Fuel system arrangement, internal combustion engine and method utilizing the fuel system arrangement and method of operating an internal combustion engine

Abstract

The invention related to fuel system arrangement (1) for an internal combustion engine (18), the arrangement comprising a primary fuel supplier (2), a secondary fuel supplier (4) and an injector device (6) for injecting liquid fuels. The injector device (6) comprises an injector needle (9), a primary fuel chamber (10), a secondary fuel chamber (11) and a nozzle (12). The injector needle (9) may assume a closed position or an open position, thereby allowing selectively injecting fuel from the primary fuel chamber (10) through the nozzle (12) and allowing mixing of the secondary fuel with the primary fuel within the primary fuel chamber (10). The injector needle (9) assumes the closed position below a predetermined closing pressure limit and maintains the open position above the predetermined closing pressure limit applied to the primary fuel chamber (10). The primary fuel supplier (2) selectively supplies fuel to the primary fuel chamber (10) with a pressure above the closing pressure limit, and the secondary fuel supplier (4) selectively supplies the secondary fuel to the secondary fuel chamber (11) with a pressure above the closing pressure limit.

Description

[0001] FUEL SYSTEM ARRANGEMENT, INTERNAL COMBUSTION ENGINE AND METHOD UTILIZING THE FUEL SYSTEM ARRANGEMENT AND METHOD OF OPERATING AN INTERNAL COMBUSTION ENGINE

[0002] Field of the disclosure

[0003] The present disclosure relates to a fuel system arrangement for an internal combustion engine, as defined in the preamble of independent claim 1. The present disclosure further relates to an internal combustion engine, a method of retrofitting a fuel system arrangement and a method of operating an internal combustion engine.

[0004] Background of the disclosure

[0005] In attempt to reduce the environmental impact of emission from internal combustion engines, especially related to large compression ignited engines, there has been an emphasis on studying the use of alternative fuels, such as methanol-based fuels and ammonia-based fuels as energy sources. Use of such alternative fuels has been discovered to entrail certain challenges, most prominently due to the different energy content and combustion characteristics of such alternative fuels in comparison to those of more traditional fuels, such as diesel fuels. These differences typically cause changes in the ignition and combustion processes.

[0006] Attempts to alleviate challenges deriving from the different characteristics of the alternative and conventional fuels have been made by using said fuels together. The addition of a conventional fuel portion is considered to act as ignition promoter, i.e., to help initiate compression ignition due to better ignition properties, in addition to improving control over the combustion process by helping maintain the necessary temperature and pressure behavior for efficient combustion of the alternative fuel. Conventional fuels typically allow easier control over the phasing and rate of combustion, influencing the overall performance and emissions.

[0007] One approach to implement such dual fuel configuration has been to inject these fuels separately using separate injectors. While allowing great control over the injection, this results in a relatively complex arrangement, which often is not suitable for retrofitting purposes or simply requires too much space to be installed on a cylinder head. Moreover, the generally weak lubrication properties of alternative fuels require additional measures to ensure trouble-free operation.

[0008] Another approach has been preparing a mixture of the fuels and then using a single injector for injecting the mixture. As such alternative fuels and traditional fuels are chemically immiscible, additional chemical emulsifiers and / or mixing arrangements have been used to achieve a mixture of a sufficiently long life. The use of emulsifiers, in turn, increases costs and poses further challenges in regards to emissions, and the control of the combustion and ignition processes.

[0009] Regardless of the structure of the dual fuel configuration, in applications using the conventional fuel as an ignition promoter, proper phasing of injection of both fuel types during each injection cycle is found to be essential. That is, injection of the alternative fuel needs to be timed with a precise delay in respect to the injection of the conventional fuel to allow steady transition between said fuels. To further promote this, an appropriate overlap period of feeds of the two fuel types is found to be beneficial. In single injector configurations, said overlap period may also be used for promoting shear mixing of the fuels within the injector prior to their injection to the combustion chamber of the engine.

[0010] The need for precise phasing of injections of the two fuel types sets further requirements for the structure of the dual fuel systems. More precisely, precise and reliable control of the injector needle responsible for controlling the injection in required, said control also being synchronized with the control of feeds of the conventional and alternative fuels to the injector needle.

[0011] Brief description of the disclosure

[0012] An object of the present disclosure is to provide a fuel system arrangement allowing mixing of otherwise immiscible fuels, as well as precise phasing of injection of primary and secondary fuels by means of respective primary and secondary fuel suppliers. It is a further object of the present disclosure to provide an internal combustion engine equipped with such a fuel system arrangement, a method of retrofitting such a fuel system arrangement to a pre-existing internal combustion engine and a method of operating an internal combustion engine comprising such a fuel system arrangement.

[0013] These objects are achieved with an injector device according to independent claim 1, an internal combustion engine according to independent claim 9, a method according to independent claim 10 and a method according to independent claim 11.

[0014] By providing a fuel system arrangement comprising a primary fuel supplier, a secondary fuel supplier and an injector device with an injector needle, wherein the injector needle is adapted to assume a closed position below a predetermined closing pressure limit and to maintain an open position above the closing pressure limit, and the primary fuel supplier and the secondary fuel supplier are adapted to selectively supply primary respectively secondary fuel with a pressure above said closing pressure limit, it is possible to precisely control injection of the two fuel types by controlling their feed to the injector device by the primary and the secondary fuel suppliers.

