Method for operating combustion engine with gaseous fuel, and computer program product and controller

Abstract

In a method for operating a combustion engine (10) with gaseous fuel, a combustion chamber is supplied with compressed air from an air supply region (16) at least temporarily by means of an exhaust gas turbocharger (24), and at least temporarily returning exhaust gas from the exhaust gas region (18) into the air supply region (16) via an exhaust gas return line (36) and an exhaust gas return valve (38) arranged in the exhaust gas return line (36). According to the invention, a first variable characterizing a target position of the exhaust gas return valve (38) is dependent at least temporarily on a second variable characterizing an actual rotational speed of the exhaust gas turbocharger (24).

Description

Technical Field

[0001] The present invention relates to a method for operating a combustion engine with gaseous fuel, a computer program product, and a controller. Background Technology

[0002] DE 10 2021 210 001 A1 describes a method for operating a combustion engine that operates with a gaseous fuel, such as hydrogen. Compressed air is supplied from an air supply area to multiple combustion chambers by means of an exhaust gas turbocharger. Gaseous hydrogen is either directly blown into the combustion chambers or also injected as port fuel injection into the intake manifold, and the hydrogen-air mixture is ignited in the combustion chambers. Exhaust gases formed during combustion are discharged from the combustion chambers to an exhaust gas region, where they drive the turbine of the exhaust gas turbocharger. The exhaust gas region is at least temporarily connected to the air supply area via an exhaust gas return line. For this purpose, an exhaust gas return valve is arranged in the exhaust gas return line. Summary of the Invention

[0003] The problem upon which this invention is based is solved by a method having the features of claim 1, and by a computer program product and controller having the features of the parallel claims. Advantageous improvements are proposed in the dependent claims.

[0004] This invention broadly relates to the high-pressure exhaust gas recirculation principle known from diesel and gasoline combustion engines. This principle is used in largely different ways and in different manners in combustion engines operating on gaseous fuels, such as hydrogen, compared to conventional diesel or gasoline combustion engines. In such combustion engines operating on gaseous fuels, high-pressure exhaust gas recirculation is at least used as a supplementary solution when the air supplied to the combustion chamber is compressed by means of a turbocharger (supercharging system). This is related to the fact that the combustion engine should operate with gaseous fuels at high air coefficients (the ratio of fresh air mass to fuel mass) in the full-load region. This places high demands on the supercharging system.

[0005] To overcome the conflict between high torque at low speeds (high "low-end torque") and high rated power at high speeds, high-pressure exhaust gas recirculation is used near rated power, or at least at medium to high speeds and under relatively high loads, to reduce the mass flow through the turbine and thus the speed of the exhaust gas turbocharger. Nevertheless, high-pressure exhaust gas recirculation also directs a high mass flow into the combustion chamber of the combustion engine, where the mass flow consists of fresh air and the recirculated exhaust gas. Combined with advantageous designs of the exhaust gas turbocharger ("turbo matching"), better synergy between the exhaust gas turbocharger and other components of the combustion engine is achieved, and / or higher power density can be achieved in the combustion chamber, thus enabling a higher rated power for the combustion engine.

[0006] A typical exhaust gas turbocharger can have a pressure differential (“scavenging differential”) between the air supply region and the exhaust region near the rated power of the combustion engine, which is unfavorable for achieving high-pressure exhaust gas recirculation. This “unfavorable differential” involves the possibility that the exhaust gas mass flow can flow completely through the exhaust gas recirculation line. This requires the pressure in the exhaust region to be greater than the pressure in the air supply region. An “unfavorable differential” exists when the pressure in the air supply region (suction pipe) is greater than the pressure in the exhaust region (exhaust manifold) because the exhaust gas itself can no longer be recirculated through the exhaust gas recirculation line. However, this can still be achieved using a so-called vibrating valve. This vibrating valve is essentially a fast-switching check valve that allows the mass flow to pass in only one direction, i.e., when the exhaust gas pressure pulses briefly reach the exhaust region with the combustion engine outlet valve open, causing the scavenging differential to reverse. The vibrating valve thus allows such pressure pulsations to pass in one direction, from the exhaust region towards the air supply region (high-pressure exhaust gas recirculation).

