WO2023218170A1

WO2023218170A1 - A hydrogen-fuelled rotary engine and improvements relating thereto

Info

Publication number: WO2023218170A1
Application number: PCT/GB2023/051196
Authority: WO
Inventors: David Walker Garside
Original assignee: Hydrogen Wankel Engines Ltd
Current assignee: Hydrogen Wankel Engines Ltd
Priority date: 2022-05-09
Filing date: 2023-05-05
Publication date: 2023-11-16
Anticipated expiration: 2024-11-09
Also published as: GB202306660D0; GB2619412A

Abstract

The invention describes a Wankel-type engine using a pressurised-air rotor cooling system incorporating a rotary valve for injecting H2 gas at high velocity very early in the compression stroke. The high flow rate valve allows use of low 112 supply pressure. The homogeneous mixture with near 100% excess air results in zero NOx emissions. A small quantity of lubricant is directly metered to the three rolling element bearings such that CO2 usage is also negligible. The single-rotor engine operates only at a single speed and is unthrottled. A turbo-compound unit installed adjacent to the single exhaust port gathers further energy. The combination of low mechanical friction and pumping losses, fast and complete combustion with H2 fuel, and a gas sealing system using precision-machined slots possessing small clearances results in high thermal efficiency power units suitable for operating as lightweight range extenders in electric-motor-driven sea, land and air vehicles.

Description

A hvdrogen-fuelled Rotary engine and improvements relating thereto

The invention to which this application relates is to a relatively high efficiency rotary engine which is fuelled by Hydrogen and, in particular, although not necessarily exclusively, to a form of engine known as a Wankel engine and to the use of the engine in a form so that the same acts as a range extender engine, the purpose of which is primarily, although not necessarily exclusively, to allow the range of travel of a vehicle with which the engine in accordance with invention is installed, is provided to be extended. Yet further the vehicle will typically already be provided with an engine or motor which is powered by electricity and the engine in accordance with this invention is provided to allow the range in terms of distance of travel of the vehicle, to be extended before the charge of the batteries of the vehicle is required.

It is known that IC engines (ICEs) fuelled with hydrogen gas (H₂) offer a potential route to providing automotive and other power units with zero NOx and near-zero carbon emissions and much effort has and still is being expended to research and create viable products using reciprocating engines.

Previous known versions, with an ‘indirect’ fuelling system, supplied the H₂ gas to the induction manifold of the engine via a ‘gas carburettor’. However, they suffered from problems of flash-back of the easily-ignited H₂ mixture in the intake system coming into contact with hot exhaust gas; and additionally, pre-ignition occurred in the combustion chamber from hot spots such as the exhaust valve, spark plug or carbon deposits.

Individual solenoid injectors are now sometimes used to supply fuel in a timed manner direct into the inlet ports which avoid, with intake and exhaust valve timing and possibly other modifications, the flash-back problems.

Supplying the fuel in this manner whilst the inlet valve is still open results in the low density H₂ gas displacing a large proportion of the normal volume of induction air. This reduction in volumetric efficiency of between 17 to 40% results in the power output from a given size and weight of engine being much reduced. In order to redress this problem a turbo charger is then required to be fitted and operate in conjunction with the engine, with a resultant increase in cost and complexity. An alternative to avoid this low volumetric efficiency weakness is to directly inject all the H2 gas into the cylinder after the inlet valves have closed. Typically, an electrical solenoid injector is used to achieve this and the injector is generally located in the cylinder head and hence is exposed to the full firing pressure and temperature of combustion. The injectors must also be capable of passing a large volume of compressed H₂ gas in a short time period and the reciprocating valve component of the typical mechanism inevitably has significant size, and therefore inertia. Furthermore, H2 gas possesses zero lubricity and negligible viscosity which results in wear problems to the valve components and the achievement of adequate durability with these types of valves is proving to be a major problem, which is yet to be resolved.

Battery-powered electric vehicles also have zero NOx or HC emissions at the point of use but provide limited vehicle range. However, the required number of batteries are heavy and the fitting of more batteries to increase the range of travel of the vehicle between charges causes the vehicle weight to increase significantly and therefore overall energy usage increases. Gasoline fuelled reciprocating type rangeextender engines have been proposed as a means of overcoming this problem, but the noise and vibration emitted by these engines which generally, for reasons of weight and cost must have few cylinders, has made them almost totally unacceptable and impractical for use in the commercial marketplace.

As an alternative, prototype range extender cars using a small single-rotor Wankel type engine have been demonstrated by three manufacturers and when test-driven by the motoring press were widely acclaimed. However, scaling up these engines for use with heavier forms of vehicles such as buses, lorries, trains and the like has been regarded as impractical

Typically, in the rotary engine, it is known to provide a triangular shaped rotor which is mounted on an eccentric shaft and geared to rotate at one third the speed of the shaft, inside an epitrochoidally shaped housing, and the apices of the rotor carry seal pieces, or so called apex seals, which slidably contact the bore of said housing.

The rotation of the rotor is such as to cause a chamber to be formed into which air is inducted and a fuel can be injected and subsequently the mixture is compressed, combusted and expanded to cause rotation of the shaft and so provide a drive force for, particularly, a vehicle. This form of engine is well-known and typically is provided with a cooling system for the rotor which can be oil based or, alternatively, relies on airflow to provide the cooling effect. An advantage of using airflow to provide cooling instead of oil is that the difficulties of preventing unwanted oil leakage from the oil cooled passages inside the rotating and orbiting rotor which thereby add to unwanted exhaust emissions, is avoided. However, with the air cooling system, a difficulty is being able to provide a sufficient cooling effect in order to ensure that the components of the engine will operate correctly.

The so-called ACR (air cooled rotor) version of the Wankel type rotary engine has many additional advantages when compared with the OCR (oil cooled rotor) version particularly in relation to fewer parts count, lower weight, lower manufacturing cost and lower mechanical friction losses. However, satisfactory cooling of the ACR type rotor generally has always presented difficulties. During early development in the 1960’s, inadequate cooling of the rotor, and particularly tire rotor bearing, necessitated that the maximum engine RPM and power output were limited to a fairly low level. For example, a 300cc chamber size engine could then reliably provide only 20 bhp or so.

During the following 30 years of development, progressive design changes were incorporated such that by 2000 this same engine size could deliver 60 bhp maximum power at 8000 rpm and provide an adequate 500 hour TBO life when powering military Unmanned Air Vehicles (UAV)

The rotor cooling system used in these prior art engines most typically employed a centrifugal fan to force air at high velocity through the rotor internals in an open circuit. The majority of the total-loss system lubricating oil was ejected into the atmosphere along with the cooling air after a single pass through the engine. This system with the associated wet oil ejection was acceptable for a UAV but totally unacceptable for any ground applications. A more recent, closed-circuit system for cooling the rotor with air is disclosed in Patent Application PCT/GB2012/052574. This design eliminates the emission of wet oil as well as reducing the rotor temperature and thereby further increasing the durability and operating life. Such engines are now suited for the duty of hydrogen-fuelled zero-emission Range Extender power units driving a generator in battery electric vehicles such as city delivery vans and buses. Larger versions with higher power maybe used in trucks or light railway systems. The required TBO of such engines is very high, being of the order 8,000 hours as a minimum.

