EP4669848A1

EP4669848A1 - Fuel injection unit for mounting on a cylinder head of a piston internal combustion engine and piston internal combustion engine with the fuel injection unit

Info

Publication number: EP4669848A1
Application number: EP23708712.7A
Authority: EP
Inventors: Matti Vaarasto; Gilles MONNET; Antti VUOHIJOKI; Yao XIAO
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2023-02-24
Filing date: 2023-02-24
Publication date: 2025-12-31
Also published as: CN120457271A; WO2024175202A1; KR20250126810A

Abstract

Invention relates to a fuel injector unit (10) for assembly to a cylinder head of an internal combustion piston engine (12) adapted for injecting first and second fuel into a combustion chamber of the internal combustion piston engine, the fuel injector unit (10) comprising in its housing (16): - a first fuel inlet (101) and a second fuel inlet (102) - a first fuel feeding section (100) comprising a hydraulically operated first valve control section (110), and a sealing fluid chamber (118) is arranged between the first fuel gallery (106) and the first valve control section (110) of the first fuel injection valve (102), - a second fuel feeding section (200) comprising a hydraulically operated second valve control section (210), wherein each one of the first valve control section (110), the second valve control section (210) and the sealing fluid chamber (118) are in continuous flow connection with a second fuel inlet for pressurized fuel (102), such that the second fuel acts as hydraulic fluid in the control sections (110, 210) and as sealing fluid in the sealing fluid chamber (118).

Description

A fuel injector unit for assembly to a cylinder head of an internal combustion piston engine and an internal combustion piston engine provided with the fuel injector unit

Technical field

[001] The present invention relates to fuel injector unit according to the preamble of claim 1 . Invention relates also to an internal combustion piston engine provided with such fuel injector unit.

Background art

[002] Internal combustion piston engines are generally provided with fuel injection systems in which means for pressurizing the fuel and control of injection timing and duration are functionally separated from each other. Fuel is fed by means of at least one high pressure fuel pump into a so-called pressure accumulator, for example a fuel rail or an accumulator space, from which the fuel is led through separate conduits into the injector or injection valve of each cylinder. These systems are commonly referred to as common rail fuel injection systems. It is also known to provide the fuel injection system with injector-wise accumulators. In practice, the operation of a fuel injector is electronically controlled, for example, by means of a hydraulic control system with a solenoid or piezoelectric valve, in order to obtain a sufficiently short and accurate injection control.

[003] It is also known in prior art to operate a piston engine by making use of different or several fuels. Typically, a gaseous fuel, such as natural gas, is used as the main fuel and liquid fuel, such as LFO or diesel fuel oil, is used as pilot fuel so as to ignite the mixture of air and gaseous fuel present in the combustion chamber of the engine.

[004] WO2017162902A1 discloses a fuel injector unit comprising two fuel feeding sections for injecting first and second fuel into a cylinder of an internal combustion piston engine. Publication discloses that it is possible to use a unique mixture of multiple fuels with one concept such as fuels with ultra-low viscosities, liquid gases, liquid alcohols (e.g. methanol, MeOH) or light fuel oil (LFO). All liquefied gases, toxic fuels or easily evaporating fuels which are not desirable to leak out from the fuel injector or more specifically from the first fuel injection valve are usable. In the second fuel feeding section the injection is controlled by making use of the second fuel whereas in the first fuel feeding section the injection is controlled by a separate control fluid. This kind of solution is therefore somewhat complicated. WO2017162902A1 discloses a sealing fluid chamber in the first injection valve between a control section and the fuel gallery of the injection valve, and the second fuel is arranged to act as sealing fluid thus minimizing the first fuel to flow from the first fuel gallery to the first control section. Even if the fuel feeding arrangement shown in WO2017162902A1 is advantageous as such, it is somewhat complicated of its structure.

[005] It is an object of the invention is to provide a fuel injector which is of simpler construction and more reliable to operate.

Disclosure of the Invention

[006] Objects of the invention can be met substantially as is disclosed in the independent claim and in the other claims describing more details of different embodiments of the invention.

[007] A fuel injector unit for assembly to a cylinder head of an internal combustion piston engine which is adapted for injecting first and second fuel into a combustion chamber of the internal combustion piston engine, the fuel injector unit comprising in its housing a first fuel inlet and a second fuel inlet, a first fuel feeding section and a second fuel feeding section.

In the fuel injector unit, the first fuel feeding section comprising o at least one first fuel injection valve for administering first fuel when in use in the engine, o a first fuel injection valve needle, o a first fuel gallery, and o a hydraulically operated first valve control section arranged at an end opposite to a needle end of the first fuel injection valve needle, wherein the first fuel gallery being provided with injection orifice or orifices opened or closed in response to position of the first fuel injection valve needle, wherein the first fuel gallery is connected to the first fuel inlet, and a sealing fluid chamber is arranged between the first fuel gallery and the first valve control section of the first fuel injection valve.

