GB2376047A

GB2376047A - Fuel injector with a protectively coated tip

Info

Publication number: GB2376047A
Application number: GB0113272A
Authority: GB
Inventors: John Mcneil
Original assignee: Finch Ltd
Current assignee: Finch Ltd
Priority date: 2001-05-31
Filing date: 2001-05-31
Publication date: 2002-12-04
Anticipated expiration: 2021-05-31
Also published as: GB0113272D0; GB2376047B

Abstract

A fuel injector 1 has a fuel injector tip 5 with an external surface that is coated with a protective layer and has one or more outwardly flaring fuel delivery nozzles 8 provided in the surface. The coating may be chromium and electroplated, and may cover substantially the entire external surface of the fuel injector tip 5. The fuel delivery nozzles 8 may flare conically outwards. The fuel used may be a dense and viscous petroleum oil, animal or vegetable oils, alcohol, or solvent fuel.

Description

Fuel Injection Devices The present invention relates to a fuel injection device, for use in compression ignition engines, which has an improved operational performance and is resistant to corrosion. The device of the invention is particularly suitable for combusting difficult-to-bum liquid fuels in a high speed compression ignition engine. The invention also relates to methods of combusting difficult-to bum petroleum fuels and waste organic solvents.

High-speed compression ignition engines typically operate at between 1500 rpm and 2500 rpm. These high performance engines are very fuel specific and will normally only operate efficiently on fuels, such as diesel oil, which have been specially formulated for this type of engine. However, it is desirable to be able to operate such engines using other potential fuels, although such fuels tend to be more difficult to bum than diesel oil. Alternative fuels include aggressive, dense and viscous petroleum oils, (such as heavy fuel oils, bunker fuel, waste mineral oils) and also waste organic solvents, (such as alcohols and ketones). It is particularly desirable to be able to effectively combust aggressive petroleum fuels and waste organic solvents that may contain contaminants of either a hazardous or a polluting nature, so that the contaminants are destroyed by the combustion process. Another potential dense viscous and aggressive fuel is pyrolysis oil. Pyrolysis oil (also known as bio-oil) is a renewable, non-fossil fuel, which is produced by the fast pyrolysis of biomass material. The properties of pyrolysis oil are described in the Applicants earlier application WO 01/07834.

The above fuels are difficult to bum because they have properties that are very different from diesel oil. For example the petroleum oils mentioned are usually dense and viscous and they tend to contain high levels of sulphur and particulate material. For example, a typical heavy fuel oil may have a density of

over 0. 99 and a viscosity of more than 900 cSt at 40oC, whereas diesel oil has a density of 0. 83 and a viscosity of about 2 cSt at 40 C. Because of their markedly different fuel specifications, compared to diesel oil, these aggressive petroleum oils are not suitable for use as fuels in standard high-speed compression ignition engines.

Heavy fuel oil is used as fuel in low-speed, large bore compression ignition engines, such as, for example, marine diesel engines. These engines usually operate at speeds of between 100 rpm and 750 rpm and they are much more tolerant of poor specification fuels than high-speed engines. Even so, the exhaust smoke from such

engines when burning heavy fuel oil tends to be black, high in particulates and heavily polluted.

Many organic solvents are either toxic or hazardous by nature and waste solvents may be further contaminated by hazardous organic materials that have been absorbed from the solvent process. Waste organic solvents therefore have to be disposed of in a carefully controlled manner to avoid potential environmental pollution and risks to human health. An established method of disposal is to incinerate the waste solvents in, for example, rotary kilns or furnaces. However, many existing chemical incinerators do not incorporate means to recover the energy that is released from the combustion of the waste solvents and a potential source of energy is lost. Accordingly, it would be desirable to be able combust waste organic solvents in a high-speed compression ignition engine because the peak temperature in the combustion chamber of the engine can reach over 2000 C and the pressure over 140 bar. Such conditions would ensure that the waste solvents, and any hazardous organic contaminants present in the solvents, would be effectively incinerated. Engines also have the advantage that the energy released from the combustion process can be easily and efficiently recovered in the form of heat and electricity.

However, like aggressive petroleum oils, organic solvents also have properties that are markedly different from diesel oil, which makes them difficult to bum in high speed compression ignition engines. For example, their viscosity, density, boiling point, flash point, calorific value, octane number, cetane number and lubricity characteristics, which are all important for efficient combustion in an engine, are very different from diesel oil. Ethanol is used in some countries as a renewable fuel additive, in spark ignition engines, by blending the ethanol with petrol, and methanol has also been considered as an alternative fuel to diesel oil.

Generally, however, organic solvents have poor ignition qualities and they are not capable of being ignited by means of compression alone in a standard diesel engine.

Usually a spark or glow plug ignition system is fitted to the engine to ignite the solvent, or, alternatively, the solvent is either co-fired or blended with a petroleum oil.

One of the problems which has been encountered by the Applicant in its attempts to combust aggressive petroleum oils, such as heavy fuel oil, in a standard high-speed compression ignition engine, is that the metal tip of the standard fuel injectors used in the engine has a tendency to become corroded and pitted. This in turn encourages solid combustion products to adhere around the fuel delivery

nozzles until a hard deposit is formed. This deposit gradually builds up around the fuel delivery nozzles, thereby restricting the flow of fuel into the combustion chamber. With the standard design of fuel injector nozzle, which has primarily been designed for use with diesel oil, it was also found that the injected spray of dense, viscous heavy fuel oil dispersed poorly into the combustion chamber, which allowed fuel to impinge on the cylinder walls and the piston heads of the engine. This resulted in inefficient combustion of the fuel, which in turn produced high levels of carbonaceous combustion products inside the combustion chamber, as well as localised corrosion of the cylinder wall, the piston head and the fuel injector nozzles. Sustained efficient combustion of such fuels was therefore not possible in a high speed compression ignition engine fitted with standard fuel injectors.

