Dual-fuel engine fuel injector, dual-fuel engine, and method for operating a dual-fuel engine

Abstract

To provide a fuel injector of a duel fuel internal combustion engine.SOLUTION: A dual fuel internal combustion engine is composed of a main body, and a nozzle needle movably guided inside of a needle guide of the main body, and has a needle fuel chamber which is connectable to a combustion chamber of a cylinder through an opening portion, opened when the nozzle needle is located on a first position, and closed when the nozzle needle is located on a second position. First piping connected to the needle combustion chamber is communicated to the inside of the main body, a first liquid fuel is introduced to the inside of the needle combustion chamber through the first piping, second piping separating from the first piping, is communicated to the inside of the main body connected to the needle fuel chamber, and a second liquid fuel is introduced to the inside of the needle fuel chamber through the second piping.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel injector for a dual-fuel internal combustion engine. Further, the present invention relates to a dual-fuel internal combustion engine and a method of operating the dual-fuel internal combustion engine.

[0002] In particular, the invention relates to the field of so-called large engines or large internal combustion engines, which have cylinders with a piston diameter of at least 140 mm, in particular at least 175 mm, such as marine engines.

[0003] Dual-fuel internal combustion engines for marine engines are already known. Prior art dual-fuel internal combustion engines are capable of operating in a first operating mode in which they burn a liquid fuel and a second operating mode in which they burn a gaseous fuel or another liquid fuel.

[0004] Patent Document 1 discloses a dual-fuel internal combustion engine having dual fuel injectors, each of which is supplied with fuel via a separate fuel pump, and a separate sealed lubrication system.

[0005] Starting from this, the present invention aims to provide a new type of fuel injector for a dual-fuel internal combustion engine and a dual-fuel internal combustion engine equipped with such a fuel injector. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102017123315 Summary of the Invention [Problem to be solved by the invention]

[0007] This object is achieved by a fuel injector according to claim 1. [Means for solving the problem]

[0008] The fuel injector is configured to deliver liquid fuel to a combustion chamber of a cylinder of a dual-fuel internal combustion engine, the fuel injector including a body, a nozzle needle movably guided within a needle guide of the body, and a needle fuel chamber defined by the body and connectable to the combustion chamber through an opening, the opening being open in a first position of the nozzle needle and closed in a second position of the nozzle needle.

[0009] A first pipe connected to the needle fuel chamber leads to the interior of the body of the fuel injector, and the first liquid fuel can be introduced into the needle fuel chamber via the first pipe. Further, a second pipe separate from the first pipe leads to the interior of the body of the fuel injector, and the second pipe is also connected to the needle fuel chamber, and the second liquid fuel can be introduced into the needle fuel chamber via the second pipe.

[0010] The fuel injector of the present invention allows for particularly efficient fuel injection into the combustion chambers of each cylinder of a dual-fuel internal combustion engine burning a liquid fuel. In certain operating modes of the dual-fuel internal combustion engine, a liquid, relatively non-ignitable fuel can be injected into the combustion chamber of each cylinder via the fuel injector, specifically together with a relatively ignitable fuel that is used to ignite another liquid, relatively non-ignitable liquid fuel. In other operating modes, the fuel injector is used exclusively to introduce the relatively ignitable liquid fuel into each combustion chamber of each cylinder. Thus, the fuel injector of the present invention functions as both a main injector and a pilot injector. A separate pilot injector can be omitted, simplifying the design of the internal combustion engine.

[0011] Preferably, the second line is coupled to the needle fuel chamber via a control element, such as a choke, to supply relatively ignitable liquid fuel to the needle fuel chamber in a predetermined manner, particularly when liquid, relatively non-ignitable fuel is introduced into the needle fuel chamber via the first line.

[0012] In a further development of the invention, the second line is further connected to the needle guide and / or to a control chamber of the control valve of the fuel injector, and a liquid, relatively ignitable fuel can be supplied to the needle guide as a barrier fluid and / or to the control chamber as an actuating fluid via the second line. The relatively ignitable liquid fuel also serves as the barrier fluid or the actuating fluid. This allows for a particularly simplified engine design. Preferably, the second line is connected to the control chamber of the control valve via a further choke. This is desirable for supplying the relatively ignitable fuel to the control chamber of the control valve in a predetermined manner.

