Patent Description:
Laminar burning velocity (also referred to as "flame speed") is a fundamental combustion property of any fuel/air mixture. As taught in SAE <NUM>-<NUM>-<NUM> formulating gasoline fuel blends having faster burning velocities can be an effective strategy for enhancing engine and vehicle performance. Faster burning fuels can lead to a more optimum combustion phasing resulting in a more efficient energy transfer and hence a faster acceleration and better performance.

Increasing ignition delay time (IDT) sufficiently to allow for optimization of spark timing during the power stroke in a spark-ignition internal combustion engine (SI-ICE) provides the best opportunity to calibrate for optimal efficiency. In addition, if the fuel is modified so that the ignition delay time increase is caused by inhibition of the chemical radical reactions that occur before the spark, and a shift of these same reactions further up the temperature/pressure trajectory of the cycle to occur after the spark, then combustion improvement can be achieved through increased flame speeds resulting in shorter burn duration. Ability to control flame speed, and burn duration collectively enable the SI-ICE to be calibrated to achieve the best balance between fuel economy, power and acceleration expressed in the term "break thermal efficiency" (BTE).

<CIT> discloses a gasoline composition comprising (a) a major amount of a mixture of hydrocarbons in the gasoline boiling range and (b) a minor amount of at least one hydrocarbon having <NUM> to <NUM> carbon atoms and containing at least one cyclopropyl group and at least one acetylenic group, said gasoline composition providing increased flame speed.

It has now surprisingly been found that the use of a particular additive component or combination of additive components in a liquid fuel composition can provide benefits in terms of increased flame speed, reduced burn duration, increased burn rate, improved power output, improved acceleration performance and improved fuel economy. Surprisingly the present invention achieves this without affecting the Ignition Delay Time (IDT).

According to the present invention there is provided a fuel composition comprising:.

wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, unsubstituted, straight chain or branched C<NUM>-C<NUM> alkyl group, OH, (CH<NUM>)nOH, (CH<NUM>)nNH<NUM>, wherein n is from <NUM> to <NUM>, provided that at least one of the X groups in each CX<NUM> group is a hydrogen atom.

It has been surprisingly found that the fuel compositions of the present invention provide increased flame speed, reduced burn duration, increased burn rate, improved power output and improved acceleration performance. Surprisingly the present invention achieves this without effecting the Ignition Delay Time (IDT).

According to yet another aspect of the present invention there is provided the use of a liquid fuel composition as described herein for improving power output.

According to yet another aspect of the present invention there is provided the use of a liquid fuel composition as described herein for improving acceleration.

According to yet another aspect of the present invention, there is provided the use of a liquid fuel composition for increasing the flame speed.

According to yet another aspect of the present invention there is provided the use of a liquid fuel composition for reducing the burn duration.

In order to assist with the understanding of the invention several terms are defined herein.

The term "power output" as used herein refers to the amount of resistance power required to maintain a fixed speed at wide open throttle conditions in Chassis Dynamometer testing.

According to the present invention, there is provided a use of a fuel composition described hereinbelow for improving the power output of an internal combustion engine. In the context of this aspect of the invention, the term "improving" embraces any degree of improvement. The improvement may for instance be <NUM>% or more, preferably <NUM>% or more, more preferably <NUM>% or more, even more preferably <NUM>% or more, especially <NUM>% or more, more especially <NUM>% or more, even more especially <NUM>% or more, of the power output of an analogous fuel formulation, prior to adding a tetraalkylethane compound, and preferably also a nitroxide radical, to it in accordance with the present invention. The improvement in power output may even be as high as <NUM>% of the power output of an analogous fuel formulation, prior to adding a tetraalkylethane compound, and preferably also a nitroxide radical, to it in accordance with the present invention.

In accordance with the present invention, the power output provided by a fuel composition may be determined in any known manner.

The term "acceleration" as used herein refers to the amount of time required for the engine to increase in speed between two fixed speed conditions in a given gear.

According to the present invention, there is provided a use of a fuel composition described hereinbelow for improving the acceleration of an internal combustion engine. In the context of this aspect of the invention, the term "improving" embraces any degree of improvement. The improvement may for instance be <NUM>% or more, preferably <NUM>% or more, more preferably <NUM>% or more, even more preferably <NUM>% or more, especially <NUM>% or more, more especially <NUM>% or more and even more especially <NUM>% or more of the acceleration provided by an analogous fuel formulation, prior to adding a tetraalkylethane compound, and preferably also a nitroxide radical, to it in accordance with the present invention. The improvement in acceleration may even be as high as <NUM>% of the acceleration provided by an analogous fuel formulation, prior to adding a tetraalkylethane compound, and preferably also a nitroxide radical, to it in accordance with the present invention.

In accordance with the present invention, the power output and acceleration provided by a fuel composition may be determined in any known manner for instance using the standard test methods as set out in SAE Paper <NUM>-<NUM>-<NUM> and SAE Paper <NUM>-<NUM>-<NUM>.

