DESC:FIELD OF THE INVENTION:
The present invention relates to a Marine Cylinder Lubricant composition with an excellent oil film retaining and scuffing prevention properties. More particularly, the present invention relates to a marine cylinder lubricant composition comprising Group I base oil, detergent, dispersant, ashless antiwear, metal deactivator; film forming agent, and pour point depressant.
BACKGROUND OF THE INVENTION:
Fuels used for marine diesel engines generally have a high sulphur content (such as, for example, at least 3.5% sulphur), which results in exhaust gases from marine diesel engines containing large amounts of sulphur oxides (SOX). The sulphur oxides react with moisture present in the exhaust gases to form sulphuric acid which corrodes the engine particularly cylinder liner area. Marine diesel cylinder lubricant compositions therefore include over-based metallic detergents to neutralize the sulphuric acid formed during combustion. Commercial marine diesel cylinder lubricant compositions generally have total base number (‘TBN’) of at least 70 (as determined using ASTM D2896) for engines running on fuels with high Sulphur content.
Environmental concerns have prompted many areas, such as coastal areas, to require the use of low sulphur fuels, i.e. fuels including less than 1.00% by weight of sulphur, which allows the use of marine diesel cylinder lubricant compositions having lower total base numbers such as, for example, 17/25/40. This therefore creates the need for ships to carry tanks for two different lubricants.
As per the MARPOL emission regulations, the global cap on bunker sulfur is 3.5 % and in emission controlled areas (ECA), it is 0.1 %. Marine Cylinder Lubricants presently used worldwide are of 70 base number (BN). However, the slowdown of the economy has reduced the goods/cargo movement through the sea freight. This resulted in slow steaming there by resulting in lower engine operating temperatures leading to higher level of acid formation. Further, in Asia Pacific region, irrespective of MARPOL regulations, the bunker fuel sulfur is on higher side (ranging from 3-4 %) resulting in higher acid formation. In order to combat this problem, shipping industry is exploring the possibility of switching to 100 BN and above Marine Cylinder Lubricants. Hence, all major OEMs like MAN DT and Wartsila insist on the use of optimized field proven 100-140 BN Marine Cylinder Lubricants in those operations in order to address the issue of slow steaming trend in the shipping business. While developing a Marine Cylinder Lubricant, apart from corrosion combat, extreme care to be given to ensure scuffing and wear preventing characteristics in the oil which makes it most suitable for Marine cylinder lubrication.
US6596673 B1 discloses Marine Cylinder Lubricant with TBN in the range 60-100 composed with an overbased metal detergent, and S or P containing compound to overcome the scuffing type mechanical wear. This patent also discloses overbased calcium salicylate in a minor amount (< 50%) of TBN > 330 and 0.4-5.0 % amine dithiophosphate and it is a part of an auxiliary additive system which also contains a sulfirised phenol. The lubricant also contains co-additives such as metal containing antiwear (AW), antioxidant (AO), defoamant, rust inhibitors and pour point depressant (PPD).
EP1803794 discloses Marine Cylinder Lubricant composition in the TBN range 60-100 which contains a phenate (> 200 TBN), sulfonate (> 250 TBN), dispersant (0.005 – 0.1 % Nitrogen) and PIBSI (Poly Isobutylene Succinimide) with molecular weight in the range of 800-8000), Zinc Dialkyl Dithio Phosphate (ZDDP) (0.007 – 0.1 % Phosphorous) for improving high temperature wear performance. Phenate to sulfonate ratio is between 22:78 to 37:63. Other additives used are antioxidant (AO), Extreme Pressure additive (EP), Friction Modifier (FM), Viscosity Index Improver (VII), Multifunctional additive (MFA), rust inhibitor, foam inhibitor and PPD.
US6339051 discloses Marine Cylinder Lubricant composition for improved piston cleanliness, reduced deposits and improved scuffing protection based on Gp I/II base oils and PIB. TBN range 40-100. The additive package comprising a detergent component or components, a antioxidant, a antiwear agent, and a dispersant. The aforesaid composition contains 4-12% PIB, detergent from phenate and/or sulfonate (> 200 TBN), PIBSI dispersant (0.5-5 %) and sulfur containing AW agent (0.1-0.5 % sulfurised isobutylene), 0.1 – 1 % aminic AO.
US 20080153723 A1 discloses Marine Cylinder Lubricant in the TBN range 5-100 with detergents selected from neutral sulfonate, neutral phenate and overbased sulfonate. It also discloses Zn containing AW, AO, rust inhibitors, PPD, demulsifier, dispersant, FM, EP agent, and multifunctional additives, studied AW property by Falex Pin and Vee Block test.

