Fuel injector

Abstract

A fuel injector for an internal combustion engine is provided. The fuel injector comprises a first valve needle arranged to control injection of a first fuel and extending along an injector longitudinal axis. The fuel injector further comprises a first control chamber associated with the first valve needle. The fuel injector further comprises an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis. The actuator assembly comprises a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis.

Description

FUEL INJECTORTechnical Field

[0001] The present application relates to a fuel injector and an internal combustion engine comprising the fuel injector.Background

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention.

[0003] Internal combustion engines for heavy-duty and industrial applications are typically fueled by diesel. However, the use of alternative, cleaner burning fuels including fuels which are in gaseous form are of increasing interest. However, because many alternative fuels such as methanol, ammonia, natural gas and hydrogen have high auto-ignition temperatures, ignition assistance is generally needed. In some engine systems including Diesel-cycle engine systems, a pilot injection of lower auto-ignition temperature fuel such as diesel fuel is used to ignite these fuels which do not reliably ignite from the heat of compression in a combustion chamber of the internal combustion engine. As used herein, the auto-ignition temperature is the lowest temperature at which a substance will spontaneously ignite without an external ignition source, such as a flame or a spark. For example, the auto-ignition temperature of normal diesel fuel in a normal atmosphere is approximately 210° C, and for natural gas it is approximately 540° C depending upon the fuel quality. In one type of the internal combustion engine, both the alternative main fuel and the pilot fuel are injected directly into the combustion chamber. Due to space constraints in an engine cylinder head, it is desirable to inject both fuels using one dual fuel injector per cylinder. The dual fuel injector is adapted to keep the two fuels separate within the injector, and to deliver independently the respective fuel at the appropriate time. Exemplary fuel injectors and methods of operating in internal combustion engine systems have been described in applicant’s earlier patents including US7373931, US8095294, US 10167786, US 11053866 as well as co-owned US 10294908 all of which are incorporated herein by reference.

[0004] Generally, the dual fuel injector is provided with a twin nozzle arrangement having inner and outer valve needles. The inner and outer valve needles are engageable at their lower ends with respective valve seats to control the flow of fuel through respective inner and outer sets of discharge holes. The outer valve needle controls injection of the gaseous fuel through the outer set of discharge holes, and the inner valve needle controls injection of diesel through the inner set of discharge holes. The inner and outer valve needles are controlled independently by two electromagnetic control valves, which are configured to control the pressure of a control fluid (such as diesel fuel) within respective control chambers for the inner and outer valve needles. The control chambers receive the upper ends of the respective needles, so that changing the pressure of the control fluid in each control chamber changes the downward (closing) force on the corresponding needle. The control chamber receiving the upper end of the outer valve needle is associated with a “a main needle control valve”. The control chamber receiving the upper end of the inner valve needle is associated with a “a pilot needle control valve”.

[0005] When the pressure of the control fluid in a control chamber is relatively high, a downward force of the fuel (gas or diesel) is greater than an upward force and the respective needle remains seated, and when the pressure of the control fluid is relatively low, the upward force overcomes the downward force, and the respective needle opens to permit fuel injection through the respective set of discharge holes. Each control chamber is connected to a source of the control fluid at a relatively high pressure. Each control valve is operable to connect the respective control chamber to a low-pressure drain passage for the control fluid. In this way, the opening of each control valve causes a reduction in the pressure of the control fluid in the corresponding control chamber, resulting in the opening of the corresponding valve needle.

[0006] In some dual fuel injectors, high pressure of the control fluid in the drain passage may interfere with timings and opening / closing rates of the main needle control valve. Moreover, pressure imbalance in the drain passage may lead to reopening of the main needle control valve at an inappropriate time. For example, when a large mass flow of the control fluid flows past the main needle control valve to drain, various fluid passages in the dual injector may experience pressure reflections at locations where injector components are coupled to one another. The presence of pressure reflections and pressure fluctuations in the drain passage may lead to improper mixing of fuels, inappropriate timing of fuel injection and other control of injection events. As the quantity of fuels delivered to the combustion chamber affects the torque output of the engine, pressure fluctuations in the drain passage of the dual fuel injector may provide anundesirable torque output of the engine. Further, improper mixing of the fuels due to pressure fluctuations in the drain passage of the dual fuel injector may also lead to undesirable exhaust emissions from the engine. Such problems of pressure reflections and pressure fluctuations in the drain passage may also be noticed in conventional fuel injectors having one or more control valves, where fluid returning to the drain passage may create an undesirable back pressure and / or uneven fluid force acting on a face of the control valve. The term “and / or” is used herein to mean “one or the other or both”.

[0007] The state of the art is therefore lacking in techniques for reducing pressure fluctuations and pressure reflections in the drain passage / drain circuit of a fuel injector. The present disclosure provides a technique for preventing pressure imbalances / pressure fluctuations and pressure reflections in the drain passage of a fuel injector, thereby improving an overall performance of the fuel injector and an internal combustion engine comprising that fuel injector.Summary

[0008] An improved fuel injector for an internal combustion engine comprises a first valve needle arranged to control injection of a first fuel. The first valve needle extends along an injector longitudinal axis. The fuel injector further comprises a first control chamber associated with the first valve needle. The fuel injector further comprises an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis. The actuator assembly comprises a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis. The fuel injector further comprises a header body disposed on the actuator assembly. The header body comprises a bottom surface that at least partially contacts the upper surface of the actuator assembly at a header body-actuator interface. The header body further comprises a return inlet extending through the header body from the header body-actuator interface. The return inlet is disposed in selective fluid communication with the first control chamber, such that the return inlet selectively receives the control fluid from the first control chamber. The fuel injector further comprises a body disposed adjacent to the actuator assembly opposite the header body and axially extending from an upper body face to an opposing lower body face. The body at least partially houses the actuator assembly. The fuel injector further comprises a barrel axially extending from an upper barrel face to an opposing lower barrel face.The barrel comprises an annular outer surface extending between the upper barrel face and the lower barrel face. The upper barrel face of the barrel at least partially contacts the lower body face of the body at a body-barrel interface. The fuel injector further comprises a nozzle disposed adjacent to the barrel opposite the body and at least partially contacting the lower barrel face of the barrel. The fuel injector further comprises a first drain passage disposed in fluid communication with the return inlet of the header body. The first drain passage comprises a first drain inlet arranged to receive the control fluid and a first drain outlet arranged to discharge the control fluid. The first drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the first drain outlet of the first drain passage is disposed below the upper barrel face and on the annular outer surface of the barrel.

[0009] An improved fuel injector for an internal combustion engine comprises a first valve needle arranged to control injection of a first fuel. The first valve needle extends along an injector longitudinal axis. The fuel injector further comprises a first control chamber associated with the first valve needle. The fuel injector further comprises an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis. The actuator assembly comprises a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis. The fuel injector further comprises a header body disposed on the actuator assembly. The header body comprises a bottom surface that at least partially contacts the upper surface of the actuator assembly at a header body-actuator interface. The header body further comprises a return inlet extending through the header body from the header body-actuator interface. The return inlet is disposed in selective fluid communication with the first control chamber, such that the return inlet selectively receives the control fluid from the first control chamber. The header body further comprises a plurality of return passages angularly spaced apart from each other about the actuator longitudinal axis and fluidly communicating with the return inlet above the bottom surface of the header body. Each return passage from the plurality of return passages is inclined to the actuator longitudinal axis and extends downwardly through the header body from the return inlet to the bottom surface. Each return passage is arranged to receive the control fluid from the return inlet.

[0010] An improved fuel injector for an internal combustion engine comprises a first valve needle arranged to control injection of a first fuel. The first valve needle extends along an injector longitudinal axis. The fuel injector further comprises a first control chamber associated with thefirst valve needle. The fuel injector further comprises an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis. The actuator assembly comprises a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis. The fuel injector further comprises a body disposed adjacent to the actuator assembly and axially extending from an upper body face to an opposing lower body face. The body at least partially houses the actuator assembly. The body comprises a first inlet arranged to receive the first fuel within the fuel injector. The fuel injector further comprises a barrel axially extending from an upper barrel face to an opposing lower barrel face. The barrel comprises an annular outer surface extending between the upper barrel face and the lower barrel face. The upper barrel face of the barrel at least partially contacts the lower body face of the body at a body-barrel interface. The fuel injector further comprises a nozzle disposed adjacent to the barrel opposite the body and at least partially contacting the lower barrel face of the barrel. The nozzle comprises a plenum interface arranged to selectively receive the first fuel from the first inlet and a set of first discharge holes disposed in fluid communication with the plenum interface. The fuel injector further comprises a plurality of high-pressure passages extending from the first inlet to the plenum interface. A cross-sectional flow area of each high-pressure passage from the plurality of high- pressure passages either decreases or remains substantially the same along its length from downstream of the first inlet as fluid flows to the plenum interface.Brief Description of the Drawings

[0011] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the apparatus, systems, and methods and, together with the general description above, and the detailed description of the specific embodiments, serve to explain the principles of the apparatus, systems, and methods.

