INTERNAL COMBUSTION ENGINE

Abstract

An internal combustion engine includes transfer passages between a pre-chamber and a main combustion chamber, and a control unit configured to control a pre-chamber supply system coupled to the pre-chamber and a main combustion chamber supply system coupled to the main combustion chamber, wherein the control unit is configured to control the pre-chamber supply system such that a supply volume exceeds a volume of the pre-chamber and that a surplus of the supply volume is communicated to the main combustion chamber, such as during a transient operating condition.

Claims

1. An internal combustion engine, comprising a main combustion chamber, a pre-chamber of smaller volume than the main combustion chamber, transfer passages which establish fluid communication between the pre-chamber and the main combustion chamber, a pre-chamber supply system equipped to supply a fuel or a first air-fuel mixture to the pre-chamber, a main combustion chamber supply system equipped to supply air or a second air fuel mixture to the main combustion chamber, and a control unit configured to closed or open loop control the pre-chamber supply system in order to supply the supply volume of the fuel or the first air-fuel mixture to the pre-chamber, wherein the control unit is configured to closed or open loop control the pre-chamber supply system, such that the supply volume exceeds the volume of the pre-chamber and that a surplus of the supply volume is communicated to the main combustion chamber through the transfer passages for mixing of the supply volume supplied to the pre-chamber with the air or the second air fuel mixture supplied to the main combustion chamber, at least during a transient operation condition.

2. The internal combustion engine according to claim 1, wherein the pre-chamber supply system comprises a pre-chamber valve, the operation of which is controlled by the control unit to time selectively open or close in order to supply the supply volume to the pre-chamber.

3. The internal combustion engine according to claim 2, wherein the pre-chamber valve is configured to realise different degrees of opening controlled by the control unit.

4. The internal combustion engine according to claim 1, wherein the pre-chamber supply system comprises: an actuator for adjusting a pressure in the pre-chamber supply system and a passive pre-chamber valve, in particular a check valve, which is actuated by a pressure difference between the pre-chamber supply system and the pre-chamber, wherein the control unit is configured to closed or open loop control the actuator.

5. The internal combustion engine according to claim 1, wherein the control unit is configured to supply the supply volume, which exceeds the volume of the pre-chamber, only during transient operation conditions.

6. The internal combustion engine according to claim 1, wherein a set fuel energy amount (E.sub.f) for combustion in the main combustion chamber is given and the control unit is configured to control the pre-chamber supply system such that a first fuel energy amount (E.sub.1) pertaining to the surplus of the supply volume communicated to the main combustion chamber and a second fuel energy amount (E.sub.2) pertaining to the air or second air fuel mixture supplied to the main combustion chamber add up to the set fuel energy amount (E.sub.f), in each combustion cycle during the transient operation condition.

7. The internal combustion engine according to claim 6, wherein the first fuel energy amount (E.sub.1) pertaining to the surplus of the supply volume communicated to the main combustion chamber at least at one point in time during the transient operation condition provides more than 90% of the set fuel energy amount (E.sub.f).

8. The internal combustion engine according to claim 2, wherein the pre-chamber supply system includes a pre-chamber rail for delivering the fuel or the first air fuel mixture to the pre-chamber, wherein the pre-chamber valve is arranged between the pre-chamber rail and the pre-chamber for supplying the fuel or the first air fuel mixture from the pre-chamber rail to the pre-chamber.

9. The internal combustion engine according to claim 1, wherein the pre-chamber supply system includes at least one of: a first volume flow control valve for controlling a first volume flow of fuel for the pre-chamber or for mixing with air to obtain the first air fuel mixture, a second volume flow control valve for controlling a second volume flow of air for mixing with the fuel to obtain the first air fuel mixture, a compressor for compressing the fuel or the first air fuel mixture, a cooling device for cooling the fuel or the first air fuel mixture, a condensate separator for removing moisture from the fuel or the first air fuel mixture, a heater for heating the fuel or the first air fuel mixture, a pressure regulator for controlling the pressure of the fuel or the first air fuel mixture, and/or a buffer for storing a storage volume of the fuel or first air fuel mixture upstream of the pre-chamber valve at a higher pressure level compared to the pressure level prevailing immediately upstream of the pre-chamber valve.

