CA2866956C

CA2866956C - Use of a viscosity improver

Info

Publication number: CA2866956C
Application number: CA2866956A
Authority: CA
Inventors: Felix Johannes BALTHASAR; Matthias Eggenstein
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2012-03-16
Filing date: 2013-03-18
Publication date: 2020-04-21
Anticipated expiration: 2033-03-18
Also published as: CN104169400B; WO2013135912A1; CA2866956A1; MY169744A; PH12014502055B1; EP2825619B1; CN104169400A; PH12014502055A1; ZA201406441B; BR112014022491B1; JP2015513603A; JP6242829B2; EP2825619A1

Abstract

Use of a viscosity-improving additive, in a diesel fuel formulation, for the purpose of increasing the compressibility of the formulation. The viscosity-improving additive may be selected from (i) olefin-based polymers (in particular styrene-based polymers); (ii) base oils naphthenic, paraffinic or synthetic; (iii) polymethacrylates; and (iv) mixtures thereof. It may be used to increase the isothermal compressibility of the diesel fuel formulation at typical fuel injection pressures and temperatures, and in turn to improve the power- related performance of a compression ignition engine running on the fuel formulation.

Description

2 PCT/EP2013/055581 USE OF A VISCOSITY IMPROVER
Field of the Invention This invention relates to the use of certain types of additive in diesel fuel formulations for new purposes.
Background to the Invention It is often desired to improve the performance of internal combustion engines through the use of modified fuels. In the past, for example, diesel fuels have been modified by the addition of relatively high density components, in order to improve the power-related performance of engines running on the fuels. In modern direct injection diesel engines a higher density fuel will typically lead to an increase in the mass of combustible material which is delivered into the combustion chamber through the engine's fixed volume fuel injectors; this in turn increases the energy made available through the combustion process.
It is not straightforward to predict how a fuel will behave in the injection system of an engine, in particular under the extremely high injection pressures (often in excess of 2000 bar) to which it will be subjected in a modern diesel engine. A diesel fuel is a complex mixture of hydrocarbons of different molecular weights and not all of these molecules will respond in the same way to increases in pressure. Moreover the geometry of the injection system can itself affect the way in which a fuel's viscosity and other properties will impact upon engine performance.
It is an aim of the present invention to provide an alternative way of improving engine performance by modifying the properties of diesel fuels, in particular through the use of fuel-compatible additives.
Statements of the Invention According to a first aspect of the present invention there is provided the use of a viscosity-improving additive, in a diesel fuel formulation, for the purpose of increasing the compressibility of the formulation.
The present invention is based on the realisation that it is possible to use additives to modify the compressibility of a diesel fuel formulation, ie the rate at which its density changes with increasing pressure. An increase in the compressibility of a fuel means that as it is subjected to increasing pressures, such as within a fuel injection system, its density will increase at a greater rate. This in turn means that at any given injection pressure, the fuel will have a higher density.
Thus, at the high pressures experienced in the injection system of a diesel engine (typically from 1600 to 2500 bar), the fuel will provide a higher energy content in each injection event. This in turn can increase the power delivery through the engine, and hence its performance.
It has surprisingly been found that viscosity-improving additives can, in addition to increasing the viscosity of a diesel fuel formulation at any given temperature and pressure, also increase its compressibility. Moreover, this effect appears to be particularly marked at the high pressures (for example in excess of 1500 or even 2000 bar) and high temperatures (for example in excess of 100 C, often up to 250 C) which are typically used in modern diesel engines.
Thus, at typical injection pressures and temperatures, a diesel fuel formulation for use according to the invention will have a higher density than in the

- 3 -absence of the viscosity-improving additive. This can yield an increase in delivered power from an engine running on the formulation. In accordance with the invention, therefore, a viscosity-improving additive may be used to improve the power-related performance of an engine running on a diesel fuel formulation, by increasing the compressibility of the formulation.
Although the additive may not increase the density of the formulation by a large amount under standard measurement conditions (for example at atmospheric pressure and either 15 or 40 C), it can increase the density by a considerably greater amount under injection conditions.
The invention is expected to have particular benefits in modern diesel engines, as the rail pressures used in such engines are continually increasing. A fuel formulation which is able to respond to increasing pressure with an increase in energy and power output can represent a promising candidate for use in high performance engines and the vehicles which they power.
The viscosity-improving additive used in the present invention may be any component, or mixture thereof, which is suitable for use in a diesel fuel formulation and which, when added to such a formulation, causes an increase in its viscosity, in particular its kinematic viscosity. A range of such components are known and commercially available.
Viscosity improvers have been used in diesel fuels in the past. WO-A-2005/054411, for example, describes the use of a viscosity-increasing component in a diesel fuel composition, for the purpose of improving the vehicle tractive effort (VTE) and/or acceleration performance of a diesel engine into which the composition is introduced.
The components used to increase the viscosity of the fuel

