Metal and especially metal containing additives have been incorporated in fuel compositions for many years. The additives may provide a number of effects on the fuel. Certain additives are known to improve the combustion properties of the fuel, for example certain additives may increase the octane number of petroleum fuels. The additives may also provide an effect during combustion, in particular during combustion in an internal combustion engine. For example metal or metal containing additives may deposit metal or metal compounds on surface of an internal combustion engine during combustion. In particular metal or metal compounds may deposit on the valves or valve seats of an internal combustion engine. Such deposits may protect these components of the engine from wear caused during operation, for example the deposits may protect the valve seats from wear and consequential recession.

It has also been found that certain metals may be deposited such that detrimental effects are observed. For example it has been found that iron or iron compounds when present at high treat rates may deposit on the spark plugs of internal combustion engines. In particular iron components may deposit on the insulating section of a spark plug and to such an extent that the insulating properties of the insulating section are degraded. When degraded to a sufficient degree, on sparking the designed spark path may not be followed and some discharge through the iron-containing deposits may occur, particularly in critical vehicles and after extended mileage. This may lead to mis- firing of the engine which may reduce efficiency, may be noticeable to the driver or may in extreme circumstances lead to reduced operability of an engine or a vehicle to which it is fitted.

We have found that when iron or an iron compound is provided in a fuel in an amount to provide iron in an amount of at least 15 mg per kg of fuel, on combustion spark plug fouling may occur and detrimental be effects observed, particularly in critical vehicles

and after extended mileage. The combustion products of iron and/or iron compounds include iron oxides. For example, when a fuel comprising ferrocene is dosed in fuel in an amount to provide 18 mg of iron per kg of fuel, misfiring of an internal combustion engine may occur. Ferrocene is a well-known metal-containing fuel additive with a significant capability to increase octane quality in unleaded gasoline. It is used as an octane trimming additive at refineries to enhance octane quality in gasoline, to assist meeting gasoline octane specifications.

It is recommended that ferrocene be added to fuel at a treat rate of no greater than 30mg Ferrocene/kg. Ferrocene comprises 30wt% iron, so this treat rate equates to 9mg Fe/kg. For octane enhancement purposes, iron added as ferrocene is used typically at a treat rate of 9mg Fe/kg. However, this treat rate may sometimes be exceeded unintentionally or intentionally to enhance octane quality in gasoline having particularly low octane rating to ensure that gasoline octane specifications are met.

It has also been found that low quality/purity iron compounds such as ferrocene compositions containing high amounts of impurities may cause spark plug fouling at treat rates below the recommended maximum of 30mg Ferrocene/kg (9mg Fe/kg) of high quality products.

There is consequently a desire to provide a means by which plug fouling caused by high iron treat rates or by impure iron compositions may be reduced and/or prevented.

In a first aspect there is provided use of potassium and/or a potassium compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a second aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) potassium and/or a potassium compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the potassium and/or a potassium compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the

iron, iron compound or combustion product thereof.

In a third aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) potassium and/or a potassium compound; and (iii) a fuel.

In a fourth aspect there is provided use of potassium and/or a potassium compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a fifth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) potassium and/or a potassium compound; and (iii) a fuel; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the potassium and/or a potassium compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The potassium is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

The term"plug fouling"will understood by one skilled in the art. It is typically taken to mean deposition on a plug which may cause operability problems or performance degradation, for example as described and tested in the present Examples.

IRON Iron or iron compounds may be added to fuels for a number of reasons. Volatile iron- containing additives may contribute to increased driveability, in both the short and long term. Initially, an octane improvement results from the use of iron materials, such as PLUTOcenRTM. Iron compounds are known to reduce in-cylinder deposits through oxidation of carbonaceous material, again, a volatile species would be expected to provide such benefits throughout the cylinder as opposed to only those parts wetted by liquid fuel. Thin films of iron containing material deposited on the cylinder walls are

suspected as providing fuel consumption and emissions reduction benefits, especially for CO, NOx and unburned hydrocarbons.

Preferably the iron and/or iron compound is an iron compound.

Preferably the iron compound is a ferrocene and/or a substituted ferrocene.

Preferably the iron and/or iron compound is a ferrocene and/or a substituted ferrocene.

Preferably the iron compound is a ferrocene.

Preferably the iron and/or iron compound is a ferrocene.

Preferably the iron compound is an iron complex selected from bis-cyclopentadienyl iron and substituted bis-cyclopentadienyl iron.

Preferably the iron and/or iron compound is an iron complex selected from bis- cyclopentadienyl iron and substituted bis-cyclopentadienyl iron.

Preferably the iron compound is bis-cyclopentadienyl iron.

Preferably the iron and/or iron compound is bis-cyclopentadienyl iron.

The iron compound may be an iron complex of bis-cyclopentadienyl or substituted bis- cyclopentadienyl complex of iron, wherein the substituents can be, for example, one or more Ci. alkyl groups, preferably Cul-2 alkyl groups. A combination of such iron complexes may also be used.

Suitable alkyl-substituted-dicyclopentadienyl iron complexes are cyclopentadienyl- (methylcyclopentadienyl) iron, cyclopentadienyl (ethyl-cyclopentadienyl) iron, bis- (methylcyclopentadienyl) iron, bis- (ethylcyclopentadienyl) iron, bis- (1, 2-dimethyl- cyclopentadienyl) iron, and bis- (1-methyl-3-ethylcyclo-pentadienyl) iron. These iron complexes can be prepared by the processes taught in US-A-2680756, US-A-2804468, GB-A-0733129 and GB-A-0763550. Another volatile iron complex is iron pentacarbonyl.

