Lubricating oil composition

Abstract

This invention provides a lubricating oil composition having a base number of at least 5mgK0H / g, measured according to the hydrochloric acid method according to JIS K2501, said lubricating oil composition comprising : ( i ) a base oil; ( ii ) a calcium detergent in an amount of more than 1000ppm of calcium based on the overall weight of the lubricating oil composition; ( iii ) a magnesium detergent selected from magnesium sulfonate, magnesium salicylate and mixtures thereof, present in an amount in the range of from 350 to 600ppm of magnesium based on the overall weight of the lubricating oil composition; wherein the magnesium detergent has a base number such that the value M of the base number (mgKOH / g) divided by the magnesium content (mass% ) present in a petroleum ether solution is greater than 50 and wherein the magnesium detergent has a particle size distribution such that D50 (nm) / D10 (nm) is no more than 1. 20.

Description

[0001] SP3129 - 1 - LUBRICATING OIL COMPOSITION Field of the Invention This invention relates to a lubricating oil composition and a process for lubricating an engine using said lubricating oil composition. 5 Background of the invention In view of the desire to reduce fuel consumption and minimise carbon footprint there is a demand to maximise fuel economy in automobiles. An important factor in the improvement of engines is enhancing the energy efficiency 10 by which they convert fuel into power. To assist with this efficiency, there is demand for lubricating oil compositions having excellent performance, providing enhanced protection while allowing heightened fuel economy. 15 Further, it is desirable to extend the time period between oil drains for a lubricating oil composition which is performing under the highly complex conditions encountered in modern engines. The use of additives such as detergents to maintain engine cleanliness is well 20 known. Neutralisation of acidic compounds is an important function of detergents. Such acidic compounds are precursors of sludge and cause engine corrosion. It is important to provide lubricating oil compositions with good initial properties, such a high initial base number 25 (BN), which are maintained throughout an extended oil life in order to allow longer oil drain intervals. The advantages of certain detergents need to be carefully balanced with other properties. For example, calcium and magnesium detergents are known to impact the 30 sulphated ash content of lubricating oil compositions as measured by ASTM D874. Sulphated ash in lubricating oil compositions may cause clogging of gasoline particulate filters. Therefore, lubricating oil compositions with lower sulphated ash contents have generally been preferred. 5 EP4083173 A1 describes a lubricating oil composition comprising calcium and magnesium detergents as well as a molybdenum compound. The lubricating oil composition is claimed to provide a suitable initial base number while reducing the friction coefficient in a wide temperature 10 range and also to provide a decreased viscosity. Summary of the Invention The present invention provides a lubricating oil composition having a base number, measured according to the hydrochloric acid method according to JIS K2501, of at 15 least 5mgKOH / g, said lubricating oil composition comprising: (i) a base oil; (ii) a calcium detergent in an amount of more than 1000ppm of calcium based on the overall weight of 20 the lubricating oil composition; (iii) a magnesium detergent, selected from magnesium sulfonate, magnesium salicylate and mixtures thereof, present in an amount in the range of from 350 to 600ppm of magnesium based on the 25 overall weight of the lubricating oil composition; wherein the magnesium detergent has a base number such that the value M of the base number (mgKOH / g) divided by the magnesium content (mass%) present in a petroleum ether 30 solution is greater than 50 and wherein the magnesium detergent has a particle size distribution such that D50(nm) / D10(nm) is no more than 1.20. The present invention also provides a process for lubricating an internal combustion engine by applying such a lubricating oil composition to the engine and operating the engine. Detailed Description of the Invention One or more specific embodiments of the present 5 disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the 10 specification. When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and 15 “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding 20 the existence of additional embodiments that also incorporate the recited features. All component amounts given here in are by weight and are based on the overall weight of the lubricating oil composition. In the context of the present invention, in a 25 case where a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100 wt%. The present inventors have found that an excellent lubricating oil composition suitable for use in a gasoline 30 engine may be provided by using a specific combination of calcium and magnesium detergent additives. It is particularly advantageous to use a magnesium detergent with a high base number to mass ratio and with a narrow particle size distribution. The lubricating oil composition of the present invention provides a high initial base number, with good base number retention after oxidation, even at low levels of sulphated ash content. The base oil in the lubricating oil composition may 5 be selected from one or more mineral oils and synthetic oils. Any suitable base oil may be used. However, one or more base oils selected from those in Group 2, 3, 4 according to the base oil categorisation of the American Petroleum Institute (API) is preferred. Even more10 preferably, the base oil comprises one or more Fischer- Tropsch derived base oil. Even more preferably, the base oil comprises one or more group 3, Fischer-Tropsch derived base oil. Most preferably, the base oil consists essentially of one or more group 3, Fischer-Tropsch 15 derived base oil. The kinematic viscosity at 100˚C of the base oil is preferably in the range of from 2.0 to 6.0 mm2 / s, more preferably in the range of from 3.0 to 5.0 mm2 / s. The lubricating oil composition preferably contains 20 in the range of from 75 to 95 mass% of base oil based on the overall weight of the lubricating oil composition. More preferably, the lubricating oil composition contains in the range of from 83 to 92 mass% of base oil base on the overall weight of the lubricating oil composition. 