[0015] List of figures

[0016] In the following the present invention will be described in more detail by way of example and with reference to the attached drawings, in which Figure 1 illustrates an internal combustion engine coupled to a primary and a secondary fuel source and with a fuel system arrangement according to a first embodiment of the present disclosure,

[0017] Figure 2 illustrates a cross-cut section of an injector device of the fuel system arrangement of Figure 1,

[0018] Figure 3 illustrates a detail of the injector device of Figure 2 in an open position of an injector needle,

[0019] Figure 4 illustrates a detail of the injector device of Figure 2 in a closed position of the injector needle,

[0020] Figure 5 illustrates a detail of the injector device according to a second embodiment of the present disclosure in the open position of the injector needle,

[0021] Figure 6 illustrates a detail of the injector device according to the second embodiment of the present disclosure in the closed position of the injector needle,

[0022] Figure 7 illustrates a detail of the injector device according to a third embodiment of the present disclosure in an intermediate position of the injector needle, and

[0023] Figure 8 illustrates the fuel system arrangement according to the present disclosure retrofitted to a pre-existing internal combustion engine coupled to a primary fuel source.

[0024] Detailed description of the invention

[0025] Figure 1 illustrates schematically an internal combustion engine 18 coupled to a primary 3 and a secondary fuel source 5 and comprising a fuel system arrangement 1 according to a first embodiment of the present disclosure. The figure is only meant for illustrating the general structure of the engine and the fuel system arrangement 1 , and reciprocal connectivity of its main structural elements, without aiming to accurately illustrate positioning or dimensions of said elements.

[0026] As illustrated in Figure 1, the fuel system arrangement 1 comprises a primary fuel supplier 2 connectable in fluid communication with the primary fuel source 3 and a secondary fuel supplier 4 connectable in fluid communication with the secondary fuel source 5. Said connections enabling fluid communication are illustrated in Figure 1 with dashed lines. Either or each of said fuel suppliers 2, 4 may comprise e.g. a fuel pump, which may be operationally connected with a valve or valve system adapted to control the supply of fuel by the fuel supplier 2, 4, the fuel pump and the valve or valve system in this case forming the fuel supplier system.

[0027] In the example of Figure 1, the primary fuel supplier 2 comprises a variable displacement pump, for example a jerk-type helix pump 19a, which may be driven by e.g. a cam of an engine camshaft and adjusted for its fuel delivery, and the secondary fuel supplier 4 comprises a constant volume pump, for example, a multi-piston pump 19b operationally connected with an electronically controlled valve 20. Said valve 20 may be e.g. an electronically operated fuel rail valve. Typically, a variable displacement pump 19a, such as helix pump is required separately for each cylinder of the engine. On the other hand, a constant volume pump 19b serves a common fuel rail which then provides fuel for several cylinders of the engine. Said primary 3 and secondary fuel source 5 may each comprise e.g. a fuel tank or fuel supply line for liquid fuels. As illustrated in Figure 1, the fuel system arrangement 1 also comprises an injector device 6 for injecting liquid fuels into a combustion chamber 18b of the internal combustion engine 18. Figure 2 illustrates a cross-cut section of the injector device 6 of the fuel system arrangement of Figure 1. As best seen in this figure, the injector device 6 comprises an injector body 7 defining an internal space 8, an injector needle 9 arranged within the internal space 8 and a primary fuel chamber 10 delimited between an outside of the injector needle 9 and the internal space 8. In said example, the primary fuel chamber 10 is provided as an annular cavity delimited at its outer side by walls of the internal space 8 and at its inner side by the injector needle 9, such that the primary fuel chamber 10 surrounds the injector needle 9. The injector device 6 also comprises a secondary fuel chamber 11 delimited between the outside of the injector needle 9 and the internal space 8. In the example of Figure 2, the secondary fuel chamber 11 is also provided as an annular cavity delimited at its outer side by the walls of the internal space 8 and at its inner side by the injector needle 9, such that the secondary fuel chamber 11 surrounds the injector needle 9. In the example of Figures 1 and 2, the primary fuel chamber 10 is arranged closer to a distal end of the injector body 7 than the secondary fuel chamber 11.

[0028] In the example of Figures 1 and 2, the injector device 6 further comprises a sealing chamber 24 delimited between the outside of the injector needle 9 and the internal space 8 of the injector body 7, the sealing chamber 24 being connected in fluid communication with a lubricant supplier 25. Said lubricant supplier 25 may comprise e.g. a pump providing a lubricant fluid with pressure to the sealing chamber 24. The lubricant may be e.g. oil, including diesel fuel oil, which may be sourced from the primary fuel supplier 2 as explained in more detail further below.

[0029] The purpose of the sealing chamber 24 is to prevent leaking of the primary fuel from the primary fuel chamber 10 into an annular gap between the injector needle 9 and the injector body 7, notably a part thereof supporting the injector needle 9. Another purpose of the sealing chamber 24 is to prevent seizing of the injector needle 9 by providing lubrication based on the properties of the lubricant. This is achieved by allowing the lubricant to penetrate from the sealing chamber 24 into an annular gap between the needle 9 and the injector body 7, so as to form a lubricating film to keep the needle 9 and the part of the injector body 7 supporting the needle 9 lubricated and sealed in temperatures and pressures experienced by the injector device 1.

[0030] In the arrangement as described, the lubricant supplier 25 is preferably adapted to supply the lubricant to the sealing chamber 24 with a pressure higher than the pressure of the secondary fuel supplied to the secondary fuel chamber 11 by the secondary fuel supplier 4, so as to avoid penetration of the secondary fuel from the secondary fuel chamber 11 to the annular gap between the needle 9 and the injector body 7 and further to the sealing chamber 24. Notably, in embodiments where a loaded spring 23 is provided to the injector device 6 for providing a closing force to the injector needle 9, pressure of the lubricant is preferably higher than said pressure of the secondary fuel, so as to prevent penetration of the secondary fuel to a housing of the loaded spring 23, said housing preferably connecting to the primary fuel supplier 2 and being also provided with the primary fuel.

