Note: Descriptions are shown in the official language in which they were submitted.
CA 02799602 2012-12-21
MARINE ENGINE LUBRICATION
FIELD OF THE INVENTION
This invention relates to the lubrication of 2-stroke and 4-stroke marine
diesel internal combustion engines, the former usually being referred to as
cross-
head engines and the latter as trunk piston engines. Respective lubricants
therefor
are usually known as marine diesel cylinder lubricants ("MDCL's") and trunk
piston
engine oils ("TPEO's").
BACKGROUND OF THE INVENTION
Cross-head engines are slow engines with a high to very high power range.
They include two separately-lubricated parts: the piston/cylinder assembly
lubricated with total-loss lubrication by a highly viscous oil (an MDCL); and
the
crankshaft lubricated by a less viscous lubricant, usually referred to as a
system oil.
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.
It is known in the art to include brightstock in MDCL's and TPEO's,
brightstock being a high viscosity oil that is highly refined and dewaxed and
that is
produced from residual stocks or bottoms. It may, for example, have a
kinematic
viscosity at 100 C of greater than 25, usually greater than 30, mm2s'1, such
as a
solvent-extracted, de-asphalted product from vacuum residuum generally having
a
kinematic viscosity at 100 C of 28-36 mm2s-I.
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Brightstock is however expensive and art describes ways of replacing it.
WO 99/64543 describes MDCL's formulated without brightstock and US
2008/0287329 describes a TPEO containing little or no brightstock.
A problem in the art is to formulate brightstock-free MDCL's and TPEO's at
reduced cost and at the same time provide improved antiwear properties.
SUMMARY OF THE INVENTION
It is now found that the use of olefin copolymers such as an amorphous
ethylene-propylene copolymer in an MDCL or a TPEO enables the above problem
to be overcome.
Thus, the present invention provides a two-stroke or four-stroke marine
engine lubricating oil composition comprising an oil of lubricating viscosity
in a
major amount and
(A) additives, in respective minor amounts; and
(B) a viscosity modifier in the form of an olefin copolymer in an amount
in the range of 0.05 - 6 mass %,
wherein the composition includes less than 0.5 mass%, preferably less than 0.1
mass%, of brightstock; preferably brightstock is completely or substantially
absent
from the composition.
In further aspects the present invention comprises:-
The use of a viscosity modifier (B) to improve the anti-wear properties of a
marine diesel cylinder lubricant or of a trunk piston engine oil which
includes less
than 0.5 mass%, preferably less than 0.1 mass%, of brightstock; preferably
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brightstock is absent or is substantially absent from the marine diesel
cylinder
lubricant or the trunk piston engine oil;
A method of lubricating a cross-head marine diesel engine comprising
supplying a lubricating oil composition including viscosity modifier (B) to
the
piston/cylinder assembly of the engine; and
A method of lubricating a trunk piston marine diesel engine comprising
supplying the composition to the engine.
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 40 or 50 mass % or more of a composition;
"minor amount" means less than 50 mass % of a composition;
"TBN" means total base number as measured by ASTM D2896.
Furthermore in this specification, if and when used:
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"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.
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.
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
The features of the invention will now be discussed in more detail below.
OIL OF LUBRICATING VISCOSITY
The lubricant composition contains a major proportion of an oil of
lubricating viscosity. Such lubricating oils may range in viscosity from light
distillate mineral oils to heavy lubricating oils. Generally, the viscosity of
the oil
ranges from 2 to 40, such as 3 to 15, mm2/sec, as measured at 100 C, and a
viscosity
index of 80 to 100, such as 90 to 95. The lubricating oil may comprise greater
than
60, typically greater than 70. mass % of the composition.
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i
Natural oils include animal oils and vegetable oils (e.g., castor 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.
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, analogues and homologues thereof.
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.
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, sebacic 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,
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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 of tetraethylene glycol and two moles of 2-ethylhexanoic
acid.
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.
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 phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate,
diethyl
ester of decylphosphonic acid) and polymeric tetrahydrofurans.
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 esterification and used without further
treatment
are unrefined oils.
Marine Diesel Cylinder Lubricant ("MDCL")
An MDCL may employ 10-35, preferably 13-30, most preferably 16-24,
mass % of a concentrate or additive package, the remainder being base stock.
It
preferably includes at least 50, more preferably at least 60, even more
preferably at
least 70, mass % of oil of lubricating viscosity based on the total mass of
MDCL.
Preferably, the MDCL has a compositional TBN (using ASTM D2896) of 40-100,
such as 50-60.
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The following may be mentioned as examples of typical proportions of
additives in an MDCL.
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Additive Mass% a.i. Mass % a.i.
(Broad) (Preferred)
detergent(s) 1-20 3-15
dispersant(s) 0.5-5 1-3
anti-wear agent(s) 0.1-1.5 0.5-1.3
pour point dispersant 0.03-1.15 0.05-0.1
base stock balance balance
Trunk Piston Engine Oil ("TPEO")
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.
Preferably, the TPEO has a compositional TBN (using D2896) of 20-60, such as
25-55.
The following may be mentioned as typical proportions of additives in a
TPEO.
Additive Mass% a.i. Mass A a.i.
(Broad) (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
When a plurality of additives is employed it may be desirable, although not
essential, to prepare one or more additive packages comprising the additives,
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whereby several additives can be added simultaneously to the base oil 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.
More detailed description of additive components is given below.
Detergents
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.