[0012] FIG. 1 is a schematic view of an internal combustion engine, according to an embodiment of the present disclosure;

[0013] FIG. 2 is a side view of a fuel injector of the internal combustion engine of FIG. 1, according to an embodiment of the present disclosure;

[0014] FIG. 3 is a sectional side view of the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0015] FIG. 4 is a partial sectional front view of the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0016] FIG. 5 is a perspective view of an actuator assembly of the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0017] FIG. 6A is a side view of aheader body of the fuel injector of FIG. 2, with some internal parts shown in dotted lines, according to an embodiment of the present disclosure;

[0018] FIG. 6B is a front view of the header body of FIG. 6A, with some internal parts shown in dotted lines, according to an embodiment of the present disclosure;

[0019] FIG. 7A is a partial front view of the header body and the actuator assembly of the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0020] FIG. 7B is a top view of the header body and the actuator assembly of FIG. 7 A, according to an embodiment of the present disclosure;

[0021] FIG. 8 is a top view of a portion of a header body and an actuator assembly of a fuel injector, according to another embodiment of the present disclosure;

[0022] FIG. 9 is a partial sectional side view of a barrel and a body of the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0023] FIG. 10A is a perspective side view of the barrel of FIG. 9, according to an embodiment of the present disclosure;

[0024] FIG. 10B is a front view of the barrel of FIG. 9, according to an embodiment of the present disclosure;

[0025] FIG. 10C is a top view of the barrel of FIG. 9, according to an embodiment of the present disclosure;

[0026] FIG. 11 A is a perspective side view of a lower cap nut, according to an embodiment of the present disclosure;

[0027] FIG. 1 IB is a sectional side view of the lower cap nut of FIG. 11 A, according to an embodiment of the present disclosure;

[0028] FIG. 12A is a perspective side view of a first line in the fuel injector of FIG. 2, according to an embodiment of the present disclosure;

[0029] FIG. 12B is a rear view of the first line of FIG. 12A, according to an embodiment of the present disclosure; and

[0030] FIG. 13 is a graph illustrating a total cross-sectional flow area of the first line of FIG. 12A versus a length of the first line as measured from the first fuel inlet of the fuel injector of FIG. 2, according to an embodiment of the present disclosure.Detailed Description

[0031] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in some embodiments”, “in an exemplary embodiment,” “in exemplary embodiments,” and “in some exemplary embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “in other embodiments,” “another embodiment,” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope of the invention.

[0032] Conditional language, such as "can," "could," or "may," unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and / or steps.

[0033] Referring to FIG. 1, there is shown an internal combustion engine 50, according to an embodiment of the present disclosure. The internal combustion engine 50 can be used for a vehicle, and can also be employed in marine, locomotive, mine haul, power generation, orstationary applications. In other words, the internal combustion engine 50 can be a light-duty engine, a medium-duty engine, a heavy-duty engine or a high horsepower (HHP) engine.

[0034] The internal combustion engine 50 is capable of being fueled by a liquid and / or gaseous fuel. In some embodiments, a gaseous fuel may serve as a main fuel for the internal combustion engine 50 and a liquid fuel may serve as a pilot fuel for the internal combustion engine 50. As used herein, a gaseous fuel is any fuel in the gas state / phase at standard temperature and pressure, which in the context of this application is defined as a temperature of zero (0) degrees Celsius (°C) and an absolute pressure of one hundred (100) kilopascals (kPa).

[0035] The internal combustion engine 50 comprises a cylinder 52. The cylinder 52 defines a cylinder axis CA along its length. The internal combustion engine 50 further comprises a cylinder head 54 disposed on the cylinder 52. The cylinder head 54 covers a top end of the cylinder 52. The internal combustion engine 50 further comprises a piston 56 movable within the cylinder 52. Particularly, the piston 56 is reciprocal within the cylinder 52. The internal combustion engine 50 further comprises a combustion chamber 58 defined by the cylinder 52, the cylinder head 54, and the piston 56.

[0036] The internal combustion engine 50 further comprises a hydraulically actuated fuel injector 100 mountable in the cylinder head 54 for directly introducing fuel into the combustion chamber 58. The fuel injector 100 extends at least partially through the cylinder head 54 into the combustion chamber 58. The fuel injector 100 is adapted to deliver independently the pilot fuel and the main fuel at their respective appropriate timings. In the illustrated embodiment of FIG. 1, the internal combustion engine 50 may operate on two fuels (for example a liquid pilot fuel and a main fuel having a higher auto ignition temperature than the pilot fuel). In other embodiments, the internal combustion engine 50 may employ a hydraulically actuated fuel injector with only a single needle that does not include a bore for a pilot needle, and the fuel injector does not require a pilot actuation mechanism. A hydraulic fluid may be employed as a pilot fuel and a hydraulic fluid inlet may also be employed as a pilot fuel inlet, whereby a match-fit or other passage operates to permit a desired flow rate of pilot fuel into a main fuel plenum. In some embodiments, a pilot fuel may be injected from a separate pilot injector (not shown), or other well-known ignition assist devices such as hot surfaces (e.g. glow plugs), spark plugs and catalytic elements can be employed instead of, or in conjunction with a pilot fuel.

[0037] It should be understood that some conventional elements of the internal combustion engine 50 are not shown for simplicity and clarity purposes. Further, only a cross-section of the internal combustion engine 50 showing the combustion chamber 58 of one cylinder (that is, the cylinder 52) is shown but those skilled in the technology will understand that the internal combustion engine 50 may comprise other components and a plurality of cylinders.

[0038] FIG. 2 is a side view of the fuel injector 100 for the internal combustion engine 50 of FIG. 1, according to an embodiment of the present disclosure. FIG. 3 is a sectional side view of the fuel injector 100. FIG. 4 is a partial sectional front view of the fuel injector 100. Referring to FIGS. 2 to 4, the fuel injector 100 is adapted to inject a first main fuel Fl and a second fuel F2 which is a pilot fuel. The first fuel Fl can be the same fuel or a different fuel from that of the second fuel; and in an exemplary embodiment the first fuel Fl is a gaseous fuel and the second fuel F2 is a liquid fuel. In some embodiments, the liquid fuel is diesel. In some embodiments, the gaseous fuel is hydrogen. In some embodiments, the gaseous fuel is selected from the group consisting of natural gas, hydrogen, propane, ethane, butane, methane, ammonia and mixtures thereof. In some other embodiments, the first fuel Fl may be a liquid fuel such as ethanol or methanol.

[0039] The fuel injector 100 comprises several members stacked on the top of each other and firmly maintained together by two or more cap nuts. The fuel injector 100 extends from a tophead 102 to a nozzle-tip 104 along an injector longitudinal axis LAI. The injector longitudinal axis LAI may overlap the cylinder axis CA (shown in FIG. 1), although this is not a requirement. From the top-head 102 to the nozzle-tip 104, following the arbitrary orientation of FIG. 3, the fuel injector 100 comprises an electrical connector 106, a header body 108, an actuator assembly 110 comprising a first control valve 112 and a second control valve 114, a body 116, a barrel 118, and a nozzle 120. The fuel injector 100 further comprises an upper cap nut 122 and a lower cap nut 124. The upper cap nut 122 couples the header body 108 at shoulder 161 to the body 116, such that the actuator assembly 110 is retained between the header body 108 and the body 116. The upper cap nut 122 is screwed to the body 116. The lower cap nut 124 couples the body 116 to the nozzle 120, such that the barrel 118 is retained between the body 116 and the nozzle 120. The lower cap nut 124 is screwed to the body 116.

[0040] The electrical connector 106 is shaped to receive a complementary connector of a command unit (not shown). The electrical connector 106 is disposed on top of the header body108. The electrical connector 106 comprises electrical pins 126 (shown in FIG. 3) from which electrical leads 128 (shown in FIG. 2) extend and are arranged in a specific bore provided in the header body 108 and in the first and second control valves 112, 114.

[0041] The body 116 comprises a first inlet 130 arranged to receive the first fuel Fl within the fuel injector 100. The nozzle 120 comprises a set of first discharge holes Hl arranged to selectively receive the first fuel Fl from the first inlet 130. The fuel injector 100 accommodates a first line LI (high-pressure passage shown in FIG. 10C) for conveying the first fuel Fl from the first inlet 130 to the nozzle-tip 104 where the first fuel Fl is directly injected into the combustion chamber 58 via the set of first discharge holes Hl . The first line LI comprises a plurality of high- pressure passages Pl, which will be described later in further detail.

[0042] The header body 108 comprises a second inlet 132 arranged to receive the second fuel F2 within the fuel injector 100. The nozzle 120 further comprises a set of second discharge holes H2 arranged to selectively receive the second fuel F2 from the second inlet 132. The fuel injector 100 further accommodates a second line L2 (shown in FIGS. 6 A and 10C) for conveying the second fuel F2 from the second inlet 132 to the nozzle-tip 104 where the second fuel F2 is directly injected into the combustion chamber 58 via the set of second discharge holes H2.