WO/2015/067723 discloses Marine Cylinder Lubricant composition comprising Gp II base stocks, 100-250 TBN salicylates and over based sulfonates. The MCL contains 0.1-35 % salicylate (100-250 BN), 0.1-34 % sulfonate (250 BN), also contain an antioxidant, ashless dispersant, detergent, rust inhibitor, dehazing agent, demulsifying agent, metal deactivating agent, friction modifier, pour point depressant, antifoaming agent, co-solvent, package compatibiliser, corrosion inhibitor, dyes, extreme pressure agent and mixtures thereof.
Most of the above discussed art on Marine Cylinder Lubricant (MCL) compositions makes use of either an extreme pressure/sulfur containing additive or zinc containing antiwear additive for scuffing and wear prevention at extreme conditions. Also, it uses amine dithiophosphate in a MCL composition to raise the onset temperature of scuffing type mechanical wear and it has 7.2 % Phosphorous, 8.7 % Sulfur and 1.2 % Nitrogen. No prior art literatures are available for 100 BN (17-150 BN) MCL composition with amine phosphate and fatty acids for scuffing prevention with promising film retaining capacity.

SUMMARY OF THE INVENTION:
Accordingly, the present invention provides a marine cylinder lubricant composition comprising:
41.6 to 88.84 weight % of Group I base oil;
25.0 to 40.0 weight % of detergent;
1.0 to 3.5 weight % of dispersant;
0.01 to 0.30 weight % of ashless antiwear;
0.05 to 0.30 weight % of metal deactivator;
0.5 to 2.50 weight % of film forming agent; and
0.1 to 0.3 weight % of pour point depressant,
wherein weight percentage being based on the total weight of the marine cylinder lubricant composition.

In one of the embodiment of the present invention, the Group I base oil is mineral oil having sulfur content in the range of 5,000 to 20,000 ppm and saturates content in the range of 85 to 89 %.

In another embodiment of the present invention, the Group I base oil is neutral base oil and bright stock base oil; wherein:
(i) the neutral base oil is having kinematic viscosity at 100 °C in the range of 5.0 to 13.0 cSt; and
(ii) the bright stock base oil is having kinematic viscosity at 100 °C in the range of 28.0 to 35.0 cSt.

In still another embodiment of the present invention, the detergent is selected from overbased phenate, overbased sulfonate and combination thereof; wherein:
(i) the overbased phenate is calcium phenate and having TBN in the range of 230-265 and 265-320 with calcium content in the range 7.5-11.0 % and 8.0-13.0 %.
(ii) the overbased sulfonate is calcium sulfonate and having TBN in the range of 395-430 with calcium content of 14.0-17.0 %.

In yet another embodiment of the present invention, the dispersant is selected from dispersant 1 having nitrogen content of 1- 2.5 % and dispersant 2 having nitrogen content of 0.85- 1.65 %.

In yet another embodiment of the present invention, the dispersant is ashless dispersant and selected from oil soluble imide of long chain hydrocarbon substituted mono or dicarboxylic acids or their anhydrides.

In still another embodiment of the present invention, the ashless antiwear is selected from phosphate, phosphite, dithiophosphate, phosphorothionate, phosphorodithionate, and amine.

In yet another embodiment of the present invention, the ashless antiwear is amine phosphate with phosphorous content in the range of 3.3-6.0 %.

In yet another embodiment of the present invention, the metal deactivator is selected from bis imidazol ether, tolu triazol, amine, benzatriazol and thiadiazol derivatives.

In yet another embodiment of the present invention, the metal deactivator is triazol compound.

In yet another embodiment of the present invention, the film forming agent is fatty acid having a chain length in the range of C10-C22 and selected from oleic acid, stearic acid, lauric acid, capric acid, vaccenic acid, erucic acid, palmitoleic acid, and linoelic acid.

In still another embodiment of the present invention, the pour point depressant is selected from wax alkylate naphthalene, wax alkylate phenol and polymethacrylate.

In still another embodiment of the present invention, the ashless antiwear is amine phosphate and film forming agent is Fatty acid.

