Field of the Invention

The present invention relates to the use of a lubricating oil composition comprising a Fischer-Tropsch derived base oil for reducing exhaust port blocking of a two-stroke engine and to a two-stroke lubricating engine oil composition having reduced exhaust port blocking. Background of the Invention

Two-stroke gasoline engines are used in motorcycles as well as in garden and recreational equipment such as lawn mowers, chain saws, string trimmers, mopeds, snow ^¬ mobiles, outboard marine motors and the like. Slow speed two-stroke diesel engines are used for marine propulsion in very large ships.

To operate a two-stroke gasoline engine the crankcase holds a mixture of two-stroke gasoline

lubricant and fuel and the crankcase serves as a

pressurization chamber to force air/fuel into the

cylinder. This necessitates the use of a lubricating composition which has been specically formulated for two- stroke engines, instead of a high viscosity lubricating oil such as those used in 4-stroke engines. The 2-stroke engine lubricant is mixed with gasoline in prescribed proportions to lubricate the crankshaft, connecting rod and cylinder walls.

Conventional two-stroke gasoline engine lubricants are typically formulated with a mineral oil base oil or synthetic base oil and a low-viscosity, low-boiling hydrocarbon solvent to enhance the miscibility of the lubricant with the gasoline.

Some two-stroke engine oils have used ester base oils with no low boiling solvent to reduce flammability and minimize smoky emissions. However these lubricants often suffer from poor oxidation stability. Other two- stroke engine oils have used polyalphaolefin base oils having improved low temperature properties. Both PAOs and ester base oils suffer from the disadvantage of being limited in supply and very expensive.

A variety of performance additives can be added to improve the overall performance of the lubricant. In particular, a two-stroke engine oil should meet the requirements set by standards setting organizations, including Japanese Automobile Standard JASO M345 2003 and International Standard ISO 1373832000(E).

Since conventional two-stroke engines tend to be rather smoky, smoke-reducing additives are often added to the lubricant. Examples of smoke-reducing additives include those that contain metals, but these tend to be undesirable from an environmental viewpoint. Other examples include synthetic basestocks, but these tend to be expensive. Polybutenes and polyisobutylenes are also commonly added for reducing smoke and as anti-scuffing agents. It is taught in WO2007/050352 that

polyisobutylenes contribute to exhaust port deposits and clogging .

It would be desirable to provide a lubricating oil composition which is suitable for use in a two-stroke engine oil and which, in particular, provides

improvements in exhaust port blocking behaviour.

At the same time, it would also be desirable to provide a 2-stroke lubricating oil composition which exhibits reduced engine wear, reduced pollution, good low-temperature performance, good gasoline miscibility, high oxidation stability, high flash points, and which meets the requirements of standard setting organizations such as Japanese Automobile Standard JASO M345 2003 and International Standard ISO 1373832000(E).

It has now surprisingly been found that by using a Fischer-Tropsch derived base oil, preferably a heavy

Fischer-Tropsch derived base oil, as a base oil in a two- stroke engine lubricating oil composition, an improved two-stroke engine lubricating oil composition is provided which exhibits, in particular, a reduction in exhaust port blocking.

Summary of the Invention

According to the present invention there is provided the use of a lubricating oil composition comprising at least one Fischer-Tropsch derived base oil for reducing exhaust port blocking of a 2-stroke engine.

According to another aspect of the present invention there is provided a 2-stroke lubricating engine oil composition comprising (i) at least one Fischer-Tropsch derived base oil having a kinematic viscosity at 100°C in the range of from 2 to 30 mm ² /s and (ii) 5 wt% or greater of a hydrocarbon solvent; wherein the lubricating engine oil composition has a Blocking Index of greater than 130 as measured by the JASO M343-92 Exhaust System Blocking Test Method.

According to yet a further aspect of the present invention there is provided a 2-stroke lubricating engine oil composition comprising (i) a first Fischer-Tropsch derived base oil having a kinematic viscosity at 100°C in the range of from 2 mm ² /s to 10 mm ² /s and (ii) a second Fischer-Tropsch derived base oil having kinematic

viscosity at 100°C in the range of from 18 mm ² /s to 30 mm ² /s; wherein the weight ratio of the first Fischer- Tropsch base oil to the second Fischer-Tropsch base oil is in the range of from 10:1 to 1:5, and wherein the lubricating engine oil composition has a Blocking Index of greater than 130 as measured by the JASO M343-92

Exhaust System Blocking Test Method.

