Aviation fuel,method of making aviation fuel,additives for aviation fuel

Abstract

Aviation fuel comprising a mixture of an aviation fuel base and at least one component of citronella oil. The fuel may comprise at least 0.01vol% of the citronella component, and may comprise no more

Description

BACKGROUND OF THE INVENTION [0001 ] The present invention relates to aviation fuels, such as gas turbine fuels.

[0002] The present invention relates to aviation fuel. More particularly, but not exclusively, the present invention, concerns an aviation fuel, a method of making an aviation fuel, use of at least one component of citronella oil as an additive in an aviation fuel, at least one component of citronella oil for use as an additive in an aviation fuel and a method of fuelling an aircraft engine.

[0003] Fuel used in aircraft is traditionally kerosene based (for example, Jet-A, Jet-A1 and Jet-B fuels). Efforts have been made to make aircraft fuels that have less of an environmental impact than traditional fuels. For example, one type of sustainable aircraft fuel (SAF) may be produced from liquid waste, such as cooking oil, and solid waste, such as packaging, paper, textiles and food scraps. A further alternative to the above-mentioned type of SAF is to add more environmentally-friendly components that are not fossil-fuel based, to traditional aircraft fuels. There may be disadvantages of using some such environmentally-friendly components, for example, if the environmentally-friendly components may otherwise have been used for some other purpose (such as for food) or if growth of the environmentally-friendly components uses resources (such as land) that could have been used for another purpose (for example, to growfood). Furthermore, some environmentally-friendly components may have an adverse effect on one or more properties of the aviation fuel.

[0004] The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved aviation fuel. SUMMARY OF INVENTION

[0005] In accordance with a first aspect of the present invention, there is provided an aviation fuel comprising a mixture of (i) an aviation fuel base and (ii) at least one component of citronella oil.

[0006] The applicant has discovered that it is possible to incorporate at least one component of citronella oil into aviation fuel. Citronella oil burns with a clean, smokeless flame, and may improve one or more characteristics of the aviation fuel. Furthermore, it is anticipated that the environmental impact of aviation fuel comprising components of citronella oil may be lower than that of aviation fuel without the one or more components of citronella oil, because citronella oil provides a biologically-producible component of the aviation fuel. The plant, lemongrass, from which citronella oil is derived may be grown in areas that are not suitable for food production. Furthermore, lemongrass captures carbon dioxide. The at least one component of citronella oil may be provided by citronella oil or a fraction of citronella oil. Such a fraction is typically obtained by fractional distillation of citronella oil. Alternatively, the at least one component of citronella oil may be provided as isolated components. For example, the at least one component of citronella oil may be provided by a fraction of citronella oil comprising citronellal. Alternatively, citronellal may be provided as an isolated component (for example, as commercially-available citronellal).

[0007] Optionally, at least 0.01 vol%, at least 0.025vol%, at least 0.05vol%, at least 0.1vol%, at least 0.5vol% and at least 1vol% of the aviation fuel is provided by the at least one component of citronella oil. The applicant anticipates that a minimum amount of the at least one component of citronella oil would be advantageous, given the beneficial properties of citronella oil mentioned above. The vol% of the at least one component of citronella oil is determined relating to the total volume of the at least one component of citronella oil and the aviation fuel base.

[0008] Optionally, no more than 10vol%, no more than 8vol%, no more than 6vol%, no more than 5vol%, no more than 3vol%, no more than 1vol%, no more than 0.8vol% and no more than 0.5vol% of the aviation fuel is provided by the at least one component of citronella oil. The applicant anticipates that, while citronella oil has advantageous properties, a maximum amount of the at least one component of citronella oil would be preferred, given some of the properties of citronella oil, such as a high viscosity compared to aviation fuel.

[0009] Optionally, from 0.025 to 1 vol%, from 0.05 to 0.8 vol% and from 0.1 to 0.5vol% of the aviation fuel is provided by the at least one component of citronella oil. The applicant anticipates that such a range provides an advantageous amount of the at least one component of citronella oil, given its properties.

