Gas injector with nozzle portion

Abstract

A nozzle portion (24, fig 1) for a gas / hydrogen injector (10, fig 1) comprises a nozzle body 26 having a central passage 14 along a central axis (A, fig 1) extending between a gas inlet and outlet; a

Description

Technical field The present invention generally relates to injection systems for internal combustion engines operating with gaseous fuels, and more specifically to injector nozzle arrangements for gas / hydrogen injectors. Background Art Fuel injectors are well known in association with internal combustion engines. They are used to inject fuel into a combustion chamber of the engine. Such fuel injectors generally comprise a nozzle body connected to an injector body. A fuel delivery passage extends from a fuel pump through the injector body to a nozzle cavity arranged in the nozzle body. The nozzle body has at least one nozzle orifice so that fuel can be injected from the nozzle cavity into the combustion chamber. A pintle is slidable in an axial central bore arranged in the nozzle body. The pintle comprises a pintle head configured to cooperate with a valve seat around the nozzle orifice to prohibit fuel flow through the nozzle orifice. The pintle is biased in closing direction by a spring. A solenoid actuator generates a magnetic field that permits actuating the valve pintle, so as to open or close the nozzle orifice to either allow or prohibit fuel flow into the combustion chamber. The nozzle body has an upper contact surface, which is pressed against a lower contact surface of the injector body. In the context of the development of hydrogen combustion engines, the technology on conventional fuel injectors (gasoline or diesel) is adapted for injection of gaseous fuel. A common issue with prior art nozzles designs is that the valve seat is susceptible to wear, in particular due to the lack of hydraulic damping compared to liquid fuel. Indeed, failure mode analyses have shown the presence of scratches on the valve seat, mainly distributed around the inner periphery of the valve seat. These scratches can in turn enable fuel to leak through them, which is of course to be avoided. This is of particular relevance for hydrogen injectors, as molecules of hydrogen are much smaller in size than molecules of traditional fuels. Hydrogen fuel is thus capable of flowing in much narrower gaps, and hydrogen injector nozzles need to be sealed tighter and more securely than traditional fuel injector nozzles accordingly. Furthermore, components of hydrogen injectors such as the valve seat need to be durable enough to prevent the formation of scratches through which hydrogen could leak. The difficulty in designing performant hydrogen injectors lies in balancing the properties of their components in a way that meets all the design requirements. Indeed, while modifying a specific property of a component may improve the performance of the design in one way, it may also significantly lower the performance in another way. For example, an increase in sealing pressure leads to a tighter seal of hydrogen, but also correlates with an increase in stress under impact load, which could lower the durability of the valve seat or the pintle head and lead to leaks. Technical problem It is thus an object of the present invention to provide an injector nozzle design with an improved pintle head to valve seat sealing contact geometry that increases the durability of the valve seat. General Description of the Invention The present invention relates to a nozzle portion for a gas injector comprising: a nozzle body extending along a central axis, the nozzle body having a central passage along the central axis extending between a proximal gas inlet and an opposite nozzle tip with a gas outlet; a valve seat at the nozzle tip surrounding the central passage, the valve seat having an edge junction with the central passage and a conical annular valve seat surface extending outwardly from the edge junction, the central passage having a diameter Di at said edge junction, the annular valve seat surface being conical with an aperture angle Av; a pintle having a pintle shaft and a pintle head, the pintle being reciprocally moveable in the central passage between a closed position in which the pintle rests on the valve seat to close gas flow therethrough and an open position raised from the valve seat to allow gas discharge from the nozzle tip; wherein the pintle head has a seat-facing side with an annular sealing surface comprised