In still another embodiment of the present invention, the marine cylinder lubricant composition has base number in the range from of 17 to 150.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1: Represents Reciprocating Friction & Wear Tester (RFWT) curves for Reference oil 1 (100 BN);
Fig. 2: Represents RFWT curves for Reference oil 2 (100 BN);
Fig. 3: Represents RFWT curves for Candidate Oil 1 (100 BN);
Fig. 4: Represents RFWT curves for Candidate Oil 2 (100 BN);
Fig. 5: Represents RFWT curves for Ref oil 3 (17 BN) and Candidate oil 3 (17 BN);
Fig. 6: Represents RFWT curves for Ref oil 4 (70 BN) and Candidate oil 4 (70 BN); and
Fig. 7: Represents RFWT curves for Ref oil 5 (140 BN) and Candidate oil 5 (140 BN).
OBJECTIVES OF THE INVENTION:
It is the primary objective of the invention is to provide Marine Cylinder Lubricant composition which has base number ranges from of 17 to 150. More particularly, the objective of invention is to provide Marine Cylinder Lubricant composition which has 100 base number.
It is further objective of the invention is to provide Marine Cylinder Lubricant composition which comprises of Group I base oils (neutral and bright stock) and other additives such as detergents, dispersants, ashless antiwear, metal deactivator, film forming agent and pour point depressant.
It is further objective of the invention is to provide MCL composition with minor amounts of phosphorous containing ashless anti wear and film forming fatty acid together with sulfonate-phenate detergents and dispersants that provides the attributes of scuffing and wear resistance.
DETAILED DESCRIPTION OF THE INVENTION:
According to the primary embodiment, the present invention relates to Marine Cylinder Lubricant composition which has base number ranges from of 17 to 150.
In preferred embodiment, the aforesaid Marine Cylinder Lubricant composition comprising Group I base oils (neutral and bright stock) and other additives which fall in the category of detergents, dispersants, ashless antiwear, metal deactivator, film forming agent and pour point depressant.
Marine Cylinder Lubricant composition is prepared by mixing the individual additives with base oils and complete mixing is achieved by stirring the mixture at 60-70 °C.
The detailed description of the base oils and additives are as follows:
1. Base oils:
The base oils used in this invention were refined Group I base oils. The Group I base oils are refined mineral oils and characterized by sulfur content greater than 300 ppm and saturates content less than 90 %. Both neutral and bright stocks were used. The neutral base oil can be characterized by kinematic viscosity at 100 °C in the range of 5.0 to 13.0 cSt and bright stock in the range of 28.0 to 35.0 cSt.

