Marine engine lubrication

Abstract

 Trunk piston marine engine crankcase lubrication is effected by a composition that includes a zinc dihydrocarbyl dithiophosphoric acid salt additive component in an amount providing in the range of 400 to 700 or to 1000 ppm P by mass to diminish loss ofBN and diminish increase of viscosity during use of the composition.

Description

FIELD OF THE INVENTION

[0001] This invention relates to the lubrication of 4-stroke marine diesel internal combustion engines, usually referred to as trunk piston engines. Lubricants therefor are usually known as trunk piston engine oils ("TPEO's").

BACKGROUND OF THE INVENTION

[0002] Trunk piston engines may be used in marine, power-generation and rail traction applications and have a higher speed than cross-head engines. A single lubricant (TPEO) is used for crankcase and cylinder lubrication. All major moving parts of the engine, i.e. the main and big end bearings, camshaft and valve gear, are lubricated by means of a pumped circulation system. The cylinder liners are lubricated partially by splash lubrication and partially by oil from the circulation systems that finds its way to the cylinder wall through holes in the piston skirt via the connecting rod and gudgeon pin. Trunk piston engines normally include a centrifuge to clean the TPEO.

[0003] Zinc dialkyl dithiophosphates ("ZDDP's") are known in the art as additives for TPEO's to provide wear protection for gears and valve train in trunk piston engines. See for example EP-A-2 123740; EP-A-1 154 099; EP-A-1 528 099; and US-A-2009/0011966.

[0004] The art does not, however, mention the effect of ZDDP on the dimunition of base number (BN) during use of the TPEO; nor its effect on viscosity increase.

SUMMARY OF THE INVENTION

[0005] It is now found that the use of ZDDP's in defined amounts in a TPEO has a beneficial effect on the BN and viscosity.

[0006] Thus, the present invention provides the use of a zinc dihydrocarbyl dithiophosphate additive in an amount providing in the range of greater than 400 to 700, or 400 to 1000, ppm P by mass in a trunk piston marine lubricating oil composition for a medium-speed compression-ignited marine engine, fueled by a heavy fuel oil, and its lubrication by the composition, the composition having a BN in the range of 20 to 60, preferably 30 to 55, the use being to diminish the loss of BN and to diminish the increase in viscosity in comparison with analogous use when the amount of zinc dihydrocarbyl dithiophosphate falls outside of the above range.

[0007] In this specification, the following words and expressions, if and when used, have the meanings ascribed below:

"active ingredients" or "(a.i.)" refers to additive material that is not diluent or solvent;

"comprising" or any cognate word specifies the presence of stated features, steps, or integers or components, but does not preclude the presence or addition of one or more other features, steps, integers, components or groups thereof; the expressions "consists of" or "consists essentially of" or cognates may be embraced within "comprises" or cognates, wherein "consists essentially of" permits inclusion of substances not materially affecting the characteristics of the composition to which it applies;

"major amount" means 50 mass % or more, preferably 60 mass % or more, even more preferably 60 mass % or more, of a composition;

"minor amount" means less than 50 mass %, preferably less than 40 mass %, even more preferably less than 30 mass %, of a composition;

"TBN" means total base number as measured by ASTM D2896. "BN" has the same meaning.

[0008] Furthermore in this specification, if and when used:

"calcium content" is as measured by ASTM 4951;

"phosphorus content" is as measured by ASTM D5185;

"sulphated ash content" is as measured by ASTM D874;

"sulphur content" is as measured by ASTM D2622;

"KV100" means kinematic viscosity at 100°C as measured by ASTM D445.

[0009] Also, it will be understood that various components used, essential as well as optimal and customary, may react under conditions of formulation, storage or use and that the invention also provides the product obtainable or obtained as a result of any such reaction.

[0010] Further, it is understood that any upper and lower quantity, range and ratio limits set forth herein may be independently combined.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The features of the invention will now be discussed in more detail below.

TRUNK PISTON MARINE ENGINE LUBRICATING OIL COMPOSITION ("TPEO")

[0012] A TPEO may employ 7-35, preferably 10-28, more preferably 12-24, mass % of a concentrate or additives package, the remainder being base stock (oil of lubricating viscosity). Preferably, the TPEO has a compositional TBN (using D2896) of 20-60, preferably 25 or 30-55.

[0013] The following may be mentioned as typical proportions of additives in a TPEO.

