Methods for operating an internal combustion engine

Abstract

The invention relates to methods for operating an internal combustion engine (ICE) powered by gaseous fuel, in particular to methods for limiting leaks of gaseous fuel. The ICE includes a gaseous fuel delivery system for supplying, via a supply line (15), a source of gaseous fuel to a fuel rail (16) through a pressure regulator (14). The source of gaseous fuel includes at least one gas tank (12). A tank isolation valve (20) is associated with each of the at least one gas tank (12). A supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section (A). According to a first aspect, the method comprises monitoring for the occurrence of a gas leak, and, if a leak is detected, operating the engine in a predetermined operating mode to limit gaseous fuel leakage, the predetermined mode being selected based on the location and / or magnitude of the leak. According to another aspect, the fuel delivery system comprises a refueling line (24) branching from the high-pressure section (A), the refueling line comprising a filling receptacle for interfacing with a refueling station and a check valve (34) at or near the connection with the high-pressure section (A). After tank refueling, a purge procedure is performed, according to which injection events are performed while the tank isolation valve(s) is / are closed, until the gas pressure in the high-pressure section has decreased to a predetermined threshold.

Description

[0001] P-DELPHI-464 / WO 1

[0002] METHODS FOR OPERATING AN INTERNAL COMBUSTION ENGINE

[0003] Technical field

[0004] The present invention generally relates to methods for operating an internal combustion engine powered by gaseous fuel, in particular to methods for limiting leaks of gaseous fuel.

[0005] Background Art

[0006] Hydrogen-fueled internal combustion engines have garnered significant attention as a sustainable alternative to conventional fossil-fueled engines, owing to their potential for zero carbon emissions during combustion. Fuel leakage is a common concern for designers of internal combustion engines powered by gaseous fuel, in particular those powered by hydrogen. Hydrogen fuel is typically stored in gas tanks at high pressures ranging from 350 to 700 bar. This pressure is reduced as it flows through a fuel delivery line to a working pressure of 5 to 40 bar for injection into the engine. This pressure reduction process introduces multiple opportunities for fuel gas leakage along the fuel delivery line.

[0007] Control and mitigation of leaks in hydrogen-fueled internal combustion engines is critical for both safety and efficiency. Hydrogen is highly flammable and has a lower ignition energy than conventional fuels, making even small leaks a significant hazard. When a leak is detected, immediate corrective actions must be taken to prevent fire, explosion, or unintended emissions. Effective leak control should enhance engine reliability, maintain optimal combustion conditions, and ensure regulatory compliance with safety and emissions standards. Implementing advanced leak detection and containment mechanisms, such as real-time sensors and automated shut-off valves, is essential for maintaining operational integrity. Addressing leaks promptly also improves fuel efficiency and reduces waste, contributing to the overall sustainability of hydrogen-powered technology.

[0008] Technical problem

[0009] It is an object of the present invention to provide a method for operating a gaseous fuel internal combustion engine that is able to mitigate fuel leaks.P-DELPHI-464 / WO 2

[0010] General Description of the Invention

[0011] The present invention is based on the single general inventive concept of a holistic method for managing fuel pressure within delineated sections of the fuel supply line. This is achieved through integrated control logic capable of managing both actual (reactive) and potential (proactive) leak risks.

[0012] This concept is embodied in two procedures that provide technically interrelated facets of the invention. The two procedures can be run independently from one another. Alternatively, they may be designed to operate synergistically (simultaneously and / or interdependent from one another). A first procedure provides a reactive leak response, wherein an actual detected leak triggers a locationdependent mitigation mode.

[0013] A second, complementary procedure provides a proactive strategy to address the potential leak risk from the high-pressure refueling line after refueling. This is achieved by actively reducing pressure in the high-pressure section by consuming residual fuel.

[0014] According to a first aspect, the invention relates to a method for operating an internal combustion engine as claimed in claim 1.

[0015] The internal combustion engine comprises a gaseous 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 source of gaseous fuel includes at least one gas tank.

[0016] The gaseous fuel delivery system includes a supply line that connects the source of gaseous fuel to the fuel rail, the pressure regulator being arranged on the supply line and configured to reduce the pressure of gas flowing to the fuel rail to a reduced pressure. A tank isolation valve is associated with each of the at least one gas tank. A gas flow control valve is arranged between the pressure regulator and the fuel rail.

[0017] A supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section, a supply line section between the pressure regulator and the gas flow control valve is referred to as medium-pressure section,P-DELPHI-464 / WO 3

[0018] and a supply line section between said gas flow control valve and the fuel rail is referred to as low-pressure section. The high-, medium- and low- pressure sections are hereinbelow collectively referred to as pressure sections.

[0019] Means for detecting gaseous fuel leaks are arranged to detect a gas leak in each of the high-pressure section, medium-pressure sections and low-pressure section. According to the invention, the method comprises monitoring the occurrence of a gas leak, and, if a leak is detected, operating the engine in a predetermined operating mode to limit gaseous fuel leakage, the predetermined mode being selected based on the location of the leak.

