CN120225772A - Method for operating an internal combustion engine for gaseous fuels - Google Patents

Abstract

The application relates to a method for operating a hydrogen internal combustion engine, comprising the steps of a) determining a combustion stability limit (lambda _Max) on the basis of operating parameters (I ₁,I₂) of the internal combustion engine, in particular the rotational speed and the required torque, B) determining a lambda setpoint value (lambda _soll) for the current air charge of the internal combustion engine, C) calculating activation signals for a plurality of control measures (A, B, C) on the basis of the lambda setpoint value lambda _soll, the combustion stability limit lambda _Max and the operating parameters (I ₁,I₂) of the internal combustion engine, d) prioritizing the control measures (A, B, C) on the basis of the activation signals, e) carrying out one or more control measures (A, B, C) on the internal combustion engine on the basis of the prioritization.

Description

Method for operating an internal combustion engine for gaseous fuels

Technical Field

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

Internal combustion engines may operate on liquid and gaseous fuels. In this case, these fuels can be introduced either directly into the combustion chamber of the internal combustion engine or into the intake tract of the internal combustion engine. In combustion methods using external ignition and when using gaseous fuels, an important regulating parameter is the so-called Lambda value (Lambda value), which represents the ratio of the amount of oxygen available to the amount of fuel in the combustion chamber. A lambda value of 1 means that the amount of oxygen present in the combustion chamber happens to burn the fuel in the combustion chamber without surplus. If less oxygen is present in the combustion chamber, the lambda value is less than 1, which is referred to as a rich fuel mixture. If there is an excess of oxygen in the combustion chamber, it is referred to as a lean mixture (lambda > 1). For example, if the amount of oxygen is twice the amount required to completely combust the gaseous fuel located there, then the lambda value is 2. An example of a lambda value adjustment is known from DE 10 2022 201 852 A1.

In the combustion of hydrogen, lambda values of greater than 1, usually much greater than 1, are always sought. This allows on the one hand to reduce fuel consumption and on the other hand to reduce nitrogen oxide emissions. However, even in the case of low power demand, the lambda value cannot be increased arbitrarily, since the combustion stability will not be guaranteed if it is increased arbitrarily. 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, a combustion stability limit exists, for example, at λ=4. Therefore, when the internal combustion engine is running, it is necessary to avoid exceeding this limit.

Very high lambda values are particularly easy to occur when the internal combustion engine is operated at medium or high load and the power demand of the internal combustion engine is reduced rapidly thereafter. At this time, only a small amount of fuel is introduced into the combustion chamber, while the air supply, which is typically done by a turbocharger, has a certain inertia, so that relatively much oxygen is still introduced into the combustion chamber. That is, this problem occurs mainly when the engine that was previously operated at a relatively high load is shifted to the low load operation. In this case, there is still a high boost pressure (Ladedruck) in the air system that was previously required in order to be able to burn the amount of hydrogen required at that time at lambda values greater than 1.

In order to avoid this problem, various measures are known. For example, the air supply can be throttled, but this can only be adjusted to the desired range after a certain delay. Furthermore, in a multi-cylinder internal combustion engine, one or more cylinders may be deactivated such that the remaining hydrogen may be distributed among the remaining cylinders and thereby more hydrogen may be introduced into each cylinder, which may reduce the lambda value within the combustion chambers. In addition, the exhaust gas recirculation may be varied, i.e. more combusted air is recirculated from the exhaust passage to the fresh air region, to bring the lambda value into the desired range. Yet another approach may be to adjust the firing angle to a later angle, but this may result in reduced efficiency.

All these measures have their particular advantages and disadvantages and, given the existing functions in the control unit, can only be distinguished from one another to a limited extent or not sufficiently specifically. This means that it is difficult to decide which measures, alone or in combination, can be used to quickly adjust the lambda value to the desired range.

Disclosure of Invention

The inventive method for operating a hydrogen internal combustion engine has the advantage that, depending on the operating point of the internal combustion engine, appropriate measures can be quickly introduced to set the lambda value of the internal combustion engine to a desired range. For this purpose, the method is carried out by first determining, based on the operating parameters of the internal combustion engine, in particular the rotational speed and the torque required, a maximum lambda value (lambda _Max value) which just meets the combustion stability limit. Then, a lambda setpoint value is determined, which is derived from the current air charge (Luftf u llung) and the fuel quantity that corresponds to the current driver's wishes. If the lambda value obtained when the driver wishes is achieved is greater than lambda _Max, the activation signal is calculated for a plurality of control measures on the basis of the lambda _Max value, the operating parameters of the internal combustion engine and the lambda setpoint value. These control measures are then prioritized according to the activation signal, and finally the control measures are implemented on the internal combustion engine according to the prioritization.

