Method of operating a gaseous fuel internal combustion engine

Abstract

The invention relates to a method of operating a gaseous fuel internal combustion engine comprising a fuel delivery system with a source of gaseous fuel supplying a fuel rail via a pressure regulator, and a plurality of fuel injectors coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders. The pressure regulator includes a movable valve member operatively coupled to an electromagnetic actuator, which is driven by a pulse-width modulated, PWM, voltage signal with a controllable duty cycle. The PWM voltage signal applied to the electromagnetic actuator has an operating frequency (FOP) corresponding to a fixed, nominal operating frequency (FOP.Nom), or set within a predetermined nominal operating frequency range, over the engine operating range, except for a plurality of engine speed intervals, where the operating frequency is modified to avoid approaching the frequency of the injection events and of at least one predetermined harmonic thereof.

Description

[0001] P-DELPHI-445 / WO 1

[0002] METHOD OF OPERATING A GASEOUS FUEL INTERNAL COMBUSTION ENGINE

[0003] Technical field

[0004] The present invention generally relates to gaseous fuel internal combustion engines and more specifically to the regulation of the pressure regulator in such engine.

[0005] Background Art

[0006] For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines since the emissions from a hydrogen engine consist mainly of water. The fuel delivery system in such engine typically comprises a gas tank assembly comprising a plurality of tanks filled with pressurized fuel gas, connected via a supply line to a fuel rail to which a plurality of fuel injectors are coupled and arranged for fuel discharge (directly or indirectly) into engine cylinders. A fuel regulator is typically arranged on the supply line to regulate the gaseous fuel pressure in the rail.

[0007] It has been observed that in such gaseous fuel engines, the pressure regulation in the fuel rail tends to become erratic at certain engine speeds.

[0008] General Description of the Invention

[0009] In order to overcome the above-mentioned problem, the present invention proposes a method of operating a gaseous fuel internal combustion engine as claimed in claim 1.

[0010] The invention relates to a method of operating a gaseous fuel internal combustion engine comprising a fuel delivery system with a source of gaseous fuel supplying a fuel rail via a pressure regulator, and a plurality of fuel injectors coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders.

[0011] The pressure regulator includes a movable valve member operatively coupled to an electromagnetic actuator (e.g. solenoid actuator), which is driven by a pulse-width modulated, PWM, voltage signal with a controllable duty cycle.P-DELPHI-445 / WO 2

[0012] According to the invention, the PWM voltage signal applied to the electromagnetic actuator has an operating frequency (FOP) corresponding to a fixed, nominal operating frequency (Fop.Nom), or set within a predetermined nominal operating frequency range, is within a predetermined range, over the engine operating range. However, for a plurality of engine speed intervals, the operating frequency is modified to avoid approaching the frequency of the injection events and of at least one predetermined harmonic thereof.

[0013] Indeed, the present inventors have found that the erratic pressure behavior in the fuel rail is due to resonance phenomena when the operating frequency of the regulator is around the injection frequency or a harmonic thereof (which depend on engine speed).

[0014] Hence, the present invention resides on the idea of locally adjusting the operating frequency of the PWM voltage signal, instead using high operating frequency to ensure that the operating frequency over the entire engine speed range. This is desired in the context of gas fuel engines, where low operating frequencies are desired for the pressure regulator.

[0015] The inventive method thus proposes a strategy where the pressure regulator operating frequency can be maintained at a fixed (constant) nominal operating frequency, e.g. lower than 250 Hz, or can be maintained in a predetermined nominal operating frequency range, over the entire engine operating range, except where locally adjusted.

[0016] For example, the fixed nominal operating frequency may be of 200 Hz, or less, in particular may be set at a value ranging from 80 to 180 Hz, and more particularly at between 100 and 150 Hz.

[0017] In case of nominal operating frequency range, it is preferably a narrow range (min to max frequency) of 10 to 50 Hz, and the upper bound of the nominal operating frequency range is no greater than 200 Hz.

[0018] In practice, the nominal operating frequency (or range) is locally adjusted to avoid frequency collision points, at engine speeds where the regulator operating frequency would approach the injection frequency or selected harmonics. The intensity of the resonance at the frequency collision points the may depend on theP-DELPHI-445 / WO 3

[0019] engine, and the skilled person may decide how many, resp. which, frequency collision points should be avoided.

[0020] In general, it is desirable to avoid the fundamental and the first harmonic(s), i.e. the injection frequency and at least the first harmonic thereof.