[0013] The dual-fuel internal combustion engine of the present invention is defined in claim 9. The method for operating the dual-fuel internal combustion engine of the present invention is defined in claim 10.

[0014] Preferred further developments of the invention can be obtained from the dependent claims and the detailed description. Exemplary embodiments of the invention are explained in detail with the aid of the drawings, but the invention is not limited to these exemplary embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] 1 depicts a marine propulsion system having a dual-fuel internal combustion engine. [Figure 2] 1 is a cross-sectional view of a fuel injector for a dual-fuel internal combustion engine. [Figure 3] FIG. 2 is a first diagram for explaining a method of operating a dual-fuel internal combustion engine. [Figure 4] FIG. 2 is a second diagram for explaining a method of operating a dual-fuel internal combustion engine. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 is a schematic diagram of a marine propulsion system 10 including a dual-fuel internal combustion engine 11 having multiple cylinders 12 .

[0017] Inside the cylinder 12, fuel is burned, specifically, in a first operating mode of the dual-fuel internal combustion engine 11, a liquid, relatively ignitable fuel (a fuel that is relatively easy to ignite), and in a second operating mode of the dual-fuel internal combustion engine 11, a liquid, relatively unignitable fuel (a fuel that is relatively difficult to ignite).

[0018] When fueled by each fuel, the dual-fuel internal combustion engine 11 generates driving power that is used in Figure 1 to drive a generator 13. The generator 13 generates electrical energy that is used to drive a propeller 14 of the vessel.

[0019] Figure 1 further illustrates a fuel delivery system 15 for the dual fuel internal combustion engine 11. Figure 2 illustrates a fuel injector 16 according to the present invention as an assembly of the fuel delivery system 15.

[0020] In each of the operating modes of the dual-fuel internal combustion engine 11, the fuel supply system 15 allows a respective liquid fuel to be supplied to the cylinders 12 of the fuel supply system 15.

[0021] The fuel supply system 15 comprises at least one fuel injector 16 , in particular a single fuel injector 16 , for each cylinder 12 .

[0022] In a first operating mode of the dual-fuel internal combustion engine 11, a relatively ignitable liquid fuel can be supplied to each of the cylinders 12 via the fuel injectors 16. Furthermore, in a second operating mode of the dual-fuel internal combustion engine 11, a relatively unignitable liquid fuel and a relatively ignitable liquid fuel for igniting the relatively unignitable liquid fuel can be supplied to each of the cylinders 12 via the fuel injectors 16.

[0023] Thus, in both the first and second operating modes, specifically in the first operating mode for exclusively introducing ignitable fuel and in the second operating mode for igniting non-ignitable liquid fuel and ignitable liquid fuel for igniting the non-ignitable liquid fuel, the same fuel injector 16 of the cylinder 12 is available. Thus, the same fuel injector 16 is utilized both as the main injector and as the pilot injector.

[0024] 2 illustrates in detail the fuel injector 16 of the present invention. As discussed above, the fuel injector 16 is utilized to introduce relatively ignitable liquid fuel into each cylinder in a first mode of operation, and to introduce relatively non-ignitable liquid fuel into each cylinder along with relatively ignitable liquid fuel in a second mode of operation. In the second mode of operation, the relatively ignitable liquid fuel is utilized to ignite the relatively non-ignitable liquid fuel.

[0025] The fuel injector 16 includes a preferably multi-part body 27 , a nozzle needle 28 , and a control valve 29 .

[0026] The nozzle needle 28 is movably guided in a needle guide 30 of the body 27. The body 27 defines a needle fuel chamber 31. The needle fuel chamber 31 is connectable to a combustion chamber 33 of each cylinder 12 via an opening 32. In a first position of the nozzle needle 28, the nozzle needle 28 closes the opening 32. In a second position of the nozzle needle 28, the nozzle needle 28 opens the opening 32.

[0027] A first pipe 34 communicates with the interior of the body 27 of the fuel injector 16 of the present invention. The first pipe 34 is connected to the needle fuel chamber 31, and the first liquid fuel can be introduced into the needle fuel chamber 31 via the first pipe 34.

[0028] In addition to the first pipe 34 connected to the needle fuel chamber 31, a second pipe 35 separate from the first pipe 34 leads to the inside of the main body 27 and is connected to the needle fuel chamber 31 independently of the first pipe 34. The second fuel can be introduced into the needle fuel chamber 31 via the second pipe 35.

