Fuel Compositions

The present invention relates to methods and uses for improving the performance of diesel engines using fuel additives. In particular the invention relates to additives for diesel fuel compositions for use in diesel engines with high pressure fuel systems.

Due to consumer demand and legislation, diesel engines have in recent years become much more energy efficient, show improved performance and have reduced emissions.

These improvements in performance and emissions have been brought about by improvements in the combustion process. To achieve the fuel atomisation necessary for this improved combustion, fuel injection equipment has been developed which uses higher injection pressures and reduced fuel injector nozzle hole diameters. The fuel pressure at the injection nozzle is now commonly in excess of 1500 bar (1.5 x 10 ⁸ Pa). To achieve these pressures the work that must be done on the fuel also increases the temperature of the fuel. These high pressures and temperatures can cause degradation of the fuel. Furthermore, the timing, quantity and control of fuel injection has become increasingly precise. This precise fuel metering must be maintained to achieve optimal performance.

Diesel engines having high pressure fuel systems can include but are not limited to heavy duty diesel engines and smaller passenger car type diesel engines. Heavy duty diesel engines can include very powerful engines such as the MTU series 4000 diesel having 20 cylinder variants designed primarily for ships and power generation with power output up to 4300 kW or engines such as the Renault dXi 7 having 6 cylinders and a power output around 240kW. A typical passenger car diesel engine is the Peugeot DW10 having 4 cylinders and power output of 100 kW or less depending on the variant.

A common problem with diesel engines is fouling of the injector, particularly the injector body, and the injector nozzle. Fouling may also occur in the fuel filter. Injector nozzle fouling occurs when the nozzle becomes blocked with deposits from the diesel fuel. Fouling of fuel filters may be related to the recirculation of fuel back to the fuel tank. Deposits increase with degradation of the fuel. Deposits may take the form of carbonaceous coke-like residues, lacquers or sticky or gum-like residues. Diesel fuels become more and more unstable the more they are heated, particularly if heated under pressure. Thus diesel engines having high pressure fuel systems may cause increased fuel degradation. In recent years the need to reduce emissions has led to the continual redesign of injection systems to help meet lower targets. This has led to increasingly complex injectors and lower tolerance to deposits. The problem of injector fouling may occur when using any type of diesel fuels. However, some fuels may be particularly prone to cause fouling or fouling may occur more quickly when these fuels are used. For example, fuels containing biodiesel and those containing metallic species may lead to increased deposits.

When injectors become blocked or partially blocked, the delivery of fuel is less efficient and there is poor mixing of the fuel with the air. Over time this leads to a loss in power of the engine and increased exhaust emissions and poor fuel economy.

Deposits are known to occur in the spray channels of the injector, leading to reduced flow and power loss. As the size of the injector nozzle hole is reduced, the relative impact of deposit build up becomes more significant. Deposits are also known to occur at the injector tip. Here they affect the fuel spray pattern and cause less effective combustion and associated higher emissions and increased fuel consumption.

In addition to these “external” injector deposits in the nozzle hole and at the injector tip which lead to reduced flow and power loss, deposits may occur within the injector body causing further problems. These deposits may be referred to as internal diesel injector deposits (or IDIDs). IDIDs may occur further up inside the injector on the critical moving parts. They can hinder the movement of these parts affecting the timing and quantity of fuel injection. Since modern diesel engines operate under very precise conditions these deposits can have a significant impact on performance.

IDIDs cause a number of problems, including power loss and reduced fuel economy due to less than optimal fuel metering and combustion. Initially the user may experience cold start problems and/or rough engine running. These deposits can lead to more serious injector sticking. This occurs when the deposits stop parts of the injector from moving and thus the injector stops working. When several or all of the injectors stick the engine may fail completely.

IDIDs are recognised as a serious problem by those working in the field and a new engine test has been developed by the industry based organisation, the Coordinating European Council (CEC). The IDID DW10C test was developed to be able to discriminate between a fuel that produces no measurable deposits and one which produces deposits that cause startability issues considered unacceptable. The objective of the test is to discriminate between fuels that differ in their ability to produce IDIDs in direct injection common rail diesel engines. The test is still under development. However a suitable merit system which may be used to evaluate fuels in this specification is described in example 15. The present inventors have studied these internal diesel injector deposits and have found that they contain a number of components. However they believe that the presence of lacquers and/or carboxylate residues lead to injector sticking.

Lacquers are varnish-like deposits which are insoluble in fuel and common organic solvents. Some occurrences of lacquers have been found by analysis to contain amide functionality and it has been suggested that they form due to the presence of low molecular weight amide containing species in the fuel.

Carboxylate residues may be present from a number of sources. By carboxylate residues we mean to refer to salts of carboxylic acids. These may be short chain carboxylic acids but more commonly long chain fatty acid residues are present. The carboxylic residues may be present as ammonium and/or metal salts. Both carboxylic acids and metals may be present in diesel fuel from a number of sources. Carboxylic acids are commonly added into fuel as lubricity additives and/or corrosion inhibitors; they may occur due to oxidation of the fuel and may form during the combustion process; residual fatty acids may be present in the fatty acid methyl esters included as biodiesel; and they may also be present as byproducts in other additives. Derivatives of fatty acids may also be present and these may react or decompose to form carboxylic acids.

Various metals may be present in fuel compositions. This may be due to contamination of the fuel during manufacture, storage, transport or use or due to contamination of fuel additives. Metal species may also be added to fuels deliberately. For example transition metals are sometimes added as fuel borne catalysts to improve the performance of diesel particulate filters.

The present inventors believe that one of the causes of injector sticking occurs when metal or ammonium species react with carboxylic acid species in the fuel. One example of injector sticking has arisen due to sodium contamination of the fuel. Sodium contamination may occur for a number of reasons. For example sodium hydroxide may be used in a washing step in the hydrodesulfurisation process and could lead to contamination. Sodium may also be present due to the use of sodium-containing corrosion inhibitors in pipelines. Another example can arise from the presence of calcium from for example interaction with or contamination with a lubricant or from calcium chloride used in salt drying processes in refineries. Other metal contamination may occur for example during transportation due to water bottoms.

Metal contamination of diesel fuel and the resultant formation of carboxylate salts is believed to be a major cause of injector sticking. The formation of lacquers is yet another major cause of injector sticking. One approach to combatting IDIDs and injector sticking resulting from carboxylate salts is to try to eliminate the source of metal contamination and/or carboxylic acids or to try to ensure that particularly problematic carboxylic acids are eliminated. This has not been entirely successful, and there is a need for additives to provide control of IDIDs.

It is an aim of the present invention to provide compositions, methods and uses which improve the performance of a diesel engine, especially a diesel engine having a high pressure fuel system. This may be achieved by combatting internal diesel injector deposits (IDIDs) and/or “external injector deposits” and/or fuel filter deposits. It is a further aim of the present invention to provide compositions, methods and uses which improve the performance of a traditional diesel engine, for example by combatting deposits. By combatting deposits we mean to include preventing or reducing the formation of deposits and/or by reducing or removing existing deposits.

Deposit control additives are often included in fuel to combat deposits, for example in the injector nozzle or at the injector tip. Additives are also used to control deposits on vehicle fuel filters. However additives which have been found to be useful to control “external deposits” and fuel filter deposits have not, for example, always been found to be effective at controlling IDIDs. A challenge for the additive formulator is to provide more effective detergents.

According to a first aspect of the invention there is provided a diesel fuel composition comprising (a) a quaternary ammonium salt additive; and (b) one or more nitrogen-free detergents; wherein the quaternary ammonium salt additive comprises the quaternised reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group; wherein each molecule of the hydrocarbyl substituted succinic acid derived acylating agent includes on average at least 1 .2 succinic acid moieties.

According to a second aspect of the present invention there is provided a method of improving the performance of a diesel engine, the method comprising combusting in the engine a diesel fuel composition comprising (a) a quaternary ammonium salt additive; and (b) one or more nitrogen-free detergents; wherein the quaternary ammonium salt additive comprises the quaternised reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group; wherein each molecule of the hydrocarbyl substituted succinic acid derived acylating agent includes on average at least 1 .2 succinic acid moieties.

According to a third aspect of the present invention there is provided the use of a combination of (a) a quaternary ammonium salt additive and (b) one or more nitrogen-free detergents to improve the performance of a diesel engine; wherein the quaternary ammonium salt additive comprises the quaternised reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group; wherein each molecule of the hydrocarbyl substituted succinic acid derived acylating agent includes on average at least 1 .2 succinic acid moieties.

Preferred features of the first, second and third aspects of the present invention will now be described.

The present invention involves the use of a combination of additives. Additive (a) is a quaternary ammonium salt which is the quaternised reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group.

For the avoidance of doubt reference to the quaternised reaction product is meant to refer to a reaction product which comprises the tertiary amine which has then been quaternised to form a quaternary ammonium group. The quaternary ammonium salt additive is formed by reacting a quaternising agent with the reaction product of a hydrocarbyl substituted succinic acid derived acylating agent and a compound able to react with said acylating agent and which includes a tertiary amine group.

As used herein, the term "hydrocarbyl substituent" or "hydrocarbyl group" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:

(i) hydrocarbon groups, that is, aliphatic (which may be saturated or unsaturated, linear or branched, e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic (including aliphatic- and alicyclic-substituted aromatic) substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring);

(ii) substituted hydrocarbon groups, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent (e.g., halo (e.g. chloro, fluoro or bromo), hydroxy, alkoxy (e.g. Ci to C4 alkoxy), keto, acyl, cyano, mercapto, amino, amido, nitro, nitroso, sulfoxy, nitryl and carboxy);

(iii) hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms. Heteroatoms include sulphur, oxygen, nitrogen, and encompass substituents as pyridyl, furyl, thienyl and imidazolyl. In general, no more than two, preferably no more than one, non-hydrocarbon substituent will be present for every ten carbon atoms in the hydrocarbyl group; typically, there will be no non-hydrocarbon substituents in the hydrocarbyl group.

Suitable hydrocarbyl substituted succinic acid derived acylating agents and means of preparing them are well known in the art. For example a common method of preparing a hydrocarbyl substituted succinic acylating agent is by the reaction of maleic anhydride with an olefin using a chlorination route or a thermal route (the so-called “ene” reaction).

Illustrative of hydrocarbyl substituent based groups include n-octyl, n-decyl, n-dodecyl, tetrapropenyl, n-octadecyl, oleyl, chloroctadecyl, triicontanyl, etc. The hydrocarbyl based substituents may be made from homo- or interpolymers (e.g. copolymers, terpolymers) of mono- and di-olefins having 2 to 10 carbon atoms, for example ethylene, propylene, butane-1 , isobutene, butadiene, isoprene, 1 -hexene, 1 -octene, etc. Preferably these olefins are 1- monoolefins. Alternatively the substituent may be made from other sources, for example monomeric high molecular weight alkenes (e.g. 1-tetra-contene), aliphatic petroleum fractions, for example paraffin waxes and cracked analogs thereof, white oils, synthetic alkenes for example produced by the Ziegler-Natta process (e.g. poly(ethylene) greases) and other sources known to those skilled in the art. Any unsaturation in the substituent may if desired be reduced or eliminated by hydrogenation according to procedures known in the art.

Preferably the hydrocarbyl substituents are predominantly saturated, that is, they contain no more than one carbon-to-carbon unsaturated bond for every ten carbon-to-carbon single bonds present. Most preferably they contain no more than one carbon-to-carbon non-aromatic unsaturated bond for every 50 carbon-to-carbon bonds present.