10. The internal combustion engine according to claim 1, wherein the main combustion chamber supply system includes an intake manifold for air or the second air fuel mixture and preferably a mixing device for providing the second air fuel mixture.

11. The internal combustion engine according to claim 1, wherein the main combustion chamber supply system includes a main compressor, a mixture cooler, and/or a throttle valve.

12. The internal combustion engine according to claim 6, wherein the pre-chamber rail is supplied by the main combustion chamber supply system through a supply channel, which branches off the main combustion chamber supply system.

13. The internal combustion engine according to claim 12, wherein the air or the second air fuel mixture supplied to the pre-chamber rail via the supply channel from the main combustion chamber supply system can be enriched with fuel in order to provide the first air fuel mixture for the pre-chamber.

14. The internal combustion engine according to claim 12, wherein the supply channel branches off the main combustion chamber supply system in fluid communication sense before or after a low-pressure mixing device for providing the second air fuel mixture and/or before or after a main compressor for creating a charge pressure for the main combustion chamber and/or before or after a mixture cooler and/or before or after a further mixture cooler, and/or before or after a throttle valve and/or in or after a part of an intake manifold common for all or a group of main combustion chambers, and/or individually for each main combustion chamber in the intake manifold and/or an intake channel of the main combustion chamber.

15. A method for operating an internal combustion engine, comprising: supplying a supply volume of a fuel or a first air fuel mixture to a pre-chamber of the internal combustion engine, which supply volume exceeds a volume of the pre-chamber; supplying air or a second air fuel mixture to a main combustion chamber of the internal combustion engine; communicating a surplus of the supply volume to a to the main combustion chamber through one or more transfer passages between the pre-chamber and the main combustion chamber; and mixing the surplus of the supply volume with the air or the second air fuel mixture in the main combustion chamber.

16. The method according to claim 15, wherein supplying the supply volume, which exceeds the volume of the pre-chamber and communicating the surplus of the supply volume to the main combustion chamber is carried out during transient operation conditions.

17. The method according to claim 16, wherein supplying the supply volume, which exceeds the volume of the pre-chamber and communicating the surplus of the supply volume to the main combustion chamber is carried out as long as an actual operation parameter of the internal combustion engine, in particular an engine revolution rate, a power of the internal combustion engine, and/or a load of the internal combustion engine differs from a set engine operation parameter by more than 1% in reference to the set engine operation parameter.

18. The method according to claim 15, wherein the method further comprises enriching the air or the second air fuel mixture supplied to a pre-chamber rail via a supply channel from a main combustion chamber supply system with fuel in order to provide the first air fuel mixture for the pre-chamber.

19. The method according to claim 15, wherein the method further comprises setting a set fuel energy amount (E.sub.f) for combustion in the main combustion chamber and controlling a pre-chamber supply system such that a first fuel energy amount (E.sub.1) pertaining to the surplus of the supply volume communicated to the main combustion chamber and a second fuel energy amount (E.sub.2) pertaining to the air or second air fuel mixture supplied to the main combustion chamber add up to the set fuel energy amount (E.sub.f), preferably in each combustion cycle during a transient operation condition.

20. The method according to claim 19, wherein the first fuel energy amount (E.sub.1) pertaining to the surplus of the supply volume communicated to the main combustion chamber at least at one point in time during the transient operation condition provides more than 10% of the set fuel energy amount (E.sub.f).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0120] Further advantages and details regarding the invention are apparent from the figures and the accompanying description of the figures. The figures show:

[0121] FIG. 1 is a schematic drawing of an embodiment of the invention,

[0122] FIG. 2 is a schematic drawing of another embodiment of the invention,

[0123] FIG. 3a, 3b are diagrams visualising the advantage of over-scavenging the pre-chamber,

[0124] FIG. 4a, 4b are diagrams on the energy share of the fuel or first air fuel mixture during over-scavenging, and

[0125] FIG. 5 is a further embodiment according to the invention visualising some branching off points for the supply channel.

