WO2002079361A1

WO2002079361A1 - Lubricant composition

Info

Publication number: WO2002079361A1
Application number: PCT/SE2001/000710
Authority: WO
Inventors: Bager Ganemi
Original assignee: Svenska Statoil Ab
Priority date: 2001-04-02
Filing date: 2001-04-02
Publication date: 2002-10-10
Also published as: DE60124319T2; US20040116307A1; DE60124319D1; EP1383852B1; EP1383852A1

Abstract

A lubricant composition comprising 90-20% by weight of A) a lubricating base oil, 10-80% by weight of B) at least one fatty acid(C1-C4)alkylester, based on A)+B), and 0.1-20% by weight of C) lubricating oil additives, the percentage of C) being based on A)+B)+C). Use of said lubricant composition as a lubricant for a two-stroke cycle engine. Fuel composition for a two-stroke cycle engine comprising a fuel together with said lubricant composition.

Description

LUBRICANT COMPOSITION

Technical field

The present invention is within the field of lubricants. More specifically, it relates to a new lubricant composition which has been found to possess outstanding properties, especially in connection with two-stroke cycle engines. Accordingly, the invention also relates to the use of said lubricant composition as a lubricant for a two-stroke cycle engine. Furthermore, the invention relates to a two-stroke cycle engine fuel comprising said novel lubricant composition.

Backcrround of the invention

The use of spark ignited two-stroke internal combustion engines is steadily increasing. Examples of apparatuses or equipments in connection with which such engines are utilised are lawn movers and other pieces of garden equipment, chain saws, pumps, electrical generators, marine outboards, snow-mobiles, motorcycles and the like. The increasing use of two-stroke cycle engines, coupled with increasing severity of those conditions under which they are to be operated, has lead to an increased demand for oils to adequately lubricate such engines. Furthermore, the lubrication of two-stroke cycle engines is associated with unique problems and techniques relative to the lubrication of other types of engines. Thus, it should generally be noted that in a two-stroke cycle engine the lubricant, in addition to imparting to the engine a proper lubricating effect, should burn or combust as completely as possible during the engine operation cycle. In other words, the characteristics desired from such a lubricant are somewhat contradictory. With reference to problems associated with two- stroke cycle engines and different attempts to solve such problems, reference is made to the following US patents: 3 004 837; 3 753 905; and 5 866 520. Although specific problems and specific solutions to such problems may be the subjects of said US patents, it could generally be said that lubricity, scuffing and scoring problems are controlled by the addition of relatively high viscosity oils such as bright stock or high molecular weight polymers. Other solutions comprise the addition of very specific additives.

Thus, the viscosity of the lubricant oil used has generally been related to the lubricity properties thereof. Therefore, a certain viscosity has been considered compulsory to achieve an adequate lubrication.

The present invention is based on a completely different approach to solve the problems referred to. Thus, it has unexpectedly been found that a specific group of fatty acid-alkyl esters can replace the lubricating base oil up to a considerable proportion thereof to give an outstanding lubricant composition for two-stroke cycle engines, in spite of the fact that said lubricant composition can be imparted a much lower viscosity than that hitherto considered necessary or proper for engines of the type referred to. As will be described more fully below said alkyl esters may be derived from vegetable oils, e.g. rapeseed oil, and concerning such esters per se reference can be made to for instance EP 626 442 Al and US 5 713 965 as prior art. From said prior art it can be seen that such esters have been proposed primarily as fuels for diesel engines. However, although they are mentioned incidentally also in connection with lubricants, the specific use according to the present invention is neither disclosed nor suggested.

Summary of the invention Contrary to the previous view that adequate lubrication for an engine is generally achieved by means of a rather viscous lubricant oil, the present invention is thus based on the finding that a specific group of fatty acid- alkyl esters can replace a considerable proportion of previously used lubricating base oils to give an outstanding new lubricant composition especially well suited for two-stroke cycle engines. Said esters may even represent the major ingredient of the base oils of such lubricant compositions, in spite of the fact that such proportions may give a lubricant composition having up to four or five times lower viscosity than lubricant compositions utilised today.

