Starting a gaseous-fuelled internal combustion engine

Abstract

Disclosed is a control system, a gaseous-fuelled internal combustion engine system, a vehicle, a method, and computer readable instructions. The control system comprises one or more processors configu

Description

TECHNICAL FIELD The present disclosure relates to a gaseous-fuelled internal combustion engine, in particular to starting this engine and subsequently running it. Aspects of the invention relate to a control system, a gaseous-fuelled internal combustion engine system, a vehicle, a method, and computer readable instructions. BACKGROUND It is known to start gaseous-fuelled internal combustion engines with an assistance from a starter motor. Use of a starter motor requires significant consumption of electrical energy. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a control system, a gaseous-fuelled internal combustion engine system, a vehicle, a method, and computer readable instructions as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for a multi-cylinder gaseous-fuelled internal combustion engine of a vehicle, the control system comprising one or more processors collectively configured to: receive one or more input signals indicative of a phase of an engine cycle; determine, from the phase, whether at least one cylinder is stopped on a power stroke; responsive to determining that at least one cylinder is stopped on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke; output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; and subsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. An advantage of using gaseous fuel injection and ignition to start the engine cycle is that electrical energy is conserved when compared to start methods which require starter motor actuation, which have significant electrical energy consumption. An advantage of using gaseous fuel in this way is that the engine cycle can be started more reliably in a cold start scenario because an ignitable fuel-air mixture can be created without requiring the combustion chamber to be pre-warmed. A further advantage of using gaseous fuel in this way is that the low ignition energy of gaseous fuels means that less pressure is required, which is difficult to generate when the engine is not rotating or without depletion of electrical energy stores. The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to: receive one or more input signals indicative of a phase of an engine cycle; determine, from the phase, whether at least one cylinder is stopped on a power stroke; responsive to determining that at least one cylinder is stopped on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke; output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; and subsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. Optionally the further fuel injection control signals comprise a fuel injection control signal to control a first injection of gaseous fuel after starting the engine cycle, wherein the first injection of gaseous fuel after starting the engine cycle is into a combustion chamber of at least one cylinder performing its first compression stroke of the engine cycle. Optionally the one or more processors are collectively configured to: output further fuel ignition control signals to control positive ignition of gaseous fuel injected into the combustion chambers of cylinders performing compression strokes. Optionally the one or more processors are collectively configured to control timing of the output of the further fuel ignition control signals to cause the positive ignition to be between 20 crank angle degrees before top dead centre and 20 crank angle degrees after top dead centre. By timing the positive ignition to be close to TDC, the combustion will happen early in the power stroke, and maximum fuel chemical energy can be therefore extracted from the combustion. Optionally the one or more processors are collectively configured to control timing of the output of the further fuel injection control signals to cause the injection of gaseous fuel to begin after intake valve closing. By timing the injection of gaseous fuel to begin after IVC, injected gaseous fuel cannot back flow in the intake manifold where it would be unavailable for combustion leading to a reduction of power generation. Optionally the one or more processors are collectively configured to control timing of the output of the further fuel injection control signals to cause injection of a target amount of gaseous fuel to be completed when or before: a difference between injection pressure and in-cylinder pressure is less than a threshold value, or a ratio between injection pressure and in-cylinder pressure is less than a threshold value. Optionally the one or more processors are collectively configured to: responsive to determining that no cylinder is stopped on a power stroke, output a starter motor control signal to control a starter motor to rotate the engine until at least one cylinder is positioned on a power stroke; responsive to at least one cylinder being positioned on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder; output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder; and subsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. Therefore the engine can always be started by injection and ignition of gaseous fuel. Optionally the one or more processors are collectively configured to: responsive to determining that no cylinder is stopped on a power stroke, output a starter motor control signal to control a starter motor to rotate the engine until one or more conditions for beginning fuel injection are met; responsive to the one or more conditions for fuel injection being met, output the further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. Therefore the engine can be started by injection and ignition of gaseous fuel where possible, but not necessarily every time. Optionally the injection of gaseous fuel is driven by a pressure under which the gaseous fuel is stored in a gaseous fuel storage tank. An advantage of driving the injection of gaseous fuel by a pressure under which it is stored in a gaseous fuel storage tank is that no accumulator is needed in the fuel rail to pressurise the fuel. Therefore fuel accumulation is fuel rail is avoided. Gaseous fuel accumulation is fuel rail can lead to issues with pre-ignition, unburnt gaseous fuel residues entering the combustion chamber, and risk of corrosion of components the gaseous fuel comes into contact with leading to damage of engine. According to an aspect of the present invention there is provided a gaseous-fuelled internal combustion engine system