The hydrocarbyl substituent of the succinic acid derived acylating agent preferably comprises at least 10, more preferably at least 12, for example at least 30 or at least 40 carbon atoms. It may comprise up to about 200 carbon atoms. Preferably the hydrocarbyl substituent of the acylating agent has a number average molecular weight (Mn) of between 170 to 2800, for example from 250 to 1500, preferably from 500 to 1500 and more preferably 500 to 1100. An Mn of 700 to 1300 is especially preferred.

The hydrocarbyl substituted succinic acid derived acylating agent may comprise a mixture of compounds. For example a mixture of compounds having different hydrocarbyl substituents may be used. Preferred hydrocarbyl-based substituents are polyisobutenes. Such compounds are known to the person skilled in the art.

Preferred hydrocarbyl substituted succinic acid derived acylating agents are polyisobutenyl succinic anhydrides. These compounds are commonly referred to as “PIBSAs” and are known to the person skilled in the art.

Conventional polyisobutenes and so-called "highly-reactive" polyisobutenes are suitable for use in the invention. Highly reactive polyisobutenes in this context are defined as polyisobutenes wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type as described in EP0565285. Particularly preferred polyisobutenes are those having more than 80 mol% and up to 100 mol% of terminal vinylidene groups such as those described in US7291758. Preferred polyisobutenes have preferred molecular weight ranges as described above for hydrocarbyl substituents generally.

Other preferred hydrocarbyl groups include those having an internal olefin for example as described in the applicant’s published application W02007/015080.

An internal olefin as used herein means any olefin containing predominantly a non-alpha double bond, that is a beta or higher olefin. Preferably such materials are substantially completely beta or higher olefins, for example containing less than 10% by weight alpha olefin, more preferably less than 5% by weight or less than 2% by weight. Typical internal olefins include Neodene 1518IO available from Shell.

Internal olefins are sometimes known as isomerised olefins and can be prepared from alpha olefins by a process of isomerisation known in the art, or are available from other sources. The fact that they are also known as internal olefins reflects that they do not necessarily have to be prepared by isomerisation.

Preferred hydrocarbyl substituted succinic acid derived acylating agents for use in preparing additive (a) of the present invention are polyisobutenyl substituted succinic anhydrides or PIBSAs. Especially preferred PIBSAs are those having a PIB molecular weight (Mn) of from 300 to 2800, preferably from 450 to 2300, more preferably from 500 to 1300.

The hydrocarbyl substituted succinic acid derived acylating agent is suitably prepared by reacting maleic anhydride with an alkene, for example a polyisobutene. The product obtained (such as a PIBSA) still includes a double bond. The maleic anhydride is present in the resultant molecule as a succinic acid moiety. The monomaleated PIBSA may have the structure (A) or (B):

The double bond in the monomaleated product can react with a further molecule of maleic anhydride to form a bismaleated PIBSA having the structure (C) or (D):

Thus it is possible to provide a hydrocarbyl group which is substituted with more than one succinic acid moiety. In such embodiments each molecule of the hydrocarbyl substituted succinic acid derived acylating agent includes more than one succinic acid moiety.

The skilled person will appreciate that the additives used in the invention typically comprise mixtures of compounds and will be prepared from a mixture of monomaleated and bismaleated PIBSAs. The PIBSAs may be defined in terms of their level of bismaleation.

One way in which this may be determined is by calculating the average number of succinic acid moieties per molecule of acylating agent.

A monomaleated PIBSA has one succinic acid moiety per module.

A bismaleated PIBSA has two succinic acid moieties per molecule. A mixture comprising monomaleated PIBSA and bismaleated PIBSA in a 1 :1 molar ratio would comprise an average of 1 .5 succinic acid moieties per molecule of PIBSA.

The average number of succinic acid moieties per molecule of acylating agent is sometimes referred to in the art as “P value”.

One way in which the P value can be determined empirically is described in relation to the examples.

The present invention relates in particular to the use of quaternary ammonium salts derived from hydrocarbyl substituted acylating agents which include an average of at least 1 .2 succinic acid moieties per molecule.

As the skilled person will appreciate, a single molecule cannot have 1 .2 succinic acid moieties. What is meant by at least 1 .2 succinic acid moieties is the mean number of succinic acid moieties per molecule of acylating agent as the sum of all the succinic acid moieties present in a sample divided by the total number of molecules of acylating agent having one or more succinic acid moieties present in the sample.

The present inventors have surprisingly found that when the quaternary ammonium salt additive is prepared from a hydrocarbyl substituted succinic acid derived acylating agent comprising on average at least 1.2 succinic acid moieties per molecule improved deposit control in diesel engines is seen when used in combination with a further nitrogen-free detergent.

Preferably the hydrocarbyl substituted succinic acid derived acylating agent comprises on average at least 1 .21 succinic acid moieties per molecule, more preferably at least 1 .22 succinic acid moieties per molecule.

In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .23 or at least 1 .24 succinic acid moieties per molecule.

In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .25, at least 1 .26 or at least 1 .27 succinic acid moieties per molecule.

In some embodiments the hydrocarbyl substituted succinic acid derived acylating agent may comprise at least 1 .28, at least 1 .29 or at least 1 .30 succinic acid moieties per molecule.

By succinic acid moiety we mean to include residues of succinic acid present in diacid or anhydride form. The hydrocarbyl substituted succinic acid derived acylating agent is reacted with a compound able to react with said acylating agent and which includes a tertiary amine group. The tertiary amine group is quaternised to provide the quaternary ammonium salt additive.

Examples of suitable compounds able to react with the hydrocarbyl substituted succinic acid derived acylating agent and which include a tertiary amine group can include but are not limited to: N,N-dimethylaminopropylamine, N,N-diethylaminopropylamine, N,N-dimethylamino ethylamine. The nitrogen or oxygen containing compounds capable of condensing with the acylating agent and further having a tertiary amino group can further include amino alkyl substituted heterocyclic compounds such as 1-(3-aminopropyl)imidazole and 4-(3- aminopropyl)morpholine, 1-(2-aminoethyl)piperidine, 3,3-diamino-N-methyldipropylamine, and 3'3-aminobis(N,N-dimethylpropylamine). Other types of nitrogen or oxygen containing compounds capable of condensing with the acylating agent and having a tertiary amino group include alkanolamines including but not limited to triethanolamine, trimethanolamine, N,N- dimethylaminopropanol, N,N-dimethylaminoethanol, N,N-diethylaminopropanol, N,N- diethylaminoethanol, N,N-diethylaminobutanol, N,N,N-tris(hydroxyethyl)amine, N,N,N- tris(hydroxymethyl)amine, N,N,N-tris(aminoethyl)amine, N,N-dibutylaminopropylamine and N,N,N'-trimethyl-N'-hydroxyethyl-bisaminoethylether; N,N-bis(3-dimethylaminopropyl)-N- isopropanolamine ; N-(3-dimethylaminopropyl)-N,N-diisopropanolamine; N'-(3- (dimethylamino)propyl)-N,N-dimethyl 1 ,3-propanediamine; 2-(2-dimethylaminoethoxy)ethanol, N,N,N'-trimethylaminoethylethanolamine and 3-(2-(dimethylamino)ethoxy) propylamine.

Preferably the compound able to react with hydrocarbyl substituted succinic acid derived acylating agent and which includes a tertiary amine group is an amine of formula (I) or (II): wherein R ² and R ³ are the same or different alkyl, alkenyl, aryl, alkaryl or aralkyl groups having from 1 to 22 carbon atoms; X is a bond or an optionally substituted alkylene group having from 1 to 20 carbon atoms; n is from 0 to 20; m is from 1 to 5; and R ⁴ is hydrogen or a Ci to C22 alkyl group. When a compound of formula (I) is used, R ⁴ is preferably hydrogen or a Ci to C alkyl group, preferably a Ci to Cw alkyl group, more preferably a Ci to Ce alkyl group. When R ⁴ is alkyl it may be straight chained or branched. It may be substituted for example with a hydroxy or alkoxy substituent. Preferably R ⁴ is not a substituted alkyl group. More preferably R ⁴ is selected from hydrogen, methyl, ethyl, propyl, butyl and isomers thereof. Most preferably R ⁴ is hydrogen.

When a compound of formula (II) is used, m is preferably 2 or 3, most preferably 2; n is preferably from 0 to 15, preferably 0 to 10, more preferably from 0 to 5. Most preferably n is 0 and the compound of formula (II) is an alcohol.

Preferably the hydrocarbyl substituted acylating agent is reacted with a diamine compound of formula (I).

R ² and R ³ are the same or different alkyl, alkenyl, aryl, alkaryl or aralkyl groups having from 1 to 22 carbon atoms. In some embodiments R ² and R ³ may be joined together to form a ring structure, for example a piperidine, imidazole or morpholine moiety. Thus R ² and R ³ may together form an aromatic and/or heterocyclic moiety. R ² and R ³ may be branched alkyl or alkenyl groups. Each may be substituted, for example with a hydroxy or alkoxy substituent.

Preferably each of R ² and R ³ is independently a Ci to Cw alkyl group, preferably a Ci to Cw alkyl group. R ² and R ³ may independently be methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, or an isomer of any of these. Preferably R ² and R ³ is each independently Ci to C4 alkyl. Preferably R ² is methyl. Preferably R ³ is methyl.

X is a bond or an optionally substituted alkylene group having from 1 to 20 carbon atoms. In preferred embodiments when X is an alkylene group this group may be straight chained or branched. The alkylene group may include a cyclic structure therein. It may be optionally substituted, for example with a hydroxy or alkoxy substituent. In some embodiments X may include a heteroatom within the alkylene chain, for example X may include an ether functionality.

X is preferably an alkylene group having 1 to 16 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, for example 2 to 6 carbon atoms or 2 to 5 carbon atoms. In some preferred embodiments X is an unsubstituted alkylene group. Most preferably X is an ethylene, propylene or butylene group, especially a propylene group.

Examples of compounds of formula (I) suitable for use herein include 1 -aminopiperidine, 1-(2- aminoethyl)piperidine, 1- (3-aminopropyl)-2-pipecoline, 1-methyl-(4-methylamino)piperidine, 4- (1 -py rro lid iny I) pi pe rid i n e , 1 -(2-aminoethyl)pyrrolidine, 2-(2-aminoethyl)-1 - methylpyrrolidine, N,N-diethylethylenediamine, N,N-dimethylethylenediamine, N,N-dibutylethylenediamine, N,N- diethyl-l,3-diaminopropane, N,N-dimethyl-1 ,3-diaminopropane, N,N,N'- trimethylethylenediamine, N,N-dimethyl-N'-ethylethylenediamine, N,N-diethyl-N'- methylethylenediamine, N,N,N'- triethylethylenediamine, 3-dimethylaminopropylamine, 3- diethylaminopropylamine, 3-dibutylaminopropylamine, N,N,N'-trimethyl- 1 ,3- propanediamine, N,N,2,2-tetramethyl-l,3-propanediamine, 2-amino-5-diethylaminopentane, N,N,N',N'- tetraethyldiethylenetriamine, 3,3'-diamino-N-methyldipropylamine, 3,3'-iminobis(N,N- dimethylpropylamine), 1-(3-aminopropyl)imidazole and 4-(3-aminopropyl)morpholine, 1-(2- aminoethyl)piperidine, 3,3-diamino-N-methyldipropylamine, 3,3-aminobis(N,N- dimethylpropylamine), 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof.

