Method for operating a gas-powered internal combustion engine

Abstract

The invention relates to a method for operating a gas-powered internal combustion engine, wherein during an inlet phase (9) in a switched-on operating state of the internal combustion engine, an oxygen-containing gas, preferably air, is introduced into at least one cylinder for combustion, and fuel is conducted to at least one injector (14) and injected from the injector (14) into the cylinder in the course of a primary injection and ignited at said point in the course of a primary ignition (1, 1'), characterized in that during a switch-off step of the internal combustion engine, the supply of fuel to the injector (14) is terminated and residual fuel in the region of the injector (14) is injected into at least one cylinder of the internal combustion engine after the primary ignition (1, 1') and before the start of the subsequent inlet phase (9) in the course of a secondary injection and ignited at said point in the course of a secondary ignition.

Description

[Technical field]

[0001] The invention relates to a method for operating a gas-powered internal combustion engine, wherein during an inlet phase in a switched-on operating state of the internal combustion engine, an oxygen-containing gas, preferably air, is introduced into at least one cylinder for combustion, and fuel is conducted to at least one injector, from which it is injected into the cylinder in the course of a primary injection and ignited therein in the course of a primary ignition. [Background technology]

[0002] It is known that in gas-operated internal combustion engines, i.e. internal combustion engines operated with fuels that are gaseous under normal atmospheric conditions, such as, for example, hydrogen, natural gas, etc., after switching off, fuel residues remain in the injector and / or in the tubes that supply the injector. Thus, after the end of the switched-on operating state, there is residual fuel present which exerts high pressure on the injector via the injector and / or the injector's supply tube. In order to reduce the resulting pressure during the switched-off state at the location, after the last normal combustion in the course of the primary ignition, the residual gases are discharged to the environment or transferred to a corresponding collection vessel. This leads to problems of fuel polluting the environment and flammable gases becoming a safety risk, or of constructional complication due to additional components.

[0003] DE 102015210756, EP 3486458 and JP 2004076698 discuss a method for operating an internal combustion engine for several further revolutions by consuming the remaining fuel in the injector during the inlet phase and primary ignition during the switch-off process in the course of the primary injection. Due to the reduction in the fuel quantity in the injector and the associated reduction in pressure in the injector, less and less is injected into the cylinder. This can lead to a failure of the primary ignition, since the small injected fuel quantity is too diluted by the incoming air in the inlet phase. This can lead to unburned fuel reaching the surroundings. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE 102015210756 [Patent Document 2] European Patent Application Publication No. 3486458 [Patent Document 3] Special Publication No. 2004076698 Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide a method which is as safe and environmentally friendly as possible and which further requires only simple construction. [Means for solving the problem]

[0006] The problem according to the invention is solved in that during the switch-off process of the internal combustion engine, the supply of fuel to the injector is terminated and the remaining fuel in the area of ​​the injector is injected in the process of secondary injection after the primary ignition and before the start of the subsequent inlet phase in at least one cylinder of the internal combustion engine and ignited in the process of secondary ignition. Effect of the Invention

[0007] This makes it possible to reduce the residual fuel without it reaching the surroundings or requiring separate fuel storage, thus eliminating the load on the injectors, and while greater technical adaptations and more complex structures are not required to implement the method, it is ensured that no unburned fuel reaches the outside and causes environmental risks or even uncontrolled ignition.

[0008] It is not important that all the remaining fuel is injected and ignited, but rather that the pressure of the remaining fuel at the relevant points is reduced, in particular to atmospheric pressure, so that dangers due to leakage of fuel, in particular hydrogen, are prevented when the internal combustion engine is switched off.

[0009] Further ignition outside the normal ignition cycle of switched-on operation, i.e. secondary ignition, burns fuel without significantly interfering with the freewheeling of the internal combustion engine. The secondary ignition preferably exerts no or only a slight force on the piston, and thus preferably does not cause any downward movement of the piston (or impede its upward movement), as occurs with primary ignition. The internal combustion engine is thus not loaded by the further ignition.

[0010] During the switch-off process, the supply of fuel to the injectors is preferably terminated and only afterwards is the remaining fuel injected and ignited in the region of the injectors, in particular in the distributor.

[0011] In this context, residual fuel that is still present in the supply line to the injector and in the injector itself after the end of the supply of fuel to the injector is meant. As a rule, the injector is supplied with fuel via a pressure reducing device, a so-called pressure regulator. A piping system for supplying the injector is preferably provided, which piping system comprises at least one pressure reducing device. The pressure reducing device is used to reduce the pressure of fuel from a fuel source, such as a fuel tank, in order to supply the fuel to the injector at a lower pressure. Preferably, the residual fuel between the at least one pressure regulator and the injector is injected and ignited according to the invention during the switch-off process.

