Method for operating an internal combustion engine and gaseous fuel injection unit

Abstract

The invention relates to a method for operating an internal combustion engine (10) provided as a medium speed gas engine or a dual fuel engine in a gaseous fuel mode. The method comprises the steps of: injecting gaseous fuel directly into a combustion chamber (14) of the engine at a maximum injection pressure which is lower than the compression end pressure of the engine (10).

Description

Technical Field

[0001] The invention relates to a method for operating an internal combustion engine configured as a medium-speed gas engine or a dual-fuel engine in a gaseous fuel mode. The invention further relates to a gaseous fuel injection unit for an internal combustion engine configured as a medium-speed gas engine or a dual-fuel engine when operating in a gaseous fuel mode, and to an internal combustion engine equipped with such a gaseous fuel injection unit. Background Art

[0002] In order to operate ships at relatively low emission levels, the use of medium speed gas engines is known. In addition, the use of reciprocating internal combustion engines operating as dual fuel engines is known, which can run on gas as well as liquid fuel. Typically, such engines can operate in gas fuel mode and liquid fuel mode as described in EP 2706 214A1.

[0003] In gaseous fuel mode, known dual-fuel engines are designed to primarily burn a gaseous fuel, such as natural gas, but typically use a small percentage of a liquid fuel, such as diesel, as a pilot fuel to initiate ignition. By doing so, the engine can operate based on a combustion process that is a cross between the Diesel cycle and the Otto cycle. More specifically, in the gaseous fuel mode of a known dual-fuel engine, a gas-air mixture is delivered to the cylinder of the engine via an intake valve during an intake stroke and then compressed during a compression stroke, wherein at the top of the compression stroke, a pilot fuel is injected and spontaneously ignites, thereby igniting the gas-air mixture to produce a powered expansion.

[0004] In contrast, in liquid fuel mode, liquid fuel, such as diesel fuel, is supplied to the engine cylinder as the only fuel (ie, energy source) in combustion. In this mode, the engine is generally operated according to the diesel cycle, wherein the liquid fuel can be directly injected into the combustion chamber.

[0005] The advantage of dual-fuel engines is that they offer a certain degree of fuel flexibility, thereby increasing the security of energy supply. In addition, dual-fuel engines generally ensure low emission levels when operating in gas fuel mode. Therefore, dual-fuel engines are increasingly used in ships, either as main engines or auxiliary engines, in order to meet IMO (International Maritime Organization) III requirements.

[0006] Known dual-fuel engines are usually operated in such a way that at the beginning of the intake stroke, a small amount of gas-air mixture is flushed into the cylinder. In this way, the cylinder is cooled to prevent the combustion chamber from being subjected to excessive combustion temperatures, which could, for example, lead to an increase in the amount of nitrogen oxides in the engine exhaust.

[0007] In order to flush the cylinder with the gas-air mixture, the inlet and outlet valves of the cylinder are usually kept open for a period of time during the intake stroke. However, by doing so, a small amount of gaseous fuel present in the gas-air mixture is expelled from the cylinder before combustion and is released into the surrounding environment. As a result, the engine can emit greenhouse gases during its operation. In the context of internal combustion engines, the expulsion of unburned fuel from the cylinder is also often referred to as "fuel leakage".

[0008] As environmental sustainability is becoming increasingly important, the latest developments are aimed at further improving the efficiency and reducing the pollutant emissions of such engines, namely greenhouse gas emissions. Summary of the invention

[0009] The object of the present invention is therefore to provide a method and a gaseous fuel injection unit which enable an internal combustion engine provided as a medium-speed gas engine or a dual-fuel engine to be operated in a more efficient manner, i.e. more environmentally friendly. To this end, the object of the present invention is to provide an internal combustion engine provided as a medium-speed gas engine or a dual-fuel engine, which is equipped with such a gaseous fuel injection unit.

[0010] These objects are solved by a method, a gaseous fuel injection unit and an internal combustion engine equipped with such a gaseous fuel injection unit as defined in the present description.Preferred embodiments are also set forth in the present description and the drawings.

[0011] Therefore, a method is provided for operating an internal combustion engine provided as a medium speed gas engine or a dual fuel engine in a gaseous fuel mode. The method comprises the steps of injecting gaseous fuel directly into a combustion chamber of the engine at a maximum injection pressure below the compression end pressure of the engine.