[0021] In embodiments, the method is implemented to avoid the injection frequency and the first three harmonics thereof. With this, the more problematic resonance phenomena can be avoided.

[0022] In embodiments, the operating frequency is adjusted (within each predetermined engine speed interval) to maintain a predefined frequency offset between the operating frequency and the injection frequency or harmonic frequency, respectively.

[0023] The predefined frequency offset may be fixed or variable, configured to ensure no overlap or resonance between the operating frequency of the pressure regulator and the frequency of the injection events.

[0024] In embodiments, within each predetermined engine speed intervals, the harmonic line corresponding to the frequency collision points is determined. This gives the reference of the frequencies to avoid around the frequency collision points.

[0025] In embodiments, the offset is positive before the respective frequency collision point and is negative after the frequency collision point.

[0026] Advantageously, a hysteresis mechanism may be applied to the operating frequency adjustment to avoid rapid fluctuations in operating frequency.

[0027] These and other embodiments of the invention are recited in the appended claims. According to another aspect, the invention relates to a fuel delivery system for a gaseous fuel internal engine, comprising a with a source of gaseous fuel supplying a fuel rail via a pressure regulator, and a plurality of fuel injectors coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, wherein the pressure regulator includes a movable valve member operatively coupled to an electromagnetic actuator, and a controlled configured to generate a pulse-width modulated, PWM, voltage signal with a controllable duty cycle that is applied to the electromagnetic actuator to control the flow rate throughP-DELPHI-445 / WO 4

[0028] the pressure regulator, and wherein the controller is configured to perform the method according to any of the preceding claims.

[0029] According to a further aspect, the invention concerns a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the present disclosure.

[0030] Brief Description of the Drawings

[0031] 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:

[0032] Fig. 1 is diagram of an embodiment of a hydrogen internal combustion engine; Fig. 2 illustrates plots of PWM Voltage signal vs. time and the corresponding solenoid current;

[0033] Fig. 3 is a plot of injection frequency, rail pressure error, and PWM signal frequency vs. engine speed;

[0034] Fig. 4 is a graph in function of engine speed, that indicates a variable and a constant PWM injection frequencies, together with the injection frequency and the first three harmonics;

[0035] Fig. 5 is a plot of a PWM voltage signal generated in accordance with the inventive method;

[0036] Fig. 6 is a detail of the graph of Fig.5;

[0037] Fig. 7 is a principle diagram of an embodiment of the present method.

[0038] Description of Preferred Embodiments

[0039] 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.1 , 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 designatesP-DELPHI-445 / WO 5

[0040] 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).

[0041] 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 portfuel configuration, where fuel is injected / discharged upstream of the intake valve into the intake air stream).

[0042] 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.

[0043] 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 with pressurized hydrogen 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 and a pressure regulator, which may be integrated in a common housing, forming a hydrogen regulation module, HRM (symbolized by the dash-lined square. The HRM may further include one or more of a pressure relief valve, a purge valve, and a fuel filter.

[0044] In the shown embodiment, the pressure regulator 44 also acts as shutoff valve. It may be configured to regulate the pressure in the fuel rail in a predetermined range,P-DELPHI-445 / WO 6

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] In the context of the invention, it may be noted that the ECU is typically configured to operate injection events, by which the fuel injectors are operated to inject predetermined fuel amounts in respective cylinders. The ECU will then also perform spark events, by which spark plugs (not shown) arranged in the respective cylinders are powered to ignite the fuel and air mixture in the cylinders. The control of injection event and spark event is part of the combustion event.

[0050] The ECU, e.g. via a controller (not shown), is further configured to drive the pressure regulator in order to regulate the downstream fuel gas pressure with the desired range, say within 2 to 40 bars.

[0051] Conventionally, the pressure regulator is piloted by means of a pulse-width modulated, PWM, voltage signal with a controllable duty cycle that is applied to the electromagnetic actuator.

[0052] Such PWM voltage signal is illustrated in Fig.1. As is conventional in the art, the PWM voltage signal is applied with a controllable duty cycle. That is, PWM signal is built as a periodic signal which alternates between "on" (high) and "off" (low) states.P-DELPHI-445 / WO 7

[0053] The “on” state is referred to as pulse. It has a predetermined pulse width, i.e. duration. Each on state is typically followed by an off state.

[0054] The duty cycle period, noted Touty is thus the total duration of one complete On+Off cycle, which is the inverse of the frequency. In the following, the frequency of the PWM voltage signal applied to the actuator of pressure regulator is noted FOP, where FOP=1 / Touty.