Additive	Mass% a.i. (Broad)	Mass % a.i. (Preferred)
detergent(s)	0.5-12	2-8
dispersant(s)	0.5-5	1-3
anti-wear agent(s)	0.1-1.5	0.5-1.3
oxidation inhibitor	0.2-2	0.5-1.5
rust inhibitor	0.03-0.15	0.05-0.1
pour point dispersant	0.03-1.15	0.05-0.1
base stock	balance	balance

[0014] When a plurality of additives is employed it may be desirable, although not essential, to prepare one or more additive packages comprising the additives, whereby several additives can be added simultaneously to the oil of lubricating viscosity to form the lubricating oil composition. Dissolution of the additive package(s) into the lubricating oil may be facilitated by solvents and by mixing accompanied with mild heating, but this is not essential. The additive package(s) will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration, and/or to carry out the intended function, in the final formulation when the additive package(s) is/are combined with a predetermined amount of base lubricant. Thus, compounds in accordance with the present invention may be admixed with small amounts of base oil or other compatible solvents together with other desirable additives to form additive packages containing active ingredients.

ZINC DIHYDROCARBYL DITHIOPHOSPHATE ADDITIVE

[0015] Dihydrocarbyl dithiophosphate metal salts may be prepared in accordance with known techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually by reaction of one or more alcohols or a phenol with P₂S₅ and then neutralizing the formed DDPA with a metal compound. For example, a dithiophosphoric acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely primary in character. To make the metal salt, any basic or neutral metal compound could be used but the oxides, hydroxides and carbonates are most generally employed. Commercial additives frequently contain an excess of metal due to the use of an excess of the basic metal compound in the neutralization reaction.

[0016] Preferred zinc dihydrocarbyl dithiophosphates are oil-soluble salts that may be represented by the following formula:

where R¹ and R² may be the same or different hydrocarbyl groups containing 1 to 18, preferably 2 to 12, carbon atoms and include groups such as alkyl, alkenyl, aryl, arylalkyl, alkaryl and cyloaliphatic groups. Particularly preferred as R¹ and R² groups are alkyl groups of 2 to 8 carbon atoms. The groups may, for example, be ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, see-butyl, amyl, n-hexyl, iso-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, propenyl and butenyl. In order to confer the salt with oil-solubility, the total number of carbon atoms (i.e. in R¹ and R²) is generally five or more.

[0017] The zinc dihydrocarbyl dithiophospate may advantageously be a zinc dialkyl dithiophosphate, such as a secondary C₆ salt.

[0018] As stated, the salt or salts provide the TPEO with greater than 400 to 700, or greater than 400 to 1000 ppm by mass of P atoms. Preferred are 450 to 700, such as 500 to 700 ppm P by mass. The co-additives will now be discussed in further detail.

METAL DETERGENT

[0019] A detergent is an additive that reduces formation of deposits, for example, high-temperature varnish and lacquer deposits, in engines; it has acid-neutralising properties and is capable of keeping finely divided solids in suspension. It is based on metal "soaps", that is metal salts of acidic organic compounds, sometimes referred to as surfactants.

[0020] A detergent comprises a polar head with a long hydrophobic tail. Large amounts of a metal base are included by reacting an excess of a metal compound, such as an oxide or hydroxide, with an acidic gas such as carbon dioxide to give an overbased detergent which comprises neutralised detergent as the outer layer of a metal base (e.g. carbonate) micelle.

[0021] The detergent is preferably an alkali metal or alkaline earth metal additive such as an overbased oil-soluble or oil-dispersible calcium, magnesium, sodium or barium salt of a surfactant selected from phenol, sulphonic acid, carboxylic acid, salicylic acid and naphthenic acid, wherein the overbasing is provided by an oil-insoluble salt of the metal, e.g. carbonate, basic carbonate, acetate, formate, hydroxide or oxalate, which is stabilised by the oil-soluble salt of the surfactant. The metal of the oil-soluble surfactant salt may be the same or different from that of the metal of the oil-insoluble salt. Preferably the metal, whether the metal of the oil-soluble or oil-insoluble salt, is calcium.

[0022] The TBN of the detergent may be low, i.e. less than 50 mg KOH/g, medium, i.e. 50-150 mg KOH/g, or high, i.e. over 150 mg KOH/g, as determined by ASTM D2896. Preferably the TBN is medium or high, i.e. more than 50 TBN. More preferably, the TBN is at least 60, more preferably at least 100, more preferably at least 150, and up to 500, such as up to 350 mg KOH/g, as determined by ASTM D2896.

[0023] Preferably, the detergent comprises an alkaline earth hydrocarbyl-substituted hydroxyl-benzoate salt such as a calcium alkylsalicylate salt.

[0024] The terms 'oil-soluble' or 'oil-dispersable' as used herein do not necessarily indicate that the compounds or additives are soluble, dissolvable, miscible or capable of being suspended in the oil in all proportions. These do mean, however, that they are, for instance, soluble or stably dispersible in oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired.