between an inner annular surface and outer annular surface, the annular sealing surface defining, in a closed position of the pintle, a sealing diameter Ds with the valve seat surface; wherein the annular sealing surface of said pintle head has a predetermined curvature radius Rs; wherein the valve seat surface and the seat-facing side of the pintle head are configured such as to form, in closed position, an annular gap that tapers from the edge junction towards the sealing diameter Ds; wherein the annular gap is such that a distance, referred to as gap opening (g), corresponding to the axial length between the edge junction and its axial projection on the seat-facing side of said pintle, is at least 5 pm. The present invention provides a nozzle portion with an improved design at the pintle I valve seat interface. Research by the present inventors has established that it is desirable to have an annular gap of controlled geometry to avoid intense wear. Indeed, the inventors have found that whereas a cone / sphere geometry is desirable, the distance between the pintle sealing surface and the facing edge at the seat periphery, herein referred to as gap opening g, is a relevant parameter. Indeed, increasing the gap opening also implies increasing the length of the valve seat surface between the edge junction and the sealing diameters. This has two main benefits: the larger sealing surface ensures that the pintle will always close in a defined area, away from the edge junction; and the controlled taper angle creates some spacing between the pintle sealing surface and edge junction, which avoids contact between the pintle and edge, thereby avoiding overstress and wear. Advantageously, the injector nozzle portion according to the invention is less susceptible to wear and fatigue, guarantees sufficient contact pressure between the pintle head and the valve seat to seal hydrogen in the injector nozzle, and keeps the head loss in the tapered gap within acceptable range. In the following, embodiments of the invention are disclosed which are considered particularly efficient to achieve the above-mentioned benefits. In embodiments, the difference between said sealing diameter Ds and said diameter Di at said edge junction is greater than 0.20, preferably greater than 5 0.32 times the sine of Av / 2, and smaller than 1.67, preferably smaller than 1.44, more preferably smaller than 0.84, still more preferably smaller than 0.72 times the sine of Av / 2. These designs provide a selection of the two diameters of interest, which control the length of the surface on which the pintle head lands, thereby improving the contact interface between pintle head and valve seat. 10 In embodiments, the curvature radius Rs of the annular sealing surface of said seat facing side of said pintle is comprised between 1 and 2 mm, preferably between 1 and 1.8 mm. CO In embodiments, the annular sealing surface of the seat facing side of the pintle extends beyond the axial projection of the edge junction on the seat-facing side 15 of the pintle. In embodiments, the annular sealing surface of said seat facing side of said pintle has a cone aperture Ai greater than 132° at its junction with the inner annular surface, preferably of at least 140°. In embodiments, wherein the annular sealing surface of said seat facing side of 20 said pintle has a cone aperture Ao smaller than 108° at its junction with the outer annular surface, preferably not more than 100°. In embodiments, the valve seat is configured such that the conical annular valve seat surface faces towards the distal end and said pintle head presses proximally onto said annular valve seat surface in closed position. 25 In embodiments, the sealing diameter Ds lies between 3.88 mm and 5.97 mm. In embodiments, the distance between said sealing diameter Ds and said edge junction along the valve seat surface is greater than 0.104 mm, preferably greater than 0.162 mm, and smaller than 0.831 mm, preferably smaller than 0.716 mm, more preferably smaller than 0.416 mm, still more preferably smaller than 30 0.358 mm. In embodiments, the diameter Di at the edge junction is greater than 3.6 mm and smaller than 5.35 mm. In embodiments, the difference between said sealing diameter Ds and said diameter Di at said edge junction is greater than 0.18 mm, preferably greater than 0.28 mm, and is smaller than 1.44 mm, preferably smaller than 1.24 mm, more preferably smaller than 0.72 mm, still more preferably smaller than 0.62 mm. For