[0031] In some embodiments, the primary fuel supplier 2 may be used instead of the lubricant supplier 25 to provide pressure to the sealing chamber 24, in which case the primary fuel supplier 2 is connected in fluid communication with the sealing chamber 24 and provides primary fuel with pressure to the sealing chamber 24. This relates to situation where the primary fuel is diesel fuel or similar having also lubricating properties in addition to providing combustible energy. In this arrangement, the same pump system providing the primary fuel to the primary fuel chamber 10 may be used for providing the primary fuel also to the sealing chamber 24, in which case a separate pressure-operated valve and / or pressure maintaining valve system and / or pressure accumulator may be provided between the primary fuel supplier 2 and the sealing chamber 24 to ensure an average, constant pressure higher than the average pressure of the secondary fuel supplied to the secondary fuel chamber 11 to be provided to the sealing chamber 24.

[0032] As illustrated in Figure 1, the primary fuel chamber 10 is connected in fluid communication with the primary fuel supplier 2 and the secondary fuel chamber 11 is connected in fluid communication with the secondary fuel supplier 4. In this arrangement, the primary fuel supplier 2 may be used to supply primary fuel to the primary fuel chamber 10 and the secondary fuel supplier 4 may be used to supply secondary fuel to the secondary fuel chamber 11. As indicated in said example, said fluid communication may be implemented through a primary fuel channel 21 and a secondary fuel channel 22 extending between the primary 10 respectively the secondary fuel chamber 11 and the outside of the injector body 7.

[0033] To better illustrate the internal structure of the injector device of Figure 2, Figure 3 illustrates a magnification of detail A of the injector device 6 of Figure 2, representing an open position of the injector needle 9, and Figure 4 illustrates a corresponding detail of the injector device 6 of Figure 2, representing a closed position of the injector needle 9. As best seen in these figures, the injector device 6 also comprises a nozzle 12 arranged at a distal end of the injector body 7, the nozzle 12 comprising a plurality of nozzle orifices 13 extending between an inside 12a of the nozzle 12 and an outside of the nozzle 12. In this arrangement, the nozzle orifices 13 enable fluid communication between its inside 12a and outside, such that the primary and the secondary fuels received to the inside 12a of the nozzle 12 may be injected through them. As illustrated in Figures 3 and 4, the injector needle 9 extends into the primary fuel chamber 10 and into the secondary fuel chamber 11, such that in the closed position, illustrated in Figure 4, the needle 9 prevents fluid communication between the primary fuel chamber 10 and the nozzle 12, and the needle 9 prevents fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11. In the open position, illustrated in Figure 3, the needle 9 allows fluid communication between the primary fuel chamber 10 and the nozzle 12, and the needle 9 allows fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11. Thereby, the needle 9 allows selectively injecting fuel from the primary fuel chamber 10 through the nozzle 12, and it also allows mixing of the secondary fuel with the primary fuel within the primary fuel chamber 10 prior to injecting fuels through the nozzle 12.

[0034] In other words, when secondary fuel is supplied to the secondary fuel chamber 11, it is guided to the nozzle 12 and further to the nozzle orifices 13 through the primary fuel chamber 10 when the injector needle 9 assumes the open position, thereby mixing with the primary fuel received to the primary fuel chamber 10. In the closed position of the injector needle 9, mixing of the primary fuel with the secondary fuel in the primary fuel chamber 10 is not enabled.

[0035] In the example of Figures 3 and 4, the injector device 6 also comprises a needle seat 14 arranged between the primary fuel chamber 10 and the inside 12a of the nozzle 12. In the closed position of the injector needle 9, the needle 9 is seated against the needle seat 14, thereby preventing the fluid communication between the primary fuel chamber 10 and the nozzle 12. In the open position of the needle 9, in turn, the injector needle 9 is spaced apart from the needle seat 14, thereby allowing the fluid communication between the primary fuel chamber 10 and the nozzle 12.

[0036] Figures 5 and 6 illustrate a detail of the injector device 6 according to a second embodiment of the present disclosure, representing the open and the closed position of the injector needle 9, respectively. As said second embodiment shares most of the characteristic features of the embodiment of Figures 1 to 4, the second embodiment is now discussed focusing mostly on differences between said embodiments.

[0037] In the arrangement according to the example of Figures 5 and 6, the injector needle 9 comprises an internal, secondary fuel passage 9a extending longitudinally along the needle 9. At a portion of the needle 9 residing in the primary fuel chamber 10, the needle 9 also comprises a plurality of needle orifices 9b for injecting secondary fuel into the primary fuel chamber 10, the needle orifices 9b extending between the internal secondary fuel passage 9a and an outside of the needle 9. Also, the injector needle 9 in said example comprises a plurality of secondary fuel inlet ducts 9c extending between the secondary fuel passage 9a and an outside of the needle 9, wherein the secondary fuel inlet ducts 9c are arranged such that in the closed position of the injector needle 9, they close from the secondary fuel chamber 11, thereby preventing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11 via the secondary fuel passage 9a. Correspondingly, in said arrangement the secondary fuel inlet ducts 9c open to the secondary fuel chamber 11 in the open position of the needle 9, thereby allowing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11 via the secondary fuel passage 9a.

