Gas injector for an internal combustion engine

Abstract

A gas injector 10 comprising an outwardly-opening pintle 26 having a hollow pintle shaft 28 and a pintle head 30. In the closed state, the pintle head engages a valve seat 24. A magnetic armature 32 is mechanically coupled to the pintle shaft. The injector comprises a proximal flexible sealing means 40 and a distal flexible sealing means 42 which extend between the injector body 12 and pintle shaft. The sealing membranes are axially spaced and are configured to sealingly isolate the axial gas passage from an intermediate portion 44 of the gas injector. The intermediate portion is adapted to contain lubricating fluid. The internal diameter of the distal sealing membrane is larger than the internal diameter of the proximal sealing membrane. A fuel delivery system using the gas injector is also claimed. The use of the gas injector is also claimed.

Description

Technical field The present invention generally relates to a gas injector for injection of gaseous fuel in an internal combustion engine. Background Art For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines. Indeed, emissions from hydrogen internal combustion engines consist mainly of water and do not comprise nearly as much pollutants as those from traditional engines. When designing hydrogen engine components, inspiration is naturally drawn from those of currently available thermal engines, which are typically powered by liquid fuel such as gasoline or diesel. In their simplest form, the fuel delivery systems of such liquid fueled combustion engines typically comprise a liquid fuel tank with a low-pressure pump, a high-pressure pump connected thereto, a fuel rail and a plurality of fuel injectors. However, the components of liquid fueled engines cannot be carelessly used in gaseous fueled internal combustion engines and must instead be adapted to meet specific technical requirements. In particular, when designing gaseous fuel delivery systems, care must be taken to anticipate possible fuel leaks and / or excessive pressure drops, which occur much more frequently with gaseous fuels than with their liquid counterparts. Moreover, gaseous fuels may lack some advantageous properties of liquid fuels such as self-lubrication or squeeze damping properties. Finally, some gaseous fuel such as hydrogen may cause embrittlement of some components, in particular components made from martensitic stainless steels. Technical problem It is an object of the present invention to provide a gas injector suitable for injection of gaseous fuel, which overcomes the aforementioned drawbacks. General Description of the Invention The present invention provides a gas injector for an internal combustion engine as claimed in claim 1. The gas injector extends along an injector axis from a proximal side to a distal side and comprises: an injector body defining a channel extending from a proximal inlet portion to a distal outlet portion having an outlet opening surrounded by a valve seat, an outwardly-opening pintle having a pintle shaft and pintle head, wherein the pintle is movable along the injector axis between a closed position, in which the pintle head engages said outlet valve seat to prevent gas flow through the outlet opening, and an open position, in which the pintle head is distally spaced from the valve seat to enable flow of gas through the outlet opening, a magnetic armature mechanically coupled to the pintle shaft in the direction of the injector axis, a spring arranged to bias the pintle towards its closed position, wherein the pintle shaft comprises a hollow length extending along the injector axis, and the pintle comprises a proximal aperture and a distal aperture, thereby defining an axial gas passage between the inlet portion and the outlet portion, a proximal flexible sealing membrane and a distal flexible sealing membrane extend between the injector body and the pintle shaft, the sealing membranes being axially spaced and configured to sealingly isolate the axial gas passage from an intermediate portion of the gas injector, the intermediate portion at least partially surrounding the pintle shaft and being adapted to contain lubricating fluid, at least one of the armature and the spring being arranged in the intermediate portion. According to the invention, an average internal diameter 02 of the distal sealing membrane is larger than an average internal diameter 01 of the proximal sealing membrane. The inventive gas injector uses sealing membranes of different dimensions -namely the distal sealing membrane being wider than the proximal sealing membrane - to counterbalance the pressure force exerted by the pressurized gas in the injector. As will be discussed in more details below, such configurations of proximal and distal sealing membranes allows optimizing the net force acting on the pintle. It may be noted that the inventors observed that for a sealing membrane having an annular shape, say e.g. for a tubular, cylindrical or conically shaped sealing membrane (with or without corrugations), it is the