example, the difference between Ds and Di may be equal to 0.28 mm, 0.62 mm, 0.72 mm, or 1.24 mm. Preferably, the central passage comprises at its distal end a cylindrical end section that connects with said valve seat at said edge junction. In embodiments, the gap opening is at least 8 pm, preferably over 10 pm. The conical annular valve seat may have a cone angle Av between 5 and 175°, preferably between 90 and 150°, more preferably between 110 and 130°. The invention further provides an injector for gaseous fuel comprising a nozzle portion according to any one of the designs detailed above, and a solenoid actuator configured to selectively actuate the pintle Brief Description of the Drawings Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein: Fig. 1 is a longitudinal cross section view of a gaseous fuel injector according to an embodiment of the invention; Fig. 2 is an enlarged view of detail X shown on figure 1; Fig. 3 is an enlarged view of selection Y in figure 2; Fig. 4 is principle drawing of the pintle head and valve seat interface in Fig.3; Fig. 5 is a principle drawing of the pintle head and valve seat interface according to a comparative design not forming part of the invention; Fig. 6 is a graph representing the theoretical sealing contact pressure for the interface designs of Figs 4 and 5; Fig. 7 is a graph representing the theoretical stresses under impact load for the interface designs of Figs 4 and 5. Detailed Description of the Drawings Figure 1 schematically shows a gas injector 10 including an embodiment of the present nozzle portion. The gas injector 10 is designed for injection of gaseous fuel, in particular hydrogen. The injector 10 comprises an injector housing 12 extending along a longitudinal axis A. The injector housing 12 has an axial cavity that defines a central passage 14 for gaseous fuel extending from a proximal end (inlet side of the injector) to an opposite distal end D (discharge end). At the proximal side P, only shown in part, a fitting (not shown) is provided for fluid connection to a gas supply pipe (not shown). The fitting connects with the central passage 14 and a filter (not shown) may be arranged in the inlet section. The injector 10 includes an actuator portion 16 located on the proximal side P. The actuator portion 16 includes a slidably arranged actuating shaft 18. The actuating shaft 18 is hollow and open ended, such that gas may flow through it. The actuating shaft 18 is integral with a magnetic armature 20, which extends radially therefrom. Reference sign 22 designates a solenoid coil which, when energized, creates a magnetic field that attracts the armature 20 in the direction of the distal side D (i.e. downwards the Figure) and hence moves the actuating shaft 18 in opening direction, as will be discussed below. Below the actuating shaft 18 is the nozzle portion 24, where a nozzle body 26 forms the distal section of the injector housing 12. At its end, or tip, the nozzle body 26 comprises a valve seat 28 that surrounds the central passage 14. The open end of the central passage 14 at the valve seat is referred as nozzle orifice 29 and forms the gas outlet of the nozzle / injector. A pintle 30 is slidably arranged in the central passage 14 relative to the nozzle body 26. The pintle 22 comprises a pintle head 32 configured to cooperate with the valve seat 28 to stop or allow the discharge of gas at the injector tip. The pintle 30 further comprises a pintle shaft 34 and a pintle perch 36 (protruding annular collar). A compression spring 38 is arranged between the nozzle body 26 and the pintle perch 36 to bias the pintle head 32 towards the proximal end P: This is the closed position (shown in Fig. 1), in which the pintle head 32 rests on the valve seat 28 thereby obturating flow through the central passage 14 downstream of the valve seat 28. Conversely, the actuating shaft 18 is configured to transfer force towards the distal end D to the pintle 30 so as to lift the pintle head 32 from valve seat 28 and thus allow gas to be discharged at the nozzle tip. Hence, when the engine control unit connected to the injector 10 triggers an injection event, the solenoid 22 is energized and the actuating shaft 18 and the pintle 30 are moved towards the distal end D, whereby the pintle head 32 is moved away from the valve seat 28, thereby unsealing the nozzle orifice 29 and discharging gas in the engine. Then, when the solenoid is deenergized, the pintle 30 is forced towards the proximal end P by