WO2024083782A1

WO2024083782A1 - Fuel compositions

Info

Publication number: WO2024083782A1
Application number: PCT/EP2023/078759
Authority: WO
Inventors: Kimberly Ann Johnson; Tushar Kanti Bera; Allen Ambwere Aradi; Varun GAUBA
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Usa, Inc.
Priority date: 2022-10-21
Filing date: 2023-10-17
Publication date: 2024-04-25

Abstract

Fuel composition comprising: (a) a gasoline base fuel suitable for use in a spark ignition internal combustion engine; and (b) a polybutene polymer, wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol and wherein greater than 30% of the polymer molecules in the polybutene polymer have a terminal vinylidene group; and (c) a tetraalkylethane compound having the formula (I): wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH2)nOH or (CH2)nNH2, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX3 group is a hydrogen atom. The fuel compositions of the present invention provide improved engine power and reduced burn duration.

Description

FUEL COMPOSITIONS

Field of the Invention

The present invention relates to a liquid fuel composition, in particular to a liquid fuel composition which provides improved engine power and which has a reduced burn duration in an internal combustion engine. The present invention also relates to methods of improving the power output of an internal combustion engine as well as increasing efficiency and reducing emissions, by fueling the internal combustion engine with the liquid fuel composition described herein below. The present invention also relates to methods of reducing the burn duration of a liquid fuel composition. Background of the Invention

In order to improve engine efficiency, power and acceleration properties of modern spark ignition interal combustion engines, these engines are increasingly being downsized and boosted as well as moving up in compression ratios.

As well as upgrading the engine hardware, it is also possible to improve engine efficiency, reduce emissions, increase power and acceleration of spark ignition engines by making changes to the fuel formulations used to fuel the engines. For example, gasoline fuel compositions containing specially formulated refinery components with high octane and flame speed/burn duration properties can deliver increases in power and/or acceleration as well as fuel economy. However, it would be desirable to be able to use market available, standard exchange gasoline fuel for upgrading power, acceleration and fuel efficiency performance . So-called high reactivity polybutene polymers have relatively high proportions (i.e. >30%) of polymer molecules having a terminal vinylidene group. US 6,048,373 discloses a fuel composition comprising a spark ignition fuel, a Mannich detergent and a polybutene having a molecular weight distribution of less than 1.4 for controlling intake valve deposits and minimizing valve sticking in spark ignition internal combustion engines. Preferred polybutenes disclosed therein have a number average molecular weight (Mn) of from about 500 to about 2000, and high reactivity polyisobutylenes (PIBs) are disclosed. Preferred treat rates for the polybutene(s) having a molecular weight distribution of 1.4 or less are stated to fall within the range of about 0.5 to about 50 ptb, preferably in the range of about 1.5 to about 40 ptb. The treat rate of the high reactivity PIB used in Example 2 is 53.2 ptb which is equivalent to about 151 ppm. However, there is no teaching in this document of the use of a low molecular weight polybutene polymer at selected treat rates for providing increased engine power and reduced burn duration.

Co-pending US patent application 63/390715 discloses a fuel composition comprising a gasoline base fuel and a high-reactivity polybutene polymer for providing improved engine power.

Co-pending US patent application 63/179767 discloses a fuel composition comprising a base fuel and a tetraalkylethane compound such as dicumene for providing improved engine power.

It has now surprisingly been found that the use of a a low molecular weight polybutene, such as a low molecular weight polyisobutylene (PIB), especially a low molecular weight, high reactivity, polyisobutylene (PIB) in combination with a selected tetraalkylethane compound in a gasoline fuel composition, preferably at selected additive treat rates, can provide synergistic benefits in terms of improved power output (increased P_max) and reduced burn duration, even when a standard exchange gasoline fuel is used. A reduction in burn duration leads to a more complete burn per cycle, which improves engine efficiency as well as lowers harmful emissions including particulate matter (PM/PN).

Summary of the Invention

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

(a) a gasoline base fuel suitable for use in a spark ignition internal combustion engine; and

(b) a polybutene polymer; wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol, wherein greater than 30% of the polymer molecules in the polybutene polymer have a terminal vinylidene group; and

(c) a tetraalkylethane compound having the formula (I): ex, ex, I I Ar“C- C—Ar ex, cXj wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX3 group is a hydrogen atom.

It has been surprisingly found that the fuel compositions of the present invention provide improved power output as reflected in increased P_max, as well as reduced burn duration of the fuel. Further the fuel compositions of the present invention exhibit excellent acceleration, energy efficiency and fuel economy.

According to another aspect of the present invention there is provided a use of a liquid fuel composition for improving power output of an internal combustion engine,wherein the liquid fuel composition comprises:

(b) a polybutene polymer; wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol, preferably wherein the polybutene is a high reactivity polybutene wherein greater than 30% of the polymer molecules in the polyisobutylene polymer have a terminal vinylidene group; and

(c) a tetraalkylethane compound having the formula (I): ex, ex,

I I

Ar~C- -C—Ar

I I

CXj ex, wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX₂ group is a hydrogen atom.

According to another aspect of the present invention there is provided a method of increasing the power output of a spark ignition internal combustion engine wherein the method comprises adding a polybutene and a tetraalkylethane compound to a gasoline base fuel to produce a gasoline fuel composition, wherein the polybutene has a number average molecular weight in the range from 200 to 10,000 g/mol, preferably wherein greater than 30% of the polymer molecules in the polybutene polymer have a terminal vinylidene group; and wherein the tetraalkylethane compound has the formula

(I):

wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX₂ group is a hydrogen atom, and combusting the fuel composition in the spark ignition internal combustion engine.