- 4 -composition include hydrocarbon diesel fuel components such as in particular Fischer-Tropsch derived diesel components, and oils, which may be mineral or synthetic in origin and may also be Fischer-Tropsch derived. US-A-2009/0241882 discloses the use of a viscosity index (VI)-improving additive, in an automotive diesel fuel composition, for the purpose of improving the acceleration performance of an engine into which the fuel composition is introduced or of a vehicle powered by such an engine.
However, such disclosures have failed to establish, or even to investigate, a link between the viscosity of a fuel formulation and its compressibility, in particular at typical fuel injection pressures. Such a link is not necessarily predictable, due to the relatively complex constitutions and properties of fuel formulations. Nor could it have been predicted, from this earlier work, that viscosity-improving additives would have an effect on fuel compressibility even at high temperatures and pressures. Earlier work on the densities and viscosities of additivated fuels has focused primarily on fuel properties measured at ambient temperature and pressure, as in many of the standard (for example ASTM) test methods, rather than investigating changes in fuel behaviour under injection conditions.
Magin et al in Energy & Fuels, vol 26, no 2, pages 1336 to 1343 in a paper entitled 'Bulk Modulus of Compressibility of Diesel/Biodiesel/HVO' found a synergistic effect leading to higher values for the bulk modulus for HVO/Diesel blends which reached a maximum for a 25% HVO content. The paper speculates that the reason for this effect is the increase of diversity of hydrocarbon structures provided by incorporating the HVO

- 5 -into the diesel, and that similarly where small amounts of HVO are utilized in fuel blends, the resultant decrease in molecular structure diversity yields significant decreases in the bulk modulus.
In accordance with the invention, the viscosity-improving additive may be an oligomeric or polymeric, in particular a polymeric, component. It may be selected from:
i. olefin-based polymers;
ii. naphthenic, paraffinic, or synthetic base oils;
iii. polymethacrylates; and iv. mixtures thereof.
It has been found that the olefin-based polymers can yield a useful increase in compressibility at only a fraction of the amount of additive than a base oil additive.
An additive of type (i) is therefore especially preferred. It is a polymer which comprises one or more olefinic monomer units. In the context of the present invention, the term "polymer" includes a copolymer. An additive of type (i) may be a copolymer, in particular a block copolymer, which may comprise a mixture of two or more olefinic monomer units. Olefinic monomer units may for example be selected from ethylene, propylene, butylene, butadiene, isoprene and styrene.
An additive of type (i) may be selected from polyisobutylenes (PIBs), poly-alpha olefins (PA05), ethylene-propylene copolymers (including both semi-crystalline and amorphous copolymers), styrene-based polymers, and mixtures thereof. It may be selected from ethylene-propylene copolymers, styrene-based polymers, and mixtures thereof.

- 6 -Suitable ethylene-propylene copolymers are available for example as LZ 706X additives (ex Lubrizol). Suitable PIBs are commercially available for example as Indopol-H
(ex INEOS). Suitable PAOs are commercially available for example as Durasyn (ex INEOS) or Synfluid (ex Chevron Phillips).
In an embodiment, the additive of type (i) comprises a styrene-based polymer, ie a polymer or copolymer which comprises one or more styrenic monomer units. It may comprise a styrene-based copolymer, for example a copolymer of at least one styrenic monomer with at least one olefinic monomer. Suitable such polymers are available for example as KratonTM D or KratonTM G additives (ex Kraton) or as SVTM additives (ex Infineum, Multisol and others). They have been used in the past as viscosity-improving and viscosity index-improving additives, including in diesel fuel formulations: see for example US-A-2009/0241882. They have also been used as additives in lubricants (see WO-A-2008/024111).
The additive of type (i) may in particular be selected from copolymers of styrenic and olefinic monomers (in particular copolymers of styrene monomers with ethylene, propylene, butylene, butadiene and/or isoprene (2-methyl-1,3-butadiene) monomers), and mixtures thereof. It may for instance be selected from polystyrene-polyisoprene copolymers, polystyrene-polybutadiene copolymers, and mixtures thereof. Such copolymers may be block copolymers, as for instance SVTM
150 (a linear polystyrene-polyisoprene di-block copolymer) or the KratonTM additives (styrene-butadiene-styrene tri-block copolymers or styrene-ethylene-butylene tri-block copolymers). They may be tapered copolymers, for instance styrene-butadiene copolymers. They may be

- 7 -stellate copolymers, as for instance SVTM 260 and SVm200 (which are polystyrene-polyisoprene star copolymers).
In an embodiment, the additive (i) is selected from polystyrene-polyisoprene copolymers and mixtures thereof.
In an embodiment, it is selected from SVTM additives and mixtures thereof, for example from SVm150, SVm200, SVm260 and mixtures thereof. In an embodiment, it is selected from SVm150, SVm260 and mixtures thereof. In an embodiment, it comprises SVTM 150.
An additive of type (ii) is most suitably a lubricant base oil, for example a naphthenic base oil derived from naphthenic crude oils. It may in particular be a mineral oil or mixture thereof, for example a naphthenic mineral base oil. The base oil, or a component thereof, may be a synthetic product such as a Fischer-Tropsch-derived component.
A base oil (ii) may for example be a Group III, Group IV or Group V base oil. In an embodiment, it is an API (American Petroleum Institute) Group V base oil. The Group V base oils include non-PAO synthetic components such as diesters, polyolesters, and alkylated hydrocarbons such as alkylated naphthenes and alkylated benzenes.
In a specific embodiment, a base oil (ii) may have a density at 15 C of from 875 to 885 kg/m3 (DIN 51 757 D;
ISO 12185), for example about 880 kg/m3. It may have a kinematic viscosity at 40 C (VK 40) of from 7.7 to 8.2 mm2/s (DIN 51 562, T.1; ISO 3104), for example about 7.9 mm2/s; and/or a kinematic viscosity at 100 C (VK 100) of about 2.1 mm2/s (ISO 3104). It may have a vapour pressure at 20 C of less than 0.01 kPa; a pour point of -60 C (DIN
ISO 3016); a flash point of 146 C (ISO 2719); and/or a

