AU2011340549A1 - Improvements of fuels by adding polymeric viscosity increasing components - Google Patents

Abstract

Use of a viscosity increasing component in a fuel composition, or a fuel composition comprising a viscosity increasing component, for the purpose of influencing the viscometric performance of a lubricant in an internal combustion engine into which the fuel composition is or is intended to be introduced.

Description

WO 2012/076652 PCT/EP2011/072204 IMPROVEMENTS OF FUELS BY ADDING POLYMERIC VISCOSITY INCREASING COMPONENTS Field of the Invention The present invention relates to influencing the viscometric performance of a lubricant in an internal combustion engine. In particular, though not exclusively, 5 the invention relates to counteracting a deterioration in the viscometric performance of a lubricant associated with the ingress of fuel into the lubricant. Background of the Invention In recent decades, the use of internal combustion 10 engines, powered by the ignition of hydrocarbon fuel, for transportation and energy generation has become more and more widespread. For example, compression ignition engines, which will be referred to further as "diesel"' engines after 15 Rudolf Diesel (who invented the first compression ignition engine in 1892) feature among the main type of engines employed for passenger cars and heavy duty applications, as well as for stationary power generation, as a result of their high efficiency. In a diesel engine 20 a fuel/air mixture is ignited by being compressed until it ignites due to the temperature increase due to compression. In spark ignition engines ("petrol") engines on the other hand, which are another widespread form of internal 25 combustion engine, a separate source of ignition, such as a spark plug, ignites the fuel. Lubricant oils ("lubricants") are used in all internal combustion engines to reduce friction between, and hence wear on, moving parts. During use of an engine, 30 however, the properties (particularly the viscometric WO 2012/076652 PCT/EP2011/072204 -2 performance) of a lubricant can gradually deteriorate over time, to a point where its performance is impaired and it has to be replaced. Much of this lubricant deterioration is due to contaminants that pass from the 5 combustion chamber into the crankcase and into the lubricant. For example, a fraction of the fuel may enter the lubricant. The ingress of fuel into the lubricant generally leads to a reduction of lubricant viscosity and/or 10 viscosity index, i.e. loss of viscometric performance, and can thus result in increased engine wear. The draining and replacement of an engine lubricant can be costly and time consuming. It would, therefore, be desirable to be able to reduce the rate of viscometric 15 performance loss, and hence to increase the interval between lubricant changes (also known as "oil drain interval"). A number of improved lubricant formulations have been proposed over the years to reduce the rate of 20 lubricant performance loss and to increase the interval between lubricant changes. Furthermore, engine designers are conscious of the problem of fuel dilution and have sought to minimise it by the incorporation of seals and the like. However, nevertheless, the loss of viscometric 25 performance in lubricants remains a problem, especially in diesel engines. It is proposed in WO 2009/080673 to use a Fischer Tropsch (FT) derived oil, particularly a Fischer-Tropsch extra heavy base oil, to mitigate loss of viscometric 30 performance of an engine oil. However significant quantities of the FT oil are required to effect a beneficial result, cf the Examples where 5 vol% of an FT extra heavy base oil is used. It would be advantageous to WO 2012/076652 PCT/EP2011/072204 -3 achieve such a result without the need for such a high amount of additive; it would be even more beneficial if it would be possible to prevent lubricant deterioration to a greater extent whilst utilising a lower additive 5 amount. It is also known to use viscosity index improving additives directly in lubricant formulations, where they are used to maintain viscosity as constant as possible particularly at high temperatures. In this use, also high 10 concentrations are utilised: typically between 1 and 20% w/w of the additive. Summary of the Invention It has now been found that, surprisingly, incorporating a polymeric viscosity index (VI) improving 15 additive into a fuel composition, and particularly a diesel fuel composition, can advantageously influence the viscometric performance of a lubricant in an internal combustion engine running on said fuel composition, even when used in the fuel composition at low concentrations. 20 The present invention is based on the appreciation that fuel dilution, which is conventionally seen as a cause of lubricant deterioration, can be made use of to influence the viscometric performance of the lubricant, by using viscosity index improving additives in the fuel. 25 In this manner, it is possible to counteract deterioration of viscometric performance in the lubricant (e.g. to achieve an increase in the interval between lubricant changes) without the need to alter the engine itself, and irrespective of the nature of the lubricant. 30 From a first aspect, the invention resides in the use of a viscosity increasing component in a fuel composition, for the purpose of influencing the viscometric performance of a lubricant in an internal WO 2012/076652 PCT/EP2011/072204 -4 combustion engine into which the fuel composition is or is intended to be introduced, wherein the viscosity increasing component is a polymeric viscosity index (VI) improving additive. 5 In the context of the present invention, "use" of a viscosity increasing component in a fuel composition means incorporating the component into the composition, typically as a blend (i.e. a physical mixture) with one or more fuel components (typically base fuels) and 10 optionally with one or more fuel additives. The viscosity index improving additive may preferably be incorporated into the fuel composition before the composition is introduced into an engine that is to be run on the composition. 15 Accordingly, the viscosity index improving additive may be dosed directly into (e.g. blended with) one or more components of the fuel composition or base fuel at the refinery. For instance, it may be pre-diluted in a suitable fuel component, which subsequently forms part of 20 the overall fuel composition. Alternatively, it may be added to a fuel composition downstream of the refinery. For example, it may be added as part of an additive package containing one or more other fuel additives. This can be particularly 25 advantageous because in some circumstances it can be inconvenient or undesirable to modify the fuel composition at the refinery. For example, the blending of base fuel components may not be feasible at all locations, whereas the introduction of fuel additives, at 30 relatively low concentrations, can more readily be achieved at fuel depots or at other filling points such as road tanker, barge or train filling points, dispensers, customer tanks and vehicles.