[0029] The first pipe 34 communicates with the partial chamber 31b of the needle fuel chamber 31 that is spaced apart from the opening 32, while the second pipe 35 communicates with the partial chamber 31b of the needle fuel chamber 31 that is formed adjacent to the opening 32, so that the needle fuel chamber 31 can be connected to the combustion chamber 33 of each cylinder 12 via the opening 32. Thus, the second pipe 35 communicates with the needle fuel chamber 31 that is adjacent to the opening 32, while the first pipe 34 communicates with the needle fuel chamber 31 that is clearly spaced apart from the opening 32. The two partial chambers 31a, 31b of the needle fuel chamber 31 are connected to each other via a choke-like constriction 40.

[0030] In a first operating mode of the dual-fuel internal combustion engine 11, a relatively ignitable liquid fuel is supplied to the first line 34 as a first fuel and to the second line 35 as a second fuel. Thus, in the first operating mode, ignitable liquid fuel is supplied to both the sub-chambers 31a and 31b of the needle fuel chamber 31.

[0031] In a second operating mode of the dual-fuel internal combustion engine 11, the relatively non-ignitable fuel can be supplied as a first fuel to the first line 34, and the relatively ignitable liquid fuel can be supplied as a second liquid fuel to the second line 35. The relatively ignitable liquid fuel is used to ignite the relatively non-ignitable fuel in the second operating mode. Thus, the relatively ignitable liquid fuel is supplied to the sub-chamber 31a of the needle fuel chamber 31, and the relatively non-ignitable liquid fuel is supplied to the sub-chamber 31b of the needle fuel chamber 31.

[0032] FIG. 1 shows a fuel tank 18 holding a relatively ignitable liquid fuel.

[0033] In the first operating mode, such relatively ignitable liquid fuel is supplied to a first line 34 of each of the fuel injectors 16 via a first fuel pump 17, also referred to as a main pump. Furthermore, in the first operating mode, relatively ignitable liquid fuel from a fuel tank 18 is supplied to a second line 35 of each of the fuel injectors 16 via a second fuel pump 24, also referred to as a pilot pump.

[0034] Preferably, the pressure provided by the second fuel pump 24 is slightly higher than the pressure provided by the first fuel pump 17 .

[0035] In a second operating mode of the dual-fuel internal combustion engine, relatively non-ignitable liquid fuel held in the second fuel tank 19 is again supplied via the first fuel pump 17 to the first line 34 of each of the fuel injectors 16, while in a second operating mode, relatively ignitable fuel from the fuel tank 18 is supplied via the second fuel pump 24 to the second line 35 of each of the fuel injectors.

[0036] 1 shows two fuel tanks 18, 19 as well as a shuttle valve 22. The fuel tank 18, adapted to hold a relatively ignitable liquid fuel, is coupled to the shuttle valve 22 via a fuel line 20, while the second fuel tank 19, adapted to hold a relatively non-ignitable liquid fuel, is coupled to the shuttle valve 22 via a fuel line 21.

[0037] Specifically, when the dual-fuel internal combustion engine 11 is operating in a first operating mode, the fuel tank 16 is coupled to the fuel pump 17 via the shuttle valve 22. In the first operating mode, the second fuel tank 19 is decoupled from the fuel pump 17. In contrast, when the dual-fuel internal combustion engine is operating in a second operating mode, the second fuel tank 19, which holds a relatively non-ignitable liquid fuel, is coupled to the first fuel pump 17 via the shuttle valve 22. In the second operating mode, the fuel tank 18, which holds a relatively ignitable liquid fuel, is decoupled from the first fuel pump 17 via the shuttle valve 22.

[0038] 1, fuel lines 23 from second fuel pump 24 extend toward cylinder 12, and fuel lines 23 are coupled to second lines 35 of each fuel injector 16. Also, fuel lines 25 from fuel pump 17 extend toward cylinder 12, and fuel lines 25 are coupled to first lines 34 of each fuel injector 16.