[0012] The piping system may also include a distributor for distributing fuel among the injectors.

[0013] The admission phase is a phase in which the admission passage is in fluid communication with the combustion chamber, i.e. the inside of the cylinder, and air or another oxygen-containing gas is admitted into the combustion chamber. The gas may be pre-compressed and / or may be doped with additives, e.g. fuel, nitrogen or other gases, liquids or solids. The fluid communication may be effected, for example, by opening at least one valve and / or by moving a piston and thus opening at least one flow passage opening. Thus, in the case of opening a valve, the admission phase begins with the start of the valve opening and ends with the end of the valve closing. The same applies to the opening of a flow passage opening due to an action.

[0014] The primary ignition is used to apply a force to the piston to drive it towards bottom dead centre when it is switched on and in operation. Typically, the primary ignition is performed at or at least close to top dead centre.

[0015] The internal combustion engine for the method described above is usually used for the operation of a motor vehicle, in particular for propelling said vehicle.

[0016] In the switched-on operating state, the engine is normally operated to provide torque for, for example, a vehicle, in particular for the movement of said vehicle, and thus refers to the normal operation of an internal combustion engine, in which fuel is continuously combusted and the piston is periodically moved from top dead center to bottom dead center or vice versa.

[0017] When the internal combustion engine is transferred from a switched-on operating situation to a stationary state, i.e. a switched-off state, such as, for example, stopping the vehicle, a switch-off process is performed in which, leaving the switched-on operating state, the internal combustion engine ceases to provide the relevant torque for the movement. Typically, the exact progression of the switch-off process is defined by the engine control program, which introduces the switch-off process, for example upon receiving a corresponding user request. During this process, the usual injection and combustion in the process of primary ignition of fuel to generate torque is terminated, since it is no longer required. The piston can perform several or partial revolutions before coming to a standstill. That is to say, the piston moves at least partially through the individual phases, such as the inlet phase or the outlet phase, even if all actively controlled actions, such as primary injection or primary ignition, are no longer performed. Typically, however, the fluid communication with the inlet and outlet channels is performed by mechanical control of valves when moving through the inlet and outlet phases or by opening fluid openings during the switch-off process.

[0018] In the switched-on operating state of the internal combustion engine, during the exhaust phase, the exhaust gases are led out of the cylinder, and the residual fuel is preferably injected and ignited from the beginning of the exhaust phase, preferably during the exhaust phase, particularly preferably in the first half of the exhaust phase, thereby allowing the burnt gases to escape from the combustion chamber immediately after the secondary ignition and preventing a pressure increase in the combustion chamber during the secondary ignition, which would undesirably affect the piston movement. It is also possible for the residual fuel to be injected and preferably also ignited at least 10 crank angles before the end of the exhaust phase, preferably at least 20 crank angles before the end of the exhaust phase.

[0019] The exhaust phase is a phase in which at least one outlet passage is in fluid communication with the combustion chamber, i.e. the cylinder interior, and exhaust gases can flow out of the combustion chamber. The fluid communication can be achieved, for example, by opening at least one valve and / or by moving the piston and thus opening at least one flow opening. Thus, when opening the valve, the exhaust phase begins with the start of the valve opening.

[0020] The exhaust and intake phases can overlap or the intake phase can even intersect with the exhaust phase, this is particularly possible in two-stroke operation, but also in four-stroke operation.

[0021] By early, we mean early in time: performing the injection early ensures that there is enough space in the cylinder to obtain ignition without significantly affecting the piston motion.

[0022] In a preferred embodiment, the ignition of the residual fuel is performed at most 20 crank angles after the start of the injection of the residual fuel, preferably at most 10 crank angles after the start of the injection of the residual fuel, which ensures that the residual fuel is distributed in the combustion chamber so that it can be mixed with the oxygen in the combustion chamber before it is ignited without losing too much time, which leads to the most complete combustion possible without affecting the movement of the piston.

[0023] Ignition of the residual fuel preferably occurs a minimum of 5 crank degrees after the start of injection.

[0024] The pressure regulator conducts fuel at a regulated pressure from the fuel tank through the distributor to the injectors, and during the switch-off process, the pressure regulator can terminate the fuel supply to the distributor, preferably before the remaining fuel is injected and ignited, thereby making it possible to precisely regulate the pressure of the fuel at the time of injection. During the switched-on operating state in the distributor, the pressure regulator sets a pressure which leads to the desired injection pressure into the cylinder. During the switch-off process, this pressure is reduced again by secondary injection and secondary ignition.

