DUAL-FUEL COMBUSTION ENGINE

Description

[0001] The invention relates to a dual-fuel internal combustion engine.

[0002] The invention presented here relates in particular to the field of so-called large engines or large internal combustion engines, whose cylinders have piston diameters of at least 140 mm, and in particular of at least 175 mm. Such large internal combustion engines include, for example, marine engines.

[0003] Dual-fuel internal combustion engines are already known as marine engines. Practically known dual-fuel internal combustion engines can operate in a first mode, in which they burn a liquid fuel, and in a second mode, in which they burn a gaseous fuel or another liquid fuel.

[0004] From DE 10 2017 123 315 A1, a dual-fuel internal combustion engine with a dual-fuel fuel injector is known. Each fuel is supplied to the dual-fuel fuel injector via a separate fuel pump. Furthermore, a separate sealing and lubricating oil system is provided.

[0005] DE 10 2014 016 927 B3 discloses a dual-fuel internal combustion engine according to the preamble of claim 1.

[0006] WO 2017 / 162 902 A1 reveals further state of the art.

[0007] There is a need for a novel dual-fuel internal combustion engine with a simple design.

[0008] Based on this, the present invention aims to create a novel dual-fuel internal combustion engine.

[0009] This problem is solved by a dual-fuel internal combustion engine according to claim 1.

[0010] The dual-fuel internal combustion engine has cylinders in which a first liquid fuel can be combusted in a first operating mode and a second liquid fuel in a second operating mode. The dual-fuel internal combustion engine has a main injection system with at least one main injector per cylinder. The main injection system supplies the cylinders with the first liquid fuel, which is relatively ignitable, in the first operating mode, and the cylinders with the second liquid fuel, which is relatively inignitable, in the second operating mode. The dual-fuel internal combustion engine also has a pilot injection system with at least one pilot injector per cylinder. The pilot injection system supplies the cylinders with the first liquid fuel to ignite the second liquid fuel in the second operating mode.The main injection system and the pilot injection system of the dual-fuel internal combustion engine according to the invention are coupled in such a way that, in the second operating mode, the first liquid fuel can be supplied to the respective main injector of the main injection system as working fluid and / or as barrier fluid, starting from the pilot injection system.

[0011] The two injection systems are therefore coupled. This is achieved in such a way that, in the second operating mode, the first liquid fuel is supplied from the pilot injection system to the respective main injector of the main injection system. In the second operating mode, the second liquid fuel is then introduced into the cylinders via this main injector, with the first liquid fuel serving as the working fluid and / or barrier fluid in the respective main injector. This working fluid or barrier fluid serves to seal and actuate the valves of the respective main injector.

[0012] In the dual-fuel internal combustion engine according to the invention, a liquid fuel is burned in each of the two operating modes. The first liquid fuel for the first operating mode is relatively readily ignitable. The second liquid fuel for the second operating mode is relatively inert. The first liquid fuel serves to ignite the second liquid fuel in the second operating mode. The dual-fuel internal combustion engine has a main injection system, which has at least one main injector per cylinder, and a pilot injection system, which has at least one pilot injector per cylinder. The main injection system can supply the cylinders with the first liquid fuel in the first operating mode and the second liquid fuel in the second operating mode.In the second operating mode, the first liquid fuel performs two functions: firstly, it ignites the second fuel, and secondly, it acts as the working fluid and / or barrier fluid in the area of ​​the respective main injector. The main injection system is coupled to the pilot injection system to also utilize the ignition fluid as the working fluid and / or barrier fluid.

[0013] According to the invention, the main injection system comprises a main pump through which, in the first operating mode, the first liquid fuel is supplied to the cylinders, and through which, in the second operating mode, the second liquid fuel is supplied to the cylinders. The pilot injection system comprises a pilot pump through which, in the second operating mode, the first liquid fuel is supplied to the cylinders for the ignition of the second liquid fuel. A first fuel tank for the first fuel is connected to the main pump via a first fuel line. A second fuel tank for the second fuel is connected to the main pump via a second fuel line. A changeover valve serves to connect the main pump to the first fuel tank via the first fuel line in the first operating mode and to the second fuel tank via the second fuel line in the second operating mode.This ensures a particularly simple design of the dual-fuel internal combustion engine according to the invention.

