The invention relates to an internal combustion engine and, more particularly, to a cylinder assembly therefor comprising a compression chamber and an external combustion chamber (precombustion chamber). The engine may have a single cylinder or be of the multi-cylinder type. The invention is applicable to an internal combustion engine having drive means such as a conventional crankshaft and connecting rod as well as crankless engines e.g. two or four stroke conventional engines, swash, wobble and rotary engines, etc. The engines to which the invention relates may be adapted to employ any one of a wide range of fuels such as petrol, gas or diesel oil.

Background of Invention

Petrol and gas engines, that undertake the compression stroke with a fuel/air mixture, are restricted to a compression ratio not exceeding about 13 : 1. To exceed this ratio may result in premature explosion of the charge before reaching top dead centre. This is often referred to as 'detonation'. Engine manufacturers have progressively increased the compression ratio as materials and fuels were developed to allow such increases. The higher the compression ratio the greater release of energy for a given quantity of fuel, and the higher the efficiency. Diesel engines enjoy much higher compression ratios, in the order of 20 : 1, by reason of the fact that the compression stroke compresses air only, not an air/fiiel mixture. Diesel oil is injected into the combustion chamber at top dead centre and continues for some time after, the heat of compression in the compressed air being more than necessary to ignite and burn the oil.

Described in my International Application No.PCT/AU92/00507 is a two-stroke internal combustion engine wherein harmful emissions (e.g. carbon monoxide, hydrocarbons and oxides of nitrogen) and heating problems normally experienced with prior two-stroke engines are minimised. To that end, the engine has a cylinder assembly comprising a

SUBSTITUTE SHEET <RULE 26)

compression chamber in which at least one piston reciprocates and a small extern combustion chamber having restricted communication with the compression chamber. I operation, a blast of high pressure scavenging air is supplied to the compression chambe The combustion chamber is supplied with a fuel/air mixture which in part passes to th compression chamber to form a fuel lean mixture with the scavenging air therein. Ignitio of the fuel mixture in the combustion chamber in turn ignites the fiαel lean mixture in th compression chamber. The arrangement is such that the operating temperatures in th compression chamber remain sufficiently low to inhibit the formation of the nitrogen oxid therein and ensure substantial complete combustion of the fuel.

Description of the Invention

To minimise harmful emissions, reduce heat and ensure substantially complete combustio of fuel, the present invention makes use of a similar cylinder assembly comprising a sma external combustion chamber (hereinafter called a "prechamber") having restricte communication with a compression chamber. However, the invention is applicable to a internal combustion engine operable in accordance with a two-stroke or a four-stroke cycl or otherwise.

According to the invention, an internal combustion engine comprises a cylinder assembl including a cylinder, at least one piston mounted for reciprocation within the cylinder, common compression chamber defined by the cylinder and piston(s), a plurality prechambers each having restricted communication with the common compression chambe each prechamber having ignition means operable to ignite fuel therein and means to contr admission of fuel to the prechambers in such a way that at any time fuel may be admitte selectively to one, some or all of the prechambers.

This control would allow combustion to take place in only one or in a selected number prechambers. Where more than one prechamber is charged with fuel, ignition of fuel ma

be effected simultaneously in the charged prechambers. Alternatively, ignition of fuel may be effected sequentially. Preferably, both simultaneous ignition and sequential ignition would be available and control means would allow a choice therebetween.

Brief Description of the Drawings

The invention is described with reference to the accompanying drawings which illustrate two embodiments of the invention. For convenience, the invention is described in relation to its application to a single cylinder internal combustion engine which operates in accordance with a two-stroke cycle. However, it is emphasised that the invention has wider application than to a single cylinder two-stroke engine. In the drawings,

Fig. 1 is a sectional view of a cylinder assembly of a two-stroke internal combustion engine having a single piston according to one embodiment of the invention; and

Fig. 2 is a sectional view of a cylinder assembly of a two-stroke internal combustion engine having opposed pistons according to a second embodiment of the invention.

Fig. 3 is a schematic diagram of an engine management system for a two stroke internal combustion engine having a cylinder assembly according to the second embodiment of the invention.