However, it has been found that the problems associated with standard fuel injectors can be overcome by means of a judiciously designed fuel injection device.

From a first aspect, therefore, the present invention provides a fuel injector comprising a fuel injector tip, the external surface of said tip being coated with a protective layer, and having one or more outwardly flaring fuel delivery nozzles provided in that surface.

Thus in accordance with the first aspect of the invention, a fuel injector tip is provided with a flaring fuel delivery nozzle and a protective coating. This combination of features produced a significant improvement in performance of the fuel injectors, and this is thought to be due to a number of factors, namely: a) The external protective coating on the injector tip helps to prevent surface corrosion ; b) The shape of the outwardly flared fuel delivery nozzle, combined with the protective coating around the nozzle orifice, allows the next injection of fuel to wash away any combustion deposits that may have formed around the nozzle; c) The narrow fuel passage tubes in the injector tip restrict the flow of the fuel and high pressure is required to spray the fuel into the combustion chamber. A high injection pressure is in any case necessary to produce effective atomisation and vaporisation of the fuel. However, when a dense, viscous fuel is forced through the same passage tube, even higher pressure is required to spray the fuel into the combustion chamber. With viscous fuel, the pressure in the injection system can build-up to an extreme level and this can have a detrimental affect on the atomisation and vaporisation of the fuel. Machining the outwardly flared nozzle into the external end of the fuel passage tube decreases the length of the tube, which in turn reduces the fuel injection pressure and compensates for the excessive build-

up in pressure that can occur with dense, viscous fuels; d) The compensated fuel injection pressure, combined with the shape of the outwardly flared fuel delivery nozzle, provides improved atomization, spray dispersion and vaporisation of dense, viscous fuels. This results in a more efficient fuel bum, which helps to limit the formation of carbonaceous combustion products inside the combustion chamber.

The injector tip may be coated with any substance which is capable of withstanding the extreme environment in the combustion chamber of an engine, that is any material which is sufficiently resistant to corrosion and heat. Chromium is preferred because it is a cost effective, corrosion resistant metal, which may conveniently be applied to the injector tip using electroplating techniques.

However, other corrosion resistant metals such as nickel, or metal alloys, including chromium or nickel alloys, could also be used to coat the injector tips.

Preferably the coating is an electroplated coating. Electroplating is a simple, cost effective method of depositing a thin layer of metal on a surface, and means for electroplating are well known in the art. However, any other known method suitable for forming a thin protective layer may be used instead. Other methods of producing thin layers of coating materials, such as dipping techniques, are well known and may be adapted to the type of protective coating used.

It is desirable that the protective layer is as thin as possible, particularly where the cost of the protective material is a factor. However, it must also be sufficiently thick to afford adequate protection against wear and corrosion, and be sufficiently uniform in thickness for the same reasons. Typically, therefore the protective layer will be about 2 to 15 microns thick, preferably 4 to 12 microns thick and most preferably between 6 and 10 microns thick.

The coating on the external surface of the injector tip should extend around the flared nozzle outlet and may advantageously cover the entire external surface of the fuel injector tip that will protrude into the combustion chamber of the engine.

The fuel passage tubes in the standard injectors used in the research work had a bore of 200 microns.

As stated above, the fuel delivery nozzle flares outwardly from this tube, i. e. its diameter or similar dimension increases towards the external surface of the fuel injector tip. The flaring may be substantially linear, such that the nozzle is effectively conical, or any other suitable profile. A conical shape is, however, preferred for ease of manufacture.

The fuel delivery nozzle can be appropriately sized to suit individual fuel specifications. For example, the maximum diameter at the external surface of the nozzle can easily be varied from about 250 to over 400 microns, and most preferably between 280 to 300 microns. For example, for heavy fuel oil it has been found that an external orifice diameter of about 300 microns gave effective atomisation and spray dispersion of the fuel. For other types of fuel, the preferred external nozzle diameter may be higher or lower than this and may readily be determined by one skilled in the art.

Typically the flare angle of the fuel delivery nozzle is between 30 and 60 , preferably about 450 (i. e. an included angle of 90 ), although other angles may be possible.

It will be appreciated that the invention also extends to a compression ignition engine incorporating an injector in accordance with the invention, and also to a method of combusting fuels in a compression ignition engine, wherein the engine is provided with a fuel injector device in accordance with the invention. The fuels may include aggressive, dense and viscous petroleum oils, such as heavy fuel oils, residual fuel oils (e. g. heavy residual fuel oil), bunker fuels and waste mineral oils, as well as other fuels such as organic solvents, animal or vegetable oils and fats, pyrolysis oils and blends and mixtures thereof.

The injector device may well help the combustion performance of certain dense, viscous fuels when the engine is operated under normal naturally aspirated conditions. However, most difficult-to-bum fuels, such as heavy fuel oil and waste solvent blends would not bum effectively in a sustained, effective manner in a highspeed engine under naturally aspirated conditions, even with the modified fuel injectors. Under these circumstances, the modified injectors would be used in conjunction with an enriched oxygen combustion atmosphere.