[0010] Components of citronella oil include, but are not limited to, citronellol (3,7-dimethyloct-6-en-1-ol), citronellal (3,7-dimethyloct-6-enal), geraniol (3,7-dimethylocta-2,6-dien-1-ol), geranyl acetate (3,7-dimethylocta-2,6-dien-1-yl acetate), limonene (1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene), methyl isoeugenol (1,2-dimethoxy-4-[(prop-1-enyl]benzene), ocimene ((3E)-3,7-Dimethylocta-1,3,7-triene, (3Z)-3,7-Dimethylocta-1,3,6-triene and (3E)-3,7-Dimethylocta-1,3,6-triene), octatriene (1,3,6-octatriene), neral ((Z)-3,7-Dimethylocta-2,6-dienal), citronellyl acetate (3,7-Dimethyloct-6~en-1 -yl acetate), elemene ((+)-a: (S)-1-lsopropyl-6-methyl-3-(propan-2-ylidene)-6-vinylcyclohex-1 -ene, (-)-£: (1 S,2S,4R)-1 -Methyl-2,4-di(prop-1 -en-2-yl)-1 -vinylcyclohexane, (-)-y: (3R,4R)-1-lsopropyl-4-methyl-3-(prop-1-en-2-yl)-4-vinylcyclohex-1-ene, (-)-6: (3R,4R)-1-lsopropyl-4-methyl-3-(prop-1-en-2-yl)-4-vinylcyclohex-1-ene), aromandrene (1,1,7-Trimethyl-4-methylenedecahydro-1 H-cyclopropa[e]azulene), germacrene ((1 F,5F,8S)-1,5-dimethyl-8-(prop-1-en-2-yl)cyclodeca-1,5-diene), elemol (2-((1 R,3S,4S)-4-Methyl-3-(prop-1-en-2-yl)-4-vinylcyclohexyl)propan-2-ol), 1,3-cyclopentadiene, eugenol (2-Methoxy-4-(prop-2-en-1-yl)phenol), geranial ((2E)-3,7-Dimethylocta-2,6-dien-1-ol), 4-nonanone, trans-p-caryophyllene ((1R,4F,9S)-4,11,11-Trimethyl-8-methylidenebicyclo[7.2.0]undec-4-ene), cadinene (a, p, y and 6 cadinene, also known as (1S,4aR,8aR)-4,7-dimethyl-1-(propan-2-yI)-1,2,4a,5,6,8a-hexahydronaphthalene [for a-cadinene], (1 S,4aR,8aR)-7-methyl-4-methylidene-1-(propan-2-yl)-1,2,3,4,4a,5,6,8a-octahydronaphthalene [for y-cadinene] and (1S,8aR)-4,7-dimethyl-1-(propan-2-yl)-1,2,3,5,6,8a-hexahydronaphthalene [for 6-cadinene]), linalool (3,7-Dimethylocta-1,6-dien-3-ol), pulegol (5-methyl-2-(propan-2-ylidene)cyclohexan-1 -ol), terpinene-4-ol acetate, cadinol (Cadin-4-en-10-ol), eudesmol (2-((2R,4aR,8aS)-4a-methyl-8-methylenedecahydronaphthalen-2-yl)propan-2-ol), dimethyloctenyl ester of butanoic acid, terpinolene (1-Methyl-4-(propan-2-ylidene)cyclohex-1-ene), phellandrene ((a): 2-Methyl-5-(propan-2-yl)cyclohexa-1,3-diene (P): 3-Methylidene-6-(propan-2-yl)cyclohex-1-ene), tricyclodecane, myrcene (7-Methyl-3-methylideneocta-1,6-diene), linalyl acetate (3,7-Dimethylocta-1,6-dien-3-yl acetate), citronellyl formate (3,7-dimethyloct-6-en-1 -yl formate), borneol (rel- ^1^,25,4^)-1,7,7-Trimethylbicyclo[2.2.1]heptan-2-ol), pinene (a and p-pinene), limonene (1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene), trimethylhexanal, cineole (1,3,3-Trimethyl-2-oxabicyclo[2.2.2]octane), trimethylhexanol, terpinene (a (4-Methyl-1 -(1 -methylethyl)-1,3-cyclohexadiene), p (4-Methylene-1-(1-methylethyl)cyclohexene), y (4-Methyl-1 -(1 -methylethyl)-1,4-cyclohexadiene), 6(1 -Methyl-4-(propan-2-ylidene)cyclohex-1-ene)), terpineol (a, p, y and 4-terpineol) and longifolene ((1 R,2S,7S,9S)~ 3,3,7-trimethyl- 8-methylenetricyclo- [5.4.0.02,9]undecane). Those skilled in the art will realise that not all of the above-listed components may be present in the aviation fuel, because the precise composition of the citronella oil, or a fraction thereof, will depend on the plant from which the oil has been extracted, the part(s) of the plant from which the oil has been extracted and, in the case of a fraction of citronella oil, the particular fraction that is used. Furthermore, due to this natural variability, there may be components of citronella oil that are present which are not listed above. As mentioned above, the at least one component of citronella oil may be provided by a fraction of citronella oil. The fraction of citronella oil may provide citronellal, optionally in the absence of one or both, and preferably in the absence of both, of geraniol and citronellol. The fraction of citronella oil may provide one or both of geraniol and citronellol (preferably both), in the absence of citronellal. [0011 ] Many of the components mentioned above exist in one or more isomeric forms, for example, as E and Z isomers, or as different stereoisomers. Optionally, only one such isomer of the multiple isomers may be present. Optionally, more than one of the multiple isomers may be present. Optionally, each of the multiple isomers may be present. For example, geraniol may exist as the E and the Z isomer at the 2 position, but in lemongrass the E isomer is usually present. Geranyl acetate is also known as 3,7-dimethylocta-2,6-dien-1-yl acetate. Geranyl acetate may exist as the E and Z isomer. Geranyl acetate may exist as the E and the Z isomer at the 2 position, but in lemongrass the E isomer is usually present. Limonene is also known as 1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene.