However it is found that a life limiting design feature of the current designs of ACR type engines, such as that shown in PCT/GB2012/052574, is the needle roller type bearing which is used for mounting the rotor on the engine eccentric shaft. Typically it has been indirectly lubricated extremely sparsely via some of the oil particles which are circulating throughout the engine at high velocity within the rotor cooling air. The bearing is located in the centre of the hot rotor and the oil particles which do enter the bearing are hot and therefore have low viscosity. Thus, in the prior art rotary engines it is found that the high centrifugal forces result in the oil forming only an extremely thin, and possibly incomplete, film on the sliding and rolling surfaces. The same forces also act on the cage of the bearing so that a hydrodynamic oil film is not created between the cage OD and the supporting bore. The resulting wear on the cage and the bore limits the life of the bearing to lower than what is required for new H2 fuelled potential uses.

Hydrogen-consuming fuel cells (FCs) have also been considered to avoid all unwanted emissions. However, despite intensive development for 60 years and more, these fuel cells still have design and technical issues, are very costly to manufacture, utilise scarce raw materials, need to be supplied with high-purity H2 gas, and require completely new forms of manufacturing systems to be adopted. Furthermore, it is found that they cannot efficiently provide vehicle heating which is important for vehicles in general and in particular multi passenger vehicles such as city centre buses and commuter trains.

The invention is also directed to further improvements to the Air- Cooled Rotary engine of a type as illustrated in the Patent application PCT/GB2009/000319 describes an ACR type of engine and, in particular, a means of improving the cooling of the rotor. In the cooling solution of this prior art patent a centrifugal fan forces a pressurised air-gas mixture, hereinafter referred to as “air”, to be circulated in a closed system at high velocity through the rotor internal passages (where heat is picked up ) and then through a heat exchanger (or ‘cooler’ ) where that heat is dissipated. In this design both the fan and the cooler are provided to be external to the engine housing and are connected by ducts. This means that considerable additional overall bulk results from this arrangement and the duct joints need to be well engineered to avoid the possibility of leakage. Additionally, the external mounted intercooler must always be located higher than the engine in order to avoid oil particles gathering in some low part of the circuit due to the effect of gravity. An alternative solution to the rotor cooling problem is disclosed in Patent application PCT/GB2012/052574 and in which both the fan and the cooler are integrated into the engine casings. The intercooler is located as an integrated part of the cool induction sector of the cast aluminium rotor housing at the highest part of the engine to ensure that all oil particles remained in circulation. These changes considerably reduce the bulk, weight, component count and manufacturing cost of the ACR engine. However, the cooling capability of the intercooler in this arrangement using cast fins to reject heat has proved to be deficient in its ability to sufficiently reduce the temperature of the circulating cooling air as it exits the rotor prior to that air re-entering the cooling passages in the rotor. Consequently, the temperature of the rotor assembly is higher than desirable. This limits the applications and possibly also durability and life of this engine type.

Furthermore, as the prior art cast fins are created as integral parts of the main cast aluminium rotor housing, so the metal thickness of the fins and the spacing between them is limited by what is practical to manufacture, most typically using a sand casting process and therefore compromises in the design have to be made. For example, thicker fins transfer more heat per fin, but thicker fins result in a reduced number of fins being provided and hence a reduced total area for transferring heat from the air to the metal. Some of the fins, particularly in larger capacity engines, are much longer than is ideal for transferring heat from the tips along the full radial length of the fins to their base where the heat is transferred to a water passage. The contact area of the fin bases with the single water passage is also somewhat limited and this reduces the rate of heat transfer at this location.

It is known that some improvement in cooling performance can be gained by machining the fin surfaces from solid rather than them being cast thereby allowing the creation of a larger number of thinner fins and, in turn, a greater total surface area as, for example, was done in high power radial reciprocating engines for aircraft. However, this type of machining is extremely costly to cany out.

As a result of the problems and limitations of the above examples, it is still found that the rotor of the ACR engine suffers from the temperature being too high and therefore with the current known designs there is no effective means of providing adequate cooling of this key component

An aim of the present invention is therefore to provide a Range Extender engine which provides a zero emissions characteristic, which possesses small size and weight, emits low noise and vibration, has high thermal efficiency, can additionally provide heat for the purpose of passenger comfort and/or is easy to manufacture using existing procedures and raw materials. A further aim is to provide the engine in a form which utilises Hydrogen as the fuel.

A key characteristic of using H2 fuel in an IC engine is that, unlike gasoline, it bums very efficiently whilst using a wide range of mixture strengths. The important relationship of NOx output with the mixture strength is provided via the frequently published graph as below:

Table A

A further aim of the present invention is to provide a solution to allow sufficient and effective lubrication of the rotor bearing to be achieved such that the life of the engine can be increased practically to the desired levels whilst at the same ensuring that the total oil supply rate to the engine and thereby the resulting carbon emissions from the engine are minimised to a negligible quantity.

A yet furflier aim of the invention is to provide a means of cooling of a rotary form of engine which avoids the deficiencies described above and is sufficiently effective to completely overcome the problem of overheating of the rotor in ACR engines.

In a first aspect of the invention there is provided a rotary engine of the so-called Wankel type wherein a 3 cornered rotor possessing arcuate flanks revolves at one third the speed of the eccentric shaft upon which it is mounted, the three comers of the rotor being in slidable contact with a two lobed epitrochoidal shaped housing bore such that the four phases of induction, compression, expansion and exhaust are created, the rotor being a pressurised-air-cooled-rotor type and wherein a mechanically driven rotary valve controls the injection of hydrogen fuel into the engine during the early part of the compression stroke of the engine such that a homogeneous mixture of fuel and air is formed prior to combustion in the following expansion stroke.

In one embodiment the rotor type is as as described in Patent PCT / GB 2012 / 052574.

In one embodiment the rotary valve which incorporates large flow areas and has an outlet or outlets which are intermittently connected to a hole or holes located in the epitrochoidal shaped surface of the induction compression chamber and via which H2 gas is injected into the compression chamber, the diameter, location, and alignment angles of the said holes being selected to best procure the homogeneous mixture.

In one embodiment injection of the required mass of H2 commences at the instant the air induction port closes and is completed during the first 100 ⁰ of the 270 “duration compression stroke. More preferably injection of the required mass of H2 commences at the instant the air induction port closes and is completed during the first 60 “whilst only requiring a low pressure supply of gas due to the large flow areas of the rotary valve.

In one embodiment the quantity of H2 gas which is injected creates a homogenous or near homogeneous mixture of air and gas where q> = 0.5 or near such that NOx emissions from the engine are zero or close to zero.