[0055] As will be understood, the current level in the actuator solenoid will vary depending on the PWM signal. Referring to Fig.2, during the on phase of PWM signal the solenoid current will increase, whereas during the off phase the solenoid current will decrease. This results in an average regulation current value IREG, that defines the operating point of the pressure regulator. That is, the position of the valve member, and hence the flow cross-section and downstream pressure, depends on IREG. The value of the average regulation current can be adapted by modifying the duration of the on phase. Otherwise stated, the pressure regulator is configured such that the flow-cross-section can be progressively adjusted from 0 to 100% by varying the regulation current IREG by changing the duty cycle ratio, i.e. % of ON time with respect to Touty (and not the frequency FOP).

[0056] < Invention >

[0057] In the context of the invention, it has been observed that in H2-ICE, the pressure regulation (via pressure regulator 44) in the fuel rail tends to become erratic at certain engine speeds.

[0058] This is illustrated in Fig.3, which is a plot of rail pressure error and of the PWM voltage signal frequency (i.e. FOP) in function of engine speed for a 4-cylinder H2-ICE.

[0059] One may note that the pressure regulator in the example of Fig.3 is operated with a constant PWM (duty cycle) frequency FOP over the entire engine range. This leads to noticeable pressure variations at predetermined operating points, which have been identified as operating points where the injection frequency, i.e. the frequency of the injection events, or a harmonic thereof, is the same or close to the frequency FOP of the PWM voltage signal.P-DELPHI-445 / WO 8

[0060] For example, for a 4-cylinder engine:

[0061] - at 4500 erpm, injection frequency is equal to 150 Hz. As the pressure regulator PWM frequency FOP is 150 Hz, a resonance appears on the rail pressure.

[0062] - at 2250 erpm, the injection frequency is equal to 75 Hz. As the pressure regulator PWM frequency FOP is 150 Hz, a resonance also appears (150 Hz is a harmonic of 75 Hz).

[0063] The present inventors have found that in the context of hydrogen engines it is desirable to operate the pressure regulator at low frequencies in order to influence a controlled ripple effect in the solenoid current that causes the valve member to oscillate around the operating position corresponding to IREG. Indeed, the fact that gaseous fuels such as hydrogen are dry gases, i.e. lacking lubricating I hydraulic effects of liquid fuels, may cause some dragging or frictional resistance issues. The oscillating effect of the valve member obtained by the use of a low frequency PWM signal permits to avoid such dragging / blocking of the pressure regulator valve. As will be understood by those skilled in the art, operating the PWM at comparatively higher frequencies tends to reduce the amplitude of the current ripple, and reduces the oscillating movement.

[0064] Accordingly, it has been found desirable to operate the pressure regulator at low PWM frequencies, an in particular at frequencies FOP lower than 250 Hz, preferably lower than 200 Hz. In the presented embodiments, the operating frequency is 150 Hz, but could be lower.

[0065] Fig. 4 is a plot of injection frequency (noted Finj.o) in function of engine speed, also illustrating the 1st, 2ndand 3rdharmonic thereof (noted Finj.i to Finj.3), for a 4-cylinder engine. The horizontal dashed line 4 represents the PWM voltage signal of constant frequency (150 Hz), whereas line 2 represents a variable PWM voltage signal. For avoidance of doubt, the injection frequency can be readily determined from the engine speed. That is, the injection frequency (lnjection_freq in Hz) can be determine from the following relation, on the assumption of one injection event per cylinder per engine cycle (i.e. 720°):

[0066]

[0067] P-DELPHI-445 / WO 9

[0068] Where Engine_Speed is the crank shaft speed in RPM and Numb_cyl is the number of engines cylinders.

[0069] As can be observed, for a constant PWM of 150 Hz, there are several engine operating points where the injection frequency or a harmonic thereof will take the value of the PWM signal frequency. Fig.4 can be compared with Fig.3, where it can be seen that the resonance phenomena in the rail pressure error correspond to the events where the injection frequency and harmonics are the same as FOP. These points are referred to as frequency collision points, noted Po where the injection frequency corresponds to FOP, and Pi, P2 and P3 where the first, second and third harmonics of the injection frequency corresponds to FOP.

[0070] One option to avoid this situation could be to use a variable PWM signal that is e.g. increased to remain above the third harmonic, as shown by line 2 in Fig.4.

