US20080066714A1

US20080066714A1 - Fuel compositions and its use

Info

Publication number: US20080066714A1
Application number: US11/533,255
Authority: US
Inventors: George Robert Lee
Original assignee: Individual
Current assignee: Shell USA Inc
Priority date: 2005-09-20
Filing date: 2006-09-19
Publication date: 2008-03-20
Also published as: EP1926803A1; AU2006298847B2; AR056079A1; BRPI0616132A2; CN101292015A; WO2007039457A1; AU2006298847A1; ZA200802308B; JP2009509019A; CA2622857A1

Abstract

A fuel composition containing a major amount of a fuel for an internal combustion engine and a minor amount of a fuel-compatible dendrimer containing from 4 to 64 terminal functional groups independently selected from amino, hydroxyl and carboxylate groups is disclosed. The use of such compositions as fuel in an internal combustion engine for controlling combustion chamber deposits is also disclosed.

Description

FIELD OF THE INVENTION

This invention relates to fuel compositions, more particularly to such compositions containing a fuel for an internal combustion engine, to their preparation and to their use in operation of internal combustion engines.

BACKGROUND OF THE INVENTION

Use of certain branched polyolefin additives in fuel and/or lubricating oil in the form of a comb, star, nanogel and structural combinations thereof is described for example in U.S. Pat. No. 6,127,481.

SUMMARY OF THE INVENTION

In one embodiment a fuel composition is provided a fuel composition comprising a major amount of a fuel for an internal combustion engine and a minor amount of a fuel-compatible dendrimer containing from 4 to 64 terminal functional groups independently selected from amino, hydroxyl and carboxylate groups.
A method of operating an internal combustion engine using such fuel components is also provided.

DETAILED DESCRIPTION OF THE INVENTION

It has now been found that incorporation in fuels for internal combustion engines of certain dendrimers can have unpredictable beneficial effects, e.g. in controlling combustion chamber deposits.
U.S. Pat. No. 6,127,481 and the published European patent application EP-A-818 525, describes a branched polyolefin additive for use in fuel and/or lubricating oil in the form of a comb, star, nanogel and structural combinations thereof in which a plurity of polyolefin arms are attached to a backbone having repeating units containing aliphatic groups, aromatic groups, heteroatom-containing groups and combinations thereof, to provide a branched polymeric additive in which the properties of the additive can be conveniently tailored to a single or multi-functional performance criteria of a fuel and/or lubricating oil composition.
In one embodiment, dendrimers are used as the backbone, and the reactive terminal groups of the dendrimer are reacted with polyolefin prearms to provide a polymeric product in which the terminal groups are polyolefinic groups. The examples wherein dendrimers are used as the backbone are Examples 15, 17, 21 and 22. In each of these examples, ethylene-propylene polymer arms are functionalised with an end group which will react with a reactive terminal group on a dendrimer, and the resulting polyolefin prearms are reacted with dendrimer such that each reactive terminal group reacts with a polyolefin prearm to form an ester, imide, amine, ether or urea linkage, thereby leaving no terminal amino, hydroxyl or carboxylate groups.
WO 96/12755 describes an oil soluble dendrimer-based cold flow improver comprising a central core linked through a plurality of polar groups to a dendritic body which is linked through a plurality of polar groups to a hydrocarbyl periphery, the periphery consisting of n-alkyl groups which contain from 8 to 1000 carbon atoms. After a desired number of reaction steps or, in the case of certain dendrimers, the limited number of reaction steps available because of steric restrictions on growth (“dense packing”), functional, n-alkyl moieties are attached through the external reactive groups of the dendrimer to form a hydrocarbyl periphery.
These dendrimer-based cold flow improvers are used in crude oil, lubricating oil or fuel oil (e.g. kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils). In fuel oils, the concentration (w/w) is 0.0001 to 1% (1 to 10,000 ppmw), preferably 0.1 to 0.2% (1000 to 2000 ppmw) (page 7, lines 5 to 17, of WO 96/12755), although the examples employ 100 to 200 ppmw (0.01 to 0.02% w/w).
WO 02/102928 describes a method for solubilising asphaltenes in an asphaltenes-containing hydrocarbon mixture by adding thereto an effective amount of a dendrimeric compound; and a hydrocarbon mixture comprising (in addition to hydrocarbons), asphaltenes and at least one dendrimeric compound.
Asphaltenes are aromatic hydrocarbons which are insoluble in n-heptane, and are generally determined in accordance with ASTM D 6560. Asphaltenes may cause problems in oil recovery and oil refining processes, by forming solid desposits or dark sludge, e.g. in oil formations, in oil-well equipment or in oil pipelines. The Examples in WO 02/102928 demonstrate solubilising of asphaltenes in crude oil, and show improved performance for dendrimers in which a proportion of terminal hydroxyl groups have been modified by reaction with poly(isobutenyl succinic anhydride in which the poly(isobutenyl) chain contained about 22 isobutylene units.
WO 97/41092 discloses alkoxy acetic acid derivatives of general formula
wherein

R is the residue of an amine, an aminoalcohol or a polyol linked to the or each —CHR′—CO— moiety via an amide or ester linkage:
R′ is hydrogen or C_1-4alkyl;
R¹is an optionally substituted hydrocarbyl group of 1 to 300 carbon atoms;
one of R²and R³is independently selected from hydrogen and optionally substituted hydrocarbyl of 1 to 10 carbon atoms, the other of R²and R³being independently selected from optionally substituted hydrocarbyl of 1 to 10 carbon atoms;
m is from 3 to 200;
n is from 0 to 20, provided that m/n is at least 1; and
p is from 1 to 5, their preparation and their use as fuel additives.