[0038] In the arrangement as described, the needle orifices 9b, the secondary fuel passage 9a and the secondary fuel inlet ducts 9c form together a pathway for the secondary fuel between the secondary 11 and the primary fuel chamber 10, said pathway enabling the fluid connection between the fuel chambers 10, 11 only in the open position of the injector needle 9. In some configurations, only one of each of the secondary fuel passage 9a and the needle orifice 9b may be provided.

[0039] In the example of Figures 1 to 4, wherein the secondary fuel passage 9a is omitted from the injector needle 9, the injector device 6 comprises a fuel passage 15 delimited between the outside of the injector needle 9 and the internal space 8, the fuel passage 15 connecting the primary fuel chamber 10 with the secondary fuel chamber 11. In this configuration, the injector needle 9 is provided at its outside with a sealing section 16 having a larger diameter than the section of the injector needle 9 adjacent to the sealing section 16, such that in the closed position of the injector needle 9, the sealing section 16 closes the fuel passage 15. Thereby, the sealing section 16 prevents in the closed position the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11. Correspondingly, in the open position of the injector needle 9, the sealing section 16 is spaced apart from the fuel passage 15, thereby allowing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11.

[0040] Figure 7 illustrates a detail of the injector device according to a third embodiment of the present disclosure, representing a predetermined intermediate position of the injector needle 9. As said third embodiment shares most of the characteristic features of the embodiments of Figures 1 to 6, the third embodiment is now discussed focusing mostly on differences between it and the previous embodiments.

[0041] In said predetermined intermediate position, the needle 9 is positioned between the closed position and the open position, wherein the needle 9 extends into the primary fuel chamber 10 and into the secondary fuel chamber 11 in such way that the needle 9 allows fluid communication between the primary fuel chamber 10 and the nozzle 12, and the needle 9 prevents fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11. Thereby, the needle 9 according to said example allows selectively injecting primary fuel through the nozzle 12 while preventing flow of the secondary fuel to the primary fuel chamber 10. In the example of Figure 7, the sealing section 16 has a diameter corresponding to the diameter of the fuel passage 15, allowing the sealing section 16 to move within the fuel passage 15 when the injector needle 9 is driven between the open position and the closed position. In this configuration, the intermediate position may be obtained such that the injector needle 9 is spaced apart from the needle seat 14 while the sealing section 16 is at least partially retained within the fuel passage 15, thereby preventing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11.

[0042] In configurations of the injector device 6 in which the injector needle 9 assumes the intermediate position as described between the closed position and the open position, an injection cycle phase is obtained at which only the primary fuel may be injected through the nozzle 12, prior to a cycle phase at which both the primary and the secondary fuel, or only the secondary fuel are injected. In this arrangement, injection of purely the primary fuel through the nozzle 12 is ensured at an early phase of each injection cycle, prior to any secondary fuel being injected. Thereby, optimized combustion characteristics of the injected fuel during the initial combustion phase are ensured e.g. for engines originally designed compatible with the primary fuel only.

[0043] In some configurations, the sealing section 16 may be arranged such that it becomes spaced apart from the fuel passage 15 simultaneously with the injector needle 9 becoming spaced apart from the needle seat 14, in which case the intermediate position as described may not be obtained. In this case, the sealing section 16 may have a diameter larger than that of the fuel passage 15, in which case it may be arranged to abut the fuel passage 15 in the closed position of the injector needle 9. In these configurations, when the injector needle 9 has not assumed the closed position, supply of the secondary fuel to the primary fuel chamber 10 may only be controlled by means of controlling the secondary fuel supplier 4.

[0044] In configurations of the injector needle 9 in which the secondary fuel passage 9a, the needle orifices 9b and the secondary fuel inlet ducts 9c are provided as disclosed above in relation to Figures 5 and 6, the intermediate position may also be enabled. In this case, the secondary fuel inlet duct or ducts 9c may be arranged such that they allow the injector needle 9 to be spaced apart from the needle seat 14 while retaining the closed state of the inlet ducts 9c from the secondary fuel chamber 11 , thereby preventing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11 via the secondary fuel passage 9a. In these configurations, the secondary fuel inlet duct or ducts 9c may be arranged to open to the secondary fuel chamber 11, thereby allowing the fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11 via the secondary fuel passage 9a, only after further movement of the injector needle 9 away from the needle seat 14.

[0045] In the injector device 6 according to the present disclosure, the injector needle 9 is adapted to assume the closed position below a predetermined closing pressure limit PCL applied to the primary fuel chamber 10. The needle 9 is also adapted to maintain the open position above the predetermined closing pressure limit PCL applied to the primary fuel chamber 10. For the sake of clarity, the injector device 6 may require a pressure even significantly or at least somewhat above the predetermined closing pressure limit PCL to be opened but when injector needle 9 has assumed the open position, it may remain open until pressure drops to or below the closing pressure limit PCL. Force for driving the injector needle 9 to the closed position and for maintaining the closed position may be provided by, for example, mechanical means using e.g. the loaded spring 23 as described above subjecting a force to the needle 9 towards the closed position, as illustrated in the example of Figure 2. The needle 9 and the primary fuel chamber 10 are preferably reciprocally shaped such that the pressure provided to the primary fuel chamber 10 subjects a force component to the needle 9 towards the open position.

