8.5mm²S; wherein the weight ratio of the first base oil component to the second base oil component is from 1:10 to 1: 1.15.

in another aspect, there is provided a method of controlling deposit formation in an internal combustion engine selected from a natural gas engine, a low speed diesel engine or a medium speed diesel engine, comprising operating said internal combustion engine with said lubricating oil composition disclosed herein.

In another aspect, there is provided a use of a lubricating oil composition as described herein for the purpose of controlling deposit formation in an internal combustion engine selected from a natural gas engine, a low speed diesel engine or a medium speed diesel engine.

Examples

The following illustrative examples are intended to be non-limiting.

To determine the effect of the base oil on deposit control in the engine, lubricating oil compositions having the formulations set forth in the examples below were prepared. The composition is prepared by mixing the base oil with the additive package according to conventional preparation methods. The properties of the base oils are listed in table 3. The deposition performance of the lubricating oil compositions was measured using the PennState micro Oxidation test (SAE Technical Paper 801362) after 35 minutes at 260 ℃.

TABLE 3

Base oil Properties