WO2014056790A1

WO2014056790A1 - Treatment of fuel

Info

Publication number: WO2014056790A1
Application number: PCT/EP2013/070673
Authority: WO
Inventors: Stian HAUGE; Aage Bjørn ANDERSEN
Original assignee: Innano As
Priority date: 2012-10-08
Filing date: 2013-10-04
Publication date: 2014-04-17
Also published as: GB201309274D0; GB201218005D0; GB2509344A

Abstract

A method for treatment of fuel and/or of a combustion process comprises the use of titanium dioxide nanoparticles, or a precursor thereof, in the fuel or the combustion process in order to treat or modify the fuel or the combustion process. The method includes introducing the titanium dioxide nanoparticles, or precursor thereof, into at least one of the fuel, the fuel and/or the air for the combustion process, a combustion apparatus of the combustion process or combustion emissions of the combustion process.

Description

TREATMENT OF FUEL

The invention relates to the treatment of modification of a fuel or a combustion process to improve the characteristics of the fuel, or the combustion process, or both. The improvement to the combustion process may include treatment of the emissions from the combustion process.

Liquid fuels are vital to transportation. Most liquid fuels in widespread use are derived from fossil fuels, for example petrol, diesel and kerosene. In order to reduce emissions from combustion of fossil fuels, which are often potentially damaging to the environment, it is desirable to reduce fuel consumption. A reduction in fuel consumption also has economic benefits and can hence decrease the cost of transportation. Similar environmental and economic benefits arise for any use of liquid fuels, for example in generators for electrical power.

Combustion processes produce emissions that are often potentially damaging to the environment. The emissions may include gases or liquids that are toxic or poisonous. This is particularly the case when the combustion process involves fossil fuels or fuels with a similar mix of hydrocarbons and the like. Technologies have been developed to manage the emissions of these types of combustion processes. Often a catalytic treatment is used, a well known example of this being the use of a catalytic converter for treatment of vehicle emissions.

Undesirable emissions from combustion processes include pollutants such as carbon monoxide (CO), carbon dioxide (C0₂), unburned hydrocarbons and nitrogen oxides (NO_x). Catalytic treatments use catalysts to stimulate chemical reactions that convert undesirable components of emissions into less toxic chemicals. For example, in a three-way catalytic converter as used in vehicles the exhaust from the engine is treated using oxidative and reducing catalysts to convert carbon monoxide, unburned hydrocarbons and NO_x into carbon dioxide (C0₂), nitrogen (N₂), and water (H₂0). Catalytic treatments are also used to treat sulphur dioxides and to degrade or break down particulate matter and organic compounds in the emissions from combustion processes.

In view of the well-known problems with combustion of fossil fuels (particularly the emission of greenhouse gasses), there is now an increasing reliance on biofuels, i.e. fuels that are derived from biological carbon fixation rather than from fossil fuels. Liquid biofuels include ethanol and biodiesel, for example. Biofuels are often blended with fossil fuels, or can be used as a replacement to fossil fuels altogether.

The International Convention for the Prevention of Pollution From Ships, 1973 as modified by the Protocol of 1978 and later amendments (MARPOL), have established maximum specific emission levels for nitrogen oxides from ships' engines and further established Sulphur Emission Control Areas (SECAs) and Emission Control Areas i.e. areas of the ocean where there are even stricter requirements on emissions of sulphur and nitrogen oxides. Emissions to air from the shipping industry are increasing as a contributor also to greenhouse gases in comparison with other such sources which are more strictly regulated. Over the last decade, the greenhouse gas contribution from the shipping sector has nearby doubled and it now accounts for some 3.3%. It is however predicted that this sector will become a major contributor over the next two decades, emitting in the range of 30% of all greenhouse gases. This scenario will not be accepted and it is expected that the international community will enforce even stricter emission regulations including those of greenhouse gases in the near future. Existing expectations and forecasted future regulative development will result in an increased demand and reliance on alternative fuels including biofuels, which have a smaller carbon footprint than fossil fuels.

Depending on the application, a fuel may need to have certain characteristics, either to enable the combustion process to operate, or to satisfy certain standards (for example, safety standards and environmental standards). Certain characteristics of a fuel can be modified by blending additives with the fuel.

The cloud point of a liquid is the temperature at which dissolved solids are no longer completely soluble. At this temperature, the dissolved solids form a precipitate, giving the liquid a cloudy appearance. In the context of liquid fuels, the cloud point refers to the temperature below which wax in diesel or biowax in biodiesels begins to precipitate out of the solution.

It is generally desirable that the cloud point of a fuel is not too high compared to expected operating temperatures. Otherwise, at cold operating temperatures, the precipitate can cause clogging of fuel filters, injectors or other parts of an engine.

Cloud point can be tested in accordance with ISO 3015: Petroleum products - Determination of cloud point.

The flash point of a fuel is the lowest temperature at which it can vaporize to form an ignitable mixture in air; that is, it is the temperature at which the vapours of the fuel ignite when a test flame is applied. The flash point of a fuel can be determined in accordance with ISO 2719-A.