comprising: a gaseous fuel storage tank; a multi-cylinder gaseous-fuelled internal combustion engine comprising: a fuel injection system configured to receive gaseous fuel from the gaseous fuel storage tank and comprising at least one injector per cylinder opening into the cylinder for direct injection, and a fuel ignition system configured to provide positive ignition in each cylinder; and the control system of any preceding claim. Optionally the fuel injection system comprises: one or more fuel rails configured to supply the injectors with gaseous fuel; a pressure reducing regulator configured to deliver gaseous fuel from the gaseous fuel storage tank to the one or more fuel rails at a reduced, regulated pressure. According to an aspect of the present invention there is provided a vehicle comprising the control system or the gaseous-fuelled internal combustion engine system of the preceding paragraphs. According to an aspect of the present invention there is provided a method for controlling a multi-cylinder gaseous-fuelled internal combustion engine of a vehicle, the method comprising: receiving one or more input signals indicative of a phase of an engine cycle; determining, from the phase, whether at least one cylinder is stopped on a power stroke; in response to determining that at least one cylinder is stopped on a power stroke, outputting a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke; outputting a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; and subsequently outputting further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. According to an aspect of the present invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform any one or more of the methods described herein. According to an aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein. According to an aspect of the present invention there is provided a control system for a gaseous-fuelled internal combustion engine, the control system comprising one or more processors collectively configured to: receive one or more input signals indicative of a phase of an engine cycle; determine, from the phase, whether at least one cylinder is stopped on a power stroke; responsive to determining that at least one cylinder is stopped on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke; output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; and subsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, maybe taken independently or in any combination that falls within the scope of the appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG 1 illustrates a schematic representation of an example of a vehicle; FIG 2 illustrates a schematic representation of an example of a gaseous-fuelled internal combustion system; FIG 3A illustrates a schematic representation of an example of a control system; FIG 3B illustrates a schematic representation of an example of a non-transitory storage medium; FIG 4 illustrates a flowchart illustrating an example of a method; FIG 5 illustrates a schematic representation of an example implementation of a method; FIG 6 illustrates a graph illustrating injection and ignition windows; FIG 7 illustrates a flowchart illustrating an example of a method; and FIG 8 illustrates a flowchart illustrating an example of a method. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles or static plant and machinery. A gaseous-fuelled internal combustion engine system 10 is schematically labelled in FIG 1. FIG 2 schematically illustrates an example gaseous-fuelled internal combustion engine system 10. The gaseous-fuelled internal combustion engine system 10 comprises a multi-cylinder gaseous-fuelled internal combustion engine 100, a gaseous fuel storage tank 130, and a control system 200 for the gaseous-fuelled internal combustion engine 100. Gaseous fuel refers to fuels which have a gaseous state under an applicable standard temperature and pressure, particularly those which relate to atmospheric or sea-level conditions. For example, gaseous fuel may refer to fuels which have a gaseous state at 20 °C and 1 atm. Examples of gaseous fuels include hydrogen, methane, and natural gas. Gaseous fuel does not refer to vaporised liquid fuels which would have a liquid state under the applicable standard temperature and pressure, for example fuels which have a liquid state at 20 °C and 1 atm such as gasoline and diesel. The multi-cylinder gaseous-fuelled internal combustion engine 100 (‘engine’) may be a hydrogen engine or a methane engine. The engine 100 differs from a liquid-fuelled engine (e g., gasoline or diesel) in several ways. The engine 100 can include, among other things: hardened and stronger moving parts and head gaskets; and gas fuel injectors rather than liquid fuel injectors. A cross-section of a cylinder 102 of the engine 100 is schematically illustrated in FIG 2. The illustrated cylinder 102 is suitable for an engine operable in a four-stroke engine cycle. The engine 100 may be operable in a four-stroke cycle. The engine 100 may alternatively be operable in a two-stroke cycle in which case the cylinder 102 may differ from the one illustrated. The cylinder 102 comprisesa plurality of valve ports 114, 118 for the combustion chamber 108, including an intake valve port 114, opened and closed by an intake valve 112, and an exhaust valve port 118, opened and closed by an exhaust valve 116. The intake valve 112 and exhaust valve 116 may both be poppet valves. The intake valve 112 and exhaust valve 116 may be actuated by cams which are rotated by the camshaft 110. The engine 100 is a reciprocating piston engine. A piston 106 is arranged to move in a reciprocating motion within the cylinder 102. Piston rings (not shown) of the piston 106 are arranged to slide along the inside surface of the cylinder 102. The piston 106 is connected to crankshaft 104 via a connecting rod and a crankpin of the crankshaft 104. Optionally, there may be provided a starter motor 150 configured to rotate engine 100 via crankshaft 104. The starter motor 150 may be provided in the form of a belt integrated starter generator (BISG) or a crank integrated motor generator (CIMG), for example. The space between the piston 106 and the valve ports 114,118 defines a combustion chamber 108. There is provided a fuel injection system 120 configured to provide direct injection of gaseous fuel into the combustion chamber 108. The gaseous fuel therefore first mixes with air inside the combustion chamber 108. This contrasts with indirect injection, such as port or manifold injection, where the gaseous fuel first mixes with the air outside the combustion chamber 108, for example in the intake valve port 114 