IMPROVED LUBRICATING OIL COMPOSITION
FIELD OF INVENTION
[0001] This invention relates to lubricating oil compositions for use in trunk piston engines. More specifically, the invention is directed to trunk piston engine oil compositions that reduce black deposits in trunk piston engines running on residual/furnace oil.
BACKGROUND OF THE INVENTION
[0002] Over the years, lubrication of trunk piston engines operating on residual fuels and engaged in captive power generation has become increasingly important. Ever increasing engine power output, declining specific lube oil consumption (SLOC), and highly fluctuating residual fuel quality have increased the stress factor manifold on this class of lubricating oils. In addition to these operational features, fuel-lubricant incompatibility in terms of the overall compositional polarity has been deduced as the root cause for many day-to-day maladies such as dirty crankcases, black rocker arm deposits, and high piston under crown deposits.
[0003] Trunk piston engine oil composition is predominantly characterized by its detergent chemistry. Usage of several types of detergents such as conventional sulphonate-phenate combination, phenates/phenolates alone, salicylates, and complex detergents is prevalent in the industry. The main idea in using these different types of detergents is that besides providing good levels of neutralization reserve, they provide optimal polarity to solubilize the raw fuel asphalt entering into crankcase as a consequence of fuel dilution. This is desired primarily because, if the fuel asphalt is not properly solubilized in the body of the lubricant matrix, it may settle down on various engine parts like crankcase, rocker arm, piston groves and cooling galleries as thick black deposit. It has been reported that every 100-micrometer increase in the thickness of these deposits in the piston cooling gallery

raises 10 deg C of piston temperature. This uninhibited rise in the piston
temperature can hamper the heat exchange leading to hot corrosion on piston tops.
In view of the foregoing, the formulations of trunk-piston engine oils need very
careful attention in the selection of detergent chemistry. However, only limited
information is available in the open literature about the composition of such
detergent mix which ensures the reduction of black deposits arising out of heavy
fuel ingress into lubricating oil.
[0004] U.S. Pat. No. 7,053,027 describes a lubricating oil composition to
resist the black deposit formation in trunk piston engine comprising aromatic
carboxylate and a zinc based antiwear additive.
[0005] WO Published Application No. 1996/026995 discloses a hydrocarbyl-
substituted phenol based lubricating oil composition to reduce black paint
formation in low- or medium-speed diesel engines.
[0006] US Published Application No. 20050014659 describes a lubricating
composition suitable for diesel engines comprising a major amount of an oil of
lubricating viscosity and a minor amount of an alkylamine-alkylphosphate
additive.
[0007] The existing art, though, catering to the core issue of controlling black
deposit formation in engines, are short on addressing issues relating to various
parameters that define an efficient lubricating oil. Most of the existing lubricating
oil compositions have an average performance record on viscosity, black deposit
filterability, dispersancy etc.
[0008] Accordingly, there is a need to develop an improved trunk piston
engine oil composition to control black deposits in trunk piston engines running on
heavy fuels which has a high performance capacity and at the same time good
effectiveness in controlling black deposit formation.

OBJECTS OF THE INVENTION
[0009] It is an object of the invention to provide an efficient lubricating oil
composition to control the black deposit formation in diesel engines
[00010] It is another object of the invention to provide an efficient lubricating
oil composition to control the black deposit formation in diesel engines running on
residual/furnace oil.
[00011] It is another object of the invention to provide an additive composition
which when added to a lubricant oil composition in desired amount is effective in
controlling the black deposit formation in diesel engines
[00012] It is yet another object of the invention to provide an additive
composition that reduces the oxidative viscosity rise in lubricants in a more
effective manner.
[00013] It is a further object of the invention to provide an additive
composition that decreases the black deposit formation to a significant extent.
[00014] It is a further object of the invention to provide an additive
composition that improves the dispersancy characteristics of the lubricant to an
extent better than the available compositions.
[00015] It is a yet another object of the invention to provide a lubricating oil
composition that is effective against a wide variety of engines.
[00016] It is a yet another object of the invention to provide a lubricating oil
composition that is effective against a wide variety of engine parts.
SUMMARY OF THE INVENTION
[00017] The present invention relates to a lubricating oil composition useful for controlling black deposit formation in diesel engines running on residual/furnace oils, wherein the lubricating oil comprises a major portion of a lubricating base oil and a minor proportion of an aromatic phenol containing thio-ether moiety, wherein the aromatic phenol is selected from a group of di- and tri-

