Hydrogen fuel injection system

Abstract

A controller for determining an injection strategy of a fuel injector in a hydrogen fuel injection system in an engine, the controller comprising: an input configured to receive an engine operating parameter and a pressure signal associated with a pressure of hydrogen fuel available for injection from the injector in the fuel injection system; a processor arranged to determine an injection strategy for the injector based on the received pressure signal and engine control parameters, the determined injection strategy comprising one or more injector control signals to control operation of the fuel injector; and an output arranged to output the one or more control signals to the fuel injector.

Description

Technical Field

[0001] The present invention generally relates to a fuel system for injecting hydrogen into an engine for combustion. The present invention also relates to a fuel injection system for injecting hydrogen. Background Art

[0002] The ecological transition indicates a drastic reduction in atmospheric CO2 emissions, and therefore the pressure to replace carbon-based fossil fuels with renewable energy sources increases. In the automotive industry, this has seen the emergence of alternative power generation devices to traditional internal combustion engines running on fossil fuels. While battery solutions have gained considerable momentum as a viable alternative to internal combustion engine technology, it does have limitations, especially when considering heavy-duty or off-road vehicles, where the size and weight of the battery is impractical with the current state of the art.

[0003] An alternative approach consists in using conventional internal combustion engine technology, but replacing the existing carbon-based fossil fuels with ecologically produced hydrogen. Extensive research has shown the feasibility of this solution and a medium-pressure hydrogen injection system has been successfully developed. This medium-pressure system injects hydrogen into the cylinder as soon as the cylinder inlet valve has closed and continues to inject until the cylinder pressure reaches a pressure limit defined by the injection pressure. This pressure limit restricts the injection window and dictates a combustion strategy of the "premixed" type initiated by the spark plug. The combustion strategy is therefore similar to that used in gasoline-type (Otto cycle) direct injection systems.

[0004] Increasing the operating pressure of hydrogen fuel injection systems is a potential way to improve engine performance and reduce fuel consumption in hydrogen internal combustion engines (ICEs). The main disadvantage of increasing injection pressure is that for typical hydrogen storage mechanisms, relying on high pressure availability limits the range of the vehicle or requires expensive and inefficient pumps / compressors.

[0005] The most common hydrogen storage mechanism for vehicles is a storage tank containing compressed gas which is refilled to 350 bar (suitable for heavy vehicles) or 700 bar (a more compact storage mechanism than heavy vehicles, but heavier. This storage mechanism is more suitable for smaller vehicles).

[0006] As fuel is used, the storage tank pressure decreases and the storage tank is generally considered empty when the pressure drops to approximately 20 bar.

[0007] For low pressure (less than about 10 bar) and medium pressure (less than about 40 bar) hydrogen injection systems, the storage tank pressure is reduced to the injector operating pressure by a gas pressure regulator before the gas is introduced into the accumulator / common rail immediately upstream of the fuel injectors.

[0008] It is against this background that the present invention has been devised. Summary of the invention

[0009] Against this background, according to one aspect of the present invention, there is provided a controller for determining an injection strategy of a fuel injector in a hydrogen fuel injection system in an engine, the controller comprising: an input end configured to receive engine operating parameters and a pressure signal associated with a pressure of hydrogen fuel available for injection from the injector in the fuel injection system; a processor configured to determine the injection strategy of the injector based on the received pressure signal and engine control parameters, the determined injection strategy comprising one or more injector control signals to control the operation of the fuel injector; and an output end configured to output the one or more control signals to the fuel injector.

[0010] The present invention provides a controller that determines an injection strategy for an injector in a hydrogen fuel injection system (single fuel injection system). The controller receives engine operating parameters (e.g., engine load and / or engine speed) and a pressure signal associated with a hydrogen fuel pressure available for injection, the fuel pressure corresponding to the fuel pressure in a storage tank. Based on the engine operating parameters and the pressure signal, an injection strategy including one or more control signals output to the fuel injector is determined. Note that the pressure signal can be associated with a current maximum pressure of hydrogen fuel available for injection from an injector in the fuel injection system.

[0011] A controller according to the above aspect of the invention can implement a hydrogen injection system and control strategy that uses the highest pressure available from the hydrogen storage system at any given time. A fuel injection system controlled by a controller according to such an aspect of the invention can operate over a pressure range from the maximum storage pressure of the fuel tank (a full tank, e.g. 700 bar) down to the minimum storage pressure (a nominally "empty" tank may be maintained at 20 bar-50 bar for architectural and refill power / time reasons).

[0012] Such an injection system and control strategy may thus take advantage of the increased engine efficiency available from high pressure injection when it is available, but still maintain the ability to operate at low injection pressures to maximize vehicle mileage.