[0020] The inventive method thus enables to take appropriate measures to limit or mitigate the impact of leaks, depending on the location of said leaks.

[0021] Any appropriate techniques may be used for detecting gaseous fuel leaks in the pressure sections, in particular pressure sensors (possibly together with temperature sensors) and hydrogen concentration sensors.

[0022] Conventionally, a leak may be identified by comparing a pressure drop to a predefined threshold. Alternatively, mass loss can be determined from pressure and temperature. So, a deviation in mass or pressure, beyond expected tolerances, is indicative of a leak within the system.

[0023] In other words, a leak in the gaseous fuel delivery system is inherently linked to a corresponding loss in pressure or mass, with the magnitude of the leak being proportional to the extent of pressure or mass reduction. So, in the following, determining if a leak is below or above a threshold is equivalent to comparing pressure loss or mass loss to a threshold.

[0024] In practice, measurements at two different time points are used to compute a delta that is compared to a threshold:

[0025] - for pressure-based determination: AP = P1 - P2;

[0026] - for mass-based leak determination: Am = ml - m2;

[0027] As can be observed, the delta is computed by subtracting the end value from the initial value, whereby a greater leak leads to a higher delta value, making it easier to compare to a threshold. When the delta exceeds a predetermined threshold, aP-DELPHI-464 / WO 4

[0028] leak is present. However, one could also compute inversely (P2-P1) and work with negative thresholds.

[0029] In embodiments, the means for detecting gaseous fuel leaks include pressure sensors arranged to measure gaseous fuel pressure in each of the high-pressure section, medium-pressure section, and low-pressure section, and / or one or more hydrogen concentration sensors arranged on the fuel delivery system.

[0030] In practice, the use of pressure sensors is convenient for leak detection, as pressure monitoring may be required for other purposes.

[0031] In embodiments, if a leak below a predetermined first threshold is detected in the high-pressure section, a restricted operating mode is activated for the engine, according to which injection events are performed while the tank isolation valve(s) are sequentially closed and opened, such that fuel pressure in the high-pressure section is maintained within a predefined pressure range that is lower than a gas tank pressure. While the restricted operating mode is active, standard fuel injection strategies can still be applied, i.e. combustion events (injection / spark) can be performed normally in response to torque demands.

[0032] It may be noted that the tank isolation valve(s) conventionally only have two discrete states (fully open or fully closed), with no partial opening possible. The inventive method thus sequentially opens and closes the tank isolation valve(s), adjusting the duration of opening and closing phases so as to keep the fuel pressure in the high-pressure section within a predefined pressure range that is lower than the gas tank pressure. By reducing the fuel pressure in the high-pressure section, possible leaks out of the high-pressure section are significantly limited.

[0033] It may further be noted that, in the context of the present strategies, each tank isolation valve(s) includes an electromechanical actuator (any appropriate technique, e.g. comprising a solenoid or electric motor) that allows remotely actuating the respective valve by the engine control unit or other controller, i.e., to open or close selected valves according to the needs of the implemented strategy. In embodiments, the predefined pressure range corresponds to an operating pressure of the pressure regulator ± 5 bar. In embodiments, the predefined pressure range corresponds to a range of from 30 and 50 bar.P-DELPHI-464 / WO 5

[0034] In embodiments, if a leak exceeding a predetermined second threshold is detected in the low-pressure section, a safe state operating mode for the engine is activated, according to which the tank isolation valve(s) and the gas flow control valve are closed, such that the high- and medium- pressure sections are isolated from the pressure source and from the low-pressure section, and subsequently a purge of the low-pressure section is performed.

[0035] In these embodiments, the engine is thus forcefully stopped by isolating the low-pressure section from the pressure source and the high- and medium- pressure sections before purging the low-pressure section. Once the low-pressure section is fully emptied, no leaks may occur therethrough.

[0036] In embodiments, if a leak exceeding a predetermined third threshold is detected in the high- and / or medium-pressure section, another safe state operating mode for the engine is activated, according to which the tank isolation valve(s) is / are closed, such that the high-, medium- and low- pressure sections are isolated from the pressure source and in communication with each other, and subsequently a purge of the high-, medium-, and / or low-pressure section is performed.

[0037] In these embodiments, the engine is thus forcefully stopped by isolating the high-, medium-, and low-pressure sections from the pressure source before purging the high-, medium-, and / or low-pressure sections, depending on where the leak is located. Once the relevant pressure section is fully emptied, no gas leaks may occur therethrough.

[0038] In embodiments, the engine further comprises at least one vent line branching from the high-, medium-, and / or low-pressure section, each vent line comprising a venting shutoff valve. Purge of a pressure section is then performed by (temporarily) opening the venting shutoff valve of the corresponding vent line. Stated otherwise, at least one or up to all three pressure sections may have a vent line branching therefrom. For cost reasons, one vent line with venting shutoff valve may be considered sufficient, in particular since in operation two or more sections can be in communication (depending on isolation valve configuration) and thus purged as a common volume.P-DELPHI-464 / WO 6

[0039] In embodiments, purge of at least the low-pressure section is performed by triggering (performing) fuel injection events through the injectors that are ignited (i.e. , the injected gas is combusted), typically just before stopping the engine.