Apart from the fact that outstanding lubricity properties are still achieved, this basically means that the new lubricant composition according to the present invention will be highly combustible and biodegradable.

In this context, it could be mentioned that when used in two-stroke cycle engines mineral oil based lubricants utilised today give high emissions to the environment, in the form of not readily biodegradable products .

Another great advantage in connection with the present invention is related to the fact that the fatty acid-alkyl esters referred to can be obtained from inexpensive and renewable vegetable sources. In other words, the new lubricant composition according to the invention is cheap as well as less harmful to the environment. Contrary thereto, natural or synthetic non- mineral oil-based lubricants available today are rather expensive, which has indeed delayed the use of more environmentally adapted products. Other advantages of the new lubricant composition should be obvious to a person skilled in the art after having read the more detailed description of the invention presented below. Description of the invention

More specifically, according to a first aspect of the present invention, there is provided a novel lubricant composition comprising

90-20 % by weight of A) a lubricating base oil and 10-80 % by weight of B) at least one fatty acid- (Ci-

C₄) alkyl ester, said percentages being based on the total weight of A) +B) .

In addition to the above-mentioned major ingredients the lubricant composition also further contains 0.1-20 % by weight of C) conventional lubricating oil additive (s) , said percentage being based on the total weight of the lubricant composition, i.e. of A) +B) +C) .

According to one embodiment of the invention the lubricant composition comprises 50-80, e.g. 60-80 or 60- 75, % by weight of said fatty acid- (Cι-C₄) alkyl ester.

As concerns said fatty acid- (C_3.-C₄) alkyl ester, a preferable embodiment thereof is represented by the case where the fatty acid portion of said ester comprises at least 60 % by weight, preferably at least 70 % by weight, of C₁₆-Ci₈-fatty acid(s).

According to one especially preferable embodiment of the lubricant composition the fatty acid- (C₁-C4) alkyl ester is derived from a vegetable oil. Examples of interesting vegetable oils in this connection are olive, peanut, corn, cottonseed, rapeseed, soybean, linseed, castor, coconut, palm, peanut, safflower, sesame, sunflower and tallow oils. The (C₁-C₄) alkyl portion of said fatty acid- (Ci-

C₄) alkyl ester may be methyl, ethyl, propyl and butyl

(with straight or branched chains where applicable) .

Methyl and ethyl are, however, preferable, methyl being especially preferable.

As rapeseed oil is common in for instance Sweden, this vegetable oil represents a cheap and easily available raw material for the ester referred to. In addition thereto, for instance the methyl ester of rapeseed oil is an easily available commercial product, that can be directly used in the lubricant composition according to the present invention. Apart from the fact that said methyl ester is cheap and easily available, it has also been found to impart outstanding properties (lubricity, combustibility, etc.) to the lubricant composition, as will be presented below in the experimental part of the description. Methods for the esterification of rapeseed oil are also known per se and can be utilized for the manufacture of said ester. Similar methods could be used for other alkyl esters and other vegetable oils. As prior art in this connection reference can be made to US 5,713,965.

The lubricating base oil used in the composition can be any one or any mixture of conventional base oils used in lubricant, preferably two-stroke, compositions. In other words, it is generally selected from lubricating natural, e.g. mineral, and synthetic oils.

Some examples of types of oils in this respect are hydrocarbon oils, alkylene oxide polymers, esters of mono- or polyfunctional carboxylic acids and polyfunctional alcohols, poly (alkylene) glycols, etc.

Especially interesting esters can be found within the following groups: Natural triglyceride esters, for instance from the following sources: castor, coconut, corn, cottonseed, linseed, olive, palm, palm kernel, peanut, rapeseed, safflower, sesame, soybean, sunflower and tallow oils; Synthetic polyol esters based on polyols such as neopentyl glycol (NPG) , trimethylol propane (TMP) and pentaerythritol (PE) , esterified with fatty acid(s), e.g. from the following sources: castor, coconut, corn, cottonseed, linseed, olive, palm, palm kernel, peanut, rapeseed, safflower, sesame, soy, sunflower and tallow oils ;

Synthetic esters based on polyalcohol (s) derived from sugar species esterified with fatty acid(s), e.g. from the following sources: castor, coconut, corn, cottonseed, linseed, olive, palm, palm kernel, peanut, rapeseed, safflower, sesame, soy, sunflower and tallow oils; and

Dimerate esters, such as esters based on dimerized fatty acids (e.g. C₃₆ dimer acid esters) and alcohols (e.g. monofunctional alcohols).