In the fuel injector unit, the second fuel feeding section comprising o a second fuel injection valve for administering second fuel when in use in the engine, o a second fuel injection valve needle, and o a second fuel gallery, and o a hydraulically operated second valve control section arranged at an end opposite to a needle end of a second fuel injection valve needle, wherein the second fuel gallery is connected to the second fuel inlet,

In the fuel injector unit according to the invention each one of the first valve control section, the second valve control section and the sealing fluid chamber are in continuous flow connection with the second fuel inlet, such that the second fuel acts as hydraulic fluid in the control sections and as sealing fluid in the sealing fluid chamber.

[008] This way the hydraulic control of valve unit is operable with the fuels only and no additional hydraulic system are needed. Additionally, the valve unit provides a safety measure such that both of the fuel injection valves are prevented from operation in case there is a malfunction in the second fuel system. In other words, the first fuel injection valve is arranged to operate dependently on the second fuel injection valve. When the second fuel is arranged to operate as control fluid for the first injection valve the first fuel can not be injected if there is a malfunction in the second fuel system which prevents a situation where the first fuel would be injected (if the control would be independent from the second fuel system) into the combustion chamber but it would not be injected due to such malfunction in the second fuel system.

[009] Combustion is also better controllable because only two different fuel materials are combusted: the first fuel and minor portion of the second fuel (as leaked sealing fluid) via the first fuel injection valve and the second fuel via the second fuel injection valve.

[0010] According to an embodiment of the invention the second valve control section and the sealing fluid chamber are in continuous flow connection with the second fuel inlet via a fuel pressure accumulator in the second fuel feeding section.

[0011] This provides even fuel pressure to the second valve control section and the sealing fluid chamber and thus trouble-free control of the first fuel injector and sealing between the fuel gallery and the control chamber.

[0012] According to an embodiment of the invention the first fuel feeding section is further provided with a first fuel pressure accumulator space arranged in the fuel injector unit between the first inlet for pressurized fuel and the first fuel gallery.

[0013] This way injection pressure of the first fuel injector can be maintained at adequate level during the injection.

[0014] According to an embodiment of the invention the first fuel feeding section is further provided with flow fuse valve in the fuel injector unit between the first fuel pressure accumulator space and the first fuel gallery.

[0015] The flow fuse will close to flow connection between the pressure accumulator and the fuel gallery in case of pressure difference increases over a predetermined level, for example due to leakage of the valve needle.

[0016] According to an embodiment of the invention the housing of the fuel injection unit comprises a cylindrical guide section for the first fuel injection valve needle and the sealing fluid chamber comprises a ring space arranged to circumscribe the first fuel injection valve needle in the guide section.

[0017] This way the sealing effect is uniform in the circumference of the needle at the location of the ring space. [0018] According to an embodiment of the invention the flow connection between the second fuel inlet and the first valve control section is arranged to extend via the sealing fluid chamber.

[0019] This provides an effect that control and sealing operations are interconnected and thus it is ensured that sealing is effective when the first injection valve is operable what comes to hydraulic control.

[0020] According to an embodiment of the invention the flow connection between the second fuel inlet for pressurized fuel and the sealing fluid chamber is arranged to extend via the first valve control section.

[0021] This also provides an effect that control and sealing operations are interconnected and thus it is ensured that sealing is effective when the first injection valve is operable what comes to hydraulic control.

[0022] According to an embodiment of the invention the first valve control section is in continuous flow connection with the second fuel inlet for pressurized fuel via a constriction.

[0023] This provides an effect that possible pressure fluctuations in the second fuel inlet are minimized.

[0024] According to an embodiment of the invention the housing of the fuel injection unit comprises a cylindrical guide section for the first fuel injection valve needle and the sealing fluid chamber comprises a ring space arranged to circumscribe the first fuel injection valve needle in the guide section and the first fuel injection valve needle is provided with flow path, such as a boring, connecting a side wall of the valve needle at a longitudinal location of the ring space to an end of the needle at the first valve control section.

[0025] This provides an effect that control and sealing operations are interconnected and thus it is ensured that sealing is effective when the first injection valve is operable what comes to hydraulic control.

[0026] According to an embodiment of the invention an annular flow path between the first fuel injection valve needle and the cylindrical guide section forms a flow path connecting the sealing fluid chamber with the first valve control section.

[0027] This way there is no need to provide flow channels to the valve needle which simplifies the structure.

[0028] According to an embodiment of the invention the first fuel injection valve needle comprises a longitudinal groove or boring forming a flow path connecting the ring space with the first valve control section.