Flash points vary depending on the specific fuel. So, for example, the flash point of petrol is typically around 43 °C, whereas the flash point of diesel varies between 52 and 96 °C. The flash point of biodiesel is greater than 130 °C.

The flash point of a fuel is relevant when considering whether the fuel can be used in a spark-ignition or compression-ignition engine. In a spark-ignition engine, the fuel is mixed with air, heated above its flash point, and then ignited by the spark plug. Petrol is suitable for use in a spark-ignition engine, because it has a low flash point.

In a compression-ignition engine, there is no ignition source. Instead, air is compressed until it has been heated above the auto-ignition temperature (the lowest temperature at which a fuel will spontaneously ignite without an external source of ignition). Once the air is heated above the auto-ignition temperature of the fuel, the fuel is injected as a high-pressure spray, and ignites. Diesel is suitable for use in a compression-ignition engine, as it has a high flash point but a low auto-ignition temperature.

The viscosity of a fuel, particularly diesel fuels which can be quite viscous, must be maintained carefully within the design range for a particular engine because the viscosity of a fuel has a significant effect on combustion quality. A high viscosity fuel leads to improper atomisation in the fuel injectors, which in turn leads to incomplete combustion.

Fuel emulsions are fuel mixtures typically comprising water and a base fuel, most commonly a diesel type fuel. Fuel emulsions can be either a micro-emulsion or a macro- emulsion, differing in terms of the particle size (water droplet size) in the emulsion. Micro- emulsions generally have particle dimensions of 10 to 100 nm, whereas macro-emulsions have particle dimensions of from 100 nm to over 1 μιη. It is also possible to use an alternative to water in the fuel emulsion.

Emulsions suffer from reduced energy density, i.e. if 10% water is introduced, the energy efficiency of the fuel is reduced volumetrically. Therefore, fuel emulsions have a practical limitation with regard to the amount of water introduced. Emulsions can also suffer from instability. In particular, macro-emulsions are prone to settling and change its particle size distribution over time. Micro-emulsions have an improved shelf life compared to macro- emulsions. The downside is the level of energy that producing a micro-emulsion requires.

The water can be mixed in the fuel at location (so shelf life is less important). The water for a fuel emulsion may also be introduced via the combustion air at the point of combustion.

The main advantages to using fuel emulsions instead of the fuel itself are environmental and economic benefits. Addition of water to the diesel process generally decreases combustion peaking temperatures and consequently reduces amount of NO_x and particulate matter emissions generated.

It will be appreciated that engine designers will design engines with a particular fuel in mind, and that fuel will need to have certain characteristics. In the case that a biofuel is used in place of the fossil fuel for which the engine was designed, the biofuel will need to exhibit those same characteristics that the engine was designed for. Therefore, a treatment that modifies the characteristics of a fuel is highly desirable.

Apart from engineering requirements, other requirements for fuels are imposed by environmental or safety concerns. ISO 8217:2005 lists the various properties for marine fuels, for example. As one example, the minimum requirement to flash point of fuels to be used in bulk aboard marine vessels is 60 °C.

According to a first aspect of the present invention, there is provided a method comprising the use of titanium dioxide nanoparticles, or a precursor thereof, in a fuel or a combustion process in order to treat or modify the fuel or the combustion process, the method including introducing the titanium dioxide nanoparticles, or precursor thereof, into at least one of the fuel, the fuel and/or the air for the combustion process, a combustion apparatus of the combustion process or combustion emissions of the combustion process.

In a preferred embodiment, the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of modifying one or more of the following properties of the fuel: cloud point or flash point. Alternatively or additionally, the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of modifying the fuel consumption rate. Surprisingly, the inventors have established that titanium dioxide nanoparticles or precursor thereof can be added to fuels to achieve these advantageous effects. Beneficial changes in one or more of these parameters can be obtained with diesel fuel and marine gas oil (MGO) as described in further detail in the Examples and similar effects will occur in other fuels including petrol, kerosene as well as heavy fuel grades.

The titanium dioxide nanoparticles or precursor thereof may be provided for the purpose of reducing the viscosity of the fuel.

Changing the viscosity of a fuel may be useful for a number of reasons. Firstly, viscosity must be maintained carefully within the design range for a particular engine because the viscosity of a fuel has a significant effect on combustion quality. Reducing the viscosity to lie within the design range for a particular engine may allow the engine to operate more efficiently, thereby reducing fuel consumption.

Secondly, heavy fuels (i.e. long-chain hydrocarbons) may require heating to achieve a desired viscosity. When viscosity can be reduced using a fuel additive, the preheating requirement may be reduced. This results in a major saving of energy, particularly in shipping, for example.

Alternatively or in addition, the titanium dioxide nanoparticles or precursor thereof may be provided for the purpose of reducing fuel consumption. Reducing fuel consumption is advantageous to reduce the amount of fuel that must be carried (for example, aboard a marine vessel), and also to reduce the combustion emissions resulting from the combustion process.