[0013] Unlike known low and medium pressure hydrogen injection systems, the controller according to the present invention does not regulate / control the hydrogen pressure available to the injector. The injector may be exposed to the fuel storage pressure within the fuel tank or isolated from the fuel tank by a shutoff valve.

[0014] In order to maintain acceptable engine performance over a continuous range of injection pressures, a controller according to aspects of the present invention may use a range of injection strategies (variations in the number of injections per cycle and the timing and injection amount of each injection). The most appropriate injection strategy may be scheduled based on the available fuel pressure and other engine operating parameters (e.g., current engine speed and desired torque). In addition to the injection strategy, the corresponding ignition strategy, including spark timing, duration, and intensity, may be varied in a similar manner to optimize overall combustion efficiency and engine performance.

[0015] Typically, the pressure of the hydrogen to be injected ranges from 10 to 700 bar, depending on the engine speed / load requirements. By injecting the hydrogen at a high injection pressure, the main injection provides efficiency benefits in terms of reduced pumping and heat losses.

[0016] The advantages of a fuel injection system including a controller according to the above aspects of the present invention are:

[0017] - System simplicity and lower cost - Compared to high pressure systems that require a compressor to maintain a high operating pressure to maximize vehicle mileage, the present arrangement enables the current pressure available from the fuel tank to be used when determining the injection strategy. Similarly, compared to low / medium pressure systems that require a regulator and possibly a heat exchanger, the fuel injection system according to aspects of the present invention provides a simpler system.

[0018] - The fuel injection system according to aspects of the invention provides a higher overall drive cycle efficiency compared to low / medium pressure systems.

[0019] - Fuel injection systems according to aspects of the present invention are flexible in that they can operate according to different injection strategies depending on the available pressure of the available hydrogen fuel (e.g., they can operate at highest efficiency if / when fuel storage and refilling facilities are maximized, but can also accommodate situations where refilling is infrequent and fuel tanks are smaller as H2 infrastructure develops and expands).

[0020] Engine operating parameters may include engine speed and / or engine load.

[0021] The processor may be configured to access a lookup table containing a plurality of injection strategies set by engine control parameters and the pressure of hydrogen fuel available for injection. The processor may be configured to select an optimal injection strategy from the plurality of injection strategies based on the received engine parameters and the received pressure signal. Alternatively, the processor may be configured to access a mathematical model configured to generate an injection strategy based on the received engine parameters and the received pressure signal.

[0022] One or more control signals in the determined injection strategy may be arranged to control the amount of fuel injected by the injector.One or more control signals in the determined injection strategy may be arranged to control the injector valve opening and closing times.

[0023] The engine may include an engine cylinder having a cylinder piston, which is driven by a crankshaft between a bottom dead center (BDC) and a top dead center (TDC) to perform a compression stroke, and the determined injection strategy may include one or more of the following: pre-injecting hydrogen fuel into a combustion chamber late in the compression stroke (for example, within 60 degrees before the cylinder piston is at top dead center); pre-injecting hydrogen fuel into the combustion chamber, followed by a main injection of hydrogen fuel into the combustion chamber late on both sides of top dead center (TDC); pre-injecting hydrogen fuel into the combustion chamber early in the compression stroke (for example, near the closing of the intake valve).

[0024] According to another aspect of the present invention, a method for determining an injection strategy of a fuel injector in a hydrogen fuel injection system in an engine is provided, the method comprising: receiving engine operating parameters and a pressure signal associated with a pressure of hydrogen fuel that can be used to inject from an injector in the fuel injection system; determining the injection strategy of the injector based on the received pressure signal and engine control parameters, the determined injection strategy comprising one or more injector control signals to control the operation of the fuel injector; and outputting the one or more control signals to the fuel injector.

[0025] According to another aspect of the present invention, a single-fuel hydrogen fuel injection system for an engine is provided, comprising: a hydrogen fuel storage tank; an accumulator rail fluidly connected to the storage tank; one or more injectors fluidly connected to the accumulator rail; a pressure sensor configured to determine the pressure of the hydrogen fuel within the fuel injection system; and a controller according to the above aspect of the present invention.

[0026] The accumulator rail may be in direct fluid communication with the hydrogen fuel storage tank.The hydrogen fuel pressure determined by the pressure sensor within the fuel injection system may correspond to the pressure within the storage tank.

