The present invention relates to methods and apparatus for improving the combustion of fuels particularly fuels that are slow to ignite such as slurries of coal or other porous carbonaceous material in an aqueous carrier liquid.

BACKGROUND ART One of the most abundant combustible fuel reserves is coal with projections that there is at least 5 times the energy reserve in coal deposits that are easily recovered, than is available in recoverable oil reserves. Coal is derived from plant or forest matter laid down eons ago, and while this invention is primarily designed for coal combustion it is also applicable to other fuels that are comprised of finely powdered porous carbonaceous materials. Such material could be timber, particularly timber sawmill dust, waste material from agriculture such as rice husks or crushed coconut husks, or even pulped paper waste, all of which are primarily carbonaceous, and have porosity.

The combustion of coal particles or any other porous carbonaceous material such as timber dust and paper waste is directly related to its surface area. As will be clear to persons skilled in the art, the greater the surface area to volume ratio of the carbonaceous material, the faster and more efficient the combustion. Therefore, it can be seen that the smaller the particles of carbonaceous material the greater the surface area to volume ratio and the faster and more efficient the combustion.

One particular disadvantage of particles of carbonaceous material such as coal is that they do not flow particularly well in a fuel distribution system. It was to overcome this disadvantage that proposals have been

made to form fine particles of carbonaceous material into slurries with water. Typically such slurries will contain 50 to 70% by weight of coal or another carbonaceous material, from 29 to 39% by weight of water and approximately 1% by weight of a surfactant or other additive. This has other disadvantages, however, as when a coal/water slurry fuel is introduced into a combustion system there is always a significant time lag where the residual heat of combustion is transferred to the coal/water slurry, first boiling off the water, then volatilising the oils and tars contained in the coal, then heating and swelling the char and finally burning the large char particles. In particular it is the period of time and quantity of energy required to boil the water surrounding the particle and in the particle voids or pores which reduces the efficiency of a coal/water slurry fined combustion process. This energy is taken from the surrounding hot gases in the combustion chamber which would otherwise produce useful work. As the coal/water slurry is being heated in the combustion chamber, the thin layer of water surrounding each particle and the water in the particle voids or pores boils off as steam. This steam leaves the particle as a wave of gas at a slightly higher pressure than the surrounding gas. This wave of steam leaving the particle produces on area of lower pressure behind it which must be filled. The surrounding air, with its constituent oxygen content, flows into and fills this area of low pressure near the surface of particle to provide oxygen for combustion of the particle. It is not until the thin layer or film of water surrounding each particle has been removed to allow oxygen to the surface of the particle that combustion may commence.

While this combustion mechanism may not apply to all particles of carbonaceous material it is likely that a

large proportion will combust as described above.

It will therefore be seen that to improve combustion of fuels consisting of particles of carbonaceous material in a carrier liquid, it is preferable to increase the surface area to volume ratio of the carbonaceous material, and/or minimise the energy lost to heating up the aqueous carrier medium.

In an effort to ameliorate the disadvantages of the prior art it is proposed to provide a method and apparatus of increasing the surface area to volume ratio of fuels consisting of particles of carbonaceous material in a carrier liquid and reduce energy loss which offers the public with a choice over the prior art and which, at least in the preferred embodiments, provides faster and more efficient and complete combustion of such a fuel. DISCLOSURE OF THE INVENTION

The first aspect of the present invention provides a method for treating a slurry containing water and porous particles of carbonaceous material, the method comprising elevating the pressure and temperature of the slurry to heat the water in the slurry including the water contained in pores or voids in the particles while maintaining the water in a liquid state and passing said slurry at the elevated pressure and temperature into an enclosed space having a pressure substantially below that of the elevated pressure and a temperature at least substantially as high as that elevated temperature such that the water in the slurry including water in the pores and voids of the particles of carbonaceous material flash boils and the particles shatter to form a number of smaller sized particles of carbonaceous material.