[0025] In this case, it is advantageous that during the switched-on operating state, the pressure of the fuel is reduced by the pressure regulator. This means that there is a higher pressure upstream of the pressure regulator than downstream of the pressure regulator, i.e. the pressure regulator reduces the pressure in the fuel flow direction. In other words, the pressure regulator reduces the pressure of the fuel during operation, so that the pressure in the fuel tank is higher than the pressure in the distributor. It is thus possible to store the fuel under high pressure with a simple pressure regulator. This allows optimal regulation of the pressure at the injector while still achieving an efficient and space-saving solution.

[0026] In this case, it is also advantageous for the fuel present in the distributor and / or injector to be injected and ignited in at least one cylinder of the internal combustion engine after the primary ignition and before the start of the subsequent admission phase during the switch-off process of the internal combustion engine, so that the pressure of the fuel present in the injector or distributor is reduced.

[0027] In particular, when the internal combustion engine is operated in four-stroke operation, it is advantageous that in the switched-on operating state, an oxygen-containing gas, preferably air, is introduced into the cylinder during the intake stroke, and fuel is passed into the cylinder, and during the switch-off step, the remaining fuel is injected and ignited into at least one cylinder of the internal combustion engine before the start of the intake stroke. The start of the intake stroke usually takes place in the region of top dead center and usually ends in the region of bottom dead center. The intake phase thus corresponds to the intake stroke in four-stroke operation.

[0028] In four-stroke operation when the internal combustion engine is switched on and in operation the gases are preferably ignited in the course of a primary ignition in one combustion stroke.

[0029] The combustion stroke is the stroke in which normal ignition occurs that drives the cylinder toward bottom dead center. Typically, the combustion stroke begins at 0 degrees crank angle, i.e., top dead center, and ends at 180 degrees, i.e., bottom dead center.

[0030] The exhaust gases may be discharged from the cylinders at the beginning or during the exhaust stroke in the switched-on operating state so that during the switch-off process the remaining fuel is injected and ignited into at least one cylinder of the internal combustion engine before the end of the exhaust stroke, thereby ensuring that the combustion chambers are again ready for primary ignition at the subsequent new start by also completely discharging the exhaust gases resulting from the secondary ignition.

[0031] The exhaust stroke is typically the stroke immediately following the combustion stroke during which the gases combusted in the combustion chamber are discharged. The exhaust stroke preferably begins at 180 degrees crank angle, i.e., bottom dead center, and ends at 360 degrees, i.e., top dead center. Typically, at least one discharge valve is opened during the exhaust stroke to provide fluid communication between the combustion chamber and one discharge passage to allow gases to escape through the discharge valve.

[0032] It is furthermore advantageous for the remaining fuel to be injected and ignited during the switch-off process at least 30 crank angle degrees before the start of the exhaust stroke, preferably at least 20 crank angle degrees before the start of the exhaust stroke, thereby providing sufficient time and space for as complete deloading of the injector as possible while still allowing a sufficient interval until the last primary ignition.

[0033] The internal combustion engine may also be operated in two-stroke operation.

[0034] In this case, it is possible that in the switched-on operating state of the internal combustion engine, exhaust gases are led out of the cylinder during the exhaust phase, and the injection of the remaining fuel during the switch-off process begins at least 15 crank angles before the start of the exhaust phase, preferably at the earliest 5 crank angles before the start of the exhaust phase, particularly preferably after the start of the exhaust phase. Although less time is available for ventilation of the injector in two-stroke operation, such a selection of the injection time nevertheless allows sufficient ventilation without influencing the piston movement.

[0035] The final ignition of a cylinder during operation of an internal combustion engine, in which residual fuel is injected and ignited during the switch-off process, is preferably carried out with a stoichiometric ignition mixture, i.e. an ignition mixture in which there is more air than is required to completely combust the fuel, i.e. a lean ignition mixture.

[0036] If several cylinders are provided, it is preferred to select for injection and ignition of the residual fuel at least one cylinder which at the beginning of the switch-off process is exactly in the aforementioned possible region for injection and ignition of the residual fuel and / or which is located just before said region, thereby enabling the pressure to be reduced as soon as possible after the switch-off signal.

[0037] It is particularly preferred to select at least one cylinder for the injection and ignition of the residual fuel which is exactly in the aforementioned possible region for the injection and ignition of the residual fuel immediately after the end of the fuel supply to the injector and / or which is located just before said region, so that it is possible to keep the switching process as short as possible and to reduce the pressure applied to the injector to a minimum.