The titanium dioxide nanoparticles or precursor thereof may be provided for the purpose of reducing the cloud point of the fuel, additionally or alternatively to the above-mentioned purposes. It is generally desirable that the cloud point of a fuel is not too high compared with operating temperatures otherwise the fuel filters, injectors or other parts of an engine can become clogged. Decreasing the cloud point of the fuel may therefore be desirable.

The titanium dioxide nanoparticles or precursor thereof may be provided for the purpose of increasing the flash point of the fuel, additionally or alternatively to the above-mentioned purposes. The flash point of a fuel is generally required, for safety reasons, to be above a certain temperature, depending on the application. For example, the flash point of fuels to be used in bulk aboard marine vessels is a minimum of 60 °C. Increasing the flash point of the fuel is therefore desirable, particularly if the flash point of the unmodified fuel is just below the threshold, but can be increased over the threshold by the provision of titanium dioxide nanoparticles, or precursor thereof. This allows for a broader range of fuels to be used.

Regardless of the threshold values set in international standards, it is in any case

advantageous to increase the flash point of the fuel, so that the fuel is safer.

The advantages discussed above may be obtained by direct modification of the fuel by introducing the titanium dioxide nanoparticles or precursor thereof to the fuel, for example by mixing in a carrier liquid or in powder form as discussed below. Alternatively the fuel properties may be modified indirectly by introducing the titanium dioxide nanoparticles or precursor thereof into the combustion air, which is then mixed with the fuel in a combustion process, or by separate introduction of the titanium dioxide nanoparticles or precursor thereof into a combustion apparatus, for example by injection into a combustion chamber.

The fuel may be a fuel emulsion. When a fuel emulsion is used, the titanium dioxide nanoparticles may be introduced via mixing with the emulsion or alternatively by mixing with the fuel or water before the emulsion is generated. In one embodiment, the titanium dioxide nanoparticles may be provided mixed with water in the combustion air, the air/water/titanium dioxide mixture being provided at the point of combustion to mix with fuel to form a fuel emulsion.

The fuel may be a biofuel. The titanium dioxide nanoparticles or precursor thereof may hence be provided in a biofuel, or in a biofuel or combustion air for a combustion process, or in the exhaust from a combustion process in which a biofuel is combusted. The biofuel may be a biofuel emulsion.

It is also possible for the fuel to be a mixture of biofuel and fossil fuel. In some fuels of this type the mixture may be an emulsion.

The titanium dioxide nanoparticles or precursor thereof may be provided in fuel for use on a marine vehicle.

In a preferred embodiment, the titanium dioxide nanoparticles comprise or consist of photocatalytic titanium dioxide semiconductor material having a band gap suitable for absorption of UV and/or visible light, and the method comprises treatment of combustion emissions of the combustion process by providing titanium dioxide nanoparticles or a precursor thereof in the fuel or the air for the combustion process or in the exhaust from the combustion process, such that when the combustion emissions are released into the environment the photocatalyst nanoparticles are carried with the emissions and result in a catalytic reaction that reduces the amount of pollutants in the emissions. This method results in a photocatalysed reaction that occurs after combustion emissions are released to the atmosphere. In the preferred embodiments titanium dioxide nanoparticles are carried with and mixed with the combustion emissions. They hence come into contact with gases, liquids and particles in the emissions and stimulate reactions that decompose toxic and/or undesirable compounds. The photocatalytic reactions are generated by light in the environment and in particular are enhanced by sunlight. The pollutants treated by the photocatalyst may include NO_x, sulphur dioxide, particle matter, uncombusted hydrocarbons and other organic compounds.

Preferably the photocatalyst comprises the semiconductor nanoparticles as a major constituent thereof, for example as at least 70% of the photocatalyst, preferably at least 90%. The photocatalyst or precursor may be introduced as a mixture with a carrier, for example it may be dispersed in a liquid as discussed below. When the photocatalyst is introduced by addition of a precursor of the photocatalyst then the precursor may comprise an organometallic solute that decomposes to photocatalyst nanoparticles when exposed to the combustion process or in the exhaust. Possible precursors include titanium tetracarboxylates or titanium tetrachloride.

Light activated catalytic treatment of undesirable components of combustion emissions has been explored in the past, but not in the context of a titanium dioxide nanoparticle additive that promotes a catalysed reaction after the emissions are released into the environment. The use of a nano-sized additive in this way generates significant advantages in the effectiveness of the treatment. The photocatalyst or precursor can be evenly dispersed throughout the fuel or air prior to combustion or in the exhaust after combustion and hence the photocatalyst is evenly distributed in the emissions resulting in treatment of all combustion products. The treatment effect continues for a long period after the emissions are released into the atmosphere.