average internal diameter that is relevant at the design stage. Indeed, the inventor have found that this average internal diameter provides a simple yet accurate estimation of the net projected surface area to consider when computing the effect of pressure on the retention force of the pintle. The ‘average internal diameter’ herein refers to the mean or average internal diameter from one end of the sealing membrane to the other. The average internal diameter of the sealing membranes can be computed by integrating the internal diameter of the sealing membrane over its length, and dividing it by its length. The term diameter is here to be understood as “generalized diameter”, i.e. the sealing membrane may have a transverse cross section of any annular shape, e.g. circular, square, triangular, hexagonal etc... The above design confers further technical advantages. Indeed, first of all, the present injector defines a straight gas passage extending throughout its length. Gas entering the gas passage at the inlet portion exits through the distal aperture near the outlet opening and upstream of the valve seat. A straight gas passage is thus provided, thereby avoiding significant pressure drops as undergone in conventional designs with solid pintle shafts, where the fuel has to flow around the pintle and through the armature and spring. Moreover, the magnetic armature may be arranged in the intermediate portion and submerged in lubricating fluid. In such a case, the closing motion of pintle generates a pressure increase of lubricating fluid on the proximal side of the armature, thereby reducing its speed towards the proximal side. This so called “squeeze damping” reduces the impact speed of the pintle against the valve seat, thereby improving the durability of the pintle head-valve seat contact interface. Furthermore, by submerging the armature and / or the spring in lubricating fluid, unwanted oscillations of moving components are better dampened, thereby preventing resonance from leading to inconsistent injections. Finally, components arranged in the intermediate portion are not in contact with hydrogen and are thus not susceptible to hydrogen embrittlement. The membranes are said to be “flexible” as they are able to deform according to the movement of the pintle in axial direction. The membranes are also, per design, fluid-tight. They can be made of metal or other appropriate material. The membranes are connected to the body or injector shaft in a fluid-tight manner. The connection of the membranes to the injector body or injector shaft may be direct or via an interposed element, in the latter case the interposed element is also connected in a fluid-tight manner to the body or shaft. In embodiments, each sealing membrane is sealingly connected to an outer surface of the pintle shaft and to an inner surface of the injector body, thereby preventing flow of fluid between the inlet, outlet and intermediate portions, and each sealing membrane is expandable and / or elastically deformable in the direction of the injector axis. In embodiments, each sealing membrane has an inner surface and an outer surface, and said inner surface is sealingly connected to the outer surface of the pintle shaft and to the inner surface of the injector body. In embodiments, the sealing membranes are corrugated bellows. The sealing membranes may be made of metal, for example austenitic stainless steel, copper, copper alloy, nickel or nickel alloy. In embodiments, the intermediate portion of the gas injector contains fluid at a pressure lower than 3 bar or at atmospheric pressure. In embodiments, the average internal diameter 02 of the distal sealing membrane, the average internal diameter 01 of the proximal sealing membrane, and the sealing diameter 03 are selected such that 0.3 <I-2- 032 0 2 2 — 012 And preferably this ratio ——— may be between 0.5 and 1. In embodiments, the injector body, pintle shaft, and the distal sealing membrane define an annular plenum chamber on the distal side, and the pintle comprises an intermediate aperture, thereby enabling gas flow between the hollow portion of the pintle shaft and said annular plenum chamber. In embodiments, each sealing membrane is sealingly connected to an outer surface of the pintle shaft and to an inner surface of the injector body, thereby preventing flow of fluid between axial gas passage and the intermediate portion, and each sealing membrane is expandable and / or elastically deformable in the direction of the injector axis. In embodiments, the proximal sealing membrane extends proximally from the proximal aperture of the pintle shaft along the injector axis. In embodiments, the armature is clearance fitted in the injector body, thereby constraining motion of the pintle to the injector axis. In embodiments, the gas injector further comprises a pole piece arranged in the intermediate volume. In embodiments, a sealable orifice is formed in the injector body, the sealable orifice being configured to enable filling of the intermediate portion with lubricant fluid. In embodiments, the pintle