The invention relates to a fuel system and method for a gas engine, and more in particular to such a system and method using high pressure gas to inject liquid diesel fuel.

Liquefied Natural Gas or LNG is seen as a viable alternative for oil based fuels as well as an enabler for CO ₂ reduction. It has become popular to run diesel engines on gas (LNG / natural gas). For ignition of the air and gas mixture a small amount of diesel fuel is injected, which only serves to ignite the lean fuel- air mixture, which would be beyond the capability of a spark plug. Due to its characteristics natural gas fuel is less suited to be directly used in compression ignition (CI) engines, or to achieve highest possible efficiency therein. Current development in using natural gas in CI engines is to inject the natural gas at the end of the compression stroke, and separately inject a small (pilot) amount of diesel fuel to ignite it. For this purpose the natural gas needs to be brought up to pressures of at least 300 bar. It may in some cases, such as In international transport, be more economical to run an engine on diesel only for a part of a journey and to run the engine on LNG for another part of the journey. There is thus a demand for fuel supply systems for convertible use using diesel fuel, or diesel fuel and gaseous fuel. Present systems have to be manually converted to run on the diesel fuel or on the diesel and gaseous fuel combination. Such systems are contemplated in US 1,857,256 to rely on blast compressors of variable capacity for injection operations. The adjustment of these compressors may be done manually to handle excess quantities of compressed gaseous fuel over the air necessary when operating on diesel fuel alone. In US20160061168 a duel fuel injector is described having a single injector for injecting both gaseous and liquid fuel to the combustion chamber. The injector is able to provide a pilot diesel fuel injection for simultaneous delivery of both diesel fuel and gaseous fuel to the combustion chamber. To that end a control chamber is provided that is in fluid communication with the injection chamber via a delivery passage. This fuel injection limits the versatility of the fuel injection control since it requires the fuel to he delivered via delivery passage in case of the gaseous fuel mode.

Accordingly it is an object of the present invention to propose an improved and simplified fuel injection system for convertible use, for a gas- diesel dual fuel engine. In a more general sense it is thus an object of the invention to overcome or reduce at least one of the disadvantages of the prior art. It is also an object of the present invention to provide alternative solutions which are less cumbersome in assembly and operation and which moreover can be made relatively inexpensively. Alternatively it is an object of the invention to at least provide a useful alternative. In a more general sense it is thus an object of the invention to overcome or reduce at least one of the disadvantages of the prior art. It is also an object of the present invention to provide alternative solutions which are less cumbersome in assembly and operation and which moreover can be made relatively inexpensively. Alternatively it is an object of the invention to at least provide a useful alternative.

To this end the invention provides a fuel injection system for a gas-diesel dual fuel engine, comprising a gaseous fuel supply, a diesel fuel supply comprising a diesel pump and an injector comprising an internal receiving volume with an injector seat and a single injection needle for performing injections of the thereto supplied fuels via the injector seat into a combustion chamber of the engine. The internal receiving volume comprises a gaseous fuel inlet fluidly connected to the gaseous fuel supply, and a diesel fuel inlet fluidly connected to the diesel fuel supply. The fuel inlet is arranged for providing fuel to the internal receiving volume in any one of two modes. One of these two modes is a dual fuel mode in which for a combustion cycle of the engine a pilot combustion amount of diesel is provided, via the fuel inlet (13), to the internal receiving volume and with a gaseous fuel is supplied by the single injection needle to the combustion chamber of the engine via the injector seat. The second of these two modes is a diesel-only mode in which, for a combustion cycle of the engine diesel fuel provided, via the fuel inlet (13), to the internal receiving volume, that is the only fuel supplied by the single injection needle to the combustion chamber of the engine via the injector seat. The system further comprises an electronic engine controller (ECU) arranged for selecting a mode of operation for the engine from the dual fuel mode and the diesel -only mode. The engine controller is arranged for. in the dual fuel mode controlling the diesel pump such that the diesel pump only supplies the pilot combustion amount of diesel fuel to the injector for a combustion cycle. The engine controller is further arranged for, in the diesel-only mode, controlling the diesel pump for supplying an operational amount of diesel, greater than the pilot combustion amount of diesel, to the combustion chamber of the engine via the injector for a combustion cycle.