[0027] It will be appreciated that preferred and / or optional features of any aspect of the invention may be incorporated into any other aspect of the invention either alone or in appropriate combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] For a better understanding of the present invention, reference will now be made, by way of example only, to the following drawings, in which:

[0029] Figure 1 is a schematic diagram of a known combustion cylinder in a hydrogen fuel system;

[0030] Figure 2 yes Figure 1 A schematic diagram of a combustion cylinder in an engine having an injector and a spark plug arrangement for initiating combustion of hydrogen gas injected into the cylinder;

[0031] Figure 3 is a schematic diagram of a known fuel injection system in a hydrogen fuel system;

[0032] Figure 4 is a schematic diagram of another known fuel injection system in a hydrogen fuel system;

[0033] Figure 5 is a schematic diagram of a fuel injection system according to an embodiment of the present invention;

[0034] Figure 6 is a diagram of possible fuel injection strategies depending on available fuel pressure according to an embodiment of the present invention;

[0035] Figure 7 is a method of operating a fuel injection system according to an embodiment of the present invention; and

[0036] Figure 8 It is a cross-sectional view of a fuel injector applicable to the embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention relates to a single fuel hydrogen fuel system for delivering hydrogen to the cylinders of an engine. The present invention solves the problem of low thermal efficiency of medium pressure hydrogen fuel injection systems because it is able to inject high pressure hydrogen into the combustion chamber. This is further enhanced in the present invention by using an injection and ignition strategy to achieve a "diffusion type" combustion of hydrogen.

[0038] In the drawings, like components are denoted by like reference numerals.

[0039] See also Figure 1 , shows a known arrangement in which a combustion cylinder 10 is located within a cylinder head (not shown) and includes at least one intake valve 12 and at least one exhaust valve 14 (one of each is shown), as in a conventional internal combustion engine arrangement. An injector 16 is centrally located on the top of the cylinder 10 between the intake valve 12 and the exhaust valve 14 and is arranged to receive a supply of pressurized hydrogen from a hydrogen source (not shown). Under the control of an engine control unit (ECU) (e.g. Figure 3 and Figure 4 1 , the injector 16 is arranged to inject hydrogen into the engine cylinder 10 according to an injection plan, which will be described in further detail below. The injector has a longitudinal center axis AA.

[0040] Cylinder piston( Figure 1The piston (not shown) can be moved within the engine cylinder 10 by a piston cycle between a bottom dead center (BDC) position and a top dead center (TDC) position by means of a crank drive (not shown). The position of the cylinder piston within the piston cycle is referenced to a crank angle (CA) relative to TDC. The convention used herein when referring to the position of the cylinder piston throughout the piston cycle is to define top dead center (TDC) as occurring at 360° CA. For example, 300° CA refers to a crank angle of 60° before TDC, and 420° CA refers to a crank angle of 60° after TDC.

[0041] Figure 2 The position of the cylinder piston 18 within the cylinder is shown. The cylinder piston 18 has a longitudinal axis BB which is ideally aligned with the injector axis AA. The upper end of the cylinder piston 18 defines, together with the walls and top of the cylinder, a combustion space 20 into which an injected spray or jet 22 of hydrogen gas is delivered by the injector 16. Adjacent to the injector 16, a spark plug 24 is located in a generally central position of the cylinder top and is arranged to produce a spark to ignite the injected hydrogen gas jet 22 within the combustion space 20. The upper end of the cylinder piston 18 is shaped to include a bowl 24 into which the hydrogen gas is injected. Figure 2 The bowl 26 shown in FIG. 1 is a well-known concave bowl for use in diesel engines. The concave bowl 26 includes sides that slope inwardly toward the central axis BB of the piston. In a diesel engine, the concave nature of the piston bowl 26 is used to optimize air-fuel mixing and subsequent combustion. In the present invention, a concave bowl may be preferred, but other piston bowl geometries may be used due to the different dynamic characteristics of hydrogen injection compared to diesel injection.

[0042] The compression ratio is typically (but not exclusively) between 14: 1 and 22: 1. The compression ratio is defined as the ratio of the swept volume of the cylinder piston to the swept volume of the combustion chamber at its minimum volume (TDC).

[0043] Reference Figure 3 , shows a known injection system for low-pressure and medium-pressure systems, in which hydrogen is injected at a pressure below about 50 bar via injectors into combustion cylinders located in the cylinder head, as in a conventional internal combustion engine arrangement.

[0044] Figure 3 A schematic diagram of a fuel injection system 30 is shown including a plurality of fuel injectors 16 in fluid communication with and supplied by an accumulator rail 35. The accumulator rail 35 is in turn in fluid communication with a hydrogen fuel reservoir in a storage tank 37. The injectors 16 are controlled by an engine control unit (ECU) 39.

