WO2006095219A1

WO2006095219A1 - Vegetable oil based fuel

Info

Publication number: WO2006095219A1
Application number: PCT/IB2005/003653
Authority: WO
Inventors: Miguel Verhein
Original assignee: Revego Ltd
Priority date: 2005-03-11
Filing date: 2005-12-02
Publication date: 2006-09-14

Abstract

The present invention relates to a fuel for a diesel engine, comprising more than 60 % by weight of a vegetable oil and 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound, a method for producing a vegetable based fuel, use of a vegetable based fuel in a diesel engine, a method for operating a diesel engine using a vegetable based fuel, and a fuel system for providing a diesel engine with a vegetable based fuel.

Description

VEGETABLE OIL BASED FUEL

Field of the invention

Background Diesel fuel is a refined petroleum product used to power a large part of the modes of transportation in use today. At the current rate of consumption of petroleum derived products, the world's reserves of non renewable fossil fuels will be exhausted within a not distant future.

In addition to the apparent problem of the world' s natural resources being limited, there is also the risk of more acute shortages and price increases due to different circumstances, such as natural disasters or war.

The use of fossil fuels also carries the inherent environmental problems associated therewith, such as a net addition in carbon dioxide contributing to global warming. Diesel fuel also produces relatively high amounts of particulate matter and toxic by-products upon combustion, e.g. SO₂.

For the above reasons, the search for alternative, more environmentally friendly fuels with the capacity to replace petroleum derived fuels in certain applications has intensified in recent years. Particular attention has been directed to the use of renewable resources, such as farm crops, for fuel production.

Furthermore, in the food industry, an increasing problem during the last years has been the disposal of used vegetable oils. Vast amounts of waste cooking oils are disposed each year by food processing and manufacturing plants as well as by domestic consumers. The environmental problems associated with disposal of large volumes of waste vegetable oils have grown to a point where they can not be overlooked.

Use of waste vegetable oils as fuel for diesel engines has been contemplated. However, pure vegetable oils have a number of disadvantages when used as engine fuels, such as excessive engine wear, fuel injector coking, and high smoke values. Also, the high viscosity of vegetable oils, compared to petroleum based diesel fuel, makes their use impractical.

Different approaches towards providing a practical way of using waste vegetable oils as diesel fuels have been sought out. Some have involved modification of the vegetable oil, chemically or physically, in order to conform the vegetable oil fuel to the specifications required for use in a conventional diesel engine. One way that has been proposed to make use of waste vegetable oil is through methyl esterification of the oil and using the methylated derivative as a fuel for diesel engines. The fuel product obtained upon methyl esterification of vegetable oil, however, suffers from a number of disadvantages, for example high production costs depending on the large amounts of methanol or ethanol required, and high plant construction costs, due to safety requirements involved in working with methanol and ethanol. Japanese patent document JP 2005105014 A discloses a diesel fuel oil provided by blending 50-85 % of a mineral oil and 15-50 % vegetable oil. As the vegetable oil, a filtered waste vegetable oil is described. Kerosene or gas oil are used to adjust the viscosity of the vegetable oil. Use of different ratios of vegetable oil and kerosene or gas oil for use in different climates is contemplated.

US patent application US 2003167682 A discloses mixing of a vegetable oil with halogenated hydrocarbons and solvents, particularly terpenoid solvents, and a petroleum diesel fuel to produce a fuel suitable for use in a diesel engine.

The approach of adding lesser amounts of vegetable oil fuel to a conventional diesel fuel only offers a partial solution to the problem. A large part of the fuel is still petroleum based. According to Japanese patent document JP 2000119685, waste food oil is activated by means of oxidation with ozone, oxygen or air for use in a fuel oil. The food oil is filtered and mixed with water for removal of water soluble contaminants . US patent application US 2004003534 discloses a process for treatment, e.g. ozone treatment, of fish oil or a mixture of fish oil and vegetable oil to produce fuel for a diesel engine. The process comprises filtration of the oil, as well as ozone treatment. The process may also comprise addition of a "vegetable additive".

