Method for operating an internal combustion engine, control device and computer program product

Abstract

In a method for operating an internal combustion engine (10) with gaseous fuel, in particular gaseous hydrogen, the fuel is injected directly and at least temporarily completely into the combustion chamber (12) with the inlet valve (20) closed, and exhaust gas flowing from the combustion chamber (12) drives a turbine (34) of an exhaust-gas turbocharger (30). It is proposed that at least a portion of the fuel quantity is injected into the combustion chamber (12) with the inlet valve (20) at least partially open, at least in certain operating conditions and depending on the rotational speed (n) of the exhaust-gas turbocharger (30).

Description

Technical Field

[0001] This invention relates to a method for operating an internal combustion engine, a control device, and a computer program product. Background Technology

[0002] DE 10 2021 210 001 A1 describes a method for operating an internal combustion engine that utilizes a gaseous fuel, such as hydrogen. The gaseous hydrogen is injected directly into the combustion chamber (DIInjection) or into the inlet passage (Port Fuel Injection), and the hydrogen-air mixture is ignited in the combustion chamber by an ignition device. The gaseous hydrogen enters a fuel accumulator line via a pressure regulator, the fuel accumulator line functioning similarly to that in an internal combustion engine with gasoline or diesel direct injection. Multiple fuel injectors are connected to the fuel accumulator line, which deliver the gaseous fuel to the combustion chamber. EP1 682 764B1 and FR 2 854 652 A1 also relate to internal combustion engines operating with gaseous fuel. Summary of the Invention

[0003] The task on which the invention is based is solved by a method, a control device, and a computer program product having the features of the parallel claims. Advantageous improvements are proposed in the dependent claims.

[0004] This invention enables protection of the exhaust gas turbocharger from exceeding its maximum permissible speed (“excess speed”) by intervening in the injection system of a turbocharged, particularly lean-operated, direct-injection hydrogen motor (“H2-DI-motor”). This danger arises in such internal combustion engines, especially within the rated power range. This invention achieves this by using low regulation delay and very directly preventing the exhaust gas turbocharger from exceeding its maximum permissible speed. This ultimately prevents damage to the exhaust gas turbocharger and consequently improves the lifespan and operational safety of the internal combustion engine.

[0005] This is based on the following considerations: gaseous hydrogen, in particular, offers the potential for CO2-free energy for both mobile and stationary applications. Internal combustion engines running on gaseous hydrogen allow for the reuse of existing technologies, preventing disruptive changes and resulting in more favorable manufacturing and maintenance costs. To ensure combustion stability and simultaneously limit nitrogen oxide emissions in such internal combustion engines, it is meaningful to operate them in lean-feed mode, i.e., with a high air-fuel ratio (the ratio of fresh air mass to fuel mass) or a high fill factor (fresh air mass +, if necessary, exhaust gas mass from the exhaust gas recirculation system, to fuel mass).

[0006] The injection of hydrogen, and therefore the supply of hydrogen to the combustion process, can occur not only before the combustion chamber ("Port Fuel Injection" or "PFI") but also directly and immediately into the cylinder ("Direct Injection"). When gaseous fuel is injected directly into the combustion chamber with a closed inlet valve, the volume of air drawn into the combustion chamber plus the exhaust gas recirculated if necessary is greater under similar boundary conditions than when hydrogen is injected before the combustion chamber with an open inlet valve (it goes without saying that the current embodiment applies not only to internal combustion engines with multiple inlet valves per combustion chamber but also to internal combustion engines with only a single inlet valve per combustion chamber; here and thereafter, the singular and plural forms of the term "inlet valve" are used synonymously). If injection occurs with an open inlet valve, a portion of the volume of the intake medium, consisting of air and, if necessary, exhaust gas recirculated, is replaced by the volume of the injected gaseous fuel, thereby reducing the fill factor. Therefore, gaseous fuel can be injected directly and at least temporarily into the combustion chamber of an internal combustion engine with the inlet valve completely closed, resulting in higher power density under the same boost pressure.

[0007] Specifically, a method is proposed for operating an internal combustion engine with gaseous fuel, particularly gaseous hydrogen. The internal combustion engine is typically of the known piston type, operating according to the 4-stroke principle. The engine typically comprises multiple cylinders, each with a combustion chamber, and each combustion chamber is typically equipped with at least one inlet valve, at least one outlet valve, a fuel injector, and at least one ignition device. In the method according to the invention, fuel is injected directly and at least temporarily into the combustion chamber with the valves completely closed, typically or in normal operation after the intake stroke. The fuel injector outlet is thus located within the combustion chamber. Exhaust gas flowing from the combustion chamber drives the turbine of an exhaust gas turbocharger. According to the invention, at least under certain operating conditions of the internal combustion engine and depending on the speed of the exhaust gas turbocharger, a portion of the fuel is injected into the combustion chamber with the inlet valve at least partially open.