[0045] The fuel injection system further includes a shutoff valve 41, which is configured to open when the engine ignition is “ON” and to close when the engine ignition is “OFF”, and a pressure regulator 44, which is located in a fuel line 46 between the storage tank 37 and the accumulator rail 35. The pressure regulator 44 is controlled by the engine control unit 39.

[0046] The accumulator rail 35 is also associated with a pressure sensor 48 that is configured to measure the pressure of the hydrogen fuel within the rail 35 .

[0047] In operation, hydrogen fuel is supplied from storage tank 37 to accumulator rail 35 and then injected into the engine by injector 16. ECU 39 receives pressure signal 50 from pressure sensor 48 and sends control signal 52 to pressure regulator 44 to regulate fuel pressure within the operating pressure range (narrower range of low pressure) of injector 16. ECU 39 then sends control signal 54 to the fuel injector based on engine operating parameters such as engine load (throttle demand from the driver) and engine speed.

[0048] It will be appreciated that during operation, the pressure sensor 48 , the ECU 39 , and the pressure regulator 44 form a feedback loop to maintain the fuel pressure within the accumulator rail 35 within an optimal pressure range for the injectors 16 .

[0049] It should be noted that Figure 3 The arrangement shown may introduce inefficiencies into the fuel injection process. For example, if the pressure of the storage tank 37 is high, the system 30 first regulates the pressure of the fuel to the operating pressure of the injector 16 and then effectively increases the fuel pressure again as the fuel is compressed in the engine cylinders. Figure 3 The arrangement requires the presence of a regulator, but may also include a heat exchanger (not shown), which will increase the complexity of the fuel injection system.

[0050] Figure 4 A schematic diagram of a known fuel injection system 30 is shown for use in a high pressure system in which hydrogen is injected via an injector at a pressure between approximately 150 bar and 300 bar into a combustion cylinder located in a cylinder head, as in an internal combustion engine arrangement. Figure 4 In, with Figure 1 , Figure 2 and Figure 3 The same reference numerals indicate equivalent / similar components / features.

[0051] Figure 4 The general injection system shown is similar to Figure 3However, instead of pressure regulator 44, fuel line 46 now includes a compressor / pump 56 which is controlled by ECU 39 (via control signal 58).

[0052] In operation, hydrogen fuel is supplied from the storage tank 37 to the accumulator rail 35 and then injected into the engine by the injector 16. Figure 3 As shown, the ECU 39 receives a pressure signal 50 from the pressure sensor 48, but Figure 4 In the case of a fuel pump 16, the required pressure in the accumulator rail 35 is at a higher level (e.g. 150 bar to 300 bar), so the ECU 39 sends a control signal 58 to the compressor / pump 56 to control and maintain the fuel pressure within the operating pressure range of the injector 16. The ECU 39 then sends a control signal 54 to the fuel injector 16 based on engine operating parameters such as engine load (throttle demand from the driver) and engine speed.

[0053] It will be appreciated that during operation, the pressure sensor 48 , the ECU 39 , and the pump / compressor 56 form a feedback loop to maintain the fuel pressure within the accumulator rail 35 within an optimal pressure range for the injectors 16 .

[0054] It should be noted that Figure 4 The arrangement shown increases the complexity of the fuel injection system because the pump / compressor 56 is required to maintain high operating pressures to maximize vehicle range.

[0055] Figure 5 A schematic diagram of a fuel injection system 60 according to an embodiment of the present invention is shown, wherein hydrogen is injected via injectors at a pressure between approximately 20 bar and 700 bar into combustion cylinders located in a cylinder head, as in a conventional internal combustion engine arrangement.

[0056] In the following description, the term "engine load" is used as a synonym for "fuel demand" and is expressed in mg of fuel. The term engine speed is normally used and is expressed in rpm. When different injection combinations or partial injections are used in each injection cycle, this combination is called an injection "strategy".

[0057] Reference Figure 5, a fuel injection system 60 according to an embodiment of the present invention includes one or more fuel injectors 16 (one of which is shown in this example), which are controlled by an engine control unit (or controller) 39 including a computer or processor 62. The controller 39 is configured to generate an injector control signal 54, which is generally in the form of an electric current, applied to the injector 64 to control the movement of the injector valve needle (not shown). For example, in a unit injector, the control signal 54 takes the form of a current waveform applied to an electromagnetic actuator to control the valve needle lift. The current is applied to the injector in the form of a waveform, and when the current in the waveform exceeds a predetermined threshold, the valve needle of the injector is opened, thereby injecting fuel into the engine cylinder. When the current in the waveform decreases to below a predetermined threshold, the valve needle is closed, thereby stopping the injection of fuel into the engine cylinder. In order to optimize the operation of the injector, the control signal 54 must be selected to start at the correct time and have the correct duration. The timing and duration of signal 54 is typically dependent on one or more engine operating parameters: a first control parameter 66 representing engine load (determined by the throttle position set by the operator) and a second operating parameter 68 representing engine speed. Both engine operating parameters are provided to an input 70 of controller 39.