[0012] Optionally, the at least one component of citronella oil comprises citronellal. Optionally, the at least one component of citronella oil comprises citronellol and geraniol. Optionally, the at least one component of citronella oil comprises at least three of citronellal, citronellol, geranyl acetate, geraniol, and limonene are present. Optionally, the at least one component of citronella oil comprises at least four of citronellal, citronellol, geranyl acetate, geraniol, and limonene are present. Optionally, the at least one component of citronella oil comprises all of citronellal, citronellol, geranyl acetate, geraniol, and limonene are present. The presence of the various component(s) of citronella oil may be determined using GC-MS (gas chromatographymass spectrometry), for example.

[0013] Optionally, the at least one component of citronella oil comprises citronellal, citronellol and geraniol. Optionally, the at least one component of citronella oil comprises citronellal, citronellol, geraniol and geranyl acetate. Citronellal, citronellol and geraniol typically provide a relatively large proportion of citronella oil.

[0014] For some citronella oils, citronellal, citronellol and geraniol may make-up at least 30vol% of citronella oil, in which case, optionally, at least 0.003vol%, at least 0.008vol%, at least 0.017vol%, at least 0.03vol%, at least 0.15vol% and at least 0.3vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0015] Optionally, no more than 3vol%, no more than 2.4vol%, no more than 1.8vol%, no more than 1.5vol%, no more than 0.9vol%, no more than 0.3vol%, no more than 0.25vol% and no more than 0.15vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0016] Optionally, from 0.008 to 0.3vol%, from 0.015 to 0.25 vol% and from 0.03 to 0.15vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0017] Optionally, citronellal, citronellol and geraniol make-up at least 40% of citronella oil, in which case optionally, at least 0.004vol%, at least 0.01 vol%, at least 0.023vol%, at least 0.04vol%, at least 0.2vol% and at least 0.4vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0018] Optionally, no more than 4vol%, no more than 3.2vol%, no more than 2.4vol%, no more than 2.0vol%, no more than 1.2vol%, no more than 0.4vol%, no more than 0.33vol% and no more than 0.2vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0019] Optionally, from 0.01 to 0.4vol%, from 0.02 to 0.33 vol% and from 0.04 to 0.20vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0020] Optionally, citronellal, citronellol and geraniol make-up at least 50% of citronella oil, in which case at least 0.005vol%, at least 0.012vol%, at least 0.025vol%, at least 0.05vol%, at least 0.25vol% and at least 0.5vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0021] Optionally, no more than 5vol%, no more than 4vol%, no more than 3vol%, no more than 2.5vol%, no more than 1.5vol%, no more than 0.5vol%, no more than 0.4vol% and no more than 0.25vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0022] Optionally, from 0.012 to 0.5vol%, from 0.025 to 0.4 vol% and from 0.05 to 0.25vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0023] Optionally, citronellal, citronellol and geraniol make-up at least 60% of citronella oil, in which case, optionally, at least 0.006vol%, at least 0.015vol%, at least 0.03vol%, at least 0.06vol%, at least 0.3vol% and at least 0.6vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0024] Optionally, no more than 6vol%, no more than 4.8vol%, no more than 3.6vol%, no more than 3vol%, no more than 1.8vol%, no more than 0.6vol%, no more than 0.48vol% and no more than 0.3vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0025] Optionally, from 0.015 to 0.6vol%, from 0.03 to 0.48 vol% and from 0.06 to 0.3vol% of the aviation fuel is provided by citronellal, citronellol and geraniol.

[0026] For the avoidance of doubt, the aviation fuel of the first aspect of the present invention is suitable for use in aircraft engines. The aviation fuel comprises an aviation fuel base, optionally selected from the list consisting or one or more of JetA, Jet A1, JetB, JP8, synthetic aviation fuel and sustainable aviation fuel. The aviation fuel base optionally comprises kerosene, such as Jet A, JP8 and Jet A-1 fuels. The aviation fuel base may optionally comprise naphtha-kerosene fuel, such as Jet B. The aviation fuel may optionally comprise an aviation fuel base comprising a synthetic aviation fuel. The aviation fuel base optionally comprises a sustainable aviation fuel. Sustainable aviation fuel typically comprises components derived from a renewable feedstock. The aviation fuel may, for example, comprise a gas turbine fuel. Such gas turbine fuels are suitable for use in gas turbine engines, such as jet aircraft engines.

[0027] The aviation fuel of the first aspect of the present invention may be made by mixing citronella oil (or a fraction thereof) and an aviation fuel base. Therefore, the aviation fuel of the first aspect of the present invention may comprise a mixture of (i) an aviation fuel base and (ii) citronella oil, or a fraction thereof. A method of making such an aviation fuel is described below in the third aspect of the present invention.

[0028] The aviation fuel may optionally have a freezing point of greater than -70°C, optionally greater than -60°C and optionally greater than -50°C. Optionally, the aviation fuel may have a freezing point of from -50°C to -35°C, for example of from -48°C to -38°C. The aviation fuel may optionally have a flash point of at least 30°C, optionally at least 35°C and optionally about 38°C.

[0029] The aviation fuel may comprise one or more of: an antioxidant, an antistatic agent, a corrosion inhibitor, an icing inhibitor, a biocide and a metal deactivator.

