The present invention is directed to an internal combustion (IC) engine.

BACKGROUND OF THE INVENTION

Known internal combustion engines in general can effectively transform about one third of the chemical energy stored in fuel into useful work. About two thirds of the remaining energy is rejected to the environment as secondary heat. A small portion of the fuel is left unburned or not fully oxidized causing carbon monoxide, hydrocarbon and particulate matter (PM) emissions that are discharged into the atmosphere.

hi view of the high level of fuel prices it is desirable to improve the efficiency of IC engines convert a greater proportion of the energy stored in the fuel to useful work than the current one third conversion efficiency.

Concurrently, it is also desirable to approach full oxidation of the fuel, hi theory, near- full oxidation of fuel will virtually transform all the chemical energy into heat, water and carbon dioxide. This in turn will leave very minimal amounts of carbon monoxide, hydrocarbon and particulate matter.

hi maximizing the release of heat from fuel, challenges also come in the form of oxides of nitrogen (NOx) emission and heat management of the engine. Accelerated and maximum heat release is likely to cause combustion temperature above 2000 Kelvin a temperature at which NOx is likely to form. The formation of NOx currently requires expensive exhaust aftertreatment systems to meet the increasingly more stringent current and future emissions legislation.

Conventional internal combustion engines tackle the problem of heat management by introducing water coolant filled radiators cooled by ambient air. Very little research has been done to tackle this problem at the source of the problem itself; the inability of the engine itself to transform all the released heat into useful work, thus resulting less heat from being rejected to the coolant and exhaust gas.

In maximizing the heat being converted into useful work, it should of course be noted that whenever the one third energy conversion efficiency is increased, the two thirds portion of the heat rejected to the surroundings will be decreased proportionately. If the two thirds portion is decreased to the very minimum, it is not impossible for radiator of a typical passenger car to decrease significantly in size or to be totally omitted. It is also possible that the exhaust gas exiting the tailpipe may approach the temperature of the ambient air.

Even if it is possible to improve the efficiency of combustion, there will still be energy being wasted as secondary heat and discharged to the environment. It is therefore also desirable to enable the remaining heat transferred to the coolant and exhaust gas to be recycled back into the combustion chamber in following combustion cycles.

SUMMARY OF THE INVENTION

One aspect of the present invention provides an internal combustion engine comprising: a cylinder; a piston located in the cylinder and connected to a crankshaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder; a fuel injector to selectively inject fuel into the combustion chamber; an oxidising agent injector to selectively inject oxidising agent into the combustion chamber; an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber; wherein the engine is configured to inject the oxidising agent in first and second distinct stages. Another aspect of the present invention provides An internal combustion engine comprising: a cylinder, a cylinder head; a piston located in the cylinder and connected to a crankshaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head; a fuel injector to selectively inject fuel into the combustion chamber; an oxidising agent injector to selectively inject oxidising agent into the combustion chamber; a coolant injector to selectively inject coolant into the combustion chamber; an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber; wherein the coolant injector is orientated to inject coolant towards the cylinder head.

Another aspect of the present invention provides an internal combustion engine comprising:

' a cylinder, a cylinder head; a piston located in the cylinder and connected to a crankshaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head; a fuel injector to selectively inject fuel into the combustion chamber; an oxidising agent injector to selectively inject oxidising agent into the combustion chamber; a coolant injector to selectively inject coolant into the combustion chamber; an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber; a coolant reservoir and a pump to supply pressurised coolant to the coolant injector, the engine further including means for heating the coolant.

Another aspect of the present invention provides an internal combustion engine comprising: a cylinder, a cylinder head; a piston located in the cylinder and connected to a crank shaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head; an oxidising agent inlet system, an exhaust gas exhaust system, a fuel inlet system and a coolant injector to selectively inject coolant into the combustion chamber, wherein the coolant injector is orientated to inject coolant towards the cylinder head.

Another aspect of the present invention provides a method of operating an internal combustion engine comprising the steps of providing: - a cylinder, a cylinder head, a piston located in the cylinder and connected to a crank shaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head, an oxidising agent inlet system, an exhaust gas exhaust system, a fuel inlet system and a coolant injector to selectively inject coolant into the combustion chamber; igniting a mixture of an oxidising agent and a fuel provided in the combustion chamber to produce a power stroke, and subsequently injecting a coolant into the combustion chamber in the absence of fuel so as to produce a further power stroke.

Another aspect of the present invention provides a method of operating an internal combustion engine comprising the steps of providing:- a cylinder, a cylinder head, a piston located in the cylinder and connected to a crank shaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head, an oxidising agent inlet system, an exhaust gas exhaust system, a fuel inlet system and a coolant injector to selectively inject coolant into the combustion chamber; providing a further cylinder, a further cylinder head, a further piston located in the cylinder, an inlet system, . . an exhaust system; igniting a mixture of an oxidising agent and fuel in said combustion chamber to provide a power stroke and heat, transferring the heat to a working fluid, injecting the working fluid into said further cylinder head to produce a further power stroke.

Another aspect of the present invention provides an internal combustion engine comprising a cylinder, a cylinder head, a piston located in the cylinder head connected to a crank shaft for reciprocal motion with respect to the cylinder, and defining a combustion chamber with the cylinder head, a fuel injector to selectively inject fuel into the combustion chamber, an oxidising agent injector to selectively inject oxidising agent into the combustion chamber, an exhaust valve to selectively open and allow exhaust gases to be expelled from the combustion chamber and means for varying the exhaust valve operating characteristic.

