Method for operating an internal combustion engine by means of gaseous fuel, computer program product and control device

Abstract

In a method for operating an internal combustion engine (10) by means of gaseous fuel, compressed air is at least temporarily fed to a combustion chamber (14) by means of an exhaust gas turbocharger (24). In the method, scavenging is also at least temporarily active. According to the invention, when scavenging is active, and depending on the result of an evaluation of a variable that characterizes a target increase in power, a measure for limiting an exhaust-gas back pressure is implemented.

Description

[0001] R.415353

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for operating an internal combustion engine with gaseous fuel, as well as computer program product and control unit

[0006] State of the art

[0007] The invention relates to a method for operating an internal combustion engine with gaseous fuel, a computer program product and a control unit.

[0008] German patent DE 10 2021 210 001 A1 describes a method for operating an internal combustion engine that runs on gaseous fuel, for example, hydrogen. Compressed air from an air supply area is supplied to a plurality of combustion chambers by means of an exhaust gas turbocharger. Gaseous hydrogen is injected directly into the combustion chambers, or it is injected into the intake ports (port fuel injection), and the hydrogen-air mixture is ignited in the combustion chambers. Exhaust gas produced during combustion is discharged from the combustion chambers into an exhaust gas section, where it drives a turbine of the exhaust gas turbocharger. Furthermore, it is known to influence the performance of the exhaust gas turbocharger by adjusting the geometry of the turbine blades of the exhaust gas turbocharger, e.g., their angle of attack. The principle of "scavenging" is also known.This refers to the overlapping opening times of the intake and exhaust valves in a combustion chamber of an internal combustion engine. This allows cooler fresh air to purge the hot exhaust gas (residual gas) present in the combustion chamber of the internal combustion engine from the cylinder.

[0009] Disclosure of invention R.415353

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[0011] The problem underlying the invention is solved by a method with the features of claim 1, as well as by a computer program product and a control unit with the features of the dependent claims. Advantageous embodiments are specified in the dependent claims.

[0012] One advantage of the invention is that the scavenging effect can be ensured even when power is demanded ("target power increase"), for example, when an increase in the torque of the internal combustion engine is desired. Combustion anomalies are avoided by preventing high exhaust backpressure and thus an increased amount of residual gas in the combustion chamber of the internal combustion engine. Furthermore, the invention allows for the rapid implementation of a power demand, i.e., a target power increase, since a high fresh air charge in the combustion chamber is achieved through rapid activation of the exhaust gas turbocharger. In addition, the invention reduces nitrogen oxide emissions and fuel consumption.

[0013] One aspect of the invention is that, when the target power output is increased, the increase in exhaust backpressure by the exhaust gas turbocharger—that is, the gas pressure between the exhaust valve and the turbine of the exhaust gas turbocharger—is delayed. This ensures that the pressure differential between the intake and exhaust valves of a combustion chamber has a direction that enables scavenging. Scavenging refers to the process by which comparatively cool fresh air scavenges the exhaust gas present in a combustion chamber by overlapping the opening times of the intake and exhaust valves, particularly at the beginning or end of a suction stroke. The increased cooling of the combustion chamber reduces the tendency for knocking and pre-ignition. Furthermore, the cylinder filling is increased, thereby improving the power output of the internal combustion engine.

[0014] In dynamic or transient operation of the internal combustion engine, particularly under load or torque demand, the exhaust gas turbocharger typically responds by means of active boost pressure control, adjusting the turbine geometry to provide the optimal boost pressure for the desired load or torque demand. This adjustment of the turbine geometry typically involves an increase in the R.415353

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[0016] The angle of attack of the turbine blades leads to increased exhaust back pressure or pressure peaks in the exhaust gas area between the exhaust valve and the turbine.

[0017] The invention ensures that the pressure downstream of the exhaust valve is lower than upstream of the intake valve, thus guaranteeing scavenging of the combustion chamber in one direction only, from the intake valve to the exhaust valve. Because scavenging is maintained even with an increase in power output, the engine's tendency to knock is reduced. Furthermore, even higher torque is possible, since the lower exhaust backpressure allows more fresh air into the combustion chamber, resulting in more efficient combustion.

[0018] The invention can be implemented in internal combustion engines with both permanent and non-permanent scavenging. In the case of permanent scavenging, the inventive measure can always be carried out when the further requirement (result of the evaluation) is met. In the case of non-permanent scavenging, the inventive measure can be carried out when scavenging is currently being performed or is currently active.