European patent application EP 1026224 Al discloses a process for treatment of vegetable oil (virgin or waste oil) to produce fuel for a diesel engine. The treatment comprises filtration, heating of the oil, adding water and/or ozone to the oil and agitating the mixture.

International patent application WO 03093400 A discloses a method for manufacturing engine fuel from waste vegetable oil comprising filtration and cracking steps.

Chemically modifying vegetable oils, e.g. via reactive mixing with ozone or other oxidative agents, in order to obtain physical properties more similar to those of conventional diesel fuel, requires use of reactive chemicals and/or special equipment, making this approach relatively awkward and costly. Japanese patent document JP 8053681 discloses a diesel fuel consisting of a vegetable or fish oil mixed with 5-50 % of a terpene compound. Additionally, if necessary, gas oil, kerosene or fuel oil may be added. A number of different approaches for lowering viscosity of the oil by heating the oil are shown in the documents discussed below.

Japanese patent document JP 2004092631 A discloses a system for reducing viscosity of a vegetable oil in a diesel engine using vegetable oil as fuel. Viscosity of the vegetable oil is reduced by heating the oil using cooling water warmed up by the engine. At startup, the engine is first warmed up running on conventional fuel. Spanish patent application ES 2181579 discloses a method and device for use of a vegetable oil as fuel in an internal combustion engine. Normal fuel is used for cold-starting the engine. When the vegetable oil fuel has been heated via a heat exchanger, the vegetable oil is used as fuel instead.

German patent application DE 10060573 discloses a system for reducing viscosity of a vegetable oil in a diesel engine using vegetable oil as fuel. Viscosity of the vegetable oil is reduced by heating the oil using an electrical heater.

German patent application DE 10105760 discloses a method for reducing viscosity of a vegetable oil in a diesel engine using vegetable oil as fuel. Viscosity of the vegetable oil is reduced by heating the oil using glow plugs .

German patent application DE 10042397 discloses a warming device for vegetable oil used as fuel in a diesel engine. The vegetable oil is heated using an electrical heater and a heat exchanger. An auxiliary electrical heater is arranged near an injection nozzle through which the fuel is injected.

In the light of the above cited prior art, there is a demand for an inexpensive, efficient and environmentally friendly alternative to petroleum derived diesel fuels.

Description of the invention An object of the present invention is to provide an inexpensive alternative fuel, produced from renewable natural resources, as a replacement for conventional petroleum based diesel fuels, which can be used in a conventional diesel engine without further modification of said engine.

Another object of the present invention is to provide a technically, environmentally and economically viable way of producing a fuel, based on renewable natural resources, using waste vegetable oil as a replacement for conventional petroleum based diesel fuels, thus reducing problems associated with disposal of waste vegetable oil today, e.g. increasing rodent populations in sewers, and jellyfish populations at sea, fed by the waste vegetable oil. Another object of the present invention is to provide a method for achieving optimum operating conditions for a vegetable oil based fuel during use in a diesel engine arrangement.

Yet another object of the present invention is to provide a fuel system for providing a diesel engine with a fuel comprising vegetable oil, said fuel system being arranged to provide optimum operating conditions for said diesel engine with said fuel .

A further object of the invention is to provide a method for producing a fuel, based on renewable natural resources, comprising vegetable oil, which fuel can be used in a conventional diesel engine. The above mentioned objects, as well as further objects of the invention, which should be apparent to a person skilled in the art after having studied the description below, are accomplished by the various aspects of the present invention.