Thus in some embodiments it is possible for a solenoid controlled oxidising agent injector to deliver stratified oxidising agent into the piston bowl as the piston approaches TDC. Fuel injector will later inject gaseous or liquid fuel into the piston bowl just before TDC. Stratification of both oxidising agent and fuel in the piston bowl will maximize combustion efficiency by making sure that oxygen and fuel molecules are in close contact with one and another.

hi other conventional diesel engine, only fuel can be stratified into the piston bowl. This leaves the inducted air to be diluted by residual exhaust gas from the previous combustion cycle before the charge is pushed into the piston bowl by the squish action from the tight clearance between piston and the cylinder head flame face. As a result, combustion efficiency is relatively less because fuel molecules have to overcome the presence of nitrogen, water and carbon dioxide before the fuel molecules can be in contact with oxygen. Such competition will decrease the chance that full oxidation of fuels to occur. Certain embodiments enable the air-to-fuel ratio to be kept at stochiometric or slightly lean at around lambda 1-1.2. Typical diesel engines require up to lambda 3 to ensure low PM, CO and HC emissions. By keeping the air-to-fuel ratio close to stochiometric, significant compression works to compress the oxidising agent and during the compression stroke can be reduced. Furthermore, by keeping the air-to-fuel ratio close to stochiometric, cheaper aftertreatment system can be used rather than the aftertreatments that normally required for lean burn combustion.

Though it is possible to operate the engine using ambient air as the oxidising agent, it is preferable that the ambient air is enriched with oxygen as much as possible or to completely replace the ambient air with high purity oxygen.

With the use of oxygen instead of ambient air is used for fuel oxidation. There will be very minimum nitrogen present in the combustion chamber. This also means that the total charge present in the combustion is relatively lower if compared to conventional spark ignition (SI) and compression ignition (CI) engines.

Such a low charge mass is not likely to absorb the heat from the fuel oxidation. Moreover, the residual gas and combustion by-products that consist of mostly carbon dioxide gas have such a low specific heat capacity. As a result, the cylinder temperature in some embodiments may increase to an unacceptable temperature unless some form of cooling agent is introduced into the combustion chamber/cylinder.

In particular, the use of either water or ammonia as the cooling agent is preferable. Both water and ammonia have relatively specific heat capacity in both liquid and gaseous form. Once introduced in the combustion chamber during or after auto- ignition has occurred, the high specific heat capacity of either water or ammonia absorbs the combustion heat to effectively lower the cylinder temperature. In some embodiments the cylinder temperature can be kept within the range of 1500-2000° Kelvin by the use of water or ammonia. To ensure that the injected coolant is not interfering with the fuel oxidation process, the coolant injector is pointing upward to the cylinder head flame face preferably to the hot spots like valve bridges and drill edges. The coolant injection spray pattern is also designed in such a way that the injected coolant does not interfere with the flame propagation.

Further efficiency improvements can be made by heating the coolant to be injected using secondary heat recovered from the engine and vehicle. The secondary heat can come from exhaust gas, coolant, oil, brake and wheel bearings. These heat sources are normally found in a typical cars, trucks and motorcycles.

For powerplant and large marine vessels, the coolant to be supplied to the engine can be first heated using heat sources outside of the engine. In particular, the heat sources can come from geothermal sources and solar. For ease of handling unpressurized water, it is preferable that the water is heated to around 90° -95° degree Celcius at atmospheric pressure. However, pressurizing the water above the atmospheric pressure can still be applied to increase the water boiling temperature which in turn will maximize the heat storage in the water.

In general, there are plenty of heat sources around for supply of heat. Unfortunately, the density of heat that can be absorbed is too small to be converted from thermal energy to either kinetic or electric energy. However in certain embodiments of the present invention, any "low grade", heat available that is capable of raising water temperature from room temperature to somewhat higher temperature is useful.

In every 10° Kelvin of water temperature increase, the water will require 10° Kelvin less to reach the boiling point. This also means that the energy required to increase the water temperature by 10° Kelvin is no longer required from burning the fuel. Inside the engine, the water will require less heat from the combustion of fuel to turn into steam. As a result, more heated water can be delivered into the engine which in turn will increase the amount of steam available to do work on the piston.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of an internal combustion engine according to one embodiment of the present invention;

Figure 2 is a perspective view illustrating the layout of a cylinder of the internal combustion engine of figure 1;

Figure 3 is a diagram illustrating the cycle of the engine of figure 1 ;

Figure 4 is a schematic diagram illustrating another embodiment of the internal combustion engine of the present invention;

Figure 5 is a cross section view illustrating the layout of certain components of the internal combustion engine of figure 1; and

Figure 6 is a plan view illustrating the layout of certain components of the internal combustion of figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 schematically illustrates a single cylinder embodiment of the internal combustion engine of the present invention indicated generally at 10 along with its ancillary heat exchange system.

The internal combustion engine 10 comprises a cylinder 12 defined by an engine block 11, a piston 14 in the cylinder defining a combustion chamber 13, two exhaust valves 16A and 16B in respective exhaust ports (only one shown (17A)) of a cylinder head 36, a crankshaft 18 and a connecting rod 21. An oxidising agent (in this embodiment oxygen gas 20), fuel (in this embodiment diesel 22) and a cylinder coolant (in this case water 24) are injected into the cylinder through the use of oxygen. Injectors 26A, 26B, fuel injector 28 and water injectors 30A, 30B respectively, and controlled electronically by an engine ECU (not shown). The piston has a depression in its upper surface defining a piston bowl 15.

Fuel and oxygen are ignited through the use of compression ignition in this embodiment. In other embodiments spark ignition may be used, with a spark plug being provided in the cylinder head. The engine 10 is operated in a two stroke cycle in which the downward stroke comprises an expansion stroke and the upward stroke comprises a hybrid of initially an exhaust stroke, followed by a compression stroke.

Oxygen is supplied from a compressed oxygen tank 32. In other embodiments an oxygen generator may be used (see figure 4). The oxygen gas 20 is pressurized to enable it to be introduced during compression stroke. In this embodiment, a separate oxygen generator (not shown) is needed to generate oxygen from the ambient air. The oxygen is later compressed into the oxygen tank at around 170-250 bar. The oxygen supplied through compressed oxygen tank 32 makes this embodiment particularly applicable for land or sea vehicle with restricted space that lacks room for an onboard oxygen generator.

Dry ambient air typically comprises about 78% nitrogen, about 21% oxygen, and just less than 1% argon with the remainder comprising various gases including carbon dioxide, helium, ozone, hydrogen, and methane amongst others. The nitrogen content of the NOx emissions of conventional internal combustion engines comes from the nitrogen in the air. By providing an oxidising agent with reduced amounts of nitrogen results in less NOx emissions.

