Startup combustion anomaly detection in hydrogen internal combustion engine

Abstract

A method for operating a hydrogen fuel powered internal combustion engine (10, fig 1) applies a startup combustion anomaly detection routine during an engine startup procedure to detect misfire and un

Description

Technical field The present invention generally relates to internal combustion engines operating on gaseous fuel such as hydrogen. The invention more particularly relates to the detection of combustion anomalies at startup. Background Art It is well known within the art that gas leakage is an important concern for designers of vehicles powered by gas-powered combustion engines, and particularly hydrogen combustion engines. Indeed, the hydrogen fuel gas is usually stored at high pressures ranging from 350 bars to 700 bars. The hydrogen storage pressure is decreased by means of regulator means to a working pressure between 5 to 40 bars, for injection within the engine. This creates multiple situations in which fuel gas leakage may occur. Furthermore, hydrogen is intrinsically very volatile and inflammable as past catastrophes have amply demonstrated, so that early and accurate detection of any kind of fuel gas leakage is of paramount importance in terms of user safety, which is in turn crucial for the commercial success of hydrogen-powered vehicles. Detecting fuel gas leakage is particularly critical during engine startup after the engine has been turned off. Leakage can occur internally, such as hydrogen seeping through the H2 shutoff valve and one or more injectors, leading to the formation of hydrogen pockets within the cylinders, which may cause unwanted combustion events during startup. External leaks can also occur, resulting in insufficient fuel delivery to the injectors and potentially causing misfires. To prevent hazardous situations, it is essential to detect any potential leaks as early as possible, ideally before the engine reaches operational conditions. Technical problem It is an object of the present invention to provide an approach that allows detecting unwanted combustions, or misfires, that may be dues to leakage or defaults in the fuel delivery system of a hydrogen internal combustion engine. General Description of the Invention The present invention relates to a method for operating a hydrogen fuel powered internal combustion engine. The engine comprising a fuel delivery system comprising a pressurized fuel source that supplies fuel to a fuel rail to which a plurality of injectors are coupled, the fuel injectors being arranged to inject fuel into respective engine cylinders. To start the engine, startup procedure is performed, which includes an activation phase, during which the starter motor is engaged and fuel injection is disabled, and a subsequent engine-starting phase, during which fuel is injected; A startup combustion anomaly detection routine is implemented during the engine startup procedure, which comprises a synchronous mode with the steps of: - monitoring a torque indicator that is influenced by output torque produced by the internal combustion engine and determined from real-time data; - detecting a combustion anomaly by comparing said torque indicator to a detection threshold. As will be detailed below, the inventive method provides techniques for early detection of combustion anomalies that can reveal leaks or defects in the fuel system. The ability to detect such situations allows the ECU to implement safety measures, e.g. interrupting the engine startup procedure or neutralizing a faulty cylinder. The term ‘synchronous’ as will be clear those killed in the art refers to the synchronization of the crankshaft, i.e. the ECU is able to determine the angular position of the crankshaft. In contrast, the asynchronous refers to the period preceding crankshaft synchronization. The synchronous mode can be applied from the moment that the crankshaft position is known / synchronized, which may be noted CK_S. In embodiments, the synchronous mode is applied upon CK_S. Alternatively, it the synchronous mode is entered from when CK_S is established and a predetermined threshold engine speed threshold SI is reached. A first sub-routine may be carried out in situations where fuel injection is disabled. The torque indicator is compared to a first threshold. If the torque indicator is greater than the first threshold, an unwanted combustion event is registered. This is of particular interest in embodiments wherein the engine startup procedure implements is configured to perform one or more spark events in the activation phase, e.g. to indeed provoke combustion of gaseous fuel that may be in the cylinder although fuel injection is disabled. Before performing those