EP2683798B1

EP2683798B1 - Use of camphene in a gasoline fuel formulations

Info

Publication number: EP2683798B1
Application number: EP12707804.6A
Authority: EP
Inventors: Richard John Price; Martin Tom CROFT; Renate UITZ
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2011-03-10
Filing date: 2012-03-12
Publication date: 2017-03-08
Anticipated expiration: 2032-03-12
Also published as: CN103415600B; JP2014507542A; CN103415600A; EP2683798A1; WO2012120147A1; AU2012224533A1

Description

Field of the Invention

This invention relates to the use of certain materials in fuel formulations for new purposes.

Background of the Invention

In the interests of the environment, and to comply with increasingly stringent regulatory demands, it is necessary to increase the amount of bio-derived components (biofuels) used in automotive fuels.
Bio-derived fuel components are derived from biological sources, which result in a reduction in "well-to-wheels" (i.e. from source to combustion) greenhouse gas emissions. In gasoline fuels for use in spark ignition (petrol) engines, the most common bio-derived components are oxygenates such as alcohols, in particular ethanol. These are typically blended with more traditional gasoline fuel components. However, the disruption of hydrogen-bonding when certain oxygenates such as ethanol are combined with gasoline hydrocarbons results in an undesirable increase in the vapour pressure of the fuel. Ethanol also impacts the distillation properties of gasoline fuels, increasing their E70 and E100 values. As a result, a gasoline base fuel typically has to be specially reformulated if it is to be blended with ethanol, to ensure that the resultant blend meets gasoline specifications around the world. This reformulation naturally increases the cost and complexity of the fuel manufacturing process, and can limit the concentration at which ethanol can practically be included in gasoline fuels.
It would be desirable to provide new fuel formulations containing high amounts of bio-derived components that could overcome or at least mitigate some of the problems associated with formulations comprising known oxygenates such as ethanol.

Statements of the Invention

It has now been found that camphene, a monoterpene component, can be used to provide a variety of beneficial advantages in gasoline fuel formulations.
Monoterpenes are a large and varied class of organic compounds, produced primarily by a wide variety of plants, particularly conifers, and also by some insects. Monoterpenes may be synthetic or naturally occurring, and may be bio-derived, particularly from gum turpentine and crude sulphate turpentine (produced by the wood pulping industry). Structurally, monoterpenes comprise isomers of C₁₀H₁₆ and may consist of two isoprene units. Monoterpenes may be linear (acyclic) or may contain rings. Acyclic monoterpenes include myrcene and ocimene, and the various stereoisomers thereof. Monocyclic monoterpenes include limonene, γ-terpinene, α- and β-phellandrene, α- and γ-terpinolene, and the various stereoisomers thereof. Bicyclic monoterpenes include 3-carene, α- and β-pinene, α-fenchene, and camphene, and the various stereoisomers thereof. Some examples of monoterpene structures are shown in Table 1 below. Table 1