[0012] In addition, a gas fuel injection unit for use in an internal combustion engine is provided, the internal combustion engine being configured as a medium-speed gas engine or a dual-fuel engine when operating in a gas fuel mode. The gas fuel injection unit comprises a gas fuel injection valve and a gas fuel feed unit, the gas fuel injection valve being configured to inject gas fuel directly into a combustion chamber of the engine, and the gas fuel feed unit being configured to supply pressurized gas fuel to the gas fuel injection valve at a maximum injection pressure lower than a compression end pressure of the engine.

[0013] For this purpose, an internal combustion engine as a medium-speed gas engine or as a dual-fuel engine is provided which is equipped with such a gas fuel injection unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0015] Figure 1 shows a schematic diagram of an internal combustion engine equipped with a gaseous fuel injection unit;

[0016] Figure 2 shows a schematic longitudinal sectional view of a cylinder head of an engine according to a first embodiment;

[0017] Figure 3 A schematic longitudinal sectional view showing a cylinder head of an engine according to a second embodiment; and

[0018] Figure 4 A graph illustrating injection events during an engine cycle for an engine cylinder is shown. DETAILED DESCRIPTION

[0019] Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings, wherein the same elements are denoted by the same reference numerals and repeated descriptions thereof may be omitted to avoid redundancy.

[0020] Figure 1 A reciprocating internal combustion engine 10, also referred to hereinafter as an "engine", is schematically shown, which may be installed in a vehicle such as a ship as a main engine or an auxiliary engine, or may be used in a power plant. In the configuration shown, the engine 10 is arranged as a dual-fuel engine. In the context of the present invention, the term "dual-fuel engine" refers to a reciprocating internal combustion engine designed to run on both gaseous fuel and liquid fuel.

[0021] The term "gaseous fuel" refers to a gaseous fuel, i.e., a fuel that is in a gaseous state under normal conditions. The gaseous fuel may include a combustible hydrocarbon gas, such as methane, propane, butane, or a mixture thereof. For example, the gaseous fuel may be provided as liquefied petroleum gas, natural gas, biogas, or any other suitable gas that may be used as a gaseous fuel. In the engine 10, the gaseous fuel may be handled or stored in a compressed and liquefied state.

[0022] The term “liquid fuel” refers to a fuel that is in a liquid state under normal conditions. The liquid fuel may be provided as diesel, biodiesel, fuel oil (eg, heavy fuel oil), or any other fuel that can be used as a liquid fuel in engine 10 .

[0023] The engine 10 is configured to operate in a gas fuel mode and a liquid fuel mode. Specifically, in the gas fuel mode, the engine 10 is designed to mainly burn gas fuel, but preferably uses a small amount or percentage of liquid fuel as a pilot fuel to start ignition. In the liquid fuel mode, the engine 10 is designed to burn only liquid fuel to produce power expansion.

[0024] Next, the structural configuration of the engine 10 is described. The engine 10 includes at least one, preferably a plurality of cylinders 12, such as eight, twelve or eighteen cylinders, which may be arranged in an inline configuration, a V-shaped configuration or any other known cylinder configuration. Each cylinder 12 is provided with a combustion chamber 14 defined by a piston 16 accommodated in the cylinder 12. The piston 16 is configured to reciprocate and move axially within the cylinder 12 and is connected to a crankshaft 18 of the engine 10 via a connecting rod 20. The cylinder 12 is covered by a cylinder head 22 that further defines the combustion chamber 14.

[0025] The engine 10 also includes a control device (not shown) that controls the actuation of the engine 10 and its components. Specifically, the control device is configured to control the supply of a desired fuel-air mixture into the combustion chamber 14. In the configuration shown, the fuel-air mixture is provided by mixing a fuel medium (i.e., a gaseous fuel and / or a liquid fuel) with an intake air (i.e., an intake charge) within the combustion chamber 14. In addition, the control device is configured to control the ignition of the fuel-air mixture supplied within the combustion chamber 14 so as to produce high temperature and high pressure gases that apply a force to the piston 16 and thereby axially move the piston, thereby rotating the crankshaft 18. To this end, the control device is configured to control the exhaust of the combustion gases from the combustion chamber 14 after combustion has occurred.