or further upstream in the intake manifold (not shown). The fuel injection system 120 comprises at least one injector 122 per cylinder 102, at least one fuel rail 124, and a pressure reducing regulator 126. The at least one injector 122 per cylinder 102 opens into the cylinder 102 for direct injection. Though the injector 122 is illustrated as being centrally mounted with respect to the combustion chamber 108, it should be appreciated that the injectors 122 can instead be side-mounted with respect to the combustion chamber 108. The injectors 122 are gas fuel injectors. Compared to liquid fuel injectors, the injectors 122 can have a nozzle design with a larger flow cross section. The nozzles may also have additional sealing against high in-cylinder pressure. The injectors 122 may be formed from different materials, for example materials than are resistant to corrosion caused by certain gaseous fuels. For example, components of the injectors 122 which would be in contact with hydrogen gas can be made of austenitic and ferritic steels, rather than for example martensitic steel, to be resistant to hydrogen embrittlement. Lower injection pressure is required for gaseous fuels than for liquid fuels such as gasoline or diesel. Accordingly, the injectors 122 can be configured to provide injection pressure of 50 bar or less. For example, the injectors 122 may be configured to provide injection pressure of around 40 bar. It will be appreciated that injectors 122 configured to provide higher injection pressures than 50 bar can be used. One or more fuel rails 124 are configured to supply the injectors 122 with gaseous fuel. A common fuel rail may be provided which supplies all injectors 122. Alternatively, each injector 122 or the injectors 122 of each cylinder 102 may be supplied by its / their own fuel rail 124. The pressure reducing regulator 126 is configured to deliver gaseous fuel from the gaseous fuel storage tank 130 to the one or more fuel rails at a reduced, regulated pressure. The pressure reducing regulator 126 can be configured to reduce the pressure of the gaseous fuel to the pressure at which it will be injected into the combustion chamber 108. In some examples the gaseous fuel storage tank 130 is configured to storage the gaseous fuel at up to 700 bar. The injection of the gaseous fuel is driven by a pressure under which the gaseous fuel is stored in a gaseous fuel storage tank 130. As a result, no accumulator is needed in the fuel rail(s) 124 to pressurise the gaseous fuel. Therefore, accumulation of gaseous fuel in the fuel rail(s) 124 is avoided. Particularly with hydrogen, it is not desirable to accumulate the fuel in the fuel rail(s) 124. This can lead to issues with pre-ignition, unburnt hydrogen residues entering the combustion chambers 102, and risk of hydrogen embrittlement leading to damage of the engine 100. In some examples, the fuel injection system may additionally comprise injectors for port or manifold injection (not shown). There is provided a fuel ignition system 140 configured to provide positive ignition. Positive ignition comprises providing a localised high temperature, sufficient to ignite the gaseous fuel-air mixture, within the combustion chamber 102 using energy supplied by a source external to the engine 100, such as a battery, for example. This contrasts with compression ignition in which the high temperature is provided by the compression of the gaseous fuel-air mixture. In some examples, positive ignition may be in the form of spark ignition using a spark plug. However, for gaseous fuels with low ignition energy, such as for example hydrogen, means other than a spark plug, including but not limited to a glow plug or hotwire, may be used to provide the positive ignition. The control system 200 for the gaseous-fuelled engine 100 will now be described with reference to FIG 3A. The control system 200 comprises one or more controllers 202. The control system 200 is configured to receive crankshaft position data from a crankshaft position sensor 105, camshaft position data from a camshaft position sensor 111, and / or other data indicative of the phase of the engine cycle. The control system 200 may then determine which cylinder 102 is stopped on its power stroke. The control system 200 may then output control signals to control the fuel injection system 120 and the fuel ignition system 140. The control signals may optionally control the starter motor 150 too. The control system 200 as illustrated in FIG 3A comprises one controller 202, although it will be appreciated that this is merely illustrative. The controller 202 comprises processing means 206 and memory means 208. The processing means 206 may be one or more electronic processing device 206 which operably execute computer-readable instructions. The memory means 208 may be one or more memory device 208. The memory means 208 is electrically coupled to the processing means 206. The memory means 208 is configured to store instructions, and the processing means 206 is configured to access the memory means 208 and execute the instructions stored thereon. The controller 202 comprises an input means 212 and an output means 214. The input means 212 may comprise an electrical input 212 of the controller 202. The output means 214 may comprise an electrical output 214 of the controller 202. The controller 202 may have an interface 204 comprising an electrical input / output I / O 212, 214, or an electrical input 212, or an electrical output 214, for receiving information and interacting with external components. The input 212 is arranged to receive a crankshaft position signal from the crankshaft position sensor 105, a camshaft position signal from the camshaft position sensor 111, and / or an engine phase signal from any other suitable sensor or controller. The crankshaft position signal and camshaft position signal are electrical signals which are indicative of the phase of the engine cycle that the engine 100 is currently in. The output 214 is arranged to output a fuel injection control signal indicative of instructions for controlling the fuel injection system 120, a fuel ignition control signal indicative of instructions for controlling the fuel ignition system 140, and optionally a starter motor control signal indicative of instructions for controlling the starter motor 150. FIG 3B illustrates a non-transitory computer-readable storage medium 300 comprising the instructions (computer software). It is to be understood that the, or each, controller 202 can comprise a control unit or computational device having one or more electronic processors (e g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unitor computational device, or alternatively different functions of the or each controller 202 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 202 to implement the control techniques described herein (including some or all of the functionality required for the method(s) described herein). The set of instructions 210 could be embedded in said one or more electronic processors 206 of the controller 202; or alternatively, the set of instructions 210 could be provided as software to be executed in the controller 202. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful. The, or each, electronic processor 206 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions 210. The, or each, electronic memory device 208 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and / or instructions therein or thereon. In an embodiment, the memory device 208 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 206 may access the memory device 208 and execute and / or use that or those instructions and information to carry out or perform some or all of the functionality and methodology described herein. The at least one memory device 208 may comprise a computer-readable storage medium (e.g., a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational devices. Examples of the form include, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such inform ation / instructions. FIG 4 illustrates a method 400 according to an embodiment of the invention. The method 400 is a method of controlling a multi-cylinder gaseous combustion engine 100 (such as illustrated in FIG 2) of a vehicle 1 (such as illustrated in FIG 1). The method 400 may be performed by the control system 200 illustrated in FIG 3A. In particular, the memory 208 may comprise computer-readable instructions 210 which, when executed by the processor 206, perform the method 400. Block 410 comprises determining a phase of an engine cycle. In particular, block 410 comprises determining a phase of the engine cycle in which the engine 100 is stopped. The phase of the engine cycle may be expressed in crank angle degrees (CAD). For a four-stroke engine cycle, the phase of the engine cycle at any given time is between 0 and 720 CAD. The phase changes by 180 CAD during the course of each stroke. The positions of pistons 106 and valves 112, 116 of each cylinder 102 are mapped to the phase of the engine cycle. Determining a phase of an engine cycle is achieved by means of receiving one or more input signals indicative of a phase of an engine cycle. The one or more input signals may include at least one from the following: an output signal from crankshaft position sensor 105, an output signal from a camshaft position sensor 111, or an output signal of an angle encoder (not shown) which may take input from either or both of the crankshaft position sensor 105 and camshaft position sensor 111. Block 420 comprises determining, from the phase, whether at least one cylinder 102 is stopped on a power stroke. The power stroke is the stroke during which force is generated to drive rotation of the crankshaft 104. In some examples, this block 420 may be performed in the form of determining, from the phase, at least one cylinder 102 stopped on a power stroke. That is, a finding that at least one cylinder 102 is stopped on a power stroke is implicit from determining which cylinder 102 or cylinders 102 is stopped on a power stroke. In some examples, the engine 100 may be configured such that there will always be at least one cylinder 102 positioned on a power stroke at any phase of the engine cycle. For example, engines 100 operable in a four-stroke engine cycle having four or more cylinders 102 can be so configured. Likewise, engines 100 operable in a two-stroke engine cycle having two or more cylinders 102 can be so configured. Where the method 400 is performed in respect of these engines 100, block 420 is performed in the form of determining, from the phase, at least one cylinder 102 stopped on a power stroke. For the avoidance of doubt, a cylinder 102 stopped on a power stroke refers to a cylinder 102 which is positioned on a power stroke when the engine 100 is at rest, i.e., not rotating. Being positioned on a power stroke means that the piston 106 is positioned such that it will move from its current position towards bottom dead centre (BDC), away from top dead centre (TDC), upon rotation of the crankshaft 104 and engine 100 in their normal direction and that the intake valve 112 is closed. The exhaust valve 116 will be closed at at least the start of the of the power stroke but in some examples may be open towards the end of the stroke. Responsive to determining that at least one cylinder 102 is stopped on a power stroke, whether explicitly or implicitly, the method 400 advances to block 430. Block 430 comprises direct injection of gaseous fuel into a combustion chamber 108 of the at least one cylinder 102 which is determined to be stopped on the power stroke. This can be achieved by means of outputting a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber 108 of the at least one cylinder 102 stopped on the power stroke. The fuel injection control signal is configured to control the fuel injection system 120 to directly inject gaseous fuel into the combustion chamber 108 of the at least one cylinder 102 stopped on its power stroke via the at least one injector 122 opening into that combustion chamber 108. In some examples gaseous fuel is directly injected into the combustion chambers 108 of all cylinders 102 which are determined to be stopped on a power stroke. Block 440 comprises positive ignition of the gaseous fuel in the combustion chamber 108 of the at least one cylinder 102 stopped on the power stroke to start the engine cycle. This can be achieved by means of outputting a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber 108 of the at least one cylinder 102 stopped on the power stroke to start the engine cycle. The fuel ignition control signal is configured to control the fuel ignition system 140 to provide positive ignition in the at least one cylinder 102 stopped on its power stroke. Gaseous fuel is ignited in the combustion chambers 108 of all cylinders 102 into which gaseous fuel was injected in block 430. Starting the engine cycle comprises starting rotation of the engine 100. Because the injection and ignition of gaseous fuel occurs in the cylinder(s) 102 stopped on a power stroke, the driving of the piston 106 towards BDC causes the engine 100 to rotate in its normal direction and therefore advances the phase of the engine cycle. Thus, in the example of a four-stroke engine cycle, the