According to yet another aspect of the present invention there is provided a method of reducing the burn duration of a liquid fuel composition in an internal combustion engine, wherein the method comprises adding a polybutene and a tetraalkylethane compound to a gasoline base fuel to produce a gasoline fuel composition, wherein the polybutene has a number average molecular weight in the range from 200 to 10,000 g/mol, preferably wherein greater than 30% of the polymer molecules in the polybutene polymer have a terminal vinylidene group; and wherein the tetraalkylethane compound has the formula (I):

wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX3 group is a hydrogen atom, and combusting the fuel composition in the spark ignition internal combustion engine Brief Description of the Drawings

Figure 1 is a graphical representation of the P_max measurements for Example 1 and its reference base fuel.

Figure 2 is a graphical representation of the Pmax measurements for Examples 2-4 and their reference base fuel.

Figure 3 is a graphical representation of the Pmax measurements for Examples 5-13 and their reference base fuel.

Figure 4 shows the average % difference in P_max and average % difference in burn duration (Al 10-90) between the test blend (Examples 5-13) and it's base fuel control at 1300 HL , IGN = 1 (IGN = ignition time).

Figure 5 is a graphical representation of the Pmax measurements for Examples 14-27 and their reference base fuel.

Figure 6 shows the average % difference in Pmax and average % difference in burn duration (Al 10-90) between the test blend (Examples 14-27) and the base fuel control at 1300 rpm, 15 IMEP, IGN at TDC. Detailed Description of the Invention

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.

The term 'P_max' as used herein refers to the direct measurement of the force generated by decomposition of the fuel.

According to the present invention, there is provided a method of improving the power output of an internal combustion engine. Also, according to the present invention, there is a method of improving the Pmax of an internal combustion engine. In the context of these aspects of the present invention, the term "improving" embraces any degree of improvement. The improvement may for instance be 0.05% or more, preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.5% or more, especially 1% or more, more especially 2% or more, even more especially 5% or more, of the power output or Pmax provided by an analogous fuel formulation, prior to adding a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound to it in accordance with the present invention. The improvement in power output or Pmax may even be as high as 10% of the power output or P_max provided by an analogous fuel formulation, prior to adding a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound to it in accordance with the present invention.

The combination of a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound may also be used to improve the acceleration of an internal combustion engine. 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. In the context of this aspect of the invention, the term "improving" embraces any degree of improvement, and may be improved by the same percentages as the power and or Pmax is increased above.

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 2005- 01-0239 and SAE Paper 2005-01-0244.

The term 'burn duration' as used herein means the time required (in engine crank angle degrees) for combustion to progress from 10% to 90% (referred to as Al 10-90 in the Examples below). The term Al 50-90 is also used in relation to burn duration and means the time required (in engine crank angle degrees) for combustion to progress from 50% to 90%.

According to the present invention, there is provided a method of reducing the burn duration of a gasoline fuel composition wherein the method comprises adding a polybutene polymer and a tetraalkylethane compound to the gasoline fuel composition, wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol and wherein the tetraalkylethane compound has the formula (I):

Ar“C- C—Ar

CX, CXj wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX3 group is a hydrogen atom, and combusting the fuel composition in the spark ignition internal combustion engine

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.

In the context of this aspect of the invention, the term "reducing the burn duration" embraces any degree of reduction. The reduction may for instance be 0.05% or more, preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.5% or more, especially 1% or more, more especially 2% or more and even more especially 4% or more, or 5% or more reduction of the burn duration provided by an analogous fuel formulation, prior to adding a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound to it in accordance with the present invention. The reduction in burn duration may even be as high as a 10% reduction of the burn duration provided by an analogous fuel formulation, prior to adding a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound to it in accordance with the present invention.

The term "flame speed" or 'laminar flame speed' (LES) refers to laminar burning velocity. LES 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' can 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. 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:

1. Stagnation flame method (up to 5-7 atm)

2. Spherically expanding method, either constant pressure or constant volume (up to 60-80 atm)

3. The heat flux method (up to 5 atm or so).

All three of these methods are described in the review publication: Egolfopoulos, F.N., Hansen, N., Ju, Y., Kohse-Hbinghaus, K., Law, C.K., and Qi, F. "Advances and challenges in laminar flame experiments and implications for combustion chemistry",Progress in Energy and Combustion Science 43 (2014) 36-67, https://doi.Org/10.1016/j.pecs.2014.04.004.

The following method for measuring flame speed in a constant volume combustion chamber (spherical bomb), ref Gillespie, L.L., M.; Sheppard, C.G.; Wooley, R, Aspects of laminar and turbulent burning velocity relevant to spark ignition engines, Journal of the Society of Automotive Engineers, 2000 (2000-01-0192).

The following method for measuring flame speed uses a net pressure method: Mittal, M., Zhu, G. and Schock H., 'Fast mass-fraction-burned calculation using the net pressure method for real-time applications', Proc. Instn Meeh Engrs, Part D: J. Automobile Engineering 223 (3) (2009): 389-394.

