Internal combustion engine

An internal combustion engine has first and second cylinders (12, 14), the first cylinder (12) having a larger swept volume than the second cylinder (14) and the second cylinder being formed in the crown of the first cylinder. First and second pistons (16, 18) are reciprocable respectively in the first and second cylinders (12, 14), the second piston (18) being formed as a protrusion on the crown of the first piston (16). The first cylinder has an air inlet (25) and an exhaust outlet (27) whilst a first fuel source (34) provides fuel to the second cylinder (14). The second piston has a crown (35) which is spaced from and connected to the crown (36) of the first piston and which has an edge (37) which is relatively thin in the axial direction compared to the spacing of the first piston crown from the second piston crown. This defines a combustion space (20) between the piston crowns and a side wall (14a) of the second cylinder (14) when the pistons are substantially at the inner dead center position. The combustion space (20) communicates with both cylinders (12,14) during part of the expansion stroke. A spark plug (52) is provided communicating with the combustion space. The ignition process is started with a spark and allowed to continue by compression ignition. After the spark ignition process begins, the flame raises the pressure and temperature of the gas in the combustion space sufficiently to cause compression-ignition of the remainder of the vaporized fuel as it ingresses into the combustion space under the action of the smaller piston and mixes with more air.

I claim:

1. An internal combustion engine comprising:

at least one set of first and second cylinders, said first cylinder having a larger swept volume than said second cylinder;

respective first and second pistons movable in said first and second cylinders;

air inlet means communicating with said first cylinder;

exhaust means communicating with said first cylinder;

a first fuel source for providing fuel to said second cylinder;

means defining a combustion space when said first and second pistons are substantially at an inner dead centre position, said combustion space communicating with both said first and second cylinders during an expansion stroke of said first and second pistons;

ignition means communicating with said combustion space;

inhibiting means for inhibiting ingression of fuel/air mixture from said second cylinder into said combustion space prior to said second piston reaching a preselected point in a compression stroke;

control means for triggering said ignition means to discharge ignition energy into said combustion space after commencement of said ingression and prior to completion of said ingression to ignite a portion of ingressing fuel thereby to raise temperature and pressure in said combustion space to levels sufficient to ignite a remainder of said fuel by compression ignition;

and means for ensuring that said pressure and temperature reached in said combustion space near an end of said compression stroke are insufficient to cause spontaneous compression ignition of fuel used.

2. An engine as claimed in claim 1 wherein said second piston has a crown which is spaced from and connected to a crown of said first piston and said crown of said second piston has an edge which is relatively small in an axial direction compared to a distance between said crown of said first piston and said crown of said second piston in said axial direction, thereby to define said combustion space between said crowns of said first and second pistons and a side wall of said second cylinder.

3. An engine as claimed in claim 2 wherein said ignition means is spark triggered compression ignition means.

4. An engine as claimed in claim 2 wherein said means for ensuring that said pressure and temperature reached in said combustion space near said end of said compression stroke are insufficient to cause spontaneous compression ignition of fuel used comprises a geometrical compression ratio of said engine, being a ratio of volumes within said first and second cylinders available for occupation by gas at outer and inner dead centre positions of said first add second pistons.

5. An engine as claimed in claim 4 wherein said means for ensuring that said pressure and temperature reached in said combustion space near said end of said compression stroke are insufficient to cause spontaneous compression ignition of fuel used further comprises throttle means for throttling air inducted by said first cylinder through said air inlet means to maintain gas pressure and temperature in said first and second cylinders at levels insufficient to cause spontaneous compression ignition of fuel used prior to ignition by said ignition means.

6. An engine as claimed in claim 2 having access means associated with said second cylinder for admitting fuel and air to said second cylinder during induction, said access means comprising a first port means opening into said second cylinder and a first valve means for controlling said port means.

7. An engine as claimed in claim 6 wherein said first fuel source is a low pressure fuel injector and is shielded by said first valve means.

8. An engine as claimed in claim 6 wherein said first port means serves as both inlet and exhaust port for said second cylinder.

9. An engine as claimed in claim 6 wherein said access means further comprises a second port means forming an exhaust port means for said second cylinder, and second valve means for controlling said second port means.

10. An engine as claimed in claim 2 having exhaust means associated with said second cylinder for exhausting exhaust gases therefrom, said exhaust means comprising exhaust port means opening into said second cylinder and exhaust valve means for controlling said exhaust port means, and wherein said first fuel source is a fuel injector for injecting fuel directly into said second cylinder.

11. An engine as claimed in claims 7 wherein said exhaust port means communicates with said air inlet means for providing exhaust gas recirculation.

12. An engine as claimed in claim 2 wherein said air inlet means and said exhaust means of said first cylinder serve respectively as a sole inlet and exhaust means for said second cylinder;

and said first fuel source is a fuel injector for delivering fuel directly into said second cylinder.