The term "flame speed" or 'laminar flame speed' (LFS) as used herein refers to laminar burning velocity. LFS is a fundamental measure of flame propagation rate without complication of mixing dynamics. However, in an engine, mixing dynamics play a role, so the measured flame speed is referred to as 'burn rate' and 'burn duration'. The terms 'burn rate' and 'burn duration' is also used herein interchangeably with 'flame speed'. Laminar Burning Velocity (LBV) is a fundamental property of a chemical component. It is defined as the rate (normal to the flame front, under laminar flow conditions) at which unburnt gas propagates to the flame front and reacts to form products.

According to the present invention, there is provided a use of a fuel composition described hereinbelow for increasing the flame speed in an internal combustion engine. In the context of this aspect of the invention, the term "increasing" embraces any degree of increase. The increase may for instance be <NUM>% or more, preferably <NUM>% or more, more preferably <NUM>% or more, and especially <NUM>% or more of the flame speed of an analogous fuel formulation, prior to adding the claimed additives to it in accordance with the present invention. The increase in flame speed may be at most <NUM>% of the flame speed of an analogous fuel formulation, prior to adding the claimed additives to it in accordance with the present invention.

However, it should be appreciated that any measurable improvement in power output, acceleration and flame speed may provide a worthwhile advantage, depending on what other factors are considered important, e.g. availability, cost, safety and so on.

In accordance with the present invention, the flame speed of a fuel composition may be determined in any known manner, for instance measurement of LFS can be performed using any one of the following three methods:.

All three of these methods are described in the review publication: <NPL>.

The following method for measuring flame speed in a constant volume combustion chamber (spherical bomb), ref <NPL>).

The following method for measuring flame speed uses a net pressure method: <NPL>.

The term 'burn duration' as used herein means the time required (in engine crank angle degrees) for combustion to progress from <NUM>% to <NUM>% (referred to as AI <NUM>-<NUM> in the Examples below). In the Examples below, the term AI <NUM>-<NUM> is also used in relation to burn duration and means the time required (in engine crank angle degrees) for combustion to progress from <NUM>% to <NUM>%.

In accordance with the present invention, the burn duration of a fuel composition may be determined in any known manner, for instance using the test method disclosed in the Examples section hereinbelow.

However, it should be appreciated that any measurable improvement in power output, acceleration, burn duration and flame speed may provide a worthwhile advantage, depending on what other factors are considered important, e.g. availability, cost, safety and so on.

The liquid fuel composition of the present invention comprises a base fuel suitable for use in an internal combustion engine, a tetraalkylethane compound and a nitroxide radical. The base fuel suitable for use in an internal combustion engine is a gasoline, and therefore the liquid fuel composition of the present invention is a gasoline composition.

The tetraalkylethane compound used herein is a compound having the formula (I):
<CHM>
wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, unsubstituted, straight chain or branched C<NUM>-C<NUM> saturated or unsaturated alkyl group, (CH<NUM>)nOH, (CH<NUM>)nNH<NUM>, wherein n is in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, more preferably in the range from <NUM> to <NUM>, even more preferably in the range from <NUM> to <NUM>, provided that at least one of the X groups in each CX<NUM> group is a hydrogen atom.

Preferably, at least two of the X groups in each CX<NUM> group is a hydrogen atom.

In an especially preferred embodiment, three of the X groups in each CX<NUM> group is a hydrogen atom.

Preferably, the Ar of the tetraalkylethane compound is an unsubstituted aromatic group, such as a phenyl, biphenyl, naphthyl or anthracyl. More preferably, Ar is an unsubstituted phenyl group. This means that for the preparation of the preferred compound of formula (I) it is possible to start out with cumene, which is commercially available. Starting with cumene, dicumene can be prepared by several known methods, as described in <CIT>.

Preferably, each X group is independently selected from a hydrogen atom and an unsubstituted, straight chain or branched, saturated or unsaturated C<NUM>-C<NUM>, more preferably C<NUM>-C<NUM>, alkyl group, provided that at least one of the X groups in each CX<NUM> group is a hydrogen atom.

More preferably, each X group is independently selected from a hydrogen atom and an unsubstituted, straight chain or branched, saturated C<NUM>-C<NUM>, preferably C<NUM>-C<NUM>, alkyl group, provided that at least one of the X groups in each CX<NUM> group is a hydrogen atom.

In one embodiment, each X group is independently selected from a hydrogen atom, and an unsubstituted straight chain, saturated C<NUM>-C<NUM>, preferably C<NUM>-C<NUM>, alkyl group, especially methyl, ethyl and propyl.

Examples of suitable tetraalkylethane compounds of Formula (I) include:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

In one embodiment herein the tetralkylethane compound is <NUM>,<NUM>' (<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>,<NUM>-ethanediyl)bis-benzene (dicumene). Dicumene is commercially available from Aldrich and various other chemical suppliers.

The tetraalkylethane compound is preferably present in the fuel composition at a level from 30ppm to <NUM> wt%, preferably from 100ppm to <NUM> wt%, more preferably from 100ppm to <NUM> wt%, even more preferably from 100ppm to 5000ppm, especially from 500ppm to 2000ppm, by weight of the fuel composition.