Monoterpene (C₁₀H₁₆) Example structures

Acyclic

Monocyclic

Bicyclic
The synthesis and extraction of these monoterpenes is well known in the art and monoterpene components comprising one or more monoterpenes are commercially available. For example, camphene and other monoterpenes can be made according to the method described in US 5,826,202 .
Monoterpenes have been described in the literature as potential fuel components:
WO 01/53437A1 proposes further reduction of vapour pressure of a fuel formulation comprising a C₃ to C₁₂ hydrocarbon component, ethanol, and a second oxygenate, by the incorporation of from 0 to 99% by volume of an individual hydrocarbon selected from C₆ to C₁₂ aliphatic or alicyclic, saturated or unsaturated hydrocarbons; suitable examples include limonene and myrcene. Limonene is also proposed for use in fuel blends in US-A-4 818 250 in an amount up to 20% by volume. Terpenes comprising at least 60%wt pinenes are proposed for use with a gasoline base fuel in EP-A1-2 290 037 , in particular as a corrosion inhibitor, in an amount from 0.1 to 40% by volume.
US-A-3 274 224 proposes the use of a small amount (from 0.33 to about 6% by weight) of terpenes comprising at least 60%wt α-pinene, to provide thermal stability for tetraethyl lead antiknock blends; camphene is mentioned as a minor impurity (4 to 8%) in one of three sources of terpenes. More recently, terpenes have been proposed in WO 2010/017099 for use as an optional component of a modified fuel comprising a base fuel, a lower alcohol and a triglyceride derived from a fatty acid, in an amount of less than 1% by volume; the modified fuel as a whole is said to provide increased horsepower and/or increased octane.
RU-2105041 C1 appears to disclose a fuel composition comprising a base fuel, a fatty acid-based soluble iron compound and 0.006 to 0.03%wt of a camphene to increase both octane number in gasolines and cetane number in diesel fuels. However since it is well known (reference Fuels and Engines, Institut Francais Du Petrole Publications, JC Guibert, 1999, chapters 3 and 4) that increase of octane number is provided by the increase of the autoignition temperature of a gasoline fuel but cetane number increase is achieved by the decrease of autoignition temperature in a diesel fuel, it is not fully understood how both can be achieved by the same component.
DE 3031158 A1 proposes the use of from 0.1 to 1% of bicyclic monoterpene hydrocarbons, amongst other options, in a mixture also containing 70 to 85% vol of water and ethanol; the mixture is used with gasoline, naphtha, gas oil or fuel oil to increase acceleration and octane number with reduced NOx in exhaust gases.
Camphene [CAS no. 79-92-5] is a monoterpene with a bicyclic structure, as shown in Table 1. It is a white crystalline solid with a boiling point of 159 °C, i.e. within the normal gasoline boiling range.
The monoterpene component comprises at least 90% or even at least 95% v/v of camphene, based on the total volume of the component. In an embodiment, the monoterpene component is substantially free of tricyclene and/or tricyclic monoterpenes. "Substantially free" may refer to a concentration of less than 2% v/v based on the total volume of the component. The monoterpene component may exclude tricyclene.
For use in a fuel formulation the monoterpene component may be obtained by any suitable method. The monoterpene component may be synthetic or naturally occurring. In a preferred embodiment, the monoterpene component is bio-derived, by which is meant that it has been obtained - either directly or indirectly - from a biological source.
The monoterpene component may advantageously comprise at least about 0.1 dpm/gC of carbon-14. It is known in the art that carbon-14 (C-14), which has a half-life of about 5,700 years, is found in bio-derived materials but not in fossil fuels. Thus, the term "bio-derived" as used herein may be defined as "comprising at least about 0.1 dpm/gC of carbon-14".
The monoterpene is used in the fuel formulation in an amount in the range of from 5 to 10 % v/v of which at least 90% by volume, more preferably at least 95% by volume, is camphene.
The monoterpene component should ideally be dissolved in the fuel formulation, suitably fully dissolved. It may be present in a carrier fluid, for example a solvent selected from alkanes (for example n-heptane or other n-alkanes, or iso-octane); alcohols (for example ethanol or butanol); ethers (for example methyl t-butyl ether or ethyl t-butyl ether); alkenes such as diisobutylene; fuel components such as alkylates, isomerates, naphthas, straight run tops, light and heavy catalytically cracked gasolines or reformates; and mixtures thereof.
The monoterpene component may be used, in accordance with the invention, in a gasoline fuel formulation (e.g. automotive). For example, it may be used in a gasoline fuel formulation comprising a base fuel, preferably as defined below. Alternatively, the monoterpene component may be used in a gasoline fuel formulation comprising a base fuel and one or more additional components, such as, for example, a bio-derived component or an oxygenate (e.g. ethanol). Preferred additional components, in particular bio-derived components and oxygenates, are described below.
It has been found that, since an individual bio-derived component (e.g. ethanol) is unlikely to embody all the physical properties desirable for inclusion in a gasoline fuel formulation, it can be advantageous to combine two or more bio-derived components in order to offset any disadvantageous properties of one with the advantageous properties of the other(s). The natures and concentrations of the components of such a combination can be chosen so as to achieve desired properties for the overall fuel formulation which contains it, and thus to increase the total bio-derived content of the formulation without unduly impairing its performance. This in turn can assist the fuel formulator in meeting increasingly stringent fuel specifications.
In one aspect, monoterpene components have been found to be effective for reducing the vapour pressure of fuel formulations. The term "vapour pressure" as used herein may refer to the dry vapour pressure equivalent (DVPE) and should be construed as such unless context requires otherwise. The DVPE of a formulation is the vapour pressure of that formulation at 37.8 °C. DVPE values may be measured using the standard test method EN 13016-1 or ASTM D4953-06 or an analogous method.
Blending rules allow for calculation of the DVPE of a blend of components from the blending DVPE values of its individual components. The blending DVPE of a fuel formulation component is a measure of how the DVPE of the fuel formulation may change with the addition of that component. To calculate the blending DVPE (bDVPE) of a component n, the following equation may be used: ${bDVPE}_{n} = {(\frac{[{({DVPE}_{base + n})}^{1.25} - {({DVPE}_{base + n})}^{1.25} (1 - v_{n})]}{v_{n}})}^{0.8}$
where bDVPE_n is the blending dry vapour pressure equivalent of a component or mixture n, DVPE_base is the dry vapour pressure equivalent of the base fuel, DVPE_base+n is the dry vapour pressure equivalent of the blend, and v_n is the volume fraction of n in the blend.
The DVPE of a blend of fuel components (for example monoterpene, ethanol and an additional bio-derived fuel component) in a base fuel may also be calculated from the relevant blending DVPE (bDVPE) values using the Chevron blend rule, which provides that: ${DVPE}^{1.25} = {DVPE}_{base}^{1.25} v_{base} + Σ {bDVPE}_{n}^{1.25} v_{n}$
where bDVPE_n and v_n are the blending DVPE and volume fraction of component n, and DVPE_base and v_base are the DVPE and volume fraction of the base fuel.