To produce a pure form of oxygen it can be separated out from air. There are two basic technologies of air separation, namely cryogenic air separation and non- cryogenic air separation. Cryogenic air separation involves the process of cooling air to several hundred degrees below zero in order to separate the component gases. Non- cryogenic air separation requires air to be forced through special materials that selectively pass or retain the oxygen or nitrogen. Thus, non-cryogenic air separation separates the oxygen constituents of air from the nitrogen constituents of air and is therefore capable of producing a gas which has a high percentage of oxygen and in particular a low percentage of nitrogen. The fact that this gas may include the other constituents of air is not significant since the other constituents of air do not create NOx emissions when burnt in an internal combustion engine. Depending upon the particular engine, the oxygen used in the present invention may be contained within a gas mixture comprising at least 50% oxygen, preferably at least 75% oxygen, or preferably at least 95% oxygen. The oxygen may be provided in a gas mixture comprising less than 5% nitrogen, preferably less than 2% nitrogen.

The engine 10 further comprises a coolant circuit 34 of a standard water/glycol that is circulated through the engine block 11 and cylinder head 36 of the engine 10 to a heat exchanger 38 (discussed in more detail below) by a water pump 40. Coolant temperature is monitored by a temperature sensor 35. The coolant circuit is advantageously pressurized to 3 bar in order that the temperature can be maintained at 130 °C. The temperature is controlled by varying the speed of the water pump 40. The engine further comprises a lubrication oil circuit 42 that introduces lubricants into the crankcase of the engine 20 and is also cooled by the heat exchanger 38.

A water pipe 44 takes water 24 from a water tank 25 and passes it through the heat exchanger 38 to remove heat from the coolant in coolant circuit 34 and from the lubrication oil in oil circuit 42. The water 24 is compressed by a high pressure water pump 46 and is passed through a high pressure heat exchanger 48 described in more detail below, before being injected under pressure into the cylinder 12 by the water injector 30.

Secondary heat from exhaust gas exits the cylinder after combustion via the exhaust ports (17A) and enters the heat exchanger 48 placed immediately downstream of the exhaust valves 16A and 16B. This recovers a substantial proportion of the secondary heat from the exhaust gas and transfers it to the pressurised water 24. At the same time, some heat needs to be retained in order to keep a 2-way catalytic converter 50 at a temperature above 300 °C for optimum pollutant conversion efficiency. For this reason, the catalytic converter 50 is located immediately downstream of the high pressure heat exchanger 48.

Remaining secondary heat in the exhaust gas is recovered using a second heat exchanger in the form of a condenser 52. This recovers water 24 from the exhaust gas and is positioned within the water tank 25. In maximizing the amount of water recovered from the exhaust gas, there should be a significant temperature difference between the exhaust gas and the heat exchanger 48. In other words, the pipe section after the catalytic converter is significantly cooled down by condenser 52. This requires insulation 54 preferably made of ceramics, to be introduced in between the catalytic converter outlet and an exhaust pipe 55 leading to the second heat exchanger 52. However, in certain embodiments a catalytic converter will not be needed in particular if the emissions are well below any legislative requirements.

In maximizing the water to be recovered from the exhaust gas, a further substantial temperature difference is created by placing the condenser 52 inside the water reservoir 25. For this purpose, the water in the water reservoir is kept at 30-40 °C by having minimum water volume to be stored in the condenser 52. Once the water has condensed and accumulated at the bottom of the condenser 52 it is circulated back into the water pipe 44 via a second pipe 56, the flow in which is controlled by a electronically controlled valve 58.

About 20% of the water may not be recovered from the exhaust gas so the water storage or water tank 25 needs to be refilled from time to time. This ratio is chosen to ensure pollutants dissolved by the water will not on the one hand build up to a concentration that may cause significant material deterioration to the pipe 55 and tank walls, and on the other hand refills do not become too frequent.

Once as much of the heat from the exhaust gas as is feasible has been recovered, the exhaust gas exiting the tail pipe is typically around 50-70 ⁰ C. As much of the heat has been taken out from the exhaust gas, it has a relatively low velocity as it exits the tailpipe.

As will be appreciated the water being injected into the cylinder can be heated by various heat sources including the condenser 52 or the high pressure heat exchanger 48, and in these circumstances exhaust heat is being used to heat the water. The heat exchanger 38 uses engine coolant heat to heat the water and engine lubricating oil (42) to heat the water. In alternative embodiments, further heat sources could be used to heat the water. For example the kinetic energy of an associated vehicle could be used e.g. when the vehicle is slowed by its brakes the brakes convert kinetic energy into thermal energy and this thermal energy could be used (e.g. by way of a heat exchanger) to heat the water. Vehicle wheel bearings generate significant amount of heat at high speed which can be used to heat up the water (e.g. via a heat exchanger). Vehicle suspension system also generates significant heat especially when the vehicle moves over bumpy surfaces and this could also be used to heat the water (e.g. via a heat exchanger).

Alternatively, solar energy could be used to heat the water. Alternatively when the engine is stationary (i.e. not mounted on a vehicle) ground source energy could be used to heat the water. Alternatively, hot coolant water from chemical processing plants, manufacturing plants, nuclear powerplants and coal powerplants can also be used to supply heat to heat the water using a heat exchanger.

As described above the coolant in coolant circuit 34 is kept separate from the water 24 and its associated circuit. Ih further embodiments the coolant circulated through the engine block 11 and/or cylinder head 36 of the engine could be injected into the combustion chamber.

As mentioned above, high pressure water pump 46 pressurizes the water to enable it to be injected. Heating of the water can occur either before water pressurization (e.g. via heat exchanger 38) or after water pressurization (e.g. via high pressure heat exchanger 48). Preferably the water is heated to near its boiling point. Thus, prior to pressurization, the boiling point of water is approximately 100 °C and therefore the temperature of the water exiting the heat exchanger 38 could be 80 ⁰ C (e.g. within 20 ⁰ C of its boiling point) or 90 ⁰ C (e.g. within 10 °C of its boiling point). Depending upon the pressure achieved by the high pressure water pump 46 the temperature of the water exiting the high pressure heat exchanger 48 could be near its boiling point, e.g. within 20 °C of its boiling point, or alternatively within 10 °C of its boiling point. By providing the water near its boiling point allows maximum recovery of heat whilst still maintaining the water as a liquid. By injecting water at near its boiling point, as it expands into the combustion chamber it will boil very quickly, thereby minimising the damping effect on the flame front. In the figure 1 embodiment the crankshaft 18 outputs to a continuous variable transmission 60, but in other embodiments other suitable transmission systems may be used.