Numerous possibilities are mentioned for the amine, aminoalcohol and polyols, representable as R(H)p, of which R in formula I represents the residue, and it is specifically stated that complex amines such as “Starburst” (trade mark) dendrimers may be used, e.g. the compound of formula [CH₂N((CH₂)₂CONH (CH₂)₂NH₂)₂]₂. This latter compound, “Starburst” (PAMAM, generation O) dendrimer, is used in Example 25 resulting in a compound of formula I wherein R is a dendrimer backbone having 3 remaining terminal amino groups.
It is specifically stated that most preferably, R(H)p is selected from the group consisting of pentaerythritol, triethylenetetramine and tris (2-aminoethyl) amine.
It can be noted (Table 1 in WO 97/41092) that the product of Example 25 is not among the most active of the materials tested, and the person skilled in the art would not have been encouraged to pursue further derivatives of dendrimers instead of polyalkylene glycol derivatives of pentaerythritol, triethylenetetramine and tris (2-aminoethyl) amine, in the quest for advantageous gasoline additives.
According to the present invention there is provided a fuel composition comprising a major amount of a fuel for an internal combustion engine and a minor amount of a fuel-compatible dendrimer containing from 4 to 64 terminal functional groups independently selected from amino, hydroxyl and carboxylate groups. It has been found that these dendrimers can have the beneficial effect of controlling combustion chamber deposits.
As described in WO 96/12755, Tomalia et al, Angew. Chem. Int. Ed. Engl., 29 (1990), 138, describe dendrimers as three-dimensional highly-ordered oligomers or polymers. They are obtainable by reiterative reaction sequences starting from an initiator core having one or more reactive sites. To each reactive site is attached one functional group only of a polyfunctional reactant. The reactant is then caused to react through its remaining functional group or groups with additional molecules either the same as the original core if it is polyfunctional or a different, polyfunctional, molecule or molecules, and so on, in each case under reaction conditions such that unwanted side reactions, for example, crosslinking, are avoided. In this way, a dendritic body is built up around the central core, each reiterative reaction sequence adding further reactants (or ‘units’) to the ends of the dendrites. Tomalia describes the manufacture of polyamidoamine (PAMAM) dendrimers; these may be made based on ammonia as a core, which is caused to react by Michael addition with methyl acrylate (Step A). The carboxyl group of the acrylate molecule is caused to react with one amino group only of ethylene diamine (Step B). The resulting triamine core cell is referred to by Tomalia as Generation O; a further repetition of steps A and B provides a hexamine, referred to as Generation 1. Further repetitions of steps A and B produce higher generations which after Generation 4 result in concentric spheres of cells, the outermost sphere carrying external reactive groups. Other dendrimers described by Tomalia include polyethylenimine, hydrocarbon, polyether, polythioether, polyamide, polyamdo-alcohol and polyarylamine dendrimers. Synthesis of such dendrimers are variously desscribed, for example, in U.S. Pat. Nos. 4,435,548, 4,507,466, 4,558,120 and 4,568,737, all of Tomalia et al (assigned to The Dow Chemical Company).
Polyamide- and ester-based dendrimers are also described by Newkome et al, J. Am. Chem. Soc., 112 (1990) 8458. Use of a long-chain alkylene dibromide as core provided a dendrimer (referred to by Newkome as an arboral) in the form of two spheres linked by an alkylene chain. U.S. Pat. No. 5,041,516 describes molecules similar to those of Tomalia, but made by a “convergent” approach, i.e., starting with the outer surface of the dendrimer, building up a wedge-shaped molecule, and finally reacting a plurality of the “wedges” with a core molecule. GB-A-1575507 describes star-shaped polymers and their use as viscosity improvers, these polymers being based on a cross-linked divinylbenzene core and isoprene branches; in EP-A-368395 such a hydrocarbon polymer is functionalized through a sulphonamide linkage to provide carboxyl terminal groups.
O'Sullivan, Chemical and Engineering News for 16^thAugust, 1993, describes a polypropylenimine dendrimer obtained by Michael addition of acrylonitrile to 1,4-diaminobutane, and reduction of the nitrile group to amino groups over Raney cobalt. Repeated four times, this procedure gives a dendrimer which theoretically has 64 amino groups. PCT Application WO 93/114147 contains a similar disclosure. The disclosures of all of the above documents are incorporated herein by reference.
The number of layers that it is possible to construct varies with the reactant as does the closeness of the packing within the dendrimer, and hence the size of channels between its branches. PAMAM dendrimers have a large internal surface area which, in proportion to the external surface area, increases with the number of generations. In contrast, polyether dendrimers have very little proportional internal surface, which reaches a maximum at Generations 3 to 4.
As indicated above, the successive layers of cells may be the same or different, and mixtures of two or more reactants, for example as described by Tomalia, Angew Chem. Int. Ed., Engl, 29 (1990) at page 148, may be used.
Aldrichimica Acta, Vol. 37, No. 2, 2004 at Pages 39 to 57 contains a review by Tomalia of dendrimers and their application as building blocks for nanoscale synthetic organic chemistry. This review is followed by a listing of PAMAM and phosphorous dendrimers available from Aldrich.
Aldrich Handbook of Fine Chemicals and Laboratory Equipment 2003-2004 United Kingdom contains listings of dendrimers available from Aldrich, including various DAB-Am dendrimers (Page 545), PAMAM dendrimers (Pages 1406 to 1408) and PAMAM-OH dendrimers (Pages 1408 and 1409). Other and similar dendrimers are available directly from Dendritech, Inc, Michigan, USA and Dendritic Nano Technologies, Inc. Michigan, USA.
Preferably, the dendrimer is at least one fuel-compatible dendrimer independently selected from DAB-Am, PAMAM and PAMAM-OH dendrimers.
The terminal functional groups are preferably individually selected from —NH₂, —OH and COOX groups, where X represents H, K or Na.
Preferably, the dendrimer contains from 4 to 32 terminal functional groups and more conveniently 8 to 16 terminal functional groups, independently selected from amino, hydroxyl and carboxylate groups.
The dendrimer is preferably present in the fuel composition in a concentration in the range from 5 ppmw to 500 ppmw, more preferably in the range from 10 ppmw to 200 ppmw, based on total composition.
It may be found useful for the fuel composition additionally to contain a fuel-compatible oxygenate co-solvent selected from C₁to C₁₄alkanols and 2-ethylhexanoic acid.
A fuel composition according to the invention preferably additionally contains a nitrogen-containing detergent containing a hydrocarbyl group having a number average molecular weight (Mn) the range 750 to 6000, in a concentration in the range 25 to 2500 ppmw based on total composition.
The fuel composition preferably contains 50 to 1500 ppmw of the nitrogen-containing detergent, and more preferably 50 to 500 ppmw thereof. Quantities in the range 80 to 250 ppmw, e.g. 100 to 150 ppmw, are very suitable.
The nitrogen-containing detergent containing a hydrocarbyl group having a number average molecular weight (Mn) in the range 750 to 6000 may be an amine, e.g. a polyisobutylene mono-amine or polyamine, such as a polyisobutylene ethylene diamine, or N-polyisobutenyl-N′,N′-dimethyl-1,3-diaminopropane, or amide e.g. a polyisobutenyl succinimide, and are variously described, for example, in U.S. Pat. No. 5,855,629 and WO 0132812. Alternatively, the nitrogen-containing detergent may be a Mannich amine detergent, for example a Mannich amine detergent as described in U.S. Pat. No. 5,725,612.
A particularly preferred nitrogen-containing detergent is hydrocarbyl amine of formula R¹—NH₂, wherein R¹represents a group R²or a group R²—CH₂— and R²represents a hydrocarbyl group having a number average molecular weight in the range 750 to 6000, preferably in the range 900 to 3000, more preferably 950 to 2000, and most preferably in the range 950 to 1350, e.g. a polybutenyl or polyisobutenyl group having a number average molecular weight in the range 950 to 1050.