In a first aspect, the present invention provides a fuel comprising more than 60 % by weight of a vegetable oil and 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound. The concentration of vegetable oil in the inventive fuel is more than 60 % by weight. In one embodiment of the invention, the concentration of vegetable oil is at least 75 % by weight. In another embodiment of the invention, the concentration of the vegetable oil is at least 95 % by weight. In yet another embodiment of the invention the concentration of vegetable based organic solvent comprising a terpene compound is 2-4 % by weight. In a more specific embodiment of the invention, the fuel consists of 95-99 % by weight of a vegetable oil and 1-5 % by weight of a vegetable based solvent comprising a terpene compound. In another more specific embodiment of the invention, the fuel consists of 96-98 % by weight of a vegetable oil and 2-4 % by weight of a vegetable based solvent comprising a terpene compound. The fuel according to the invention may additionally comprise additional components, such as a petroleum or vegetable based fuels, or combustible solvents, at a concentration of 1-39 % by weight, to the extent that this is possible with regard to the content of the principal components.

The vegetable oil based fuel according to the invention may comprise any naturally occurring or synthetically modified type of vegetable oil. Non- limiting examples of useful fats and oils are soybean oil, rapeseed oil, oiticica oil, tung oil, castor oil, tall oil, olive oil, palm oil, safflower oil, sesame oil, sunflower oil, linseed oil, babassu oil, coconut oil, palm kernel oil, corn oil, cottonseed oil, groundnut oil, and mixtures of two or more thereof.

In certain embodiments of the present invention, said vegetable oil may be "recycled", i.e. an oil or a mixture of two or more oils, which has previously been used, e.g. in processing or preparation of foodstuffs, such as deep frying or preservation. In this respect, the present invention provides a simple and environmentally beneficial approach towards solving the problem of disposal of increasing amounts of waste vegetable oil emerging from food processing and production.

The fuel according to the present invention further comprises 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound, examples of which include but are not limited to turpentine and other vegetable extracts containing terpenes and terpenoids, e.g. monoterpenes, such as α-ρinene and β-pinene, nerol, citral, camphor, menthol and limonene, sesquiterpenes, such as nerolidol and farnesol, diterpenes, such as phytol, and mixtures of two or more terpenes.

In one embodiment of the invention, the vegetable based organic solvent is turpentine. Turpentine is also known e.g. as oil of turpentine, gum turpentine, spirits of turpentine, turps, pine oil or fir oil. In some embodiments, the use of a vegetable based organic solvent as an additive in the inventive fuel affords a fuel which is 100 % vegetable based, and hence does not contribute at all to the increase of CO2 in the atmosphere and global warming resulting therefrom. Another advantage of the fuel according to the present invention is the price. A number of vegetable oil based fuels have been suggested in the past, which have been either too expensive to provide a realistic option to petroleum based fuels at the present time, or which have carried inherent disadvantages, such as engine wear or incomplete combustion. The present invention provides a fuel that is inexpensive, due to the use of inexpensive raw materials and processing methods.

In a second aspect thereof, the present invention provides use of a fuel as defined above in a diesel engine.

In a third aspect of the present invention, a method is provided for operating a diesel engine, comprising the steps of:

a) providing a fuel as defined above, b) heating said fuel prior to injection into the diesel engine, c) injecting said fuel into the diesel engine.

In one embodiment, in step b) , the fuel is heated to a temperature of 48-100 ⁰C, preferably to a temperature of 65-100 °C, more preferably to a temperature of 80-85 ⁰C and most preferably to a temperature of about 83 ⁰C, prior to injection into the diesel engine. In a more specific embodiment, said heating is effected in a fuel filter. In another more specific embodiment, said heating is effected using warm engine coolant from the engine cooling system. In yet another embodiment, said heating is effected electrically. The possibility to control the temperature of the fuel being injected into the engine allows optimization of the conditions of combustion, and thereby optimization of the combustion. This results in an exhaust from the engine containing less harmful components. Vegetable oils intrinsically comprise less components liable to give rise to toxic exhausts upon combustion, such as halogens, sulfur and heavy metals, compared to conventional petroleum based fuels, such as diesel fuel or gasoline. The inventive fuel in combination with heating of the fuel prior to injection into the engine provides a method giving very low emissions of harmful components, such as THC : s and SO₂, as disclosed in the example below. Heating also lowers the viscosity of the vegetable oil based fuel, circumventing problems associated with using a high viscosity fuel in an internal combustion engine.