In some preferred embodiments the compound of formula (I) is selected from from N,N-dimethyl- 1 ,3-diaminopropane, N,N-diethyl-1 ,3- diaminopropane, N,N-dimethylethylenediamine, N,N- diethylethylenediamine, N,N-dibutylethylenediamine, 3-(2-(dimethylamino)ethoxy) propylamine, or combinations thereof.

Examples of compounds of formula (II) suitable for use herein include alkanolamines including but not limited to triethanolamine, N,N-dimethylaminopropanol, N,N-diethylaminopropanol, N,N- diethylaminobutanol, triisopropanolamine, 1-[2-hydroxyethyl]piperidine, 2-[2- (dimethylamine)ethoxy]-ethanol, N-ethyldiethanolamine, N-methyldiethanolamine, N- butyldiethanolamine, N,N-diethylaminoethanol, N,N-dimethyl amino- ethanol, 2-dimethylamino- 2-methyl-1 -propanol, N,N,N'-trimethyl-N'-hydroxyethyl-bisaminoethylether; N,N-bis(3- dimethylaminopropyl)-N-isopropanolamine ; N-(3-dimethylaminopropyl)-N,N- diisopropanolamine; N'-(3-(dimethylamino)propyl)-N,N-dimethyl 1 ,3-propanediamine; 2-(2- dimethylaminoethoxy)ethanol, and N,N,N'-trimethylaminoethylethanolamine.

In some preferred embodiments the compound of formula (B2) is selected from Triisopropanolamine, 1-[2-hydroxyethyl]piperidine, 2-[2-(dimethylamine)ethoxy]-ethanol, N- ethyldiethanolamine, N-methyldiethanolamine, N-butyldiethanolamine, N,N- diethylaminoethanol, N,N-dimethylaminoethanol, 2-dimethylamino-2-methyl-1 -propanol, or combinations thereof.

An especially preferred compound of formula (I) is N,N-dimethyl-1 ,3-diaminopropane (dimethylaminopropylamine) .

When a compound of formula (B2) is reacted with a succinic acylating agent the resulting product is a succinic ester. When a succinic acylating agent is reacted with a compound of formula (B1) in which R ⁴ is hydrogen the resulting product may be a succinimide or a succinamide. When a succinic acylating agent is reacted with a compound of formula (B1) in which R ⁴ is not hydrogen the resulting product is an amide. To form the quaternary ammonium salt additive (a) the hydrocarbyl substituted succinic acid derived acylating agent is reacted with a compound able to react with said acylating agent and which includes a tertiary amine group. This reaction product is then quaternised by reaction with a quaternising agent.

The reaction product of the acylating agent and compound which includes a tertiary amine group is preferably reacted with at least one molar equivalent of quaternising agent per mole of tertiary amine group present in the reaction product.

Preferably the reaction product of the acylating agent and compound which includes a tertiary amine group is reacted with more than one molar equivalent of quaternising agent per mole of tertiary amine group present in the reaction product, preferably at least 1 .2 molar equivalents of quaternising agent per mole of tertiary amine group, more preferably at lleast 1.5 molar equivalents of quaternising agent, suitably at least 1 .7 molar equivalents of quaternising agent, for example at least 1 .9 molar equivalents of quaternising agent.

Preferably the reaction product of the acylating agent and compound which includes a tertiary amine group is reacted with two or more molar equivalents of quaternising agent per mole of tertiary amine group present in the reaction product, preferably at least 2.1 molar equivalents of quaternising agent.

In some embodiments the reaction product of the acylating agent and compound which includes a tertiary amine group is reacted with more than 2.2 molar equivalents of quaternising agent per mole of tertiary amine group present in the reaction product, for example from 2.3 to 4 molar equivalents, from 2.3 to 3 molar equivalents, or from 2.3 to 2.7 or from 2.5 to 3 molar equivalents.

Any suitable quaternising agent may be used. The quaternising agent may suitably be selected from esters and non-esters.

Suitable quaternising agents include esters of a carboxylic acid, dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, alkyl nitrites, alkyl nitrates, hydroxides, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

In some preferred embodiments, quaternising agents used to form the quaternary ammonium salt additives of the present invention are esters. Preferred ester quaternising agents are compounds of formula (III): in which R is an optionally substituted alkyl, alkenyl, aryl or alkylaryl group and R1 is a C1 to C22 alkyl, aryl or alkylaryl group. The compound of formula (III) is suitably an ester of a carboxylic acid capable of reacting with a tertiary amine to form a quaternary ammonium salt.

Suitable quaternising agents include esters of carboxylic acids having a pKa of 3.5 or less.

The compound of formula (III) is preferably an ester of a carboxylic acid selected from a substituted aromatic carboxylic acid, an a-hydroxycarboxylic acid and a polycarboxylic acid.

In some preferred embodiments the compound of formula (III) is an ester of a substituted aromatic carboxylic acid and thus R is a substituted aryl group.

Preferably R is a substituted aryl group having 6 to 10 carbon atoms, preferably a phenyl or naphthyl group, most preferably a phenyl group. R is suitably substituted with one or more groups selected from carboalkoxy, nitro, cyano, hydroxy, SR5 or NR5R6. Each of R5 and R6 may be hydrogen or optionally substituted alkyl, alkenyl, aryl or carboalkoxy groups. Preferably each of R5 and R6 is hydrogen or an optionally substituted C1 to C22 alkyl group, preferably hydrogen or a C1 to C16 alkyl group, preferably hydrogen or a C1 to C10 alkyl group, more preferably hydrogen or a C1 to C4 alkyl group. Preferably R5 is hydrogen and R6 is hydrogen or a C1 to C4 alkyl group. Most preferably R5 and R6 are both hydrogen. Preferably R is an aryl group substituted with one or more groups selected from hydroxyl, carboalkoxy, nitro, cyano and NH2. R may be a poly-substituted aryl group, for example trihydroxyphenyl. In some embodiments R may be a hydrocarbyl substituted aryl group, for example an alkyl substituted aryl group. In some embodiments R may be an aryl group substituted with a hydroxy group and a hydrocarbyl group, such as an alkyl group, for example as described in EP2631283.

Preferably R is a mono-substituted aryl group. Preferably R is an ortho substituted aryl group. Suitably R is substituted with a group selected from OH, NH2, NO2 or COOMe. Preferably R is substituted with an OH or NH2 group. Suitably R is a hydroxy substituted aryl group. Most preferably R is a 2-hydroxyphenyl group. Preferably R ¹ is an alkyl, aralkyl or alkaryl group. R ¹ may be a C1 to C16 alkyl group, preferably a C1 to C10 alkyl group, suitably a C1 to C8 alkyl group. R ¹ may be C7 to C16 aralkyl or alkaryl group, preferably a C7 to C10 aralkyl or alkaryl group. R ¹ may be methyl, ethyl, propyl, butyl, pentyl, benzyl or an isomer thereof. Preferably R ¹ is benzyl or methyl. Most preferably R ¹ is methyl.

Especially preferred compounds of formula (III) are lower alkyl esters of salicylic acid such as methyl salicylate, ethyl salicylate, n and i propyl salicylate, and butyl salicylate, preferably methyl salicylate.

In some embodiments the compound of formula (III) is an ester of an a-hydroxycarboxylic acid. In such embodiments the compound has the structure: wherein R7 and R8 are the same or different and each is selected from hydrogen, alkyl, alkenyl, aralkyl or aryl. Compounds of this type suitable for use herein are described in EP 1254889.

Examples of compounds of formula (III) in which RCOO is the residue of an a-hydroxycarboxylic acid include methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2- hydroxyisobutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2-hydroxy-2-methylbutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of 2-hydroxy-2-ethylbutyric acid; methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, benzyl-, phenyl-, and allyl esters of lactic acid; and methyl-, ethyl-, propyl-, butyl-, pentyl- , hexyl-, allyl-, benzyl-, and phenyl esters of glycolic acid. Of the above, a preferred compound is methyl 2-hydroxyisobutyrate.

In some embodiments the compound of formula (III) is an ester of a polycarboxylic acid. In this definition we mean to include dicarboxylic acids and carboxylic acids having more than 2 acidic moieties. In such embodiments RCOO is preferably present in the form of an ester, that is the one or more further acid groups present in the group R are in esterified form. However embodiments in which not all acid groups are esterified are within the invention. Mixed esters of polycarboxylic acids may also be used. Preferred esters are C1 to C4 alkyl esters.

The ester quaternising agent may be selected from the diester of oxalic acid, the diester of phthalic acid, the diester of maleic acid, the diester of malonic acid or the diester of citric acid. One especially preferred compound of formula (III) is dimethyl oxalate. In preferred embodiments the compound of formula (III) is an ester of a carboxylic acid having a pKa of less than 3.5. In such embodiments in which the compound includes more than one acid group, we mean to refer to the first dissociation constant.

The ester quaternising agent may be selected from an ester of a carboxylic acid selected from one or more of oxalic acid, phthalic acid, salicylic acid, maleic acid, malonic acid, citric acid, nitrobenzoic acid, aminobenzoic acid and 2, 4, 6-trihydroxybenzoic acid.

Preferred ester quaternising agents include dimethyl oxalate, methyl 2-nitrobenzoate and methyl salicylate.

In some preferred embodiments, quaternising agents used to form the quaternary ammonium salt additives of the present invention are esters selected from dimethyl oxalate, methyl 2- nitrobenzoate and methyl salicylate, preferably dimethyl oxalate and methyl salicylate.

Suitable non-ester quaternising agents include dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, alkyl nitrites, alkyl nitrates, hydroxides, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

In some embodiments the quaternary ammonium salt may be prepared from, for example, an alkyl or benzyl halide (especially a chloride) and then subjected to an ion exchange reaction to provide a different anion as part of the quaternary ammonium salt. Such a method may be suitable to prepare quaternary ammonium hydroxides, alkoxides, nitrites or nitrates.

Preferred non-ester quaternising agents include dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl susbsituted epoxides in combination with an acid, alkyl halides, alkyl sulfonates, sulfones, hydrocarbyl substituted phosphates, hydrocarbyl substituted borates, N-oxides, chloroacetic acid or salts thereof, or mixtures thereof.

Suitable dialkyl sulfates for use herein as quaternising agents include those including alkyl groups having 1 to 10, preferably 1 to 4 carbons atoms in the alkyl chain. A preferred compound is dimethyl sulfate.

Suitable benzyl halides include chlorides, bromides and iodides. The phenyl group may be optionally substituted, for example with one or more alkyl or alkenyl groups, especially when the chlorides are used. A preferred compound is benzyl bromide. Suitable hydrocarbyl substituted carbonates may include two hydrocarbyl groups, which may be the same or different. Each hydrocarbyl group may contain from 1 to 50 carbon atoms, preferably from 1 to 20 carbon atoms, more preferably from 1 to 10 carbon atoms, suitably from 1 to 5 carbon atoms. Preferably the or each hydrocarbyl group is an alkyl group. Preferred compounds of this type include diethyl carbonate and dimethyl carbonate.

Suitable hydrocarbyl substituted epoxides have the formula: , 2, R3 and R4 is independently hydrogen or a hydrocarbyl group having 1 to 50 carbon atoms. Examples of suitable epoxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide and stilbene oxide. The hydrocarbyl epoxides are used as quaternising agents in combination with an acid.

The hydrocarbyl substituted succinic acylating agent includes two acyl groups. In some embodiments only one of these groups reacts with the compound of formula (I) or formula (II) to form a compound having an ester or an amide functional group and a free carboxylic acid. In these embodiments if an epoxide is used as the quaternising agent, a separate acid does not need to be added. However in other embodiments an acid for example acetic acid may be used.