[0026] More specifically, in order to control the above-described gas exchange and combustion within cylinder 12 during operation, engine 10 includes a charge air supply unit 24 , a liquid fuel injection unit 26 , an exhaust gas discharge unit 28 , and a gas fuel injection unit 30 .

[0027] As for the substance, the charge air supply unit 24 is configured for guiding charge air into the combustion chamber 14. Therefore, the charge air supply unit 24 comprises a charge air feed unit 32 for providing charge air intake, which is guided through an intake valve 34 via a charge air line 36. The intake valve 34 opens into the combustion chamber 14 and is configured for regulating the supply of charge air into it. The charge air feed unit 32 may comprise at least one turbocharger unit configured for pressurizing and thereby charging the intake air guided therethrough, i.e. fresh air from outside the engine 10, which is then fed into the charge air line 36.

[0028] The liquid fuel injection unit 26 is configured to inject liquid fuel into the combustion chamber 14. To this end, the liquid fuel injection unit 26 includes a liquid fuel injection valve 38 configured for injecting the liquid fuel directly into the combustion chamber 14 of the engine 10. The liquid fuel injection unit 26 may further include a fuel pump configured to draw the liquid fuel from a storage container or tank and pressurize the liquid fuel received thereby, which is then directed to the liquid fuel injection valve 38. Specifically, during operation of the engine 10, the pressurized liquid fuel supplied to the liquid fuel injection valve 38 may be raised by the fuel pump to a minimum pressure level that is higher than the compression end pressure of the engine 10.

[0029] In the context of the present invention, the term "compression end pressure" refers to the pressure prevailing in the combustion chamber 14 before ignition begins, particularly immediately before ignition begins. More specifically, the compression end pressure may refer to the pressure prevailing in the combustion chamber 14 when the cylinder 12 is at its top dead center during operation.

[0030] The exhaust gas discharge unit 28 is configured for discharging combustion gases from the combustion chamber 14 , ie after combustion of the fuel-air mixture. To control the discharge of the combustion gases, an exhaust valve 40 is provided which variably opens and closes an orifice of an exhaust line 42 leading to the combustion chamber 14 .

[0031] The basic structure and basic mode of operation of the engine 10 and its components, i.e. the control device, the charge air supply unit 24, the liquid fuel injection unit 26 and the exhaust gas discharge unit 28, are well known to those skilled in the art and are therefore not further described. Instead, the features of the engine 10 (i.e. its gaseous fuel injection unit 30) and its operation in connection with the present invention are addressed below.

[0032] As described above, the engine 10 includes a gas fuel injection unit 30 configured to inject pressurized gas fuel into the combustion chamber 14. The term "pressurized gas fuel" refers to a compressed or pressurized liquefied gas fuel and / or a compressed or pressurized gaseous gas fuel.

[0033] Specifically, the gaseous fuel injection unit 30 includes a gaseous fuel injection valve 44 configured to inject the gaseous fuel directly into the combustion chamber 14 of the engine 10 .

[0034] In the context of the present invention, the expression "injecting the gaseous fuel directly into the combustion chamber 14" means that the gaseous fuel is injected into the combustion chamber 14 before mixing with the charge air or intake air. In other words, in the proposed configuration, the gaseous fuel is not premixed with the air before being supplied to the combustion chamber 14, for example in a separate intake port. For this purpose, the gaseous fuel injection valve 44 is arranged such that it opens into the combustion chamber 14, such as from Figure 1 Visible in.

[0035] By proposing an engine 10 configured to inject gaseous fuel directly into its combustion chamber 14, the supply of gaseous fuel to the combustion chamber 14 and thereby intake air variation and combustion may be more precisely controlled, which allows the engine 10 to be operated in a more efficient manner.

[0036] The gaseous fuel injection unit 30 further includes a gaseous fuel feed unit 46 configured to supply pressurized gaseous fuel to the gaseous fuel injection valve 44. Specifically, as will be explained in more detail below, the gaseous fuel feed unit 46 is configured to supply pressurized gaseous fuel to the gaseous fuel injection valve 44 at a maximum injection pressure that is lower than the compression end pressure of the engine 10.