[0007] This invention provides a novel method for controlling and / or regulating high-pressure exhaust gas recirculation. A key signal used in this method is the rotational speed of the exhaust gas turbocharger, or a parameter characterizing that speed. The method according to this invention enables relatively easy control and / or regulation of high-pressure exhaust gas recirculation, which operates without complex modeling schemes. Furthermore, this invention achieves a closed control loop for boost pressure that allows for corrective intervention, for example, to protect specific components.

[0008] Specifically, this is achieved through methods used to operate a combustion engine with gaseous fuel. Such a combustion engine is typically very similar to, and even almost identical in construction to, a classic gasoline combustion engine, being a four-stroke piston combustion engine. However, instead of injecting liquid gasoline into the combustion chamber, gaseous fuel, such as gaseous hydrogen, is instead blown directly into the corresponding combustion chamber or into its air supply area (suction pipe). The combustion engine can have multiple cylinders with multiple combustion chambers.

[0009] As in known gasoline combustion engines, in the method according to the invention, compressed air is supplied from the air supply region to the combustion chamber, at least temporarily, by means of an exhaust gas turbocharger. The air supply region can be formed or comprised, for example, by a so-called "intake manifold." An inlet valve and the combustion chamber are arranged downstream of the air supply region, and the compressor of the exhaust gas turbocharger is arranged upstream of the air supply region. The compressor compresses the drawn-in ambient air, and the compressed air is then supplied to the combustion chamber through the inlet valve.

[0010] As in known gasoline combustion engines, in the method according to the invention, exhaust gas is at least temporarily diverted from the exhaust gas region to the air supply region via an exhaust gas recirculation line and an exhaust gas recirculation valve arranged in the exhaust gas recirculation line. However, unlike in known gasoline combustion engines, such high-pressure exhaust gas recirculation is less used for NOx reduction or elimination throttling in combustion engines operating with gaseous fuels, and more as a supplementary means of controlling / regulating the air in the exhaust gas turbocharger or compressed air supply region.

[0011] An exhaust gas return valve is an exhaust gas return valve that has at least a closed position and an open position, but preferably also an exhaust gas return valve that can have an intermediate position between the closed and open positions. Typically, the exhaust gas return valve has a signal-controlled actuator, such as an electromagnetic actuator, which generates the adjusting movement of the exhaust gas return valve. Typically, the exhaust gas return valve is controlled by a duty cycle signal, which characterizes the target position of the exhaust gas return valve. For this purpose, for example, the duty cycle can be converted into a corresponding angle of the exhaust gas return valve by a component driver of the exhaust gas return valve. Alternatively, the actual position of the exhaust gas return valve may follow the target position.

[0012] In the method according to the invention, a first parameter characterizing the target position of the exhaust gas recirculation valve depends at least temporarily on a second parameter characterizing the actual rotational speed of the exhaust gas turbocharger. The actual rotational speed can be detected, for example, by means of a sensor, but it can also be provided, for example, according to a software model, such as based on model-based boost pressure regulation. Therefore, control and, if necessary, regulation can be achieved by the method according to the invention, with the second parameter as its input and the first parameter as its output. The second parameter is a signal of the exhaust gas turbocharger's rotational speed or can be based on that signal. The second parameter can be provided, for example, by a model, such as a portion of existing boost pressure regulation, or by a sensor.

[0013] One improved approach proposes that the first parameter is obtained at least using a characteristic curve, with the second parameter supplied indirectly or directly to the characteristic curve. This is easily implemented. When other parameters besides the second parameter are needed to obtain the first parameter, multiple characteristic curves or one or more families of characteristic curves can be used. The characteristic curves can define almost any desired relationship between the first and second parameters. Such a relationship can be, for example, a step function, a continuous function, or a constant function.