[0030] In accordance with a second aspect of the present invention, there is provided an aviation fuel comprising a mixture of (i) an aviation fuel base and (ii) citronella oil or a fraction thereof. [0031 ] The applicant has discovered that it is possible to incorporate citronella oil or a fraction thereof, into aviation fuel. Citronella oil burns with a clean, smokeless flame, and may improve one or more characteristics of the aviation fuel. Furthermore, it is anticipated that the environmental impact of aviation fuel comprising components of citronella oil may be lower than that of aviation fuel without the components of citronella oil, because citronella oil provides a biologically-producible component of the aviation fuel. The plant, lemongrass, from which citronella oil is derived may be grown in areas that are not suitable for food production. Furthermore, lemongrass captures carbon dioxide. A fraction of citronella oil may be used instead of citronella oil, although this may be less convenient, because the citronella oil is subject to fractional distillation to obtain the fraction.

[0032] The aviation fuel base may have one or more of the features of the aviation fuel base described above in relation to the aviation fuel of the first aspect of the present invention.

[0033] Optionally, at least 0.01 vol%, at least 0.025vol%, at least 0.05vol%, at least 0.1vol%, at least 0.5vol% and at least 1vol% of the aviation fuel is provided by citronella oil or a fraction thereof. The applicant anticipates that a minimum amount of citronella oil or a fraction thereof would be advantageous, given the beneficial properties of citronella oil mentioned above.

[0034] Optionally, no more than 10vol%, no more than 8vol%, no more than 6vol%, no more than 5vol%, no more than 3vol%, no more than 1vol%, no more than 0.8vol% and no more than 0.5vol% of the aviation fuel is provided by citronella oil or a fraction thereof. The applicant anticipates that, while citronella oil has advantageous properties, a maximum amount of citronella oil, or fraction thereof, would be preferred, given some of the properties of citronella oil, such as a high viscosity compared to aviation fuel.

[0035] Optionally, from 0.025 to 1 vol%, from 0.05 to 0.8 vol% and from 0.1 to 0.5vol% of the aviation fuel is provided by citronella oil or a fraction thereof. The applicant anticipates that such a range provides an advantageous amount of citronella oil, given its properties.

[0036] The aviation fuel of the second aspect of the present invention may comprise one or more features of the aviation fuel of the first aspect of the present invention.

[0037] In accordance with a third aspect of the present invention, there is provided a method of making an aviation fuel comprising mixing (i) an aviation fuel base and (ii) at least one component of citronella oil.

[0038] As mentioned above, the applicant has discovered that it is possible to incorporate citronella oil, or a fraction thereof, into aviation fuel. Citronella oil burns with a clean, smokeless flame, and may improve one or more characteristics of the aviation fuel. The method of the third aspect of the present invention may therefore comprise mixing (ii) an aviation fuel base and (ii) citronella oil or a fraction thereof.

[0039] The method of the third aspect of the present invention may comprise a method of making an aviation fuel according to the first or second aspect of the present invention. Therefore, the method of the third aspect of the present invention may comprise one or more features of the aviation fuel of the first or second aspect of the present invention. For example, the aviation fuel base may have one or more of the features of the aviation fuel base described above in relation to the aviation fuel of the first aspect of the present invention.

[0040] The method may optionally comprise mixing at least 0.01 vol%, at least 0.025vol%, at least 0.05vol%, at least 0.1vol%, at least 0.5vol% and at least 1 vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least one component of citronella oil and the aviation fuel base. The applicant anticipates that a minimum amount of the at least one component of citronella oil would be advantageous, given the beneficial properties of citronella oil mentioned above. The at least one component of citronella oil may optionally be provided by citronella oil or a fraction thereof. The method may thereof optionally comprise mixing at least 0.01vol%, at least 0.025vol%, at least 0.05vol%, at least 0.1vol%, at least 0.5vol% and at least 1vol% of citronella oil, or a fraction thereof, with the aviation fuel base, the vol% of the citronella oil, or a fraction thereof, being calculated relative to the total volume of the citronella oil, or a fraction thereof, and the aviation fuel base. The applicant anticipates that a minimum amount of citronella oil, or a fraction thereof, would be advantageous, given the beneficial properties of citronella oil mentioned above. [0041 ] The method may optionally comprise mixing no more than 10vol%, no more than 8vol%, no more than 6vol%, no more than 5vol%, no more than 3vol%, no more than 1vol%, no more than 0.8vol% and no more than 0.5vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least one component of citronella oil and the aviation fuel base. The applicant anticipates that, while citronella oil has advantageous properties, a maximum amount of the at least one component of citronella oil would be preferred, given some of the properties of citronella oil, such as a high viscosity compared to aviation fuel. The at least one component of citronella oil may optionally be provided by citronella oil or a fraction thereof. The method may optionally comprise mixing no more than 10vol%, no more than 8vol%, no more than 6vol%, no more than 5vol%, no more than 3vol%, no more than 1vol%, no more than 0.8vol% and no more than 0.5vol% of citronella oil, or a fraction thereof, with the aviation fuel base, the vol% of the citronella oil, or a fraction thereof, being calculated relative to the total volume of the citronella oil, or a fraction thereof, and the aviation fuel base. The applicant anticipates that, while citronella oil has advantageous properties, a maximum amount of the citronella oil, or a fraction thereof, would be preferred, given some of the properties of citronella oil, such as a high viscosity compared to aviation fuel.