Suitable iron complexes are bis-cyclopentadienyl iron and/or bis- (methylcyclo-pentadienyl) iron.

A highly preferred iron complex is ferrocene (i. e. bis-cyclopentadienyl iron).

The co-ordination chemistry relevant to the solubilisation of transition metals, including iron, in hydrocarbon solvents, e. g. diesel fuel, is well known to those skilled in the art (see e. g. WO-A-87/01720 and WO-A-92/20762).

A wide range of so-called"substituted ferrocenes"are known and may be used in the present invention (see e. g. Comprehensive Organic Chemistry, Eds. Wilkinson et al., Pergamon 1982, Vol. 4: 475-494 and Vol. 8: 1014-1043). Substituted ferrocenes for use in the invention include those in which substitution may be on either or both of the cyclopentadienyl groups. Suitable substituents include, for example, one or more Cl-5 alkyl groups, preferably Cr 2 alkyl groups.

Particularly suitable alkyl-substituted-dicyclopentadienyl iron complexes (substituted ferrocenes) include cyclopentadienyl (methylcyclopentadienyl) iron, bis- (methylcyclopentadienyl) iron, bis- (ethylcyclopentadienyl) iron, bis- (1, 2- dimethylcyclopentadienyl) iron and 2, 2-diethylferrocenyl-propane.

Other suitable substituents that may be present on the cyclopentadienyl rings include cycloalkyl groups such as cyclopentyl, aryl groups such as tolylphenyl, and acetyl groups, such as present in diacetyl ferrocene. A particularly useful substituent is the hydroxyisopropyl group, resulting in (a-hydroxyisopropyl) ferrocene. As disclosed in WO-A-94/09091, (a-hydroxyisopropyl) ferrocene is a room temperature liquid.

Ferrocenes linked by a"bridge"may used in the present invention. Suitable compounds are taught in PCT/GB01/03897 and PCT/GB2002/004002.

Other organometallic complexes of iron may also be used in the invention, to the extent that these are fuel soluble and stable. Such complexes include, for example, iron pentacarbonyl, di-iron nonacarbonyl, (1,3-butadiene)-iron tricarbonyl, and (cyclopentadienyl)-iron dicarbonyl dimer. Salts such as di-tetralin iron tetraphenylborate (Fe (C, oH12) 2 (B (C6H5) 4) 2) may also be employed.

As a result of a combination of their solubility, stability, high iron content and, above all, volatility, the substituted ferrocenes are particularly preferred iron compounds for use in the invention. Ferrocene itself is an especially preferred iron compound on this basis.

Ferrocene of suitable purity is sold in a range of useful forms as PLUTOcenRTM and as solutions, SatacenRTM both by Octel Deutschland GmbH.

The iron compounds for use in the invention need not feature iron-carbon bonds in order to be fuel soluble and stable. Salts may be used; these may be neutral or overbased.

Thus, for example, overbased soaps including iron stearate, iron oleate and iron naphthenate may be used. Methods for the preparation of metal soaps are described in The Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed, Vol. 8: 432-445, John Wiley & Sons, 1993. Suitable stoichiometric, or neutral, iron carboxylates for use in the invention include the so-called'drier-iron'species, such as iron tris (2-ethylhexanoate) [19583-54-1].

Iron complexes not featuring metal-carbon bonds and not prepared using carbonation may also be used in the invention provided these are adequately fuel soluble and stable.

Examples include complexes with p-diketonates, such as tetramethylheptanedionate.

Iron complexes of the following cheating ligands are also suitable for use in the invention: aromatic Mannich bases such as those prepared by reaction of an amine with an aldehyde or ketone followed by nucleophilic attack on an active hydrogen containing compound, e. g. the product of the reaction of two equivalents of (tetrapropenyl) phenol, two of formaldehyde and one of ethylenediamine, * hydroxyaromatic oximes, such as (polyisobutenyl)-salicylaldoxime. These may be prepared by reaction of (polyisobutenyl) phenol, formaldehyde and hydroxylamine ; Schiff bases such as those prepared by condensation reactions between aldehydes or ketones (e. g. (tert-butyl)-salicylaldehyde) and amines (e. g. dodecylamine). A tetradentate ligand may be prepared using ethylenediamine (half equivalent) in place of dodecylamine ; substituted phenols, such as 2-substituted-8-quinolinols, for example 2-dodecenyl-8- quinolinol or 2-N-dodecenylamino-methylphenol ; substituted phenols, such as those wherein the substituent is NR2 or SR in which R

is a long chain (e. g. 20-30 C atoms) hydrocarbyl group. In the case of both a-and p- substituted phenols, the aromatic rings may beneficially be further substituted with hydrocarbyl groups, e. g. lower alkyl groups; carboxylic acid esters, in particular succinic acid esters such as those prepared by reaction of an anhydride (e. g. dodecenyl succinic anhydride) with a single equivalent of an alcohol (e. g. triethylene glycol) ; acylated amines. These may be prepared by a variety of methods well known to those skilled in the art. However, particularly useful chelate are those prepared by reaction of alkenyl substituted succinates, such as dodecenyl succinic anhydride, with an amine, such as N, N'-dimethyl ethylene diamine or methyl-2-methylamino-benzoate ; amino-acids, for example those prepared by reaction of an amine, such as dodecylamine, with an a, p-unsaturated ester, such as methylmethacrylate. In cases where a primary amine is used, this may be subsequently acylated, such as with oleic acid or oleyl chloride ; hydroxamic acids, such as that prepared from the reaction of hydroxylamine with oleic acid, linked phenols, such as those prepared from condensation of alkylated phenols with formaldehyde. Where a 2: 1 phenol : formaldehyde ratio is used the linking group is CH2.