25 The lubricating oil composition comprises a calcium detergent in an amount that provides at least 1000ppm by weight of calcium on the basis of the overall weight of the lubricating oil composition. Preferably the calcium detergent is present in an amount that provides at most 30 2000ppm by weight, more preferably at most 1500ppm by weight of calcium on the basis of the overall weight of the lubricating oil composition. The calcium detergent preferably comprises one or more calcium salt selected from the group consisting of calcium salicylate calcium sulfonate and calcium phenate salts. In a preferred embodiment the calcium detergent is a calcium salicylate. The base number of the calcium detergent is 5 preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, and further preferably 150 mgKOH / g or more, and is preferably 500 mgKOH / g or less, more preferably 400 mgKOH / g or less, and further preferably 300 mgKOH / g or less. 10 The lubricating oil composition also comprise a magnesium detergent which is a magnesium sulfonate or magnesium salicylate detergent present in an amount in the range of from 350 to 600ppm of magnesium based on the overall weight of the lubricating oil composition. 15 In the case where the magnesium detergent is magnesium sulfonate, the base number of the magnesium sulfonate is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, further preferably 300 mgKOH / g or more, and still further preferably 350 mgKOH / g 20 or more, and is preferably 650 mgKOH / g or less, more preferably 500 mgKOH / g or less, and further preferably 450 mgKOH / g or less. In the case where the magnesium-based detergent is magnesium salicylate, the base number of the magnesium 25 salicylate is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, further preferably 200 mgKOH / g or more, and still further preferably 300 mgKOH / g or more, and is preferably 500 mgKOH / g or less, more preferably 450 mgKOH / g or less, and further preferably 400 30 mgKOH / g or less. The magnesium-based detergent has a base number such that the value M of the base number (mgKOH / g), measured by the hydrochloric acid method according to JIS K2501, divided by the magnesium content (mass%) present in a petroleum ether solution is greater than 50, preferably greater than 55, more preferably greater than 60. Further, the magnesium-based detergent has a particle sized distribution such that the value of 5 D50(nm) / D10(nm) is no more than 1.20. The particle size of the magnesium-based detergent was measured in a petroleum ether solution using dynamic light method with zeta- potential and particle size analyser ELSZ-2000 (Otsuka Electronics Co., Ltd.). In this measurement, D50 is the 10 median particle diameter and D10 is the tenth centile diameter, i.e. the diameter which 10% of the particle are smaller than. As well as t he calci um and magnesi um-based detergents, the lubricating oil compositions preferably 15 also comprise one or more oil-soluble molybdenum compounds. More preferably, the one or more oil-soluble molybdenum compounds comprise one or more molybdenum dithiocarbamate (MoDTC) compounds. Most preferably, the one or more oil-soluble molybdenum compounds is / are one or 20 more molybdenum dithiocarbamate (MoDTC) compounds. Molybdenum dithiocarbamate (MoDTC) can be represented by structures I (dinuclear) and II (trinuclear). I In structure I and structure II, R is suitable a linear or branched paraffinic chain containing from 4 to 20 carbon atoms. The one or more oil-soluble molybdenum compounds present in the lubricating composition are included at a 5 level sufficient to provide from greater than 350ppm to no more than 1000 ppm of molybdenum, by mass based on the overall weight of the lubricating oil composition. The lubricating oil composition may also contain one or more additional additive suitable for use in an engine 10 oil composition. Examples of such additives include antioxidants, ashless dispersants, pour point depressants, viscosity index improvers, anti-wear agents, extreme pressure agents, rust inhibitors, anti-foaming agents, metal deactivators, and demulsifier. Such additives may be 15 used alone or as a combination of two or more types thereof. Examples of the antioxidant include an amine-based antioxidant, a phenol-based antioxidant, a sulfur-based antioxidant, and a phosphorus-based antioxidant. Among 20 these, an amine-based antioxidant and a phenol-based antioxidant are preferably used, and both an amine-based antioxidant and a phenol-based antioxidant are more preferably used in combination. Examples of the amine-based antioxidant include a 25 diphenylamine-based antioxidant, such as diphenylamine and an alkylated diphenylamine having an alkyl group having 3 to 20 carbon atoms; and a naphthylamine-based antioxidant, such as an α-naphthylamine and a phenyl-α-naphthylamine substituted with an alkyl group having 3 to 20 carbon 30 atoms. Examples of the phenol-based antioxidant include a monophenol-based antioxidant, such as 2,6-di-tert-butyl-4- methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; a diphenol-based antioxidant, such as 4,4'- methylenebis(2,6-di-tert-butylphenol) and 2,2'- methylenebis(4-ethyl-6-tert-butylphenol); and a hindered phenol-based antioxidant. 