[0029] According to an embodiment of the invention the first fuel injection valve needle is biased towards its closing direction by a mechanical spring which is arranged at the end of valve control section of the needle.

[0030] According to an embodiment of the invention the first fuel injection valve needle is biased towards its closing direction by a mechanical spring which is arranged at least partially in the fuel gallery of the first fuel feeding section.

[0031] According to an embodiment of the invention the second fuel feeding section is configured to administer fuel with one injection so as to provide maximum energy which is equal to the energy contained in fuel administered by one injection of the first fuel feeding section.

[0032] It may be said that according to this particular embodiment the second fuel feeding section is configured to administer fuel to up to 100% of maximum fuel injection amount of the first fuel feeding section. This way the engine may be kept running at viable loads even in a case of malfunction in the first fuel feeding section.

[0033] According to an embodiment of the invention the first fuel injection valve needle comprises a piston part at the end of valve control section of the needle which has diameter greater than diameter of the valve needle, and that housing of the fuel injection unit comprises a cylindrical guide section which has a first section arranged to guide the valve needle and a second section arranged to guide the piston part, wherein the piston part comprises a flow path from its annular face to its end face. [0034] According to an embodiment of the invention the housing of the injector unit is a multipart assembly, wherein crossover locations of the first fuel feed channel of the first fuel feeding section at the boundaries between the parts in the multi-part assembly comprises a hydraulic leakage bar circumscribing the feed channel and a sealing space of the hydraulic leakage bar is directly connected with the second pressure accumulator space by a sealing fluid channel, which is fluidly connected at its end, opposite to the end connected to the second pressure accumulator space, to the second fuel gallery by means of a connecting channel such that the connecting channel and the sealing fluid channel form a parallel flow path with the second fuel feed channel from the second pressure accumulator space to the second fuel gallery.

[0035] Invention also provides an internal combustion piston engine which is comprising a fuel injector unit according to the invention.

[0036] According to an embodiment of the invention the body of the injector unit is a multi-part assembly, wherein crossover location of the first fuel feed channel of the first fuel feeding section at the boundaries between the parts in the multipart assembly comprises a hydraulic leakage bar circumscribing the feed channel.

[0037] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings

[0038] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which Figure 1 illustrates a fuel injector unit according to an embodiment of the invention,

Figure 2 illustrates a fuel injector unit according to another embodiment of the invention, and

Figures 3- 9 disclose alternative embodiments of the first fuel injection valve applicable for use in the first fuel feeding section of the injector according to an embodiment of the invention.

Detailed Description of Drawings

[0039] Figure 1 depicts schematically a fuel injector unit 10 which is configured for assembly to a cylinder head of an internal combustion piston engine (not shown in the figure 1). The fuel injector unit 10 is adapted for injecting first and second fuel to the internal combustion piston engine in independently controllable manner. That is accomplished such that the fuel injector unit 10 comprises a first fuel feeding section 100 and a second fuel feeding section 200, both arranged in a housing 16 of the injector unit 10.

[0040] The fuel injector unit 10 comprises a first fuel inlet 101 and a second fuel inlet 201 which are coupled with a source of first and second fuel sources when assembled to an engine. The source of the first fuel is configured to deliver fuel at a predetermined pressure to the injector unit 10. The first fuel usable in the fuel injector unit 10 is preferably one of, or an applicable blend of, the following: Liquefied natural gas (LNG), Liquefied petroleum gas (LPG), ammonia, hydrogen, bio or synthetic fuel or carbon-neutral methane and methanol. The first fuel may be injected into the engine in liquid or gaseous phase, depending on the fuel and the actual setup. Particularly, it is possible to use a unique mixture of multiple fuels with one unit such as fuels with ultra-low viscosities, liquid gases, liquid alcohols (e.g. methanol, MeOH) or light fuel oil (LFO). Invention gives benefits for all liquefied gases, toxic fuels or easily evaporating fuels which are not desirable to leak out from the fuel injector or more specifically from the first fuel injection valve. In general, the first fuel is such that it will not ignite alone in the engine, and therefore the first fuel can also be referred to as lower reactivity fuel. The second fuel is preferably one of or an applicable blend of the following: Light fuel oil (LFO), bio diesel, marine diesel oil (MDO) or a corresponding synthetic liquid fuel. The second fuel is used as igniting the first fuel, and it is such that compression ignition will occur and therefore the second fuel is a fuel capable of autoignition at the design compression pressure/temperature of the engine. Therefore, the second fuel can also be referred to as higher reactivity fuel.