Therefore in certain embodiments of the method of the invention, an enriched oxygen atmosphere may be provided in the combustion chamber of the engine. This is advantageous in that higher combustion temperatures can be reached using oxygen enrichment, thus ensuring more complete destruction of any potentially hazardous material in the fuels. Oxygen enrichment in internal combustion engines has been the subject of considerable past research, most of which has concentrated on how oxygen enrichment could affect the level of different emissions in the engine exhaust. Published research includes'Effect of oxygen enrichment on the performance and emissions of IDI diesel engines'by J Ghojel et al (1983) and'Exhaust emissions and performance of a spark ignition

engine using oxygen enriched air'by A A Quader (1978).

Furthermore, related research work has been carried out into the disposal of tallow animal fat and waste cooking oil, by means of combustion in compression ignition engines and using an enriched oxygen combustion atmosphere. This research is described in the Applicant's earlier application WO 99/02405.

The skilled person will be able to readily determine whether or not oxygen enrichment would be beneficial, depending on the nature of the fuel and the type of compression ignition engine. For example, medium fuel oil may bum adequately in a high-speed compression ignition engine without oxygen enrichment, whereas heavy fuel oil will not. Heavy fuel oils are capable of being burned in naturally aspirated low-speed, wide bore compression ignition engines, however, enriching the combustion atmosphere in this type of engine with oxygen would undoubtedly further improve the efficiency of the combustion process.

Common solvents, such as alcohols and ketones, cannot be combusted in naturally aspirated high-speed compression ignition engines because these types of solvent will not ignite by means of compression only. However, with an enriched oxygen combustion atmosphere these types of solvents are capable of being ignited by means of compression only. The combustion of such solvents can be further improved by blending the solvents with a fuel that is suitable for use in this type of engine. For example, if the solvents were blended with petroleum based diesel oil, an enriched oxygen combustion atmosphere may not be necessary. However, if the solvents were blended with a non-fossil fuel, such as vegetable oil, then oxygen enrichment would probably be required to provide efficient sustained combustion.

Where oxygen enrichment is required, it is preferred that the combustion atmosphere in the engine is enriched with oxygen to between 3% and 10% above naturally aspirated conditions (i. e. between 24% oxygen, 76% nitrogen and 31% oxygen, 69% nitrogen) and more preferably between 4% and 5% above naturally aspirated conditions (i. e. between 25% oxygen, 75% nitrogen and 26% oxygen, 74% nitrogen).

The level of oxygen enrichment may be controlled in dependence on an analysis of the exhaust gases from the engine, or it may be controlled in dependence on the carbon monoxide level in the exhaust gas, or both. For example, the level of oxygen enrichment could be controlled so as to maintain the carbon monoxide concentration in the exhaust gas at a predetermined level.

For environmental reasons, it is preferred that the level of nitrogen oxides in the exhaust gas is abated by means of, for example, selective catalytic reduction

with ammonia. Preferably also, the engine is operated at its optimum constant speed.

In the case of viscous petroleum oils, the fuel would normally be hot filtered, centrifuge clarified and then heated to high temperatures of up to 130 C, before being injected into the engine, to provide mobility. Trials have established that the injector device described in the invention performs reliably even when very hot aggressive fuels are delivered to the fuel injector.

Examples of solvents which are suitable for disposal according to the

method of the invention include alcohols such as methanol, ethanol, I-propanol, 2propanol, and so forth, and ketones such as acetone, methyl ethyl ketone, etc, which are widely used as solvents in the pharmaceutical, chemical and related industries.

Other organic chemicals, including esters, ethers, glycol ethers and aliphatic, alicyclic and aromatic hydrocarbons, are also used as industrial solvents and can be combusting according to the present invention. Suitable solvents may be in a virgin (uncontaminated) or waste state, or combinations of virgin and waste solvents may be used. Organic solvent wastes from industrial processes may either be a single stream of a particular solvent or a mixture of different solvents. For example, a typical mixed solvent waste stream may include alcohols, ketones and some hydrocarbons. Waste solvents may also contain water.

Some alcohols, and associated chemicals derived from such alcohols, can be produced from biomass material, for example by the fermentation of sugars and starches, as well as from fossil based petrochemicals. When produced from biomass, alcohols provide a potential source of renewable energy. A major benefit of a renewable based fuel is that when it is burned it has a neutral greenhouse gas impact on the environment, as new plants grown to produce more of the renewable fuel are able to absorb the carbon dioxide that has been released to the atmosphere during the combustion process. Thus, in a preferred embodiment, alcohols and their derivatives produced from biomass material may be combusted according to the invention.

However, a problem with combusting solvents is that they have poor levels of lubricity, which causes excessive wear on the fuel injection system, i. e. the fuel pumps and fuel injectors of the engine. The solvents therefore need to be blended with a suitable substance to provide lubricity. For example, to overcome this drawback, ethanol has been blended with petrol to provide a fuel for internal combustion engines, and in this instance the petrol provides the lubricity required for efficient operation of the fuel injection systems. However, using a petroleum oil as the blending medium has the disadvantage that it is a fossil fuel and when burned

it has a detrimental greenhouse gas impact on the environment. Thus from an environmental point of view, it is preferred in a method of the invention that the waste organic solvents are blended with a renewable non-fossil liquid fuel rather than with a petroleum oil. In particular, where alcohol is concerned, it is possible to produce alcohol by the fermentation of plant materials, and the resulting fuel blend could well be largely derived from renewable sources.

It has been recognised by the Applicant that animal and vegetable oils or fats have sufficient lubricity to enable standard fuel pumps and fuel injectors to perform efficiently, without component wear, during sustained engine operation. Animal and vegetable oils and fats in virgin or waste states would therefore be better media to blend with organic solvents, instead of petroleum oils, as the resulting blended fuel would be either largely or partly derived from non-fossil renewable sources. Waste cooking oil, which generally consists of either vegetable oils or a mixture of vegetable oils and animal fats, would be suitable as a blending agent. The blending agents may be heated and filtered as necessary before, during or after blending with the solvents.