[0071] Unfortunately, this would imply PWM frequencies above 200 Hz already from 11 GO-1150 RPM. And above 400 Hz from about 2600 RPM. This strategy is not desirable, since, as explained above, for reasons of reliability, low PWM frequencies are preferred.

[0072] Accordingly, in the present embodiment of the inventive method / strategy, a PWM voltage signal is applied to the regulator / actuator, which has an operating frequency FOP that is fixed (constant) over the engine operating range, except for a plurality of predetermined engine speed intervals, where the PWM operating frequency is modified to avoid approaching (i.e. being the same as or close to) the frequency of the injection events and of one or more predetermined harmonics thereof.

[0073] This is illustrated in Figs. 5 and 6. In the example, the pressure regulator is normally operated at a constant / fixed low frequency, namely of 150 Hz. This is the nominal operating frequency, noted Fop.Nom. For ease of explanation, the PWM voltage signal frequency is generally referred to as FOP; whereas the desired fixed operating frequency is referred to as nominal operating frequency, noted Fop.Nom.

[0074] As can be seen, the PWM voltage signal has a frequency FOP that corresponds to Fop.nom (150 Hz) over most of the engine operating range (the RPM).

[0075] The frequency FOP of the PWM voltage signal is however modified locally to avoid that FOP corresponds to the injection frequency (i.e. fundamental) or one of the first three harmonics thereof.P-DELPHI-445 / WO 10

[0076] This may advantageously be done by locally modifying the frequency FOP such as to maintain a predetermined frequency offset between FOP and the injection frequency, resp the selected harmonics. This modification of FOP is typically around the frequency collision points Pi, hence over given engine speed intervals.

[0077] Stated otherwise, the PWM frequency FOP is locally modified from the nominal operating frequency Fop.nom within so-called frequency adjustment windows (FAW), where the FOP is increased and / or decreased to maintain a predefined offset between FOP and the injection frequency or a harmonic thereof. The frequency FOP is said to be modified ‘locally’ since the FAW extends over a limited engine speed interval. Similarly, the term window is used to mean that the modification occurs over a given engine speed interval.

[0078] As can be observed, the engine speed interval of each FAW typically spans over 200 to 500 RPM, or e.g. over an engine speed interval that may represent between 2 to 15% of the engine operating range (ratio of respective FAW interval over max. engine speed), and generally less than 10% of the maximum engine speed.

[0079] More specifically, it has been observed that the most critical frequency collision points are those corresponding to Po, Pi, P2 and P3, i.e. the fundamental injection frequency and the first three harmonics thereof.

[0080] In the present strategy, the operating frequency FOP is thus adjusted within four frequency adjustment windows FAW, designated FAWo to FAW3. Each FAW includes (encompasses) a respective frequency collision point Po to P3. The reference to the frequency collision point is made for ease of explanation, since obviously due to the present strategy these points are avoided since the frequency FOP is modified to avoid approaching any of Finj.O to Finj.3.

[0081] Within each FAW, the pressure regulator frequency FOP is thus modified in such manner to that it does not approach too close from the injection frequency, respectively an injection frequency harmonic.

[0082] Any appropriate adjustment strategy can be used.

[0083] One approach may consist in adding an offset (positive or negative) to the nominal PWM signal frequency Fop.Nom to ensure a predetermined frequency difference with respect to the injection frequency or harmonic.P-DELPHI-445 / WO 11

[0084] This can be written as Fop=Fop.Nom + Offsetl

[0085] The value of Offsetl can be calibrated to be below the maximum desired operating frequency (here 200 Hz) and sufficiently spaced from the respective injection frequency line over the length of the FAW.

[0086] Another approach may involve dynamically (variably) modifying the frequency FOP with respect to the respective harmonic line within the FAW.

[0087] The term harmonic line refers to the values of the fundamental or harmonic frequency over the engine speed interval around each frequency collision point. So, in general, the harmonic line corresponding to each frequency collision point may be determined, and the FOP may be incrementally modified to maintain a substantially constant offset between FOP and the respective harmonic line (represented by dotted line) over the engine speed interval corresponding to the FAW.

[0088] In one embodiment, shown in the Figs., the FOP is dynamically (incrementally) modified to maintain a constant offset relative to the harmonic line, with a hysteresis function to prevent oscillatory adjustments.

[0089] This is best seen in Fig.6, where it can be observed that within each FAW, FOP is first increased up to the collision point Pi, to maintain a predetermined positive offset with respect to the harmonic line. Then at the collision point, FOP is decreased to maintained a negative offset with respect to the harmonic line, until FOP returns to F OP. Norn- The switching point between positive and negative offset as well as hysteresis position can be adjusted relative to Pi, if desirable.