A system is thus described which readily allows an engine to operationally switch to rely on different fuels with a smooth transition, e.g. by just providing a balanced pressure between the liquid fuel supply and gaseous fuel supply . The system here also beneficially relies, in the diesel- only mode on diesel to be injected under pressure of the diesel pump itself without the aid of an air or gas blast compressor. It should be understood that diesel fuel may be seen as any fuel that would rely on compression ignition in an internal combustion engine. The pilot amount of diesel fuel is chosen such that it is merely sufficient to start the ignition of the co -injected gaseous fuels. The pilot amount is, in itself, insufficient to allow work to be derived from the engine without the addition of other fuels. The gaseous fuel can be anything that will burn, i.e, may be vaporized LNG, and CMG and propane.

In one embodiment the electronic controller is arranged for controlling the diesel pump such that, in the diesel-only mode, an internal fuel receiving volume of the injector is substantially entirely filled with diesel fuel for an injection. It is to be understood that the volume is filled prior to injection and thus while the injector remains closed to the combustion chamber of the engine. The system further may comprise a selective barrier means disposed in the gaseous fuel inlet for preventing the incursion of diesel fuel into the gaseous fuel supply. This beneficially prevents the build up diesel fuel in the gaseous fuel inlet with diesel fuel, such as during diesel-only operations. Preventing such incursions sees an increased torque control of the engine upon switching between modes of operation. The controller may he arranged for controlling the diesel pump such that, at least in the diesel-only mode, the diesel fuel is supplied to the injector at a pressure which is higher than a pressure of gaseous fuel at the gaseous fuel inlet. In such an embodiment the selective harrier means may he a check- valve. Beneficially the check valve does not require active opening and closing based on injection timing. In a preferred embodiment the gaseous fuel pump may be a high pressure pump or compressor which generates a pressure A in the range of 300 - 500 bar wherein pressure A is at least 150% of a peak firing pressure of the combustion chamber. The diesel pump may in said preferred embodiment also he a high pressure diesel pump which generates diesel pressures in the range of 300 - 2500 bar. The diesel pump would in such a case be arranged to generate a higher pressure than the gaseous fuel pump, at least during the diesel- only operations, or even during all modes. Beneficially, the mode of operations would in such an embodiment be determined by the operation of the diesel fuel pump at this higher pressure. This simplifies switching between modes as no pump settings need to be changed. It can be understood that in such an embodiment, when the diesel is supplied to the injector, the check valve remains closed simply due to over pressure. In the dual fuel· mode the pump pressure may be controlled to only supply the pilot amount of diesel prior to injection and to stop providing diesel beyond that amount such that the gaseous fuel may be allowed to come in through the check valve and purge and atomize the pilot amount of diesel from the injector into the engine.

A metering unit for metering diesel fuel being supplied to the injector can he comprised in the system to increase torque control during the dual fuel mode. The controller would in such a case be arranged for, in the dual fuel mode, using the metering unit to control the diesel pump to dose only the pilot combustion amount of diesel to the injector for an injection. Optionally the metering unit is an inlet metering valve for metering diesel fuel entering the diesel fuel pump, or an outlet metering valve for metering diesel fuel exiting the diesel fuel pump.

The injector may comprise an injection needle and an actuator arranged for actuating the injection needle for opening and closing the injector to the combustion chamber. The controller is arranged for controlling a timing of the injection by opening and closing of the injector via the actuator. The timing of injection comprises moment of injection in a combustion cycle and duration of injection. A single injection needle system allows for the simultaneous injection of gaseous fuel and diesel fuel using a single injection nozzle. This solution is relatively inexpensive and assembly is less cumbersome than tradition injectors, such an injectors carrying parallel injection needles. Air intake into the engine may occur via a separate injection or inlet means. Herein only fuel injection to an engine is discussed.

The engine can be arranged as a standard piston-type engine. The engine would in such a case comprise a crankshaft, wherein the combustion chamber is formed by a firing cylinder and a piston, and wherein the piston is connected to the crankshaft. The controller can. in such a situation, be arranged to control the timing of the injection independently of the position of the crankshaft. More particularly, when considering the single needle injector, the needle can also be opened and closed independently of the engine crankshaft position by means of either a hydraulic servo mechanism (as in current common rail injectors) or directly by means of e.g. piezo elements. The signal for opening and closing of the needle comes from the engine controller which controls both start of injection and the injected quantity. A benefit is that moments of injection can be chosen separate from the crankshaft position so as to allow injection timing to differ between the two modes at the end of a compression stroke. This increases duel efficiency.

In another aspect of the invention an engine assembly comprises a gas- diesel dual fuel engine having a combustion chamber and the system as discussed above. Such an engine assembly may be comprises in a vehicle such as a car, truck, boat or other vehicles. The vehicle may be provided with a user area or cabin fitted with a user interface to allow the user to select the mode of operation of the engine. Such a user interface would be communicatively arranged with the controller for selecting the mode of operation based on user input. In yet another aspect of the invention the method steps of operating the engine assembly in either of the two modes.