[0043] In some embodiments, each hole H2 of the set of second discharge holes H2 is arranged to align with a corresponding hole Hl of the set of first discharge holes Hl. In some embodiments, each hole H2 of the set of second discharge holes H2 is arranged to discharge the second fuel F2 between two adjacent holes Hl of the set of first discharge holes Hl.

[0044] The fuel injector 100 further comprises first and second valve needles 134, 136 arranged to control injection of the first and second fuels Fl, F2, respectively. In the exemplary embodiment shown in Fig. 3, each of the first and second valve needles 134, 136 extends along the injector longitudinal axis LAI. However, in other embodiments the first and second valve needles 134, 136 may be concentrically arranged off-set from the injector longitudinal axis LAI and / or arranged adjacent to each other. Each of the first and second valve needles 134, 136 is movably received within the nozzle 120. The second valve needle 136 is shown in FIG. 3 concentrically guided in a bore provided inside the first valve needle 134. The first valve needle 134 is a hollow needle adapted to open or close the set of first discharge holes Hl arranged at the nozzle-tip 104 of the fuel injector 100. The second valve needle 136 is a plain needle, or innerneedle, adapted to open or close the set of second discharge holes H2 arranged at the nozzle-tip 104 of the fuel injector 100.

[0045] The fuel injector 100 further comprises first and second control chambers 138, 140 associated with the first and second valve needles 134, 136, respectively. The nozzle 120 defines the second control chamber 140. The fuel injector 100 further comprises a plug 142 arranged at an end of the second valve needle 136 distant from the set of second discharge holes H2. The plug 142 seals the bore enclosing the second valve needle 136. The second control chamber 140 is defined between a top end of the second valve needle 136 and the plug 142. The fuel injector 100 further comprises a second spring 146 disposed between the plug 142 and the second valve needle 136. The second spring 146 biases the second valve needle 136 in a closed position of the set of second discharge holes H2.

[0046] The barrel 118 defines the first control chamber 138. The first control chamber 138 is a cylindrical recess arranged above the first valve needle 134 within the barrel 118. The fuel injector 100 further comprises a first spring 144 disposed between a top face of the first control chamber 138 and the plug 142. The first spring 144 biases the first valve needle 134 in a closed position of the set of first discharge holes Hl.

[0047] FIG. 5 is a perspective view of the actuator assembly 110. Referring to FIGS. 3 to 5, the actuator assembly 110 axially extends from an upper surface 148 to an opposing lower surface 150 along an actuator longitudinal axis LA2. The first control valve 112 comprises a first valve body 152 defining the upper surface 148 of the actuator assembly 110. In other words, the first control valve 112 forms the upper surface 148 of the actuator assembly 110. The first valve body 152 comprises a corresponding assembly of a solenoid (not shown), an armature 1522, and a spool 1524 (best shown in FIG. 4) for functioning of the first control valve 112. The second control valve 114 comprises a second valve body 154 defining the lower surface 150 of the actuator assembly 110. In other words, the second control valve 114 forms the lower surface 150 of the actuator assembly 110. The second valve body 154 comprises a corresponding assembly (not shown for illustrative purposes) of a solenoid, an armature, and a spool for functioning of the second control valve 114.

[0048] The header body 108 is disposed on the actuator assembly 110. The header body 108 comprises a bottom surface 158 that at least partially contacts the upper surface 148 of the actuatorassembly 110 at a header body-actuator interface 160. The body 116 is disposed adjacent to the actuator assembly 110 opposite the header body 108. The body 116 axially extends from an upper body face 166 to an opposing lower body face 168 along the injector longitudinal axis LAI. The body 116 at least partially houses the actuator assembly 110. The body 116 comprises a recess 170 disposed at the upper body face 166 and at least partially receiving the second control valve 114 therein.

[0049] The first control valve 112 of the actuator assembly 110 is arranged to vary the pressure of a control fluid in the first control chamber 138 so as to cause opening and closing movements of the first valve needle 134 along the injector longitudinal axis LAI. In some embodiments, the second fuel F2 is the control fluid. The fuel injector 100 defines a first control path 155 (shown in FIGS. 3 and 10C) to convey the control fluid to the first control chamber 138. When the pressure of the control fluid in the first control chamber 138 drops below a first threshold, the first valve needle 134 is lifted to open the set of first discharge holes Hl. The first control valve 112 may be controlled to vary the pressure of the control fluid in the first control chamber 138 based on application requirements. In some embodiments, the first control valve 112 is a two-way valve, and in other embodiments the first control valve 112 is a three-way valve. In operation, a two- way valve generally results in higher fluid volumes discharged to drain than with a three-way valve since high pressure control fluid continues to supply a control chamber rather than being blocked (as in a three-way valve), albeit in a two-way valve the high pressure control fluid is supplied through a restriction to the control chamber slower than the control fluid exits to drain.

[0050] The second control valve 114 of the actuator assembly 110 is arranged to vary the pressure of the control fluid in the second control chamber 140 so as to cause opening and closing movements of the second valve needle 136 along the injector longitudinal axis LAL The fuel injector 100 defines a second control path 156 (shown in FIG. 10C) to convey the control fluid to the second control chamber 140. When the pressure of the control fluid in the second control chamber 140 drops below a second threshold, the second valve needle 136 is lifted to open the set of second discharge holes H2. The second control valve 114 may be controlled to vary the pressure of the control fluid in the second control chamber 140 based on application requirements. In some embodiments, the second control valve 114 is a three-way valve. For embodiments having the first control valve 112 as a two-way valve and the second control valve 114 as a three-way valve, the first control valve 112 may have a relatively higher volume of fluid to manage.

[0051] FIG. 6A is a side view of the header body 108 of the fuel injector 100 of FIG. 2, with some internal parts shown in dotted lines. FIG. 6B is a front view of the header body 108, with some internal parts shown in dotted lines. FIG. 7A is a partial front view of the header body 108 and the actuator assembly 110. FIG. 7B is a top view of the first control valve 112 of the actuator assembly 110 with a plurality of return passages 164 (drain passages) of the header body 108 overlay ed for reference.

[0052] Referring to FIGS. 3 to 7B, the header body 108 further comprises a return inlet 162 extending through the header body 108 from the header body-actuator interface 160. The return inlet 162 is disposed in selective fluid communication with the first control chamber 138, such that the return inlet 162 selectively receives the control fluid from the first control valve 112 and the first control chamber 138. The return inlet 162 is adapted to receive the control fluid from the first control chamber 138 at least via the first control path 155.

[0053] The header body 108 further comprises the plurality of return passages 164 angularly spaced apart from each other about the actuator longitudinal axis LA2. The plurality of return passages 164 fluidly communicate with the return inlet 162 above the bottom surface 158 of the header body 108. Each return passage 164 from the plurality of return passages 164 is inclined to the actuator longitudinal axis LA2. Each return passage 164 extends downwardly through the header body 108 from the return inlet 162 to the bottom surface 158. Each return passage 164 is arranged to receive the control fluid from the return inlet 162. In some embodiments, the plurality of return passages 164 are approximately evenly radially spaced and angularly separated from each other about the actuator longitudinal axis LA2. In the illustrated embodiment of FIGS. 7A and 7B, the plurality of return passages 164 comprise a pair of return passages 164 angularly separated by approximately 180 degrees. The pair of return passages 164 are therefore disposed diametrically opposite to each other with reference to the actuator longitudinal axis LA2 (best shown in FIG. 7B). Also shown in FIGS. 7A and 7B are first control valve seat 1526, drain orifice feed 1527, and first control valve sealing pad 1528.

[0054] FIG. 8 is a top view of a portion of a header body 108’ and the actuator assembly 110 of a fuel injector 100’ with the return passages 164 of header body 108’ overlayed for reference, according to another embodiment of the present disclosure. The fuel injector 100’ is substantially similar to the fuel injector 100 of FIGS. 3 and 4, with common components being referred to by the same numerals. Further, the header body 108’ of the fuel injector 100’ is substantially similarto the header body 108 shown in FIG. 7B. However, in the header body 108’, the plurality of return passages 164 comprise three return passages angularly separated by approximately 120 degrees. Therefore, referring to FIGS. 7B and 8, the plurality of return passages 164 comprise the pair of return passages 164 angularly separated by approximately 180 degrees, or three return passages 164 angularly separated by approximately 120 degrees. In other embodiments, the plurality of return passages 164 may comprise more than three return passages 164.

[0055] Referring again to FIGS. 3 to 7B, the actuator assembly 110 further comprises a plurality of arcuate protrusions 172 disposed at a perimeter 175 of the upper surface 148 and angularly spaced apart from each other about the actuator longitudinal axis LA2. Each of the plurality of arcuate protrusions 172 contacts the bottom surface 158 of the header body 108, such that an axial gap G1 is formed between the bottom surface 158 of the header body 108 and the upper surface 148 of the first control valve 112 of actuator assembly 110. The axial gap G1 is arranged to receive the control fluid from the plurality of return passages 164.

