HYDROGEN COMBUSTION ENGINE

Abstract

Hydrogen combustion engine (100) with at least one closed control loop (101), with a sensor (103) for measuring the relative air-fuel ratio and / or the NOx concentration in the exhaust gas (105), which is arranged downstream of a catalyst (107); and a control unit (109) for controlling the amount of fuel supplied (111), the ignition angle, and / or the intake air mass flow based on the measured air-fuel ratio and / or the NOx concentration in the closed control loop (101).

Description

[0001] The invention relates to a hydrogen combustion engine and a method for controlling a hydrogen combustion engine.

[0002] Hydrogen combustion engines often operate with lean air / fuel ratios to achieve the desired fuel efficiency. However, lean engine operation can produce nitrogen oxides (NOx). NOx are conventionally reduced to elemental nitrogen and oxygen in aftertreatment systems. The efficiency and effectiveness of these aftertreatment systems, however, depend on the operating conditions of the hydrogen combustion engine. Measuring the relative air / fuel ratio with a lambda sensor positioned upstream in the exhaust gas before a catalytic converter is not possible with these hydrogen combustion engines because the measurement accuracy is affected by the hydrogen content in the exhaust gas.

[0003] The hydrogen combustion engine according to the invention, with at least one closed control loop, comprises a sensor for measuring the relative air-fuel ratio and / or the NOx concentration in the exhaust gas, which is arranged downstream of a catalyst, and a control unit for controlling the amount of fuel supplied, the ignition timing, and / or the intake air mass flow based on the measured air-fuel ratio and / or the NOx concentration in the closed control loop. The hydrogen combustion engine offers the technical advantage that the relative air-fuel ratio in the closed control loop can be influenced by controlling the amount of fuel supplied, thereby reducing nitrogen oxide emissions and the risk of abnormal combustion phenomena, such as knocking of the hydrogen combustion engine.

[0004] In an advantageous embodiment, the sensor (103) is a lambda probe or a NOx sensor. This offers the technical advantage that the relative air-fuel ratio and / or the NOx concentration in the exhaust gas can be determined using a simple and reliable method.

[0005] In an advantageous embodiment, the control unit is configured to adjust the supplied fuel quantity such that the relative air-fuel ratio remains above a predetermined lower limit. This adjustment can occur, for example, during a positive transient load change of the hydrogen combustion engine. This offers the technical advantage of ensuring, in a simple manner, that the predetermined lower limit of the relative air-fuel ratio is never undercut. This reduces NOx emissions and the risk of abnormal combustion phenomena, such as knocking or pre-ignition of the hydrogen combustion engine.

[0006] In a further advantageous embodiment, the control unit is configured to adjust the ignition timing and / or the amount of fuel supplied such that the NOx concentration remains below a predetermined upper limit. This adjustment can be made, for example, during a positive transient load change of the hydrogen combustion engine. This offers the technical advantage of ensuring, in a simple manner, that the predetermined upper limit of the NOx concentration is never exceeded. In this way, NOx emissions can be monitored and the risk of abnormal combustion phenomena, such as knocking or pre-ignition of the hydrogen combustion engine, can be reduced.

[0007] In a further advantageous embodiment, the control unit is configured to adjust the intake air mass flow such that the relative air-fuel ratio is at a setpoint or within a setpoint range. This offers the technical advantage that the steady-state setpoint of the relative air-fuel ratio can be easily adjusted without significantly affecting the engine torque.

[0008] In a further advantageous embodiment, the control unit is configured to increase an inlet pressure or an inlet airflow during the positive transient load change. This offers the technical advantage of achieving a steady-state airflow requirement.

[0009] In a further advantageous embodiment, the control unit is configured to calculate a maximum fuel quantity for the cylinder based on the supplied air quantity and / or a lower limit of the relative air-fuel ratio. This offers the technical advantage of easily limiting the fuel quantity even at the beginning of a positive transient load change. This can be done, for example, before the lambda sensor or the NOx sensor has acquired extensive measurements of the relative air-fuel ratio or the NOx concentration in the exhaust gas.

[0010] In a further advantageous embodiment, the control unit is configured to calculate the ignition timing and / or a lower limit of the relative air-fuel ratio from an upper limit of the NOx concentration. This can be done, for example, using an inverse NOx model. This offers the technical advantage that the upper limit of the NOx concentration is taken into account in the ignition timing of the hydrogen engine and in the lower limit of the relative air-fuel ratio, even without direct control.

[0011] In a further advantageous embodiment, the control unit is configured to detect a steady state when the inlet pressure, the inlet airflow, and / or the air-fuel ratio are within a predetermined range, such as over a predetermined period. This offers the technical advantage that the steady state can be easily detected and the control system can be quickly adjusted.

