Title of Invention

A DILUENT COMPOSITION FOR TWO-CYCLE ENGINE LUBRICATING OILS

Abstract

The present invention relates to a diluent composition for two-cycle engine lubricating oils comprising a hydrocarbon mixutre having a content of bicycle or higher polycyclic aromatic hydrocarbon having two or more aromatic rings or condensed rings per molecule of 1.0% by volume or less and a sulphur content of 0.015% by weight or less, and having a distillation end point of at most 320 degree c. 5

Full Text

The present invention relates to a diluent composition for providing two-cycle engine lubricating oils with improved two-cycle engine oil-cleaning properties and little exhaust smoke, and with which exhaust system clogging {closing-up of the exhaust system) does not readily occur, and two-cycle engine lubricating oils which contain said diluent. Two-cycle gasoline engines in small two-wheeled vehicles and the like do not generally have a moving valve system such as a cam and tappet, and so they are advantageous compared with 4-stroke gasoline engines in that they are smaller and lighter, have a higher output with respect to the amount of exhaust, can be produced at lower cost, and so forth. However, two-cycle engines are disadvantageous in that both fuel and lubricating oil are aspirated into the combustion chamber and combusted, and so combustion residue comprising lubricating oil that has not been totally combusted in the combustion chamber readily builds up in the piston ring grooves and piston skirts, and a decrease in engine output and ignition plug contamination become more likely as these combustion chamber deposits increase (reference: Iridologist, Vol. 38, No. 2, p. 101 (1993)). Exhaust gas containing large amounts of such lubricating oil combustion residue results in the generation of large amounts of exhaust smoke from the exhaust pipe in the short term, and a build-up of tar-like residue in the exhaust pipe, clogging of the exhaust pipe and a subsequent decrease in engine output in the long term. Moreover, exhaust gas containing large amounts of combustion residue is environmentally-undesirable, and even if exhaust gas catalysts or the like are provided in such engines from now on, there is the fear that the surface of the catalyst will become coated, decreasing catalytic activity considerably. Furthermore, as the exhaust system becomes clogged, the exhaust pressure in the engine increases and the engine output decreases markedly. The provision of a two-cycle engine lubricating oil which allows smooth combustion, inhibits the production of uncombusted gas and, at the same time, improves engine-cleaning properties and exhaust performance and prevents clogging of the exhaust system, is very important for maintaining a good two-cycle engine performance over long periods. Lubricating oil compositions used for two-cycle engines usually comprise a mineral oil-based or synthetic base oil, an engine-lubricating base oil such as polyisobutylene or a detergent dispersant, and a petroleum-based hydrocarbon diluent for improving the miscibility with the fuel and facilitating combustion. This diluent is usually produced by taking the light oil fraction or kerosene obtained by the normal pressure distillation of crude oil as the starting material, then subjecting this to hydrogenation and desulphurization to remove impurities such as sulphur and nitrogen. Generally, compound compositions for petroleum-based hydrocarbon diluents used in two-cycle engine oils comprise aromatic compounds and saturated hydrocarbons such as paraffins and naphthenes. They also contain small amounts of organosulphur compounds, in which sulphur atoms are bonded to Chef abovementioned hydrocarbon compounds. Japanese Unexamined Patent Application Nos. S53-5783 (5 May 1978) and S54-16040 (19 December 1979) relate to diluents and lubricating oils for two-cycle gasoline engines which result in little exhaust smoke and little exhaust clogging. These techniques relate to two-cycle gasoline engine oils containing from 5 to 50% by weight of a petroleum-based and/or synthetic hydrocarbon diluent having a boiling point of from 150 to 300°C, with a stipulated temperature range for the diluent boiling fraction. Common two-cycle engine lubricating oils differ from lubricating oils or other internal combustion engines such as 