Thus the non-fossil fuel that forms the blending medium could be either waste animal or waste vegetable oils and fats or a mixture of waste animal and vegetable oils and fats. As well as fuel derived from waste sources, the method of the invention could equally apply to mixtures of virgin solvents and virgin animal or vegetable based oils and fats, and to combinations of virgin and waste based materials.

Many industrially produced organic solvents tend to be volatile liquids with relatively low boiling points and it is therefore preferable that the solvents are blended with other fuels at as low a temperature as possible to avoid evaporation of the solvents. An advantage of waste cooking oil, as a blending medium, is that it is liquid at low temperatures and only needs to be heated to about 30 to 400C to make it mobile enough for injection into an engine.

By contrast, tallow animal fat has a melting point of27 C and it has to be heated to about 600C before it is mobile enough to be injected into an engine.

Tallow is, however, miscible with waste cooking oil and a combination of tallow and waste cooking oil, in appropriate proportions, would be an alternative blending medium.

Laboratory tests showed that alcohols are not readily miscible with either tallow or vegetable oils, which are desirable fuel blend mediums, even when the mixture is gently heated and stirred. However, if the alcohol is first mixed with a

ketone, such as methyl ethyl ketone, the resulting mixture is then miscible with both tallow and vegetable oil. Mixtures of alcohols, methyl ethyl ketone and filtered waste cooking oil, gently heated to no more than 40oC, resulted in a homogeneous blended fuel that was mobile enough for direct injection into a compression ignition engine.

Typically, then, a solvent fuel blend for combustion in a compression ignition engine could for example consist of a gently heated mixture of alcohols, ketones and a non-fossil liquid fuel, such as filtered waste cooking oil, or a mixture of cooking oil and tallow.

Where solvents are concerned, the composition of the fuel blend will be dependent on the particular solvents in the mixture. Thus, the composition of a blend may vary between about 20 to 30% alcohol (s), 20 to 30% ketone (s) and 40 to 60% of a fuel providing the necessary lubricity, such as non-fossil fuels. Particularly preferred as constituents are waste alcohols, waste ketones and waste cooking oil respectively. Typically the blend could, for example, be a mixture of 25% alcohol, 25% methyl ethyl ketone and 50% waste cooking oil and preferably the mixture contains either waste alcohol or waste ketone or both. Waste solvent streams from the pharmaceutical and chemical industries may already largely be a mixture of alcohols and ketones, although such waste solvent streams may also contain varying amounts of other organic solvents and water. The final composition of the mixture will be dependent on an analysis of the individual alcohol and ketone solvents to be included in the fuel blend and their miscibility with the waste cooking oil.

Other miscible organic solvents, preferably waste solvents, including esters (such as ethyl and isopropyl acetate), ethers (such as isopropyl ether), glycol ethers, aliphatic and alicyclic hydrocarbons (such as n-hexane and cyclohexane) and aromatic hydrocarbons (such as benzene and toluene), could also be added, in suitable proportions, to the fuel blend.

The amount of these other solvents that could be included in the mixture will again be dependent on an analysis of the actual waste solvents and their miscibility with the other constituents in the mixture. Generally, however, the amount of other waste organic solvents that could be added to an alcohol, ketone and waste cooking oil mixture would probably represent no more than 20% of the total composition of the final fuel blend.

A further problem is that any of these fuels, particularly waste solvents, and indeed waste cooking oil, may contain water. When blending waste solvents and waste cooking oil, a small amount of water may be miscible with the blended fuel.

However, where large amounts of water are present, these will need to be emulsified with the blended fuel before the fuel is injected into the engine. Emulsification can be achieved by either rapidly stirring or agitating the fuel blend before injection into the engine or by adding a small amount of a suitable emulsifying agent to the fuel blend whilst it is being stirred.

A further important consideration is to be able to recover the energy released during the combustion process by using the heat and power produced to generate electricity. Disposal in the manner described, by means of combustion in a compression ignition engine, allows the energy released from the combustion process to be easily and efficiently recovered in the form of heat and electricity.

Thus, energy from the combustion process can be harnessed by coupling the engine to a generator to generate electricity and by using the hot exhaust gas from the engine to raise steam in a boiler and using the steam to drive a generator to produce electricity.

Accordingly, viewed from a further aspect, the invention provides a combustion system comprising a compression ignition engine in accordance with the invention. If necessary or desired, the combustion system further comprises oxygen enrichment apparatus for supplying an enriched oxygen atmosphere to the combustion chambers of the engine and it preferably comprises a supply of fuel for disposal by combustion in accordance with the invention. Such fuels include aggressive petroleum oils, pyrolysis oils, organic solvents and other fuels described herein, such as those that are blended with a non-fossil liquid fuel. The fuels described should if necessary be suitably prepared prior to combustion, that is heated and treated so as to remove solid material from the furet Viewed from a yet further aspect, the invention provides a disposal system for waste or unwanted fuels, such as waste organic solvents, and in particular waste solvents that may be contaminated with hazardous material, by means of combustion in a compression ignition engine in accordance with the invention.

Preferably also, the disposal system comprises any one or any combination of the following: means to blend the solvents in appropriate proportions with a non-fossil liquid fuel; means to agitate the blended fuel; means to supply the fuel to the engine; and means for supplying an enriched oxygen atmosphere to the combustion chamber of the engine.