Detailed Description of the Drawings

Illustrated in Fig. 1 is a cylinder assembly of a two-stroke internal combustion engine having a single piston 8 adapted to reciprocate in a cylinder 4. Piston 8 is connected to a conventional connecting rod and suitable drive means (not shown). The drive means may be a conventional crankshaft, swash plate, wobble plate, cam, etc. Cylinder 4 is formed with two prechambers 3 in addition to main compression chamber 6. Prechambers 3 are

spaced from compression chamber 6 but are connected thereto by a narrow passage 9 providing restricted communication between the prechambers 3 and compression chamber

A spark plug 1 is mounted on each prechamber 3 for ignition of fuel/air mixture therein. The fiiel/air mixture is fed into each prechamber 3 through an inlet port controlled by poppet valve 2. The air may be supplied by a blower (not shown). The drawings do not illustrate the means by which fuel is supplied to the prechambers. If fuel injection is adopted, the injector may inject fuel into each inlet manifold adjacent to poppet valve 2 or directly into prechambers 3. Alternatively, carburation is also applicable.

The fuel mixture strength in prechambers 3 is most likely to be in the order of 'stoichiometric' mixture. This is defined as a combustible mixture having exact proportions for complete combustion. There is no point in the mixture being richer than stoichiometric as this would cause carbon deposition on the spark plug. The mixture diminishes in strength from the spark plug through to the compression chamber.

A blast of high pressure scavenging air is forced into compression chamber 6 through an inlet port controlled by poppet valve 5. Scavenging air together with the products of combustion exit compression chamber 6 by way of one or more exhaust ports 7. Opening and closing of exhaust ports 7 is effected by piston 8 as it reciprocates in cylinder 4. Prechambers 3 are scavenged by opening poppet valves 2 before injecting fuel.

Poppet valves 2 may be operated electronically from an engine management computer. This would eliminate an inflexible cam operated system. An electronic system would allow computer control for optimum performance and efficiency. During operation, the computer would be free to open and close the poppet valves early or late, or open them partially or fully. Further, in circumstances where not all prechambers are in operation, the poppet valves of the prechambers not in use need not be operated. In any event, fuel would not be

injected into those prechambers. The advantage, apart from efficiency, would be that, if fuel entered a non functioning prechamber, it would not be combusted and that would cause high hydrocarbon emission if allowed to escape with the exhaust.

To supply a large volume of high pressure scavenging air, a blower (not shown) is provided. The same blower may be used to supply air for the fuel mix as well as air for scavenging purposes, and, if desired for supercharging. The blower may be driven by the engine and, if desired, may be turbo exhaust assisted. The provision of a large charge of high pressure air ensures an adequate throughput of scavenging air to not only purge the cylinder but also to cool it below the minimum temperature at which nitrogen oxide gases are formed but maintain a temperature capable of consuming hydrocarbon gases (i.e. the temperature limits would be 650 to 1650 degrees Celsius). Effective cooling is due in part to the fact that the scavenging air moves in a spiral path down the internal wall of compression chamber 6.

The inlet ports for the air/fuel mixture are relatively small in comparison with the other ports. Preferably, the inlet port for scavenging air and the exhaust ports 7 are larger than those employed in conventional engines of the same size. Larger air inlet and exhaust ports facilitate the supply of an adequate throughput of scavenging air.

Assume fuel is admitted to both prechambers 3 and ignited simultaneously, the engine operates throughout a complete two-stroke cycle in the following manner. It is assumed that the cycle commences with piston 8 at bottom dead centre and commencing to rise in cylinder 4. Poppet valve 5 is closed shutting off the ingress of scavenging air. Compression chamber 6 would then be filled with substantially clean air. Prechambers 3 would also be scavenged and poppet valves 2 would close. Fuel may then be supplied by "in the head" injection. Alternatively, when poppet valves 2 are open, a fuel/air mixture may be fed into prechambers 3.

The charge may proceed from prechambers 3, along passages 9 and into compression chamber 6 depending on the power and revolutions required during the operation of the engine. However, exhaust ports 7 close as piston 8 ascends before the fuel mixture is able to descend to that point in compression chamber 6. In any event, it is not necessary for the fuel mixture to descend more than the halfway point as the only purpose for entry of fuel into compression chamber 6 is to undergo dilution with the remaining air in order to provide a lean mix. The lean mix with excess oxygen in compression chamber 6 promotes complete combustion of all fuel. If a supercharge is required, poppet valves 2 must remain open until piston 8 has completely shut off exhaust ports 7.