[0037] In the context of the present invention, the term “injection pressure” refers to the pressure that prevails in the pressurized gaseous fuel as it is discharged from the gaseous fuel injection valve 44 into the combustion chamber 14 .

[0038] Furthermore, in order to be able to inject the gaseous fuel into the combustion chamber 14, the pressurized gaseous fuel has an injection pressure, i.e. a maximum injection pressure, which is greater than the actual pressure prevailing in the combustion chamber 14 when injected into the combustion chamber 14 by means of the gaseous fuel injection valve 44. In other words, during an injection event of the gaseous fuel, when discharged from the gaseous fuel injection valve 44, the injection pressure of the pressurized gaseous fuel is greater than the pressure prevailing in the combustion chamber 14.

[0039] In order to provide the pressurized gaseous fuel, the gaseous fuel feed unit 46 may include a gas compressor or pump (not shown) for pressurizing the gaseous fuel to be supplied to the gaseous fuel injection valve 44. Specifically, the gas compressor or pump may be any type capable of sucking the gaseous fuel from the storage tank and pumping the gaseous fuel received thereby to the gaseous fuel injection valve 44 through the gaseous fuel pipeline 48 under high pressure. The gas compressor or pump may be further configured to be driven by the engine 10 or the electric motor. Therefore, the gaseous fuel feed unit 46 may further include a gaseous fuel storage tank (not shown), which is configured to store the gaseous fuel in a liquefied state that can be fluidically connected to the gas compressor or pump. For example, the gaseous fuel storage tank may be configured to store the gaseous fuel at a storage pressure of approximately 2 bar to 16 bar.

[0040] Figure 2 A longitudinal cross-sectional view of a cylinder head 22 of an engine according to a first embodiment is schematically shown. As described above, the gas fuel injection valve 44 is arranged so that it opens into the combustion chamber 14. For this purpose, in the illustrated configuration, the gas fuel injection valve 44 is integrated into the cylinder head 22. Specifically, as shown in FIG. Figure 2As shown, the gaseous fuel injection valve 44 opens in a lateral region of the combustion chamber 14, more specifically in a lateral top region of the combustion chamber 14. In other words, the gaseous fuel injection valve 44 is arranged laterally in a portion 49 of the cylinder head 22 defining the combustion chamber 14.

[0041] Figure 3 Schematically shows a longitudinal cross-sectional view of an engine cylinder head 22 according to a second embodiment. Figure 2 Compared to the embodiment shown, the gaseous fuel injection valve 44 is integrated in the cylinder head 22 so that it opens into the combustion chamber 14 at a central region of the combustion chamber 14, more specifically at a central top region of the combustion chamber 14. In other words, the gaseous fuel injection valve 44 is centrally arranged in the portion 49 of the cylinder head 22 that defines the combustion chamber 14. In the shown configuration, the gaseous fuel injection valve 44 is arranged separately from the liquid fuel injection valve 38. Specifically, as shown in FIG. Figure 3 As shown, the gaseous fuel injection valve 44 is arranged adjacent to the liquid fuel injection valve 38. Alternatively, the gaseous fuel injection valve 44 and the liquid fuel injection valve 38 may be combined so that the gaseous fuel and the liquid fuel may be injected into the combustion chamber 14 via the same valve opening or bore provided in the cylinder head 22. In such a configuration, the valve opening may lead to a pre-combustion chamber so that the gaseous or liquid fuel injected via the valve opening is directed through the pre-combustion chamber before being directed into the combustion chamber 14.

[0042] The gaseous fuel injection unit 30 further comprises an actuation unit (not shown) configured to control actuation of the gaseous fuel injection valve 44 within an engine cycle of the engine cylinder 12. The term "engine cycle" refers to a repetitive and predetermined sequence of strokes of the engine cylinder 12 during which the piston 16 of the cylinder reciprocates between its bottom dead center and top dead center.

[0043] Hereinafter, the operation of the engine 10, and in particular with respect to the operation of the gaseous fuel injection unit 30 thereof, will be referred to. Figure 4 Further explanation: Figure 4 A diagram of injection events during an engine cycle is shown when engine 10 is operating in a gaseous fuel mode.

