Method for operating a combustion engine for gaseous fuels
Patent Information
- Application Number
- EP2023801412
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-11-08
- Filing Date
- 2023-11-06
- Publication Date
- 2025-09-17
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Internal combustion engines operating on hydrogen face challenges in maintaining combustion stability when switching to low load operation, as the lambda value (X value) exceeds the desired range due to inertia in air supply and high boost pressure, leading to instability and inefficiency.
A method that dynamically adjusts control measures such as cylinder deactivation, ignition timing, and exhaust gas recirculation based on real-time operating parameters to maintain the X value within a stable range, prioritizing effective interventions to quickly respond to load changes and ensure optimal combustion.
Enables rapid and precise control of the X value, preventing combustion stability limits from being exceeded, improving engine response and torque build-up during load changes, and reducing nitrogen oxide emissions.
Smart Images
Figure 1.1
Abstract
Description
[0001] title
[0002] Method for operating an internal combustion engine for gaseous fuels
[0003] The invention relates to a method for operating an internal combustion engine, preferably an internal combustion engine for gaseous fuels, in particular for hydrogen.
[0004] State of the art
[0005] Internal combustion engines can be operated with liquid and gaseous fuels. The fuels can be introduced either directly into the combustion chamber of an internal combustion engine or into the engine's intake tract. In spark-ignition combustion processes and the use of gaseous fuels, an important control variable is the so-called lambda value (X value), which indicates the ratio of available oxygen to the amount of fuel in the combustion chamber. A lambda value of X = 1 means that exactly the amount of oxygen is present in the combustion chamber to completely burn the fuel present there. If there is less oxygen in the combustion chamber, the X value is less than 1 and the mixture is referred to as rich. If there is an excess of oxygen in the combustion chamber, the mixture is referred to as lean (X > 1).For example, if twice as much oxygen is present as is required for the complete combustion of the gaseous fuel present there, the X-value is 2. An example of a control of the X-value is known from DE 10 2022 201 852 Al.
[0006] When burning hydrogen, the aim is always to achieve an X-value greater than 1, usually significantly greater than 1. This not only keeps fuel consumption low but also reduces nitrogen oxide emissions. However, even at low power requirements, the X-value cannot be arbitrarily large, as otherwise combustion stability can no longer be guaranteed. This combustion stability limit depends on the operating point of the internal combustion engine, i.e. in particular on the speed and the amount of hydrogen currently available in the combustion chamber. The combustion stability limit depends on the operating point, for example, at X = 4. When operating the internal combustion engine, exceeding this limit must therefore be avoided.
[0007] Very high X values can occur particularly when the combustion engine has been operating under medium or heavy load and then the power requirement of the combustion engine is reduced very quickly. In this case, only a small amount of fuel is introduced into the combustion chamber, while the air supply, which usually runs via a turbocharger, has a certain inertia, so that a relatively large amount of oxygen continues to be introduced into the combustion chambers. The problem therefore mainly occurs when switching to low-load operation if the engine was previously operating under a relatively high load. In this case, there is still a high boost pressure in the air system, which was previously required to burn the quantities of hydrogen required there with X values greater than 1.
[0008] Various measures are known to avoid this problem. For example, the air supply can be throttled, but this only brings the X-value into the desired range with a certain delay. Furthermore, in multi-cylinder combustion engines, one or more cylinders can be switched off, so that the remaining hydrogen is distributed among the remaining cylinders and more hydrogen is introduced per cylinder, which lowers the X-value in these combustion chambers. In addition, the exhaust gas recirculation can be modified, i.e. more burned air from the exhaust tract is returned to the fresh air region in order to bring the X-value into the desired range. Another measure can be adjusting the ignition angle to a later one, which leads to poorer efficiency.
[0009] All of these measures have specific advantages and disadvantages, and with the existing functionality in the control unit, they can only be differentiated from one another to a limited extent or not sufficiently specifically. This means that it is difficult to decide which measure, individually or in combination, will quickly bring the X-value back into the desired range.
[0010] Advantages of the invention
[0011] The method according to the invention for operating a hydrogen combustion engine has the advantage that, depending on the operating point of the combustion engine, the correct measure can be quickly initiated to bring the X-value of the combustion engine into a desired range. For this purpose, the method is carried out with the following steps: First, a maximum X-value is determined based on the operating parameters of the combustion engine, in particular the speed and the requested torque, which just meets the combustion stability limit (XMax value). Subsequently, an X-setpoint value is determined, which results from the current air charge and the fuel quantity that corresponds to the current driver command. If an X-value greater than XMax results when implementing the driver command, activation signals for a variety of control measures are calculated based on the XMax value, the operating parameters of the combustion engine, and the X-setpoint value.The control measures are then prioritized based on the activity signals and finally control measures are implemented on the combustion engine depending on the prioritization.