Moreover, the treatment effect will occur not only with the emissions from combustion of the fuel, but also with other emissions that the nanoparticles come into contact with in the environment. Hence, even if not all vehicles on a road are using the titanium dioxide doped fuel the general air quality around the road will be improved by treatment of all vehicle emissions by the photocatalytic titanium dioxide particles from just a proportion of the total number vehicles. Similarly, treatment of factory emissions or other pollutants will occur in regions where the photocatalysts are introduced into the environment by the current method, even if the emissions do not themselves result from combustion of a fuel that is modified in the claimed manner.

The nanoparticulate photocatalyst treatment may be a stand-alone treatment for the emissions but it may also be used in addition to other treatments, for example to augment the action of a catalytic converter in order to ensure that any pollutants remaining in combustion emissions released to the atmosphere continue to be degraded and broken down. Further fuel conditioning processes may also be included in combination with the nanoparticulate photocatalyst treatment, for example the injection of water. Advantageously the nanoparticles can be mixed with water which is then injected into the combustion chamber.

The method of the first aspect has advantages for any combustion process/combustion apparatus, including, for example, internal combustion and external combustion engines, heating devices, gas flares and similar waste/safety combustion processes, and so on. There are particular benefits in relation to vehicle engines, where emissions are a significant concern for consumers. This will include engines for land vehicles, but also marine engines and aviation engines, including jet engines, gas turbines and rockets. The nanoparticles can pass through a combustion apparatus of this type without adversely affecting the combustion process.

The titanium dioxide nanoparticles or precursor may be introduced into the fuel or the combustion air prior to combustion. Typically the fuel will be a hydrocarbon fuel product. The fuel product may be a gas or a liquid, or a liquefied gas, for example LPG.

Titanium dioxide has well established effectiveness as a photocatalyst and is widely available in various forms. Also, it can be readily produced in nano-sized particles, for example by hydrothermal synthesis of anatase to produce delaminated anatase inorganic nanotubes and titanate nanoribbons. The titanium dioxide preferably has a band gap corresponding to UVA and visible light. The band gap may for example be 2-3 eV.

The titanium dioxide may comprise nanodimensional particles with any shape but preferably other than long fibres. The maximum length may be 200 nm, more preferably 100 nm. It is preferred to avoid long fibres due to the similarity to asbestos fibres, which may give rise to potentially the same risks as asbestos fibres. The nano-dimensional particles may have a thickness or diameter of 1 to 100 nm, more preferably 1 to 30 nm. Nanoparticles with a mixture of sizes may be used. The titanium dioxide nanoparticles may be produced by precipitation into solid state from gaseous or liquid precursors and dispersed in the fuel, or produced in the exhaust, during combustion or upon exposure to the environment from precursors dissolved in the fuel.

The titanium dioxide nanoparticles may preferably be doped, or treated to change the structure or size of the nano particles in order that they cover a broad range of energies absorbable from sunlight.

The titanium dioxide nanoparticles or precursor may be introduced into the combustion emissions after combustion. This means that the titanium dioxide nanoparticles or precursor can be added in a controlled manner without the need for any adaptation or modification to the combustion apparatus or fuel delivery systems. Instead, it is only necessary to adapt the combustion process to allow for introduction of the titanium dioxide nanoparticles or precursor into the exhaust gas.

In preferred embodiments, the titanium dioxide nanoparticles or precursor is introduced into the fuel or air prior to combustion. The properties of the fuel are improved during combustion as discussed above. Passage of the titanium dioxide nanoparticles or precursor through the combustion process promotes effective dispersal of the nanoparticles throughout the combustion emissions. In this case, the titanium dioxide nanoparticles or precursor is introduced into the fuel or air before it reaches a combustion apparatus. For example, it may be added to the fuel by the manufacturer or vendor at the point of manufacture or at the point of sale. Alternatively, it may be added by consumer, for example by mixing an additive into a fuel tank. This has the advantage that the combustion apparatus needs no modification to permit the use of the titanium dioxide nanoparticles and to obtain the benefits of the emissions treatment. Any conventional engine will be able to make use of a fuel augmented by the titanium dioxide nanoparticles treatment described herein.

The method may include introducing the titanium dioxide nanoparticles or precursor by injection into a fuel delivery system of the combustion apparatus, an engine for example, or by direct injection into a combustion chamber. When the titanium dioxide nanoparticles or precursor is introduced in the combustion apparatus then the combustion apparatus may control the amount of titanium dioxide nanoparticles or precursor based on characteristics of the combustion process. In some cases it may not be appropriate for the ratio of titanium dioxide nanoparticles or precursor to the volume of hydrocarbon product to be constant, as would be the case if the titanium dioxide nanoparticles or precursor was mixed with the hydrocarbon product outside of the combustion apparatus. When the combustion apparatus introduces the titanium dioxide nanoparticles or precursor then this ratio can advantageously be controlled based on characteristics of the combustion process, for example based on engine speed and/or based on measurements of properties of the combustion emissions.