In one embodiment the engine operates unthrottled, such that no throttle mechanism is required to be fitted or alternatively a wide open throttle, (W OT) can be used, and generally at a single RPM thereby enabling precise optimisation of all engine design features at this selected operating point in order to achieve the highest thermal efficiency.

In one embodiment a compound expansion turbine is mounted immediately adjacent to the single exhaust port of the engine, the exhaust port and turbine entry being designed for the turbine to capture some of the blow-down energy as the port is first opened together with the following expansion energy, this energy being returned to the power unit via either a mechanical drive to the engine shaft or via supplying additional electrical energy from an electrical generator driven by the turbine shaft In one embodiment the rotor is mounted on the eccentric of the engine shaft via a needle roller type bearing, the bearing casing incorporating or being axially adjacent to side walls such that a trough is formed which contains the needles, the needle cage and lubricating oil and, resulting from the continuously acting outward centrifugal forces which operate on the contents of this trough, thereby maintains a certain depth of oil in the trough whenever the engine is rotating. In one embodiment the lubricating this oil is supplied into the ID of the bearing via a radial hole in the eccentric connected at its inner end to an axial hole in the centre of the engine shaft, tins hole being supplied with oil from a metering pump which feeds the oil into an entry hole at one end the eccentric shaft.

In one embodiment the engine includes a rotor bearing and the side wall at the end which is at the upstream side of the approaching rotor cooling air has an ID with only a very small radial clearance to the OD of the eccentric shaft such that the rotor bearing is effectively sealed from any unwanted dust particles or debris which may be entrained in the cooling airstream; and the side wall at the downstream end has an ID somewhat larger than the eccentric diameter of the shaft which ensures that the trough is filled with oil to the depth of that sidewall, the depth being selected to provide optimum lubrication of the needle cage and the rolling elements in combination with achieving low energy losses which may be related to oil churning.

In one embodiment the said lubricating oil leaves the trough via the radial clearance at the ID of the downstream side wall and enters the fast moving circulating airstream to be then carried to all other surfaces in the engine which require lubrication.

In one embodiment the engine includes an intercooler for reducing the temperature of the circulating air and where the compact size of the intercooler allows it to be located horizontally within the outer profile and axial width of the rotor housing of the engine at or near the highest point of the engine, and its construction does not possess any wells or depressions for any of the oil particles in the airstream to reside and thereby fail to continue circulating. Typically the intercooler consists of a plurality of parallel and horizontal metal tubes and aligned in planes parallel to the plane of the rotor housing, heat being removed from the internal surfaces of the tubes via the liquid coolant which is also employed to remove heat from the main housings of the engine. In one embodiment thin and closely-spaced copper or aluminium separate fins are mounted on the tubes in planes at 90 º to the tubes, or more preferably the fins consist of long thin strips of copper or aluminium which are spirally and edge mounted on the tubes generally lying in the plane of the circulating air requiring to be cooled, the fins providing a large surface area thereby enabling the transfer of heat from the circulating airstream to the liquid coolant in an efficient manner.

The engine as herein described may be utilised as a hydrogen fuelled CHP unit.

In one embodiment the gas is injected into the engine via the rotary valve which is rotating at half the speed of the eccentric shaft. Thus, in one embodiment the gas is injected into the engine with the valve rotating at twice the engine speed.

In one embodiment the engine as herein described is incorporated as part of a power unit which drives with an integrated or semi integrated electrical generator, which provides electrical energy to the batteries of land, water or air vehicles which are fitted with electric drive motors, the function of the power unit being to assist in maintaining the desired level of charge in the batteries and thereby acting as a range extender for such vehicles.

In a further aspect of the invention there is provided a Wankel-type rotary engine including an ACR type cooling system, said engine including a rotor and the rotor and engine create a compression chamber and wherein at least one valve is provided and controlled so as to commence injection of Hydrogen (H₂) into the said compression chamber of the engine at, or soon after, the instant that an inductionair port of the engine closes, so as to complete the injection of the required amount of H₂ gas early during the compression stroke of the engine.

In one embodiment the full compression stroke of the engine occupies substantially 270° of the rotation of an eccentric shaft on which the rotor is mounted to rotate therewith.

Typically the injection of the said required amount of H₂ gas is achieved substantially within the first 90° , or third, of the rotation of the rotor during the said compression stroke.

Preferably the injection of the H₂ commences substantially at the instant of closure of the said at least one induction air port.

In one embodiment the said rotor is gas-cooled. In one embodiment the engine incorporates a rotary valve unit which includes the said at least one valve, to control the supply of H₂ gas directly into the compression chamber and by which the introduction of the required amount of H₂ gas is completed in a very short time period during the early part of the compression phase.

Typically, the said valve has an outlet which is connected to a hole or holes located in an epitrochoidal surface of the induction chamber and which inject the H₂ gas at high velocity.

Typically, the hole positioning and axis of alignment and the resulting plumes of H₂ with entrained air are selected to create a satisfactorily homogenised mixture throughout the said chamber prior to the completion of the compression phase.

In one embodiment, in order to increase the power output and particularly to increase the thermal efficiency, an expansion turbine maybe mounted immediately adjacent to an exhaust port of the engine and thereby provides a turbo compounding system which captures some of the normally-wasted early blow-down high velocity gas as the port opens as well as the later expansion energy. It returns that energy to the power unit either with a mechanical drive to the engine shaft or as additional electrical energy via a turbo-shaft-mounted high-speed generator.

Typically there is provided a single exhaust port.

In one embodiment the engine shaft drives a main electrical generator which supplies energy to one or more batteries of the vehicle with which the engine in accordance with the invention is provided.

In one embodiment the power unit is operated only at a single selected RPM and single WOT load and is fuelled with a constant air + hydrogen gas mixture strength of, for example, φ =0.5 or in the range of 0.35-0.6, with the 0.5 value generally being the richest mixture which provides near-zero No_x emissions. Use of the 0.5 value or near also, very valuably, generally provides the highest thermal efficiency.

In one embodiment, no throttle disc and spindle, or throttle control mechanism is required and is not fitted.

In accordance with a further aspect of the invention there is provided a vehicle which includes a first source of power which drives the vehicle and a second source of energy and wherein this second source of energy is a Wankel-type rotary engine as herein described.

Typically the first source of power is one or more electric motors provided with electrical power from one or more batteries carried on the vehicle. Typically, during operation of the vehicle, if energy from the second source is not required it is switched off and the vehicle progresses using power from the first source alone.

In one embodiment, if, during operation of the vehicle, energy from the second source is required, a management system of the vehicle controls operation of said second source and manages the provision and distribution of energy therefrom to the batteries of the vehicle.

Typically the selective operation of the second source and the management system of the vehicle allows the overall range of distance of travel of the vehicle which is possible between charging the batteries for the first source, to be increased in comparison to an equivalent single power source vehicle.