Figure 2 shows the layout of certain components of the engine 10 in more detail. It can be seen that the cylinder head 36 comprises two exhaust valves 16A and 16B in order that the exhaust gases may exit the combustion chamber 13 in a relatively unhindered manner. The cylinder further comprises two water injectors 30A and 30B that are directed upwardly and are positioned in the wall of the cylinder (not shown in Figure 2) so as to spray the water in the direction of hot spots in the cylinder, and in particular the exhaust valves 16 and area between the exhaust valves (the exhaust valve bridge). In order for the geometry of this arrangement to be feasible, recesses 58 are provided in the piston 14 at locations corresponding to the water injectors 30 so that the flow of water from the injector 30 is not impeded when the piston is around top dead centre (TDC). The recesses are sized to be slightly larger than the water injector opening in the cylinder. This ensures that injected water does not hit the edge of the recess and ensures that water is not deflected into the gap above the piston ring between the piston and the cylinder wall.

In more detail, as best seen in figure 5 the water injector 30A has an axis A which is orientated to inject the water upwardly. For the avoidance of doubt, the term "upwardly" and similar terms should be considered with regard to the normal positioning of reciprocating internal combustion engines. Thus, the cylinder 12 defines a central axis and the term upwardly and similar terms should be considered with regard to this axis. In particular, the top dead-centre position of the piston (i.e. the position of the piston when it is furthest away from the crankshaft) and the bottom dead-centre position of the piston (i.e. the position of the piston when it is closest to the crankshaft) determine "upwardly", rather than the actual physical orientation of the engine in space.

As shown in figure 5 the axis A is angled at angle B relative to the central axis of the cylinder bore. In this case angle B is approximately 60 degrees. In this case the top of the combustion chamber 13, as defined by the cylinder head 36 is flat. Water is therefore injected towards the cylinder head. In this case the cylinder head 36 is a separate component from the engine block 11. The cylinder head 36 is clamped onto the cylinder block 11 by fixings, such as bolts, in a conventional manner. As will be appreciated, the water injector 3 OA is mounted in the cylinder block .11. The cylinder 12 includes a hole 62 through which water is injected.

The piston includes a top (or first) piston land 63, a second piston land 64 and a third piston land 65. The first and second piston lands are separated by a piston ring groove 66 which receives a piston ring 66A in a conventional manner. The second and third lands are separated by a piston ring groove 67 which receives a piston ring 67A in a conventional manner. The top land 63 is generally annular and has a top surface 68. The land 63 includes a recess 69 A adjacent injector 30A and a recess 69B adjacent injector 30B. The recess is generally U-shaped with the bottom of the U-shape being angled at angle C relative to a centre line of the cylinder 12. hi this case angle C is approximately 30 degrees. As best seen in figure 5, the piston is at the top dead-centre position, i.e. is at its highest position within the bore. It will be appreciated that the top 68 of the top piston land 63 is positioned above the hole 62. Furthermore, the bottom 90 of the top piston land, i.e. the top of the first ring groove 66 is positioned below the hole 62 when the piston is at its top dead-centre position.

The recess 69A allows water to be injected even when the top 68 of the piston land is above the hole 62. Arranging for the hole 62 to always be positioned above the top piston ring groove 66 ensures that the top piston ring 66A never passes over the hole 62 and therefore there is no danger of the end of the top piston becoming jammed in hole 62.

It will be appreciated that the recess 69A acts as a deflector to redirect injected water towards the cylinder head 36, This is because the bottom of the recess 69A is angled at angle C which is a smaller angle than angle B of the injector. As such, water injected through hole 62 will strike the recess and be. deflected upwardly. Since water injection commences after the piston has reached TDC, as the piston moves down, the recess at the piston will spread the injected water over wider surface area of the cylinder head flame face and the recess will act to "fan out" the injected water so as to help avoid overcooling of the cylinder head flame face by the injected water.

As best seen in figure 6, the top 68 ^' of the piston land is generally annular with an external diameter slightly smaller than the diameter of the cylinder 12 and having an internal diameter which defines the edge of the piston bowl 15. Significantly both recess 69 A and 69B are positioned wholly outside of the inner diameter. When the top 68 of the piston land approaches the cylinder head 36 it creates a "squish" band, as is known. By ensuring that the recess 69A is not sufficiently large that it reaches the inner diameter of the top 68 ensures that the squish effect of the squish band is maintained.

The orientation of the water injector 30A is such that water is injected both upwardly (as best seen in figure 5) and in a chordal manner (as best seen in figure 6). For the avoidance of doubt, the term "chord" refers to a straight line connecting two points on the cylinder bore, the straight line not being a diameter. The injector 30B is similarly orientated and injects water both upwardly and in a chordal manner. As best seen in figure 6, injector 30A injects water towards a region of the cylinder head 36 positioned between exhaust valves 16A and 16B, i.e. it injects water towards the bridge of the cylinder head between the exhaust valves. This is advantageous since this bridge can become hot and by directing water towards it the water acts to cool the bridge.

In further embodiments, water can be directed to other hot spots within the combustion chamber, in particular the water could be directed towards the exhaust valve itself.

Also illustrated in figure 2 is a conventional diesel fuel injector 28 which is flanked either side by two oxygen injectors 26A and 26B that are positioned so as to promote the optimal mixing of oxygen with the diesel fuel in the cylinder.