[0039] In particular, when the dual-fuel internal combustion engine 11 is suitably operated in a first operating mode, the first line 34 and the second line 35 of each fuel injector 16 are coupled to the fuel tank 18, thereby providing a relatively ignitable liquid fuel to both the first line 34 and the second line 35 of each fuel injector 16. In particular, when the dual-fuel internal combustion engine 11 is operated in a second operating mode, the first line 34 is coupled to the second fuel tank 19 and the second line 35 of each fuel injector 16 is coupled to the fuel tank 18, thereby providing a relatively non-ignitable liquid fuel to the needle fuel chamber 31 of each fuel injector 16 via the first line 34 and a relatively ignitable liquid fuel to the needle fuel chamber 31 of each fuel injector 16 via the second line 35 in the second operating mode.

[0040] Since the pressure in the second pipe 35 is slightly higher than the pressure in the first pipe 34, in the second operating mode, relatively ignitable fuel can be introduced in a predetermined manner from the second pipe 35 into the sub-chamber 31a of the needle fuel chamber 31. The needle fuel chamber 31, specifically the sub-chamber 31a of the needle fuel chamber 31, is connected to the second pipe 35 via the choke 26. By setting the dimension of the choke 26, the amount of relatively ignitable fuel introduced into the sub-chamber 31 in the second operating mode can be adjusted in a predetermined manner. To achieve this, specifically, in the second operating mode, relatively ignitable liquid fuel from the second pipe 35 is introduced into the sub-chamber 31a, and relatively non-ignitable liquid fuel from the first pipe 34 is introduced into the sub-chamber 31b of the needle fuel chamber 31. During injection operation, in the second operating mode, the relatively ignitable fuel enters the combustion chamber 33 first, followed by the relatively non-ignitable liquid fuel, so that the relatively ignitable liquid fuel can be ignited in a predetermined manner in the second operating mode.

[0041] In a preferred exemplary embodiment of the fuel injector 16 according to the present invention, shown in FIG. 2, the second line 35 of the fuel injector 16 is connected via a choke 26 to the partial chamber 31a of the needle fuel chamber 31 and also to the needle guide 30 and the control chamber 36 of the control valve 29 of the fuel injector 16. Thus, in both operating modes of the dual-fuel internal combustion engine 11, the relatively ignitable fuel can be supplied not only to the needle fuel chamber 31 but also to both the needle guide 30 and the control chamber 36 of the control valve 29 via the second line 35. The relatively ignitable fuel serves as a barrier fluid in the region of the needle guide 30 and as an actuating fluid in the region of the control chamber 36 of the control valve 29. As shown in FIG. 2, the second line 35 of each fuel injector 16 is connected via a further choke 37 to the control chamber 36 of the control valve 29.

[0042] As mentioned above, the pressure in the second line 35 is greater than the pressure in the first line 34. Therefore, in the region of the needle guide 30, a particularly advantageous barrier effect of the barrier fluid can be ensured.

[0043] In a particularly preferred embodiment of the fuel injector 16, the second line 35 not only serves to supply ignitable fuel towards the needle fuel chamber 31, but also towards the needle guide 30 and the control chamber 36 of the control valve 29, so that the ignitable fuel is used as barrier fluid and actuation fluid, thereby making it possible to particularly simplify the construction of the internal combustion engine.

[0044] As can be seen from FIG. 2, the needle guide 30 is positioned between the needle fuel chamber 31 and the control chamber 36 of the control valve 29, specifically between the partial chamber 31b of the needle fuel chamber 31 and the control chamber 36 of the control valve 29.

[0045] 2, a spring chamber 38 receiving a spring 39 is positioned between the needle guide 30 and the control chamber 36. The spring 39 biases the nozzle needle 28 into a closed position.

[0046] The relatively ignitable liquid fuel is preferably a liquid fuel having a lubricity WSD of 100 μm to 300 μm, preferably 100 μm to 200 μm. The relatively ignitable fuel is preferably a diesel fuel. The relatively unignitable liquid fuel is preferably a liquid fuel having a lubricity WSD of 300 μm to 820 μm, preferably 400 μm to 820 μm. The relatively unignitable fuel is preferably ethanol or methanol.