In the method of providing fuel to a gas-diesel dual fuel engine for a dual fuel combustion cycle the following occurs. A pilot amount of diesel fuel and only this amount of diesel fuel is supplied to the injector from the diesel fuel supply. During the step of supplying the pilot amount of fuel to the injector, the injector remains closed to the combustion chamber. In a subsequent step high pressure gaseous fuel is supplied to the injector as main fuel for the engine. Subsequently still the injector, at the end of a compression stroke, is opened and kept open for an amount of time to simultaneously supply gaseous fuel and diesel fuel to the combustion chamber of the engine and allow the atomization of the diesel fuel into the combustion chamber by means of the gaseous fuel such that the gaseous fuel is used both as main fuel, as well as an atomizing medium for the pilot amount of diesel. Optionally the controller is arranged to adjust the torque of the engine by adjusting the amount of time the injector is open to the combustion chamber. The injection time being in this case proportional to the amount of combustibles injected into the engine. The user may by a torque control unit, such as a speed paddle indicate the desired torque to the controller which changes the torque accordingly. The method may- be repeated during each engine stroke while the engine is in the duel fuel mode.

More in particular herein is thus described a first method of providing fuel to a gas-diesel dual fuel engine for a combustion cycle. The method comprises steps a) - e) which are elaborated herein below. First step: providing the gas-diesel dual fuel engine comprising a gaseous fuel supply, a diesel fuel supply comprising a diesel pump, an injector for performing injections of the thereto supplied fuels into a combustion chamber of the engine. The injector comprises an inner volume for receiving diesel and gaseous fuels therein, a gaseous fuel inlet fluidly connected to the gaseous fuel supply, and a diesel fuel inlet fluidly connected to the diesel fuel supply via the diesel pump. The engine also comprises in this example an electronic engine controller arranged for controlling the diesel pump and the injector. For completeness sake it here given that the injector can he controlled via control signals from the controller to an actuator of an injection needle of the injector. It can be understood that this step more in general concerns providing an engine assembly according to a previous aspect of the invention. Further steps relate to engine operations, rather than to provision of engine elements.

Step a) using the controller to control the diesel pump into supplying only a pilot amount of diesel directly into the internal receiving volume of the injector, e.g, by metering through an appropriate diesel pressure, which is just above the gas pressure. At the same moment the injector is also filled with gas, which has a slightly lower pressure, thus balancing a diesel pressure and a gas pressure for a required metering. Alternatively a small volume of diesel can he metered directly.

Step h) collecting the pilot amount of diesel in the internal receiving volume of the injector.

Step c) using the controller to control the injector needle such that the internal receiving volume becomes fluidly connected to the combustion chamber. More particularly the raising of the injection needle via the actuator opens the inner volume to the combustion chamber.

Step d) supplying gaseous fuel to the injector, at least while the injector needle is in open position, such that the gaseous fuel can he used both as main fuel for a combustion stroke of the combustion cycle, as well as an atomizing medium. The injection timing, which includes both moment of injection and duration of injection, can be, in any of the modes of operation be controlled by the engine controller. The moment of injection may, regardless of mode of operation, be anywhere from directly after a compression stroke and prior to a following combustion stroke. The duration of injection preferably does not extend to the moment of combustion. The duration of the injection determines the amount of gaseous fuel that is injected. The moment at which the injector is closed may he a function of a user selected torque requirement of the engine.

Step e) using the controller to close the injector. In the method of providing fuel to a gas-diesel dual fuel engine for a diesel-only combustion cycle the following occurs. An internal receiving volume of the injector is substantially entirely filled, via a fuel inlet fluidly connected to the diesel pump, with diesel fuel for an injection, while the injector remains closed to the combustion chamber. The injector is opened at the end of a compression stroke and is kept open for an amount of time to supply the diesel fuel under the diesel fuel pressure alone as a main fuel to the combustion chamber, and the injector is then closed to end the injection cycle. The method may be repeated during each engine stroke while the engine is in the diesel-only mode. More in particular herein is thus described a second method of providing fuel to a gas-diesel dual fuel engine for a combustion cycle, The method comprises steps i) - iii) which are elaborated herein below.

Step i) using the controller to control the pump to substantially entirely fill, via the fuel inlet, directly into the internal receiving volume of the injector with diesel fuel for an injection, e.g. by increasing the diesel pressure above the gas pressure.

Step ii) using the controller to control the injector needle in open position to supply the diesel fuel, via the fuel inlet of the internal receiving volume under the diesel fuel pressure alone to the combustion chamber, such that the diesel fuel can be used as a main fuel for a combustion stroke of the combustion cycle.