The monoterpene component may be used, for example, in fuel formulations having a DVPE of 100 kPa or less. The DVPE of such fuel formulations may be 90 or 95 or 80 or - in particular where it is intended for use as a summer grade fuel - 70 or 60 kPa or less. The use of a monoterpene component according to the invention has been found to be particularly beneficial in fuel formulations having a DVPE of 45 kPa or more, such as, for example 50 or 55 or 60 kPa or more.
As aforesaid, fuel formulations typically comprise a base fuel and may also contain additional components such as bio-derived or oxygenate components. The monoterpene component may be used, according to the invention, for the purpose of reducing the vapour pressure of a fuel formulation to a level below the vapour pressure of a bio-derived or oxygenate component comprised in the fuel formulation. Preferably, the monoterpene component may be used for the purpose of reducing the vapour pressure of the formulation to a level below the vapour pressure of a mixture of a base fuel and a bio-derived or oxygenate component comprised in the fuel formulation. In some embodiments, the monoterpene component may even be used for the purpose of reducing the vapour pressure of the formulation to a level below the vapour pressure of a base fuel comprised in the fuel formulation.
Generally, it is desirable for fuel formulations comprising a base fuel to have a vapour pressure that is no greater than the vapour pressure of the base fuel alone. Thus, in a preferred embodiment of the invention, the monoterpene component is used in such a fuel formulation, optionally further comprising a bio-derived component or oxygenate, to adjust or reduce the DVPE of the fuel formulation such that there is no increase in DVPE relative to the base fuel. That is to say: $ΔDVPE \leq 0 kPa$
where ΔDVPE is the difference between the DVPE of the overall fuel formulation and that of the base fuel. The ΔDVPE may also be the difference between the DVPE of the overall fuel formulation and that of the same formulation in the absence of a monoterpene component and any additional bio-derived or oxygenate component(s).
To provide a fuel formulation which closely matches the specifications of its base fuel, the monoterpene component may advantageously be used for the purpose of adjusting or reducing the vapour pressure of the fuel formulation to be neutral or close to neutral with respect to the vapour pressure of the base fuel. By "neutral or close to neutral" is meant that the vapour pressure of the formulation is adjusted to lie within plus or minus 15%, preferably plus or minus 10% of the vapour pressure of the base fuel.
Vapour pressure (DVPE) is an indicator of volatility: the higher the vapour pressure, the more volatile the fuel. Similarly, certain other fuel properties such as distillation properties (e.g. as discussed below), boiling points (e.g. initial and final boiling points), and alternative measurements of vapour pressure, such as air-saturated vapour pressure (ASVP), are dependent on DVPE. These properties, and indeed all fuel formulation properties dependent on vapour pressure are embraced by the term "vapour pressure" as used herein. Reducing the vapour pressure of a fuel formulation may hence comprise influencing or adjusting any fuel property dependent on vapour pressure.
The distillation properties of a fuel formulation may be expressed in terms of E-values and T-values. For example, the E70 value for a formulation is the volume percentage of the formulation that has been distilled at 70°C, whilst the E100 value is the volume percentage of the formulation that has been distilled at 100°C. Both E70 and E100 values, as well as other E-values, can be measured using the standard test method EN ISO 3405.
Likewise, the T70 value for a formulation is the temperature on its distillation curve at which 70% of its volume has evaporated at standard atmospheric pressure, whilst the T100 value for a formulation is the temperature on its distillation curve at which 100% of its volume has evaporated at standard atmospheric pressure. Both T70 and T100 values, as well as other T-values, can be measured using the standard test method EN ISO 3405.
It is also possible to calculate blending E-values and T-values. For example, blending E-values can be calculated using the following equation: ${bE 70}_{n} = \frac{{E 70}_{blend} - {E 70}_{base} (1 - v_{n})}{v_{n}}$
where bE70n is the blending E70 value for component n in the relevant blend, v_n is the volume fraction of the component n in the blend; E70_base is the E70 value of the base fuel; and E70_blend is the E70 value of the blend containing the base fuel and component n.
The distillation properties, for example E70 or E100, of a fuel formulation may be calculated from the blending E70 (bE70) values for a fuel formulation using linear blending rules, which provide for example that: ${E 70}_{blend} = {E 70}_{base} v_{base} + Σ {bE 70}_{n} v_{n}$
where bE70_n and v_n are the blending E70 and volume fraction of component n, and E70_{base fuel} and v_base fuel are the E70 and volume fraction of the base fuel.
Use of the monoterpene component according to the first aspect may preferably be for the purpose of influencing or adjusting the E70 and E100 values of the fuel formulation. In an embodiment, the monoterpene component, or particularly the combination or use of the monoterpene component with any additional bio-derived components or oxygenates in the fuel formulation, does not significantly alter the E70 and E100 values for the fuel formulation as a whole compared to the values for a base fuel of the formulation alone. By the term "not significantly alter the E70 and E100 values" is meant that both the E70 value and the E100 value of the fuel formulation are maintained within 25%, or within 20%, or within 15%, of both the E70 value and the E100 value of the base fuel, and/or that the value of (E70 + E100) for the fuel formulation is maintained within 15%, or within 10%, or within 5% of the value of (E70 + E100) for the base fuel.
In an embodiment the monoterpene component is used for the purpose of achieving: $- 20 % v / v \leq (ΔE 70 + ΔE 100) \leq 20 % v / v,$
where ΔE70 is the difference between the E70 of the overall fuel formulation and that of the same formulation in the absence of the monoterpene component and any additional bio-derived component(s) or oxygenate(s); and ΔE100 is the difference between the E100 of the overall fuel formulation and that of the same formulation in the absence of any monoterpene component and the additional bio-derived component(s) or oxygenate(s). Alternatively ΔE70 may be seen as the difference between the E70 of the overall fuel formulation and that of the base fuel alone, and ΔE100 as the difference between the E100 of the overall fuel formulation and that of the base fuel alone.
It may be preferred that: $- 15 % v / v \leq (ΔE 70 + ΔE 100) \leq 15 % v / v,$
or that: $- 10 % v / v \leq (ΔE 70 + ΔE 100) \leq 10 % v / v,$
or that: $- 5 % v / v \leq (ΔE 70 + ΔE 100) \leq 5 % v / v,$
or that: $- 1 % v / v \leq (ΔE 70 + ΔE 100) \leq 1 % v / v,$
or in cases that : $ΔE 70 + ΔE 100 = 0 % v / v .$
These constraints may be seen as a need for ΔE70 to counter, at least partially, ΔE100. For example, where a formulation includes both ethanol and an additional bio-derived component or oxygenate X, suitable relative concentrations for its components may be calculated so as to satisfy the following equation: $\sum_{n = 1}^{n = 3} v_{fn} bE 70_{n} - E 70_{base} = E 100_{base} - \sum_{n = 1}^{n = 3} v_{fn} bE 100_{n}$
wherein:

