GB2468130A

GB2468130A - Diesel fuel compositions

Info

Publication number: GB2468130A
Application number: GB0903164A
Authority: GB
Inventors: Ian Mcrobbie; Jacqueline Reid
Original assignee: Innospec Ltd
Current assignee: Innospec Ltd
Priority date: 2009-02-25
Filing date: 2009-02-25
Publication date: 2010-09-01
Also published as: GB0903164D0

Abstract

A diesel fuel composition comprises one or more performance enhancing additives, intended to address the problem of fouling of injector body and nozzles, selected from:(I) the Mannich reaction product of an optionally substituted phenol, ammonia and an aldehyde;(II) the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400;(III) an antioxidant compound; and(IV) the combination of the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier.

Description

Fuel Compositions The present invention relates to fuel compositions and additives therefor. In particular the invention relates to additives for diesel fuel compositions, especially those suitable 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 108 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.

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 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 DW1O having 4 cylinders and a power output of 100 kW or less depending on the variant.

In all of the diesel engines relating to this invention, a common feature is a high pressure fuel system. Typically pressures in excess of 1350 bar (1.35 x 108 Pa) are used but often pressures of up to 2000 bar (2 x 108 Pa) or more may exist.

Two non-limiting examples of such high pressure fuel systems are: the common rail injection system, in which the fuel is compressed utilizing a high-pressure pump that supplies it to the fuel injection valves through a common rail; and the unit injection system which integrates the high-pressure pump and fuel injection valve in one assembly, achieving the highest possible injection pressures exceeding 2000 bar (2 x 108 Pa). In both systems, in pressurizing the fuel, the fuel gets hot, often to temperatures around 100°C, or above.

In common rail systems, the fuel is stored at high pressure in the central accumulator rail or separate accumulators prior to being delivered to the injectors. Often, some of the heated fuel is returned to the low pressure side of the fuel system or returned to the fuel tank. In unit injection systems the fuel is compressed within the injector in order to generate the high injection pressures. This in turn increases the temperature of the fuel.

In both systems, fuel is present in the injector body prior to injection where it is heated further due to heat from the combustion chamber. The temperature of the fuel at the tip of the injector can be as high as 250 -350 °C.

Thus the fuel is stressed at pressures from 1350 bar (1.35 x 108 Pa)to over 2000 bar (2 x 108 Pa) and temperatures from around 100°C to 350°C prior to injection, sometimes being recirculated back within the fuel system thus increasing the time for which the fuel experiences these conditions.

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 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. Increased degradation of the fuel may also cause increased corrosion in the fuel system including the fuel lines and pump.

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 have been found to produce injector fouling more readily. Diesel fuels containing metallic species may also lead to increased deposits. Metallic species may be deliberately added to a fuel in additive compositions or may be present as contaminant species. Contamination occurs if metallic species from fuel distribution systems, vehicle distribution systems, vehicle fuel systems, other metallic components and lubricating oils become dissolved or dispersed in fuel.

Transition metals in particular cause increased deposits, especially copper and zinc species.

These may be typically present at levels from a few ppb (parts per billion) up to SOppm, but it is believed that levels likely to cause problems are from 0.1 to SOppm, for example 0.1 to lOppm.

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, increased exhaust emissions, poor fuel economy and increased maintenance costs.

As the size of the injector nozzle hole is reduced, the relative impact of deposit build up becomes more significant. By simple arithmetic a 5 pm layer of deposit within a 500 pm hole reduces the flow area by 4% whereas the same 5 pm layer of deposit in a 200 pm hole reduces the flow area by 9.8%.

At present, nitrogen-containing detergents may be added to diesel fuel to reduce coking.

Typical nitrogen-containing detergents are those formed by the reaction of a polyisobutylene-substituted succinic acid derivative with a polyalkylene polyamine. However newer engines including finer injector nozzles are more sensitive and current diesel fuels may not be suitable for use with the new engines incorporating these smaller nozzle holes.

In order to maintain performance with engines containing these smaller nozzle holes much higher treat rates of existing additives would need to be used.

The present inventor has developed diesel fuel compositions which when used in diesel engines with high pressure fuel systems provide improved performance compared with diesel

fuel compositions of the prior art.

According to a first aspect of the present invention there is provided a diesel fuel composition comprising one or more performance enhancing additives selected from: (I) the Mannich reaction product of an optionally substituted phenol, ammonia and an aldehyde; (II) the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400; (Ill) an antioxidant compound; and (IV) the combination of the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier.

The fuel composition of the first aspect of the present invention may comprise one or more of additives (I), (II), (Ill) and (IV) in any combination.

For example, the fuel composition may comprise additive (I) but be substantially free of additives (II), (Ill) and (IV).

The fuel composition may comprise additive (II) but be substantially free of additives (I), (Ill) and (IV).

The fuel composition may comprise additive (Ill) but be substantially free of additives (I), (II) and (IV).

The fuel composition may comprise additive (IV) but be substantially free of additives (I), (II) and (Ill).

The fuel composition may comprise additive (I) along with any combination of additives (II), (Ill) and (IV). For example it may comprise a mixture of additives (I) and (II), additives (I) and (Ill), additives (I) and (IV), additives (I), (II) and (Ill), additives (I), (II) and (IV) or additives (I), (Ill) and (IV).

The fuel composition may comprise additive (II) along with any combination of additives (I), (Ill) and (IV).

The fuel composition may comprise additive (Ill) along with any combination of additives (I), (II) and (IV).

The fuel composition may comprise additive (IV) along with any combination of additives (I), (II) and (Ill).