[0014] In one improved embodiment, the first parameter is obtained at least from the output parameter of the characteristic curve filtered by a first low-pass filter, such as a PT1-filter. This, in particular, reduces signal noise and prevents unwanted adjustment movements.

[0015] In one improved embodiment, the second parameter is also derived from the actual rotational speed, filtered by a second low-pass filter, such as a PT1-filter. This reduces unwanted adjustment movements. The low-pass filter preferably has a direction-dependent time constant.

[0016] One improved scheme proposes that the time constant of the first low-pass filter is greater than that of the second low-pass filter, preferably approximately ten times the time constant of the second low-pass filter. This has proven to be particularly significant.

[0017] One improved scheme proposes that the relationship between the first and second parameters has a hysteresis. This hysteresis prevents the continuous opening / closing of the exhaust gas return valve under critical conditions.

[0018] One improved solution proposes that the target position of the exhaust gas evacuation valve is open when the actual (increased) speed of the exhaust gas turbocharger reaches or exceeds a first limit, and the target position is closed when the actual (decreased) speed of the exhaust gas turbocharger reaches or falls below a second limit, where the second limit is less than the first limit. Here, the term "open position" does not necessarily mean that it must always be operated with a 100% duty cycle. Other values ​​are also conceivable. This improved solution is a particularly easy way to implement the mentioned hysteresis.

[0019] In one improved embodiment, it is proposed that the target velocity of the adjustment movement of the exhaust gas return valve in the closing direction is different from, preferably larger than, the target velocity of the adjustment movement along the opening direction. Therefore, the adjustment movement of the exhaust gas return valve is performed via a so-called "ramp," whereby the exhaust gas return valve opens continuously for a desired time period without abrupt opening, and closes continuously for the same desired time period without abrupt closing, but this desired time period is typically different from the opening situation. However, it is also conceivable in principle that the target velocities during opening and closing are the same. Instead of the aforementioned ramp, the filter with a direction-dependent time constant mentioned above can also be used.

[0020] The present invention also relates to a computer program product comprising commands that, when executed by a processor, cause the processor to perform at least one of the methods described above.

[0021] Furthermore, the present invention relates to a controller for controlling and / or regulating the operation of a combustion engine, the controller comprising at least one processor, at least one memory, and at least one computer program product of the type described above stored in the memory. Attached Figure Description

[0022] Embodiments of the present invention will now be explained with reference to the accompanying drawings. The drawings show: Figure 1 A schematic diagram of a combustion engine operating on gaseous fuel is shown, the combustion engine having an exhaust gas turbocharger, an exhaust gas recirculation line, and an exhaust gas recirculation valve; Figure 2 This demonstrates control using characteristic curves. Figure 1 Block diagram of the exhaust gas return valve; Figure 3 It shows Figure 2 The characteristic curves correlate a first parameter characterizing the target position of the exhaust gas return valve with a second parameter characterizing the actual rotational speed of the exhaust gas turbocharger. Figure 4A graph is shown, plotted over time. Figure 3 The first parameter characterizing the target position of the exhaust gas return valve; and Figure 5 The alternative characteristic curve (without hysteresis) is shown to be similar to... Figure 3 The curve graph. Detailed Implementation