Especially preferred epoxide quaternising agents are propylene oxide and styrene oxide, optionally in combination with an additional acid.

Suitable alkyl halides for use herein include chlorides, bromides and iodides.

Suitable alkyl sulfonates include those having 1 to 20, preferably 1 to 10, more preferably 1 to 4 carbon atoms.

Suitable sulfones include propane sulfone and butane sulfone.

Suitable hydrocarbyl substituted phosphates include monoalkyl phosphates, dialkyl phosphates, trialkyl phosphates and O,O-dialkyl dithiophospates. Preferred alkyl groups have 1 to 12 carbon atoms.

Suitable hydrocarbyl substituted borate groups include alkyl borates having 1 to 12 carbon atoms. Preferred alkyl nitrites and alkyl nitrates have 1 to 12 carbon atoms.

Preferably the non-ester quaternising agent is selected from dialkyl sulfates, benzyl halides, hydrocarbyl substituted carbonates, hydrocarbyl substituted epoxides optionally in combination with an additional acid, chloroacetic acid or a salt thereof, and mixtures thereof.

Especially preferred non-ester quaternising agents for use herein are hydrocarbyl substituted epoxides in combination with an acid. These may include embodiments in which a separate acid is provided or embodiments in which the acid is provided by the tertiary amine compound that is being quaternised. Preferably the acid is provided by the tertiary amine molecule that is being quaternised.

Preferred quaternising agents for use herein include dimethyl oxalate, methyl 2-nitrobenzoate, methyl salicylate, chloroacetic acid or a salt thereof, and styrene oxide or propylene oxide optionally in combination with an additional acid.

In some embodiments mixtures of two or more quaternising agents may be used.

To form some preferred quaternary ammonium salt additives of the present invention the compound of formula (III) is reacted with a compound formed by the reaction of a hydrocarbyl substituted succinic acid acylating agent and an amine of formula (I) or (II).

The compounds of formula (I) or formula (II) are as described above.

The amine of formula (I) or (II) is reacted with a hydrocarbyl substituted succinic acid derived acylating agent such as a succinic acid or succinic anhydride.

Suitably approximately one equivalent of amine is added per succinic acid moiety present in the acylating agent. The ratio of amine used will thus typically depend on the average number of succinic acid moieties present in each molecule of the acylating agent.

An especially preferred quaternary ammonium salt for use herein is formed by reacting methyl salicylate or dimethyl oxalate with the reaction product of a polyisobutylene-substituted succinic anhydride having a PIB molecular weight of 700 to 1300 and dimethylaminopropylamine; wherein the polyisobutylene-substituted succinic anhydride includes on average at least 1 .2 succinic acid moieties per molecule. US2012/0010112 describes an acid-free process for preparing quaternized nitrogen compounds, wherein a) a compound comprising at least one oxygen- or nitrogen-containing group reactive with the anhydride and additionally comprising at least one quaternizable amino group is added onto a polycarboxylic anhydride compound, and b) the product from stage a) is quaternized using an epoxide quaternizing agent without an additional acid. Such methods could be used to prepare the quaternary ammonium salt additives of the present invention.

The present invention also involves the use of (b) a nitrogen-free detergent. Any suitable nitrogen-free detergent may be used.

Preferred nitrogen-free detergents for use herein are copolymeric nitrogen containing detergents and polycarboxylic acids and/or esters thereof.

In some embodiments the nitrogen-free detergent is a copolymeric nitrogen-free detergent.

Preferred copolymeric nitrogen-free detergents comprise a-olefin derived units and maleic anhydride derived units.

By a-olefin derived units we mean to refer to units of the copolymer derived from a-olefin monomers. By maleic anhydride derived units we mean to refer to units of the polymer derived from maleic anhydride monomers.

To form the copolymeric nitrogen-free detergents the a-olefin and maleic anhydride are preferably reacted in a molar ratio of from 5:1 to 1 :5, preferably from 2:1 to 1 :2, for example about 1 :1.

Preferred a-olefins have from 6 to 36 carbons atoms, preferably from 12 to 30 carbon atoms, more preferably from 20 to 24 carbon atoms. Mixtures of a-olefins may be used. As the skilled person will appreciate, commercial sources of a-olefins often comprise mixtures of compounds.

In some embodiments the copolymeric nitrogen-free detergents may comprise only units derived from a-olefin monomers and units derived from maleic anhydride monomers.

In some embodiments the copolymeric nitrogen-free detergent may further comprise units derived from one or more further monomers. Suitable further monomers which may be included used to prepare the copolymeric nitrogen-free detergents include:

- ethylenically unsaturated mono- or dicarboxylic acids or derivatives thereof;

- further aliphatic or cycloaliphatic olefins having at least 4 carbon atoms;

- vinyl esters; - vinyl ethers;

- (meth)acrylic esters of alcohols, preferably alcohols having at least 5 carbon atoms;

- allyl alcohols or ethers thereof;

- monomers derived from acrylic acid and other monomers derived from methacrylic acid or an ester thereof; and

- monomers derived from other a, p ethylene-saturated acids and esters thereof.

In some embodiments the maleic anhydride derived units present in the copolymeric nitrogen- free detergents may be unhydrolysed. In other embodiments the maleic anhydride derived units may be hydrolysed or partially hydrolysed to provide some or all of the maleic anhydride derived units in diacid form.

In some embodiments the maleic anhydride units may be post-reacted to provide further derivatisation, for example to form esters.

Suitable nitrogen-free copolymeric detergents for use herein include those described in US10150927, US2017/0130153, US2019/0249099, EP3609990, US11085001 ,

WO2018007486 and US2020056109.

In some embodiments the nitrogen-free detergent component (b) comprises a polycarboxylic acid or an ester thereof.

The polycarboxylic acid may be selected from any acid including one or more acid groups.

Preferably the nitrogen-free detergent comprises at least one hydrocarbyl group having at least 5 carbon atoms. In embodiments in which the nitrogen free detergent is an ester the hydrocarbyl group may from part of the acid derived portion of the molecule and/or part of the alcohol derived portion of the molecule.

When the nitrogen-free detergent comprises an ester it may comprise a monoester, diester, a polyester, or mixtures thereof. In preferred embodiments at least one ester group is not esterified.

When the nitrogen-free detergent comprises an ester it may be prepared from a free polycarboxylic and/or an anhydride thereof.

Any suitable polycarboxylic acid may be used. Suitable polycarboxylic acids include optionally substituted succinic acid, phthalic acid, citric acid, itaconic acid, citraconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, isocitric acid, 2-hydroxycitric acid, malic acid, tartaric acid, 2-hydroxyadipic acid, 2-hydroxyglutaric acid, aconitic acid, and anhydrides and/or isomers thereof.

In some embodiments the nitrogen-free detergent comprises the reaction product of an alcohol having at least 5 carbon atoms and a polycarboxylic acid having no more than 5 carbon atoms per carboxylic acid group, or an anhydride thereof or a polycarboxylic acid compound of formula (I): or an anhydride thereof, wherein wherein each of n and m may be 0 or a positive integer.

In such embodiments the polycarboxylic acid or anhydride thereof may be selected from citric acid, itaconic acid, citraconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, isocitric acid, 2-hydroxycitric acid, malic acid, tartaric acid, 2-hydroxyadipic acid, 2-hydroxyglutaric acid, aconitic acid, and anhydrides and/or isomers thereof.

Preferably the alcohol is a compound of formula H-(OR) _n -OR ¹ , wherein R is an optionally substituted alkylene group; R ¹ is an optionally substituted hydrocarbyl group; and n is 0 or a positive integer.

Preferably the alcohol is selected from: alkanols of formula CH3(CH2)xOH wherein x is from 4 to 23, preferably from 9 to 19; branched or cyclic alkyl alcohols in which n is 0; alkenyl alcohols in which n is 0; glycol ethers in which n is not 0.

More preferably the alcohol is selected from an an alcohol of formula R ¹ OH wherein R ¹ is a (preferably branched) alkyl group having 8 to 30 carbon atoms;

- an alcohol of formula R ¹ OH wherein R ¹ is an alkenyl group having 8 to 30 carbon atoms; and

- an alcohol of formula H-(OR) _n -OR ¹ wherein n is from 1 to 24, R is ethylene, propylene or isopropylene, and R ¹ is an unsubstituted alkyl group having 8 to 30, preferably 12 to 24, carbon atoms. For example the alcohol may be selected from hexanol, heptanol, octanol, nonanol, decanol, dodecanol, tetradecanol, cetyl alcohol, stearyl alcohol, 2-ethyl-1 -butanol, 2-ethyl-1 -hexanol, 2- ethyl-1 -heptanol, 2-propylheptanol, 2-ethyl-1 -decanol, 2-hexyl-1 -decanol, 2-octyl-1 -decanol, 2- hexyl-1 -dodecanol, 2-octyl-1 -dodecanol, 2-decyl-1 -tetradecanol, isotridecanol, cyclohexanol, cyclooctanol, benzyl alcohol, citronellol, oleyl alcohol, 9-decen-1-ol, cis-3-hexen-1-ol, trans-2- hexen-1-ol, 5-hexen-1-ol, 6-methyl-5-hepten-2-ol, 1-octen-3-ol, trans-2-octen-1-ol, 10-undecen- 1-ol and compounds of formula CH3(CH2)xO(CH2CH(CH3)O) _y H or an isomer thereof wherein x is from 10 to 15, and y is from 10 to 20.

Suitably the polycarboxylic acid or anhydride thereof and the alcohol are reacted in a molar ratio of from 2:1 to 1 :2.

Further preferred features of such esters are described in W02021/090020 and WO 2021/090021.

In some embodiments the nitrogen-free detergent (b) comprises a polymer of formula (IV): wherein n is at least 4, x may be 0 or a positive integer, y may be 0 or a positive integer and each R is independently hydrogen or an optionally substituted hydrocarbyl group provided that at least 10% of all R groups are not hydrogen.

Such polymers may be prepared by reacting dicarboxylic acid of formula (V): (V) or an anhydride thereof with an alcohol; and polymerising the resultant reaction product.

The dicarboxylic acid or anhydride thereof is suitably selected from itaconic acid, itaconic anhydride, 2-methylene glutaric acid, 2-methylene glutaric anhydride, 2-methylene adipic acid, 2-methylene adipic anhydride and isomers and/or mixtures thereof.

The alcohol may be selected from: short chain alcohols having 1 to 3 carbon atoms; short chain polyols having 2 or 3 carbon atoms; alkanols of formula CH3(CH2)aOH or an isomer thereof wherein a is from 4 to 23; branched or cyclic alkyl alcohols in which m is 0 and R ¹ has 6 to 24 carbon atoms; alkenyl alcohols in which n is 0 and R ¹ has 6 to 24 carbon atoms; glycol ethers in which m is not 0; and mixtures thereof.

In preferred embodiments the alcohol is selected from hexanol, octanol, nonanol, decanol, dodecanol, tetradecanol, cetyl alcohol, stearyl alcohol, 2-ethyl-1 -butanol, 2-ethyl-1 -hexanol, 2- ethyl-1 -heptanol, 2-propylheptanol, 2-ethyl-1 -decanol, 2-hexyl-1 -decanol, 2-octyl-1 -decanol, 2- hexyl-1 -dodecanol, 2-octyl-1 -dodecanol, 2-decyl-1 -tetradecanol, isotridecanol, cyclohexanol, cyclooctanol, and benzyl alcohol.

In some embodiments the additive of formula (IV) is the polymerised reaction product of itaconic acid or an anhydride thereof and a mixture of isopropanol and 2-ethylhexanol.