It has surprisingly been found that the use of

Fischer-Tropsch derived base oil, preferably heavy

Fischer-Tropsch derived base oil, in the 2-stroke

lubricating oil compositions herein provides reduced exhaust port blocking.

The use of a Fischer-Tropsch derived base oil allows replacement of polyisobutylenes on a viscometric basis.

It is to be expected that the same benefit would be manifest in a 2-stroke diesel engine, especially a 2- stroke slow speed marine diesel engine.

The 2-stroke lubricating oil compositions according to the present invention also provide reduced engine wear, increased lubricity, reduced pollution, an improved smoke index, good low-temperature performance,

satisfactory gasoline miscibility, high oxidation

stability, high flash points and reduced flammability .

The 2-stroke engine oil of the present invention also meets the requirements of Japanese Automobile

Standard JASO M345 2003 and International Standard ISO 1373832000 (E) .

Detailed Description of the Invention

The 2-stroke lubricating oil composition for use herein comprises at least one Fischer-Tropsch derived base oil.

Fischer-Tropsch derived base oils are known in the art. By the term "Fischer-Tropsch derived" is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To- Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition are those as for example

disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO

00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

The Fischer-Tropsch derived base oil preferably has a kinematic viscosity at 100°C in the range of from 2 mm ² /s to 30 mm ² /s. The total amount of Fischer-Tropsch derived base oil in the lubricating oil composition is preferably in the range of from 5 wt% to 99 wt~6 , more preferably from 10 wt% to 99 wt%.

In one embodiment of the present invention the lubricating oil composition comprises a light Fischer-

Tropsch derived base oil having a kinematic viscosity at 100°C in the range of from 2 mm ² /s to 10 mm ² /s,

preferably in the range of from 2 mm ² /s to 4 mm ² /s. In one embodiment, the light Fischer-Tropsch derived base oil is present at a level of from 5 wt% to 60 wt%, preferably at a level of from 20 wt% to about 60 wt%.

In another embodiment of the present invention the lubricating oil composition comprises a heavy Fischer- Tropsch derived base oil having a kinematic viscosity at 100°C in the range of from 12 mm ² /s to 30 mm ² /s,

preferably in the range of from 18 mm ² /s to 22 mm ² /s.

The heavy Fischer-Tropsch derived base oil is preferably present at a level of from 5 wt% to about 60 wt%, preferably from 10 wt% to 50 wt%.

In a preferred embodiment of the present invention the lubricating oil composition comprises a heavy

Fischer-Tropsch derived base oil having a kinematic viscosity at 100°C in the range of from 12 mm ² /s to 30 mm ² /s, preferably in the range of from 18 mm ² /s to 22 mm ² /s, and less than 2 wt% of a light Fischer-Tropsch base oil having a kinematic viscosity at 100°C in the range of from 2 mm ² /s to 10 mm ² /s. In the latter

embodiment, the lubricating oil composition is preferably free of light Fischer-Tropsch derived base oil having a kinematic viscosity at 100°C in the range of 2 mm ² /s to 20 mm ² /s.

In yet another embodiment of the present invention, the lubricating oil composition comprises a mixture of a first Fischer-Tropsch oil which is a light Fischer

Tropsch base oil having a kinematic viscosity at 100°C in the range of from 2 mm ² /s to 10 mm ² /s, preferably in the range of from 2 mm ² /s to 4 mm ² /s, and a second Fischer- Tropsch base oil which is a heavy Fischer-Tropsch base oil having a kinematic viscosity at 100°C in the range of from 12 mm ² /s to 30 mm ² /s, preferably in the range of from 18 mm ² /s to 22 mm ² /s. In the latter embodiment, it is preferred that the weight ratio of the first Fischer- Tropsch derived base oil and the second Fischer-Tropsch derived base oil is in the range of from 10:1 to 1:5, more preferably in the range of from 1.98:1 to 0.01:1.