In addition to the tetraalkylethane compound described above, it is also preferable to include a nitroxide radical in the fuel compositions of the present invention. It has been found that by using a combination of a tetraalkylethane compound and a nitroxide radical improvements in power, acceleration, flame speed, burn duration properties can be obtained.

As used herein, the term 'nitroxide radical' refers to stable nitroxide free radicals. Nitroxide radicals may have either a heterocyclic or linear structure. Suitable nitroxide radicals for use herein have the formula (II):
<CHM>
wherein R<NUM>, R<NUM>, R<NUM> and R<NUM> are individually selected from an alkyl group or a hetero atom substituted alkyl group, and wherein R<NUM> and R<NUM> are any atom or group except hydrogen which can covalently bond to carbon.

R<NUM>, R<NUM>, R<NUM> and R<NUM> may be the same or different and, in some embodiments, include <NUM> carbon atoms to <NUM> carbon atoms. Preferably, R<NUM>, R<NUM>, R<NUM> and R<NUM> are individually selected from a methyl group, an ethyl group, or a propyl group.

R<NUM> and R<NUM> may be any atom or group except hydrogen which can bond covalently to carbon, although some groups may reduce the stabilizing power of the nitroxide structure and are undesirable. In some embodiments, R<NUM> and R<NUM> are individually selected from halogen, cyano, - COOR wherein R is alkyl or aryl, -CONH<NUM>, -S-C<NUM>H<NUM>, -S-COCH<NUM>, -OCOC<NUM>H<NUM>, carbonyl, alkenyl where the double bond is not conjugated with the nitroxide moiety or alkyl of <NUM> to <NUM> carbon atoms. R<NUM> and R<NUM> may also form a ring of <NUM> carbon atoms or <NUM> carbon atoms and up to two heteroatoms, such as O, N or S by R<NUM> and R<NUM> together. Examples of suitable compounds having the structure above and in which R<NUM> and R<NUM> form part of the ring are pyrrolidine-<NUM>-oxys, piperidinyl-<NUM>-oxys, the morpholines and piperazines. Particular examples wherein the R<NUM> and R<NUM> above form part of a ring are <NUM>-hydroxy-<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-piperindino-<NUM>-oxy and pyrrolin-<NUM>-oxyl. In some embodiments, suitable R<NUM> and R<NUM> groups are individually selected from methyl, ethyl and propyl groups.

Another example of a suitable nitroxide radical may include, but is not limited to, a nitroxide radical having the structure of a six-membered ring of Formula (III) as follows:
<CHM>
wherein R<NUM>, R<NUM>, R<NUM> and R<NUM> are individually selected from alkyl groups or hetero atom substituted alkyl, and wherein R<NUM> and R<NUM> are individually selected from -CR'R'-, wherein each R' is individually selected from hydrogen, a hydroxide group, an alkyl group, or an alkoxy group. The alkyl (or heteroatom substituted) groups R<NUM>, R<NUM>, R<NUM> and R<NUM> may be the same of different and, in some embodiments, include <NUM> carbon atom to <NUM> carbon atoms. In some embodiments, R<NUM>, R<NUM>, R<NUM> and R<NUM> are individually selected from methyl, ethyl or propyl groups. In some embodiments, each R' may be the same or different and, in some embodiments, include <NUM> carbon atoms to <NUM> carbon atoms. In some embodiments, each R' is individually selected from methyl, ethyl, or propyl groups.

An example of a suitable hydroxide of Formula (III) includes <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-piperidinyloxy free radical, commonly referred to as TEMPO, which may also be referred to as <NUM>,<NUM>,<NUM>,<NUM>,-tetramethyl-piperidino-<NUM>-oxy, <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidine <NUM>-oxyl or <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidinyloxy, of Formula (IV) as follows:
<CHM>.

TEMPO is commercially available from Aldrich and other chemical suppliers.

Another example of a suitable nitroxide radical may include, but is not limited to, a nitroxide radical having the structure of a six-membered ring of Formula (V) as follows:
<CHM>
wherein R<NUM>, R<NUM>, R<NUM> and R<NUM> of Formula (V) are individually selected from alkyl groups or hetero atom substituted alkyl, and wherein R<NUM>, R<NUM>, R<NUM> of Formula (V) are individually selected from -CR'R'-, wherein each R' is individually selected from hydrogen, a hydroxide group, an alkyl group, or an alkoxy group. The alkyl (or heteroatoms substituted) groups R<NUM>, R<NUM>, R<NUM>, and R<NUM> of Formula (V) may be the same or different and, in some embodiments, R<NUM>, R<NUM>, R<NUM> and R<NUM> of Formula (V) are individually selected from methyl, ethyl, or propyl groups. In some embodiments, each R' may be the same or different and, in some embodiments, include <NUM> carbon atoms to <NUM> carbon atoms. In some embodiments, each R' is individually selected from methyl, ethyl or propyl groups.