WO 2012/076652 PCT/EP2011/072204 -5 Accordingly, the "use" of the first aspect of the invention may also encompass the supply of a polymeric viscosity index improving additive together with instructions for its use to achieve one of the benefits 5 of the present invention, e.g. counteracting performance loss of a lubricant of an engine into which the fuel composition is or is intended to be introduced. The viscosity index improving additive may therefore be supplied as a component of a formulation which is 10 suitable for and/or intended for use as a fuel additive, without departing from the scope of the invention. By way of example, the viscosity index improving additive may be incorporated into an additive formulation or package along with one or more other fuel additives. The one or 15 more fuel additives may be selected from any useful additive, such as detergents, anti-corrosion additives, esters, poly-alpha olefins, long chain organic acids, components containing amine or amide active centres, and mixtures thereof, as is known to the person of skill in 20 the art. Instead, or in addition, the "use" of the first aspect of the invention may involve running an engine on the fuel composition containing the viscosity index improving additive, typically by introducing the fuel 25 composition into a combustion chamber of the engine. Accordingly, the "use" of the first aspect of the invention may also encompass the supply of a fuel composition comprising a polymeric viscosity index improving additive together with instructions for its use 30 to achieve one of the benefits of the present invention, e.g. influencing the viscometric performance of a lubricant of an engine into which the fuel composition is or is intended to be introduced.

WO 2012/076652 PCT/EP2011/072204 -6 From a second aspect, the invention resides in the use of a fuel composition comprising a polymeric viscosity index improving additive in an internal combustion engine for the purpose of influencing the 5 viscometric performance of a lubricant of the engine. In the context of the invention, "influencing" the viscometric performance of a lubricant embraces any alteration of the viscometric performance compared to viscometric performance in the absence of the viscosity 10 index improving additive in the fuel under otherwise identical conditions. Influence on viscometric performance may be measured, for example, by comparing viscometric performance in a lubricant when using the invention, with 15 viscometric performance when the same engine is run on an otherwise identical fuel composition not including the viscosity index improving additive. The difference in viscometric performance represents the influence of using the viscosity index improving additive (or the fuel 20 comprising said additive). Preferably, influencing the viscometric performance may comprise counteracting deterioration (or loss) of the viscometric performance of the lubricant associated with ingress of the fuel composition into the lubricant. It 25 may also comprise preserving and/or maintaining viscometric performance. In the context of the invention, the term "counteracting deterioration" (e.g. of viscometric performance) embraces mitigating, slowing down, reducing 30 or even stopping (i.e. reducing to zero) deterioration (or the rate of loss). Counteracting deterioration of lubricant performance also embrace mitigation, to at least a degree, of an increase in deterioration due to WO 2012/076652 PCT/EP2011/072204 another cause, e.g. the presence of other certain fuel components. "Counteracting deterioration" according to the invention is not restricted to any particular mechanism of action. 5 Counteraction of deterioration of viscometric performance may be measured by a comparison over a given engine running time or engine running distance. For example, counteraction of deterioration may be determined by comparing deterioration of viscometric performance in 10 a lubricant when using the invention with the deterioration when the same engine is run on an otherwise identical fuel composition prior to adding a polymeric viscosity index improving additive to it. The difference (e.g. mitigation, slowing down, reduction or stopping) in 15 deterioration represents the counteraction. The deterioration of viscometric performance may be measured over a predetermined time period (i.e. engine running time), in particular a period that begins at the time of introduction of the (previously unused) lubricant 20 fluid into the engine..Deterioration may, for example, be measured over a period of 100 hours or more of engine running time, or 200 hours or more, or 250 hours or more, for example 300 or 400 or 500 hours or more, following the introduction of the lubricant fluid into the engine. 25 Alternatively deterioration may be measured over a predetermined engine running distance, in particular beginning at the time of introduction of the (previously unused) lubricant fluid into the engine. Deterioration may for example be measured over 5000 engine miles or 30 more, or 8000 engine miles or more, or 10000 engine miles or more, or 13000 or 15000 engine miles or more, following the introduction of the lubricant fluid into the engine.

WO 2012/076652 PCT/EP2011/072204 -8 Deterioration may accordingly be expressed as a change per unit engine running time or as a change per unit engine running distance. The present invention may, for example, involve 5 adjusting the effects of the fuel composition on viscometric performance of a lubricant, by means of the viscosity index improving additive, in order to meet a desired target. In the context of the invention, "viscometric 10 performance" may preferably embrace all properties and effects of the lubricant that vary in dependence on its kinematic viscosity at 100C (VK 100, as measured by EN ISO 3104). References in this specification to viscosity are, unless otherwise specified, intended to mean VK 100. 15 The viscometric performance (or properties) of the lubricant may embrace one or more of: lubricant viscosity at 40 0 C (VK 40) or 1000C (VK 100) or any other temperature, lubricant SAE viscosity grade, lubricant viscosity index (e.g. SAE scale), lubricant fluid changes 20 or oil drain interval, engine lubrification, lubricant lifetime or lifespan, engine friction, and engine wear. Since all expressions of viscometric performance vary in dependence on VK 100, viscometric performance may conveniently be measured based on VK 100, for instance 25 using the standard test method EN ISO 3104. From two or more such measurements, the deterioration of viscometric performance over a particular period of time or a particular distance can be calculated, as described above. 30 Other expressions of viscometric performance may also provide an indication of viscometric performance, based on relevant standard measurements, preferably EN ISO, where available.