[0056] The first control valve 112 of the actuator assembly 110 further comprises a plurality of ports 174. Each port 174 from the plurality of ports 174 is defined between a corresponding pair of arcuate protrusions 172 from the plurality of arcuate protrusions 172. Each port 174 is arranged to receive the control fluid from the axial gap Gl. The upper cap nut 122 defines an upper annular space 176 around the actuator assembly 110. The upper annular space 176 is in fluid communication with the plurality of ports 174 of the actuator assembly 110. The upper annular space 176 is arranged to receive the control fluid through the plurality of ports 174. In the illustrated embodiment of FIG. 7B, the plurality of ports 174 comprise six ports 174. In other embodiments, the plurality of ports 174 may comprise four, five, seven, or any other number of ports 174.

[0057] The plurality of return passages 164 allow for a more even distribution of the control fluid across the upper surface 148 of the first control valve 112 and better distributes the control fluid to each port 174. In conventional fuel injectors, the control fluid may not be distributed to each port and may instead discharge towards a single port, thereby choking the single port. In the fuel injector 100, as the plurality of return passages 164 are arranged to distribute the control fluid to each port 174, there is a tower pressure imbalance and reduced pressure reflections caused by the high velocity flow of the control fluid from the return inlet 162 to the plurality of returnpassages 164 to the upper annular space 176 via the plurality of ports 174. In other words, the control fluid flows in an efficient manner from the return inlet 162 to the upper annular space 176.

[0058] Splitting the flow of the control fluid from the return inlet 162 to the plurality of return passages 164 mitigates pressure reflections caused from the uneven distribution of the control fluid as it flows to the upper annular space 176 which in turn provides improved injection timing and fuel quantity thereby improving injector performance. The plurality of return passages 164 also reduces the velocity of the control fluid from the return inlet 162, which in turn leads to efficient distribution of the control fluid across the upper surface 148 of the actuator assembly 110. The reduced velocity of the control fluid further reduces pressure fluctuations caused by the flow of the control fluid from the return inlet 162 to the upper annular space 176. Therefore, there is minimal undesirable back pressure and / or uneven fluid forces acting on the upper surface 148 of the actuator assembly 110, which may otherwise affect opening and closing of the first valve needle 134 and the second valve needle 136 being controlled by the actuator assembly 110. Similarly, the plurality of return passages 164, the plurality of arcuate protrusions 172, and the plurality of ports 174 may also be installed in a hydraulically actuated monofuel or single needle injector and result in substantially similar advantages of improved injector performance particularly for gaseous fuels being injected in an internal combustion chamber at high pressures.

[0059] FIG. 9 is a partial sectional side view of the barrel 118 and the body 116 of the fuel injector 100 of FIG. 2. FIG. 10A is a side view of the barrel 118. FIG. 10B is a front view of the barrel 118. FIG. 10C is atop view of the barrel 118. Referring again to FIGS. 3 to 10C, the barrel 118 axially extends from an upper barrel face 178 to an opposing tower barrel face 180. The upper barrel face 178 of the barrel 118 at least partially contacts the lower body face 168 of the body 116 at a body-barrel interface 182. The barrel 118 comprises an annular outer surface 184 (also shown in FIG. 10 A) extending between the upper barrel face 178 and the lower barrel face 180.

[0060] The nozzle 120 is disposed adj acent to the barrel 118 opposite the body 116 and at least partially contacts the lower barrel face 180 of the barrel 118. The fuel injector 100 further comprises a first drain passage 186a and a second drain passage 186b spaced spart from the first drain passage 186a. The first drain passage 186a is disposed in fluid communication with the return inlet 162 of the header body 108. The first drain passage 186a comprises a first drain inlet 187a (shown in FIG. 3) arranged to receive the control fluid and a first drain outlet 188a (shown in FIG. 9) arranged to discharge the control fluid from the fuel injector 100. The second drainpassage 186b comprises a second drain inlet 187b (shown in FIG. 3) arranged to receive the control fluid from at least the second control chamber 140 and the second control valve 114 and a second drain outlet 188b (shown in FIG. 9) arranged to discharge the control fluid from the fuel injector 100.

[0061] The first drain passage 186a extends through the body 116, crosses the body-barrel interface 182, and extends along the annular outer surface 184 of the barrel 118, such that the first drain outlet 188a of the first drain passage 186a is disposed below the upper barrel face 178 and on the annular outer surface 184 of the barrel 118. The second drain passage 186b extends through the body 116, crosses the body-barrel interface 182, and extends along the annular outer surface 184 of the barrel 118, such that the second drain outlet 188b of the second drain passage 186b is disposed below the upper barrel face 178 and on the annular outer surface 184 of the barrel 118.

[0062] The first drain inlet 187a is formed in the body 116 and disposed in fluid communication with the upper annular space 176. Thus, the first drain inlet 187a receives the control fluid from the upper annular space 176. In the illustrated embodiment of FIGS. 3 and 9, the fuel injector 100 comprises two drain passages (that is, the first drain passage 186a and the second drain passage 186b). However, in some other embodiments, the fuel injector 100 may comprise more than two drain passages, and in other embodiments (such as a monofuel an / or single needle injector), the fuel injector 100 may comprise a single drain passage (that is, the first drain passage 186a).

[0063] In some embodiments, the first drain passage 186a comprises a first drilled passage 190a extending through the body 116 from the upper body face 166 to the lower body face 168. The first drilled passage 190a of the first drain passage 186a forms the first drain inlet 187a at the upper body face 166, such that the first drain inlet 187a is in fluid communication with the upper annular space 176. Thus, the first drilled passage 190a of the first drain passage 186a is arranged to receive the control fluid from the upper annular space 176 via the first drain inlet 187a.

[0064] In some embodiments, the second drain passage 186b may optionally comprise a second drilled passage 190b extending through the body 116 from the upper body face 166 to the lower body face 168. In some embodiments, the second drain inlet 187b is formed in the body 116 and disposed in fluid communication with the upper annular space 176. In which case, the second drilled passage 190b of the second drain passage 186b forms the second drain inlet 187bat the upper body face 166, such that the second drain inlet 187b is in fluid communication with the upper annular space 176. Thus, the second drilled passage 190b of the second drain passage 186b is arranged to receive the control fluid from the upper annular space 176 via the second drain inlet 187b. In other embodiments, the second drain passage 186b extends through the body 116 from the upper body face 166 (at the lower surface 150 of the second control valve 114) to the lower body face 168 and does not fluidly communicate with the upper annular space 176.

[0065] In some embodiments, the first drain passage 186a may extend through the body 116, such that the first drain passage 186a does not cross the body-barrel interface 182. In such a case, the first drain outlet 188a is disposed above the upper barrel face 178. In some embodiments, the second drain passage 186b may extend through the body 116, such that the second drain passage 186b does not cross the body -barrel interface 182. In such a case, the second drain outlet 188b is disposed above the upper barrel face 178.

[0066] In some embodiments, the barrel 118 further comprises a first notch 192a and a second notch 192b spaced apart from the first notch 192a. The first notch 192a forms a portion of the first drain passage 186a in the barrel 118. The first notch 192a extends from the upper barrel face 178 along the annular outer surface 184 of the barrel 118 and forms the first drain outlet 188a below the upper barrel face 178. The first notch 192a is disposed in fluid communication with the first drilled passage 190a of the first drain passage 186a and arranged to receive the control fluid from the first drilled passage 190a at the body-barrel interface 182.

[0067] The second notch 192b forms a portion of the second drain passage 186b in the barrel 118. The second notch 192b extends from the upper barrel face 178 along the annular outer surface 184 of the barrel 118 and forms the second drain outlet 188b below the upper barrel face 178. The second notch 192b is disposed in fluid communication with the second drain passage 186b and arranged to receive the control fluid from the second drain passage 186b at the body-barrel interface 182. As shown in FIG. 10C, in some embodiments, each of the first notch 192a and the second notch 192b has a semi-circular cross-section in a plane perpendicular to the injector longitudinal axis LAI .

[0068] By extending the first drain outlet 188a of the first drain passage 186a and the second drain outlet 188b of the second drain passage 186b below the upper barrel face 178 and on the annular outer surface 184 of the barrel 118, pressure fluctuations and pressure reflections in thefirst drain passage 186a and the second drain passage 186b are reduced in comparison to the conventional injectors where the drain passage extends only up to an upper barrel face. Pressure fluctuations and pressure reflections in the first drain passage 186a and the second drain passage 186b are minimized which could otherwise affect fueling accuracy of the injector 100.

[0069] FIG. 11 A is a perspective side view of the lower cap nut 124. FIG. 1 IB is a sectional side view of the lower cap nut 124. Referring to FIG. 3 and FIGS. 9 to 1 IB, the lower cap nut 124 comprises a first exit hole 194a extending therethrough. The lower cap nut 124 further comprises a second exit hole 194b extending therethrough and angularly spaced apart from the first exit hole 194a about the injector longitudinal axis LAI. The lower cap nut 124 defines a lower annular space 196 (shown in FIG. 9) around the barrel 118. The lower annular space 196 is disposed in fluid communication with each of the first exit hole 194a and the second exit hole 194b.