[0040] To recap, purging can be achieved by injection / combustion of the fuel gas, or by venting through a vent line with venting shutoff valve that is branched off from the supply line. In practice it may be desirable to have a vent line to be able to purge through that vent line if the engine has stalled.

[0041] In embodiments, the internal combustion engine is coupled to a starter motor powered by a battery to crank the engine, and if an injector leak is detected, a safe startup operating mode for the engine is activated, whereby a startup sequence is initiated at engine start, according to which the engine is cranked over a predetermined angular range before performing injection events and / or triggering spark events (so before implementing combustion). This produces a scavenging effect, by which air is fed to the cylinders to replace gaseous fuel. The predetermined angular range may be between 720° and 1440° (i.e., 2 to 4 full turns). For example, the angular range may correspond to 2, 2.5., 3, 3.5, or 4 turns, or greater.

[0042] The inventors have found that, while the engine is stopped, injector leakage may result in the presence of significant amounts of residual gaseous fuel in corresponding engine cylinders. If a spark event is triggered, said residual gaseous fuel may be ignited, which may result in undesired and unexpected torque generation and may damage the engine. To solve this issue, the engine is cranked for at least 2 turns using its starter motor, such that the residual gaseous fuel is evacuated through the exhaust system of the vehicle. This cranking can be part of the engine startup procedure, and is thus performed before fuel pressure is established in the fuel rail and before starting injection and spark events.

[0043] In embodiments, the fuel delivery system further comprises a refueling line branching from the high-pressure section, the refueling line comprising a filling receptacle for interfacing with a refueling station and a check valve at or near the connection with the high-pressure section. The check valve is configured as oneway valve to only allow flow from the refueling line to the high-pressure section. The check valve is advantageously arranged near the connection with the high-pressure section. In practice, depending on the overall configuration, the check valve may beP-DELPHI-464 / WO 7

[0044] positioned at a distance of up to 0.5 m from the connection point, or up to 1.0 m, 1.5 m, or 2.0 m from the connection point. The check valve may be the last component on the refueling line before the connection point to the high-pressure section.

[0045] According to this method, following refueling of the gas tanks, a purge procedure is performed, according to which injection events are performed while the tank isolation valve(s) is / are closed, until the gas pressure in the high-pressure section has decreased to a predetermined fourth threshold. Then the tank isolation valves are opened.

[0046] The inventors have found that, following refueling of the gas tanks, it is preferable for the tank shutoff valves to remain closed, such that fuel is drawn from the system itself, including residual fuel in the refueling line due to the previous / recent refueling operation rather than from the gas tanks. Indeed, refueling lines are not able to store gaseous fuel as reliably as dedicated gas tanks. Following a refueling operation, it is thus preferable to decrease the gas pressure in the refueling line to decrease possible leaks therethrough and only start drawing fuel from the gas tanks once the gas pressure in the refueling line has decreased to an acceptable level, which may be detected by, e.g., monitoring pressure in the high-pressure section. The check valve at the connection (connection point) of the refueling line to the high-pressure section prevents gas from flowing into the refueling line after reopening of the tank isolation valves.

[0047] According to another aspect, the invention provides a method for operating an internal combustion engine according to claim 11.

[0048] In embodiments, the gas flow control valve includes a shutoff valve and / or a pressure regulator.

[0049] In embodiments, detection of a possible leak in the gaseous fuel delivery system is performed by monitoring the gaseous fuel pressure and temperature in at least one of the high-, medium-, and low- pressure sections, determining a first fuel quantity in a pressure section at a first instant and a second fuel quantity in said pressure section at a subsequent second instant based on said gaseous fuel pressure and temperature, computing a fuel quantity delta from a difference between the secondP-DELPHI-464 / WO 8

[0050] fuel quantity and the first fuel quantity, and concluding the occurrence of a leak if the fuel quantity delta is greater than a threshold.

[0051] In embodiments, detection of a possible leak in the gaseous fuel delivery system is performed by monitoring the gaseous fuel pressure in at least one of the high-, medium-, and low- pressure sections, computing a fuel pressure delta from a difference between a value of a pressure sample at a first instant and a value of a pressure sample at a second instant, and concluding the occurrence of a leak if the fuel pressure delta exceeds a threshold.

[0052] Alternative and complementary methods for detecting leaks and determining their location and optionally magnitude are known in the art, and will thus not be discussed further.

[0053] The invention further provides a computer program (and / or computer readable medium) comprising instructions that, when the program is executed by a computer, cause the computer to carry out the method as described above. The invention further provides a control unit having stored thereon said computer program.