The fuel composition may comprise a mixture of additives (II) and (Ill), additives (II) and (IV), additives (Ill) and (IV) or additives (II), (Ill) and (IV).

The fuel composition may comprise a mixture of additives (I), (II), (Ill) and (IV).

Additive (I) is the reaction product of a Mannich reaction between an optionally substituted phenol, an aldehyde and ammonia.

The aldehyde is preferably an aliphatic aldehyde, preferably having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, for example 1 or 2 carbon atoms.

Most preferably the aldehyde is formaldehyde.

The optionally substituted phenol used to make additive (I) may be substituted with 0 to 4 groups on the aromatic ring (in addition to the phenol OH). For example it may be a tn-or di-substituted phenol. Preferably the phenol is a mono-substituted phenol. Substitution may be at the ortho, and/or meta, and/or para position(s).

Each phenol moiety may be ortho, meta or para substituted with the aldehyde/amine residue.

Compounds in which the aldehyde residue is ortho or para substituted are most commonly formed. Mixtures of compounds may result. In preferred embodiments the starting phenol is para substituted and thus the ortho substituted product results.

The phenol may be substituted with any common group, for example one or more of an alkyl group, an alkenyl group, an alkynl group, a nitryl group, a carboxylic acid, an ester, an ether, an alkoxy group, a polyoxyalkyl group, a halo group, a further hydroxyl group, a mercapto group, an alkyl mercapto group, an alkyl sulphoxy group, a sulphoxy group, an aryl group, an arylalkyl group, a substituted or unsubstituted amine group or a nitro group.

Preferably the phenol carries one or more optionally substituted alkyl substituents. The alkyl substituent may be optionally substituted with, for example, hydroxyl, halo, (especially chloro and fluoro), alkoxy, alkyl, mercapto, alkyl sulphoxy, aryl or amino residues. Preferably the alkyl group consists essentially of carbon and hydrogen atoms. The substituted phenol may include a alkenyl or alkynyl residue including one or more double and/or triple bonds. Most preferably the phenol used to prepare additive (I) is an alkyl substituted phenol group in which the alkyl chain is saturated. The alkyl chain may be linear or branched. Preferably the phenol is a monoalkyl phenol, especially a para-substituted monoalkyl phenol.

Preferably the phenol used to prepare additive (I) comprises an alkyl substituted phenol in which the phenol carries one or more alkyl chains having a total of less 28 carbon atoms, preferably less than 24 carbon atoms, more preferably less than 20 carbon atoms, preferably less than 18 carbon atoms, preferably less than 16 carbon atoms and most preferably less than 14 carbon atoms.

Preferably the or each alkyl substituent of the phenol has from 4 to 20 carbons atoms, preferably 6 to 18, more preferably 8 to 16, especially 10 to 14 carbon atoms. In a particularly preferred embodiment, component (c) is a phenol having a C12 alkyl substituent.

Preferably the or each substituent of the phenol used to prepare additive (I) has a molecular weight of less than 400, preferably less than 350, preferably less than 300, more preferably less than 250 and most preferably less than 200. The or each substituent of phenol component (c) may suitably have a molecular weight of from 100 to 250, for example 150 to 200.

Molecules of the phenol used to prepare additive (I) preferably have a molecular weight on average of less than 1800, preferably less than 800, preferably less than 500, more preferably less than 450, preferably less than 400, preferably less than 350, more preferably less than 325, preferably less than 300 and most preferably less than 275.

The Mannich reaction products of additive (I) may include a mixture of compounds. However as will be appreciated by the skilled person the proportion of each component present in the composition may be manipulated by varying the reaction conditions and the ratio of the reagents used.

Additive (I) may include oligomeric Mannich reaction products. Additive (I) may include polymeric Mannich reaction products.

In embodiments in which additive (I) comprises polymeric or oligomeric species, these preferably have a number average molecular weight of less than 10000, preferably less than 7500, more preferably less than 2000, suitably less than 1500. In some embodiments, the number average molecular weight may be less than 900, suitably less than 850, for example less than 800.

The Mannich reaction product of additive (I) is the product of a reaction between an aldehyde, ammonia and an optionally substituted phenol. These may be reacted in a ratio of 1:1:1 (aldehyde: ammonia: phenol) to provide molecules having the structure shown in figure (i): OH R1 NH2 R/> (i) wherein each R is an optionally substituted alkyl group, for example having I to 24 carbon atoms, n is from 0 to 4 and is preferably 1, and R1 is the aldehyde residue and is preferably hydrogen. Regioisomers of the compounds shown in figure (i) may also be present.

The Mannich reaction product may be formed by reacting the aldehyde, ammonia and phenol in ratio of 2:2:1 to give compounds of formula (ii): R1 OH R1 H2N NH2 R7> (ii) wherein each R is an optionally substituted alkyl group, for example having 1 to 24 carbon atoms, n is from 0 to 3 and is preferably 1, and R1 is the aldehyde residue and is preferably hydrogen. Regioisomers of the compounds shown in figure (ii) may also be present.

Additive (I) may include molecules formed by reaction of the aldehyde, ammonia and phenol in a ratio of 2:1:2 to give compounds of formula (iii): OH R1 R1 OH

N

H I

R (iii)

wherein each R is an optionally substituted alkyl group, for example having 1 to 24 carbon atoms, each n is from 0 to 4 and each is preferably 1, and R1 is the aldehyde residue and is preferably hydrogen. Regioisomers of the compounds shown in figure (iii) may also be present.