[0070] Further, the lower annular space 196 is disposed in fluid communication with the first drain outlet 188a and arranged to receive the control fluid from the first drain passage 186a. The first exit hole 194a is arranged to receive the control fluid from the lower annular space 196 and convey the control fluid from the fuel injector 100. The lower annular space 196 is disposed in fluid communication with the second drain outlet 188b and arranged to receive the control fluid from the second drain passage 186b. The second exit hole 194b is arranged to receive the control fluid from the lower annular space 196 and convey the control fluid from the fuel injector 100. In the illustrated embodiment of FIGS. 3, 9, and 11 A, the lower cap nut 124 comprises two exit holes (that is, the first exit hole 194a and the second exit hole 194b). However, in other embodiments, the lower cap nut 124 may comprise more than two exit holes. The control fluid can be returned to a liquid tank via the first exit hole 194a and the second exit hole 194b. Although the first and second exit holes 194a, 194b are shown in alignment with the first and second drain passages 188a, 188b, respectively in FIGS. 3 and 9, this is not a requirement and the first and second exit holes 194a, 194b may be annular spaced as much as 90 degrees from the respective first and second drain passages 188a, 188b.

[0071] In comparison to fuel injectors with a single exit hole for discharge of the control fluid from the fuel injector, the fuel injector 100 with two exit holes (that is, the first exit hole 194a and the second exit hole 194b) formed in the lower cap nut 124 experiences minimal pressure reflections caused from control fluid flow in the first drain passage 186a and the second drain passage 186b thereby improving the consistency of pressure of the control fluid in the first drainpassage 186a and the second drain passage 186b, and maintaining the desired flow rate of the control fluid in the first drain passage 186a and the second drain passage 186b.

[0072] Referring again to FIG. 10C, the fuel injector 100 further comprises a sealing-fluid supply line arranged to seal the plurality of high-pressure passages Pl at least at the body -barrel interface 182, so as to prevent leakage of the first fuel Fl from the plurality of high-pressure passages Pl . The pressure of the liquid sealing fluid should be sufficient so that the leakage of the first fuel Fl from the high-pressure passages Pl is prevented. In some embodiments, the sealingfluid supply line comprises a liquid sealing fluid. In some embodiments, the liquid sealing fluid is the second fuel F2. When the liquid sealing fluid is the second fuel F2, the first fuel Fl (that is, within the high-pressure passages Pl) is pressurized to a pressure slightly less than that of the pressure of the second fuel F2 (that is, the liquid fuel) to prevent leakage of the first fuel past a fluid seal cavity in the fuel injector 100.

[0073] FIG. 12A is a perspective side view of the first line LI in the fuel injector 100 of FIG. 2, according to an embodiment of the present disclosure. FIG. 12B is a rear view of the first line LI. Referring to FIGS. 3, 10C, 12A, and 12B, the nozzle 120 further comprises a plenum interface 198 arranged to selectively receive the first fuel Fl from the first inlet 130. The plenum interface 198 is in fluid communication with the set of first discharge holes HL In other words, the set of first discharge holes Hl receives the first fuel Fl from the plenum interface 198.

[0074] As already mentioned, the fuel injector 100 comprises the plurality of high-pressure passages Pl extending from the first inlet 130 to the plenum interface 198. The first line LI extends from the first (main fuel) inlet 130 in a single short portion that splits to form the plurality of high-pressure passages PL The plurality of high-pressure passages Pl extend at least downwardly through the body 116 and the barrel 118 prior to entering the nozzle 120. In the illustrated embodiment of FIGS. 12A and 12B, the high-pressure first line LI splits into two and then four high-pressure passages PL In other embodiments, the plurality of high-pressure passages Pl may comprise three, five, or any other number of high-pressure passages Pl depending on application requirements and availability of space in the fuel injector 100.

[0075] FIG. 13 is a graph 202 illustrating a total cross-sectional flow area Al of the first line LI shown in FIG. 12A versus a length SI of the high-pressure first (main fuel) line LI as it extends from the high-pressure main fuel inlet 130 (that is, the first inlet 130) to the plenum interface 198.The total cross-sectional flow area Al of the first line LI is the sum of the cross-sectional flow area of each of the plurality of high-pressure passages Pl at a particular segment length SI as measured from the first inlet 130. The length SI is expressed in arbitrary units in the abscissa. The total cross-sectional flow area Al is expressed in arbitrary units in the ordinate.

[0076] In some embodiments, the total cross-sectional flow area Al of the first line LI either decreases or remains substantially the same along its length SI from the first inlet 130 to the plenum interface 198. Moreover, the cross-sectional flow area of each high-pressure passage Pl either decreases or remains substantially the same along its length SI from the first inlet 130 to the plenum interface 198. As shown in FIG. 12A, the cross-sectional flow area of each high-pressure passage Pl progressively decreases in a plurality of steps 200 along its length SI from the first inlet 130 to the plenum interface 198. This results in the total cross-sectional flow area Al of the first line LI remaining substantially constant and then subsequently decreasing in the total cross- sectional flow area Al at steps 200 as the high pressure fuel flows from the high pressure main fuel inlet 130 to the plenum interface 198, illustrated in FIG. 13 moving downstream from the high pressure fuel inlet 130 plotted on the left side of length SI abscissa to the plenum interface 198 plotted on the right side of Length SI abscissa.

[0077] The reduced cross-sectional flow area of each high-pressure passage Pl along its length SI from the first inlet 130 to the plenum interface 198 provides additional space for drain passages (that is, the first drain passage 186a and the second drain passage 186b) to extend below the upper barrel face 178 prior to exiting the barrel 118. The additional space provided by the reduced cross- sectional flow area of each high-pressure passage Pl may also be used to accommodate various fluid passages, such as a fluid passage for supply of additives.

[0078] The reduced cross-sectional flow area of each high-pressure passage Pl, and the reduction of the total cross-sectional flow area Al of the first line LI as the first fuel Fl flows downstream from the first inlet 130 to the plenum interface 198 results in reduced pressure reflections and pressure waves in the fluid passages of the first line LI in the fuel injector 100 during operation. The reduced cross-sectional flow area of each high-pressure passage Pl also allows for higher pressures to be achieved in the first line LI without increasing the size of the fuel injector 100. Therefore, the reduced cross-sectional flow area of each high-pressure passage Pl and the reduction of the total cross-sectional flow area Al of the first line LI as the first fuel Fl flows downstream from the first inlet 130 to the plenum interface 198 provides an improvedperformance of the fuel injector 100 related to injection timings and opening / closing rates of the first valve needle 134 and the second valve needle 136.

[0079] Referring to FIGS. 1 to 13, the fuel injector 100 comprises various features such as the plurality of return passages 164, the plurality of arcuate protrusions 172, the plurality of ports 174, the first drain passage 186a, the second drain passage 186b, the first notch 192a, the second notch 192b, the first exit hole 194a, and the second exit hole 194b. Such features of the fuel injector 100 help reduce pressure fluctuations and pressure reflections in fluid passages (that is, drain passages) and interface regions where injector components are coupled to each other. As pressure fluctuations and pressure reflections are reduced or eliminated, control of fluid pressure within the injector is improved along with timings and opening / closing rates of the first valve needle 134 and the second valve needle 136, leading to more refined timing of fuel injection, effective control of injection events, and minimizing or reducing leakage of fluids from their respective fluid passages within the fuel injector 100. As the quantity and timing of fuels delivered to the combustion chamber 58 impacts the torque output of the internal combustion engine 50, the reduced pressure fluctuations in the drain passages of the fuel injector 100, alone or in combination with the reduced pressure waves in the first line LI provides improved injector performance and a desirable torque output of the internal combustion engine 50. Improved timing of the first fuel Fl and the second fuel F2 injections also leads to improved exhaust emissions from the internal combustion engine 50.

[0080] Alternatively, in some embodiments, the fuel injector 100 may be a monofuel and / or single needle injector adapted to inject fuel from a single fuel passage. For example, in some embodiments, the fuel injector 100 may not comprise the second valve needle 136, and other features associated with the second valve needle 136 (such as the second control chamber 140, the set of second discharge holes H2, the second control valve 114, the second spring 146, and associated passages). In this circumstance, first valve needle 134 is not required to be hollow but can remain so to reduce the mass of the first valve needle.