4-cycle engines in that they do not contain organometallic compounds which are not readily combustible or substances which combust to form ash, such as the antioxidant zinc dialkyldithiophosphate (ZnDTP) or oil-soluble molybdenum compounds because the lubricating oil mixes with the fuel and lubricates each part, and because a mixed gas comprising air and fuel containing some of the lubricating oil is combusted. Although, by way of exception, metallic detergents are generally used, the amounts used are generally limited because the metal-containing compound contaminates the spark plug electrodes which generate electrical sparks to the mixed gas to cause ignition (reference: Tribologist, Vol. 38, No. 2, p. 101 (1993)). The present invention aims to provide a two-cycle engine lubricating oil which allows smooth combustion, inhibits the production of uncombusted gas and exhaust smoke and, at the same time, improves engine-cleaning properties and exhaust performance, prevents clogging of the exhaust system and allows a good engine output performance to be maintained for long periods, and the necessary diluent composition therefor. Thus, as a result of diligent research into developing a two-cycle engine oil with good cleaning properties that results in little exhaust clogging and little exhaust gas, the present inventors perfected the present invention upon discovering that the important factor for overcoming these problems is not the boiling point range of the diluent, as focused on in the abovementioned published patent literature, but the sulphur content and bicyclic or higher polycyclic aromatic content of the aromatic hydrocarbons (test method as stipulated by the UK Petrochemical Association IP 391/90) contained in the diluent. Specifically, the first embodiment of the present invention relates to a diluent composition for two-cycle engine lubricating oils characterized by comprising a hydrocarbon mixture having a bicyclic or higher polycyclic aromatic hydrocarbon content of 1.0% by volume or less and a sulphur content of 0.015% by weight or less. Conventionally it was thought that all aromatic hydrocarbons were difficult to combust completely and readily formed partially oxidized and combusted compounds. However, it has been found that monocyclic aromatic hydrocarbons dissolve the sludge formed in engines, have an engine-cleaning effect and are an important component for improving the cleaning properties of two-cycle engine oils, whereas the bicyclic or higher polycyclic aromatic hydrocarbons contained in the diluent have a larger molecular weight, a higher boiling point and are chemically more stable than the other hydrocarbon components in the diluent, and they have two or more aromatic rings or condensed rings per molecule and are highly unsaturated, and so it is the bicyclic or higher polycyclic aromatic hydrocarbons that are difficult to combust completely in the engine and readily form partially oxidized and combusted compounds. These partially oxidized and combusted bicyclic or higher polycyclic aromatic hydrocarbons stick to the insides of the combustion chamber and in the piston ring grooves in the engine and result in a deterioration in engine-cleaning properties, they also accumulate in the exhaust system, which tends to cause exhaust clogging, and they result in the production of black smoky exhaust. Moreover it is thought that the organosulphur compounds contained in the diluent also undergo oxidation rather than combustion, forming organosulphonyl compounds and sulphonate compounds which contaminate the engine, and that rather than undergo combustion they interact with water vapour to form exhaust smoke-forming nuclei, corrode the exhaust pipe and result in an increase in the amount of exhaust smoke. Thus another embodiment of the present invention relates to the above diluent composition further having a monocyclic aromatic hydrocarbon content of 20% by volume or more. The diluents according to the first and second embodiments of the present invention are hydrocarbon-based diluents, suitable for use with a wide range of two-cycle engine oils for land and small sea craft, and the like. Diluents of the present invention preferably have a JIS K2265 Tag closed-cup test flash point of 40°C or more, preferably 70°C or more, a JIS K2254 normal pressure distillation test end