[0044] Specifically, in Figure 4In the illustrated diagram, the abscissa of the diagram depicts the crank angle expressed in degrees after top dead center (ATDC). The ordinate on the left side of the diagram shows the associated normalized lift of each valve (i.e., the intake valve 34, the liquid fuel injection valve 38, and the gaseous fuel injection valve 44), wherein the ordinate on the right side shows the associated cylinder pressure prevailing in the combustion chamber 14. More specifically, to show the normalized lift of each valve, the diagram includes an intake valve lift curve 52 representing the lift of the intake valve 34, a liquid fuel injection valve lift curve 54 representing the lift of the liquid fuel injection valve 38, and a gaseous fuel injection valve lift curve 56 representing the lift of the gaseous fuel injection valve 44 during an engine cycle. In addition, to show the cylinder pressure prevailing in the combustion chamber 14, the diagram further includes a cylinder pressure curve 58 showing the pressure level prevailing in the combustion chamber 14 during an engine cycle.

[0045] As described above, during operation of the engine 10, gaseous fuel is injected directly into the combustion chamber 14 at a maximum injection pressure that is less than the compression end pressure of the engine. Figure 4 4 is shown by the gaseous fuel injection valve lift curve 56. During the engine cycle, the step of injecting the gaseous fuel is started when the exhaust valve 40 for discharging the exhaust gas from the combustion chamber 14 is in the closed state. In other words, the actuation unit of the gaseous fuel injection unit 30 is configured to actuate the gaseous fuel injection valve 44 so that the injection of the gaseous fuel into the combustion chamber 14 is prevented when the exhaust valve 40 is operated in the open position. Therefore, the actuation unit of the gaseous fuel injection unit 30 is configured to actuate the gaseous fuel injection valve so that the injection of the gaseous fuel into the combustion chamber 14 is performed when the exhaust valve 40 is operated in the closed position.

[0046] In this way, leakage of gaseous fuel, ie, unburned gaseous fuel, can be effectively prevented, thereby contributing to more efficient and more environmentally friendly operation of the engine.

[0047] like Figure 4 As shown, in the engine cycle, the step of injecting the gaseous fuel is performed before the step of starting the ignition in the combustion chamber, and in the illustrated structure, this step is performed by injecting the liquid fuel as the pilot fuel into the combustion chamber 14. In other words, the actuation unit of the gaseous fuel injection unit 30 is configured to actuate the gaseous fuel injection valve 44 so that in the engine cycle of the cylinder 12, the gaseous fuel injection valve 44 operates in the open position for injecting the gaseous fuel into the combustion chamber 14 before the ignition in the combustion chamber 14 starts. In addition, the actuation unit is configured to actuate the gaseous fuel injection valve 44 so that in the engine cycle, the gaseous fuel injection valve 44 operates in the closed position to prevent the gaseous fuel from being injected into the combustion chamber 14 when the ignition in the combustion chamber starts.

[0048] As described above, in the illustrated configuration, ignition of the fuel-air mixture in the combustion chamber 14 is initiated by injecting liquid fuel as a pilot fuel into the combustion chamber 14, which in turn Figure 4 54. Alternatively, the ignition of the fuel-air mixture in the combustion chamber 14 can be initiated by a high-voltage spark released into the combustion chamber 14 or its antechamber. In particular, such an ignition program can also be implemented in medium-speed gas engines.

[0049] In the step of directly injecting the gaseous fuel, the gaseous fuel is injected with a maximum injection pressure, which is no more than three quarters or half of the compression end pressure of the engine 10, and is greater than or equal to twice the actual compression pressure that prevails in the combustion chamber 14, and the actual compression pressure is associated with the corresponding crank angle position. In the illustrated configuration, the compression end pressure of the engine 10 may be less than 250 bar, in particular less than 200 bar. For example, the compression end pressure may be 150 bar. The gaseous fuel may be injected at a maximum injection pressure in the range of 5 bar to 100 bar. Specifically, the gaseous fuel may be injected at a maximum injection pressure in the range of 10 bar to 50 bar. Since in the proposed solution, the maximum injection pressure is relatively low compared to known fuel injection devices, the proposed gas fuel injection unit 30 may have a less complex design.