Step iii) using the controller to control the injector needle in closed position.

In one further method according to the invention there is a method for operating an engine assembly according to a previous aspect of the invention. The method comprises the step of using the controller for selecting the mode of operation to be the dual fuel mode and performing, for each subsequent combustion cycle, at least method steps a) - f) according to the first method or using the controller for selecting the mode of operation to be the diesel- only mode and performing, for each subsequent combustion cycle, at least method steps i) - iii) according to the second method. Optionally, the user selects the mode of operation via a corresponding human interface, wherein the interface is communicatively connected to the controller for receiving such user input. Further advantageous aspects of the invention will become clear from the appended description and in reference to the accompanying drawings, in which;

Figure 1 schematically illustrates a fuel system according to the invention;

Figure 2 schematically illustrates an engine assembly comprising an engine and the fuel system according to the invention;

Figure 3 also schematically illustrates a fuel system according to the invention; Figures 4A, 4B schematically show the injector during method steps in the dual fuel mode; and

Figures 5 A, 5B schematically show the injector during method steps in the diesel-only mode;

Figure 6 schematically shows the method steps for operating the fuel system according to the invention in a dual fuel mode; and for operating the fuel system according to the invention in a diesel -only mode;

Figure 7 shows an illustrative graph how the dual fuel modes are controlled by a diesel pressure of the diesel supply. Typical gas pressure is 300 to 500 bar, with diesel pressure being up to +/-100 bar higher in dual fuel mode. In diesel mode (right side) the diesel pressure is typically 800 to 2500 bar;

Figure 8 schematically shows alternative actuation embodiments of the injector needle. Figure 1 shows a schematic view of a fuel injection system 1 according to the invention. The system 1 has a gaseous fuel supply 3, a diesel fuel supply 5 and an injector 7. This gaseous fuel supply consists of a liquefied natural gas (LNG) source 2, a high pressure fuel pump 8 and a subsequently an evaporator 10, In an alternative embodiment the gaseous fuel supply may consist of a compressed natural gas (CNG) source and a high pressure gaseous fuel pump instead In both eases the high pressure gaseous fuel pump is able to supply the particular gaseous fuel from the gaseous fuel supply 3 to the injector 7 at a pressure of e.g. 300 bar. This pressure is merely an example. The gaseous fuel may for example be supplied to the injector with a pressure in the range of 300 - 500 bar. This value applies to modern CI-engines that have a pressure on full load above e.g. 200 bar. Preferably the gaseous fuel is supplied to the injector 7 at a pressure of at least 150% of a peak firing pressure of the combustion chamber 101. The diesel supply can be either a pressure controlled or volume controlled system. The purpose of the diesel supply is to deliver a controlled amount of diesel fuel into the sole injector between two injection operations. The diesel fuel supply 5 has a diesel fuel source 4, and a diesel fuel pump 6 which is in this example a high pressure diesel fuel pump. The diesel pump 6 draws diesel fuel from the diesel fuel source 4. The diesel pump 6 is further arranged to, in use supply the diesel, e.g, at 1000 bar pressure. However, said pump could more in general arranged for operating at a pressure in the range from 300 - 2500 bar, wherein the pressure may be purposefully chosen to exceed the pressure with which gaseous fuel supply is supplied to the injector 7. The injector 7 has an injector seat 20, defining an internal receiving volume of the injector 7, and an injection needle 21 which acts as a valve for, in use, selectively opening and closing the injector, in particular the inner volume of the injector, to a combustion chamber 101 of an engine 100. The injector 7 further has an actuator 23 arranged for moving the injection needle 21 from a closed position into an open position and vice versa. In this example the actuator may have a hydraulic servo mechanism which draws diesel from the diesel fuel supply for its hydraulic operations. Alternatively, the actuator can be a piezoelectric mechanism. The actuator 23 is in this example arranged to draw electricity from an electrical source (not shown, but customary), such as a car battery. An electronic engine controller 15, also part of the system, is arranged to control the timing of the injection hy means of controlling the position of the injection needle 21 at any given moment in a combustion cycle via the actuator 23. The controller 15 may also draw its electrical energy from the same electrical source as the actuator. The timing of injection can he understood to encompass the moment of injection in a combustion cycle and the duration of injection. The duration of injection here being the time that passes between an opening and a subsequent closing of the injector 7. The system 1 thus provides fuel to the engine in particular the combustion chamber 101 of the engine 100 during the injection. The system is arranged for providing fuel to the engine in any one of a) a dual fuel mode in which, for a combustion cycle of the engine, a pilot combustion amount of diesel and a gaseous fuel are supplied to the combustion chamber of the engine via the injector 7, and b) a diesel-only mode in which for a combustion cycle of the engine diesel fuel is the only fuel supplied to the combustion chamber of the engine via the injector 7. The pilot combustion amount of diesel is an amount of diesel which is sufficient for providing a pilot ignition flame for the gaseous fuel during a combustion stroke of the engine. The pilot diesel amount is chosen such that, in itself, the amount is insufficient for driving the engine assuming the engine is without load.