spring 38 and the pintle head 32 is snapped back against the valve seat 28, thereby sealing the nozzle orifice 29. Figure 2 shows an enlarged view of detail X in Figure 1. In particular, the pintle head 32 and the valve seat 28 of the nozzle orifice 29 are visible. Figure 3 further shows an enlarged view of detail Y of Figure 2. As can be seen, the central passage 14 ends connects with the outwardly extending valve seat 28 at the nozzle orifice 29 via an edge junction 40. The valve seat 28 is here a conical surface of aperture angle Av that defines a corresponding annular valve seat surface (hence also designated 28). Angle Av may in general be comprised between 5 and 175°. Injector 10 is designed as an outwardly opening injector, whereby valve seat 28 faces away from the proximal end, in the direction of gas discharge. The pintle head 32 in contrast has a seat-facing side 42 with an annular sealing surface 44 having a predetermined radius of curvature Rs and arc length Ls. The annular sealing surface 44 is comprised between an inner annular surface 46 and outer annular surface 48. The inner annular surface 46 is tangent to the inward end of the annular sealing surface 44 and defines a conical surface with aperture angle Ai. The outer annular surface 48 is tangent to the outward end of the annular sealing surface 44 and defines a conical surface with aperture angle Ao. The cone angle of the valve seat 28, the cone angle of the inner annular surface 46 and the cone angle of the outer annular surface 48 are indicated with respect to the central axis A and thus respectively noted Av / 2, Ai / 2 and Ao / 2. In the closed position, the pintle head’s annular sealing surface 44 is pressed against the valve seat surface 28; they contact each other according to a circular contact line, in a gas sealed manner. This circular contact line has a predetermined diameter, referred to as Ds - sealing diameter. It may be noted that both the pintle and the nozzle body are typically made of metal, e.g. stainless steel. The sealing line is thus achieved by a metal to metal seal. A high contact pressure is required to provide a hydrogen seal, which is achieved by the return spring and the value of Rs. In the context of hydrogen injection, with operating pressures ranging up to 50 bar, in consideration of hydraulic and spring forces, it is desirable that the sealing diameter Ds is positioned at a controlled distance from the central passage. In particular, it is desirable that the difference between the sealing diameter Ds and said diameter Di at the edge junction 40 is greater than 0.20*sin(Av / 2) and smaller than 1.67*sin(Av / 2). Figure 4 is a principle drawing representing the interface between pintle head 32 and valve seat 28 in closed position. The same reference signs are used as in Figs 1-3. The diameters Di and Ds are indicated relative to longitudinal axis A and hence noted as Di / 2 and Ds / 2. The cone angle of the valve seat 28 is indicated with respect to the central axis A and thus noted Av / 2. One will recognize the end section of the central passage 14, which is here cylindrical. The central passage 14 ends with nozzle orifice 29 at its distal end, where it is surrounded by valve seat 28. The cylindrical central passage 14 and the conical valve seat 28 are discontinuous and form an edge junction 40. The pintle head 32 is here only represented by an arc corresponding to the annular sealing surface 44 of curvature radius Rs. As can be seen, the valve seat surface 28 and the seat-facing side 42 of said pintle head 32 are configured such as to form, in closed position, a tapering annular gap 50 that decreases from the edge junction 40 towards the sealing diameter Ds. Reference sign g designates the gap opening, i.e. the distance corresponding to the axial length between the edge junction 40 and its axial projection on the seatfacing side of the pintle. To improve the interface durability, the gap is preferably at least 5 pm, more preferably at least 8 pm or over 10 pm. The relevance of this parameter is explained in the following. The distance Lv between the edge junction 40 and the seal diameter Ds along the peripheral wall of the valve seat 28 depends on the valve seat angle, the sealing diameter Ds and the diameter Di at edge junction 40. The gap g between the pintle head 32 and the edge junction 40 along line A’ (parallel to the axis A and hence to the axis of motion of the pintle X) can be determined from the distance Lv along the