WO 2012/076652 PCT/EP2011/072204 -9 Where the present invention is used to counteract deterioration of viscometric performance, the counteraction may advantageously lead to a reduction in deterioration of VK 100 of at least 1 %, preferably of at 5 least 5 %, for example of at least 10 or 15 or 20 or 25% or in cases even 30%, compared to the deterioration observed when running the engine on the fuel composition prior to incorporation of the viscosity index improving additive, for example based on any of the time periods or 10 distances mentioned hereinabove. The invention may be used for the purpose of reducing the frequency of lubricant fluid changes, and/or of increasing an interval between lubricant fluid changes (oil drain interval). As described above, lubricant fluid 15 changes are necessary whenever the properties and/or performance of the fluid deteriorate to such an extent as to impair its performance, and/or to impede satisfactory functioning of the engine which the fluid is used to lubricate. In particular, the viscosity index improving 20 additive, or the fuel composition comprising it, may be used to reduce the frequency of lubricant fluid changes that are necessary due to changes in the viscosity or viscosity index of the fluid. Where the present invention is used to increase an interval between lubricant fluid 25 changes needed, the increase may be of at least 10 or 20 %, preferably of at least 50 or 60 or 70 or 80 %, in cases of at least 90 or even 100 %, compared to the intervals required when running the engine on a fuel composition without the viscosity increasing component. 30 The point at which a lubricant change is deemed necessary should be evaluated in each case using the same criteria, which may preferably include the kinematic viscosity of the fluid (e.g. at 100*C).

WO 2012/076652 PCT/EP2011/072204 - 10 A third aspect of the invention provides for the use of a polymeric viscosity index improving additive in a fuel composition, or the use of a fuel composition comprising the polymeric viscosity index improving 5 additive, for the purpose of influencing, preferably counteracting a deterioration of, one or more of: viscosity; viscosity index; fluid change frequency or oil drain interval; or lifetime or lifespan; of a lubricant in an internal combustion engine into which the fuel 10 composition is or is intended to be introduced. A fourth aspect of the invention provides for the use of a polymeric viscosity index improving additive in a fuel composition, or the use of a fuel composition comprising the polymeric viscosity index improving 15 additive, for the purpose of influencing, preferably counteracting a deterioration of, one or more of: lubrification; lifetime; friction; or wear of or in an internal combustion engine into which the fuel composition is or is intended to be introduced. 20 A fifth aspect of the invention provides a method of operating an internal combustion engine, and/or a system (for example an automotive vehicle) which is powered by such an engine, which method involves introducing into a combustion chamber of the engine a fuel composition 25 containing a polymeric viscosity index improving additive for one or more of the purposes defined in any one of the first to the fourth aspects of the present invention. The engine may preferably be a diesel engine. It may be of the direct injection type, for example of the rotary 30 pump, in-line pump, unit pump, electronic unit injector or common rail type, or of the indirect injection type. A sixth aspect of the invention provides a method of achieving a target viscometric performance associated WO 2012/076652 PCT/EP2011/072204 - 11 with a lubricant of an internal combustion engine, the method comprising powering the engine using a fuel composition comprising a polymeric viscosity index improving additive. 5 The VI improving additive used in the fuel composition in accordance with the present invention is polymeric in nature. The VI improving additive may, for example, comprise a copolymer tha-t contains one or more olefin monomers (or monomer blocks), typically selected 10 from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers. The VI improving additive may, for example, be selected from: a) styrene-based copolymers, in particular block copolymers, for example those available as 15 Kraton(TM) D or Kraton(TM) G additives (ex. Kraton) or as SV(TM) additives (ex. Infineum, Multisol or others). Particular examples include copolymers of styrenic and ethylene/butylene monomers, for instance polystyrene polyisoprene copolymers and polystyrene-polybutadiene 20 copolymers. Such copolymers may be block copolymers, as for instance SV(TM) 150 (a polystyrene-polyisoprene di block copolymer) or the Kraton(TM) additives (styrene butadiene-styrene tri-block copolymers or styrene ethylene-butylene block copolymers). They may be tapered 25 copolymers, for instance styrene-butadiene copolymers. They may advantageously be stellate copolymers, as for instance SV (TM) 260 (a styrene-polyisoprene star copolymer) or SV (TM) 200 (a divinylbenzene-polyisoprene star copolymer); b) other block copolymers based on 30 ethylene, butylene, butadiene, isoprene or other olefin monomers, for example ethylene-propylene copolymers; c) polyisobutylenes (PIBs); d) polymethacrylates (PMAs); e) poly alpha olefins (PAOs); and f) mixtures thereof.