next stroke performed by the cylinder(s) 102 previously stopped on a power stroke will be an exhaust stroke. Block 450 is performed subsequent to block 440, after the engine cycle has started. Block 450 comprises injection of gaseous fuel into combustion chambers 108 of cylinders 102 performing compression strokes. That is, after the engine cycle is started as a result of performance of block 440, subsequent injections of gaseous fuel are timed so that the gaseous fuel enters the combustion chambers 108 of the cylinders 102 during each cylinder’s compression strokes. This can be achieved by means of outputting further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes. The further fuel injection control signals comprise a fuel injection control signal to control a first injection of gaseous fuel after starting the engine cycle and comprise subsequent fuel injection control signal to control subsequent injection of gaseous fuel while the engine is running. The further fuel injection control signals are configured to control the fuel injection system 120 to inject gaseous fuel into the combustion chambers 108 of cylinders 102 performing compression strokes. This can be achieved via the injectors 122 opening into the 10 combustion chambers 108 (direct injection) or via other injectors which may be comprised in the fuel injection system 120 and which are configured to inject gaseous fuel into the intake manifold or the intake valve port (indirect injection). In some examples, the first injection of gaseous fuel after starting the engine cycle is into a combustion chamber 108 of a cylinder 102 performing its first compression stroke of the engine cycle. In some examples, the first injection of gaseous fuel after starting the engine cycle is specifically into a combustion chamber 108 of a cylinder 102 performing a compression stroke as a next stroke after a stroke on which it was stopped. For example, in an engine 100 operable in a four-stroke engine cycle, the first injection of gaseous fuel after starting the engine cycle is into a combustion chamber 108 of a cylinder 102 which was stopped on its intake stroke and occurs when this cylinder 102 is performing its first compression stroke of the engine cycle. In these examples, the first injection of gaseous fuel after starting the engine cycle is therefore not into the cylinder 102 which is stopped on its compression stroke and performs the remaining part of its compression stroke upon starting the engine cycle, but is instead into the combustion chamber 108 of the cylinder 102 which performs the first full compression stroke after starting the engine cycle and occurs during this first full compression stroke. An instance of these examples is shown in FIG 5. Block 460 comprises positive ignition of gaseous fuel injected into the combustion chambers 108 of cylinders 102 performing compression strokes. This can be achieved by means of outputting further fuel ignition control signals to control positive ignition of gaseous fuel injected into the combustion chambers of cylinders performing compression strokes. The further fuel ignition control signals are configured to control the fuel ignition system 140 to provide positive ignition in the cylinders into which gaseous fuel has been injected. The timing of injections of gaseous fuel after starting the engine cycle and of positive ignitions of that gaseous fuel may be defined with respect to the phase of the engine cycle, which continues to be indicated by input signals received as described in block 410. It is determined, from the phase, when a cylinder 102 is on its compression stroke and the fuel injection system 120 is controlled to inject the gaseous fuel into that cylinder 102 responsive to that determination. The fuel ignition system 140 is controlled to positively ignite that gaseous fuel either during the same compression stroke into which the gaseous fuel was injected or during the immediately following power stroke. Further details on the timing of the injection of gaseous fuel during the compression stroke and the ignition of that gaseous fuel are described later with respect to FIG 6. There may be delays between outputting further control signals to the fuel injection system 120 (e.g., the further fuel injection control signals) and injection. There may be delays between outputting further control signals to the fuel ignition control system (e.g., the further fuel ignition control signals) and ignition. The timing of the output of these further control signals can therefore be controlled based on knowledge of these delays as well as the timings for injection and ignition. The delays may be translated into phase offsets in dependence on the rotational speed of the engine 100. The timing of the output of these further control signals can therefore also be defined with respect to the phase of the engine cycle. Blocks 410 to 440 provide an improved direct start method for the engine 100. Direct starts beneficially conserve electrical energy when compared to start methods which require starter motor actuation. The use of a starter motor to rotate an engine consumes significant electrical energy and requires the provision of a starter motor which takes up space and adds weight. A starter motor may also have issues operating in extreme (hot or cold) climates. However, there can be difficulties with direct starts. The present utilisation of gaseous fuel to achieve direct start makes the starting of the engine cycle more reliable in a cold start scenario because an ignitable fuel-air mixture can be created without requiring the combustion chamber to be pre-warmed. The low ignition energy of gaseous fuels (in particular but not exclusively hydrogen) means that less pressure is required, which is difficult to generate when the engine 100 is not rotating or without depletion of electrical energy stores. FIG 5 illustrates an example of the method 400 implemented for a four-cylinder engine 100 operable in a four-stroke engine cycle. Each column relates to a single cylinder. The first column relates to a first cylinder 102_1. The second column relates to a second cylinder 102_2. The third column relates to a third cylinder 102_3. The fourth column relates to a fourth cylinder 102_4. In the following description features referenced using a reference number without a subscript index (e.g., 102) in FIG 2 are referenced using the reference number with an appended numerical index (e.g., 102_1) when referring to that feature in a specific cylinder, where the appended numerical index indicates the cylinder in question. The reference number without an appended numerical