- 8 -polycyclic aromatic compound (PCA) content of about 1%
w/w (IP 346).
Base oils, in particular mineral base oils, are widely available, for example from the Shell group of companies. They have been used in the past to increase the viscosity and density of racing diesel fuels.
In an embodiment, the additive of type (ii) comprises the lubricant base oil HNR40D, which is a naphthenic mineral base oil, available from the Shell group of companies.
Additives of type (iii) are available for example as ViscoplexTM 1-300 (ex Evonik), which is used as a pour point depressant and as a viscosity modifier in lubricants.
In an embodiment of the invention, the viscosity-improving additive is selected from olefin-based polymers; base oils; and mixtures thereof. In an embodiment, it is selected from styrene-based polymers;
base oils; and mixtures thereof. In an embodiment, it comprises a styrene-based polymer or mixture thereof.
An additive of the type (i) to (iv) may be used, according to the invention, in the form of an additive composition which contains both the active ingredient (for example an olefin-based polymer) and a suitable carrier fluid. Carrier fluids (in particular carrier solvents) include for example mineral oils, aromatic hydrocarbon solvents such as ShellsolTM A150 (ex Shell), other hydrocarbons and hydrocarbon mixtures with boiling points within the normal diesel boiling range, fatty acid alkyl esters (in particular fatty acid methyl esters), and mixtures thereof.
Such an additive composition may comprise one or more additional active substances, for example selected

- 9 -from substances which are active as detergents, dehazers, anti-corrosion additives, antifoam additives, lubricity improvers, cold flow improvers, cetane improvers, and mixtures thereof, in particular from substances which are active as detergents, dehazers, anti-corrosion additives, antifoam additives, and mixtures thereof.
In an embodiment, the viscosity-improving additive is a viscosity index-improving additive, ie a component which, when added to a diesel fuel formulation, causes an increase in its viscosity index VI. The VI of a fuel formulation is a measure of the rate of change of the viscosity of the formulation with temperature. A fuel formulation with a relatively high VI will exhibit a smaller reduction in its viscosity than will a fuel formulation with a relatively low VI, over any given increase in temperature.
Viscosity index-improving additives (also referred to as VI improvers) are already known in lubricant formulations, where they are used to maintain viscosity as constant as possible over a desired temperature range by increasing viscosity at higher temperatures. They are typically based on relatively high molecular weight, long chain polymeric molecules that can form conglomerates and/or micelles. These molecular systems expand at higher temperatures, thus further restricting their movement relative to one another and in turn increasing the viscosity of the system.
Known VI improvers include polymethacrylates (PMAs), polyisobutylenes (PIBs), ethylene-propylene copolymers and other olefin copolymers (0CPs), and styrene/olefin copolymers such as those referred to above. Thus, many of the viscosity-improving additives (i) and (iii) are also

- 10 -capable of acting as VI-improving additives in diesel fuel formulations.
In WO-A-01/48120, certain of these types of additive are proposed for use in diesel fuel compositions, for the purpose of improving the ability of an engine to start at elevated temperatures. They have not however, to our knowledge, been proposed for use in increasing the compressibility of a diesel fuel formulation.
In accordance with the invention, the viscosity-improving additive may be used in the diesel fuel formulation at an (active matter) concentration of 0.01%
w/w or greater, or of 0.05% w/w or greater, or of 0.1%
w/w or greater. In cases it may be used at an (active matter) concentration of 0.5 or 1% w/w or greater. It may be used at an (active matter) concentration of up to 30%
w/w, or of up to 25 or 20 or 15% w/w, or more suitably up to 10% w/w or up to 7.5 or 5 or 2.5% w/w. In cases it may be used at an (active matter) concentration of up to 1 or 0.5% w/w, such as from 0.01 to 0.5% w/w or from 0.05 to 0.5% w/w.
In a first specific embodiment, in particular when the viscosity-improving additive is of type (i) or (iii), and more particularly when it is an ethylene-propylene copolymer or styrene-based polymer, most particularly a styrene-based polymer, its (active matter) concentration in the diesel fuel formulation may be 0.01% w/w or greater, or 0.025 or 0.05% w/w or greater, or 0.1% w/w or greater. In this embodiment the (active matter) concentration of the additive may be up to 0.5% w/w, or up to 0.4 or 0.3 or 0.2% w/w, such as from 0.01 to 0.5%
w/w or from 0.04 to 0.2% w/w or from 0.05 to 2% w/w. In preferred embodiments, an additive of type (i) is used in the diesel fuel formulation in a concentration in the