[0054] According to a further aspect, the invention provides an internal combustion engine as claimed in claim 21. The engine comprises a gaseous 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 source of gaseous fuel including at least one gas tank. The gaseous fuel delivery system includes a supply line that connects the source of gaseous fuel to the fuel rail, the pressure regulator being arranged on the supply line and configured to reduce the pressure of gas flowing to the fuel rail to a reduced pressure. A tank isolation valve is associated with each of the at least one gas tank. A gas flow control valve is arranged between the pressure regulator and the fuel rail. The supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section, the supply line section between the pressure regulator and the gas flow control valve is referred to as medium-pressure section, and the supply line section between said gas flow control valve and the fuel rail is referred to as low-pressure section. Pressure sensors are arranged to measure the gaseous fuel pressure in each of the high-pressure, medium-pressure, and low-pressure sections. Preferably, temperatureP-DELPHI-464 / WO 9

[0055] sensors are also arranged to measure the gaseous fuel temperature in each of the sections.

[0056] The internal combustion engine is coupled to a starter motor powered by a battery to crank the engine. Advantageously, the fuel delivery system further comprises a refueling line branching from the high-pressure section, said refueling line comprising a filling receptacle for interfacing with a refueling station and a check valve at or near the connection with the high-pressure section. The engine comprises the control unit configured to implement the methods and techniques according to the present disclosure.

[0057] In embodiments, at least one pressure section has a vent line branching therefrom, possibly at least two pressure sections have a vent line branching therefrom, and even all pressure sections may have a vent line branching therefrom.

[0058] Methods and techniques disclosed herein have been developed in the context of hydrogen powered internal combustion engines. It can, however, be applied to other gaseous fuels (e.g., CNG, etc.) and gaseous fuels mixtures (e.g., including a given percentage of hydrogen).

[0059] Brief Description of the Drawings

[0060] Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0061] FIG.1 is a schematic view of a gaseous fuel delivery system;

[0062] FIG.2 is a schematic view of another gaseous fuel delivery system;

[0063] FIG.3 is a flowchart of a method according to an embodiment of the invention; and FIG.4 is a flowchart of a method according to another embodiment the invention.

[0064] Description of Preferred Embodiments

[0065] FIG.1 illustrates a gaseous fuel delivery system 10 suitable for implementing the present methods and strategies. The system 10 includes multiple gas tanks 12i (two in this example — 12i and 122) that store gaseous fuel (e.g., hydrogen) as a source of gaseous fuel. The pressure of the gas tanks is referred to as tank pressure orP-DELPHI-464 / WO 10

[0066] supply pressure, also noted Ptank. The supply pressure may be around 350 to 700 bar, which corresponds to typical filling pressures.

[0067] The system 10 also comprises at least one pressure regulator 14 that reduces the fuel gas pressure to a predetermined level and a fuel rail 16 that supplies the fuel gas to multiple injectors 18. A supply line 15 connects the source of gaseous fuel to the fuel rail via the pressure regulator 14. The system here comprises four fuel injectors 18, though the number may vary. Although not shown, the fuel injectors 18 are arranged to deliver gaseous fuel to combustion chambers defined by cylinders of an internal combustion engine.

[0068] The pressure regulator 14 is configured to reduce the upstream / inlet pressure (at Ptank) to a lower pressure level that is predetermined, typically between 30 and 50 bar. The pressure regulator 14 here is a mechanical pressure regulator.

[0069] A tank isolation valve 20i is associated with each gas tank 12i to selectively enable or disable gaseous fuel flow from the corresponding gas tanks. Each tank isolation valve 20i is thus positioned directly downstream of the associated tank 12i to control the flow of fuel gas to the fuel rail 16 through the pressure regulator 14.

[0070] A gas flow control valve 22 is arranged between the pressure regulator 14 and the fuel rail 16 to selectively enable or disable fuel flow therethrough. The gas flow control valve 22 here takes the form of a rail isolation valve, but may alternatively be a (electronic) pressure regulator or a combination of shutoff valve and pressure regulator.

[0071] The tank isolation valves 20i and the gas flow control valve 22 are typically configured as on / off valves that are able to operate in either fully open or fully closed configuration. They include an electromechanical actuator (e.g., electric motor or solenoid actuator) that allows for remote actuation of the valve member. The isolation valves may typically be normally closed valves.

[0072] The section of the system 10 between the tank isolation valves 20i and the pressure regulator 14 is referred to as the high-pressure section, noted A; the section between the pressure regulator 14 and the rail isolation valve 22 is referred to as the medium-pressure section, noted B; and the section between the rail isolation valve 22 and the fuel rail 16 is referred to as the low-pressure section, noted C.P-DELPHI-464 / WO 11

[0073] The high-, medium-, and low-pressure sections (A, B, and C) are connected in series with a pressure separator (either pressure regulator or isolation valve) arranged at the interface between adjacent sections. Hence, gas may only flow from one section to an adjacent section via a respective isolation valve or regulator. The isolation valves 20, 22 enable flow (in either direction) from one section to an adjacent section when in open state. In closed state, fuel cannot flow through the isolation valve, and flow between sections is prevented.