The present invention also provides an apparatus for treating a slurry containing water and porous particles of carbonaceous material the apparatus comprising a pressurizing means, heat transfer means and injection

means, the pressurizing means being adapted to elevate the pressure of the slurry, the heat transfer means being adapted to heat the slurry to an elevated temperature wherein, at the pressure applied by the pressurizing means the water in the slurry including the water contained in pores or voids of the particles is maintained in a liquid state, the injection means being adapted to deliver the slurry at the elevated temperature and pressure into an enclosed space having a pressure substantially below the elevated pressure and a temperature at least substantially as high as the elevated temperature such that, the water in the slurry including the water contained in the pores and voids of the particles of carbonaceous material flash boils and the particles shatter to form a number of smaller sized particles of carbonaceous material.

As outlined above, most carbonaceous particles such as coal, timber dust, etc, have voids which may be filled with all types of matter, such as air, water, hydrocarbon gas, tar, oil or other volatiles. When such porous particles of carbonaceous material are used to form a slurry, some of the water in the slurry may enter these voids. If the slurry is placed under pressure more water is forced into these voids.

Not all carbonaceous material is suitable for use with the present inventive method and apparatus.

According to the present invention, for the shattering of the carbonaceous particle to occur it must have some pores or voids which are filled with water at an elevated temperature and pressure. If the particle of carbonaceous material does not contain any pores or voids, or these pores or voids collapse at the elevated temperature and pressure required by the present invention, the steam shattering cannot take place.

Most coals are suitable for use with the present invention since they contain some pores or voids. Some

coals or other carbonaceous materials however, do not contain any pores or voids and/or the pores or voids collapse upon heating and pressurization and become plastic or tar like, at higher temperatures or pressures. It is therefore preferable that these types of coals are treated at lower temperatures and pressures. Such lower temperatures and pressures reduce the efficiency of the treatment, however, and these types of coal are therefore less desirable. It is preferable to use coals with a high porosity. The chemical cleaning process using caustic soda followed by an acid wash (known as the CSIRO "Ultra-Clean" Coal Process) on the Hydrofluoric Acid Process (developed by Hitachi) both produce coal which is particularly suitable for this process. These processes produce a coal which is highly porous, has less ash and therefore less wear and less slag in the combustion process and which is particularly suitable for shattering into shards etc since the pores and voids formed by this process are elongated due to the mineral oxides which are removed, being formed as layers in the coal seam.

The particles of carbonaceous material in the slurry are preferably below 70 microns in size. The size of the particles e.g. coal used for the inventive method and apparatus may be chosen in accordance with the type of engine, that the slurry is to fuel. In larger slower moving engines larger size coal particles may be used. In smaller faster engines, smaller particles are preferred. In a further embodiment of the invention the slurry contains particles of 10-1 microns temperature while maintaining the water in the slurry including the water in the pores.

It has been found that finer particles of coal obtained during conventional coal washery operation often have greater porosity and other desirable characteristics

for this process. These fine particles usually disposed of as "washery fines" are potentially very suitable for inclusion in a carrier liquid for the present process.

When coal is used as the carbonaceous material, the smaller coal particles produced by shattering of larger coal particles, according to the present invention, are usually in the form of thin fingers or shards of coal. These shards have a much higher surface area to volume ratio than the unshattered coal particles leading to an increase in surface area available for combustion and thereby producing faster burning of the carbonaceous material.

When the particles of carbonaceous material are shattered according to the present invention not only is the surface area available for combustion increased but a proportion of the material shattered is flung about the combustion chamber in such a way that at least some of the water surrounding each particle separates from the surface of the particle and allows the oxygen contained in the surrounding air to reach the surface of the particle and for combustion to commence. This separation of water from the particles of carbonaceous material is assisted by the fact that a large proportion of the particles are irregular in shape. Movement and tumbling of an irregular shaped particle such as a shard through space tends to break through its surrounding layer of water more easily than a regular shaped particle. The surrounding water may also be flung off the particle or blown off the particle by its movement through the gas filled enclosed space. The raising of pressure and temperature of the slurry may be accomplished by several different methods. In one embodiment of the present invention, the temperature of the slurry is raised by heat transfer with the hot exhaust gases leaving a combustion process where the small particles of carbonaceous material, resulting from this

aspect of the present invention, are burnt.