5 Examples of the ashless dispersant include a succinimide compound, such as an alkenylsuccinimide, a boron-containing succinimide compound, such as a boron- containing alkenylsuccinimide, a benzylamine compound, a boron-containing benzylamine compound, a succinate ester 10 compound, and a monovalent or divalent carboxylic acid amide represented by a fatty acid or succinic acid. Examples of the pour point depressant include an ethylene-vinyl acetate copolymer a polymethacrylate, and a polyalkylstyrene. 15 Examples of the viscosity index improver include polymers, for example, a non-dispersive polymethacrylate, a dispersive polymethacrylate, an olefin-based copolymer (such as an ethylene-propylene copolymer), a dispersive olefin-based copolymer, and a styrene-based copolymer 20 (such as a styrene-diene copolymer and a styrene-isoprene copolymer). Examples of the anti-wear agent or the extreme pressure agent include a sulfur-containing compound, such as a zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, 25 zinc dithiocarbamate, a sulfide compound, a sulfurized olefin compound, a sulfurized fat or oil compound, a sulfurized ester compound, a thiocarbonate compound, a thiocarbamate compound, and a polysulfide compound; a phosphorus-containing compound, such as a phosphite ester 30 compound, a phosphate ester compound, a phosphonate ester compound, and amine salts and metal salts thereof; and a sulfur and phosphorus-containing anti-wear agent, such as a thiophosphite ester compound, a thiophosphate ester compound, a thiophosphonate ester compound, and amine salts and metal salts thereof. Examples of the rust inhibitor include a fatty acid, an alkenyl succinate half ester, a fatty acid soap, an 5 alkylsulfonate salt, a polyhydric alcohol fatty acid ester, a fatty acid amine, oxidized paraffin, and an alkyl polyoxyethylene ether. Examples of the anti-foaming agent include a silicone oil and an acrylate type anti-foaming agent. 10 Examples of the metal deactivator include a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, an imidazole-based compound, and a pyrimidine-based compound. Examples of the demulsifier include an anionic 15 surfactant, such as a sulfate ester salt of castor oil and a petroleum sulfonate salt; a polyoxyalkylene polyglycol and a dicarboxylate ester thereof; and an alkylene oxide adduct of an alkylphenol-formaldehyde polycondensate. In one preferred embodiment, the lubricating oil 20 composition also comprises one or more further additives selected from dispersants, antioxidants, viscosity modifiers and antiwear agents. The invention will now be further illustrated by reference to the following non-limiting examples. 25 Examples Lubricating oil compositions as set out in Tables 1 to 4 were blended by standard methods. The following components were used. Base oil – a Fischer-Tropsch derived, group III base oil 30 with a KV100 of 4cSt. Addpack 1 – an additive package containing ZnDTP, a dispersant and an antioxidant as well as a magnesium sulfonate with a value of M of at least 50 and a D50(nm) / D10(nm) of no more than 1.20. Addpack 2 - an additive package containing ZnDTP, a dispersant and an antioxidant as well as a magnesium sulfonate with a value of M of less than 50 and a D50(nm) / D10(nm) of more than 1.20. 5 Addpack 3 – an additive package containing ZnDTP, a dispersant, an antioxidant and no detergent. Mg sulfonate 1 - a magnesium sulfonate with a value of M of at least 50 and a D50(nm) / D10(nm) of no more than 1.20. Mg salicylate 1 – a magnesium salicylate with a value of M 10 of at least 50 and a D50(nm) / D10(nm) of no more than 1.20. Mg sulfonate 2 - a magnesium sulfonate with a value of M of less than 50 and a D50(nm) / D10(nm) of more than 1.20. Calcium salicylate – a calcium salicylate with base number (ASTM D2896) of 160 mgKOH / g. 15 Viscosity modifier – commercially available as Viscoplex® 3-201 (ex. Evonik). MoDTC – a molybdenum dialkyldithiocarbamate commercially available as Sakuralube® 525 (ex. Adeka). The lubricating oil compositions were each evaluated 20 and assessed according to the standards set out below. The results are reported in Tables 1 to 4. Kinematic viscosity at 40˚C (KV40) was measured according to ASTM D445. Kinematic viscosity at 100˚C (KV100) was measured 25 according to ASTM D445. Viscosity index (VI) was measured according to ASTM D2270. Tapered Bearing Simulator viscosity at 150˚C (TBS150) was measured according to ASTM D4683. Acid number (AN) was measured according to JIS K2501. 30 Base Number (BN HCl) was measured according to JIS K2501. Base number (BN HClO4) was measured according to ASTM D2896. Mass% of calcium, magnesium, molybdenum, phosphorus and zinc were measured according to ICP, JPI05S-38. Sulphated ash content was measured according to ASTM D874. NOx bubbling test was conducted following SAE technical paper No. 881577. 150 mL of test oil was put into a glass vessel. Nitrogen gas containing 0.8 vol% NO, and wet air 5 were blown into the vessel at the rates of 5.7 and 15 L / hr, respectively. The temperature of the oil was kept at 150˚C for 48 hours. After the NOx bubbling test, acid number, base number (HCl) and base number (HClO4) were measured according to the same methods as the fresh oil. 10 The results are shown in Tables 1 to 4.

