Method for operating an internal combustion engine

Abstract

The invention relates to a method for operating an internal combustion engine (2). The method comprises the steps of: detecting a load requested by the internal combustion engine (2); determining an operating situation of a system (1) comprising the internal combustion engine (2); selecting an operating mode from a set of predefined operating modes based on the determined operating situation, wherein each of the operating modes specifies a fuel injection characteristic into at least one combustion chamber of the internal combustion engine (2) for a plurality of possible operating points; and operating the internal combustion engine (2) by injecting gaseous fuel into the at least one combustion chamber according to the fuel injection characteristic specified by the selected operating mode at the requested load. The invention further relates to a system (1) with an internal combustion engine (2).

Description

The invention relates to a method for operating an internal combustion engine. The invention further relates to a system having an internal combustion engine.DE 10 2022 118 732 A1 discloses a hydrogen injection system, an internal combustion engine which can be operated with hydrogen and a method for controlling a hydrogen injection system.The method according to the invention for operating an internal combustion engine comprises the following steps:detecting a load demanded by the internal combustion engine;determining an operating situation of a system comprising the internal combustion engine;selecting an operating mode from a set of predefined operating modes on the basis of the ascertained operating situation, each of the operating modes defining a fuel introduction characteristic in at least one combustion chamber of the internal combustion engine for a plurality of possible operating points; andoperating the internal combustion engine by injecting gaseous fuel into the at least one combustion chamber according to the fuel introduction characteristic predefined by the selected operating mode at the required load.The gaseous fuel is, for example, hydrogen.The method can be used to operate an internal combustion engine of a vehicle, a generator or another comparable system.The internal combustion engine is, for example, a conventional internal combustion engine which is designed as reciprocating piston engines according to the Otto principle and can be operated with gaseous fuel, for example hydrogen.The load requested by the internal combustion engine is requested by a driver by operating an accelerator pedal, for example. Preferably, a load demand gradient is detected simultaneously, i.e. how fast the demanded load changes.The operating situation of the system which is determined characterizes, for example, a state of charge and / or pressure of a fuel accumulator of the system or a load jump, that is to say a sudden change in the requested load.Because an operating mode for operating the internal combustion engine is selected and set as a function of the operating situation, the internal combustion engine can be operated with a fuel input characteristic that is optimum for the respective operating situation. In a simplified form, the times and / or time periods in which fuel is injected into the at least one combustion chamber of the internal combustion engine can be adapted to the respective operating situation in order to achieve operating situation-specific goals. If, for example, the state of charge and / or pressure of the fuel accumulator is low, the remaining range can be maximized by selecting the appropriate operating mode and correspondingly adapting the fuel injection. In the event of a load jump, on the other hand, the time until the requested target load is reached can be minimized by selecting the appropriate operating mode and correspondingly adapting the fuel injection.In a preferred embodiment, the set of predefined operating modes comprises at least the following operating modes:a direct injection mode which specifies that fuel is injected into the at least one combustion chamber at each of the possible operating points while an inlet valve of the combustion chamber is closed;a pilot valve closure injection mode which specifies that fuel is injected into the at least one combustion chamber at each of the possible operating points while the inlet valve of the combustion chamber is at least partially open; anda dual operating mode which specifies for at least one of the possible operating points that fuel is injected into the at least one combustion chamber while the inlet valve of the combustion chamber is at least partially opened and which specifies for at least one other of the possible operating points that fuel is injected into the at least one combustion chamber while the inlet valve of the combustion chamber is closed.The direct injection mode preferably specifies a fuel injection characteristic into the at least one combustion chamber of the internal combustion engine, which corresponds to a direct injection (DI) known from conventional diesel and spark ignition engines. An advantage of this type of injection is that very high power densities can be achieved.The pre-valve closure