[0050] If you can Figure 4 As collected from the graph depicted in FIG. 1 , the step of injecting the gaseous fuel is performed in the range of -150° to -15° after the top dead center. Alternatively, the step of injecting the gaseous fuel into the combustion chamber 14 may be performed in the range of -360° to -15° after the top dead center. Specifically, in order to ensure that the step of injecting the gaseous fuel is completed before the step of igniting the fuel-air mixture within the engine cycle, the step of injecting the gaseous fuel is completed below -15° after the top dead center.

[0051] In an alternative embodiment, the engine 10 may be configured as a medium speed gas engine. In the context of the present invention, the term "medium speed gas engine" refers to an internal combustion engine that runs on gaseous fuel and runs at a speed in the range of 500 rpm to 1400 rpm, preferably at a speed of about 750 rpm or 1000 rpm. Typically, such an engine is operated in a gas fuel mode, wherein the gaseous fuel as the only fuel is burned in the combustion chamber.

[0052] When provided as a medium-speed gas engine, the use of the above-mentioned liquid fuel injection unit in the engine 10 is omitted. Instead, the engine 10 is provided with a spark plug unit configured to initiate ignition of the fuel-air mixture in the combustion chamber 14 by a high-pressure spark released into the combustion chamber 14 or into a pre-combustion chamber. In its respective engine cycle, the step of directly injecting the gaseous fuel is preferably performed at the same timing and the same injection pressure, as described above, in particular as combined Figure 4 described.

[0053] It is obvious to those skilled in the art that these embodiments and projects only describe examples of multiple possibilities. Therefore, the embodiments shown here should not be understood to constitute restrictions on these features and configurations. Any possible combination and configuration of the features can be selected according to the scope of the present invention.

[0054] A method for operating an internal combustion engine provided as a medium speed gas engine or a dual fuel engine in a gaseous fuel mode may be provided. The method may include the steps of injecting gaseous fuel directly into a combustion chamber of the engine at a maximum injection pressure below the compression end pressure of the engine.

[0055] By proposing a method of injecting gaseous fuel directly into the combustion chamber of an engine, the supply of gaseous fuel, i.e. with respect to its timing and amount, can be controlled more accurately than in known engines (e.g. known dual-fuel engines in which the gaseous fuel is premixed with the intake air before being introduced into the combustion chamber).

[0056] The proposed method can be used to operate an engine used as a main engine or an auxiliary engine in a ship or a power plant. However, the method is not limited to these applications.

[0057] In a further development, the method may be provided such that the step of injecting gaseous fuel directly into the combustion chamber is started when an exhaust valve of the engine for venting or exhausting exhaust gas from the combustion chamber is in a closed state within an engine cycle of a cylinder of the engine.

[0058] In this way, the proposed method can prevent unburned gaseous fuel from being discharged through the exhaust valve at the beginning of the intake stroke within the engine cycle. In other words, slippage of unburned gaseous fuel can be prevented. As a result, the proposed method can contribute to a more environmentally friendly engine operation.

[0059] The method may further comprise the step of initiating ignition of the fuel-air mixture in the combustion chamber, wherein the step of directly injecting the gaseous fuel may be performed before the step of initiating ignition in the combustion chamber within an engine cycle of the cylinder.

[0060] Specifically, when the engine is configured as a dual fuel engine, the step of starting ignition in the combustion chamber may be performed by injecting a pilot fuel, such as a liquid fuel, into the combustion chamber. Alternatively or additionally, the step of starting ignition in the combustion chamber may be performed by discharging a high voltage spark into the combustion chamber or a pre-combustion chamber thereof.

[0061] When the engine is provided as a medium speed gas engine, the step of starting ignition in the combustion chamber may be performed by discharging a high voltage spark into the combustion chamber or into its antechamber.

[0062] In a further development, the step of directly injecting the gaseous fuel may be performed so that the gaseous fuel is injected at a maximum injection pressure no greater than three quarters or half of the compression end pressure of the engine. In addition, the maximum injection pressure may be greater than or equal to twice the actual compression pressure of the engine that prevails in the combustion chamber during the injection event.

[0063] Alternatively or additionally, the step of directly injecting the gaseous fuel may be performed such that the gaseous fuel is injected with a maximum injection pressure in the range of 5 bar to 100 bar, in particular in the range of 10 bar to 50 bar. In addition, the compression end pressure of the engine may be less than 250 bar, in particular less than 200 bar or 150 bar.