Advantageously, when the titanium dioxide nanoparticles or precursor is added to the fuel or combustion air then the mechanism for treatment of the fuel, the combustion process, and/or the emissions is carried through the combustion process and exits already well distributed within and mixed with the emissions. This means that it is possible to effectively treat the emissions for combustion processes where the exhaust is not contained, for example in jet engines or rockets. Moreover, it means that there can be fewer design constraints for an exhaust system of an engine or the like. An emissions treatment system, which may restrict flow of exhaust, need not be built into the exhaust system since the treatment can occur after the combustion emissions exit the combustion apparatus.

An additional advantage of including the titanium dioxide nanoparticles or precursor additive in the fuel itself, i.e. when the additive is mixed with the fuel before it is passed to the combustion device, is that in the event that the fuel is spilled or otherwise inadvertently released into the environment then the photocatalytic process can act to break down and disperse the hydrocarbons, assuming that the precursor does not rely solely on the combustion process to decompose it to the photocatalytic titanium dioxide nanoparticles . Thus, for example, if there was a fuel spill on land or water and the fuel included a photocatalyst as described herein then the exposure of the fuel to the air and to sunlight would result in catalysed and accelerated continuous degradation and dispersion of fuel.

The titanium dioxide nanoparticles or precursor may be introduced as a powder or as a suspension in a liquid, for example in water. For example, a powder or liquid suspension may be dispersed into the fuel by the manufacturer or vendor of the fuel. It may be most convenient to supply the nanoparticles or precursor as a suspension in a liquid that is then mixed with the fuel.

In one preferred embodiment the titanium dioxide nanoparticles or precursor is mixed with water and the water with dispersed nanoparticles is mixed with the fuel, introduced into the emissions after combustion or the air prior to combustion (for example via an atomised spray) or injected into the combustion chamber and hence mixed with the combustion air and fuel prior to ignition. It is known to inject water into the combustion chamber of internal combustion engines in order to cool the combustion chamber. For a compression engine this enables greater compression ratios and better detonation characteristics. The power output and efficiency of the engine can be increased and NO_x and carbon monoxide emissions reduced. Thus, combining the introduction of the titanium dioxide nanoparticles with water injection provides a way to enhance performance whilst also enhancing treatment of the emissions. Moreover, existing engines already adapted for water injection could easily be augmented with the titanium dioxide nanoparticles simply by adding them to the water supply.

Example fuels include gasoline, bunker fuels, diesel fuel, fuel oils, jet fuel, kerosene, biofuels, and other similar products used as fuels for combustion processes.

Advantageously, when titanium dioxide acting as a photocatalyst is added to fuel, then exposure to ultraviolet (UV) and/or visible light will generate oxidising agents acting as a biocide that may prevent bacterial growth or may kill bacteria in the fuel. This is a particularly advantageous for biofuels, which are vulnerable to bacterial growth. Hence, titanium dioxide may be added to fuels, most advantageously to biofuels, for the purpose of allowing treatment by UV and/or visible light to kill bacteria. A preferred embodiment is a method of treatment of a fuel including the step of exposing the fuel to UV and or visible light.

According to a second aspect of the present invention, there is provided an additive for a fuel, for the fuel or combustion air for a combustion process, or for the exhaust from the combustion process, the additive including titanium dioxide nanoparticles or a precursor thereof.

In a preferred embodiment, the titanium dioxide nanoparticles or a precursor thereof modify the cloud point or flash point of the fuel. Alternatively or additionally, the titanium dioxide nanoparticles or precursor thereof modify the fuel consumption rate. The additive may have the effects discussed above and in preferred embodiments the additive has features as discussed above in relation to the method of the first aspect.

Preferably, the titanium dioxide nanoparticles comprise or consist of a photocatalytic titanium dioxide semiconductor material having a band gap suitable for absorption of UV and/or visible light or a precursor of the photocatalyst, such that when emissions from a combustion process with the additive are released into the environment the titanium dioxide photocatalyst nanoparticles result in a catalytic reaction that reduces the amount of pollutants in the emissions.

In a preferred embodiment the additive is a fuel additive. Alternatively it may be an additive intended for introduction to the combustion process via the combustion air or into the exhaust. Advantageously, when the additive comprises the titanium dioxide nanoparticles itself, or when the precursor decomposes to the titanium dioxide nanoparticles upon exposure to the atmosphere then a similar treatment effect will be obtained in the event of a spill of a fuel with the additive. Thus the spilled fuel will be broken down by the action of the titanium dioxide nanoparticle photocatalyst when the fuel is exposed to the environment and the photocatalytic effect occurs.

The titanium dioxide nanoparticles may have characteristics as discussed above.

The additive may comprise the nanoparticles in a powder form or as a suspension in a liquid. One preferred embodiment comprises the nanoparticles as a suspension in a liquid, which may be water as discussed above.

The additive may comprise a precursor of the titanium dioxide nanoparticles, for example, an organometallic solute that decomposes to titanium dioxide nanoparticleswhen exposed to the combustion process, as discussed above.