[0012] In a further advantageous embodiment, the control unit is configured to perform closed-loop control or adjustment of the target air mass based on the measured relative air-fuel ratio. This can be done, for example, in the steady-state condition of the hydrogen combustion engine. This offers the technical advantage of reducing deviations of the relative air-fuel ratio from its steady-state target value.

[0013] In a further advantageous embodiment, the hydrogen combustion engine includes a pressure sensor for measuring the intake pressure. This offers the technical advantage that the pressure sensor can be used for control when no sensor signal for the relative air-fuel ratio or the NOx concentration is available, or when the measured sensor signal for the relative air-fuel ratio or the NOx concentration exhibits excessive fluctuations or inaccuracies.

[0014] In another advantageous embodiment, the hydrogen combustion engine is a lean hydrogen engine. This offers the technical advantage that the formation of nitrogen oxides in lean hydrogen engines can be controlled in a simple manner.

[0015] A vehicle according to the invention with a hydrogen combustion engine achieves the same technical advantages as a hydrogen combustion engine.

[0016] The inventive method for controlling a hydrogen combustion engine with at least one closed control loop comprises the steps of measuring the relative air-fuel ratio and / or the NOx concentration in the exhaust gas by means of a sensor arranged downstream of a catalyst; and controlling the amount of fuel supplied, the ignition timing, and / or the intake air mass flow rate based on the air-fuel ratio and / or the measured NOx concentration in the closed control loop. This method achieves the same technical advantages as the hydrogen combustion engine.

[0017] Exemplary embodiments of the invention are explained in more detail with reference to the following figures. These show: Fig. 1 a schematic representation of a hydrogen combustion engine with a closed control loop; Fig. 2. A graphical representation of various operating parameters of a hydrogen combustion engine; and Fig. 3 a schematic representation of a method for controlling a hydrogen combustion engine with a closed control loop.

[0018] Fig. Figure 1 shows a schematic representation of a hydrogen combustion engine 100 with a closed-loop control system 101. Air is directed into the combustion chamber 119 via a throttle valve 117. The air is filtered by an air filter 121 and cooled by a charge air cooler 123 (CAC). Gaseous hydrogen is supplied under increased pressure via a hydrogen injector 125 (common rail) directly into the combustion chamber 119 and mixed with the incoming air. The resulting charge mixture is ignited by spark plugs and ignition coils, thus driving the hydrogen combustion engine 100.

[0019] The resulting exhaust gas 105 drives a variable-geometry turbocharger 127 (VGT) and is routed to the exhaust system via the catalyst 107 and an exhaust silencer 129. The catalyst 107 is, for example, an oxidation catalyst (OC), a three-way catalyst (TWA), or a passive NOx absorber (PNA). The turbocharger 127 drives a compressor 131, which increases the pressure of the supplied air to the required level.

[0020] The relative air-fuel ratio λ in the exhaust gas is measured by a lambda sensor 103 or a NOx sensor, which is located downstream of the catalyst 107. The lambda sensor 103 determines the residual oxygen content in the exhaust gas compared to the oxygen content of a reference, usually the ambient air. From this, the air-fuel ratio λ (ratio of combustion air to fuel) can be determined and adjusted. Corresponding measured values ​​for the air-fuel ratio are transmitted as a feedback signal to the control unit 109. In addition to the relative air-fuel ratio, a NOx sensor can also determine the NOx concentration in the exhaust gas and supply corresponding measured values ​​to the control unit 109.

[0021] The electronic control unit 109 uses the received measured values ​​to control or adjust the amount of fuel supplied 111, ensuring that a predefined lower limit of the relative air-fuel ratio is not undercut during a positive transient load change of the hydrogen combustion engine 100; and / or to control or adjust the ignition timing and the amount of fuel supplied, ensuring that a predefined upper limit of the NOx concentration is not exceeded. The control or adjustment of the amount of fuel supplied 111 and the ignition timing, in turn, influences the relative air-fuel ratio and the NOx concentration in the exhaust gas. In this way, the closed control loop 101 is established based on the measured values, and the air-fuel ratio remains above the predefined lower limit and the NOx concentration remains below the predefined upper limit.

[0022] The exhaust gas downstream of the catalyst 107 is free of hydrogen, so the lambda sensor or the NOx sensor 103 is suitable for control downstream of the catalyst 107. This arrangement of the lambda sensor or the NOx sensor 103 ensures higher measurement accuracy.

[0023] Fig. Figures 2a to 2d show graphical representations of various operating parameters of the hydrogen combustion engine, namely a time course of the torque in Nm ( Fig. 2a), a time course 135 of the relative air-fuel ratio in the exhaust gas ( Fig. 2b), a time course 137 of the supplied air mass in mg per stroke (mgs / str - milligrams per stroke) ( Fig. 2c) and a time course of 139 of the fuel mass in mg per stroke ( Fig. 2d). These operating parameters are shown during a steady-state operating condition in areas A and C, and during a positive transient load step in the dynamic operating condition of the hydrogen combustion engine 100 in area B.