Where a 1: 1 ratio is employed, the linking group is CH20CH2 ; alkylated, substituted pyridines, such as 2-carboxy-4-dodecylpyridine ; borated acylated amines. These may be prepared by reaction of a succinic acylating agent, such as poly (isobutylene) succinic acid, with an amine, such as tetraethylenepentamine. This procedure is then followed by boronation with a boron oxide, boron halide or boronic acid, amide or ester. Similar reactions with phosphorus acids result in the formation of phosphorus-containing acylated amines, also suitable for providing an oil-soluble iron chelate for use in the invention; pyrrole derivatives in which an alkylated pyrrole is substituted at the 2-position by OH, NH2, NHR, COsH, SH or C (O) H. Particularly suitable pyrrole derivatives include 2- carboxy-t-butylpyrroles ; 'su sulphonic acids, such as those of the formula R'SO3H, where R'is a C, to about C60 hydrocarbyl group, e. g. dodecylbenzene sulphonic acid; organometallic complexes of iron, such as ferrocene, substituted ferrocenes, iron naphthenate, iron succinates, stoichiometric or over-based iron soaps (carboxylate or sulphonate), iron picrate, iron carboxylate and iron-diketonate complexes.

Suitable iron picrates for use in the invention include those described in US-A-4,370, 147 and US-A-4,265, 639.

Other iron-containing compounds for use in the invention include those of the formula M (R) x. nL wherein: M is an iron cation; R is the residue of an organic compound RH in which R is an organic group containing an active hydrogen atom H replaceable by the metal M and attached to an O, S, P, N or C atom in the group R; x is 2 or 3; n is 0 or a positive integer indicating the number of donor ligand molecules forming a dative bond with the metal cation; and L is a species capable of acting as a Lewis base.

To observe the advantages of the present invention, the iron and/or an iron compound will be present in an amount to provide enough iron such that plug fouling will occur. This will typically be will iron in an amount of at least 15 mg per kg of fuel. However, as explained herein this amount may be lower when an iron containing composition comprising impurities is provided.

In one aspect the iron and/or an iron compound provides iron in an amount of at least 18 mg per kg of fuel.

In one aspect the iron and/or an iron compound provides iron in an amount of at least 22.5 mg per kg of fuel.

In one aspect the iron and/or an iron compound provides iron in an amount of at least 30 mg per kg of fuel.

In one aspect the iron and/or an iron compound provides iron in an amount of from 15 to 30 mg per kg of fuel.

POTASSIUM Preferably the potassium and/or potassium compound is a potassium compound.

A very extensive range of compounds have been claimed to be suitable as a means to provide alkali metals, in particular potassium, in fuel-soluble forms for various purposes including gasoline soluble forms for use as VSR additives.

Potassium salts used may be acidic, neutral or basic (that is over-based, hyperbased or superbased).

Acidic salts may be prepared with an excess of organic acid over potassium, neutral salts react essentially stoichiometric quantities of acid and base and basic salts contain an excess of cations, and are typically prepared by'blowing'a suspension of metal base in a solution of organic acid with gaseous CO2.

In aspects of the present invention colloidal suspensions of inorganic salts of potassium may be used.

Suitable organic acids for use in preparing the potassium compound are extensively reviewed in W087/01126 to Johnston et al. These include sulphur acids, carboxylic acids and phosphorus acids.

Some workers have expressed fears that catalyst poisoning may limit the usefulness of the phosphorus acids.

In one aspect the potassium compound is prepared from a sulphur acid.

Sulphur acids include sulphonic, sulphamic, thiosulphonic, sulphenic, sulphinic, partial ester sulphuric, sulphurous and thiosulphuric acids. The sulphur acids may be aliphatic or aromatic, including mono-or poly-nuclear aromatic acids or cycloaliphatic compounds. A typical example is alkylbenzene sulphonic acid salt of potassium.

Sulphonates from detergent manufacture by-products are frequently encountered.

Carboxylic acids include aliphatic, cycloaliphatic and aromatic mono-and poly-basic carboxylic acids, naphthenic, alkyl or alkenyl cyclopentanoic and hexanoic acids and the corresponding aromatic acids. Branched chain carboxylic acids, including 2- ethylhexanoic acid and propylene tetramer substituted maleic acids may be used.

Carboxylic acid fractions featuring various, mixed hydrocarbon chains, such as tall oils which also contain rosins are also encountered. A typical carboxylic acid is the potassium salt of alkyl-arylamide of carboxylic acid (CAS 686603-91-8).

Salts of phenols (generally referred to as phenates) may be used. These are of the general formula : (R*) a- (Ar*)- (OH) m where R* is an aliphatic group of 4 to 400 C atoms, a is an integer of 1-4, Ar* is a polyvalent aromatic hydrocarbon nucleus of up to about 14 C atoms and m is an integer from 1-4, provided that there are at least about 8 C atoms per acid equivalent provided by the R* groups. The R* groups may be substituted provided that this does not alter the essentially hydrocarbon character of the groups.