In a fourth aspect thereof, the invention provides a method for operating a diesel engine, in which method a fuel as defined above is used in a diesel engine arrangement comprising a diesel engine, a fuel tank, a fuel line, a fuel filter and an engine cooling system comprising a recirculating engine coolant, the method comprising the steps:

a) a first heating of the fuel to a first temperature effected in the fuel tank, and b) a second heating of the fuel to a second temperature effected in the fuel filter using warm engine coolant from the engine cooling system.

In an embodiment, said second temperature is in the range of 48-100 ⁰C, preferably in the range of 65-100 ⁰C, more preferably in the range of 80-85 ⁰C and most preferably said second temperature is about 83 °C.

In another embodiment said first temperature is in the range of 35-44 ⁰C and said second temperature is in the range of 48-100 ⁰C, preferably in the range of 65-100 °C, more preferably in the range of 80-85 ⁰C, and most preferably about 83 °C.

Use of a sequential heating process, such as provided by this aspect of the invention, allows a more accurate control of the final temperature of the fuel before injection thereof into the engine. Accurate control of the temperature as provided by the present invention is essential in obtaining optimal combustion conditions and thereby optimal combustion with a minimum of undesired combustion by-products. In an embodiment of the invention, the fuel lines are also heated. In some embodiments, the heating of the fuel filter and/or the fuel tank and/or the fuel lines may also be effected electrically.

The fuel filter, in which the second heating of the inventive fuel is effected in step b) , is constructed so as to allow heat from engine coolant to be transferred to the fuel, via a heat exchanging arrangement. Heating in the fuel filter enables accurate regulation of the temperature of the fuel being injected into the engine. The temperature of the fuel as it leaves the fuel filter may be controlled to an error margin of about 1 ⁰C.

When using recycled vegetable oil as an ingredient in a fuel according to the present invention, it is very important to remove particulate matter originating from the vegetable from the fuel oil before injecting it into the engine. Therefore, it is important to select a suitable fuel filter for use in a fuel system according to the present invention. Recycled vegetable oil also generally comprises water in different concentrations. Water in fuel used in an internal combustion engine, even in small amounts, can be very harmful to the engine. It is therefore of desirable that water present in the vegetable oil fuel of the invention can be removed prior to injection into the engine. In the fuel system of the present invention, this may e.g. be achieved by the use of a fuel filter utilizing a turbine centrifuge, in which water and particulate matter is separated from the vegetable oil fuel to an extent allowing injection of the filtrated vegetable oil fuel into the engine, without risk of damage to the engine. Other types of fuel filters may of course also be used.

A fifth aspect of the present invention provides a fuel system for providing a diesel engine with a fuel, said fuel system comprising a fuel tank containing a fuel according to the first aspect of the invention, an engine cooling system comprising a recirculating engine coolant, a fuel line connecting the tank with the engine, and a fuel filter arranged on said fuel line, said fuel filter being arranged with said cooling system so as to allow heat transfer in the fuel filter from the recirculating engine coolant to the fuel provided from the fuel tank to the engine.

In an embodiment, said fuel tank is arranged with said cooling system so as to allow heat transfer from the recirculating engine coolant to the fuel contained in the fuel tank. In another embodiment, said fuel line is also heated.

In yet another embodiment, said fuel system further comprises a second fuel tank containing a second fuel for a diesel engine and a second fuel line connecting said second fuel tank with the engine, wherein said first and second fuel line are provided with electromagnetically operated valves that can be opened or closed independently of each other or simultaneously.

In a further embodiment, said second fuel is a petroleum based diesel fuel.