In addition to the Fischer-Tropsch derived base oil, the lubricating composition herein may comprise one or more additional base oils. There are no particular limitations regarding the additional base oil (s) which can be used in the lubricating composition of the present invention, and various conventional mineral oils, synthetic oils as well as naturally derived esters such as vegetable oils may be conveniently used.

The additional base oil may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils; thus, the term "base oil" may refer to a mixture containing more than one base oil or base stock. Mineral oils include liquid petroleum oils and solvent- treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Suitable base oils for use in the lubricating oil compositions herein are Group I-III mineral base oils, Group IV poly-alpha olefins (PAOs) , and Group V base oils.

By "Group I", "Group II", "Group III" "Group IV" and "Group V" base oils are meant lubricating oil base oils according to the definitions of American Petroleum

Institute (API) for categories I-V. These API categories are defined in API Publication 1509, 16th Edition,

Appendix E, April, 2007.

Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs) , dibasic acid esters, polyol esters, polyalkylene glycols (PAGs) , alkyl naphthalenes and dewaxed waxy isomerates. API Group III hydrocarbon base oils sold by the Shell Group under the designation "Shell XHVI" (trade mark) may be conveniently used.

Poly-alpha olefin base oils (PAOs) and their

manufacture are well known in the art. Preferred poly- alpha olefin base oils that may be used in the

lubricating compositions may be derived from linear C2 to C32, preferably C6 to Ci6, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1- octene, 1-decene, 1-dodecene and 1-tetradecene .

The total amount of base oil incorporated in the lubricating composition is preferably present in an amount in the range of from 60 to 99 wt.%, more preferably in an amount in the range of from 65 to 98 wt . % and most preferably in an amount in the range of from 70 to 95 wt.%, with respect to the total weight of the lubricating composition.

Preferably, the finished lubricating composition has a kinematic viscosity in the range of from 2 to 30 mm ² /s at 100 °C, more preferably in the range of from 3 to 20 mm ² /s, most preferably in the range of from 4 to 15 mm ² /s .

Preferably, the lubricating oil composition

comprises 5 wt% or greater of a volatile hydrocarbon solvent. The inclusion of such a solvent is for the purpose of improving the miscibility and/or solubility of base oil and additives with gasoline or other fuel.

Preferably the volatile hydrocarbon solvent is present in the composition at a level in the range of 5 to 40 wt%, preferably in the range of 10 wt% to 30 wt%, more preferably in the range of from 20 wt% to 30 wt%, by weight of the total composition.

Examples of suitable volatile hydrocarbon solvents include kerosene, Exxsol D80 commercially from Exxon Mobil Chemical Company, Shellsol D70 commercially

available from Shell International Chemical Company and Fischer-Tropsh kerosene commercially available from Shell International Petroleum Company.

Another preferred component for use in the

lubricating compositions herein is a smoke-suppression agent. In a preferred embodiment, the smoke-suppression agent is an olefinically unsaturated polymer selected from the group consisting of polybutene, polyisobutylene or a mixture of polybutene and polyisobutylene, which has a number average molecular weight of 400 to 2200 and a terminal olefin content of at least 60 mol%, based on the total number of double bonds in the polymer. These types of smoke-suppression agents are taught in EP-A-1743932.

An example of a smoke-suppression agent is that commercially available from BASF Corporation under the tradename Glissopal (RTM) 1000, an approximately 1000

Dalton poly-isobutylene . Other examples would be poly- butylenes of similar molecular weight supplied by Ineos Oligomers under the trade name Indopol.

The smoke-suppression agent is preferably present in the composition at a level in the range of from 5% to

70%, preferably in the range of from 10% to 55%, by weight of the total composition.

One or more detergent/dispersant additive packages may be included in the lubricating oil composition of the present invention, preferably in an amount of from 1 to

25 wt%, more preferably from 3 to 20 wt%, based on the total weight of composition. Ashless, low-ash or ash- containing additives may be used for this purpose.

Suitable ashless additives include polyamide, alkenylsuccinimides , boric acid-modified

alkenylsuccinimies , phenolic amines and succinate

derivatives or combinations of any two or more such additives .

Suitable ash-containing detergent/dispersant

additives include alkaline earth metal (e.g. magnesium, calcium, barium) , salicylate, sulfonate, phosphonates or phenates or combinations of any two or more such

additives .