Viewed from yet a further different aspect, the invention also provides an electricity generating system comprising a generator coupled to a compression ignition in accordance with the invention. Preferably, said system comprises a

supply of fuel for disposal by combustion in accordance with the invention. Such fuels should be suitably prepared and preferred fuels include the aggressive petroleum oils, organic solvents and other fuels described herein, such as those that are blended with a non-fossil liquid fuel. If necessary or desired, an enriched oxygen atmosphere may be provided in the combustion chamber of the engine, and in a preferred embodiment, there is an electricity generating system comprising a steam generator that utilises steam from a boiler heated by the hot exhaust gas coming from the engine.

It will be appreciated by those skilled in the art that the method of the invention would equally apply to low-speed wide bore compression ignition engines, as well as to high-speed engines, as they both operate in a similar manner.

As mentioned above, the fuel injector of the invention is particularly suitable for difficult-to-bum fuels that require an enriched oxygen combustion atmosphere to facilitate efficient combustion. However, the fuel injector device described by the invention may well have applications to improve the combustion of certain dense and viscous fuels, such as, for example, medium fuel oils in compression ignition engines operating under normal, naturally aspirated conditions.

It will also be appreciated that certain difficult to bum fuels may not require the use of an adapted fuel injector in accordance with the invention although they may require an enriched oxygen combustion atmosphere to facilitate combustion.

Accordingly, from a further aspect the invention provides a method of disposing of waste organic solvents comprising burning said solvents in an enriched oxygen atmosphere in a compression ignition engine and from a yet further aspect, the invention also provides a method of combusting aggressive petroleum oils comprising burning said oils in an enriched oxygen atmosphere in a compression ignition engine.

The invention also extends to fuel blends for combustion in accordance with the invention. A preferred fuel blend comprises between about 20 to 30% alcohol (s), 20 to 30% ketone (s) and 40 to 60% of a fuel providing lubricity, preferably a non-fossil fuel.

Some preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which Figure la illustrates schematically, in cross-section view, a conventional design of fuel injector used in a Lister-Petter engine; Figure Ib is an enlarged cross-section view of the tip of the of injector

described in Figure 1 a.

Figure 1 c is a cross-sectional view of a fuel injector device in accordance with the present invention; Figure 2 shows smoke density filter papers which illustrate the exhaust smoke coming from the Lister-Petter engine with alternative fuels and oxygen concentrations.

Figure 3 is a schematic illustration of a typical combustion and energy recovery system which may be operated using a combustion engine modified with the fuel injection device of the present invention and alternative fuels.

With reference to Figure la, a conventional steel fuel injector 1, typical of the type used for diesel fuelled engines, is shown located in the cylinder head 4 of a compression ignition engine. The needle 2 inside the injector 1 is in the closed position. When the needle 2 is raised inside the injector, fuel from the fuel pump is allowed, under pressure, to enter the injector 1 through a fuel supply line 3. The tip 5 of the injector protrudes through the cylinder head 4 into the combustion chamber 30 of the cylinder.

Figure 1 b shows an enlarged cross-section view of the steel tip of the fuel injector of Figure la. Upward movement of needle 2 allows fuel to be injected, under pressure, into the combustion chamber through a fuel delivery passage 6. The timing of the movement of needle 2 is finely controlled, so that fuel is injected into the combustion chamber at the precise point when the piston has reached the correct position in its cycle inside the engine cylinder. For ease of illustration in Figure lb, only one fuel delivery passage 6 is shown in the injector tip 5,-but in practise there are typically four or more fuel delivery passages spaced around the tip 5 of the injector. In the standard fuel injector, passage 6, which has a diameter of about 200 microns, is bored straight through the wall 32 of the tip 5 into the fuel chamber 34 located inside the injector, as shown in Figure lb. A nozzle orifice 36 is formed by the outermost section of the passage.

Figure 1 c shows a detail of an injector in accordance with the invention. In this case, the end of the passage 6 has been machined to form a conical fuel delivery nozzle 8. The outside diameter of the nozzle 8 can be between about 250 and 400 microns. After machining the cone, the external surface 38 of the injector tip 5 was then completely electroplated with chromium, to a thickness of about 6 microns, to provide a corrosion resistant coating 7 as illustrated in Figure 1 c. The coating 7 extends onto the walls of the nozzle 8, but does not obstruct the passage 6. This construction helps minimise corrosion of the tip 5 and improves the dispersion

of the fuel within the combustion chamber 30. Any sooty carbon deposits which form around the nozzles of fuel injectors will be washed into the combustion chamber during the next injection of fuel.

Fuel injectors, in accordance with the invention, may be used in any compression ignition engine. Preferably, however, they are used in an engine incorporating an energy recovery system, which is described with reference to the schematic illustration given in Figure 3.

In this embodiment, waste alcohol solvent, which has been analysed and filtered, is stored in a tank 9. Waste ketone solvent, such as methyl ethyl ketone, which has been analysed and filtered, is stored in a tank 10. Filtered waste cooking oil is stored in a tank 11 at a temperature of no more than 30 C.

Alcohol solvent from the tank 9, ketone solvent from the tank 10 and waste cooking oil from the tank 11 are gradually blended together in a tank 12, in the desired proportions. The tank 12 is gently heated to no more than 30 C and the blend is mixed by stirrer 13. Small amounts of other miscible waste organic solvents, including esters, ethers, glycol ethers and aliphatic, alicyclic and aromatic hydrocarbons, can be added, in appropriate proportions, to the solvent blend in the tank 12.