n = 1 is a monoterpene component
n = 2 is ethanol,
n = 3 is the additional bio-derived component or oxygenate X,
v_fn is the volume fraction of the component represented by n in the ternary mixture of a monoterpene, ethanol and X,
bE70_n is the blending E70 value of the component represented by n,
bE100_n is the blending E100 value of the component represented by n,
E70_base is the E70 value of the base fuel, and
E100_base is the E100 value of the base fuel.

For example, using the equations given above, a blend containing ethanol as well as a monoterpene component can be tailored to have acceptable distillation properties, as can a blend containing one or more additional bio-derived components or oxygenates with a monoterpene component, a base fuel and optionally ethanol.
It has also been found that monoterpenes can contribute positively to other properties of fuel formulations. Thus, a second aspect, resides in the use of a monoterpene component which comprises camphene in a fuel formulation, for the purpose of improving or maintaining one or more properties of the fuel formulation selected from: lubricity, oxidative stability, deposit-forming tendency, elastomer compatibility and especially octane number relative to the relevant property in: (i) a bio-derived or oxygenate component comprised in the fuel formulation; and/or (ii) a mixture of a base fuel and a bio-derived or oxygenate component comprised in the fuel formulation and/or (iii) a base fuel comprised in the fuel formulation.
Use according to the second aspect may in particular be for the purpose of achieving a desired target property, particularly by mitigating a detrimental effect on the property of other bio-derived or oxygenate components, such as ethanol, within the formulation.
The lubricity of a fuel formulation can be assessed by any suitable method. One such method involves measuring the wear scar produced on an oscillating ball from contact with a stationary plate whilst immersed in the formulation. This "wear scar" may be measured for example using the test described in Example 4 below. An "improvement" in the lubricity of a formulation may be manifested for example by a lower degree of wear scar, or of other friction-induced damage, in two relatively-moving components which are exposed to the formulation.
The oxidative stability of a fuel formulation can be assessed by any suitable method. One such method involves measuring the concentration of peroxides in the fuel formulation before storage and upon storage of the fuel formulation at various temperatures and time intervals. For example, peroxide concentration may be measured initially, and may then be measured again after a three-month storage of the fuel formulation at 0-2 °C. A similar experiment may be performed with the storage occurring at 40 °C. Peroxide concentrations, which provide a suitable metric for the oxidative stability of a fuel formulation, can be measured using the standard test method SMS 359 or an analogous method.
The oxidative stability of a fuel formulation can also be assessed using the induction period after a period of storage at a specified temperature (e.g. 3 months at 0-2 °C or 40 °C). The induction period, which provides a suitable metric for the oxidative stability of a fuel formulation, can be measured using the standard test method EN ISO 7536 or an analogous method.
It has also been found that surprisingly the inclusion of a monoterpene in a fuel formulation can improve or maintain deposit-forming tendencies of the fuel formulation. By 'improve or maintain deposit-forming tendencies' is meant that there is a decreased or equal tendency of the monoterpene-containing fuel formulation to form deposits, particularly gum deposits, relative to the relevant reference point.
The deposit-forming tendencies of a fuel formulation can be assessed by any suitable method. One such method is the MIHPT (multiple inclined hot plate rig test) method. This method uses an intake valve deposit simulator test corresponding closely to that described in SAE Paper 890215, Daneshgari et al, "The Influence of Temperature upon Gasoline Deposit Build-Up on the Intake Valves", Detroit, USA, 27 February to 3 March 1989, and is described in Example 6 below.
It has further been found that the inclusion of a monoterpene component in a fuel formulation can improve or maintain elastomer compatibility. Elastomer compatibility is a measure of a fuel formulation's tendency to cause elastomer-damaging effects, ie effects that reduce the ability of an elastomeric material to function correctly in a fuel-consuming system and/or in the presence of the fuel formulation. An example of an elastomer damaging effect is swelling of the elastomer when in contact with the fuel formulation. Elastomer damage also includes a change (typically a reduction) in the hardness and/or flexibility of the elastomer when in contact with the fuel formulation.
Elastomer swell measurements in particular provide a measure of the compatibility of elastomeric materials, such as are used in fuel pump seals and other engine components, with a fuel component or formulation. Generally this compatibility is evaluated by assessing changes in the properties of an elastomer due to its immersion in a test fluid. The elastomer swelling effects of a fuel formulation may for instance be assessed by measuring the increase or percentage increase in volume or mass of an elastomeric material on immersion in the formulation for a predetermined period of time. A smaller volume or mass increase indicates a reduction in elastomer swelling effects. This assessment may for example be carried out for nitrile and/or fluorocarbon elastomers. A standard test method such as DIN 51605-1 or ISO 1817:1998 may be used to measure elastomer swell effects. Changes in the hardness and/or flexibility of an elastomeric material may be assessed using standard test methods such as the Shore hardness test or TMS 556.
It has further been found that the inclusion of a monoterpene component, especially one which comprises camphene, in a fuel formulation can improve or maintain an octane number of the formulation.
Octane number may refer to research octane number (RON) and/or motor octane number (MON). The research octane number (RON) may be measured by any suitable method. It can be measured using the standard test methods ASTM D2699 or EN 25164 or analogous methods such as PrEN ISO 5164. The motor octane number (MON) may be measured by any suitable method. It can be measured using the standard test methods ASTM D2700 or EN 25163 or analogous methods such as PrEN ISO 5163.
The effectiveness of the monoterpene component in improving or maintaining octane number depends on the one hand on the octane number of the fuel formulation to which it is added and on the other hand on the structure of the monoterpene(s) present in the monoterpene component.
Advantageously, the monoterpene component may be used to maintain or improve the octane number of a fuel formulation having a RON of 100 or less or 99 or 98 or 95 or less and/or a MON of 95 or less, or 90 or 88 or less.
With regard to the structure of the monoterpene(s) it has been found that, surprisingly, camphene is especially effective in improving or maintaining the octane number (especially RON) of fuel formulations. Accordingly, a third, preferred, aspect, resides in use of camphene in a fuel formulation for the purpose of improving, maintaining or achieving a target octane number of the fuel formulation.
In other words the third aspect embraces use of camphene in a fuel formulation to achieve: $ΔRON \geq 0$
where ΔRON is the difference between the RON of the camphene-containing fuel formulation and that of the base fuel alone. The ΔRON may also be the difference between the RON of the overall fuel formulation and that of the same formulation in the absence of camphene and any additional bio-derived or oxygenate component(s).
Blending RON and MON values may be calculated in an analogous fashion to blending E-values, as discussed above: ${bP}_{n} = \frac{[P_{base + n} - P_{base} (1 - v_{n})]}{v_{n}}$
where P is the relevant fuel property, for example RON or MON; v_n is the volume fraction of component n in the blend; and base is the base fuel.
The RON of a blend may be calculated from the blending values using linear blending rules, such that: ${RON}_{blend} = {RON}_{base} v_{base} + Σ {bRON}_{n} v_{n}$
where bRON_n and v_n are the blending RON and volume fraction of component n, and RON_base and v_base are the RON and volume fraction of the base fuel. MON values can be calculated from the respective blending values in a similar manner.
It is noted that the purposive uses may alternatively be expressed as methods of achieving one or more target properties in a fuel formulation by blending an effective amount of a monoterpene, especially camphene, component with the fuel formulation.
For instance, a fourth aspect, resides in a method of achieving a target vapour pressure in a fuel formulation, the method comprising blending an effective amount of a monoterpene component with the fuel formulation.
Similarly, a fifth aspect, resides in a method of achieving a target lubricity, oxidative stability, deposit-forming tendency, elastomer compatibility or octane number in a fuel formulation, the method comprising blending an effective amount of a monoterpene component which comprises camphene with the fuel formulation.
A sixth aspect provides a method of achieving a target octane number in a fuel formulation, the method comprising blending an effective amount of camphene with the fuel formulation.
The advantageous properties of monoterpenes, and camphene in particular, enable the formulation of fuels having a high concentration of bio-derived components.
Thus, a seventh aspect provides the use of a bio-derived monoterpene component which comprises camphene, in a fuel formulation, particularly a fuel formulation comprising another bio-derived component or oxygenate, for the purpose of increasing the bio-derived content of the formulation without, or without unduly, increasing the vapour pressure of the formulation.
An eighth aspect, provides the use of a bio-derived monoterpene component which comprises camphene, in a fuel formulation, particularly a fuel formulation comprising another bio-derived component or oxygenate, for the purpose of increasing the bio-derived content of the formulation without, or without unduly, reducing an octane number of the formulation.
A ninth aspect provides the use of a monoterpene which comprises camphene in a gasoline fuel formulation, for the purpose of replacing, at least partially, a bio-derived component and/or an oxygenate in the formulation. In an embodiment, the monoterpene component is biologically derived. The monoterpene component may thus be used as a substitute for at least some of the bio-derived component or oxygenate which would otherwise have been included in the formulation, for example so as to achieve a desired target specification such as a minimum bio-derived content. For instance, a quantity of biologically derived monoterpene component may be included in a fuel formulation in place of the same or a similar quantity of ethanol, allowing a target minimum bio-derived content to be achieved but without, or with fewer of, the drawbacks associated with the use of ethanol alone.
A tenth aspect, resides in a fuel formulation obtainable by or resulting from the use or method of any of the first to ninth aspects of the invention.