In some embodiments the additive of formula (IV) is the polymerised reaction product of itaconic acid or an anhydride thereof and 2-ethylhexanol.

In preferred embodiments the additive of formula (IV) is the polymerised reaction product of itaconic acid or an anhydride thereof and 2-ethylhexanol wherein the polymer has a weight average molecular weight of from 2000 to 50000, preferably from 4000 to 30000, more preferably from 5000 to 20000, for example from 6000 to 15000, suitably from 8000 to 12000.

Weight average molecular weight may be measured by gel permeation chromatography. In some embodiments the nitrogen-free detergent (b) comprises an ester compound which is the reaction product of an optionally substituted polycarboxylic acid or an anhydride thereof and an alcohol or formula H-(OR) _n -OR ¹ , wherein R is an optionally substituted alkylene group; R ¹ is hydrogen or an optionally substituted hydrocarbyl group, and n is 0 or a positive integer; wherein n is not 0 when R ¹ is hydrogen.

In such embodiments the optionally substituted polycarboxylic acid or anhydride thereof is a hydrocarbyl substituted succinic acid or a hydrocarbyl substituted succinic anhydride.

Preferably each R is ethylene or propylene, preferably -CH2CH2- or -CH(CH3)CH2-, more preferably -CH(CH3)CH2-; and n is from 1 to 30.

Preferably the polycarboxylic acid or anhydride thereof includes an optionally substituted alkyl or alkenyl group having 6 to 100 carbon atoms.

Preferably the polycarboxylic acid or anhydride is a succinic acid or anhydride thereof having a polyisobutenyl substituent having a number average molecular weight of 100 to 5000.

Preferably the optionally substituted polycarboxylic acid or hydrocarbyl substituted anhydride and alcohol of formula H-(OR) _n -OR ¹ are reacted in a ratio of from 1.5:1 to 1 :1.5.

In some embodiments the optionally substituted polycarboxylic acid or hydrocarbyl substituted anhydride and alcohol of formula H-(OR)n-OR ¹ are reacted in a ratio of from 2.5:1 to 1 .5:1 and R ¹ is hydrogen.

In some embodiments n is 0 and R ¹ is a Ce to C30 alkyl group.

In some embodiments R ¹ is hydrogen.

In some embodiments n is 1 or more and R ¹ is a C4 to C30 alkyl group.

In some embodiments the nitrogen-free detergent additive (b) comprises the reaction product of a succinic acid or anhydride of formula (A3) or (A4): and an alcohol of formula H-(OR) _n -OR ¹ ; wherein R ² is an alkyl or alkenyl group having 6 to 36 carbon atoms or a polyisobutenyl group having a number average molecular weight of from 200 to 1300; wherein the alcohol of formula H-(OR) _n -OR ¹ is selected from:

- ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, trehalose, sorbitol, glycerol, pentaerythritol, trimethylolpropane, 1 ,3-propanediol, 1 ,2-butanediol, 1 ,3-butanediol, 1 ,4- butanediol, 1 ,6-hexanediol, neopentyl glycol and a polyethylene or polypropylene glycol having a number average molecular weight of 300 to 1200; or a C6 to C24 ether thereof; and

- benzyl alcohol, tetradecanol, butanol, 2-butanol, isobutanol, octanol, 2-ethylhexanol, hexanol, cyclohexanol, cyclooctanol, 2-propylheptanol, 2-ethyl-1 -butanol and isopropanol.

The nitrogen-free detergent may comprise the reaction product of a succinic acid or anhydride of formula (A3) or (A4) and an alcohol of formula H-(OR) _n -OR ¹ ; wherein R ² is a polyisobutenyl group having a number average molecular weight of from 700 to 1300; wherein the alcohol of formula H-(OR) _n -OR ¹ is selected from:

- butanediols, tripropylene glycol and polypropylene glycols having a number average molecular weight of from 300 to 600; and

- tetradecanol, butanol and 2-ethylhexanol.

Further preferred features of embodiments in which the nitrogen-free detergent is an ester compound which is the reaction product of an optionally substituted polycarboxylic acid or an anhydride thereof and an alcohol or formula H-(OR) _n -OR ¹ are described in WO2018/178680, WO2018/178678, WO2018/178695, WO2018/178674 and WO2018/178687.

In some especially preferred embodiments, the nitrogen-free detergent (b) comprises a hydrocarbyl substituted succinic acid.

The hydrocarbyl substituent preferably comprises at least 10, more preferably at least 12 carbon atoms. It may comprise up to about 200 carbon atoms. In some embodiments the hydrocarbyl substituent is an alkyl or alkenyl group having 6 to 40 carbon atoms, preferably 10 to 38 carbon atoms, more preferably 16 to 36 carbon atoms, suitably 18 to 26 carbon atoms, for example 20 to 24 carbon atoms.

Preferred hydrocarbyl substituents are polyisobutenes known in the art.

Conventional polyisobutenes and so-called "highly-reactive" polyisobutenes are suitable for use in the invention. Highly reactive polyisobutenes in this context are defined as polyisobutenes wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type as described in EP0565285. Particularly preferred polyisobutenes are those having more than 80 mol% and up to 100 mol% of terminal vinylidene groups such as those described in EP1344785.

In some embodiments the R ² has a molecular weight of from 100 to 5000, preferably from 300 to 4000, suitably from 450 to 2500, for example from 500 to 2000 or from 600 to 1500.

In some embodiments the substituted succinic acid or anhydride thereof may comprise a mixture of compounds including groups R ² of different lengths. In such embodiments any reference to the molecular weight of the group R ² relates to the number average molecular weight for the mixture.

In some embodiments the hydrocarbyl substituent is a polyisobutenyl group, preferably having a number average molecular weight of from 100 to 5000, preferably from 200 to 2400, suitably from 220 to 1400.

In some embodiments the hydrocarbyl substituent is a polyisobutenyl group having a number average molecular weight of from 400 to 700.

In some embodiments the hydrocarbyl substituent is a polyisobutenyl group having a number average molecular weight of from 180 to 400.

In some embodiments the hydrocarbyl substituent is a polyisobutenyl group having a number average molecular weight of from 800 to 1200.

Most preferably the nitrogen-free detergent (b) comprises polyisobutenyl-substituted succinic acid wherein the polyisobutenyl group has a number average molecular weight of from 600 to 1300. Suitable treat rates of (a) the quaternary ammonium salt additive and (b) the one or more nitrogen-free detergents may depend on the type of fuel used and different levels of additive may be needed to achieve different levels of performance.

Suitably the quaternary ammonium salt additive (a) is present in the diesel fuel composition in an amount of from 0.1 to 10000 ppm, preferably from 1 to OOppm, preferably from 5 to 500 ppm, for example 5 to 250 ppm or 5 to 100 ppm.

Suitably the additive (b) is present in the diesel fuel composition in an amount of from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm. Preferably from 5 to 250 ppm, for example 5 to 100 ppm.

Each of additive (a) and additive (b) may be provided as a mixture of compounds. The above amounts refer to the total of all such compounds present in the composition.

For the avoidance of doubt the above amounts refer to the amount of active additive compound present in the composition and ignore any impurities, solvents or diluents which may be present.

The weight ratio of additive (a) to additive (b) is preferably from 1 :10 to 10:1 , preferably from 1 :4 to 4:1 , more preferably from 1 :2 to 2:1 .

In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of (a) a quaternary ammonium salt additive and from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm, of a copolymeric nitrogen-free detergent comprising a-olefin derived units and maleic anhydride derived units.

In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of (a) a quaternary ammonium salt additive and from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of the reaction product of an alcohol having at least 5 carbon atoms and a polycarboxylic acid having no more than 5 carbon atoms per carboxylic acid group, or an anhydride thereof selected from citric acid, itaconic acid, citraconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, isocitric acid, 2-hydroxycitric acid, malic acid, tartaric acid, 2-hydroxyadipic acid, 2-hydroxyglutaric acid, aconitic acid, and anhydrides and/or isomers thereof.

In some embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of (a) a quaternary ammonium salt additive and from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 250 ppm, for example 5 to 100 ppm of an ester compound which is the reaction product of an optionally substituted succinic acid or an anhydride thereof and an alcohol or formula H- (OR)n-OR ¹ , wherein R is an optionally substituted alkylene group; R ¹ is hydrogen or an optionally substituted hydrocarbyl group, and n is 0 or a positive integer; wherein n is not 0 when R ¹ is hydrogen.

In preferred embodiments the diesel fuel composition comprises from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm, for example 5 to 100 ppm of (a) a quaternary ammonium salt additive; from 0.1 to 10000 ppm, preferably from 1 to 1000 ppm, preferably from 5 to 500 ppm, for example 5 to 100 ppm of a hydrocarbyl substituted succinic acid, preferably a polyisobutenyl substituted succinic acid, suitably having a PIB number average molecular weight of 600 to 1300.

The diesel fuel composition used in the present invention may include one or more further additives such as those which are commonly found in diesel fuels. These include, for example, antioxidants, additional dispersants I detergents, metal deactivating compounds, wax antisettling agents, cold flow improvers, cetane improvers, dehazers, stabilisers, demulsifiers, antifoams, corrosion inhibitors, lubricity improvers, dyes, markers, combustion improvers, metal deactivators, odour masks, drag reducers and conductivity improvers. Examples of suitable amounts of each of these types of additives will be known to the person skilled in the art.

In some embodiments the diesel fuel composition may comprise one or more detergents, especially one or more nitrogen containing detergents. Suitable such additives are known to the person skilled in the art.

By diesel fuel we include any fuel suitable for use in a diesel engine, either for road use or nonroad use. This includes, but is not limited to, fuels described as diesel, marine diesel, heavy fuel oil, industrial fuel oil etc.

The diesel fuel composition of the present invention may comprise a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 1 10°C to 500°C, e.g. 150°C to 400°C. The diesel fuel may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and refinery streams such as thermally and/or catalytically cracked and hydro-cracked distillates.

The diesel fuel composition used in the present invention may comprise non-renewable Fischer- Tropsch fuels such as those described as GTL (gas-to-liquid) fuels, CTL (coal-to-liquid) fuels and OTL (oil sands-to-liquid). The diesel fuel composition used in the present invention may comprise a renewable fuel such as a biofuel composition or biodiesel composition.

The diesel fuel composition may comprise 1st generation biodiesel. First generation biodiesel contains esters of, for example, vegetable oils, animal fats and used cooking fats. This form of biodiesel may be obtained by transesterification of oils, for example rapeseed oil, soybean oil, safflower oil, palm oil, corn oil, peanut oil, cotton seed oil, tallow, coconut oil, physic nut oil (Jatropha), sunflower seed oil, used cooking oils, hydrogenated vegetable oils or any mixture thereof , with an alcohol, usually a monoalcohol, in the presence of a catalyst.

The diesel fuel composition may comprise second generation biodiesel. Second generation biodiesel is derived from renewable resources such as vegetable oils and animal fats and processed, often in the refinery, often using hydroprocessing such as the H-Bio process developed by Petrobras. Second generation biodiesel may be similar in properties and quality to petroleum based fuel oil streams, for example renewable diesel produced from vegetable oils, animal fats etc. and marketed by ConocoPhillips as Renewable Diesel and by Neste as NExBTL.

The diesel fuel composition used in the present invention may comprise third generation biodiesel. Third generation biodiesel utilises gasification and Fischer-Tropsch technology including those described as BTL (biomass-to-liquid) fuels. Third generation biodiesel does not differ widely from some second generation biodiesel, but aims to exploit the whole plant (biomass) and thereby widens the feedstock base.