An embodiment of a fuel system according to the invention is disclosed in Figure 1. The fuel system comprises a diesel engine (1), a fuel tank containing a vegetable oil based fuel according to the invention (2) , a fuel line (3) leading from the fuel tank to a fuel filter (4) and from said fuel filter via an electromagnetic three-way (10) valve to the fuel inlet of the diesel engine. The fuel system further comprises an engine cooling system (5), containing an engine coolant. The engine coolant is heated by the engine in the cooling system. The heated coolant leaving the engine is led to the fuel filter (4) and used in a heat exchanging arrangement in the fuel filter to heat vegetable oil based fuel present in the filter. The engine coolant used to heat the vegetable oil based fuel in the fuel filter

(4) is then led to the fuel tank containing the vegetable oil based fuel and used to heat the fuel present in said fuel tank before being recirculated to the engine. The fuel system according to this embodiment further comprises a second fuel tank (6), a fuel line (7) leading from said fuel tank to the fuel inlet of the diesel engine via a conventional diesel fuel filter (8) , and via the electromagnetic three-way valve (10). Excess fuel is returned to a second electromagnetic three-way valve (11) via a return fuel line (12) .

The electromagnetic three-way valves (10, 11) are arranged to allow switching between the different fuels contained in the two fuel tanks. The first valve (10) directs one of the fuels to the engine fuel inlet, stopping the flow of the other fuel into the engine. The second valve (11) allows excess fuel from the engine to be returned to the appropriate fuel filter (4) or (8) depending on which fuel, i.e. vegetable oil based fuel or diesel fuel, is in use.

In a further aspect of the present invention, a method for producing a vegetable oil based fuel for use in a diesel engine is provided, said method comprising the steps of:

a) providing a vegetable oil, b) filtrating said vegetable oil under a pressure A, c) filtrating said vegetable oil under a pressure B, d) mixing said vegetable oil with an amount of 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound,

wherein said pressure A is higher than said pressure B.

In an embodiment, the amount of vegetable based organic solvent comprising a terpene compound is 2-4 % by weight. In another embodiment said vegetable oil is a recycled vegetable oil. In yet another embodiment said vegetable based organic solvent comprising a terpene compound is turpentine. In an embodiment of the inventive method for production of a vegetable oil based fuel, the filtration in step b) is performed using a filter with a pore size of 20-100 μm. In another embodiment, the filtration in step b) is performed using a filter with a pore size of 30-80 μm. In yet another embodiment, the filtration in step b) is performed using a filter with a pore size of 5-10 μm.

In a an embodiment of the inventive method for production of a vegetable oil based fuel, the filtration in step c) is performed using a filter with a pore size of 20-100 μm. In another embodiment, the filtration in step c) is performed using a filter with a pore size of 30-80 μm. In yet another embodiment, the filtration in step c) is performed using a filter with a pore size of 5-10 μm.

In a further embodiment of the method for production of a vegetable oil based fuel above, said pressure A is a pressure within the range of 0,001-250 bar and said pressure B is a pressure within the range of 0,001-250 bar. Preferably, said pressure A is a pressure within the range of 1-250 bar and said pressure B is a pressure within the range of 0,001-5 bar. More preferably, said pressure A is a pressure within the range of 5-250 bar and said pressure B is a pressure within the range of 1-5 bar .

The filtration steps b) and c) in this aspect of the invention may be performed in any order, i.e. first b) , then c) or first c) , then b) . The steps b) and c) may also be performed repeatedly, e.g. b) , c) , b) , c) , or b) , b) , c) , c) , in any possible combination.

