The present invention relates to lubricating oil compositions and in particular to lubricating oil compositions suitable for medium- or low-speed diesel engines, typically the four-stroke trunk-piston engine.

Lubricating oils for medium- or low-speed diesel engines are known and will typically contain a range of additives which will perform a variety of functions, for example they may comprise dispersants to minimise deposit formation in various parts of the engine, or detergent additives. However contamination of these lubricating oil compositions with unburnt residual fuel oil is a problem recognised in the industry. This leads to severe engine cleanliness problems in service which is sometimes referred to as "black paint". The problem is particularly widespread in 4-stroke trunk-piston engines where dirty cam boxes and crankcases are encountered. However, the problem is not confined to 4-stroke engines. 2- stroke cross-head engines can also suffer from the problem. These 2-stroke engines will usually use two separate lubricating oils, one for the crankcase and one for the cylinder, but it is in the crankcase where the heavy deposits potentially occur.

It might be expected that the problem would be overcome simply by using more of the conventional dispersant additive in the lubricating oil but this measure has met with very limited success. We have now found that the aforementioned problem is solved by including in the lubricating oil compositions a hydrocarbyl- substituted phenol.

Thus according to the present invention there is provided a lubricating oil composition suitable for use in low or medium speed diesel engines comprising a fuel oil with a residual oil content characterised in that the lubricating oil composition further comprises a "black paint" reducing amount of a hydrocarbyl-

substituted phenol.

The lubricating oil composition of the present invention will be suitable for use in either a low- or medium-speed engine especially a marine diesel engine. Typically such an engine can be a 4-stroke trunk piston engine having an engine speed of 50-1,000 rpm, e.g. 100-500 rpm, and a brake horse-power (BHP) per cylinder of 10-3,000 preferably 250-2,000. The engine can also be a 2-stroke cross-head engine having a speed of 40-1,000 rpm preferably 100-500 rpm, and a BHP per cylinder of 100-8,000.

In a further aspect of the present invention there is provided a method of reducing deposits in a low- or medium-speed diesel engine comprising lubricating the moving parts of the engine with a lubricating oil composition suitable for use in such an engine which comprises a fuel oil with a residual oil content characterised in that the lubricating oil composition further comprises a "black paint" reducing amount of a hydrocarbyl-substituted phenol. The lubricating oil compositions of the present invention will have a TBN in the range 0.1 to lOOmgKOH g. Where the composition is to be used in a 4- stroke trunk piston engine the TBN is preferably in the range 5-70, more preferably 8-50mgKOH/g; where it is to be used in a 2-stroke cross-head engine and particularly for the crankcase, the TBN of the composition is preferably in the range 0.1 to 15, more preferably 1 to 10 mgKOH/g.

The lubricating oil composition of the present invention will usually be a monograde lubricant, i.e. one which exhibits little or no viscosity index improvement properties, e.g. an SA30 oil.

As regards the lubricating oil, this may be any oil suitable for the lubrication of a low- or medium-speed diesel engine, particularly a marine diesel engine. The lubricating oil may suitably be an animal, a vegetable or a mineral oil. Suitably the lubricating oil is a petroleum-derived lubricating oil, such as a naphthenic base, paraffin base, or mixed base oil. Alternatively, the lubricating oil may be a synthetic lubricating oil. Suitable synthetic lubricating oils include synthetic ester lubricating oils, which oils include diesters such as di-octyl adipate, di-octyl sebacate and tri-decyl adipate, or polymeric hydrocarbon lubricating oils, for example liquid polyisobutene and poly-alpha olefins. Commonly, a mineral oil is employed. The oil may be suitable for lubricating a low- or medium-speed marine diesel engine without adjustment of its viscosity. If viscosity adjustment is required it may be achieved by the addition of, for example, bright stock. The lubricating oil

will generally comprise greater than 70% by weight, typically greater than 80% by weight of the composition.

The lubricating oil composition will be contaminated with a fuel oil which has a residual oil content. Such a fuel oil will be suitable for use as a diesel fuel oil. Fuel oils can in general be divided into two main categories - distillates and heavy fuels. Distillates consist of one or more distilled fractions. Heavy fuels are fuels which comprise at least a proportion of a residual oil, that is an oil which remains after the distilled fractions have been removed from an unrefined oil. The composition of the residual oil will vary with the composition of the starting oil which is usually a crude oil and will also vary depending upon the distillation conditions. However, by its nature residual oil is of high molecular weight and high boiling point and the man skilled in the art will know what is meant by residual oil. Heavy fuels can also comprise, in addition to residual oil, distillates. However, heavy fuels will generally comprise at least 90%, for example at least 95%, typically at least 99% by weight residual oil. The present invention is concerned with lubricating oil compositions that are contaminated with a heavy fuel. The amount of heavy fuel in the lubricating oil composition will vary. Typically the composition will comprise between 0.1 to 10, e.g. 0.3 to 5, especially 0.5 to 3%, by weight heavy fuel oil which as defined above is a fuel oil which has a residual oil content.

The hydrocarbyl-substituted phenol may be a mono-hydrocarbyl-substituted phenol or a poly-hydrocarbyl-substituted phenol or a mixture of both mono- and poly-substituted phenols. The hydrocarbyl-substituent is preferably an alkyl group which may be branched or unbranched. Suitable alkyl groups contain from 4 to 50, preferably from 9 to 29, carbon atoms. A particularly suitable alkyl phenol is the predominantly Ci2-.alkyl phenol obtained by alkylating phenol with propylene tetramer. A particularly suitable poly-substituted phenol is dinonyl phenol.