point of 320^0 or less, preferably 270""C or less, a bicyclic or higher polycyclic aromatic hydrocarbon (according to the test method IP 391/90, stipulated by the UK Petrochemical Association) content of 1.0% by volume or less, and a sulphur content of 0.015% by weight or less. Moreover, it is particularly preferable for the diluents to have a 10% residual carbon content (according to test method JIS K2270) of 0.1% by weight or less. Diluents with these characteristics can be produced by subjecting crude oil to normal pressure distillation separation and a high-level hydrogenation desulphurization treatment. When the diluent is used to prepare a two-cycle engine lubricating oil, the anticipated normal ambient temperature is less than iC^C, so if the flash point is 40°C or more, there is little adverse effect on actual operations, and operational efficiency is good when the engine oil is manufactured. Moreover, as it is generally stipulated (as shown in the Automobile Technology Corporation"s automobile regulation M345-93) that the flash point of two-cycle engine oils containing such diluents be 70°C or higher, this also necessitates that the flash point of any admixed diluent be 40°C or higher, preferably 70°C or higher. A normal pressure distillation test end point of 320°C or less is required because it is preferable for the diluent to vaporize below the temperature of the metal surface in the two-cycle engine combustion chamber. Moreover, in order to prevent residue originating from the diluent remaining in the engine and adversely affecting engine-cleaning properties when the diluent is vaporized in the engine, the residual carbon content of the diluent is preferably low, at 0.1% by weight or less. If diluents of the present invention have the abovementioned characteristics it is possible to achieve the aims of the present invention using synthetic hydrocarbon-based diluents, petrochemical hydrocarbon-based diluents or mixtures of these diluents. When diluents of the present invention are used for two-cycle engine oils in practice, suitable amounts of various additives such as polybutene and detergent dispersants may be added to the mineral oil-based and/or synthetic base oil if necessary, and these diluents can be added at from 5 to 40% by weight, preferably from 10 to 30% by weight, per 100% by weight of the resulting product. When diluent is admixed into two-cycle engine oil in larger amounts than mentioned above, it is possible to decrease the two-cycle engine exhaust smoke (according to the JASO M342-92 test) and increase the exhaust smoke index, but it is feared that the low-temperature engine-cleaning properties and the initial torque index {according to the JASO M340-92 lubricating test) will be lowered and at the low temperature drag torque in the engine (engine friction) will increase. Therefore, the viscosity of the two-cycle engine oil manufactured product is generally such that it has a kinematic viscosity at 100°C of 6.5 mm^/s or more, as stipulated by the ISO (International Standards Organization) and JASO M345-93 regulations. Moreover, if there is a large diluent component in the two-cycle engine oil, the viscosity of the composition is lower and so a large amount of macromolecular polybutene having a number average molecular weight of 1000 or more or a high-viscosity base oil must be added to maintain a product viscosity of 6.5 mm^/s or more. In such cases, the lubricating oil is aspirated into the engine, then the diluent is vaporized at the engine surface, the high-viscosity base oil and macromolecular polybutene remains on the surface, and the drag torque of the engine (engine friction) is increased. Also, when large amounts of high-viscosity base oil or macromolecular polybutene compound having a number average molecular weight of 1000 or more are admixed, complete combustion is difficult to achieve and uncombusted products form readily in the engine, due to their high melting points and high molecular weights. Consequently, such diluents must be used at 40% by weight or less per 100% by weight of two-cycle engine oil product. Examples of detergent dispersants used in two-cycle engine oils include metallic detergent dispersants such as sulphonates, phenates and salicylates, and ashless dispersants such as succinimide, succinic acid esters and ethylene propylene