Method for operating internal combustion engine for gaseous fuel

Abstract

The invention relates to a method for operating a hydrogen internal combustion engine, comprising the following method steps: a) determining a combustion stability limit (Lambda Max) on the basis of operating parameters (I1, I2) of the internal combustion engine, in particular a rotational speed and a required torque; b) determining a lambda desired value (lambda soll) for a current air charge of the internal combustion engine; c) calculating activation signals for the plurality of control measures (A, B, C) on the basis of the lambda desired value lambda soll, the combustion stability limit lambda Max and the operating parameters (I1, I2) of the internal combustion engine; d) prioritizing the control measures (A, B, C) in accordance with the activation signal; e) implementing one or more control measures (A, B, C) on the internal combustion engine according to the priority ranking.

Description

Field of the Invention

[0001] The present invention relates to a method for operating an internal combustion engine, preferably an internal combustion engine for gaseous fuels, in particular for hydrogen. Background Art

[0002] Internal combustion engines can be operated with liquid and gaseous fuels. Here, these fuels can be introduced either directly into the combustion chamber of the internal combustion engine or into the intake duct of the internal combustion engine. In combustion methods with external ignition and when using gaseous fuels, an important adjustment parameter is the so-called Lambda value (λ value), which represents the ratio of the amount of oxygen available in the combustion chamber to the amount of fuel. A λ value of 1 means that the amount of oxygen present in the combustion chamber is exactly sufficient to burn the fuel in the combustion chamber without residue. If there is less oxygen in the combustion chamber, then the λ value is less than 1, and this is called a rich fuel mixture. If there is an excess of oxygen in the combustion chamber, it is called a lean fuel mixture (λ > 1). For example, if the amount of oxygen is twice the amount required to completely burn the gaseous fuel located there, then the λ value is 2. An example of λ value adjustment can be found in DE 10 2022 201 852A1.

[0003] When burning hydrogen, a λ value greater than 1 is always pursued, usually much greater than 1. This can reduce fuel consumption on the one hand and nitrogen oxide emissions on the other hand. However, even in the case of low power demand, the λ value cannot be increased arbitrarily because: if it is increased arbitrarily, combustion stability cannot be guaranteed. The combustion stability limit depends on the operating point of the internal combustion engine, in particular on the rotational speed and the current available amount of hydrogen in the combustion chamber. Depending on the operating point, the combustion stability limit exists, for example, at λ = 4. Therefore, when the internal combustion engine is operating, it is necessary to avoid exceeding this limit.

[0004] When the internal combustion engine is operating at medium or high load and then the power requirement of the internal combustion engine rapidly decreases, very high λ values are particularly likely to occur. At this time, only a small amount of fuel is introduced into the combustion chamber, while the air supply usually carried out by a turbocharger has a certain inertia, so relatively more oxygen is still introduced into the combustion chamber. That is, this problem mainly occurs when an engine that was previously operating at a relatively high load switches to low-load operation. In this case, there is still the following high boost pressure in the air system: the high boost pressure was required to be able to burn the amount of hydrogen required at that time with a λ value greater than 1.

[0005] To avoid this problem, various measures are known. For example, the air supply can be throttled, but this can only adjust the λ value to the desired range after a certain delay. In addition, in a multi-cylinder internal combustion engine, one or more cylinders can be deactivated, so that the remaining hydrogen is distributed to the remaining cylinders, and thus more hydrogen is introduced into each cylinder, which reduces the λ value in these combustion chambers. Additionally, the exhaust gas recirculation can be changed, i.e., more of the burned air is recirculated from the exhaust duct to the fresh air area to bring the λ value into the desired range. Another measure can be to adjust the ignition angle to a later angle, but this results in a reduction in efficiency.

[0006] All of these measures have their specific advantages and disadvantages, and under the existing functions in the control unit, they can only be distinguished from each other to a limited extent or not sufficiently specifically. This means that it is difficult to decide which measure, used alone or in combination, can quickly adjust the λ value to the desired range. Summary of the Invention

[0007] The method for operating a hydrogen internal combustion engine according to the invention has the following advantages: the correct measures can be quickly introduced according to the operating point of the internal combustion engine to adjust the λ value of the internal combustion engine to the desired range. For this purpose, the method is implemented by the following steps: First, based on the operating parameters of the internal combustion engine, in particular the rotational speed and the required torque, the maximum λ value (λ Max value) is determined, which just meets the combustion stability limit. Then, the desired λ value is determined, which is derived from the current air filling and the fuel quantity that conforms to the current driver's wish. If the λ value obtained when realizing the driver's wish is greater than λ Max , then based on the λ Max value, the operating parameters of the internal combustion engine, and the desired λ value, activation signals are calculated for a plurality of control measures. Then, these control measures are prioritized according to the activation signals, and finally the control measures are implemented on the internal combustion engine according to the prioritization.