After poppet valves 2 close, piston 8 continues to rise in cylinder 4 on the compression stroke. The air in cylinder 4 is compressed in compression chamber 6 , passages 9 and prechambers 3. However, the dimensions of each passage 9 are such that the fuel/air mix adjacent to spark plug 1 remains sufficiently rich for it to be ignited by spark with a consequent explosion. The remaining charge, having been made lean by mixing with scavenging air, is ignited by the burning of the richer charge and burns without detonation.

The relationship of prechambers 3 and compression chamber 6 is such that separate zones with a significant temperature difference result. In the first place, a high temperature zone is produced near the centre of the explosion in each prechamber 3. Secondly, there is a zone of significantly lower temperature in compression chamber 6. As a consequence, there is effective separation of the high temperature zone in each prechamber 3 and the excess oxygen from the leaner mix in compressor chamber 6. The temperature of the excess oxygen is sufficiently low (below 1650 degrees Celsius) to inhibit formation of nitrogen oxides. Furthermore, due to the excess oxygen, substantially complete combustion is achieved resulting in the absence of carbon monoxide and hydrocarbons from the exhaust emissions. Another consequence is that reciprocation of piston 8 in cylinder 4 is a relatively cool operation so that the engine avoids the traditional heating problems normally associated with two-stroke engines.

The power stroke then follows with blowdown taking place as piston 8 exposes exhaust ports 7. Poppet valve 5 now opens and scavenging air is forced into compression chamber 6 to fully purge it with clean air and to cool cylinder 4. Poppet valves 2 open to admit scavenging air to prechambers 3.

When only one of the prechambers 3 is operative, fuel is not admitted into the other prechamber 3 and its spark plug is not fired. Otherwise, operation of the engine is the same.

The cylinder arrangement illustrated in Fig.2 is for use with horizontally opposed pistons. The reference numerals used in the figure and the operating principal remain the same as for Fig.l except poppet valve 5 of Fig.1 is replaced by open ports 5 which are opened and closed by one of the reciprocating pistons 8. Ports 5 are arranged in cylinder 4 such that exhaust ports 7 are uncovered just before ports 5 so as to allow blowdown.

Although in each embodiment illustrated in Figs. 1 and 2 there are only two prechambers 3, a greater number of prechambers may be provided in communication with a compression chamber 6. The prechambers may be of different volumes as required for maximum efficiency.

Each prechamber 3 incorporates means for admitting fuel and the number of prechambers receiving fuel at any given instant may be controlled by the power demand of the engine. This control allows combustion to take place in only one, some or all prechambers 3. For example, during engine idle, only one prechamber 3 may be supplied with fuel, the remaining prechambers having their individual injectors (or other means of admitting fuel) isolated electronically or by other suitable means, and the poppet valves may also be isolated. As power demand increases, additional prechambers would be progressively brought into service by admission of fuel.

The use of a plurality of prechambers with simultaneous ignition enables the fuel/air mixture to be divided into multiple small charges or volumes and each charge to be combusted efficiently in an excess of air. An air throttle is not required, allowing the cylinder pressure to maintain maximum value at all times, including engine idle as is the case in a diesel engine. This feature allows high thermal efficiency and low emissions even during engine idle.

Instead of firing simultaneously, the spark plugs may be fired in sequence to ignite each charged prechamber in series during the power stroke. During idle or low power output, it may not be necessary to admit fuel to all prechambers and in that case the operation may be little different from the case of simultaneous ignition. However, in the upper power range there is significant difference.

Sequential ignition extends the duration of high cylinder pressure well into the power stroke providing a prolonged application of positive work on the drive means. This simulates diesel engines which have improved torque output relative to fuel/gas engines due to the injection of fuel continuing into the power stroke. The result of sequential ignition of the fuel charges in the prechambers is a more prolonged application of force on the drive means long after top dead centre. Conventional engines, with ignition of the entire mixture at or close to top dead centre, deliver maximum force to the drive means when it is in the most ineffective position to convert this force into rotation. The ability to ignite part of the air/fiiel charge at a point when the engine mechanism is able to apply a greater mechanical advantage to the output shaft is of immense significance. By selecting an appropriate sequence for fuel ignition, a highly prolonged power stroke pressure and thermal efficiency is achieved.