The hot exhaust gases from any combustion process leave the combustion chamber at high temperature. By conducting a heat exchange between these hot exhaust gases and the slurry, the temperature of the incoming slurry may be increased in a cost effective manner. Such a heat transfer with the hot exhaust gases of the combustion process may be advantageously accomplished by circulating the slurry around an exhaust outlet of the combustion process prior to entry into the enclosed area of reduced pressure or by circulating an intermediate heat transfer liquid such as a molten salt around an exhaust outlet for subsequent heat exchange with the slurry.

The enclosed space of reduced pressure may also be at a substantially higher temperature than the elevated temperature of the slurry leading to quicker and more complete flash boiling of the water in the pores or voids of the carbonaceous material. Further, the enclosed space of reduced pressure may, in fact be the combustion chamber of a combustion process in which the smaller particles of carbonaceous material are burnt. For example, in a diesel engine the combustion chamber is approximately at 10-40 atmospheric (Atm) pressure. By increasing the pressure of the coal/water slurry above these levels, shattering of the coal particles may be accomplished by injection of the hot pressurized slurry directly into the combustion chamber.

The present invention may operate best within a band of temperature and pressure for any one apparatus but is always sensitive to variations in the fuel. As the term coal covers such a wide variety of material no one system is applicable to all coals. The present invention is applicable to most coking coals and many thermal coals. Some coals will have characteristics that make them unsuitable, such as low plastic temperatures, or tendency

to form tars that clog the system or jam moving parts as discussed above.

The upper limit of temperature and pressure for this steam explosion technique is imposed by the supercritical point of water, which is about 320 degrees Centigrade at about 220 atmospheres. Beyond this point the solvent power of water is markedly increased, and the structure of the coal or carbonaceous material and its porosity would be subject to change. There is no clear cut line between the area of near critical solubility and the area where the structural integrity of the coal or carbonaceous particle is unchanged. There is an area, which varies with the fuel, and pressures and temperatures where there is a pessimism reaction. That is where the carbonaceous fuel is still largely solid, or even agglomerated, but is plastic enough to change the porosity structure.

The lower limit is the temperature and pressure that will cause acceptable steam shattering of the porous fuel. As the pressure in a diesel engine combustion chamber for example is 20-40 atmospheres the elevated pressure of the slurry must be significantly greater. An elevated pressure of 70-80 atmospheres (which would give 40-50 atm. differential) or greater would be desirable for rapid shattering, which is equivalent to the slurry being heated to about 285 degrees C. Some carbonaceous material may soften and become plastic or tar like below 320 degrees C. for example most cellulose materials will break down and lose its porous nature at somewhat lower temperature.

In a second aspect, the present invention provides a method for combusting a slurry containing water and particles of a carbonaceous material in a diesel engine comprising the steps of injecting the slurry into a combustion space defined within the diesel engine toward a

target means located on an exhaust valve of the engine and maintained at an elevated temperature wherein a proportion of smaller, lighter particles of carbonaceous material combust prior to impact with the target means, and a proportion of larger, heavier particles of carbonaceous material impact on the target means and shatter to form a number of smaller particles, which subsequently combust. The present invention also provides in this second aspect a diesel engine which is adapted to combust a fuel slurry containing water and porous particles of carbonaceous material and which comprises a combustion space, a fuel injection means, and means to ignite the fuel, the improvement comprising said injection means being adapted to produce a flow of particles of carbonaceous material in said combustion space, a target means located on an exhaust valve of the engine and maintained at an elevated temperature, being positioned on the path of flow of the particles of carbonaceous material such that in use, a proportion of lighter, smaller particles of carbonaceous material will be combusted prior to impact with the target means and a proportion of heavier, larger particles of carbonaceous material will impact of the target means and shatter to form a number of smaller particles which subsequently combust. In this second aspect of the present invention, a proportion of the larger, heavier particles of carbonaceous material, which are slow to combust, are broken down to smaller sizes as a result of impact with a target means located within the combustion space. This impact shatters the particles reducing their size and thereby increasing the surface area to volume ratio of each particle and the total surface area of carbonaceous material available for combustion. Such an increase in available surface area increases the speed and efficiency of combustion.