[0008] Depending on the turbocharger's speed, typically at relatively high speeds, at least a portion, and if necessary, all, of the fuel is injected during the intake stroke with the inlet valve still open, unlike the typical method where fuel is injected with the inlet valve completely closed. The injected fuel thus occupies a portion of the combustion chamber volume, making it unusable for the intake fresh air (and, if necessary, exhaust gas in the exhaust gas recirculation section). This reduces the air-fuel ratio, or fill factor, correspondingly reducing the power density during combustion in the combustion chamber, and subsequently lowering the energy contained in the exhaust gas. Therefore, less energy is available for the turbine driving the turbocharger, thereby preventing the maximum permissible speed of the turbocharger from being exceeded.

[0009] In the improved design, when the exhaust gas turbocharger's speed reaches or exceeds a first limit, at least a portion or all of the fuel is injected into the combustion chamber with the inlet valve at least partially open. This is easily achievable in terms of control technology. However, as an alternative or additional solution, it is also possible to use a characteristic curve that depends on the exhaust gas turbocharger's speed, for example, controlling the proportion of the portion of fuel to the total fuel volume. Here, a filter can be used if necessary to improve the stability of the control.

[0010] To address this, the improved design incorporates a feature where, when the exhaust gas turbocharger's speed reaches or exceeds a first limit, the start of fuel injection is advanced to a point where the inlet valve is still at least partially open. This is also easily achievable technically. The inlet valve can therefore be closed during fuel injection into the combustion chamber, or the injection can occur while the inlet valve is fully open. However, as an alternative or additional solution, it is also conceivable that the injection is divided into multiple partial injections, for example, starting and ending one partial injection before the inlet valve closes, and starting another partial injection after the inlet valve has closed.

[0011] The improved design incorporates a method where, when the exhaust gas turbocharger's speed reaches or falls below a second limit, the amount of fuel injected is reduced while the inlet valve is at least partially open, or fuel injection is terminated while the inlet valve is at least partially open. This ensures that the measures according to the invention are only implemented when there is a risk of reaching or exceeding the exhaust gas turbocharger's maximum permissible speed. This guarantees combustion stability and achieves low nitrogen oxide emissions.

[0012] The improved scheme is characterized by a second limit value being smaller than the first limit value. This hysteresis helps prevent vibration or continuous switching.

[0013] The improved scheme sets up a system in which, under the defined operating conditions, the amount or a portion of fuel is injected with the inlet valve at least partially open, depending on the rotational speed of the exhaust gas turbocharger. These defined operating conditions are also specified by at least a predetermined fill factor. This avoids undesirable side effects of the method according to the invention, such as problems with combustion stability and increased nitrogen oxide emissions.

[0014] The present invention also relates to a control device having a processor and a memory, wherein a computer program product is stored in the memory, the computer program product including commands that, when the computer program product is executed by the control device, cause the control device to perform the methods of the above type.

[0015] The present invention also relates to a computer program product comprising commands that, when implemented by a microprocessor, cause the microprocessor to perform the methods of the above type. Attached Figure Description

[0016] Embodiments of the present invention will now be explained with reference to the accompanying drawings. The drawings show: Figure 1 A schematic diagram of an internal combustion engine is shown, which has multiple combustion chambers and inlet valves and fuel injectors associated with these combustion chambers; Figure 2 A graph is shown, in which the curve is plotted about the crankshaft angle. Figure 1 The opening stroke of the combustion chamber inlet valve of the internal combustion engine during the suction stroke and the opening state of the fuel injector in the combustion chamber; Figure 3 A graph is shown, plotting the rotational speed of the exhaust gas turbocharger over time; and Figure 4 It shows the method for running Figure 1 The flowchart of the method for developing an internal combustion engine. Detailed Implementation

[0017] Internal combustion engines Figure 1 Reference numeral 10 is used in the accompanying drawings. The internal combustion engine is a classic piston-four-stroke internal combustion engine, which, exemplarily, has five cylinders and five combustion chambers 12. Each combustion chamber 12 is assigned a fuel injector 14, which injects gaseous fuel, exemplarily hydrogen, directly into the combustion chamber 12 assigned to the gaseous fuel. The outlet of the fuel injector 14 is thus located directly in the combustion chamber 12. The fuel injector 14 is connected to a fuel accumulator 16, which is supplied with gaseous fuel by a fuel system (not shown further). The pressure in the fuel accumulator 16 is detected by a pressure sensor 18.