In some embodiments additive (I) may comprise the polymeric or oligomeric compounds having the structure shown in figure (iv): r 11 1 R2JfR3 LR>< ix (iv) wherein each R is an optionally substituted alkyl group, for example having 1 to 24 carbon atoms; each n is from 0 to 3 and each is preferably 1; R1 is the aldehyde residue and is preferably hydrogen; x is from 1 to 50, preferably from I to 25 and most preferably from 1 to 10; R2 is either hydrogen or NH2; and R3 is either hydrogen or a group of formula CHR1Ar in which Ar is the residue of an optionally sustituted phenol. Regioisomers of the compounds shown in figure (iv) may also be present, and as the skilled person will appreciate oligomers and polymers typically contain a mixture of compounds.

Additive (I), when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.lppm, preferably at least lppm, for example at least Sppm. It may suitably be present in an amount of at least loppm, preferably at least 2oppm, more preferably at least 25ppm, for example at least 3Oppm. It may be present in an amount of at least 4Oppm or at least 5Oppm.

Additive (I) may be present in an amount of up to S000ppm, preferably up to l000ppm, more preferably up to SOOppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

Additive (II) is the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400. For the avoidance of doubt, the succinic acylating agent used to form additive (II) has a molecular weight of less than 400. The product formed upon reaction with a nitrogen-containing compound may have a higher molecular weight.

Preferably the succinic acylating agent used in the preparation of additive (II) has a molecular weight of less than 350, preferably less than 325, for example less than 300.

The succinic acylating agent is preferably a subsitutued succinic acid, a monosuccinate ester, succinic anhydride or succinic chloride. More preferably the succinic acylating agent is a substitutued succinic acid or succinic anhyd ride.

The succinic acylating agent preferably has an optionally substituted alkyl or alkenyl residue, preferably having from 1 to 20 carbon atoms, more preferably from 2 to 18 carbon atoms, for example from 6 to 16 carbon atoms. In especially preferred embodiments, the succinic acylating agent has a C12 alkyl subsituted. Most preferably it is dodecylsuccinic anydride.

The succinic acylating agent is reacted with a nitrogen-containing compound. Preferred nitrogen containing compounds include ammonia, hydrazine and amines, especially ammonia and amines. Amines suitable for reaction with the succinic acylating agent to form additive (II) include monoamines, for example optionally substituted alkyl amines; and polyamines, for example polyethylene polyamines.

Suitable amines for use in forming additive (II) include hydroxy-substituted amines, for example 3-amino-propanol and aminoethylethanolamine; Cl to C4 alkyl amines, for example methylamine; and polyamines, for exam pie ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine and dimethylaminopropylamine.

Commercially available sources of polyamines typically contain mixtures of isomers and/or oligomers, and products prepared from these commercially available mixtures fall within the scope of the present invention.

Preferred nitrogen containing compounds for reaction with the succinic acylating agent include hydrazine, ethylenediamine and 3-aminopropanol. Especially preferred are ethylenediamine and 3-aminopropanol.

The acylated nitrogen compounds of additive (II) may suitably be formed by the reaction of a molar ratio of succinic acylating agent: nitrogen containing compound of from 10:1 to 1:10, preferably from 5:1 to 1:5, suitably from 2:1 to 1:4, more preferably from 2:1 to 1:2 and most preferably from 2:1 to 1:1. This type of compound and the preparation thereof is well known to those skilled in the art.

Additive (II), when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.lppm, preferably at least lppm, for example at least 5ppm.

It may suitably be present in an amount of at least loppm, preferably at least 2Oppm, more preferably at least 25ppm, for example at least 3oppm. It may be present in an amount of at least 4Oppm or at least 50 ppm.

Additive (II) may be present in an amount of up to 5000ppm, preferably up to l000ppm, more preferably up to 500ppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

Additive (Ill) may be selected from any antioxidant known for use in diesel fuel. Preferred antioxidants include phenolic antioxidants and phenylenediamine antioxidants. Also useful are naturally occurring antioxidants for example tocopherol (vitamin E and derivatives thereof); and nitroxide compounds, for exam pie 2,2,6,6-tetramethylpiperid me-i -oxyl (TEMPO), 4-hydroxy-TEMPO, 4-oxo-TEMPO etc. By phenolic antioxidant additive we mean to include any compound which contains a phenol moiety i.e., a benzene ring which is substituted with a hydroxyl group. This may be a very simple compound, for example a benzene diol, alkyl substituted phenol or a benzene triol.

Alternatively the phenolic antioxidant may be part of a more complex molecule. It may include two phenol moieties, for example, see the compounds disclosed in US 2006/0219979.

Suitable phenolic antioxidant compounds for use in the present invention include those of formula (v): R1 R2 ii --(OH)n R3 (v) wherein R1 is selected from an optionally substituted alkyl or alkenyl group, an aryl group, an ester, a carboxylic acid, an aldehyde, a ketone, an ether, an alcohol, an amine or an amide; R2 and R3 are independently selected from hydrogen, an optionally substituted alkyl or alkenyl group, an aryl group, an ester group, a ketone, an aldehyde, a carboxylic acid, an ether, an alcohol, an amine or an amide; and n is an integer from 1 to 5.

Preferably R1 is an alkyl group, preferably having 1 to 9 carbon atoms, and may be straight chained or branched. Preferably R1 is selected from methyl, ethyl, isopropyl, and tertiarybutyl.

R1 and R2 may together form a cyclic substituent, either alkyl or aryl. R2 and R3 are preferably hydrogen or an alkyl group having 1 to 9 carbon atoms. Preferably R2 and R3 are independently selected from hydrogen, methyl, ethyl, tertiarybutyl and isopropyl. Preferably n is 1,2 or 3.