head comprises a pin-shaped attachment portion that is fitted inside a distal axial open end of said pintle shaft, thereby closing the latter. In embodiments, the pintle head comprises a comprises a tubular attachment portion and the distal end of the pintle shaft is engaged inside or around said tubular attachment portion. In embodiments, the distal aperture is arranged in the pintle shaft upstream of the tubular attachment portion, or the distal aperture is arranged at the level of the tubular attachment and extends through the pintle shaft and tubular attachment. In embodiments, the gas injector further comprises a solenoid arranged to generate, when energized, a magnetic field that distally attracts said magnetic armature. The invention further provides a fuel delivery system comprising a fuel tank configured to store pressurized fuel (gas fuel in gaseous or liquefied state), and a fuel rail fluidly coupled to at least one gas injector as described above. In embodiments, the fuel delivery systems further comprises pressure regulating means configured to decrease the pressure of fuel flow therethrough, wherein the pressure regulating means is serially connected between the fuel tank and the fuel rail. The present invention has been developed in the context of optimizing hydrogen combustion engines, it is applicable to other gaseous fuels, e.g. CNG, gaseous greenfuel or biofuel, etc. The gas injector may further be used for the injection of compressed air. Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a cross sectional view of an embodiment of the inventive gas injector; Fig. 2 is a schematic view of a gaseous fuel delivery system comprising the inventive gas injector; Figs. 3a-d are principle views of alternative configurations of the pintle. Description of Preferred Embodiments Figure 1 shows a first embodiment of the gas injector 10 according to the present invention. The gas injector 10 is adapted to inject a gaseous fuel, in particular hydrogen (H2) or natural gas (CH4), into a combustion chamber of an internal combustion engine (not shown). The term “gaseous fuel” generally includes combustible fluids which are in their gaseous state when exposed to nominal operating conditions of the injector and the engine, e.g. pressure and temperature. Regarding more specifically hydrogen as gaseous fuel for an ICE, it typically consists of a gas with at least 90% hydrogen (H2), preferably pure hydrogen with no more than 2% impurities. In other applications, such as in engines with a precombustion chamber, the present gas injector 10 can also be used to inject pressurized (dry) air into the combustion chamber. The gas injector 10 is mostly symmetrical about an injector axis A and comprises an injector body 12, which may be made of one or several pieces. The injector 10 includes an inlet portion 14 on a proximal side P and an outlet portion 18 on a distal side D, where an outlet opening 22 is surrounded by a valve seat 24. The inlet portion 14 is typically fluidly coupled (directly or via pipe) to a fuel rail 106 at the proximal side P for supply of pressurized gaseous fuel to the gas injector 10. When installed on the engine, the injector body portion with the outlet portion 18, i.e. lower body 12.b, is arranged in a bore in the cylinder head, which opens into a combustion chamber (not shown) of the engine. The injector body 12 defines a channel 20, which extends along injector axis A from the inlet portion 14 to the outlet portion 18. The channel 20 forms an internal, elongate cavity that extends throughout the injector body 12, from an inlet opening 21 to the outlet opening 22. Depending on the design, the channel 20 may comprise sections of different shapes or cross-sections along its length. Where the body is made of several pieces, they are assembled together in a fluid-tight manner. The valve seat 24 defines an annular surface that faces outwardly, i.e. away from the channel 20, and which may typically be a conical surface. A pintle 26 is axially movable between closed and open positions to control flow of gaseous fuel through the outlet opening 22. The pintle 26 comprises a pintle shaft 28, which extends along the injector axis A and is moveably received inside channel 20, and a pintle head 30, which radially protrudes from the pintle shaft 28 at the distal end thereof. Pintle head 30 forms a valve member (or plug) that is adapted to cooperate with the valve seat 24. When the pintle 26 is in its closed position (as shown in Fig. 1), the pintle head 30 engages the valve seat 24, thereby preventing gas flow through the outlet opening 22. Conversely, when the pintle 26 is in its open position (not shown), the pintle head 30 is distally spaced from the valve seat 24, thereby enabling fuel flow through the outlet opening 22. It may be noted that the pintle head 30 is located downstream (in gas flow direction) of the valve seat 24 and the pintle 26 opens in flow direction; hence the gas injector 10 is said to open outwardly. Reference sign 36 designates a solenoid coil that cooperates with a magnetic