[0038] The invention will now be described with reference to the drawings, in which: FIG. [Brief description of the drawings]

[0039] [Figure 1] 1 shows a schematic structure of a fuel pipe of an internal combustion engine for carrying out the method according to the invention in a first embodiment; [Figure 2a] Schematic diagram of the piston position in a cylinder of an internal combustion engine during implementation of the method according to the invention in a second embodiment as a function of the crank angle in four-stroke operation. [Figure 2b] 5 is a schematic diagram of the piston position in a cylinder of an internal combustion engine during implementation of the method according to the invention in a third embodiment as a function of the crank angle in two-stroke operation; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] In Fig. 1 a fuel supply system for an internal combustion engine having six cylinders is diagrammatically shown. Fuel is stored under high pressure in a gas tank 16. A pipe 11 connects the gas tank 16 to a pressure regulator 12 which, during switched-on operation of the internal combustion engine, conducts the fuel into a distributor 13 which is connected to the pressure regulator and which regulates the pressure of the supplied fuel. The pressure regulator 12 can be configured, for example, as an adjustable valve.

[0041] The distributor 13 is connected to six injectors 14, each assigned to one cylinder. It is also possible that at least two injectors 14 are assigned to at least one cylinder. During switched-on operation, via the pressure regulator 12 it is possible to regulate the pressure that the fuel exerts on the injectors 14 and thus the pressure with which the fuel enters the cylinder during injection.

[0042] In FIG. 2a, the piston position y in the cylinder of an internal combustion engine between top dead center and bottom dead center is shown as a function of the crank angle x of the crankshaft. At a crank angle of 0 degrees, the cylinder is at top dead center. In the region of top dead center, preferably at top dead center, a primary ignition 1 is performed, which drives the piston downwards by igniting the mixture of air and fuel previously introduced and compressed by the primary ignition. A combustion stroke 2 extending from 0 degrees to a crank angle of 180 degrees is followed by an exhaust stroke 3, during which the discharge valve of the cylinder is opened so that the burnt gases can escape. Meanwhile, the piston again moves towards top dead center 4 by 360 degrees, at which point no primary ignition is performed. At this point, the first rotation of the crankshaft and the exhaust stroke 3 ends, with the discharge valve closing. At the same time, the inlet valve opens so that preferably compressed air can enter the cylinder, and the piston again moves towards bottom dead center 5 in the course of a second rotation. At this point, the inlet valve closes again and the intake stroke 6, which stretches from the beginning of the inlet valve opening to the end of its closure, is completed. During the intake stroke 6, fuel injection by the injector 14 also takes place in switched-on operation. The intake stroke 6 is followed by a compression stroke 7, which stretches from bottom dead center to top dead center, at which point the next primary ignition and thus the next combustion stroke begins.

[0043] During the switch-off process, the primary ignition and injection of fuel are terminated so that the piston is no longer pushed down in the combustion stroke. Shortly thereafter, the piston moves several times due to the thrust force, which causes the valve to open and close accordingly. In addition, the pressure regulator 12 is also closed during the switch-off process.

[0044] As soon as the regulator is closed, a cylinder that is just in the combustion stroke and / or just in the window 8 is selected and, during the window 8, the residual fuel between the regulator 12 and the injector 14 is injected into the cylinder. This secondary injection reduces the pressure in the distributor 13.

[0045] The window 8 for injecting the residual fuel starts in this embodiment 30 degrees, i.e. 150 degrees of crank angle, before the start of the exhaust stroke during the last combustion stroke of the cylinder, which ends with the closing of the discharge valve and thus the end of the exhaust stroke 3. It is preferred that the ignition of the residual fuel is carried out 20 degrees, or preferably 10 degrees, after the injection of the residual fuel, so that the fuel can be distributed in the cylinder chamber. In this case, it is advantageous for the injection to be carried out at the latest 20 degrees of crank angle, preferably 10 degrees of crank angle, before the end of the exhaust stroke 3.

[0046] In figure 2b, the position of a piston between top and bottom dead centre in a cylinder of an internal combustion engine as a function of the crank angle of the piston is shown in another embodiment similar to that of figure 2a, so that only the most important differences will be described here and identical features will be given the same reference numerals.

[0047] The internal combustion engine illustrated in Fig. 2b is operated with cross-flow scavenging in two-stroke operation. Primary ignition 1 is performed at top dead center, i.e. at 0 degrees crank angle. During the downward movement of the piston towards bottom dead center (at 180 degrees), it opens an opening so that fluid communication is established between the discharge passage in the cylinder and the combustion chamber of that cylinder. This is illustrated by point 9a. From this point on, the exhaust phase 8 begins, during which the burnt gases can escape from the combustion chamber.