[0064] In a further development, the step of injecting the gaseous fuel may be performed within a range of 360° to 15° before the top dead center of the cylinder within the engine cycle. In addition, the step of directly injecting the gaseous fuel may be performed so that it is completed at 15° or 30° before the top dead center of the cylinder.

[0065] In addition, a gas fuel injection unit for use in an internal combustion engine that is configured as a medium-speed gas engine or a dual-fuel engine when operating in a gas fuel mode may be provided. The gas fuel injection unit may include a gas fuel injection valve configured to inject gas fuel directly into a combustion chamber of the engine and a gas fuel feed unit configured to supply pressurized gas fuel to the gas fuel injection valve at a maximum injection pressure that is lower than a compression end pressure of the engine.

[0066] The gaseous fuel injection unit can be used in particular for carrying out the operation of the above-mentioned engine.Therefore, the technical features described in conjunction with the above-mentioned method can also relate to and be applied to the proposed gaseous fuel injection unit, and vice versa.

[0067] The gaseous fuel injection unit may further include an actuation unit configured to control actuation of a gaseous fuel injection valve within an engine cycle of a cylinder of the engine, wherein the actuation unit may be configured to actuate the gaseous fuel injection valve so as to prevent gaseous fuel from being injected into the combustion chamber when the exhaust valve of the cylinder is operating in an open position.

[0068] Furthermore, the actuation unit may be configured to actuate the gaseous fuel injection valve such that, within an engine cycle of a cylinder of the engine, the gaseous fuel injection valve operates in an open position for injecting gaseous fuel into the combustion chamber before ignition in the combustion chamber begins, and operates in a closed position for preventing gaseous fuel from being injected into the combustion chamber when ignition in the combustion chamber begins.

[0069] The gas fuel feeding unit may include a gas compressor configured to pressurize the gas fuel to be supplied to the gas fuel injection valve. In addition, the gas compressor may be configured to be driven by an engine or an electric motor.

[0070] The gaseous fuel injection valve can be integrated in a cylinder head of the engine so that, in the installed state in the engine, the gaseous fuel injection valve opens into the combustion chamber in a lateral or central region of the combustion chamber.

[0071] In addition, an internal combustion engine may be provided. The internal combustion engine is preferably arranged as a medium speed gas engine or a dual fuel engine. In addition, the engine may be equipped with a gas fuel injection unit as described above, the gas fuel injection unit being configured to inject gas fuel directly into the combustion chamber of the engine when the engine is running in gas fuel mode.

[0072] Since the proposed internal combustion engine is equipped with the above-mentioned gas fuel injection unit, the technical features described in conjunction with the above-mentioned method or gas fuel injection unit may also relate to and be applied to the proposed internal combustion engine, and vice versa.

[0073] Industrial Applicability

[0074] With reference to the accompanying drawings and the accompanying description, a method for operating an internal combustion engine and a corresponding gaseous fuel injection unit are proposed. The method and the gaseous fuel injection unit as described above can be applied to an internal combustion engine arranged as a medium-speed gas engine or a dual-fuel engine. The proposed method can replace conventional operating methods. Therefore, the proposed gaseous fuel injection unit can replace conventional gaseous fuel supply units and can be used as a replacement or retrofit component.

Claims

1. A method for operating an internal combustion engine (10) provided as a medium speed gas engine or a dual fuel engine in a gaseous fuel mode, comprising the following steps: A gaseous fuel is directly injected into a combustion chamber (14) of the engine at a maximum injection pressure lower than the compression end pressure of the engine (10), wherein in the step of directly injecting the gaseous fuel, the gaseous fuel is injected at such a maximum injection pressure that is no greater than three quarters of the compression end pressure of the engine (10) and greater than twice the actual compression pressure prevailing in the combustion chamber (14), the actual compression pressure being associated with the corresponding crank angle position.

2. The method of claim 1, wherein the maximum injection pressure is no greater than half of a compression end pressure of the engine (10).

3. The method according to claim 1, wherein the step of directly injecting the gaseous fuel is started when, in an engine cycle of a cylinder (12) of the engine (10), an exhaust valve (40) of the cylinder (12) for discharging exhaust gas from the combustion chamber (14) is in a closed state.