DETAILED DESCRIPTION

[0126] FIG. 1 schematically shows a first embodiment of an internal combustion engine 1 according to the invention, here a gas engine. The main combustion chambers 2 are embodied as cylinders with a reciprocating piston (not shown). Four main combustion chambers 2 are shown purely exemplary. Large modern gas engines usually have significantly more cylinders.

[0127] Air or a second air fuel mixture is supplied to the main combustion chambers 2 through a main combustion chamber supply system 7, which in this embodiment includes a low-pressure mixing device 19. Alternatively or additionally, the main combustion chamber supply system 7 could include a mixing device downstream of the main compressor 20.

[0128] The main compressor 20 in this embodiment is a driven by a drive shaft driven by an exhaust turbine (both not shown) and thus is part of a turbo charger.

[0129] The main combustion chamber supply system 7 according to this embodiment further includes a mixture cooler 21 and a throttle valve 22.

[0130] The intake manifold 18 delivers the second air fuel mixture, or alternatively only air, to the cylinder-individual intake channels 26. In order to not impede the visual clarity of the drawing, the reference numeral is shown only for one intake channel 26.

[0131] As pointed out in the beginning of this document, ignition performance can be improved with pre-chambers 3. In this embodiment, one pre-chamber 3 is present for each main combustion chamber 2. The transfer passages 4, which provide fluid communication between each pre-chamber 3 and the respective main combustion chamber 2, are indicated schematically.

[0132] Fuel or a first air fuel mixture is supplied to the pre-chambers 3 through the pre-chamber supply system 5.

[0133] The first air fuel mixture can be created by branching off air or second air fuel mixture from the main combustion chamber supply system 7 via a supply channel 23 (or more supply channels), and potentially adding fuel and/or air through a first volume flow control valve 10 for adding fuel and/or a second volume flow control valve 11 for adding air. Conventionally, the first air fuel mixture is richer in fuel (i.e., lower lambda) than second air fuel mixture in order to achieve better ignition properties in the pre-chambers 3, although embodiments where a first air fuel mixture with a higher lambda than the second air fuel mixture or where the first air fuel mixture and the second air fuel mixture are the same are in principle conceivable.

[0134] The supply channel 23 in this embodiment branches off the main combustion chamber supply system 7 between the mixture cooler 21 and the throttle valve 22 in fluid communication sense. Three dashed lines show three other examples of where the supply channel 23 branches off the main combustion chamber supply system 7, namely [0135] between the low-pressure mixing device 19 and the main compressor 20, [0136] between the main compressor 20 and the mixture cooler 21, [0137] after the throttle valve 22 in the common part of the intake manifold 18.

[0138] In other embodiments, the supply channel 23 could branch off cylinder-individually from the intake channels 26 of the main combustion chambers 2. More possible branching off points are visualized in and described in connection with FIG. 5.

[0139] Combinations of the different options for where the supply channel 23 branches off the main combustion chamber supply system 7 are of course conceivable.

[0140] A further possibility is to omit the supply channel 23 entirely and provide the fuel and/or first air fuel mixture fresh by mixing the fuel with air from a fuel source (or just providing fuel).

[0141] As pointed out earlier, the fuel or fuel composition for the first air fuel mixture and the fuel or fuel composition for the second air fuel mixture can be the same fuel or different fuels or fuel compositions.

[0142] In one conceivable embodiment, the main combustion chamber supply system 7 only supplies air to the main combustion chambers 2 and the pre-chamber supply system 5 provides only fuel or the first air fuel mixture to the pre-chambers 3. The pre-chamber 3 is then over-scavenged in order to provide the necessary fuel component for the combustion in the main combustion chamber 2.