[0058] According to an embodiment of the present invention, Figure 5 The controller / ECU 39 shown in FIG. 1 uses the engine operating parameters (66, 68) and the hydrogen fuel pressure within the fuel system 60 determined by the pressure sensor 48 to determine the injection strategy of the injector 64. Thus, during operation, the controller receives the engine control parameters (66, 68) and a pressure signal 72 from the pressure sensor 48 via an input 70, the pressure signal 72 being associated with the pressure of the hydrogen fuel available for injection from the injector 64 in the fuel injection system. Note that in FIG. Figure 5 In the illustrated fuel injection system 60 , there is no pressure regulator 44 or pump / compressor 56 between the storage tank 37 and the fuel rail 35 . It should therefore be appreciated that the fuel rail 35 and the fuel injectors 16 are exposed to the fuel pressure within the storage tank 37 .

[0059] The processor 62 is then configured to determine an injection strategy for the injector 64 based on the received pressure signal 72 and the engine control parameters (66, 68), the determined injection strategy including one or more injector control signals 54 to control the operation of the fuel injector 64. The control signal 54 is output to the fuel injector 64 via an output 74 of the ECU / controller 39.

[0060] The engine operating parameters used by the processor to determine the injection strategy include engine load and engine speed. The processor 62 can use the received engine operating parameters (66, 68) and the received pressure signal 72 to select the most appropriate / optimal injection strategy for the vehicle's engine / fuel injection system 60 from a lookup table 76 containing multiple injection strategies set by engine control parameters and the pressure of the hydrogen fuel available for injection. [The lookup table 76 is shown as Figure 5 part of the controller 39 in the vehicle, but may be located elsewhere within the vehicle with which the processor 62 communicates].

[0061] As an alternative to the lookup table 76, the processor 62 may communicate with a mathematical model 78 configured to generate an injection strategy based on the received engine parameters (66, 68) and the hydrogen fuel pressure determined by the pressure sensor 48 within the fuel injection system 60. [The mathematical model 78 is in Figure 5 39, but may be located elsewhere within the vehicle with the processor 62 in communication].

[0062] The injection strategy determined by the processor 39 includes fuel quantity parameters as well as fuel timing and ignition parameters. The injector control signal 54 determined by the lookup table 76 or mathematical model 78 is configured to control the fuel quantity parameters of the hydrogen fuel injected by the injector 64 and may include control signals for controlling the opening and closing of the injector valve and controlling the ignition timing.

[0063] and Figure 3 and Figure 4 Compared to the fuel injection system shown in FIG. 1 , the accumulator rail 35 in the fuel injection system according to an embodiment of the present invention is not maintained within the optimal pressure range for the injector. Instead, the pressure within the accumulator rail 35 varies from a maximum pressure corresponding to the pressure when the tank 37 is full to a minimum pressure corresponding to the pressure when the tank 37 is nearly empty. The injection strategy determined by the processor 39 according to an embodiment of the present invention is changed so that an appropriate control signal 54 can be output to the fuel injector 16 to enable fuel injection to occur within a pressure range between approximately 20 bar and 700 bar.

[0064] Figure 6 A range of possible injection strategies 80 are shown as a function of fuel pressure and crank angle, which can be selected as the optimal strategy. As mentioned above, a crank angle of 360 degrees corresponds to top dead center. Figure 6 Intake valve 16 is closed by approximately 220 degrees.

[0065] Three general injection strategy types are shown: a premixed injection strategy 82, in which fuel is injected early in the cycle (e.g., near the beginning of intake valve closing); a premixed injection strategy 84, in which hydrogen fuel is injected relatively late in the injection cycle (i.e., near top dead center); and a pilot / main injection strategy 86, in which a pilot injection is performed before TDC, followed by a main injection after TDC.

[0066] from Figure 6 As can be seen in FIG. 1 , more injection strategies are available when the available fuel supply pressure is high. The late and early selections of premixed injection shown are the limits of a range, and single or multiple injections may be used within this range.

[0067] When the available fuel supply pressure is low, the choices of injection strategies are more limited, especially at higher engine loads.

[0068] Higher engine efficiencies are possible when available fuel pressure is high, and it is expected that vehicle operators will maintain the availability of high fuel pressures through more regular storage tank refills and / or larger storage tanks on the vehicle if / when possible.

[0069] At lower available fuel pressures (tank near empty), engine efficiency drops but is still comparable to typical low- and medium-pressure injection systems.