[0014] According to a further development of the invention, a branch line diverges from the pilot injection system upstream of each pilot injector and preferably opens into the main injection system in the region of the respective main injector. In the second operating mode, the pressure in the branch line leading from the pilot injection system to the main injection system is higher than the pressure in the region of the respective main injector of the main injection system. Such a coupling of the two injection systems via the branch line is particularly preferred. In this way, in the second operating mode, the first fuel, which serves as working fluid and / or barrier fluid in the region of the respective main injector, can be easily supplied from the pilot injection system to the main injection system.

[0015] According to a further development of the invention, a pressure reducer is integrated into each branch line to limit the pressure in that branch line. The pressure reducer limits the pressure in the respective branch line.

[0016] Preferred embodiments of the invention are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1: a schematic of a ship propulsion system with a dual-fuel internal combustion engine; Fig. 2: a section of the dual-fuel internal combustion engine in the area of ​​a cylinder.

[0017] Fig. 1 Figure 10 shows a highly schematic representation of a ship propulsion system 10, which includes a dual-fuel internal combustion engine 11 with several cylinders 12. Fuel is burned in the cylinders 12; in a first operating mode of the dual-fuel internal combustion engine, a first liquid fuel is burned, and in a second operating mode of the dual-fuel internal combustion engine, a second liquid fuel is burned.

[0018] When the respective fuel is burned, the dual-fuel internal combustion engine generates drive power, which is then used in Fig. 1 This is used to drive a generator 13. The generator 13 produces electrical energy which is used to drive a ship's propeller 14.

[0019] Fig. 1 further shows a fuel supply system 15 of the dual-fuel internal combustion engine 11. Fig. 2 Figure 1 shows further components of the fuel supply system 15. The fuel supply system 15 allows the respective liquid fuel to be supplied to the cylinders 12 of the dual-fuel internal combustion engine 11 in the respective operating mode. The fuel supply system 15 of the dual-fuel internal combustion engine 11 has a main injection system and a pilot injection system.

[0020] The main injection system, which has at least one main injector 16 per cylinder 12 (see Fig. 2 ) includes, in the first operating mode, the cylinders 12 can be supplied with the first liquid fuel, which is relatively readily ignitable, and in the second operating mode, the second liquid fuel, which is relatively inert. Thus, it shows Fig. 2 a main injector 16 of a cylinder 12. Through this main injector 16, the first liquid fuel can be injected into the cylinder 12 in the first operating mode, and the second liquid fuel can be injected into the cylinder 12 in the second operating mode. Although it is preferable for cost reasons to inject the first liquid fuel into the respective cylinder 12 of the dual-fuel internal combustion engine via the same main injector 16 in the first operating mode and the second liquid fuel in the second operating mode, it is alternatively possible for each cylinder 12 to have a separate main injector for each of the two liquid fuels. The in Fig. 2 However, the embodiment shown, in which the same main injector 16 is used in the first operating mode to inject the first liquid fuel and in the second operating mode to inject the second liquid fuel into the respective cylinder, is preferred.

[0021] According to Fig. 2 The respective liquid fuel can be supplied to the respective main injector 16 via a main pump 17, which therefore delivers the first liquid fuel in the first operating mode and the second liquid fuel in the second operating mode towards the respective main injector 16.

[0022] Fig. 1 Figure 1 shows a first fuel tank 18 for storing the first liquid fuel and a second fuel tank 19 for storing the second liquid fuel. The first fuel tank 18 can be connected to the main pump 17 via a first fuel line 20 and the second fuel tank 19 via a second fuel line 21, using a changeover valve 22.