Preferred phenolic antioxidant compounds for use in the present invention are substituted benzene compounds having 1 or more hydroxy substituents. Examples include tertiarybutylhyd roquinone (TBHQ or MTBHQ), 2,5-di-tertiarybutylhydroquinone (DTBHQ), pyrogallol, pyrocatechol 2,6-di-tert-butyl-4-methylphenol (BHT), propylgallate and tertiarybutylcatechol.

Preferred phenylenediamine antioxidants suitable for use in the present invention include those of formula (vi): R5 R1 R3 \i/ R2 R6/R (vi) wherein R1, R2, R3, R4, R5, R6 and R7 are each independently selected from an optionally substituted alkyl or alkenyl group, an aryl group, an ester, a carboxylic acid, an aldehyde, a ketone, an ether, an alcohol, an amine or an amide. Preferably R1 is hydrogen. Preferably R3 is hydrogen. Preferably R2 is an alkyl group, preferably having 1-10 carbon atoms. More preferably R2 is an alkyl group having 1-5 carbon atoms. Preferably R2 is selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secbutyl and tertiarybutyl. Most preferably R2 is isopropyl or secbutyl. Preferably R4 is an alkyl group, preferably having 1-10 carbon atoms.

More preferably R4 is an alkyl group having 1-5 carbon atoms. R4 is preferably selected from methyl, ethyl, propyl, isopropyl, secbutyl, butyl, tertiarybutyl and isobutyl. Most preferably R4 is isopropyl or sec butyl.

R5, R6 and R7 are preferably selected from hydrogen or alkyl groups, more preferably from hydrogen and alkyl groups having 1-10 carbon atoms, more preferably from hydrogen and alkyl groups having 1-5 carbon atoms. Preferably R5, R6 and R7 are independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, tertiarybutyl, secbutyl and isobutyl. Most preferably R5 is hydrogen. Most preferably R6 is hydrogen. Most preferably R7 is hydrogen.

In some preferred embodiments additive (Ill) comprises a phenolic antioxidant compound, especially a hindered phenolic antioxidant compound. By hindered phenolic antioxidant, we refer to a phenol compound which is preferably ortho-substituted. It may also be para In an especially preferred embodiment additive (Ill) comprises phenylenediamine.

Additive (Ill), when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.1 ppm, preferably at least 1 ppm, for example at least Sppm.

Additive (Ill) may be present in an amount of up to 5000ppm, preferably up to l000ppm, more preferably up to 500ppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

Additive (IV) comprises, in combination, the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier. For the avoidance of doubt, the succinic acylating agent used to form additive (IV) has a molecular weight of more than 700. The product formed upon reaction with a nitrogen-containing compound may have a higher molecular weight.

Preferably the succinic acylating agent used in the preparation of additive (IV) has a molecular weight of at least 800, preferably at least 900, for example at least 950.

It may suitably have a molecular weight of up to 5000, preferably up to 2500, more preferably up to 2000, for example up to 1500, preferably up to 1300, more preferably up to 1200.

The succinic acylating agent is preferably a subsitutued succinic acid, a monosuccinate ester, succinic anhydride or succinic chloride. More preferably the succinic acylating agent is a substitutued succinic acid or succinic anhydride.

The succinic acylating agent preferably has an optionally substituted alkyl or alkenyl residue.

Preferably it is substituted with a larger alkyl chain, for example those having in excess of 50 carbon atoms. Particularly preferred compounds are those in which the succinic acylating agent is substituted with a hydrocarbyl residue 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-i, isobutene, butadiene, isoprene, i-hexene, 1-octene, etc. Preferably these olefins are 1-monoolefins. The hydrocarbyl substituent may also be derived from the halogenated (e.g. chlorinated or brominated) analogs of such homo-or interpolymers.

Alternatively the substituent may be made from other sources which are well known to those skilled in the art.

Especially preferred are succinic acylating agents substituted with a polyisobutene residue of molecular weight of between 600 and 5000, for example between 650 and 2500, preferably between 700 and 2000, most preferably between 800 and 1200.

The succinic acylating agent is reacted with a nitrogen-containing compound. Preferred nitrogen containing compounds include ammonia, hydrazine and amines. Amines suitable for reaction with the succinic acylating agent to form additive (IV) include monoamines, for example optionally substituted alkyl amines; and polyamines, for example polyethylene polyami nes.

Suitable amines for use in forming additive (IV) include hydroxy-substituted amines, for example 3-amino-propanol and aminoethylethanolamine; Cl to C4 alkyl amines, for example methylamine; and polyamines, for exam pie ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine and dimethylaminopropylamine.

Especially preferred nitrogen containing compounds for reaction with the succinic acylating agent include hydrazine, ethylenediamine and aminoethylethanolamine.

The acylated nitrogen compounds of additive (IV) may suitably be formed by the reaction of a molar ratio of succinic acylating agent: nitrogen containing compound of from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2 and most preferably from 2:1 to 1:1.

This type of compound and the preparation thereof is well known to those skilled in the art.

Additive (IV) comprises the combination of the reaction product of a nitrogen-compound and a succinic acylating agent having a molecular weight of more than 700 (an acylated nitrogen compound) and a polyether carrier. Preferred polyether carriers are alkyl ethoxylates and alkyl propoxylates.

Suitably the ratio of acylated nitrogen compound to polyether carrier is from 1:99 to 99:1, preferably from 75:25 to 25:75, for example from 60:40 to 40:60.