[0018] Air enters combustion chamber 12 through inlet valves 20 associated with each combustion chamber 12 (it goes without saying that the following embodiments apply not only to internal combustion engines 10 with multiple inlet valves 20 per combustion chamber 12 as currently present, but also to internal combustion engines with only one inlet valve per combustion chamber). An air manifold 22 is arranged upstream of the inlet valves 20, and a throttle valve 24 is arranged upstream of the air manifold. A turbocharger air cooler 26 and the compressor 28 of the exhaust gas turbocharger 30 are arranged upstream of the throttle valve 24. Combustion exhaust gas from combustion chamber 12 reaches the turbine 34 of the exhaust gas turbocharger 30 through outlet valve 31 and exhaust manifold 32. Sensor 35 detects the rotational speed of the exhaust gas turbocharger 30. An exhaust gas return line 36 branches off upstream of the turbine 34, and the exhaust gas return line is guided to the air manifold 22 through an exhaust gas return valve 38 and an exhaust gas return cooler 40.

[0019] The mixture of gaseous fuel and air present in the combustion chamber 12 is ignited by the ignition device 42. The piston of the internal combustion engine 10 (not shown) acts on the crankshaft 44 (shown only symbolically), the position and speed of which are detected by the crankshaft sensor 46.

[0020] The operation of the internal combustion engine 10 is controlled and regulated by a control device. A controller 48 is primarily part of this control device, which receives signals from numerous sensors within the internal combustion engine 10, such as pressure sensor 18, speed sensor 35, and crankshaft sensor 46. The controller 48 operates different actuators of the internal combustion engine 10, primarily controlling the fuel injector 14. For this purpose, the controller 48 mainly comprises a processor and a memory. The memory stores a computer program product with program code, including commands that, when implemented by the control device, cause the control device to perform different methods, primarily as described below. Figures 2-4 The method explained.

[0021] exist Figure 2 The vertical axis on the left represents the open position H1 of the inlet valve 20 of the combustion chamber 12, which is considered here as an example. The corresponding curve is... Figure 2 The figure is marked with reference numeral 50. The vertical axis on the right represents the open state H2 of the fuel injector 14 associated with the combustion chamber 12 exemplarily considered herein. The corresponding curve is shown in... Figure 2 The figures are labeled 52 and 54. The horizontal axis is... Figure 2 The value in 'W' represents the crankshaft angle W of crankshaft 44 over the entire working cycle, i.e., a crankshaft angle from 0° to 720°. The suction stroke typically extends from approximately 360° to approximately 540° of crankshaft angle. As can be seen from curve 50, during such a suction stroke, inlet valve 20 opens and closes.

[0022] In the internal combustion engine 10, gaseous fuel is injected directly into the combustion chamber 12 via fuel injector 14. Typically, and at least temporarily, the gaseous fuel is injected entirely during the compression stroke with the inlet valve 20 closed, i.e., at a crankshaft angle between approximately 540° and approximately 720°. This corresponds to curve 52, shown as a dashed line.

[0023] Under defined operating conditions and depending on the rotational speed n of the exhaust gas turbocharger 30 detected by sensor 35, at least a portion of the fuel (currently, exemplary, the entire amount) is injected into the combustion chamber 12 with the inlet valve 20 at least partially open, i.e., currently, exemplary, with a crankshaft angle in the range of approximately 400° to approximately 500°. This corresponds to curve 54 shown as a solid line.

[0024] Currently, the rotational speed n of the exhaust gas turbocharger 30 is detected by sensor 35. However, it is also possible to determine the rotational speed of the exhaust gas turbocharger 30 using a software model. Furthermore, as described above, under certain operating conditions, a portion of the fuel is injected into the combustion chamber with the inlet valve 20 at least partially open, depending on the rotational speed of the exhaust gas turbocharger 30. These determined operating conditions can be defined, for example, by the expected fill factor when fuel is injected with the inlet valve 20 open. The fill factor corresponds to the quotient obtained by dividing the mass of fresh air plus, if necessary, the mass of exhaust gas from the exhaust gas recirculation section by the mass of fuel.

[0025] Depend on Figure 3 The effect of injecting at least a portion of the fuel when the inlet valve 20 is at least partially open can be observed: there, the vertical axis represents the rotational speed n of the exhaust gas turbocharger 30. The horizontal axis represents time t. If high power of the internal combustion engine 10 is required during operation, for example in a motor vehicle, and the internal combustion engine is operating, for example, within its rated power range, then the rotational speed n of the exhaust gas turbocharger increases. Here, fuel is initially injected during the compression stroke when the inlet valve 20 is closed, corresponding to... Figure 2 Curve 52 in the diagram.