The liquid fuel composition of the present invention comprises a base fuel suitable for use in an internal combustion engine, a low molecular weight, preferably high reactivity, polybutene and a tetraalkylethane compound. Typically, the base fuel suitable for use in an internal combustion engine is a gasoline or a diesel fuel, and therefore the liquid fuel composition of the present invention is typically a gasoline composition or a diesel fuel composition. Preferably, the base fuel is a gasoline base fuel.

The polybutene for use herein is preferably a high reactivity polybutene. A high reactivity polybutene is a polybutene having a relatively high proportion, i.e. greater than 30%, of polymer molecules having a terminal vinylidene group. The term 'polybutene' as used herein includes polymers made from pure or substantially pure 1- butene or isobutene, and polymers made from mixtures of two or all three of 1-butene, 2-butene and isobutene, as well as including polymers containing minor amounts, preferably less than 10% by weight, more preferably less than 5% by weight, of C2, C3, and C5 and higher olefins as well as diolefins. In a preferred embodiment, the polybutene is a polyisobutene (also referred to as 'polyisobutylene') preferably wherein at least 90% by weight, more preferably at least 95% by weight, of the polymer is derived from isobutene.

In a particularly preferred embodiment, the polybutene is a high reactivity polyisobutylene.

In one embodiment, the high reactivity polybutene has greater than 40% of polymer molecules having a terminal vinylidene group.

In another embodiment, the high reactivity polybutene polymer has greater than 50% of polymer molecules having a terminal vinylidene group.

In a preferred embodiment, the high reactivity polybutene has more than 85% of its double bonds located in the terminal position of the molecule.

The high reactivity polybutene polymer for use herein preferably has a molecular mass distribution of 1.5 or greater, preferably 1.6 or greater, more preferably 1.7 or greater, even more preferably 1.8 or greater.

The polybutene polymer is present at a level of from 500ppm to 5000ppm. In one embodiment, the polybutene polymer is present at a level of from 1000 ppm to 5000 ppm. In another embodiment the polybutene polymer is present at a level of from 2500 to 5000 ppm, by weight of the fuel composition. Examples of preferred levels of polybutene include lOOOppm, 2500ppm and 5000ppm, by weight of the fuel composition.

One or more polybutene polymer can be used in the fuel compositions herein. When more than one polybutene polymer is used herein, the total level of polybutene polymer is the same as the ranges given in the previous paragraph.

The polybutene polymer for use herein is a low molecular weight polybutene polymer. As used herein the term 'low molecular weight polybutene' means a polybutene polymer having a number average molecular weight (M_n) in the range from 200 to 10,000 g/mol, preferably from 500 to 5000 g/mol, more preferably from 1000 to 5000 g/mol. In one embodiment of the invention, the polybutenes, preferably high reactivity polybutenes, for use herein have a number average molecular weight (M_n) from 1000 to 2300 g.mol. In another embodiment of the invention, the polybutenes for use herein have a number average molecular weight (M_n) from 2300 to 5000 g/mol. The number average molecular weight of the polybutene polymer can be determined using Gel Permeation Chromatography.

The high reactivity polybutenes for use herein may be bioderived or non-bioderived. In one embodiment of the invention, the polybutene is a low molecular weight, high reactivity polyisobutylene which is derived from

100% renewable feedstock.

The high reactivity polybutenes for use herein preferably contain less than 1 mg/kg of chlorine.

In one embodiment, the high reactivity polybutene polymer for use herein has a kinematic viscosity at 100°C of 190 mm²/s or greater, preferably in the range of 190 mm²/s to 1500 mm²/s, more preferably in the range from 430 to 1500 mm²/s.

A preferred high reactivity polybutene for use herein has an alpha olefin content of greater than 85%.

Suitable high reactivity polybutenes for use herein include those commercially available from BASF under the tradename Glissopal (RTM) such as Glissopal (RTM) 1000, Glissopal (RTM) 1300 and Glissopal (RTM) 2300.

Glissopal (RTM) 1000 has a number average molecular weight (M_n) of 1000 g/mol, a molecular mass distribution (M_w/M_n) of 1.6, an alpha olefin content of greater than 85%, a kinematic viscosity at 100°C of 190 mm²/s and a chlorine content of less than 1 mg/kg.

Glissopal (RTM) 1300 has a number average molecular weight (M_n) of 1300 g/mol, a molecular mass distribution (M_w/M_n) of 1.7, an alpha olefin content of greater than 85%, a kinematic viscosity at 100°C of 190 mm²/s and a chlorine content of less than 1 mg/kg.

Glissopal (RTM) 2300 has a number average molecular weight (M_n) of 2300, a molecular mass distribution (M_w/M_n) of 1.6, an alpha olefin content of greater than 85%, a kinematic viscosity at 100°C of 190 mm²/s and a chlorine content of less than 1 mg/kg.

Also suitable for use herein are Glissopal (RTM) 1000, 1300 and 2300 BMBcert (TM) which are low molecular weight, highly reactive polyisobutenes derived from 100% renewable feedstock, commercially available from BASF.

The polybutene polymer may be blended together with any other additives in addition to the tetraalkylethane compound 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 tetraalkylethane compound used herein is a compound having the formula (I):

wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 saturated or unsaturated alkyl group, (CH2)nOH, (CH2)nNH2, wherein n is in the range from 1 to 9, preferably in the range from 1 to 6, more preferably in the range from 1 to 4, even more preferably in the range from 1 to 3, provided that at least one of the X groups in each CX3 group is a hydrogen atom.