[0008] A control measure is an intervention in the control of an internal combustion engine to adjust the λ value to a desired value or keep it within a desired range. For this purpose, various control measures are feasible: deactivating one or more cylinders (if the internal combustion engine has multiple cylinders), adjusting the ignition timing, or changing the air supply to the combustion chamber. Changing the air supply also includes changing the exhaust gas recirculation, i.e., changing the proportion of the post-combustion combustion air recirculated from the exhaust passage to the fresh air supply of the internal combustion engine. By considering the activation signal, it is possible to determine which control measure can most effectively adjust the λ value within the desired range. This is very important when the load of the internal combustion engine changes, especially when switching from a relatively high load to a low load and then back to a high load. Here, during the application process of the internal combustion engine, certain control measures can also be given higher priority from the beginning. Through these control measures, the response characteristics of the internal combustion engine can also be improved, especially after rapid load changes.

[0009] In a first advantageous configuration, the activation signal is determined based on the engine speed of the internal combustion engine and the required torque. Depending on the state of the internal combustion engine, the effectiveness of the individual control measures in adjusting the λ value within the desired range may vary. This is taken into account by the calculated activation signal, which is a measure of effectiveness, in order to be able to identify and implement the most effective measure. The order of the measures can also be influenced by the application of the internal combustion engine, such that certain measures can be introduced preferentially from the beginning.

[0010] In another advantageous configuration, the activation signals for the control measures are normalized. This allows the activation signals of the individual control measures to be compared and the most effective control measure to be reliably determined.

[0011] In another advantageous configuration, in the case of a multi-cylinder internal combustion engine, the control measure is to deactivate cylinders. If one or more cylinders are no longer supplied with fuel, i.e., deactivated, the supplied fuel (such as hydrogen or other gaseous fuels) is distributed to the remaining cylinders. With the air supply remaining unchanged, this reduces the λ value, thus moving away from the λ Max limit, and the engine continues to operate within the optimal range.

[0012] In another advantageous configuration, the control measure is to change the boost pressure. For example, the boost pressure can be influenced by changing the turbocharger or changing the throttle valve. This reduces the amount of air entering the combustion chamber, which also reduces the λ value.

[0013] In another advantageous configuration, the exhaust gas recirculation is changed by correspondingly adapting the exhaust gas recirculation characteristic field. This allows more or less exhaust gas to be reintroduced into the combustion chamber, thereby reducing the oxygen content in the combustion chamber in order to quickly adjust the λ value within the desired range.

[0014] In another advantageous configuration, the ignition time point is changed as a control measure. In this way, the desired torque of the internal combustion engine can be achieved under normal combustion and with a suitable lambda value. Description of the Drawings

[0015] Figure 1 Shows the variation process of the lambda value and the boost pressure when the load of the internal combustion engine changes,

[0016] Figure 2 Shows the corresponding torque of the internal combustion engine,

[0017] Figure 3 Shows the flow chart of the control of the internal combustion engine according to the present invention. Detailed Description of the Invention

[0018] Internal combustion engines for gaseous fuels usually operate with excess air in the combustion chamber, that is, there is more oxygen in the combustion chamber than is required to burn the gaseous fuel. This reduces nitrogen oxide emissions and improves combustion, especially in internal combustion engines operating with gaseous hydrogen. When switching from medium or high load to low load, that is, when the fuel supply is rapidly reduced due to the driver's wish, there will be high excess air in the combustion chamber because the regulation of the supply of oxygen in the air to the combustion chamber is relatively lagged and will continue to operate for some time after the amount of hydrogen has decreased, especially when the air supply is carried out through a turbocharger. This results in a significant increase in the lambda value, that is, the ratio of fuel to oxygen in the air in the combustion chamber increases. A lambda value of 1 exactly corresponds to the amount of oxygen required for complete combustion of the gaseous fuel. If there is more oxygen, then the lambda value is greater than 1 (lean fuel mixture).

[0019] However, the lambda value cannot be increased arbitrarily: when a specific maximum lambda value (lambda Max ) is reached, the combustion stability limit is reached, and normal combustion can be carried out until this limit. Further increasing the lambda value, that is, having a higher excess oxygen in the combustion chamber, will lead to unstable combustion. In the case of unstable combustion, the internal combustion engine can only produce insufficient torque or even cannot ignite. Figure 1 The variation process of the lambda value with time during load change is plotted. It should be noted that in this figure, the lambda value increases from top to bottom. The reduction in the amount of hydrogen supplied to the combustion chamber due to the change in the driver's wish causes: at time point t1, the lambda value rapidly rises from 2 to 4. By making corresponding interventions in the internal combustion engine, it is ensured that the combustion stability limit (lambda = 4 in this example) is not exceeded, and thus the combustion remains stable. In contrast, the boost pressure p of the engine decreases with a delay, as Figure 1As shown by curve p1 in the figure. In this figure, the boost pressure increases from bottom to top, as shown by the p-axis on the right. If the driver demands more power at time point t2, then the λ value drops and quickly returns to the optimal range of λ = 2. Here, the boost pressure p also rises with a delay and finally reaches the initial value again.