Phosphorus acids may also be used, for example the phosphonic and thiophosphonic acids prepared by reaction of P2S5 with petroleum fractions such as bright stock or with polymeric materials prepared from C2 to C6 mono-olefins, such as poly- (butenes).

Appropriate technology for preparation of a range of phosphorus additives is referenced in WO 87/01126.

EP 207,560 and EP 555,006 describe ranges of succinic acid derivatives, substituted on at least one of the alpha carbon atoms with a C20 to Csoo hydrocarbyl group, optionally connected to the other alpha-carbon atom by a hydrocarbon moiety of from 1 to 6 carbon atoms. Such derivatives may be further derivatised by reaction of one carboxyl group with an alcohol or an amine preparing, respectively, the hemi-ester or the amide.

A typical succinic acid derivative is the potassium salt of the hemi-ester of alkenyl PIBSA.

Preferred acid salts are those of potassium with the succinic acid derivatives, as described immediately above, or of alkyl benzene sulphonic acids, especially dodecyl benzene sulphonic acid.

Neutral salts are preferred. Salts which are resistant to extraction into aqueous phases are preferred.

The alternative of providing a fuel-stable colloidal suspension of a metal salt having a mean particle size of 1 micron, preferably 0.5 micron or less is illustrated in US-A- 5,090, 966 to Crawford et al. An emulsion of a solution of a suitable metal salt, whether potassium borate, carbonate, bicarbonate or acetate is prepared, optionally using an emulsifying agent is prepared in some carrier oil. The solvent is then removed, typically

by heating whilst subjecting to rapid agitation. Preferred in-situ preparations of metal borate products, preferred carrier oils and preferred emulsifying agents are set out in the Patent. Such colloidal suspensions are also preferred sources of potassium for use according to the invention.

Mixtures of any or all of the above-mentioned acids may be employed in order to provide a fuel-soluble and stable source of potassium ions. Potassium ions may be employed as a mixture of solution and colloidal suspension sources.

In one preferred aspect the potassium compound is a potassium sulphonate.

In one preferred aspect the potassium and/or potassium compound provides potassium in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the potassium and/or potassium compound provides potassium in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the potassium and/or potassium compound provides potassium in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the potassium and/or potassium compound provides potassium in an amount of from 6 to 12 mg per kg of fuel.

POTASSIUM AND IRON In one preferred aspect the ratio by weight of potassium to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of potassium to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of potassium to iron is from 1: 5 to 1: 1.

FURTHER ASPECTS LEAD We have also found that the potassium and/or a potassium compound of the present invention may be supplemented with or may be entirely replaced by lead or a lead compound.

Thus in a sixth aspect there is provided use of lead and/or a lead compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a seventh aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) lead and/or a lead compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the lead and/or a lead compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the iron, iron compound or combustion product thereof.

In a eighth aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) lead and/or a lead compound; and (iii) a fuel.

In a ninth aspect there is provided use of lead and/or a lead compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a tenth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) lead and/or a lead compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel

with a spark plug, such that the lead and/or a lead compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The lead is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

S BLOCK METALS We have also found that the potassium and/or a potassium compound of the present invention may be supplemented with or may be entirely replaced by a metal selected from the s block of the periodic table ("an s block metal") or a compound comprising a metal selected from the s block of the periodic table ("an s block compound").

Thus in a eleventh aspect there is provided use of an s block metal and/or an s block compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a twelfth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) an s block metal and/or an s block compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the s block metal and/or s block compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the iron, iron compound or combustion product thereof.

In a thirteenth aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) an s block metal and/or an s block compound; and (iii) a fuel.

In a fourteenth aspect there is provided use of an s block metal and/or an s block compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a fifteenth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) an s block metal and/or an s block compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the s block metal and/or s block compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The s block metal is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

MANGANESE We have also found that the potassium and/or a potassium compound of the present invention may be supplemented with or may be entirely replaced by manganese or a manganese compound.

Thus in a sixteenth aspect there is provided use of manganese and/or a manganese compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a seventeenth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) manganese and/or a manganese compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the manganese and/or manganese compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the iron, iron compound or combustion product thereof.

In a eighteenth aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) manganese and/or a manganese compound; and (iii) a fuel.

In a nineteenth aspect there is provided use of manganese and/or a manganese compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a twentieth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) manganese and/or a manganese compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the manganese and/or manganese compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The manganese is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

CERIUM We have also found that the potassium and/or a potassium compound of the present invention may be supplemented with or may be entirely replaced by cerium or a cerium compound.

Thus in a twenty first aspect there is provided use of cerium and/or a cerium compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a twenty second aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) cerium and/or a cerium compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the cerium and/or cerium compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the iron,

iron compound or combustion product thereof.

In a twenty third aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) cerium and/or a cerium compound; and (iii) a fuel.

In a twenty fourth aspect there is provided use of cerium and/or a cerium compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a twenty fifth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) cerium and/or a cerium compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the cerium and/or cerium compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The cerium is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

PHOSPHORUS We have also found that the potassium and/or a potassium compound of the present invention may be supplemented with or may be entirely replaced by phosphorus or a phosphorus compound.