Preferably, at least two of the X groups in each CX3 group is a hydrogen atom.

In an especially preferred embodiment, three of the X groups in each CX3 group is a hydrogen atom.

Preferably, the Ar of the tetraalkylethane compound is a substituted or unsubstituted aromatic group, such as a phenyl, biphenyl, naphthyl, thienyl 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 US4,072,811. Preferably, each X group is independently selected from a hydrogen atom and an unsubstituted, straight chain or branched, saturated or unsaturated C1-C6, more preferably C₁-C₃, alkyl group, provided that at least one of the X groups in each CX3 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 C1-C6, preferably C1-C3, alkyl group, provided that at least one of the X groups in each CX₃ group is a hydrogen atom. In one embodiment, each X group is independently selected from a hydrogen atom, and an unsubstituted straight chain, saturated C1-C6, preferably C1-C3, alkyl group, especially methyl, ethyl and propyl. Examples of suitable tetraalkylethane compounds of Formula (I) include:

In one embodiment herein the tetralkylethane compound is 1,1'(1,1,2,2-tetramethyl-l,1-ethanediyl)bis- benzene 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 10 wt%, preferably from 100ppm to 5 wt%, more preferably from 100ppm to 1 wt%, even more preferably from 100ppm to 5000ppm. In one embodiment, the tetraalkylethane is present at a level from 313ppm to 5000ppm, by weight of the fuel composition. The tetraalkylethane compound may be blended together with any other additives in addition to the polybutene polymer 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 0.1 to 99.8 wt%, more preferably in the range of from 5 to 50 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 15 ppmw (parts per million by weight) to 10 %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: (i) at least 100 ppmw (ii) at least 200 ppmw (iii) at least 300 ppmw (iv) at least 400 ppmw (v) at least 500 ppmw (vi) at least 600 ppmw (vii) at least 700 ppmw (viii) at least 800 ppmw (ix) at least 900 ppmw (x) at least 1000 ppmw (xi) at least 2500ppmw (xii) at most 5000ppmw (xiii) at most 10000 ppmw (xiv) at most 2 %wt. (xv) at most 5 %wt. A further preferred additive for use in the fuel compositions herein, in combination with the tetralkylethane compound and the polybutene polymer is an alkylbenzene compound having the f n each R1-R6 gr R1 R2ormula (II) wherei R R65 R4 R3ently selected from hydrogen and a C₁-C₆

alkyl group, wherein at least one of the R1-R6 groups is a C1-C6 alkyl group. In preferred embodiments herein, three R1-R6 groups in the alkylbenzene compound are independently selected from a C1-C6 alkyl group. In one embodiment herein the alkylbenzene compound is a trimethylbenzene compound. In another embodiment, the alkykbenzene compound is 1,3,5-trimethylbenzene. 1,3,5-trimethylbenzene is commercially available from Aldrich and other chemical suppliers. In another embodiment, the alkylbenzene compound is a mixture of trimethylbenzene isomers (known as mesitylene). The alkylbenzene compound is preferably present in the fuel composition at a level from 30ppm to 2 wt%, preferably from lOOppm to 1 wt%, more preferably from lOOppm to 5000ppm, even more preferably from 500ppm to 2000ppm, by weight of the fuel composition.

In one embodiment, the alkylbenzene compound, the tetraalkylethane compound and the polybutene polymer 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.

In the liquid fuel compositions of the present invention, if the base fuel used is a gasoline, then 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'.The gasoline may also comprise various levels of bio-components and bio-streams at any level while maintaining appropriate analytical specifications. The bio-components may come from any biomass conversion processes including variations of uncatalyzed and catalyzed biomass pyrolyses, hydro-thermal liquefaction, non-thermal biomass conventions such as microbe catalyzed biochemical processes, etc. Any biomass suitable as feedstock to these processes is ideal.

Gasolines typically comprise mixtures of hydrocarbons boiling in the range from 25 to 230°C (EN- ISO 3405), 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 80, for instance in the range of from 80 to 110, preferably the RON of the gasoline will be at least 90, for instance in the range of from 90 to 110, more preferably the RON of the gasoline will be at least 91, for instance in the range of from 91 to 105, even more preferably the RON of the gasoline will be at least 92, for instance in the range of from 92 to 103, even more preferably the RON of the gasoline will be at least 93, for instance in the range of from 93 to 102, and most preferably the RON of the gasoline will be at least 94, for instance in the range of from 94 to 100 (EN 25164); the motor octane number (MON) of the gasoline may conveniently be at least 70, for instance in the range of from 70 to 110, preferably the MON of the gasoline will be at least 75, for instance in the range of from 75 to 105, more preferably the MON of the gasoline will be at least 80, for instance in the range of from 80 to 100, most preferably the MON of the gasoline will be at least 82, for instance in the range of from 82 to 95 (EN 25163).

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 0 to 40 percent by volume based on the gasoline (ASTM D1319); preferably, the olefinic hydrocarbon content of the gasoline is in the range of from 0 to 30 percent by volume based on the gasoline, more preferably, the olefinic hydrocarbon content of the gasoline is in the range of from 0 to 20 percent by volume based on the gasoline.