[0042] The method may optionally comprise mixing from 0.025 to 1 vol%, from 0.05 to 0.8 vol% and from 0.1 to 0.5vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least one component of citronella oil and the aviation fuel base. The applicant anticipates that such a range provides an advantageous amount of the at least one component of citronella oil, given its properties. The at least one component of citronella oil may optionally be provided by citronella oil or a fraction thereof. The method may optionally comprise mixing from 0.025 to 1 vol%, from 0.05 to 0.8 vol% and from 0.1 to 0.5vol% of citronella oil, or a fraction thereof, with the aviation fuel base, the vol% of the citronella oil, or fraction thereof, being calculated relative to the total volume of the citronella oil, or fraction thereof, and the aviation fuel base. The applicant anticipates that such a range provides an advantageous amount of the citronella oil, or fraction thereof, given its properties.

[0043] The composition of citronella oil is now discussed. Citronella oil may optionally be extracted from lemongrass plants of the genus Cymbopogon, for example Cymbopogon nardus or Cymbopogon winterianus, optionally by heating the leaves of the lemongrass plant. The composition of the citronella oil depends, to a certain extent, on the particular lemongrass from which the citronella oil is extracted. For example, the citronella oil may be of a Ceylon chemotype or a Java chemotype. Java chemotype typically comprises more citronellal than the Ceylon chemotype.

[0044] The precise composition of the citronella oil depends on many factors, such as the precise nature of the plant from which the citronella oil is extracted, the season, and when the plant is harvested.

[0045] For example, there are two citronella oil chemotypes, Java and Ceylon. Table 1 below shows illustrative amounts in wt% of several key components of citronella oil. Chemotype Wt% citronellal Wt% geraniol Wt% geranyl acetate Wt% citronellol Wt% limonene Wt% methyl isoeugenol Ceylon 5-15 18-20 2 6-8 9-11 7-11 Java 32-45 21-24 3-8 3-8 1-4 0 Table 1 - typical composition of Ceylon and Java citronella oil Those skilled in the art will realise that citronella oil comprises many components other than those listed in Table 1.

[0046] Other compositions of citronella oil are described in Pineiro et al, “Insecticidal activity of citronella grass essential oil on FranklinieIla schultzei and Myzus persicae”, Ciencia e Agrotecnologia, 37(2), 138-144, April 2013; Kanza et al., “Comparison of the separation process of crude citronella oil usingvacuum fractionation distillation on a pilot plant scale and laboratory scale”, 2021, IOP Conf. Ser.: Earth Environ. Sci., 733, 012013; Verma et al., “Qualitative performance of Java citronella (Cymbopogon winterianus Jowitt) cultivars in Kumaon Himalaya”, Journal of Medicinal and Aromatic Plant Sciences, 31 (4), 2009, 321-325 and Hamzah et aL, "Comparison of citronella oil extraction methods from Cymbopogon nardus grass by ohmic-heated hydro-distillation, hydro-distillation, and steam distillation," BioRes. 9(1), 256-272. Fractional distillation may be used to provide a fraction of citronella oil. The composition of the fraction will depend on the fraction selected. For example, as indicated in in N. Fitri et al., “Identification of Citronella Oil Fractions as Efficient Bio-Additive for Diesel Engine Fuel”, Designs, 2022, vol. 6, pg. 15, a first fraction may comprise citronellal, without significant amounts of citronellol or geraniol, while a second fraction comprise citronellol and geraniol, without significant amounts of citronellal.

[0047] The method may comprise storing, conveying and / or mixing the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) in a volume defined by a material resistant to citronella oil, such as a fluorinated material, such as a fluorosilicone or a fluoroelastomer, such as Viton®. The method may comprise mixing the aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) remote from an aircraft. The method may comprise storing the aviation fuel priorto supplyingthe aviation fuel to an aircraft fuel tank, optionally for at least 24 hours.

[0048] The method may comprise mixing the aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) on an aircraft. For example, the method may comprise mixing the aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) upstream of an aircraft engine. The method may comprise mixingthe aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) downstream of an aircraft fuel tank in which the aviation fuel base is stored, and optionally downstream of a receptacle for the storage of the at least one component of citronella oil. The receptacle for the storage of the at least one component of citronella oil may comprise a material resistant to citronella oil, such as those mentioned above. The method may comprise mixingthe aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) in a mixing region. The mixing region may be defined by a material resistant to citronella oil, such as those mentioned above.

[0049] The method may comprise mixing the aviation fuel base with the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) adjacent to an aircraft, immediately prior to, or during, fuelling of an aircraft fuel tank. The method may comprise addingthe at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) to the aviation fuel base upstream of an aircraft fuel tank during fuelling of the aircraft fuel tank. The method may comprise introducing the at least one component of citronella oil (for example, as provided by citronella oil or a fraction thereof) into a flow of aviation fuel base upstream of an aircraft fuel tank to form the aviation fuel, and providing the aircraft fuel tank with the aviation fuel.

[0050] In accordance with a fourth aspect of the present invention, there is provided use of at least one component of citronella oil as an additive in an aviation fuel, optionally a gas turbine fuel.