[0074] Pressure and temperature sensors are arranged to monitor fuel pressure and temperature inside of each of the high-, medium-, and low-pressure sections A, B, and C. Each gas tank 12 may also be fitted with sensors to monitor fuel pressure and temperature therein. In the drawings, the pressure and temperature sensors are indicated P and T, respectively. In the embodiment of FIG.1, each section is provided with sensors for measuring the fuel gas pressure and temperature therein. Preferably, sensors configured to measure pressure and temperature values of fuel gas in a given section are arranged at a central location of said given section, such that the measured fuel gas pressure and temperature values will have a high probability of being representative of the operating conditions in said section.

[0075] In other embodiments, the temperature of the fuel gas enclosed within a given section may be estimated from at least one temperature value related to an engine component that is adjacent to the at least one section, e.g. an adjacent section or a component of the motor itself, such that no temperature sensor is required in that section. Indeed, temperature of fuel in a given section may be computed using a value measured in the vicinity of the given section and applying a temperature variation gradient. For example, the temperature of the injection rail can be calculated from an already measured engine temperature value.

[0076] Pressure and temperature signals are sent to an engine control unit (ECU), not shown. ECUs are electronic control systems used to regulate and optimize the operation of an internal combustion engine. An ECU comprises one or more processor units, memory units, input / output (I / O) interfaces, and communication modules configured to execute control algorithms for regulating engine operation. Alongside the aforementioned pressure and temperature sensors signals, the ECU may process various sensor inputs, including but not limited to engine speed,P-DELPHI-464 / WO 12

[0077] temperature, air intake, and fuel composition, to dynamically adjust parameters such as fuel injection timing, ignition timing, and air-to-fuel ratio. The ECU may control fuel injection based on real-time operating conditions to ensure efficient combustion, reduce emissions, and enhance overall engine performance. Additionally, the ECU may be configured to interface with pressure regulators, injection rails, and other fuel system components to manage fuel flow and maintain optimal pressure levels.

[0078] The gaseous fuel delivery system 10 further comprises a refueling line 24 for refilling the gas tanks 12. The refueling line 24 may comprises a first filter 26, a first check valve 28, an optional refueling isolation valve 30, a second filter 32, and a second check valve 34. A pressure sensor is arranged after the first check valve 28. The refueling line 24 branches from the high-pressure section A, interfacing therewith via the second check valve 34. The refueling line 24 is thus delimited on one end by the second check valve 34, and on the other end by a filling receptacle 36. The filling receptacle 36 is accessible by a user by opening a filling door. Advantageously, the second check valve 34 is arranged close to the gas tanks 12, thereby minimizing the volume of the high-pressure section A. For example, the second check valve 34 can be arranged at a connection point CP24 between the refueling line 24 and the high-pressure section A, or at a predetermined distance L34 from the connection point CP24, e.g., between 0.5 and 2.0 m.

[0079] Fuel from a filling station enters the refueling line 24 via the filing receptacle 36 at a pressure equal to or greater than the working pressure of the gas tank (e.g. 350 to 700 bar). Fuel then flows through the first filter 26, the first check valve 28, and the second filter 32, before entering the high-pressure section A through the second check valve 34. Fuel then flows through the high-pressure section into the respective gas tanks 12.

[0080] It may be noted that, although only illustrated for the first gas tank 12.1, a bypass with a check valve 21 is typically connected before and after each gas isolation valve 20i. The check valve 21 only allows flow from section A towards the respective gas tank 20. A manual shut-off valve 23 is also typically mounted on the gas tank or close by. During refilling, the engine is typically stopped and the isolation valves 20 are closed. The gaseous fuel thus flows from the refueling line 24 into section AP-DELPHI-464 / WO 13

[0081] through the second check valve 34 and then flows into the respective gas tanks via the respective bypasses with check valves 21.

[0082] FIG.2 shows another gaseous fuel delivery system 10’ suitable for implementing the present methods and strategies. This gaseous fuel delivery system 10’ is similar to that of FIG.1 , comprising all of the features discussed above, and further comprises vent lines 25 branching off of each of the high-, medium-, and low-pressure sections. These vent lines may be used to purge different pressure sections, as will be explained below.

[0083] Although not shown, the internal combustion engine is conventionally coupled to a starter motor powered by a battery. The starter motor is coupled to the engine during startup to crank the engine and initiate engine operation. The startup motor is typically decoupled from the engine after cranking it over an angular range that is sufficient to initiate engine operation.

[0084] <Leak mitigation>

[0085] FIG.3 illustrates a flowchart of embodiments of methods for operating an internal combustion engine according to the invention. As previously mentioned, control and mitigation of leaks in gaseous fueled internal combustion engines is critical for both safety and efficiency. As such, when a leak is detected, the inventive method switches to various operating modes depending on the location and / or the magnitude of the detected leak, thereby appropriately reducing possible leaks. When no leak is detected, the engine remains in normal operation, as is conventional in the art.