[0143] A pre-chamber rail 9 delivers the fuel or first air fuel mixture from where fuel or first air fuel mixture is provided (in the embodiment of FIG. 1 after the second volume flow control valve 11) to the pre-chambers, while the pre-chamber rail 9 possibly branches off into pre-chamber individual sections before reaching the pre-chamber valves 6. The supply channel 23 can also be viewed as part of the pre-chamber rail 9.

[0144] In the embodiment of FIG. 1, the following functional units are in the flow path in the pre-chamber rail 9: [0145] the first volume flow control valve 10, [0146] the second volume flow control valve 11, [0147] the compressor 12, [0148] a compressor 12 for raising the pressure in the pre-chamber rail 9, [0149] a cooling device 13, [0150] a condensate separator 14, [0151] a heater 15, [0152] a pressure regulator 16, and [0153] a buffer 17.

[0154] These functional units can be used to condition the fuel or the first air fuel mixture in the pre-chamber rail 9 with the desired pressure and/or temperature and/or humidity.

[0155] The functional units do not have to be arranged in the fluid communication sequence as depicted in FIG. 1. As an example, FIG. 2 shows a different possible embodiment of the invention, where the first volume flow control valve 10 is arranged after the second volume flow control valve 11 and the buffer 17 is arranged before the pressure regulator 16 (both in fluid communication sense).

[0156] Referring to both FIG. 1 and FIG. 2, the buffer 17 can for example be a volume which can be closed off upstream and optionally downstream using valves in order to store some of the fuel or first air fuel mixture in the pre-chamber rail 9 at a raised pressure. The raised pressure can be reached as previously described by making use of a further pump and/or compressor and/or by making use of pressure changes in the pre-chamber rail 9 and time selectively opening and closing the valves for shutting off the buffer volume.

[0157] The pre-chamber valves 6 can time selectively opened or closed, possibly at controllable opening degrees, in order to admit the fuel or first air fuel mixture to the pre-chambers.

[0158] For this, the control unit 8 open or closed loop controls the pre-chamber valves 6. Of course, signal connections are present between the control unit 8 and the pre-chamber valves 6, but they are not depicted in FIG. 1 and FIG. 2 in order to not impede the viewability of the figures.

[0159] In preferred embodiments, the control unit 8 controls the pre-chamber valves 6 such that the amount of fuel or first air fuel mixture from the pre-chamber rail 9 entering the pre-chambers 3 exceeds the volume of each of the pre-chambers 3 (over-scavenging).

[0160] A surplus of fuel or first air fuel mixture will then be communicated into the main combustion chambers 2, where it will mix with the air or second air fuel mixture in the main combustion chambers 2.

[0161] Preferably, during transient operation conditions, this can raise the amount of fuel (relative to the amount of air) in the main combustion chamber 2 in order to provide more power for a short period of time. Since the pre-chamber supply system 5 can more easily be adapted to react quicker and provide more fuel, in this way a faster reaction to transient operation conditions can be realised.

[0162] Of course, it is also possible in this way to reduce the amount of fuel or the amount of fuel in the first air fuel mixture in order to quickly reduce the amount of fuel in the main combustion chambers 2, in the event that a reduced power is required from the internal combustion engine 1.

[0163] Both FIG. 1 and FIG. 2 can be embodied differently by using a passive pre-chamber valve, e.g., in form of check valves with a pre-load.

[0164] In such embodiments, the control unit 8 can control (with the corresponding signal connections) the pressure regulator 16, the buffer 17, and/or the compressor 12 to produce a higher pressure in the pre-chamber rail 9 directly before (in fluid communication sense) the passive pre-chamber valves 6. This higher pressure will cause the pre-chamber valves 6 to stay open for a longer amount of time achieving the overspilling of the pre-chamber 3 according to certain embodiments of the invention.