In preferred embodiments, the acylated nitrogen compound is suspended or dissolved in the polyether carrier. However, embodiments in which the acylated nitrogen compound and the carrier are added separately to the diesel fuel composition are also within the scope of the present invention.

Additive (IV), when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.lppm, preferably at least lppm, for example at least 5ppm.

Additive (IV) may be present in an amount of up to 5000ppm, preferably up to l000ppm, more preferably up to 500ppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

Preferably the total amount of additives (I), (II), (III) and (IV) present in the fuel composition is at Jeast 0.ippm, preferably at least ippm, for example at least 5ppm. It may suitably be present in an amount of at least lOppm, preferably at least 2Oppm, more preferably at least 25ppm, for example at least 30 ppm. They may be present in an amount of at least 4Oppm or at least 5Oppm.

Suitably the total amount of additives (I), (II), (Ill) and (IV) present in the fuel composition is less than l0000ppm, preferably less than 5000ppm, more preferably less than l000ppm, preferably less than 500ppm, for example less than 400ppm. Suitably they may in total be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

In some preferred embodiments the fuel composition further comprises a further performance enhancing additive (V), in addition to the one or more of additives (I), (II), (III) and (IV) present in the composition. Additive (V) is the product of a Mannich reaction between: (a) an aldehyde; (b) a polyamine; and (c) an optionally substituted phenol, in which the or each substituent of the phenol component (c) has an average molecular weight of less than 400. Preferred features of additive (V) are as defined in the applicant's copending application PCT1GB20081050864.

Preferably additive (V) has a number average molecular weight of less than 10000, more preferably less than 7500, preferably less than 2000, more preferably less than 1500.

Suitably the number average molecular weight of additive (V) is from 300 to 2000, preferably from 300 to 1500, more preferably from 400 to 1300. Preferably additive (V) has a number average molecular weight of less than 900, more preferably less than 850 and most preferably less than 800.

Preferably the aldehyde component (a) used to make additive (V) is an aliphatic aldehyde having ito 10 carbon atoms. Most preferably the aldehyde is formaldehyde.

Polyamine component (b) is preferably a polyalkylene polyamine. Most preferably the polyamine is a polyethylene polyamine.

Preferably the polyamine has 2 to 15 nitrogen atoms, preferably 2 to 8 nitrogen atoms.

In some especially preferred embodiments the polyamine reactants used to make the Mannich reaction products of additive (V) include an optionally substituted ethylene diamine residue.

Polyamine (b) used to make additive (V) is preferably selected from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, propane-i,2-diamine, 2(2-amino-ethylamino) ethanol, and N',N'-bis (2-aminoethyl) ethylenediamine (N(CH2CH2NH2)3). Most preferably the polyamine comprises tetraethylenepentamine or especially ethylenediamine.

Optionally substituted phenol component (c) used to make additive (V) is preferably a mono-substituted phenol. In preferred embodiments the phenol is para substituted.

Preferably component (c) comprises an alkyl substituted phenol in which the phenol carries one or more alkyl chains having a total of less 28 carbon atoms, preferably less than 24 carbon atoms, more preferably less than 16 carbon atoms Preferably the or each alkyl substituent of component (c) has from 8 to 16 carbon atoms, especially 12 carbon atoms.

Molecules of component (c) used to make additive (V) preferably have a molecular weight on average of less than 400, more preferably less than 300.

Additive (V) of the present invention is preferably the reaction product obtained by reacting components (a), (b) and (c) in a molar ratio of from 10:1:10 to 0.1:1:0.1, preferablyfrom 5:1:5 to 0.1:1:0.1, more preferablyfrom 3:1:3 to 0.5:1:0.5.

Some preferred compounds used as additive (V) in the present invention are formed by reacting components (a), (b) and (c) in a molar ratio of 2 parts (a) to 1 part (b) � 0.2 parts (b), to 2 parts (c) � 0.4 parts (c); preferably approximately 2:1:2 (a: b: c). These are commonly known in the art as bis-Mannich reaction products.

In other preferred embodiments additive (V) includes the reaction product of one mole of aldehyde with one mole of polyamine and one mole of phenol. Additive (V) may contain a mixture of compounds resulting from the reaction of components (a), (b), (c) in a 2:1:2 molar ratio and a 1:1:1 molar ratio. Alternatively or additionally the performance enhancing additive may include compounds resulting from the reaction of 1 mole of optionally substituted phenol with 2 moles of aldehyde and 2 moles of polyamine.

Additive (V), when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.1 ppm, preferably at least I ppm, for example at least 5ppm.

Additive (V) may be present in an amount of up to 5000ppm, preferably up to l000ppm, more preferably up to 500ppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm The fuel composition of the present invention may comprise a mixture of two or more of any of each type of additives (I), (II), (III), (IV) and (V). In this specification, any definitions of amounts of each additive present in the composition refer to the total amount of all additives of this type.

In some preferred embodiments the fuel composition further comprises a nitrogen containing detergent. Suitable nitrogen containing detergents include those disclosed in the applicant's co-pending application flu mber PCT1GB20081050864.

This nitrogen containing detergent may be present in addition to the performance enhancing additives (I), (II), (Ill), (IV) and (V), some of which may have been described in the prior art as having detergent properties.

Preferred nitrogen-containing detergents are the reaction product of a carboxylic acid-derived acylating agent and an amine. Such compounds are well known to those skilled in the art.