The nitroxide radical is preferably present in the fuel composition at a level from 30ppm to <NUM> wt%, preferably from 100ppm to <NUM> wt%, more preferably from 100ppm to 5000ppm, even more preferably from 500ppm to 2000ppm, by weight of the fuel composition.

The tetraalkylethane compound and, when present, the nitroxide radical may be blended together with any other additives e.g. additive performance package(s) to produce an additive blend. The additive blend is then added to a base fuel to produce a liquid fuel composition.

The amount of performance package(s) in the additive blend is preferably in the range of from <NUM> to <NUM> wt%, more preferably in the range of from <NUM> to <NUM> wt%, by weight of the additive blend.

Preferably, the amount of the performance package present in the liquid fuel composition of the present invention is in the range of <NUM> ppmw (parts per million by weight) to <NUM> %wt, based on the overall weight of the liquid fuel composition. More preferably, the amount of the performance package present in the liquid fuel composition of the present invention additionally accords with one or more of the parameters (i) to (xv) listed below:.

In the liquid fuel compositions of the present invention, the base fuel used is a gasoline. The gasoline may be any gasoline suitable for use in an internal combustion engine of the spark-ignition (petrol) type known in the art, including automotive engines as well as in other types of engine such as, for example, off road and aviation engines. The gasoline used as the base fuel in the liquid fuel composition of the present invention may conveniently also be referred to as 'base gasoline'.

Gasolines typically comprise mixtures of hydrocarbons boiling in the range from <NUM> to <NUM> (EN-ISO <NUM>), the optimal ranges and distillation curves typically varying according to climate and season of the year. The hydrocarbons in a gasoline may be derived by any means known in the art, conveniently the hydrocarbons may be derived in any known manner from straight-run gasoline, synthetically-produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydro-cracked petroleum fractions, catalytically reformed hydrocarbons or mixtures of these.

The specific distillation curve, hydrocarbon composition, research octane number (RON) and motor octane number (MON) of the gasoline are not critical.

Conveniently, the research octane number (RON) of the gasoline may be at least <NUM>, for instance in the range of from <NUM> to <NUM>, preferably the RON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, more preferably the RON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, even more preferably the RON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, even more preferably the RON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, and most preferably the RON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM> (EN <NUM>); the motor octane number (MON) of the gasoline may conveniently be at least <NUM>, for instance in the range of from <NUM> to <NUM>, preferably the MON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, more preferably the MON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM>, most preferably the MON of the gasoline will be at least <NUM>, for instance in the range of from <NUM> to <NUM> (EN <NUM>).

Typically, gasolines comprise components selected from one or more of the following groups; saturated hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons, and oxygenated hydrocarbons. Conveniently, the gasoline may comprise a mixture of saturated hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons, and, optionally, oxygenated hydrocarbons.

Typically, the olefinic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline (ASTM D1319); preferably, the olefinic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline, more preferably, the olefinic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline.

Typically, the aromatic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline (ASTM D1319), for instance the aromatic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline; preferably, the aromatic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline, for instance the aromatic hydrocarbon content of the gasoline is in the range of from <NUM> to <NUM> percent by volume based on the gasoline. In one embodiment herein the gasoline base fuel comprises less than <NUM> vol% of aromatics, based on the total base fuel. In another embodiment herein, the gasoline base fuel comprises less than <NUM> vol% of aromatics having <NUM> carbon atoms or greater, based on the total base fuel.

The benzene content of the gasoline is at most <NUM> percent by volume, more preferably at most <NUM> percent by volume, especially at most <NUM> percent by volume based on the gasoline.

The gasoline preferably has a low or ultra low sulphur content, for instance at most <NUM> ppmw (parts per million by weight), preferably no more than <NUM> ppmw, more preferably no more than <NUM>, even more preferably no more than <NUM> and most preferably no more than even <NUM> ppmw.

The gasoline also preferably has a low total lead content, such as at most <NUM>/l, most preferably being lead free - having no lead compounds added thereto (i.e. unleaded).

When the gasoline comprises oxygenated hydrocarbons, at least a portion of non-oxygenated hydrocarbons will be substituted for oxygenated hydrocarbons (match-blending) or simply added to the fully formulated gasoline (splash-blending). The oxygenate content of the gasoline may be up to <NUM> percent by weight (EN <NUM>) (e.g. ethanol per se) based on the gasoline. For example, the oxygenate content of the gasoline may be up to <NUM> percent by weight, preferably up to <NUM> percent by weight, more preferably up to <NUM> percent by weight. Conveniently, the oxygenate concentration will have a minimum concentration selected from any one of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> percent by weight, and a maximum concentration selected from any one of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> percent by weight.