[0051] The use may be as an emissions-reducing additive, such as a soot-reducing additive, a carbon monoxide-reducing additive, a carbon dioxide-reducing additive, an unburnt hydrocarbon-reducing additive and / or a NOx-reducing additive. Citronella oil burns very cleanly, generating relatively small amounts of soot, NOx, carbon monoxide, carbon dioxide and unburnt hydrocarbon. The at least one component of citronella oil may have one or more of the features described above in relation to the aviation fuels of the first and second aspects of the present invention, or in relation to the method of the third aspect of the present invention. The use of the fourth aspect of the present invention may optionally comprise use of citronella oil, or a fraction thereof, as an additive in an aviation fuel, optionally a gas turbine fuel.

[0052] The use may be as a viscosity-enhancing additive. Citronella oil has a relatively high viscosity compared to aviation fuel.

[0053] In the use of the fourth aspect of the present invention, the aviation fuel may have one or more of the features described above in relation to the aviation fuel of the first or second aspect of the present invention and / or in relation to the method of the third aspect of the present invention.

[0054] In accordance with a fifth aspect of the present invention, there is provided at least one component of citronella oil for use as an aviation fuel additive, optionally for use as a gas turbine fuel additive.

[0055] The at least one component of citronella oil may be for use as an emissions-reducing additive, such as a soot-reducing additive, a carbon monoxide-reducing additive, a carbon dioxide-reducing additive, an unburnt hydrocarbon-reducing additive and / or a NOx-reducing additive. Citronella oil burns very cleanly, generating relatively small amounts of soot, NOx, carbon monoxide, carbon dioxide and unburnt hydrocarbon. The at least one component of citronella oil may have one or more of the features described above in relation to the aviation fuels of the first and second aspects of the present invention, or in relation to the method of the third aspect of the present invention. Optionally, citronella oil, or a fraction thereof, may be for use as an additive in an aviation fuel, optionally a gas turbine fuel.

[0056] The at least one component of citronella oil (and optionally citronella oil, or a fraction thereof) may be for use may be as a viscosity-enhancing additive. Citronella oil has a relatively high viscosity compared to aviation fuel.

[0057] The at least one component of citronella oil may have one or more of the features described above in relation to the aviation fuel of the first or second aspect of the present invention, the method of the third aspect of the present invention and / or the use of the fourth aspect of the present invention.

[0058] In accordance with a sixth aspect of the present invention, there is provided a method of fuelling an aircraft engine (optionally a jet engine), the method comprising providingthe aircraft engine with an aviation fuel comprising at least one component of citronella oil, or a mixture of (i) an aviation fuel base and (ii) citronella oil or a fraction thereof.

[0059] The aviation fuel may comprise one or more of the features described above in relation to the aviation fuel of the first or second aspect of the present invention. The aviation fuel may comprise the aviation fuel of the first or second aspect of the invention. For example, the aviation fuel may comprise an aviation fuel base. The method of fuelling an aircraft engine may comprise the method of the third aspect of the present invention. The method of the third aspect of the present invention may, for example, comprise mixing an aviation fuel base with citronella oil, or a fraction thereof, on an aircraft.

[0060] In the method of the sixth aspect of the present invention, the aircraft engine may be one of two, three or four aircraft engines provided on an aircraft. Optionally, the aircraft engine may be a jet engine, and the jet engine may be one of two, three or four jet engines provided on a jet engine aircraft. The aircraft may be a wide-bodied aircraft or a narrow-bodied aircraft. [0061 ] The aircraft may have a length of at least 25m, optionally at least 30m, optionally at least 35m and optionally at least 40m.

[0062] The aircraft may have a wingspan of at least 25m, optionally at least 30m and optionally at least 35m.

[0063] The aircraft may be a passenger aircraft. The aircraft may have a capacity of at least 60 passengers, optionally at least 80 passengers, optionally at least 100 passengers, optionally at least 120 passengers, optionally at least 140 passengers and optionally at least 160 passengers.

[0064] In accordance with a seventh aspect of the present invention, there is provided an aviation fuel comprising at least one component of citronella oil. The aviation fuel of the seventh aspect of the present invention may comprise an aviation fuel base. The at least one component of citronella oil may be provided by citronella oil or a fraction of citronella oil. The aviation fuel of the seventh aspect of the present invention may comprise one or more features of the aviation fuels of the first or second aspect of the present invention. The at least one component of citronella oil may comprise one or more of the features describe above in relation to the aviation fuel of the first aspect of the present invention. The aviation fuel base may comprise one or more of the features described above in relation to the aviation fuel of the first or second aspect of the present invention. The aviation fuel of the seventh aspect of the present invention may be made in accordance with the method of the third aspect of the present invention, and may be used in the method of the sixth aspect of the present invention.