- 11 -range of from 0.01 to 2% w/w, more preferably from 0.01 to 1% w/w, and especially from 0.01 to 0.5% w/w, for example from 0.01 to 0.2% w/w, or from 0.04 to 0.2% w/w.
It is a significant advantage that the increase in compressibility can be provided by such viscosity-improving additives at such low concentrations as are typically associated with fuel additives. This is, for example, preferred in order to minimise the impact of the invention on fuel preparation and handling processes.
In a second specific embodiment, in particular when the viscosity-improving additive is of type (ii), its concentration in the diesel fuel formulation may be 1%
w/w or greater, or 2% w/w or greater, or in cases 5 or 10% w/w or greater. In this embodiment the concentration of the additive may be up to 30% w/w, or up to 25 or 20 or 15% w/w, suitably up to 10% w/w or up to 7.5 or 5%
w/w, such as from 1 to 10% w/w or from 1 to 5% w/w. Such viscosity-improving additives may thus be included in fuel formulations at concentrations typically associated with fuel components. Ideally, in such a case, the additive will not be detrimental to the properties of the overall formulation, ie the overall formulation will still comply with relevant applicable standards such as EN 590 or ASTM D975, even though it has a higher density and compressibility under injection temperatures and pressures.
A diesel fuel formulation used according to the invention (ie a diesel fuel formulation in which a viscosity-improving additive is or has been used in accordance with the invention) may comprise, in addition to the viscosity-improving additive, one or more diesel fuel components and/or additives, as are known in the

12 PCT/EP2013/055581 art. It may for example comprise a diesel base fuel or mixture thereof.
A diesel base fuel may be any fuel component, or mixture thereof, which is suitable and/or adapted for use in a diesel fuel formulation and therefore for combustion within a compression ignition (diesel) engine. It will typically be a liquid hydrocarbon middle distillate fuel, more typically a gas oil. It may be petroleum-derived. It may be or contain a kerosene fuel component.
Alternatively it may be synthetic: for instance it may be the product of a Fischer-Tropsch condensation. It may be derived, either directly or indirectly, from a biological source such as plant biomass. It may be or include an oxygenate such as a fatty acid alkyl ester, in particular a fatty acid methyl ester (FAME) such as rapeseed methyl ester or palm oil methyl ester.
A diesel base fuel will typically boil in the range from 150 or 180 to 370 C (ASTM D86 or EN ISO 3405). It will suitably have a measured cetane number (ASTM D613) of from 40 to 70 or from 40 to 65 or from 51 to 65 or 70.
It will suitably have a density of from 750 to 900 kg/m3, or from 800 to 860 kg/m3, or more suitably from 820 to 845 kg/m3, at 15 C (ASTM D4052 or EN ISO 3675), and/or a VK 40 of from 1.5 to 6.0 mm2/s or from 2.0 to 4.5 mm2/s (ASTM D445 or EN ISO 3104).
Where a fuel formulation used according to the invention comprises a diesel base fuel, the concentration of the base fuel in the formulation may be 60% v/v or greater, or 65 or 70 or 75 or 80 or 85 or 90% v/v or greater, or in cases 95% v/v or greater. Its concentration may be up to 99.99% v/v, or up to 99.95 or 99.9% v/v, or up to 99.8 or 99.5% v/v, or up to 99 or 98 or 95% v/v. The base fuel may represent the major part of

- 13 -the fuel formulation: after inclusion of the viscosity-improving additive, and any further (optional) fuel components and additives, the diesel base fuel may therefore represent the balance to 100%.
A diesel fuel formulation used according to the invention will suitably comply with applicable current standard diesel fuel specification(s) such as for example EN 590 (for Europe) or ASTM D975 (for the USA). By way of example, the overall formulation may have a density from 820 to 845 kg/m3 at 15 C; a 195 boiling point (ASTM D86 or EN ISO 3405) of 360 C or less; a measured cetane number of 40 or greater, ideally of 51 or greater; a VK40 from 2 to 4.5 mm2/s; a flash point (ASTM D93 or EN ISO
2719) of 55 C or greater; a sulphur content (ASTM D2622 or EN ISO 20846) of 50 mg/kg or less; a cloud point (IP
219) of less than -10 C; and/or a polycyclic aromatic hydrocarbons (PAH) content (EN 12916) of less than 11%
w/w. It may have a lubricity, measured using a high frequency reciprocating rig for example according to ISO
12156 and expressed as a "HFRR wear scar", of 460 pm or less. Relevant specifications may however differ from country to country, from season to season and from year to year, and may depend on the intended use of the formulation. Moreover a formulation used according to the invention may contain individual fuel components with properties outside of these ranges, since the properties of an overall blend may differ, often significantly, from those of its individual constituents.
A fuel formulation used according to the invention may comprise one or more fuel or refinery additives, in particular additives which are suitable for use in automotive diesel fuels. Many such additives are known and commercially available. The formulation may for