armature 32 (typically an annular piece made of magnetic steel) to actuate the pintle 26. The armature 32 is mechanically coupled to the pintle shaft 28, such that it moves therewith in the direction of the injector axis A. In embodiments, the armature 32 is fixedly attached to the pintle shaft 28, e.g. by welding (as is the case here), press-fit, screwing, or through form combination. Hence, the pintle shaft 28 extends from the pintle head 30 up to the armature 32, and in the presented embodiment extends proximally beyond the armature 32. A core spring 34 surrounding the pintle shaft 28 is arranged to bias the pintle 26 towards its closed position. In the embodiment of Fig. 1, the core spring 34 is arranged distally from a pintle perch 29 (radial protrusion), with its proximal end engaging the latter and its distal end engaging a shoulder of the injector body 12. Other spring configurations can be considered. In use, to perform an injection event where gas is discharged through the outlet opening 22, the solenoid 36 is energized to create a magnetic field that attracts the armature 32 in the distal direction and causes the pintle 26 to move distally in an open position, when the force due to the magnetic field overcomes the spring force. Reference sign 38 designates a pole piece arranged distally from the armature 32 to enhance and shape the magnetic field. To guide the magnetic field, a nonmagnetic ring may be incorporated in the main body; alternatively, the wall thickness of the armature body 12 can be locally reduced to form a so-called shunt. The pintle shaft 28 comprises a hollow length 28.1 extending from proximal side P to the distal side D. The pintle 26 further comprises a proximal aperture 26.1 and a distal aperture 26.2. As will be understood, the pintle shaft 28 defines an axial gas passage that enables to convey gas from the inlet portion 14 to the outlet portion 18. In this embodiment, the pintle shaft 28 is realized as a straight tube having a proximal axial open end which forms the proximal aperture 26.1, and an opposite distal axial closed end. The distal aperture 26.2 is laterally or radially arranged, here about the distal end of the pintle shaft 28. The distal aperture 26.2 may be formed by a single hole or by a plurality of holes in the peripheral wall of the pintle shaft 28 proximal to the pintle head 30. The size and number of the holes may depend on the application. When the pintle 26 is moved distally, a flow passage is opened between the pintle head 30 and valve seat 24, through which gaseous fuel is discharged. The present injector 10 thus provides a design with a straight gas passage extending throughout the injector length. Gas entering the gas passage at the inlet portion 14 exits through the distal aperture 26.2 near the outlet opening 22 and upstream of the valve seat 24. A straight gas passage is thus provided, thereby avoiding significant pressure drops as undergone in conventional designs with solid pintle shafts, where the fuel has to flow around the pintle and through the armature and spring. At the top of the pintle shaft 28, i.e. at the proximal side P, gaseous fuel enters through the axially located proximal aperture 26.1. On the distal side D, the gas exists the pintle shaft 28 via aperture 26.2 upstream of the valve seat 24. The valve seat 24 surrounds the outlet opening 22, such that when the pintle 26 is in the closed position, flow through the outlet opening 22 is prevented, and an inner volume 18.1 of the outlet portion 18 defines a plenum chamber in fluid communication with the inner volume 28.1 of the hollow pintle shaft 28. Conversely, when the pintle 26 is in the open position, the chamber 18.1 is open and pressurized gaseous fuel is discharged in the engine’s combustion chamber. It will be appreciated that the gas injector 10 further comprises a proximal and a distal sealing membrane 40, 42, which are elastically deformable along the injector axis A. The sealing membranes 40, 42 have a generally tubular shape, with one end sealingly connected to an outer surface of the pintle shaft 28 and the opposite end sealingly connected to an inner surface of the injector body 12. The membranes have fluid-tight walls and are connected in a fluid-tight manner at both ends. In the embodiment of figure 1, each sealing membrane 40, 42 has the form of a bellow sealingly welded at one end to the pintle shaft 28 and at the other end to the injector body 12. Each sealing membrane 40, 42 ensures low-friction, fluid-tight sealing between the injector body 12 and the pintle shaft 28. The proximal and distal sealing membranes 40, 42 thus sealingly isolate the inlet portion 14 and the outlet portion 18 from an intermediate portion 44, within which the core spring 34, pintle perch 29, armature 32 and pole piece 38 are advantageously arranged. In other words, gaseous fuel flowing through the injector 10 never enters the intermediate portion 44, and instead flows along the axial gas passage from the inlet portion 14 through the inner volume 28.1 of the pintle shaft 28 and the distal