Preferably the lubricating base oil is selected from environmentally friendly natural or synthetic esters, such as those types disclosed above. Most preferably such esters are selected from the above-mentioned synthetic polyol and sugar polyalcohol fatty acid esters. Thus, by the present invention it has become possible to replace a considerable proportion of such generally expensive esters with easily available and inexpensive fatty acid- alkylesters without any significant impairment of lubricity properties.

In other words the use of environmentally friendly lubricants are considerably expedited by the present invention. As to the additive (s) C) a preferred range thereof is 0.1-10 % by weight, for instance 0.1-5 % by weight, based on the weight of A)+B)+C) . As mentioned above such additive (s) can be chosen completely along the lines of the prior art, for instance in connection with two-stroke cycle engines and for purposes similar to those of the prior art. However, it may well be emphasized once more that lubricity base ingredients A) and B) of the lubricant composition impart such good properties to the lubricant composition that some or many conventional additives may be reduced or even omitted in the composition. When utilized, they are, however, preferably selected among lubricity improvers, viscosity improvers, combustion improvers, corrosion and/or oxidation inhibiting agents, pour point depressing agents, extreme pressure agents, antiwear agents, antifoam agents, detergents, dispersants, antioxidants and metal passivators completely along the lines of the prior art.

One preferable additive to be used in the lubricant composition claimed is, however, polyisobutylene and derivates thereof, for instance in an amount of 2-10, such as 3-8, % by weight, based on the weight of A) +B) +C) . Examples of derivates of polyisobutylene are amine and succinic acid derivates thereof .

As was mentioned above, the viscosity of the lubricant composition is generally much lower than that of previously known lubricants for similar purposes . Generally this means that the (kinematic) viscosity thereof, at 100°C, is within the range of 1-10 cSt . Preferably said viscosity is within the range of 1-6 cSt and more preferably within the range of 2-5 cSt . Although the lubricant composition according to the present invention is presented especially in connection with lubrication of two-stroke cycle engines, it is not per se restricted to such use only. Thus, it may well be useful as a lubricant for other engines or in industrial applications. However, since the lubrication of two- stroke cycle engines is especially interesting, another aspect of the present invention is represented by the use of the lubricant composition as defined above for the lubrication of, or as a lubricant for, a two-stroke cycle engine .

As one of the advantages with the lubricant composition is that it is of a relatively low viscosity, one preferable embodiment of said use is in connection with an engine where the lubricant composition is supplied to said engine separately from the fuel for the same. That is, a separate lubrication of a two-stroke cycle engine is more easily achieved by means of a low viscosity lubricant composition, the pumpability at low temperature being a great advantage as compared to today's high viscosity lubricants.

However, as can be gathered from the above- mentioned, the lubricant composition may well be combined or mixed directly into the fuel for a two-stroke cycle engine, as is common practice today. Therefore, still another aspect of the present invention is represented by a fuel composition for a two-stroke cycle engine, which comprises a fuel for said engine together with a lubricant composition as defined above. A preferable embodiment of such a fuel composition is a composition wherein said lubricant composition constitutes 0.5-4, more preferably 1-3, such as 1-2, % by weight, based on the weight of said fuel. The present invention will now be further described in a non-limiting way by the following working examples showing the manufacture of representative lubricant compositions according to the invention as well as characteristics and uses thereof.

Examples

For the evaluation of the lubricity properties of the lubricant composition according to the present invention a sample thereof, SI, was prepared and tested at two different laboratories. At one laboratory said sample SI was also compared with a commercial mineral-oil based two-stroke engine oil, S2, and at the other laboratory sample SI was compared with a commercial, synthetic and biodegradable ester-based two stroke engine oil, S3.