oxide copolymers. Of these, sulphonate detergents and succinimide, or combinations of salicylate detergents and succinimide, are particularly suitable. Polybutene compounds having a number average molecular weight of from 500 to 1000 are added if necessary. Mineral-based base oils and/or synthetic base oils based on esters and the like are used as the lubricating base oil. An especially preferred base oil is a base oil having as main component a base oil of a kinematic viscosity of from 4 to 20 mm^/s at 100°C, a viscosity index of 75 or more, a condensed polycyclic aromatic hydrocarbon {DMSO extract) content of less than 1.0% by weight and a sulphur content of 1.0% wt or less. Another preferred base oil is a base oil of a kinematic viscosity of from 4 to 20 mm^/s at lOCC, a viscosity index of 75 or more, a condensed polycyclic, aromatic hydrocarbon (DMSO extract) content of less than 1.0% by weight and a sulphur content of 1.2% wt or less, when used in combination with from 0.1 to 2.0 parts by weight of phenolic antioxidant per 100 parts of weight of base oil. The present invention is described in more detail below by means of working examples and comparative examples, although the present invention is not limited to these. Test oils were prepared by combining various diluents of the present invention with mineral-based base oil, detergent dispersant, polybutene and pour point lowering agent, and these test oils were subjected to the cleaning properties test (JASO M341-92), exhaust smoke test (JASO M342-92), exhaust system clogging test (JASO M343-92) and lubricating test (JASO M340-92) for two-cycle gasoline engine lubricating oils. The compositions and test results for the various test oils are shown in the tables. Note 1: The hydrocarbon type test was performed according to test method IP 391-90 (high speed liquid chromatography) stipulated by the UK Petrochemical Association. When JIS K0124 (high speed liquid chromatography analysis measurements) was also performed, JIS K0124 was taken as standard. Table 1 Unit Test method Diluent 1 Diluent 2 Diluent 3 Diluent 4 Kinematic viscosity mm^/s JIS K2283 1.2 1.2 1.2 3.8 40""C Density (15=C) g/cm^ JIS K2249 0.79 0.81 0.79 0.81 Plash point °Q JIS K2265 Tag closed-cup flash point test 46 74 70 136 Distillation end point "C JIS K2254 Normal pressure distillation test 232 228 226 334 Sulphur content % by weight JIS K2541 Radiation exci¬tation method 0.230 0.001 or less 0.080 0.001 or less Copper plate corrosion JIS K2513 1 or less 1 or less 1 or less 1 or less (50°C, 3h) 10% residue oil carbon % by weight JIS K2270 0.1 or less 0.1 or less 0.1 or less 0.1 or less content Monocyclic aromatic % by volume IP-391/90 and 17.3 22.5 0.5 0.5 component Bicyclic aromatic % by volume JIS K 0124"°" "" 2.3 1.6 0.1 0.1 component Tricyclic or higher % by volume 0.1 or 0.1 or 0.1 or 0.1 or aromatic component lower lower lower lower Comments Hydrogena- Hydrogena- Hydrogena- Hydrogena- tion desul- tion desul- tion desul- tion desul- phurization phurization phurization phurization treatment treatment treatment treatment Table 2 Unit Test method Diluent 5 Diluent 6 Diluent 7 Kinematic viscosity 40^0 mm^/s JIS K2283 1.2 1.2 2.5 Density (15°C) g/cm^ JIS K2249 0.79 0.79 0.80 Flash point °C JIS K2265 Tag closed-cup flash point test 48 73 84 Distillation end point °C JIS K2254 Normal pressure distillation test 226 248 285 Sulphur content % by weight JIS K2541 Radiation excitation method 0.004 0 . 001 or lower 0.001 or lower Copper plate corrosion JIS K2513 1 or lower 1 or lower 1 or lower 10% residue oil carbon content % by weight JIS K2270 0.1 or lower 0 .1 or lower 0,1 or lower Monocyclic aromatic component Bicyclic aromatic component Tricyclic or higher aromatic component % by volume % by volume % by volume IP-391/90 and JIS K 0124"*"" ^" 22.0 0.4 0.1 or lower 0.4 0.1 0 .1 or lower 0.4 0.1 0,1 or lower Comments Hydrogenat ion Hydrogenat ion Hydrogenation 1 N -H U jj 0 s ^ (U a e i-H 4J =) S (8 m 0 0) OJ -H M ■d 4-1 4J 4.) 