aperture 26.2, to the inner volume 18.1 of the outlet portion 18. Hence, none of the gas flowing through the injector 10 flows around the armature 32, pole piece 38 and core spring 34, which are normally regions of the flow where high pressure drops tend to occur. Moreover, as the intermediate portion 44 is sealingly isolated from the axial gas passage, its volume may be filled with a lubricating fluid. Said lubricating fluid is typically a liquid having advantageous lubricating and squeeze damping properties, such as a low viscosity synthetic oil with appropriate doping additives. In the shown embodiment, the bellows are provided with fixing rings at both ends, indicated 40.1 and 42.1, i.e. the bellow is fixed in a gas-tight manner (e.g. welding) to the fixing ring, and in turn fixedly and sealably connected to the pintle shaft or body. The inventors have found that configurations of proximal and distal sealing membranes 40,42 can be improved to optimize the net force acting on the pintle 26. Indeed, the intermediate portion 44 is sealingly isolated from the axial gas passage and contains lubricating fluid at a pressure considerably lower than the gas present in the latter. This difference in pressure biases the pintle in a direction depending on the average internal diameters 01, 02 of the proximal and the distal sealing membranes 40, 42. More specifically a force F = (Paas-Pfiuid)*^*Wl2-022] is exerted on the pintle by this difference in pressure, where Pgas is the pressure of the gaseous fuel in the axial gas passage, Pfiuid is the pressure of the lubricating fluid in the intermediate portion 44, 01 is the average internal diameter of the proximal sealing membrane 40, and 02 is the average internal diameter of the distal sealing membrane 42. As mentioned above, the average internal diameter provides a simple yet accurate estimation of the net projected surface area to consider when computing the effect of pressure on the retention force of the pintle. As apparent from Fig. 1, using a distal sealing membrane 42 of larger diameter increases the transversal surface surrounding the pintle shaft 28. In the shown variant, this additional / increased surface is a portion of the distal surface of attachment ring 42.1, and corresponds to the annular surface -noted SAd- between the dashed lines 01 and 02. The net retention force acting on the pintle 26 can then be defined as F = CSL - Pgas 4 * 032 - (Pgas - Pfluid) * | * (012 - 022) where CSL is the core spring load of the spring 34, 03 is the sealing diameter on the valve seat 24, and -Pgas * * 032 corresponds to the pressure of the gaseous fuel acting on the pintle head 30. The in-cylinder pressure is here ignored (low when the injector opens) but could be taken into account. Conventionally, the sealing diameter 03 corresponds to the diameter of the contact line between the valve seat 24 and pintle head 30. The surface of the pintle head within that diameter is exposed to the gas pressure inside the passage 20. The above equation may be rewritten as F = CSL - Pgas * * (032 + 012 - 022) - Pfluid * | * (012 - 022) Whilst the pintle remain in its closed position, both CSL and Pfiuid (012 - 022) are constant, but Pgas may vary. In other words, the retention force depends on the gaseous fuel pressure. This results in variations of the retention force on the pintle 26, which may cause undesired injector behaviours. More specifically, when large variations of the retention force are possible, the core spring load must be high to ensure that the retention force is always large enough to ensure proper sealing at the nominal pressure for the gaseous fuel. However, high core spring load and retention force may result in spring failure and valve seat wear, as the impact speed of the pintle head 30 on the valve seat 24 during a closing motion of the injector 10 increases accordingly. By selecting 01 and 02 such that 012 <022, it is possible to decrease variations of the net retention force. In a preferred embodiment 022 - 012 = 032, resulting in a perfectly pressure-balanced injector, wherein the retention force is constant and independent from the gaseous fuel pressure in the gas passage. Advantages of a decrease in variations of the net retention force includes: enabling a reduction of spring load, thereby reducing valve seat wear and risk of spring failure, enabling an increase of the working pressure range for the gaseous fuel, thereby improving flow capability, decreasing the required solenoid force, thereby decreasing the required drive power, enabling an increase of the sealing diameter 03 to increase the flow rate or reduce the pintle stroke, etc. In embodiments, the lubricating fluid in the intermediate portion 44 is at atmospheric pressure, i.e. Pfiuid = 0. The average internal diameter of each sealing membranes 40, 42 can be computed by integrating the internal diameter of the sealing membrane (i.e. the diameter of the sealing membrane on its surface exposed to gas pressure) over its length, and dividing it by its length. Preferably, 01 and 02 are selected such that 022-012 1.2 >— ....................