Further, shattering of the particle leads to liberation of the water trapped in the pores and voids of the particles. This water quickly evaporates in the combustion space leaving the existing heat of combustion to burn the remaining particles of carbonaceous material. In accordance with the present invention not all the particles of carbonaceous material in the slurry injected into the combustion space will strike the target means. Most carbonaceous materials have a reasonably consistent density. Larger particles will therefore be heavier than smaller particles. A proportion of the larger, heavier particles of carbonaceous material, with the greatest mass and lowest surface area to volume ratio, will hold their velocity of injection best and therefore strike the target means with the greatest momentum. Some of the smaller, lighter particles of carbonaceous material will slow down as they move toward the target means. This slowing down in the combustion chamber leads to combustion of the smaller particles prior to impact with the target means such that they do not strike the target means at all.

In a preferred embodiment the slurry is injected into a clerestory chamber which is in substantially unrestricted communication with the cylinder of a diesel engine. As used hereinafter the term "clerestory combustion chamber" refers to a combustion space in the cylinder head of a diesel engine, which is in substantially unrestricted communication with the cylinder of the engine, the exhaust valve of the engine being contained in the clerestory chamber. The clerestory chamber is preferably designed to provide a controlled turbulence to mix the particles of carbonaceous material and carrier liquid with the available oxygen in the clerestory combustion chamber. By providing such controlled turbulent mixing in the clerestory chamber, a layer of relatively stagnant gas is

produced on the inner surface of the clerestory chamber to prevent excessive loss of the heat of combustion to the walls of the clerestory combustion chamber.

In another embodiment of the present invention the target means is positioned on one side of the clerestory combustion chamber, the fuel injection means being positioned on an opposed side of the clerestory combustion chamber. In this way, the particles of carbonaceous material are injected substantially directly at the target means.

The target means is positioned on a surface of an exhaust valve facing into the combustion chamber, so that the heat of the exhaust gases raises the temperature of the target means which in turn raises the temperature of the particles of carbonaceous material impacting on the target means. The exhaust valve on which the target means sits is preferably insulated from the walls of the clerestory combustion chamber by means of an insulating valve seat made of stabilised zirconia thereby maintaining the exhaust valve and target at the highest possible temperature.

While the target may simply be a point on the exhaust valve against which some of the carbonaceous particles impact, it may also comprise a raised position on the exhaust valve protruding toward the combustion space. By protruding into the combustion space the shattered fuel particles are mixed with the greatest available oxygen in the air, and the combustion is maintained away from the walls of the combustion chamber. The target and exhaust valve may be machined as one piece from the same material to prevent separation of the target and exhaust valve, through heating and cooling of metals with different expansion rates. It is also possible to have the target made from a wear resistant material where the joining technology is able to reliably cope with thermal stress

over very many cycles.

BRIEF DESCRIPTION OF DRAWINGS

In order that the nature of the present invention may be more clearly understood preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figures 1 - 3 are side elevational views of a coal particle subjected to treatment according to a first embodiment of the present invention; Figure 4 is a flow diagram of a diesel engine according to a second embodiment of the present invention; Figure 5 is a partial plan view of a cylinder head of a diesel engine according to a fourth embodiment of the present invention; Figure 6 is a side elevational view through section B-B of Figure 5;

Figure 7 is a side elevational view through section C-C of Figure 5;

MODES FOR CARRYING OUT THE INVENTION Referring firstly to Figures 1 - 3, Figure 1 shows a coal particle 20 in a slurry. While the present invention is suitable for slurries with any type of porous particle of carbonaceous material in an aqueous carrier liquid, coal is shown here for the sake of illustration. The coal particle has pores and voids 21 throughout its volume. As previously outlined there are several types of physical or chemical processes to increase the porosity of coal or other carbonaceous materials. The voids and pores in the coal are at least partially filled with water in the slurry. The coal particle may be thought of as porous with narrow passages connecting the voids to the surface.