Typically, the aromatic hydrocarbon content of the gasoline is in the range of from 0 to 70 percent by volume based on the gasoline (ASTM D1319), for instance the aromatic hydrocarbon content of the gasoline is in the range of from 10 to 60 percent by volume based on the gasoline; preferably, the aromatic hydrocarbon content of the gasoline is in the range of from 0 to 50 percent by volume based on the gasoline, for instance the aromatic hydrocarbon content of the gasoline is in the range of from 10 to 50 percent by volume based on the gasoline. In one embodiment herein the gasoline base fuel comprises less than 10 vol% of aromatics, based on the total base fuel. In another embodiment herein, the gasoline base fuel comprises less than 2 vol% of aromatics having 9 carbon atoms or greater, based on the total base fuel.

The benzene content of the gasoline is at most 10 percent by volume, more preferably at most 5 percent by volume, especially at most 1 percent by volume based on the gasoline.

The gasoline preferably has a low or ultra low sulphur content, for instance at most 1000 ppmw (parts per million by weight), preferably no more than 500 ppmw, more preferably no more than 100, even more preferably no more than 50 and most preferably no more than even 10 ppmw.

The gasoline also preferably has a low total lead content, such as at most 0.005 g/1, 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 85 percent by weight (EN 1601) (e.g. ethanol per se) based on the gasoline. For example, the oxygenate content of the gasoline may be up to 35 percent by weight, preferably up to 25 percent by weight, more preferably up to 10 percent by weight. Conveniently, the oxygenate concentration will have a minimum concentration selected from any one of 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 percent by weight, and a maximum concentration selected from any one of 12, 8, 7.2, 5, 4.5, 4.0, 3.5, 3.0, and 2.7 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, 2- propanol, butanol, tert-butanol, iso-butanol and 2- butanol), ethers (preferably ethers containing 5 or more carbon atoms per molecule, e.g., methyl tert-butyl ether and ethyl tert-butyl ether) and esters (preferably esters containing 5 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.S.A., 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 100 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 85 percent by volume; up to 70 percent by volume; up to 65 percent by volume; up to 30 percent by volume; up to 20 percent by volume; up to 15 percent by volume; and, up to

10 percent by volume, depending upon the desired final formulation of the gasoline. Conveniently, the gasoline may contain at least 0.5, 1.0 or 2.0 percent by volume oxygenated hydrocarbons.

Examples of suitable gasolines include gasolines which have an olefinic hydrocarbon content of from 0 to 20 percent by volume (ASTM D1319), an oxygen content of from 0 to 5 percent by weight (EN 1601), an aromatic hydrocarbon content of from 0 to 50 percent by volume (ASTM D1319) and a benzene content of at most 1 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 CO2, and blends thereof which each other or with fossil-derived gasoline streams and components. Suitable examples of such fuels include:

1) Biomass derived: a. Straight run bio-naphthas from hydrodeoxygenation of biomass, and b. cracked and/or isomerized products of syn-wax (biomass gasification to syngas (CO/H2) then to syn-wax by the Fischer-Tropsch (FT) process, which is then hydrocracked/hydroisomerized to yield a slate of products including cuts in the gasoline distillation range.

2) CO2 derived: a. CO2 + H2 syngas (CO/H2) by modified water/gas shift reaction, then to syn-wax by the FT process), which is then hydrocracked/hydroisomerized to yield a slate of products including cuts in the gasoline distillation range.

3) Methanol derived: a. Biomass gasification to syngas (CO/H2), then to Methanol and then gasoline by the MTG process (MTG is 'methanol-to-gasoline' process). To reduce the carbon intensity of the fuel further, the H2 used in all processes would be renewable (green) H2 from electrolysis of water using renewable electricity such as from wind and solar.

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 W02009/077606, W02010/028206, WO2010/000761, European patent application nos. 09160983.4, 09176879.6, 09180904.6, and US patent application serial no. 61/312307. 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 low molecular weight, preferably high reactivity, polybutene and the tetraalkylethane compound. 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 US Patent No. 5,855,629.

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 1 percent by weight, more preferably in the range from 5 to 2000 ppmw, advantageously in the range of from 300 to 1500 ppmw, such as from 300 to 1000 ppmw.

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; dehazers; anti-knock additives; metal deactivators; solvents; carrier fluids; diluents; 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 2,4-di-tert- butylphenol or 3,5-di-tert-butyl-4-hydroxy- phenylpropionic acid; anti-static agents; metallocenes such as ferrocene; methylcyclopentadienylmanganese tricarbonyl; lubricity additives, such as certain fatty acids, alkenylsuccinic esters, bis(hydroxyalkyl) fatty amines, hydroxyacetamides or castor oil; and also dyes (markers). Suitable such additives are disclosed in US Patent No. 5,855,629. Amines may also be added, if appropriate, for example as described in WO 03/076554. 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 W02009/50287, 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 85 to 20000 and at least one polar moiety selected from:

(Al) mono- or polyamino groups having up to 6 nitrogen atoms, of which at least one nitrogen atom has basic properties;

(A6) polyoxy-Cg- to -C4-alkylene groups which are terminated by hydroxyl groups, mono- or polyamino groups, in which at least one nitrogen atom has basic properties, or by carbamate groups; (A8) moieties derived from succinic anhydride and having hydroxyl and/or amino and/or amido and/or imido groups; and/or

(A9) moieties obtained by Mannich reaction of substituted phenols with aldehydes and mono- or polyamines.