[0023] Combustion engine in Figure 1 Reference numeral 10 is generally used in the accompanying drawings. The combustion engine includes an engine block 12, which exemplarily has four cylinders, each with a combustion chamber 14. Each combustion chamber 14 has at least one inlet valve (not shown) and an outlet valve (not shown), as well as an ignition device (not shown). The combustion chamber 14 is connected to an air supply area 16 via the inlet valve. The combustion chamber 14 is connected to an exhaust gas area 18 via the outlet valve. A throttle valve 18 (“throttle valve”) is arranged generally upstream of the combustion chamber 14 in the air supply area 16 along the air flow direction 17. A booster air cooler 20 is arranged upstream of the throttle valve 18 in the air supply area 16. An exhaust gas turbocharger compressor 22 is arranged upstream of the booster air cooler 20 in the air supply area 16, and the compressor is connected upstream to the external environment via an air filter 26. The actual rotational speed of compressor 22, and therefore overall exhaust gas turbocharger 24, is currently exemplarily detected by speed sensor 27. In embodiments not shown, it is also possible to provide the actual rotational speed via a software model.

[0024] Generally viewed downstream of combustion chamber 14 along the exhaust gas flow direction 17, the exhaust gas region includes the turbine 28 of an exhaust gas turbocharger 24, which drives compressor 22. The exhaust gas turbocharger 24 also typically includes an exhaust gas bypass valve 30, which can be active or passive. Optionally, the turbine 28 of the exhaust gas turbocharger 24 can have variable turbine geometry; however, this is not shown in detail here. Downstream of turbine 28, exhaust gas region 18 includes an exhaust gas retreatment unit 32 and a muffler 34.

[0025] An exhaust gas return line 36 branches off from the exhaust gas region 18 between the outlet valve of the combustion chamber 14 and the turbine 28 of the exhaust gas turbocharger 24. This exhaust gas return line leads to the air supply region 16, specifically to the area between the inlet valve and the throttle valve 18 of the combustion chamber 14. Looking from the exhaust gas region 18, an exhaust gas return valve 38 is first arranged in the exhaust gas return line 36.

[0026] Along the exhaust gas flow direction 40, in the exhaust gas return line 36, downstream of the exhaust gas return valve 38, an exhaust gas return cooler 42 is arranged in the exhaust gas return line 36. Again, downstream of the exhaust gas return cooler 42, in the exhaust gas return line 36, a reed valve 44 is arranged. Such a reed valve 44 is also called a tongue valve. This relates to a single, unilaterally acting check valve. It typically comprises one or more thin, flexible reeds made of metal or plastic, which can open in one direction to allow gas flow and then automatically close to prevent backflow. Currently, the reed valve 44 blocks towards the exhaust gas region 18 and opens towards the air supply region 16.

[0027] The controller 46 also belongs to the combustion engine 10, and is used to control and / or regulate the operation of the combustion engine 10. The controller includes at least one processor 48 and at least one memory 50. A computer program product is stored in the memory 50, and when the computer program product is implemented, the controller 46 implements specific methods, which will be described in more detail below. Furthermore, the controller 46 receives signals from various sensors, and generates control signals for various actuators. The controller 46 primarily receives signals from the speed sensor 27, and generates control signals for the exhaust gas return valve 38.

[0028] The combustion engine 10 typically operates as follows: Fresh air is drawn in through air filter 26, compressed by compressor 22, cooled in booster air cooler 20, and supplied to the corresponding combustion chamber 14 (along with the recirculated exhaust gas if necessary) along the flow direction 17 during the suction stroke, depending on the position of throttle valve 18. During the compression stroke, the supplied air and, if necessary, the recirculated exhaust gas are compressed. Gaseous fuel, such as hydrogen, is blown directly into the combustion chamber 14, or, in embodiments not described herein, into air supply area 16, and the mixture of gaseous fuel and air (and exhaust gas, see below) is ignited in the combustion chamber 14 by an ignition device. The piston defining the corresponding combustion chamber 14 is thus placed in motion, driving a crankshaft (not shown) during the power stroke.

[0029] The exhaust gases generated by combustion are discharged from the corresponding combustion chamber 14 through the corresponding outlet valve along the flow direction 17 into the exhaust gas area 18 (exhaust stroke). The exhaust gases drive the turbine 28 and then enter the external environment after the exhaust gas retreatment device 32 and the muffler 34. A portion of the exhaust gases can be returned to the air supply area 16 along the flow direction 40 through the exhaust gas return line 36.