[0165] FIG. 3a and FIG. 3b show a comparison of the engine load capability of an internal combustion engine according to the prior art (FIG. 3a) and an internal combustion engine 1 according to embodiments of the invention when an increased power requirement is present. As the comparison of FIG. 3a and FIG. 3b clearly shows the internal combustion engine 1 according to embodiments of the invention (FIG. 3b) is able to more quickly adapt to greater increases in power requirements (greater load step, shorter recovery time).

[0166] How this works is shown in FIGS. 4a and 4b, where the energy contribution from the fuel or first air fuel mixture from the pre-chamber (PC, for pre-chamber) and the second air fuel mixture (MC, for main combustion chamber) is shown over time. Again, FIG. 4a refers to an internal combustion engine according to the prior art and FIG. 4b refers to an internal combustion engine according to embodiments of the invention.

[0167] The increasing load request is shown as grey curve in both FIG. 4a and FIG. 4b.

[0168] Because the over-scavenging of the pre-chamber can very quickly (quicker than the main combustion chamber supply system 7) increase the amount of fuel (and therefore the amount of energy which can be generated by the combustion in the main combustion chamber) in the main combustion chamber, the internal combustion engine according to embodiments of the invention can react quicker to the changed torque or load request than the internal combustion engine according to the prior art.

[0169] It should be noted that the Y-axis (Energy share [%]) is normalized to the set fuel energy amount E.sub.f desired at each point in time. Upon occurrence of a higher torque request, the set fuel energy amount E.sub.f is raised in order to deal with the higher load/torque required. Relatively speaking, the energy share MC introduced into the main combustion chamber 2 therefore drops sharply at that point in time.

[0170] It should also be noted that the energy share PC rises at exactly the same time, but are drawn slightly next to each other in order to ensure clarity of the depiction.

[0171] FIG. 5 shows a further embodiment of the invention visualising different branching off points for the supply channel 23.

[0172] The pre-chamber supply system 5 is only partly shown and can otherwise be embodied as in FIG. 1 or FIG. 2. Furthermore, the pre-chamber rail 9 can separate in, e.g., two sub-branches for supplying pre-chambers 3 for, e.g., two cylinder banks which is shown symbolically.

[0173] Additionally, the pre-chamber rail 9 can comprise various orifices 25 either in a common part of the pre-chamber rail 9 for all main combustion chamber 2 (in this case cylinders with reciprocating pistons) or in cylinder-individual parts of the pre-chamber rail 9. Such orifices can serve to create a defined pressure drop in the pre-chamber rail 9 as needed.

[0174] The main combustion chamber supply system 7 comprises [0175] a main compressor 20 which is driven by an exhaust gas turbine 24 through a drive shaft to embody a turbo charger, [0176] a mixture cooler 21, [0177] a further mixture cooler 21a, [0178] a throttle valve 22, and [0179] a common part for all the main combustion chambers 2 of the intake manifold 18.

[0180] The main combustion chambers 2 are connected to the intake manifold 18 through cylinder-individual intake channels 26 (which are here not furnished with reference numerals in order to not overburden the figure).

[0181] Each pre-chamber 3 is associated with one main combustion chamber 2 as is shown symbolically.

[0182] Each branching off point A, B, C, D, and E is symbolised with a box and the according letter. The supply channel 23 common for all pre-chambers 3 for branching off points A, B, C, and D would run from the respective point to the common pre-chamber rail 9, which is symbolised only for branching off point A, but would be embodied analogously for the other branching off points B, C, and D.

[0183] Branching off point E would be a cylinder-individual branching off point where the pre-chamber supply system 5 would comprise cylinder-individual pre-chamber rails 9 for each cylinder.

[0184] The branching off points are: [0185] A directly after the main compressor 20 and before the mixture cooler 21, [0186] B between the mixture cooler 21 and the further mixture cooler 21a, [0187] C after the throttle valve 22, [0188] D in the common part of the intake manifold 18, [0189] E cylinder-individual branching off in the intake channel 26 for each cylinder.