In one embodiment the Wankel type engine which forms the second source has a single rotor.

In one embodiment the said engine includes a bearing lubrication system to allow lubricating oil to be supplied directly into the rotor bearing via an entry into an axial central bore preferably via a free non-drive end of a main eccentric shaft of the engine.

In one embodiment the supply of lubricating oil to the engine is supplied via a metering pump into said bore.

In one embodiment the shaft includes the axial bore which, possesses a tapered increasing diameter which connects with a radial hole or holes through the eccentric of the shaft to the inner race of the rotor bearing.

Typically, the centrifugal forces acting on the oil in the tapered bore results in all of the supplied oil immediately passing directly into the needle bearing assembly.

In one embodiment rings or shoulders, possibly of steel, are fitted to the rotor bore adjacent to each end of the bearing. In one embodiment, on the upstream side, where the main circulating cooling airstream is axially approaching the outside of bearing, the ID of the ring or shoulder has only a very small radial clearance to the OD of the eccentric of the shaft such that the cavity containing the rotor bearing is effectively totally sealed from this airstream at that end.

In one embodiment the needles of the bearing are typically 4mm diameter.

In one embodiment the shoulder at the downstream end has an ID which is typically 2 to 5mm larger than the diameter of the eccentric on the shaft where the needle bearing is operating. Hence an annular trough is formed by tire ID of the bearing outer race surface and the two end shoulders. Typically, when the engine is running, a continually acting centrifugal radially outward force acts on the bearing needles and on the oil in the trough, these components rotating at a speed midway between the speed of rotation of the shaft and the speed of rotation of the rotor. This ensures that the trough is filled with oil to the depth of the radially inward protrusion of the downstream shoulder. The bearing needle rollers and needle cage operate in this trough of oil. The OD of the bearing cage is now hydrodynamically supported with a substantial oil film thickness due to the rotation speed of the cage relative to the rotor bore.

Typically, the level of oil which is provided is selected so as to provide greatest energy efficiency of the engine when operated.

In one embodiment the oil leaves the trough via the radial gap at the ID of the downstream plate and enters the fast-moving cooling air stream to then be carried to all the other surfaces in the engine which require lubrication. The oil entering into the trough via the supply hole from the centre of the eccentric shaft is always new clean oil supplied via the metering pump taking oil from an external tank such that the rotor bearing is now always free of any wear debris or corrosive particles or previously used oil.

As a result of the improvements herein described the bearing is now operating in an ideal environment; and the life of the bearing assembly will now achieve that predicted by the bearing manufacturers for a correctly installed and operated rolling element type bearing and the TBO will meet the needs of the Range Extender users.

In one embodiment the engine is provided with an intercooler system which is accommodated substantially within the outer profile of the rotor housing to provide compactness to the overall engine assembly.

Typically the intercooler system includes a plurality of tubes which are substantially circular in cross section and arranged so as to be substantially parallel.

Typically, the cooling medium is water which has previously passed through a main radiator fitted for rejecting heat from the main engine housings.

In one embodiment the means to provide extended external surfaces to the tubes which aid the transfer of heat from the heated gas which is exiting the cooling passages in the rotor are a plurality of sheet metal or metal alloy plates which are engaged with the external surface of said tube with each plate typically forming a fin.

In one embodiment the plate includes a substantially centrally located aperture which receives a tube there through. In one embodiment the plates are provided in the form of shoulders and are formed of copper.

In one embodiment to avoid the possibility for air to partially bypass some areas between the circular shaped plates lightweight nylon or similar tubes of negligible cost and weight can be attached or inserted between the plates at spaced locations on the edge of the same and which effectively occupy and block the areas through which the air may flow and thereby force a greater proportion of the air to pass between the fins.

In an alternative embodiment the plates are provided with a series of straight edges as the outer profile which then provides a larger total fin area in a given size of intercooler than is the case with using shoulders. The relative advantages of using square fins, or the alternative of adding the compensating plastic tubes with the circular fins can be instantly seen by examining the drawings. Note that the square fins would be somewhat more expensive to manufacture and assemble on the tubes than the circular shoulders as they have to be accurately circumferentially aligned. This increased cost is particularly true because the circular shoulders can be formed, not as individual shoulders successively and individually pressed on to the tube, but can be created by using a single strip of copper sheet, the width of the strip being equal to the desired height of the fins. This strip is then deformed and edge wound as a spiral to make firm contact with the OD of the water tubes. The result in terms of the area exposed to the air is effectively identical to employing individual shoulders.

The said plates maybe pressed or otherwise located on to the outside of the tubes so as to be in contact with the tubes and allow the high rate of heat transfer from the plates to the tubes.

In one embodiment, the tubes are located in a transverse plane of the engine such that axially flowing rotor cooling air from the fan exit passes parallel to and between the fins mounted on the external walls of the tubes.

The fins have a very large surface area in contact with the air, and the use of copper material, which possesses a very high coefficient of heat transfer, ensures a high rate of heat transfer from the air to the fins and from the fins to the outer walls of the tubes on which they are mounted.

The radial dimension of the fins is not high such that the heat transferred to the fin tips from the air has only a short distance to travel before transfer to the tube wall. In one embodiment the total contact area between the cooling water and the walls of the tubes which receive the heat from the fins is much greater than with the known existing arrangement.

Furthermore, the overall heat transfer capability of the cooling apparatus is many times greater than the conventional system which uses cast fins and occupies no greater volume nor does it impose a higher flow resistance to the cooling air than the conventional systems.

In accordance with a further aspect of the invention there is provided a rotary engine including a bearing lubrication system to allow lubricating oil to be supplied directly into the rotor bearing via an entry into an axial central bore at a free, non-drive, end of a main eccentric shaft of the engine said oil provided from an annular shaped trough.

In accordance with a yet further aspect of the invention there is provided a rotary engine including a housing, a rotor located to rotate within a compression chamber in the housing and wherein the engine includes an intercooler system for the rotor and wherein said intercooler system is substantially accommodated within the outer profile of the said housing.

Typically the rotary engine in these further aspects can be used in conjunction with the features and embodiments of the first aspect ion combination or independently as described herein.

The invention is applicable to a wide range of engine sizes. Applications include use with vehicles in the form of city taxis, city delivery vans, buses and, using multiple units, heavy trucks and light railways systems. It is envisaged that use of the invention will allow what previously were impractical uses of electrically powered vehicles, e.g. for longer routes or longer distances, will now be practical and achievable.