Examples of oxygenated hydrocarbons that may be incorporated into the gasoline include alcohols, ethers, esters, ketones, aldehydes, carboxylic acids and their derivatives, and oxygen containing heterocyclic compounds. Preferably, the oxygenated hydrocarbons that may be incorporated into the gasoline are selected from alcohols (such as methanol, ethanol, propanol, <NUM>-propanol, butanol, tert-butanol, iso-butanol and <NUM>-butanol), ethers (preferably ethers containing <NUM> or more carbon atoms per molecule, e.g., methyl tert-butyl ether and ethyl tert-butyl ether) and esters (preferably esters containing <NUM> or more carbon atoms per molecule); a particularly preferred oxygenated hydrocarbon is ethanol.

When oxygenated hydrocarbons are present in the gasoline, the amount of oxygenated hydrocarbons in the gasoline may vary over a wide range. For example, gasolines comprising a major proportion of oxygenated hydrocarbons are currently commercially available in countries such as Brazil and U. , e.g. ethanol per se and E85, as well as gasolines comprising a minor proportion of oxygenated hydrocarbons, e.g. E10 and E5. Therefore, the gasoline may contain up to <NUM> percent by volume oxygenated hydrocarbons. E100 fuels as used in Brazil are also included herein. Preferably, the amount of oxygenated hydrocarbons present in the gasoline is selected from one of the following amounts: up to <NUM> percent by volume; up to <NUM> percent by volume; up to <NUM> percent by volume; up to <NUM> percent by volume; up to <NUM> percent by volume; up to <NUM> percent by volume; and, up to <NUM> percent by volume, depending upon the desired final formulation of the gasoline. Conveniently, the gasoline may contain at least <NUM>, <NUM> or <NUM> percent by volume oxygenated hydrocarbons.

Examples of suitable gasolines include gasolines which have an olefinic hydrocarbon content of from <NUM> to <NUM> percent by volume (ASTM D1319), an oxygen content of from <NUM> to <NUM> percent by weight (EN <NUM>), an aromatic hydrocarbon content of from <NUM> to <NUM> percent by volume (ASTM D1319) and a benzene content of at most <NUM> percent by volume.

Also suitable for use herein are gasoline blending components which can be derived from sources other than crude oil, such as low carbon gasoline fuels from either biomass or CO<NUM>, and blends thereof which each other or with fossil-derived gasoline streams and components. Suitable examples of such fuels include:.

Particularly suitable for use herein are gasoline blending components which can be derived from a biological source. Examples of such gasoline blending components can be found in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

Whilst not critical to the present invention, the base gasoline or the gasoline composition of the present invention may conveniently include one or more optional fuel additives, in addition to the essential tetraalkylethane compound and the essential nitroxide radical mentioned above. The concentration and nature of the optional fuel additive(s) that may be included in the base gasoline or the gasoline composition of the present invention is not critical. Non-limiting examples of suitable types of fuel additives that can be included in the base gasoline or the gasoline composition of the present invention include anti-oxidants, corrosion inhibitors, detergents, dehazers, antiknock additives, metal deactivators, valve-seat recession protectant compounds, dyes, solvents, carrier fluids, diluents and markers. Examples of suitable such additives are described generally in <CIT>.

Conveniently, the fuel additives can be blended with one or more solvents to form an additive concentrate, the additive concentrate can then be admixed with the base gasoline or the gasoline composition of the present invention.

The (active matter) concentration of any optional additives present in the base gasoline or the gasoline composition of the present invention is preferably up to <NUM> percent by weight, more preferably in the range from <NUM> to <NUM> ppmw, advantageously in the range of from <NUM> to <NUM> ppmw, such as from <NUM> to <NUM> ppmw.

As stated above, the gasoline composition may also contain synthetic or mineral carrier oils and/or solvents.

Examples of suitable mineral carrier oils are fractions obtained in crude oil processing, such as brightstock or base oils having viscosities, for example, from the SN <NUM> - <NUM> class; and also aromatic hydrocarbons, paraffinic hydrocarbons and alkoxyalkanols. Also useful as a mineral carrier oil is a fraction which is obtained in the refining of mineral oil and is known as "hydrocrack oil" (vacuum distillate cut having a boiling range of from about <NUM> to <NUM>, obtainable from natural mineral oil which has been catalytically hydrogenated under high pressure and isomerized and also deparaffinized).

Examples of suitable synthetic carrier oils are: polyolefins (poly-alpha-olefins or poly (internal olefin)s), (poly)esters, (poly)alkoxylates, polyethers, aliphatic polyether amines, alkylphenol-started polyethers, alkylphenol-started polyether amines and carboxylic esters of long-chain alkanols.

Examples of suitable polyolefins are olefin polymers, in particular based on polybutene or polyisobutene (hydrogenated or nonhydrogenated).