[0002] Table 1 - Examples 1 to 3 (inventive) 1 2 3 Viscosity grade 0W-8 0w-16 0W-20 M 63 63 63 D50 (nm) 1.3 1.3 1.3 D50 / D10 1.18 1.18 1.18 Base oil (mass%) 89.10 82.80 79.60 Addpack 1 (mass%) 7.30 7.30 7.30 Addpack 2 (mass%) - - - Addpack 3 (mass%) - - - Mg sulfonate 1(mass%) - - - Mg salicylate 1(mass%) - - - Mg sulfonate 2(mass%) - - - Calcium salicylate(mass%) 2.00 2.00 2.00 Viscosity modifier(mass%) 1.00 7.30 10.50 MoDTC(mass%) 0.60 0.60 0.60 Total (mass%) 100 100 100 KV40 mm2 / s 23.72 27.00 28.93 KV100 mm2 / s 5.087 6.639 7.712 VI 149 218 257TBS150mPa・s 1.75 2.38 2.70AN mgKOH / g 1.83 1.75 1.71 BN HCl mgKOH / g 5.53 5.90 5.65 BN HClO4 mgKOH / g 7.10 7.21 7.24 Ca mass% 0.117 0.120 0.120 Mg mass% 0.051 0.052 0.053 Mo mass% 0.057 0.057 0.059 P mass% 0.068 0.065 0.062 Zn mass% 0.079 0.082 0.083 Sulphated ash mass% 0.77 0.77 0.77 NOx bubbling, AN 2.41 2.33 2.29 150˚C, after 48 h BN HCl 1.89 2.18 2.32 BN HClO4 5.86 5.97 6.04 Table 2 – Examples 4 to 6 (inventive) 4 5 6 Viscosity grade 0W-8 0W-8 0W-20 M 63 78 78 D50 (nm) 1.9 3.1 3.1 D50 / D10 1.19 1.19 1.19 Base oil (mass%) 89.15 89.03 79.53 Addpack 1 (mass%) - - - Addpack 2 (mass%) - - - Addpack 3 (mass%) 6.700 6.700 6.700 Mg sulfonate 1(mass%) 0.550 - - Mg salicylate 1(mass%) - 0.670 0.670 Mg sulfonate 2(mass%) - - - Calcium salicylate(mass%) 2.00 2.00 2.00 Viscosity modifier(mass%) 1.00 1.00 10.50 MoDTC(mass%) 0.60 0.60 0.60 Total (mass%) 100 100 100 KV40 mm2 / s 23.65 23.93 29.11 KV100 mm2 / s 5.082 5.129 7.793 VI 149 150 259TBS150mPa・s 1.74 1.76 2.71AN mgKOH / g 2.07 1.98 1.97 BN HCl mgKOH / g 5.44 5.92 5.91 BN HClO4 mgKOH / g 7.26 7.33 7.43 Ca mass% 0.117 0.117 0.120 Mg mass% 0.051 0.050 0.052 Mo mass% 0.057 0.057 0.058 P mass% 0.069 0.069 0.064 Zn mass% 0.079 0.079 0.083 Sulphated ash mass% 0.80 0.78 0.78 NOx bubbling, AN 2.46 2.51 2.31 150˚C, after 48 h BN HCl 1.54 2.27 2.58 BN HClO4 6.22 6.35 6.34 Table 3 – Examples 7 to 9 (comparative) 7 8 9 Viscosity grade 0W-8 0W-20 0W-20 M 63 63 78 D50 (nm) 1.3 1.9 3.1 D50 / D10 1.18 1.19 1.19 Base oil (mass%) 91.10 79.90 79.90 Addpack 1 (mass%) 7.30 - - Addpack 2 (mass%) - - - Addpack 3 (mass%) - 6.700 6.700 Mg sulfonate 1(mass%) - 0.300 - Mg salicylate 1(mass%) - - 0.300 Mg sulfonate 2(mass%) - - - Calcium salicylate(mass%) - 2.00 2.00 Viscosity modifier(mass%) 1.00 10.50 10.50 MoDTC(mass%) 0.60 0.60 0.60 Total (mass%) 100 100 100 KV40 mm2 / s 22.66 28.63 28.77 KV100 mm2 / s 4.911 7.573 7.608 VI 147 253 253TBS150mPa・s 1.69 2.59 2.59AN mgKOH / g 1.55 1.91 1.83 BN HCl mgKOH / g 2.19 4.24 4.76 BN HClO4 mgKOH / g 3.92 6.28 6.05 Ca mass% <0.001 0.110 0.107 Mg mass% 0.052 