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 85 to 20000, especially from 113 to 10000, in particular from 300 to 5000. Typical hydrophobic hydrocarbon radicals, especially in conjunction with the polar moieties (Al), (A8) and (A9), include polyalkenes (polyolefins), such as the polypropenyl, polybutenyl and polyisobutenyl radicals each having Mn of from 300 to 5000, preferably from 500 to 2500, more preferably from 700 to 2300, and especially from 700 to 1000.

Non-limiting examples of the above groups of detergent additives include the following:

Additives comprising mono- or polyamino groups (Al) are preferably polyalkenemono- or polyalkenepolyamines based on polypropene or conventional (i.e. having predominantly internal double bonds) polybutene or polyisobutene having Mn of from 300 to 5000. 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, diethylene- triamine, triethylenetetramine or tetraethylenepentamine. Corresponding additives based on polypropene are described in particular in WO-A-94/24231. 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 5 to 100, with nitrogen oxides or mixtures of nitrogen oxides and oxygen, as described in particular in WO-A-97/03946. 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 DE-A-196 20 262. Additives comprising polyoxy-C₂-C₄-alkylene moieties (A6) are preferably polyethers or polyetheramines which are obtainable by reaction of C₂- to C₆₀-alkanols, C₆- to C₃₀-alkanediols, mono- or di-C₂-C₃₀-alkylamines, C₁-C₃₀- alkylcyclohexanols or C₁-C₃₀-alkylphenols with from 1 to 30 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 EP-A-310 875, EP- A-356 725, EP-A-700 985 and US-A-4 877 416. 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 300 to 5000 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 US-A-4849572.

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 300 to 5000. Such "polyisobutene-Mannich bases" are described in particular in EP-A-831141.

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 300 to 5000. 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 low molecular weight, preferably high reactivity, polybutene polymer and the essential tetraalkylethane compound 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 of a combination of a low molecular weight, preferably high reactivity, polybutene having a number average molecular weight of from 500 to 10,000 g/mol and a tetraalkylethane compound, provides synergistic benefits in terms of improved power and increased P_max of an internal combustion engine being fuelled by the liquid fuel composition containing said polybutene, relative to the internal combustion engine being fuelled by the liquid base fuel. In a preferred embodiment herein, an improvement in power can be observed at low load and low speed conditions (such as at 1300 rpm and 11.5 bar) as well as at high load and high speed conditions (such as at 3300 rpm and 12.4 bar).

It has also surprisingly been found that the the use of a combination of a low molecular weight, preferably high reactivity, polybutene having a number average molecular weight of from 500 to 10,000 g/mol and a tetraalkylethane compound provides synergistic benefits in terms of reduced burn duration of the liquid fuel composition containing said polybutene, relative to the internal combustion engine being fuelled by the liquid base fuel.

Preferably, the internal combustion engine herein is a spark ignition internal combustion engine operating in either PFI (Port fuel injection) or GDI (gasoline direct injection) mode.

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.

Examples

Examples 1-13

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) in PFI mode. 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 1 to 13).

All fuel compositions used an E10 base fuel (containing 10% ethanol) meeting North American maingrade specification ASTM D4814 containing no performance additive. Example 1 used an E10 base fuel having a RON of 92.3, Examples 2-4 used an E10 base fuel having a RON of 96.7 and Examples 5-13 used an E10 base fuel having a RON of 96.5.

High reactivity polyisobutylene (HR-PIB) and/or dicumene were added into the base fuel at the treat rates indicated in Tables 1 and 2 below. Some of the Examples also included mesitylene, as indicated. Mesitylene is a mixture of trimethylbenzene isomers. Tables 1 and 2 also show the RON and MON values for each fuel formulation.

Table 1

Examples Additives Dose, ppm RON MON RON- wt% MON

E10 base fuel — — 92.3 96.6 5.7 (RON 92.3)

1 PIB 5000/5000 91.3 84.9 6.4

(1000)/dicumene

E10 base fuel — — 96.7 85 11.7 (RON 96.7)

2 dicumene 5000 95 83.9 11.1

3 PIB 5000/5000 94.4 83.4 11

(1000)/dicumene

4 PIB (1000) 5000 96.4 85 11.4

Table 2

Examples Additives Dose, ppm RON MON RON- wt% MON

E10 base fuel — — 96.5 86 10.5 (RON 96.5)

5 dicumene 5000 94.1 84.1 10

Mesitylene 5000

PIB (1000) 5000

6 dicumene 2500 95 84.6 10.4 mesitylene 5000

PIB (1000) 5000

7 dicumene 1250 95.5 85 10.5

Mesitylene 2500

PIB (1000) 5000

8 Dicumene 625 95.8 85.5 10.3 mesitylene 1250

PIB (1000) 2500

9 Dicumene 625 95.8 85.6 10.2

PIB (1000) 2500

10 Dicumene 313 96 85.8 10.2

PIB (1000) 1000

11 PIB (1000) 5000 96.5 86 10.5

12 PIB (1000) 2500 96.4 86.1 10.3

13 PIB (1000) 1000 96.4 86.2 10.2

Test Conditions The engine used for these experiments was the Gasoline single cylinder engine in PFI mode. This engine was manufactured by AVL and based on the EA8882.OL Audi TFSI/VW TSI (Euro 6). The single cylinder bench engine details are shown in Table 3 below.