When using a vegetable oil, especially when using a recycled vegetable oil, as a fuel for an internal combustion engine, it is very important that the vegetable oil is free from solid contaminants, which may cause damage or excessive wear of the engine, as well as build-up of deposits of solid material in different parts of the engine, leading to uneven performance or requiring undue maintenance of the engine. Depending on the degree of purity of the vegetable oil used as starting material to provide the inventive fuel, different measures of purification of the oil may be required. The method provided by the invention for producing a vegetable oil based fuel for use in a diesel engine allows use of vegetable oils within a wide range of degree of purity. The inventive method provides filtration of the vegetable oil starting material under high pressure and under low pressure alternately. High pressure filtration may for example be achieved by passing the vegetable oil through a filter of a certain pore size under high pressure obtained by the use of low diameter tubing and high pressure pumps. The high pressure may be as described above. Low pressure filtration may be achieved by passing the vegetable oil through a filter of a certain pore size at close to or below normal atmospheric pressure. This treatment of filtration at different pressures results in a fuel with better combustion properties and cleaner combustion .

By use of the term "fuel" herein is meant any liquid or gaseous combustible substance, which can be used to provide power to an internal combustion engine upon combustion. Examples of fuels include, but are not limited to diesel, gasoline, kerosene and vegetable oil.

By use of the term "diesel engine" herein is meant any internal combustion engine normally designed to operate on conventional petroleum based diesel fuel. By use of the term "vegetable oil" herein is meant a naturally occurring composition comprised mainly of glycerol esters of fatty acids such as, but not limited to, caproic, caprylic, capric, lauric, myristic, palmitic, palmitoleic, stearic, isostearic, oleic, linoleic, linolenic, arachidic, gadoleic, behenic and erucic acids and combinations thereof, as well as synthetically modified derivatives thereof. Non-limiting examples of useful fats and oils are soybean oil, rapeseed oil, oiticica oil, tung oil, castor oil, tall oil, olive oil, palm oil, safflower oil, sesame oil, sunflower oil, linseed oil, babassu oil, coconut oil, palm kernel oil, corn oil, cottonseed oil, groundnut oil, and mixtures of two or more thereof.

By use of the term "recycled vegetable oil" herein is meant a vegetable oil as defined above, that has previously been used for a purpose other than as fuel. Non-limiting examples of sources for waste vegetable oil include different processes involved in food preparation, such as frying and conservation.

By use of the term "terpene compound" herein, is meant a naturally occurring organic compound, biologically built from the naturally occurring monomer called isoprene, CsH₈, which is found as a volatile oil in plants. By use of the term "terpene compound" herein, we also mean a terpenoid compound, i.e. alcohols, aldehydes, ketones or carboxylic acids of terpenes. Examples of terpene compounds include, but are not limited to, monoterpenes, such as α-pinene and β-pinene, nerol, citral, camphor, menthol and limonene, sesquiterpenes, such as nerolidol and farnesol, diterpenes, such as phytol, and mixtures of two or more terpenes. By use of the term "vegetable based organic solvent comprising a terpene compound" herein is meant an organic solvent comprising a terpene as defined above, which solvent has not, directly or indirectly, been derived from a petroleum raw material. Examples of such "vegetable based organic solvents comprising a terpene compound" include but are not limited to turpentine and other vegetable extracts containing terpenes and terpenoids, e.g. monoterpenes, such as α-pinene and β- pinene, nerol, citral, camphor, menthol and limonene, sesquiterpenes, such as nerolidol and farnesol, diterpenes, such as phytol, and mixtures of two or more terpenes . Brief description of the drawings

Figure 1 shows a scheme of the components present in a fuel system according to an embodiment of the invention.

Example

To determine the usefulness of the vegetable oil based fuel according to the invention, the following experiment was performed.

In a conventional diesel engine (Mitsubishi L200 4X4, 4D56 (Turbo variable, Intercooler) , year of manufacture 1998) , two different fuels, a vegetable oil based fuel according to the present invention (a) and a conventional petroleum based diesel fuel (b) , were evaluated with regard to the content of a number of components present in the exhaust fumes produced upon combustion of the fuels in the diesel engine.

The vegetable oil based fuel (a) consisted of 96,8 % by weight of a recycled, filtrated vegetable oil (mixture of different vegetable oils, mainly sunflower oil) and 3,2 % of turpentine (industrial grade).