1 C tZ QJ N e ■H 4-1 U nJ P 0) si u ft 4J rH a n u) 0 Note 2: Molecular weight measurement conditions were as follows: Toso G2000H*L*1, G3000H*L*1, G4000H*L*1, G5000H*L*1 was used as the column; tetrahydrofuran was used as the solvent; flow rate 1.0 mm/min; temperature iO°C: detector R. I, Integrator Chromatopac C-R4A (Shimazu). Table 3 Polybutene A Polybutene B Base oil Detergent dispersant Pour point lowering agent Kinematic viscosity 40""C, mm^/s 650 4000 99.2 " Kinematic viscosity 100°C, mm^/s 31 115 11.2 78.2 " Viscosity index - - 98 - - Number average molecular weight"""* ^^ 665 910 ^ " Elemental analysis results Sulphur, % by weight O.ODl or lower 0.001 or lower 0.2 0.001 or lower 0.001 or lower Nitrogen, % by weight 0.001 or lower 0,001 or lower 0.001 or lower 1.09 0.001 or lower Ca, % by weight 0.001 or lower 0.001 or lower 0.001 or lower 0.45 0. 001 or lower Compounds, other comments Isobutylene copolymer Isobutylene copolymer Mineral-based solvent- purified base oil Mixture comprising succinimide-based dispersant and calcium salicylate-based detergent Polymethacrylate- based macromole- cular pour point lowering agent Hote 3: Performed according to the cleaning property test method for two-cycle gasoline engine lubricating oils Automobile Regulation M341-92, Automobile Technology Corporation, the higher the numerical value for the cleaning property index of the test oil, the less the contamination inside the engine due to the accumulation of varnish, carbon and the like. Note 4: Performed according to the exhaust smoke test method for two-cycle gasoline engine lubricating oils Automobile Regulation M342-92, the higher the numerical value for the exhaust smoke index of the test oil, the smaller the amount of visible smoke produced from the exhaust pipe due to the two-cycle oil. Note 5: Performed according to the exhaust system clogging test method for two-cycle gasoline engine lubricating oils Automobile Regulation M343-92, the higher the numerical value for the clogging factor of the test oil, the less the clogging of the exhaust route due to the accumulation of substances originating from the two-cycle oil in the exhaust system. Note 6: Performed according to the lubrication test method for two-cycle gasoline engine lubricating oils Automobile Regulation M340-92, the higher the numerical value for the lubrication index of the test oil, the better the lubrication of the moving parts {between the piston and the cylinder) in the engine, due to the two-cycle oil. Moreover, the higher the numerical value of the initial torque index of the test oil, the lower the resistance of the moving parts in the engine at the beginning of the test, due to the two-cycle oil. Table 4 Comparative Comparat ive Comparative Comparative Example 1 Example 2 Example 3 Example 4 Test oil composition Diluent 1 % by weight 20.0 Diluent 2 % by weight 20.0 Diluent 3 % by weiqht 20.0 Diluent 4 % by weight 20.0 Diluent 5 % by weight Diluent 6 % by weiqht Diluent 7 % by weiqht Polybutene A % by weiqht 13.6 13.6 13.6 13.6 Polybutene B % by weight 22.0 22.0 22.0 22.0 Base oil % by weiqht 39.8 39.8 39.8 39.8 Detergent dispersant % by weight 4.4 4.4 4.4 4.4 Pour point lowering % by weight 0.2 0.2 0.2 0.2 agent Total % by weight 100.0 100.0 100.0 100.0 Test oil JIS K2283 kinematic ram^/s 8.3 8.4 8.4 12.1 charact¬eristics viscosity (100°C) JIS K2265 flash point °C 70 98 94 160 JIS K2272 sulphate % by weight 0.07 0.07 0.07 0.07 ash two-cycle gasoline engine lubricating oil performance appraisal JASO M 341-92 cleaning property Cleaning test""" =" property index 76 92 78 92 JASO M 342-92 exhaust smoke test"""" JASO M 340-92 exhaust system clogging test""" ^" JASO M 340-92 lubrication test"""^ *" JASO M 340-92 lubrication test""" ^" Exhaust smoke index Clogging index 68 74 72 98 75 78 72 109 Lubrication index Initial torque 93 103 101 98 index 92 98 98 100 Table 5 Working Example 1 Working Example 2 Working Example 3 Test oil composition Diluent 1 % by weight Diluent 2 % by weight Diluent 3 % by weight Diluent 4 % by weight Diluent 5 % by weight 20,0 Diluent 6 % by weight 20.0 Diluent 7 % by weight 20.0 Polybutene A % by weight 13.6 13.6 13.6 Polybutene B % by weight 22,0 22.0 22.0 Base oil % by weight 39.8 39.8 39.8 Detergent dispersant % by weight 4.4 4.4 4.4 Poor point lowering agent % by weight 0.2 0.2 0.2 Total % by weight 100.0 100.0 100.0 Test oil character¬istics JIS K2283 kinematic viscosity (IOQOC) mm^/s 8.3 8.4 10.3 JIS K2265 flash point "C 72 98 118 JIS K2272 sulphate ash % by weight 0.07 0.07 0.07 two-cycle gasoline engine lubricating oil performance appraisal JASO M 341-92 cleaning property test""" ^" Cleaning property index 110 105 106 JASO