> 0.3 032 More preferably, this ratio may be between 0.5 and 1. In this embodiment, the proximal sealing membrane 40 is welded at one end to the pintle shaft, extends proximally from the proximal aperture 26.1 of the pintle shaft 28 along the injector axis A, and is welded at the other end to the injector body 12 near the inlet. Hence the axial gas passage between the inlet portion 14 and the outlet portion 18 is defined by both the proximal sealing membrane 40 and the hollow pintle shaft 28. Alternatively, the pintle shaft 28 could extend higher up proximally, and the proximal sealing membrane 40 could axially overlap with the pintle shaft 28. Likewise, the distal sealing membrane 42 is welded at one end to the pintle perch, and at its other end to the injector body. On the proximal side, axial guiding of the pintle 26 may be achieved by a controlled annular clearance between armature 32 and injector body 12, or between the pintle shaft 28 and the pole piece 38. On the distal side, axial guiding of the pintle 26 may be achieved by a controlled annular clearance between pintle shaft 28 and injector body 12, at the level of radial protrusion 47. As can be observed, the injector body 12, pintle shaft 28 and the distal sealing membrane 42 define an annular chamber 46 on the distal side. An intermediate aperture 26.3 is formed on the pintle shaft 28 to enable fluid communication between the hollow portion 28.1 of the pintle shaft 28 and said annular chamber 46, thereby preventing local variations of gas pressure during motion of the pintle 26. The injector body 12 is typically made of metallic material, in particular steel or stainless steel. As core spring 34 is immersed in lubricants, it is not susceptible to hydrogen embrittlement and can thus be made of conventional martensitic stainless steels. In other words, only the sealing membranes 40, 42, the valve seat 24 and the pintle 26 are in direct contact with hydrogen. These components could thus be made of austenitic stainless steels, thereby reducing the risk of hydrogen embrittlement. The sealing membranes 40 can be made of metal, preferably austenitic stainless steel, copper (alloy), nickel (alloy); however, these should not be construed as limiting and other appropriate materials may be employed. The valve seat 24 can be made integral with the injector body 12 or can be a prefabricated piece securely fixed thereon in a gas-tight manner, e.g. by welding, as shown on figure 1. Likewise, the pintle head 30 can be made integral with the pintle shaft 28 or can be a pre-fabricated piece securely fixed thereon, e.g. by interference fit, welding, etc. When the clearance between the armature 32 and the injector body 12 is low, the armature 32 divides the intermediate portion 44 in a proximal sub-portion and a distal sub-portion. The armature 32 may then comprises an axial through-hole (not represented), to promote flow of lubricating fluid between said proximal sub-portion and said distal sub-portion. The armature 32 and / or the injector body 12 may define a plenum chamber when the pintle is in its closed position. The volume of said plenum chamber decreases during the closing motion of the pintle, resulting in a pressure increase on the proximal side of the armature. A sealable orifice 48 is formed in the injector body 12 to enable filling of the intermediate portion (44) with lubricant fluid. Figure 2 shows a schematic view of a gaseous fuel delivery system 100 comprising a fuel tank 102, a pressure regulator 104 (e.g. electronic), and a fuel rail 106 coupled (directly or indirectly) to a plurality of inventive gas injectors 10 as described above. The pressure regulator 104 is serially connected between the gaseous fuel tank 102 and the fuel rail 106 by means of piping 108. The pressure regulator 104 is configured to decreases the flow pressure upstream thereof to a nominal working pressure range, e.g. around 5 to 40 bar. The gaseous fuel tank 102 is configured to store pressurized fuel at pressures of up to 700 bars, which may be in a liquid or a gaseous state. Within the tank 102, the fuel is typically gaseous, but could also be liquefied and discharged in gaseous form into line 108. In general, the gaseous fuel tank 102 includes an associated mechanical pressure reducer to discharge gaseous fuel at a pressure between 25 and 50 bar into line 108. 5 Turning to Figs 3a-3d, possible alternative embodiments of the pintle design are shown, with different configurations for the distal aperture 26.2. Specifically, the pintle shaft 28 may be inserted in a blind bore formed in the pintle head 30, as shown on figure 3a-c. The distal aperture 26.2 may be formed through both the pintle shaft 28 and the pintle head 30, as shown on figure 3b, the recess may be formed 10 exclusively through the pintle head 30, as shown on figure 3c, and the pintle head 30 may comprise a through-hole surrounding a filled portion of the pintle shaft 28, the filled portion being distal to the distal opening 26.2 and preventing flow through the pintle head 30.