[0070] Figure 6 Pressure curves representing in-cylinder pressure at high and low loads are shown. It can be seen that the in-cylinder pressure is highest near TDC, but depends on engine load and boost pressure.

[0071] The hydrogen fuel pressure should be higher than the in-cylinder pressure to allow injection to occur. Ideally, the hydrogen fuel pressure is significantly higher than the in-cylinder pressure to achieve a high hydrogen fuel flow rate.

[0072] It should be noted that low hydrogen fuel ratios result in low hydrogen pressure injection limited to early timing. Higher hydrogen fuel pressures enable late premixing as well as pilot and late strategies.

[0073] When the hydrogen fuel pressure is greater than about 2 times the in-cylinder pressure, then the cylinder pressure has no effect on the injected fuel flow, and this is the preferred injection environment as it allows for maximum flexibility in the injection strategy.

[0074] Figure 7 A method of operating a fuel injection system according to an embodiment of the present invention is shown.

[0075] In step 90, the processor 62 within the controller 39 receives the engine operating parameters and the pressure signal. In step 92, the processor determines an injection strategy for the injector based on the received engine operating parameters (66, 68) and the pressure signal 72. In step 94, the injector control signal 54 is output to the fuel injector 64.

[0076] Figure 8 A first embodiment of a fuel injector 100 for gaseous fuel of an internal combustion engine is shown. Figure 8 The fuel injector 100 is suitable for use as Figure 5 The fuel injector 100 is of the inwardly opening type and includes an injection nozzle 110 having a generally cylindrical nozzle body 112 through which a nozzle bore 114 extends. The nozzle bore 114 terminates in one or more nozzle outlets 116 that extend through the thickness of the wall of the nozzle body 112 to enable fluid communication between the nozzle bore 114 and an environment external to the fuel injector 100.

[0077] At the end of the injection nozzle 110 opposite the nozzle outlet 116, the nozzle body 112 defines a shoulder region 118 having an increased outer diameter when compared to the remainder of the nozzle body 112. The shoulder region 118 engages with a housing 120 such that the nozzle body 112 extends and protrudes through an opening 122 of the housing 120. The housing 120 contains the other components of the fuel injector 100, which are retained within the housing 120 by a nut 124.

[0078] The fuel injector 100 includes a valve needle assembly 130 operable to control the delivery of fuel through at least one nozzle outlet 116. The valve needle assembly 130 includes a valve needle 132 received within the nozzle bore 114 and engaged with a seat region 115 of the injection nozzle 110 defined at a junction between the nozzle bore 114 and the at least one nozzle outlet 116. This defines a "closed" position of the valve needle assembly 130, preventing fuel from flowing out of the fuel injector 100 through the nozzle outlet 116 in use. Conversely, an "open" position of the valve needle assembly 130 is defined when the valve needle 132 is not engaged with the seat region 115, thereby allowing fuel to flow out of the nozzle outlet 116 via the nozzle bore 114 in use.

[0079] The valve needle assembly also includes a valve needle return spring 134 operably engaged with the valve needle 132. The valve needle return spring 134 provides a return force acting on the valve needle 132, forcing the valve needle 132 to engage with the valve seat area 115. The valve needle assembly may also include a pull tube 136 operably engaged with the valve needle 132 and extending through the fuel injector 100 away from the nozzle 110 and the valve needle assembly 130. A pull tube return spring 137 is connected to an engagement area 138 of the pull tube 136 to keep the pull tube 136 engaged with the valve needle 132.

[0080] The pull tube 136 is surrounded by a substantially cylindrical gas tube that substantially fills the space between the housing 120 and the pull tube 132. The gas tube includes first and second actuator devices 140, 150 that are axially arranged in series along the longitudinal axis L of the fuel injector 100. Each actuator device 140, 150 includes a coil 142, 152 that is concentrically mounted on a body 144, 154 in a radially outer region of the respective actuator device 140, 150. The actuator devices 140, 150 also include armatures 146, 156 that are located radially inward of the coils 142, 152 for generating a magnetic field. The first armature 146 is slidably mounted on the pull tube 136, with a gap 148 provided between the first armature 146 and the engagement region 138 of the pull tube 136. The second armature 156 is directly mounted on the pull tube 136 so that it engages with the outer surface of the pull tube 136 and couples the motion of the two components.