Commercially available two-stroke lubricant

detergent/dispersant additive packages include, for example,

Lubrizol 400, Lubrizol 6827, Lubrizol 6830, Lubrizol 600, Lubrizol 606, Oronite OLOA 9333, Oronite OLOA 340A, Oronite OLOA 6721 and Oronite OLOA 9357. The lubricating composition may further comprise additional additives such as anti-wear additives,

lubricity additives, extreme pressure agents, anti ^¬ oxidants, friction modifiers, viscosity index improvers, pour point depressants, rust or corrosion inhibitors, defoaming agents and seal fix or seal compatibility agents .

The above-described additives may be present at a level in the range of from 0.005% to 15%, preferably from 0.005% to 6%, by weight of the lubricating oil

composition .

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail. Specific examples of such additives are described in for example Kirk-Othmer

Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

To operate a two-stroke gasoline engine the

crankcase holds a mixture of two-stroke gasoline

lubricant and fuel. The recommended mix ratio of two- stroke gasoline engine lubricant and fuel are specified by the engine manufacturer. The fuels useful in two- stroke gasoline engines are well known to those skilled in the art and usually contain a major portion of a normally liquid fuel such as a hydrocarbonaceous

petroleum distillate fuel, e.g. spark ignition engine fuel as defined by ASTM D4814-07, or motor gasoline as defined by ASTM D439-89. Such fuels can also contain non-hydrocarbonaceous materials such as alcohols, ethers, organo nitro compounds and the like. Examples of

suitable fuels include, but are not necessarily limited to methanol, ethanol, diethyl ether, methylethyl ether, nitro methane and liquid fuels derived from vegetable and mineral sources such as corn, switch grass, alpha shale and coal. Examples of such fuel mixtures are

combinations of gasoline and ethanol, diesl fuel and ether, gasoline and nitro methane, etc. The fuel is preferably lead-free gasoline.

Two-stroke gasoline engine lubricants are typically used in admixture with fuels in amounts of about 20 to 250 parts by weight of fuel per 1 part by weight of lubricating oil, preferably in the range from 30 to 100 parts by weight of fuel per 1 part by weight of

lubricant .

It is important that the two-stroke lubricating oil composition of the present invention meets the

requirements set by standards setting organizations, including Japanese Automobile Standard JASO M345:2003 and

International Standard ISO 1373832000 (E) .

In particular, it has been found that the

lubricating oil compositions of the present invention provide an improved benefit in terms of reduced exhaust port blocking. Such a benefit can be measured by the standard test method JASO 343-92.

In particular, in preferred embodiments, the

lubricating oil compositions of the present invention have a Blocking Index of greater than 130, preferably greater than 140, as measured by JASO 343-92.

The lubricating compositions may be conveniently prepared by admixing the additives that are usually present in lubricating compositions, for example as herein before described, with mineral and/or synthetic base oil.

The present invention will now be described by reference to the following Examples which are not intended to limit the scope of the invention in any way. Examples

Example 1 and Comparative Example A

To determine the effect of GTL base oil on exhaust port blocking behaviour in a two-stroke motorcycle engine, two-stroke motorcycle oils were prepared having the formulations set out in Table 1 below. The

formulations were prepared by mixing the additives with the base oils according to conventional preparation methods. To determine the effect of each composition on exhaust system port blocking the Blocking Index for each example was measured using the Exhaust System Blocking test method JASO M343-92.

The results of these tests are shown in Table 1. Table 1

1. Mineral API Group I base oil commercially available from Shell Pernis Refinery, Rotterdam

2. Mineral API Group I base oil commercially available from Shell Pernis Refinery, Rotterdam

3. Heavy Fischer-Tropsch base stock having a kinematic viscosity at 100°C of 19 cSt as prepared according to US-

A-7354508.

4. Polybutylene having a molecular weight of 950

5. ShellSol D70B solvent commercially available from Shell International Chemical Company, Rotterdam, The Netherlands

6. 2-stroke performance additive package commercially available from Infineum, Milton Hill, Oxfordshire, UK containing aminic dispersant, antioxidants (mixed

hindered phenols and aminic antioxidants) , and over-based detergents from the range calcium phenate and calcium salicylates .