The diesel fuel composition may contain blends of any or all of the above diesel fuel compositions.

In some embodiments the diesel fuel composition used in the present invention may be a blended diesel fuel comprising bio-diesel. In such blends the bio-diesel may be present in an amount of, for example up to 0.5%, up to 1 %, up to 2%, up to 3%, up to 4%, up to 5%, up to 10%, up to 20%, up to 30%, up to 40%, up to 50%, up to 60%, up to 70%, up to 80%, up to 90%, up to 95% or up to 99%.

In some embodiments the diesel fuel composition may comprise a secondary fuel, for example ethanol. Preferably however the diesel fuel composition does not contain ethanol.

The diesel fuel composition of the present invention may contain a relatively high sulphur content, for example greater than 0.05% by weight, such as 0.1 % or 0.2%. However in preferred embodiments the diesel fuel has a sulphur content of at most 0.05% by weight, more preferably of at most 0.035% by weight, especially of at most 0.015%. Fuels with even lower levels of sulphur are also suitable such as, fuels with less than 50 ppm sulphur by weight, preferably less than 20 ppm, for example 10 ppm or less.

As mentioned above, various metal species may be present in fuel compositions. This may be due to contamination of the fuel during manufacture, storage, transport or use or due to contamination of fuel additives. Metal species may also be added to fuels deliberately. For example transition metals are sometimes added as fuel borne catalysts, for example to improve the performance of diesel particulate filters.

The present inventors believe that problems of injector sticking occur when metal or ammonium species, particularly sodium species, react with carboxylic acid species in the fuel.

Sodium contamination of diesel fuel and the resultant formation of carboxylate salts is believed to be a major cause of injector sticking.

In preferred embodiments the diesel fuel compositions used in the present invention comprise sodium and/or calcium. Preferably they comprise sodium. The sodium and/or calcium is typically present in a total amount of from 0.01 to 50 ppm, preferably from 0.05 to 5 ppm preferably 0.1 to 2ppm such as 0.1 to 1 ppm.

Other metal-containing species may also be present as a contaminant, for example through the corrosion of metal and metal oxide surfaces by acidic species present in the fuel or from lubricating oil. In use, fuels such as diesel fuels routinely come into contact with metal surfaces for example, in vehicle fuelling systems, fuel tanks, fuel transportation means etc. Typically, metal-containing contamination may comprise transition metals such as zinc, iron and copper; other group I or group II metals and other metals such as lead.

The presence of metal containing species may give rise to fuel filter deposits and/or external injector deposits including injector tip deposits and/or nozzle deposits.

In addition to metal-containing contamination which may be present in diesel fuels there are circumstances where metal-containing species may deliberately be added to the fuel. For example, as is known in the art, metal-containing fuel-borne catalyst species may be added to aid with the regeneration of particulate traps. The presence of such catalysts may also give rise to injector deposits when the fuels are used in diesel engines having high pressure fuel systems. Metal-containing contamination, depending on its source, may be in the form of insoluble particulates or soluble compounds or complexes. Metal-containing fuel-borne catalysts are often soluble compounds or complexes or colloidal species.

In some embodiments, the diesel fuel may comprise metal-containing species comprising a fuel- borne catalyst. Preferably, the fuel borne catalyst comprises one or more metals selected from iron, cerium, platinum, manganese, Group I and Group II metals e.g., calcium and strontium. Most preferably the fuel borne catalyst comprises a metal selected from iron and cerium.

In some embodiments, the diesel fuel may comprise metal-containing species comprising zinc. Zinc may be present in an amount of from 0.01 to 50 ppm, preferably from 0.05 to 5 ppm, more preferably 0.1 to 1 .5 ppm.

Typically, the total amount of all metal-containing species in the diesel fuel, expressed in terms of the total weight of metal in the species, is between 0.1 and 50 ppm by weight, for example between 0.1 and 20 ppm, preferably between 0.1 and 10 ppm by weight, based on the weight of the diesel fuel.

Preferably the method and use of the present invention provide an improvement in the performance of a diesel engine. This improvement in performance is suitably selected from one or more of: a reduction in power loss of the engine; a reduction in external diesel injector deposits; a reduction in internal diesel injector deposits; an improvement in fuel economy; a reduction in fuel filter deposits; a reduction in emissions; and an increase in maintenance intervals.

The method and use of the present invention improve the performance of a diesel engine. Preferably the method and use improve the performance of a modern diesel engine having a high pressure fuel system.

Such diesel engines may be characterised in a number of ways.

Such engines are typically equipped with fuel injection equipment meeting or exceeding “Euro 5” emissions legislation or equivalent legislation in US or other countries. Such engines are typically equipped with fuel injectors having a plurality of apertures, each aperture having an inlet and an outlet.

Such engines may be characterised by apertures which are tapered such that the inlet diameter of the spray-holes is greater than the outlet diameter.

Such modern engines may be characterised by apertures having an outlet diameter of less than 500pm, preferably less than 200pm, more preferably less than 150pm, preferably less than 100pm, most preferably less than 80pm or less.

Such modern diesel engines may be characterised by apertures where an inner edge of the inlet is rounded.

Such modern diesel engines may be characterised by the injector having more than one aperture, suitably more than 2 apertures, preferably more than 4 apertures, for example 6 or more apertures.

Such modern diesel engines may be characterised by an operating tip temperature in excess of 250°C.

Such modern diesel engines may be characterised by a a fuel injection system which provides a fuel pressure of more than 1350 bar, preferably more than 1500 bar, more preferably more than 2000 bar. Preferably, the diesel engine has fuel injection system which comprises a common rail injection system.

The method and use of the present invention preferably improve the performance of an engine having one or more of the above-described characteristics.

The method and use of the present invention improve the performance of an engine. This improvement in performance is suitably achieved by reducing deposits in the engine.

The present invention may therefore provide a method of combating deposits in an engine comprising combusting in said engine a fuel composition of the first aspect.

Combating deposits may involve reducing or the preventing of the formation of deposits in an engine compared to when running the engine using unadditised fuel. Such a method may be regarded as achieving “keep clean” performance. Combating deposits may involve the removal of existing deposits in an engine. This may be regarded as achieving “clean up” performance.

In especially preferred embodiments the method of the sixth aspect of the present invention may be used to provide “keep clean” and “clean up” performance.

As explained above deposits may occur at different places within a diesel engine, for example a modern diesel engine.

The present invention is particularly useful in the prevention or reduction or removal of internal deposits in injectors of engines operating at high pressures and temperatures in which fuel may be recirculated and which comprise a plurality of fine apertures through which the fuel is delivered to the engine. The present invention finds utility in engines for heavy duty vehicles and passenger vehicles. Passenger vehicles incorporating a high speed direct injection (or HSDI) engine may for example benefit from the present invention.

The present invention may also provide improved performance in modern diesel engines having a high pressure fuel system by controlling external injector deposits, for example those occurring in the injector nozzle and/or at the injector tip. The ability to provide control of internal injector deposits and external injector deposits is a useful advantage of the present invention.

Suitably the present invention may reduce or prevent the formation of external injector deposits. It may therefore provide “keep clean” performance in relation to external injector deposits.

Suitably the present invention may reduce or remove existing external injector deposits. It may therefore provide “clean up” performance in relation to external injector deposits.

Suitably the present invention may reduce or prevent the formation of internal diesel injector deposits. It may therefore provide “keep clean” performance in relation to internal diesel injector deposits.

Suitably the present invention may reduce or remove existing internal diesel injector deposits. It may therefore provide “clean up” performance in relation to internal diesel injector deposits.

The removal or reduction of IDIDs according to the present invention will lead to an improvement in performance of the engine. The improvement in performance of the diesel engine system may be measured by a number of ways. Suitable methods will depend on the type of engine and whether “keep clean” and/or “clean up” performance is measured.

An improvement in “keep clean” performance may be measured by comparison with a base fuel. “Clean up” performance can be observed by an improvement in performance of an already fouled engine.

The effectiveness of fuel additives is often assessed using a controlled engine test.

In Europe the Co-ordinating European Council for the development of performance tests for transportation fuels, lubricants and other fluids (the industry body known as CEC), has developed a test for additives for modern diesel engines such as HSDI engines. The CEC F-98- 08 test is used to assess whether diesel fuel is suitable for use in engines meeting new European Union emissions regulations known as the “Euro 5” regulations. The test is based on a Peugeot DW10 engine using Euro 5 injectors, and is commonly referred to as the DW10 test. This test measures power loss in the engine due to deposits on the injectors, and is further described in example 17.

Preferably the use of the fuel composition of the present invention leads to reduced deposits in the DW10 test. For “keep clean” performance a reduction in the occurrence of deposits is preferably observed.

For “clean up” performance removal of deposits is preferably observed. The DW10 test is used to measure the power loss in modern diesel engines having a high pressure fuel system.

Suitably the use of a fuel composition of the present invention may provide a “keep clean” performance in modern diesel engines, that is the formation of deposits on the injectors of these engines may be inhibited or prevented. Preferably this performance is such that a power loss of less than 5%, preferably less than 2% is observed after 32 hours as measured by the DW10 test.

In some embodiments, the present invention may provide a power gain. Suitably when combusting a fuel composition according to the present invention a power gain in the DW10 test is observed compared to when combusting an unadditised base fuel and with clean injectors. Suitably a power gain of at least 0.5%, preferably at least 1 % is achieved within 4 hours, preferably within 2 hours. Suitably the use of a fuel composition of the present invention may provide a “clean up” performance in modern diesel engines, that is deposits on the injectors of an already fouled engine may be removed. Preferably this performance is such that the power of a fouled engine may be returned to within 1 % of the level achieved when using clean injectors within 16 hours, preferably 12 hours, more preferably 8 hours as measured in the DW10 test.

Preferably rapid “clean-up” may be achieved in which the power is returned to within 1 % of the level observed using clean injectors within 4 hours, preferably within 2 hours.

In some preferred embodiments, clean up may also provide a power increase. Thus a fouled engine may be treated to remove the existing deposits and provide an additional power gain.

Clean injectors can include new injectors or injectors which have been removed and physically cleaned, for example in an ultrasound bath.

The present invention may improve the performance of a diesel engine by combatting internal diesel injector deposits or IDIDs in the injectors of a severely fouled engine.

The present invention may clean up internal diesel injector deposits caused by lacquers and/or carboxylate residues.

The present invention may clean up internal diesel injector deposits caused by amide lacquers and/or carboxylate residues.

The present invention may clean up internal diesel injector deposits caused by lacquers.

The present invention may clean up internal diesel injector deposits caused by amide lacquers.

Preferably the present invention clean up internal diesel injector deposits caused by carboxylate residues. Carboxylate residues are typically present as metal or ammonium salts.

“Clean-up” of a fouled engine may provide significant advantages. For example, superior clean up may lead to an increase in power and/or an increase in fuel economy and/or reduced emissions. In addition removal of deposits from an engine, in particular from injectors may lead to an increase in interval time before injector maintenance or replacement is necessary thus reducing maintenance costs.

In some preferred embodiments, clean up may also provide a power increase. Thus a fouled engine may be treated to remove the existing deposits and provide an additional power gain. The removal of IDIDs according to the present invention will lead to an improvement in performance of the engine.

The improvement in performance of the diesel engine system may be measured by a number of ways.

“Clean up” performance can be observed by an improvement in performance of an already fouled engine.