[0081] Each body 144, 154 includes two distinct regions: a first radially inner region 144a, 154a and a second region 144b, 154b radially located between the radially inner region 144a, 154a and the corresponding coil 142, 152, such that the second region 144b, 154b effectively surrounds the coil 142, 152. Each first region 144a, 154a has a high magnetic permeability, while the second region 144b, 154b has a low magnetic permeability. Figure 2 As shown, the radial extent of the armature 146, 156 outward from the longitudinal axis L corresponds to the radial extent of the second region 144b, 154b inward. Thus, each first region 144a, 154a includes a sub-region 144c, 154c that is aligned with the armature 146, 156 parallel to the longitudinal axis L. As will be described in further detail below, the low magnetic permeability of the second region 144b, 154b effectively acts as a barrier to the passage of magnetic flux, thereby limiting the "wasted" magnetic flux that does not act on the armature 146, 156.

[0082] When discussing the value of the magnetic permeability, it is worth considering that the magnetic permeability of the material varies depending on the applied magnetic field H, wherein the magnetic permeability reaches a maximum value at small but non-zero values ​​of H, and then decreases and tends to 1 as the material becomes magnetically saturated. The relevant values ​​of the magnetic permeability of the first region 144a, 154a and the second region 144b, 154b are therefore dependent on the strength of the magnetic field applied by the coils 142, 152. All values ​​subsequently mentioned hereinafter should be considered to represent the values ​​of the magnetic permeability of the corresponding region 144a, 144b, 154a, 154b in use when it is affected by the magnetic field of the coils 142, 152.

[0083] The second region 144b, 154b should have as low a magnetic permeability as possible. Therefore, the second region will ideally have a relative magnetic permeability (defined as the ratio of the magnetic permeability of the material to the magnetic permeability of free space, μ0) of 1 or as close to it as possible. Annealed 316 austenitic stainless steel meets this standard well, but may be too soft for the structural requirements of the structure of the gas tube 120. Mechanical hardening Mechanical treatment of 316 stainless steel will also harden it magnetically and increase its magnetic permeability. Therefore, in practice, the relative magnetic permeability of the second region 144b, 154b is at most 50. Preferably, the relative magnetic permeability of the second region 144b, 154b is at most 40, at most 25, or at most 10.

[0084] With respect to the first regions 144a, 154a (including sub-regions 144c, 154c), while it is desirable that the first regions 144a, 154a have as high a permeability as possible, the required compromise in terms of magnetic properties and material properties limits this. However, the relative permeability of the first regions 144a, 154a is at least 500, preferably at least 1000. The first regions 144a, 154a therefore have a permeability (or equivalently a relative permeability) that is at least one order of magnitude greater than the permeability of the second regions 144b, 154b. It should be noted that while the absolute values ​​of the permeabilities of the first and second regions 144a, 144b, 154a, 154b are important, it is the relationship between them that is most critical, so that the desired effect of generating preferred and sub-preferred paths for magnetic flux can be achieved.

[0085] In operation, current is passed through the coils 142, 152. This generates a magnetic field through the center of each coil 142, 152, wherein the magnetic flux lines are substantially parallel to the longitudinal axis L within the coil. Due to their increased magnetic permeability compared to the second regions 144b, 154b, the magnetic flux lines preferentially pass through the first regions 144a, 154a, and in particular through the sub-regions 144c, 154c thereof. As a result of the magnetic flux passing through the sub-regions 144c, 154c, a force is exerted on the armature 146, 156, which acts to move the armature 146, 156 away from the nozzle 110.

[0086] Since the first armature 146 is slidably mounted on the pull tube 136, the first armature 146 slides upward along the pull tube 136 (i.e., away from the injection nozzle 110) and closes the gap 148 before engaging with the engagement area 138 of the pull tube 136. With the first armature 146 now engaged with the engagement area 138, both armatures 146, 156 are coupled to the pull tube 136, and further upward movement of the armatures 146, 156 causes the valve needle assembly 130 to move against the action of the return force provided by the valve needle return spring 134, and thus acts to move the valve needle assembly 130 to the open position. In this way, the coils 142, 152 and the first and second actuator devices 140, 150 are used to apply an opening force to the valve needle assembly 130. The action of the slidable first armature 142 generates an impact when engaging with the engagement area 138, thereby providing an additional force that assists in the initial opening of the valve needle assembly 130.

[0087] When the valve needle assembly 130 is in the open position, fuel is allowed to flow out of the fuel injector 100 via the nozzle bore 114 and the nozzle outlet 116. When the fuel has been injected, the supply of current to the coils 142, 152 is stopped. This stops the generation of magnetic flux by the coils 142, 152, and thus the force acting on the first and second actuator arrangements 140, 150 is removed. The action of the valve needle return spring 134 then returns the valve needle assembly 130 to the closed position, thereby preventing further delivery of fuel from the nozzle 110.