- 14 -example comprise one or more additives selected from detergents, dehazers, anti-corrosion additives, antifoam additives, cetane improvers such as 2-ethylhexyl nitrate (2-EHN), antistatic additives, lubricity additives, conductivity additives, cold flow additives, and combinations thereof. It may comprise one or more additives selected from detergents, dehazers, anti-corrosion additives, antifoam additives, and mixtures thereof. Such additives may each be included at an (active matter) concentration of up to 300 ppmw (parts per million by weight), for example of from 50 to 300 ppmw.
A fuel formulation used according to the invention should be suitable and/or adapted for use in a compression ignition (diesel) internal combustion engine.
It may in particular be an automotive fuel formulation.
In an embodiment, it is suitable and/or adapted for use in a diesel engine which operates using high fuel injection pressures, for example pressures greater than about 1800 bar or of about 2000 bar or greater. Such an engine may for example be of the common rail or unit injector type, and/or of the type referred to as "Euro 5".
In embodiments, the present invention may be used to prepare at least 1,000 litres of the additive-containing diesel fuel formulation, or at least 5,000 or 10,000 or 20,000 or 50,000 litres.
In accordance with the invention, the viscosity-improving additive is used for the purpose of increasing the compressibility of a diesel fuel formulation. It may in particular be used to increase the compressibility of the formulation at a pressure of 1000 bar or greater, or of 1500 bar or greater, or of 2000 bar or greater, for

- 15 -example from 1000 to 2500 bar or from 1500 to 2500 bar or from 2000 to 2500 bar. It may be used to increase the compressibility of the formulation at a temperature of 100 C or greater, or of 150 C or greater, or of from 100 to 250 C or from 100 to 200 C or from 100 to 175 C or from 100 to 150 C. In an embodiment, the viscosity-improving additive is used to produce a diesel fuel formulation which has an increased compressibility at a pressure of from 2000 to 2500 bar and a temperature of from 100 to 150 C, in particular at a pressure of 2000 bar and a temperature of 150 C.
In the present context, "compressibility" is suitably isothermal compressibility, ie the rate of change of density with pressure at a constant temperature.
The isothermal compressibility of a fuel formulation may be assessed using any suitable method, for instance as described in the examples below. Its reciprocal, referred to as the bulk modulus, is typically defined as the ratio of the change in pressure to the relative change in density at constant temperature. Isothermal compressibility and bulk modulus may thus be assessed by measuring the density of the fuel formulation at a range of pressures and observing the way in which the density changes with pressure. The results may for example be plotted on a graph of density against pressure. The density measurements should be taken at a constant temperature, for example a temperature to which the fuel formulation might typically be subjected in the injection system of a diesel engine. In particular, the density measurements may be taken at a constant temperature which is in the range from 40 to 200 C, or in the range from 40

- 16 -to 150 C, or in the range from 100 to 150 C, such as at about 150 C.
The density of a fuel formulation may be measured using a standard test method such as ASTM D4052 or an analogous method.
The invention may be used to achieve any degree of increase in the compressibility of the fuel formulation, and/or to achieve a desired target compressibility, for example a target set by an applicable regulatory standard, or a target set by a user (which includes a handler, keeper or distributor) or potential user of the formulation. The increase in compressibility will typically be as compared to the compressibility of the formulation prior to adding the viscosity-improving additive to it.
The invention may be used to achieve a desired increase in compressibility at a specific temperature, or within a specific range of temperatures. It may be used to achieve a desired increase in compressibility at a specific pressure, or within a specific range of pressures.
"Achieving" a desired target property also embraces - and in an embodiment involves - improving on the relevant target. Thus, for example, the viscosity-improving additive may be used to produce a diesel fuel formulation which has a compressibility higher than a desired target value.
The increase in compressibility of the diesel fuel formulation may be as compared to the compressibility of the formulation, and/or of an otherwise analogous fuel formulation intended (eg marketed) for use in an analogous context, prior to the realisation that the viscosity-improving additive could be used in the way

- 17 -provided by the present invention, or prior to adding the viscosity-improving additive to the formulation in accordance with the invention. Thus, the increase may be as compared to the compressibility of the diesel fuel formulation without the viscosity-improving additive. At a given pressure and temperature, the increase in compressibility may for example be 0.5% or more, or 0.75 or 1% or more, or in cases 2.5 or 3 or 4 or 5% or more, of the compressibility which it is desired to improve upon. At a given pressure and temperature, the increase in compressibility may for example be up to 20%, or up to or 10%, or up to 7.5 or 5%, of the compressibility which it is desired to improve upon.
The invention may additionally or alternatively be 15 used to adjust any property of the diesel fuel formulation which is equivalent to or associated with its compressibility, for instance to effect an increase in a desired property or behaviour and/or a reduction in an undesired property or behaviour. In particular, an increase in compressibility may be manifested by an improvement in the performance of a fuel-consuming system (in particular a diesel engine) running on the fuel formulation. Such an improvement may for example comprise a higher delivered torque under steady state conditions (ie at constant engine speed and load), shorter acceleration times, and/or a higher power output (manifested for example by a higher brake mean effective pressure). It may thus be manifested by an improvement in one or more power-related aspects of the performance of the fuel-consuming system. In accordance with the invention, the viscosity-improving additive may be used in a diesel fuel formulation for the purpose of achieving one or more of these effects, in particular to improve