[0025] The lubricant compositions of this invention comprise defined individual (i.e. separate) components that may or may not remain the same chemically before and after mixing.

[0026] It may be desirable, although not essential, to prepare one or more additive packages or concentrates comprising the additives, whereby the additives can be added simultaneously to the oil of lubricating viscosity to form the lubricating oil composition. Dissolution of the additive package(s) into the lubricating oil may be facilitated by solvents and by mixing accompanied with mild heating, but this is not essential. The additive package(s) will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration, and/or to carry out the intended function in the final formulation when the additive package(s) is/are combined with a predetermined amount of base lubricant.

[0027] Thus, the additives may be admixed with small amounts of base oil or other compatible solvents together with other desirable additives to form additive packages containing active ingredients in an amount, based on the additive package, of, for example, from 2.5 to 90, preferably from 5 to 75, most preferably from 8 to 60, mass % of additives in the appropriate proportions, the remainder being base oil.

OTHER CO-ADDITIVES

[0028] The lubricating oil composition of the invention may comprise further additives. Such additional additives may, for example, include ashless dispersants, other metal detergents, other anti-wear agents, such as anti-oxidants such as aminic or phenolic anti-oxidants, and demulsifiers.

OIL OF LUBRICATING VISCOSITY

[0029] The lubricating oils present as a major proportion of the TPEO may range in viscosity from light distillate mineral oils to heavy lubricating oils. Generally, the viscosity of the oil ranges from 2 to 40 mm²/sec, as measured at 100°C.

[0030] Natural oils include animal oils and vegetable oils (e.g., caster oil, lard oil); liquid petroleum oils and hydrorefined, solvent-treated or acid-treated mineral oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale also serve as useful base oils.

[0031] Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkybenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulphides and derivative, analogs and homologs thereof.

[0032] Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic lubricating oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-polyiso-propylene glycol ether having a molecular weight of 1000 or diphenyl ether of poly-ethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C₃-C₈ fatty acid esters and C₁₃ Oxo acid diester of tetraethylene glycol.

[0033] Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of such esters includes dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles oftetraethylene glycol and two moles of 2-ethylhexanoic acid.

[0034] Esters useful as synthetic oils also include those made from C₅ to C₁₂ monocarboxylic acids and polyols and polyol esters such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.

[0035] Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and silicate oils comprise another useful class of synthetic lubricants; such oils include tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes and poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid esters of phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

[0036] Unrefined, refined and re-refined oils can be used in lubricants of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations; petroleum oil obtained directly from distillation; or ester oil obtained directly from an esterification and used without further treatment would be an unrefined oil. Refined oils are similar to unrefined oils except that the oil is further treated in one or more purification steps to improve one or more properties. Many such purification techniques, such as distillation, solvent extraction, acid or base extraction, filtration and percolation are known to those skilled in the art. Re-refined oils are obtained by processes similar to those used to provide refined oils but begin with oil that has already been used in service. Such re-refined oils are also known as reclaimed or reprocessed oils and are often subjected to additional processing using techniques for removing spent additives and oil breakdown products.

[0037] The American Petroleum Institute (API) publication "Engine Oil Licensing and Certification System", Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998 categorizes base stocks as follows:

a) Group I base stocks contain less than 90 percent saturates and/or greater than 0.03 percent sulphur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1.

b) Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1.

c) Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur and have a viscosity index greater than or equal to 120 using the test methods specified in Table E-1.

d) Group IV base stocks are polyalphaolefins (PAO).

e) Group V base stocks include all other base stocks not included in Group I, II, III, or IV.

[0038] Analytical Methods for Base Stock are tabulated below:

PROPERTY	TEST METHOD
Saturates	ASTM D 2007
Viscosity Index	ASTM D 2270
Sulphur	ASTM D 2622
	ASTM D 4294
	ASTM D 4927
	ASTM D 3120

[0039] As examples of the above oils, there may be mentioned the Group I and Group II oils. Also, there may be mentioned those of the above oils containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur as the oil of lubricating viscosity, eg Group II, III, IV or V. They also include basestocks derived from hydrocarbons synthesised by the Fischer-Tropsch process. In the Fischer-Tropsch process, synthesis gas containing carbon monoxide and hydrogen (or 'syngas') is first generated and then converted to hydrocarbons using a Fischer-Tropsch catalyst. These hydrocarbons typically require further processing in order to be useful as a base oil. For example, they may, by methods known in the art, be hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized and dewaxed. The syngas may, for example, be made from gas such as natural gas or other gaseous hydrocarbons by steam reforming, when the basestock may be referred to as gas-to-liquid ("GTL") base oil; or from gasification of biomass, when the basestock may be referred to as biomass-to-liquid ("BTL" or "BMTL") base oil; or from gasification of coal, when the basestock may be referred to as coal-to-liquid ("CTL") base oil.