injection mode preferably specifies a fuel injection characteristic which is comparable to a suction pipe injection (PFI: Port Fuel Injection). However, the injection itself does not have to be carried out using a conventional PFI injection nozzle. Injection directly into the respective combustion chamber is also possible. In contrast to direct injection (DI), however, the inlet valve is at least partially open when fuel is introduced into the combustion chamber. Expressed in simplified form, the fuel introduction into the respective combustion chamber therefore takes place earlier in relation to the ignition time in comparison with the direct injection mode. This in turn improves the mixture formation and the efficiency of the fuel usage overall. Hereinafter, this type of injection is also referred to simply as PFI injection.The dual mode of operation, expressed in simplified terms, represents a combination of the direct injection mode and the pre-valve closure injection mode and combines their respective advantages.By the three said operating modes a selection of possible fuel injection characteristics is provided which can be applied in numerous different operating situations. Nevertheless, the operating modes mentioned should of course not be understood as restrictive.In one variant of the method, a state of charge of at least one fuel accumulator, for example a hydrogen accumulator, of the system is determined as the operating situation, and the operating mode is selected as a function of the determined state of charge.If the ascertained state of charge is below a predefined charging threshold value, the pre-valve closure injection mode is preferably selected as the operating mode. As a result, the remaining fuel can be used very efficiently. If the method is used, for example, in a hydrogen-operated vehicle, a longer range can be achieved in comparison with the direct injection mode with the remaining hydrogen.In a further variant of the method, a load demand gradient is detected as the operating situation and the operating mode is selected as a function of the detected load demand gradient.If the load demand gradient determined is above a predefined gradient threshold value, the direct injection mode is preferably selected as the operating mode. In other words, in the event of a strong increase in the required load, a direct injection of fuel into the at least one combustion chamber of the internal combustion engine is selected and set in a short time. Due to the high attainable power densities in this type of injection, the power provided by the internal combustion engine can be increased within a short time and the target value of the required load can be quickly reached.In a further variant embodiment of the method, it is provided that a check is made as to whether a requested load corresponds to a load applied by the internal combustion engine, and that the selection of the operating mode takes place as a function of the result of the check.If the check reveals that the load applied by the internal combustion engine corresponds to the requested load, the dual operating mode is preferably selected as the operating mode. As a result, the internal combustion engine can be operated in normal operation with the type of injection which is advantageous for the current operating point.During current operation in a low-load range, for example at less than 30% of the full load of the internal combustion engine, the fuel injection can take place while the inlet valve of the combustion chamber is at least partially opened (PFI injection). During current operation in a high load range, for example at more than 80% of the full load of the internal combustion engine, the fuel injection can take place while the inlet valve of the combustion chamber is closed (DI injection). During current operation between 30% and 80% of the full load, it may be provided that the fuel injection is started while the inlet valve of the combustion chamber is at least partially opened and is only ended after the inlet valve is already fully closed. Expressed in simplified terms, a mixed mode (PFI / DI injection) can thus be provided in a medium-load range of the internal combustion engine.In a further variant of the method, it is provided that, at least in one operating mode from the predefined set of operating modes, a fuel injection (post injection) takes place for at least one operating point.For example, in the direct injection mode, a fuel reinjection can be provided for at least one of the operating points, preferably for all operating points.Alternatively or additionally, the fuel injection can also be adjusted as a function of the aforementioned load demand gradient. Fuel injection takes place, for example, when the load demand gradient is above a predefined gradient threshold value.By means of the fuel injection, the required load can be provided even more quickly by the internal combustion engine.Furthermore, it can be provided that when the operating situation is ascertained, a check is made as to whether the internal combustion engine is shut off or is shut off, and that the pilot valve closure injection mode is selected as the operating mode if the check reveals that the internal