The control measure is an intervention in the control of the internal combustion engine to adjust the lambda value to a desired value or to remain within a desired range. For this purpose, various control measures are possible, such as deactivating one or more cylinders (if the internal combustion engine has a plurality of cylinders), adjusting the ignition point in time 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 combusted combustion air recirculated from the exhaust passage to the fresh air supply of the internal combustion engine. By taking the activation signal into account it can be determined which control measure is most effective in adjusting the lambda value to the desired range. This is very important when the load of the combustion engine changes, in particular when switching from a relatively high load to a low load and then back again to a high load. In this case, certain control measures can also be given higher priority from the beginning during the application of the internal combustion engine. By these control measures, the response characteristics of the internal combustion engine can also be improved, in particular after rapid load changes.

In a first advantageous embodiment, the activation signal is determined as a function of the engine speed of the internal combustion engine and the torque required. The effectiveness of the individual control measures in adjusting the lambda value to the desired range may vary depending on the state of the internal combustion engine. 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 measures. The sequence of the measures can also be influenced by the application of the internal combustion engine, so that certain measures can be introduced first.

In a further advantageous embodiment, the activation signal of the control measure is normalized (normiert). In this way, the activation signals of the individual control measures can be compared and the most effective control measure can be reliably determined.

In a further advantageous embodiment, in the case of a multi-cylinder internal combustion engine, the control measure is to deactivate the cylinders. If one or more cylinders are no longer fueled, i.e., deactivated, then the supplied fuel (e.g., hydrogen or other gaseous fuel) may be distributed to the remaining cylinders. This reduces the lambda value, leaving the lambda _Max limit, with the air supply unchanged, and the engine continues to operate in the optimum range.

In a further advantageous embodiment, the control means is to vary the boost pressure. For example, boost pressure may be affected by changing the turbocharger or changing the throttle valve. Thus the air entering the combustion chamber is reduced, which also reduces the lambda value.

In a further advantageous embodiment, the exhaust gas recirculation is changed by adapting the exhaust gas recirculation characteristic field (Abgasr u ckf u hrungskennfeld) accordingly. 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 lambda value to within the desired range.

In a further advantageous embodiment, the ignition point is changed as a control measure. In this way, the desired torque of the internal combustion engine can be achieved with normal combustion and a suitable lambda value.

Drawings

Figure 1 shows the course of the lambda value and boost pressure as the load of the engine changes,

Figure 2 shows the corresponding torque of the internal combustion engine,

Fig. 3 shows a flow chart of the control of an internal combustion engine according to the invention.

Detailed Description

Internal combustion engines for gaseous fuels typically operate with excess air in the combustion chamber, that is, with an amount of oxygen in the combustion chamber that is greater than the amount of oxygen required to combust the gaseous fuel. This reduces nitrogen oxide emissions and improves combustion, particularly in internal combustion engines operating with gaseous hydrogen. When switching from medium or high load to low load, i.e. when the fuel supply is rapidly reduced due to the driver's wishes, a high excess of air occurs in the combustion chamber, since the regulation of the supply of the combustion chamber with oxygen in the air is relatively late and continues to operate for a period of time after the hydrogen amount has been reduced, in particular when the air supply is performed by means of a turbocharger. This results in a significant increase in lambda value, i.e. an increase in the ratio of fuel to oxygen in the air in the combustion chamber. Lambda value 1 corresponds exactly to the amount of oxygen required for complete combustion of the gaseous fuel. If more oxygen is present, the lambda value is greater than 1 (lean mixture).