WO 2012/076652 PCT/EP2011/072204 - 12 Other examples of suitable viscosity index improvers are disclosed in Japanese Patents Nos. 954077, 1031507, 1468752, 1764494 and 1751082. Yet further examples include the dispersing-type VI improving additives, which 5 comprise copolymerised polar monomers containing nitrogen and oxygen atoms alkyl aromatic-type VI improving additives; and certain pour point depressants known for use as VI improving additives. Of the above, additives of type (a) and (b), or 10 mixtures thereof, are preferred, in particular additives of type (a). As aforesaid, the invention makes use of fuel dilution to influence the viscometric performance of the lubricant. Since fuel dilution typically occurs through 15 one or more pistons of the engine, i.e. in a high shear environment, to enhance the efficiency with which the viscosity improving component used in the fuel composition is delivered to (and retained within) the lubricant, the viscosity improving component, and in 20 particular the preferred VI improving additives, used according to the invention may advantageously have a stellate (i.e. star-like) structure and/or may form star like clusters (micelles). It is thought that a stellate structure, and in particular the formation of star-like 25 clusters, enhances shear resistance, which means that a greater proportion of such VI improving additives in fuel is made available to influence the viscometric properties of the lubricant. The kinematic viscosity at 400C (VK 40, as measured 30 by EN ISO 31041 of the VI improving additive may suitably be 40 mm2/s or greater, preferably 100 mm2/s or greater, more preferably 1000 mm2/s or greater. Its density at 15*C (EN ISO 3675) may suitably be 600 kg/m3 or greater, WO 2012/076652 PCT/EP2011/072204 - 13 preferably 800 kg/m3 or greater. Its sulphur content (EN ISO 20846) may suitably be 1000 mg/kg or lower, preferably 350 mg/kg or lower, more preferably 10 mg/kg or lower. 5 Suitably, the VI improving additive may be used at a concentration in the range of from 0.01% w/w to 0.5% w/w based on the total weight of the fuel composition. For example, the VI improving additive may be used at a concentration in the range of from: (i) 0.01% w/w to 1.0% 10 w/w; (ii) 0.05% w/w to 0.7% w/w; or (iii) 0.1% w/w to 0.5% w/w; based on the total weight of the fuel composition. The fuel compositions may contain any number of additional useful additives known to the person of skill 15 in the art. In some embodiments, two or more viscosity increasing components may be used, such as a VI improving additive and a high viscosity fuel or oil component, e.g. a refinery product, which has a higher kinematic viscosity than the base fuel of the fuel composition. In 20 another embodiment there may be two or more VI improving additives of the same or different structural class, provided one is a polymeric VI improving additive. An example of a VI improving additive of another class is an inorganic compound, for example a zeolite. 25 In the present context, an internal combustion engine may be, for example, a compression ignition ("diesel") engine or a spark ignition ("petrol") engine. As aforesaid, all such engines suffer from fuel dilution, i.e. ingress of fuel into the lubricant. Preferably, the 30 engine may permit a fuel dilution of at least 3%, preferably 6%, most preferably 10% w/w fuel in the lubricant in at least one operational mode and/or operational span.

WO 2012/076652 PCT/EP2011/072204 - 14 The use according to the first aspect of the invention is contemplated in (or may comprise the use of) any fuel composition that is suitable for use in (i.e. to power) the internal combustion engine into which it is or 5 is intended to be introduced. The fuel composition may, for example, be an automotive fuel composition, for use in powering an automotive vehicle. The fuel composition may comprise petroleum derived components ("distillate"), and/or synthetically derived, 10 e.g. Fischer-Tropsch derived, components. As used herein, the term "Fischer-Tropsch derived" means that a material is, or derives from, a synthesis product of a Fischer Tropsch condensation process. A Fischer-Tropsch derived fuel component of use in the present invention may be 15 obtained directly from the refining or the Fischer Tropsch reaction, or indirectly for instance by fractionation or hydrotreating of the refining or synthesis product to give a fractionated or hydrotreated product. A Fischer-Tropsch derived fuel or fuel component 20 will therefore be a hydrocarbon stream in which a substantial portion, except for added hydrogen, is derived directly or indirectly from a Fischer-Tropsch condensation process. The Fischer-Tropsch process converts carbon monoxide and hydrogen into longer chains, 25 which are usually paraffinic hydrocarbons. The carbon monoxide and hydrogen may themselves be derived from organic, inorganic, natural or synthetic sources, such as from natural gas or from organically derived methane. Fischer-Tropsch derived components may be obtained by 30 converting gas, biomass or coal to liquid (XtL), specifically by gas to liquid conversion (GtL), or from biomass to liquid conversion (BtL). Any form of Fischer- WO 2012/076652 PCT/EP2011/072204 - 15 Tropsch derived fuel component may be used as a base component in accordance with the invention. The fuel composition may preferably contain no more than 5000 ppmw (parts per million by weight) of sulphur, 5 typically from 2000 to 5000 ppmw, or from 1000 to 2000 ppmw, or alternatively up to 1000 ppmw. The composition may, for example, be a low or ultra low sulphur fuel, or a sulphur free fuel, for instance containing at most 500 ppmw, preferably no more than 350 ppmw, most preferably 10 no more than 100 or 50 or even 10 ppmw, of sulphur. It has been found that fuel dilution is particularly pronounced in compression ignition engines powered by diesel fuel. Without wishing to be bound by theory, it is thought that the relatively high boiling points of many 15 diesel fuel components (e.g. compared to gasoline fuel components) make such components less likely to evaporate and escape the lubricant following their ingress. This can lead to a build-up of fuel components in the lubricant, which, in the absence of viscosity increasing 20 components in the fuel, can in turn cause an increased deterioration of the viscometric properties of the lubricant. Based on the appreciation that diesel fuel is particularly likely to affect the viscometric properties 25 of the lubricant, the use according to the invention may preferably be in (or comprise the use of) a diesel fuel composition suitable and/or adapted and/or intended for use in a compression ignition (diesel) engine. Such a diesel fuel composition may comprise one or more diesel 30 fuel components of conventional type, typically comprising liquid hydrocarbon middle distillate fuel oil(s), for instance petroleum derived gas oils. In general, such fuel components may be organically or WO 2012/076652 PCT/EP2011/072204 - 16 synthetically derived, and are suitably obtained by distillation of a desired range of fractions from a crude oil. Such gas oils may be processed in a hydrodesulphurisation (HDS) unit so as to reduce their 5 sulphur content to a level suitable for inclusion in a diesel fuel composition. They will typically have boiling points within the usual diesel range of 150 to 410*C or 170 to 370*C, depending on grade and use. In some cases, the fuel composition will include one or more cracked 10 products obtained by splitting heavy hydrocarbons. Diesel fuels contained in the a diesel composition will typically have a density of from 750 to 900 kg/m 3 , preferably from 800 to 860 kg/m, at 15 0 C (ASTM D-4052 or EN ISO 3675) and/or a kinematic viscosity at 40*C (VK 40) 15 of from 1.5 to 6.0 centistokes (mm 2 /s) (ASTM D-445 or EN ISO 3104). The fuel composition may be a diesel fuel composition that comprises a Fischer-Tropsch derived diesel fuel component, typically a Fischer-Tropsch 20 derived gas oil. In the context of reducing carbon emissions, it is increasingly desirable for diesel fuel to contain one or more so-called "biofuel" components, which may typically be oxygenates. Thus, in beneficial embodiments of the 25 invention, the diesel fuel composition may consist of or comprise a biofuel component or an oxygenate component, such as a vegetable oil, hydrogenated vegetable oil or vegetable oil derivative (e.g. a fatty acid ester, in particular a fatty acid methyl ester, FAME), or another 30 oxygenate such as an acid, ketone or ester. The biofuel or oxygenate may preferably be bio-derived, i.e. comprise at least about 0.1 dpm/gC of carbon-14. It is known in the art that carbon-14 (C-14), which has a half-life of WO 2012/076652 PCT/EP2011/072204 - 17 about 5,700 years, is found in bio-derived materials but not in fossil fuels. It has been found that fuel dilution in internal combustion engines particularly affects lubricant 5 performance when the fuel composition comprises a biofuel, particularly an oxygenate. The ingress of diesel fuel compositions comprising biofuel components, especially esters of either a carboxylic acid or a vegetable oil such as FAME, has been found to have a 10 particularly detrimental effect on lubricant performance. Without wishing to be bound by theory, it is thought that biofuels/oxygenates, in particular esters of either a carboxylic acid or a vegetable oil, and most particularly FAME, can accumulate relatively quickly in the lubricant 15 due to their relatively high boiling points. Furthermore, biofuels/oxygenates, in particular esters of either a carboxylic acid or a vegetable oil, and most particularly FAME, have surprisingly been found to lower the viscosity (i.e. viscometric performance) of lubricant beyond even 20 levels predicted by viscometric models. Accordingly, to address such increased losses in viscometric performance, the use according to the invention is preferably contemplated in, or may preferably comprise the use of, a fuel composition 25 (advantageously a diesel fuel composition), comprising an oxygenate (advantageously an ester of either a carboxylic acid or a vegetable oil, most advantageously FAME) optionally having a high amount of polar components, measurable for example with reference to unreacted acid 30 (Acid value greater than 0.5 mg/KOH/g) or, particularly in the context of FAME, more than 0.8% w/w monoglycerates.