[0030] Because the exhaust gas is drawn back into the air supply region 16, where there is a relatively high pressure due to compression achieved by the compressor 22, this type of exhaust gas recirculation is also called high-pressure exhaust gas recirculation. Such high-pressure exhaust gas recirculation is used less for NOx reduction or elimination throttling in hydrogen combustion engines, and is instead more often used for supplementary control or regulation of the boost system, that is, supplementary control or regulation of air compression achieved by the compressor 22 in the air supply region 16.

[0031] The exhaust gas recirculation valve 38 is a controlled or regulated valve, thus its position can be influenced by an actuator (not shown). Specifically, the exhaust gas recirculation valve 38 can occupy both an open and a closed position. Here, the adjustment movement of the exhaust gas recirculation valve 38 is achieved at a desired target speed, respectively. To manipulate the exhaust gas recirculation valve 38, the controller 46 generates a first parameter characterizing the target position of the exhaust gas recirculation valve 38. This first parameter is typically the duty cycle. The first parameter depends on a second parameter characterizing the actual rotational speed of the exhaust gas turbocharger 24, and this second parameter is currently, exemplarily, generated using the signal from the speed sensor 27. The second parameter can also be provided alternatively via a software model, as mentioned above, for example, through model-based boost pressure regulation. Now refer to... Figure 2 To elaborate on this point in more detail.

[0032] The first parameter mentioned above represents the target position of the exhaust gas return valve 38 in the form of duty cycle. Figure 2 Reference numeral 52 is used in the accompanying drawings. The first parameter is the output parameter of the first low-pass filter 54 (PT1 filter), which obtains the output parameter of characteristic curve 58 as input parameter 56. The first low-pass filter 54 operates with a time constant 60. The output parameter 62 of the second low-pass filter 64 (PT1 filter) is supplied to characteristic curve 58. The second low-pass filter obtains the speed signal (actual speed) of the speed sensor 27 as input parameter 66, which is exemplarily taken as input. The second low-pass filter 64 operates with a time constant 68. The time constant 60 is exemplarily greater than the time constant 68. Exemplarily, the time constant 60 can be greater than the time constant 68 by a factor of 10.

[0033] Now for reference Figure 3 A more detailed explanation of characteristic curve 54: Characteristic curve 54 operates at a first limit value n1 and a second limit value n2. As an initial state assumption: the actual rotational speed n of the turbocharger 24 (according to the attached figure, reference numeral 66, or...) Figure 2The output parameter (or second parameter 62) representing the actual rotational speed is relatively low; and the duty cycle T is 0% (the duty cycle is used to control the exhaust gas return valve 38 and in this regard, the output parameter 56 or the first parameter 52 representing the target position of the exhaust gas return valve 38 after filtering is involved), so the exhaust gas return valve 38 is closed.

[0034] When the actual speed n of the turbocharger 24, or the corresponding output parameter 62 of the second low-pass filter 64, rises and reaches or exceeds the first limit value n1, the characteristic curve 58 generates a duty cycle T of x%. This duty cycle can be 100%, but it is not necessary. In this duty cycle, the target position of the exhaust gas recirculation valve 38 corresponds to the open position. The exhaust gas recirculation valve 38 is thus opened when the first limit value n1 is exceeded. When the actual speed n of the turbocharger 24 then decreases and reaches or falls below the second limit value n2, the characteristic curve 58 generates a duty cycle T of 0%. In this duty cycle, the target position of the exhaust gas recirculation valve 38 corresponds to the closed position. If the limit value n2 is reached or falls below, then the exhaust gas recirculation valve 38 closes. It is identified that there is a hysteresis in the relationship between the first parameter (duty cycle T) and the second parameter (actual speed n), i.e., the difference between n2 and n1. However, in principle, a hysteresis-free relationship between the first parameter and the second parameter can also be conceived, as exemplarily in… Figure 5 As shown in the diagram.