alkyl substituted compounds with a minimum carbon chain length of C7-C16, and the thio-ether is selected from a group comprising of iso-alkyl substituted aromatic hydrocarbon with a carbon chain length of C16-C22.
DETAILED DESCRIPTION OF THE INVENTION
[00018] The present invention describes an improved lubricating oil composition that has good efficacy to keep the fuel asphalt dispersed in the body of the lubricant and to prevent plate out of the fuel asphalt as black deposit on the engine parts. Accordingly, this invention provides an optimized lubricating oil formulation in SAE 40 viscosity grade having a total base number (TEN) varying from 38 to 45 mg KOH/g for use in trunk piston engines running on heavy fuel oils. The trunk piston engines can be marine engines, propulsion engines, stationary power generation engines and continuous power generation engines. Further, the lubricating oil composition of the present invention can be used for lubrication of engine parts including piston, cylinder liner, cam rocker arm, fuel injector, piston under crown, big and small bearings, and piston skirt. [00019J In an embodiment, the lubricating oil composition comprises of 70 to 86 %wt of a solvent extracted, dewaxed and hydrofinished mineral lubricating oil base stock, 13 to 25 %wt of a core additive composition, 2 to 8 %wt of a detergent-dispersant booster additive composition, and 0.1 to 2.5 %wt of a synergistic additive composition comprising of an aromatic phenol containing thio-ether moiety. The lubricating oil composition can include 0.03 to 0.30 %wt of pour point depressant additive of the high molecular weight polymethacrylate type. [00020] In an embodiment, the lubricating base oil is selected from a group comprising of solvent extracted, dewaxed, hydrofinished mineral oils with kinematic viscosity in the range of 60 to 150 centistokes at 40 deg C and 8-16cSt @ 100 C, the preferred range being 9-13 cSt at 100 deg C.

[00021] In an embodiment, the core additive composition of the proposed lubricating oil composition comprises of 15 to 25 %wt of an alkaline earth metal aromatic carboxylate detergent with a TBN in the range of 140 to 180 mg KOH/g, 60 to 80 %wt of alkaline earth metal salts of alkyl substituted aromatic phenols with a TBN in the range of 150 to 450 mg KOH/g, 3 to 9 %wt of an ashless dispersant having a nitrogen content varying from 0.5 to 3.0 %wt, and 2 to 7 %wt of a zinc organo-phosphorus compound. In an embodiment, the core additive composition is present in the lubricating oil composition in an amount ranging from 13.5 to 19%wt.
[00022] In an embodiment, the alkaline earth metal aromatic carboxylate detergent can be highly polar and can have an alkyl hrdoxylate group either in ortho- or in para position or in a mix of both positions. The aromatic rings can have an alkyl group substitution, wherein the alkyl group is normal- or iso- and having an average chain length of CIO to C12. The average molecular weight of this detergent can vary in the range of 250-550. In an embodiment, the alkaline earth metal aromatic carboxylate is calcium aromatic carboxylate. In yet another preferred embodiment, the alkaline earth metal aromatic carboxylate is calcium alkyl substituted aryl ethanoate.
[00023] In an embodiment, the alkaline earth metal salts of alkyl substituted aromatic phenols can have medium polarity and have alkyl group substitution in the aromatic rings, wherein the alkyl group has an average chain length of C8 to C12. In a preferred embodiment, the alkaline earth metal salts of alkyl substituted aromatic phenols is a calcium salt of alkyl substituted, aromatic phenols. [00024] In an embodiment, the zinc organo-phosphorus compound of the core additive composition can be an alkyl substituted sulphurised zinc phosphate, wherein the alkyl group may be a primary or secondary or mixed primary and secondary alkyl group.