Preferred acylated nitrogen-containing compounds of this class are those made by reacting a poly(isobutene)-substituted succinic acid-derived acylating agent (e.g., anhydride, acid, ester, etc.) wherein the poly(isobutene) substituent has between about 12 to about 200 carbon atoms with a mixture of ethylene polyamines having 3 to about 9 amino nitrogen atoms per ethylene polyamine and about 1 to about 8 ethylene groups. These acylated nitrogen compounds are formed by the reaction of a molar ratio of acylating agent: amino compound of from 10:1 to 1:10, preferablyfrom 5:1 to 1:5, more preferablyfrom 2:1 to 1:2 and most preferablyfrom 2:1 to 1:1.

Especially preferred nitrogen-containing detergents are those formed by the reaction of a succinic acid-derived acylating agent having a polyisobutene substituent with a molecular weight of from 500 to 1200, preferably 600 to 1000, for example 650 to 850 and a polyethylene polyamine having from 3 to 8, preferably 4 to 7 nitrogen atoms.

Suitable nitrogen containing detergents for use herein include those described in U.S. Pat. Nos. 3,172,892; 3,219,666; 3,272,746; 3,310,492; 3,341,542; 3,444,170; 3,455,831; 3,455,832; 3,576,743; 3,630,904; 3,632,511; 3,804,763, 4,234,435 and U56821307.

1 0 The nitrogen containing detergent, when present, is preferably present in the fuel composition of the present invention in an amount of at least 0.lppm, preferably at least lppm, for example at least 5ppm. It may suitably be present in an amount of at least 1 Oppm, preferably at least 2Oppm, more preferably at least 25ppm, for example at least 3Oppm. It may be present in an amount of at least 4oppm or at least 50 ppm.

The nitrogen containing detergent may be present in an amount of up to 5000ppm, preferably up to l000ppm, more preferably up to SOOppm, for example up to 400ppm. Suitably it may be present in an amount of up to 300ppm, preferably up to 200ppm, for example up to lOOppm.

In some embodiments the diesel fuel composition may comprise a mixture of two or more nitrogen-containing detergents. In such embodiments, the above amounts refer to the total amount of all such detergents present in the composition.

In some preferred embodiments the diesel fuel composition of the present invention further comprises a metal deactivating compound. Any metal deactivating compound known to those skilled in the art may be used and include, for example, the substituted triazole compounds of figure (vii) wherein R and R' are independently selected from an optionally substituted alkyl group or hydrogen. 0 R/N

NR2) NR'2 (vii) Preferred metal deactivating compounds are those of formula (viii):

OHOH

(viii) wherein R1, R2 and R3 are independently selected from an optionally-substituted alkyl group or hydrogen, preferably an alkyl group having from 1 to 4 carbon atoms or hydrogen. R1 is preferably hydrogen, R2 is preferably hydrogen and R3 is preferably methyl. n is an integer from 0 to 5, most preferably 1.

A particularly preferred metal deactivator is N,N'-disalicyclidene-1,2-diaminopropane, and has the formula shown in figure (ix): -bN-J$IoH HO' (ix) Another preferred metal deactivating compound is shown in figure (x):

H H O (x)

The metal deactivating compound, where present, is preferably present in an amount of less than lOOppm, and more preferably less than 5Oppm, preferably less than 3Oppm, more preferably less than 20, preferably less than 15, preferably less than 10 and more preferably less than Sppm. The metal deactivator is preferably present as an amount of from 0.0001 to 5oppm, preferably 0.001 to 20, more preferably 0.01 to loppm and most preferably 0.1 to 5ppm.

The diesel fuel composition of 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, dispersants, detergents, wax anti-settling agents, cold flow improvers, cetane improvers, dehazers, stabilisers, demulsifiers, antifoams, corrosion inhibitors, lubricity improvers, dyes, markers, combustion improvers, odour masks, drag reducers and conductivity improvers.

In particular, the composition of the present invention may further comprise one or more additives known to improve the performance of diesel engines having high pressure fuel systems. Such additives are known to those skilled in the art and include, for example, the compounds described in EP 1900795, EP 1887074, EP 1884556 and WO 2006/135881.

In this specification where amounts of any additive are given, this refers to the actual amount of that additive as the active agent and does not include any diluent which may be present.

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 110°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 of 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 of the present invention may comprise a renewable fuel such as a biofuel composition or biodiesel composition.

The diesel fuel composition may comprise first 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 25 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 of 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 a greater proportion of the 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 of 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.

Preferably, the diesel fuel has a sulphur content of at most 0.1% by weight, more preferably of at most 0.05% by weight, suitably 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 SOppm sulphur by weight, preferably less than 2Oppm, for example lOppm or less.

As detailed above the problem of engine fouling is particularly apparent in fuel compositions comprising a metal-containing species and thus the method of the present invention may be particularly applicable when such fuels are used.

Commonly when present, metal-containing species will 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 will comprise transition metals such as zinc, iron and copper and others such as lead.

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. Such catalysts are often based on metals such as iron, cerium, Group I and Group II metals e.g., calcium and strontium, either as mixtures or alone. Also used are platinum and manganese. 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 metal-containing species comprises a fuel-borne catalyst.

In some embodiments, the metal-containing species comprises zinc.

The amount of metal-containing species in the diesel fuel compositions of the present invention, expressed in terms of the total weight of metal in the species, may be between 0.01 and 50 ppm by weight, for example between 0.1 and 10 ppm by weight, based on the weight of the diesel fuel.