Thus in a twenty sixth aspect there is provided use of phosphorus and/or a phosphorus compound for prevention and/or inhibition of, and/or ameliorating the adverse effects of, fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a twenty seventh aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i)

iron and/or an iron compound, (ii) phosphorus and/or a phosphorus compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the phosphorus and/or phosphorus compound prevents and/or inhibits, and/or ameliorates the adverse effects of, fouling of the spark plug by the iron, iron compound or combustion product thereof.

In a twenty eighth aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) phosphorus and/or a phosphorus compound; and (iii) a fuel.

In a twenty ninth aspect there is provided use of phosphorus and/or a phosphorus compound for prevention and/or inhibition of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof.

In a thirtieth aspect there is provided a method for preventing and/or inhibiting of fouling of a spark plug of an internal combustion engine by iron, an iron compound or a combustion product thereof, comprising; (a) providing a fuel composition comprising (i) iron and/or an iron compound, (ii) phosphorus and/or a phosphorus compound; and (iii) a fuel ; (b) combusting the fuel composition in an internal combustion engine by igniting the fuel with a spark plug, such that the phosphorus and/or phosphorus compound prevents and/or inhibits fouling of the spark plug by the iron, iron compound or combustion product thereof.

The phosphorus is present in amount to provide the required reduction and/or prevention of, and/or amelioration of the adverse effects of, spark plug fouling.

LEAD Preferably the lead and/or lead compound is a lead compound.

A broad range of lead compounds have been claimed to be suitable as a means to deliver lead, in fuel-soluble forms, for various purposes including gasoline soluble forms for use as anti-knock additives.

In a preferred aspect the lead compound is a tetraalkyl lead compound.

In a preferred aspect the lead and/or lead compound is a tetraalkyl lead compound.

Usually the tetraalkyl lead compound will be a tetra-lower alkyl lead, such as tetramethyl lead, tetraethyl lead (otherwise, commonly known as"TEL"), dimethyl ethyl lead, dimethyl diethyl lead, tri-ethyl methyl lead, tetraisopropyl lead, and the like, including mixtures thereof.

There are numerous references to tetraalkyl lead compounds-such as TEL-in the art.

For example, reference may be made to any one of the following US patents: 1705723, 1798593,2004160, 2029301,2000069, 241453,2400383, 2043224,3151142, 2515821, 2477465,2464398, 1645375,1652812, 1661809,1661810, 1717961,1907701, 1962173 and 2686799 (the contents of which are incorporated herein by reference).

The tetraalkyl lead compound is typically prepared by known processes wherein lead/sodium alloy (PbNa) is reacted with an alkyl halide.

There are numerous references to the preparation of tetraalkyl lead compounds-such as TEL-in the art. For example, reference may be made to any one of the following US patents: 2411453,1661809 and 1661810 (the contents of which are incorporated herein by reference).

Preferably, the tetraalkyl lead compound is TEL.

Typically, the TEL is prepared by the reaction of lead/sodium alloy (PbNa) with ethyl chloride.

The tetraalkyl lead compound and the iron complex can be used in conjunction with at least one lead scavenger-such as a poly-halo-hydrocarbon lead scavenger. A typical lead scavenger comprises from 2 to 8 carbon atoms and from 2 to 3 halogen atoms and has a boiling point less than 300°C, preferably less than 210°C. Suitable scavengers are ethylene dibromide and ethylene dichloride. A preferred scavenger is dichloroethane or dibromoethane.

In one preferred aspect the lead and/or lead compound provides lead in an amount of at

least 3 mg per kg of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of from 6 to 12 mg per kg of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of at least 0. 01g per litre of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of at least 0.015g per litre of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of at least 0.03g per litre of fuel.

In one preferred aspect the lead and/or lead compound provides lead in an amount of at least 0.05g per litre of fuel.

LEAD AND IRON In one preferred aspect the ratio by weight of lead to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of lead to iron is from 1: 12 to 1: 1.

In one preferred aspect the ratio by weight of lead to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of lead to iron is from 1: 5 to 1: 1.

S BLOCK Preferably the s block metal or the s block metal of the s block compound is selected from magnesium and calcium.

The s block metal may be magnesium.

The s block metal may be calcium.

Preferably the s block metal and/or s block metal compound is an s block metal compound.

A very extensive range of compounds have been claimed to be suitable as a means to provide s block metals, in particular magnesium and/or calcium, in fuel-soluble forms for various purposes.

The s block metal or the s block compound may be delivered in a manner analogous to that given above in respect of potassium. Each of the forms of potassium disclosed above may be used to provide the analogous s block compound, such as the analogous calcium or magnesium compound.

Particularly preferred s block compounds are overbased carboxylic acid salts of the respective s block metal, such as overbased carboxylic acid salts of magnesium and/or calcium.

In one preferred aspect the s block metal and/or s block compound provides the s block metal in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the s block metal and/or s block compound provides the s block metal in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the s block metal and/or s block compound provides the s block metal in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the s block metal and/or s block compound provides the s block metal in an amount of from 6 to 12 mg per kg of fuel.

In one preferred aspect the calcium and/or calcium compound provides calcium in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the calcium and/or calcium compound provides calcium in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the calcium and/or calcium compound provides calcium in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the calcium and/or calcium compound provides calcium in an amount of from 6 to 12 mg per kg of fuel.

In one preferred aspect the magnesium and/or magnesium compound provides magnesium in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the magnesium and/or magnesium compound provides magnesium in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the magnesium and/or magnesium compound provides magnesium in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the magnesium and/or magnesium compound provides magnesium in an amount of from 6 to 12 mg per kg of fuel.