[0086] First strategy - M1

[0087] When a leak below a first threshold is detected in the high-pressure section A, a restricted operating mode (M1) is activated for the engine. This first threshold can be set to define an acceptable leakage level at which the engine can still be operated. In mode M1, the tank isolation valves 20 are sequentially closed and opened, thereby limiting the quantity of fuel flowing to the high-pressure section, andP-DELPHI-464 / WO 14

[0088] injection events are performed, which reduces the pressure in the high-pressure section A. That is, the tank isolation valves 20 are operated in synchronism (typically simultaneously), successively on / off, to achieve a kind of regulation of the pressure to a pressure level below Ptank. In doing so, fuel pressure in the high-pressure section A is thus maintained within a predefined pressure range that is lower than a gas tank pressure (e.g., between 30 and 50 bar, and / or within the operating pressure of the pressure regulator ± 5 bar), thereby reducing leaks.

[0089] It may be noted that the tank isolation valves 20 are typically shut-off valves, i.e. , designed to have only two operating positions: open or closed. The pressure regulation effect carried out in this first strategy is thus obtained by continuously toggling the tank isolation valves between on and off positions to achieve the desired pressure in the high-pressure section. In practice, the duration of the off-state of the shut-off valves will thus vary depending on the Ptank, on the desired pressure in section A, and on the current engine fuel consumption.

[0090] Second strategy - M2

[0091] When a leak exceeding a second threshold is detected in the low-pressure section C, a safe state operating mode (M2) for the engine is activated. Here the second threshold detects a leak beyond an acceptable level. In mode M2, the tank isolation valve(s) and the gas flow control valve are closed, such that the high- and mediumpressure sections A, B are isolated from the pressure source and from the low-pressure section C. Subsequently a purge of the low-pressure section C is performed, and the engine is forcefully shutdown.

[0092] When the gaseous fuel system comprises vent lines as shown on FIG.2, purge of the low-pressure section C may be performed through the vent line. Otherwise, purging may be performed through the injectors, by performing injection events while the engine is running before stoppingv

[0093] Third strategy - M3

[0094] When a leak exceeding a third threshold is detected in the high- and / or mediumpressure sections, a safe state operating mode (M3) for the engine is activated.P-DELPHI-464 / WO 15

[0095] The tank isolation valves are closed, such that the high-, medium-, and low-pressure sections are isolated from the pressure source and in communication with each other. That is, while the tank isolation valves 20 are closed, the regulator 14 and flow control valve 22 are not operated to achieve a pressure separation between the sections: they remain in fluid communication. Subsequently a purge of the high-, medium-, and / or low-pressure sections is performed, and the engine is forcefully shutdown. When the gaseous fuel delivery system comprises venting lines 25 with associated shut-off valves 27 as shown on FIG.2, purge of the pressure sections may be performed through any of the vent lines 25, and is preferably performed through the vent line 25 corresponding to the pressure-section in which the leak was detected. Otherwise, purging may be performed through the injectors, by performing injection events while the engine is stopped.

[0096] As will be understood, one vent line 25 is sufficient to purge all three sections A, B, and C, since they are in fluid communication. That is the three sections can be purged through a single vent line 25 or by performing injection events with the fuel injectors. The end of each purge line 25 may be configured to either vent directly to the atmosphere or be connected to a canister or similar storage device for collecting the purged gas.

[0097] Fourth strategy - M4

[0098] When an injector leak is detected, a safe startup operating mode for the engine is activated (M4). A specific startup sequence is initiated at engine start, according to which the engine is cranked, e.g., for 2 to 4 full turns using its starter motor. Such cranking enables evacuation of any residual gaseous fuel present in engine cylinders (due to injector leaks) or admission and / or exhaust lines through the exhaust system of the vehicle before triggering any injection or spark events. So, the cranking is conducted longer than usual, until fuel injection is started.

[0099] No injection events or spark events are performed during this startup sequence. Also, pressure in the fuel rail is established only after this startup sequence.

[0100] In the context of this strategy, injector leaks may be detected based on pressure or fuel quantity variation in the fuel rail, in particular while the engine is stopped. ForP-DELPHI-464 / WO 16

[0101] example, as the vehicle is parked, a reduction of fuel pressure or fuel quantity in the fuel rail that is observed a predetermined time period (minutes or hours) can indicate that fuel has leaked through the injectors into the engine.

[0102] Fifth strategy - M5

[0103] As shown in FIG.4, following refueling of the gas tanks, a post-refueling restricted mode (M5) for the engine is activated. Injection events are performed while the tank isolation valves 20 are (remain closed - they are typically closed while the engine is off) closed such that fuel is drawn from residual fuel in the refueling line from the previous refueling operation, rather than the gas tanks. When the gas pressure PA in the high-pressure section A has decreased to a fourth threshold TH4, the tank isolation valves 20 may be reopened and engine operation proceeds as is conventional / usual, or according to one of the restricted modes as described above. This restricted mode enables to decrease the gas pressure in the refueling line 24 to reduce possible leaks therethrough.