combustion engine is shut off or is shut off. As a result, the gas pressure acting on the injection nozzle and thus also the leakage of fuel, for example hydrogen, into the respective combustion chamber after the internal combustion engine has been shut down can be reduced.The system according to the invention comprises an internal combustion engine and a fuel injection device for injecting fuel into the internal combustion engine, wherein the fuel injection device comprises at least one injection nozzle which is designed to inject fuel into a combustion chamber of the internal combustion engine when an inlet valve of the combustion chamber is closed, and having a control unit which is designed to carry out a method according to the invention.The advantages mentioned for the method according to the invention apply in the same way to the system according to the invention.Preferred exemplary embodiments are explained in more detail with reference to the following figures. This showsFIG. 1 shows a schematic representation of an exemplary embodiment of a system according to the invention with an internal combustion engine and a fuel injection device;FIG. 2 is a schematic illustration of the internal combustion engine and fuel injection device of the system of FIG. 1 ;FIG. 3 is a schematic illustration of an alternative embodiment of the internal combustion engine and the fuel injection device;FIG. 4 shows a diagram schematically showing a) a DI injection; b) a PFI injection; and c) a superimposed or dual PFI / DI injection into a combustion chamber of the internal combustion engine of the system from FIG. 1 ;FIG. 5 shows a characteristic diagram of a dual operating mode which, for a plurality of possible operating points, specifies in each case a fuel introduction characteristic into a combustion chamber of the internal combustion engine of the system from FIG. 1 ;FIG. 6 shows a characteristic diagram of a direct injection mode which, for a plurality of possible operating points, specifies in each case a fuel introduction characteristic into a combustion chamber of the internal combustion engine of the system from FIG. 1 ;FIG. 7 shows a characteristic diagram of a pilot valve closure injection mode which, for a plurality of possible operating points, specifies in each case a fuel introduction characteristic into a combustion chamber of the internal combustion engine of the system from FIG. 1 ; andFIG. 8 is a diagram schematically showing a DI injection with fuel reinjection into a combustion chamber of the internal combustion engine of the system from FIG. 1.The system 1 shown in FIG. 1 is a vehicle and comprises an internal combustion engine 2 which is designed to be operated with fuel, for example with hydrogen.The system 1 further comprises a fuel storage device 3, a fuel injection device 4 which during operation draws fuel from the fuel storage device 3 and supplies it to the internal combustion engine 2, and a control device 5 for controlling the fuel supply.The internal combustion engine 2 and the fuel injection device 4 are shown in more detail in FIG. 2.The internal combustion engine 2 is designed as a reciprocating piston engine and has four combustion chambers 6. Furthermore, the internal combustion engine 2 comprises an intake tract 7 with a throttle valve 8, by means of which the supply air can be regulated. Each of the combustion chambers 6 comprises an inlet valve and an outlet valve. Since such valves are known from the prior art, their illustration has been omitted in FIG. 2 for reasons of clarity.The fuel injection device 4 comprises a direct injection device 9 having four direct injection nozzles 10 which are assigned to the respective combustion chambers 6 and are designed to directly jet fuel into the respective combustion chambers 6. The direct injection device 9 is designed as an accumulator injection device and has a common distributor pipe 11 for supplying fuel to the four direct injection nozzles 10.Furthermore, the fuel injection device 4 comprises an intake duct injection nozzle 12 for injecting fuel into the intake tract 7 of the internal combustion engine 2.Alternatively, a plurality of intake channel injection nozzles 12 can also be provided, wherein one of the intake channel injection nozzles 12 is assigned to each of the combustion chambers 6.The fuel injection device 4 shown in FIG. 2 comprises a distributor pressure regulator 13 for regulating the pressure in the common distributor pipe 11 and a low-pressure regulator 14 for regulating the pressure of the intake duct injection nozzle 12.Furthermore, the fuel injection device 4 comprises a shut-off valve 15 for shutting off the fuel supply and a pressure relief valve 16, with which fuel can be discharged in a controlled manner at too high a pressure in the fuel injection device 4.FIG. 3 shows a schematic illustration of an internal combustion engine 2 and a fuel injection device 4 in an alternative embodiment variant, which can be used for operating the system 1 instead of the arrangement shown in FIG. 2. The internal combustion engine 2 and the fuel injection device 4 from FIG. 3 substantially correspond to those from FIG. 2, so that only the differences will be discussed below. The same reference