Table 3

Parameter: Details:

Manufacturer AVL

Displaced Volume 454 cm³

Cylinders 1

Stroke 86 mm

Bore 82 mm

Compression ratio Variable 8-12, (10:1 chosen)

Number of valves 2 inlet; 2 outlet

Maximum engine speed 5000 rpm (3300 rpm chosen)

Aspiration Slightly Boosted (max 2.5 bar absolute)

Injection PFI (solenoid injector)

Other IMEP up to 25 bar, Max. peak pressure 130 bar continuous

The engine test conditions are detailed below in

Table 4

Engine Speed IMEP Intake Intake Exhaust Fuel Fuel test [RPM] [Bar] pressure temp. back pressure temp conditions [mbara] [°C] pressure [bar] [°C] [mbara]

1300HL 1300 11.5 1110 35 1080 3 25

1300ML 1300 8 905 35 1080 3 25

3300HL 3300 12.4 1205 35 1850 3 25

The test protocol below was run with base fuel and one test fuel (one of Examples 1-13) per day:

• Warm up engine and line out on base fuel • Run baseline spark sweep: 1300 ML, HL, 3000 ML (ML = medium load; HL = high load)

• Switch to test fuel and flush 30 litre • Test: spark sweep at three different conditions (1300 rpm, IMEP: 11.5 bar and 8 bar; and 3300 rpm, IMEP: 12.4 bar)

• End.

Each test fuel blend was screened twice, once in each of two randomized loops. Average maximum pressure (Pmax) measurements were taken and the results are shown in Figures 1-4.

Figure 1 is a graphical representation of the Pmax measurements for Example 1 and its reference base fuel (the Example number being on the x axis and Pmax being on the y axis).

Figure 2 is a graphical representation of the Pmax measurements for Examples 2-4 and their reference base fuel (the Example number being on the x axis and Pmax being on the y axis).

Figure 3 is a graphical representation of the Pmax measurements for Examples 5-13 and their reference base fuel (the Example number being on the x axis and P_max being on the y axis).

Figure 4 shows the average % difference in P_max and average % difference in burn duration (Al 10-90) between the test blend and it's base fuel control at 1300 HL , IGN = 1 (IGN = ignition time). In Figure 4, the Example number is on the x axis and the average % difference in burn duration and average % difference in P_max is on the y axis. Examples 14-27

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) in GDI mode. 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 14 to 27).

All fuel compositions used an E10 base fuel (containing 10% ethanol) meeting North American maingrade specification ASTM D4814 containing no performance additive having a RON of 96.5. High reactivity polyisobutylene (HR-PIB) and/or dicumene were added into the base fuel at the treat rates indicated in Table 5 below. Some of the Examples also included mesitylene, as indicated. Mesitylene is a mixture of trimethylbenzene isomers. Table 5 also shows the RON and MON values for each fuel formulation.

Table 5

Examples Additives Dose, ppm RON MON RON- wt% MON

E10 base fuel — — 95.7 84.4 11.3 (RON 95.7)

14 PIB (1000) 2500 95.7 84.4 11.3

15 Mesitylene 625 95.8 84.4 11.4

PIB (1000) 1250

16 Mesitylene 1250 96 84.4 11.6

PIB (1000) 1250

17 Mesitylene 1250 95.9 84.5 11.4

PIB (1000) 2500

18 dicumene 625 95.3 84.3 11

PIB (1000) 1250

19 dicumene 625 95.2 84.4 10.8

Mesitylene 625

20 dicumene 625 95.3 84.4 10.9

PIB (1000) 2500

21 dicumene 625 95.3 84.3 11

Mesitylene 1250

PIB (1000) 1250

22 dicumene 625 95.3 84.2 11.1

Mesitylene 1250

PIB (1000) 2500

23 dicumene 1250 95 84 11

24 dicumene 1250 95 83.8 11.2

PIB (1000) 2500 25 dicumene 1250 95 84.1 10.9

Mesitylene 625

PIB (1000) 1250

26 dicumene 1250 95 83.8 11.2

Mesitylene 625

PIB (1000) 2500

27 dicumene 1250 95 83.9 11.1

Mesitylene 1250

Test Conditions

The engine used for these experiments was the Gasoline single cylinder engine in GDI mode. This engine was manufactured by AVL and based on the EA8882.0L Audi

TFSI/VW TSI (Euro 6). The single cylinder bench engine details are shown in Table 6 below.

Table 6

Parameter: Details:

Manufacturer AVL

Displaced Volume 454 cm³

Cylinders 1

Stroke 86 mm

Bore 82 mm

Compression ratio Variable 8-12, (10:1 chosen)

Number of valves 2 inlet; 2 outlet

Maximum engine speed 5000 rpm (3300 rpm chosen)

Aspiration Slightly Boosted (max 2.5 bar absolute)

Injection GDI mode

Other IMEP up to 25 bar, Max. peak pressure 130 bar continuous

The engine test conditions are detailed below in

Table 7

1300HL 1300 15 1300 40 25 200 25

2000ML 2000 13.5 1200 40 45 200 25

3300HL 3300 16.2 1400 40 200 200 25 The test protocol below was run with base fuel and one test fuel (one of Examples 14-27) per day:

• Warm up engine and line out on base fuel

• Run baseline spark sweep: 1300 ML, 2000 ML and 3000 ML (ML = medium load; HL = high load)

• Switch to test fuel and flush 30 litre

• Test: spark sweep at three different conditions (1300 rpm, IMEP: 15 bar; 2000 rpm, IMEP: 13.5 bar; and 3300 rpm, IMEP: 16.2 bar)

• End.