[0019] Specifically, the invention relates to a method for operating an internal combustion engine with gaseous fuel. Such an internal combustion engine typically serves to power a motor vehicle and is typically very similar, if not identical in many respects, in construction to classic gasoline internal combustion engines, i.e., as a four-stroke piston internal combustion engine. However, instead of liquid gasoline being injected into the combustion chambers, gaseous fuel, for example, gaseous hydrogen, is injected directly into the respective combustion chambers of the internal combustion engine, or it is injected into the intake ports (port fuel injection). The internal combustion engine can have several cylinders with multiple combustion chambers.

[0020] As with known gasoline internal combustion engines, in the method according to the invention, compressed air from an air supply area is supplied to a combustion chamber at least temporarily by means of an exhaust gas turbocharger. R.415353

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[0022] The air intake area can be formed, for example, by or encompass a so-called "intake manifold." Downstream of the air intake area are the intake valve and combustion chamber; upstream of the air intake area is the compressor of an exhaust gas turbocharger. This compressor compresses the intake air, and this compressed air is then fed into the combustion chamber via the intake valve(s).

[0023] In the operation of the internal combustion engine according to the invention, scavenging is active at least temporarily. This means that scavenging can be active permanently or only during certain operating phases of the internal combustion engine. Typically, the internal combustion engine has intake and exhaust valves for this purpose, the timing of which can be changed – for example, by adjusting a camshaft – so that scavenging is present, i.e., active, during certain operating phases of the internal combustion engine.

[0024] According to the invention, when scavenging is active, and depending on the result of an evaluation of a parameter that characterizes a target power increase ("transient indicator"), a measure is implemented to limit exhaust back pressure. "Limited" in this context means that the exhaust back pressure is lower with the measure than without it. The evaluation of the parameter that characterizes a target power increase helps to determine whether a target power increase (i.e., a required dynamic or transient operation, for example, due to a load or torque demand) is present at all and / or what the extent of the target power increase is.

[0025] In the simplest case, the result of the evaluation is either "Yes, there is a target performance increase" or "No, there is no target performance increase." In another case, the result of the evaluation is either "the target performance increase or the quantity characterizing it is so large (for example, is higher than a limit value) that the measure is justified" or "the target performance increase or the quantity characterizing it is not so large (for example, is not higher than a limit value) that the measure is justified." If there is no target performance increase or the target performance increase is not higher than a limit value, the result is R.415353.

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[0027] If the parameter characterizing the performance increase is not sufficiently large, the measure will not be implemented. However, it is also conceivable that the scope of the measure depends on the value of the parameter characterizing the target performance increase, for example, according to a characteristic curve.

[0028] The proposed modification involves a measure that directly or indirectly reduces the power output of a turbine in the exhaust gas turbocharger. This is easily implemented and directly affects the exhaust backpressure. "Reduced" in this context means that the power output of the exhaust gas turbocharger turbine is lower with the modification than without it.

[0029] Typically, the turbine output of the exhaust gas turbocharger is lower than the maximum possible output due to this measure.

[0030] Further training requires that the measure be at least one from the following group: limiting the target angle of attack of the turbine blades of the exhaust gas turbocharger or a parameter characterizing the target angle of attack; limiting a target value for boost pressure; limiting a target value for a filling coefficient; limiting a target value for exhaust back pressure. From this list, the measure "limiting the target angle of attack of the turbine blades of the exhaust gas turbocharger or a parameter characterizing the target angle of attack" is particularly preferred. The parameter characterizing the target angle of attack could, for example, be a control signal, such as a duty cycle, for an actuator that can adjust the angle of attack of the turbine blades. The listed measures are easy to implement.

[0031] Further training stipulates that the parameter characterizing the target performance increase ("transient indicator") must be at least one of the following: difference between actual boost pressure and boost pressure during steady-state operation of the internal combustion engine; difference between actual filling coefficient and filling coefficient during steady-state operation of the internal combustion engine; difference between actual and target power output of the internal combustion engine; gradient of a target torque; gradient of a target injection quantity; gradient of an actual engine speed; intervention of a limit on the filling coefficient for transient operation of the internal combustion engine; gradient of a target R.415353

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[0033] Boost pressure. From this list, the parameters "difference between an actual boost pressure and a boost pressure during steady-state operation of the internal combustion engine" and "difference between an actual filling coefficient and a filling coefficient during steady-state operation of the internal combustion engine" are particularly preferred. The "filling coefficient" preferably characterizes the ratio of the total cylinder charge to the injected fuel and takes into account both the fresh air present in the combustion chamber and, if present, exhaust gas that enters the combustion chamber with the fresh air via exhaust gas recirculation.