S BLOCK AND IRON In one preferred aspect the ratio by weight of s block metal to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of s block metal to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of s block metal to iron is from 1: 5 to 1: 1.

MANGANESE Preferably the manganese and/or manganese compound is a manganese compound.

The most desirable general type of manganese carbonyl compounds utilised in accordance with this invention comprise organomanganese polycarbonyl compounds.

For best results, use should be made of a cyclopentadienyl manganese tricarbonyl compound of the type described in U. S. Pat. Nos. 2,828, 417 and 3,127, 351. Thus use can be made of such compounds as cyclopentadienyl manganese tricarbonyl, methylcyclopentadienyl manganese tricarbonyl, ethylcyclopentadienyl manganese tricarbonyl, dimethylcyclopentadienyl manganese tricarbonyl, trimethylcyclopentadienyl manganese tricarbonyl, propylcyclopentadienyl manganese tricarbonyl, isopropylcyclopentadienyl manganese tricarbonyl, butylcyclopentadienyl manganese tricarbonyl, pentylcyclopentadienyl manganese tricarbonyl, hexylcyclopentadienyl manganese tricarbonyl, ethylmethylcyclopentadienyl manganese tricarbonyl, dimethyloctylcyclopentadienyl manganese tricarbonyl, dodecylcyclopentadienyl manganese tricarbonyl, indenyl manganese tricarbonyl, and like compounds in which the cyclopentadienyl moiety contains up to about 18 carbon atoms.

A preferred organomanganese compound is cyclopentadienyl manganese tricarbonyl.

Particularly preferred for use in the practice of this invention is methylcyclopentadienyl manganese tricarbonyl.

Methods for the synthesis of cyclopentadienyl manganese tricarbonyls are well documented in the literature. See for example, in addition to U. S. Pat. Nos. 2,818, 417 and 3,127, 351 noted above, U. S. Pat. Nos. 2,868, 816; 2,898, 354; 2,960, 514; and 2,987, 529, among others.

Other organomanganese compounds which may be employed include the non-ionic diamine manganese tricarbonyl halide compounds such as bromo manganese tricarbonyl halide compounds such as bromo manganese dianiline tricarbonyl and bromo manganese dipyridine tricarbonyl, described in U. S. Pat. No. 2,902489 ; the acyl manganese tricarbonyls such as methylacetyl cyclopentadienyl manganese tricarbonyl and benzoyl methyl cyclopentadienyl manganese tricarbonyl, described in U. S. Pat No.

2,959, 604; the aryl manganese pentacarbonyls such as phenyl manganese

pentacarbonyl, described in U. S. Pat. 3,007, 953; and the aromatic cyanomanganese dicarbonyls such as mesitylene cyanomanganese dicarbonyl, described in U. S. Pat. No.

3,042, 693. Likewise, use can be made of cyclopentadienyl manganese dicarbonyl compounds of the formula RMn (CO) 2L, where R is a substituted or unsubstituted cyclopentadienyl group having 5 to 18 carbon atoms, and L is a ligand, such as an olefin, an amine, a phosphine, SO2, tetrahydrofuran, or the like. Such compounds are referred to, for example in, Herberhold, M. , Metal s-Complexes, Vol. II, Amsterdam, Elsevier, 1967 or Giordano, P. J. and Weighton, M. S., Inorg. Chem., 1977,16, 160. Manganese pentacarbonyl dimer (dimanganese decarbonyl) can also be employed if desired.

Preferably the manganese compound is a manganese complex.

Preferably the manganese compound is selected from cyclopentadienyl manganese tricarbonyl and substituted cyclopentadienyl manganese tricarbonyl.

The manganese compound may cyclopentadienyl manganese tricarbonyl and substituted cyclopentadienyl manganese tricarbonyl, wherein the substituents can be, for example, one or more C15 alkyl groups, preferably C, 2 alkyl groups. A combination of such manganese complexes may also be used.

Preferably the manganese compound is methylcyclopentadienyl manganese tricarbonyl.

Preferably the manganese and/or the manganese compound is selected from cyclopentadienyl manganese tricarbonyl and substituted cyclopentadienyl manganese tricarbonyl.

Preferably the manganese and/or the manganese compound is methylcyclopentadienyl manganese tricarbonyl.

In one preferred aspect the manganese and/or manganese compound provides manganese in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the manganese and/or manganese compound provides manganese in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the manganese and/or manganese compound provides manganese in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the manganese and/or manganese compound provides manganese in an amount of from 6 to 12 mg per kg of fuel.

MANGANESE AND IRON In one preferred aspect the ratio by weight of manganese to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of manganese to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of manganese to iron is from 1: 5 to 1: 1.

CERIUM Preferably the cerium and/or cerium compound is a cerium compound.

The cerium metal or the cerium compound may be delivered in a manner analogous to that given above in respect of potassium. Each of the forms of potassium disclosed above may be used to provide the analogous cerium compound.

Preferred sources of cerium include overbased cerium salts, particularly cerium oxide, otherwise known as ceria. Such overbased cerium salts are often referred to as sols, that is, suspensions of finely divided cerium salt crystals comprising surface-bound sulphonic or especially carboxylic acids. An example of a suitable sulphonic acid would be dodecylbenzene sulphonic acid. Examples of suitable carboxylic acids would include long-chain fatty acids, such as C12 to C24 fatty acids, especially the naturally occurring mixtures of acids known as tall-oil fatty acids.