2. Detergents:
Detergents generally comprise a polar head with a long hydrophobic tail. A hydrophobic tail is an entity which has no solubility in polar solvents such as water but dissolves in non polar solvents such as paraffin. In the present invention, the paraffinic part is lubricating base oil. The polar head comprises a metal salt of an acidic organic compound. Such overbased detergents may have a TBN of about 150 or greater, and typically will have a TBN of from about 230 to about 450 or more. The detergents that may be used include oil soluble sulfonates, phenates, salicylates, acetates, thiophosphonates and naphthenates of alkaline or alkaline earth metals e.g. barium, calcium, magnesium, sodium, lithium and potassium. The most common metals used are calcium and magnesium. Particularly convenient neutral and overbased sulfonaets detergents are having TBN from about 20 to 450, calcium phenates and sulfurised phenates having TBN in the range of 150-300. Combination of detergents either neutral or over-based may be used. Metal-containing or ash-forming detergents function as both detergents to reduce or remove deposits and as acid neutralizers or rust inhibitors, thereby reducing wear and corrosion and extending engine life. The detergents used in present invention may fall in the category of mixtures of overbased phenates and sulfonates. The calcium phenates used in this invention have TBN in the range of 230-265 and 265-320 with calcium content in the range 7.5-11.0 % and 8.0-13.0 %. The calcium sulfonate has a TBN in the range of 395-430 with calcium content of 14.0-17.0 %.
3. Total Base Number (TBN)
TBN is the amount of acid (perchloric acid or hydrochloric acid) needed to neutralize all or part of a lubricant’s basicity, expressed as KOH equivalents.
4. Dispersants:
The ashless dispersants employed in Marine Cylinder Lubricant of present invention may fall in the category of imides. Succinimide dispersants are a type of carboxylic dispersant. The two dispersants used in this invention differ by nitrogen content. Dispersant 1 and 2 can be characterized by the nitrogen content of 1- 2.5 % and 0.85- 1.65 % respectively. These nitrogen containing ashless dispersants also contribute to the BN of finished product. Representative examples of ashless dispersants include, but are not limited to, amides, amines, alcohols or ester polar moieties attached to polymer backbones via bridging groups. An ashless dispersant of the present invention may be, for example, selected from oil soluble imides, of long chain hydrocarbon substituted mono or dicarboxylic acids or their anhydrides. Succinimide dispersants are a type of carboxylic dispersant. The succinimide dispersants normally contain nitrogen in form of imide functionality, although the amide functionality may be in the form of amine salts, amines, imidazolines as well as mixtures thereof.
5. Ashless antiwear:
Examples for ashless antiwear additives are phosphates, phosphites, dithiophosphates, phosphorothionate and phosphorodithionate. The antiwear additive may also include an amine such as secondary or tertiary amine. The ashless antiwear used in this invention may be an amine type phosphate with phosphorous content 3.3-6.0 %.
6. Metal Deactivator:
Examples for metal deactivators include bis imidazol ethers, tolu triazols, amines, benzatriazol and thiadiazol derivetives. It normally added to a concentration in the range from into 0.05-0.30 % by weight. The metal deactivator used in this invention is triazol type compound.
7. Film forming agent:
Examples for fatty acids may include oleic acid, stearic acid, lauric acid, capric acid, vaccenic acid, erucic acid, palmitoleic acid, linoelic acid etc. The Fatty acid used in this invention is having a chain length in the range of C10-C22.
8. Pour point depressants (PPD):
Pour point depressants are critical components that prevent wax fractions from forming large crystal networks which inhibit lubricant flow at cold temperatures. Examples are wax alkylate naphthalene, wax alkylate phenols and polymethacrylates.

Advantages of the present invention:
The present invention has the following advantages over the prior arts:
(i) Marine Cylinder Lubricant composition eliminates the requirement of extreme pressure and ash forming anti wear additives for the purpose of scuffing and wear prevention.
(ii) Extremely promising film retention, scuffing prevention and anti-wear credentials have been achieved through a unique composition of detergent-dispersant and ashless antiwear-film forming additives.
(iii) Marine Cylinder Lubricant composition also requires only minor quantities of ashless anti-wear additive (in the range 0.01-0.1 wt. %).
Example 1A (100 BN MCL):
The invention can be illustrated with the following examples where the Reciprocating Friction & Wear Tester (abbreviated as RFWT) data of candidate oils (100 BN) were compared with the respective reference oils.
Reciprocating Friction & Wear Tester is used in the present invention to qualitatively assess the oil films formed by lubricating oils under simulated conditions of load, speed temperature and geometry of contact. It simulates the actual contact parameters experienced in all engine. The performance of a given candidate is assessed in terms of change in Contact potential (from the 50mV applied across the contact) and Friction coefficient being continuously measured during the test.
When the oil film is not able to withstand the temperature and load conditions, it may undergo breakdown leading to metal to metal contact. Since, the Oil film is a poor conductor of electricity, when it breaks down, metal to metal contact occurs which causes the contact potential to dip to very low values. When the film is intact, the contact potential is quite high close to the applied value (50mV), so a qualitative assessment of the film as measured under the simulated conditions becomes possible.
Each sample was tested in RFWT whereby contact potential was measured as a function of temperature and load. This test is designed to examine the ability of the oil to form the lubricant film between the moving parts and to retain the film at severe conditions. It involves lubricating stationary specimen with the test oil while subjecting it to a moving specimen under an applied load. The temperature is raised from 50 to 150 °C and load from 50-300 Newton during a time period of 2.30 hrs. The moving specimen has a frequency of 50 Hz.
Table-1