However, the lambda value cannot be raised arbitrarily, and when a specific maximum lambda value (lambda _Max) is reached, a combustion stability limit is reached up to which normal combustion can take place. Further increases in lambda values, i.e. higher excess oxygen in the combustion chamber, can lead to combustion instabilities, in which the internal combustion engine can only produce insufficient torque or even fail to ignite. Fig. 1 plots the time course of lambda values as the load changes. It is noted that the lambda value increases from top to bottom in this figure. A decrease in the supply amount of hydrogen supplied to the combustion chamber due to a change in the driver's desire causes a rapid rise in the lambda value from 2 to 4 at time t 1. By appropriate intervention in the internal combustion engine it is ensured that the combustion stability limit (λ=4 in this example) is not exceeded and combustion is thus kept stable. In contrast, the boost pressure p of the engine is decreased with a delay, as shown by a curve p1 in fig. 1. In this figure, the boost pressure increases from bottom to top, as indicated by the right p-axis. If the driver again requires more power at time t2, the lambda value will drop and quickly return to the optimal range of lambda=2. Here too, the boost pressure p rises with a delay and eventually reaches an initial value again.

The corresponding torque M in this example is shown in fig. 2. At time t1, torque M decreases until a significantly lower level is reached due to the reduced hydrogen supply. At time point t2, as the hydrogen supply amount increases, the torque M rises again (curve I) until the initial value is reached again. However, due to air conditioning hysteresis, the power or torque does not rise immediately. The torque build-up after power reduction can also be improved by the measures taken, as shown by curve p ₂ in fig. 1 and curve II in fig. 2. The magnitude of the boost pressure drop is not as great as in normal control, which accelerates the power build-up at time point t 2. This is advantageous especially when the power demand changes rapidly.

By means of the method according to the invention, an adjustment of the lambda value can be achieved such that the lambda value does not reach or exceed the combustion stability limit. The combustion stability limit is dependent on the state of the internal combustion engine, in particular on the rotational speed of the internal combustion engine and the torque prevailing. From these values, the current combustion stability limit (λ _Max) can be determined and compared with the expected value of λ (λ _soll). The lambda setpoint value is a lambda value which is derived from the current driver's desire (pedal position), the current air charge of the combustion chamber or of the intake tract, and other requirements (for example transmission or ESP interventions).

The lambda _Max value and the lambda setpoint value are used together with the current operating parameters of the internal combustion engine (i.e. the motor speed, the torque prevailing and possibly other parameters, such as the intake air temperature) to prioritize the possible interventions of the internal combustion engine. Thus, each possible measure is assigned an activation signal that represents the effectiveness in influencing the lambda value to keep it in the desired range within the combustion stability limits.

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 highest, then a corresponding number of cylinders will be deactivated and no fuel will be supplied thereto. The remaining fuel is distributed to the other cylinders, thereby lowering the lambda value there and ensuring optimal combustion. If several measures are ascertained by the control unit from the prioritization, for example, the cylinders are deactivated and the ignition point is changed, several measures can also be introduced simultaneously.

The method of the present invention is shown in flow chart form in fig. 3. State variables I ₁、I₂, etc. characterize the state of the internal combustion engine, such as the torque present, the driver's wishes present and the rotational speed. The combustion stability limit lambda _Max, which should not be exceeded during operation of the internal combustion engine, is thus determined. The lambda desired value (lambda _soll) is determined from the current driver's desire (i.e., pedal position) and the current air charge in the intake passage. Other requirements, such as transmission or ESP interventions, are also contemplated herein. In this case, using the two lambda values (lambda _soll,λ_Max), the activation signals are calculated and prioritized in the control unit P and finally one or more measures A, B or C are introduced.

By means of the measures introduced, the torque build-up after a power reduction can also be improved, as shown by the curve p ₂ in fig. 1 and the curve II in fig. 2. The magnitude of the boost pressure drop is not as great as in normal control, which accelerates the power build-up at time point t 2. This is advantageous especially when the power demand changes rapidly.

Claims (7)

1. A method for operating a hydrogen internal combustion engine, comprising the following method steps:

-determining a combustion stability limit (lambda _Max) based on an operating parameter (I ₁,I₂) of the internal combustion engine, in particular the rotational speed and the required torque;

-determining a lambda desired value (lambda _soll) for the current air charge of the internal combustion engine;

-calculating activation signals for a plurality of control measures (a, B, C) based on said lambda desired value lambda _soll, said combustion stability limit lambda _Max and said operating parameter (I ₁,I₂) of the internal combustion engine;

-prioritizing the control measures (a, B, C) according to an activation signal;

-implementing one or more control measures (a, B, C) on the internal combustion engine according to said prioritization.

2. The method of claim 1, wherein the activation signal is determined based on an engine speed of the internal combustion engine and a requested torque.

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

4. A 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 the cylinders.

5. A method according to any one of claims 1-3, characterized in that one control measure is to vary the boost pressure.

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