[0034] The invention also relates to a computer program product comprising instructions which, when the program is executed by a computer, cause it to execute one of the methods described above.

[0035] The invention also relates to a control unit for controlling and / or regulating the operation of an internal combustion engine, 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.

[0036] One embodiment of the invention is explained below with reference to the accompanying drawing. The drawing shows:

[0037] Figure 1 shows a schematic diagram of an internal combustion engine powered by gaseous fuel, with an exhaust gas turbocharger;

[0038] Figure 2 shows a flowchart of a method for operating the internal combustion engine of Figure 1;

[0039] Figure 3 is a diagram showing the actual torque of the internal combustion engine from Figure 1 over time with a target power increase under three different operating scenarios;

[0040] Figure 4 is a diagram showing the filling coefficient of the internal combustion engine of Figure 1 over time at the target power increase and the three operating scenarios of Figure 3; R.415353

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[0042] Figure 5 is a diagram showing the angle of attack of a turbine of the exhaust gas turbocharger of the internal combustion engine of Figure 1 over time during the target power increase and the three operating scenarios of Figure 3;

[0043] Figure 6 is a diagram showing the boost pressure of the internal combustion engine from Figure 1 over time at the target power increase and the three operating scenarios from Figure 3; and

[0044] Figure 7 is a diagram showing the exhaust back pressure of the internal combustion engine of Figure 1 over time during the target power increase and the three operating scenarios of Figure 3.

[0045] In Figure 1, an internal combustion engine is designated by reference numeral 10. It typically serves to power a motor vehicle and comprises an engine block 12 with, by way of example, four cylinders, each with a combustion chamber 14. Each combustion chamber 14 has at least one intake valve (not shown) and at least one exhaust valve (not shown), as well as at least one ignition device (not shown). The intake valve associated with a combustion chamber 14 connects it to an air supply area 16. The exhaust valve associated with a combustion chamber 14 connects it to an exhaust gas area 18.

[0046] In the airflow direction 17, viewed upstream of the combustion chamber 14, a throttle valve 18 (“throttle flap”) is arranged in the air supply area 16. Upstream of the throttle valve 18, an intercooler 20 is arranged in the air supply area 16. Upstream of the intercooler 20, a compressor 22 of an exhaust gas turbocharger 24 is arranged in the air supply area 16, which is in turn connected to the outside environment upstream via an air filter 26.

[0047] In the direction of exhaust gas flow 17, viewed downstream of the combustion chamber 14, the exhaust gas section 18 comprises a turbine 28 of the exhaust gas turbocharger 24, which drives the compressor 22. For example, the exhaust gas turbocharger 24 also includes an actuator 30 with which the angle of attack of the turbine blades of the turbine 28 can be adjusted (variable).

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[0049] Turbine geometry”). Downstream of the turbine 28, the exhaust gas section 18 includes an exhaust gas aftertreatment device 32 and a silencer 34.

[0050] Between the exhaust valves of the combustion chambers 14 and the turbine 28 of the exhaust gas turbocharger 24, an exhaust gas recirculation line 36 branches off from the exhaust gas section 18 and opens into a section of the air supply section 16 located between the inlet valve of the combustion chambers 14 and the throttle valve 18. From the perspective of the exhaust gas section 18, a check valve 38, designed as a reed valve, is initially arranged in the exhaust gas recirculation line 36. In this case, the reed valve 38 blocks the exhaust gas section 18 and opens it towards the air supply section 16.

[0051] In the exhaust gas flow direction 40, viewed downstream of the reed valve 38 in the exhaust gas recirculation line 36, an exhaust gas recirculation cooler 42 is arranged in the exhaust gas recirculation line 36. Further downstream of the exhaust gas recirculation cooler 42, an exhaust gas recirculation valve 44 is arranged in the exhaust gas recirculation line 36. In an embodiment not shown, the reed valve is arranged downstream of the exhaust gas recirculation cooler and the exhaust gas recirculation valve is arranged upstream of the exhaust gas recirculation cooler.

[0052] The internal combustion engine 10 also includes a control unit 46, which can control and / or regulate the operation of the internal combustion engine 10. This unit comprises at least one processor 48 and at least one memory 50. A computer program is stored in the memory 50, the execution of which causes the control unit 46 to carry out a specific procedure, which is described in more detail below. For this purpose, the control unit 46 receives signals from various sensors and generates control signals for various actuators. Among other things, the control unit 46 receives signals from an accelerator pedal 52, with which an operator can set a desired power output of the internal combustion engine 10, and it generates control signals for the actuator 30.