Blended fuel is transferred from the tank 12 to a work-in-progress tank 14, which is also gently heated to no more than 40oC. The fuel in tank 14 is agitated, for example, by a high speed propeller stirrer 15, to ensure that any water in the mixture is emulsified with the blended fuel. If necessary a small amount of a suitable emulsifying agent can be added to the blended fuel in the tank 14 to aid emulsification. The blended fuel is then pumped to the fuel injectors as described in Figure 1 c, located in the cylinder head of the compression ignition engine 16.

A different fuel may also be combusted in the engine 16, for example an aggressive petroleum oil, such as heavy fuel oil. In this embodiment, hot oil which has been filtered and centrifuge clarified is stored in a heated storage tank 26. The oil is heated such that it is sufficiently mobile to be injected into the engine. For a typical heavy fuel oil this would require a temperature of about 130 C. The hot oil is then pumped to the fuel injectors as described in Figure 1 c, located in the cylinder head of the engine 16.

The fuel injectors as described in Figure le, in the engine 16 would be designed to suit the particular fuel being delivered into the combustion chambers of the engine 16. Thus if different fuels are being combusted, it may be desirable to change the design of the delivery nozzles of the injectors from fuel to fuel.

Air rich in oxygen is pumped from a gas separation unit (not shown) to a valve 18 that controls the concentration of oxygen in the air supply to the engine 16 by selectively admitting atmospheric air to the oxygen rich air. The oxygen enriched air, typically containing 26% oxygen, is then introduced by the control valve 18 into the air intake manifold of the engine 16.

The combustion of the fuel in the engine 16 forces the engine pistons up and down and this movement is transmitted to a drive shaft, which operates an electricity generator 17.

A sensor 19 in the engine exhaust monitors the emission levels of carbon monoxide and nitrogen oxides, as well as the exhaust gas temperature. Once the system is set up and the engine is running at its optimum speed and power output, deviations in engine performance will be indicated by changes in the carbon monoxide level detected by sensor 19. The engine operation will therefore be controlled by the carbon monoxide measurement detected by the sensor 19, as well as by the engine management systems, the sensor 19 being linked to control valve 18, to enable the oxygen level to be adjusted, if necessary, to maintain efficient engine operation.

The exhaust gas passes to an abatement system 21, such as a selective catalytic reduction unit, where the concentration of nitrogen oxides in the exhaust is reduced by ammonia to an acceptable environmental level.

The hot exhaust gas is then used to raise steam in a steam boiler 22, the steam being used to drive a steam generator 23, which generates more electricity.

Steam is also passed through a heat exchanger 24 to produce hot water and the engine coolant is also passed through a heat exchanger 20 to produce hot water. The hot water is advantageously used in heating the fuel tanks.

Aggressive petroleum fuel oil usually contains high levels of sulphur, and therefore sulphur dioxide will be present in the exhaust gas. This may be abated by means of an alkaline scrubber, prior to the exhaust gas being released to the atmosphere through a chimney 25.

The efficacy of the present invention was assessed by performing combustion trials, using a high-speed Lister-Petter compression ignition engine.

This particular diesel engine is a two cylinder, four stroke engine, with direct fuel injection and a nominal capacity of one litre. The engine was run at the optimum speed, 2300 rpm, and the engine and fuel injection timing conditions as recommended by the engine manufacturer for operation with diesel fuel oil.

In a first trial, heavy fuel oil was hot filtered and centrifuge clarified prior to combustion, to remove large sized particulate material that could have blocked the engine fuel injectors. The resulting fuel had a density of 0.99 at 15 C and a viscosity of 926 cSt at 40 C. The fuel oil was heated to 130 C, to provide adequate mobility, before being supplied to the standard fuel injectors fitted to the engine.

It was not possible to combust the heavy fuel oil effectively under naturally aspirated conditions.

With oxygen enrichment, although the heavy fuel oil could be burned, it was not possible to maintain combustion effectively because of a deterioration in the performance of the standard fuel injectors. There was evidence of localised corrosion of the injector tips and hard deposits were forming on the tips and nozzles of the fuel injectors, thereby restricting flow of fuel to the combustion chambers of the engine, as well as on the cylinder walls and piston heads of the engine.

However, by using fuel injectors in accordance with the invention, e. g. an external fuel delivery nozzle diameter of about 300 microns and chromium coated tips, it was found that the aggressive heavy fuel oil could be run in a sustained manner, at a power output of 9-kWe, in an oxygen rich combustion atmosphere consisting of 26% oxygen, 74% nitrogen, in the Lister-Petter research engine. At the end of a prolonged engine run, inspection of the fuel injectors and the engine cylinders showed no evidence of corrosion on the injector tips, nor were solid deposits formed around the fuel delivery nozzles or within the cylinders of the engine. The exhaust smoke was relatively clean as illustrated in the smoke density filter paper in Figure 2b.

With regard to the combustion of solvents, combusting a mixture of ethanol and methyl ethyl ketone in the trial engine fitted with standard injectors, showed that with oxygen enrichment it was possible to ignite the solvents in the test engine by means of compression only. However, the actual combustion was not entirely satisfactory as the solvents tended to detonate after ignition, which resulted in an engine performance that was less smooth and less efficient than when diesel oil was used as fuel.

More importantly, the organic solvents in question have very poor lubricity properties compared to petroleum oils. The standard fuel pumps and fuel injectors on the test engine had been designed primarily for diesel oil and the trials indicated that the performance of the fuel pumps and the fuel injectors deteriorated when using solvents as fuel.

Both the fuel pumps and the fuel injector needles showed evidence of

mechanical wear when solvents were run for prolonged periods in the engine under enriched oxygen conditions. The tips of the fuel injectors also exhibited signs of corrosion and there was a tendency for hard deposits to form around the nozzles of the fuel injectors when burning organic solvents. In contrast, there was no evidence of component wear or deposit build-up when diesel oil was run in the test engine for the same period of time in an enriched oxygen atmosphere.