Other preferred cerium compounds would include neutral carboxylate salts of the acids described above. Further preferred compounds would include-diketonate salts, especially salts of 2, 2,6, 6-tetramethylheptane-3, 5-dione (TMHD).

In one preferred aspect the cerium and/or cerium compound provides cerium in an amount of at least 3 mg per kg of fuel.

In one preferred aspect the cerium and/or cerium compound provides cerium in an amount of from 3 to 20 mg per kg of fuel.

In one preferred aspect the cerium and/or cerium compound provides cerium in an amount of from 5 to 15 mg per kg of fuel.

In one preferred aspect the cerium and/or cerium compound provides cerium in an amount of from 6 to 12 mg per kg of fuel.

CERIUM AND IRON In one preferred aspect the ratio by weight of cerium to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of cerium to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of cerium to iron is from 1: 5 to 1: 1.

PHOSPHORUS Preferably the phosphorus and/or phosphorus compound is a phosphorus compound.

Preferably the phosphorus and/or the phosphorus compound is an amine salt of a phosphorus based acid.

All references in the present specification to ValvemasterRTM in the context of phosphorus compounds may be read to mean an amine salt of a phosphorus based acid and/or the reaction product of the following reaction C, 3 alcohol + P205--> organic acid organic acid + amine o amine salt of a phosphorus based acid and/or a product described in US-A-4720288.

Thus in a preferred aspect the phosphorus based acid is obtainable or obtained from the

reaction of (i) the reaction of a C13 alcohol and P205 to form an organic acid and (ii) the reaction of the organic acid and an amine.

PHOSPHORUS AND IRON In one preferred aspect the ratio by weight of phosphorus to iron is from 1: 20 to 1: 1.

In one preferred aspect the ratio by weight of phosphorus to iron is from 1: 10 to 1: 1.

In one preferred aspect the ratio by weight of phosphorus to iron is from 1: 5 to 1: 1.

FUEL In a third aspect there is provided a fuel composition comprising (i) iron and/or an iron compound in an amount to provide iron in an amount of at least 15 mg per kg of fuel ; (ii) potassium and/or a potassium compound; and (iii) a fuel.

The term'fuel'covers compositions containing a major amount of gasoline base fuel suitable for use in spark-ignition engines. This includes hydrocarbon base fuels boiling in the so-called gasoline boiling range of 30 to 230°C. These base fuels may comprise mixtures of saturated, olefinic and aromatic hydrocarbons. They can be derived from straight-run gasoline, synthetically produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbon feedstocks, hydrocracked petroleum fractions or catalytically reformed hydrocarbons. Motor gasolines are defined by ASTM 48/4-01, aviation gasolines typically have a narrower boiling range of 37 to 165°C. The gasoline may also contain various blending components designed to provide octane number, such as MTBE, TAME or ETBE as non-limiting examples. A proportion of the hydrocarbons may also be replaced for example by alcohols, ethers (as above), esters or ketones. Generally the octane number of the gasoline will be greater than 65.

Preferably the fuel is gasoline.

The fuel may further comprise performance-enhancing additives. A non-limiting list would include corrosion inhibitors, rust inhibitors, gum inhibitors, anti-oxidants, solvent oils, anti-static agents, dyes, anti-icing agents, ashless dispersants and detergents.

The fuel additives according to the invention may be added as part of a package to the fuel. prior to combustion. This may be done at any stage in the fuel supply chain (for example, at the refinery or distribution terminal) or may be added via a dosing device on- board the vehicle, either to the fuel or even separately direct into the combustion chamber or inlet system. The fuel additives may be added to the fuel in the vehicle fuel tank by the user, a so-called'aftermarket'treatment.

The invention further comprises an additive solution for addition to a fuel. Such an additive might be dosed at any stage in the fuel supply chain prior to combustion of the fuel. The fuel additives of the invention may be dosed to the fuel at any stage in the fuel supply chain. Preferably, each additive is added to the fuel close to the engine or combustion systems, within the fuel storage system for the engine at the refinery, distribution terminal or at any other stage in the fuel supply chain, including aftermarket use.

How an additive solution is to be employed significantly influences the optimum formulation. For example, the additive may be added to the fuel at the refinery or at the distribution terminal. Here the iron and potassium components may be added together or separately, providing an additional valuable flexibility in use. If added together, they will be dissolved in the minimum amount of fuel compatible solvent commensurate with the need to provide a pumpable solution and avoid crystallisation/separation of any of the components at low temperatures, e. g. about-30°C.

Where the advantages of separate addition are desired, the iron material such as PLUTOcenE is added at the refinery as a blending component for octane trimming, to meet the required product octane specification, thus fulfilling the well known and valuable role to the refiner of an octane enhancing agent. The potassium component such as ValvemasterRT" KT can be added to the finished fuel at the distribution terminal, for example in order to produce a product known to those in the Industry as a"lead replacement gasoline" (LRG) or"lead replacement petrol" (LRP).

Where, however, the additive combination is intended to be added as an'aftermarket' treatment, the volume of solvent used will be such as to provide a non-viscous solution, suitable for use in a dispenser bottle or syringe pack. The concentration of iron and

phosphorus and/or potassium will be such that some convenient and easily recalled treat rate (e. g. about 1 cm3 per litre of fuel) is required. In any case the solvents to be used should be readily fuel soluble and compatible, including with respect to boiling point range, and preferably will have flash points in excess of 62°C for ease of storage.