Specific examples of the invention are now described with reference to the accompanying drawings; wherein

Fig 1 shows an external view of an engine assembly in accordance with one embodiment of the invention;

Fig 2 shows a cross-section through the rotary valve assembly of the engine assembly of Figure 1;

Fig 3 shows a profile of the flow area through the rotary valve versus shaft angle;

Fig 4 shows a transverse Section through the working chambers of the engine together with the rotary valve assembly, the rotor flank profiles at the typical start and end of H2 injection; and the blow-down / expander turbine unit adjacent to the exhaust port;

Fig 5 shows a transverse section of the compression chamber and rotor with a jet of fuel and entrained air at the mid-point of the injection phase and when the flow area through tire rotary valve is at a maximum;

Fig 6 shows a radial view of multiple fuel sprays entering the compression chamber early in the injection phase;

Figure 7 shows a section through a prior art ACR engine assembly with a fan, the location of the intercooler and the airflow through the centre of the rotor being illustrated;

Figure 8 shows illustrates an axial view of the prior art type of intercooler of Figure 7 with cast fins;

Figure 9 shows a similar axial view as Figure 8 but with the intercooler apparatus in accordance with the invention shown in place of the prior art intercooler apparatus;

Figure 10A shows a transverse section of a short sample of a water tube with pressed on individual circular shoulder plates to form fins in accordance with one embodiment of the invention;

Figure 10B shows an axial view of a water tube with individual square pressed-on plates to form fins in accordance with one embodiment of the invention;

Figure IOC shows a part-cross section short of a sample of a water tube with spirally wound circular fins in accordance with one embodiment of the invention;

Figure 11 shows a cross section view of an intercooler assembly with 4 tubes with circular plates forming fins either individually circular or spirally wound type in accordance with one embodiment of the invention;

Figure 12 shows an axial cross-section view with 4 circular fins with added plastic air flow guide tubes in accordance with one embodiment of the invention;

Figure 13 shows an axial cross-section view of 4 tubes with square pressed on plates forming fins; in accordance with one embodiment of the invention;

Figure 14 shows an intercooler in accordance with one embodiment of the invention for use with larger ACR engines and which employs a nine tube configuration with 6 blocking tubes in accordance with one embodiment of the invention; Fig 15 shows a cross section of a type of engine with which the embodiments of the invention can be implemented;

Fig 16 shows a view of a prior art design of rotor bearing;

Fig 17 shows a part view of the bore in the eccentric shaft which supplies oil to the bearing in accordance with one embodiment of the invention; and

Fig 18 shows an enlarged cross section of the rotor bearing assembly in accordance with one embodiment of the invention.

Referring firstly to Figure 1 the engine unit in accordance with one embodiment of the invention includes a main rotor housing 1 with end plates 15 and 16 and an engine drive shaft with drive flange 2 with balance weight 3. A tooth-belt drive pulley 4 is mounted on the engine shaft and drives, via belt 5 at precisely 50%, engine speed pulley 6 which is mounted on the shaft of the rotary valve assembly 7.

Hydrogen fuel is supplied from a fuel tank and a pressure control valve, (not shown), to the rotary valve entry union 8. A liquid coolant entry union 9 and induction air entry ram pipe 10 are also shown. The assembly 11 is an expander turbine with exhaust gas exit 12 mounted, typically immediately adjacent to the engine exhaust exit at 13 and the expander turbine is connected to directly drive an electrical generator 14 which may be integrated with the turbine.

Figure 2 illustrates both transverse and axial sections through the rotary valve and it shows how the valve body 7 has a rotor 22 which has a small radial clearance between its OD and the bore of the valve body. The entry port 23 and exit port 24 communicate with the slot 25 in the rotor.

The rotor revolves at a speed of 50% of that of the engine shaft with a precise timing setting driven by the pulley 6 of which only the hub is shown. Shaft extensions 28 are supported and accurately radially located in the body by bearings 27. Lip seals are also provided which prevent H₂ gas escaping.

Figure 3 illustrates the values 31 of the varying flow area as it rotates in the valve body. At the start 32 and the end 33 of fuel injection the flow value is zero and the maximum flow area value at 34 is midway between the start and end of injection. The Figure shows the flow area through the rotary valve to be pyramid shaped as line 31. This results ftom the slot width in the valve spindle being selected to be the same width as the slot in the housing. By selecting the slots to be different widths line 31 can be a different shape with a lower maximum value but with a flat top.

Figure 4 illustrates a cross section of the engine assembly on the mid-plane of the engine rotor. The position of the rotor flank profile 41 is at the start of injection into the engine compression chamber 48 which coincides with a rotor apex 43 just closing the induction port 44. The position of the rotor flank profile 42 is passing the fuel entry hole or holes 45 at the instant when the injection of fuel ceases. The expander turbine body 11 contains a turbine rotor 46, the assembly being mounted very close to the engine exhaust duct 47. Spark plug or plugs are shown in a general position at 48.

Figure 5 is a cross section of the engine assembly when the rotor flank 51 is positioned at the mid point between start and finish of fuel injection and the rate of flow is at or near to the maximum. The fuel jet or jets form a plume 52 with the entrained air in the compression chamber and are approaching the end of the engine compression chamber 48 at the greatest distance from the point of the fuel entry.

Figure 6 is a view into the engine compression chamber 48 at right angles to the engine mainshaft axis 61. The rotary valve body has a manifold passage 62 which distributes the fuel to one or more passageways 64 through the engine rotor housing 1 to the injector holes 45 on the rotor housing epitrochoidal shaped bore surface 65. The injector hole 45 may inject the fuel in parallel sprays or in a splayed, non-parallel, arrangement.

The engine as described in accordance with this invention can utilise features of previous engines of this general type, for example as described in the patent application PCT/ GB2012/052574 and US8424504. These describe a system for cooling the rotor with pressurised and hence denser air than ambient air. This possesses a higher coefficient of heat transfer from the heated rotor to this cooling air which is circulated through the rotor internal finned passages and then through a heat exchanger where the gathered heat is rejected. The above cited patents describe eariier unsatisfactory systems.

One advantage of the engine as described in the above mentioned patent application is that the rotor temperature is reduced when compared to earlier ACR systems which used ambient air pressure. More importantly it allows a very small quantity of lubricating oil to be fed to a single point in the closed continually recirculating system. The fast-moving circulating cooling air distributes these oil particles to all areas where lubrication is required and continues to recirculate each particle of oil through the system many hundreds of times before eventually the oil migrates from the internal passages in the rotor into the working chambers. It therefore lubricates and assists the sealing quality of the gas seals before being vapourised and generally burned as it passes though the exhaust port of the engine, this being the oily exit route. When compared to the better-known Oil Cooled Rotor type of Wankel engine (OCR) very significant advantages are that the ACR type of engine is smaller, lighter weight and consists of fewer components; and is therefore lower cost to manufacture. More importantly it also avoids the need for a bulky oil sump and the need for periodic oil changes which is of particular advantage when one considers that a range-extender engine may be located in a remote, possibly sound-proofed enclosure. Furthermore, the ACR form of engine avoids the fundamental problem of oil leakage from within the rotating and orbiting OCR type rotor, a problem which becomes more severe as the engine wears.