M 342-92 exhaust smoke test"""" Exhaust smoke index 98 94 94 JASO M 343-92 exhaust system clogging test"°" ^" Clogging index 138 121 130 JASO M 340-92 lubrication test""" ^" Lubrication index 98 105 102 JASO M 340-92 lubrication test"°" ^" Initial torcfue index 100 98 100 Hydrocarbon-based diluent having a flash point of 40°C or more and a normal pressure distillation test end point of 320°C or less were used for Comparative Examples 1, 2 and 3, and Working Examples 1, 2 and 3, respectively. A diluent having a bicyclic or higher polycyclic aromatic hydrocarbon content of more than 1.0% by volume and a sulphur content of more than 0.015% by weight per 100% of diluent was used in the test oil of Comparative Example 1. A diluent having a sulphur content of 0.015% by weight or less and a bicyclic or higher polycyclic aromatic hydrocarbon content of more than 1.0% by volume per 100% by weight of diluent was used in the test oil of Comparative Example 2. A diluent having a bicyclic or higher polycyclic aromatic hydrocarbon content of 1.0% by volume or less and a sulphur content of more than 0.015% by weight per 100% of diluent was used in Comparative Example 3. A comparison of Working Example 1 and Comparative Examples 2 and 3 shows that when a diluent having a bicyclic or higher polycyclic aromatic hydrocarbon content of more than 1.0% by volume and a sulphur content of 0.015% by weight or less per 100% of diluent is used, it is clear that the aims are met in that the engine-cleaning properties are improved and there is a decrease in black smoke and exhaust system clogging. A hydrocarbon-based diluent having a flash point of 40°C or more, a normal pressure distillation test end point of more than 320°C and a bicyclic or higher polycyclic aromatic hydrocarbon content of 1.0% by volume or less and a sulphur content of 0.015% by weight or less per 100% of diluent was used in the test oil of Comparative Example 4. This shows that when diluents having a normal pressure distillation test end point of more than 320°C are used, there are cases where the aims cannot be met because large amounts of exhaust smoke are produced and the exhaust smoke index is low, even though the bicyclic or higher polycyclic aromatic hydrocarbon content is 1.0% by volume or lower and the sulphur content is 0.015% by weight or lower. A hydrocarbon-based diluent composition having a flash point of 40°C or more, a normal pressure distillation test end point of more than 320°C or less, a monocyclic aromatic hydrocarbon content of 20% by volume or more, a bicyclic or higher polycyclic aromatic hydrocarbon content (IP 319/90 test method) of 1,0% by volume or less, a sulphur content of 0.015% by weight or less and comprising, as other components, paraffin-based and naphthene-based saturated hydrocarbons was used in the test oil of Working Example 1. In this working example, there was clearly a marked improvement in engine-cleaning properties, a large decrease in exhaust smoke and exhaust clogging, and a considerable improvement in the cleaning property, exhaust smoke and clogging indices, and the present aims were met. 1 Diluent composition for two-cycle engine lubricating oils comprising a hydrocarbon mixture having a bicyclic or higher polycyclic aromatic hydrocarbon content of 1.0% by volume or less and a sulphur content of 0.015% by weight or less, and having a distillation end point of at most 320°C.. 2. Diluent composition for two-cycle engine lubricating oils according to claim 1, further having a monocyclic aromatic hydrocarbon content of 20% by volume or more. 3. Diluent composition according to Claim 1 or 2, having a JIS K2265 Tag closed-cup test flash point of 40°C or more, a JIS K2254 normal pressure distillation test end point of 320°C or less and a 10% residue residual carbon content {JIS K2270) of 0.1% by weight or less. 4. Lubricating oil for two-cycle engines characterized in that it contains from 5 to 40% by weight of the diluent composition disclosed in any of Claims 1 to 3 and has a flash point of 70°C or more. 5. Diluent composition substantially as hereinbefore described with reference to the accompanying drawings. 6, Lubricating oil for two-cycle engines substantially as hereinbefore described with reference to the accessioning drawings.

Documents:

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