[0024] Steady-state operation occurs when no additional torque is requested. In this case, the requested torque 141 and the generated torque 133 are equal. The hydrogen combustion engine 100 is driven at a constant speed. Steady-state operation occurs, for example, when a vehicle is traveling at a constant speed.

[0025] In steady-state operation, the relative air-fuel ratio in the exhaust gas is constant. In steady-state operation, the air-fuel ratio can then be controlled with an open-loop system to adjust the fuel quantity supplied based on a predetermined steady-state setpoint. At lean relative air-fuel ratios, for example, greater than 2, NOx emissions are lower, and the accuracy requirements for the control of the relative air-fuel ratio are correspondingly lower. Furthermore, the setpoint for the air-fuel ratio can be adjusted depending on the operating conditions of the hydrogen combustion engine and may therefore differ over time.

[0026] In steady-state operation, the time profile 137 of the supplied air mass is also constant and corresponds to a predetermined target value 145 for the supplied air mass. The target value 145 for the supplied air mass can also be adjusted depending on the operating situation of the hydrogen combustion engine 100 and therefore may also differ in its time profile. The same applies to the time profile 139 of the supplied fuel mass and the target value 147 for the fuel mass.

[0027] In the dynamic operating state, which lies between the two steady-state operating states, a torque is abruptly requested. This generates a positive transient load step. The requested torque 141 and the generated torque differ in this case, and the speed of the hydrogen combustion engine 100 increases until the requested torque 141 and the generated torque again match (range B in Fig. 2a).

[0028] Since the relative air-fuel ratio drops abruptly during the positive transient load change in the dynamic operating state due to an increase in the amount of fuel supplied, the control unit 109 regulates the amount of fuel supplied 111 based on the measured air-fuel ratio using a closed-loop control system 101. The air-fuel ratio is regulated so that it does not fall below a predefined lower limit 113. With a NOx sensor, the ignition timing and the amount of fuel supplied 111 can also be regulated or adjusted based on the measured NOx concentration to prevent exceeding a predefined upper limit.

[0029] At the start of the dynamic operating state, the setpoint 143 for the air-fuel ratio, the setpoint 145 for the supplied air mass, and the setpoint 147 for the supplied fuel mass can also be changed by the control unit 109. Accordingly, the time profile 137 of the supplied air mass and the time profile 139 of the supplied fuel mass also increase in the dynamic operating state.

[0030] A maximum upper limit 149 for the supplied fuel mass can be calculated by the control unit 109 from the lower limit 113 of the relative air-fuel ratio and the actual supplied air mass. The actual supplied air mass can be calculated from a filling model using an intake pressure sensor. At the beginning of the transient load change, this value limits the fuel mass and is adjusted as soon as the controls for the relative air-fuel ratio and / or the NOx concentration are active.

[0031] During the transient load change, the intake pressure and / or intake airflow are increased, for example by opening the throttle valve 117 (de-throttling or boosting), to achieve the steady-state target intake airflow. The target intake airflow is determined by the steady-state target fuel mass and the relative air-fuel ratio. Since the intake pressure and intake airflow cannot be used to control the relative air-fuel ratio during the transient load change, the fuel mass is used as the control variable. This ensures that the lower limit 113 of the air-fuel ratio is maintained. The feedback signal from the lambda sensor or the NOx sensor 103 is used for this purpose.

[0032] The controls for the amount of fuel supplied and the ignition timing to maintain the air-fuel ratio and / or the NOx concentration can be activated permanently or only during a transient load change.

[0033] In the case of a transient load change, the control loop 101 can be activated for a predetermined time after a load demand reaches the lower limit value 113, or when a measured relative air-fuel ratio reaches the lower limit value 113. The signal for the control loop 101 is generated either by the lambda sensor or the NOx sensor 103 in the exhaust gas of the hydrogen combustion engine 100.

[0034] The control loop 101 can be deactivated when the control unit 109 detects that the actual inlet pressure, the inlet airflow, or the relative air-fuel ratio has reached the steady-state range. The control unit 109 detects this, for example, when the values ​​resume a constant course after a positive transient load change and remain within a predetermined range for a specified period of time.

[0035] In contrast, during continuous or steady-state operation of the hydrogen combustion engine, the control unit can activate closed-loop control or adjustment of the target air mass based on the measured relative air-fuel ratio. Using the intake airflow to regulate the relative air-fuel ratio has a lesser impact on engine torque compared to using the fuel flow and is therefore less noticeable to the operator. The adjustment of the target value for the intake airflow is limited by the expected tolerances in the intake airflow measurement. A plausibility check of the intake airflow and exhaust gas recirculation (EGR) can be performed to account for model and sensor tolerances.