According to a second aspect of the present invention there is provided the use of an additive in a diesel fuel composition to improve the engine performance of a diesel engine having a high pressure fuel system using said diesel fuel composition, wherein the additive is selected from one or more of: (I) the Mannich reaction product of an optionally substituted phenol, ammonia and an aldehyde; (II) the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400; (III) an antioxidant compound; and (IV) the combination of the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier.

Preferred aspects of the second aspect are as defined in relation to the first aspect.

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

Use of the performance enhancing additives of the present invention in this test provides a fuel giving a power loss of less than 10%, preferably less than 5%, preferably less than 4% for example less than 3%, less than 2% or less than 1%.

Preferably the use of a fuel composition of the first aspect in a diesel engine having a high pressure fuel system reduces the power loss of that engine by at least 2%, preferably at least 10%, preferably at least 25%, more preferably at least 50% and most preferably at least 80% compared to the base fuel.

The improvement in performance of the diesel engine having a high pressure fuel system may be measured by an improvement in fuel economy.

Improvement in performance may also be assessed by considering the extent to which the use of the performance enhancing additive reduces the amount of deposit on the injector of an engine having a high pressure fuel system.

By reducing the level of deposits in the injectors the present invention may reduce the need for injector maintenance, thus reducing maintenance costs.

Direct measurement of deposit build up is not usually undertaken, but is usually inferred from the power loss mentioned earlier or fuel flow rates through the injector.

An alternative measure of deposits can be obtained by removing the injectors from the engine and placing in a test rig. A suitable test rig is the DIT 31. The DIT31 has three methods of testing a fouled injector: by measuring the back pressure, the pressure drop or the injector time.

To measure the back pressure, the injector is pressurised to 1000 bar (108 Pa). The pressure is allowed to fall and the time taken for the pressure to drop between 2 set points is measured.

This tests the integrity of the injector which should maintain the pressure for a set period. If there is any failure in performance, the pressure will fall more rapidly. This is a good indication of internal fouling, particularly by gums. For example, a typical passenger car injector may take a minimum of 10 seconds for the pressure to drop between the two set points.

To measure the pressure drop, the injector is pressurised to 1000 bar (108 Pa). The pressure is allowed to fall and at a set point (750 bar -7.5 x i07 Pa) fires. The drop in pressure during the firing period is measured and is compared to a standard. For a typical passenger car injector this may be 80 bar (8 x 106 Pa). Any blockage in the injector will cause a lower pressure drop than the standard.

During the pressure drop measurement the time that the injector opens for is measured. For typical passenger car injectors this may be 10 ms�1 ms. Any deposit may impinge this opening time causing the pressure drop to be affected. Thus a fouled injector may have a shortened opening time as well as a lower pressure drop.

The present invention is particularly useful in the reduction of deposits on 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 use of the second aspect may improve the performance of the engine by reducing the deposits on an injector having an aperture with a diameter of less than 500 pm, preferably less than 200 pm, more preferably less than 150 pm. In some embodiments the use may improve the performance of the engine by reducing deposits on an injector with an aperture having a diameter less than 100 pm, preferably less than 80 pm. The use may improve the performance of an engine in which the injector has more than one aperture, for example more than 4 apertures, for example 6 or more apertures.

Within the injector body, clearances of only 1-2 pm exist between moving parts and there have been reports of engine problems in the field caused by injectors sticking and particularly injectors sticking open. Control of deposits in this area can be very important.

The use of the second aspect may improve the performance of the engine by reducing deposits including gums and lacquers within the injector body.

The use of the second aspect may also improve the performance of the engine by reducing deposits in the vehicle fuel filter.

A reduction of deposits in a vehicle fuel filter may be measured quantitatively or qualitatively.

In some cases this may only be determined by inspection of the filter once the filter has been removed. In other cases, the level of deposits may be estimated during use.

Many vehicles are fitted with a fuel filter which may be visually inspected during use to determine the level of solids build up and the need for filter replacement. For example, one such system uses a filter canister within a transparent housing allowing the filter, the fuel level within the filter and the degree of filter blocking to be observed.

It has been surprisingly been found that when using the fuel compositions of the present invention the level of deposits in the fuel filter are considerably reduced compared with fuel compositions which do not contain the performance enhancing additive of the invention. This allows the filter to be changed much less frequently and can ensure that fuel filters do not fail between service intervals. Thus the use of the present invention may lead to reduced maintenance costs.

Suitably the use of the performance enhancing additive of the present invention allows the interval between filter replacement to be extended, suitably by at least 5%, preferably at least 10%, more preferably at least 20%, for example at least 30% or at least 50%.

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 new test 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 named CEC-F-98-08 (Direct Injection, Common Rail Diesel Engine Nozzle Coking Test). The test is based on a Peugeot DW1O engine using Euro 5 injectors, and will hereinafter be referred to as the DW1O test.

Preferably the use of the performance enhancing additives of the present invention leads to reduced deposits in the DW1O test.

Using this test the inventor found that the use of the performance enhancing additives of the invention in a diesel fuel composition resulted in a reduction in power loss compared with the same fuel not containing the performance enhancing additive.

Deposits on injectors of an engine having a high pressure fuel system may also be measured using a hot liquid process simulator (or HLPS). This equipment allows the fouling of a metallic component, typically a steel or aluminium rod to be measured.

The HLPS equipment, which is generally known to those skilled in the art, includes a fuel reservoir from which fuel is pumped under pressure and passed over a heated stainless steel tube. The level of deposit on the tube after a certain period can then be measured. This is considered a good way of predicting how a much fuel would deposit on an injector. The equipment was modified to allow fuel to recirculate.