[0026] If the speed n of the exhaust gas turbocharger 30 reaches the first limit value G1, then the fuel injection into the combustion chamber 12 is based on... Figure 2Curve 54 is advanced, so the injection is now, exemplarily, performed with the inlet valve 20 at least partially open. The volume of gaseous fuel thus replaces the corresponding volume of the intake medium, typically consisting of fresh air and, if necessary, recirculated exhaust gas. This reduces the total filler volume in combustion chamber 12, thereby reducing the exhaust gas volume flow. This, in turn, causes a very direct reduction in the rotational speed n of the exhaust gas turbocharger 30, or prevents it from rising further to a value significantly greater than G1.

[0027] If the rotational speed n is less than the second limit value G2, then the amount of fuel injected with the inlet valve 20 at least partially open is reduced again, or in other words, the fuel injection with the inlet valve 20 open currently terminates, and then transitions to the corresponding... Figure 2 The injection curve 52. During the time period dT, the function described above is activated, thereby injecting fuel into the combustion chamber 12 at least partially with the inlet valve 20 open. It can be seen that the second limit value G2 is less than the first limit value G1, thereby achieving hysteresis and improving the stability of the function.

[0028] According to the function described above, under defined operating conditions and depending on the rotational speed n of the exhaust gas turbocharger 30, at least a portion of the fuel is injected into the combustion chamber 12 with the inlet valve 20 at least partially open. Now, referring again... Figure 4 The function described is as follows: In function block 56, the current speed n of the exhaust gas turbocharger 30 is compared with a first limit value G1. If the speed n is less than the limit value G1, then it jumps back to the beginning of function block 56.

[0029] If the rotational speed n reaches or exceeds the limit value G1, then in function block 58, it is checked whether the following operating conditions exist, in which activation of the function described above is meaningful. For example, it is checked whether the expected fill factor under the condition of activating the function is within the allowable range. If this is the case, then the function is activated in function block 60, and at least a portion of the fuel is injected with the inlet valve 20 at least partially open. Conversely, if it is determined in function block 58 that activation of the function described above is not meaningful, then by means of function block 62, an alternative measure is taken to ensure that the rotational speed n of the exhaust gas turbocharger 30 does not exceed the maximum allowable value. For example, the exhaust gas return valve 38 can be manipulated to allow more exhaust gas to return to the combustion chamber 12, thereby reducing the quality of fresh air.

Claims

1. A method for operating an internal combustion engine (10) with a gaseous fuel, particularly gaseous hydrogen, wherein the fuel is injected directly and at least temporarily completely into a combustion chamber (12) with a closed inlet valve (20), and wherein exhaust gas flowing from the combustion chamber (12) drives a turbine (34) of an exhaust gas turbocharger (30), characterized in that, At least under defined operating conditions and depending on the rotational speed (n) of the exhaust gas turbocharger (30), at least a portion of the fuel is injected into the combustion chamber (12) with the inlet valve (20) at least partially open.

2. The method according to claim 1, characterized in that, When the speed (n) of the exhaust gas turbocharger (30) reaches or exceeds the first limit value (G1), at least a portion of the fuel is injected into the combustion chamber (12) with the inlet valve (20) at least partially open.

3. The method according to claim 2, characterized in that, When the rotational speed (n) of the exhaust gas turbocharger (30) reaches or exceeds the first limit value (G1), the start of fuel injection is advanced to the point when the inlet valve (20) is still at least partially open.

4. The method according to at least one of the preceding claims, characterized in that, When the speed (n) of the exhaust gas turbocharger (30) reaches or falls below the second limit value (G2), the amount or part of the fuel injected with the inlet valve (20) at least partially open is reduced, or the fuel injection is terminated with the inlet valve (20) at least partially open.

5. The method according to claim 2 or 3 in combination with claim 4, characterized in that, The second limit value (G2) is less than the first limit value (G1).

6. The method according to at least one of the preceding claims, characterized in that, The determined operating conditions depend on the rotational speed (n) of the exhaust gas turbocharger (30) and the injection of at least a portion of the fuel with the inlet valve (20) at least partially open. The determined operating conditions are also defined by at least the expected fill factor.

7. A computer program product comprising commands that, when the program is executed by a computer, cause the computer to perform the method according to at least one of the preceding claims.

8. A controller (48) for controlling and / or regulating the operation of an internal combustion engine (10), the controller comprising at least one processor, at least one memory, and at least one computer program product according to claim 7 stored in the memory.

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