[0040] Preferably, the oil of lubricating viscosity in this invention contains 50 mass % or more said basestocks. It may contain 60, such as 70, 80 or 90, mass % or more of said basestock or a mixture thereof. The oil of lubricating viscosity may be substantially all of said basestock or a mixture thereof.

[0041] It may be desirable, although not essential, to prepare one or more additive packages or concentrates comprising additives, whereby additives can be added simultaneously to the oil of lubricating viscosity to form the TPEO.

[0042] The final formulations as a trunk piston engine oil may typically contain 30, preferably 10 to 28, more preferably 12 to 24, mass % of the additive package(s), the remainder being the oil of lubricating viscosity. The trunk piston engine oil may have a compositional TBN (using ASTM D2896) of 20 to 60, such as, 30 to 55. For example, it may be 40 to 55 or 35 to 50.

[0043] The treat rate of additives contained in the lubricating oil composition may for example be in the range of 1 to 2.5, preferably 2 to 20, more preferably 5 to 18, mass %.

EXAMPLES

[0044] The present invention is illustrated by but not limited to the following examples.

TPEO'S

[0045] A first set of TPEO's was formulated comprising two TPEO's which differed only in the amount of secondary C₆ ZDDP they contained and base oil to balance. Each TPEO contained a mixture of overbased calcium salicylate detergents, a mixture of aminic and phenolic anti-oxidants, and other co-additives. They contained the same amounts of base oil to balance.

[0046] Each TPEO was tested in a bulk oil oxidation test where the oil was contaminated with 0.5 % HFO (Heavy Fuel Oil) and subjected to oxidising conditions for 120 hours. The test was the DKA oxidation test (CEC L-48-00) in which BN and viscosity change were assessed.

[0047] The results are tabulated below:

Example	% ZDDP (expressed as ppm P)	BN Initial	BN End	BN Change	KV100 Initial	KV100 End	KV100 Change
Ref 1	374	55.24	55.01	6%	15.45	19.07	23%
Inv 1	544	52.61	51.68	2%	15.45	17.72	15%

[0048] The results show that the example of the invention (Inv 1), which contained more ZDDP, exhibited both a lower reduction in BN and a lower increase in KV100 than the comparison example (Ref 1).

[0049] The second set of TPEO's was subject to the same procedure as described above for the first set. The second set comprised two TPEO's differing only in the amounts of the same ZDDP and the base oil.

[0050] The results are tabulated below:

Example	% ZDDP (expressed as ppm P)	BN Initial	BN End	BN Change	KV100 Initial	KV100 End	KV100 Change
Ref 2	408	48.32	46.07	5%	14.17	16.6	18%
Inv 2	544	54.87	51.93	5%	14.65	15.81	8%

[0051] The results show that the example of the invention (Inv 2), which contained more ZDDP, exhibited the same reduction in BN and a lower increase in KV100 than the comparison example (Ref 2).

Claims

1. The use of a zinc dihydrocarbyl dithiophosphate additive in an amount providing in the range of greater than 400 to 700, or 400 to 1000, ppm P by mass in a trunk piston marine lubricating oil composition for a medium-speed compression-ignited marine engine, fueled by a heavy fuel oil, and its lubrication by the composition, the composition having a BN in the range of 20 to 60, preferably 30 to 55, the use being to diminish the loss of BN and to diminish the increase in viscosity in comparison with analogous use when the amount of zinc dihydrocarbyl dithiophosphate falls outside of the above range.

2. The use of claim 1 where the composition comprises an oil of lubricating viscosity, in a major amount, containing 50 mass % or more of a basestock containing greater than or equal to 90 % saturates and less than or equal to 0.03 % sulphur.

3. The use of claim 1 or claim 2 where the composition contains an overbased alkyl-substituted hydroxybenzoate calcium salt detergent additive, such as a calcium salicylate.

4. The use of any of claims 1 to 3 where the composition contains one or more co-additives selected from aminic or phenolic anti-oxidants and from ashless dispersants.

5. The use of any of claims 1 to 4 where the zinc dihydrocarbyl dithiophosphate is a secondary C₆ alkyl salt.

6. The use of any of claims 1 to 5 where said range is from 450 to 700, such as from 500 to 700, ppm P by mass.

7. A trunk piston marine lubricating oil composition for a medium-speed compression-ignited marine engine including a zinc dihydrocarbyl dithiophosphate additive in an amount providing in the range of greater than 400 to 700 or to 1000 ppm P by mass in the composition.

8. The composition of claim 7 where the range is from 450 to 700, such as 500 to 700, ppm P by mass.