[0104] Leak detection

[0105] Leak detection in the fuel delivery system 10, 10’ can be particularly carried out by tracking of pressure loss or quantity loss.

[0106] Pressure loss tracking can be implemented by comparing the pressure in a given section of the fuel delivery system between two time points. This approach is particularly efficient if the temperature remains substantially constant and there is no fuel injection. Alternatively, the injection fuel quantity (if injection / combustion is operated) should be accounted for to compensate the pressure measure at the second time point.

[0107] Quantity loss tracking can be conducted by monitoring the fuel quantity, measured in mass or moles, over two time points. Mass or molar quantities are derived using the perfect gas law, incorporating pressure and temperature. Fuel leakage for a respective section may be identified by comparing the quantities measured at different time points against a predefined threshold.

Claims

P-DELPHI-464 / WO 17Claims1. A method for operating an internal combustion engine comprising a gaseous fuel delivery system with a source of gaseous fuel supplying a fuel rail (16) via a pressure regulator (14), and a plurality of fuel injectors (18) coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, the source of gaseous fuel including at least one gas tank (12);wherein the gaseous fuel delivery system includes a supply line (15) that connects the source of gaseous fuel to the fuel rail, the pressure regulator being arranged on the supply line and configured to reduce the pressure of gas flowing to the fuel rail to a reduced pressure;wherein a tank isolation valve (20) is associated with each of the at least one gas tank (12);wherein a gas flow control valve (22) is arranged between the pressure regulator and the fuel rail;wherein a supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section (A), a supply line section between the pressure regulator and the gas flow control valve is referred to as medium-pressure section (B), and a supply line section between said gas flow control valve and the fuel rail is referred to as low-pressure section (C);wherein means for detecting gaseous fuel leaks are arranged to detect a gas leak in each of the high-pressure section, medium-pressure section, and low- pressure section;the method comprising monitoring the occurrence of a gas leak, and, if a leak is detected, operating the engine in a predetermined operating mode to limit gaseous fuel leakage, the predetermined mode being selected based on the location and / or magnitude of the leak.

2. The method according to the preceding claim, whereby if a leak below a first threshold is detected in the high-pressure section, a restricted operating modeP-DELPHI-464 / WO 18is activated for the engine, according to which injection events are performed while the tank isolation valve(s) are sequentially closed and opened, such that fuel pressure in the high-pressure section is maintained within a predefined pressure range that is lower than a gas tank pressure.

3. The method according to the previous claim, whereby the predefined pressure range corresponds to an operating pressure of the pressure regulator plus or minus 5 bar.

4. The method according to claim 2, whereby the predefined pressure range corresponds to a range of from 30 and 50 bar.

5. The method according to any of the preceding claims, whereby if a leak exceeding a second threshold is detected in the low-pressure section, a safe state operating mode for the engine is activated, according to which the tank isolation valve(s) and the gas flow control valve are closed, such that the highland medium- pressure sections are isolated from the pressure source and from the low-pressure section, and subsequently a purge of the low-pressure section is performed.

6. The method according to any of the preceding claims, whereby if a leak exceeding a third threshold is detected in the high- and / or medium-pressure sections, a safe state operating mode for the engine is activated, according to which the tank isolation valve(s) is / are closed, such that the high-, medium-, and low- pressure sections are isolated from the pressure source and in communication with each other, and subsequently a purge of the high-, medium- , and / or low-pressure sections is performed.

7. The method according to claim 5 or 6, the gaseous fuel delivery system further comprising at least one vent line branching from the high-, medium-, and / or low- pressure section, each vent line comprising a venting shutoff valve;whereby purge of a pressure section is performed by opening the venting shutoff valve of the corresponding vent line.P-DELPHI-464 / WO 198. The method according to claims 5 or 6, whereby purge of at least the low- pressure section is performed by triggering fuel injections through the injectors while the engine is being stopped.

9. The method according to any of the preceding claims, whereby the internal combustion engine is coupled to a starter motor powered by a battery to crank the engine; andwhereby if an injector leak is detected, a safe startup operating mode for the engine is activated, whereby a startup sequence is initiated at engine start, according to which the engine is cranked for at least 2 to 4 turns before performing injection events and / or triggering spark events.

10. The method according to any of the preceding claims, wherein the fuel delivery system further comprises a refueling line (24) branching from the high-pressure section (A) at a connection point, said refueling line comprising a filling receptacle (36) for interfacing with a refueling station and a check valve (34) at or near the connection point with the high-pressure section (A);whereby, after tank refueling, a purge procedure is performed, according to which injection events are performed while the tank isolation valve(s) is / are closed, until the gas pressure in the high-pressure section has decreased to a fourth threshold.