numerals are used for identical or functionally identical components.In contrast to the fuel injection device 4 shown in FIG. 2, the variant shown in FIG. 3 does not have a suction channel injection nozzle 12. The fuel is therefore injected into the respective combustion chambers 6 exclusively by the direct injection device 9 or the direct injection nozzles 10.The control unit 5 of the system 1 is designed and configured to carry out a method according to the invention for operating the internal combustion engine 2. An exemplary embodiment of the method is explained below.In a first step of the method, control unit 5 detects a load requested by internal combustion engine 2. This can be done, for example, by evaluating an accelerator pedal position. At the same time, a load demand gradient is also detected, i.e. how fast the demanded load changes.In a second step of the method, control unit 5 ascertains at least one operating situation of system 1, for example, a charge state of fuel accumulator 3.Alternatively or additionally, the control device 5 can determine in the second step of the method whether a load jump is present in the requested load. For this purpose, the control device 5 compares the load demand gradient with a predefined gradient threshold value.In a third step of the method, control unit 5 selects an operating mode from a set of predefined operating modes on the basis of the ascertained operating situation.Each of the operating modes specifies a fuel introduction characteristic 17 in each case for a plurality of possible operating points of the internal combustion engine 2 in the respective combustion chambers 6 of the internal combustion engine 2.For the purpose of illustration, FIG. 4 schematically shows various possible fuel introduction characteristics 17 over the crank angle, that is to say as a function of the piston position in the respective combustion chambers 6, in a diagram.The diagram shows, in addition to the fuel introduction characteristics 17, an inlet valve opening state 18 and an outlet valve opening state 19.FIG. 4 a) shows a DI injection. The fuel is introduced into the respective combustion chambers 6 with the inlet valve fully closed by means of the direct injection nozzles 10.FIG. 4 b ) shows a PFI injection. The fuel is introduced into the respective combustion chambers 6 when the inlet valve is at least partially open. For this purpose, the suction channel injection nozzle 12 can be used. Alternatively or additionally, the fuel can also be injected into the respective combustion chambers 6 by means of the direct injection nozzles 10 during the PFI injection, in particular if, as in the alternative embodiment variant shown in FIG. 3, no suction duct injection nozzle 12 is provided.FIG. 4 c ) shows a superimposed or dual PFI / DI injection. In this type of injection, the introduction of fuel into the respective combustion chambers 6 is started, while the respective inlet valves are at least partially opened. The fuel introduction is only ended after the closing of the respective inlet valves.In the exemplary embodiment, the set of predefined operating modes from which the operating mode to be set is selected comprises at least the following operating modes:a direct injection mode which specifies that fuel is injected into the respective combustion chambers 6 at each of the possible operating points, while the inlet valves assigned to the combustion chambers 6 are closed;a pilot valve closure injection mode which specifies that fuel is injected into the respective combustion chambers 6 at each of the possible operating points, while the inlet valves assigned to the combustion chambers 6 are at least partially opened; anda dual operating mode which specifies for at least one of the possible operating points that fuel is injected into the respective combustion chambers 6, while the inlet valves assigned to the combustion chambers 6 are at least partially open, and which specifies for at least one further of the possible operating points that fuel is injected into the respective combustion chambers 6, while the inlet valves assigned to the combustion chambers 6 are closed.The operating modes are predefined, for example, in the form of characteristic fields which the control device 5 can access.FIG. 5 shows a first simplified characteristic diagram in tabular form, which characterizes the dual operating mode.Each of the entries in the tabular characteristic map describes a possible operating point of the internal combustion engine 2 in the dual operating mode. The operating points are characterized in each case by the current rotational speed and the mean pressure of the internal combustion engine 2 (BMEP-Brake Mean Effective Pressure) corresponding to the load.The characteristic map specifies a fuel entry characteristic 17 for each of the operating points. In the table, this is given simply as a percentage numerical value.The table value "100" corresponds to a complete PFI injection, as shown in FIG. 4 b). The fuel is therefore introduced into the respective combustion chambers 6 when the inlet valve is at least partially open.The table value "0" corresponds to a complete DI injection, as shown in FIG. 4 a). The fuel is therefore introduced