index is used when referring to the features as a class (or set) or for a non-specific cylinder. Each row represents particular phases in the engine cycle. At any given phase in the engine cycle, each of the cylinders 102 is on a different stroke. The first row represents the phase of the engine cycle on which the engine 100 is stopped. The first cylinder 102_1 is stopped on its intake stroke. The second cylinder 102_2 is stopped on its compression stroke. The third cylinder 102_3 is stopped on its exhaust stroke. The fourth cylinder 102_4 is stopped on its power stroke. In accordance with blocks 430 and 440 of the method 400, gaseous fuel 502 is injected into the combustion chamber 108_4 of the fourth cylinder 102_4 and a localised high temperature 504 suitable for igniting the injected gaseous fuel 502 is produced in this combustion chamber 108_4. The second row represents the phases of the engine cycle in which rotation of the engine 100 is just beginning. At this phase, the respective pistons 106 are moving but are still completing the strokes on which they were stopped. The movement of the pistons 106 is driven by the expanding combustion mixture 506 in the combustion chamber 108_4 of the fourth cylinder 102_4, which was created by the ignition of the injected gaseous fuel 502. This is driving the piston 106_4 towards BDC. The motion of the piston 106_4rotates the crankshaft 104 which causes the motion of the other pistons 106. In this example, no further injection or ignition occurs during the phases represented by the second row. However, in other examples gaseous fuel may be injected into the combustion chamber 108^2 of the second cylinder 102 2 which is finishing its compression stroke. The third row represents the phases of the engine cycle in which the cylinders 102 are performing their first full strokes after the starting of the engine cycle. In other words, each cylinder 102 is performing the next stroke after the stroke on which it was stopped. The first cylinder 102_1 is performing its compression stroke. In accordance with block 450 of the method 400, gaseous fuel 502 is injected into the combustion chamber 108_1 of the first cylinder 102_1. In the example shown a localised high temperature 504 suitable for igniting the injected gaseous fuel 502 is produced in this combustion chamber 108_1, in accordance with block 460 of the method 400, during the same compression stroke. However, it is to be appreciated that the localised high temperature 504 suitable for igniting the injected gaseous fuel 502 may instead be produced in this combustion chamber 108_1 during the immediately following power stroke depicted in the fourth row of FIG 5. The fourth row represents the phases of the engine cycle in which the cylinders 102 are performing their second full strokes after the starting of the engine cycle. The movement of the pistons 106 is now being further driven by the expanding combustion mixture 506 in the combustion chamber 108_1 of the first cylinder 102_1, which is now on its power stroke. The third cylinder 102_3 is performing its compression stroke. In continuing accordance with block 450 of the method 400, gaseous fuel 502 is injected into the combustion chamber 108_3 of the third cylinder 102_3. In the example shown a localised high temperature 504 suitable for igniting the injected gaseous fuel 502 is produced in this combustion chamber 108_3, in accordance with block 460 of the method 400, during the same compression stroke. However, as before, it is to be appreciated that the localised high temperature 504 suitable for igniting the injected gaseous fuel 502 may instead be produced in this combustion chamber 108_3 during the immediately following power stroke. FIG 6 illustrates an example of an injection window 602 for injecting the gaseous fuel into the combustion chambers 108 of cylinders 102 performing compression strokes, in accordance with block 450 of the method 400, and an example of an ignition window 604 for igniting that gaseous fuel, in accordance with block 460 of the method 400. FIG 6 also shows in-cylinder pressure on the y-axis with respect to phase of the engine cycle in crank angle degrees (CAD) on the x-axis. In particular, FIG 6 shows variation of in-cylinder pressure (line 608) over the compression stroke 610 and subsequent power stroke 612 in an example of the engine 100. The injection window 602 represents the earliest phase at which injection of the gaseous fuel should begin and the latest phase by which the injection of the gaseous fuel should be completed. In some examples, the earliest phase at which injection of the gaseous fuel should begin is a phase at which intake valve closing (I VC) occurs. In these examples, direct injection of gaseous fuel into the combustion chambers 108 of cylinders 102 performing compression strokes is provided via the injectors 122 which open into the combustion chambers 108. By timing the injection of gaseous fuel to begin after IVC, injected gaseous fuel cannot back flow in the intake manifold where it would be unavailable for combustion leading to a reduction of power generation. In some examples, the latest phase by which the injection of the gaseous fuel should be completed is a phase 614 at which a difference between the injection pressure that the injectors 122 are configured to provide and the in-cylinder pressure is less than a threshold value ('the threshold pressure difference’). That is, the latest phase by which the injection of the gaseous fuel should be completed is the phase 614 at which the in-cylinder pressure reaches a value 616 which is less than the injection pressure by the threshold pressure difference. Alternatively, the latest phase by which the injection of the gaseous fuel should be completed is a phase at which a ratio between the injection pressure that the injectors 122 are configured to provide and the in-cylinder pressure is less than a threshold value ('the threshold pressure ratio’). The threshold pressure difference (or ratio) represents the pressure difference (or ratio) at which injector choking begins to occur. The threshold pressure difference (or ratio) therefore depends on the design of the injectors 122 which are used in the fuel injection system 120. Once injector choking begins, it is no longer reliably possible to inject more gaseous fuel. Accordingly, injection of a target amount of gaseous fuel should be completed before the phase at which the threshold pressure difference (or ratio) is reached. Therefore, injection of the gaseous fuel should be begun at an earlier phase which is dependent on the rotational speed of the engine 100 and the