The diesel engine was operated alternately on fuels (a) and (b) . The vehicle used in the study was provided with a fuel system according to an embodiment of the invention as shown in Figure 1, including a first fuel tank (2) containing the vegetable oil based fuel (a), and a second fuel tank (6) containing the diesel fuel (b) and a three-way valve (10) on the fuel lines (5, 7) leading from the fuel tanks to the injection unit of the engine (1) allowing regulation of which of the fuels, (a) or (b) , to be fed to the engine.

Fuel (a) was provided using a fuel system according to the present invention, wherein the fuel was heated in a fuel filter prior to injection into the engine, using warm engine coolant from the engine cooling system to heat the fuel in said filter. The temperature of the vegetable oil based fuel upon injection into the engine was approximately 83 ⁰C.

Fuel (b) was provided to the engine in a conventional way, via a diesel fuel filter, without heating of the fuel prior to injection into the engine.

Exhaust fumes from the engine were analyzed for THC (total hydrocarbons), SO₂ and CO₂. THC, SO₂ and CO₂ were evaluated according to the standard testing procedures EPA (US Environmental Protection Agency) N° 1, VDI 3481 and EPA CTM-30.

Measurements were conducted at engine rotational speeds of 2000 and 3000 rpm. All measurements were performed in triplicate in order to provide values with statistical significance. Measurements were performed at ambient temperature and pressure. The results of the measurements are presented in Table 1 below.

Table 1.

1 ) Value too low to detect

2 ) Calculated C0₂-concentration

The results in Table 1 show that with a vegetable oil based fuel according to the invention, a lower total hydrocarbon content (THC) was produced, compared to the conventional diesel fuel, indicating better combustion. The levels of sulfur dioxide were significantly lower for the vegetable oil based fuel than for the diesel fuel. The levels of sulfur dioxide in the exhaust from the vegetable oil based fuel were actually to low to be determined by the methods used in this study. No differences in the behavior of the engine when running on the vegetable oil based fuel and when running on the diesel fuel were observed. The color of the exhaust gas, and the amount of smoke was the same for the two fuels. The conclusion of the study is that the vegetable oil based fuel of the invention can be used in combination with a fuel system according to the invention as a cleaner, Cθ₂~neutral substitute for conventional petroleum based diesel fuels without further modification of the diesel engine.

Claims

1. Fuel for a diesel engine, comprising more than 60 % by weight of a vegetable oil and 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound.

2. Fuel according to claim 1, comprising at least 75 % by weight of a vegetable oil.

3. Fuel according to claim 2, comprising at least 95 % by weight of a vegetable oil.

4. Fuel according to any one of the preceding claims, comprising 2-4 % by weight of a vegetable based organic solvent comprising a terpene compound.

5. Fuel according to any one of the preceding claims, consisting of 95-99 % by weight of a vegetable oil and 1-5 % by weight of a vegetable based organic solvent comprising a terpene compound.

6. Fuel according to any one of the preceding claims, consisting of 96-98 % by weight of a vegetable oil and 2-4 % by weight of a vegetable based organic solvent comprising a terpene compound.

7. Fuel according to any one of the preceding claims, wherein said vegetable oil is a recycled vegetable oil.

8. Fuel according to any one of the preceding claims, wherein said vegetable based organic solvent comprising a terpene compound is turpentine.

9. Use of a fuel according to any one of the preceding claims in a diesel engine.

10. Method for operating a diesel engine, comprising the steps of:

a) providing a fuel according to any one of claims 1- 8, b) heating said fuel prior to injection into the diesel engine, c) injecting said fuel into the diesel engine.

11. Method according to claim 10, wherein in step b) said fuel is heated to a temperature in the range of 48-100 ⁰C.

12. Method according to claim 11, wherein in step b) said fuel is heated to a temperature in the range of 65- 100 ⁰C.

13. Method according to claim 12, wherein in step b) said fuel is heated to a temperature in the range of 80-

85 ⁰C.