0.026 0.021 Mo mass% 0.058 0.054 0.054 P mass% 0.069 0.062 0.062 Zn mass% 0.081 0.073 0.073 Sulphated ash mass% 0.42 0.63 0.64 NOx bubbling, AN 2.07 2.28 2.40 150˚C, after 48 h BN HCl 0.41 1.22 1.39 BN HClO4 2.73 4.82 4.50 Table 4 – Examples 10 to 13 (comparative) 10 11 12 13 Viscosity grade 0W-8 0W-8 0W-8 0W-8 M 23 41 23 23 D50 (nm) 2.4 4.4 2.4 2.4 D50 / D10 1.26 1.26 1.26 1.26 Base oil (mass%) 89.10 89.17 87.24 84.45 Addpack 1 (mass%) - - - - Addpack 2 (mass%) 7.30 - 8.76 10.95 Addpack 3 (mass%) - 6.700 - - Mg sulfonate 1(mass%) - - - - Mg salicylate 1(mass%) - - - - Mg sulfonate 2(mass%) - 0.53 - - Ca salicylate(mass%) 2.00 2.00 2.40 3.00 VM(mass%) 1.00 1.00 1.00 1.00 MoDTC(mass%) 0.60 0.60 0.60 0.60 Total (mass%) 100 100 100 100 KV40 mm2 / s 23.72 23.70 24.92 26.87 KV100 mm2 / s 5.088 5.091 5.27 5.580 VI 149 150 151 153 TBS150mPa・s1.74 1.75 1.80 1.90AN mgKOH / g 1.93 1.98 2.22 2.62 BN HCl mgKOH / g 4.23 4.43 5.06 6.17 BN HClO4 mgKOH / g 7.14 7.14 8.57 10.7 Ca mass% 0.118 0.117 0.140 0.173 Mg mass% 0.051 0.048 0.061 0.076 Mo mass% 0.057 0.057 0.056 0.056 P mass% 0.069 0.068 0.082 0.102 Zn mass% 0.080 0.079 0.095 0.116 Sulphated ashmass% 0.77 0.75 0.90 1.10 NOx AN 2.51 2.48 2.59 2.97 bubbling, 150˚C, after BN HCl 1.18 1.21 2.07 2.84 48 h BN HClO4 5.46 5.82 7.89 9.97 Examples 1 to 6 (inventive) show high base number (HCl) above 5.0mgKOH / g in fresh oil and above 1.5 mgKOH / g after NOx bubbling. The sulphated ash contents for these examples are equal or lower to 0.85 mass%. This level of 5 sulphated ash can prevent gasoline particulate filter clogging. Example 7 (comparative) does not contain any calcium detergent and provided an unsuitably low initial base number (HCl) which would lead to a poor capability in neutralisation of acid in use. Comparative Examples 8 and 10 9, containing less than 350 ppm of magnesium also provided unsuitably low initial base numbers. Comparative Example 10 demonstrates the use of a magnesium sulfonate detergent with a low value of M and a value of D50 / D10 of greater than 1.20. This example also provides an unsuitably low 15 initial base number. The same is true for comparative example 11, with a different magnesium detergent also with M and D50 / D10 values outside the range required for the present invention. Increasing the magnesium content using the same magnesium-based detergent as in comparative 20 example 10, in order to achieve the desirable initial base number (see comparative examples 12 and 13) lead to an unacceptably high level of sulphated ash content (greater than 0.85 mass%) for these lubricating oil compositions.