[0035] exist Figure 4 The time plot is used to control the duty cycle T of the exhaust gas recirculation valve 38. At time t1, the first limit value n1 is reached or exceeded as the speed n of the exhaust gas turbocharger 24 increases. Figure 3 Thus, the duty cycle T increases from 0% to 100% within the time period dt1 with a corresponding gradient g1. The exhaust gas recirculation valve 38 therefore does not open abruptly, but gradually. At time t2, the exhaust gas turbocharger 24 reaches or falls below the second limit value n2 as its speed n decreases. Figure 3 Therefore, the duty cycle T decreases from 100% to 0% within the time period dt2 with a corresponding gradient g2. The exhaust gas return valve 38 thus does not close abruptly, but gradually. However, the time period dt2 is shorter than the time period dt1. Therefore, the target speed g2 of the adjustment movement of the exhaust gas return valve 38 along the closing direction is different from, and thus a higher, target speed compared to, the target speed g1 of the adjustment movement of the exhaust gas return valve 38 along the opening direction.

[0036] refer to Figure 3 and Figure 4One embodiment has been described in which the relationship between the duty cycle T and the rotational speed n of the exhaust gas turbocharger 24 is a step function. It goes without saying that in other embodiments not shown, the relationship could be continuous, for example, proportional, at least within the range of rotational speed n.

Claims

1. A method for operating a combustion engine (10) with gaseous fuel, wherein compressed air is supplied to the combustion chamber from an air supply region (16) at least temporarily by means of an exhaust gas turbocharger (24), and wherein exhaust gas is at least temporarily drawn back from an exhaust gas region (18) to the air supply region (16) via an exhaust gas return line (36) and an exhaust gas return valve (38) arranged in the exhaust gas return line (36), characterized in that, The first parameter (52) characterizing the target position of the exhaust gas return valve (38) depends at least temporarily on the second parameter (62) characterizing the actual rotational speed (n) of the exhaust gas turbocharger (24).

2. The method according to claim 1, characterized in that, The first parameter (52) is obtained at least by means of the characteristic curve (58), and the second parameter is supplied to the characteristic curve.

3. The method according to claim 2, characterized in that, The first parameter (52) is obtained at least from the output parameter (56) of the characteristic curve (58) filtered by the first low-pass filter (54).

4. The method according to at least one of the preceding claims, characterized in that, The second parameter (62) is also obtained from the actual rotational speed (n) filtered by the second low-pass filter (64).

5. The method according to claims 3 and 4, characterized in that, The time constant (60) of the first low-pass filter (54) is greater than the time constant (68) of the second low-pass filter (64), preferably about ten times the time constant (68) of the second low-pass filter (64).

6. The method according to at least one of the preceding claims, characterized in that, The relationship between the first parameter (52) and the second parameter (62) is lag-dependent.

7. The method according to claim 6, characterized in that, When the actual speed (n) of the exhaust gas turbocharger (24) reaches or exceeds the first limit value (n1), the target position of the exhaust gas return valve (38) is the open position, and when the actual speed (n) of the exhaust gas turbocharger (24) reaches or falls below the second limit value (n2), the target position of the exhaust gas return valve (38) is the closed position, wherein the second limit value (n2) is less than the first limit value (n1).

8. The method according to at least one of the preceding claims, characterized in that, The target speed of the adjustment movement of the exhaust gas return valve (38) along the closing direction is a different target speed from the target speed of the adjustment movement along the opening direction, preferably a larger target speed.

9. A computer program product comprising commands that, when executed by a processor (48), cause the processor to perform the method according to at least one of the preceding claims.

10. A controller (46) for controlling and / or regulating the operation of a combustion engine (10), comprising at least one processor (48), at least one memory (50), and at least one computer program product according to claim 9 stored on said memory.

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