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.
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,
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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.
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.
Anti-oxidants
The trunk piston diesel engine lubricant composition may include at least one
anti-oxidant. The anti-oxidant may be aminic or phenolic. As examples of
amines
there may be mentioned secondary aromatic amines such as diarylamines, for
example diphenylamines wherein each phenyl group is alkyl-substituted with an
alkyl group having 4 to 9 carbon atoms. As examples of anti-oxidants there may
be
mentioned hindered phenols, including mono-phenols and bis-phenols.
Preferably, the anti-oxidant, if present, is provided in the composition in an
amount of up to 3 mass %, based on the total amount of the lubricant
composition.
Other additives such as pour point depressants, anti-foamants, metal rust
inhibitors, pour point depressants and/or demulsifiers may be provided, if
necessary.
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.
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Moreover, the additional incorporation of other additives may also permit
incorporation of higher levels of a particular additive, if desired.
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.
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.
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.
The final formulations may typically contain about 5 to 40 mass % of the
additive packages(s), the remainder being base oil.
VISCOSITY MODIFIER
In this invention, as stated above, a viscosity modifier (B) is additionally
provided.
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Viscosity modifiers impart high and low temperature operability to a
lubricating oil and permit it to remain relatively viscous at elevated
temperatures and
also exhibit acceptable viscosity or fluidity at low temperatures.
In this invention olefin copolymers (0CP's) are used. Examples of ranges in
the composition include 0.1-6, 0.1-5, 0.1-4, mass % and lower limits of 1 or 2
mass %.
These may be copolymers of two or more monomers of C2 to C30, e.g. C2 to
C8, olefins, including both alpha-olefins and internal olefins, which may be
straight
or branched, aliphatic, aromatic, alkyl-aromatic, or cycloaliphatic.
Frequently, they
are of ethylene with C3 to C30 olefins, particularly preferred being
copolymers of
ethylene and propylene. They may also be copolymers of C6 and higher alpha
olefins and terpolymers of styrene, e.g. with isoprene and/or butadiene and
hydrogenated derivatives thereof.
Preferred OCP' s are ethylene copolymers containing 15 to 90, preferably 30
to 80, mass % of ethylene and 10 to 85, preferably 20 to 70, mass % of one or
more
C3 to C28, preferably C3 to C18, more preferably C3 to C8, alpha-olefins. Such
OCP's
may have a degree of crystallinity of less than 25 mass %, as determined by x-
ray
and differential scanning calorimetry. As indicated above, copolymers of
ethylene
and propylene are most preferred. Other alpha-olefins suitable in place of
propylene,
or in combination with ethylene and propylene to form a terpolymer or
tetrapolymer,
for example, include: 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-
nonene,
1-decene; and branched chain alpha-olefins such as 4-methyl-1-pentene, 4-
methyl-l-
hexene, 4-methyl pentene-1, 4, 4-dimethyl-l-pentene, 6-methylheptene-1, and
mixtures thereof.
There may also be included terpolymers and tetrapolymers of ethylene, said
C3 to C28 alpha-olefin, and a non-conjugated diolefin or mixtures of such
diolefins.
The non-conjugated diolefin is generally present as 0.5 to 20, preferably 1 to
7, mole
percent of the total moles of ethylene and alpha-olefin.
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=
EXAMPLES
The present invention is illustrated by, but in no way limited to, the
following examples.
MDCL's
A set of MDCL's was formulated, each containing 20.89 mass A of the same
additives in the proportions and having a TBN of about 70. The set comprised a
control consisting of additives and base oil; a reference consisting of
additives, base
oil and brightstock; and an inventive MDCL consisting of additives, base oil
and
viscosity modifier. The additives were additives known in the art and used in
proportions known in the art for conferring MDCL properties. The viscosity
modifier was an olefin copolymer in the form of amorphous ethylene-propylene
copolymer. The brightstock was a Group I bright stock with a kinematic
viscosity of
>20cSt at 100 C. The base oil was a Group 1 base oil.
TPEO's
A set of TPEO's was formulated, each containing 16 mass % of the same
additives in the same proportions and having a TBN of about 40. The set
comprised
a control consisting of additives and base oil; a reference consisting of
additives,
base oil and bright stock; and an inventive MDCL consisting of additives, base
oil
and viscosity modifier. The additives were additives known in the art and used
in
proportions known in the art for conforming TPEO properties. The viscosity
modifier and brightstock were as used in the MDCL's. The base oil was a Group
1
base oil.
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TESTING & RESULTS
Samples of the above formulations were tested using a PCS Instruments high
frequency reciprocating rig (HFRR) on a standard protocol comprising the
following
conditions:
= 120 minutes
= 20 Hz reciprocation of 1mm stroke length
= 200g load using standard equipment manufacturer supplied steel
substrates.
Each test was repeated two further times and the recorded wear measurement was
the average of these values.
The HFRR data for the compositions are summarized in the table below.
Table
TPEO Additive Base oil Brightstock OCP Result
(mass A) (mass %) (mass %) (mass %) (wear vol
Control 16 84 5,584
Reference 16 75.5 8.5 8,279
1 16 82.67 1.33 5,359
MDCL
Control 20.89 79.11 33,960
Reference 20.89 58.89 20.22 3,940
2 20.89 77.61 3.17 2,953
The above results show that the use of an amorphous olefin copolymer additive
gives advantageous results when compared with brightstock at much lower
additive
treat levels in the formulation.
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