The base fuel component of a fuel formulation in the context of the invention is typically a liquid hydrocarbon distillate gasoline fuel component, or mixture of such components, containing hydrocarbons that boil in the range from 0 to 250°C (ASTM D86 or EN ISO 3405) or from 20 or 25 to 200 or 230°C. The optimal boiling ranges and distillation curves for such base fuels will typically vary according to the conditions of their intended use, for example the climate, the season and any applicable local regulatory standards or consumer preferences.
The hydrocarbon fuel component(s) in the base fuel may be obtained from any suitable source. They may for example be derived from petroleum, coal tar, natural gas or wood, in particular petroleum.
Alternatively they may be synthetic products such as from a Fischer-Tropsch synthesis. Conveniently they may be derived in any known manner from straight-run gasoline, synthetically-produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydrocracked petroleum fractions, catalytically reformed hydrocarbons or mixtures of these.
Typically, base fuels comprise components selected from one or more of the following groups: saturated hydrocarbons, olefinic hydrocarbons, and aromatic hydrocarbons. Typically, the olefinic hydrocarbon content of a base fuel is in the range from 0 to 40% v/v; it may for instance be in the range from 0 to 30% v/v. Typically, the aromatic hydrocarbon content of a base fuel is from 0 to 70% v/v; it may for instance be from 10 to 60% v/v.
The benzene content of a base fuel is typically at most 10% v/v, or at most 5% v/v, or at most 1% v/v. Typically, the saturated hydrocarbon content of a base fuel is at least 40% v/v; it may for instance be from 40 to 80% v/v.
The base fuel suitably has a low or ultra low sulphur content, for instance at most 1000 ppmw (parts per million by weight) of sulphur, or no more than 500 ppmw, or no more than 100 ppmw, or no more than 50 or even 10 ppmw. It also suitably has a low total lead content, such as at most 0.005 g/l; in an embodiment it is lead free ("unleaded"), ie having no lead compounds in it.
A base fuel will typically have a research octane number (RON) (ASTM D2699 or EN 25164) of 80 or greater, or of 85 or 90 or 93 or 94 or 95 or 98 or greater, for example from 80 to 110 or from 85 to 115 or from 90 to 105 or from 93 to 102 or from 94 to 100. In some embodiments of the invention a monoterpene component may advantageously be used in a fuel formulation comprising a base fuel having a RON of 115 or less, or of 105 or 102 or 100 or 99 or even 98 or less.
Similarly, a base fuel will typically have a motor octane number (MON) (ASTM D2700 or EN 25163) of 70 or greater, or of 75 or 80 or 84 or 85 or greater, for example from 70 to 110 or from 75 to 105 or from 84 to 95. In some embodiments of the invention a monoterpene component may advantageously be used in a fuel formulation comprising a base fuel having a MON of 110 or less, or of 105 or 100 or 95 or 90 or even 88 or less.
A base fuel will typically have an E70 value of 10% v/v or greater, or of 14 or 15 or 20 or 22% v/v or greater. Its E70 value might typically be up to 55% v/v, or up to 51 or 50 or 48% v/v. Its E70 value might for example be from 10 to 55% v/v, or from 14 to 51% v/v, or from 14 to 50% v/v, or from 20 to 50% v/v. In an embodiment, it has an E70 value of from 20 to 48% v/v. In an alternative embodiment, it has an E70 value of from 22 to 50% v/v.
The base fuel will typically have an E100 value of 35% v/v or greater, or of 40 or 45 or 46% v/v or greater. Its E100 value might typically be up to 75% v/v, or up to 72 or 71% v/v. Its E100 value might for example be from 35 to 75% v/v, or from 40 to 72% v/v, or from 40 to 71% v/v, or from 46 to 71% v/v.
The base fuel may be a reformulated base fuel, for example one which has been reformulated so as to accommodate the addition of an oxygenate such as ethanol.
The specific distillation curve, hydrocarbon composition, RON and MON of the base fuel are not however critical for the purposes of its use in the present invention.
A base fuel might typically have a density from 0.720 to 0.775 kg/m³ at 15°C (ASTM D4052, EN ISO 3675, or EN ISO 12185. For use in a summer grade gasoline fuel, a base fuel might typically have a vapour pressure at 37.8°C (DVPE) of from 45 to 70 kPa or from 45 to 60 kPa (EN ISO 3405, EN 13016-1 or ASTM D4953-06). For use in a winter grade fuel it might typically have a DVPE of from 50 to 100 kPa, for example from 50 to 80 kPa or from 60 to 90 kPa or from 65 to 95 kPa or from 70 to 100 kPa.
Examples of suitable base fuels include those having an olefinic hydrocarbon content of from 0 to 20% v/v (ASTM D1319), and/or an aromatic hydrocarbon content of from 0 to 50% v/v (ASTM D1319), and/or a benzene content of at most 1% v/v. In an embodiment of the invention, the base fuel complies with the current European gasoline fuel standard EN 228. In an embodiment, it complies with the current US gasoline fuel standard ASTM D4814-08b.
The concentration of the base fuel may be up to 99.99% v/v, or up to 99.95% v/v, or up to 99.9 or 99.5% v/v based on the total volume of the fuel formulation. It may be up to 99% v/v, for example up to 98 or 95 or 90% v/v, or in cases up to 85 or 80 or 75 or 70 or 65 or 60% v/v based on the total volume of the fuel formulation. The base fuel will typically represent the major proportion, i.e. more than 50% v/v, of a fuel formulation
A fuel formulation may also contain one or more additional fuel components. Optionally the fuel formulation may comprise at least one additional fuel component which causes an increase in vapour pressure relative to the vapour pressure of the base fuel.
The fuel formulation may include one or more gasoline fuel additives, of the type well known in the art.
The fuel formulation may contain one or more additional bio-derived components. Such additional fuel components may have boiling points within the normal gasoline boiling range, and in the case of bio-derived components will have been derived - whether directly or indirectly - from biological sources. The, or each, additional bio-derived fuel component may comprise at least about 0.1 dpm/gC of carbon-14.
The formulation may contain one or more oxygenates, which may for example be selected from alcohols, ethers (including cyclic ethers), esters, carboxylic acids and their derivatives, aldehydes, ketones, and mixtures thereof. In an embodiment, the formulation contains one or more oxygenates selected from alcohols, ethers, esters and mixtures thereof. In an embodiment, it contains one or more oxygenates selected from alcohols, ethers and mixtures thereof. Such oxygenates are suitably bio-derived components.
Alcohols suitable for inclusion in a fuel formulation in the context of the invention include C1 to C5 saturated or unsaturated alcohols, in particular C1 to C4 aliphatic alcohols such as ethanol and butanol. In particular, a formulation may include ethanol. It may include ethanol and one or more - for example one - additional bio-derived components. It may include ethanol and one or more - for example one - additional oxygenates.
Ethers suitable for inclusion in a fuel formulation include dialkyl ethers, in particular alkyl t-butyl ethers, more particularly (C1 to C3 alkyl) t-butyl ethers such as methyl t-butyl ether and ethyl t-butyl ether. Other suitable ethers include furans; C5 and C5+ ethers having boiling points below 210°C; and C7 ethers - in particular ethyl ethers - such as 2-ethoxy-2-methylbutane and 1-ethoxy-3-methylbutane. In particular, a formulation may include ethanol together with one or more ethers selected from (C1 to C3 alkyl) t-butyl ethers and mixtures thereof.
Where a fuel formulation contains a bio-derived or oxygenate component, especially ethanol, the bio-derived/oxygenate or ethanol concentration may for example be 1 or 2 or 5% v/v or greater, or 8 or 10 or 15 or 20 or 25 or 30% v/v or greater, based on the total volume of the formulation. The ethanol or bio-derived/oxygenate concentration may be up to 50% v/v, or up to 45 or 40 or 35% v/v. In cases it may be up to 30 or 25 or 20 or 15 or 10% v/v. The amount of oxygenate is usefully such as to provide a fuel formulation having an oxygen content of from 0 to 5% w/w (EN 1601).
In a formulation useful in the invention and containing a bio-derived or oxygenate component, the volume ratio of the monoterpene component to the ethanol or bio-derived/oxygenate component may be for example 1:100 or greater, or 1:50 or 1:10 or greater, for example 1:5 or 1:2 or greater, or 1:1 or 1.5:1 or greater. It may be up to 5:1, or up to 4:1 or 3:1 or 2:1 or 1:1. In particular where the formulation does not contain any additional bio-derived components or oxygenates, the volume ratio of the monoterpene component to ethanol may be 1:1 or greater, or 1.2:1 or greater, or 1.5:1 or greater, or 1.8:1 or greater; in this case the ratio may for example be up to 5:1, or up to 4:1 or 3:1 or 2.5:1, for example from 1.5:1 to 3:1.
Where the formulation includes a combination of a monoterpene component and ethanol, or a combination of a monoterpene component, ethanol and one or more additional bio-derived components or oxygenates, the concentration of the combination in the formulation may be 3 or 4 or 5% v/v or greater. The concentration of the combination may be up to 50% v/v, or up to 40 or 30% v/v, or up to 25 or 20 or 15 or 10% v/v. These concentrations are for the combination as a whole in the overall fuel formulation, even if one or more components of the combination are in practice added individually when preparing the formulation.
The formulation resulting from uses according to the invention should be suitable for use in a spark ignition (petrol) internal combustion engine. It may in particular be suitable for use as an automotive fuel.
The RON of a formulation resulting from the uses of the invention is suitably 80 or greater. It may be 85 or 90 or 93 or 94 or 95 or 98 or 98.4 or greater. The RON may for example be from 80 to 110 or from 85 to 115 or from 90 to 105 or from 93 to 102 or from 94 to 100.
The MON of a fuel formulation resulting from the uses of the invention is suitably 70 or greater, or 75 or 80 or greater. It may be 84 or 85 or greater. The MON may for example be from 70 to 110 or from 75 to 105 or from 84 to 95.
In the present context, "achieving" a desired target property also embraces - and in an embodiment involves - improving on the relevant target. Thus, for example, a monoterpene component may be used to produce a fuel formulation that has an octane number above a desired target value, or a vapour pressure below a desired target value.
In the context of the present invention, "use" of a monoterpene component in a fuel formulation means incorporating a monoterpene component into the formulation, typically as a blend (i.e. a physical mixture) with one or more other fuel components such as a base fuel and optionally one or more additional bio-derived components or oxygenates. The monoterpene may conveniently be incorporated before the formulation is introduced into an engine or other system that is to be run on the formulation.
"Use" of a monoterpene component in the ways described above may also embrace supplying the monoterpene component together with instructions for its use in a fuel formulation to achieve the purpose(s) of any of the aspects of the invention. The monoterpene component may itself be supplied as part of a composition which is suitable for and/or intended for use as a fuel additive, in which case the monoterpene component may be included in such a composition for the purpose of influencing its relevant effects on a fuel formulation.
The present invention will now be further described with reference to the following non-limiting examples.