[0047] In addition to the fuel injector 16 of the present invention, the present invention also relates to a dual-fuel internal combustion engine 11, in which each cylinder 12 of the dual-fuel internal combustion engine 11 is equipped with at least one, preferably a single, fuel injector 16 of the present invention. The fuel injector 16 enables a relatively ignitable fuel to be supplied to the cylinder 12 in a first operating mode, and enables a relatively ignitable fuel and a relatively non-ignitable fuel to be supplied to the cylinder 12 in a second operating mode, with the relatively ignitable fuel being used to ignite the relatively non-ignitable fuel.

[0048] The present invention further relates to a method for operating a dual-fuel internal combustion engine 11. In a first mode of operation, a relatively ignitable fuel is supplied exclusively to the cylinders 12 via each of the fuel injectors 16, and specifically to the combustion chamber 33 of each of the cylinders 12. In contrast, in a second mode of operation, both a relatively ignitable fuel and a relatively unignitable fuel are introduced via each of the fuel injectors 16 to the combustion chamber 33 of each of the cylinders 12, and in the second mode of operation, the relatively ignitable fuel is utilized to ignite the relatively unignitable fuel.

[0049] FIG. 3 illustrates the possibility of introducing relatively ignitable fuel and relatively unignitable fuel into the combustion chamber 33 of each cylinder 12 in the second operating mode. Accordingly, FIG. 3 illustrates the amount of fuel injected into the cylinder 12 over time t in the second operating mode. Injection begins at time t1 and ends at time t2. In the second operating mode, relatively ignitable fuel collects in the partial chamber 31a and relatively unignitable fuel collects in the partial chamber 31b. Therefore, in the second operating mode, the relatively ignitable fuel from the first partial chamber 31a is first introduced into the combustion chamber 33 of each cylinder 12 between times t1 and t3, followed by the relatively unignitable fuel from the partial chamber 31b between times t3 and t2. The relatively unignitable fuel is ignited via the relatively ignitable fuel.

[0050] 4 illustrates an alternative procedure for injecting fuel using a fuel injector 16 according to the present invention. In FIG. 4, relatively unignitable fuel from partial chamber 31a is first injected and ignited into the combustion chamber 33 of each cylinder 12 between times t1 and t3 to prime the combustion chamber 33. After time t3, with a time offset Δt, the actual main injection begins at time t4, again introducing first relatively ignitable fuel from partial chamber 31a and then relatively unignitable fuel into the combustion chamber 33 of each cylinder 12. Thus, in FIG. 4, injection is divided into a pre-injection from time t1 to t3, followed by a main injection from time t4 to t2.

[0051] With the present invention, a separate pilot injector can be omitted. Via one and the same fuel injector 16, liquid fuel can be introduced into the combustion chamber 33 of each cylinder 12 in both operating modes of the dual-fuel internal combustion engine 11.

[0052] The relatively ignitable fuel, which in the second operating mode is used to ignite the relatively unignitable fuel, is stored in a partial chamber 31a of the needle fuel chamber 31, which is formed adjacent to the opening 33 or adjacent to the needle seat of the nozzle needle 38. Thus, in each injection cycle in the second operating mode, the relatively ignitable fuel first enters the combustion chamber 33 of each cylinder 12, and then the relatively unignitable fuel is properly ignited and burned via the relatively ignitable fuel. Furthermore, the relatively ignitable fuel preferably serves as a barrier fluid and a working fluid, in particular as a barrier fluid in the region of the needle guide 30 and as a working fluid in the region of the control valve 29.

[0053] This is particularly relevant in the field of so-called large engines or large internal combustion engines, in which the piston diameter of the cylinder is at least 140 mm, in particular 175 mm. Such large internal combustion engines are, for example, marine engines. In the present invention, these are embodied as dual-fuel internal combustion engines. [Explanation of symbols]

[0054] 10. Marine Propulsion Systems 11 Dual-fuel internal combustion engine 12 cylinders 13. Generator 14 Ship propellers 15 Fuel supply system 16 fuel injector 17 Fuel pump 18 Fuel Tank 19 Fuel Tank 20 Fuel piping 21 Fuel piping 22 Shuttle valve 23 Fuel piping 24 Fuel pump 25 Fuel piping 26 Chalk 27 Main Unit 28 Nozzle needle 29 Control valve 30 Needle guide 31 Needle fuel chamber 31a Partial room 31b Partial chamber 32 Opening 33 Combustion chamber 34 Piping 35 Piping 36 Control Room 37 Chalk 38 Spring chamber 39 Spring 40 Stenosis