into the respective combustion chambers 6 when the inlet valve is closed.Table values which lie in the range between "0" and "100" characterize the PFI proportion in the case of superimposed or dual PFI / DI injection, as shown in FIG. 4 c ).In Fig. 6, a second simplified map is shown in tabular form characterizing the direct injection mode. In this operating mode, the table value "0" is assigned to each of the possible operating points. Thus, at all possible operating points, a DI injection always takes place.FIG. 7 shows a third simplified characteristic diagram in tabular form, which characterizes the pre-valve closure injection mode. In this operating mode, the table entry "0" is not assigned to any of the possible operating points. Pure DI injection is therefore not provided at any of the possible operating points in this operating mode. In other words, at each of the operating points, a fuel injection takes place with the inlet valve at least partially open. At very high requested loads or medium pressures, as shown in FIG. 7, a PFI / DI injection can also be provided.In a fourth step of the method, the control unit 5 operates the internal combustion engine 2 by injecting fuel into the respective combustion chambers 6 in accordance with the fuel introduction characteristic 17 predefined by the selected operating mode at the required load and the current rotational speed.The selection and setting of an operating mode matching the respective operating situation from the predefined set of operating modes is explained below by way of example.The internal combustion engine 2 of the system 1 shown in FIG. 1 is operated as standard in the dual operating mode. Depending on the required load and the current rotational speed of the internal combustion engine 2, the fuel is introduced by a PFI injection, a PFI / DI injection or a pure DI injection.During operation, fuel is consumed and the state of charge of the fuel accumulator 3 falls.If the state of charge of the fuel accumulator 3 falls below a predefined charging threshold value, for example 5%, the control unit 5 selects the pre-valve closure injection mode in the third step of the method. In this operating mode, the fuel injection is effected at least partially by PFI injection at each of the possible operating points. Pure DI injection is avoided and the remaining range of the system 1 designed as a vehicle that can be achieved with the remaining fuel is thereby increased.If, on the other hand, the state of charge of the fuel accumulator 3 is above the predefined charging threshold value and at the same time the load demand gradient is above a predefined gradient threshold value, the control device 5 selects the direct injection mode in the third step of the method. In other words, a change from the dual operating mode to the direct injection mode thus takes place when a load jump is detected in the requested load. An arrow is drawn in FIG. 5, which represents such a load jump of the requested load at a current rotational speed of 1000 rpm.The fuel injection is effected by pure DI injection on account of the operating mode change into the direct injection mode, as shown in FIG. 6. As a result, particularly high power densities can be achieved and the required load can be provided in a comparatively short time.During operation of the system 1, the control unit 5 checks, continuously or at regular intervals, whether the required load corresponds to the load provided by the internal combustion engine 2.If, for example, after a load jump and operation of the internal combustion engine 2 in the direct injection mode, the check reveals that the requested load is provided completely or at least approximately completely by the internal combustion engine 2, the standard dual operating mode can be selected and set again for the further operation. In the event of a further load jump, the control device 5 can then again initiate a change to the direct injection mode.In the exemplary embodiment, the control unit 5 also checks, when detecting the operating situation, whether the internal combustion engine 2 is shut off or is shut off.When the check reveals that the internal combustion engine 2 is shut off or is shut off, the control device 5 selects the pilot valve closure injection mode as the operating mode.Since no DI injection is provided in this operating mode, the gas pressure in the distributor pipe 11 can be lowered. As a result, the leakage of fuel through the direct injection nozzles 10 into the respective combustion chambers 6 and thus also the risk of misfires upon a renewed start of the internal combustion engine 2 can be reduced.FIG. 8 shows a further possible fuel introduction characteristic 17 over the crank angle, at which the fuel is injected into the combustion chambers 6 of the internal combustion engine 2 by a DI injection with a subsequent fuel post-injection 20.The fuel is therefore introduced analogously to the example explained with reference to FIG. 4 a), with the difference that additional fuel is injected subsequently.It can be provided that the fuel reinjection 20 is adjusted as a function of the aforementioned load demand gradient. Fuel is re-injected, for example, when the load demand gradient is above a