time that it will take to inject the target amount of gaseous fuel. An example of the injection window 602 is between 170 CAD before TDC and 60 CAD before TDC. In some examples, the timing of the output of the further fuel injection control signals is controlled in order to cause injection of the gaseous fuel to begin and complete within the injection window 602 of each cylinder 102. Timing of the output of the further fuel injection control signals is controlled to cause the injection of gaseous fuel to begin after IVC. Timing of the output of the further fuel injection control signals is controlled to cause injection of a target amount of gaseous fuel to be completed when or before: a difference between injection pressure and in-cylinder pressure is less than a threshold value, or a ratio between injection pressure and in-cylinder pressure is less than a threshold value. The fuel injection system 120 is controlled, by the further fuel injection control signals, to begin and complete injection of gaseous fuel within the injection window 602 of each cylinder 102. The ignition window 604 represents the earliest and latest phases at which positive ignition of the gaseous fuel injected during the compression strokes should occur. The positive ignition should occur between 20 CAD before TDC and 20 CAD after TDC. By timing the positive ignition to be close to TDC, the combustion will happen early in the power stroke, and maximum fuel chemical energy can be therefore extracted from the combustion. An early ignition in the compression stroke would result in severe knocking as the piston 102 is moving up towards TDC while the combustion would try to move the piston down towards BDC and may also result in poor gaseous fuel-air mixing quality resulting in poor engine efficiency and unburned residuals. In some examples, the timing of the output of the further fuel ignition control signals is controlled in order to cause positive ignition at a phase within the ignition window 604 of each cylinder 102. Timing of the output of the further fuel ignition control signals is controlled to cause the positive ignition to be between 20 CAD before TDC and 20 CAD after TDC. The fuel ignition control system 140 is controlled, by the further fuel ignition control signals, to positively ignite the gaseous fuel at a phase within the ignition window 604 of each cylinder 102. FIG 7 illustrates a further example of the method 400 illustrated in FIG 4. Block 410 is as described in the foregoing. Block 420 is also as described in the foregoing. However, in this further example, responsive to determining that no cylinder 102 is stopped on a power stroke, the method 400 advances to block 470 rather than block 430. Block 470 comprises rotating the engine 100 using the starter motor 150 until at least one cylinder 102 is positioned on a power stroke. This can be achieved by means of outputting a starter motor control signal to control the starter motor 150 to rotate the engine 100 until at least one cylinder 102 is positioned on a power stroke. While method 400 comprises stopping the starter motor 150 from driving rotation of the engine 100 once at least one cylinder 102 is positioned on a power stroke, it does not necessarily require the starter motor 150 to stop rotation of the engine 100 once at least one cylinder 102 is positioned on a power stroke. However, in some examples, the method 400 does comprises controlling the starter motor 150 to stop rotation of the engine 100 once at least one cylinder 102 is positioned on a power stroke. In those examples, block 470 comprises rotating the engine 100 using the starter motor 150 until at least one cylinder 102 is stopped on a power stroke. Once at least one cylinder 102 is positioned on a power stroke, whether rotation of the engine 100 is stopped or not, the method 400 advances to block 430’. Block 430’ is identical to block 430 if rotation of the engine 100 is stopped, whether by control of the starter motor 150 or by friction. If the engine 100 is still rotating, block 430’ differs from block 430 only in that the fuel injection system 120 is controlled to directly inject gaseous fuel into a combustion chamber 108 of the at least one cylinder 102 positioned, rather than stopped, on the power stroke. In all other respects it is as described in the foregoing. Block 440’ is identical to block 440 if rotation of the engine 100 is stopped, whether by control of the starter motor 150 or by friction. If the engine 100 is still rotating, block 440’ differs from block 440 only in that the fuel ignition system 140 is controlled to positively ignite the gaseous fuel in the combustion chamber 108 of the at least one cylinder 102 positioned, rather than stopped, on the power stroke. If the engine 100 is still rotating, the timing of the positive ignition may be controlled to occur before exhaust valve opening, which may occur at a late phase of the power stroke. In all other respects it is as described in the foregoing. Blocks 450 and 460 are as described in the foregoing. FIG 8 illustrates a further example of the method 400 illustrated in FIG 4. Block 410 is as described in the foregoing. Block 420 is also as described in the foregoing. However, in this further example, responsive to determining that no cylinder 102 is stopped on a power stroke, the method 400 advances to block 480 rather than block 430. Block 480 comprises rotating the engine 100 using the starter motor 150. This can be achieved by means of outputting a starter motor control signal to control the starter motor 150 to rotate the engine 100. Block 490 comprises determining whether one or more conditions for beginning fuel injection are met. In some examples, the one or more conditions for beginning fuel injection comprise a predetermined rotational speed of the engine 100 having been reached or exceeded. Once the one or more conditions for beginning fuel injection are met, the method advances to blocks 450 and 460 as described in the foregoing. The starter motor 150 may cease to drive rotation of the engine once fuel injection and ignition has begun. It will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non- 5 programmable ASIC, Boolean logic circuitry, etc. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. 10 The blocks illustrated in the FIGs 4 and 7 may represent steps in a method and / or sections of code in the computer program 210. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted. Features described in the preceding description may be used in combinations other than the combinations explicitly described. 15 Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