[0081] While particular elements, embodiments, and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims

What is claimed is:

1. A fuel injector for an internal combustion engine, the fuel injector comprising: a first valve needle arranged to control injection of a first fuel, the first valve needle extending along an injector longitudinal axis; a first control chamber associated with the first valve needle; an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis, the actuator assembly comprising a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis; a header body disposed on the actuator assembly, the header body comprising a bottom surface that at least partially contacts the upper surface of the actuator assembly at a header body-actuator interface and a return inlet extending through the header body from the header body-actuator interface, wherein the return inlet is disposed in selective fluid communication with the first control chamber, such that the return inlet selectively receives the control fluid from the first control chamber; a body disposed adjacent to the actuator assembly opposite the header body and axially extending from an upper body face to an opposing lower body face, the body at least partially housing the actuator assembly; a barrel axially extending from an upper barrel face to an opposing lower barrel face, the barrel comprising an annular outer surface extending between the upper barrel face and the lower barrel face, wherein the upper barrel face of the barrel at least partially contacts the lower body face of the body at a body -barrel interface; a nozzle disposed adj acent to the barrel opposite the body and at least partially contacting the lower barrel face of the barrel; and a first drain passage disposed in fluid communication with the return inlet of the header body, the first drain passage comprising a first drain inlet arranged to receive the control fluid and a first drain outlet arranged to discharge the control fluid, wherein the first drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the first drain outlet of the first drain passage is disposed below the upper barrel face and on the annular outer surface of the barrel.

2. The fuel inj ector of claim 1 , wherein the header body further comprises a plurality of return passages angularly spaced apart from each other about the actuator longitudinal axis and fluidlycommunicating with the return inlet above the bottom surface of the header body, wherein each return passage from the plurality of return passages is inclined to the actuator longitudinal axis and extends downwardly through the header body from the return inlet to the bottom surface, and wherein each return passage is arranged to receive the control fluid from the return inlet.

3. The fuel injector of claim 2, wherein the plurality of return passages are approximately evenly radially spaced and angularly separated from each other about the actuator longitudinal axis.

4. The fuel injector of claim 2, wherein the plurality of return passages comprise a pair of return passages angularly separated by approximately 180 degrees, or three return passages angularly separated by approximately 120 degrees.

5. The fuel injector of claim 2, wherein the actuator assembly further comprises: a plurality of arcuate protrusions disposed at a perimeter of the upper surface and angularly spaced apart from each other about the actuator longitudinal axis, each of the plurality of arcuate protrusions contacting the bottom surface of the header body, such that an axial gap is formed between the bottom surface of the header body and the upper surface of the actuator assembly, wherein the axial gap is arranged to receive the control fluid from the plurality of return passages; and a plurality of ports, wherein each port is defined between a corresponding pair of arcuate protrusions from the plurality of arcuate protrusions and arranged to receive the control fluid from the axial gap.

6. The fuel injector of claim 5, further comprising an upper cap nut coupling the header body to the body, such that the actuator assembly is retained between the header body and the body, wherein the upper cap nut defines an upper annular space around the actuator assembly, the upper annular space being in fluid communication with the plurality of ports of the actuator assembly and arranged to receive the control fluid through the plurality of ports, and wherein the first drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

7. The fuel injector of claim 6, wherein the first drain passage comprises a first drilled passage extending through the body from the upper body face to the lower body face, wherein the first drilled passage of the first drain passage forms the first drain inlet at the upper body face, such that the first drain inlet is in fluid communication with the upper annular space.

8. The fuel injector of claim 7, wherein the barrel further comprises a first notch forming a portion of the first drain passage in the barrel, wherein the first notch extends from the upper barrel face along the annular outer surface of the barrel and forms the first drain outlet below the upper barrel face, and wherein the first notch is disposed in fluid communication with the first drilled passage of the first drain passage and arranged to receive the control fluid from the first drilled passage at the body-barrel interface.

9. The fuel injector of claim 8, further comprising a lower cap nut coupling the body to the nozzle, such that the barrel is retained between the body and the nozzle, wherein the lower cap nut comprises a first exit hole extending therethrough, wherein the lower cap nut defines a lower annular space around the barrel disposed in fluid communication with the first exit hole, the lower annular space being in fluid communication with the first drain outlet and arranged to receive the control fluid from the first drain passage, and wherein the first exit hole is arranged to receive the control fluid from the lower annular space and convey the control fluid from the fuel injector.

10. The fuel injector of claim 9, further comprising: a second valve needle arranged to control injection of a second fuel, the second valve needle extending along the injector longitudinal axis; and a second control chamber associated with the second valve needle; wherein the actuator assembly further comprises a second control valve arranged to vary the pressure of the control fluid in the second control chamber so as to cause opening and closing movements of the second valve needle along the injector longitudinal axis.

11. The fuel injector of claim 10, further comprising a second drain passage spaced apart from the first drain passage, the second drain passage comprising a second drain inlet arranged to receive the control fluid from at least the second control chamber and a second drain outlet arranged to discharge the control fluid, wherein the second drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the second drain outlet is disposed below the upper barrel face and on the annular outer surface of the barrel.

12. The fuel injector of claim 11, wherein the second drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

13. The fuel injector of claim 11, wherein the second drain passage comprises a second drilled passage extending through the body from the upper body face to the lower body face, wherein the second drilled passage of the second drain passage forms the second drain inlet at the upper body face, such that the second drain inlet is in fluid communication with the upper annular space.

14. The fuel injector of claim 11, wherein the barrel further comprises a second notch spaced apart from the first notch and forming a portion of the second drain passage in the barrel, wherein the second notch extends from the upper barrel face along the annular outer surface of the barrel and forms the second drain outlet below the upper barrel face, and wherein the second notch is disposed in fluid communication with second drain passage and arranged to receive the control fluid from the second drain passage at the body-barrel interface.

15. The fuel injector of claim 14, wherein each of the first notch and the second notch has a semi-circular cross-section in a plane perpendicular to the injector longitudinal axis.

16. The fuel injector of claim 14, wherein the lower cap nut comprises a second exit hole extending therethrough and angularly spaced apart from the first exit hole about the injector longitudinal axis, wherein the lower annular space is disposed in fluid communication with the second exit hole and the second drain outlet and arranged to receive the control fluid from the second drain passage, and wherein the second exit hole is arranged to receive the control fluid from the lower annular space and convey the control fluid from the fuel injector.

17. The fuel injector of claim 10, wherein each of the first and second valve needles is movably received within the nozzle.

18. The fuel injector of claim 10, wherein the second valve needle is concentrically guided in a bore provided inside the first valve needle.

19. The fuel injector of claim 10, wherein the nozzle defines the second control chamber.

20. The fuel injector of claim 10, wherein the first control valve forms the upper surface of the actuator assembly, and wherein the second control valve forms the lower surface of the actuator assembly.

21. The fuel injector of claim 10, wherein the body comprises a recess disposed at the upper body face and at least partially receiving the second control valve therein.

22. The fuel injector of claim 10, wherein the header body further comprises a second inlet arranged to receive the second fuel within the fuel injector, and wherein the nozzle further comprises a set of second discharge holes arranged to selectively receive the second fuel from the second inlet.

23. The fuel injector of claim 22, wherein the second fuel is the control fluid.

24. The fuel injector of claim 23, wherein the second fuel is a liquid fuel.

25. The fuel injector of claim 22, wherein the body further comprises a first inlet arranged to receive the first fuel within the fuel injector, and wherein the nozzle further comprises a plenum interface arranged to selectively receive the first fuel from the first inlet and a set of first discharge holes disposed in fluid communication with the plenum interface.

26. The fuel injector of claim 25, further comprising a plurality of high-pressure passages extending from the first inlet to the plenum interface, and wherein a cross-sectional flow area of each high-pressure passage from the plurality of high-pressure passages either decreases or remains substantially the same along its length from the first inlet to the plenum interface.

27. The fuel injector of claim 26, wherein the cross-sectional flow area of each high-pressure passage progressively decreases in a plurality of steps along its length from the first inlet to the plenum interface.

28. The fuel injector of claim 26, further comprising a sealing-fluid supply line arranged to seal the plurality of high-pressure passages at least at the body-barrel interface, so as to prevent leakage of the first fuel from the plurality of high-pressure passages.

29. The fuel injector of claim 28, wherein the sealing-fluid supply line comprises a liquid sealing fluid.

30. The fuel injector of claim 29, wherein the liquid sealing fluid is the second fuel.

31. The fuel injector of claim 25, wherein each hole of the set of second discharge holes is arranged to align with a corresponding hole of the set of first discharge holes.

32. The fuel injector of claim 25, wherein each hole of the set of second discharge holes is arranged to discharge the second fuel between two adj acent holes of the set of first discharge holes.

33. The fuel injector of any preceding claim, wherein the first fuel is a gaseous fuel.

34. The fuel injector of claim 33, wherein the gaseous fuel is hydrogen.

35. The fuel injector of any preceding claim, wherein the barrel defines the first control chamber.

36. A fuel injector for an internal combustion engine, the fuel injector comprising: a first valve needle arranged to control injection of a first fuel, the first valve needle extending along an injector longitudinal axis; a first control chamber associated with the first valve needle; an actuator assembly axially extending from an upper surface to an opposing tower surface along an actuator longitudinal axis, the actuator assembly comprising a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis; and a header body disposed on the actuator assembly, the header body comprising: a bottom surface that at least partially contacts the upper surface of the actuator assembly at a header body-actuator interface; a return inlet extending through the header body from the header body-actuator interface, wherein the return inlet is disposed in selective fluid communication with the first control chamber, such that the return inlet selectively receives the control fluid from the first control chamber; and a plurality of return passages angularly spaced apart from each other about the actuator longitudinal axis and fluidly communicating with the return inlet above the bottom surface of the header body, wherein each return passage from the plurality of return passages is inclined to the actuator longitudinal axis and extends downwardly through the header body from the return inlet to the bottom surface, wherein each return passage is arranged to receive the control fluid from the return inlet.