[0012] Control measures are interventions in the control system of the combustion engine in order to bring the X-value to the desired value or to maintain it within a desired range. Various control measures are possible for this: shutting down one or more cylinders (if the combustion engine has multiple cylinders), adjusting the ignition timing, or changing the air supply to the combustion chambers. Changing the air supply also includes changing the exhaust gas recirculation, i.e., the proportion of burned combustion air that is returned from the exhaust tract to the fresh air supply of the combustion engine. By taking the activation signals into account, the control measure that most effectively brings the X-value into the desired range can be determined.This is important during load changes of the combustion engine, especially when switching from a relatively high load to a low load and then back to a high load. Certain control measures can also be given higher priority from the outset during a combustion engine calibration. These control measures can also improve the responsiveness of the combustion engine, especially after rapid load changes.
[0013] In a first advantageous embodiment, the activation signals are determined depending on the engine speed and the requested torque of the combustion engine. Depending on the condition of the combustion engine, individual control measures can be used more or less effectively to bring the X-value into the desired range. This is taken into account by the calculated activation signal, which is a measure of effectiveness, so that the most effective measure can be identified and implemented. The sequence of measures can also be influenced by an application of the combustion engine, so that individual measures are initiated preferentially from the outset.
[0014] In a further advantageous embodiment, the activation signals of the control measures are standardized. This allows a comparison of the activation signals of the individual control measures and a reliable determination of the most effective control measure.
[0015] In a further advantageous embodiment, the control measure is a deactivation of cylinders in multi-cylinder engines. If one or more cylinders are no longer supplied with fuel, i.e., deactivated, the supplied fuel - for example, hydrogen gas or another gaseous fuel - is distributed among the remaining cylinders. With a constant air supply, this results in a reduction of the X value, so that the X Ma x-limit is removed and the engine continues to run in an optimal range.
[0016] In a further advantageous embodiment, the control measure is a change in the boost pressure. The boost pressure can be influenced, for example, by adjusting the turbocharger or the throttle valve. This allows less air to enter the combustion chambers, which also lowers the X-value. In a further advantageous embodiment, the exhaust gas recirculation is modified by adjusting the exhaust gas recirculation map accordingly. This allows more or less exhaust gas to be recirculated back into the combustion chamber, thus reducing the oxygen occupancy of the combustion chamber and quickly bringing the X-value into the desired range.
[0017] In a further advantageous embodiment, the ignition timing is changed as a control measure. This allows the target torque of the combustion engine to be achieved with proper combustion and a suitable X value.
[0018] drawing
[0019] Fig. 1 shows a curve of the X-value and the boost pressure during a load change of the internal combustion engine, Fig. 2 shows the associated torque of the internal combustion engine and Fig. 3 shows a flow diagram of the control of the internal combustion engine according to the invention.
[0020] Description of the embodiments
[0021] Internal combustion engines for gaseous fuels usually operate with an excess of air in the combustion chamber, i.e. there is more oxygen than is required to burn the gaseous fuel. This reduces nitrogen oxide emissions and improves combustion, particularly in internal combustion engines powered by gaseous hydrogen. When transitioning from a medium or high load to a low load, i.e. when the fuel supply is throttled back very quickly due to the driver's wishes, there is a high excess of air in the combustion chamber. This is because the control for supplying the combustion chamber(s) with atmospheric oxygen is relatively sluggish and continues for some time after the amount of hydrogen has been reduced, particularly if the air supply is provided via a turbocharger. This leads to a significant increase in the X-value, i.e. the ratio of fuel to atmospheric oxygen in the combustion chamber.An X-value of 1 corresponds exactly to the amount of oxygen required for complete combustion of the gaseous fuel. If more oxygen is present, the X-value is greater than 1 (lean mixture). However, the X-value cannot be increased arbitrarily: at a certain maximum X-value (ΔMax), the combustion stability limit is reached, up to which normal combustion can take place. A further increase in the X-value, i.e. an even greater excess of oxygen in the combustion chamber, leads to unstable combustion, in which the combustion engine only develops insufficient torque or no longer ignites at all. Fig. 1 shows a curve of the X-value over time, as it occurs during a load change. It should be noted that the X-value increases from top to bottom in this diagram. Due to a reduction in the H2 supply to the combustion chambers due to the changed driver command, the X-value increases rapidly from 2 to 4 at time t1.Appropriate interventions in the combustion engine ensure that the combustion stability limit – in this example X = 4 – is not exceeded, thus ensuring stable combustion. In contrast, the engine's boost pressure p decreases only after a delay, as can be seen from the curve pi in Fig. 1. In this illustration, the boost pressure increases from bottom to top, as shown on the p-axis on the right. If the driver requests more power again at a time t2, the X value decreases and quickly returns to the optimal range at X = 2. The boost pressure p also increases after a delay and finally returns to the initial value.