[0046] The primary fuel supplier 2 according to the present disclosure is adapted to selectively supply the primary fuel from the primary fuel source 3 to the primary fuel chamber 10 of the injector device 6 with a pressure above the closing pressure limit PCL, and the secondary fuel supplier 4 is adapted to selectively supply the secondary fuel from the secondary fuel source 5 to the secondary fuel chamber 11 of the injector device 6 with a pressure above the closing pressure limit PCL. Thereby, the pressure of the primary fuel selectively supplied by the primary fuel supplier 2, as well as the pressure of the secondary fuel selectively supplied by the secondary fuel supplier 4, may be used for maintaining the injector needle 9 in the open position previously assumed, as in the open position, pressure from the secondary fuel chamber 11 is communicated to the primary fuel chamber 10, thereby allowing the injector needle 9 to remain in the open position. As compared to the closed position, in the open position a different, increased surface area of the needle 9 becomes exposed to the pressure of the primary and / or the secondary fuel, thereby affecting the minimum pressure needed to keep the injector needle 9 in the open position. The injector needle 9 in said example is adapted to maintain the open position when at least one of the primary fuel supplier 2 and the secondary fuel supplier 4 is arranged to supply the primary respectively the secondary fuel with the pressure above the closing pressure limit PCL.

[0047] The injector needle 9 according to the examples of Figures 1 to 7 is adapted to assume the open position above a predetermined opening pressure limit POP applied to the primary fuel chamber 10, wherein the opening pressure limit POP is higher than the closing pressure limit PCL. In other words, in the arrangement of said examples the pressure required for opening the injector needle 9 is greater than the pressure required for maintaining the needle 9 in the open position. In this arrangement, the primary fuel supplier 2 is adapted to selectively supply the primary fuel from the primary fuel source 3 to the primary fuel chamber 10 with a pressure above the opening pressure limit POP, SO as to ensure that the injector needle 9 assumes the open position when the primary fuel is supplied. In this arrangement, lower pressure is required of the secondary fuel supplied by the secondary fuel supplier 4 to the primary fuel chamber 10 to maintain the injector needle 9 in the open position, namely a pressure that is only above the closing pressure limit PCL. Correspondingly, pressure only exceeding the closing pressure limit PCL needs to be provided by the primary fuel supplier 2 after the injector needle 9 has assumed the open position.

[0048] Said selective supply of the primary and of the secondary fuel may be controlled by means of e.g. directly controlling a fuel pump comprised in the primary 2 respectively the secondary fuel supplier 4, or by controlling a valve or valve system controlling the supply of fuel from a fuel pump to the injector device 6. In the example of Figure 1, the fuel system arrangement 1 further comprises a control unit 17 adapted to control the primary fuel supplier 2 and the secondary fuel supplier 4 for controlling the selective supply of the primary fuel and the secondary fuel. In this arrangement, said controlling is arranged such that in a first phase, the primary fuel supplier 2 is controlled to supply the primary fuel and the secondary fuel supplier 4 is controlled to not supply the secondary fuel. In other words, in said first phase only the primary fuel is supplied to the primary fuel chamber 10 of the injector device 6. In praxis, the first phase as described may correspond to a pilot fuel injection phase preceding a main fuel injection phase.

[0049] In said example, the control unit 17 is adapted to further control the fuel suppliers 2, 4 such that in a second phase, subsequent to the first phase, the primary fuel supplier 2 and the secondary fuel supplier 4 are controlled to supply the primary respectively the secondary fuel. In other words, in said second phase both the primary and the secondary fuel are supplied to the injector device 6, representing an overlap period of the two fuel feeds. As the injector needle 9 at this point is in the open position, shear mixing of the secondary fuel with the primary fuel within the primary fuel chamber 10 takes place prior to the fuel mixture being injected through the nozzle 12, and the needle 9 allows the fuel mixture from the primary fuel chamber 10 to be injected through the nozzle 12. As both the primary fuel supplier 2 and the secondary fuel supplier 4 are adapted to supply the primary respectively the secondary fuel with a pressure above the closing pressure limit PCL, the injector needle 9 at the second phase maintains the open position.

[0050] In said example, the control unit 17 is adapted to further control the fuel suppliers 2, 4 such that in a third phase, subsequent to the second phase, the secondary fuel supplier 4 is controlled to supply the secondary fuel and the primary fuel supplier 2 is controlled to not supply the primary fuel. In other words, in said third phase only the secondary fuel is supplied to the injector device 6, the secondary fuel being supplied to the secondary fuel chamber 11. As the injector needle 9 at this point is in the open position, fluid communication between the primary fuel chamber 10 and the secondary fuel chamber 11 is enabled, and pressure from the secondary fuel chamber 11 is communicated to the primary fuel chamber 10. Thereby, flow of the secondary fuel to the primary fuel chamber 10 is enabled, and the injector needle 9 remains in the open position allowing the secondary fuel from the primary fuel chamber 10 to be injected through the nozzle 12.

[0051] In said example, the control unit 17 is adapted to further control the fuel suppliers 2, 4 such that in a fourth phase, subsequent to the third phase, the primary fuel supplier 2 and the secondary fuel supplier 4 are controlled to not supply the primary respectively the secondary fuel. At this phase, no pressure is provided by the fuel suppliers 2, 4 to the primary fuel chamber 10, thereby causing the pressure within the chamber to fall below the closing pressure limit PCL. Thereby, the injector needle 9 at this point assumes the closed position, preventing fluid communication between the primary fuel chamber 10 and the nozzle 12, as well as between the primary fuel chamber 10 and the secondary fuel chamber 11. Thereby, further injection of fuel through the nozzle 12 is interrupted.