WO 2012/076652 PCT/EP2011/072204 - 18 Where the fuel composition contains a biofuel component or oxygenate, the biofuel or oxygenate component may be present in quantities of between 1% and 99% w/w, for example. In one embodiment the fuel 5 comprises at least 2% w/w biofuel or oxygenate, such as between 2% and 75% w/w. In some cases the biofuel or oxygenate is present at between 2% and 45% w/w, such as between 3% and 35% w/w, between 4% and 25% w/w, or between 5% and 15% w/w. In one beneficial embodiment the 10 biofuel or oxygenate component is FAME. In a preferred application FAME is present at 5% w/w to 15% w/w based on the total weight of the fuel composition. In diesel fuel compositions, the base fuel may itself comprise a mixture of two or more diesel fuel 15 components of the types described above. The fuel composition may also be a gasoline (petrol) fuel composition. Such gasoline fuel compositions are well known in the art. It has been found that certain engine operating 20 cycles, such as diesel particulate filter (DPF) regeneration and, in the case of automotive engines, city driving, led to particularly high levels of fuel dilution. Therefore, use according to the invention may preferably be for the purpose of influencing the 25 viscometric performance of a lubricant (as described anywhere herein) during a particulate filter regeneration cycle and/or a city driving cycle of the internal combustion engine. In the context of the present invention, the 30 lubricant may be any lubricant fluid, typically an oil, which is suitable and/or adapted and/or intended for use in an internal combustion engine, in particular a diesel engine. Typical lubricant fluids are composed primarily WO 2012/076652 PCT/EP2011/072204 - 19 of one or more base oils, which may be selected from any of the synthetic (lubricating) oils, mineral oils, natural oils or mixtures thereof. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated 5 mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic/naphthenic type, which may be further refined by hydrofinishing processes and/or dewaxing. Synthetic base oils include Fischer-Tropsch derived base oils, as well as olefin oligomers (PAOs), dibasic acid 10 esters, polyol esters and dewaxed waxy raffinates. For use in an internal combustion engine, a base oil will suitably contain less than 1 %wt, preferably less than 0.1 %wt, of sulphur, as determined, for instance, by ASTM D-2622, D-4294, D-4927 or D-3120. It will suitably 15 have a viscosity index of more than 80, preferably of more than 120, as measured according to ASTM D-2270. It may conveniently have a VK 100 of from 3.8 to 26 centistokes (mm 2 /s) (ASTM D-445). A lubricant fluid for use in an internal combustion 20 engine might suitably have a VK 100 of from 2 to 80 centistokes (mm 2 /s), preferably from 3 to 70 centistokes (m2/S) or from 4 to 50 centistokes (mm 2 /s) Natural oils suitable for use as base oils include both animal and vegetable oils (e.g. castor or lard oil); 25 liquid petroleum oils; and hydrorefined, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils. 30 Alkylene oxide polymers and interpolymers and derivatives thereof, in which the terminal hydroxyl groups have been modified by esterification, etherification, etc, constitute another class of known WO 2012/076652 PCT/EP2011/072204 - 20 synthetic lubricating oils. These are exemplified by polyoxyalkylene polymers prepared by polymerisation of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g. methyl 5 polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polyethylene glycol having a molecular weight of 500-1000, diethyl ether of polypropylene glycol having a molecular weight of 1000 15001; and mono-and polycarboxylic esters thereof, for 10 example, the acetic acid esters, mixed C3-C8 fatty acid esters and the C13 oxo acid diester of tetraethylene glycol. Another suitable class of synthetic lubricating oils comprises the esters formed by reacting dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinic 15 acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adip+-c acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with a variety of alcohols (e.g. butyl alcohol, hexyl alcohol, dodecyl alcohol, 2 20 ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of these esters include dibutyl adipate, di (2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl 25 phthalate, didecyl phthalate, dieicosyl sebacate, the 2 ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2- ethylhexanoic acid. 30 Esters useful as synthetic oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, WO 2012/076652 PCT/EP2011/072204 - 21 trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol. Silicon-based oils, such as the polyalkyl-, polyaryl-, polyalkoxy, or polyaryloxysiloxane oils and 5 silicate oils, comprise another useful class of synthetic lubricating oils; they include tetraethyl silicate, tetraisopropyl silicate, tetra- (2-ethylhexyl) silicate, tetra- (4-methyl~2-ethyl-hexyl) silicate, tetra- (p tertbutylphenyl) silicate, hexa- (4-methyl- 2-pentoxy) 10 disiloxane, poly (methyl) siloxanes and poly (methylphenyl) siloxanes. Other synthetic lubricating oils include liquid esters of phosphorous-containing acids (e.g. tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric 15 tetrahydrofurans. Lubricant fluids may typically contain additives as known in the art, for example oxidation inhibitors (antioxidants), dispersants, seal fix or seal compatibility agents, and/or detergents. They may also 20 include other lubricant additives that perform specific functions not provided by the main components. These additional additives include, but are not limited to, corrosion inhibitors, VI improving additives, pour point depressants, zinc dialkyldithiophosphates, anti-wear 25 agents, anti-foam agents, and/or friction modifiers. Suitable additives are described in US-A-5320765 and US B-6528461. Suitable oxidation inhibitors include, for example, copper antioxidants, phenolic compounds and/or aminic compounds. Suitable dispersants include, for 30 example, succinimides. Suitable detergents include, for example, salicylate, phenate and sulphonate detergents. Suitable anti-wear additives include zinc dithiophosphates.