[0022] The corresponding torque M for this example is shown in Fig. 2. At time t1, the torque M decreases due to the throttled hydrogen supply until it reaches a significantly lower level. At time e, the torque M increases again due to the increased supply of H2 (curve I) until the initial value is reached again. However, the power or torque does not increase instantaneously due to the sluggish air control. The measures introduced can also improve the build-up of torque after a reduction in power, as shown by curves p2 in Fig. 1 and curve II in Fig. 2. The boost pressure does not drop as much as with normal control, which accelerates the power build-up at time t2. This is particularly advantageous when the power requirement changes quickly.
[0023] With the method according to the invention, the X value can be controlled in such a way that the X value does not reach or exceed the combustion stability limit. The combustion stability limit depends on the state of the internal combustion engine, in particular on the speed and the currently applied torque of the internal combustion engine. Using these values, the current combustion stability limit can be determined (XMax) and compared with an X setpoint (X S0 n). The X-setpoint is the X-value resulting from the current driver input (pedal position), the current air charge in the combustion chambers or intake tract, and other requirements, such as transmission or ESP intervention.
[0024] The "Max" value and the "X" setpoint are used together with the current operating parameters of the combustion engine—i.e., the engine speed, the applied torque, and possibly other variables, such as intake air temperature—to prioritize the multitude of possible interventions on the combustion engine. Each of the possible measures is assigned an activation signal that indicates its effectiveness in influencing the X value to keep it within the desired range on this side of the combustion stability limit.
[0025] The possible measures, such as ignition timing adjustment, air system intervention (throttle valve position), or cylinder suppression, are prioritized based on the activation signal in order to ultimately select one or more measures. If, for example, cylinder suppression has the highest priority for the current condition and taking into account the combustion stability limit XMax, the corresponding number of cylinders are suppressed and no longer supplied with fuel. The remaining fuel is thus distributed among the remaining cylinders, which lowers the X value there and ensures optimal combustion. Several measures can also be initiated simultaneously, such as cylinder deactivation and a change in the ignition timing, if this is determined by the control unit based on the prioritization.
[0026] The method according to the invention is shown as a flow chart in Fig. 3. The state variables li, h, ... characterize the state of the combustion engine, such as the applied torque, the current driver command, and the speed. From this, the combustion stability limit XMax is determined, which should not be exceeded during operation of the combustion engine. The X setpoint (X S0 n) is determined from the current driver input—i.e., the pedal position—and the current air charge in the intake tract. Other requirements, such as transmission or ESP interventions, are also taken into account here. These two X values (Ä. so ii, ÄMax) the activation signals are then calculated and prioritized in the control unit P and finally one or more of the measures A, B or C are initiated.
[0027] The implemented measures also improve torque buildup after a power reduction, as shown by curves P2 in Fig. 1 and curve II in Fig. 2. The boost pressure does not drop as much as with normal control, accelerating the power buildup at time ts. This is particularly advantageous during rapid changes in power demand.
Claims
Claims 1. Method for operating a hydrogen combustion engine with the following process steps: - Determine a combustion stability limit (X Ma x) based on the operating parameters (li, b) of the internal combustion engine, in particular the speed and the requested torque, - Determine the lambda setpoint (X S0 n) for the current air charge of the combustion engine, - Calculation of activation signals of a variety of control measures (A, B, C) based on the lambda setpoint X S0 n, the combustion stability limit ÄMax and the operating parameters (li, b) of the combustion engine, - Prioritization of control measures (A, B, C) based on the activation signals, - Implementation of one or more control measures (A, B, C) depending on the prioritization on the combustion engine.
2. Method according to claim 1, characterized in that the activation signals are determined as a function of the engine speed and the requested torque of the internal combustion engine.
3. Method according to claim 1, characterized in that the activation signals of the control measures are standardized.
4. Method according to one of claims 1 to 3, characterized in that the control measure is a deactivation of cylinders in multi-cylinder engines.
5. Method according to one of claims 1 to 3, characterized in that the control measure is the change of the boost pressure. Method according to one of claims 1 to 3, characterized in that the control measure is the modification of the exhaust gas recirculation characteristic map. Method according to one of claims 1 to 3, characterized in that the control measure is the modification of the ignition timing.