Hydrocarbyl-substituted phenols are well-known commercial materials which are usually manufactured by alkylating phenol at elevated temperature in the presence of an acidic catalyst.

In addition to the lubricating oil and the hydrocarbyl-substituted phenol the composition of the invention may contain other additives, chief amongst which is a dispersant.

Although any type of dispersant may be employed in the composition, a suitable dispersant is one derived from a hydrocarbyl-substituted succinic acid or

anhydride by reaction with an amine, i.e. a hydrocarbyl-substituted succinimide, e.g. a polyisobutene (PIB) succinimide. Such succinimides are well known in the art.

Succinimide production is described in, for example, US-A-2,992,708; US- A-3,018,291; US-A-3,024,237; US-A-3, 100,673; US-A-3,219,666; US-A- 3,172,892 and US-A-3, 272,746.

Succinimide dispersants which are mono- or bis- succinimides may be employed.

The amount of dispersant present in the low- or medium-speed diesel engine lubricating oil composition of the present invention may suitably be in the range from 0.01 to 5.0, preferably from 0.1 to 2.5% by weight based on the weight of the composition.

In addition to the foregoing the composition may additionally contain additives conventionally employed in low- or medium-speed diesel engine lubricating oil compositions. Examples of such additives include detergents, foam inhibitors, extreme pressure/antiwear agents, rust inhibitors, antioxidants, and the like. Detergents generally employed in the compositions of the invention include hydrocarbyl-substituted alkaline earth metal phenates, salicylates, naphthenates, sulphonates or carboxylates, which may be normal or overbased materials. The detergent, in addition to providing detergency, is generally employed to adjust the total base number of the composition to a desired value, typically about 30mg KOH/g.

A preferred composition according to the present invention comprises from 0 to 5.0%, preferably from 0.10 to 3.0%, by weight of a hydrocarbyl-substituted succinimide dispersant; sufficient of a hydrocarbyl-substituted alkaline earth metal phenate, salicylate, naphthenate, sulphonate or carboxylate detergent to adjust the TBN to a value in the range from 8 to 50mgKOH/g for use in a 4-stroke trunk piston engine or to a value in the range from 1 to lOmgKOH/g for use in a 2-stroke cross-head marine engine; from 0.5 to 10%, preferably from 2.0 to 5.0% by weight of a hydrocarbyl-substituted phenol; from 0.1 to 10%, typically from 0.5 to 3% by weight heavy fuel oil (i.e. a fuel oil which has a residual oil content); and, comprising the remainder of the composition, a low- or medium-speed diesel engine lubricating oil.

The composition of the invention may be prepared by diluting a concentrate comprising a solution of the hydrocarbyl-substituted phenol and optionally the

other additives referred to hereinbefore in a suitable carrier with low- or medium- speed diesel engine lubricating oil. As the carrier there may be employed any solvent for the phenol which is compatible both with the lubricating oil and with the use of the composition. The carrier may be any inert hydrocarbon solvent. The hydrocarbyl-substituted phenol may suitably be present in the concentrate in an amount in the range from 0.1 to 20% by weight.

The use of a hydrocarbyl-substituted phenol as described hereinabove for reducing black paint in low- or medium- speed diesel engines is a further embodiment of the present invention. The invention will now be further illustrated by reference to the following

Examples. In the Examples the total sediment content of residual fuel contaminated compounded oils is determined.

In the test method, ten grams of the test oil which has previously been subjected to ageing at 100°C for 24hr is filtered through a filter medium. After solvent washing and drying the total sediment on the filter medium is weighed. The test is carried out in duplicate. Results

The mass percentage of Total Sediment to the nearest 0.01% m/m is calculated using:- S = M1 - M2 x l00

M3 where S = Total Sediment in % m/m

Ml = Mass of filter medium after filtration in g M2 = Mass of filter medium before filtration in g M3 = Mass of sample filtered in g.

In the following Comparison Test and Examples all percentages are percentages by weight. Comparison Test

A fully formulated 30TBN trunk piston engine oil lubricant at SAE40 containing a hydrocarbyl-substituted calcium phenate detergent (ex. Adibis) (X) and 20% residual fuel was tested in the Adibis Test Method for "black paint".

The result of the Test is given in the accompanying Table. Example 1

The Comparison Test was repeated except that in addition 0.66% by weight of the alkyl phenol product obtained by alkylating phenol with propylene

tetramer was added.

The result of the Test is given in accompanying Table. Example 2

The Comparison Test was repeated except that in addition 1.48% by weight of the alkyl phenol product obtained by alkylating phenol with propylene tetramer (as used in Example 1) was added.

The result of the Test is given in the accompanying Table. Example 3

The Comparison Test was repeated except that in addition 2.54% by weight of the alkyl phenol product obtained by alkylating phenol with propylene tetramer (as used in Example 1) was added.

The result of the Test is given in the accompanying Table. Example 4

The Comparison Test was repeated except that in addition 3.95% by weight of the alkyl phenol product obtained by alkylating phenol with propylene tetramer (as used in Example 1 ) was added.

The result of the Test is given in the accompanying Table.

TABLE

It can be seen from the Table that addition of alkyl phenol leads to a marked reduction in sediment.