[0088] The different magnetic characteristics of the first region 144a, 154a and the second region 144b, 154b optimize the path of the magnetic flux generated by the current through the coils 142, 152. By creating a preferential path for the magnetic flux to pass only through the armatures 146, 156, the configuration of the first and second actuator devices 140, 150 enables more efficient use of the generated magnetic flux. This means that either less energy is wasted to generate the same force, or a higher total actuation force can be generated to act on the valve needle assembly 130, allowing the injection pressure to be increased. Therefore, the competing magnetic and mechanical demands on the system can be alleviated by using regions with different magnetic permeabilities.

[0089] While it may be the case that different regions of the body 144, 154 have different magnetic permeabilities due to the first region 144a, 154a and the second region 144b, 154b being made of different materials, it may also be the case that the first and second regions 144a, 144b, 154a, 154b may be formed from one material that has undergone different treatments to produce different magnetic permeabilities. For example, this may be different thermal or mechanical treatments that may be applied to separate components made of the same material, or even to a single continuous body 142, 152.

[0090] It is understood that other embodiments of the invention can be envisaged without departing from the scope of the appended claims.

Claims

1. A controller (39) for determining an injection strategy of a fuel injector (64) in a hydrogen fuel injection system in an engine, the controller comprising: an input (70) configured to receive engine operating parameters (66, 68) and a pressure signal (72) associated with a pressure of hydrogen fuel available for injection from the injector (64) in the fuel injection system; a processor (62) configured to determine an injection strategy (80) for the injector (64) based on the received pressure signal (72) and engine control parameters (66, 68), the determined injection strategy including one or more injector control signals (54) to control operation of the fuel injector; An output terminal (74) is configured to output the one or more control signals (54) to the fuel injector.

2. The controller (39) according to claim 1, wherein: The engine operating parameters include engine speed (68).

3. A controller (39) according to claim 1 or 2, wherein: The engine operating parameters include engine load (66).

4. A controller (39) according to any one of the preceding claims, wherein: The processor is configured to access a lookup table (76) containing a plurality of injection strategies (80) set by engine control parameters and a pressure of hydrogen fuel available for injection.

5. The controller (39) according to claim 4, wherein: The processor is configured to select an optimal injection strategy from the plurality of injection strategies based on received engine parameters (66, 68) and a received pressure signal (72).

6. A controller (39) according to any one of claims 1 to 3, wherein: The processor (62) is configured to access a mathematical model (78) configured to generate an injection strategy (80) based on the received engine parameters and the received pressure signal.

7. A controller (39) according to any one of the preceding claims, wherein: The one or more control signals (54) in the determined injection strategy are arranged to control the amount of fuel injected by the injector (64).

8. A controller (39) according to any one of the preceding claims, wherein: The one or more control signals (54) in the determined injection strategy are arranged to control injector valve opening and closing times.

9. A controller (39) according to any one of the preceding claims, wherein: The engine comprises an engine cylinder (10) having a cylinder piston (18), the cylinder piston (18) being driven by a crankshaft between a bottom dead center (BDC) and a top dead center (TDC) to perform a compression stroke, the determined injection strategy comprising one or more of the following: pre-injecting hydrogen fuel into the combustion chamber late in the compression stroke; a pilot injection of hydrogen fuel into the combustion chamber followed by a main injection of hydrogen fuel into the combustion chamber at a later time on either side of top dead center (TDC); Hydrogen fuel is pre-injected into the combustion chamber early in the compression stroke.

10. A method for determining an injection strategy (80) of a fuel injector (64) in a hydrogen fuel injection system in an engine, the method comprising: receiving (90) engine operating parameters (66, 68) and a pressure signal (72) associated with a pressure of hydrogen fuel available for injection from the injector (64) in the fuel injection system; determining (92) an injection strategy (80) of the injector (64) based on the received pressure signal and engine control parameters, the determined injection strategy including one or more injector control signals (54) to control operation of the fuel injector; The one or more control signals (54) are output (94) to the fuel injector.

11. A single-fuel hydrogen fuel injection system for an engine, comprising: Hydrogen fuel storage tank (37); an accumulator rail (35) in fluid communication with the storage tank; one or more ejectors (64) in fluid communication with the accumulator rail; a pressure sensor (48) configured to determine a pressure of hydrogen fuel within the fuel injection system; A controller (39) according to any one of claims 1 to 9.

12. The single fuel hydrogen fuel injection system according to claim 11, wherein: The accumulator rail (35) is in direct fluid communication with the hydrogen fuel storage tank.

13. The single-fuel hydrogen fuel injection system according to claim 11 or 12, wherein: The pressure of the hydrogen fuel in the fuel injection system determined by the pressure sensor corresponds to the pressure in the storage tank (37).

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