WO 2012/076652 PCT/EP2011/072204 - 22 Examples of lubricating base oils, and of additives for use in lubricant fluids, are described at pages 15 to 23 of WO-A-2007/128740. Throughout the description and claims of this 5 specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, -additives, components, integers or steps. 10 Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as 15 singularity, unless the context requires otherwise. Preferred features of each aspect of the present invention may be as described in connection with any of the other aspects. Other features of the present invention will become apparent from the following 20 examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings} . Thus, features, integers, characteristics, compounds, chemical moieties 25 or groups described in conjunction with a particular aspect, embodiment or example of the present invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Moreover, unless stated 30 otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

WO 2012/076652 PCT/EP2011/072204 - 23 The following examples illustrate the use of polymeric VI improving additives in fuel compositions, in accordance with the present invention, and assess their effects orr-the properties of lubricant oils in engines 5 running on the fuel compositions. Example 1 The viscometric properties of a lubricant in a compression ignition engine were observed whilst running the engine on two different fuels. 10 One of the fuels, Fuel A, consisted of only base fuel made up of regular mineral diesel including 5%v FAME (without any performance additives). The properties of Fuel A are summarised in Table 1: Table 1 Fuel Property Test method Density @ 15 (g/ml) 838.6 DIN EN ISO 12185 Viscosity @ 40'C 3.1726 DIN EN ISO 3104 (mm 2 / ) Distillation (*C) DIN EN ISO 3405 IBP 171.9 10% 226.0 30% 259.5 50% 283.6 70% 310.0 90% 341.5 95% 354.6 Final Boiling Point 363.8 The other fuel, Fuel B, consisted of Fuel A plus 15 0.5% w/w of a viscosity increasing component, specifically viscosity index (VI) improving additive SV (TM) 200, a divinylbenzene-polyisoprene star copolymer. Table 2A illustrates the effect of the addition of the viscosity increasing component.