The electronic engine controller 15 arranged for selecting a mode of operation for the engine from a) the dual fuel mode and b) the diesel-only mode.

In one embodiment the controller may- select the mode of operation corresponding to a user input on a desired mode of operation selected from the modes a) and b). To this end the system may he provided with a human interface 22 which is communicatively connected to the controller 15 for receiving the user input.

In another embodiment the controller may select the mode of operation based on the availability of gaseous fuel. To this end, the controller 15 can be arranged to detect the sufficient availability of gaseous fuel via a corresponding fuel level sensor (not shown but customary). The controller would in this example be arranged to select the dual fuel mode, only when in use the controller detects via the fuel level sensor, the sufficient availability of gaseous fuel. The controller would in this example, select the diesel-only mode when in use the controller detects, via the fuel level sensor, the insufficient availability of gaseous fuel. A predetermined minimum fuel level may be used by the sensor to compare a fuel level sensor measured fuel level, wherein a measured fuel level equal to and above the minimum fuel level constitutes sufficient availability, and wherein a measured fuel level below the minimum fuel level constitutes insufficient availability.

More in general the controller may he arranged for selecting the mode of operation based on an external signal, such as a user signal, or fuel availability signal.

The controller 15 is arranged for controlling, in the dual fuel mode, the diesel pump 6 such that the diesel pump only supplies the pilot combustion amount of diesel fuel to the injector 7 for an injection for any given combustion cycle. There are various ways in which the diesel pump could he controlled in order to supply only the pilot combustion amount of diesel to the injector.

It is for example an option to actuate the diesel pump for a predetermined amount of time which corresponds to the diesel pump supplying an amount of diesel which only partially fills the inner volume defined by the injector seat 20 prior to injection.

In one embodiment a metering unit 19 can be used for the precise metering of the pilot combustion amount. The pilot combustion amount is here too only sufficient to partially fill the inner volume defined by the injector seat 20 and supplied prior to injection. The controller 15 is in this example arranged for, in the dual fuel mode, using the metering unit 19 to control the diesel pump 6 to dose only the pilot combustion amount of diesel to the injector 7 prior to injection. The optional metering unit 19 is in Figure 1 shown as an outlet metering valve to the diesel pump. Alternatively, this could be an inlet metering valve to the diesel pump. During injection, in the dual fuel mode, the gaseous fuel carries and atomizes the pilot amount of diesel from the injector seat into the combustion chamber 101 of the engine. Injection is here defined as the time period from an opening of the injector to the combustion chamber 101 of the engine 100 and the subsequent closing of the injector. The controller is further arranged for, in the diesel-only mode, controlling the diesel p ump 6 for supplying an operational amount of diesel, greater than the pilot combustion amount of diesel, to the combustion chamber 101 of the engine 100 via inlet 13 of the injector 7 for a combustion cycle. In the diesel only mode diesel fuel is supplied to substantially entirely fill the volume defined by the injector seat 20 prior to injection. By diesel pressure only diesel fuel is further sprayed into the combustion chamber via the injector diming injection.

In this example the diesel fuel pressure exceeds that of the gaseous fuel pressure. This prevents gaseous fuel from also being injected alongside diesel without the gaseous fuel supply being fluidly disconnected from or being shut off from the injector. The system may have a selective barrier means 17 disposed in the gaseous fuel inlet 11 for preventing the incursion of diesel fuel into the gaseous fuel supply 3. This selective barrier means is in this example a valve that closes on overpressure, also known as check- valve.

Optional elements are shown in dashed lines --- . Elements which are communicatively connected are connected via dashed- dotted lines -, -,- .

In the example of Figure 1 the injector has an inner volume of 10 mm3, about, but not necessary, equal to the injected quantity at idle. The pilot amount of diesel fuel is typically between 0.5 - 3 times idle fuel flow. Figure 2 shows an engine assembly 1000 of a gas- diesel dual fuel engine 100 and the system according to Figure 1. In the Figure also a vehicle 2000, in particular a truck, is shown comprising the assembly 1000. Although not shown in the Figure, there may optionally be provided a human interface 22, as shown in Figure 1. in the passenger cabin that is arranged to allow a user to input the mode of operation which is to be selected by the controller. Such a human interface could be a switch, but could also be a touch screen.