7. Antioxidant commercially available from CIBA

Speciality Chemicals, Berne, Switzerland

Examples 2-4 and Comparative Example B

To determine the effect of GTL base oil on exhaust port blocking behaviour in two-stroke engines, two-stroke motorcycle oils were prepared having the formulations set out in Table 2 below. The formulations were prepared by mixing the additives with the base oils according to conventional preparation methods. Various measurements were made on each of the engine lubricants using the test methods detailed in Table 2. The results of these tests are set out in Table 2.

Table 2

8. 2-stroke performance additive package containing aminic dispersant, antioxidants (mixed hindered phenols and aminic antioxidants) , over-based detergents from the range calcium phenates and calcium salicylates

9. antioxidant commercially available from CIBA

Speciality Chemicals, Berne, Switzerland

10. Lubricity additive commercially available from

Infinenum, Milton Hill, Oxfordshire, UK

11. Mineral Group I base oil commercially available from Shell Pernis Refinery, Rotterdam

12. Mineral Group I base oil commercially available from Shell Pernis Refinery, Rotterdam

13. Fischer-Tropsch base stock having a kinematic viscosity at 100°C of 19 cSt prepared according to the method of US-A-7354508.

14. Fischer-Tropsch base stock having a kinematic viscosity at 100°C of 3 cSt prepared according to the method of US-A-7354508.

Example 5 and Comparative Examples C and D

2-stroke engine oil compositions were prepared having the formulations set out in Table 3. The

formulations were prepared by mixing the additives with the base oils according to conventional preparation methods. In order to determine the exhaust port blocking behaviour the 2 stroke engine oil compositions were subject to the Exhaust Port Blocking Test Method JASO

The results are shown in Table 3 below

15. 2 stroke solvent ShellSol D70B solvent, commercially available from Shell Chemicals, The Netherlands

16. Polybutylene having a molecular weight of 950

17. Mineral API Group I base oil commercially available from Shell Pernis Refinery, Rotterdam

18. brightstock commercially available from Shell Pernis Refinery, Rotterdam 19. Heavy Fischer-Tropsch base stock having a kinematic viscosity at 100°C of 19 cSt.

20. A (brightstock) residual aromatic extract

commercially available from Shell Pernis Refinery,

Netherlands

21. 2-stroke performance additive package containing aminic dispersant, antioxidants (mixed hindered phenols and aminic antioxidants) , over-based detergents from the range calcium phenates and calcium salicylates

22. antioxidant commercially available from CIBA

Speciality Chemicals, Berne, Switzerland

Discussion

The examples show that a heavy residual GTL base oil (19cSt kinematic viscosity at 100 C) in combination with polybutylene (PB) gives a better port blocking

performance than a formulation containing solely PB as heavy base stock component, which demonstrates that heavy residual GTL base oil is an effective partial

polybutylene replacement. In Example 1 the major change in the formulation compared to Comparative Example A was to reduce PB and replace with a heavy residual GTL base oil. A minor modification was made to the API Gp I high viscosity index (HVI) base stock to maintain iso- viscometrics .

In Comparative Example B and Examples 2 to 4, it can be seen that a light GTL base oil (GTL-3) gives an improvement in port blocking performance compared to an all mineral (API Gp I) analogue formulation. Further, the Example 4 shows that use of the combination of light and heavy Fischer-Tropsch base oils, light Fischer-

Tropsch base oil GTL-3 together with heavy Fischer- Tropsch base oil GTL-19, gives an exceptional improvement in port blocking performance compared to the standard (API Gp I) mineral oil based formulation under iso- viscous conditions. Examples 2 to 4 are all 2 stroke oil formulations containing no PB, and yet suitable port blocking behaviour is obtained.

In Comparative Examples C and D and Example 5, the standard 2 stroke engine oil formulation, which normally had a polybutylene content of 35 wt%, was re-formulated to 25wt % polybutylene in the formulation together with a replacement amount of a heavy base stock component. It was noted that there was an improvement in the port blocking propensity of the 2-stroke formulation, for a range of heavy base oils, in the order GTL-19> brightstock

(HVI-650)> residual aromatic extract (Flavex 595).