According to the present invention, prior to entry into the combustion chamber of an engine (see for example Figures 5 - 7) the slurry is placed under pressure, forcing more water into voids 21. The temperature of the

slurry is also raised, while the water in the coal particle voids or pores is maintained as a liquid.

The heated and pressurised coal/water slurry is then transferred to an enclosed area having substantially reduced pressure and a temperature substantially as high as the slurry. This reduction in pressure with no corresponding drop in temperature causes flash boiling of the water in the coal particle voids. Not wishing to be bound by any scientific theory, it appears that this decrease in pressure initially leads to swelling of the particle 20 as shown in Figure 2, due to the build up of steam in the voids 21. Additionally, a certain amount of steam 22 will escape along with some of the volatiles 23 in the coal such as tar and oil escaping with the steam cloud.

As seen in Figure 3, a fraction of a second after this initial expansion of the coal particle 20, steam pressure in the coal particle voids builds rapidly to such an extent that the coal particle 20 is shattered into a number of smaller particles or shards 24 with the remaining coal volatiles being expressed as fine droplets 25.

This increase in the surface area of coal particles leads to an increase in the speed, efficiency and cleanliness of the combustion process.

Additionally, since the water in the voids of the porous particle is liberated no heat of combustion is lost to heating this water to boil it off prior to combustion of the smaller particles. Further, the fine droplets of volatiles expressed from the particle burn more easily than the coal and may form several points for initiation of combustion in a combustion chamber.

To provide even greater efficiency, it is possible that heating of the coal/water slurry is achieved by heat

exchange with the hot exhaust gases leaving a combustion process, for example, a combustion process in which the carbonaceous particles are burnt.

Figure 4 illustrates an embodiment of the inventive process operating in an enclosed combustion engine. A coal/water slurry 70 at ambient temperature and pressure is pumped from a fuel tank 71 to an engine compartment and then into a fuel delivery system by an engine driven piston pump 72 preferably driven off an engine auxiliary drive shaft (not shown) . This small piston pump 72 forces the slurry 70 into a "common rail" system of capillary tubing still at ambient temperature.

The pressurised coal/water slurry is then heated by being fed through a heat exchange unit 76 that may be heated by engine coolant or any other heat transfer medium 77 circulated by pump 80 around a heat transfer circuit. The heat transfer medium 77 is heated by the hot exhaust gases of combustion in heat exchange unit 78. Alternatively, the slurry may be pumped through a coil of the capillary tubing that surrounds the exhaust outlet 75. The pressure level within the fuel delivery system is preferably maintained at a preset level of between 100 and 200 Atm by a pressure relief valve 81 close to piston pumps 72. Valve 81 would vent overflow of the coal/water slurry back to the main fuel tank.

The pressure of the fuel delivery system is such that boiling of the coal/water slurry is suppressed at quite high temperatures. However, the energy to cause rapid production of steam is available once the pressure of the slurry is rapidly lowered. There may also be some extraction of volatile material from the coal upon pressure reduction of the slurry, depending on the coal type.

Such a pressure reduction is achieved by injecting the heated and pressurised coal/water slurry 70 into an

area of reduced pressure and a temperature substantially as high as the slurry. One such area is the combustion chamber itself. For example in a diesel engine the combustion chamber is at 10 - 40 Atm. At the point that the injection means 73 is opened, the coal/water slurry is released from a pressure of 100 - 200 Atm into the combustion chamber 74 where the pressure will be from 10 - 40 Atm and the temperature will in fact be higher than the injected slurry. This will cause the water in the voids or pores of the carbonaceous material to turn to steam very rapidly. As coal for example has up to 20% of its volume as voids, these voids serve as detonation points for the water to almost instantaneously boil to steam and explode the coal particles.