spark events, the ECU may put the fuel delivery system under pressure, with injectors closed. A second sub-routine may be implemented when the fuel injection is enabled. The torque indicator may be compared to a second detection threshold, and if the torque indicator is smaller than the second threshold, a misfire event is registered. The torque indicator may be determined from real-time data, from which output torque can be derived. In embodiments, the torque indicator is determined from at least one of the following parameters: engine speed, crankshaft angular velocity, crankshaft acceleration, exhaust gas pressure, a Fourier torque metric derived from Fourier analysis applied to crankshaft rotational data. The engine speed and crankshaft angular velocity crankshaft acceleration and Fourier torque metric are determined from crankshaft rotational data obtained from a speed sensor. Exhaust gas pressure may be determined from pressure sensor in the exhaust manifold / system. Fourier torque metric may be determined using Discrete Fourier transformation of crankshaft rotation for one or more harmonic(s), based on crankshaft speed sensor signal (instantaneous speed). The computation may be based on speed data on the two last engine cycles, or on speed data covering the angular interval from combustion on one cylinder to combustion TDC on the next cylinders (in firing order). In embodiments, the torque indicator is the crankshaft acceleration, determined over at least part of a combustion angular interval. For example, the crankshaft acceleration may be determined from an engine speed sensor signal as the difference of speed between crank angles CA.l and CA.2 over the corresponding time period. CAI is generally set with respect to the beginning of a combustion segment, and CA2 is set with respect to the end of a combustion segment. In embodiments, an asynchronous mode that may be implemented during the activation phase and before crankshaft synchronization, whereby an unwanted combustion event is registered in case the engine speed exceeds a third threshold. In embodiments, the said synchronous mode is applied up to a predetermined engine speed S2 that is higher than engine starter nominal speed and below idle, in particular 480 to 550 RPM. In embodiments, the synchronous mode is applied up from a predetermined engine speed SI, in particular 50 to 150 RPM. The present invention has been developed for application to hydrogen operated engines, wherein the fuel gas is essentially hydrogen, i.e. with a concentration above 90vol.% and above 95 vol.%. It’s the term “hydrogen fuel powered” engine is however to be understood as an engine operating on (essentially pure) gaseous hydrogen, but also where hydrogen is mixed with another combustion gas (e.g. CNG) and may represent a minor amount of the gaseous fuel. The invention also relates to an internal combustion engine powered with hydrogen fuel, said engine comprising a plurality of cylinders and a fuel delivery system comprising a pressurized fuel source that supplies a fuel rail to which a plurality of injectors are coupled, each fuel injector arranged to inject fuel into a respective engine cylinder, the engine further comprising a starter, an engine speed sensor, and a control unit, wherein the control unit is configured to implement the method according to the present disclosure. According to another aspect, the invention relates to a computer program product comprising instructions which, when the program is executed by an engine control unit comprising a processor, cause the engine control unit to carry out the method according to the present disclosure. These and other embodiments of the invention are recited in the appended claims. Brief Description of the Drawings Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein: Fig. lisa diagram of an embodiment of a hydrogen internal combustion engine; Fig. 2 is a flowchart implementing routine R2 of the synchronous mode; Fig. 3 is a flowchart implementing routine R3 of the synchronous mode; Fig. 4 is a flowchart implementing routine RI of the asynchronous mode; Fig. 5 is a plot of engine speed vs. time during the engine startup phase; and Fig. 6 is a plot of ICA vs. engine speed showing correlation between ICA and combustion events. Description of Preferred Embodiments Embodiments of the present invention will now be described in the context of a hydrogen internal combustion engine. The engine 10 is schematically illustrated on Fig.l, in a simplified manner. The engine configuration is conventional and will only be briefly described. The engine 10 comprises an engine block 12 with a plurality of cylinders 14 (only one being shown in the Figure). A piston 16 is reciprocally disposed within