[0023] In the first operating mode, the changeover valve 22 connects the first fuel tank 18 or the first fuel line 20 to the main pump 17 to supply the first fuel 18 to the cylinders 12 of the dual-fuel internal combustion engine. In this first operating mode, the changeover valve 22 disconnects the second fuel tank 19 from the main pump 17 of the main injection system.

[0024] In the second operating mode, however, the changeover valve 22 assumes a switching position in which the second fuel tank 19 is connected to the main pump 17 via the second fuel line 21 in order to supply the second fuel to the cylinders 12 of the dual-fuel internal combustion engine 11 in this second operating mode. In this second operating mode, the first fuel tank 18 is then disconnected from the main pump 17 of the main injection system.

[0025] As previously explained, the first liquid fuel is relatively readily ignitable, and the second liquid fuel is relatively inert. To ignite the second liquid fuel in the second operating mode in the area of ​​the respective cylinder 12, the dual-fuel internal combustion engine has a pilot injection system, which has at least one pilot injector 23 for each cylinder 12.

[0026] In the second operating mode, the pilot injection system can supply the first liquid fuel to the cylinders 12 of the dual-fuel internal combustion engine 11 to ignite the second liquid fuel.

[0027] The pilot injection system has, in addition to at least one pilot injector 23 per cylinder 12, a pilot pump 24, which, in the second operating mode, supplies the respective pilot injector 23 with the first liquid fuel from the first fuel tank 18. A further fuel line 27 extends from the first fuel tank 18 towards the cylinders 12, and the pilot pump 24 is connected to this further fuel line 27.

[0028] In the dual-fuel internal combustion engine 11 according to the invention, as Fig. 2 the main injection system and the pilot injection system are coupled in such a way that the first liquid fuel in the second operating mode can be supplied from the pilot injection system, which comprises at least one pilot injector 23 and the pilot pump 24 for each cylinder 12, to the respective main injector 16 of the main injection system, wherein the first liquid fuel in the second operating mode serves as working fluid and / or as barrier fluid in the area of ​​the respective main injector 16.

[0029] This shows Fig. 2 A branch line 25 branches off from the pilot injection system upstream of the respective pilot injector 23 and preferably leads directly to the respective main injector 16 of the main injection system of the respective cylinder 12, and preferably opens into the main injection system in the region of the respective main injector 16. Viewed in the delivery direction of the pilot injection system, the branch line 25 branches off downstream of the pilot pump 24 and upstream of the respective pilot injector 23 in order to supply the first liquid fuel to the respective main injector 16 of the main injection system as working fluid and / or barrier fluid in the second operating mode.

[0030] In the second operating mode, the pressure in the respective branch line 25 leading from the pilot injection system to the main injection system is higher than the pressure in the area of ​​the respective main injector 16, preferably by a defined pressure offset. This ensures that the first liquid fuel can always be reliably supplied to the respective main injector 16 in the second operating mode.

[0031] In Fig. 2 A pressure reducer 26 is integrated into the branch line 25 shown there. This limits the pressure in the respective branch line 25 downstream of the pressure reducer 26 to a defined level.

[0032] The first liquid fuel, which is relatively ignitable, is preferably a liquid fuel having a lubricity WSD between 100 µm and 300 µm, particularly advantageously between 100 µm and 200 µm. The second liquid fuel, which is relatively inignitable, is preferably a liquid fuel having a lubricity WSD between 300 µm and 820 µm, particularly advantageously between 400 µm and 820 µm. The first liquid fuel is preferably diesel fuel. The second liquid fuel is preferably ethanol or methanol.

[0033] In the dual-fuel internal combustion engine 11 according to the invention, which burns a liquid fuel in each of its two operating modes, the first liquid fuel serves in the second operating mode, on the one hand, to ignite the second liquid fuel and, on the other hand, as working fluid and / or barrier fluid in the area of ​​the respective main injector 16. In the second operating mode, the main injector 16 and pilot injector 23 of the respective cylinder 12 therefore use the first liquid fuel, on the one hand, as ignition oil, which is introduced into the cylinder 12 via the respective pilot injector 23, and, on the other hand, as working oil and / or barrier oil in the area of ​​the main injector 16.