The nitrogen-containing detergents are known materials and may be prepared by known methods or by methods analogous to known methods. For example, U.S. Pat. No. 4,832,702 describes the preparation of polybutenyl and polyisobutenyl amines from an appropriate polybutene or polyisobutene by hydroformylation and subsequent amination of the resulting oxo product under hydrogenating conditions.
Suitable hydrocarbyl amines are obtainable from BASF A.G., under the trade mark “Kerocom”.
Whilst the fuel for an internal combustion engine may be gasoline, diesel fuel, aviation gasoline or aviation gas turbine fuel, the fuel is preferably gasoline or diesel fuel, most preferably gasoline.
In the case where a fuel composition according to the invention is a gasoline composition, in addition to a nitrogen-containing detergent, the gasoline composition may additionally contain one or more carrier fluids, corrosion inhibitors, anti-oxidants, dyes, dehazers, metal deactivators, detergents other than a nitrogen-containing detergent containing a hydrocarbyl group as defined above (e.g. a polyether amine), friction modifiers, diluents and markers.
Particularly suitable carrier fluids are polyolefins, e.g. polyisobutylene and polyalphaolefins, and polyoxyalkylene compounds. Carrier fluids may conveniently be employed in total concentrations in the range 20 to 8000 ppmw, e.g. 50 to 500 ppmw.
Polyalphaolefin carrier fluids are primarily trimers, tetramers and pentamers, and synthesis of such materials is outlined in Campen et al. “Growing use of synlubes”, Hydrocarbon Processing, February 1982, Pages 75 to 82. The polyalphaolefin may be unhydrotreated, but it is preferably a hydrogenated oligomer. The polyalphaolefin is preferably derived from an alphaolefinic monomer containing from 8 to 12 carbon atoms. Furthermore, it preferably has viscosity at 100° C. in the range 6×10⁻⁶to 1×10⁻⁵m²/s (6 to 10 centistokes). Polyalphaolefins derived from decene-1 are very suitable. Polyalphaolefins having a viscosity at 100° C. of 8×10⁻⁶m²/s (8 centistokes) are very suitable.
Polyoxyalkylene carrier fluids, which are very effective, preferably have the formula II
wherein R³and R⁴independently represent hydrogen atoms or hydrocarbyl, preferably C_1-40hydrocarbyl, e.g. alkyl, cycloalkyl, phenyl or alkyl-phenyl groups, each R⁵independently represents an alkylene, preferably C_2-8alkylene, group, and p is such that Mn of the polyoxyalkylene compound is in the range 400 to 3000, preferably 700 to 2000, more preferably 1000 to 2000.
Preferably R³represents a C_8-20alkyl group and R⁴represents a hydrogen atom. R³preferably represents a C_8-18alkyl group, more preferably a C_8-15alkyl group. R³may conveniently be a mixture of C_8-15alkyl groups.
In the formula II the groups R⁵are preferably 1,2 alkylene groups. Preferably each group R⁵independently represents a C_2-4alkylene group, e.g. an ethylene, 1,2-propylene or 1,2-butylene group. Very effective results have been obtained when each group R⁵represents a 1,2-propylene group.
Number average molecular weights, e.g. of hydrocarbons such as polyalkenes, may be determined by several techniques which give closely similar results. Conveniently Mn may be determined by vapour phase osmometry (VPO) (ASTM D 3592) or by modern gel permeation chromatography (GPC), e.g. as described for example in W. W. Yau, J. J. Kirkland and D. D. Bly, “Modern Size Exclusion Liquid Chromatography”, John Wiley and Sons, New York, 1979. Where the formula of a compound is known, the number average molecular weight can be calculated as its formula weight.
Typical of gasolines suitable for use in spark ignition engines are mixtures of hydrocarbons having boiling points in the range from 25° C. to 232° C. and comprising mixtures of saturated hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons. Preferred are gasoline blends having a saturated hydrocarbon content ranging from 40 to 80 percent volume, an olefinic hydrocarbon content ranging from 0 to 30 percent volume and an aromatic hydrocarbon content ranging from 10 to 60 percent volume. The gasoline can be derived from straight run gasoline, polymer gasoline, natural gasoline, dimer- or trimerised olefins, synthetically produced aromatic hydrocarbon mixtures from thermally or catalytically reformed hydrocarbons, or from catalytically cracked or thermally cracked petroleum stocks, or mixtures thereof. The hydrocarbon composition and octane level of the gasoline are not critical. The octane level, (R+M)/2, will generally be above 85. Any conventional gasoline can be used. For example, in the gasoline, hydrocarbons can be replaced by up to substantial amounts of conventional alcohols or ethers conventionally known for use in gasoline, including biofuel components, or of ester biofuel components such as ethyl levulinate.
The gasoline is preferably lead-free, and this may be required by law. Where permitted, lead-free anti-knock compounds and/or valve-seat recession protectant compounds (e.g. known potassium salts, sodium salts or phosphorous compounds) may be present.
Modern gasolines are inherently low-sulphur fuels, e.g. containing less than 200 ppmw sulphur.
In this specification, amounts (concentrations) (% v) (ppmw) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials.
A gasoline composition in accordance with the invention may be prepared by a process which comprises bringing into admixture the gasoline and the fuel-compatible dendrimer, and any other components, such as nitrogen-containing detergent.
If desired, the fuel-compatible dendrimer, and any additional components such as nitrogen-containing detergent, fuel-compatible oxygenate co-solvent, corrosion inhibitors, anti-oxidants, etc., as listed above, may be co-mixed, preferably together with suitable diluent(s), in an additive concentrate, and the additive concentrate may be dispersed into gasoline, in suitable quantity to result in a gasoline composition of the invention.
In the case in which a fuel composition according to the invention is a diesel fuel composition, the fuel for an internal combustion engine is a diesel fuel, which may typically comprise liquid hydrocarbon middle distillate gas oil(s), for instance petroleum derived gas oils. Such fuels will typically have boiling points with the usual diesel range of 150 to 400° C., depending on grade and use. They will typically have a density from 750 to 900 kg/m³, preferably from 800 to 860 kg/m³, at 15° C. (e.g. ASTM D4502 or IP 365) and a cetane number (ASTM D613) of from 35 to 80, more preferably from 40 to 75. They will typically have an initial boiling point in the range 150 to 230° C. and a final boiling point in the range 290 to 400° C. Their kinematic viscosity at 40° C. (ASTM D445) might suitably be from 1.5 to 4.5 mm²/s.
Optionally, non-mineral oil based fuels, such as bio-fuels or Fischer-Tropsch derived fuels, may also form or be present in the diesel fuel composition.
The amount of Fischer-Tropsch derived fuel used in a diesel fuel composition may be from 0.5 to 100% v of the overall diesel fuel composition, preferably from 5 to 75% v. It may be desirable for the composition to contain 10% v or greater, more preferably 20% v or greater, still more preferably 30% v or greater, of the Fischer-Tropsch derived fuel. It is particularly preferred for the composition to contain 30 to 75% v, and particularly 30 or 70% v, of the Fischer-Tropsch derived fuel. The balance of the fuel composition is made up of one or more other fuels.
The Fischer-Tropsch product will suitably contain more than 80 wt % and more suitably more than 95 wt % iso and normal paraffins and less than 1 wt % aromatics, the balance being naphthenics compounds. The content of sulphur and nitrogen will be very low and normally below the detection limits for such compounds. For this reason the sulphur content of a diesel fuel composition containing a Fischer-Tropsch product may be very low.
The diesel fuel composition preferably contains no more than 5000 ppmw sulphur, more preferably no more than 500 ppmw, or no more than 350 ppmw, or no more than 150 ppmw, or no more than looppmw, or no more than 50 ppmw, or most preferably no more than 10 ppmw sulphur.