Another lubricant composition according to the present invention, Sll, was also prepared and tested at an independent laboratory, where it was also compared with said commercial mineral-oil based two-stroke engine oil S2.

Samples SI and S 11 according to the present invention were prepared by mixing the following components in the following percentages:

Component Amount (% by weight) SI Sll

Lubricating base oil: 25.0 15.0

(Sugar-C -C₁₈-fatty acid ester) Fatty acid- (C_3.-C₄) alkyl ester: 62.3 77.7

(Rapeseed-methyl ester) Additives : Paraffinic solvent 5.0 0.8

Calcium alkyl phenate 0.3 0.3

Calcium sulfonate 0.3 0.3

Polyisobutylene 4.0 3.0

Derivative of polyisobut :yylleennee 0.4 0.4 and succinic acid

Polyisobutylene amine 2.5 2.5

Poly alkyl methacrylate 0.2 -

The kinematic viscosities of SI and Sll (according to ASTM D 445) were 10.40 cSt at 40°C and 3.15 cSt at 100°C (SI), and 7.74 cSt at 40°C and 2.65 cSt at 100°C, respectively (Sll) .

Example 1

Detergency and Rincrstickincr test on a Husqvarna 346 Two

Stroke Chainsaw Engine This test on a Husqvarna 346 two stroke chainsaw engine is a high temperature detergency test with resistance against ringsticking as the main result information. Samples SI and S2 were tested under identical conditions and the test results are presented below. The tests were carried out with an oil-gasoline mixture containing 2% by volume of oil. The kinematic viscosity of S2 (ASTM D 445) was 58 cSt at 40°C and 9.2 cSt at 100°C.

The test consists of a breaking in phase and a high temperature load phase. The engine is held at full throttle at 8400 r/min, except for 5 idle phases (5 min) ,

To get a test approval, no ringsticking or seizure should have occured. Nine items are rated from 1 (lowest rating) to 5 (highest rating) . All ratings should be above 2. +/- accounts for 0,25.

No factors are used, but the most important item is ^,λ4:Ring & Ringland" . A clear ringsticking gives automatically rating 1.

Sometimes two grades are used for the same item. Then the first focuses on the amount of deposits and the other one focuses on the effect it has on engine function.

The test results are presented in Table 1.

Table 1

Comparison of lubricity performances between samples SI and S2

Oil sample SI S2

Test approved Yes Yes

Ringsticking No ^" NO

. _ _.. ^

Scuffing No

Classification

1) Piston top 4-/3 4-/3

2 ) Topϊand 3 3

3) Piston skirt 3/2^".5 ^" ^" 3.5

4) Ring + ringland ^~ 3.5 ^~ ^"3^".5

5) Piston pin ^"3 ^{~ "}3

_ ^

6) Pin bearing ^~~ 3

7) Combustion chamber 3.5/3-^"" 3^~.5/3-

8) Exhaust port ^~3 3

9) Sparkplug 3 ^" 3

SUM 1 (high) 28.75 29.25

SUM 2 (low) 26.75 27.75 Example 2

Testing of two-stroke oil for snowmobile motors, type

Rotax 253

The measurements of the technical qualities of the two samples, SI and S3, were made according to the procedure which is described in the following published document :

"Meddelande 3415, Tv taktsoljor for snόskotermotorer" , published by the Swedish Machinery Testing Insti tute, 1994 .

As in the Laboratory 1 testing the tests were carried out with an oil-gasoline mixture containing 2% by volume of oil. The kinematic viscosity of S3 (ASTM D 445) was 42 cSt at 40°C and 8.3 cSt at 100°C.

Mark-setting of coatings in the motor was carried out after a running cycle of 5 hours . Eight items were rated from 1 (lowest rating) to 5 (highest rating) . The test results are presented in Table 2.