[0036] If a control error of the relative air-fuel ratio is higher than would be expected based on the tolerances and cannot be caused by inaccuracies in the air path, the supplied fuel mass 111 can be adjusted to achieve the steady-state range. Furthermore, it can be determined whether a general fuel fault of the injectors exists if, in addition, a valid signal from the lambda sensor or the NOx sensor 103 is present. This can be determined by using a second lambda sensor or NOx sensor 103, which is located further downstream in the aftertreatment system.

[0037] The hydrogen combustion engine 100 corrects errors in the amount of fuel supplied and the actual intake airflow to ensure the correct air-fuel ratio and NOx emissions. During transient operation, the amount of fuel supplied and / or the ignition timing are adjusted, while during steady-state operation, the intake airflow, or a model of the intake airflow in the cylinder used to calculate the maximum limit, is corrected accordingly.

[0038] Fig.Figure 3 shows a schematic representation of a method for controlling the hydrogen combustion engine 100 with the closed-loop control system 101. In step S101, the relative air-fuel ratio in the exhaust gas is first measured using the lambda sensor 103 or the NOx sensor, which is located downstream of the catalyst 107. In the subsequent step S102, the amount of fuel supplied 111 is controlled in the closed-loop control system 101 based on the measured air-fuel ratio.

[0039] This method offers the advantage of ensuring that the relative air-fuel ratio can be easily maintained above a predefined critical lower limit of 113. A drop below this lower limit of 113 can generate high NOx emissions that exceed the potential urea dosing and conversion capacity of the SCR aftertreatment system. A similar and additional control loop for adjusting the ignition timing and fuel quantity based on the measured NOx concentration can ensure that NOx emissions do not exceed a predefined critical upper limit.

[0040] The process reduces unusual combustion phenomena, such as knocking and premature ignition, and limits NOx emissions. Abnormal combustion during dynamic operation is minimized, for example, during a positive transient load change. Furthermore, engine tolerances that develop over the lifetime of the hydrogen combustion engine 100 can be compensated for by controlling the relative air-fuel ratio. This process enables a steady-state relative air-fuel ratio to be maintained by controlling or adjusting the intake airflow, for example, by adjusting the intake pressure, cylinder filling, or the mixture via the throttle valve.Control can also be based on the turbocharger 127 with variable geometry (VGT), exhaust gas recirculation (EGR), variable valve timing (VVT) and / or variable valve lift (WL).

[0041] All features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the object according to the invention in order to simultaneously realize their advantageous effects.

[0042] All process steps can be implemented by devices suitable for executing the respective process step. All functions performed by tangible features can constitute a process step of a process.

Claims

[1] Hydrogen combustion engine (100) with at least one closed control loop (101), with: - a sensor (103) for measuring the relative air-fuel ratio and / or the NOx concentration in the exhaust gas (105), which is arranged downstream of a catalyst (107); and - a control unit (109) for controlling the supplied fuel quantity (111), the ignition angle and / or the intake air mass flow on the basis of the measured air-fuel ratio and / or the NOx concentration in the closed control loop (101). [2] Hydrogen combustion engine (100) according to claim 1, wherein the sensor (103) is a lambda sensor or a NOx sensor. [3] Hydrogen combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is designed to adapt a supplied fuel quantity (111) such that the relative air-fuel ratio is above a predetermined lower limit (113). [4] Hydrogen combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is designed to adapt an ignition timing and / or a supplied fuel quantity (111) such that the NOx concentration is below a predetermined upper limit. [5] Hydrogen combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is designed to adapt an intake air mass flow such that the relative air-fuel ratio lies in a target range. [6] Hydrogen combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is configured to increase an intake pressure or an intake air flow during the positive transient load step. [7] Hydrogen internal combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is designed to calculate a maximum fuel quantity for the cylinder based on a supplied air quantity and / or a lower limit of the relative air-fuel ratio. [8] Hydrogen internal combustion engine (100) according to one of the preceding claims, wherein the control unit (109) is designed to calculate the ignition timing and / or a lower limit of the relative air-fuel ratio from an upper limit of the NOx concentration. [9] Hydrogen internal combustion engine (100) according to claim 5, wherein the control unit (109) is configured to detect a steady state when the intake pressure, the intake air flow and / or the air-fuel ratio are within a predetermined range. [10] Method for controlling a hydrogen combustion engine (100) with at least one closed control loop (101), comprising the steps: - measuring (S101) the relative air-fuel ratio and / or the NOx concentration in the exhaust gas by means of a sensor (103) arranged downstream of a catalyst (107); and - Controlling (S102) the supplied fuel quantity (111), the ignition timing and / or the intake air mass flow on the basis of the air-fuel ratio and / or the measured NOx concentration in the closed control loop (101).

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