Example 1

A number of commercially available monoterpene components were blended with a commercially available unleaded gasoline base fuel from Germany, GBF2.

The properties of GBF2 are summarised in Table 2 below.

Table 2

Fuel property	*Units*	*GBF2*
RON (PrEN ISO 5164)		98.2
MON (PrEN ISO 5163)		87.5
DVPE (EN ISO 3405)	kPa	63.3
Density @ 15°C (EN 12185)	g/kg	746.7
Initial boiling point (EN ISO 3405)	°C	33.0
T5	°C	47.5
T10	°C	54.6
T20	°C	66.4
T30	°C	78.7
T40	°C	92.0
T50	°C	103.3
T60	°C	111.7
T70	°C	120.2
T80	°C	132.6
T85	°C	142.7
T90	°C	154.8
T95	°C	168.7
Final boiling point	°C	194.4
Total recovery	% v/v	97.8
Percent residue	% v/v	1.1
Corrected loss	% v/v	1.1
E50	% v/v	6.7
E70	% v/v	23.0
E100	% v/v	46.9
E125	% v/v	74.9
E150	% v/v	88.0
E180	% v/v	97.1

Of the monoterpene components used, myrcene (95% purity), S(-) limonene (96% purity), and camphene (95% purity) were sourced from Sigma-Aldrich; ocimene (90% purity), α-pinene (98% purity) and β-pinene (99% purity) from Aldrich; and R(+) limonene (97% purity) from Sigma. Myrcene and ocimene are acyclic monoterpenes. Limonene is a monocyclic monoterpene. Pinene and camphene are bicyclic monoterpenes.

DVPE values were measured in accordance with EN ISO 3405 for various monoterpenes when blended at 10% v/v with the base fuel GBF2. These values are shown in Table 3 below.

Table 3

*Added component*	Concentration of added component (% v/v)	*DVPE (kPa)*	E70 (% v/v)	E100 (% v/v)	E150 (% v/v)
None (GBF2 alone)	-	63.3	23.0	46.9	88.0
Ethanol	10	69.4	40.3	52.5	89.0
Myrcene	10	58.8	19.9	40.6	81.3
Ocimene	10	58.3	20.2	41.3	80.1
S(-)Limonene	10	58.3	19.6	40.7	79.9
R(+)Limonene	10	58.8	19.9	41.0	80.4
α-Pinene	10	58.6	19.1	40.3	84.9
β-Pinene	10	58.3	19.4	40.4	82.1
Camphene	10	56.2	18.9	40.2	83.8

Table 3 illustrates that all monoterpenes tested reduce the DVPE in the 10% v/v blend, relative to base fuel alone and relative to the ethanol 10 % v/v blend, reflecting the relatively high boiling point of these molecules. The high reduction of 6 kPa (from 63.3 kPa for the base fuel to 56.2 kPa for the base fuel + 10% v/v camphene) for the camphene blend in particular was unexpected.
Furthermore, all monoterpenes tested reduce the E70, E100 and E150, relative to base fuel alone and relative to the ethanol 10 % v/v blend.
Therefore using monoterpenes in the fuel formulation can compensate the impact of ethanol on the vapour pressure and distillation properties of the fuel formulation. This means that through combining monoterpenes, and especially camphene, with ethanol containing base-fuel no further adjustment for DVPE and E70 and E100 is needed (e.g. to the base fuel).