Furthermore, the ACR type of engine has much lower mechanical friction losses than the OCR type as shown in Table B below:

It allows a smaller R/e ratio for the basic geometry. This results in a more compact combustion chamber with a 15% or so reduction in the surface / volume ratio with consequently lower heat loss during combustion. The reduced R/e ratio also provides increased turbulence of the air/fuel mixture around TDC thereby speeding up combustion and further reducing SFC.

The use of a rotary valve unit in accordance with the engine of the current invention rather than multiple solenoid injectors as generally previously employed, enables precisely timed injection of the gaseous H₂ feel at a fast rate and high velocity direct into the compression chamber very early in the compression phase. Start of injection is at the instant the induction port closes. In general, completion of injection is prior to the compression stroke having only reduced the chamber volume by 15-20% from that volume which existed at time of the induction port closing.

The provision of this relatively fest and early injection means that the H₂ gas and air have more time available during the remaining part of the compression stroke to allow formation of a homogeneous mixture. Furthermore, the pressure and density of the air in the chamber are low at the beginning of the compression stroke and so the jets of feel penetrate more easily into the more distant end of the chamber Also, the required supply pressure of the H₂ into the rotary valve can be lower, being typically only 2 to 4 bar (gauge). Hence a larger percentage of the pressurised gas H₂ gas contained in the vehicle fuel tank can be utilised with no additional pump being required.

The volumetric efficiency of all Wankel type rotary engines is generally higher than reciprocating engines due to the absence of an inlet valve and the general absence of limitations on the flow area and shape of the induction system. The engine in accordance with this invention, with single-RPM and WOT-only has a particularly high volumetric efficiency for several further reasons, including no throttle disc or its accompanying spindle is required or fitted, the volume displacement and drag of adding any fuel into the induction air is eliminated and the length and diameter of the induction ram pipe can be precisely optimised for this single rpm.

Furthermore, no cold starting system is required for this gaseous fuel. The main electrical generator cranks the engine to its chosen RPM, a fuel supply valve is opened, a magneto ignition system automatically supplies the required sparks, and the engine runs at its normal maximum output instantly. The engine is stopped merely by turning off a fuel valve.

When turbochargers are fitted to diesel or gasoline type reciprocating engines the turbine is generally fed from an exhaust manifold which has collected the exhaust gasses from all of the, typically multiple, cylinders. It is inevitable that the initial high- velocity blow-down from each individual exhaust valve opening is largely dissipated. There is also some heat loss in the manifold from this gas before it arrives at entry to the expander turbine.

This single-rotor engine allows the gas entry of the expander turbine to be located very close to the exhaust port. As the exhaust port of a Wankel engine opens much faster that an exhaust valve of a reciprocating engine a considerable quantity of blow- down energy can be recovered by the turbine in accordance with this invention, as well as energy recovered in expansion of the hot exhaust gasses down to atmospheric pressure. In this single speed and load engine these features can be precisely optimised without the usual severe compromises which are obligatory with an engine which must operate throughout a wide load and speed range.

Furthermore, in alternative power sources, such as in turbocharged gasoline or diesel engines all or most of the turbine energy is used to drive a compressor. No compressor is required to be fitted to the engine in accordance with the invention and all of the turbine energy is available. Hence, to increase the shaft power of the range extender engine, a significant amount of additional energy can be gathered thereby improving the overall thermal efficiency of this engine. The addition of the turbine expander also beneficially reduces the level of exhaust noise.

Larger swept volume units of this engine, which will assist in the reduction of both gas leakage and heat loss during combustion, may enable the thermal efficiency to be further increased. Thereby the overall efficiency levels which can be achieved by conventional fuel cells may be well exceeded by use of the invention in accordance with this application.

It is envisaged that heavy trucks or light trains may use Range Extender multiple power units of perhaps 2000cc or greater working chamber capacity engines providing 100 to 150kW, or more, each. The use of multiple units can possess operational advantages.

Although this patent application discusses use of the apparatus in vehicles it should be appreciated that the use of the apparatus is not so limited. For example, the apparatus may also be advantageously used when consuming Hydrogen fuel in Combined Heat and Power (CHP) units.

It should be noted that although this patent application discusses engines with single rotors this does not exclude arrangements with multi rotors.

Referring now to Fig 7 and 8 these figures illustrate a prior art ACR engine and in particular a section parallel to the main shaft axis and of a type shown in for example the patent application PCT/GB2012/052574. This assembly has an unsatisfactory intercooler system. In the assembly side plates 101 and 102 with rotor housing 103 enclose a rotor 104 mounted on eccentric shaft 105. A centrifugal fan impellor 106 mounted on 105 circulates cooling air streams 107 through axial passages 108 in the rotor where heat is picked up and then through cast fins 109 where heat is rejected. The majority of the fins are typically mounted on a single generally rectangular cast water passage 110 where the water makes only limited thermal contact with the base of the fins 109.

Fig 8 is a part axial view of the same engine. Cooling water generally after exiting the main radiator (not shown) enters at 120 and passes through cast passage 121 where it collects heat conducted from the fins 123 and leaves at 122 to thereafter cool the engine main housings (not shown) in the hot zone of the engine. The base of Fins 123 are mounted on the wall of 121.

Fig 9 illustrates the improved intercooler apparatus in accordance with one embodiment of the invention where a large number of short copper plates are mounted at spaced locations on multiple parallel tubes 131 to form external fins 134. Cooling water entering at 130 passes through the tubes 131 and leaves at outlet 133. The air to be cooled passes through the fins 114 at right angles to this view where heat is rejected. The total surface area of the fins which are contacted by the air streams passing between them is very much higher than previous designs. The resistance to air flow is low to match the limited pressure capability of the engine- speed centrifugal fan and thereby to maximise the air volume flow through the rotor internal passages.

Fig 10A shows a short section of a piece of a tube 131 with individual copper fins 134 mounted on the tube. The radial length of the fins is not high. Copper material which possesses a particularly high value of thermal conductivity and therefore is attractive to be used to manufacture the fins 134. These fins make high contact with the airstream and also with the full periphery of the water cooled tube on which they are mounted.

Figure 10B shows an axial view of an individual fin 138 which in this embodiment possesses a square outer profile rather than the circular profile of fin 134. These fins 118 present a larger area of contact with the air than circular fins 134 with the same major dimensions.

Fig IOC shows another method used to create the fins and in this case there is shown in part section a single piece of metal strip 119 spirally wound along the tube and attached thereto, to provide parallel circular OD profile fins 134 and edge mounted on tube 131.

Fig 11 shows an arrangement of four parallel tubes 141 with circular fins formed by plates 134 or with strip 139 as shown in Figs 10A and 10C, respectively mounted on the tubes 141. Approaching air streams 143 pass largely through the fins 142 but some of the air streams tend to diverge slightly to pass somewhat more through the spaces outside the periphery of the fins as shown at 144, 145, 146 .