[0065] It will, of course, be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. DESCRIPTION OF THE DRAWINGS

[0066] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings of which:

[0067] Figure 1 shows the chemical structures of various compounds that are typically found in citronella oil;

[0068] Figure 2 shows a schematic representation of an aircraft comprising a jet engine for use in an example of an embodiment of a method in accordance with the present invention;

[0069] Figure 3 shows a schematic representation of a fuelling arrangement for use in an example of an embodiment of a method in accordance with the present invention; and

[0070] Figure 4 shows a schematic representation of an example of an embodiment of a method in accordance with the present invention. DETAILED DESCRIPTION

[0071] An example of an embodiment of method of making, in accordance with the third aspect of the present invention, an aviation fuel (in this case, a gas turbine fuel) in accordance with the first and second aspects of the present invention will now be described byway of example only. 10 litres of citronella oil is mixed with 1990 litres of Jet A1 aviation fuel to provide a jet fuel comprising 0.5vol% citronella oil and 99.5vol% Jet A1 aviation fuel base. The gas turbine fuel so made can then be delivered to the aircraft. This example also illustrates the use of citronella oil as an additive to gas turbine fuel.

[0072] The citronella oil used is of a Java chemotype, and has the following major components, as previously determined using GC-MS: 24% citronellal, 29% geraniol, 2% geranyl acetate, 17% citronellol, 1 % limonene, 6% terpinene-4-ol acetate, 5% elemol and 3% cadinol. The approximate vol% of each component in the gas turbine fuel is therefore about: 0.12vol% citronellal, 0.15vol% geraniol, 0.01vol% geranyl acetate, 0.085vol% citronellol, 0.005vol% limonene, 0.025vol% elemol and 0.015vol% cadinol. The chemical structure of each of the components is shown in Figure 1. Both stereoisomers of citronellol are shown, whereas only one stereoisomer of each of limonene, elemol and cadinol is shown. Geraniol and geranyl acetate are shown as E-isomers in Figure 1. The composition of the citronella oil used in the above-example was previously determined using GC-MS. Conversely, it is possible to investigate the presence of components of citronella oil in gas turbine fuel using GC-MS, therefore suggesting that the gas turbine fuel is a mixture of a gas turbine fuel base and citronella oil. In this connection, accordingto Babushok at al, the components of citronella oil mention above have retention indices on a slightly polar, 5% phenol on polysiloxane column, such as HP-5MS or DB-5HT, as shown in Table 2. Compound Retention index Citronellal 1153.7 Geraniol 1254.9 Geranyl acetate 1379.9 Citronellol 1228.1 Limonene 1029.5 Terpinene-4-ol acetate 1302.1 Elemol 1547.5 Cadinol 1651.9 Table 2 - Retention indices for components of citronella oil The retention index indicates the time order in which the various components are observed in the gas chromatogram, the higher the retention index, the higher the retention time. The area of the GC peak indicates the amount of compound present in the sample. Mass spectrometry facilitates further identification of compound. Since the gas turbine fuel base comprises various hydrocarbons, GC peaks associated with those hydrocarbons would be observed, the timing positions of those peaks depending on the molecular weight and molecular structure. The area of the GC peaks would indicate the amount of each gas turbine fuel base compound present.

[0073] Citronella oil burns very cleanly, generating relatively small amounts of soot, NOx, carbon monoxide, carbon dioxide and unburnt hydrocarbon. Citronella oil may therefore be used as an emissions-reducing additive, such as a soot-reducing additive, a carbon monoxide-reducing additive, a carbon dioxide-reducing additive, an unburnt hydrocarbon-reducing additive and / or a NOx-reducing additive. Furthermore, citronella oil has a viscosity that is significantly higher than that of aviation fuel, and therefore Citronelle oil may be used as a viscosity-enhancing additive, if increased viscosity is desirable.

[0074] While it is anticipated that that the citronella oil will typically be incorporated into the aviation fuel remote from the aircraft, so that the additive-containing fuel is stored and delivered to the aircraft, this need not be the case, as will now be explained. A further example of an embodiment of a method of making, in accordance with the third aspect of the present invention, an aviation fuel (in this case, a gas turbine fuel) in accordance with the first and second aspects of the present invention will now be described byway of example only with reference to Figure 2. Gas turbine fuel base in the form of Jet A1 aviation fuel is stored in the fuel tank 2 of an aircraft 1. Citronella oil is stored separately in on-board additive tanks 3, 3’. Citronella oil is fed from additive tank 3, 3’ to blending regions 4,4’ where it is blended with Jet A1 aviation fuel on board the aircraft. The blended fuel with the additive added is delivered to engines 5, 6 where it is burned.

[0075] A further example of another embodiment of a method of making, in accordance with the third aspect of the present invention, an aviation fuel (in this case, a gas turbine fuel) in accordance with the first and second aspects of the present invention will now be described byway of example only with reference to Figures 3 and 4. Gas turbine fuel base, in the form of Jet A1 aviation fuel is delivered to the fuel tank 2 of aircraft 1 from fuel bowser 10 via fuel line 11. Citronella oil is introduced into fuel line 11 at introduction point 12 from citronella oil container 13. The gas turbine fuel comprising the citronella oil is then delivered to fuel tank 2. Schematically, referring to Figure 4, the method 100 of making gas turbine fuel comprises introducing 101 the citronella oil into a flow of gas turbine fuel base upstream of an aircraft fuel tank to form the gas turbine fuel, and providing 102 the aircraft fuel tank with the gas turbine fuel.