[0041] The first fuel feeding section 100 in the fuel injector unit 10 is configured for injecting main fuel of the engine. Typically, the main fuel brings about at least 90% of power of the engine. In the embodiment of the figure 1 the first fuel feeding section 100 comprises a first fuel injection valve 102 for administering first fuel into a combustion chamber of the engine. There is also a first fuel injection valve needle 104 in the in the first fuel injection valve, which needle 104 is arranged coaxially into a cylindrical space provided for the needle 104. Further a first fuel gallery 106 is arranged in the space for the needle 104 and provided with injection orifices 108 in the injector housing which are opened or closed in response to position of the first fuel injection valve needle 104. The first fuel gallery 106 is in flow connection with the first fuel inlet 101 by means of a first fuel feed channel 112. The first fuel feed channel is provided with a fist pressure accumulator space 114 and a flow fuse valve 116 such that the flow fuse valve 116 is arranged between the pressure accumulator 114 and the first fuel gallery 106. The first fuel gallery 106 is therefore in flow connection with the first fuel inlet 101 via the first pressure accumulator space and the flow fuse valve 115. The flow fuse valve 116 limits and finally prevents the fuel flow from the first pressure accumulator space to the fuel gallery in case of malfunction of the injector, for example when the valve needle fails to close properly, based on pressure difference between the fuel gallery and the first pressure accumulator space. The first pressure accumulator space 114 and the flow fuse 116 are also arranged within the housing 16 of the injector unit 10.

[0042] There is also a hydraulically operated first valve control section 110 arranged at an end, opposite to a needle end of the first fuel injection valve needle 104. There is a first control space 120 on top of the first needle 104 into which pressurized control fluid is admitted for controlling position of the needle. In this case second fuel is used as the control fluid, which is explained later. Pressure of the fluid causes a closing force to the needle whereas the fuel pressure in the gallery 106, together with a biasing spring 122, causes opening force to the needle. In closed position, where the needle 104 closes the orifices 108, the closing force is greater than the opening force. When the orifices 108 are to be opened the pressure in the control space 120 is relieved which changes the force balance such that the needle 104 moves away from the orifices 108, upwards in the figure 1. There is a first return channel 124 extending from the control space 120 to a first control valve 126. The first control valve 126 is an on-off solenoid valve which is operated either for maintaining pressure, or relieving pressure from the control space 120. The return channel 124 extends further to a fuel outlet 103 of the injector unit 10.

[0043] Additionally, there is a sealing fluid chamber 118 in connection with the first valve needle 104. The sealing fluid chamber 118 is arranged around the valve needle 104, to fully circumscribe the needle, longitudinally (axially) between the first fuel gallery 106 and the first valve control section 110 of the first fuel injection valve 102. More particularly the housing 16 of the fuel injection unit comprises a cylindrical guide section for the first fuel injection valve needle 104, wherein the sealing fluid chamber 118 comprises an annular ring space arranged to circumscribe the first fuel injection valve needle 104 in the guide section. The sealing fluid chamber 118 is separated, to an extent of practically being feasible, from the first fuel gallery 108. The sealing fluid chamber 118 is in continuous flow connection with the second fuel inlet 201 of the injector unit 10. There is also a flow connection arranged between the sealing fluid chamber 118 and the control space 120, such that when in use, the second fuel may flow from the sealing fluid chamber to the control space 120 so as to act as pressurized control fluid of the needle 104 as referred to above. The flow connection comprises flow channel 105 arranged to the needle 104, which channel opens to an end surface of the needle. The flow channel 105 is formed by such a that the first fuel injection valve needle 104 is provided with a borings, connecting a side wall of the valve needle at a longitudinal location of the sealing fluid chamber 118, such as a ring space, to an end of the needle at the first valve control space 120. The sealing fluid chamber provides more reliable sealing between the fuel gallery 106 and the first control space 120. Pressure in the second fuel feeding section 200 is maintained higher than the fuel pressure in the first fuel feeding section 100 so as to have the sealing fluid system to operate as intended. The pressure difference may be for example 5 MPa - 20Mpa.

[0044] The continuous flow connection of the sealing fluid chamber 118 to the second fuel inlet 201 can also be understood as direct flow connection in the sense that there are no such means between the sealing fluid chamber 118 and the fuel inlet 201 which may close the flow connection in flow direction towards the sealing fluid chamber totally, such as a closing valve or a like, still there may be one or more throttles or a like for reducing and/or adjusting pressure. Operation of the sealing fluid chamber is such that second fuel is admitted to the chamber and predetermined pressure of the second fuel is maintained substantially constantly in the sealing fluid chamber. The pressure in the sealing fluid chamber is equal to or higher than injection pressure of the first fuel and this way first fuel to flow from the first fuel gallery to the first control space is prevented. Small leakage of the second fuel, which possible occurs, into the first fuel gallery 106, is combusted in the engine together with the first fuel.