[0020] The corresponding torque M in this example is Figure 2 shown. At time point t1, due to the reduced hydrogen supply, the torque M drops until it reaches a significantly lower level. At time point t2, due to the increased hydrogen supply, the torque M rises again (curve I) until it reaches the initial value again. However, due to the air conditioning lag, the power or rather the torque does not rise immediately. By the measures taken, the torque build-up after power reduction can also be improved, as Figure 1 shown by curve p2 in and Figure 2 curve II in. The drop in boost pressure is not as large as in normal control, which speeds up the power build-up at time point t2. This is especially beneficial when the power demand changes rapidly.

[0021] By the method of the present invention, the regulation of the λ value can be achieved so that the λ value does not reach or exceed the combustion stability limit. Here, the combustion stability limit depends on the state of the internal combustion engine, especially on the rotational speed of the internal combustion engine and the currently existing torque. Using these values, the current combustion stability limit (λ Max ) can be determined and compared with the desired λ value (λ soll ). Here, the desired λ value is the λ value derived from the current driver's wish (pedal position), the current air filling amount in the combustion chamber or intake passage, and other requirements (such as transmission or ESP intervention).

[0022] The λ Max value and the desired λ value, together with the current operating parameters of the internal combustion engine (i.e., the motor speed, the currently existing torque, and possibly other parameters such as the intake air temperature), are used to prioritize the possible multiple intervention measures for the internal combustion engine. Thereby, an activation signal is assigned to each possible measure, and this activation signal represents the effectiveness in terms of influencing the λ value to keep it within the desired range within the combustion stability limit.

[0023] The possible measures (such as ignition angle adjustment, air system intervention (throttle position), or cylinder deactivation) are prioritized according to the activation signal to finally select one or more measures. For example, for the current state and considering the combustion stability limit λ Max, if the priority of cylinder deactivation is the highest, then the corresponding number of cylinders will be deactivated and no fuel will be supplied to them. The remaining fuel will be distributed to other cylinders, thereby reducing the λ value there and ensuring optimal combustion. If multiple measures, such as cylinder deactivation and changing the ignition time point, are obtained through priority sorting by the control unit, multiple measures can also be introduced simultaneously.

[0024] The method of the present invention is shown in Figure 3 in the form of a flow chart. State variables I1, I2, etc. characterize the state of the internal combustion engine, such as the currently present torque, the current driver's desire, and the rotational speed. From this, the combustion stability limit λ that should not be exceeded during the operation of the internal combustion engine is determined. Max . The λ desired value (λ soll ) is determined from the current driver's desire (i.e., the pedal position) and the current air filling amount in the intake duct. Other requirements, such as transmission or ESP intervention, are also considered here. Here, using these two λ values (λ soll , λ Max ), an activation signal is calculated and prioritized in the control unit P, and finally one or more measures A, B, or C are introduced.

[0025] Through the introduced measures, the torque build-up after power reduction can also be improved, as shown by the curves p2 in Figure 1 and the curve II in Figure 2 . The magnitude of the boost pressure drop is not as large as in normal control, which accelerates the power build-up at time point t2. This is particularly advantageous when the power demand changes rapidly.

Claims

1. A method for operating a hydrogen internal combustion engine, comprising the following method steps: - Determine the combustion stability limit (λ Max ) based on the operating parameters (I1, I2) of the internal combustion engine, in particular the rotational speed and the required torque; - Determine the λ desired value (λ soll ) for the current air filling quantity of the internal combustion engine; - Based on the λ expected value λ soll , the combustion stability limit λ Max and the operating parameters (I1, I2) of the internal combustion engine, calculate the activation signals of various control measures (A, B, C); - Prioritize these control measures (A, B, C) according to an activation signal; - Implement one or more control measures (A, B, C) on the internal combustion engine according to the prioritization.

2. The method according to claim 1, wherein Determine the activation signal according to the engine speed and the required torque of the internal combustion engine.

3. The method according to claim 1, characterized in that, Normalize the activation signal of the control measure.

4. The method according to any one of claims 1 to 3, characterized in that In the case of a multi-cylinder engine, one control measure is to deactivate a cylinder.

5. The method according to any one of claims 1 to 3, characterized in that, One control measure is to change the boost pressure.

6. The method according to any one of claims 1 to 3, characterized in that, One control measure is to change the exhaust gas recirculation characteristic field.

7. The method according to any one of claims 1 to 3, characterized in that One control measure is to change the ignition time point.

Images