WO 2012/076652 PCT/EP2011/072204 - 24 Table 2A Fuel Properties Density @15 Viscosity @40 (kg/m3) (mm2/S) Fuel A 838.2 3.779 Fuel B 838.5 4.910 Fuel A and Fuel B were successively used (in respective "runs") to power a Mercedes Benz OM646 common rail diesel engine, having the properties shown in Table 2B under identical engine operating conditions for 10 5 hours. Table 2B Vehicle C 220 CDI, E 220, Construction period CDI 2004-2007 Cylinder 4 DOHC Displacement 2148 cm 3 Power 110 kW @ 4200 1min Torque 340 Nm @ 2000 1/min Compression 1 : 18 Engine management Bosch EDC Emission standard EU 4 Injection-system Common Rail 3 - 1600 bar,Piezo ,Injector Exhaust DPF, lambda probe, EGR For each run, the engine was lubricated by previously unused lubricant in the form of a mineral oil based SAE 5W-30 low ash engine oil. For both Fuel A and Fuel B, the engine operating 10 conditions were monitored at all times and kept as set out in Table 3. Table 3 Engine speed r/min 1500 Engine torque Nm 26 Start of Main Injection "bTDC -10 (Crank Angle) Start of Post Injection *bTDC -38 (Crank Angle) Quantity Post Injection mm 3 /stroke 10 (fuel) WO 2012/076652 PCT/EP2011/072204 - 25 To shorten test duration, operating conditions were chosen, for which the fuel dilution rate into the engine oil is high, e.g. soot filter regeneration mode. The engine was run continuously under- steady state conditions 5 with active post injection at low engine speed and engine load, to simulate operating conditions for soot filter regeneration (high exhaust gas temperature) . For that purpose the injection timings of the main and post injections were delayed compared to normal operation. The 10 ratio of the injected fuel quantity between main and post injection was 2/3. During running of the engine with Fuel A and Fuel B, every two hours oil samples were taken to analyse the engine oil viscosity (at 100 0 C as per DIN EN 3104, VK 15 100). The results of the analysis are shown in Table 4. For security reasons the engine was under idle conditions when the oil samples were taken. Table 4 Run Time (h) Fuel A (VK 100) Fuel B (VK 100) (MM2/S) (mm 2 /S) 0 11.71 11.71 2 10.83 10.92 4 10.35 10.57 6 9.91 10.25 8 9.63 10.00 10 9.25 9.84 It was additionally noted that the amount of fuel in the engine oil was substantially identical, greater than 20 10% w/w, after 10h in each run. This indicates that a moderate level of fuel dilution occurred during both runs. The results of Table 4 show that, when using Fuel B the viscosity of the lubricant is less affected by the 25 thinning effect of fuel dilution. The final viscosity, after 10 hours testing differs from Fuel A by 0.58%.

WO 2012/076652 PCT/EP2011/072204 - 26 When using the base Fuel A, under the test conditions the lubricant viscosity is so affected by fuel dilution, that its end viscosity value is below 9.3 mM 2 /s, the defined limit between SAE 30 (the class in 5 which the oil belongs originally) and SAE 20. Being in an SAE class lower, the oil is recommended to be changed. By contrast, when using Fuel B which includes VI improving additive, the lubricant remained within its initial SAE viscosity range. 10 The use of VI improving additive therefore leads to an increased oil drain interval (ODI). The use of the viscosity increasing fuel component compensates the dilution caused by fuel, and brings a longer ODI and a better protection. 15 The presence of FAME (Fatty Acid Methyl Esters) in diesel fuels tends to make the oil dilution effect even worse, since FAME will be enriched in the lubricant; Table 4 illustrates that this effect can be overcome according to the invention. 20 Example 2 The viscometric properties of a lubricant in a compression ignition engine powered vehicle were observed whilst running the vehicle on two different fuels. One of the fuels, Fuel A, consisted of only base 25 fuel made up of regular mineral sulphur free (<10 ppm) winter diesel including 7%v FAME (with performance additives). The other fuel, Fuel B, consisted of Fuel A plus 0.2% w/w of a viscosity increasing component, 30 specifically viscosity index (VI) improving additive SV (TM) 150, a polystyrene-polyisoprene di-block copolymer having a tendency to form star-like clusters (micelles) in solution.

WO 2012/076652 PCT/EP2011/072204 - 27 A pair of cars (VW-Golf 2.0 TDI from 2009) ran in parallel for 25 000 km on the same routes and at the same time. One car was fuelled with Fuel A and the other with Fuel B to compare the impact on the lubricants (engine 5 oils), which were identical, previously unused mineral oil based low ash SAE 5W-30. The lubricant was regularly analysed for fuel dilution and viscosity (at 100*C as per DIN EN 3104, VK 100). 10 After 25 000km, the car run on Fuel A is taken for a further test (Transfer Test) in which it is powered by Fuel B and driven for only about 2000 km. However, during the Transfer Test, shortening test operating conditions were chosen, for which the fuel dilution rate into the 15 engine oil is high, namely soot filter regeneration mode (as in Example 1). 20 filter regenerations are triggered followed by a short trip of driving on the road (100 km) . The engine oil was analysed for fuel dilution and viscosity (at 100"C as per DIN EN 3104, VK 100). This 20 test represents a city driving cycle with short trips and high load of the soot particle filter. The viscosity and fuel dilution measurement results are shown in Table 5. Table 5 % Fuel VK 100 (mm 2 /s) VK 100 (mm2/s) VK 100 Dilution Golf without Golf with VI (mm 2 /s) Golf in VI improving improving from lubricant additive additive Transfer Test 0.5 11.82 11.82 11.91 3 10.82 3.4 10.7 4.3 10.72 4.5 10.26 5.4 10.47 5.5 10.04 5.8 9.69 6.4 9.68 WO 2012/076652 PCT/EP2011/072204 - 28 Table 5 (continued) % Fuel VK 100 (mm 2 /s) VK 100 (MM2/s) VK 100 Dilution Golf without Golf with Vi (mM 2 /s) Golf in VI improving improving from lubricant additive additive Transfer Test 6.6 9.31 8 9.15 7 9 7.5 9.12 7.9 9.75 8.4 9.56 9.6 9.33 13 8.50 As expected, the viscometric performance of the lubricant deteriorated in all three tests due to fuel dilution. However, after running for 25 000 km in comparable conditions, the impact of Fuel B on the 5 lubricant viscosity is 0.3 to 0.4 mm 2/S less than with Fuel A. Thus Fuel B counteracts, more specifically mitigages, the deterioration. Furthermore, in the Transfer Test (which simulates a city driving cycle or DPF regeneration), surprisingly, 10 Fuel B is able to counteract the deterioration in viscometric performance even more effectively. It is noted that if the Transfer Test had been conducted over 25 000 km the influence (specifically the counteracting effect) of Fuel B could be seen even more 15 clearly. With the same fuel dilution the viscosity of the lubricant would decrease by about 2 nm 2 /s less and clearly stay in the viscosity range of the SAE class. In summary, Example 2 shows that low viscosity of the lubricant and possible engine damage can be avoided 20 by the use of a viscosity increasing component, (specifically a VI improving additive) in fuels. Such use is particularly beneficial during a city driving cycle and during DPF regeneration.