The base diesel fuel may itself be additivated (additive-containing) or unadditivated (additive-free). If additivated, e.g. at the refinery, it will contain minor amounts of one or more additives selected for example from anti-static agents, pipeline drag reducers, flow improvers (e.g. ethylene/vinyl acetate copolymers or acrylate/maleic anhydride copolymers) and wax anti-settling agents (e.g. those commercially available under the Trade Marks “PARAFLOW” (e.g. PARAFLOW™ 450, ex Infineum), “OCTEL” (e.g. OCTEL™ W 5000, ex Octel) and “DODIFLOW” (e.g. DODIFLOW™ V 3958, ex Hoechst).
Detergent-containing diesel fuel additives are known and commercially available, for instance from Infineum (e.g. F7661 and F7685) and Octel (e.g. OMA 4130D). Such additives may be added to diesel fuels at relatively low levels (their “standard” treat rates providing typically less than 100 ppmw active matter detergent in the overall additivated fuel composition) intended merely to reduce or slow the build up of engine deposits.
The additive may contain other components in addition to the nitrogen-containing detergent. Examples are lubricity enhancers; dehazers, e.g. alkoxylated phenol formaldehyde polymers such as those commercially available as NALCO™ EC5462A (formerly 7D07) (ex Nalco) and TOLAD™ 2683 (ex Petrolite); anti-foaming agents (e.g. the polyether-modified polysiloxanes commercially available as TEGOPREN™ 5851 and Q 25907 (ex Dow Corning), SAG™ TP-325 (ex OSi) and RHODORSIL™ (ex Rhone Poulenc)); ignition improvers (cetane improvers) (e.g. 2-ethylhexyl nitrate (EHN), cyclohexyl nitrate, di-tert-butyl peroxide and those disclosed in U.S. Pat. No. 4,208,190 at column 2, line 27 to column 3, line 21); anti-rust agents (e.g. that sold commercially by Rhein Chemie, Mannheim, Germany as “RC 4801”, a propane-1,2-diol semi-ester of tetrapropenyl succinic acid, or polyhydric alcohol esters of a succinic acid derivative, the succinic acid derivative having on at least one of its alpha-carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group containing from 20 to 500 carbon atoms, e.g. the pentaerythritol diester of polyisobutylene-substituted succinic acid); corrosion inhibitors; reodorants; anti-wear additives; anti-oxidants (e.g. phenolics such as 2,6-di-tert-butyiphenol, or phenylenediamines such as N,N′-di-sec-butyl-p-phenylenediamine); and metal deactivators.
It is particularly preferred that the diesel fuel additive include a lubricity enhancer, especially when the fuel composition has a low (e.g. 500 ppmw or less) sulphur content. In the additivated diesel fuel composition, the lubricity enhancer is conveniently present at a concentration between 50 and 1000 ppmw, preferably between 100 and 1000 ppmw. Suitable commercially available lubricity enhancers include EC 832 and PARADYNE™ 655 (ex Infineum), HITEC™ E580 (ex Ethyl Corporation), VEKTRON™ 6010 (ex Infineum) and amide-based additives such as those available from the Lubrizol Chemical Company, for instance LZ 539 C. Other lubricity enhancers are described in the patent literature, in particular in connection with their use in low sulphur content diesel fuels, for example in:
the paper by Danping Wei and H. A. Spikes, “The Lubricity of Diesel Fuels”, Wear, III (1986) 217-235;
WO-A-95/33805—cold flow improvers to enhance lubricity of low sulphur fuels;
WO-A-94/17160—certain esters of a carboxylic acid and an alcohol wherein the acid has from 2 to 50 carbon atoms and the alcohol has 1 or more carbon atoms, particularly glycerol monooleate and di-isodecyl adipate, as fuel additives for wear reduction in a diesel engine injection system;
U.S. Pat. No. 5,490,864—certain dithiophosphoric diester-dialcohols as anti-wear lubricity additives for low sulphur diesel fuels; and
WO-A-98/01516—certain alkyl aromatic compounds having at least one carboxyl group attached to their aromatic nuclei, to confer anti-wear lubricity effects particularly in low sulphur diesel fuels.
It is also preferred that the diesel fuel additive contain an anti-foaming agent, more preferably in combination with an anti-rust agent and/or a corrosion inhibitor and/or a lubricity additive.
Unless otherwise stated, the (active matter) concentration of each such additional component in the additivated diesel fuel composition is preferably up to 10000 ppmw, more preferably in the range from 5 to 1000 ppmw, advantageously from 75 to 300 ppmw, such as from 95 to 150 ppmw.
The (active matter) concentration of any dehazer in the diesel fuel composition will preferably be in the range from 1 to 20 ppmw, more preferably from 1 to 15 ppmw, still more preferably from 1 to 10 ppmw, advantageously from 1 to 5 ppmw. The (active matter) concentration of any ignition improver present will preferably be 600 ppmw or less, more preferably 500 ppmw or less, conveniently from 300 to 500 ppmw.
If desired, the additive components, as listed above, may be co-mixed, preferably together with suitable diluent(s), in a diesel fuel additive concentrate, and the additive concentrate may be dispersed into the fuel, in suitable quantity to result in a composition of the present invention.
In the case of a diesel fuel, for example, the additive will typically contain a detergent, optionally together with other components as described above, and a diesel fuel-compatible diluent, which may be a carrier oil (e.g. a mineral oil), a polyether, which may be capped or uncapped, a non-polar solvent such as toluene, xylene, white spirits and those sold by companies of the Shell Group under the trade mark “SHELLSOL”, and/or a polar solvent such as an ester and, in particular, an alcohol, e.g. hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixtures such as those sold by companies of the Shell Group under the trade mark “LINEVOL”, especially LINEVOL™ 79 alcohol which is a mixture of C_7-9primary alcohols, or the C_12-14alcohol mixture commercially available from Sidobre Sinnova, France under the trade mark “SIPOL”.
The total content of the additives may be suitably between 0 and 10000 ppmw and preferably below 5000 ppmw.
The present invention further provides a method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine or fuel composition according to the invention, as defined above.
The present invention also provides use of a fuel composition of the invention, preferably a gasoline composition, as fuel in an internal combustion engine (in the case of gasoline, a spark-ignition engine) for controlling combustion chamber deposits.
The present invention will be further understood from the following illustrative examples in which, unless otherwise indicated, parts and percentages are by weight (ppmw is parts per million by weight) and temperatures are in degrees Celsius.
In the examples, base gasoline was an unleaded gasoline (95 ULG) of RON 95.3, MON 85.3 and having sulphur content (ASTM D 2622-94) of 48 ppmw, aromatics content of 33.2% v/v and olefins content of 11.9% v/v (ASTM D 6623-01 (procedure C)), density (DIN 51757/V4) 743 kg/m³distillation (ISO 3405/88) IBP 25-30.5° C., 10% v/v 40-50° C., 50% v/v 99-100° C., 95% v/v 178-181° C. and FBP 204-206° C.
Detergent-containing gasoline was the above base gasoline into which was incorporated, at a package concentration of 380 ppmw, a standard commercial gasoline additive package, containing a polyisobutyleneamine detergent, a synthetic carrier oil and a conventional corrosion inhibitor, corresponding closely to additive package PI of Example 3 of DE-A-19955651. The polyisobutyleneamine detergent was a polyisobutylene monoamine (PIPBA) ex BASF, in which the polyisobutylene (PIB) chain has a number average molecular weight of approximately 1000. The synthetic carrier oil was a polyether carrier being a polyoxypropylene glycol hemiether, containing 15 to 30 propylene oxide units prepared using a mixture of alkanols in the C_5-15range as initiators, and having Mn in the range 1000 to 2000. The additive package contained about 68% non-volatile matter, about 27% w of the package being the PIBA and 40% w of the package being carrier fluid.
Base diesel fuel had sulphur content (IP 373) of 39 ppmw, cloud point −6° C., cetane number (IP 380/94) of 55.9, density at 15° C. 831 kg/m³, distillation (IP 123) IBP 171° C., 10% 211° C., 50% 277° C., 90% 328° C. and FBP 359° C.
Detergent-containing diesel fuel contained the above base diesel fuel together with a commercial performance package containing detergent, anti-foam, anti-oxidant and anti-corrosion additives, in addition to necessary commercial cold-flow improver, cetane improver (2-ethylhexyl nitrate), anti-static agent, lubricating improver and pipeline drag reducer.