- 18 -the power-related performance of an engine in which the fuel formulation is, or is intended to be, used. It may be used to increase the combustion energy generated with each injection of the fuel formulation into a combustion chamber of an engine running on the formulation.
An improvement in the power-related performance of a fuel-consuming system may also embrace mitigation, to at least a degree, of a decrease in acceleration performance due to another cause, in particular due to another fuel component or additive included in the fuel formulation on which the system is running. By way of example, a fuel formulation may contain one or more components intended to reduce its overall density so as to reduce the level of emissions which it generates on combustion; a reduction in density can result in loss of engine power, but this effect may be overcome or at least mitigated by the use of a viscosity-improving additive in accordance with the present invention.
An improvement in power-related performance may also embrace restoration, at least partially, of performance which has been reduced for another reason such as the use of a fuel containing an oxygenated component (for example a so-called "biofuel"), or the build-up of combustion-related deposits in the engine (typically in the fuel injectors).
In the context of the present invention, "use" of a viscosity-improving additive in a diesel fuel formulation means incorporating the additive into the formulation, typically as a blend (ie a physical mixture) with one or more other diesel fuel components, for example a diesel base fuel and optionally one or more other diesel fuel additives. The viscosity-improving additive will conveniently be incorporated before the formulation is

- 19 -introduced into an engine or other system which is to be run on the formulation. Instead or in addition, the use of a viscosity-improving additive may involve running a fuel-consuming system, typically an internal combustion engine, on a diesel fuel formulation containing the additive, typically by introducing the formulation into a combustion chamber of an engine. It may involve running a vehicle which is driven by a fuel-consuming system, on a diesel fuel formulation containing the additive. In such cases the fuel-consuming system is suitably a compression ignition (diesel) engine.
"Use" of a viscosity-improving additive in the ways described above may also embrace supplying the additive together with instructions for its use in a diesel fuel formulation in order to increase the compressibility of the formulation. The additive may itself be supplied as part of a composition which is suitable and/or adapted and/or intended for use as a fuel additive, in which case the viscosity-improving additive may be included in such a composition for the purpose of influencing its effects on the compressibility of a diesel fuel formulation.
In general, references to "adding" a component to, or "incorporating" a component in, a fuel formulation may be taken to embrace addition or incorporation at any point during the production of the formulation or at any time prior to its use. Thus, for example, the viscosity-improving additive may be incorporated into a diesel base fuel at the refinery, or more suitably it may be added to a diesel fuel formulation at the depot, downstream of the refinery.
A diesel fuel formulation used according to the invention may be marketed with an indication that it benefits from an improvement due to the inclusion of the

- 20 -viscosity-improving additive, in particular a higher compressibility and/or an improvement in the power-related performance of an engine which is running on the fuel formulation. The marketing of such a formulation may comprise an activity selected from (a) providing the formulation in a container that comprises the relevant indication; (b) supplying the formulation with product literature that comprises the indication; (c) providing the indication in a publication or sign (for example at the point of sale) that describes the formulation; and (d) providing the indication in a commercial which is aired for instance on the radio, television or internet.
The improvement may be attributed, in such an indication, at least partly to the presence of the viscosity-improving additive. The invention may involve assessing the relevant property (in particular the compressibility) of the formulation during or after its preparation. It may involve assessing the relevant property both before and after incorporation of the viscosity-improving additive, for example so as to confirm that the additive contributes to the relevant improvement in the formulation.
Similarly, a diesel fuel additive composition containing a viscosity-improving additive may, in accordance with the invention, be marketed with an indication that it benefits from an improvement due to the inclusion of the viscosity-improving additive, the improvement being the ability of the composition to increase the compressibility of a diesel fuel formulation in which it is used, and/or to improve the power-related performance of an engine which is running on such a diesel fuel formulation.

- 21 -Throughout the description and claims of this 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.
Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following 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 or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.
Where upper and lower limits are quoted for a property, for example for the concentration of a fuel component, then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.
In this specification, references to fuel and fuel component properties are - unless stated otherwise - to properties measured under ambient conditions, ie at atmospheric pressure and at a temperature of from 16 to

22 or 25 C, or from 18 to 22 or 25 C, for example about 20 C.
The present invention will now be further described with reference to the following non-limiting examples.

Example 1 Diesel fuel formulations were prepared, in accordance with the invention, by blending a diesel base fuel with four viscosity-improving test additives. The additives were:
a. SVTM 150, a fuel additive containing a polystyrene-polyisoprene block copolymer, ex-Infineum.
b. SVTM 200, a fuel additive containing a polystyrene-polyisoprene star copolymer, ex-Infineum.
c. SVTM 260, a fuel additive containing a styrene-polyisoprene star copolymer, ex-Infineum.
d. HNR40D, a lubricant base oil, ex Shell.
The base fuel was a zero sulphur diesel fuel (ex Shell), which conformed to the European diesel fuel specification EN 590. It contained 7% v/v of rapeseed methyl ester (RME), together with standard refinery additives. It had a VK 40 of 2.86 mm2/s (DIN EN ISO
3104), and a density at 40 C of 817.28 kg/m3 (DIN EN ISO
12185).
HNR4OD is a highly refined API Group V mineral oil, ex Shell. It is manufactured from naphthenic crude oils via a process involving vacuum distillation and hydrotreatment. It has a density at 15 C of 880 kg/m3 (ISO 12185); a VK 40 of 7.9 mm2/s (ISO 3104); a VK 100 of 2.1 mm2/s (ISO 3104); a flash point of 146 C (ISO 2719);
a polycyclic aromatic compound (PCA) content (IP 346) of 1% w/w; and a colour index (ASTM 1500) of less than 0.5.
The test additives were incorporated into the base fuel at a treat rate of 0.04% w/w and 0.2% w/w for the SVTM 150; 0.2% w/w for the SVTM 200; 0.15% w/w for the SVTM
260 and 26% w/w for the HNR40D.