Thus with a coal/water slurry that has a majority of its coal particles at about 50 microns, after this steam explosion process, the particles will have a much smaller particle size and more jagged shape. This increases the surface area available for combustion quite substantially and reduces the amount of water in the combustion chamber which must be boiled off prior to combustion of the carbonaceous material.

The hot exhaust gases of the combustion chamber 74 leave through exhaust outlets 75 to heat exchange unit 78 and the energy produced by combustion is transformed into work 79.

As shown in Figure 4 the thermal energy required to raise the temperature of the coal/water slurry 70 is preferably extracted from the hot combustion gases in the exhaust of a diesel engine by the transfer of heat from the hot exhaust gases to an intermediate heat transfer liquid 77 in a heat exchanger system.

The heat transfer liquid 77 is pumped through the exhaust heat exchange unit 78, which may be a casing

surrounding the exhaust passage, or a heat exchange tubing that has a capillary flow through it. The heat exchange unit 78 may line the walls of the exhaust passage 75 and/or protrude into the gas flow. The heat exchange unit 78 may also be fitted with fins or protrusions to increase its surface area for heat transfer into the fluid. Fins fitted to the exhaust heat exchange unit 78 may also impart motion to the exhaust gas 75 to enable better flow and/or more efficient heat recovery.

Heat transfer liquid 77 enters the exhaust heat exchange unit 78 at the point furthest from the combustion and is directed to the point closest to the combustion i.e. counter current heat exchange. The liquid 77 may be any suitable material that is a liquid at the working temperature of the system. As the density of energy that can be transferred by a volume of liquid is an efficiency factor in this system the liquid that has greatest capacity to transfer thermal energy relative to its volume is desired. Some metals and metal alloys are liquid in the temperature ranges considered; 150 to 450 degrees Centigrade (C), but a eutectic salt mix is a particularly suitable liquid for heat transfer.

The heat transfer liquid 77 is then pumped from the heat exchange unit 78 in the exhaust or flue gas stream to a point where the heat may be transferred to the coal water slurry in heat exchange unit 76. The coal/water slurry has before this heat transfer, been bought to a high pressure, by means of a displacement pump 72 at ambient temperature, or a temperature less than 100 degrees C. The level of this pressure is higher than the boiling point of the coal/water slurry at the maximum temperature possible by the heat transfer mechanism so that the water in the voids or pores of the particle is maintained as a liquid. This maximum temperature of the

heat transfer mechanism will vary from system to system depending on efficiency of combustion and efficiency of heat recovery, and transfer.

In the process of the present invention a majority of preheating of the incoming fuel has been achieved from waste heat, before combustion, and thus combustion is more rapid and efficient. The transfer of heat from the waste end of the combustion cycle into this system of preheating under pressure, is a beneficiation of the fuel that allows higher thermal efficiencies to be achieved. This is because there is more heat to do work, and less heat vented to atmosphere.

In a diesel engine the time available for combustion is limited by the engine speed. Rapid combustion of fine shards of shattered coal increases combustion efficiency, and reduces wear particles of unburned char reaching the piston ring/cylinder wall interface.

In practice there will be shards of differing sizes and shapes evolved, depending on coal type and preparation. Beginning with a suitable vitrinite coal, reduced to be all less than 20 microns, the majority of shards should have a mass of less than that of a regular particle of two microns diameter. The vast majority (by number count) will be sub-micron. The abovementioned inventive method and apparatus may be used in conjunction with a second aspect of the present invention as shown in Figures 5-7.

Figures 5-7 illustrate a cylinder head 10 of a diesel engine according to a fourth embodiment of the present invention. In Figures 5-7 the exhaust 11 and inlet valves 12 are preferably actuated by direct cam shaft action by cam shafts in line above the valve access but not shown in the drawings.

The injection of fuel by injection means 13 may also be controlled by cam shaft actuation, which is preferably

variable in its timing allowing for advance and retardation of the fuel injection timing, or is actuated by electromechanical control solenoid.