[0048] In the course of further downward movement of the piston, it further opens the opening, so that it creates a fluid communication between the inlet passage and the combustion chamber, preferably in the crankcase, by which the pre-compressed air can reach the combustion chamber, which point is illustrated as point 10a and represents the beginning of the inlet phase 10, during which fresh air can enter the combustion chamber.

[0049] Thus, after the piston has passed bottom dead center, it first ends the inlet phase 10 by terminating the fluid communication to the inlet passage (point 10b) and then the outlet passage is closed (point 9b) to end the exhaust phase 9. After the piston has again reached top dead center, the next primary ignition 1' is initiated in switched-on operation.

[0050] The introduction of the switch-off step is carried out as explained in Fig. 2a. As soon as the regulator 12 is closed, the residual fuel between the regulator 12 and the injector 14 is injected just between the primary ignition 1 and the window 8 and / or into the cylinders present in the window 8. This secondary injection reduces the pressure in the distributor 13. In this embodiment, the window 8 starts at 15 crank angle degrees before the start of the exhaust phase 9 (point 9a) and ends with the start of the inlet phase 10 (point 10a).

Claims

1. 1. A method for operating a gas-powered internal combustion engine, in which during an inlet phase (9) in a switched-on operating state of the internal combustion engine, an oxygen-containing gas, preferably air, is introduced into at least one cylinder for combustion, and fuel is conducted to at least one injector (14) and injected from said injector (14) into said cylinder in the course of a primary injection and ignited at said point in the course of a primary ignition (1, 1'), characterized in that during a switch-off step of the internal combustion engine, the supply of fuel to said injector (14) is terminated and residual fuel in the region of said injector (14) is injected into at least one cylinder of the internal combustion engine after the primary ignition (1, 1') and before the start of the subsequent inlet phase (9) in the course of a secondary injection and ignited at said point in the course of a secondary ignition.

2. 2. The method according to claim 1, characterized in that in a switched-on operating state of the internal combustion engine, exhaust gases are led out of the cylinder during an exhaust phase (10) and, during the switch-off step, the residual fuel is injected and ignited from the start of the exhaust phase (10), preferably during the exhaust phase (10), particularly preferably in the first half of the exhaust phase (10).

3. 3. The method according to claim 1 or 2, characterized in that the ignition of the residual fuel is performed at most 20 crank angles after the start of the injection of the residual fuel, preferably at most 10 crank angles after the start of the injection of the residual fuel.

4. 4. The method according to claim 1, characterized in that a pressure regulator (12) conducts fuel at a regulated pressure from a fuel tank (16) via a distributor (13) to a number of injectors, and during the switch-off step, the pressure regulator (12) terminates the fuel supply to the distributor (13), preferably before the residual fuel is injected and ignited.

5. 5. The method according to claim 4, characterized in that during the switch-off process of the internal combustion engine, the fuel present inside the distributor (13) and / or the injector is injected and ignited into at least one cylinder of the internal combustion engine after the primary ignition (1, 1') and before the start of the subsequent admission phase (9).

6. 6. The method according to claim 1, wherein the internal combustion engine is operated in four-stroke operation, and wherein in the switched-on operating state, an oxygen-containing gas, preferably air, is introduced into the cylinders during the intake stroke (2), fuel is conducted into the cylinders, and during the switch-off step, the residual fuel is injected and ignited into at least one cylinder of the internal combustion engine before the start of the intake stroke (2).

7. 7. The method according to claim 6, characterized in that in the switched-on operating state, exhaust gases are led out of the cylinder at the beginning or during the exhaust stroke (3) and during the switch-off step the residual fuel is injected and ignited into at least one cylinder of the internal combustion engine before the end of the exhaust stroke (3).

8. 8. A method according to claim 6 or 7, characterized in that the residual fuel is injected and ignited during the switch-off step at least 30 crank angle degrees before the start of the exhaust stroke (3), preferably at least 20 crank angle degrees before the start of the exhaust stroke (3).

9. 6. A method according to any one of claims 1 to 5, characterised in that the internal combustion engine is operated in two-stroke operation.

10. 9. The method according to claim 8, characterized in that in the switched-on operating state of the internal combustion engine, exhaust gases are led out of the cylinder during an exhaust phase (3) and the injection of the residual fuel during the switch-off step is started at least 15 crank angle degrees before the start of the exhaust phase (3), preferably at the earliest at least 5 crank angle degrees before the start of the exhaust phase (3), particularly preferably at least from the start of the exhaust phase (3).

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