13. An engine as claimed in claim 8 wherein said first port means communicates with a closed volume.

14. An engine as claimed in claim 13 wherein said closed volume is variable.

15. An engine as claimed in claim 13 wherein said closed volume communicates with said air inlet means by way of a valve for controlling gas pressure in said closed volume.

16. An engine as claimed in claim 13 wherein said closed volume communicates with atmosphere by way of a valve and a fan for controlling gas pressure in said closed volume,

17. An engine as claimed in claim 2 wherein a second fuel source, in the form of a high pressure liquid fuel injector, is located such that when said crown of said second piston is at or near said inner dead centre position said second fuel source can deliver to said combustion space a quantity of fuel under pressure in addition to fuel supplied to said second cylinder by said first fuel source.

18. An engine as claimed in claim 17 having means for controlling said first fuel source to deliver a proportion of a total fuel quantity to be delivered into said second cylinder into a space above said crown of said second piston starting and finishing when said second piston is at predetermined positions spaced from said inner dead centre position, and for controlling said second fuel source to deliver a further proportion of said total fuel quantity into said combustion space when said first and second pistons are subsequently at or near said inner dead centre position.

19. An engine as claimed in claim 2 wherein said first fuel source is a high pressure fuel injector positioned in said side wall of said second cylinder for delivering fuel directly into said second cylinder both above and below said crown of said second piston.

20. An engine as claimed in claim 2 wherein a second fuel source and a throttle valve are provided in said air inlet means of said first cylinder for providing a spark ignitable fuel/air mixture to enable said engine to operate in a conventional spark ignition mode.

21. An engine as claimed in claim 2 wherein said edge of said second piston crown is radially spaced from an adjacent wall of said second cylinder to define a gap therebetween which comprises said inhibiting means.

22. An engine as claimed in claim 2 wherein said second cylinder is formed at an end thereof remote from said first cylinder with means defining a by-pass around said edge of said crown of said second piston when said second piston is at or adjacent said inner dead centre position.

23. An engine as claimed in claim 22 wherein said by-pass means is a groove which is formed in said wall of said second cylinder and extends over at least a portion of a circumference of said second cylinder.

24. A method of operating an internal combustion engine wherein the engine has:

at least one set of first and second cylinders, said first cylinder having a larger swept volume than said second cylinder;

respective first and second pistons movable in said first and second cylinders;

air inlet means communicating with said first cylinder;

exhaust means communicating with said first cylinder;

a first fuel source for providing fuel to said second cylinder;

means defining a combustion space when said first and second pistons are substantially at an inner dead centre position, said combustion space communicating with both said first and second cylinders during an expansion stroke of said first and second pistons;

ignition means communicating with said combustion space;

inhibiting means for inhibiting ingression of fuel/air mixture from said second cylinder into said combustion space prior to said second piston reaching a preselected point in a compression stroke;

control means for triggering said ignition means;

and means for ensuring that a pressure and temperature reached in said combustion space near an end of said compression stroke are insufficient to cause spontaneous compression ignition of fuel used;

wherein the method comprises:

introducing a first preselected quantity of fuel into said second cylinder during an induction and/or said compression stroke of said engine;

and discharging ignition energy into said combustion space after commencement of Said ingression and prior to completion of said ingression to ignite a portion of ingressing fuel thereby to raise said temperature and pressure in paid combustion space to levels sufficient to ignite a remainder of said fuel by compression ignition.

25. A method as claimed in claim 24 wherein said second piston has a crown which is spaced from and connected to a crown of said first piston and said crown of said second piston has an edge which is relatively small in an axial direction compared to a distance between said crown of said first piston and said crown of said second piston in said axial direction, thereby to define said combustion space between said crowns of said first and second pistons and a side wall of said second cylinder.

26. A method as claimed in claim 25 further comprising:

injecting a second preselected quantity of liquid fuel under high pressure into said combustion space towards said end of said compression stroke for ignition by compression ignition.

27. A method as claimed in claim 26 wherein said first preselected quantity of fuel is injected into said second cylinder during said induction stroke.

28. A method as claimed in claim 26 wherein said first preselected quantity of fuel is introduced into an inlet duct communicating with said second cylinder through an inlet valve which opens during said induction stroke.

29. A method as claimed in claim 26 wherein said second fuel is diesel fuel and said first fuel is a volatile fuel other than diesel fuel.

30. A method as claimed in claim 29 wherein said first fuel is gasoline.

31. A method as claimed in claim 25 further comprising introducing a further preselected quantity of fuel into said first cylinder during said induction stroke whilst controlling a quantity of air inducted into said first cylinder to provide a preselected fuel/air ratio mixture in said first cylinder thereby to provide with said first preselected quantity of fuel a substantially stoichiometric overall fuel/air ratio.

32. A method as claimed in claim 31 wherein said preselected fuel/air ratio is substantially stoichiometric.

33. A method as claimed in claim 25 wherein air inducted into said first cylinder is throttled to control said temperature and pressure at said end of said compression stroke to levels insufficient to cause compression ignition prior to said discharge of said ignition energy into said combustion space.