[0090] It may be noted that the inventive method can be implemented in various manners in the ECU.

[0091] One possibility is to monitor in real time the frequency collision points Pi and adjust FOP as required to avoid approaching them. A principle diagram is presented in Fig.

[0092] 7. Step S2 indicates that the pressure regulator is operated at the nominal operating frequency Fop.Nom. The engine speed is monitored to determine the injection frequency and harmonics thereof at step S4. At step S6 it is checked whether FOPP-DELPHI-445 / WO 12

[0093] approaches a frequency collision point Pi. If the test is negative, the regulator is still operated at the nominal frequency Fop.Nom.

[0094] In the affirmative, the operating frequency FOP is adjusted (step S8) to avoid being same or similar to the current frequency collision point Pi. The adjustment can be done using the strategies disclosed above.

[0095] When the test at S6 becomes No, the operating frequency FOP returns to the nominal value Fop.Nom.

[0096] According to another approach, the inventive method can be operated based on a regulator frequency map that defines the regulator operating frequency FOP in function of engine speed, and where said map is configured such that the frequency FOP is constant except for a plurality of engine speed intervals, where the operating frequency is modified to avoid approaching predetermined frequency collision points.

Claims

P-DELPHI-445 / WO 13Claims1. A method of operating a gaseous fuel internal combustion engine comprising a fuel delivery system with a source of gaseous fuel supplying a fuel rail via a pressure regulator, and a plurality of fuel injectors coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, whereinthe pressure regulator includes a movable valve member operatively coupled to an electromagnetic actuator, which is driven by a pulse-width modulated, PWM, voltage signal with a controllable duty cycle,characterized in that the PWM voltage signal applied to the electromagnetic actuator has an operating frequency (FOP) corresponding to a fixed, nominal operating frequency (Fop.Nom), or set within a predetermined nominal operating frequency range, over the engine operating range,except for a plurality of engine speed intervals, where the operating frequency is modified to avoid approaching the frequency of the injection events and of at least one predetermined harmonic thereof.

2. The method according to claim 1 or 2, wherein the PWM operating frequency is modified within four distinct engine speed intervals, that corresponding to frequency collision points between the nominal operating frequency and the injection frequency, first harmonic, second harmonic and third harmonic of the injection frequency, respectively.

3. The method according to any of the preceding claims, wherein within each predetermined engine speed interval, the operating frequency is adjusted to maintain a predefined frequency offset between the operating frequency and the injection frequency or harmonic frequency, respectively.

4. The method according to any of the preceding claims, wherein the predefined frequency offset is fixed or variable, configured to ensure no overlap orP-DELPHI-445 / WO 14resonance between the operating frequency of the pressure regulator and the frequency of the injection events.

5. The method according to any of claims 3 or 4, wherein within each predetermined engine speed intervals, the harmonic line corresponding to the frequency collision points is determined.

6. The method according to any of claims 3 to 5, wherein the operating frequency is adjusted in such manner that the offset is positive before the respective frequency collision point and is negative after the frequency collision point.

7. The method according to claim 6, further comprising applying a hysteresis mechanism to the operating frequency adjustment to avoid rapid fluctuations in operating frequency.

8. The method according to any of claims 3 to 7, wherein said frequency offset is of at least 5 or 10 Hz, and preferably no more than 20 or 25 Hz.

9. The method according to any of the preceding claims, wherein said predetermined engine speed intervals span over 100 to 500 RPM.

10. The method according to any of the preceding claims, wherein the operating frequency is maintained below 200 Hz over the entire speed range.

11. The method according to any of the preceding claims, wherein the nominal operating frequency is set to a fixed value between 80 and 160 Hz, in particular between 100 and 150 Hz.

12. A fuel delivery system for a gaseous fuel internal engine, comprising a with a source of gaseous fuel supplying a fuel rail via a pressure regulator, and a plurality of fuel injectors coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, wherein the pressure regulator includes a movable valve member operatively coupled to an electromagnetic actuator, and a controlled configured to generate a pulse-width modulated, PWM, voltage signal with a controllable duty cycle that is applied to the electromagnetic actuator to control the flow rate through the pressureP-DELPHI-445 / WO 15regulator, and wherein the controller is configured to perform the method according to any of the preceding claims.

13. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1 to 11.

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