[00025] In another embodiment, the detergent-dispersant booster additive composition used in the proposed lubricating oil composition comprises of 70 to 88 %wt of alkaline earth metal salts of alkyl substituted aromatic phenols with a TEN in the range of 200 to 450 mg KOH/g, and 10 to 20 %wt of a mixture of amino-polyolefmic dispersants having a nitrogen content varying from 0.5 to 3.5 %wt. In a preferred embodiment, the alkaline earth metal salts of alkyl substituted aromatic phenols is a calcium salt of alkyl substituted aromatic phenols. In yet another embodiment, the detergent-dispersant booster additive composition is present in the lubricating oil composition in a preferred range of 2.5 to 6.0 %wt. [00026] The synergistic additive composition comprises of an aromatic phenol containing thio-ether moiety, wherein the aromatic phenol is selected from a group of di- and tri- alkyl substituted compounds with a minimum carbon chain length of C7-C16, and the thio-ether is selected from a group comprising of iso-alkyl substituted aromatic hydrocarbon with a chain length of C16-C22. In an embodiment, the synergistic additive composition further comprises of at least one additive selected from a group comprising of overbased detergents, ash-containing detergents, ashless-detergents, ashless dispersants, pour point depressants, extreme pressure agents, antiwear agents, rust inhibitors, metal deactivators, supplemental antioxidants, corrosion inhibitors, and anti-foam agents. In an embodiment, the synergistic additive composition is present in a preferred range of 0.3 to 1.5 %wt. [00027] The lubricating oil composition of the present invention provides remarkable control on black deposit formation in diesel engines running on residual/furnace oils and has demonstrated exceptional results when compared to the existing lubricating oil compositions with known additive compositions. [00028] Tables 1, 2 and 3 illustrate the results of a comparative analysis of various parameters conducted to assess the effectiveness of the synergist additive composition of the present invention vis-a-vis the conventional compositions. The experiments were conducted with three such conventional additive compositions

viz., phenolic antioxidant (PHAO), aminic antioxidant (AMAO), and mixed amine-phenol antioxidant (AMPHAO). A Reference Oil without any antioxidant was also included in the experiments (RSMK). The synergist additive composition of the present invention is an aromatic phenol containing thio-ether moiety and was labeled as ISMK (PHTH) for experimental purposes. The results were analyzed on periodical basis and the use of the synergist additive composition of the present invention was found to be most efficient when compared to the conventional compositions, particularly over a long period of time. [00029] Table 1 illustrates the percentage rise in viscosity of different additive compositions with respect to time. The lesser the increase in viscosity, the more stable the composition is to oxidation. The rise in viscosity was found to be lowest with the use of the synergist additive composition of the present invention after 168 hrs of oxidative aging at 165 deg C, which represents the actual field condition.
TABLE - 1 Viscosity Increase

(Table Removed)
[00030] Table 2 illustrates the effect of such additive compositions on black deposit filterability. As elucidated herein, the synergist additive composition of the

present invention provides the lowest percentage of total sediments over an extended time period after 168 hrs of oxidative aging at 165 deg C, which represents the actual field condition, which represents the actual field condition.
TABLE – 2
Black Deposit Filterability

(Table Removed)
[00031] Table 3 compares the effect of additive compositions on dispersancy. The viscosity rise was found to be lowest with the synergist additive composition of the present invention indicating the highest dispersancy of the said composition.
TABLE – 3
Lamp Black Dispersancy