4. The method according to claim 1, further comprising the step of initiating ignition of a fuel-air mixture in the combustion chamber (14), wherein the step of directly injecting the gaseous fuel is performed before the step of initiating ignition in the combustion chamber (14) during an engine cycle of a cylinder (12) of the engine.

5. The method according to claim 4, wherein the step of starting ignition in the combustion chamber (14) is performed by injecting a pilot fuel into the combustion chamber (14).

6. The method according to any one of claims 1 to 5, wherein in the step of directly injecting the gaseous fuel, the gaseous fuel is injected at a maximum injection pressure in the range of 5 bar to 100 bar. 7 . The method of claim 6 , wherein in the step of directly injecting the gaseous fuel, the gaseous fuel is injected at a maximum injection pressure in the range of 10 bar to 50 bar.

8. The method according to any one of claims 1 to 5, wherein the compression end pressure of the engine (10) is less than 250 bar.

9. The method according to claim 8, wherein the compression end pressure of the engine (10) is less than 200 bar.

10. The method according to claim 9, wherein the compression end pressure of the engine (10) is less than 150 bar.

11. The method according to any one of claims 1 to 5, wherein the step of directly injecting the gaseous fuel is performed within an engine cycle of a cylinder (12) of the engine within a range of 360° to 15° before top dead center of the cylinder (12).

12. Method according to any one of claims 1 to 5, wherein the step of directly injecting the gaseous fuel is performed at 15° before top dead center of the cylinder (12) within an engine cycle of the cylinder of the engine.

13. A gas fuel injection unit (30) for use in an internal combustion engine (10), the internal combustion engine being configured as a medium speed gas engine or a dual fuel engine when operating in a gas fuel mode, the gas fuel injection unit comprising: - a gaseous fuel injection valve (44) configured for injecting gaseous fuel directly into a combustion chamber (14) of the engine (10), and - a gaseous fuel feed unit (46) configured to supply pressurized gaseous fuel to the gaseous fuel injection valve (44) at a maximum injection pressure that is lower than the compression end pressure of the engine (10), wherein the maximum injection pressure is not greater than three quarters of the compression end pressure of the engine (10) and is greater than twice the actual compression pressure prevailing in the combustion chamber (14), the actual compression pressure being associated with the respective crank angle position.

14. The gas fuel injection unit according to claim 13, wherein the maximum injection pressure is not greater than half of the compression end pressure of the engine (10).

15. The gaseous fuel injection unit according to claim 13, further comprising an actuation unit, which is configured to control actuation of the gaseous fuel injection valve within an engine cycle of a cylinder (12) of the engine (10), wherein the actuation unit is configured to actuate the gaseous fuel injection valve so that gaseous fuel is prevented from being injected into the combustion chamber (14) when the exhaust valve (40) of the cylinder (12) is operated in an open position.

16. A gas fuel injection unit according to claim 15, wherein the actuation unit is configured to actuate the gas fuel injection valve (44) so ​​that within an engine cycle of a cylinder (12) of the engine (10), the gas fuel injection valve (44) operates in an open position for injecting the gas fuel into the combustion chamber (14) before ignition in the combustion chamber (14) starts, and operates in a closed position for preventing gas fuel from being injected into the combustion chamber (14) when ignition in the combustion chamber (14) starts.

17. The gas fuel injection unit according to any one of claims 13 to 16, wherein the gas fuel feed unit (46) comprises a gas compressor configured to pressurize the gas fuel to be supplied to the gas fuel injection valve (44) and configured to be driven by the engine (10) or the electric motor.

18. A gas fuel injection unit according to any one of claims 13 to 16, wherein the gas fuel injection valve (44) is integrated in the cylinder head (22) of the engine (10) so that in the installed state in the engine, the gas fuel injection valve (44) opens into the combustion chamber (14) in a lateral or central area of ​​the combustion chamber (14).

19. An internal combustion engine (10) configured as a medium-speed gas engine or a dual-fuel engine, the internal combustion engine being equipped with a gas fuel injection unit (30) according to any one of claims 13 to 18, the gas fuel injection unit being configured to inject gas fuel directly into a combustion chamber (14) of the engine (10) when the engine (10) is operated in a gas fuel mode.

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