The engine is of a piston- type. Accordingly, the combustion chamber 101 is defined by a cylinder 102 and piston 103 of a diesel engine. Merely for illustration only a single cylinder and piston pair 102, 103 is shown. The engine may in reality comprise a plurality of cylinder and piston pairs each defining a combustion chamber. In such case the engine may comprise a plurality of injectors, one such injector being associated with each cylinder and piston pair. The injectors could each be connected to the gaseous and diesel fuel supplies in the same manner as the injector 7 shown in Figure 1. The invention is not to he construed as limited to a single piston carrying engine or piston engines per se. The injection system may also be used in other non-piston engines, such as a Wankel engine.

In Figure 2 the engine 100 comprises a crankshaft 105, wherein the combustion chamber 101 is formed by a firing cylinder 102 and a piston 103. The piston is arranged for moving within the firing cylinder 102 and is connected to the crankshaft. In this example the controller is arranged for controlling the timing of injection independently of a position of the crankshaft 105. Not all elements of the system 1 are shown in Figure 2. Figure 3 shows the same system 1. It is herein most important that it is noted that the engine controller may perform its tasks of switching between operational modes without providing a control signal to the gas supply. The needle control mechanism can in Figure 3 also be seen to optionally draw diesel fuel lor hydraulic operations of a hydraulic servo mechanism. Hereinafter there will be discussed (See Fig 6 in conjunction with Figures 4a, 4b, 5a and 5b) the methods M1, M2 of operating the engine 100 in an assembly 1000 e.g. as shown in Figure 2 in a) the dual fuel mode and b) the diesel- only mode. An advantage of the depicted arrangement is that a single injector needle can be used to inject both gaseous and diesel fuel. This allows for a smaller injector that will he easier to fit within an existing engine design. Furthermore, fuel supply of a dual fuel mode is simplified since the injector needle can be timed to control both timing and injected quantity of gaseous fuel. In the dual - gaseous - fuel mode the diesel pilot supply system only provides a pilot amount of diesel to the injector. Atomizing occurs under influence of the gaseous pressure. This has the benefit that the diesel pilot system delivery timing does not need to match exact ignition timing but can be controlled in a substantially continuous supply mode.

Figure 6 shows a method M1 for providing fuel to the engine 100, in the assembly 1000 as shown in Figure 2, for a combustion cycle in which the dual fuel mode is selected by the controller 15,

In a first step M1S1 the injector 7 is closed to the combustion chamber 101. In this example the control unit controls the actuator keep the injector closed to the combustion chamber. The first step M1S1 leads to a second step M1S2.

In a second step M1S2 a pilot amount of diesel fuel is supplied to the injector from the diesel fuel supply. In this example the control unit controls the diesel pump and optional metering means to dose the pilot amount of diesel fuel to the injector. The second step M1S2 leads to a third step M1S3. This can also he seen in Figure 4A

In a third step M1S3 a gaseous fuel is supplied at high pressure to the injector as main fuel for the engine. The gaseous fuel may, in use, constantly be pressurizing the inner volume of the injector. The controller would thus not he required to regulate the gaseous fuel pump or compressor. The third step M1S3 leads to a fourth step M1S4. In a fourth step M1S4 the injector is opened to the combustion chamber. This happens at the end of a compression stroke. The injector is kept open for an amount of time to simultaneously supply gaseous fuel and diesel fuel to the combustion chamber of the engine. In this step the gaseous fuel flushes diesel fuel from the injector. The gaseous fuel atomizes the diesel fuel into the combustion chamber. The fourth step M1S4 leads to a fifth step M1S5. This can also be seen in Figure 4B.

In a fifth step M1S5 the injector is closed. In this example the control unit controls the actuator to again close the injector to the combustion chamber ending the providing of fuel for this particular combustion cycle of the engine. The method is set to repeat with each combustion cycle.

In this example the engine 100 will after the fifth step proceed to a combustion of the fuels together with air, which is separately entered into the combustion chamber from the method of fuel injection M1. The engine can be seen to have an air inlet 107. After combustion the exhaust products are evacuated through an outlet 109.

The controller may be arranged to. in the dual fuel mode adjust the torque of the engine by adjusting the amount of time the injector is open to the combustion chamber.