Claims

SP3129 - 17 - C L A I M S 1. A lubricating oil composition having a base number, measured according to the hydrochloric acid method according to JIS K2501, of at least 5mgKOH / g, said lubricating oil composition comprising 5 (i) a base oil; (ii) a calcium detergent in an amount of more than 1000ppm of calcium based on the overall weight of the lubricating oil composition; (iii) a magnesium detergent, selected from magnesium 10 sulfonate, magnesium salicylate and mixtures thereof, present in an amount in the range of from 350 to 600ppm of magnesium based on the overall weight of the lubricating oil composition; 15 wherein the magnesium detergent has a base number such that the value M of the base number (mgKOH / g) divided by the magnesium content (mass%) present in a petroleum ether solution is greater than 50 and wherein the magnesium detergent has a particle size distribution such that 20 D50(nm) / D10(nm) is no more than 1.

20.

2. A lubricating oil composition as claimed in Claim 1, wherein the base oil is a Fischer-Tropsch derived group III base oil.

3. A lubricating oil composition as claimed in Claim 1 or 25 Claim 2, also comprising one or more oil-soluble molybdenum compounds in an amount sufficient to provide from greater than 350ppm to more than 1000ppm of molybdenum by mass based on the overall weight of the lubricating oil composition.

4. A lubricating oil composition as claimed in any one of Claims 1 to 3, wherein the calcium-based detergent is a calcium salicylate.

5. A lubricating oil composition as claimed in any one of 5 Claims 1 to 4, wherein the sulphated ash content of the lubricating oil composition is no more than 0.85 mass%.

6. A lubricating oil composition as claimed in any one of Claims 1 to 5, also comprising one or more further additives selected from dispersants, antioxidants, 10 viscosity modifiers and antiwear agents.

7. A process for lubricating an internal combustion engine by applying a lubricating oil composition according to any one of Claims 1 to 6 to the engine and operating the engine. 15

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