[0076] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0077] The Examples above describe an aviation fuel made by mixing a gas turbine fuel base with citronella oil. Whilst it is anticipated that this would be a convenient method of producing such a gas turbine fuel, a person skilled in the art could add the key components of citronella oil (for example, citronellal, geraniol, geranyl acetate, citronellol and limonene) as separate components i.e. not as citronella oil.

[0078] The Examples above describe an aviation fuel in the form of a gas turbine fuel. The aviation fuel of the present invention need not be a gas turbine fuel. For example, the aviation fuel may be suitable for other aircraft engines, such as piston engines.

[0079] The Examples above describe an aviation fuel comprising citronella oil. Those skilled in the art will realise that the aviation fuel need not comprise citronella oil per se. The aviation fuel may, for example, comprise at least one component of citronella oil. The at least one component of citronella oil may, for example, be provided as a fraction of citronella oil. For example, as described in N. Fitri et al., “Identification of Citronella Oil Fractions as Efficient Bio-Additive for Diesel Engine Fuel”, Designs, 2022, vol. 6, pg. 15, one such fraction may comprise citronellal, in the absence of citronellol and geraniol. An alternative fraction may comprise citronellol and geraniol, in the absence of citronellal. Alternatively, the at least one component of citronella oil may be provided as an isolated component. For example, commercially-available citronellal may be incorporated into the aviation fuel.

[0080] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. An aviation fuel comprising a mixture of (i) an aviation fuel base and (ii) at least one component of citronella oil.

2. The aviation fuel according to claim 1, comprising at least 0.01 vol% of the at least one component of citronella oil, and optionally at least 0.05vol% of the at least one component of citronella oil.

3. The aviation fuel according to any preceding claim, comprising no more than 10vol% of the at least one component of citronella oil.

4. The aviation fuel according to claim 3, comprising no more than 5vol% of the at least one component of citronella oil.

5. The aviation fuel according to claim 4, comprising no more than 1vol% of the at least one component of citronella oil.

6. The aviation fuel according to claim 1, comprising from 0.025 to 1 vol% of the at least one component of citronella oil.

7. The aviation fuel according to claim 6, comprising from 0.1 to 0.5vol% of the at least one component of citronella oil.

8. An aviation fuel comprising a mixture of (i) an aviation fuel base and (ii) citronella oil, or a fraction thereof.

9. The aviation fuel accordingto any preceding claim, wherein the at least one component of citronella oil comprises at least three, optionally at least four, and optionally each, of citronellal, citronellol, geranyl acetate, geraniol, and limonene.

10. The aviation fuel accordingto any preceding claim comprising one or more of: an antioxidant, an antistatic agent, a corrosion inhibitor, an icing inhibitor, a biocide and a metal deactivator.11 .The aviation fuel accordingto any preceding claim, wherein the aviation fuel is a gas turbine fuel.12.The aviation fuel accordingto any preceding claim, wherein said aviation fuel base is selected from the group consisting of JetA, JetA-1, Jet B, JP8, synthetic aviation fuel and sustainable aviation fuel.

13. A method of making an aviation fuel comprising mixing (i) an aviation fuel base and (ii) at least one component of citronella oil.

14. he method according to claim 13, comprising mixing at least 0.05vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least component of citronella oil and the aviation fuel base.

15. The method accordingto claim 13 or claim 14, comprising mixing no more than 1vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least one component of citronella oil and the aviation fuel base.

16. A method accordingto any of claims 13 to 15, comprising mixing from 0.025 to 1 vol%, optionally from 0.05 to 0.8 vol% and optionally from 0.1 to 0.5vol% of the at least one component of citronella oil with the aviation fuel base, the vol% of the at least one component of citronella oil being calculated relative to the total volume of the at least one component of citronella oil and the aviation fuel base.

17. A method accordingto any of claims 13 to 16, comprising mixing the aviation fuel base and the at least one component of citronella oil on an aircraft, optionally upstream of an aircraft engine.

18. A method accordingto claim 17, comprising mixing the aviation fuel base and the at least one component of citronella oil downstream of an aircraft fuel tank in which the aviation fuel base is stored, and optionally downstream of a receptacle for the storage of the at least one component of citronella oil.

19. The method accordingto any of claims 13 to 16, comprising mixing the aviation fuel base with the at least one component of citronella oil adjacent to an aircraft, immediately prior to, or during, fuelling of an aircraft fuel tank.

20. The method accordingto any of claims 13 to 19, comprising mixing (i) an aviation fuel base with (ii) citronella oil or a fraction thereof.

21. Use of at least one component of citronella oil as an additive in an aviation fuel, optionally as an emissions-reducing additive.

22. Use of citronella oil or a fraction thereof as an additive in an aviation fuel, optionally as an emissions-reducing additive23. At least one component of citronella oil for use as an aviation fuel additive, optionally as an emissions-reducing additive.

24. Citronella oil or a fraction thereof for use as an aviation fuel additive, optionally as an emissions-reducing additive25. A method of fuelling an aircraft engine, the method comprising providing the aircraft engine with (i) an aviation fuel comprising at least one component of citronella oil, or (ii) an aviation fuel comprising a mixture of an aviation fuel base and citronella oil or a fraction thereof.s