Fig 12 shows the same arrangement of tube and fins 141 as Fig 11 but with three sets of three thin-wall plastic tubes 161A,B and C; 162A.B and C,: 163A,B and C, added and located in the spaces such that the airstreams 164 now are forced to pass to a greater extent between the fins. Thereby they more efficiently transfer heat to the fins than would be the situation of Fig 11. If only the three central tubes 162A, B, C, were fitted then this more simple system of only fitting 3 tubes would largely achieve the same benefits of fitting 6 or 9 tubes.

Fig 13 shows a similar arrangement of four tubes 170 fitted with individual fins 711 which in this embodiment have a rectangular shape. This is the most compact arrangement because it offers the largest area of fins which are contacted by the air to be cooled. All the airstreams are constantly in contact with the fin surfaces without the addition of guidance tubes.

The arrangement of Fig 12 with tubes, 162A, 162B and 162C only being fitted, is generally preferred as it provides the best compromise between cooling performance and complexity. It should be noted that fitting only these three central tubes is particularly easy because they can just be dropped into place in the spaces between the tubes as shown and are thereby located and retained with no requirements for locating or holding brackets; whereas adding the tubes 161 and 163 may require such brackets.

Fig 14 shows an arrangement suitable for a larger and higher power engine of perhaps 150 bhp or so particularly suitable as a zero emission H2 fuelled Range extender engine in accordance with this invention. The rotor housing contains nine water cooled tubes 181 with spirally wound copper fins 182. This assembly would be typically mounted transversely to the main shaft axis and horizontally at the higher part of the engine assembly. Eight plastic tubes 183 would be fitted as illustrated to guide the air streams 84 to largely pass between the copper fins 182.

It should be noted that while Figure 11 illustrates a 2 x 2 and Fig 14 a 3 x3 configuration of the finned tubes, many alternative arrangements are possible such as 2 x 1 or 3 x 2 or 4 x 2, etc and can be used to suit the particular cooling effect and/or engine size required.

The key factors which provide the improved performance and cooling effect in accordance with the invention are the improved heat transfer efficiency of an air-to- water heat exchange where the total surface area of the fins which provide contact with the air to be cooled is very high and the flow resistance to the air stream passing between the fins is relatively low so that a given fan pressure results in high volume flow and high velocity of the airstream.

Furthermore, as the length of the fins is relatively short the required cooling effect can be achieved in a compact arrangement.

The coefficient of heat transfer of the fin material which is used, such as copper, is high and there is good contact area and a high rate of heat transfer between the base of the fins and the cooling tubes upon which they are mounted.

Furthermore, the total flow area for the liquid coolant and the total contact area of the coolant with the ID of the tubes is excellent. Referring now to Figures 15 and 16 there is illustrated a general arrangement of conventional air cooled rotor type of engine. Side plates 201 and 202, along with rotor housing 203, enclose a rotor 204 which is eccentrically mounted on shaft 205. A centrifugal fan 206 is directly mounted on shaft 205 and circulates cooling air streams 207 through an intercooler 208 and through internal cooling passages 211 in the rotor. A small quantity of oil from a metering pump (not shown) is injected via hole 209, with the purpose being to have the fast-moving circulating air then distributing it to all internal surfaces of the engine which require lubrication.

Fig 16 showsaprior art rotor bearing as used in the engine of Fig 15. An ‘M’ shaped proprietary needle cage 212 contains needle rollers 213 which radially support shaft 205 in a hardened outer race 214. Cage 212 is axially located with side plates 215 fastened to the eccentric of shaft 204. Cooling air streams 7 containing oil particles pass through parallel axial holes 216 in the eccentric of shaft 204, through passages in the rotor body (not shown in this view) and some small quantity through small axial passages in the bearing assembly 212/ 213.

Figures 17 and 18 illustrate the lubrication system in accordance with one embodiment of the current invention. Figure 17 illustrates oil 234 now supplied from an oil metering pump (not shown) via tube 232 which is mounted in the engine end cover plate 233. A tubular piece 235 having a taper bore is inserted in the bore of the shaft 204. Alternatively, the taper bore could be an integral part of the eccentric shaft. Centrifugal force forces the oil 234 to move axially along the tapered bore of 235 to exit through the radial hole 236 which opens into the needle bearing assembly (not shown) which is mounted on diameter 237.

Fig 18 shows an enlarged section view of the revised rotor bearing assembly and its lubrication system. Bearing needles 242 rolling on the eccentric diameter of shaft 205, and guided with a cage assembly (not shown), radially support the rotor 204 which is fitted with a hardened bearing outer race 214.

A steel ring 243 is fastened as shown on to the rotor 204 by screws at 245. The ID dimension of ring 243 is only very slightly larger than the OD of shaft eccentric 237 such that a minimum radial clearance exists at that point. The clearance will be the minimum which can be economically manufactured bearing in mind the required tolerances of the two diameters. If necessary, the ID of 243 could have an abradable coating which would enable a smaller clearance to be created. The cooling air stream 207 with any contained debris particles or products of combustion is now prevented from passing into the bearing assembly by the ring 243. At the opposing end of the needle bearing, ring 246 has an ID which is typically 25% to 50% of a needle diameter radially distant from the OD of the shaft eccentric 237 and leaves a radial gap 249.

Arrow 248 indicates the direction of tire centrifugal force which acts on the shaft and all the components of the needle bearing and on the oil. A trough is created between the two plates 243 and 246 which contains the cage and needles and the spaces around them are all filled from the oil supply 234. When the oil depth exceeds the radial height of ring 246 above the ID of outer race 214 then the oil will escape out of the trough at 249 and enter the air stream to lubricate other parts of the engine.

As an illustrative example of the relevant centrifugal forces, if the eccentric shaft is rotating at speed N then the rotor has speed 1/3 N and the bearing cage assembly' at 2/3 N. So, although regions of tire rotor are subjected to ‘negative’ values of acceleration as they pass the minor axis of the epitrochoidal bore, this does not apply to the needle bearing assembly or its entrained oil due to their rotational speed being twice that of the rotor. This results in the formation of a stable ‘oil bath’ in the annular trough for the needles and cage where the centrifugal force in the operating engine is always acting in the direction to hold the oil in the trough up to the depth controlled by the ID dimension of plate 246. The needles and guidance cage are now always rotating and sliding in ‘solid’ oil which eliminates any wear problem, particularly of the cage OD and bore of the rotor where the cage OD is sliding.

Thus, a key feature of the invention is that a trough of oil, typically annular in shape, is provided for the rotor bearing with a depth of oil, greater than typically 1 or 2 mm or so, is created in an engine which employs a total-loss type lubrication system where the total supply rate of the oil is only of the order of 15 cc per hour in smaller size, and perhaps 60 cc per hour in larger size, Range-Extender type engines.

The very high speed rotation of the individual needles will now result in some small energy loss due to viscous friction of operating in ‘solid’ oil. However, this loss will be more than offset by the reduction in friction of the cage OD which was sliding with near to zero lubrication in currently known systems. In accordance with the invention, tire cage will be now operating with full hydrodynamic support and negligible energy loss. The elimination of friction heat in this area is also beneficial. The silver plating used previously, generally added to tire cage surfaces in order to reduce the friction losses in existing designs will now be no longer required.