[0034] This applies in particular to the area of ​​so-called large engines or large internal combustion engines, whose cylinders have piston diameters of at least 140 mm, and in particular at least 175 mm. Such large internal combustion engines include, for example, marine engines. In the invention, these are designed as dual-fuel internal combustion engines. Reference symbol list

[0035] 10 Ship's propulsion system 11 Dual-fuel internal combustion engine 12 Cylinder 13 Generator 14 Ship's propeller 15 Fuel supply system 16 Main injector 17 Main pump 18 Fuel tank 19 Fuel tank 20 Fuel line 21 Fuel line 22 Changeover valve 23 Pilot injector 24 Pilot pump 25 Branch line 26 Pressure reducer 27 Fuel line

Claims

1. A dual-fuel internal combustion engine (11), having cylinders (12), in which in a first operating mode a first liquid fuel and in a second operating mode a second liquid fuel is combustible, having a main injection system comprising at least one main injector (16) for each cylinder (12), via which the cylinders (12) can be supplied with the first liquid fuel, which is relatively ignitable, in the first operating mode and via which the cylinders (12) can be supplied with the second liquid fuel which is relatively low-ignitable, in the second operating mode, having a pilot injection system comprising at least one pilot injector (23) for each cylinder (12), via which in the second operating mode the cylinders (12) of the internal combustion engine can be supplied with the first liquid fuel for igniting the second liquid fuel, wherein the main injection system and the pilot injection system are coupled in such a manner that in the second operating mode, emanating from the pilot injection system, the first liquid fuel can be supplied to the respective main injector (16) of the main injection system as working fluid and / or as barrier fluid, the main injection system comprises a main pump (17), via which in the first operating mode the first liquid fuel can be supplied to the cylinders (12), and via which in the second operating mode the second liquid fuel can be supplied to the cylinders (12), the pilot injection system comprises a pilot pump (24), via which in the second operating mode the cylinders (12) can be supplied with the first liquid fuel for igniting the second liquid fuel, characterised by a first fuel tank (18) for the first fuel, which can be coupled to the main pump (17) via a first fuel line (20), by a second fuel tank (19) for the second fuel, which can be coupled to the main pump (17) via a second fuel line (21), a shuttle valve (22) in order to couple in the first operating mode the main pump (17) via the first fuel line (20) to the first fuel tank (18) and in the second operating mode the main pump (17) via the second fuel line (21) to the second fuel tank (19).

2. The dual-fuel internal combustion engine according to Claim 1, wherein upstream of the respective pilot injector (23) a respective branch line (25) branches off the pilot injection system, via which in the second operating mode the first liquid fuel can be supplied as working fluid and / or as barrier fluid to the respective main injector (16).

3. The dual-fuel internal combustion engine according to Claim 2, wherein the respective branch line (25), in the region of the respective main injector (16), leads into the main injection system.

4. The dual-fuel internal combustion engine according to Claim 2 or 3, wherein in the respective branch line (25) a pressure reducer (26) is integrated in order to limit the pressure in the respective branch line (25).

5. The dual-fuel internal combustion engine according to any one of the Claims 2 to 4, wherein in the second operating mode a pressure in the respective branch line (25) leading from the pilot injection system to the main injection system is greater than a pressure in the region of the respective main injector (16) of the main injection system.

6. The dual-fuel internal combustion engine according to Claim 2, wherein the respective branch line (25) branches off the pilot injection system upstream of the respective pilot injector (23) and downstream of the pilot pump (24).

7. The dual-fuel internal combustion engine according to any one of the Claims 1 to 6, wherein the first liquid fuel has a lubricity WSD between 100 µm and 300 µm, preferentially between 100 µm and 200 µm, wherein the second liquid fuel has a lubricity WSD between 300 µm and 820 µm, preferentially between 400 µm and 820 µm.

8. The dual-fuel internal combustion engine according to any one of the Claims 1 to 7, wherein the first liquid fuel is a diesel fuel, wherein the second liquid fuel is ethanol or methanol.