Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic sulfur compound – wherein the sulfur is single bonded...
Reexamination Certificate
1998-06-11
2002-01-15
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic sulfur compound, wherein the sulfur is single bonded...
C508S291000, C508S563000, C508S577000, C585S002000, C585S003000, C585S004000, C585S005000
Reexamination Certificate
active
06339051
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to diesel engine cylinder oils.
BACKGROUND OF THE INVENTION
In large, slow speed diesel engines of the crosshead type used in marine and heavy stationary applications, the cylinders are lubricated separately from the other engine components. The cylinders are lubricated on a total loss basis with the cylinder oil being injected separately to quills on each cylinder by means of lubricators positioned around the cylinder liner. Oil is distributed to the lubricators by means of pumps which are, in modern engine designs, actuated to apply the oil directly onto the rings to reduce wastage of the oil. The high stresses encountered in these engines and the use of heavy residual fuels create the need for lubricants with a high detergency and neutralizing capability even though the oils are exposed to thermal and other stresses only for short periods of time. Residual fuels commonly used in these slow speed diesel engines typically contain significant quantities of sulfur which, in the combustion process, combines with water to form sulfuric acid, the presence of which leads to corrosive wear. Cylinder oils contain high alkalinity reserves for neutralizing this acid, which is reflected in the total base number (TBN) of these oils, typically in the range of at least 40mg KOH/g, usually from 60 to 100 mg KOH/g, which is normally adequate with fuels containing two to three percent sulfur. When higher sulfur residual fuels are being used cylinder oils with TBN values of about 70 are normally used although oils with TBN values up to and exceeding 100 mg KOH/g may be used, especially with high peak cylinder power ratings of 3,500 kw per cylinder or more.
A requirement of these cylinder oils is that they should be thin enough to spread quickly over the cylinder surface but yet thick enough to provide a continuous hydrodynamic film that will not evaporate off the walls of the upper cylinder when exposed to high combustion temperatures. Normally, oils with a viscosity grade of SAE 50 are satisfactory for lubricating both older and newer types of engine although heavier oils such as SAE 60 are contemplated. The SAE 50 grade corresponds to oils with kinematic viscosities within the range of 18.5 to 21.9 cS (100° C.), with the lower end of the range being set by engine builder specifications and the upper limit by the SAE grade sepecification. Similarly, the SAE 60 oils will have kinematic viscosities extending over the range 21.9 to 26.1 cS (100° C.). The SAE 50 oils therefore correspond to a nominal 20 cS (100° C.) oil, and the SAE 60 oils to a nominal 24 cS (100° C.) oil; oils of these grades represent the nominal viscosity targets for the oils of the present invention. Another requirement for the oils is that they should not produce deposits which will lead to port fouling. For this reason, good oxidation and thermal stability are required, manifested in actual performance by low piston ring groove packing as well as by reduced liner wear and minimized port fouling tendency.
In order to achieve the desired viscosity in the final product, relatively heavy base oils are required. Bright stock may be used to supplement the viscosity of medium heavy neutrals if extra heavy neutrals are not available to provide the desired basestock viscosity. However, bright stocks are generally unsatisfactory in cylinder oil performance because of their poor oxidative and thermal stability and although other high viscosity oils could be used to boost the basestock viscosity, for example, high viscosity synthetic polyalphaolefin (PAO's), these are very costly, given the total loss usage of the cylinder oil. Another alternative would be to increase the viscosity contribution from the additives by an increased dispersant treat rate but again, the economics are not favorable to this as a technical solution.
SUMMARY OF THE INVENTION
We have now developed improved diesel cylinder oils, useful in marine and heavy, low speed stationary diesels, which can be made from medium to medium heavy neutral base oils, typically from 300 to 500 SUS without the need for extra heavy neutrals and which can be formulated without the use of bright stock in order to provide the desired final viscosity. Compared to current commercial products, the oils according to the present invention exhibit improved deposit characteristics, improved piston cleanliness, and improved load carrying as well as providing protection against corrosive, friction and abrasive wear under severe operating conditions. In use, they are expected to result in improved engine wear characteristics as indicated by piston ring wear, cylinder liner wear, and piston ring groove packing. Port cleanliness will also be improved.
According to the present invention, the diesel cylinder oils are produced with a kinematic viscosity in the range from 15 to 27 cS (100° C.), corresponding to viscosity grades of SAE 50 or SAE 60. For these viscosity grades, the kinematic viscosity will normally be from 18.5 to 21.9 generally 19 to 21 cS (100° C.) for a nominal 20 cS oil (SAE 50) and from 21.9 to 26.1 cS (100° C.) for a nominal 24 cS oil (SAE 60). The viscosity index of the improved oils is at least 95 and usually at least 100 and may be higher, typically from 105 to 120 with most of the oils having a viscosity index in the range of 105 to 115.
The present cylinder oils use a neutral base stock of not more than 725 SUS viscosity, eliminating the need to go to extra heavy neutral base oils of higher viscosity. Normally, the base stock will comprise at least 60 wt. percent of the finished oil, usually 60 to 70 percent by weight. Because of the unique viscosity control system used in the present oils, there is no need for bright stock (which typically has a viscosity of at least 25 cS at 100° C. and in most cases at least 30 cS at 210° F.) to be used in order to obtain the desired final viscosity. Because of the its inferior stability, bright stock is not a preferred option for viscosity control and if used at all, for example with the lightest neutrals, should be used in only minor amounts, typically not more than ten percent by weight of the formulation. The neutrals used as the main component of the oil will normally have viscosities in the range of 300 to 700, preferably 300 to 600 SUS (100° F.) although with the lower viscosity neutrals, it will be necessary to use a higher treat rate for the viscosity control component and possibly also of the other additives in order to achieve the final product viscosity.
The neutral base stocks will normally be API Group I or Group II base stocks; in view of the total loss usage of the cylinder oils, there is no advantage to the use of the higher quality Group III base stocks and, in fact, because of additive solvency problems associated with the highly paraffinic character of the Group III stocks, they are not normally preferred. Group I base stocks contain less than 90 percent saturates and/or greater than 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120. Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur with a viscosity index greater than or equal to 80 and less than 120.
A feature of the present cylinder oils is the use of polyisobutylene (PIB) in combination with the neutral base stock. The amount of PIB will normally be from 1 to 20 wt. percent of the finished oil, generally from 2 to 15 wt. percent, and in most cases from 4 to 12 wt. percent of the finished oil. Polyisobutylene is a commercially available material from several manufacturers. The PIB used in the present formulations is a viscous oil-miscible liquid, with a weight molecular weight in the range of 1,000 to 8,000, usually 1,500 to 6,000, and a viscosity in the range of typically 2,000 to 5,000 or 6,000 cS (100° C.) (ASTM D-445). In most cases, the molecular weight will be in the range of 2,000 to 3,000 or 5,000 and the kinematic viscosity should be selected to be in the range of 3,000 to 4,500 cS. The more visc
Carey Vincent M.
Fogarty John T.
Keen Malcolm D.
Medley Margaret
Mobil Oil Corporation
Toomer Cephia D.
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