The engine management sysyem illustrated in Fig. 3 is of a kind currently in use to manage the operation of internal combustion engines. The system comprises an engine management computer 18 which analyses signals from a number of engine sensors and controls the fuel

injectors, the ignition system and other actuators according to data, pertinent to the particular engine being managed, stored in the programmable memory of the computer. Control of the fuel injectors determines the amount of fuel injected and the time when the fuel is injected. Control of the ignition system includes the time at which the computer fires the spark plugs. In the present management system, other activators controlled by computer 18 include the poppet valves to the prechambers and the blower. The data, which is pertinent to the particular engine being managed, stored in the programmable memory of the computer includes information sufficient to identify the engine being managed such as the number of cylinders, ignition type, sensor types, injector current, and so forth.

Parts of the cylinder assembly are indicated by the same reference numerals that are used in Fig. 2. Additional components include an air blower 10 which is used to supply air via an air flow control valve 11 to compression chamber 6 through air inlet port 5 and to prechambers 3 and, when required, for supercharge.

Separate electronic poppet valve control means 19 operates to open and close each poppet valve 2 by computer command. Control means 19 is also able to fully open or partially open each valve 2, or open each valve 2 early or late, on computer demand to assist in maximum efficiency. When less than the full number of prechambers are to operate, computer 18 determines the prechambers and signals valve control means 19 accordingly.

A first position sensor 21 detects when the pistons are at top dead centre and signals the management computer 18 accordingly. If there is more than one cylinder, one particular cylinder may be chosen for this purpose. There is also a main shaft position sensor 22 which sends a signal to computer 18 at every, say, 30 degrees of rotation of the fly wheel. The purpose of this is to detect any irregular angular velocity at idle. Computer 18 fires spark plugs 1 and electronic fuel injectors 12 on the basis of this information. Computer 18 also activates electronic poppet valve control means 19 to operate poppet valves 2 on the same information. A further position sensor 20 signals computer 18 information concerning

accelerator position and computer 18 determines how many prechambers 3 operate in these particular circumstances. In particular, the computer 18 determines the correct number of precombustion chambers 3 to operate for the given power output. Computer 18 ensures that spark is fed only to those prechambers 3 that have been supplied with fuel.

Exhaust emissions, knock, fuel efficiency and engine temperature may also be controlled by computer 18 and appropriate sensors may be installed. Those sensors may include sensor 13 adapted to measure the temperature of the ambient air before it enters blower 10 and sensor 14 adapted to measure the pressure and temperature of the air exiting blower 10. An analyser 15 may be employed to analyse the exhaust gases outputted from exhaust port 7. Similarly, sensor 16 may be used to measure the temperature of the exhaust gases flowing from exhaust ports 7. A further sensor 17 may be included to measure the temperature and/or pressure within the cylinder 4. A further sensor 23 may be employed to detect any knock associated with cylinder 4. As a result of such parameters being fed into computer 18, blower 10 will have air pressure and flow under computer control. Control valve 11 will direct air according to instructions received from computer 18 to exhaust port 5 and prechambers 3 to control exhaust emissions, detonation, fuel efficiency and engine temperature.

The effect of computer operation of spark, fuel injection and poppet valve advance and retard in conjunction with flow control from the blower is to optimise the efficiency attained in all relevant areas.

The computer 18 may be switched from its normal mode to a sequential mode. In this latter mode, data stored in the computer memory serves to fire the spark plugs in sequence, say, the order of one or two milliseconds apart. The actual delay would be dependant upon engine type, engine revs., loading and so forth.

Modifications of the details described would be readily apparent to those skilled in the art and any changes may be made without departing from the broad inventive concepts herein described. For example, in Fig.1, the roles of the inlet controlled by poppet valve 5 and the exhaust ports 7 may be reversed. As another example, it is possible in Fig.2 to have both ports 5 and 7 acting as exhaust ports with all air being admitted to the compression chamber via poppet valves 2 in the prechambers. Shortly before poppet valves 2 close, fuel is injected into this flow. Since the fuel is admitted at the last instant, stratification of the mixture is is achieved. Alternatively, fuel may be injected directly into the prechamber shortly after the exhaust ports are closed by the pistons. In the case of four-stroke engines, as with other engines, a supply of air is admitted to the compression chamber to control its temperature between the limits of 650 and 1650 degrees celsius to limit the formation of oxides of nitrogen.