- 23 -The densities of the resultant formulations, and of the unadditivated base fuel, were measured at 100 C using a density sensor, at a series of pressures from 0 to 2500 bar (relative to atmospheric) in steps of 250 bar. The experiment was then repeated at 150 C.
The results are shown in Tables 1 and 2 below, for the measurements taken at 100 C and 150 C respectively.
The figures in the tables are the base fuel and fuel formulation densities, in kg/m3. A pressure designated "0" corresponds to ambient pressure (1 bar).
Table 1 - Densities at 100 C
Pressure Base Base Base Base Base Base (bar) fuel fuel + fuel + fuel + fuel + fuel +
alone SVul SVul SVul SVD, IINR4OD

(2696 (0.0496 (0.296 (0.296 (0.1596 w/w) w/w) w/w) w/w) w/w) 776.13 777.08 777.09 777.46 777.55 789.18 250 797.70 798.61 798.67 798.83 799.16 810.39 500 816.13 817.24 817.41 817.27 817.85 828.99 750 832.32 833.75 834.07 833.58 834.43 845.66 1000 846.83 848.67 849.13 848.29 849.39 860.83 1250 860.03 862.31 862.93 861.72 863.07 874.79 1500 872.16 874.91 875.7 874.11 875.71 887.77 1750 883.42 886.66 887.61 885.65 887.49 899.90 2000 893.95 897.68 898.79 896.47 898.53 911.33 2250 903.85 908.07 909.34 906.66 908.95 922.15 2500 913.20 917.92 919.36 916.31 918.83 932.43

- 24 -Table 2 - Densities at 150 C
Pressure Base Base Base Base Base Base (bar) fuel fuel + fuel + fuel + fuel + fuel +
alone SVul SVD, SVD, SVD, IINR4OD

(2696 (0.0496 (0.296 (0.296 (0.1596 w/w) w/w) w/w) w/w) w/w) 741.85 743.15 742.51 743.14 743.44 755.88 250 769.10 771.51 770.72 770.86 771.95 783.29 500 791.41 794.95 794.14 793.73 795.49 806.41 750 810.49 815.12 814.38 813.41 815.75 826.60 1000 827.27 832.97 832.33 830.79 833.66 844.64 1250 842.33 849.05 848.54 846.43 849.80 861.02 1500 856.04 863.74 863.37 860.72 864.54 876.07 1750 868.66 877.31 877.08 873.9 878.16 890.05 2000 880.38 889.95 889.87 886.17 890.84 903.13 2250 891.34 901.80 901.88 897.68 902.73 915.44 2500 901.66 912.99 913.22 908.52 913.95 927.09 The measured densities were used to calculate the isothermal compressibilities of the base fuel and the test formulations, at each pressure and temperature.
Isothermal compressibility at temperature T (KT) is defined as a fractional volume reduction divided by the associated change in pressure, according to the following formula:
KT = - 1 . (3v) vo (3p) where V is the volume of the relevant fuel sample at temperature T and pressure P. and VO is the volume of the same sample at temperature T and ambient pressure (1 atmosphere).
For the present purposes, it can be defined according to the formula:

19*Ap KT
where p is the density of the fuel sample at temperature T and pressure P.

- 25 -The results are shown in Tables 3 and 4 below, for the experiments conducted at 100 C and 150 C
respectively. The figures in the table are KT values times 1E-6, per bar. Again, a pressure designated as "0"
corresponds to ambient pressure (1 bar).
Table 3 - Isothermal Compressibilities at 100 C
Pressure Base Base Base Base Base Base (bar) fuel fuel fuel fuel fuel fuel +

SVIK SVIK SVIK SVIK (2696 150 150 200 260 w/w) (0.0496 (0.296 (0.296 (0.1596 w/w) w/w) w/w) w/w) 121.62 120.27 120.39 119.56 120.72 115.69 250 96.61 97.03 97.46 96.16 97.32 95.03 500 80.14 81.31 81.86 80.43 81.51 80.62 750 68.46 69.97 70.57 69.12 70.13 70.01 1000 59.76 61.41 62.02 60.59 61.53 61.87 1250 53.01 54.72 55.31 53.94 54.81 55.42 1500 47.64 49.34 49.91 48.61 49.42 50.19 1750 43.25 44.92 45.48 44.23 44.99 45.87 2000 39.61 41.23 41.76 40.58 41.29 42.22 2250 36.53 38.10 38.61 37.49 38.15 39.12 2500 33.89 35.42 35.9 34.83 35.46 36.44 Table 4 - Isothermal Compressibilities at 150 C
Pressure Base Base Base Base Base Base (bar) fuel fuel fuel fuel fuel fuel +