predefined gradient threshold value.It is furthermore conceivable that in at least one operating mode from the predefined set of operating modes, a fuel reinjection 20 is provided for at least one of the possible operating points.For example, it can be provided that in the direct injection mode, a fuel reinjection 20 takes place at one, several or preferably all operating points.The fuel injection 20 makes it possible to provide the required load from the internal combustion engine 2 even quickly.Of course, the exemplary embodiments mentioned should not be understood as restrictive. A fuel injection 20 can also take place in the dual operating mode or in the pilot valve closure injection mode.In principle, the exemplary embodiment of the method according to the invention explained on the basis of the figures can also be used for operating internal combustion engines 2 that are not in-vehicle. For example, internal combustion engines 2 comprised by generators or other units can also be operated using the method.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2022 118 732 A1

[0002]

Claims

Method for operating an internal combustion engine (2), comprising the steps of: - detecting a load demanded by the internal combustion engine (2); - determining an operating situation of a system (1) which comprises the internal combustion engine (2); - selecting an operating mode from a set of predefined operating modes on the basis of the determined operating situation, wherein each of the operating modes specifies a fuel introduction characteristic (17) into at least one combustion chamber (6) of the internal combustion engine (2) for a plurality of possible operating points; and - operating the internal combustion engine (2) by injection of gaseous fuel into the at least one combustion chamber (6) in accordance with the fuel introduction characteristic (17) specified by the selected operating mode at the demanded load.Method according to Claim 1, wherein the set of predefined operating modes comprises at least the following operating modes: a direct injection mode which specifies that fuel is injected into the at least one combustion chamber (6) at each of the possible operating points while an inlet valve of the combustion chamber (6) is closed; a pilot valve closure injection mode which specifies that fuel is injected into the at least one combustion chamber (6) at each of the possible operating points while the inlet valve of the combustion chamber (6) is at least partially open; and a dual operating mode which specifies for at least one of the possible operating points that fuel is injected into the at least one combustion chamber (6) while the inlet valve of the combustion chamber (6) is at least partially open and which specifies for at least one further of the possible operating points that fuel is injected into the at least one combustion chamber (6) while the inlet valve of the combustion chamber (6) is closed.Method according to Claim 1 or 2, wherein a state of charge of at least one fuel store (3) of the system (1) is determined as the operating situation, and wherein the selection of the operating mode takes place as a function of the determined state of charge.Method according to Claim 2 in combination with Claim 3, wherein the pre-valve closure injection mode is selected as the operating mode if the ascertained state of charge is below a predefined charging threshold value.Method according to one of the preceding claims, wherein a load demand gradient is determined and wherein the selection of the operating mode takes place as a function of the determined load demand gradient.Method according to Claim 2 in combination with Claim 5, wherein the direct injection mode is selected as the operating mode if the load demand gradient determined is above a predefined gradient threshold value.Method according to one of the preceding claims, wherein it is checked whether a requested load corresponds to a load applied by the internal combustion engine (2), and wherein the selection of the operating mode takes place as a function of the result of the check.Method according to one of the preceding claims, wherein, in at least one operating mode from the predefined set of operating modes, a fuel reinjection 20 is provided for at least one of the possible operating points.Method according to one of the preceding claims, wherein when the operating situation is ascertained it is checked whether the internal combustion engine (2) is switched off or is switched off, and wherein the pre-valve closure injection mode is selected as the operating mode if the check reveals that the internal combustion engine (2) is switched off or is switched off.System comprising an internal combustion engine (2) and a fuel injection device (4) for injecting fuel into the internal combustion engine (2), wherein the fuel injection device (4) comprises at least one direct injection nozzle (10) which is designed to inject fuel into a combustion chamber (6) of the internal combustion engine (2) when an inlet valve of the combustion chamber (6) is closed, and having a control unit (5) which is designed to carry out a method according to one of Claims 1 to 9.

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