Figure 6 shows a plan view of the internal combustion engine 10. Certain components, most notably the cylinder head and the fuel injector 28 have been removed for clarity. It can be seen that, in plan view, the axis of the water injectors 3OA and 30B and the axis of the oxygen injectors 26A and 26B are all orientated in a chordal manner relative to the cylinder 12 and relative to the piston bowl 15. hi particular the water injectors 3OA and 3OB and oxygen injectors 26A and 26B are not orientated radially relative to the cylinder 12 and piston bowl 15. It will also be appreciated that the axis of water injector 30A is offset to the right of the centre of the piston (when considering the axis of water injector 30A). Similarly, the axis of water injector 30B is offset to the right of the centre of the piston (when considering the axis of water injector 30. Similarly, the axis of oxygen injector 26A is offset to the right of the centre of the piston (when considering the axis of the oxygen injector 26 A. Similarly the axis of the water injector 26B is offset to the right of the centre of the piston when considering the axis of water injector 26B. As such, when water is injected by either water injector 30A or 30B (as will be further described below) the injected water will tend to swirl the gas currently in the combustion chamber in an anticlockwise direction. Similarly, when oxygen is injected by either oxygen injected 26 A or 26B the injected oxygen will also tend to swirl the gas within the combustion chamber in an anticlockwise direction. Thus, the water injectors 30A and 30B and the oxygen injector 26A and 26B are all positioned so as to promote swirl within the combustion chamber. In this case the swirl is promoted in an anticlockwise direction (when viewing from above), though in further embodiments the swirl could be promoted in a clockwise direction by reorientating the water injectors and oxygen injectors.

As mentioned above, the oxygen will typically be pressurised in the oxygen tank at around 170 to 250 bar. The oxygen can be injected at the pressure of the oxygen tank.

Alternatively a regulator (not shown) can be provided between the oxygen tank and the injector to reduce the injection pressure of the oxygen. The injection pressure of the oxygen will depend upon the engine and also the time when injection occurs

(relative to the piston position) but typically the oxygen will be injected at a pressure of 50 bar or above, alternatively 100 bar or above.

Referring back to Figure 1, with water being injected upward onto the cylinder head 36 hot spots, the heat rejection to the coolant is significantly lower by comparison with a conventional IC engine. Even so, engine coolant may still needed to cool off critical areas like exhaust valve bridge, oxygen injectors 26 A and 26B and cylinder head flame face. Cooling of engine block 11 may still needed but it is limited to only the top part of the wall of the cylinder 12.

Since there is still significant heat being ^" rejected to the engine coolant, there is significant heat that can be recovered and delivered back into the combustion chamber. In a variant of the engine 10 of Figure 1, the coolant radiator is placed inside the water tank 25 to ensure large temperature difference between the engine coolant and the water inside the reservoir which also serves as the cooling medium.

A temperature sensor 19 is located near the hottest spot at the cylinder head to provide temperature reading to the ECU for feedback. The control system of the ECU controls the flow rate of the coolant pump 40 and thus the amount of coolant entering and exiting the engine can be controlled to ensure optimum heat rejection from the coolant to the water reservoir and also from the combustion heat to the water coolant.

With reference to figure 3 the cycle of the engine operation can be explained as followed.

As the expansion stroke takes place, the exhaust valves 16A and 16B are opened (EVO) just before bottom dead centre (BDC) or at BDC (180° crank angle). There is no clear need for the exhaust valves to be opened much earlier for "blowdown" operation as the use of substantially pure oxygen 20 (or 90% pure oxygen) reduces the charge mass by up to 78% relative to other conventional (IC) engines using air. Moreover, the use of substantially pure oxygen eliminates the need to run the engine lean which is normally required in conventional diesel engine.

To minimize oxygen consumption, a stochiometric oxygen to fuel (OF) ratio is preferred. However, to maximize the combustion efficiency, the oxygen can be increased by up to 20% from stochiometric value. A wide range lambda sensor (not shown) can be used to monitor the OF ratio during the engine operation. As the exhaust valves 16 are opened, the combustion byproducts together with the injected water (see below), which is now in vapor state, is discharged to the exhaust ports 17 and later to the atmosphere. The amount of residual charge remaining in the cylinder is controlled by adjusting the crank angle at which the exhaust valves are closed.

The crank angle of the cycle where the exhaust valves 16 are closed also determines the effective compression ratio of the engine 10, and can be advanced or retarded from the baseline using a suitable variable valve timing mechanism controlled by the ECU. Such variation enables the compression work to be optimized depending on engine rpm and load. Compared to conventional IC engines, the compression work in this embodiment of the present invention is limited and it is only needed to raise the cylinder temperature to about 150-200 °C above the autoignition temperature.

By limiting the compression work, it is also possible to keep the cylinder pressure low by comparison with a conventional diesel IC engine. With maximum cylinder pressure being kept at 100-120 bar instead of the more usual 180-200 bar, engine parts can be designed with less structural reinforcement.

The exhaust valves typically close (EVC) between 1/3 to 4/5 of the total compression stroke (i.e. a crank angle of between 216° and 324°). Compared to a conventional four stroke engine which uses the entire compression stroke doing compression work, the engine of the present invention utilizes only 4/5 to 1/3 of the upward stroke for compression work. This in turn consumes less engine power and cylinder pressure can be kept low when the diesel fuel 22 is being ignited.

With this exhaust valve 16 opening and closing arrangement, it is possible to optimize the effective compression ratio in accordance to engine rpm and load. At the same time, the expansion ratio can be maximized as the exhaust valves will only be opened near to BDC. Over the range of rpm and load, the exhaust valves are only opened to enable the cylinder pressure at BDC to be kept below 5 bar. By keeping the cylinder pressure low at BDC, there is no significant resistance to the piston 14 as the piston moves up. As the exhaust valves are opened, the exhaust valve lift may also be varied depending on engine rpm and load. By varying the exhaust valve lift to relatively lower lift than what is normally done in other conventional IC engines (e.g. down as low as 1 mm), it is possible for higher content of exhaust gas to be retained without having to close the exhaust valves early. In retaining the exhaust gas inside the cylinder, a significant amount of heat can be retained which is useful in raising the cylinder 12 temperature above the autoignition temperature in the next compression stroke. As hot exhaust gas is retained in the cylinder 12, it provides both mass and an elevated charge temperature which can further minimize compression work required to raise the cylinder temperature about 150-200 °C above the fuel autoignition temperature.