[0045] The second fuel feeding section 200 is configured for injecting a so- called pilot fuel of the engine, at least during a normal operation. Typically, the pilot fuel amount is such that it ensures ignition of the main fuel. In the embodiment of the figure 1 the second fuel feeding section 200 comprises a second fuel injection valve 202 for administering second fuel into a combustion chamber of the engine. There is also a second fuel injection valve needle 204 in the in the second fuel injection valve, which needle 204 is arranged coaxially into a cylindrical space provided for the needle 204. Further a second fuel gallery 206 is arranged in the space for the needle 204 and provided with injection orifices 208 in the injector housing which are opened or closed in response to position of the second fuel injection valve needle 204. The second fuel gallery 206 is in flow connection with the second fuel inlet 201 by means of a second fuel feed channel 212. The second fuel feed channel 212 is provided with a second pressure accumulator space 214 between the second fuel gallery and the second fuel inlet 201 . The second fuel gallery 206 is therefore in flow connection with the second fuel inlet 201 via the second pressure accumulator space 214. The second pressure accumulator space 214 is also arranged within the housing 16 of the injector unit 10. There is also a hydraulically operated second valve control section 210 in the fuel injector unit 10 arranged at an end, opposite to a needle end, of the second fuel injection valve needle 204. There is a second control space 220 arranged on top of the second needle 204 into which pressurized control fluid is admitted, in this embodiment from the second fuel gallery 206. There is a flow connection arranged from the second fuel gallery 206 to the control space 220, such that when in use, the second fuel may flow to the control space 220 so as to act as pressurized control fluid of the needle 204. The flow connection comprises flow channel 205, such as borings, arranged to the needle 204, which channel opens to an end surface of the needle. The second fuel feeding section may be designed so that it is capable of delivering fuel into a combustion chamber of the engine as an amount representing even 70-100% of the energy to run the engine at its design load. However, the most important function of the second fuel is promoting or providing ignition of the main fuel.

[0046] Also, in this embodiment the second fuel is used as the control fluid of the second valve 202. In other words, the second fuel feeding section 200 utilizes the second fuel as the control fluid of the valve as well. Pressure of the second fuel in the second control space 220, together with a biasing spring 222 of the needle 204, causes a closing force to the needle 204 whereas the fuel pressure in the second fuel gallery 206 causes opening force to the needle. In closed position, where the needle 204 closes the orifices 208, the closing force is greater than the opening force. When the orifices 208 are to be opened the pressure in the control space 220 is relieved which changes the force balance such that the needle 204 moves away from the orifices 208, upwards in the figure 1 , and opens the orifices 208. There is a second return channel 224 extending from the second control space 220 to a second control valve 226. The second control valve 226 is an on-off solenoid valve which is operated either for maintaining pressure, or relieving pressure from the control space 220. The return channel 224 extends further to a fuel outlet 103 of the injector unit 10. More particularly, in the embodiment of the figure 1 the first return channel 124 and the second return channel 224 are combined within the valve unit 10 and a combined return channel 224’ connects the first return channel 124 and the second return channel 224 to the fuel outlet 103. [0047] The sealing fluid chamber 118 in the first is in continuous flow connection with the second fuel inlet 201 via a sealing fluid feed channel 128. The sealing fluid feed channel 128 extends between the sealing fluid chamber 118 and the second fuel pressure accumulator 214. In other words, the sealing fluid chamber 118 is in continuous flow connection with the second fuel inlet 201 the second pressure accumulator 214 in the second fuel feeding section. This ensures that the pressure in the sealing fluid chamber is substantially even, such that pulses created by operation of the second valve needle 204 is not transmitted to the sealing fluid chamber 118, at least to such extent that it would disturb viable operation of the sealing fluid chamber. There is a check valve 130 arranged to allow flow of the second fuel only in a direction towards the sealing fluid chamber 118 and prevent transmission of pressure pulses from the first fuel feeding section 100 to the second fuel feeding section 200. The check valve 130 prevent also back flow of the fuel from the sealing fluid chamber 118 to the second pressure accumulator 214 when the second needle 204 is opening and/or open and pressure in the second pressure accumulator 214 may be temporarily decreased. During the closing movement of the needle, the first control space 120 is filled with second fuel which flows from the sealing fluid chamber 118 to the control space 120 via the flow channel 105 in the needle and the pressure in the first control space increases substantially to pressure level of the second pressure accumulator 214.