The additive solution may optionally contain additional components beyond the iron and potassium compounds. These components include corrosion inhibitors, rust inhibitors, gum inhibitors, anti-oxidants, solvent oils, anti-static agents, dyes, anti-icing agents, ashless dispersants and detergents as a non-limiting list. Where any additional component is employed, the use of detergents, especially poly- (butenyl) succinimide based detergents, is preferred.

The fuel composition of the present invention may contain further components to address the problems of valve seat recession (VSR). For example, the fuel composition may contain phosphorus or a phosphorus compound. The phosphorus or phosphorus compound may be as described above.

The invention will now be further described in further detail by way of example only.

EXAMPLE It will be shown that the combination of ferrocene and a potassium compound has demonstrated a clear and unexpected benefit by inhibiting spark plug fouling at high iron treat rates in engine tests.

It will also be shown that the combination of ferrocene and a lead compound has demonstrated a clear and unexpected benefit by inhibiting spark plug fouling at high iron treat rates in engine tests.

Vehicle : The test vehicle is a Suzuki Baleno 1.6 litre PFI. It is operated with Bosch FR7 DCX spark plugs with a 1. 1mm spark gap (a spark plug in common use).

Test Cycle : The test cycle used for mileage accumulation with the vehicle was completed using a Labeco Mileage Accumulation Dynamometer. The cycle was representative of low duty urban operation of the vehicle. It consisted of

3 minutes at 68kmph, 1 minute at 110kmph, 30 seconds idle, 1 minute at 18kmph repeated for around 6.5 hours.

The cycle represented a mileage of 366.6 km and was repeated 30 times for 11,000 km (the 10,000 km plug change interval of the vehicle plus 10%). The vehicle was assessed for performance at intervals of around 3000,6000, 9000 and 11, 000 km. Test intervals were selected on the expected severity of the test fuels. Trouble free operation at 11,000 km is rated as a pass.

Protocol for Assessment of Plug Performance Plug performance is tested by a skilled driver driving the vehicle on the road. A preplanned test route is used on which it is possible to evaluate the vehicle performance under acceleration under load at low and high vehicle speeds. Any occurrence of misfire is recorded.

Subsequent evaluation of plugs by visual inspection for signs of tracking and by use of a ChampionRTM spark plug tester is used to confirm any mis-fires reported by the driver.

Test results The recommended treat rate for PLUTOcenRT" G is 30ppm. Treat rates significantly above this are not normally economically attractive and have been suggested as a cause of spark plug mis-fire after extended mileage in critical vehicles. The following confirm this: ADDITIVES PASS/FAIL Iron Additive Iron Additive Iron Treat Potassium Additive Potassium Treat Rate Rate (ppm) Treat Rate (ppm) (ppm) PLUTOcen G 60 18-Fail PLUTOcenRTM G 75 22.5 - - Fail PLUTOcen «'M G 100 30 Fail ADDITIVES PASS/FAIL Iron Additive Iron Additive Iron Treat Potassium Additive Potassium Treat Rate Rate (ppm) Treat Rate (ppm) (ppm) PLUTOcenRTM G 50 15 ValvemasterRTM KT 3 Pass PLUTOcen G 50 15 Valvemaster KT 12 Pass PLUTOcen G 60 18 Valvemaster KT 6 Pass PLUTOcenRTM G 100 30 ValvemasterRTM KT 10 Pass PLUTOcenRTM G 60 18 potassium sulphonate 12 Pass PLUTOcen G 75 22. 5 potassium sulphonate 12 Pass PLUTOcen G 100 30 potassium sulphonate 12 Pass

PLUTOcenRTM G is ferrocene available from the Octel Deutschland GmbH ValvemasterRTM KT is a potassium sulphonate available from the Associated Octel Company Limited ADDITIVES PASS/FAIL Iron Additive Iron Additive Iron Treat Lead Additive Lead Treat Treat Rate Rate (ppm) Rate (g/l) (ppm) PLUTOcen"G 60 18--Fail PLUTOcenRTM G 75 22.5 - - Fail PLUTOcenK'G 100 30-Fail PLUTOcen v G 60 18 TEL-CB 0. 05 Pass PLUTOcenRTM G 60 18 TEL-CB 0.015 Pass TEL-CB is a tetraethyl lead available from the Associated Octel Company Limited ADDITIVES PASS/FAIL Iron Additive Iron Additive Iron Treat Cerium Additive Cerium Treat Rate Rate (ppm) Treat Rate (ppm) (ppm) PLUTOcen G 45 13. 5 Fail PLUTOcenRTM G 45 13.5 TX3024 6 Pass

TX3024 is an overbased Ce soap obtainable from Octel Gamlen SA. ADDITIVES PASS/FAIL Iron Additive Iron Additive Iron Treat Phosphorus Phosphorus Treat Rate Rate (ppm) Additive Treat Rate (ppm) (ppm) PLUTOcen"""'G 45 13. 5-Fail PLUTOcen « M G 45 13. 5 VM1 Improvement9

VM1, or ValvemasterRTM is a phosphorus-based anti-Valve Seat Recession (VSR) additive available from the Associated Octel Company Limited.

§ Improvement in this instance means that although the target 11,000 kms distance was not reached, the onset of misfire was only noted at greater distances than in the 45 ppm PLUTOcenRTM G test.

All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in chemistry or related fields are intended to be within the scope of the following claims.