each cylinder 14, moveable between a bottom dead center BDC and top dead center TDC, and connected to a crankshaft 18 through a rod 20. The cylinders 14 are closed by a cylinder head 22, whereby a combustion chamber 24 is defined by the piston, cylinder and cylinder head. Reference sign 26 designates an intake valve that is opened to allow fresh air inlet (from intake manifold 30) into the combustion chamber 24 (typically during an intake stroke). An exhaust valve 28 allows opening the combustion chamber 24 towards the exhaust system (not shown) to evacuate combustion gases (typically exhaust stroke). Each intake valve 26 is connected to an air intake manifold 30 via a respective intake port 32 provided in the cylinder head 22. In this embodiment, a fuel injector 34 (per cylinder) is arranged in so-called direct injection configuration; the fuel injector 34 is configured to selectively inject / discharge predetermined fuel quantities directly into the combustion chamber 24 (alternatively, the fuel injectors may be arranged in port-fuel configuration, where fuel is injected / discharged upstream of the intake valve into the intake air stream). Typically, the fuel injector 34 comprises a nozzle (or valve) portion that comprises a seat member with one or more injection holes; and a valve member is arranged to be moveable between a closed position, resting on the seat member to prevent fuel injection, and an open position, raised from the seat member and hence authorizing fuel flow towards the injection holes. The fuel injector typically comprises an electromechanical actuator that is configured to move the valve member. For example, the electromechanical actuator may comprise a solenoid that generates a magnetic field capable of pulling (lifting) the valve member off the seat member. For this purpose, a magnetic armature may be provided to cooperate with valve member; for example, the valve member may include a needle shaft and the armature surrounds the latter. The fuel injectors 34 are part of a gaseous fuel delivery system 40, wherein the fuel injectors 34 are coupled to a fuel rail 42, which is fed from a pressurized fuel gas source 48. It may comprise one or more cylinders / tanks containing gaseous (or liquid) fuel such as hydrogen. A supply pipe 43 connects the pressurized fuel gas source to the fuel rail, and may include serially connected components such as a shut-off valve 46, a pressure regulator 44, which may be integrated in a common housing, forming a hydrogen regulation module, HRM. The HRM may further include one or more of a pressure relief valve, a purge valve, and a fuel filter. The pressure regulator 44 may be configured to regulate the pressure in the fuel rail in a predetermined range, e.g. from 2 to 40 bars (other pressure ranges are however possible). The lower range, e.g. 2-20 bars may be used for port fuel injection, whereas the upper range 20-40 bars may be used for direct fuel gas injection. The engine 10 further typically includes a crankshaft speed sensor 50, that comprises a magnetic sensor 50.1 (e.g. hall effect sensor) in conjunction with a toothed wheel 50.2. As is known in the art, the toothed wheel 40.2 is fixed to the crankshaft, whereas the sensor 50.1 is fixed to the engine block 12 and detects changes in the magnetic field as the wheel 50.2 rotates. The magnetic sensor 50.1 detects the presence (tooth) and absence (gap) of the metal teeth, generating a voltage pulse each time a tooth passes. The frequency of these pulses corresponds to the rotational speed of the crankshaft. Engine operation is conventionally controlled by an engine control unit ECU (including a processor and a memory) that receives signals from various sensors and operates engine systems / components according to predetermined strategies. The ECU receives the pulses from magnetic sensor 50.1 and processes them to determine the exact position of the crankshaft and its rotational speed. The crankshaft speed sensor 50 is also used by the ECU to effect so-called crankshaft synchronization CK_S, whereby the ECU aligns its internal timing with the crankshaft's position and speed to manage engine functions, in particular fuel injection, spark ignition, and valve timing. < INVENTION > Hydrogen is more prone to leakage due to its extremely small molecular size, high diffusivity, and low viscosity, which allow it to escape through tiny cracks, pores, or seals that block larger gases. As the hydrogen gas is under pressure in the system, it may leak through shut off valves or via the injectors while the engine is parked. This may cause anomalies in the engine startup sequence, and the present method allows detecting these anomalies, hence allowing early detection of possible faults