Examples of suitable polyethers or polyetheramines are preferably compounds comprising polyoxy-C<NUM>-C<NUM>-alkylene moieties which are obtainable by reacting C<NUM>-C<NUM>-alkanols, C<NUM>-C<NUM>-alkanediols, mono- or di-C<NUM>-C<NUM>-alkylamines, C<NUM>-C<NUM>-alkylcyclohexanols or C<NUM>-C<NUM>-alkylphenols with from <NUM> to <NUM> mol of ethylene oxide and/or propylene oxide and/or butylene oxide per hydroxyl group or amino group, and, in the case of the polyether amines, by subsequent reductive amination with ammonia, monoamines or polyamines. Such products are described in particular in <CIT>, <CIT>, <CIT> and <CIT>. For example, the polyether amines used may be poly-C<NUM>-C<NUM>-alkylene oxide amines or functional derivatives thereof. Typical examples thereof are tridecanol butoxylates or isotridecanol butoxylates, isononylphenol butoxylates and also polyisobutenol butoxylates and propoxylates, and also the corresponding reaction products with ammonia.

Examples of carboxylic esters of long-chain alkanols are in particular esters of mono-, di- or tricarboxylic acids with long-chain alkanols or polyols, as described in particular in <CIT>. The mono-, di- or tricarboxylic acids used may be aliphatic or aromatic acids; suitable ester alcohols or polyols are in particular long-chain representatives having, for example, from <NUM> to <NUM> carbon atoms. Typical representatives of the esters are adipates, phthalates, isophthalates, terephthalates and trimellitates of isooctanol, isononanol, isodecanol and isotridecanol, for example di-(n- or isotridecyl) phthalate.

Further suitable carrier oil systems are described, for example, in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>, which are incorporated herein by way of reference.

Examples of particularly suitable synthetic carrier oils are alcohol-started polyethers having from about <NUM> to <NUM>, for example from about <NUM> to <NUM>, C<NUM>-C<NUM>-alkylene oxide units, for example selected from propylene oxide, n-butylene oxide and isobutylene oxide units, or mixtures thereof. Non-limiting examples of suitable starter alcohols are long-chain alkanols or phenols substituted by long-chain alkyl in which the long-chain alkyl radical is in particular a straight-chain or branched C<NUM>-C<NUM>-alkyl radical. Preferred examples include tridecanol and nonylphenol.

Further suitable synthetic carrier oils are alkoxylated alkylphenols, as described in <CIT>.

Mixtures of mineral carrier oils, synthetic carrier oils, and mineral and synthetic carrier oils may also be used.

Any solvent and optionally co-solvent suitable for use in fuels may be used. Examples of suitable solvents for use in fuels include: non-polar hydrocarbon solvents such as kerosene, heavy aromatic solvent ("solvent naphtha heavy", "Solvesso <NUM>"), toluene, xylene, paraffins, petroleum, white spirits, those sold by Shell companies under the trademark "SHELLSOL", and the like. Examples of suitable co-solvents include: polar solvents such as esters and, in particular, alcohols (e.g. t-butanol, i-butanol, hexanol, <NUM>-ethylhexanol, <NUM>-propyl heptanol, decanol, isotridecanol, butyl glycols, and alcohol mixtures such as those sold by Shell companies under the trade mark "LINEVOL", especially LINEVOL <NUM> alcohol which is a mixture of C<NUM>-<NUM> primary alcohols, or a C<NUM>-<NUM> alcohol mixture which is commercially available).

Dehazers/demulsifiers suitable for use in liquid fuels are well known in the art. Non-limiting examples include glycol oxyalkylate polyol blends (such as sold under the trade designation TOLAD™ <NUM>), alkoxylated phenol formaldehyde polymers, phenol/formaldehyde or C<NUM>-<NUM> alkylphenol/-formaldehyde resin oxyalkylates modified by oxyalkylation with C<NUM>-<NUM> epoxides and diepoxides (such as sold under the trade designation TOLAD™ <NUM>), and C<NUM>-<NUM> epoxide copolymers cross-linked with diepoxides, diacids, diesters, diols, diacrylates, dimethacrylates or diisocyanates, and blends thereof. The glycol oxyalkylate polyol blends may be polyols oxyalkylated with C<NUM>-<NUM> epoxides. The C<NUM>-<NUM> alkylphenol phenol/- formaldehyde resin oxyalkylates modified by oxyalkylation with C<NUM>-<NUM> epoxides and diepoxides may be based on, for example, cresol, t-butyl phenol, dodecyl phenol or dinonyl phenol, or a mixture of phenols (such as a mixture of t-butyl phenol and nonyl phenol). The dehazer should be used in an amount sufficient to inhibit the hazing that might otherwise occur when the gasoline without the dehazer contacts water, and this amount will be referred to herein as a "haze-inhibiting amount. " Generally, this amount is from about <NUM> to about <NUM> ppmw (e.g. from about <NUM> to about <NUM> ppm), more preferably from <NUM> to <NUM> ppmw, still more preferably from <NUM> to <NUM> ppmw, advantageously from <NUM> to <NUM> ppmw based on the weight of the gasoline.