Blending DVPE values obtained for each of the monoterpene components when blended with GBF2 were calculated according to Equation 1 above and are shown in Table 4 below.

Table 4

*Added component*	Concentration of added component (% v/v)	*bDVPE (kPa)*
None (GBF2 alone)	-	63.3
Ethanol	10	119.7
Myrcene	10	11.6
Ocimene	10	3.0
S(-)Limonene	10	3.0
R(+)Limonene	10	11.6
α-Pinene	10	8.4
β-Pinene	10	3.0
Camphene	10	0*

*bDVPE data on 10% v/v blends indicates a physically impossible negative vapour pressure for the camphene - containing blend. The blending DVPE of these components has consequently been assigned as zero.

As further evidenced by the blending DVPE values above, using monoterpenes in a fuel formulation can compensate the impact of ethanol on the vapour pressure and distillation properties of the fuel formulation. All of the monoterpenes blended at 10 % v/v with base fuel have a lower blending DVPE than the base fuel alone and the base fuel plus 10 % v/v ethanol. This means that through combining monoterpenes and especially camphene, with ethanol containing base-fuel no further adjustment for DVPE is needed (e.g. to the base fuel).

Example 2

A number of monoterpene components were blended with GBF2. The monoterpene components and base fuel were the same as those detailed in Example 1 above.
RON and MON values were measured (using the standard test methods PrEN ISO 5164 and PrEN ISO 5163 respectively) for each of the resultant blends of 5 and 10% v/v monoterpene component. RON and MON values were also recorded for the base fuel alone, and for blends of 5 and 10% v/v ethanol in the base fuel.

The RON and MON results are shown in Table 5 below.

Table 5

*Added component*	Concentration of added component (% v/v)	*RON*	*MON*
None (GBF2 alone)	-	98.2	87.5
Ethanol	5	99.5	88.0
Ethanol	10	100.4	88.2
Myrcene	5	98.2	85.0
Myrcene	10	97.4	82.9
Ocimene	5	97.6	85.7
Ocimene	10	97.1	84.3
S(-)Limonene	5	98.1	86.2
S(-)Limonene	10	97.8	83.5
R(+)Limonene	5	97.4	86.1
R(+)Limonene	10	98.0	85.2
α-Pinene	5	97.4	85.7
α-Pinene	10	96.9	84.9
β-Pinene	5	97.2	85.4
β-Pinene	10	96.9	83.6
Camphene*	5	97.8	87.0
Camphene	10	98.4	86.9

* = not according to the invention

These measurements allowed the calculation of blending RON and MON values (bRON and bMON respectively) of the neat component based on the data provided for the 10 % v/v blends of ethanol and of each of the monoterpenes in accordance with Equation 6 above. These values are provided in Table 6 below. Note that it is not possible to measure the octane values of the neat components since this is performed using engine tests for which the neat components cannot be used as the test fuel.

Table 6

*Added component*	*bRON*	*bMON*
Ethanol	120.2	94.5
Myrcene	90.2	41.5
Ocimene	87.2	55.5
S(-)Limonene	94.2	47.5
R(+)Limonene	96.2	64.5
α-Pinene	85.2	61.5
β-Pinene	85.2	48.5
Camphene	100.2	81.5

Tables 5 and 6 illustrate the superior octane properties of camphene compared to the other monoterpenes tested. Its blending RON is significantly higher than those of the other monoterpenes. Since its blending RON is >98.2 at 10% v/v there is no RON penalty when camphene is blended with a base fuel such as GBF2. By contrast, there is a small RON penalty and larger MON penalty when adding the other monoterpenes to the base fuel. Thus, camphene can be seen to be superior to the other monoterpenes in terms of its fit with typical gasoline fuel octane number specifications, making it particularly suitable for use as a gasoline fuel component.

Example 3

The elastomer swell caused by the eight formulations prepared in Example 2 was assessed using the standard test method DIN 51605-1 (measurements taken in triplicate and averaged). The elastomer tested was the nitrile elastomer SRE-NBR 34. The results are shown in Table 7 below.

Table 7

*Added component*	Concentration of added component (% v/v)	*Increase in volume (%)*	*Increase in mass (%)*
None (GBF2 alone)	-	31.2	20.0
Ethanol	10	44.5	28.3
Myrcene	10	30.6	19.6
Ocimene	10	31.1	20.2
S(-)Limonene	10	30.9	19.9
R(+)Limonene	10	30.6	19.8
α-Pinene	10	29.9	19.1
β-Pinene	10	29.8	19.0
Camphene	10	29.8	19.1

These data show that each of the monoterpenes and especially camphene causes significantly less elastomer swell than ethanol, and indeed that each has an elastomer compatibility similar to that of the base fuel alone. Thus, each of the monoterpenes and especially camphene could be substituted for at least a proportion of the ethanol in an ethanol/base fuel blend, in order to mitigate the elastomer damaging effects caused by the ethanol.

Example 4

Gasoline fuel formulations were prepared by blending the base fuel GBF2 with 10% v/v of each of the monoterpene components and ethanol, as in Example 3.
The lubricity of each of the prepared formulations, and of the base fuel itself, was then assessed using the following test method, which is a HFRR (high friction reciprocating rig) wear scar test based on ISO 12156. A sample of the fuel or blend under test was placed in a test reservoir which was maintained at a specified test temperature. A fixed steel ball was held in a vertically mounted chuck and forced against a horizontally mounted stationary steel plate with an applied load. The test ball was oscillated at a fixed frequency and stroke length while the interface with the plate was fully immersed in the fluid reservoir. The metallurgies of the ball and plate, and the temperature, load, frequency, and stroke length were as specified in ISO 12156. The ambient conditions during the test were then used to correct the size of the wear scar generated on the test ball to a standard set of ambient conditions, again as per ISO 12156. The corrected wear scar diameter provides a measure of the test fluid lubricity: the lower the wear scar diameter, the higher the lubricity improvement.

The results are shown in Table 8 below.

Table 8

*Added component*	Concentration of added component (% v/v)	*Wear scar diameter (µm)*
None (GBF2 alone)	-	886
Ethanol	10	765
Myrcene	10	900
Ocimene	10	779
S(-)Limonene	10	815
R(+)Limonene	10	747
α-Pinene	10	864
β-Pinene	10	896
Camphene	10	800

These results show an improvement in lubricity for all monoterpene containing blends, with the exception of the myrcene blend.

Example 5

A gasoline fuel formulation for use according to the invention was prepared by dissolving 10 % v/v camphene in a commercially available unleaded gasoline base fuel from Germany, GBF2 (see Example 1).
The camphene was sourced from Sigma-Aldrich. It had a purity of 95%.

The properties of the resultant formulation are shown, alongside those of the base fuel alone, in Table 9 below.