37. The fuel injector of claim 36, wherein the plurality of return passages are approximately evenly radially spaced and angularly separated from each other about the actuator longitudinal axis.

38. The fuel injector of claim 36, wherein the plurality of return passages comprise a pair of return passages angularly separated by approximately 180 degrees, or three return passages angularly separated by approximately 120 degrees.

39. The fuel injector of claim 36, wherein the actuator assembly further comprises: a plurality of arcuate protrusions disposed at a perimeter of the upper surface and angularly spaced apart from each other about the actuator longitudinal axis, each of the plurality of arcuate protrusions contacting the bottom surface of the header body, such that an axial gap is formed between the bottom surface of the header body and the upper surface of the actuator assembly, wherein the axial gap is arranged to receive the control fluid from the plurality of return passages; and a plurality of ports, wherein each port is defined between a corresponding pair of arcuate protrusions from the plurality of arcuate protrusions and arranged to receive the control fluid from the axial gap.

40. The fuel injector of claim 39, further comprising a first drain passage disposed in fluid communication with the return inlet of the header body, the first drain passage comprising a first drain inlet arranged to receive the control fluid and a first drain outlet arranged to discharge the control fluid.

41. The fuel injector of claim 40, further comprising: a body disposed adjacent to the actuator assembly opposite the header body and axially extending from an upper body face to an opposing lower body face, the body at least partially houses the actuator assembly; a barrel axially extending from an upper barrel face to an opposing lower barrel face, the barrel comprising an annular outer surface extending between the upper barrel face and the lower barrel face, wherein the upper barrel face of the barrel at least partially contacts the lower body face of the body at a body -barrel interface; and a nozzle disposed adj acent to the barrel opposite the body and at least partially contacting the lower barrel face of the barrel;wherein the first drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the first drain outlet of the first drain passage is disposed below the upper barrel face and on the annular outer surface of the barrel.

42. The fuel injector of claim 41, further comprising an upper cap nut coupling the header body to the body, such that the actuator assembly is retained between the header body and the body, wherein the upper cap nut defines an upper annular space around the actuator assembly, the upper annular space being in fluid communication with the plurality of ports of the actuator assembly and arranged to receive the control fluid through the plurality of ports, and wherein the first drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

43. The fuel injector of claim 42, wherein the first drain passage comprises a first drilled passage extending through the body from the upper body face to the lower body face, wherein the first drilled passage of the first drain passage forms the first drain inlet at the upper body face, such that the first drain inlet is in fluid communication with the upper annular space.

44. The fuel injector of claim 43, wherein the barrel further comprises a first notch forming a portion of the first drain passage in the barrel, wherein the first notch extends from the upper barrel face along the annular outer surface of the barrel and forms the first drain outlet below the upper barrel face, and wherein the first notch is disposed in fluid communication with the first drilled passage of the first drain passage and arranged to receive the control fluid from the first drilled passage at the body-barrel interface.

45. The fuel injector of claim 44, further comprising a lower cap nut coupling the body to the nozzle, such that the barrel is retained between the body and the nozzle, wherein the lower cap nut comprises a first exit hole extending therethrough, wherein the lower cap nut defines a lower annular space around the barrel disposed in fluid communication with the first exit hole, the lower annular space being in fluid communication with the first drain outlet and arranged to receive the control fluid from the first drain passage, and wherein the first exit hole is arranged to receive the control fluid from the lower annular space and convey the control fluid from the fuel injector.

46. The fuel injector of claim 45, further comprising: a second valve needle arranged to control injection of a second fuel, the second valve needle extending along the injector longitudinal axis; and a second control chamber associated with the second valve needle;wherein the actuator assembly further comprises a second control valve arranged to vary the pressure of the control fluid in the second control chamber so as to cause opening and closing movements of the second valve needle along the injector longitudinal axis.

47. The fuel injector of claim 46, further comprising a second drain passage spaced apart from the first drain passage, the second drain passage comprising a second drain inlet arranged to receive the control fluid from at least the second control chamber and a second drain outlet arranged to discharge the control fluid, wherein the second drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the second drain outlet is disposed below the upper barrel face and on the annular outer surface of the barrel.

48. The fuel injector of claim 47, wherein the second drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

49. The fuel injector of claim 47, wherein the second drain passage comprises a second drilled passage extending through the body from the upper body face to the lower body face, wherein the second drilled passage of the second drain passage forms the second drain inlet at the upper body face, such that the second drain inlet is in fluid communication with the upper annular space.

50. The fuel injector of claim 47, wherein the barrel further comprises a second notch spaced apart from the first notch and forming a portion of the second drain passage in the barrel, wherein the second notch extends from the upper barrel face along the annular outer surface of the barrel and forms the second drain outlet below the upper barrel face, and wherein the second notch is disposed in fluid communication with the second drain passage and arranged to receive the control fluid from the second drain passage at the body-barrel interface.

51. The fuel injector of claim 50, wherein each of the first notch and the second notch has a semi-circular cross-section in a plane perpendicular to the injector longitudinal axis.

52. The fuel injector of claim 50, wherein the lower cap nut comprises a second exit hole extending therethrough and angularly spaced apart from the first exit hole about the injector longitudinal axis, wherein the lower annular space is disposed in fluid communication with the second exit hole and the second drain outlet and arranged to receive the control fluid from thesecond drain passage, and wherein the second exit hole is arranged to receive the control fluid from the lower annular space and convey the control fluid from the fuel injector.

53. The fuel inj ector of claim 46, wherein each of the first and second valve needles is movably received within the nozzle.

54. The fuel injector of claim 46, wherein the second valve needle is concentrically guided in a bore provided inside the first valve needle.

55. The fuel injector of claim 46, wherein the nozzle defines the second control chamber.

56. The fuel injector of claim 46, wherein the first control valve forms the upper surface of the actuator assembly, and wherein the second control valve forms the lower surface of the actuator assembly.

57. The fuel injector of claim 46, wherein the body comprises a recess disposed at the upper body face and at least partially receiving the second control valve therein.

58. The fuel injector of claim 46, wherein the header body further comprises a second inlet arranged to receive the second fuel within the fuel injector, and wherein the nozzle further comprises a set of second discharge holes arranged to selectively receive the second fuel from the second inlet.

59. The fuel injector of claim 58, wherein the second fuel is the control fluid.

60. The fuel injector of claim 59, wherein the second fuel is a liquid fuel.

61. The fuel injector of claim 58, wherein the body further comprises a first inlet arranged to receive the first fuel within the fuel injector, and wherein the nozzle further comprises a plenum interface arranged to selectively receive the first fuel from the first inlet and a set of first discharge holes disposed in fluid communication with the plenum interface.

62. The fuel injector of claim 61, further comprising a plurality of high-pressure passages extending from the first inlet to the plenum interface, and wherein a cross-sectional flow area ofeach high-pressure passage from the plurality of high-pressure passages either decreases or remains substantially the same along its length from the first inlet to the plenum interface.

63. The fuel injector of claim 62, wherein the cross-sectional flow area of each high-pressure passage progressively decreases in a plurality of steps along its length from the first inlet to the plenum interface.

64. The fuel injector of claim 62, further comprising a sealing-fluid supply line arranged to seal the plurality of high-pressure passages at least at the body-barrel interface, so as to prevent leakage of the first fuel from the plurality of high-pressure passages.

65. The fuel injector of claim 64, wherein the sealing-fluid supply line comprises a liquid sealing fluid.

66. The fuel injector of claim 65, wherein the liquid sealing fluid is the second fuel.

67. The fuel injector of claim 61, wherein each hole of the set of second discharge holes is arranged to align with a corresponding hole of the set of first discharge holes.

68. The fuel injector of claim 61, wherein each hole of the set of second discharge holes is arranged to discharge the second fuel between two adj acent holes of the set of first discharge holes.