Components Ref oil 1
(100 BN) Ref oil 2
(100 BN) Candidate oil 1
(100 BN) Candidate oil 2
(100 BN)
Gp I 600 N (in weight %) 47.8-66.5 49.5-63.5 36.6-69.54 34.6-70.34
Gp I 150 BS (in weight %) 6.5-19.2 5.5-17.5 8.0-18.2 7.0-18.7
Commercial package (in weight %) 20.0-22.5 31.0-33.0 0.00 0.00
Overbased Detergent 1 (TBN < 400) (in weight %) 0.00 0.00 1.0-5.0 1.0-5.0
Overbased Detergent 2 (TBN > 150) (in weight %) 0.00 0.00 10.0-20.0 10.0-20.0
Overbased Detergent 3 (TBN > 150) (in weight %) 7.0-10.5 0.00 0.00 0.00
Overbased Detergent 4 (TBN > 250) (in weight %) 0.00 0.00 10.0-15.0 10.0-15.0
Dispersant 1 (Nitrogen 0.90-1.35 %) (in weight %) 0.00 0.00 0.8-2.0 0.8-2.0
Dispersant 2 (Nitrogen 1.00-1.80 %) (in weight %) 0.00 0.00 0.00 0.2-1.50
Tolu triazol (in weight %) 0.00 0.00 0.05-0.30 0.05-0.30
Amine phosphate (in weight %) 0.00 0.00 0.01-0.10 0.01-0.10
Fatty acid (in weight %) 0.00 0.00 0.5-2.50 0.5-2.50
PPD (in weight %) 0.00 0.00 0.1-0.3 0.1-0.3

Table 1a
Components Ref oil 1
(100 BN) Ref oil 2
(100 BN) Candidate oil 1
(100 BN) Candidate oil 2
(100 BN)
Gp I 600 N (in weight %) 52.10 54.00 50.40 53.90
Gp I 150 BS (in weight %) 19.00 14.50 17.50 14.20
Commercial package (in weight %) 21.20 31.50 0.00 0.00
Overbased Detergent 1 (TBN < 400) (in weight %) 0.00 0.00 3.10 2.64
Overbased Detergent 2 (TBN > 150) (in weight %) 0.00 0.00 13.80 15.27
Overbased Detergent 3 (TBN > 150) (in weight %) 7.70 0.00 0.00 0.00
Overbased Detergent 4 (TBN > 250) (in weight %) 0.00 0.00 12.94 12.44
Dispersant 1 (Nitrogen 0.90-1.35 %) (in weight %) 0.00 0.00 0.80 0.90
Dispersant 2 (Nitrogen 1.00-1.80 %) (in weight %) 0.00 0.00 0.00 0.30
Tolu triazol (in weight %) 0.00 0.00 0.10 0.05
Amine phosphate (in weight %) 0.00 0.00 0.03 0.03
Fatty acid (in weight %) 0.00 0.00 1.20 0.80
PPD (in weight %) 0.00 0.00 0.13 0.10

Both the reference oils were prepared from commercially available additive package. The commercial package as mentioned in the above tables 1 and 1a contains detergent (s), dispersant (s), anti-oxidant and film forming additive (s), pour point depressant etc. The reference oils differ in the aspect that the Ref oil 2 contains an overbased phenate as TBN booster. Candidate oils differ from each other in the aspect of Dispersant 2.
Results:
Ref Oil 1: Dip in contact potential observed at initial rise of temperature and load. Film breakage and film regaining observed at high temperature and load conditions.
Ref Oil 2: Comparatively better performance as compared to Ref oil 1. Less film breakage at high temperature and load conditions.
Candidate Oil 1: Film breakage observed only at the initial stages of temperature and load followed by excellent film retention at higher temperature and load.
Candidate Oil 2: Excellent film formation with almost nil film breakage at all phases of temperature and load. No evidence of film breakage even at severe load and temperature conditions.
Both the candidate oils were performing far superior to reference oils with respect to film forming and film retaining properties. Candidate oil 2 was the most promising blend with nil film breakage.
The RFWT curves are shown in fig. 1, 2, 3 and 4. A good RFWT graph will have less number of dips in the curve (especially at high temperature & load conditions). RFWT curves of candidate oils 1 & 2 (100 BN) have less number of dips as compared to reference oils 1 & 2 (100 BN) which explains comparatively better film forming and film retaining properties of candidate oils 1 & 2.

Example 1B (17 BN, 70 BN & 140 BN MCL)
The invention can further be illustrated with the following examples, where the reference and candidate oils (17 BN, 70 BN & 140 BN) were compared by RFWT test with the experimental conditions prescribed earlier.