Table 2

Comparison of lubricity performances between samples SI and S3

The checkpoints and ratings were the following:

Upper and lower Merit 5 Ring fully free piston ring

4 Ring movable, sluggish 3 Ring movable, very sluggish 2 ring stuck, less than half of circumference ring stuck, more than half of circumference

Ringland Merit 5 Fully clean or discoloured surface

4 Thin coating between rings

3 Discoloured surface below lower ring

2 Thin coating below lower ring

1 Thick coating below lower ring

Under crown Merit 5 Quite clean

4 Coatings, up to the size of a circle, 0 20mm 3 Coatings, up to the size of a circle, 0 25mm 2 Coatings, up to the size of a circle, 0 30mm 1 Completely covered with coatings

Upper ring Merit 5 Surface quite clean groove

4 Thin, evenly distributed coatings 3 Smaller deposits 2 Larger, hard deposits 1 Thick coatings around the whole circumference

Crow land Merit 5 Thin, even and gray coatings

4 Gray varnish coatings with small deposits gray varnish coatings with bigger deposits

2 Thick, shiny and black coatings 1 Thick, shiny and black coatings with deposits

Inside cylinder Merit 5 Quite clean or discoloured 4 < 1/3 of surface with coatings 3 > 1/3 of surface with coatings 2 Surface quite covered with coatings 1 Hard coatings along the wall of the cylinder

Exhaust port Merit 5 No coatings near the cylinderwall, thin coatings further out in the port 4 No coatings near the cylinderwall, thick coatings or the whole width of the port 3 Small, thin coatings near the cylinder wall, part of the width of the port 2 Thick coatings near the cylinder wall, part of the width of the port 1 Thick coatings near the cylinder wall all over the width of the port

Furthermore, the cold flow properties of SI and S3 were estimated as follows.

The flow-out speeds for the oils, cooled down to -25°C and taken out into room temperature (20°C) , were estimated to 5.70 ± 0.05 ml/min for sample SI and 0.97 ± 0.05 ml/min for sample S3.

Example 3 Detergency and Ringsticking test on a Husqvarna 242 Two

Stroke Chainsaw Engine

This test on a HVA 242 chainsaw engine is similar to the test disclosed in Example 1 performed on a HVA 346 chainsaw engine and reference can thus be made to said Example 1 concerning test details.

Samples Sll and S2 were tested under identical conditions and the test results are presented in Table 3.

The tests were carried out with an oil-gasoline mixture containing 2% by volume of oil. Values in brackets ( ) show tendency and are not included in the sum.

Table 3

Comparison of lubricity performances between samples Sll and S2

Oil sample Sll S2

Test approved Yes Yes

Ringsticking No No

Scuffing No No Classification

Piston top 4 4/4 - Topiand 3 ( + ) ^" 3 + Piston skirt ^{" ""} 3V/3 - 3 + ( + ) Ring + ringland ^""3 2 . 5 + Piston pin 3 ^" 3 Pin bearing 3 - 3 + ( + ) ^"

_ _ ^ Combustion chamber 3 /3 - Exhaust port 3 /3 - ^{' "} 3^" Sparkplug 3 ^" 3

SUM 1 (high) 28 28.75

SUM 2 (low) 27.25 28.5

Example 4

Husgvarna 232 E-tech Scrub Cutter engine test

Samples of Sll and S2 were also tested according to the following test procedure:

This test on HVA 232 E-tech scrub cutter was developed to sort out the detergency for two-stroke oils at low engine temperatures. The test procedure is chosen to create a high rpm range at low load. As the HVA 232 E- tech during these conditions has a rather high amount of backflow from the cylinder down into the transfer ducts, it creates tough conditions for the oil in the crankcase . More specifically the test includes the following: After a 15 min braking in phase the carburettor H- needle is set to give:

3% CO at 8400 r/min (steady state) .

The setting is done with a muffer without any catalytic converter. During the actual test cycle a Cat- muffler is used. The test cycle has the following sequence: 2s full throttle > 3s idle.

This continues for 50h (36 000 cycles) . The only load is the inertia from a 4 -egged grass-cutter. The L- needle is set to give max 12 000 (+/-500) r/min. The lowest speed normally lies around 6 OOOr/min.