in the fuel system. Fig. 5 is a plot of crankshaft speed vs. time during engine startup. The engine startup typically comprises two phases piloted by the ECU. Activation phase. The crankshaft is initially at rest. The starter motor is activated (Starter on) to start rotating the crankshaft (i.e. cranking). Fuel injection is disabled during the activation phase. Rapidly, the crankshaft position is synchronized, noted CK_S, giving access to the crankshaft angular position and hence allowing to discriminate cylinders and combustion cycle phases. Engine-starting phase. This phase follows the activation phase. Fuel injection is enabled and hence coordinated fuel events and ignition spark events (i.e. activation of spark plug to emit one or more sparks) are operated: the engine speed (RPM) increases progressively to reach a self-sustaining combustion. The starter motor is disengaged (Starteroff) when a predetermined engine speed is reached. The invention provides a startup anomaly detection routine that comprises a synchronous mode with the steps of: - monitoring a torque indicator that is influenced by output torque produced by the internal combustion engine and determined from real-time data; - detecting a combustion anomaly by comparing said torque indicator to a detection threshold. <Synchronous Mode> This mode may be activated on or after crankshaft synchronization, i.e. from the moment the ECU has synchronized the angular position of the crankshaft. Preferably, the synchronous mode is activated when CK_S is done and a predetermined engine speed SI is reached. In the present embodiment, the torque indicator is the instantaneous crankshaft acceleration index, hereinafter noted ICA, that represents crankshaft acceleration over at least part of a combustion angular interval. The instantaneous crankshaft acceleration index, hereinafter noted ICA, permits detecting the occurrence of a crankshaft acceleration after the spark event, as would be expected for a proper combustion. The ICA is here calculated for an angular interval that typically starts before TDC of the respective cylinder and extends over a part of the combustion segment. It can be calculated as _ 2 ~ Speed-cA.i 1G / 1 — . At where SpeedcA i is the engine speed (RPM) at a crankshaft angle noted cai, which is about combustion TDC; SpeedcK.2 is the engine speed at a crankshaft angle noted CA2 after TDC. Its can be measured after 50% of the combustion segment; and At is the difference of time period separating the two speed measurements SpeedcA i and SpeedcA.2. For example, crank angle CAI may be in the range of [-50°; 10] with respect to the combustion TDC. CA2 is an angle that is set at an angular position in the second half of the combustion segment. Altogether, the interval [CAI; CA2] may extend over a range of 90°C to 120°C beyond the combustion TDC. The term ‘combustion segment’ conventionally refers to the portion of an internal combustion engine's operating cycle during which combustion occurs within a cylinder. This segment is characterized by the ignition of the air-fuel mixture and consequent production of torque. The combustion segment is typically defined as the crankshaft angle range spanning from the onset of ignition to the point where combustion pressure significantly declines. As indicated above, the synchronous detection mode is applied from CK_S and hence may already be implemented during the activation phase, i.e. while fuel injection (Fuel inj.) is disabled. Hence, should an increase of ICA be observed, it must be caused by hydrogen combustion. In order to perform a leakage check of the fuel delivery system, it is possible to perform a spark event in one or more cylinders during the activation phase, in particular after CK_S. Should hydrogen be present in the cylinder(s), it would cause combustion event(s) that can be observed from the evolution of ICA. It may be noted that some engine startup procedures strategies are configured to perform one or more spark events during the activation phase (i.e. before fueling is enabled), and in particular after the fuel delivery system is pressurized with injectors closed. Should hydrogen be present in a cylinder, it would cause a combustion event that can be observed by comparing ICA to a threshold TH1. In the engine-starting phase, fueling is enabled (Fuel inj enabled) and predetermined patterns of injection events and spark events are performed to get the engine running in self-sustained mode. Here, the synchronous mode can be advantageously applied to determine the occurrence of misfires, by comparing ICA to a threshold TH2. It should be noted that the use the ICA in the context of the inventive method is of particularly relevance, as this parameter has been