This provides an engine with either a triple overhead cam shaft with cam shafts geared together and driven at half the crank shaft speeds, or a double overhead camshaft with a drive for signals to the electromechanical solenoid.

It is preferable that if the fuel used comprises a coal/water slurry, the coal is a chemically leached product with a very low ash content (typically less than 0.5%). It should be noted however that any fuel consisting of a slurry containing water and porous particles of carbonaceous material, may be used in the inventive process. In leaching coal, the inorganic and mineral content is removed leaving voids that are larger than unleached coal and a low ash level which is desirable in reducing engine wear and particulate emissions.

The fuel injection means 13 directs the slurry comprising porous particles of carbonaceous material in water, onto a target means 14 within the combustion chamber 15. A proportion of smaller, lighter particles will burn prior to impact with the target means 14. A proportion of larger, heavier particles of carbonaceous material in the fuel will hold their speed of injection better and strike the target means 14, breaking up into smaller particles which subsequently combust more easily. It is preferable according to the present invention to provide a clerestory chamber 16, in communication with a cylinder of the diesel engine (not shown) for mixing the fuel with oxygen from inlet 12 prior to combustion.

This clerestory chamber 16 is designed to provide controlled turbulence to mix the incoming fuel charge with oxygen from inlet 12 prior to combustion. It is preferable that the clerestory chamber 16 be maintained at

the highest temperature possible. Excessive turbulence in the clerestory chamber 16 leads to scrubbing away, from the inner surface of the chamber walls, of a relatively stagnant layer of gas which acts as an insulating layer to prevent excessive loss of heat of combustion to the chamber walls. It is therefore preferable to inject the slurry at a moderate velocity into the controlled turbulence produced by the clerestory chamber.

This clerestory combustion chamber 16 may be attached to the cylinder cover 17 by studs (not shown) with heat resistant gaskets therebetween. Cooling and lubrication of the exhaust valve stem is by a flow of lubricant. The cylinder cover like the cylinder is cooled by either air or liquid coolant. The fuel/air turbulence in the clerestory chamber 16 is preferably controlled and moderate, to produce a very thin, relatively stagnant layer of gas on the inner surface of the chamber walls, which acts as an insulating layer to prevent excessive loss of heat of combustion to the chamber walls, this is possible due to the open and unrestricted access of the cylinder to the combustion chamber. If the velocity of the fuel injected is excessive the solid particles may cause severe erosive wear of the fuel injector system. It is therefore preferable to inject the slurry at a moderate velocity into the controlled turbulence produced by the clerestory chamber. The steam explosion of the particles of carbonaceous material also acts to break up and mix the fuel stream, unlike the very high pressure injection or violently turbulent air required in traditional diesel engine systems.

The fuel injection is a simple stream of slurry at modest velocity so as to reduce the energy available in the particles of carbonaceous material. Solid particles at high velocity have the power to create unwanted erosive wear and as such the system may be designed to minimise

the velocity of the incoming fuel.

As shown in Figure 7, the target means 14 is positioned on the face of the exhaust valve 11 facing into the clerestory chamber 16. In this way the target means 14 may be maintained at an elevated temperature. It is also preferable to position the fuel injection means 13 on an opposed side of the clerestory chamber 16 such that the slurry is injected directly at the target means 14. The exhaust valve 11 and target means 14 may be constructed as one piece from the same material or alternatively from different materials joined, for example, by friction welding. The target means 14 for example may be constructed from a very hard material, such as tungsten carbide and coated with a harder material such as titanium nitride for even greater wear resistance.

The target means 14 is preferably upstanding from the surrounding surface of the exhaust valve 11 so that the impact of the particles of carbonaceous material with the target means 14 occurs near the centre of the clerestory combustion chamber 16.