[0052] In praxis, said steps from the first phase to the fourth phase represent one fuel injection cycle by the fuel system arrangement 1, said injection cycles being performed recurrently during operation of the internal combustion engine 18. The control unit 17 may be synchronized with e.g. frequency of a camshaft of the engine, or in some implementations, the camshaft may form an integral part of the control unit 17, wherein it may directly control one or both of the primary 2 and the secondary fuel supplier 4. In some implementations, one or both of the primary 2 and the secondary fuel supplier 4 may be controlled by the control unit 17 by means of electronically controlling a valve or valve system adapted to control the supply of fuel by the fuel suppliers 2, 4.

[0053] Preferably, the secondary fuel supplier 4 is adapted to supply the secondary fuel to the secondary fuel chamber 11 with a pressure higher than the pressure of the primary fuel supplied to the primary fuel chamber 10 by the primary fuel supplier 2. In said arrangement, backflow of the primary fuel into the secondary fuel line may be prevented in the open position of the injector needle 9, and appropriate shear mixing of the primary and the secondary fuel in the primary fuel chamber 10 may be ensured when the secondary fuel becomes forced into the primary fuel chamber 10. In this case, the pressure provided by each of the fuel suppliers 2, 4 may temporarily reach higher value than the opening pressure limit POP.

[0054] The internal combustion engine 18 comprising the fuel system arrangement 1 according to the present disclosure may be operated by a sequence of phases. In a first phase, only primary fuel is supplied to the primary fuel chamber 10 of the injector device 6 with a pressure above the opening pressure limit POP of the injector needle 9, causing the injector needle 9 to assume the open position for fuel injection. In a second phase, secondary fuel and the primary fuel are supplied to the primary fuel chamber 10 with a pressure above the closing pressure limit PCL, causing mixing of the secondary fuel with the primary fuel within the primary fuel chamber 10 prior to the fuel injection. As disclosed above, in said second phase the secondary fuel is preferably supplied to the primary fuel chamber 10 via the secondary fuel chamber 11 of the injector device 6 with a pressure higher than the pressure of the primary fuel supplied to the primary fuel chamber 10 by the primary fuel supplier 2. In this case, the pressure provided by each of the fuel suppliers 2, 4 may temporarily reach a value higher than the opening pressure limit POP but during said second phase the pressure of the primary fuel drops below that of the secondary fuel, the latter remaining longer above the closing pressure limit PCL.

[0055] In a third phase, only the secondary fuel is supplied to the primary fuel chamber 10 with a pressure above the closing pressure limit PCL for the fuel injection, and in a fourth phase, the supply of fuel to the primary fuel chamber 10 is interrupted, causing the injector needle 9 to assume the closed position. Thereby, the fuel injection is interrupted. For example, the control unit 17 arrangement as described above may be utilized for the operating the internal combustion engine 18.

[0056] In the fuel system arrangement 1 of the present disclosure, the primary fuel may be used as a so-called pilot fuel having a small relative volume portion during each injection cycle, the pilot fuel being mainly responsible for initiating each fuel injection and -combustion cycle during operation of the internal combustion engine 18. Depending on the given use situation, the primary fuel may also have a large relative volume portion and be used as the primary energy source of the engine. Volume of each fuel supplied during each injection cycle may be arranged to be adjustable, such that the volume portion of the primary fuel respective to the volume portion of the secondary fuel may be adjusted to adapt the consumption of each fuel type to their available supply in a given use case or refueling situation. For example, in a situation where the secondary fuel, e.g. a so-called alternative fuel such as a methanol-based fuel or an ammonia-based fuel is readily available, the relative volume portion of the primary fuel, e.g. a conventional diesel fuel, may be kept low during each injection cycle. In some situations, the relative volume portions of the two fuel types may be reversed, or the volume portion of the secondary fuel may even be completely omitted.

[0057] In a preferred arrangement according to the present disclosure, Light Fuel Oil (LFO), such as conventional diesel fuel is used as the primary fuel. In this case, the secondary fuel is preferably sustainable fuel (SuFu), such as alcohol-, methanol-based fuel or carbon-free fuel such as ammonia-based fuel. In this arrangement, the fuel system arrangement 1 according to the present disclosure may be easily adapted to a pre-existing, conventional internal combustion engine setup, such that a variable fraction of the conventional fuel may be substituted with the sustainable fuel when desired. In this arrangement, the overlap period of the two fuel supplies during each injection cycle may be advantageously used for ensuring a smooth transition from the conventional LFO fuel as pilot injection to the sustainable fuel main injection, said fuels typically having different combustion characteristics and energy contents.

[0058] Figure 8 illustrates the fuel system arrangement 1 according to the present disclosure retrofitted to a pre-existing internal combustion engine 18a with a primary fuel supplier 2a coupled to a pre-existing injector device 6a and primary fuel source 3. Such retrofitting enables a conventional single fuel internal combustion engine to be reconfigured for dual fuel use, for example, with relatively few component replacements and changes to the overall configuration.