confirmed to reliably correlate with the occurrence (respectively absence) of combustion at low engine speed. Fig.6 shows is a plot of ICA vs. engine RPM based on experimentation. It shows that in case of actual combustion, the ICA is significantly above ICA values measured where combustion did not occur. Based on experimentation, it is thus possible to set the level of the threshold TH that allows discriminating between combustion and non-combustion. Such experimental test also allows optimizing the configuration of the ICA, namely by adjusting angles CAI and CA2, and depending on engine configuration (number of engine cylinders). <Asynchronous Mode> Advantageously, the method includes an asynchronous mode, which is implemented before the crankshaft synchronization, i.e. up to CK_S (or CK_S + SI). In this asynchronous mode, unwanted combustion is detected based on engine speed. Indeed, in the early activation phase, the crankshaft is put into movement (from the rest / standstill position) by the starter motor; the crankshaft movement is detected by the speed sensor 50 but there is no angular synchronization. The speed threshold, noted TH3, is set at a value that is greater than the speed that should normally be reached using the starter motor in the activation phase. Hence, in case engine speed becomes greater than TH3, it is attributed to an unwanted combustion. To sum up, the present method allows for anomaly detection using several modes, that are advantageously activated in sequence. Asynchronous mode, indicated RI in Fig.5 and illustrated in Fig 4. This mode is applied at the start of the activation phase and before CK_S (or until CK_S and SI). Engine speed is monitored and compared to a speed threshold TH3. If engine speed is greater than TH3, then an unwanted combustion is registered. Since the engine is not yet synchronized, the fault be may be registered as ‘Unwanted Combustion On Unknown Cylinder’ fault. For example, a counter Cuc.3 may be incremented, that counts the number of unwanted combustions occurring with cylinder assignation. As from CK_S, the synchronous mode is applied and relies on ICA. In a first phase, the synchronous mode is applied to detect unwanted combustions. It starts already during the activation phase as soon as engine is synchronized CK_S (or CK_S + SI) and spans until the Fuel inj. is enabled. There, ICA is compared to a threshold THE If ICA is greater than TH1, then an unwanted combustion is registered in the ECU. The unwanted combustion event is registered for the corresponding cylinder, in particular by incrementing a cylinder specific counter Cue. This first phase is noted R2 in Fig.5, and illustrated in Fig. 3. In a second phase (noted R3), that begins when the fuel injection is enabled, the synchronous mode is used to detected misfires. This second phase is noted R3 in Fig.5, and illustrated in Fig. 4. There, ICA is compared with a second threshold. If ICA is lower than TH2, then a misfire event is registered in the ECU. The misfire event is registered for the corresponding cylinder, in particular by incrementing a cylinder specific counter Cmis. Thresholds TH1 and TH2 may be the same or different. They can set by calibration, as explained above in relation to Fig.6. The synchronous mode R3 may be kept active until the engine runs stably, in particular until it is stable at idling speed. Preferably, mode R3 is stopped when a predetermined engine speed S2 is reached. Speed S2 is set at a value where it is considered that mode R3 based on ICA is no longer robust enough and should be replaced by another mode. When R3 is stopped, a conventional torque-based monitoring strategy can be used to detect misfires. The present startup combustion anomaly detection routine allows early detection of events such as misfires and unwanted combustions, which could be hazardous. For example, it is possible to detect unwanted combustion events at a stage where fueling is disabled, arising from internal fuel leakage. Furthermore, the method allows detecting misfires and even pinpointing the misfires events to the actual cylinder(s). Early detection of misfire events during the engine startup procedure the cylinder and potentially the exhaust line from filling with hydrogen, which could otherwise create a hydrogen-filled volume prone to explosive behavior, and possibly leak out and accumulate in enclosed spaces, such as a garage or parking area. Hence, the inventive method provides techniques for early detection of combustion anomalies that can reveal leaks or defects in the fuel system. The ability to detect such situations allows the ECU to implement some safety measures, e.g. interrupting the engine startup procedure or neutralizing a faulty cylinder.