[0053] The internal combustion engine 10 also features intake and exhaust valves whose timing can be adjusted, for example by an adjustable camshaft (not shown). A corresponding actuator R.415353

[0054] - 9 - for camshaft adjustment is designated by reference numeral 54 in Figure 1. This is also controlled by the control unit 46. The timing of the intake and exhaust valves of a combustion chamber 14 can be coordinated so that the internal combustion engine 10 operates with so-called "scavenging," at least during certain operating phases. This refers to an overlap of the opening times of the intake and exhaust valves of a combustion chamber, allowing cooler fresh air to scavenge the hot exhaust gas from the combustion chamber 14.

[0055] The internal combustion engine 10 typically operates as follows: Fresh air is drawn in through the air filter 26, compressed by the compressor 22, cooled in the charge air cooler 20, and, according to the position of the throttle valve 18, fed along the flow direction 17 to a respective combustion chamber 14 via a respective intake valve. Gaseous fuel, for example hydrogen, is then, by way of example, injected directly into the combustion chamber 14, and the mixture of gaseous fuel and air (and recirculated exhaust gas, see below) is ignited in the combustion chamber 14 by an ignition device. In an embodiment not shown, the fuel is injected into the intake ports (port fuel injection). This sets a piston, which delimits the respective combustion chamber 14, in motion, driving a crankshaft (not shown).

[0056] Exhaust gas produced by combustion is expelled from the respective combustion chamber 14 through a corresponding exhaust valve into the exhaust gas area 18 in the direction of flow 17. The exhaust gas drives the turbine 28 and then, after passing through the exhaust gas aftertreatment system 32 and the silencer 34, is released into the outside environment. A portion of the exhaust gas can be recirculated along the direction of flow 40 through the exhaust gas recirculation line 36 into the air supply area 16.

[0057] During a suction stroke of the piston associated with combustion chamber 14, the intake valve is open. Additionally, if scavenging is activated, the exhaust valve associated with combustion chamber 14 is also preferably open at the beginning of a suction stroke. This causes any hot residual gas present in combustion chamber 14 to be expelled by the R.415353 flowing into combustion chamber 14 from the intake valve.

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[0059] Gas (fresh air + recirculated exhaust gas) is flushed out of combustion chamber 14 via the exhaust valve.

[0060] A specific procedure for operating the internal combustion engine 10 will now be explained with reference to Figure 2: After a start block 56, a decision block 58 checks whether scavenging is active. If the answer is no, the system returns to the start block 56. Otherwise, a value (transient indicator) is evaluated in a function block 60, which characterizes a target power increase. Such a power increase can be requested, for example, by the operator by pressing the accelerator pedal 52. The evaluation can include checking whether a request for a power increase, i.e., a target power increase, exists at all. It can also include checking the extent of this increase, i.e., how large the requested power increase is.

[0061] The parameter that characterizes the target power increase is at least one from the following group: the difference between an actual boost pressure in the air supply area 16 and a boost pressure in the air supply area 16 during steady-state operation of the internal combustion engine 10; the difference between an actual filling coefficient and a filling coefficient in the combustion chambers 14 during steady-state operation of the internal combustion engine 10 (the "filling coefficient" preferably characterizes the ratio of the total cylinder charge to the injected fuel and takes into account both the fresh air present in the combustion chamber 14 and, if present, exhaust gas that has entered the combustion chamber 14 with the fresh air via exhaust gas recirculation); the difference between an actual power output and a target power output of the internal combustion engine 10, in particular between an actual torque and a target torque; the gradient of a target torque of the internal combustion engine 10;Gradient of a target injection quantity of gaseous fuel, for example hydrogen, into the combustion chambers 14;

[0062] Gradient of an actual rotational speed of a crankshaft of the internal combustion engine 10; intervention of a limit of the filling coefficient for a transient operation of the internal combustion engine 10; gradient of a target boost pressure in the air supply area 16. R.415353

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[0064] In decision block 64, it is checked whether, based on the result of the evaluation in block 62, a measure should be taken to limit the exhaust back pressure in the exhaust gas section 18. If the answer in block 62 is "no," the system returns to the starting block 56. If the answer in decision block 62 is "yes," a corresponding measure is taken in block 64. The measure is at least one of the following: limiting the target angle of attack of the turbine blades of the exhaust gas turbocharger 24 or a parameter characterizing the target angle of attack; limiting a target value for a boost pressure in the air supply section 16; limiting a target value for a filling coefficient in the combustion chambers 14; limiting a target value for an exhaust back pressure in the exhaust gas section 18.

[0065] The procedure then ends in a final block 66.