In a third aspect the invention provides a fuel comprising the additive described above. The fuel may be as discussed above. In preferred embodiments the fuel and fuel additive are mixed before being passed to the combustion apparatus, for example they may be arranged to be supplied pre-mixed to a fuel tank of a vehicle. The invention extends to a container filled with the fuel and additive mixture. In this context the term container should be understood to exclude parts of a combustion apparatus, for example excluding the combustion chamber and so on.

Viewed from a fourth aspect, the invention provides a method comprising use of a photocatalyst or precursor thereof as an additive for a combustion process in order to treat emissions of the combustion process, the photocatalyst comprising nanoparticles of a semiconductor material having a band gap suitable for absorption of UV and/or visible light, such that when emissions from the combustion process are released into the environment the photocatalyst nanoparticles are carried with the emissions and result in a catalytic reaction that reduces the amount of pollutants in the emissions. The inventors have realised that irrespective of the type of photocatalyst used it is advantageous to use a photocatalyst to reduce combustion emissions and this new use of photocatalytic nanoparticles is not known in the prior art. The photocatalyst preferably comprises titanium dioxide and may be as discussed above in connection with the first aspect of the invention. The nanoparticles may have characteristics as discussed above. The method may comprise introduction of the photocatalyst or precursor as described above in connection with the first aspect and preferred features thereof. In a preferred embodiment the

photocatalyst is used as an additive for fuel, preferably an additive introduced into the fuel prior to the combustion process.

Certain preferred embodiments will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows the results of a NO_x flow test comparing levels in emissions for untreated diesel and diesel with a nanoparticle additive in accordance with a first example where the emissions were not exposed to the environment;

Figure 2 shows the results of a NO flow test for the first example;

Figure 3 shows the results of a N0₂ flow test for the first example;

Figure 4 shows the results of a C0₂ flow test for the first example;

Figure 5 shows the results of a NO_x flow test comparing levels in emissions for untreated diesel and diesel with a nanoparticle additive in accordance with a second example where the emissions were exposed to UV light simulating exposure to the environment;

Figure 6 shows the results of a NO flow test for the second example; and

Figure 7 shows the results of a N0₂ flow test for the first example.

Preferred embodiments of the invention involve introducing a photocatalytic nano-sized additive, which can be added before, during or after a process of combustion, to catalyse decomposition processes after combustion. Nanoparticles of the photocatalyst remain in the emissions from the combustion process and when they are released to the atmosphere then the photocatalyst is activated. Advantages include the reduction of NO_x, S0₂ and particle matter emission to and in the air by stimulation of reduction and oxidation reactions, which are promoted via the photocatalyst when the combustion emissions are exposed to sunlight and to air. Furthermore, by the use of titanium dioxide nanoparticles it is possible to achieve advantageous modifications of the fuel or of the combustion process.

The principle of operation relies on photo-induced generation of valence band holes and conduction band electrons in a semiconductor which has a suitable band gap for absorption of UV and visible light. The holes oxidize water molecules in air to hydroxyl radicals and peroxide ions. The electrons reduce oxygen dissolved in the water or the air to the same hydroxyl radicals and peroxide ions. The hydroxyl radicals and peroxide ions are strong oxidizing agents and will reduce the amount of environmentally harmful compounds after combustion and help the degeneration of fuel in the event of a spill. The oxidants are short-lived and act most efficiently close to the photocatalyst surface.

The photocatalyst can be nanoparticles of titanium dioxide, in the crystalline forms of rutile and/or anatase. The nanoparticles may be produced by solvothermal or hydrothermal syntesis or anodization in an electrolytic solution

The activity of the photocatalyst may be enhanced by providing active sites for the reduction by electrons, namely metallic or other electron conducting phases deposited as nanoparticles.

The following examples illustrate the use of the titanium nanoparticles in diesel fuel. It will of course be understood that the invention in its broad form is not limited to the specific features of the examples and in particular that alternative fuels can be used along with alternative forms and amounts of the nanoparticles.

EXAMPLE 1

In a first example a nano modified fuel was made by dispersing titanium dioxide nano powder - P-25 directly in to diesel fuel. Nano particles were perfectly evenly distributed in the fuel, with a size distribution equal to the P-25 nano powder, and with a concentration of 100ppm. The nano modified fuel was combusted and the emissions measured by a Testo 350 Maritime emission sensor. A diesel water pump was used for combustion. Nano modified fuel was added directly in the fuel tank and engine conditions were stabilized by applying a fixed load, which could be controlled by a valve mounted in the water pump flow stream. The measurements lasted for 120 minutes, and the measuring probe was placed in a container, which formed a part of the exhaust gas system. The container had a volume of 250 L and due to this it took some time before the system stabilized. Light was not permitted into the container.

The results of this test are shown in Figure 1 to 4, which illustrate the levels of NO_x, NO, N0₂ and C0₂ respectively for the exhaust emissions from the diesel water pump. The C0₂ level was measured as a percentage and the other measurements use parts per million (ppm). The horizontal axis shows the test time, in seconds. In each case the results for the test with nanoparticles added to the fuel are shown along with the results of the same test carried out with standard, untreated diesel fuel. As noted above, since the container had a volume of 250 L it takes time before the system stabilises, as shown by the steady rise in pollutant content from 0 seconds up to about 800 seconds. After this time the system is stable.