Thus the present invention provides the use of a performance enhancing additive as defined in relation to the first aspect to reduce the deposits from a diesel fuel. This may be measured with a hot liquid process simulator.

Although the diesel fuel compositions of the present invention provide improved performance of engines operating at high temperature and pressures, they may also be used with traditional diesel engines. This is important because a single fuel must be provided that can be used in new engines and older vehicles.

In addition to the prevention or reduction of the occurrence of injector fouling as described above, the present inventor has also found that compositions of the present invention may be used to remove some or all of the deposits which have already formed on injectors. This is a further way by which an improvement in performance may be measured.

Thus, the present invention further provides the use of a diesel fuel composition of the first aspect to remove deposits formed in a high pressure diesel engine.

According to a third aspect of the present invention there is provided a method of removing deposits from a diesel engine, the method comprising combusting in the engine a diesel fuel composition of the first aspect.

The method of the third aspect of the present invention involves "clean-up" of the injectors.

Removal of deposits from the injectors may lead to an increase in power output of the engine.

"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. 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.

The increase in power output is a significant advantage provided by the present invention. In some cases where rapid removal of deposits is achieved, the resultant increase in power will be readily observable by a user which will lead to increased consumer satisfaction.

Preferably the method of the present invention provides an increase in power of an engine of at least 1% after running the engine for 32 hours, preferably an increase in power of at least 2%, for example at least 3%, suitably at least 4%, for example at least 5%. In this definition the percentage increase in power is measured with respect to the power output of the engine immediately prior to running the engine according to the method of the third aspect of the 1 0 present invention.

Suitably the method of the present invention provides an increase in power of an engine of at least 1% after running the engine for 24 hours, preferably an increase in power of at least 2%, for example at least 3%, suitably at least 4%, for example at least 5%.

Suitably the method of the present invention provides an increase in power of an engine of at least 1% after running the engine for 12 hours, preferably an increase in power of at least 2%, for example at least 3%, suitably at least 4%, for example at least 5%.

Suitably the method of the present invention provides an increase in power of an engine of at least 1% after running the engine for 5 hours, preferably an increase in power of at least 2%, for example at least 3%, suitably at least 4%, for example at least 5%.

In some embodiments the method of the present invention may provide an increase in power of at least 1% after running the engine for 1 hour, preferably an increase in power of at least 2%, for example at least 3%, suitably at least 4%, for example at least 5%.

The present invention removes deposits from a fouled engine, in particular a fouled injector. It is an aim of preferred embodiments to remove as many of the deposits as possible and thus restore the power output of the engine to the level obtained when clean injectors are fitted.

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

Suitably after running the engine according to the method of the present invention for at least 32 hours, the engine has a power output of at least 90% of the power output obtained when using clean injectors, suitably at least 93%, for example at least 95%, preferably at least 97%, for example at least 98%.

Suitably after running the engine according to the method of the present invention for at least 24 hours, the engine has a power output of at least 90% of the power output obtained when using clean injectors, suitably at least 93%, for example at least 95%, preferably at least 97%, for example at least 98%.

Suitably after running the engine according to the method of the present invention for 12 hours, the engine has a power output of at least 90% of the power output obtained when using clean injectors, suitably at least 93%, for example at least 95%, preferably at least 97%, for example at least 98%.

Suitably after running the engine according to the method of the present invention for at least 5 hours, the engine has a power output of at least 90% of the power output obtained when using clean injectors, suitably at least 93%, for example at least 95%, preferably at least 97%, for example at least 98%.

In some embodiments after running the engine according to the method of the present invention for 1 hour, the engine has a power output of at least 90% of the power output obtained when using clean injectors, suitably at least 93%, for example at least 95%, preferably at least 97%, for example at least 98%.

Any feature of any aspect of the invention may be combined with any other feature, where appropriate.

Claims

C'aims 1. A diesel fuel composition comprising one or more performance enhancing additives selected from: (I) the Mannich reaction product of an optionally substituted phenol, ammonia and an aldehyde; (II) the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400; (Ill) an antioxidant compound; and (IV) the combination of the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier.
2. A diesel fuel composition according to claim 1 which comprises performance enhancing additive (I).
3. A diesel fuel composition according to claim 1 or claim 2 which comprises performance enhancing additive (II).
4. A diesel fuel composition according to any preceding claim which comprises performance enhancing additive (Ill).
5. A diesel fuel composition according to any preceding claim which comprises performance enhancing additive (IV).
6. A diesel fuel composition according to any preceding claim which comprises a further performance enhancing additive (V), wherein additive (V) is the product of a Mannich reaction between: (a)an aldehyde; (b)a polyamine; and (c) an optionally substituted phenol, in which the or each substituent of the phenol component (c) has an average molecular weight of less than 400.
7. A diesel fuel composition according to any preceding claim which further comprises one or more nitrogen containing detergents, and/or one or more metal deactivating compounds.
8. The use of an additive in a diesel fuel composition to improve the engine performance of a diesel engine having a high pressure fuel system using said diesel fuel composition, wherein the additive is selected from one or more of: (I) the Mannich reaction product of an optionally substituted phenol, ammonia and an aldehyde; (II) the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of less than 400; (Ill) an antioxidant compound; and (IV) the combination of the reaction product of a nitrogen-containing compound and a succinic acylating agent having a molecular weight of more than 700 and a polyether carrier.
9. The use according to claim 8 wherein the improvement in performance is due to a reduction in the level of deposits from the fuel.
10. A method of removing deposits from a diesel engine, the method comprising combusting in the engine a diesel fuel composition as claimed in any of claims 1 to 7.