A controlled engine test which has been developed to assess the control of IDIDs is commonly known as the DW10C test. This test assesses the ability of a fuel composition to prevent the formation of IDIDs that lead to injector sticking.

The DW10C test procedure was developed by CEC as a “keep clean” procedure test and thus may be used to measure the “keep clean” performance of an engine. However it is often modified and used as a clean up procedure and thus can also be used to measure the “clean up” performance of an engine.

The DW10C test is described in example 15. Reference herein to the DW10C test means the test method described in example 15. A modified version of this test adapted to measure clean up, is described in example 16. This modified test was used to test the additives of the invention.

In the DW10C test the performance of the engine is rated using a merit score. The maximum score is 10 and a score in excess of 9.5 indicates an exceptional performance. A score of less than 8 indicates that the engine is severely fouled and likely contains very high levels of IDIDs.

Very surprisingly additive combinations according to the present invention have been found to perform exceptionally well in the DW10C test when used to clean up a severely fouled engine.

By a severely fouled engine we mean to refer to an engine which would achieve a merit rating of less than 8 In the DW10C test.

In particular the method and use of the present invention can clean up IDIDs from an engine with a level of fouling equivalent to a rating of less than 8 in the DW10C test.

Preferably the use and method according to the present invention provide a score in a DW10C clean up test in excess of 9.8, preferably in excess of 9.9 when introduced to an engine having a merit score of less than 8, following the treatment with an equivalent fuel absent the additive. As is described in example 8, some additive combinations of the present invention may achieve a score of 10 in the DW10C test when used to clean up an engine with a level of fouling to give a merit score of less than 8, for example less than 7.8 or less than 7.6, following treatment with an equivalent fuel absent the additive.

The present invention provides improved performance in modern diesel engines having a high pressure fuel system by controlling internal diesel injector deposits and external injector deposits, for example those occurring in the injector nozzle and/or at the injector tip. The ability to provide control of internal injector deposits and external injector deposits is a useful advantage of the present invention.

The diesel fuel compositions of the present invention may also provide improved performance when used with traditional diesel engines. Preferably the improved performance is achieved when using the diesel fuel compositions in modern diesel engines having high pressure fuel systems and when using the compositions in traditional diesel engines. This is important because it allows a single fuel to be provided that can be used in new engines and older vehicles.

For older engines an improvement in performance may be measured using the XUD9 test. This test is described in relation to example 18.

Suitably the use of a fuel composition of the present invention may provide a “keep clean” performance in traditional diesel engines, that is the formation of deposits on the injectors of these engines may be inhibited or prevented. Preferably this performance is such that a flow loss of less than 50%, preferably less than 30% is observed after 10 hours as measured by the XUD-9 test.

Suitably the use of a fuel composition of the present invention may provide a “clean up” performance in traditional diesel engines, that is deposits on the injectors of an already fouled engine may be removed. Preferably this performance is such that the flow loss of a fouled engine may be reduced by 10% or more within 10 hours as measured in the XUD-9 test.

The benefits provided by the present invention mean that engines need to be serviced less frequently, leading to cost savings and an increase in maintenance intervals.

The additives of the present invention may provide a further benefit in addition to those listed above. For example the additive may provide lubricity benefits and/or corrosion inhibition and/or cold flow improvement. The present invention may also combat deposits on vehicle fuel filters. This may include reducing or preventing the formation of deposits (“keep clean” performance) or the reduction or removal of existing deposits (“clean up” performance).

The invention will now be further defined with reference to the following non-limiting examples.

Raw materials

The polyisobutylene used in the synthesis examples was purchased under the trade mark HRPB1000 (Daelim, South Korea) and had a number average molecular weight (M _n ) of approximately 1 ,000 and a terminal vinylidene content > 80 % ( ¹³ C NMR).

Analytical Methods

The acid value of PIBSA was determined by non-aqueous titration against lithium methoxide solution (ca 0.1 M in toluene/methanol) using thymol blue (0.4 % w/v in 1 ,4-dioxane) as the indicator. The titre of lithium methoxide solutions was regularly confirmed by titration against analytical grade benzoic acid.

The residual maleic anhydride content of polyisobutylenesuccinic anhydride (PIBSA) was measured by quantitative FTIR against a calibration curve. The characteristic absorbance at 696 cm' ¹ was used for the analysis.

The residual (unreacted) polyisobutylene content of polyisobutylenesuccinic anhydride (PIBSA) was measured by quantitative HPLC against a polyisobutylene standard, under normal phase column conditions (eluent : isohexane).

The ‘P value’ (average number of succinyl residues per polyisobutylene side chain, in the sample) is calculated as follows :

Where ‘PIB MW is the number average molecular weight (Mn) and PIB content is the residual (unreacted) polyisobutylene content as described above.

The derivation of this equation is described below.

PIB content is measured as a percentage by weight (g/100g).

Example 1 - Preparation of polyisobutylenesuccinic anhydride (PIBSA) - inventive 700 g (0.7 mol) of polyisobutylene (M _n 1000) was charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer. The starting material was heated to 120 °C with stirring and nitrogen inerting was repeated. The reaction temperature was increased to 190 °C and maleic anhydride (82.4g, 0.84 mol, 1.2 eq) was charged over 1 hour. After maintaining a temperature of 190 °C for a further 1 hour, the temperature was increased to 200 - 208 °C and held in this range for 8 hours. Vacuum (< 30 mbar) was then applied for 2.5 hrs, whilst maintaining the reaction temperature, which reduced the level of residual maleic anhydride to < 0.05 wt%. The reaction mass was cooled to < 80°C then discharged from the reactor.

Example 2 - Preparation of PIBSA - comparative

The synthesis procedure was substantially identical to Example 1 and used the same grade of polyisobutylene (M _n 1000). The charge of maleic anhydride was reduced (1 eq relative to polyisobutylene) and the reaction was held between 190 - 210 °C during the 8 hour heating period. Residual maleic anhydride was also measured as < 0.05 wt%.

The properties of the reaction products of Examples 1 and 2 are summarised in Table 1.

Table 1

Example 3 - Additive Q1 - inventive

PIBSA prepared according to Example 1 was charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer and heated to 120 °C. 3-(dimethylamino)propylamine (DMAPA) (1 eq relative to anhydride groups) was charged slowly, maintaining the reaction temperature between 120 - 130 °C. After stirring at 120 °C for a further 1 hr, the reaction temperature was increased to 140 °C and held for 3 hrs with concurrent distillation of water. Methyl salicylate (2.1 eq relative to anhydride groups) was added in a single portion and heating was continued at 140 °C for 10 hours. The reaction mass was diluted with Aromatic 150 solvent to provide an overall solids content of 60 wt% prior to discharging from the reactor. Example 4 - Additive Q2 - comparative

PIBSA prepared according to Example 2 was charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer and heated to 90 °C. 3-(dimethylamino)propylamine (DMAPA) (1 eq relative to anhydride groups) was charged slowly, maintaining the reaction temperature between 90 - 100 °C. After stirring at 90 - 100 °C for a further 1 hr, the reaction temperature was increased to 140 °C and held for 4 hrs with concurrent distillation of water. 2-ethylhexanol was added to adjust the solids content to 60 wt% then methyl salicylate (1 eq relative to anhydride groups) was added in a single portion and heating was continued at 140 °C for 15 hours. The reaction mass was cooled to 60 °C prior to discharging from the reactor.

Example 5 - Additive Q3 - inventive

PIBSA according to Example 1 was charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer and heated to 120 °C. 3-(dimethylamino)propylamine (DMAPA) (1 eq relative to anhydride groups) was charged slowly, maintaining the reaction temperature between 120 - 130 °C. After stirring at 120 °C for a further 1 hr, the reaction temperature was increased to 140 °C and held for 3 hrs with concurrent distillation of water. The reaction mass was cooled to room temperature, then acetic acid (0.71 eq relative to anhydride groups), 2-ethylhexanol (1.34 eq relative to anhydride groups) and water (0.81 eq relative to anhydride groups) were added. The reaction mass was heated to 75 °C and propylene oxide (2.39 eq relative to anhydride groups) was added over 3 hrs via a dropping funnel. Heating was continued for 4 hrs. The reaction mass was diluted with Aromatic 150 solvent to provide an overall solids content of 60 wt% prior to discharging from the reactor.

Example 6 - Additive Q4

PIBSA according to Example 2 was used. Formation of the DMAPA succinimide and subsequent quaternization using propylene oxide / AcOH was carried out in identical manner to Example 5. Reactant charges were calculated relative to anhydride groups in the PIBSA starting material.

Example 7 - Additive Q5 - inventive

PIBSA according to Example 1 (1 part) and Caromax 20 (1 part) were charged to a nitrogen flushed, jacketed reactor fitted with an overhead stirrer and heated to 80 °C to ensure proper mixing, then cooled to room temperature. 3-(dimethylamino)propylamine (DMAPA) (1 eq relative to anhydride groups in the PIBSA starting material) was added over 3 hrs, maintaining the reaction temperature below 40 °C. The reaction mass was stirred for a further 4 hrs, then propylene oxide (2 eq relative to anhydride groups) was added over 3 hrs, then the reaction mass stirred at room temperature for 4 hrs. After nitrogen sparging to remove residual propylene oxide, the reaction mass was discharged from the reactor.

Example 8 - Additive Q6 - comparative

PIBSA according to Example 2 was used. Formation of the DMAPA succinamide and subsequent quaternization using propylene oxide was carried out in identical manner to Example 7. Reactant charges were calculated relative to anhydride groups.

Example 9 - Additive A1

Additive A1 was prepared as follows:

A mixture of alkenes having 20 to 24 carbon atoms was heated with 1 .2 molar equivalents of maleic anhydride. On completion of the reaction excess maleic anhydride was removed by distillation. The anhydride value of the substituted succinic anhydride product was measured as 2.591 mmolg ^-1 .

This product was then heated with one molar equivalent of 2-ethyl hexanol, and the reaction was monitored by FTIR.

Example 10 - Additive A2

Additive A2 was prepared by hydrolysing the compound prepared according to example 2. Hydrolysis was carried out by heating the material obtained in example 2 with a slight molar excess of water at 90 to 95°C. The acid value of the product was determined to be 1.50 mmol/g by titration against 0.1 N lithium methoxide in toluene.

Example 11 - Additive A3

A 500 mL, 3-neck round bottom flask was fitted with a magnetic stirrer, condenser, Dean - Stark apparatus, gas inlet I outlet, stirrer hotplate and oil bath. Oleyl alcohol (206.19 g, 0.768 mol), itaconic acid (100 g, 0.768 mol) and p-toluenesulfonic acid (0.439 g, 2.30 mmol) were combined and heated to 165 °C (internal temperature). The reaction mass was held at 165 °C for 6 hours and water was removed. The reaction mass became homogenous and a colour change to orange was observed. After cooling to room temperature, the reaction mass was transferred to a 2 L separating funnel and toluene (270 mL) was added. The toluene - diluted reaction mass was washed with 1 : 1 water- methanol (1 x 540 mL), the organic phase separated and volatiles removed on the rotary evaporator, providing a viscous orange liquid (257.6 g). The acid value of Additive A3 was 2.0 mmollT I g.

Example 12 - Additive A4

Additive A4 was prepared by following the procedure set out in synthesis example 1 of US2017/0130153.

Example 13

Additive formulations F1 to F10 were prepared by mixing 50:50 ratios by weight of the crude products from examples 3-12 as identified table 2.

Table 2

Example 14

Fuel compositions were prepared by adding additives formulations F1 to F10 to diesel fuel.

The diesel fuel complied with the RF06 base fuel, the details of which are given in table 3 below.