After the test, three areas as below are rated:

1) Crank and crankcase

2) Piston skirt

3) Ring and Ring groove

Rating is from 1 to 5 with l=bad and 5=Excellent . The results are presented in Table 4. Table 4

CONCLUSIONS As can be seen from Tables 1-4 the novel lubricant composition according to the present invention works extremely well in two-stroke engines and matches currently used commercial two-stroke engine oils which are mineral oil-based or synthetic ester-based. Furthermore, as has been said above, the main components of the novel lubricant composition are readily biodegradable and derivable from renewable sources as well as much cheaper than currently used biodegradable synthetic ester products. In addition thereto, its low viscosity generally means advantages within this technical field.

Claims

1. A lubricant composition, preferably for a two- stroke cycle engine, comprising 90-20 % by weight of A) a lubricating base oil,

10-80 % by weight of B) at least one fatty acid- {C_- C_) alkyl ester, said percentages being based on the total weight of A) +B) and 0.1-20 % by weight, of C) lubricating oil additive (s) , said percentage being based on the total weight of A) +B) +C) .

2. A lubricant composition according to claim 1, which comprises 50-80 % by weight of said fatty acid- (C_- C₄) alkyl ester.

3. A lubricant composition according to any one of the preceding claims, wherein the fatty acid portion of said fatty acid- (C_!-C₄) alkyl ester comprises at least 60 % by weight, preferably at least 70 % by weight, of Cι₆-Cι₈ fatty acid(s) .

4. A lubricant composition according to any one of the preceding claims, wherein said fatty acid- (Cι-C₄) alkyl ester is derived from a vegetable oil.

5. A lubricant composition according to claim 4, wherein said vegetable oil is selected from olive oil, peanut oil, corn oil, cottonseed oil, rapeseed oil, soybean oil, linseed oil, castor oil, coconut oil, palmoil, peanut oil, safflower oil, sesame oil, sunflower oil and tallow oil .

6. A lubricant composition according to claim 5, wherein said vegetable oil is rapeseed oil .

7. A lubricant composition according to any one of the preceding claims, wherein the (Cι-C₄) alkyl portion of said fatty acid- (Cι-C ) alkyl ester is methyl or ethyl, preferably methyl .

8. A lubricant composition according to claim 7, wherein said fatty acid- (C_!-C₄) alkyl ester is rapeseed oil methyl ester.

9. A lubricant composition according to any one of the preceding claims, wherein said lubricating oil additive (s) is (are) present in an amount of 0.1-10 % by weight, based on the total weight of A) +B) +C) .

10. A lubricant composition according to any one of the preceding claims, wherein said lubricating base oil is selected from synthetic polyol-fatty acid esters and sugar polyalcohol -fatty acid esters.

11. A lubricant composition according to claim 10, wherein said fatty acid esters are derivable from castor, coconut, corn, cottonseed, linseed, olive, palm, palm kernel, peanut, rapeseed, safflower, sesame, soy, sunflower and/or tallow oils.

12. A lubricant composition according to any one of the preceding claims, wherein said additives are selected from lubricity improvers, viscosity improvers combustion improvers, corrosion and/or oxidation inhibiting agents, pour point depressing agents, extreme pressure agents, antiwear agents, antifoam agents, detergents, dispersants, antioxidants and metal passivators.

13. A lubricant composition according to claim 12, wherein said additive comprises polyisobutylene and/or derivatives thereof.

14. A lubricant composition according to claim 13, wherein said polyisobutylene or derivative (s) thereof is present in an amount of 2-10, preferably 3-8, % by weight .

15. A lubricant composition according to any one of the preceding claims, which has a viscosity, at 100°C, within the range of 1-10, preferably 1-6, more preferably

2-5, cSt.

16. Use of the lubricant composition as defined in any one of claims 1-15 as a lubricant for a two-stroke cycle engine.

17. Use according to claim 16, wherein said lubricant composition is supplied to said two-stroke cycle engine separately from the fuel for said engine .

18. A fuel composition for a two-stroke cycle engine, which comprises a fuel for said engine together with a lubricant composition as defined in any one of claims 1-15.

19. A fuel composition according to claim 18, wherein said lubricant composition constitutesO .5-4 , preferably 1-3, more preferably 1-2, % by weight, based on the weight of said fuel .