Table 9

*Fuel property*	*Test method*	*GBF2*	**GBF2 + 10 %v/v camphene**
DVPE (kPa)	EN ISO 3405	63.3	56.2
RON	PrEN ISO 5164	98.2	98.4
MON	PrEN ISO 5163	87.5	86.9
Density @ 15 °C (kg/m³)	EN 12185	746.7	759.3
Initial Boiling Point (°C)	EN ISO 3405	33.0	35.5
Final Boiling Point (°C)	EN ISO 3405	194.4	191.7
Residue (% v/v)	EN ISO 3405	1.1	1.1
Recovery (% v/v)	EN ISO 3405	97.8	98.0
Loss (% v/v)	EN ISO 3405	1.1	0.9
T10 (°C)	EN ISO 3405	54.6	58.3
T20 (°C)	EN ISO 3405	66.4	71.6
T30 (°C)	EN ISO 3405	78.7	85.8
T40 (°C)	EN ISO 3405	92.0	99.8
T50 (°C)	EN ISO 3405	103.3	110.4
T60 (°C)	EN ISO 3405	111.7	119.1
T70 (°C)	EN ISO 3405	120.2	129.4
T80 (°C)	EN ISO 3405	132.6	143.8
T90 (°C)	EN ISO 3405	154.8	157.5
T95 (°C)	EN ISO 3405	168.7	168.0
E70 (% v/v)	EN ISO 3405	23.0	18.9
E100 (% v/v)	EN ISO 3405	46.9	40.2
E150 (% v/v)	EN ISO 3405	88.0	83.8
E180 (% v/v)	EN ISO 3405	97.6	97.5
Unwashed gum (mg/100mL)	IP 131	29.0	25.8
Induction period (min) initial and after 3 m storage, 0-2°C	EN ISO 7536	>1000	>1000
Peroxides (mg/l) initial and after 3 m storage, 0-2°C	SMS 359	0	0

It can be seen from Table 9 that inclusion of camphene, at around 10% v/v, enables maintenance of the boiling points and octane values of the base fuel, while reducing the DVPE of the base fuel and further reducing or maintaining the distillation profile of the base fuel.

Example 6

To test deposit formation tendency, another gasoline fuel formulation was prepared by dissolving 10 % v/v camphene in a commercially available unleaded gasoline base fuel GBF1. GBF1 had an octane (RON) rating of 95.
A MIHPT (multiple inclined hot plate rig test) method was used to measure the deposit-forming tendency of the resultant formulation.
The test rig utilised four inclined plates in parallel. The plates were strips of sandblasted aluminium, each 50 cm long and 2.5 cm wide, each having a 3 mm wide, 1 mm deep central groove along its length. These plates were mounted in the rig at an angle of 3 degrees relative to the horizontal. The temperature at the top end of each plate was maintained at 400°C, whilst at the middle of each plate it was maintained at 250°C.
The test samples each contained 100 ml of the relevant fuel or fuel formulation. They were delivered at a rate of 0.6 ml/minute from glass syringes fitted with 20 gauge steel hypodermic Luer lock needles into the groove at the top end of each plate. Once sample delivery was complete, the plates were allowed to cool to ambient temperature (20°C) and were washed with n-heptane until the run-off liquid was clear. They were then left to dry before assessment of any deposit present.
Assessments were made using a SeeScan™ Marker Image Analyser with 512*512 image memory coupled to a Sony™/SeeScan™ CCD camera equipped with Nikon™ f55 macro lens. The plate being assessed was lit by two 12V tungsten lamps mounted at a linear distance of 22 cm from the point on the plate upon which the camera was focused and at angles of 33 degrees and 147 degrees relative to the plate.
An image was captured of a clear portion of each plate. A second image was then captured of the section of the plate containing deposit. The image analyser divides, pixel by corresponding pixel, the deposit image by the clean image and automatically measures the area and optical density of deposit at the pixels contained within the overall measuring frame, and calculates an integrated optical density for the image, the numerical value of which is recorded as a test rating.
A fuel with a high deposit-forming tendency would typically have a MIHPT scan rating of greater than 200. The GBF1 base fuel was determined to have an MIHPT rating of 142, whilst the GBF1 base fuel mixed with 10 %v/v camphene gave a rating of 87. These results reflect the lower deposit-forming tendency of the camphene-containing fuel formulation, further demonstrating the suitability of camphene as a fuel component. For comparison purposes, the MIHPT rating for GBF2 alone was measured as 71.

Discussion of Examples

The results of Examples 1 to 6 show that monoterpenes are suitable for reducing the vapour pressure of fuel formulations and that they have a number of further beneficial effects on fuel formulation properties.
It is evident that a blend containing an oxygenate such as ethanol as well as a monoterpene component and base fuel can be tailored to have acceptable properties. Therefore, in accordance with the present invention, a monoterpene component may be used to enhance the overall bio-derived content of fuel formulations.
Camphene has been found to be particularly useful in fuel formulations, being capable of lowering DVPE and acting as an octane booster. It is apparent from Examples 1 to 6 that blends of camphene with a gasoline base fuel can have octane numbers, DVPEs and distillation properties within ranges which are acceptable for use in spark ignition (petrol) engines, and indeed which conform to current gasoline standards such as EN 228. Such blends can also benefit from enhanced lubricity.
Using the equations given above, a blend containing ethanol as well as camphene and base fuel can be tailored to have acceptable properties, as can a blend containing one or more additional bio-derived components or oxygenates with camphene, a gasoline base fuel and optionally ethanol.
The addition of camphene also has no negative impact on oxidative stability, whilst the MIHPT results indicate that camphene has a low tendency to form engine inlet valve deposits.

Claims

Use in the range of from 5% v/v to 10% v/v, based on total volume, of a monoterpene component which comprises at least 90 % by volume of camphene, in a gasoline fuel formulation for the purpose of improving or maintaining research octane number (RON) of the fuel formulation.
Use according to claim 1, wherein the fuel formulation comprises a gasoline base fuel and a bio-derived or oxygenate component.
Use according to claim 2, wherein the bio-derived or oxygenate component is ethanol.
Use according to any one of claims 1 to 3, wherein camphene is used in the fuel formulation to achieve: $ΔRON > 0$
where ΔRON is the difference between the RON of the camphene-containing fuel formulation and that of the base fuel alone.
Use according to any preceding claim, for the concurrent purpose of improving or maintaining lubricity of the gasoline fuel formulation.
Use according to any preceding claim, for the concurrent purpose of improving or maintaining the deposit-forming tendency of the gasoline fuel formulation.
Use according to any preceding claim, for the concurrent purpose of improving or maintaining elastomer compatibility of the gasoline fuel formulation.
Use according to any preceding claim, for the concurrent purpose of reducing the vapour pressure of the gasoline fuel formulation.