Table: 2
Components Ref oil 3
(17 BN) Candidate oil 3
(17 BN) Ref oil 4
(70 BN) Candidate oil 4
(70 BN) Ref oil 5
(140 BN) Candidate oil 5
(140 BN)
Gp I 600 N (in weight %) 70.0-81.5 32.3-49.64 49.0-63.0 35.65-52.99 46.2-52.5 37.1-56.84
Gp I 150 BS (in weight %) 2.0-10.0 45.5-50.5 17.0-28.0 27.8-32.65 0.0 0.0
Gp I 150 N (in weight %) 0.00 0.00 0.00 0.00 7.0-10.3 2.5-6.7
Commercial package (in weight %) 16.5-20.0 0.00 20.0-23.0 0.00 40.5-43.5 0.00
Overbased Detergent 1 (TBN < 400) (in weight %) 0.0 0.15-1.5 0.0 1.5-3.5 0.0 3.0-6.0
Overbased Detergent 2 (TB N > 150) (in weight %) 0.0 1.5-4.5 0.0 9.0-12.0 0.0 20.0-24.5
Overbased Detergent 4 (TBN > 250) (in weight %) 0.0 1.5-4.5 0.0 7.0-9.5 0.0 16.0-19.0
Dispersant 1 (N 0.90-1.35 %) (in weight %) 0.0 0.8-2.0 0.0 0.8-2.0 0.0 0.8-2.0
Dispersant 2 (N 1.00-1.80 %) (in weight %) 0.0 0.25-1.50 0.0 0.25-1.50 0.0 0.2-1.50
Tolu triazol (in weight %) 0.0 0.05-0.30 0.0 0.05-0.30 0.0 0.05-0.30
Amine phosphate (in weight %) 0.0 0.01-0.10 0.0 0.01-0.10 0.0 0.01-0.10
Fatty acid (in weight %) 0.0 0.5-2.50 0.0 0.5-2.50 0.0 0.5-2.50
PPD (in weight %) 0.0 0.1-0.3 0.0 0.1-0.3 0.0 0.1-0.3

Table 2a

Components Ref oil 3
(17 BN) Candidate oil 3
(17 BN) Ref oil 4
(70 BN) Candidate oil 4
(70 BN) Ref oil 5
(140 BN) Candidate oil 5
(140 BN)
Gp I 600 N (in weight %) 73.30 42.19 54.73 45.36 49.00 50.59
Gp I 150 BS (in weight %) 7.50 48.09 23.27 30.25 0.0 0.0
Gp I 150 N (in weight %) 0.00 0.00 0.00 0.00 8.00 4.00
Commercial package (in weight %) 19.20 0.00 22.00 0.00 43.00 0.00
Overbased Detergent 1 (TBN < 400) (in weight %) 0.0 0.35 0.0 2.50 0.0 3.95
Overbased Detergent 2 (TB N > 150) (in weight %) 0.0 3.69 0.0 9.80 0.0 21.50
Overbased Detergent 4 (TBN > 250) (in weight %) 0.0 1.95 0.0 8.50 0.0 16.35
Dispersant 1 (N 0.90-1.35 %) (in weight %) 0.0 1.50 0.0 1.70 0.0 1.35
Dispersant 2 (N 1.00-1.80 %) (in weight %) 0.0 0.70 0.0 0.35 0.0 0.75
Tolu triazol (in weight %) 0.0 0.15 0.0 0.10 0.0 0.13
Amine phosphate (in weight %) 0.0 0.03 0.0 0.04 0.0 0.03
Fatty acid (in weight %) 0.0 1.25 0.0 1.30 0.0 1.25
PPD (in weight %) 0.0 0.10 0.0 0.10 0.0 0.10
The reference oils were prepared from commercially available additive packages. The commercial package as mentioned in the above tables 2 and 2a contains detergent (s), dispersant (s), anti-oxidant and film forming additive (s), pour point depressant etc.