Table 3

Property Units Limits Method

Min Max

Cetane Number 52.0 54.0 EN ISO 5165

Density at 15°C kg/m ³ 833 837 EN ISO 3675

Distillation

50% v/v Point 245

95% v/v Point 345 350

FBP 370

Flash Point °C 55 EN 22719 Cold Filter Plugging °C -5 EN 116 Point

Viscosity at 40°C mm ² /sec 2.3 3.3 EN ISO 3104

Polycyclic Aromatic % m/m 3.0 6.0 IP 391

Hydrocarbons

Sulphur Content mg/kg 10 ASTM D 5453

Copper Corrosion 1 EN ISO 2160

Conradson Carbon Residue on % m/m 0.2 EN ISO 10370 10% Dist. Residue

Ash Content % m/m 0.01 EN ISO 6245

Water Content % m/m 0.02 EN ISO 12937

Neutralisation (Strong Acid) mg KOH/g 0.02 ASTM D 974

Number

Oxidation Stability mg/mL 0.025 EN ISO 12205

HFRR (WSD1.4) pm 400 CEC F-06-A-96

Fatty Acid Methyl Ester prohibited

Example 15

The ability of additives of the invention to remove ‘Internal Diesel Injector Deposits’ (IDIDs) may be measured according to the test method CEC F-110-16, available from the Co-ordinating European Council. The test uses the PSA DW10C engine.

The engine characteristics as follows:

The test fuel (RF06) is dosed with 0.5mg/kg Na in the form of Sodium Naphthenate + 10mg/kg Dodecyl Succinic Acid (DDSA).

The test procedure consists of main run cycles followed by soak periods, before cold starts are carried out.

The main running cycle consist of two speed and load set points, repeated for 6hrs, as seen below.

The ramp limes of 30 seconds are included in dse duration of each step.

During the main run, parameters including, Throttle pedal position, ECU fault codes, Injector balance coefficient and Engine stalls are observed and recorded.

The engine is then left to soak at ambient temperature for 8hrs.

Afterthe soak period the engine is re-started. The starter is operated for 5 seconds; if the engine fails to start the engine is left for 60 seconds before a further attempt. A maximum of 5 attempts are allowed.

If the engine starts the engine is allowed to idle for 5 minutes. Individual exhaust temperatures are monitored and the maximum Temperature Delta is recorded. An increased variation in Cylinder-to-Cylinder exhaust temperatures is a good indication that injectors are suffering from I DID. Causing them to either open slowly or stay open to long.

An example below of all exhaust temperatures with <30°C deviation, indicating no sticking caused by IDID.

The complete test comprises of 6x Cold Starts, although the Zero hour Cold Start does not form part of the Merit Rating and 5x 6hr Main run cycles, giving a total of 30hrs engine running time. The recorded data is inputted into the Merit Rating Chart. This allows a Rating to be produced for the test. Maximum rating of 10 shows no issues with the running or operability of the engine for the duration of the test.

An example below:

The propensity of the test fuel to cause injector deposits (IDID) is evaluated through the following criteria:

□ Cold start parameters:

1 . Number of failed starts.

2. Exhaust temperature deviation from standard value for cylinders 1 to 4

□ Main run parameters

1 . Number of engine stalls

2. Number of IDID related ECU faults generated during main run

3. Pedal position drift on low speed phases

4. Injector balancing

Note: 1st Cold start (#0) is run with Flush fuel and is not rated

The rating can be summarized as follows:

1/ Cold Start (for start #1 to #5):

Startability rating:

□ 1st start: merit = 5 / each fail brings a “-1 ” merit discount.

Maximum Exhaust Ports Temperature deviation rating:

□ merit = 5 if T<30°C i 2 if 30°C<T<50°C i 0 if T>50°C.

Cold Start Rating range: 0 -> 10 for each Cold Start (5 Cold Starts rated in total)

2/ Main Run (for run #1 to #5):

Operability rating:

□ merit = 5 if no stall and no IDID related ECU Fault, each IDID related ECU fault brings a “-1 ” merit discount (after 5th ECU Fault Reset -> Next cold start).

□ merit = 0 if stall (Then -> Next Cold Start).

Maximum Pedal Position:

□ merit = 5 if P<25% i 2 if 25%<P<40% i 0 if P>40%

Maximum Injector Balancing Factror deduction:

□ merit = 5 if IB<20rpm i 2 if 30rpm<IB<20rpm i 0 if IB>30rpm Main Run Rating range: 0 -> 5 for each Main Run (5 in total)

Maximum global rating value: 75 (ie: 5x 10 + 5x 5).

Global rating = 10 x (Cold Start + Main Run Rating values) / 75

Resulting in 0 to 10 merit scale

Example 16

The ability of additives of the invention to clean up IDIDs may be assessed according to a modification of the DW10C test described in example 12.

The In-House Clean-Up Method developed starts by running the engine using reference diesel (RF06) dosed with 0.5mg/kg Na + l Omg/Kg DDSA until an exhaust temperature Delta of >50°C is observed on the Cold Start. This has repeatedly been seen on the 3 ^rd Cold Start which follows the second main run, 12hrs total engine run time.

Once the increased Exhaust temperature Delta is observed, the engine fuel supply is swapped to reference diesel, dosed with 0.5mg/kg Na (as sodium naphthenate) + l Omg/kg DDSA + the Candidate sample. The fuel is flushed through to the engine and allowed to commence with the next Main run.

The ability of the Candidate additive to prevent any further increase in deposits or to remove the deposits can then be determined as the test continues.

Example 17

The performance of fuel compositions of example 14 in modern diesel engines having a high pressure fuel system may be tested according to the CECF-98-08 DW 10 method. This is referred to herein as the DW10B test.

The engine of the injector fouling test is the PSA DW10BTED4. In summary, the engine characteristics are:

Design: Four cylinders in line, overhead camshaft, turbocharged with EGR

Capacity: 1998 cm ³

Combustion chamber: Four valves, bowl in piston, wall guided direct injection

Power: 100 kW at 4000 rpm

Torque: 320 Nm at 2000 rpm

Injection system: Common rail with piezo electronically controlled 6-hole injectors. Max. pressure: 1600 bar (1 .6 x 10 ⁸ Pa). Proprietary design by SIEMENS VDO

Emissions control: Conforms with Euro IV limit values when combined with exhaust gas posttreatment system (DPF)

This engine was chosen as a design representative of the modern European high-speed direct injection diesel engine capable of conforming to present and future European emissions requirements. The common rail injection system uses a highly efficient nozzle design with rounded inlet edges and conical spray holes for optimal hydraulic flow. This type of nozzle, when combined with high fuel pressure has allowed advances to be achieved in combustion efficiency, reduced noise and reduced fuel consumption, but are sensitive to influences that can disturb the fuel flow, such as deposit formation in the spray holes. The presence of these deposits causes a significant loss of engine power and increased raw emissions.

The test is run with a future injector design representative of anticipated Euro V injector technology.

It is considered necessary to establish a reliable baseline of injector condition before beginning fouling tests, so a sixteen hour running-in schedule for the test injectors is specified, using nonfouling reference fuel.

Full details of the CEC F-98-08 test method can be obtained from the CEC. The coking cycle is summarised below.

1 . A warm up cycle (12 minutes) according to the following regime:

2. 8 hrs of engine operation consisting of 8 repeats of the following cycle for expected range see CEC method CEC-F-98-08

3. Cool down to idle in 60 seconds and idle for 10 seconds

4. 4 hrs soak period

The standard CEC F-98-08 test method consists of 32 hours engine operation corresponding to 4 repeats of steps 1-3 above, and 3 repeats of step 4. ie 56 hours total test time excluding warm ups and cool downs.

Example 18

The effectiveness of the additives of the invention in older traditional diesel engine types may be assessed using a standard industry test - CEC test method No. CEC F-23-A-01 .

This test measures injector nozzle coking using a Peugeot XUD9 A/L Engine and provides a means of discriminating between fuels of different injector nozzle coking propensity. Nozzle coking is the result of carbon deposits forming between the injector needle and the needle seat. Deposition of the carbon deposit is due to exposure of the injector needle and seat to combustion gases, potentially causing undesirable variations in engine performance.

The Peugeot XUD9 A/L engine is a 4 cylinder indirect injection Diesel engine of 1 .9 litre swept volume, obtained from Peugeot Citroen Motors specifically for the CEC PF023 method.

The test engine is fitted with cleaned injectors utilising unflatted injector needles. The airflow at various needle lift positions have been measured on a flow rig prior to test. The engine is operated for a period of 10 hours under cyclic conditions.

The propensity of the fuel to promote deposit formation on the fuel injectors is determined by measuring the injector nozzle airflow again at the end of test, and comparing these values to those before test. The results are expressed in terms of percentage airflow reduction at various needle lift positions for all nozzles. The average value of the airflow reduction at 0.1 mm needle lift of all four nozzles is deemed the level of injector coking for a given fuel.

Example 19

A diesel fuel composition F1 1 was prepared by dosing 36 ppm active additive Q1 and 20 ppm active additive A2 into an RF06 base fuel meeting the specification of example 14.

The ability of this fuel to clean up deposits on from a fouled traditional engine was demonstrated following the procedure set out in example 18.

The test method of example 18 was carried out on the base fuel to provide “dirty up” of the engine. The test method was then repeated but starting with the dirty injectors and using the diesel fuel composition F11 comprising 36 ppm Q1 and 20 ppm A2.

The results are shown in table 4:

Example 20

Additive A5 was prepared as follows: To a 1 L reactor charged with 2-ethylhexanol (250g, 1.918 moles) was added toluene (215.7g) and heated to 90°C. To the stirred liquid was added itaconic acid (250g, 1.921 moles) and p- toluenesulfonic acid (3.31 g). The reaction was heated towards 120°C, whilst removing water by distillation over 7 hours. The products where cooled to room temperature and unreacted itaconic and p-toluenesulfonic acid removed by filtration and washing with water. The toluene was removed on a rotary evaporator to leave a yellow/orange liquid (2-ethylhexyl itaconate, 412.9g)

To a 250ml reactor was charged 2-ethylhexyl itaconate (120g) was added cyclohexane (51 ,43g) and the reactor contents sparged with Nitrogen for 1 hour whilst heating to 80°C. Trigonox 25- C75 (0.685g, 0.5wt, %, tert-Butyl peroxypivalate) was added and the reaction was mixed at 80°C for 1 hour before adding further Trigonox 25-C75 (0.685g) and heating for a further 3 hours at 80°C. The cyclohexane was removed on a rotary evaporator and Aromatic 150 (69.7g) added to leave a clear amber viscous liquid (184.4g, Mw 10932, acid value of 2.4 mmolH+Zg).

Example 21

A diesel fuel composition F12 was prepared by dosing 30 ppm active additive Q1 and 14 ppm active additive A4 into an RF06 base fuel meeting the specification of example 14.

Diesel fuel composition F12 was tested according to the CEC F-98-08 DW10B test method described in example 17, modified to measure clean up performance as outlined below.

A first 32 hour cycle was run using new injectors and RF-06 base fuel having added thereto 1 ppm Zn (as neodecanoate). This resulted in a level of power loss of 4.04% due to fouling of the injectors.

A second 32 hour cycle was then run as a ‘clean up’ phase. The dirty injectors from the first phase were kept in the engine and the fuel changed to RF-06 base fuel having added thereto 1 ppm Zn (as neodecanoate) and the test additive. This restored the power to a loss of 1.78% compared to the power obtained when using clean injectors.