Each test fuel blend was screened twice, once in each of two randomized loops. Average maximum pressure (Pmax) measurements were taken and the results are shown in Figures 5 and 6.

Figure 5 is a graphical representation of the Pmax measurements for Examples 14-27 and their reference base fuel. In Figure 5, the Example number is on the x axis and the Pmax is on the y axis).

Figure 6 shows the average % difference in Pmax and average % difference in burn duration (Al 10-90) between the test blend (Examples 14-27) and the base fuel control at 1300 rpm, 15 IMEP, IGN at TDC. In Figure 6, the Example number is on the x axis and the average % difference in burn duration and average % difference in Pmax is on the y axis. Discussion

Use of a combination of dicumene and HR-PIB have been found to provide increased P_max (related to increased power) in the engine tests of the Examples at various engine conditions, i.e. at both low speed/low load and high load/high speed conditions. This demonstrates that the fuel formulations of the present invention can be used both for retail customers and for motor sports applications.

Claims

C L A I M S

1. Fuel composition comprising:

(b) a polybutene polymer; wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol and wherein greater than 30% of the polymer molecules in the polybutene polymer have a terminal vinylidene group; and

(c) a tetraalkylethane compound having the formula (I):

5

Ar ■C- C—-Ar

I I

CXj CX; wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX₂ group is a hydrogen atom.

2. Fuel composition according to Claim 1 wherein greater than 40% of the polymer molecules in the polybutene polymer have a terminal vinylidene group.

3. Fuel composition according to Claim 1 or 2 wherein greater than 50% of the polymer molecules in the polybutene polymer have a terminal vinylidene group.

4. Fuel composition according to any of Claims 1 to 3 wherein the polybutene polymer has a number average molecular weight in the range from 500 to 5,000 g/mol.

5. Fuel composition according to any of Claims 1 to 4 wherein the polybutene polymer has a number average molecular weight in the range from 1000 to 2300 g/mol.

6. Fuel composition according to any of Claims 1 to 5 wherein the polybutene polymer is a polyisobutylene polymer.

7 . Fuel composition according to any of Claims 1 to 6 wherein the polybutene polymer is present at a level from 1000 ppm to 5000 ppm, by weight of the fuel composition.

8 . Fuel composition according to any of Claims 1 to 7 wherein the tetraalkylethane compound is present at a level from 200 ppm to 5000 ppm, by weight of the fuel composition.

9. Fuel composition according to any of Claims 1 to 8 wherein Ar of the tetraalkylethane compound is a substituted or unsubstituted aromatic group selected from phenyl, biphenyl, naphthyl, thienyl or anthracyl.

10. Fuel composition according to any of Claims 1 to 9 wherein Ar is an unsubstituted phenyl group.

11. Fuel composition according to any of Claims 1 to 10 wherein each X is independently selected from a hydrogen atom, unsubstituted, straight chain or branched Ci-Ce alkyl group, provided that at least one of the X groups in each CX3 group is a hydrogen atom.

12. Fuel composition according to any of Claims 1 to 11 wherein the tetralkylethane compound is 1,1'(1,1,2,2- tetramethyl-1,1-ethanediyl)bis-benzene.

13. Use of a liquid fuel composition for improving power output of an internal combustion engine,wherein the liquid fuel composition comprises:

(a) a gasoline base fuel suitable for use in a spark ignition internal combustion engine;

(b) a polybutene polymer; wherein the polybutene polymer has a number average molecular weight in the range from 200 to 10,000 g/mol, and preferably wherein the polybutene is a high reactivity polybutene wherein greater than 30% of the polymer molecules in the polyisobutylene polymer have a terminal vinylidene group; and

(c) a tetraalkylethane compound having the formula (I): ex, ex, I I Ar“C- C—Ar ex, cXj wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX₂ group is a hydrogen atom.

14. A method of increasing the power output of a spark ignition internal combustion engine wherein the method comprises adding a polybutene and a tetraalkylethane compound to a gasoline base fuel to produce a gasoline fuel composition, wherein the polybutene polymer is added at a level from 1000 ppm to 5000 ppm by weight of the gasoline fuel composition, and wherein the tetraalkylethane compound is added at a level from 200 ppm to 5000 ppm by weight of the gasoline fuel composition, wherein the polybutene has a number average molecular weight in the range from 200 to 10,000 g/mol and preferably wherein the polybutene is a high reactivity polybutene wherein greater than 30% of the polymer molecules in the polyisobutylene polymer have a terminal vinylidene group and wherein the tetraalkylethane compound has the formula (I): CX, exJ

I ■ I

Ar““C- C"—Ar

I I

CX, exJ wherein Ar represents an aryl group and each X is independently selected from a hydrogen atom, substituted or unsubstituted, straight chain or branched C1-C12 alkyl group, (CH₂)_nOH or (CH₂)_nNH₂, wherein n is in the range of 1 to 9, provided that at least one of the X groups in each CX3 group is a hydrogen atom, and combusting the fuel composition in the spark ignition internal combustion engine.

15. Method according to Claim 14 wherein the spark ignition internal combustion engine operates in PFI or GDI mode.