EXAMPLES 1 to 19

The following dendrimers were tested for compatibility with base gasoline and/or base diesel fuel, using fuel-soluble oxygenate co-solvents. Where an Aldrich Number is given, the dendrimer is obtainable from Aldrich companies, e.g. Aldrich Chemical Co., Milwaukee, Wis., USA or Sigma-Aldrich Company Ltd., Gillingham, Dorset, UK (Source: Aldrich Handbook of Fine Chemicals and Laboratory Equipment 2003-2004 United Kingdom).

DAB-Am Dendrimers

A: Aldrich No. 46,069-9; DAB-Am-4, Polypropylenimine tetraamine Dendrimer, Generation 1.0; [—CH₂CH₂N[(CH₂)₃NH₂]₂]₂; Formula weight 316. Contains 4 surface primary amino groups.
B: Aldrich No. 46,072-9; DAB-Am-8, Polypropylenimine octaamine, Dendrimer, Generation 2.0; [—CH₂CH₂N[(CH₂)₃N[(CH₂)₃NH₂]₂]₂]₂; Formula weight 773. Contains 8 surface primary amino groups.
C: Aldrich No. 46,907-6; DAB-Am-16, Polypropylenimine hexadecaamine Dendrimer, Generation 3.0; [—CH₂CH₂N[CH₂)₃N[(CH₂)₃N[(CH₂)₃NH₂]₂]₂]₂]₂; Formula weight 1687. Containing 16 surface primary amino groups.
D: Aldrich No. 46,908-4; DAB-Am-32, Polypropylenimine dotriacontaamine Dendrimer, Generation 4.0; [—CH₂CH₂N[(CH₂)₃N[(CH₂)₃N[(CH₂)₃N[(CH₂)₃NH₂]₂]₂]₂]₂]₂; Formula weight 3514. Contains 32 surface primary amino groups.