(TABLE REMOVED)
EXAMPLE
The present invention is further explained in the form of following examples. However, these examples should not be construed as limiting the scope of the invention.
Example 1
A particular blend of the above proposed composition was prepared wherein base oil content was 78.9 %wt, dosage of core additive composition was 17.0 %wt, dosage of the detergent-dispersant booster additive composition was 3.5 %wt, dosage of pour point depressant was 0.1 %wt, and dosage of the synergistic additive composition was 0.5 %wt. The resulting lubricating oil composition exhibited a superior performance in terms of various performance parameters when compared to field-tested lubricating oil presently employed for trunk piston engines operating on residual fuels.
Table - 4 below gives the test data for the example of performance enhancement of the present invention (ISMK-40) over the reference oil (RSMK-40) of same viscosity and total base number range.
TABLE -4
(Table Removed)
ADVANTAGES OF THE INVENTION
(1) The present invention describes a lubricating oil composition for controlling
black deposit formation in diesel engines using a synergist additive composition
comprising an aromatic phenol containing thio-ether moiety.
(2) The synergist additive composition of the present invention has been
experimentally proved to be superior in terms of various parameters over the
existing available compositions, particularly in viscosity rise, black deposit
filterability and lamp black dispersancy.
(3) The lubricating oil composition of the present invention is effective against
a wide variety of engines and engine parts.

WE CLAIM
1. A lubricating oil composition for controlling black deposit formation in diesel
engines comprising
a major proportion of a lubricating base oil; and
a minor proportion of an additive composition comprising of an aromatic phenol containing thio-ether moiety, wherein the aromatic phenol is selected from a group of di- and tri- alkyl substituted compounds with a minimum carbon chain length of C7-C16, and the thio-ether is selected from a group comprising of iso-alkyl substituted aromatic hydrocarbon with a carbon chain length of C16-C22.
2. The lubricating oil composition as claimed in claim 1, wherein the lubricating
base oil is present in the lubricating oil composition in an amount ranging from
about 70 to 86 %wt, further wherein the aromatic phenol containing thio-ether
moiety is present in the lubricating oil composition in an amount ranging from
about 0.1 to2.5%wt.
3. The lubricating oil composition as claimed in claim 1, wherein the lubricating
base oil is selected from a group comprising of solvent extracted, dewaxed,
hydrofmished mineral oils with a kinematic viscosity in the range of 60 to 150
centistokes at 40 deg C and and 8-16cSt at 100 deg C.
4. The lubricating oil composition as claimed in claim 1, where the lubricating oil
composition is of SAE 40 viscosity grade having a total base number (TEN)
ranging from about 38 to 45 mg KOH/g for use in trunk piston engines running on
heavy fuel oils.
5. The lubricating oil composition as claimed in claim 1, wherein the minor
proportion further comprises a core additive composition comprising of 15 to 25

%wt of an alkaline earth metal aromatic carboxylate detergent of 140 to 180 mg KOH/g total base number (TEN), 60 to 80 %wt of alkaline earth metal salts of alkyl-substituted aromatic phenols of 150 to 450 mg KOH/g TEN, 3 to 9 %wt of an ashless dispersant, and 2 to 7 %wt of a zinc organo-phosphorus compound.
6. The lubricating oil composition as claimed in claim 5, wherein the core additive
composition is present in the lubricating oil composition in an amount ranging
from about 13.0 to 25.0 %wt.
7. The lubricating oil composition as claimed in claim 5, wherein the alkaline earth
metal aromatic carboxylate detergent is substituted with a alkyl hydroxylate group
either in the ortho- or para- position or a mix of both positions.
8. The lubricating oil composition as claimed in claim 5, wherein the alkaline
earth metal aromatic carboxylate detergent is substituted with an alkyl group in
aromatic rings, further wherein, the alkyl group is normal- or iso-, having an
average chain length of C10 to C12.
9. The lubricating oil composition as claimed in claim 5, wherein the alkaline earth
metal aromatic carboxylate detergent has an average molecular weight in the range
of 250 to 550.
10. The lubricating oil composition as claimed in claim 5, wherein the alkaline
earth metal aromatic carboxylate detergent is a calcium carboxylate detergent.
11. The lubricating oil composition as claimed in claim 5, wherein the alkaline
earth metal aromatic carboxylate detergent is a calcium alkyl substituted aryl
ethanoate detergent.