Further customary additives for use in gasolines are corrosion inhibitors, for example based on ammonium salts of organic carboxylic acids, said salts tending to form films, or of heterocyclic aromatics for nonferrous metal corrosion protection; antioxidants or stabilizers, for example based on amines such as phenyldiamines, e.g. p-phenylenediamine, N,N'-di-sec-butyl-p-phenyldiamine, dicyclohexylamine or derivatives thereof or of phenols such as <NUM>,<NUM>-di-tert-butylphenol or <NUM>,<NUM>-di-tert-butyl-<NUM>-hydroxy-phenylpropionic acid; anti-static agents; metallocenes such as ferrocene; methylcyclo-pentadienylmanganese tricarbonyl; lubricity additives, such as certain fatty acids, alkenylsuccinic esters, bis(hydroxyalkyl) fatty amines, hydroxyacetamides or castor oil; and also dyes (markers). Amines may also be added, if appropriate, for example as described in <CIT>. Optionally anti valve seat recession additives may be used such as sodium or potassium salts of polymeric organic acids.

The gasoline compositions herein can also comprise a detergent additive. Suitable detergent additives include those disclosed in <CIT>, incorporated herein by reference.

Preferred detergent additives for use in the gasoline composition herein typically have at least one hydrophobic hydrocarbon radical having a number-average molecular weight (Mn) of from <NUM> to <NUM><NUM> and at least one polar moiety selected from:.

The hydrophobic hydrocarbon radical in the above detergent additives, which ensures the adequate solubility in the base fluid, has a number-average molecular weight (Mn) of from <NUM> to <NUM><NUM>, especially from <NUM> to <NUM><NUM>, in particular from <NUM> to <NUM>. Typical hydrophobic hydrocarbon radicals, especially in conjunction with the polar moieties (A1), (A8) and (A9), include polyalkenes (polyolefins), such as the polypropenyl, polybutenyl and polyisobutenyl radicals each having Mn of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and especially from <NUM> to <NUM>.

Non-limiting examples of the above groups of detergent additives include the following:
Additives comprising mono- or polyamino groups (A1) are preferably polyalkenemono- or polyalkenepolyamines based on polypropene or conventional (i.e. having predominantly internal double bonds) polybutene or polyisobutene having Mn of from <NUM> to <NUM>. When polybutene or polyisobutene having predominantly internal double bonds (usually in the beta and gamma position) are used as starting materials in the preparation of the additives, a possible preparative route is by chlorination and subsequent amination or by oxidation of the double bond with air or ozone to give the carbonyl or carboxyl compound and subsequent amination under reductive (hydrogenating) conditions. The amines used here for the amination may be, for example, ammonia, monoamines or polyamines, such as dimethylaminopropylamine, ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine. Corresponding additives based on polypropene are described in particular in <CIT>.

Further preferred additives comprising monoamino groups (A1) are the hydrogenation products of the reaction products of polyisobutenes having an average degree of polymerization of from <NUM> to <NUM>, with nitrogen oxides or mixtures of nitrogen oxides and oxygen, as described in particular in <CIT>.

Further preferred additives comprising monoamino groups (A1) are the compounds obtainable from polyisobutene epoxides by reaction with amines and subsequent dehydration and reduction of the amino alcohols, as described in particular in <CIT>.

Additives comprising polyoxy-C<NUM>-C<NUM>-alkylene moieties (A6) are preferably polyethers or polyetheramines which are obtainable by reaction of C<NUM>- to C<NUM>-alkanols, C<NUM>- to C<NUM>-alkanediols, mono- or di-C<NUM>-C<NUM>-alkylamines, C<NUM>-C<NUM>-alkylcyclohexanols or C<NUM>-C<NUM>-alkylphenols with from <NUM> to <NUM> mol of ethylene oxide and/or propylene oxide and/or butylene oxide per hydroxyl group or amino group and, in the case of the polyether-amines, by subsequent reductive amination with ammonia, monoamines or polyamines. Such products are described in particular in <CIT>, <CIT>, <CIT> and <CIT>. In the case of polyethers, such products also have carrier oil properties. Typical examples of these are tridecanol butoxylates, isotridecanol butoxylates, isononylphenol butoxylates and polyisobutenol butoxylates and propoxylates and also the corresponding reaction products with ammonia.

Additives comprising moieties derived from succinic anhydride and having hydroxyl and/or amino and/or amido and/or imido groups (A8) are preferably corresponding derivatives of polyisobutenylsuccinic anhydride which are obtainable by reacting conventional or highly reactive polyisobutene having Mn of from <NUM> to <NUM> with maleic anhydride by a thermal route or via the chlorinated polyisobutene. Of particular interest are derivatives with aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine. Such additives are described in particular in <CIT>.

Additives comprising moieties obtained by Mannich reaction of substituted phenols with aldehydes and mono- or polyamines (A9) are preferably reaction products of polyisobutene-substituted phenols with formaldehyde and mono- or polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine or dimethylaminopropylamine. The polyisobutenyl-substituted phenols may stem from conventional or highly reactive polyisobutene having Mn of from <NUM> to <NUM>. Such "polyisobutene-Mannich bases" are described in particular in <CIT>.