PAMAM Dendrimers

E: Aldrich No. 41,238-4; PAMAM Dendrimer, Generation 1; [—CH₂N[CH₂CH₂CONHCH₂CH₂N(CH₂CH₂CONHCH₂CH₂NH₂)₂]₂]₂; Formula weight 1429. Contains 8 surface primary amino groups.
F: Aldrich No. 41,240-6; PAMAM Dendrimer, Generation 2; [—CH₂N [CH₂CH₂CONHCH₂CH₂N [CH₂CH₂CONHCH₂CH₂N (CH₂CH₂CONHCH₂CH₂NH₂)₂]₂]₂]₂; Formula weight 3256. Contains 16 surface primary amino groups.
G: Aldrich No. 41,242-2; PAMAM Dendrimer, Generation 3; Formula weight 6909; contains 32 surface primary amino groups.
H: Aldrich No. 41,237-6; PAMAM Dendrimer, Generation 0.5; [—CH₂N[CH₂CH₂CONHCH₂CH₂N(CH₂CH₂COONa)₂]₂]₂; Formula weight 1269; contains 8 surface carboxylate groups.
I: Aldrich No. 41,239-2; PAMAM Dendrimer, Generation 1.5; [—CH₂N[CH₂CH₂CONHCH₂CH₂N[CH₂CH₂CONHCH₂CH₂N(CH₂CH₂COONa)₂]₂]₂]₂; Formula weight 2935; contains 16 surface carboxylate groups.
J: Aldrich No. 47,783-4; PAMAM-OH Dendrimer, Generation 2; [—CH₂N [CH₂CH₂CONHCH₂CH₂N [CH₂CH₂CONHCH₂CH₂N (CH₂CH₂CONHCH₂CH₂OH)₂]₂]₂]₂; Formula weight 3272; contains 16 surface hydroxyl groups.
K: Aldrich No. 47,784-2; PAMAM-OH Dendrimer, Generation 3; Formula weight 6941; contains 32 surface hydroxyl groups.
L: Aldrich No. 47,785-0; PAMAM-OH Dendrimer, Generation 4; Formula weight 14279; contains 64 surface hydroxyl groups.
M: (Comparative Example) Technical grade PAMAM-OH Dendrimer, Generation 2, ex. Dendritech, Inc., Michigan, USA, containing 16 surface groups, found by proton nuclear magnetic resonance (NMR) to be 55% —OH and 45% —COOH, in number.
N: Dendrimer M (250 ml of a 25% w/w solution of M in methanol) was passed through a chromatography column (150 g aluminium oxide in methanol) at a rate of 1 ml/minute, followed by column washing (300 ml methanol). The relative proportions of —OH and —COOH surface groups in the resulting Dendrimer N were found by NMR to be 82% —OH and 18% —COOH, in number.
O: Mixed amino/hydroxyl surface group dendrimer prepared by partial oxidation of PAMAM Dendrimer, Generation 2, available as special order ex Dendritech, Inc. having relative proportions of —NH₂to —OH surface groups, as determined by NMR, of 50% —NH₂and 50% —OH, by number.
P: Mixed amino/hydroxyl group dendrimer prepared by partial oxidation of PAMAM Dendrimer, Generation 2, available as special order ex Dentritech, Inc., having relative proportions of —NH₂to —OH surface groups, as determined by NMR of 85% —NH₂and 15% —OH, by number.

Cyclotriphosphazene Dendrimers (Comparative Examples)

Q: Aldrich No. 55201-1; Cyclotriphosphazene—PMMH-6 Dendrimer, Generation 0.5; N₃P₃(OC₆N₄CHO)₆; Formula weight 861; contains 6 surface aldehyde (—CHO) groups.
R: Aldrich No. 55206-2; Cyclotriphosphazene-PMMH-12 Dendrimer, Generation 1.5; N₃P₃(OC₆H₄CH═NN(CH₃)P(S)(OC₆H₄CHO)₂)₆; Formula weight 2853; contains 12 surface aldehyde (—CHO) groups.

Thiophosphoryl Dendrimers (Comparative Examples)

S: Aldrich No. 55176-7; Thiophosphoryl-PMMH-3 Dendrimer, Generation 0.5; S═P (OC₆H₄CHO)₃; Formula weight 426; contains 3 surface aldehyde (—CHO) groups.
T: Aldrich No. 55167-8; Thiophosphoryl-PMMH-6 Dendrimer, Generation 1.5; S═P(OC₆H₄CH═NN(CH₃)P(S)(OC₈H₄CHO)₂)₃; Formula weight 1422; contains 6 surface aldehyde (—CHO) groups.

Fuel-soluble oxygenate co-solvents used were methanol (for gasoline), 2-ethylhexanol (for gasoline and diesel fuel) and 2-ethylhexanoic acid (for diesel fuel). Co-solvent: dendrimer ratios from 5:1 to 400:1 by weight were used.
Results are given in Table 1 following:

TABLE 1

			Co-solvent; dendrimer
Example	Dendrimer	Co-solvent	ratio (w/w)	Fuel

1	A	2-ethylhexanol	10:1 and above	gasoline and diesel
2	B	2-ethylhexanol	10:1 and above	gasoline and diesel
3	C	2-ethylhexanol	10:1 and above	Gasoline and diesel
4	D	2-ethylhexanol	10:1 and above	gasoline and diesel
5	E	methanol	5:1 and above	gasoline
6	F	methanol	5:1 and above	gasoline
7	G	Methanol	5:1 and above	gasoline
8	H	methanol	400:1 and above	gasoline
9	I	methanol	400:1 and above	gasoline
10	J	methanol	5:1 and above	gasoline
11	K	methanol	5:1 and above	gasoline
12	L	methanol	5:1 and above	gasoline
13	J	2-ethylhexanoic acid	90:1 and above	diesel
14	K	2-ethylhexanoic acid	90:1 and above	diesel
15	L	2-ethylhexanoic acid	90:1 and above	diesel
16	N	methanol	80:1 and above	gasoline
17	N	2-ethylhexanoic acid	90:1 and above	diesel
18	O	methanol	80:1 and above	gasoline
19	P	methanol	80:1 and above	gasoline
Comparative A	M	none effective	—	gasoline, diesel
Comparative B	Q	none effective	—	gasoline, diesel
Comparative C	R	none effective	—	gasoline, diesel
Comparative D	S	none effective	—	gasoline, diesel
Comparative E	T	none effective	—	gasoline, diesel