Results:
The entire candidate oils performed well in the RFWT test; especially the 17 BN candidate oil is far superior to reference oil in film retention properties. The corresponding 17 BN reference oil was poor in maintaining the film thickness. After the film break-up in the initial phase of load-temperature profile, all the candidate oils regained the film quickly with superior film retention qualities at extreme experimental conditions of high load and temperature. The reference oils were showing sharp dip in the curve which evidences the week film thickness.
The RFWT curves are shown in fig. 5, 6 and 7. Comparatively better oil will have less number of dips in the curve (especially at high temperature & load conditions). Curves of all candidate oils (17, 70 & 140 BN) have less number of dips as compared to reference oils (17, 70 & 140 BN) which explains comparatively better film forming and film retaining properties of candidate oils.
Example 2
The invention can further be illustrated by the EHD film thickness studies of the candidate and reference oils of 100 BN. EHD film thickness studies of the above mentioned reference and candidate oils were conducted at 100 °C and 20 Newton load.
EHD film thickness is measured by a EHD 2 thin film measurement system which is a fully automated computer controlled instrument for film thickness measurements over a range of speeds, loads and temperatures in different regimes of lubrication.
The instrument measures the film thickness (physical film separation) between a 19.05 diameter steel ball and a rotating glass disk by optical interferometry. The system measures the wavelength of the predominant colour in the central plateau of the contact. Since the wavelength of light varies from one colour of the spectrum to other, this is used to calculate the film thickness. The film thickness varies with speed enabling us to also assess the films being formed in the different regimes of lubrication present in the contact zone.

Results
Ref Oil 1 Ref Oil 2 Candidate Oil 1 Candidate Oil 2
363 nm 345 nm 379 nm 380 nm
Candidate oils perform better in forming thicker films as compared to reference oils.
,CLAIMS:1. A marine cylinder lubricant composition comprising:
41.6 to 88.84 weight % of Group I base oil;
25.0 to 40.0 weight % of detergent;
1.0 to 3.5 weight % of dispersant;
0.01 to 0.30 weight % of ashless antiwear;
0.05 to 0.30 weight % of metal deactivator;
0.5 to 2.50 weight % of film forming agent; and
0.1 to 0.3 weight % of pour point depressant,
wherein weight percentage being based on the total weight of the marine cylinder lubricant composition.

2. The composition as claimed in claim 1, wherein the Group I base oil is mineral oil having sulfur content in the range of 5,000 to 20,000 ppm and saturates content in the range of 85 to 89 %.

3. The composition as claimed in claim 1, wherein the Group I base oil is neutral base oil and bright stock base oil; wherein:
(i) the neutral base oil is having kinematic viscosity at 100 °C in the range of 5.0 to 13.0 cSt; and
(ii) the bright stock base oil is having kinematic viscosity at 100 °C in the range of 28.0 to 35.0 cSt.

4. The composition as claimed in claim 1, wherein the detergent is selected from overbased phenate, overbased sulfonate and combination thereof; wherein:
(i) the overbased phenate is calcium phenate and having TBN in the range of 230-265 and 265-320 with calcium content in the range 7.5-11.0 % and 8.0-13.0 %.
(ii) the overbased sulfonate is calcium sulfonate and having TBN in the range of 395-430 with calcium content of 14.0-17.0 %.

5. The composition as claimed in claim 1, wherein the dispersant is selected from dispersant 1 having nitrogen content of 1- 2.5 % and dispersant 2 having nitrogen content of 0.85- 1.65 %.

6. The composition as claimed in claim 1, wherein the dispersant is ashless dispersant and selected from oil soluble imide of long chain hydrocarbon substituted mono or dicarboxylic acids or their anhydrides.

7. The composition as claimed in claim 1, wherein the ashless antiwear is selected from phosphate, phosphite, dithiophosphate, phosphorothionate, phosphorodithionate, and amine.

8. The composition as claimed in claim 1, wherein the ashless antiwear is amine phosphate with phosphorous content in the range of 3.3-6.0 %.

9. The composition as claimed in claim 1, wherein the metal deactivator is selected from bis imidazol ether, tolu triazol, amine, benzatriazol and thiadiazol derivatives.

10. The composition as claimed in claim 1, wherein the metal deactivator is triazol compound.

11. The composition as claimed in claim 1, wherein the film forming agent is fatty acid having a chain length in the range of C10-C22 and selected from oleic acid, stearic acid, lauric acid, capric acid, vaccenic acid, erucic acid, palmitoleic acid, and linoelic acid.

12. The composition as claimed in claim 1, wherein the pour point depressant is selected from wax alkylate naphthalene, wax alkylate phenol and polymethacrylate.

13. The composition as claimed in claim 1, wherein the ashless antiwear is amine phosphate and film forming agent is fatty acid.

14. The composition as claimed in claim 1, wherein the marine cylinder lubricant composition has base number in the range from of 17 to 150.