To improve this situation, a waste cooking oil was added to the solvent mixture to improve its lubricity. Combustion trials were carried out with a fuel blend consisting of 25% waste alcohol, 25% waste methyl ethyl ketone and 50% filtered waste cooking oil using the aforementioned Lister-Petter engine. The engine was fitted with fuel injectors in accordance with the invention, i. e. having fuel delivery nozzles with an external diameter of about 250 microns and chromium coated injector tips. The engine was run at its optimum speed, 2300 rpm, and the engine and fuel injection timing conditions as recommended by the engine manufacturer for continuous running with diesel fuel oil. The engine was operated in a special test rig where the mechanical load consisted of a high power direct current motor with a variable field voltage. The engine manufacturer recommended that the most favourable power output for continuous running at 2300 rpm was 9kWe, when using diesel oil as fuel.

The engine was first run naturally aspirated (i. e. 21% oxygen, 79% nitrogen) at a power output of9-kWe using diesel oil as fuel, to establish the normal engine operating parameters, including the exhaust emissions of carbon monoxide and nitrogen oxides, the exhaust smoke density and the exhaust temperature. Carbon monoxide in the exhaust gas indicates incomplete combustion-and the level of carbon monoxide in the exhaust gas therefore provides a good indication of the efficiency of the combustion process. A smoke density filter paper is illustrated in Figure 2a.

The solvent fuel blend was prepared by gently heating and stirring the mixture prior to being introduced to the engine, which was then run for short periods of time at a power output of9-kWe, under different oxygen concentrations, starting at a 5% enriched oxygen combustion atmosphere, i. e. 26% oxygen, 74% nitrogen. The oxygen content was then reduced in 1% steps until naturally aspirated conditions were reached, i. e. 21% oxygen, 79% nitrogen.

At 5% oxygen enrichment, the solvent fuel blend ignited by means of compression only and burned cleanly, as illustrated in the smoke density filter paper in Figure 2d and efficiently, with a carbon monoxide concentration in the exhaust

gas of 370 ppm. As the oxygen concentration in the air supply to the engine was decreased, the combustion of the solvent fuel blend gradually became less efficient and the exhaust smoke became increasingly polluted.

Under naturally aspirated conditions, the solvent fuel blend burned very poorly. The concentration of carbon monoxide in the exhaust gas had increased to 650 ppm and the exhaust smoke coming from the engine was black and high in particulates, as illustrated in the smoke density filter paper shown in Figure 2c.

The results of these short engine combustion trials suggested that the

optimum oxygen level required to efficiently combust the waste solvent fuel blend L was in the region of 4 to 5% enrichment, i. e. 25% oxygen, 75% nitrogen to 26% oxygen, 74% nitrogen.

A prolonged engine run was then carried out using the aforementioned solvent fuel blend, the modified injectors and a combustion atmosphere of 26% oxygen, 74% nitrogen. The prolonged run confirmed that combustion could be sustained smoothly and without loss of power.

When the fuel injectors were dismantled after the prolonged run there was no evidence of either corrosion on the injector tips or of deposit build-up around the fuel delivery nozzles. There was also no indication of mechanical wear to either the fuel pump or the fuel injector needles.

Table 1 below compares the results of the following prolonged engine runs: 1. Diesel oil under naturally aspirated combustion conditions, i. e. 21% oxygen, 79% nitrogen, with the engine having standard fuel injectors and running at 9-kWe power output. The diesel oil was delivered to the engine at ambient temperature.

2. Heavy fuel oil under enriched oxygen combustion conditions, i. e. 26% oxygen, 74% nitrogen, with the engine having specially designed fuel injectors and running at 10 kWe power output. The heavy fuel oil had been hot filtered and centrifuge clarified to produce a fuel with a density of 0.99 and a viscosity of 926 cSt at 40 C.

The heavy fuel oil was delivered to the engine at a temperature of 130 C.

3. A blended fuel consisting of 25% waste alcohol, 25% waste methyl ethyl ketone and 50% waste cooking oil under enriched oxygen combustion conditions, i. e. 26% oxygen, 74% nitrogen, with the engine having specially designed fuel injectors and running at 9-kWe power output. The constituents of the fuel blend had been pre- filtered and the fuel was delivered to the engine at a temperature of no more than 40 C.

Table 1 Results of Prolonged Engine Trials

Properties Diesel Oil Solvent Blend Heavy Fuel Oil 21% Oxygen 26% Oxygen 26% Oxygen Actual power output 9 9 10 kWe Power output 1.0 1.0 1.1 Relative CO emission 1.0 1.0 1.2 Relative NOx emission 1.0 2.4 2.7 Relative Exhaust temperature 428 432 556 C

For ease of comparison, most of the results in Table 1 are given as figures relative to the naturally aspirated engine running on diesel oil.

The results of the engine tests confirmed that the blend of waste solvents and waste cooking oil could be combusted efficiently in an enriched oxygen combustion atmosphere. With the fuel injectors of the invention, combustion could also be sustained for long periods without loss of power. The emission of carbon monoxide in the exhaust was similar to that of naturally aspirated diesel oil, although the exhaust smoke was much cleaner, as illustrated by the smoke density filter papers given in Figures 2a and 2d.

With the fuel injectors in accordance with the invention, and oxygen enrichment, the heavy fuel oil could be combusted efficiently,-and in a sustained manner, even at a power output 10% higher than the optimum level recommended for diesel oil. At this increased power output, the measured carbon monoxide emission level, 460 ppm, was well below specified environmental limits and the exhaust smoke remained relatively clean.