[0048] As is becomes clear in the figure 1 the first fuel injection valve needle 104 comprises a piston part 107 at the end of valve control section of the first valve needle 104. The piston part comprises a cylindrical part which has diameter greater than diameter of the valve needle such that it delimits the sealing fluid chamber from the first control space 120. The housing 16 of the fuel injection unit comprises a cylindrical guide section for accommodate the piston part therein and which is arranged to guide the valve needle. The piston part 107 comprises a flow path 105 from its annular face to its end face. This way the flow connection between the second fuel inlet 201 for pressurized fuel and the first valve control section 110, more precisely the first control space 120, is arranged to extend, or run, via the sealing fluid chamber 118. [0049] Figure 2 discloses the first fuel feeding section 100 and the second fuel feeding section 200 similar to that shown in the figure 1 and certain additional preferred features of the fuel injector unit 10. The injector unit 10 is configured for assembly to a cylinder head of an internal combustion piston engine 12. The housing of the injector unit 10 is an assembly of separate housing parts 16.1- 16. N i.e. a multi-part assembly. The channels extending inside the housing 16 will therefore run from one housing part to another housing part and a crossover between the housing parts is sealed. As it becomes clear from the figure 2 at least the first fuel feed channel 112, the second fuel feed channel 212, the first fuel return channel 124 and the second fuel return channel 224 extend through more than one housing part 16.1-16.N and thus there are more than one crossover locations as well.

The crossover locations of the first fuel feed channel 112 of the first fuel feeding section 100 at the boundaries between the housing parts 16.1 -16. N in the multipart assembly comprises a hydraulic leakage bar 302 circumscribing the feed channel. In practise this means that the first fuel feed channel section which is, when in use, substantially at injection pressure, is sealed at the crossover location with the hydraulic leakage bar 302. The hydraulic leakage bar 302 comprises a sealing space 304 arranged around the fuel feed channel, surrounding the fuel feed channel radially at a distance from the channel 112 sealing system so that there is a land area between the channel 112 and the sealing 302. In the land area the parts of the housing are in preferably contact with each other. The sealing space 304 is preferably annular, and it is formed e.g. by providing groove or grooves to the housing parts facing each other. Hydraulic leakage bar 302 is filled with pressurized (when in use) second fuel such that there is a sealing fluid channel 306 which connects the second fuel system 200 at its high-pressure section, that is the section in which the fuel is at injection pressure when in use, with the hydraulic leakage bar 302. Preferably the sealing fluid channel 306 connects the sealing space 304 directly with the second pressure accumulator space 214 with a constant diameter channel. This way the pressure fluctuations in the sealing space 304 are minimized. The sealing fluid channel 306 is provided with a mechanical sealing 402, where the housing parts 16.1 - 16.N are in direct (metal to metal) contact with each other, at the crossover locations. The sealing fluid channel 306 is in flow connection with the second pressure accumulator space 214 and each one of the sealing spaces 304. When the sealing spaces 304 are connected in series to the sealing fluid channel 306, the sealing fluid channel 306 is preferably fluidly connected at its end, opposite to the end connected to the second pressure accumulator space 214, to the second fuel gallery 206 by means of a connecting channel 306’. The connecting channel 306’ and the sealing fluid channel 306 form a parallel flow path with the second fuel feed channel 212 from the second pressure accumulator space 214 to the second fuel gallery 206. This way the second fuel can be fed, to act as sealing fluid in the sealing spaces 304, from both ends of an array of the sealing spaces 304 coupled in series. This has an effect of providing more even pressure in the sealing spaces 304.

[0050] With regard to the second fuel feed channel 211 , which also extends from one housing part to another housing part, the sealing at the crossover locations comprises a mechanical sealing 402, such as a o-ring or a like pressed between the housing parts. Also, the first and the second return channels 124,224,224’ are provided with corresponding mechanical sealings at the crossover location of the channels. Preferably only the crossover locations of the first fuel feed channel 112 are provided with hydraulic leakage bar 302 whereas the other crossover locations are provided with mechanical sealing.

[0051] Figures 3 - 9 disclose alternative embodiments of the first fuel injection valve 102 which are applicable for use in the first fuel feeding section 100 of the injector unit 10. All of these embodiments of the first fuel injection valve 102 comprise a sealing fluid chamber 118 in connection with the first valve needle 104. The sealing fluid chamber 118 is arranged around the valve needle 104, to fully circumscribe the needle, longitudinally (axially) between the first fuel gallery 106 and the first valve control section 110 of the first fuel injection valve 102. More particularly the housing 16 of the fuel injection unit comprises a cylindrical guide section for the first fuel injection valve needle 104, wherein the sealing fluid chamber 118 comprises a ring space arranged to circumscribe the first fuel injection valve needle 104 in the guide section. The sealing fluid chamber 118 is arranged in fluid communication with the second pressure accumulator space 214 of the second fuel feeding section 200 and also with the first control space 120. This way the second fuel feeding [0052] In the embodiment of the figure 3 the sealing fluid chamber 118 is arranged to receive sealing fluid i.e. the second fuel via a gap, or an annular flow path, between the needle and its housing from the first control space 120. In other words, the flow connection between the second fuel inlet for pressurized fuel and the sealing fluid chamber is arranged to extend via the first valve control section. The between the needle and its housing in the region between the sealing fluid chamber 118 and the first control space is greater than in the region between the sealing fluid chamber 118 and the fuel gallery 106.