The variation of lift described in the previous paragraph may be done without any changes to the duration of exhaust valve opening. In the prior art (for example the BMW Valvetronic system) the exhaust valve lift is varied in proportion to changes to the valve opening duration. By having low valve lift combined with constant and long exhaust valve opening duration, it is possible to retain the exhaust gas without significant increase in cylinder pressure as the piston moves upward.

A ID simulation has shown that it is possible to lower the valve lift for the purpose of retaining the exhaust gas without causing the cylinder pressure to significantly increase. This demonstrates that there is no significant increase in pumping work. It is believed this phenomenon may be caused by the relatively lower charge mass due to the use of oxygen rather than ambient air.

Once the exhaust valves are fully closed, about 50-70% of the total oxygen required in the cycle is injected at high pressure between OVOl and OVCl by the oxygen injector 26A. The first gas injection will take place around 30 degree before TDC and occurs rapidly, e.g. in a 10°-20° range.

This will be followed by fuel injection commencing at 5-15° before TDC (FVO) and ceasing at 5-10° after TDC (FVC). The diesel fuel ignites substantially immediately after leaving the fuel injector 28. The remaining 30-50% of the total oxygen required is injected by the oxygen injector 26B from 2-3° before TDC (OVO2) and ceasing at 5-15° after TDC. This enables the oxygen used up for fuel oxidation to be replaced. With such a powerful injection pressure, much of the combustion byproduct is also believed to be cleared out from the piston bowl 15. This measure makes it possible to have oxygen constantly available inside the piston bowl 15 for complete fuel oxidation.

As mentioned above, the oxygen may be stored in tank 20 at up to 250 bar. When the engine 10 is a vehicle engine, such as a car, the oxygen within tank 32 will be at ambient temperature, by way of example 10 ⁰ C. As the oxygen is injected into the cylinder it will have expanded, i.e. the pressure drop between the oxygen in tank 32 and the oxygen having just being injected into the combustion chamber 30 could be over 200 bar. This pressure drop causes cooling of the injected oxygen, on occasions to less than 0 °C. This cooling can effect flame propagation, particularly on engine start up. As such it is advantageous to inject the oxygen in two distinct stages. The first stage may, by way of example, inject about 50 to 70% of the total oxygen required (as described above) which creates cooling within the cylinder. By injecting fuel auto-ignition will occur thereby heating the cylinder head. Once the fuel has auto-ignited it is then possible to inject the remainder of the oxygen. This can be contrasted with injecting all the oxygen in a single injection which may result in significant cooling of the combustion chamber and therefore a failure to auto-ignite the fuel. Because of the relatively short time delayed between end of the first injection of oxygen and the start of the second injection of oxygen it is preferable to provide two oxygen injectors, one which only injects oxygen in the first distinct stage and the other which only injects oxygen in the second distinct stage, hi this way each injector is only required to open and close once during an engine cycle.

Consideration of figure 3 shows the following: OVOl occurs before the piston has reached TDC. OVOl occurs approximately 40 degrees before TDC, though in further embodiments OVOl could occur between 50 degrees and 30 degrees before TDC. OVOl occurs after the exhaust valve has closed EVC. OVOl starts before the fuel is injected (FVO). OVCl occurs before the piston has reached top dead-centre. OVCl occurs approximately 25 degrees before TDC but in further embodiments OVCl could occur between 35 degrees and 15 degrees before TDC. OVCl occurs before the fuel valve opens (FVO). 0V02 start near top dead- centre, in this case before top dead centre. In further embodiments OVO2 could occur between 15 degrees before top dead-centre and five degrees after top dead-centre. 0V02 occurs after the fuel valve is opened (FVO). OVC2 occurs after the piston has passed top dead-centre. In further embodiments 0VC2 could occur between the piston reaching top dead-centre and the piston reaching 15 degrees after top dead- centre. 0VC2 occurs before the fuel valve is closed (FVC). 0VC2 occurs before water is injected (WVO). The fuel valve opens (FVO) after the first distinct stage has stopped and before the second distinct stage has started. In further embodiments alternative opening and closing of the various injectors and valves could occur.

With the use of oxygen stratified together with diesel substantially inside the piston bowl 15, the heat release is significantly faster compared to conventional diesel engine and the ignition delay is believed to be low. Firstly, since the compression work is minimised, the cylinder pressure is around 30-40 bar and this will significantly cause the diesel boiling point not to be raised as high as it will be when subjected to cylinder pressure of 70-100, bar which is normally found in conventional diesel IC engine. As the boiling point drops, the injected diesel fuel vaporizes relatively earlier. Secondly, once it vaporizes, the fuel easily finds oxygen as it is in plentiful supply by being stratified in the piston bowl 15.

With minimum ignition delay in an oxygen rich combustion chamber, the amount of premixed combustion will be less. Thus there is less sudden heat release that will be detrimental to engine components. The amount of diesel fuel being combusted through diffusion combustion is believed to be high. Thus it is possible to further control the release of heat by controlling the flow rate of diesel fuel coming out of the injector 28.

Water is injected from the water injectors 30 once 50% mass of fuel has been burned which occurs at around 0-15° after TDC. This differs from the prior art in which water is injected before fuel is ignited. By introducing water only after 50% mass fraction burn is reached, there is minimal flame suppression by water, which can otherwise cause partial oxidation that is detrimental to fuel consumption and emission formations. To further minimize flame suppression, the water is injected upwards toward the cylinder head 36, preferably toward hot spots as described above. In the prior art the water injectors inject water into the piston bowl.

Though fuel oxidation, flame development and heat release happen relatively quickly, it takes time for all this process to occur. By the time water molecules reach the flame development region, typically the maximum amount of fuel has been burned and maximum amount of heat has been released in the combustion chamber. Moreover, with the cylinder temperature quickly rising, especially near the flame development region, it is likely that the water molecules to have turned from liquid to vapor state. This reduces the flame suppression rate by the water.

The amount of water injected into the cylinder 12 depends mostly on the need to limit the maximum cylinder temperature to 1800 Kelvin. Depending on the engine rpm and load, the maximum cylinder temperature can occur at between 0° to 45° crank angle.