It can clearly be seen that the addition of the titanium dioxide nanoparticles results in a reduction in pollutants from the very start of the test compared to the pollutants in the emissions from the untreated diesel. This is thought to be as a consequence of the viscosity reduction discussed above, although other factors may also be contributing, such as non-photolytic catalytic effects.

It will also be see that the ongoing difference in pollutants between the untreated and treated fuels does not change significantly relative to the overall amount of pollutants. This shows that when the emissions are stored without light, then no significant further treatment effect occurs.

EXAMPLE 2

In a second example a nano modified fuel was made by dispersing titanium dioxide nano powder - P-25 directly in to diesel fuel. Nano particles were perfectly distributed in the fuel, with a size distribution equal to the P-25 nano powder, and with a concentration of

100ppm. The nano modified fuel was combusted and the emissions measured by a Testo 350 Maritime emission sensor. A diesel water pump used for combustion. Nano modified fuel was added directly in the fuel tank and engine conditions was stabilized by applying a fixed load, which could be controlled by a valve mounted in the water pump flow stream. The

measurement lasted for 120 minutes, and the measuring probe was placed in a box, which was part of the exhaust system. This method results in a photocatalysed reaction that occurs after combustion emissions are released to the atmosphere in this case a closed system with a volume of 250L. The nanoparticles are carried with and mixed with the combustion emissions. They hence come into contact with gases, liquids and particles in the emissions and stimulate reactions that decompose toxic and/or undesirable compounds. The photocatalytic reactions are enhanced by sunlight and were simulated by artificial UV-light with a specific energy level of 360 nm.

The results of Example 2 are shown in Figures 5 to 7, which illustrate the levels of NO_x, NO and N0₂ respectively for the exhaust emissions from the diesel water pump. The measurements are in parts per million (ppm) with the horizontal axis showing the test time, in minutes. Once again the results for the nanoparticle augmented fuel are shown along with the results of the same test carried out with standard, untreated diesel fuel. For this test, the stabilisation period is not evident since the full two hour test is shown along the horizontal axis.

As with Example 1 the addition of the titanium dioxide nanoparticles results in a reduction in pollutants from the very start of the test compared to the pollutants in the emissions from the untreated diesel. Moreover, the exposure to UV light can be seen to further reduce the content of the pollutants as time passes.

EXAMPLE 3

In a third example a nanoparticle-modified fuel was made by dispersing titanium dioxide nanoparticles (Product number 718467-100G, produced by Sigma-Aldrich Company Ltd) with an average particle size of 21 nm in to diesel fuel. 12g of nanoparticles were mixed with 150 L of diesel fuel (produced by Shell). The nanoparticle-modified fuel was combusted in a Scania

DC1 1 diesel engine with the following characteristics:

Manufacturer: SCANIA

Model: DC1 102

Number of cylinders: 6

Stroke: 140 mm

Bore: 127 mm

Displacement: 10.7 dm³

Rated torque: 1750 Nm @ 1080-1500 rpm

Rated power: 280 kW @ 1800 rpm

The engine was run in accordance with a test cycle according to ISO 8178 test cycle

D2. The following load points were run during the tests: 1500 rpm/ 10% torque, 1500 rpm/ 25% torque, 1500 rpm/ 50% torque, 1500 rpm/ 75% torque, 1500 rpm/ 83% torque.

The same test procedure was also carried out on diesel fuel without any nanoparticle additive, and the results were compared. Table 1 shows the percentage reduction in fuel consumption in the modified fuel (with the nanoparticle additive) compared to unmodified fuel.

The reduction in fuel consumption is particularly pronounced at low loads. It is speculated that a possible mechanism for the reduction in fuel consumption could be a reduction of the friction losses between the piston rings and cylinder wall in the modified fuel.

Table 1

EXAMPLE 4

Two different fuels were modified by including titanium dioxide nanoparticles (Product number 718467-1 OOG, produced by Sigma-Aldrich Company Ltd) with an average particle size of 21 nm. The nanoparticles were added in a ratio of 0.08 g per litre of fuel. A number of tests were run to determine characteristics of the nanoparticle-modified fuel. For comparison, the same tests were carried out on unmodified fuel (i.e. fuel without the nanoparticles). The flash point of the fuels was determined following the test procedure of ISO 2719-A. The cloud point of the fuels was measured in accordance with the test procedure of ISO 3015. The results are shown in Table 2.

As will be seen, the introduction of nanoparticles resulted in an increase of between 4 % and 6 % in the flash point of the fuel. The cloud point of the nanoparticle-modified fuel was also reduced, but the exact cloud point could not be determined by the test equipment. .