EXAMPLE 20 to 26

Combustion Chamber Deposit Tests

Combustion chamber deposit tests were run using Mercedes Benz C200 saloon cars with M 111-945, 1998 cc, 4-cylinder, 16 valve engines, compression ratio 10.4:1, 100 Kw at 5500 rpm, of accumulated mileage in the range 25,000 to 50,000 miles.
Mileage was accumulated on a standard 250 mile (400 km) circuit of 64 miles (102 km) at constant 60 mph (96 kph) followed by 78 miles (125 km) of urban driving at 30 to 60 mph (48 to 96 kph), followed by 108 miles (173 km) at constant 60 mph (96 kph).
Vehicles were left overnight at 20° C., to ensure that additive blends were added to warm fuel and to ensure that combustion chamber deposits were measured at constant engine block temperature. Where vehicles were allowed to stand for periods greater than 12 hours, the exhaust system was blocked to minimise possible effects in the engine from external humidity.
Combustion chamber deposits were assessed by measuring average piston centre combustion chamber deposits thickness through sparking plug aperture at piston top dead centre (TDC), using a Fischer Isoscope MP2 Probe, standardised prior to use against manufacturer-supplied standard films of known thickness. Average piston centre combustion chamber deposit thickness has been found previously to correlate closely to average total combustion chamber deposit weight, and therefore is a meaningful parameter.
For each assessment, piston was hand-cranked to TDC, and the probe was moved around the circumference of the spark plug aperture to give 20 measurements which were averaged to give a value for that cylinder. The spark plug was replaced, and measurements were successively done in similar manner for the other 3 cylinders.

EXAMPLE 20

Vehicles were run for 500 to 6000 miles (800 to 9600 kilometres) on detergent-containing gasoline. Average combustion chamber deposit thickness was then measured as above. (“Start”) Seven vehicles were then switched to base gasoline and run for 500 miles (800 kilometres), before deposit thickness was again measured (“End”). One vehicle was switched instead to base gasoline containing 50 ppm Dendrimer J, dosed as a 1:5 w/w solution of Dendrimer J in methanol, and run for 400 miles (640 kilometres).
Results are given in Table 2 following:

TABLE 2

	Average
	piston centre
	thickness
Gasoline	(microns)	End/

Example	Gasoline prior to test	Switched to	Start	End	start %

20	Detergent-containing	Dendrimer J	40.3	21.0	52.0
Comp. F	Detergent-containing	Base	83.4	71.4	85.6
		gasoline
Comp. G	Detergent-containing	Base	51.4	52.1	101.3
		gasoline
Comp. H	Detergent-containing	Base	38.0	39.1	102.9
		gasoline
Comp. I	Detergent-containing	Base	49.5	49.6	100.2
		gasoline
Comp. J	Detergent-containing	Base	37.1	38.5	103.8
		gasoline
Comp. K	Detergent-containing	Base	39.5	38	96.2
		gasoline
Comp. L	Detergent-containing	Base	39.8	43.4	109.0
		gasoline

From Table 2 it can readily be seen that switching from a gasoline containing a standard detergent package to a base gasoline containing Dendrimer J gave a remarkable reduction by 48% of combustion chamber deposit thickness over 400 miles (640 kilometres) (1 tank of fuel).

EXAMPLES 21 to 23

Vehicles were run (i) for a minimum of 500 miles (800 kilometres) on base gasoline, followed by (ii) 1000 miles (1600 kilometres) on base gasoline plus additive, followed by (iii) a further 500 miles (800 kilometres) on base gasoline Deposit thickness was measured after (i) (Start), at 500 miles (800 kilometres) and 1000 miles (1600 kilometres) in (ii), and after (iii) (End). Dendrimer N was used in (ii), at 200 ppmw, 50 ppmw and 10 ppmw, in different vehicles, and one vehicle was run using detergent-containing gasoline for comparison purposes. Dendrimer N was dosed into base gasoline as a 1:80 w/w solution of Dendrimer N in methanol.
Results are given in Table 3 following.

	TABLE 3

	Average piston centre thickness

			500 miles	1000 miles
	Base gasoline plus	Start	(800 kilometers)	(1600 kilometers)	End

Examples	additive	Microns	Microns	% of Start	Microns	% of Start	Microns	% of Start

21	200 ppmw Dendrimer N	51.5	26.8	52%	24.9	48.3%	26.4	51.3%
22	50 ppmw Dendrimer N	74.4	58.8	79%	51.5	69.2%	57.6	77.4%
23	10 ppmw Dendrimer N	33.9	26.3	77.6%	28.8	85.2%	33.6	99.3%
Comp. M	Detergent-containing	38	40.9	107.4%	42.4	111.6%	35.8	94%
	gasoline

It will be observed that for detergent-containing gasoline, combustion chamber deposit thickness increased by more than 11% over 1000 miles (1600 kilometres), whereas for base gasoline containing Dendrimer N, combustion chamber deposit thicknesses reduced according to concentration of Dendrimer N. Thus after 1000 miles (1600 kilometres) (2 tanks of fuel) of base gasoline containing Dendrimer N, combustion chamber deposit thickness reduced by over 51% for 200 ppmw concentration, by over 30% for 50 ppmw concentration and by over 14% for 10 ppmw concentration. In each case, combustion chamber deposit thickness reverted towards Start levels upon switching back to base gasoline.

EXAMPLE 24 to 26

Vehicles were run (i) for 2500 miles (4000 kilometres) on detergent-containing gasoline, followed by (ii) 1250 miles (2000 kilometres on test gasoline, followed by (iii) a further 750 miles (1200 kilometres) on detergent-containing gasoline. Average combustion chamber deposit thickness was measured after (i) (Start), at 750 miles (1200 kilometres) and 150 miles (2000 kilometres) in (ii) and after (iii) (End). Dendrimers N, O and P, dosed as 1:80 w/w solutions of dendrimer in methanol, were dosed into detergent-containing gasoline (DTG) at a concentration of dendrimer of 100 ppmw, in different vehicles, and one vehicle was run throughout on detergent-containing gasoline, for comparison purposes.
Results are given in Table 4 following:

	TABLE 4

	Average piston centre thickness

	Dendrimer		750 miles	1250 miles
	in Test	Start	(1200 kilometers)	(2000 kilometers)	End

Examples	gasoline	Microns	Microns	% of Start	Microns	% of Start	Microns	% of Start