[0059] The method of retrofitting, as illustrated in Figure 8, comprises a step of first removing the pre-existing injector device 6a of the internal combustion engine 18a. Then, the method may be continued by providing the fuel system arrangement 1 according to the present disclosure such that the fuel system arrangement 1 incorporates the primary fuel supplier 2a of the pre-existing internal combustion engine 18a. In praxis, said providing the fuel system arrangement 1 comprises arranging the injector device 6 of the fuel system arrangement 1 according to the present disclosure to replace the pre-existing injector device 6a and providing the secondary fuel supplier 4 according to the present disclosure. In this arrangement, said primary fuel supplier 2a connects in fluid communication with the primary fuel chamber 10 of the injector device 6. According to a preferred embodiment illustrated in Figure 8, the primary fuel supplier 2a of the pre-existing internal combustion engine 18a comprises cylinder specific jerk-type pumps 26, preferably being adjustable for their stroke (jerk) volume, and the secondary fuel supplier 4 of the fuel system arrangement 1 being now retrofitted to the preexisting engine 18a comprises a common rail system 27 serving several, preferably all cylinders of the engine. In the arrangement as described, the pre-existing jerk-type pumps 26 may be easily adapted to the fuel system arrangement 1 according to the present disclosure, wherein the jerk-type pumps 26 may be driven by e.g. a cam of the engine camshaft. Also, the common rail system 27 enables a plurality of injector devices 6 according to the present disclosure to be included in the engine construction such that the same common rail system 27 may be employed for supplying the secondary fuel to each of the cylinder-specific injector devices 6. Supply of the secondary fuel by the common rail system 27 may be controlled e.g. by a valve or a valve system 28, and a separate pressure pump system 29 may be provided to provide the supply pressure to the common rail system 27, as illustrated in Figure 8.

[0060] It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

Claims1. A fuel system arrangement (1) for an internal combustion engine (18), the arrangement comprising: a primary fuel supplier (2) connectable in fluid communication with a primary fuel source (3), a secondary fuel supplier (4) connectable in fluid communication with a secondary fuel source (5), and an injector device (6) for injecting liquid fuels into a combustion chamber (18b) of the internal combustion engine (18), the injector device (6) comprising: an injector body (7) defining an internal space (8), an injector needle (9) arranged within the internal space (8), a primary fuel chamber (10) delimited between an outside of the injector needle (9) and the internal space (8), the primary fuel chamber (10) being connected in fluid communication with the primary fuel supplier (2), a secondary fuel chamber (11) delimited between the outside of the injector needle (9) and the internal space (8), the secondary fuel chamber (11) being connected in fluid communication with the secondary fuel supplier (4), a nozzle (12) arranged at a distal end of the injector body (7), the nozzle (12) comprising a plurality of nozzle orifices (13) extending between an inside (12a) of the nozzle (12) and an outside of the nozzle (12), wherein the injector needle (9) extends into the primary fuel chamber (10) and into the secondary fuel chamber (11), such that: in a closed position, the needle (9) prevents fluid communication between the primary fuel chamber (10) and the nozzle (12), and the needle (9) prevents fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11), and in an open position, the needle (9) allows fluid communication between the primary fuel chamber (10) and the nozzle (12), and the needle (9) allows fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11), thereby allowing selectively injecting fuel from the primary fuel chamber (10) through the nozzle (12), and allowing mixing of the secondary fuel with the primary fuel within the primary fuel chamber (10) prior to injecting fuels through the nozzle (12), characterized in that the injector needle (9) is adapted to assume the closed position below a predetermined closing pressure limit (PCL) applied to the primary fuel chamber (10) and to maintain the open position above the predetermined closing pressure limit (PCL) applied to the primary fuel chamber (10), the primary fuel supplier (2) is adapted to selectively supply the primaryfuel from the primary fuel source (3) to the primary fuel chamber (10) with a pressure above the closing pressure limit (PCL), the secondary fuel supplier (4) is adapted to selectively supply the secondary fuel from the secondary fuel source (5) to the secondary fuel chamber (11) with a pressure above the closing pressure limit (PCL), and in the open position, pressure from the secondary fuel chamber (11) is communicated to the primary fuel chamber (10), thereby allowing the injector needle (9) to remain in the open position.

2. The fuel system arrangement (1) according to claim 1, characterized in that the injector needle (9) is adapted to assume the open position above a predetermined opening pressure limit (POP) applied to the primary fuel chamber (10), wherein the opening pressure limit (POP) is higher than the closing pressure limit (PCL), and the primary fuel supplier (2) is adapted to selectively supply the primary fuel from the primary fuel source (3) to the primary fuel chamber (10) with a pressure above the opening pressure limit (POP).

3. The fuel system arrangement (1) according to claim 1 or 2, characterized in that the injector needle (9) is adapted to maintain the open position when at least one of the primary fuel supplier (2) and the secondary fuel supplier (4) is arranged to supply the primary respectively the secondary fuel with a pressure above the closing pressure limit (PCL).

4. The fuel system arrangement (1) according to any one of the claims 1 to 3, characterized in that the injector device (6) further comprises a needle seat (14) arranged between the primary fuel chamber (10) and the inside (12a) of the nozzle (12), wherein: in the closed position, the injector needle (9) is seated against the needle seat (14), thereby preventing the fluid communication between the primary fuel chamber (10) and the nozzle (12), and in the open position, the injector needle (9) is spaced apart from the needle seat (14), thereby allowing the fluid communication between the primary fuel chamber (10) and the nozzle (12).

5. The fuel system arrangement (1) according to any one of the claims 1 to 4, characterized in that the injector needle (9) comprises: an internal, secondary fuel passage (9a) extending longitudinally along the needle (9),at a portion of the needle (9) residing in the primary fuel chamber (10), one or more needle orifices (9b) extending between the internal secondary fuel passage (9a) and an outside of the needle (9), for injecting secondary fuel into the primary fuel chamber (10), and one or more secondary fuel inlet ducts (9c) extending between the secondary fuel passage (9a) and an outside of the needle (9), wherein the secondary fuel inlet duct (9c) is arranged such that: in the closed position, the secondary fuel inlet duct (9c) closes from the secondary fuel chamber (11), thereby preventing the fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11) via the secondary fuel passage (9a), and in the open position, the secondary fuel inlet duct (9c) opens to the secondary fuel chamber (11), thereby allowing the fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11) via the secondary fuel passage (9a).