1. A control system for a multi-cylinder gaseous-fuelled internal combustion engine of a vehicle, the control system comprising one or more processors collectively configured to:receive one or more input signals indicative of a phase of an engine cycle;determine, from the phase, whether at least one cylinder is stopped on a power stroke;responsive to determining that at least one cylinder is stopped on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke;output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; andsubsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes.

2. The control system of claim 1, wherein the further fuel injection control signals comprise a fuel injection control signal to control a first injection of gaseous fuel after starting the engine cycle,wherein the first injection of gaseous fuel after starting the engine cycle is into a combustion chamber of at least one cylinder performing its first compression stroke of the engine cycle.

3. The control system of claim 1 or 2, wherein the one or more processors are collectively configured to: output further fuel ignition control signals to control positive ignition of gaseous fuel injected into the combustion chambers of cylinders performing compression strokes.

4. The control system of claim 3, wherein the one or more processors are collectively configured to control timing of the output of the further fuel ignition control signals to cause the positive ignition to be between 20 crank angle degrees before top dead centre and 20 crank angle degrees after top dead centre.

5. The control system of any preceding claim, wherein the one or more processors are collectively configured to control timing of the output of the further fuel injection control signals to cause the injection of gaseous fuel to begin after intake valve closing.

6. The control system of any preceding claim, wherein the one or more processors are collectively configured to control timing of the output of the further fuel injection control signals to cause injection of a target amount of gaseous fuel to be completed when or before: a difference between injection pressure and in-cylinder pressure is less than a threshold value, or a ratio between injection pressure and in-cylinder pressure is less than a threshold value.

7. The control system of any preceding claim, wherein the one or more processors are collectively configured to: responsive to determining that no cylinder is stopped on a power stroke, output a starter motor control signal to control a starter motor to rotate the engine until at least one cylinder is positioned on a power stroke;responsive to at least one cylinder being positioned on a power stroke, output a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder;output a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder; andsubsequently output further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes.

8. The control system of any of claims 1 to 6, wherein the one or more processors are collectively configured to:responsive to determining that no cylinder is stopped on a power stroke, output a starter motor control signal to control a starter motor to rotate the engine until one or more conditions for beginning fuel injection are met;responsive to the one or more conditions for fuel injection being met, output the further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes.

9. The control system of any preceding claim, wherein the injection of gaseous fuel is driven by a pressure under which the gaseous fuel is stored in a gaseous fuel storage tank.

10. A gaseous-fuelled internal combustion engine system comprising:a gaseous fuel storage tank;a multi-cylinder gaseous-fuelled internal combustion engine comprising:a fuel injection system configured to receive gaseous fuel from the gaseous fuel storage tank and comprising at least one injector per cylinder opening into the cylinder for direct injection, anda fuel ignition system configured to provide positive ignition in each cylinder; and the control system of any preceding claim.

11. The gaseous-fuelled internal combustion engine system of claim 10, wherein the fuel injection system comprises:one or more fuel rails configured to supply the injectors with gaseous fuel;a pressure reducing regulator configured to deliver gaseous fuel from the gaseous fuel storage tank to the one or more fuel rails at a reduced, regulated pressure.

12. A vehicle comprising the gaseous-fuelled internal combustion engine system of claim 10 or 11 or the control system of any of claims 1 to 9.

13. A method for controlling a multi-cylinder gaseous-fuelled internal combustion engine of a vehicle, the method comprising: receiving one or more input signals indicative of a phase of an engine cycle;determining, from the phase, whether at least one cylinder is stopped on a power stroke;in response to determining that at least one cylinder is stopped on a power stroke, outputting a fuel injection control signal to control direct injection of gaseous fuel into a combustion chamber of the at least one cylinder stopped on the power stroke;outputting a fuel ignition control signal to control positive ignition of the gaseous fuel in the combustion chamber of the at least one cylinder stopped on the power stroke to start the engine cycle; andsubsequently outputting further fuel injection control signals to control injection of gaseous fuel into combustion chambers of cylinders performing compression strokes.

14. Computer readable instructions which, when executed by a computer, are arranged to perform the method according to claim 13.Application No: GB2313052.9Examiner:Mr Alastair KellyClaims searched: 1-14Date of search: 28 February 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-6, 9-14 US2010 / 192879 Al [PURSIFULL] See abstract and figures and note column 2, lines 56-67 A - US2014 / 297162 Al [SURNILLA] See abstract and figures and note paragraph [0067], [0073] A - US2014 / 345563 Al [MCALISTER] See abstract and figures and note paragraph [0173] A - JP2005315231 A [SURNILLA] See abstract and figures and note paragraphs [0010], [0013] A - JP2013252725 A [NISSAN] See abstract and figures and note paragraphs [0002], [0024], [0025], [0028] A - JP2005016356 A [MAZDA] See abstract and figures A - JP2007239490 A [NISSAN] See abstract and figures and note paragraphs [0006], [0025] A - WO2015 / 004514 Al [TOYOTA] See abstract and figures and note paragraphs page 14, lines 9-15Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB. EP, WO &US patent documents classified in the follow ing areas of the UKCX :Worldwide search of patent documents classified in the following areas of the IPC____________ F02D_____________________________________________________ The following online and other databases have been used in the preparation of this search report SEARCH- PATENTInternational Classification:Subclass Subgroup Valid From F02D 0041 / 06 01 / 01 / 2006 F02D 0041 / 00 01 / 01 / 2006Application No: GB2313052.9Examiner: Mr Alastair KellyClaims searched: 6-14Date of search: 21 May 2024Patents Act 1977Further Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance Y 6 at least US 7463967 B2 (ANCIMER et al.) See abstract and figures and note column 5, line 58 to column 6, line 4 Y 6 at least US 8095294 Bl (GRIFFITHS et al.) See abstract and figures and note column 3, lines 31 to 56 Y 6 at least CN 114183267 A (WEICHAI POWER SHARE LTD COMPANY) See abstract and figures and note paragraphs [0004]-[0010] Y 6 at least US 7000600 Bl (YAMADA et al.) See abstract and figures and note column 3, lines 1 to 38 Y 6 at least US2010 / 192879 Al [PURSIFULL] See abstract and figures and note column 2, lines 56-67Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:________________________________________________Subclass Subgroup Valid FromSubclass Subgroup Valid From F02D 0041 / 06 01 / 01 / 2006 F02D 0041 / 00 01 / 01 / 2006

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