Table 2

Claims

CLAIMS:

1. A method comprising the use of titanium dioxide nanoparticles, or a precursor thereof, in a fuel or a combustion process in order to treat or modify the fuel or the combustion process, the method including introducing the titanium dioxide nanoparticles, or precursor thereof, into at least one of the fuel, the fuel and/or the air for the combustion process, a combustion apparatus of the combustion process or combustion emissions of the combustion process.

2. The method as claimed in claim 1 , wherein the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of modifying one or more of the following properties of the fuel: cloud point; or flash point; and/or for modifying the fuel consumption rate.

3. The method as claimed in claim 2, wherein the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of reducing fuel consumption.

4. The method as claimed in claim 2 or 3, wherein the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of reducing the cloud point of the fuel.

5. The method as claimed in claim 2, 3 or 4, wherein the titanium dioxide nanoparticles or precursor thereof are provided for the purpose of increasing the flash point of the fuel.

6. A method according to any preceding claim, wherein the titanium dioxide nanoparticles comprise or consist of photocatalytic titanium dioxide semiconductor material having a band gap suitable for absorption of UV and/or visible light, and the method comprises treatment of combustion emissions of the combustion process by providing titanium dioxide nanoparticles or a precursor thereof in the fuel or the air for the combustion process or in the exhaust from the combustion process, such that when the combustion emissions are released into the environment the photocatalyst nanoparticles are carried with the emissions and result in a photocatalytic reaction that reduces the amount of pollutants in the emissions.

7. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is introduced into the fuel as a mixture with a carrier.

8. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is introduced into the air for the combustion process, for example by atomisation of a carrier liquid containing the nanoparticles.

9. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is injected into a combustion chamber of the combustion process.

10. A method as claimed in any preceding claim, wherein the titanium dioxide are introduced by addition of a precursor and the precursor comprises an organometallic solute that decomposes to photocatalyst nanoparticles when exposed to the combustion process or in the exhaust.

1 1. A method as claimed in any preceding claim, wherein the nanoparticles have a thickness or diameter of 1 to 100 nm

12. A method as claimed in any preceding claim, wherein the nanoparticles have a thickness or diameter of optionally 1 to 30 nm.

13. A method as claimed in any preceding claim, wherein the nanoparticles have a maximum dimension of 200 nm.

14. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is introduced into the fuel before it reaches the combustion apparatus.

15. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is added to the fuel by the manufacturer or vendor at the point of manufacture or at the point of sale.

16. A method as claimed in any preceding claim, wherein the titanium dioxide or precursor is added by consumer, for example by mixing an additive into a fuel tank.

17. A method as claimed in any preceding claim, wherein the fuel comprises one of gasoline, bunker oil, diesel fuel, fuel oil, jet fuel, kerosene or biofuel.

18. A method as claimed in any preceding claim, wherein the fuel is biofuel.

19. A method as claimed in any preceding claim, wherein the fuel is a fuel or a biofuel emulsion.

20. A method as claimed in any preceding claim, wherein the fuel is for use on a marine vehicle.

21. An additive for a fuel, for the fuel and/or combustion air for a combustion process, or for the exhaust from the combustion process, the additive including titanium dioxide nanoparticles or a precursor thereof.

22. An additive according to claim 21 , wherein the titanium dioxide nanoparticles or precursor thereof modify one or more of the following properties of the fuel: cloud point or flash point; and/or modify the fuel consumption rate.

23. An additive as claimed in claim 21 or 22, wherein the titanium dioxide nanoparticles comprise or consist of a photocatalytic titanium dioxide semiconductor material having a band gap suitable for absorption of UV and/or visible light or a precursor of the photocatalyst, such that when emissions from a combustion process with the additive are released into the environment the titanium dioxide photocatalyst nanoparticles result in a catalytic reaction that reduces the amount of pollutants in the emissions..

24. An additive as claimed in claim 21 , 22 or 23, wherein the additive is a fuel additive

25. A fuel comprising an additive as claimed in claim 24.

26. The fuel of claim 25 stored in a container.

27. A method comprising use of a photocatalyst or precursor thereof as an additive for a combustion process in order to treat emissions of the combustion process, the photocatalyst comprising nanoparticles of a semiconductor material having a band gap suitable for absorption of UV and/or visible light, such that when emissions from the combustion process are released into the environment the photocatalyst nanoparticles are carried with the emissions and result in a catalytic reaction that reduces the amount of pollutants in the emissions.

28. A method as in claim 27 wherein the photocatalyst comprises titanium dioxide.

29. A method as claimed in claim 27 or 28 wherein the photocatalyst or precursor is used as an additive for a combustion process.

30. A method as claimed in claim 29, wherein the photocatalyst or precursor is introduced into the fuel or combustion air prior to the combustion process.

31. A method of use of titanium dioxide nanoparticles, or a precursor thereof, substantially as hereinbefore described.

32. An additive for a fuel, for the fuel and/or combustion air for a combustion process, or for the exhaust from the combustion process, or a fuel comprising an additive for a combustion process substantially as hereinbefore described.