11. A method for operating an internal combustion engine comprising a gaseous fuel delivery system with a source of gaseous fuel supplying a fuel rail (16) via a pressure regulator (14), and a plurality of fuel injectors (18) coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, the source of gaseous fuel including at least one gas tank (12);wherein the gaseous fuel delivery system includes a supply line (15) that connects the source of gaseous fuel to the fuel rail (16), the pressure regulator being arranged on the supply line and configured to reduce the pressure of gas flowing to the fuel rail to a reduced pressure; wherein a tank isolation valve (20)P-DELPHI-464 / WO 20is associated with each of the at least one gas tank; wherein a gas flow control valve (22) is arranged between the pressure regulator and the fuel rail;wherein a supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section (A);whereby the fuel delivery system further comprises a refueling line (24) branching from the high-pressure section (A) at a connection point, said refueling line comprising a filling receptacle (36) for interfacing with a refueling station and a check valve (34) at or near the connection point with the high- pressure section (A);whereby, after tank refueling, a purge procedure is performed, according to which injection events are performed while the tank isolation valve(s) is / are closed, until the gas pressure in the high-pressure section has decreased to a fourth threshold.

12. The method according to claim 10 or 11, wherein said purge procedure is performed at or after the first engine start following tank refueling.

13. The method according to any of the preceding claims, whereby the gas flow control valve includes a shutoff valve and / or a pressure regulator.

14. The method according to any of the preceding claims, wherein pressure sensors are arranged to measure gaseous fuel pressure in each of the high-pressure section, medium-pressure section, and low-pressure section; and wherein monitoring occurrence of a gas leak is based on monitoring the gaseous fuel pressure in said sections.

15. The method according to claim 14, whereby detection of a possible leak in the gaseous fuel delivery system is performed by monitoring the gaseous fuel pressure and temperature in at least one of the high-, medium-, and low- pressure sections;P-DELPHI-464 / WO 21determining a first fuel quantity in a pressure section at a first instant and a second fuel quantity in said pressure section at a subsequent second instant based on said gaseous fuel pressure and temperature;computing a fuel quantity delta from a difference between the second fuel quantity and the first fuel quantity;concluding an occurrence of a leak if the fuel quantity delta is greater than a threshold.

16. The method according to claim 14, whereby detection of a possible leak in the gaseous fuel delivery system is performed by monitoring the gaseous fuel pressure in at least one of the high-, medium-, and low- pressure sections;computing a fuel pressure delta from a difference between a value of a pressure sample at a first instant and a value of a pressure sample at a second instant; andconcluding an occurrence of a leak if the fuel pressure delta exceeds a threshold.

17. The method according to any of the preceding claims, wherein one or more hydrogen concentration sensors are arranged on the fuel delivery system, and wherein an occurrence of a gas leak is determined based on the measurements from the hydrogen concentration sensor(s).

18. The method according to any of the preceding claims, wherein each tank isolation valve and optionally the gas flow control valve includes an electrochemical actuator for remote actuation.

19. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 1 to 18.

20. Control unit having stored thereon the computer program of the previous claim.P-DELPHI-464 / WO 2221. An internal combustion engine comprising a gaseous fuel delivery system with a source of gaseous fuel supplying a fuel rail (16) via a pressure regulator (14), and a plurality of fuel injectors (18) coupled to the fuel rail and arranged to perform injection events that discharge fuel into respective engine cylinders, the source of gaseous fuel including at least one gas tank (12); and wherein the gaseous fuel delivery system includes a supply line (15) that connects the source of gaseous fuel to the fuel rail, the pressure regulator being arranged on the supply line and configured to reduce the pressure of gas flowing to the fuel rail to a reduced pressure; wherein a tank isolation valve (20) is associated with each of the at least one gas tank; wherein a gas flow control valve (22) is arranged between the pressure regulator and the fuel rail;wherein the supply line section between the tank isolation valve(s) and the pressure regulator is referred to as high-pressure section (A), the supply line section between the pressure regulator and the gas flow control valve is referred to as medium-pressure section, and the supply line section between said gas flow control valve and the fuel rail is referred to as low-pressure section;wherein means for detecting gaseous fuel leaks are arranged to detect a gas leak in each of the high-pressure section, medium-pressure section, and low- pressure section; wherein the internal combustion engine is coupled to a starter motor powered by a battery to crank the engine;wherein the engine comprises the control unit of the previous claim.

22. The engine according to claim 21, wherein the fuel delivery system further comprises a refueling line (24) branching from the high-pressure section (A) at a connection point, said refueling line comprising a filling receptacle (36) for interfacing with a refueling station and a check valve (34) at or near the connection point with the high-pressure section.

23. The engine according to claim 21 or 22, wherein said means for detecting gaseous fuel leaks include pressure sensors arranged to measure gaseous fuel pressure in each of the high-pressure section, medium-pressure section, andP-DELPHI-464 / WO 23low-pressure sections, and / or one or more hydrogen concentration sensors are arranged on the fuel delivery system.

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