Claims

1. A method for operating a hydrogen fuel powered internal combustion engine, said engine comprising a fuel delivery system comprising a pressurized fuel source that supplies fuel to a fuel rail to which a plurality of injectors are coupled, the fuel injectors being arranged to inject fuel into respective engine cylinders,whereby a startup combustion anomaly detection routine is applied during implementation of an engine startup procedure, the startup procedure including an activation phase, during which the starter motor is engaged and fuel injection is disabled, and a subsequent engine-starting phase, during which fuel is injected;said startup combustion anomaly detection routine comprising:a synchronous mode with the steps of:- monitoring a torque indicator that is influenced by output torque produced by the internal combustion engine and determined from real-time data;- detecting a combustion anomaly by comparing said torque indicator to a detection threshold.

2. The method according to claim 1, wherein fuel injection is disabled, whereby if said torque indicator is greater than a first threshold, an unwanted combustion event is registered.

3. The method according to claim 2, wherein the startup procedure performs one or more spark events during the activation phase.

4. The method as claimed in any of claims 1 to 3, wherein fuel injection is enabled, whereby the torque indicator is compared to a second detection threshold, and if the torque indicator is smaller than said second threshold, a misfire event is registered.

5. The method as claimed in any of claims 1 to 4, wherein the torque indicator is determined from at least one of the following parameters: engine speed, crankshaft angular velocity, crankshaft acceleration, in-cylinder pressure, exhaust gas pressure, a Fourier torque metric determined from engine velocity.

6. The method as claimed in any of claims 1 to 4, wherein the torque indicator is the crankshaft acceleration, determined over at least part of a combustion angular interval.

7. The method as claimed in claim 6, wherein the crankshaft acceleration is determined from an engine speed sensor signal based on the formula_ SpeedCA 2 — SpeedCA11G ri — .Atwherein SpeedcA. i is the engine speed at a crankshaft angle noted CA. 1; SpeedcA.2 is the engine speed at a crankshaft angle noted CA2; and At is the difference of time period separating the two speed measurements SpeedcA. i and SpeedcA.2; andwherein CAI is set with respect to the beginning of a combustion segment, and CA2 is set with respect to the end of a combustion segment.

8. The method as claimed in claim 6, wherein CAI is set within an crank angle internal of [-50°; 10°] with respect to combustion Top Dead Center and the interval CAI to CA2 spans at least 90°.

9. The method as claimed in any one of claims 1 to 8, comprising an asynchronous mode that is implemented during said activation phase and before crankshaft synchronization, whereby an unwanted combustion event is registered in case the engine speed exceeds a third threshold.

10. The method as claimed in any one of claims 1 to 9, wherein said synchronous mode is applied up to a predetermined engine speed S2 that is higher than engine starter nominal speed and below idle, in particular 480 to 550 RPM.

11. The method as claimed in any one of claims 1 to 10, wherein said synchronous mode is applied up from a predetermined engine speed SI, in particular 50 to 150 RPM.

12. The method as claimed in any one of claims 1 to 11, wherein based on detection of a combustion anomaly or after a predetermined number of combustion anomalies have been register, modifying the status of one or more engine components or processes and / or actuating one or more components, in particular aborting the startup procedure or deactivating a cylinder.

13. An internal combustion engine powered with hydrogen fuel, said engine comprising a plurality of cylinders and a fuel delivery system comprising a pressurized fuel source that supplies a fuel rail to which a plurality of injectors are coupled, each fuel injector arranged to inject fuel into a respective engine cylinder, the engine further comprising astarter, an engine speed sensor, and a control unit, wherein the control unit is configured to implement the method according to any of the preceding claims.

14. A computer program product comprising instructions which, when the program is executed by an engine control unit comprising a processor, cause the engine control unit to carry out the method of any of claims 1 to 11.

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