It is also desirable to keep the exhaust gas temperature at 1000 Kelvin or above at the point where the exhaust valve 16 is to be opened.

Another criterion for the total water mass to be injected in every cycle is the maximum allowable material temperature limit. To minimise the occurrence of engine parts overheating, the temperature 19 sensor is utilised to monitor heat build-up in the combustion chamber. During the entire range of the engine operation, if the heat sensor senses the material temperature to be close to the material limit, extra water mass is injected to cool down the surface temperature.

As a result of these considerations, the mass of water to be injected is in the range of approximately 3 to 15, typically 5 to 12 times the amount of mass of fuel injected. In this context, the flow rate of the fuel injector 28 is timed to. enable as much as 15 times the water mass to be injected within approximately 20-30° of crank angle after the water injection starts, even when the engine is operating at its maximum operating speed.

As the combustion heat is being absorbed by the injected water 24. The water quickly changes state from liquid to vapor state. Expansion occurs when water changes state from liquid to vapor, which causes the cylinder pressure to increase and the piston to be pushed down to BDC.

Water 24 to be injected is heated in the high pressure heat exchanger 48 potentially until it is close to its boiling point. The high pressure positive displacement water pump 46 pressurizes the water line enabling the boiling point to be raised significantly above 100°. With the water pressure raised to 150 bar, the water boiling temperature is raised from 100 ⁰ C to approximately 340 °C. This makes it possible for the water to be heated close to 300 ⁰ C without causing the water to turn from liquid to vapor.

It is known that the pumping work required to raise the pressure inside a constant volume is 10 times less for water in liquid state if compared to water in vapor state. This is why it is important for water to remain in liquid state until the water is discharged into the combustion chamber 13.

With a temperature as high as 300 °C, the cylinder pressure of below 100 bar lowers the water boiling point from 340 ⁰ C to slightly below 300 °C. Considering that water absorbs heat from the combustion, the water temperature will be raised further causing the water to change state from liquid to vapor almost immediately after it leaves the injectors 30.

hi other embodiments, it is possible to use a slightly lower water temperature to enable the injector material to withstand the elevated temperature of water, hi this scenario, the time taken for the water to change state from liquid to vapor will be relatively longer. However, the same amount of water will be able to reduce the cylinder temperature to a lower temperature compared to when the higher temperature injected water. In other embodiments, it is possible to inject pressurized heated water into the combustion chamber as the sole means of moving the piston downward during a particular power stroke by temporarily stopping the fuel and oxidizer injections. By way of example, by keeping the water line pressurized to up to 150 bar, it is possible to heat up the water to 330° Celcius without boiling. As the cylinder approaches TDC, more water can be injected when compared to the normal engine operation. As the cylinder pressure during the water injection is significantly below 150 bar, the water at 330° Celcius will boil and flash into steam. Since the volume of water expands by 1600 times as it turns from liquid to vapour state, the piston will be pushed downward.

This application is useful for multi-cylinder applications during vehicle braking where the control system can alternate between the normal engine firing and solely steam powered operation. By alternating these 2 modes, the heat from previous engine firing can benefit the "steam" only operation by making sure that the cylinder surroundings are hot. The use of alternating these 2 modes can also be applied to the conventional 4-stroke engines during the expansion stroke.

Alternatively, an auxiliary cylinder can be integrated to the primary engine to solely run on steam. To maximize the work that can be extracted, the separate cylinder can run at relatively lower engine speed for example at 1:5 auxiliary cylinder to primary engine speed ratio. To avoid parasitic losses when water temperature is low, the auxiliary cylinder can be connected to the primary engine using one-way clutch (also known as an over running clutch or a free wheel clutch) thus the auxiliary cylinder can be left at standstill when it is not needed.

Considering gas expansion, the expansion of water in vapor form is about 2.5 times the expansion of carbon dioxide when subjected to the same temperature. When compared to Nitrogen, the expansion of water in vapor form is about 1.5 times. This results in water in vapor form being a better medium for gas expansion in a reciprocating engine and in turbines.

hi terms of heat absorption, water in liquid form has a heat capacity of 4.18 kJ/(kgK). Water in vapor form has a heat capacity of 1.52 kJ/(kgK) at 100 °C. Carbon dioxide gas has a heat capacity of 0.63 kJ/(kgK). Nitrogen gas has a heat capacity of 0.74 kJ/(kgK). Thus, water in both liquid and vapor form can absorb heat much better, compared to other gases which are normally present in conventional IC engines.

Water has the further advantage of being cheap and abundant and provides an improved way for minimizing heat being transferred to the surrounding metal and engine coolant of engine 10. As more heat is absorbed by injected water, more work is done on the piston 14 leaving less heat to be rejected to the atmosphere via exhaust gas and engine coolant. Furthermore, the portion of heat that is rejected to the engine coolant and exhaust gas, is recovered to some extent by the heat exchanger 38.

Figure 4 illustrates an IC engine 110 according to a second embodiment of the present invention in schematic form. The basic layout and principles of operation of the engine 110 are similar to those of engine 10, and where possible, similar parts are labelled by like numerals, but with the addition of the prefix "1". Only differences with respect to the first embodiment are discussed in depth.

The engine 110 is adapted for use in applications where a greater amount of space is available by comparison with engine 10, such as in static electric generators and large ships. Consequently it may be used to burn heavy fuel oil, where the increased availability of oxygen and reduced amount of nitrogen in the combustion process minimises the amount of NOx produced, which has traditionally been a problem with this fuel. In addition the high sulphur content of such fuels is dissolved in the injected water rather than being emitted as sulphur dioxide.

As the injected- water dissolves sulphur dioxide, sulphuric acid will be formed which can be detrimental to engine parts and the water pipeline. This requires the water 24 and 124 to have pH higher than 7 through addition of additive or alkali by a suitable injection system (not shown). Such additive or alkali solution is required to neutralize sulphuric acid formation in the water line.