24	N	44.1	48.6	110.1%	50.4	114.2%	59.3	134.5%
25	O	68.2	59.1	86.7%	58.3	85.5%	65.8	96.4%
26	P	57.2	49.4	86.3%	49	85.6%	59	103.1%
Comp. N	—	50.5	65	128.7%	71.5	141.7%	79.4	157.4%

It will be observed that deposit thickness increased continuously for detergent-containing gasoline over the 2000 miles (3200 kilometres) of the test. For Dendrimer N, the rate of increase of deposit thickness was slowed to an increase of 14.2% over 1250 miles (2000 kilometres), compared with 41.7% increase for detergent-containing gasoline without dendrimer. In the case of Dendrimers O and P, there was an actual reduction of deposit thickness by more than 14% over 1250 miles (2000 kilometres) relative to start. In each case, over the final 750 miles (1200 kilometres), run on detergent-containing gasoline, the deposit thickness increase by at least 11% (11% where no dendrimer had previously been used, 17.6% where Dendrimer N had previously been used, 12.8% where dendrimer O had previously been used and 20.4% where Dendrimer P had previously been used).

COMPARATIVE EXAMPLE

Detergency Testing

Intake Valve Deposit Simulator Test—Inclined Hot Plate Rig

This simulator test corresponds closely to that described in SAE Paper 890215, Daneshgari et al., “The Influence of Temperature upon Gasoline Deposit Build-Up on the Intake Valves”, Detroit, USA, 27 Feb. to 3 Mar. 1989. The test rig utilises four inclined plates in parallel. The plates are strips of sandblasted aluminium 50 cm long and 2.5 cm wide, having a central groove along their lengths 3 mm wide and 1 mm deep, mounted in the rig at an angle of 3 degrees relative to the horizontal. The temperature at the top end of each plate is maintained at 400° C. and at the middle of each plate is maintained at 250° C.
Gasoline samples, containing test materials at a concentration of 50 parts per million by weight (ppmw) of dendrimer in base gasoline, are prepared, and 100 ml portions of the gasoline samples are delivered at a rate of 0.6 ml/minute from glass syringes fitted with 20 gauge steel hypodermic Luer lock needles into the groove at the top end of each plate. Once delivery is complete, after about 2 hours and 40 minutes, the plates are allowed to cool to ambient temperature (20° C.) and are washed with n-heptane until the run-off liquid is clear, and are then left to dry before assessment of any deposit present.
Assessment is made using a “SEESCAN” (trade mark) Marker Image analyser with 512*512 image memory coupled to a “SONY”/“SEESCAN” (trade marks) CCD camera equipped with NIKON (trade mark) f55 Macro lens. Lighting of the plate being assessed is by two 12 v Tungsten lamps mounted at a linear distance of 22 cm from the point on the plate upon which the camera is focused and at angles of 33 degrees and 147 degrees relative to the plate.
A clear portion of the plate is moved under the camera and an image thereof captured. The section of the plate containing deposit is then moved beneath the camera and an image thereof is captured. The image analyser divides, pixel by corresponding pixel, the deposit image by the clean image and automatically measures the area and optical density of deposit at the pixels contained within overall measuring frame, and calculates an integrated optical density for the image, the numerical value of which is recorded as a test rating.
Results of this test are given in Table 5 as follows:

	TABLE 5

	MIHPT Rating

		Relative to Base
Dendrimer present	Rating	Gasoline

(Base gasoline)	132	1
A	382	2.9
C	353	2.7
F	322	2.4
J	363	2.8
K	202	1.5
N	357	2.8
O	220	1.7
P	233	1.8
(Detergent-containing	0	0
gasoline)

Dendrimers A and C were dosed as 1:10 w/w solutions of dendrimer in 2-ethyihexanol; and Dendrimers F, J, K, N, O and P were dosed as 1:80 w/w solutions of dendrimer in methanol.
It is readily apparent from Table 4, that these dendrimers do not exhibit detergent activity in gasoline.
This is by contrast with the disclosure of U.S. Pat. No. 6,127,481, wherein certain branched polyolefin polymers in the form of a comb, star, nanogel, or structural combinations thereof are disclosed as fuel additives. In U.S. Pat. No. 6,127,481 polyolefin pre-arms may be reacted with dendrimers (Columns 21 to 28) to provide polyolefin-terminated compounds such as Examples 15, 17d, 21b and 22, which are shown, in Example 26, Table 6, to be dispersant, detergent additives in gasoline, giving reduced intake valve deposits but increased combustion chamber deposits, relative to base gasoline.

Claims

1. A fuel composition comprising a major amount of a fuel for an internal combustion engine and a minor amount of a fuel-compatible dendrimer containing from 4 to 64 terminal functional groups independently selected from amino, hydroxyl and carboxylate groups.

2. The fuel composition of claim 1 which further comprises a fuel-compatible oxygenate co-solvent selected from C₁to C₁₄alkanols and 2-ethylhexanoic acid.

3. The fuel composition of claim 1 wherein the dendrimer is at least one fuel-compatible dendrimer independently selected from DAB-Am, PAMAM and PAMAM-OH dendrimers.

4. The fuel composition of claim 1 wherein the dendrimer contains from 4 to 32 terminal functional groups.

5. The fuel composition of claim 1 wherein the dendrimer is present in a concentration in the range from 5 ppmw to 500 ppmw based on total composition.

6. The fuel composition of claim 5 wherein the dendrimer is present in a concentration in the range from 10 ppmw to 200 ppmw based on total composition.

7. The fuel composition of claim 1 further comprises a nitrogen-containing detergent having a hydrocarbyl group having a number average molecular weight (Mn) in the range of 750 to 6000, in a concentration in the range of 25 to 2500 ppmw based on total composition.

8. The fuel composition of claim 1 wherein the fuel for an internal combustion engine is gasoline.

9. The fuel composition of claim 5 wherein the dendrimer contains from 4 to 32 terminal functional groups.

10. The fuel composition of claim 9 wherein the dendrimer is at least one fuel-compatible dendrimer independently selected from DAB-Am, PAMAM dn PAMAM-OH dendrimers.

11. A method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine a fuel composition of claim 1.

12. A method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine a fuel composition of claim 2.

13. A method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine a fuel composition of claim 3.

14. A method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine a fuel composition of claim 4.

15. A method of operating an internal combustion engine which comprises introducing into the combustion chambers of said engine a fuel composition of claim 9.