[0053] In the embodiment of the figure 4 the sealing fluid chamber 118 is arranged to receive the second fuel through the sealing fluid feed channel 128, which has a branch line 128’ connected to the first control space 120. In the branch, there is arranged a local flow constriction in the flow area, such as an orifice or other local reduction in cross sectional area in the branch line.

[0054] In the embodiment of the figure 5 the sealing fluid chamber 118 is arranged to receive the second fuel through the sealing fluid feed channel 128. The first control space 120 is connected with the sealing fluid chamber via a flow channel 105 arranged to the needle 104, which channel opens to an end surface of the needle. The flow channel 105 is formed by such a that the first fuel injection valve needle 104 is provided with borings, connecting a side wall of the valve needle at a longitudinal location of the sealing fluid chamber 118, such as a ring space, to an end of the needle at the first valve control space 120.

[0055] Figure 6 discloses a fuel injection valve otherwise similar to that shown in the figure 5 except that the spring 122 is arranged in the control space 120 instead of the fuel gallery 106.

[0056] Additionally, in the figures 3 - 5 it is shown that the mechanical spring is arranged in the fuel gallery of the injection valve, whereas in the embodiment of the figures 6-9 the mechanical spring is arranged in the control space 120 the injection valve.

[0057] Further, in the embodiments shown in the figures 7 - 9 the first fuel injection valve needle comprises a piston part 140 at the control space end of the needle which piston part 140 has diameter greater than diameter of the valve needle, and the housing of the fuel injection unit comprises a cylindrical guide section which has a first section 142 arranged to guide the valve needle and a second section 144 arranged to guide the piston part 140.

[0058] In the figure 7 the piston part comprises an axially directed flow path 105 extending from its lower annular face in the position of the figure, to its end face at its upper end in position of the figure. The flow path is provided with a constriction which makes possible that the pressure in the control space can be lowered suitably when the first control valve 126 is opened. The sealing fluid chamber 118 is in direct communication with the second pressure accumulator 214. There is a branch line 128” which connects the space below the piston part 140 bordered by the lower annular face to the second pressure accumulator 214.

[0059] This way the flow connection between the second fuel inlet 201 for pressurized fuel and the first control space 120, is arranged to extend, or run, via the flow path 105.

[0060] The embodiment in the figure 8 is otherwise similar to the embodiment disclosed in the figure 7 but here the second pressure accumulator 214 is directly connected with the space below the piston part 140 bordered by the lower annular face while the sealing fluid chamber 118 is connected with said space via a flow channel 105’ arranged to the valve needle 104 such channel opens at immediate vicinity to the annual face of the piston part 140 and at axial location of the sealing fluid chamber 118. The flow channel 105’ is preferably an inclined boring through the needle.

[0061] The embodiment in the figure 9 is otherwise similarto the embodiment disclosed in the figure 8 but here the sealing fluid chamber 118 is connected with the space below the piston part 140 bordered by the lower annular face to the second pressure accumulator 214 via an annular flow path between the first fuel injection valve needle 104 and cylindrical guide section of the injection unit. [0062] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is obvious to the skilled person that, along with the technical progress, the basic idea of the invention can be implemented in many ways. The invention and its embodiments are thus not limited to the examples and samples described above but they may vary within the contents of patent claims and their legal equivalents. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

1 . A fuel injector unit (10) for assembly to a cylinder head of an internal combustion piston engine (12) adapted for injecting first and second fuel into a combustion chamber of the internal combustion piston engine, the fuel injector unit (10) comprising in its housing (16): a first fuel inlet (101) and a second fuel inlet (201) a first fuel feeding section (100) comprising o at least one first fuel injection valve (102) for administering first fuel when in use in the engine, o a first fuel injection valve needle (104), o a first fuel gallery (106), and o a hydraulically operated first valve control section (110) arranged at an end opposite to a needle end of the first fuel injection valve needle (104), wherein the first fuel gallery (106) being provided with injection orifice or orifices (108) opened or closed in response to position of the first fuel injection valve needle (104), and wherein the first fuel gallery (106) is connected to the first fuel inlet (101), and wherein a sealing fluid chamber (118) is arranged between the first fuel gallery (106) and the first valve control section (110) of the first fuel injection valve (102), a second fuel feeding section (200) comprising o a second fuel injection valve (202) for administering second fuel when in use in the engine (12), o a second fuel injection valve needle (204), o a second fuel gallery (206), o a hydraulically operated second valve control section (210) arranged at an end opposite to a needle end of a second fuel injection valve needle (204), wherein the second fuel gallery (206) is connected to the second fuel inlet (102), characterized in that each one of the first valve control section (110), the second valve control section (210) and the sealing fluid chamber (118) are in continuous flow connection with the second fuel inlet (201), such that the second fuel acts as hydraulic fluid in the control sections (110, 210) and as sealing fluid in the sealing fluid chamber (118).