Claims

1. 1. A fuel injector (16) for a dual-fuel internal combustion engine (11), the fuel injector (16) being configured to supply fuel to a combustion chamber (33) of a cylinder (12) of the dual-fuel internal combustion engine (11), comprising: The dual-fuel internal combustion engine (11) A main body (27); a nozzle needle (28) movably guided within a needle guide (30) of the body (27); a needle fuel chamber (31) formed by the body (27) and connectable to the combustion chamber (33) of the cylinder (12) through an opening (32), the opening (32) being open when the nozzle needle (28) is in a first position and closed when the nozzle needle (28) is in a second position; It has The needle fuel chamber (31) comprises a first partial chamber (31b) and a second partial chamber (31a) connected to each other via a narrowed portion (40), a first pipe (34) connected to the first partial chamber (31b) communicates with the inside of the main body (27), and a first liquid fuel is introduced into the inside of the first partial chamber (31b) through the first pipe (34); a second pipe (35) separate from the first pipe (34) communicating with the interior of the main body (27) connected to the second partial chamber (31 a), and a second liquid fuel being introduced into the second partial chamber (31 a) through the second pipe (35).

2. 2. The fuel injector of claim 1, wherein the second line (35) is coupled to the needle fuel chamber (31) via a control element.

3. The needle fuel chamber (31) adjacent to the opening (32) forms the second partial chamber (31a) connected to the second pipe (35) via the control element (26), 3. The fuel injector according to claim 2, wherein the needle fuel chamber (31) is connectable to the combustion chamber (33) of the cylinder (12) through the opening (32).

4. the second pipe (35) is coupled to the needle guide (30) of the fuel injector (16); 4. The fuel injector according to claim 1, wherein the second liquid fuel can be supplied to the needle guide (30) as a barrier fluid via the second pipe (35).

5. the second pipe (35) is coupled to a control chamber (36) of a control valve (29) of the fuel injector (16); 5. A fuel injector according to claim 1, wherein the second liquid fuel can be supplied to the control chamber (36) as an actuating fluid via the second pipe (35).

6. 6. A fuel injector according to claim 5, characterized in that the second line (35) is connected to the control chamber (36) of the control valve (29) via a choke (37).

7. 7. A fuel injector according to claim 5 or 6, characterized in that the needle guide (30) is positioned between the needle fuel chamber (31) and the control chamber (36) of the control valve (29).

8. The fuel injector is a dual fuel injector, In a first operating mode of the dual-fuel internal combustion engine, a relatively ignitable fuel is supplied to the first line (34) as a first fuel and to the second line (35) as a second fuel; 8. The fuel injector of claim 1, wherein in a second operating mode of the dual-fuel internal combustion engine, a relatively non-ignitable fuel is supplied as a first fuel to the first line (34) and a relatively ignitable fuel is supplied as a second fuel to the second line (35) for igniting the relatively non-ignitable fuel.

9. A dual-fuel internal combustion engine (11), a plurality of cylinders in which a relatively ignitable liquid fuel is combusted in a first operating mode of the dual-fuel internal combustion engine (11) and a relatively non-ignitable liquid fuel is combusted in a second operating mode; an injection system comprising at least one fuel injector (16) for each of said cylinders (12); In the dual fuel internal combustion engine, In the first mode of operation, relatively ignitable fuels can be supplied via the injection system as a first liquid fuel and a second liquid fuel; in the second operating mode, a relatively non-ignitable fuel can be supplied through the injection system as a first liquid fuel, and a relatively ignitable fuel can be supplied through the injection system as a second liquid fuel for igniting the relatively non-ignitable fuel; A dual fuel internal combustion engine, characterized in that each of said fuel injectors (16) is a fuel injector according to any one of claims 1 to 8.

10. 10. A method for operating a dual-fuel internal combustion engine (11) according to claim 9, comprising: In the first operating mode, the relatively ignitable fuel is introduced into the combustion chamber (33) of each of the cylinders via each of the fuel injectors (16); In the second operating mode, the relatively ignitable fuel and the relatively non-ignitable fuel are introduced into the combustion chamber (33) of each of the cylinders via the respective fuel injectors (16); The method of claim 1, wherein in the second mode of operation, the relatively ignitable fuel is utilized to ignite the relatively unignitable fuel.

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