6. The fuel system arrangement (1) according to any one of the claims 1 to 4, characterized in that the injector device (6) further comprises a fuel passage (15) delimited between the outside of the injector needle (9) and the internal space (8), the fuel passage (15) connecting the primary fuel chamber (10) with the secondary fuel chamber (11), and the injector needle (9) is provided at its outside with a sealing section (16) having a larger diameter than the section of the injector needle (9) adjacent to the sealing section (16), such that: in the closed position, the sealing section (16) closes the fuel passage (15), thereby preventing the fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11), and in the open position, the sealing section (16) is spaced apart from the fuel passage (15), thereby allowing the fluid communication between the primary fuel chamber (10) and the secondary fuel chamber (11).

7. The fuel system arrangement (1) according to any one of the claims 1 to 6, characterized in that the injector needle (9) extends into the primary fuel chamber (10) and into the secondary fuel chamber (11), such that: in a predetermined intermediate position between the closed position and the open position, the needle (9) allows fluid communication between the primary fuel chamber (10) and the nozzle (12), and the needle (9) prevents fluid communication between the primary fuel chamber (10) and thesecondary fuel chamber (11), thereby allowing selectively injecting primary fuel through the nozzle (12) while preventing flow of the secondary fuel to the primary fuel chamber (10).

8. The fuel system arrangement (1) according to any one of the claims 1 to 7, characterized in that the fuel system arrangement (1) further comprises a control unit (17) adapted to control the primary fuel supplier (2) and the secondary fuel supplier (4) for controlling the selective supply of the primary fuel and the secondary fuel, such that: in a first phase, the primary fuel supplier (2) is controlled to supply the primary fuel and the secondary fuel supplier (4) is controlled to not supply the secondary fuel, in a second phase, the primary fuel supplier (2) and the secondary fuel supplier (4) are controlled to supply the primary respectively the secondary fuel, in a third phase, the secondary fuel supplier (4) is controlled to supply the secondary fuel and the primary fuel supplier (2) is controlled to not supply the primary fuel, and in a fourth phase, the primary fuel supplier (2) and the secondary fuel supplier (4) are controlled to not supply the primary respectively the secondary fuel.

9. The fuel system arrangement (1) according to any one of the claims 1 to 8, characterized in that the secondary fuel supplier (4) is adapted to supply the secondary fuel to the secondary fuel chamber (11) with a pressure higher than the pressure of the primary fuel supplied to the primary fuel chamber (10) by the primary fuel supplier (2).

10. The fuel system arrangement (1) according to any one of the claims 1 to 9, characterized in that the injector device (6) further comprises a sealing chamber (24) delimited between the outside of the injector needle (9) and the internal space (8) of the injector body (7), the sealing chamber (24) being connected in fluid communication with the primary fuel supplier (2) or a lubricant supplier (25).

11. The fuel system arrangement (1) according to claim 10, characterized in that the primary fuel supplier (2) or the lubricant supplier (25) is adapted to supply the primary fuel or, respectively, lubricant to the sealing chamber (24) with an average pressure higher than the pressure of the secondary fuel supplied to the secondary fuel chamber (11) by the secondary fuel supplier (4).

12. The fuel system arrangement (1) according to any one of the claims 1 to 11, characterized in that the primary fuel is Light Fuel Oil (LFO) and the secondary fuel is sustainable fuel (SuFu).

13. An internal combustion engine (18), characterized in that the internal combustion engine(18) comprises the fuel system arrangement (1) according to any one of the claims 1 to 11.

14. A method of retrofitting a fuel system arrangement (1) to a pre-existing internal combustion engine (18a) having a primary fuel supplier (2a) coupled to a pre-existing injector device (6a), characterized by steps of: removing the pre-existing injector device (6a) of the internal combustion engine (18a), and providing the fuel system arrangement (1) according to any one of the claims 1 to 11, such that the fuel system arrangement (1) incorporates the primary fuel supplier (2a) of the pre-existing internal combustion engine (18a), said primary fuel supplier (2a) connecting in fluid communication with the primary fuel chamber (10) of the injector device (6) of the fuel system arrangement (1).

15. The method according to claim 14, characterized in that the primary fuel supplier (2a) of the pre-existing internal combustion engine (18a) comprises jerk-type pumps (26), and the secondary fuel supplier (4) of the fuel system arrangement (1) comprises a common rail system (27).

16. A method of operating an internal combustion engine (18) comprising the fuel system arrangement (1) according to claim 2, characterized by steps of: in a first phase, supplying only primary fuel to the primary fuel chamber (10) of the injector device (6) of the fuel system arrangement (1) with a pressure above the opening pressure limit (POP) of the injector needle (9), causing the injector needle (9) to assume the open position for fuel injection, in a second phase, supplying secondary fuel and the primary fuel to the primary fuel chamber (10) with a pressure above the closing pressure limit (PCL), causing mixing of the secondary fuel with the primary fuel within the primary fuel chamber (10) prior to the fuel injection, in a third phase, supplying only the secondary fuel to the primary fuel chamber (10) with a pressure above the closing pressure limit (PCL) for the fuel injection, and in a fourth phase, interrupting the supply of fuel to the primary fuel chamber (10), causing the injector needle (9) to assume the closed position interrupting the fuel injection.

17. The method according to claim 16, characterized in that in the second phase, the secondary fuel is supplied to the primary fuel chamber (10) via the secondary fuel chamber (11) of the injector device (6) of the fuel system arrangement (1) with a pressure higher than the pressure of the primary fuel supplied to the primary fuel chamber (10) by the primary fuelsupplier (2).

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