2. A fuel injector unit (10) according to claim 1 , characterized in that the second valve control section (210) and the sealing fluid chamber (118) are in continuous flow connection with the second fuel inlet (102) via a second pressure accumulator (214) in the second fuel feeding section (200).

3. A fuel injector unit (10) according to claim 1 , characterized in that the first fuel feeding section (100) is further provided with a first fuel pressure accumulator space (114) arranged in the fuel injector unit (10) between the first inlet for pressurized fuel and the first fuel gallery (106).

4. A fuel injector unit (10) according to claim 3, characterized in that the first fuel feeding section (100) is further provided with flow fuse valve (126) in the fuel injector unit (10) between the first fuel pressure accumulator space (114) and the first fuel gallery (106).

5. A fuel injector unit (10) according to anyone of the preceding claims, characterized in that the housing (16) of the fuel injection unit (10) comprises a cylindrical guide section for the first fuel injection valve needle (104) and the sealing fluid chamber (118) comprises a ring space arranged to circumscribe the first fuel injection valve needle (104) in the guide section.

6. A fuel injector unit (10) according to anyone of the preceding claims 1 - 5, characterized in that the flow connection between the second fuel inlet and the first valve control section (110) is arranged to extend via the sealing fluid chamber (118).

7. A fuel injector unit (10) according to anyone of the preceding claims 1 - 5, characterized in that the flow connection between the second fuel inlet (201) for pressurized fuel and the sealing fluid chamber (118) is arranged to extend via the first valve control section (110).

8. A fuel injector unit (10) according to anyone of the preceding claims 1 - 5, characterized in that the first valve control section (110) is in continuous flow connection with the second fuel inlet (201) for pressurized fuel via a constriction.

9. A fuel injector unit (10) according to claim 6 or 7, characterized in that the first fuel injection valve needle (104) is provided with flow path, such as a boring, connecting a side wall of the valve needle at a longitudinal location of the sealing fluid chamber (118) to an end of the needle at the first valve control section (110).

10. A fuel injector unit (10) according to claim 6 or 7, characterized in that an annular flow path between the first fuel injection valve needle (104) and the cylindrical guide section forms a flow path connecting the sealing fluid chamber (118) with the first valve control section (110).

11. A fuel injector unit (10) according to claim 6 or 7, characterized in that the first fuel injection valve needle (104) comprises a longitudinal groove forming a flow path connecting the sealing fluid chamber (118) with the first valve control section (110).

12. A fuel injector unit (10) according to anyone of the preceding claims, characterized in that the first fuel injection valve needle (104) is biased towards its closing direction by a mechanical spring which is arranged at the end of valve control section of the needle.

13. A fuel injector unit (10) according to anyone of the preceding claims 1- 11 , characterized in that the first fuel injection valve needle (104) is biased towards its closing direction by a mechanical spring which is arranged at least partially in the fuel gallery of the first fuel feeding section.

14. A fuel injector unit (10) according to anyone of the preceding claims, characterized in that the second fuel feeding section (200) is configured to administer fuel with one injection so as to provide maximum energy which is equal to the energy contained in fuel administered by one injection of the first fuel feeding section.

15. A fuel injector unit (10) according to anyone of the preceding claims, characterized in that first fuel injection valve needle (104) comprises a piston part at the end of valve control section of the needle which has diameter greater than diameter of the valve needle, and that housing (16) of the fuel injection unit (10) comprises a cylindrical guide section which has a first section arranged to guide the valve needle and a second section arranged to guide the piston part, wherein the piston part comprises a flow path from its annular face to its end face.

16. A fuel injector unit (10) according to the claim 2, characterized in that the housing (16) of the injector unit (10) is a multipart assembly, wherein crossover locations of the first fuel feed channel of the first fuel feeding section (100) at the boundaries between the parts in the multi-part assembly (16.1 ,16.2, 16. N) comprises a hydraulic leakage bar (302) circumscribing the feed channel (112) and a sealing space (304) of the hydraulic leakage bar (302 is directly connected with the second pressure accumulator space (214) by a sealing fluid channel (306), which is fluidly connected at its end, opposite to the end connected to the second pressure accumulator space (214), to the second fuel gallery (206) by means of a connecting channel 0306’ such that the connecting channel (306’) and the sealing fluid channel (306) form a parallel flow path with a second fuel feed channel from the second pressure accumulator space (214) to the second fuel gallery (206).

17. An internal combustion piston engine (12) comprising a fuel injector unit (10) according to anyone of the preceding claims.