[0066] The physical effects of the method described in Figure 2 will now be explained in more detail with reference to Figures 3-7. In Figures 3-7, a first operating scenario without scavenging and without the action of functional block 64 from Figure 2 is shown by a dotted line. A second operating scenario with scavenging, but without the action of functional block 64 from Figure 2, is shown by a dashed line in Figures 3-7. A third operating scenario with scavenging and with the action of functional block 64 from Figure 2 is shown by a solid line in Figures 3-7.

[0067] In all figures, at time t1, the operator of the internal combustion engine 10 requests an increase in power ("target power increase"), for example by pressing the accelerator pedal 52. Figure 3 shows an initial rapid increase in the torque T of the internal combustion engine 10 in all three operating scenarios, followed by a brief dip and then a subsequent increase to the desired torque. It is evident that in the third operating scenario, the torque T increases more rapidly than in the other two scenarios.

[0068] The filling coefficient L (ratio of the mass of fresh air and recirculated exhaust gas in combustion chamber 14 to the injected amount of fuel) plotted in Figure 4 drops sharply to a minimum value Lmin at time t1. R.415353

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[0070] This limit is adhered to because the amount of fuel injected is limited.

[0071] Figure 5 shows that in the third operating scenario, at time t1, the angle of attack A of the turbine blades of turbine 28 of the exhaust gas turbocharger 24 is adjusted by actuator 30 only up to a value A1 that is smaller than the maximum possible angle of attack Amax. The action taken by functional block 64 in Figure 2 in the third operating scenario is therefore to limit the target angle of attack of the turbine blades of the exhaust gas turbocharger 24 to the value A1. In the other two operating scenarios, however, the angle of attack is adjusted up to the larger angle of attack Amax.

[0072] Figure 6 shows that limiting the target angle of attack and the corresponding limitation of the actual angle of attack A to the value A1 initially has no significant influence on the boost pressure P1 in the air supply area 16. Only when conditions gradually return to steady state is the boost pressure P1 in the air supply area 16 slightly lower in the third operating scenario than in the other two operating scenarios.

[0073] Figure 7 is of particular importance: it shows that, due to the action of functional block 64, the exhaust back pressure P2 in the exhaust gas area 18 is, at least initially, significantly lower in the third operating scenario than in the other two operating scenarios. The exhaust back pressure is therefore lower due to the action of functional block 64 (third operating scenario) than it would be without this action (first and second operating scenarios). This allows scavenging to be carried out reliably despite the requested power increase. More fresh air thus enters the combustion chamber 14, leading to more combustion and therefore more torque T. The positive effect of scavenging thus outweighs the negative effect of the smaller angle of attack of the turbine blades, as reflected in the higher torque T shown in Figure 3 for the third operating scenario compared to the other two.

Claims

R.415353 - 13 - Claims 1. Method for operating an internal combustion engine (10) with gaseous fuel, in which compressed air is supplied to a combustion chamber (14) at least temporarily by means of an exhaust gas turbocharger (24) and in which scavenging is active at least temporarily, characterized in that when scavenging is active, and depending on the result of an evaluation of a quantity that characterizes a target power increase, a measure is carried out by which an exhaust gas back pressure is limited.

2. Method according to claim 1, characterized in that the measure indirectly or directly reduces the power of a turbine of the exhaust gas turbocharger (24).

3. Method according to at least one of claims 1 or 2, characterized in that the measure is at least one of the following group: Limiting the target angle of attack of the turbine blades of the exhaust gas turbocharger (24) or a quantity characterizing the target angle of attack; Limiting a target value for a boost pressure; Limiting a target value for a filling coefficient; Limiting a target value for an exhaust back pressure.

4. Method according to at least one of the preceding claims, characterized in that the parameter characterizing the target power increase is at least one of the following group: difference between an actual boost pressure and a boost pressure in steady-state operation of the internal combustion engine (10); difference between an actual filling coefficient and a filling coefficient in steady-state operation of the internal combustion engine (10); difference between an actual power output and a target power output of the internal combustion engine (10); gradient of a target torque; gradient of a target injection quantity; gradient of an actual R.415353 - 14 - Engine speed (10); intervention of a limiting of the filling coefficient for transient operation of the internal combustion engine (10); gradient of a target boost pressure.

5. Computer program product, comprising instructions that are used in the execution of the Programs by a computer cause it to execute the method according to at least one of the preceding claims.

6. Control unit (46) for controlling and / or regulating the operation of an internal combustion engine (10), comprising at least one processor (48), at least one memory (50) and at least one computer program product stored on the memory (50) according to claim 5.

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