Claims

1. A gas injector (10) for an internal combustion engine, extending along an injector axis (A) from a proximal side (P) to a distal side (D) and comprising:an injector body (12) defining a channel (20) extending from a proximal inlet portion (14) to a distal outlet portion (18) having an outlet opening (22) surrounded by a valve seat (24);an outwardly-opening pintle (26) having a pintle shaft (28) and pintle head (30);wherein the pintle (26) is movable along the injector axis (A) between a closed position, in which the pintle head (30) engages said outlet valve seat (24) to prevent gas flow through the outlet opening (22), and an open position, in which the pintle head (30) is distally spaced from the valve seat (24) to enable flow of gas through the outlet opening (22);a magnetic armature (32) mechanically coupled to said pintle shaft (28) in the direction of the injector axis (A);a spring (34) arranged to bias said pintle (26) towards its closed position;wherein the pintle shaft (28) comprises a hollow length (28.1) extending along the injector axis, and the pintle comprises a proximal aperture (26.1) and a distal aperture (26.2), thereby defining an axial gas passage between the inlet portion (14) and the outlet portion (18);a proximal flexible sealing membrane (40) and a distal flexible sealing membrane (42) extend between the injector body (12) and the pintle shaft (28), the sealing membranes (40, 42) being axially spaced and configured to sealingly isolate the axial gas passage from an intermediate portion (44) of the gas injector (10),the intermediate portion (44) at least partially surrounding the pintle shaft (28) and being adapted to contain lubricating fluid,at least one of said armature (32) and said spring (34) being arranged in said intermediate portion;characterized in that an average internal diameter 02 of the distal sealing membrane (42) is larger than an average internal diameter 01 of the proximal sealing membrane (40).