14. Method according to claim 13, wherein in step b) said fuel is heated to a temperature of about 83 ⁰C.

15. Method according to any one of claims 10-14, wherein said heating is effected in a fuel filter.

16. Method according to any one of claims 10-15, wherein said heating is effected using warm engine coolant from the engine cooling system.

17. Method according to any one of claims 10-16, wherein said heating is effected electrically.

18. Method for operating a diesel engine, in which method a fuel according to any one of claims 1-8 is used in a diesel engine arrangement comprising a diesel engine, a fuel tank, a fuel line, a fuel filter and an engine cooling system comprising a recirculating engine coolant, the method comprising the steps:

19. Method according to claim 18, wherein said first temperature is in the range of 35-44 °C.

20. Method according to any one of claims 18-19, wherein said second temperature is in the range of 48-100 ⁰C.

21. Method according to claim 20, wherein said second temperature is in the range of 65-100 ⁰C.

22. Method according to claim 21, wherein said second temperature is in the range of 80-85 ⁰C.

23. Method according to claim 22, wherein said second temperature is about 83 ⁰C.

24. Fuel system for providing a diesel engine with a fuel, said fuel system comprising a fuel tank containing a fuel according to any one of claims 1-8, an engine cooling system comprising a recirculating engine coolant, a fuel line connecting the tank with the engine, and a fuel filter arranged on said fuel line, said fuel filter being arranged with said cooling system so as to allow heat transfer in the fuel filter from the recirculating engine coolant to the fuel provided from the fuel tank to the engine .

25. Fuel system according to claim 24, wherein said fuel tank is arranged with said cooling system so as to allow heat transfer from the recirculating engine coolant to the fuel contained in the fuel tank.

26. Fuel system according to any one of claims 24- 25, wherein said fuel line is also heated.

27. Fuel system according to any one of claims 24- 26, further comprising a second fuel tank containing a second fuel for a diesel engine and a second fuel line connecting said second fuel tank with the engine, wherein said first and second fuel line are provided with electromagnetically operated valves that can be opened or closed independently of each other or simultaneously.

28. Fuel system according to claim 27, wherein said second fuel is a petroleum based diesel fuel.

29. Method for producing a vegetable oil based fuel for use in a diesel engine, which method comprises the steps of:

a) providing a vegetable oil, b) filtrating said vegetable oil under a pressure A, c) filtrating said vegetable oil under a pressure

B, and d) mixing said vegetable oil with an amount of 1-5 % by weight, based on the total weight of the mixture, of a vegetable based organic solvent comprising a terpene compound,

wherein said pressure A is higher than said pressure B.

30. Method according to claim 29, wherein the amount of vegetable based organic solvent comprising a terpene compound is 2-4 % by weight.

31. Method according to any one of claims 29-30, wherein said vegetable oil is a recycled vegetable oil.

32. Method according to any one of claims 29-31, wherein said vegetable based organic solvent comprising a terpene compound is turpentine.

33. Method according to any one of claims 29-32, wherein the filtration in step b) is performed using a filter with a pore size of 20-100 μm.

34. Method according to any one of claims 29-33, wherein the filtration in step b) is performed using a filter with a pore size of 30-80 μm.

35. Method according to any one of claims 29-32, wherein the filtration in step b) is performed using a filter with a pore size of 5-10 μm.

36. Method according to any one of claims 29-35, wherein the filtration in step c) is performed using a filter with a pore size of 20-100 μm.

37. Method according to any one of claims 29-36, wherein the filtration in step c) is performed using a filter with a pore size of 30-80 μm.

38. Method according to any one of claims 29-35, wherein the filtration in step c) is performed using a filter with a pore size of 5-10 μm.

39. Method according to any one of claims 29-38, wherein said pressure A is a pressure within the range of 0,001-250 bar.

40. Method according to any one of claims 29-39, wherein said pressure B is a pressure within the range of 0,001-250 bar.

41. Method according to any one of claims 29-40, wherein steps b) and/or c) are performed repeatedly.