Increasing the value of the radial gap 249 as in Fig 18 will reduce the depth of oil in the trough and hence reduce oil churning. The value of the radial gap 249 will be selected to provide the optimum depth of oil in the trough taking into account both the eneigy loss due to oil churning and the requirement for optimum lubrication. It should be noted that although the drawings show that the rings 243 and 249 are separate pieces attached to the rotor with screws 245, this is not to imply that a design of rotor bearing could not be created which employs an outer race for the bearing where these pieces are integral with the outer race.

To achieve the full predicted catalogue life, the manufactures of rolling element type bearings stress the need for:

Excellent lubrication no excessive temperature such that the metallurgy of the inner or outer races or rolling elements is adversely affected no foreign particles or debris or corrosive elements enter the bearings. the lubricant does not become aged such that its characteristics deteriorate.

The invention as herein described achieves all of these requirements for the first time in the ACR type Wankel engine. As a result, the achievement of very high TBOs with this engine is now possible. Other rolling element bearings in the core engine are the two main bearings. These are typically the spherical roller type and located in the two end plates. They are not subject to direct heat from the rotor. However to avoid the possibility of wear particles or combustion gases entering the bearings they can be enclosed in substantially sealed chambers. The two bearings can each individually be directly supplied with a few cc’s of oil per hour. This is quite practical to achieve using a proprietary mass-produced and low cost oil metering pump which would typically possess a main outlet supplying 95 % or so of its output to the rotor bearing and two other outlets which supply 2.5 % to each main bearing.

Claims

1.A rotary engine of the so-called Wankel type wherein a 3 cornered rotor possessing arcuate flanks revolves at one third the speed of the eccentric shaft upon which it is mounted, the three comers of the rotor being in slidable contact with a two lobed epitrochoidal shaped housing bore such that the four phases of induction, compression, expansion and exhaust are created, the rotor being a pressurised-air- cooled-rotor type and wherein a mechanically driven rotary valve controls the injection of hydrogen fuel into the engine during the early part of the compression stroke of the engine such that a homogeneous mixture of fuel and air is formed prior to combustion in the following expansion stroke.

2. An engine according to claim 1 wherein the rotary valve which incorporates large flow areas and has an outlet or outlets which are intermittently connected to a hole or holes located in the epitrochoidal shaped surface of the induction compression chamber and via which H2 gas is injected into the compression chamber, the diameter, location, and alignment angles of the said holes being selected to best procure the homogeneous mixture.

3.An engine according to claim 2 wherein injection of the required mass of H2 commences at the instant the air induction port closes and is completed during the first 100 “of the 270° duration compression stroke.

4 An engine according to claim 2 or 3 wherein injection of the required mass of H2 commences at the instant the air induction port closes and is completed during the first 60° whilst only requiring a low pressure supply of gas due to the large flow areas of the rotary valve.

5.An engine according to any of the preceding claims where the quantity of H2 gas which is injected creates a homogenous or near homogeneous mixture of air and gas where (p = 0.5 or near such that NOx emissions from the engine are zero or close to zero.

6 An engine according to any of the preceding claims which operates unthrottled with no throttle mechanism fitted or a wide open throttle (WOT) fitted, and at a substantially single RPM thereby enabling precise optimisation of all engine design features at this selected operating point in order to achieve the highest thermal efficiency.

7.An engine according to any of the preceding claims wherein a compound expansion turbine is mounted immediately adjacent to the single exhaust port of the engine, the exhaust port and turbine entry being designed for the turbine to capture some of the blow-down energy as the port is first opened together with the following expansion energy, this energy being returned to the power unit via either a mechanical drive to the engine shaft or via supplying additional electrical energy from an electrical generator driven by the turbine shaft

8. An engine according to any of the preceding claims wherein the rotor is mounted on the eccentric of the engine shaft via a needle roller type bearing, the bearing casing incorporating or being axially adjacent to side walls such that a trough is formed which contains the needles, the needle cage and lubricating oil and, resulting from the continuously acting outward centrifugal forces which operate on the contents of this trough, thereby maintains a certain depth of oil in the trough whenever the engine is rotating.

9 An engine according to the preceding claim wherein the lubricating oil is supplied into the ID of the bearing via a radial hole in the eccentric connected at its inner end to an axial hole in the centre of the engine shaft , this hole being supplied with oil from a metering pump which feeds the oil into an entry hole at one end the eccentric shaft.

10.An engine including a rotor bearing according to claim 8 and 9 wherein the side wall at the end which is at the upstream side of the approaching rotor cooling air has an ID with only a very small radial clearance to the OD of the eccentric shaft such that the rotor bearing is effectively sealed from any unwanted dust particles or debris which may be entrained in the cooling airstream; and the side wall at the downstream end has an ID somewhat larger than the eccentric diameter of the shaft which ensures that the trough is filled with oil to the depth of that sidewall, the depth being selected to provide optimum lubrication of the needle cage and the rolling elements in combination with achieving low energy losses which may be related to oil churning.

11. An engine according to claims 9 or 10 wherein the said lubricating oil leaves the trough via the radial clearance at the ID of the downstream side wall and enters the fast moving circulating airstream to be then carried to all other surfaces in the engine which require lubrication.

12 An engine according to any of the preceding claims whereby the engine includes an intercooler for reducing the temperature of the circulating air and where the compact size of the intercooler allows it to be located horizontally within the outer profile and axial width of the rotor housing of the engine at or near the highest point of the engine, and its construction does not possess any wells or depressions for any of the oil particles in the airstream to reside and thereby fail to continue circulating.

13 An engine according to claim 12 wherein the intercooler consists of a plurality of parallel and horizontal metal tubes and aligned in planes parallel to the axis of the rotor, heat being removed from the internal surfaces of the tubes via the liquid coolant which is also employed to remove heat from the main housings of the engine.

14. An engine including an intercooler according to claim 13 wherein thin and closely-spaced copper or aluminium separate fins are mounted on the tubes in planes at 90 'to the tubes, or more preferably the fins consist of long thin strips of copper or aluminium which are spirally and edge mounted on the tubes generally lying in the plane of the circulating air requiring to be cooled, the fins providing a large surface area thereby enabling the transfer of heat from the circulating airstream to the liquid coolant in an efficient manner.

15 An engine as described in any of the preceding claims wherein the engine is utilised as a hydrogen fuelled CHP unit.

16. An engine according to any of the preceding claims wherein the gas is injected into the engine via the rotary valve which is rotating at half the speed of the eccentric shaft.

17. A power unit including an engine.as described in any of the preceding claims which drives an integrated or semi integrated electrical generator, which provides electrical energy to tire batteries of land, water or air vehicles which are fitted with electric drive motors, the function of the power unit being to assist in maintaining the desired level of charge in the batteries and thereby acting as a range extender for such vehicles.