Figure 6 further shows a method M2 for providing liquid fuel only to the engine 100, in the assembly 1000 as shown in Figure 2. for a combustion cycle in which the diesel-only mode is selected by the controller 15. In a first step M2S1 the injector 7 is closed to the combustion chamber 101. In this example the control unit controls the actuator keep the injector closed to the combustion chamber. The first step M2S1 leads to a second step M2S2,

In a second step M2S2 the liquid fuel is supplied to the injector 7, preferably at a pressure at or above a pressure with which the gaseous fuel supply would otherwise be provided to the gaseous fuel inlet. The gaseous fuel may in such a ease be allowed to remain in active supply to the injector throughout any selected mode of operation. This is opposed to a situation in which a gas compressor or gaseous fuel pump needs to be switched off. The liquid fuel being higher in pressure continuously prevents gas from being injected by keeping the check valve closed. Even when the injector is opened, the liquid fuel pressure alone may be enough for gaseous fuel to be prevented from passing the check valve, or in absence of the check valve, from reaching the injector during diesel only operations. The second step M2S2 leads to a third step M2S3.

In a third step M2S3 the receiving volume of the injector is substantially entirely filled with diesel fuel for an injection. The third step M2S3 leads to a fourth step M2S4. Tills can also be seen in Figure 5 A.

In a fourth step M2S4 the injector is opened at the end of a compression stroke of a combustion cycle and kept open for an amount of time to supply the diesel fuel under the diesel fuel pressure alone as a main fuel to the combustion chamber. The fourth step M2S4 leads to a fifth step M2S5. This can also be seen in Figure 5B.

In the fifth step M2S5 the injector is closed. In this example the control unit controls the actuator to again close the injector to the combustion chamber ending the providing of fuel for this particular combustion cycle of the engine. The method is set to repeat with each combustion cycle.

In this example the engine 100 will after the fifth step proceed to a combustion of diesel fuel together with air, which is separately entered into the combustion chamber from the method of fuel injection M1.

The controller may also he arranged to, in the diesel- only mode, adjust the torque of the engine by adjusting the amount of time the injector is open to the combustion chamber. Alternatively the controller may he arranged to control the pressure with which the diesel pump supplies diesel to the injector, such as by adjusting the voltage to the diesel pump.

Figure 7 shows an illustrative graph how the dual fuel modes are controlled by a diesel pressure of the diesel fuel supply. At lower pressures of the diesel supply indicated as ‘gas operation’ in the first fuel mode a diesel fuel pressure controller controls the diesel pump into supplying only a pilot amount of diesel to the injector due to the relatively low diesel pressure, that is partly counter acted by the gas pressure. This results in the provision of a pilot amount of diesel collected in the inner volume of the injector. At intermittent times in accordance with the motor stroke cycle, the controller opens the injector by lifting the injector needle such that the inner volume becomes fluidly connected to the combustion chamber; and at the same time, due to the gaseous fuel pressure, while the injector is open, the gaseous fuel is used both as main fuel lor a combustion stroke of the combustion cycle, together with the pilot amount of diesel. Due to the diesel pressure, in this gas operated phase, diesel fuel may continue to flow into the injector, filling it up. During injection diesel will also flow from the diesel system directly into the injector because the diesel pressure is above the gas pressure. If the difference between diesel pressure and gas pressure is raised further the injector pressure will increase above the gas pressure during injection, causing the check valve to close. In that case only diesel fuel will he injected.

In the second fuel mode, the diesel- only mode, at higher pressures of the diesel supply, the controller controls the diesel pump to substantially entirely fill the internal receiving volume of the injector with diesel fuel for an injection. The check valve may close directly under influence of the diesel pressure (e.g. a mechanical valve), but may also be electronically or otherwise controlled. The diesel only operation may act in a substantially higher pressure range than the gas operation e.g, at 1000 - 2500 bar pressure. In this pressure regime diesel fuel is supplied under the diesel fuel pressure alone to the combustion chamber by actuation of the injector needle such that the diesel fuel can be used as a main fuel for a combustion stroke of the combustion cycle.