SVIK SVIK SVIK SVIK (2696 150 150 200 260 w/w) (0.0496 (0.296 (0.296 (0.1596 w/w) w/w) w/w) w/w) 165.46 170.83 169.48 167.09 171.77 160.09 250 122.37 127.45 127.31 124.69 127.98 123.05 500 97.09 101.64 101.94 99.46 101.98 99.93 750 80.46 84.53 85.00 82.72 84.76 84.13 1000 68.70 72.35 72.89 70.8 72.52 72.64 1250 59.94 63.23 63.80 61.89 63.36 63.91 1500 53.16 56.16 56.73 54.96 56.26 57.06 1750 47.75 50.51 51.06 49.44 50.59 51.53 2000 43.35 45.89 46.43 44.92 45.96 46.98 2250 39.69 42.05 42.57 41.16 42.11 43.17 2500 36.60 38.80 39.30 37.98 38.85 39.93

- 26 -Tables 1 and 2 show that the viscosity-improving additives increase the density of the base fuel, in particular at higher pressures. Moreover, the difference between the density of the additivated base fuel and that of the base fuel alone increases with increasing pressure, indicating an increase in the compressibility of the base fuel when combined with the relevant additive. This increase in compressibility, compared to that of the base fuel alone, is clearly seen in the Table 3 and 4 data. It is apparent at both measurement temperatures, in particular at 150 C, which confirms the likely utility of the present invention under typical fuel injection conditions.
When the Table 1 results are plotted on a graph of density against pressure, the curves for the additivated fuel formulations can be seen to diverge from the curve for the base fuel alone, in particular at higher pressures above about 1000 bar. The rate of change of density with pressure (ie the compressibility) is, at such higher pressures, significantly greater for the five additivated formulations than for the unadditivated base fuel. The increase in compressibility, at any given pressure, is greater with the SVTM 150 and SVTM 260 than with the SVTM 200. Indeed the SVTM 150 has an effect even at a treat rate as low as 0.04% w/w. Similar comments apply to the Table 2 results, where the divergence of the curves is enhanced compared to that seen at 100 C.
The base fuel/HNR4OD blend has a much higher initial density than the base fuel alone. Its density remains greater than that of the base fuel at all pressures, but again its rate of change of density with increasing pressure has been shown to be higher than that of the base fuel alone, at both 100 and 150 C. However the use

- 27 -of base oil HNR4OD to improve isothermal compressibility requires a far greater amount of the additive (in these examples 26% w/w), whereas for each of the olefin-based polymer additives a benefit in compressibility is provided when using a significantly lower amount - 0.2%
w/w or lower.
Overall, these results confirm the known relationship between isothermal compressibility and pressure, ie that the compressibility decreases with increasing pressure. What they also show, however, which was not previously appreciated, is that a small amount of a suitable viscosity-improving additive can influence the way in which the compressibility of a diesel fuel formulation changes over the range of typical fuel injection pressures, resulting in higher fuel densities under injection conditions.
Thus, the present invention can provide a way of increasing the compressibility of a diesel fuel formulation, in many cases through the use of relatively small quantities of diesel fuel-compatible additives. An increase in compressibility means that, at the higher pressures to which it is subjected in the fuel injection system of an engine, the fuel formulation will have a greater density and will thus deliver, through the volumetrically-calibrated injection system, a greater combustion energy. In this way, the additivated fuel can be used to improve the power-related performance of a diesel engine.

Claims

- 28 -

1. Use of a viscosity-improving additive, in a diesel fuel formulation, for the purpose of increasing the isothermal compressibility of the formulation at a pressure of from 1,500 to 2,500 bar, wherein the viscosity-improving additive is an olefin-based polymer or a lubricant naphthenic base oil, and the isothermal compressibility of the formulation is the rate of change of density with pressure at a constant temperature.

2. Use of the viscosity-improving additive according to claim 1, wherein the olefin-based polymer is selected from polyisobutylenes (PIBs), poly-alpha olefins (PAOs), ethylene-propylene copolymers, styrene-based polymers, and mixtures thereof.

3. Use of the viscosity-improving additive according to claim 2, wherein the olefin-based polymer comprises a styrene-based polymer.

4. Use of the viscosity-improving additive according to claim 3, wherein the styrene-based polymer is a copolymer of at least one styrenic monomer with at least one olefinic monomer.

5. Use of the viscosity-improving additive according to any one of claims 1 to 4, wherein the viscosity-improving additive is a viscosity index-improving additive.

6. Use of the viscosity-improving additive according to any one of claims 1 to 5, wherein the viscosity-improving additive is used in the diesel fuel formulation at an active matter concentration of in the range of from 0.01 to 2% w/w.

7. Use of the viscosity-improving additive according to claim 6, wherein the viscosity-improving additive is used at a concentration of in the range of from 0.01 to 1% w/w.

8. Use of the viscosity-improving additive according to claim 7, wherein the viscosity-improving additive is used at a concentration of in the range of from 0.01 to 0.5% w/w.

9. Use of the viscosity-improving additive according to claim 8, wherein the viscosity-improving additive is used at a concentration of in the range of from 0.01 to 0.2% w/w.

10. Use of the viscosity-improving additive according to any one of claims 1 to 9, wherein the viscosity-improving additive is used for the purpose of increasing the isothermal compressibility of the diesel fuel formulation at a temperature of from 100 to 200°C.