As to be expected, in an enriched oxygen combustion atmosphere the level of nitrogen oxides in the exhaust was higher than with naturally aspirated combustion. Nitrogen oxides in the exhaust can, however, be reduced by well established abatement techniques, such as selective catalytic reduction with ammonia.

From the above it will be seen that the invention enables aggressive, dense and viscous petroleum oils, such as heavy fuel oil, heavy residual fuel oils, bunker fuel and waste mineral oil to be effectively combusted in a compression ignition

engine. The combustion of dense, viscous, acidic pyrolysis oil may also benefit from the invention.

The invention also provides an effective and safe method of disposing of waste organic solvents, such as alcohols and ketones.

The lubricity of solvents such as those above can be improved by blending the solvents with a suitable oil before combustion. The oil would provide the lubricity required to protect the mechanical parts in the engine fuel delivery system, whilst a blend of solvents and oil would also result in controlled combustion, without detonation, providing a smoother and more efficient engine performance.

Preferably the blending oils are from a renewable source.

Claims

Claims 1. A fuel injector comprising a fuel injector tip, the external surface of said tip being coated with a protective layer, and having one or more outwardly flaring fuel delivery nozzles provided in that surface.
2. A fuel injector as claimed in claim 1 wherein said tip is coated with chromium.
3. A fuel injector as claimed in claim 1 or 2 wherein said coating is an electroplated coating.
4. A fuel injector as claimed in any preceding claim wherein said coating is about 2 to l5 microns thick, preferably 4 to 12 microns thick and most preferably between about 6 and 10 microns thick.
5. A fuel injector as claimed in any preceding claim wherein the coating covers substantially the entire external surface of the fuel injector tip that protrudes into the combustion chamber of the engine.
6. A fuel injector as claimed in any preceding claim wherein said fuel delivery nozzle flares conically outwards.
7. A fuel injector as claimed in any preceding claim wherein the external diameter of the outwardly flared nozzle is from about 250 to over 400 microns, and most preferably 250 to 300 microns.
8. A compression ignition engine incorporating a fuel injector as claimed in any preceding claim.
9. A method of combusting a fuel, wherein said fuel is burned in a compression ignition engine as claimed in claim 8.

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10. A method as claimed in claim 9 wherein said fuel is an aggressive, dense and viscous petroleum oil such as heavy fuel oil, residual fuel oil, bunker fuel, and waste mineral oil, or pyrolysis oil or an organic solvent, or an animal or vegetable oil or fat, or blends and mixtures thereof.
11. A method as claimed in claim 9 or 10 wherein said solvent fuel includes alcohols such as methanol, ethanol, I-propanol, and 2-propanol, and ketones such as acetone, and methyl ethyl ketone.
12. A method as claimed in claim 11 wherein said solvent fuel is produced from biomass material.
13. A method as claimed in any one of claims 9 to 12 wherein said solvent fuel includes, ethers, glycol ethers, and aliphatic, alicyclic and aromatic hydrocarbons
14. A method as claimed in any of claims 9 to 13 wherein said solvent fuel is a waste solvent.
15. A method as claimed in any of claims 9 to 14 wherein said solvent fuel is blended with a substance to improve its lubricity.
16. A method as claimed in claim 15 wherein said blending substance is a renewable non-fossil liquid fuel.
17. A method as claimed in claim 16 wherein said blending substance is an animal or vegetable oil or fat.
18. A method as claimed in claim 17 wherein said blending substance is waste cooking oil.
19. A method as claimed in any of claims 15 to 18 wherein the composition of the fuel blend is about 20 to 30% alcohol (s), 20 to 30% ketone (s) and 40 to 60% of

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a substance to provide lubricity.
20. A method as claimed in any of claims 9 to 19 further comprising emulsifying any water in the fuel.
21. A method as claimed in any of claims 9 to 20 wherein an enriched oxygen atmosphere is provided in the combustion chamber of the engine.
22. A method as claimed in claim 21 wherein the combustion atmosphere of the engine is enriched with oxygen to between 3% and 10% above naturally aspirated conditions (i. e. between 24% oxygen, 76 nitrogen and 31% oxygen, 69% nitrogen).
23. A method as claimed in claims 21 wherein the combustion atmosphere in the engine is enriched with oxygen to between 4% and 5% above naturally aspirated conditions (i. e. between 25% oxygen, 75% nitrogen and 26% oxygen, 74% nitrogen).
24. A method as claimed in claims 21 to 23 wherein the level of nitrogen oxides in the exhaust gas is abated, for example, by selective catalytic reduction with ammonia.
25. A method as claimed in any of claims 9 to 24 wherein the engine is coupled to an electrical generator.
26. A method as claimed in any of claims 9 to 25 wherein exhaust gas from the engine is used to raise steam in a boiler and the steam is used to produce electricity in a steam generator.
27. An electricity generating system comprising a compression ignition engine as claimed in claim 8 coupled to an electrical generator.
28. A disposal system for waste or unwanted fuels, such as waste organic

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solvents, and in particular waste solvents that may be contaminated with hazardous material, by means of combustion in an enriched oxygen atmosphere in a compression ignition engine as claimed in claim 8.
29. A method of disposing of waste organic solvents, and in particular waste solvents that may be contaminated with hazardous material, comprising burning blends of said solvents with a non-fossil oil or fat in an enriched oxygen atmosphere in a compression ignition engine as claimed in claim 8.
30. A method of combusting aggressive petroleum oils comprising burning said oils in an enriched oxygen atmosphere in a compression ignition engine as claimed in claim 8.