Figure 8 shows a further elaboration on the various ways the injection needle 21 can be controlled to open or close the seat 20 for performing injections, via the injector seat 20 into a combustion chamber 101 of an engine. In Figure 8a an electrical actuation is depicted, wherein the injection needle 21 may be controlled electrically e.g. by controller 15 via a solenoid 90 that actuates the injection needle 21 from a closed position where it closes injector seat 20, to an open position, where the controller 15 control the injector needle such that the internal receiving volume becomes fluidly connected to the combustion chamber 101,

In Figure 8b an hydraulic control is illustrated via a three way valve 91, that is actuated by a controller 151. In this way, high pressure fuel supply 5, pressured by a fuel pump 6 is parallel circuited to directly fill the internal receiving volume 80 via fuel inlet 13, and to actuate the injector needle 21 to a closed position by ‘high’ pressure received from the fuel supply 5. When controller 151 releases the three way valve 91 to connect to a ‘low pressure’ receiving element 131 (i.e. lower pressure than the pressure received from fuel supply 13), injector needle (21) is released to an open position. The element 131 fluidly connect to a receptacle, drain or sump. Both embodiments A, B illustrate a fuel inlet 13 that is at all times directly fluidly connected to the internal receiving volume 80, both in the in a first fuel mode wherein the controller 15, 151 is controlled to control the diesel pump into supplying only a pilot amount of diesel via fuel inlet (13), directly into the internal receiving volume, wherein the pilot amount of diesel is collected in the internal receiving volume 80 of the injector; and wherein the controller is used to control the injector needle such that the internal receiving volume becomes fluidly connected to the combustion chamber; while at the same time supplying gaseous fuel to the injector, at least while the injector needle 21 is in open position, such that the gaseous fuel is used both as main fuel for a combustion stroke of the combustion cycle together with the pilot amount of diesel, and similarly, in a second fuel mode, wherein the controller 15 is used to control the pump 6 to substantially entirely fill, via fuel inlet (18) the internal receiving volume 80 of the injector with diesel fuel for an injection; and wherein the controller is used to supply the diesel fuel under the diesel fuel pressure alone to the combustion chamber, such that the diesel fuel can be used as a main fuel for a combustion stroke of the combustion cycle. Relative to the hydraulic actuation illustrated in Figure 8b, the electric actuation of Figure 8b has a benefit of decoupling the needle 21 control from the fuel supply to the internal receiving volume, so it the needle actuation might he using another fluid / gas or even a complete different needle actuation mechanism can be used (e.g. direct actuation by piezo elements). In contrast in Figure 8b the liquid fuel supply is used to simultaneously control the needle 21 and the fuel supply via fuel inlet 13. This sets a constraint on the minimal diesel pressure that can be used, otherwise the injector seat (20) may not be closed well. In contrast, in Figure 8a other means to control the needle 21 may work a well. For instance, the needle could he directly actuated by means of an magnet or piezo element, instead of a 3 -way valve 91 and a low pressure return 131. Furthermore, by only supplying high pressure fuel to the internal receiving volume 80, such as done in Figure 8a a larger freedom is obtained for determination of diesel vs gas quantity by pressure balancing. In particular, diesel pressure can be varied over a wider range as it only is adjusted relative to the gas supply through the internal receiving volume. Thus the diesel only mode can he seamlessly engaged by just (only) increasing the diesel pressure, which in general can he performed very quickly. This makes it possible to gas mode to diesel mode for example during acceleration. Going quickly and seamlessly from diesel mode to mixed mode and vice versa can be advantageous when gas supply is limited or if full load operation on gas is impossible due to gas pressures being too low, or when sucb conditions would reverse. Additionally, by using a single fuel inlet 13 for both modes the number of passages and check valves is reduced, and in both fuel modes, the same fuel feed mechanism and control is used.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description and drawings appended thereto. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will he appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. References to published material or sources of information contained in the text should not be construed as concession that this material or information was part of the common general knowledge in this country or abroad. Each document, reference or patent publication cited in this text should be read and considered by the reader as part of this text, and for reasons of conciseness the contents thereof is not repeated, duplicated or copied in this text. It will be dear to the skilled person that the invention is not limited to any embodiment herein described and that modifications are possible which may be considered within the scope of the appended claims. Also kinematic inversions are considered inherently disclosed and can be within the scope of the invention. In the claims, any reference signs shall not be construed as limiting the claim. The terms 'comprise', 'comprising' and ‘including’ when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus expression as 'including' or 'comprising' as used herein does not exclude the presence of other elements, integers, additional structure or additional acts or steps in addition to those listed. Furthermore, the words ‘a’ and ‘an’ shall not he construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. Features that are not specifically or explicitly described or claimed may ad ditionally be included in the structure of the in vention without departing from its scope. Expressions such as: "means for ..." should be read as: "component configured for ..." or "member constructed to ..." and should be construed to include equivalents for the structures disclosed. The use of expressions like: "critical", "preferred" "especially preferred" etc. is not intended to limit the invention. To the extend that structure, material or acts are considered to be essential they are inexpressively indicated as such. Additions, deletions, and modifications within the purview of the skilled person may generally be made without departing from the scope of the invention, as determined by the claims.