2. The gas injector (10) according to any of the preceding claims, wherein the intermediate portion (44) of the gas injector (10) contains fluid at a pressure lower than 3 bar, preferably about atmospheric pressure.

3. The gas injector (10) according to any of the preceding claims, wherein the average internal diameter 02 of the distal sealing membrane (42), the average internal diameter 01 of the proximal sealing membrane (40), and the sealing diameter 03 are selected such that 0.3 <1-2-4. The gas injector (10) according to any of the preceding claims, wherein the injector body (12), pintle shaft (28), and the distal sealing membrane (42) define an annular plenum chamber (46) on the distal side, and wherein the pintle (26) comprises an intermediate aperture (26.3), thereby enabling gas flow between the hollow portion (28.1) of the pintle shaft (28) and said annular plenum chamber (46).

5. The gas injector (10) according to any of the preceding claims, wherein each sealing membrane (40, 42) is sealingly connected to an outer surface of the pintle shaft (28) and to an inner surface of the injector body (12), thereby preventing flow of fluid between axial gas passage and the intermediate portion (44); andwherein each sealing membrane (40, 42) is expandable and / or elastically deformable in the direction of the injector axis (A).

6. The gas injector (10) according to any of the preceding claims, wherein the proximal sealing membrane (40) extends proximally from the proximal aperture (26.1) of the pintle shaft (28) along the injector axis (A).

7. The gas injector (10) according to any of the preceding claims wherein the sealing membranes (40, 42) are corrugated bellows.

8. The gas injector (10) according to any of the preceding claims wherein the sealing membranes (40, 42) are made of metal, preferably austenitic stainless steel, copper, copper alloy, nickel or nickel alloy.

9. The gas injector (10) according to any of the preceding claims, wherein each sealing membrane (40, 42) has an inner surface and an outer surface, and wherein said inner surface is sealingly connected to the outer surface of the pintle shaft (28) and to the inner surface of the injector body (12).

10. The gas injector (10) according to any of the preceding claims, wherein the armature (32) is clearance fitted in the injector body (12), thereby constraining motion of the pintle (26) to the injector axis (A).

11. The gas injector (10) according to any of the preceding claims, further comprising a pole piece (38) arranged in the intermediate volume (44).

12. The gas injector (10) according to any of the preceding claims, wherein a sealable orifice (48) is formed in the injector body (12), the sealable orifice (48) being configured to enable filling of the intermediate portion (44) with lubricant fluid.

13. The gas injector (10) according to any of the preceding claims, wherein the pintle head (30) comprises a pin-shaped attachment portion that is fitted inside a distal axial open end of said pintle shaft (28), thereby closing the latter.

14. The gas injector (10) according to claim 13, wherein the pintle head (30) comprises a comprises a tubular attachment portion and the distal end of the pintle shaft (28) is engaged inside or around said tubular attachment portion.

15. The gas injector (10) according to claim 14, wherein the distal aperture (26.2) is arranged in the pintle shaft (28) upstream of the tubular attachment portion; or the distal aperture (26.2) is arranged at the level of the tubular attachment and extends through the pintle shaft (28) and tubular attachment.

16. The gas injector (10) according to any of the preceding claims, further comprising a solenoid arranged to generate, when energized, a magnetic field that distally attracts said magnetic armature.

17. Fuel delivery system (100) comprising a fuel tank (102) configured to store pressurized fuel, and a fuel rail (106) fluidly coupled to at least one gas injector (10) according to any of the preceding claims.

18. Fuel delivery system (100) according to claim 17, further comprising pressure regulating means (104) configured to decrease the pressure of fuel flow therethrough, wherein the pressure regulating means (104) is serially connected between the fuel tank (102) and the fuel rail (106).

19. Use of the gas injector as claims in any one of claims 1 to 16 for the injection of gaseous fuel or compressed air.

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