Preferably, the detergent additive used in the gasoline compositions of the present invention contains at least one nitrogen-containing detergent, more preferably at least one nitrogen-containing detergent containing a hydrophobic hydrocarbon radical having a number average molecular weight in the range of from <NUM> to <NUM>. Preferably, the nitrogen-containing detergent is selected from a group comprising polyalkene monoamines, polyetheramines, polyalkene Mannich amines and polyalkene succinimides. Conveniently, the nitrogen-containing detergent may be a polyalkene monoamine.

In the above, amounts (concentrations, % vol, ppmw, % wt) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials.

The liquid fuel composition of the present invention can be produced by admixing the essential tetraalkylethane compound and nitroxide radical with a gasoline base fuel suitable for use in an internal combustion engine. Since the base fuel to which the essential fuel additive is admixed is a gasoline, then the liquid fuel composition produced is a gasoline composition.

It has surprisingly been found that the use a combination of a tetraalkylethane compound and, preferably, a nitroxide radical as described herein in liquid fuel compositions provides benefits in terms of improved power, improved acceleration, reduced burn duration, increased flame speed and improved fuel economy of an internal combustion engine being fuelled by the liquid fuel composition containing said tetraalkylethane compound and, preferably said nitroxide radical, relative to the internal combustion engine being fuelled by the liquid base fuel.

The present invention will be further understood from the following examples. Unless otherwise stated, all amounts and concentrations disclosed in the examples are based on weight of the fully formulated fuel composition.

The goal of these experiments was to screen a set of additives with potential for combustion enhancing properties using the gasoline single cylinder engine (GSCE). Combustion enhancement could be shown in basically two modes: pre-ignition delay (octane boosting, important for reduced knock at high compression ratio) or flame speed improver (shortened burn duration leading to improved power).

A number of fully formulated fuel compositions are provided below (Examples <NUM> to <NUM>).

All fuel compositions use the same base fuel. The base fuel is an E10 fuel (containing <NUM>% ethanol) meeting North American maingrade specification ASTM D4814 containing no performance additive.

TEMPO and/or dicumene were added into the base fuel at the treat rates indicated in Table <NUM> below. Table <NUM> also shows the RON and MON values for each fuel formulation.

The engine used for these experiments was the Gasoline single cylinder engine. This engine was manufactured by AVL and based on the EA888 <NUM> Audi TFSI/VW TSI (Euro <NUM>). The single cylinder bench engine details are shown in Table <NUM> below.

The engine test conditions are detailed below in Table <NUM>.

The test protocol below was run with base fuel and one test fuel (one of Examples <NUM>-<NUM>) per day:.

Each test fuel blend was screened twice, once in each of two randomized loops.

Pmax, burn duration and exhaust temperature measurements were taken and the results are shown in Tables <NUM>, <NUM>, <NUM> and <NUM> below. Table <NUM> shows the average % difference in Pmax between the test blend and it's base fuel control at <NUM> HL, IGN = <NUM> (IGN = ignition time). <FIG> is a graphical representation of the experimental data set out in Table <NUM> for Examples <NUM> to <NUM> (the Example number being on the x axis and the average % difference in Pmax being on the y axis). Table <NUM> shows the average % difference in burn duration between the test blend and it's base fuel control at <NUM> HL, IGN=<NUM>. <FIG> is a graphical representation of the experimental data set out in Table <NUM> for Examples <NUM> to <NUM> (the Example number being on the x axis and the average % difference in burn duration being on the y axis). <FIG> shows a comparison of the time required (in engine crank angle degrees) for combustion to progress from <NUM>% to <NUM>% across a range of ignition timing for Example <NUM> and the base fuel. Lower AI <NUM>-<NUM>% values (Mass Fraction Burn) means faster burning fuel (condition <NUM> rpm, <NUM> IMEP). Table <NUM> shows the Exhaust Temperature and the % difference in Exhaust Temperature between the test blend and it's base fuel control (at <NUM> HL, IGN=<NUM>). <FIG> is a graphical representation of the experimental data set out in Table <NUM> for Examples <NUM> to <NUM> (the Example number being on the x axis and the average % difference in Exhaust Temperature being on the y axis). Table <NUM> shows the average % difference in burn duration (AI50-<NUM>) between the test blend and it's base fuel control at <NUM> HL, IGN=<NUM>. <FIG> is a graphical representation of the experimental data set out in Table <NUM> for Examples <NUM> to <NUM> (the Example number being on the x axis and the average % difference in burn duration being on the y axis).

As can be seen from Table <NUM> and <FIG>, the average time required for the latter half of combustion (AI50-<NUM>) was shortened.

Claim 1:
Fuel composition comprising:
(a) a base fuel suitable for use in an internal combustion engine, wherein the base fuel is a gasoline base fuel; and
(b) a tetraalkylethane compound having the formula (I):
<CHM>
wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, unsubstituted, straight chain or branched C<NUM>-C<NUM> alkyl group, (CH<NUM>)nOH or (CH<NUM>)nNH<NUM>, wherein n is in the range of <NUM> to <NUM>, provided that at least one of the X groups in each CX<NUM> group is a hydrogen atom.