69. The fuel injector of any one of claims 36 to 68, wherein the first fuel is a gaseous fuel.

70. The fuel injector of claim 69, wherein the gaseous fuel is hydrogen.

71. The fuel injector of claim 41, wherein the barrel defines the first control chamber.

72. A fuel injector for an internal combustion engine, the fuel injector comprising: a first valve needle arranged to control injection of a first fuel, the first valve needle extending along an injector longitudinal axis; a first control chamber associated with the first valve needle; an actuator assembly axially extending from an upper surface to an opposing lower surface along an actuator longitudinal axis, the actuator assembly comprising a first control valve arranged to vary the pressure of a control fluid in the first control chamber so as to cause opening and closing movements of the first valve needle along the injector longitudinal axis; anda body disposed adjacent to the actuator assembly and axially extending from an upper body face to an opposing lower body face, the body at least partially housing the actuator assembly, the body comprising a first inlet arranged to receive the first fuel within the fuel injector; a barrel axially extending from an upper barrel face to an opposing lower barrel face, the barrel comprising an annular outer surface extending between the upper barrel face and the lower barrel face, wherein the upper barrel face of the barrel at least partially contacts the lower body face of the body at a body -barrel interface; a nozzle disposed adj acent to the barrel opposite the body and at least partially contacting the lower barrel face of the barrel, the nozzle comprising a plenum interface arranged to selectively receive the first fuel from the first inlet and a set of first discharge holes disposed in fluid communication with the plenum interface; and a plurality of high-pressure passages extending from the first inlet to the plenum interface, and wherein a cross-sectional flow area of each high-pressure passage from the plurality of high- pressure passages either decreases or remains substantially the same along its length from the first inlet to the plenum interface.

73. The fuel injector of claim 72, wherein the cross-sectional flow area of each high-pressure passage progressively decreases in a plurality of steps along its length from the first inlet to the plenum interface.

74. The fuel injector of claim 72, further comprising a header body disposed on the actuator assembly, the header body comprising: a bottom surface that at least partially contacts the upper surface of the actuator assembly at a header body-actuator interface; a return inlet extending through the header body from the header body-actuator interface, wherein the return inlet is disposed in selective fluid communication with the first control chamber, such that the return inlet selectively receives the control fluid from the first control chamber; and a plurality of return passages angularly spaced apart from each other about the actuator longitudinal axis and fluidly communicating with the return inlet above the bottom surface of the header body, wherein each return passage from the plurality of return passages is inclined to the actuator longitudinal axis and extends downwardly through the header body from the return inlet to the bottom surface, wherein each return passage is arranged to receive the control fluid from the return inlet.

75. The fuel injector of claim 74, wherein the plurality of return passages are approximately evenly radially spaced and angularly separated from each other about the actuator longitudinal axis.

76. The fuel injector of claim 74, wherein the plurality of return passages comprise a pair of return passages angularly separated by approximately 180 degrees, or three return passages angularly separated by approximately 120 degrees.

77. The fuel injector of claim 74, wherein the actuator assembly further comprises: a plurality of arcuate protrusions disposed at a perimeter of the upper surface and angularly spaced apart from each other about the actuator longitudinal axis, each of the plurality of arcuate protrusions contacting the bottom surface of the header body, such that an axial gap is formed between the bottom surface of the header body and the upper surface of the actuator assembly, wherein the axial gap is arranged to receive the control fluid from the plurality of return passages; and a plurality of ports, wherein each port is defined between a corresponding pair of arcuate protrusions from the plurality of arcuate protrusions and arranged to receive the control fluid from the axial gap.

78. The fuel injector of claim 77, further comprising a first drain passage disposed in fluid communication with the return inlet of the header body, the first drain passage comprising a first drain inlet arranged to receive the control fluid and a first drain outlet arranged to discharge the control fluid, wherein the first drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the first drain outlet of the first drain passage is disposed below the upper barrel face and on the annular outer surface of the barrel.

79. The fuel injector of claim 78, further comprising an upper cap nut coupling the header body to the body, such that the actuator assembly is retained between the header body and the body, wherein the upper cap nut defines an upper annular space around the actuator assembly, the upper annular space being in fluid communication with the plurality of ports of the actuator assembly and arranged to receive the control fluid through the plurality of ports, and wherein the first drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

80. The fuel injector of claim 79, wherein the first drain passage comprises a first drilled passage extending through the body from the upper body face to the lower body face, wherein the first drilled passage of the first drain passage forms the first drain inlet at the upper body face, such that the first drain inlet is in fluid communication with the upper annular space.

81. The fuel injector of claim 80, wherein the barrel further comprises a first notch forming a portion of the first drain passage in the barrel, wherein the first notch extends from the upper barrel face along the annular outer surface of the barrel and forms the first drain outlet below the upper barrel face, and wherein the first notch is disposed in fluid communication with the first drilled passage of the first drain passage and arranged to receive the control fluid from the first drilled passage at the body-barrel interface.

82. The fuel injector of claim 81, further comprising a lower cap nut coupling the body to the nozzle, such that the barrel is retained between the body and the nozzle, wherein the lower cap nut comprises a first exit hole extending therethrough, wherein the lower cap nut defines a lower annular space around the barrel disposed in fluid communication with the first exit hole, the lower annular space being in fluid communication with the first drain outlet and arranged to receive the control fluid from the first drain passage, and wherein the first exit hole is arranged to receive the control fluid from the lower annular space and convey the control fluid from the fuel injector.

83. The fuel injector of claim 82, further comprising: a second valve needle arranged to control injection of a second fuel, the second valve needle extending along the injector longitudinal axis; and a second control chamber associated with the second valve needle; wherein the actuator assembly further comprises a second control valve arranged to vary the pressure of the control fluid in the second control chamber so as to cause opening and closing movements of the second valve needle along the injector longitudinal axis.

84. The fuel injector of claim 83, further comprising a second drain passage spaced apart from the first drain passage, , the second drain passage comprising a second drain inlet arranged to receive the control fluid from at least the second control chamber and a second drain outlet arranged to discharge the control fluid, wherein the second drain passage extends through the body, crosses the body-barrel interface, and extends along the annular outer surface of the barrel, such that the second drain outlet is disposed below the upper barrel face and on the annular outer surface of the barrel.

85. The fuel injector of claim 84, wherein the second drain inlet is formed in the body and disposed in fluid communication with the upper annular space.

86. The fuel injector of claim 85, wherein the second drain passage comprises a second drilled passage extending through the body from the upper body face to the tower body face, wherein the second drilled passage of the second drain passage forms the second drain inlet at the upper body face, such that the second drain inlet is in fluid communication with the upper annular space.

87. The fuel injector of claim 83, wherein the barrel further comprises a second notch spaced apart from the first notch and forming a portion of the second drain passage in the barrel, wherein the second notch extends from the upper barrel face along the annular outer surface of the barrel and forms the second drain outlet below the upper barrel face, and wherein the second notch is disposed in fluid communication with the second drain passage and arranged to receive the control fluid from the second drain passage at the body-barrel interface.

88. The fuel injector of claim 87, wherein each of the first notch and the second notch has a semi-circular cross-section in a plane perpendicular to the injector longitudinal axis.

89. The fuel injector of claim 87, wherein the lower cap nut comprises a second exit hole extending therethrough and angularly spaced apart from the first exit hole about the injector longitudinal axis, wherein the tower annular space is disposed in fluid communication with the second exit hole and the second drain outlet and arranged to receive the control fluid from the second drain passage, and wherein the second exit hole is arranged to receive the control fluid from the tower annular space and convey the control fluid from the fuel injector.

90. The fuel injector of claim 83, wherein each of the first and second valve needles is movably received within the nozzle.

91. The fuel injector of claim 83, wherein the second valve needle is concentrically guided in a bore provided inside the first valve needle.

92. The fuel injector of claim 83, wherein the nozzle defines the second control chamber.

93. The fuel injector of claim 83, wherein the first control valve forms the upper surface of the actuator assembly, and wherein the second control valve forms the tower surface of the actuator assembly.

94. The fuel injector of claim 83, wherein the body comprises a recess disposed at the upper body face and at least partially receiving the second control valve therein.

95. The fuel injector of claim 83, wherein the header body further comprises a second inlet arranged to receive the second fuel within the fuel injector, and wherein the nozzle further comprises a set of second discharge holes arranged to selectively receive the second fuel from the second inlet.

96. The fuel injector of claim 95, wherein the second fuel is the control fluid.

97. The fuel injector of claim 96, wherein the second fuel is a liquid fuel.

98. The fuel injector of claim 95, further comprising a sealing-fluid supply line arranged to seal the plurality of high-pressure passages at least at the body-barrel interface, so as to prevent leakage of the first fuel from the plurality of high-pressure passages.

99. The fuel injector of claim 98, wherein the sealing-fluid supply line comprises a liquid sealing fluid.

100. The fuel injector of claim 99, wherein the liquid sealing fluid is the second fuel.

101. The fuel injector of claim 95, wherein each hole of the set of second discharge holes is arranged to align with a corresponding hole of the set of first discharge holes.

102. The fuel injector of claim 95, wherein each hole of the set of second discharge holes is arranged to discharge the second fuel between two adj acent holes of the set of first discharge holes.

103. The fuel injector of any one of claims 72 to 102, wherein the first fuel is a gaseous fuel.

104. The fuel injector of claim 103, wherein the gaseous fuel is hydrogen.

105. The fuel injector of any one of claims 72 to 104, wherein the barrel defines the first control chamber.

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