The apparatus of Figures 5-7 may be used in conjunction with the steam explosion method shown in Figures 1 - 4 and as described above. The steam explosion step may take place between the injection means 13 and impact on the exhaust valve target 14 or at that point when the impact with the hot metal target 14 raises the temperature further (see Figure 7) . Upon impact the stream of coal/water slurry will have become a cloud of steam, fine droplets of volatiles escaping from the coal particles and sub-micron coal particles which may be quickly spread about the clerestory combustion chamber shown in Figures 5-7.

Where the coal steam shattering process has less than desired efficiency i.e. a reasonable proportion of particles left unshattered for some reason, then these

particles may be attacked by using a target means within the combustion chamber as shown in Figures 5 - 7.

The target smashing process is selective as the largest particles, which have the greatest mass, and the lowest ratio of surface area to mass would hold the velocity of injection best, and thus the smaller, lighter, shattered shards would slow down in the clerestory chamber and combust prior to impact with the target means.

The unshattered particles would smash against this hot target being fragmented and raised in temperature by forced association with the hot metal. There is thus a transfer of heat energy from the "target" to the particle in a very short time, and a smashing of the particle into smaller fragments. The inventive process is suitable for a "rich combustion - lean burn" combustion, to reduce nitrous oxide formation. The water, as steam in the combustion chamber also reduces the maximum temperature of combustion, thereby reducing the potential to form nitrous oxides. A coal/water slurry is usually 50% to 70% coal solids by weight.

Finally, as this system depends for part of the ignition energy being provided by the high heat levels within the combustion chamber and a very high temperature of the exhaust valve, then there must be a special provision for starting from cold.

The present invention is most suitable where the combustion of the particles of carbonaceous material may be carried out for long periods of time without stopping and cooling down. Starting from cold may be by a separate injection system where a starting fluid of liquid diethyl ether and diesel fuel, taken from a second small fuel tank is injected. This fuel is injected at a preset reduced volume till the exhaust valve has reached a temperature that is sufficient to autoignite the coal/water slurry.

This start up procedure allows for the warm up of the exhaust valve and the coiled capillary that lines the exhaust port. At the same time it has the beneficial effect of not allowing full power output till full lubrication flow is established.

Alternatively the diesel engine shown in figure 4 may be started from cold by the following steps. 1) The coal water slurry is brought up to pressure (of about 200 atmospheres) by a small displacement pump. 2) The heat transfer liquid is brought up to temperature by electrical heating which brings the slurry to the temperature (of about 350 degrees C.) where the steam shattering will take place; and the temperature and pressure will ignite both the volatile tar oils and the shattered shards.

3) A pencil type glow plug is brought up to temperature of about 1,100 degrees C. by internal electrical heating.

4) The engine coolant is brought up to temperature of about 90 degrees C. by electrical heaters. 5) The clerestory combustion chamber may be heated to about 200 degrees C. by electrical heaters. 6) Engine is cranked and fuel is injected.

At the first injection of fuel there is combustion initiated by the glow plug, but the speed of combustion is slower than in normal operation which results in the temperature of the exhaust gas being higher when it passes the exhaust valve.

This causes the exhaust valve and clerestory combustion chamber to heat up rapidly to a point where the majority of the fuel is self igniting on injection, and the exhaust valve serves as a hotter point for the shattering and ignition of any material not shattered and ignited by the temperature and pressure in the combustion chamber. The clerestory shape of the combustion chamber shown

in Figures 5 - 7 whilst designed for direct access of the fuel to the exhaust valve, does not require any smaller valves than would be used in a standard 2 valve per cylinder engine. However, the isolation of the exhaust valve in the clerestory chamber from the main chamber, and thus inflow of cool inlet air, limits heat loss to the inlet charge. Therefore the inlet charge is of maximum density, and the exhaust valve retains its heat for donating to the coal/water slurry. The invention allows for efficient combustion in a wide variety of engines from small automotive types where the cylinder capacity may be as small as 350cc to large slow speed 4 stroke engines where the cylinder capacity may be 20 litres per cylinder or more. It is equally applicable to two stroke uniflow engines where the clerestory head (with its horizontal axis) can replace the normal vertical axis exhaust valve.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.