The greater space availability enables a non-cryogenic oxygen generator (not shown) to be used in situ. Gas pressure exiting the oxygen generator is normally low at slightly above atmospheric pressure. Through line 172, the oxygen will be fed into a turbocharger 170 where the gas pressure will be raised further prior to being compressed by a reciprocating compressor to 25 bar. An electronically controlled low pressure electric water pump 176 will draw in condensed water from the condenser 152 and the water will exit the nozzle 178. The turbocharger 170 sucks in both oxygen and water into the turbo unit for further compression. As gas compression will also elevate the charge temperature, the supplied water cools off the charge.

The oxygen is fed in a direction Y where it is then further compressed to the desired injection pressure by a reciprocating pump 180 driven from the crankshaft 118 by CVT 160. The CVT 160 enables the reciprocating pump speed to be varied at various engine rpm and load. Such a variation in reciprocating pump speed is important during idle where the turbocharger 170 does not contribute much in raising the charge pressure. In this embodiment, the crankshaft has a further output to a propeller 182

A secondary air pump 174 supplies ambient air to the turbocharger turbine outlet. Turbine outlet is chosen as the point of entry for the secondary air as this will enable the secondary air to mix well with the exhaust gas prior to the charge entry to the catalytic converter. A one way valve (not shown) prevents exhaust gas from entering the secondary air pump. The supplied ambient air provides supplementary oxygen to the 2 way catalytic converter 150 which is useful in increasing the catalyst conversion efficiency involving hydrocarbon and carbon monoxide.

Water exiting the heat exchanger 138 also flows through the turbocharger 170 turbine unit. As the turbine unit is constantly in contact with the exhaust gas, significant heat can be extracted from the turbine which further elevates the water temperature.

It will be appreciated that the engines of the present invention provides numerous advantages over the prior art. Primarily , the use of water in the combustion cycle that has been heated by exhaust gases enables more efficient utilisation of the fuel, the use of higher concentrations of oxygen in the oxidising agent minimises harmful emissions (in particular particulates and NOx) and enables fuel burn to be better controlled and cheaper two-way catalytic converters to be used. Further benefits can be derived by using the engine equipped with the described inventions wherein the water to be injected is wastewater that is high in hydrocarbon impurities so that the hydrocarbons in the wastewater act as an additional fuel supply and are burnt. Biohazards wastewater from chemical plants or hospitals can also be injected into the combustion chamber.

It will be understood that numerous changes may be made within the scope of the present invention. The engine may be used and adapted to burn other fuels such as petroleum (gasoline), biodiesels, bioethanols, compressed natural gas and methanol. The engine may be adapted to run on a four stroke cycle and may use multiple cylinders and pistons in various configurations, such as V, W or boxer configurations. Presently, inline six and boxer four cylinder configurations are preferred due to their improved balance. In addition, an inline four cylinder engine with a 90 degree crankshaft configuration is envisaged (instead of flat plane crankshaft). This enhances smoothness and may eliminate the need for balancer shafts.

As mentioned above, the cylinder coolant is water 24. In further embodiments alternative cylinder coolants, such as ammonia, could be used.

The coolant injector system has been described above in relation to the engine shown in figure 1 and the engine shown in figure 4. Injecting coolant is equally applicable to many types of internal combustion engine including spark ignition engines and combustion ignition engines, two stroke engines, four stroke engines, engines with conventional poppet inlet valves and poppet exhaust valves, engines where the fuel is premixed in a carburettor, engines where the fuel is premixed by being injected into an inlet tract upstream of an inlet valve. The advantageous features of orientating a coolant injector to inject coolant towards the cylinder head as hearing described, and in particular as mentioned in certain of the appended dependent claims are equally applicable to any of the above mentioned engine types.

The engines describes above all have fixed exhaust valve operating characteristics, that is to say the exhaust valve opens at the same point, closes at the same ^" point, lifts the same amount, has an opening ramp characteristic and a closing ramp characteristic the same on each occasion the valve is opened. In further embodiments any of the above mentioned engines could be provided with variable exhaust valve operating characteristics. For example, the exhaust valve opening point or closing point could be varied, the exhaust valve opening duration could be varied, or the exhaust valve lift could be varied between successive exhaust strokes. Where two exhaust valves are provided in a cylinder the exhaust valve operating characteristic of one exhaust valve could be different from the other during a particular exhaust stroke.

By way of example the exhaust valve could open anywhere between 1 degree and 10 degree before bottom dead centre, the exhaust valve could close anywhere between 100 degrees and 45 degrees before top deadcentre, the exhaust valve could close later during idle operation then during full load operation, or the exhaust valve lift could be lowered during idle operation than full load operation.

Exhaust valve operating characteristics could be varied by an ECU controlling a solenoid which opens and closes the exhaust valve, alternatively an ECU controlling a hydraulically operated exhaust valve, or an ECU controlling a pneumatically operated exhaust valve. Alternatively, the means for varying the exhaust valve operating characteristics could be a cam system such as is shown in EP 1300551, or in US5636603, or in any other known of cam operated variable valve system.

As will be appreciated the fuel is injected directly into the combustion chamber. As will be appreciated the water is injected directly into the combustion chamber. As will be appreciated the oxidising agent is injected directly into the combustion chamber. As will be appreciated the injected oxidising agent is the sole source of oxidising agent after start up (e.g. the engine does not include traditional inlet valves).

hi some embodiments a water temperature sensor can be provided to determine the temperature of the water just prior to inj ection.

hi some embodiments two fuel injectors can be provided. A first fuel injector may inject a first fuel of a higher cetane value prior to a second fuel injector injecting a second fuel of a lower cetane value. In some embodiments both fuels are ignited by auto ignition. Injecting a first fuel of a higher cetane value requires a lower auto ignition temperature which allows more energy to be extracted from the previous power stroke. Once the first fuel has started to burn the temperature within the combustion chamber increases, in particular to a temperature at or above the auto ignition temperature of the second fuel, which can then be injected and will auto ignite. Thus preferably the first fuel is injected when the combustion chamber conditions are such as to be below the auto ignition temperature of the second fuel. In this way power can be produced by using low grade fuels, e.g. fuels with a low cetane value. Such fuels tend to be cheaper than higher grade fuels. The first fuel may be a high grade of fuel such as a diesel fuel. The second fuel may be a fuel derived from plants, such as a biomass fuel. The second fuel may be pyrolysis oil.