12. The lubricating oil composition as claimed in claim 5, wherein the alkaline
earth metal salts of alkyl-substituted aromatic phenols are of medium polarity
having alkyl group substitution in aromatic rings, wherein the alkyl group has an
average chain length of C8 to C12.
13. The lubricating oil composition as claimed in claim 5, wherein the alkaline
earth metal salts of alkyl-substituted aromatic phenols is a calcium salt of alkyl-
substituted aromatic phenols.
14. The lubricating oil composition as claimed in claim 5, wherein the ashless
dispersant have a nitrogen content varying from 0.5 to 3.0 %wt.
15. The lubricating oil composition as claimed in claim 5, wherein the zinc organo-
phosphorus compound is an alkyl substituted sulphurised zinc phosphate, wherein
the alkyl group may be a primary or secondary or mixed primary and secondary
alkyl group.
16. The lubricating oil composition as claimed in claim 1, wherein the minor
proportion further comprises of a detergent-dispersant booster additive
composition comprising of 70 to 88 %wt of alkaline earth metal salts of alkyl-
substituted aromatic phenols of 200 to 450 mg KOH/g TEN, and 10 to 20 %wt of
a mixture of amino-polyolefinic dispersants having nitrogen content in the range of
0.5 to 3.5 %wt.
17. The lubricating oil composition as claimed in claim 16, wherein the detergent-
dispersant booster additive composition is present in the lubricating oil
composition in an amount ranging from about 2.0 to 8.0 %wt.

18. The lubricating oil composition as claimed in claim 16, wherein the alkaline
earth metal salts of alkyl-substituted aromatic phenols is a calcium salt of alkyl-
substituted aromatic phenols.
19. The lubricating oil composition as claimed in claim 1, wherein the minor
proportion further comprises of a high molecular weight polymethacrylate type
pour point depressant additive in an amount ranging from about 0.03 to 0.30 %wt.
20. The lubricating oil composition as claimed in claim 1, wherein the additive
composition further comprises of at least one additive selected from a group
comprising of overbased detergents, ash-containing detergents, ashless-detergents,
ashless dispersants, pour point depressants, extreme pressure agents, antiwear
agents, rust inhibitors, metal deactivators, supplemental antioxidants, corrosion
inhibitors, and anti-foam agents.
21. A method of controlling black deposit formation in a diesel engine, the said
method comprising providing a lubricating oil composition comprising:
70 to 86 %wt of lubricating base oil;
13.0 to 25 % wt of a core additive composition comprising of 15 to 25 %wt of an alkaline earth metal aromatic carboxylate detergent of 140 to 180 mg KOH/g TEN, 60 to 80 %wt of an alkaline earth metal salts of alkyl substituted aromatic phenols of 150 to 450 mg KOH/g TEN, 3 to 9 %wt of an ashless dispersant having a nitrogen content varying from 0.5 to 3.0 %wt, and 2 to 7 %wt of a zinc organo-phosphorus compound;
2.0 to 8.0 %wt of a detergent-dispersant booster additive composition comprising of 70 to 88 %wt of alkaline earth metal salts of alkyl-substituted aromatic phenols of 200 to 450 mg KOH/g TEN, and 10 to 20 %wt of a mixture of

amino-polyolefinic dispersants having nitrogen content in the range of 0.5 to 3.5 %wt;
0.1 to 2.5 %wt of additive composition comprising of an aromatic phenol containing thio-ether moiety, wherein the aromatic phenol is selected from a group of di- and tri- alkyl substituted compounds with a minimum carbon chain length of C7-C16, and the thio-ether is selected from a group comprising of iso-alkyl substituted aromatic hydrocarbon with a chain length of C16-C22 and;
0.03 to 0.30 %wt of a high molecular weight polymethacrylate type pour point depressant additive.
22. The method as claimed in claim 21, wherein the lubricating oil composition is
used for lubrication of engine parts including piston cylinder liner, cam.
rockerarm, fuel injector, Piston under crown, big and small bearings, and piston
skirt in a trunk piston diesel engine.
23. The method as claimed in claim 21, wherein the diesel engine is selected from
a group comprising of marine engines, propulsion engines, stationary power
generation engines and continuous power generation engines.