WO 2012/076652 PCT/EP2011/072204 - 29 Example 3 The viscometric properties of a lubricant in a compression ignition engine were observed whilst running the engine on three different fuels. 5 Fuel A consisted of a regular mineral diesel fuel containing 5%v FAME; Fuel B consisted of Fuel A plus 5%v of a Fischer-Tropsch derived extra heavy base oil, as described in the Examples of WO 2009/080673; Fuel C consisted of Fuel A plus 0.5% w/w of a viscosity 10 increasing component, specifically viscosity index (VI) improving additive SV (TM) 200, a divinylbenzene polyisoprene star copolymer. The three fuels were used in running an engine as described in Example 1, wherein for each fuel the engine 15 operating conditions were kept as set out in Table 3 in Example 1. During running of the engine, every two hours engine oil samples were taken to analyse the engine oil viscosity VK100 (viscosity at 100C as per DIN EN 3104). 20 The results of the analysis are shown in Table 6. Table 6 Run Time (h) Fuel A (VK Fuel B (VK Fuel C (VK 100) (mm 2 /s) 100) (mm 2 /s) 100) (mm 2 /s) 0 11.71 11.71 11.71 2 10.83 10.95 10.92 4 10.35 10.53 10.57 6 9.91 10.14 10.25 8 9.63 9.77 10.00 10 9.25 9.44 9.84 It can be seen from the results of Table 6 that while use of both fuels that incorporate a viscosity increasing component reduces the deterioration of the VK100 viscosity of the engine oil, Fuel C which 25 incorporates a far smaller amount of the polymeric VI improving additive gives rise to a far reduced WO 2012/076652 PCT/EP2011/072204 - 30 deterioration of viscosity than the significantly greater amount of a Fischer-Tropsch heavy base oil viscosity increasing component incorporated into Fuel B. It is surprising that a smaller amount of polymer in Fuel C 5 provides a greater mitigating effect on the lubricating oil viscosity deterioration.

Claims (12)

1. Use of a viscosity increasing component in a fuel composition, or of a fuel composition comprising a viscosity increasing component, for the purpose of influencing the viscometric performance of a lubricant in 5 an internal combustion engine into which the fuel composition is or is intended to be introduced, wherein the viscosity increasing component is a polymeric viscosity index (VI) improving additive.

2. Use according to claim 1 or claim 2, wherein 10 influencing the viscometric performance comprises counteracting deterioration of the viscometric performance associated with ingress of the fuel composition into the lubricant.

3. Use according to claim 2, wherein counteracting 15 deterioration comprises mitigating the deterioration or mitigating an increase in the deterioration.

4. Use according to any one of claims 1 to 3, wherein the viscometric performance of the lubricant is defined as one or more of: lubricant viscosity, lubricant 20 viscosity grade, lubricant viscosity index, lubricant fluid change or oil drain interval, lubricant lifetime or lifespan, and engine lubrification.

5. Use according to any one of claims 1 to 4, wherein the VI improving additive comprises a block copolymer, 25 which contains one or more monomer blocks selected from ethylene, propylene, butylene, butadiene, isoprene and styrene monomers.

6. Use according to claim 5, wherein the VI improving additive comprises a polystyrene-polyisoprene di-block 30 copolymer or a divinylbenzene-polyisoprene WO 2012/076652 PCT/EP2011/072204 - 32 stellate copolymer.

7. Use according to any one of claims 1 to 6 wherein the VI improving additive is used at a concentration in the range of from 0.01% w/w to 0.5% w/w based on the 5 total weight of the fuel composition.

8. Use according to claim 7, wherein the VI improving additive is used at a concentration of between: (i) 0.01% w/w and 1.0% w/w; (ii) 0.05% w/w and 0.7% w/w; or 10 (iii) 0.1% w/w and 0.5% w/w; based on the total weight of the fuel composition.

9. Use according to any one of claims 1 to 8, wherein the fuel composition is a diesel fuel composition.

10. Use according to any one of claims 1 to 9, wherein 15 the fuel composition comprises an ester of a carboxylic acid, a vegetable oil or a hydrogenated vegetable oil.

11. A method of operating an internal combustion engine and/or a vehicle which is powered by such an engine, which method involves introducing into a combustion 20 chamber of the engine a fuel composition obtained with the use according to any one of claims I to 10.

12. A method of achieving a target viscometric performance associated with a lubricant of an internal combustion engine, the method comprising powering the 25 engine using a fuel composition comprising a viscosity increasing component, which is a polymeric viscosity index improving additive.