peripheral wall of the valve seat 28, the valve seat angle Av and curvature radius Rs of the pintle annular sealing surface 44. It may be noted that in this embodiment the annular sealing surface 44 extends beyond projection of the edge junction on the pintle along axis A’. That is, the annular sealing surface 44 extends inwardly beyond projection axis A’. In other words, the annular sealing surface 44 connects with inner annular surface 46 at a diameter smaller than Di. <Preferred Parameters> Preferably, the valve seat has an aperture angle Av comprised between 110° and 130°, in particular 119°, 120° or 121 °. The pintle sealing surface 44 may have a curvature radius Rs comprised between 1 mm and 1.8 mm. The nozzle orifice diameter Di at edge junction 40 may be comprised between 3.6 mm and 5.35 mm. The seal diameter Ds may be comprised between 3.88 mm and 5.97 mm. With these parameters, Lv may be comprised between 0.104 mm and 0.831 mm and the gap opening g is greater than 5 pm and even 8 or 10 pm and above. Furthermore, as it will be clear from the discussion below, nozzle arrangements having such a configuration increase the contact pressure between the pintle head and the valve seat. The hydrogen sealing capabilities of injectors having such nozzle arrangement is therefore improved. <Example A> An exemplary embodiment is described in the following. The valve seat has an angle Av=119°. The pintle sealing surface 44 has a curvature radius Rs=1 mm. The nozzle orifice diameter at edge junction 40 is Di=3.62 mm. The seal diameter is Ds=3.9 mm With these parameters, Lv=0.162 mm and the gap opening g=14.1 pm. <Comparative example B> In order to better illustrate the effects of the invention, Fig.5 shows an alternative interface design (not forming part of the invention) where the central channel ends with a chamfer (conical section) before the edge junction. For ease of description, same reference signs are used as in Fig.4, with addition of the chamfer 52. The valve seat has an angle Av=120°. The pintle sealing surface 44 has a curvature radius Rs=2 mm. The nozzle orifice diameter at edge junction 40 is Di=3.9 mm. The seal diameter is Ds=4.0 mm With these parameters, Lv=0.057 mm and the gap opening g=0.9 pm. Figure 6 is a graph of the theoretical sealing contact pressure for the interfaces of Figs.4 and 5 measured at 41 bar. The probability density is plotted vs. sealing max contact pressure (1: inventive design of Fig.4; 2: comparative design of Fig.5). Comparison between the two plots shows that the minimum sealing pressure of design A is 7% greater than the minimum sealing pressure of comparative design B. The difference in sealing pressures is most likely due to the difference between the radii of the quasi-spherical portions of the pintle heads of the embodiments of Fig. 4 and 5. Fig. 8 is a graph representing the theoretical stresses under impact load for the interfaces of Fig. 4 and 5. Comparison between the two plots shows that the 5 stress under impact load of the design according to inventive example A is 12% greater than the stress under impact load of the comparative design B, but remains lower than 50% of the elastic limit. This difference is again most likely due to the difference in radii of the quasi-spherical portions of the pintle heads of the embodiments of Fig. 4 and 5. 10 Therefore, another advantage of the design according to the invention is to increase the sealing contact pressure, i.e. the tightness of the seal, whilst keeping the stress under impact load within safety range.

Claims

1. Nozzle portion (24) for a gas injector (10) comprising:a nozzle body (26) extending along a central axis (A), said nozzle body (26) having a central passage (14) along the central axis (A) extending between a 5 proximal gas inlet and an opposite nozzle tip with a gas outlet;a valve seat (28) at said nozzle tip surrounding said central passage (14), the valve seat (28) having an edge junction (40) with the central passage (14) and a conical annular valve seat surface (28) extending outwardly from the edge junction (40), the central passage (14) having a diameter Di at said edge 10 junction (40), the annular valve seat surface (28) being conical with an aperture angle Av;a pintle (30) having a pintle shaft (34) and a pintle head (32), the pintle (30) CO being reciprocally moveable in said central passage (14) between a closedCM position in which the pintle (30) rests on the valve seat (28) to close gas flow15 therethrough and an open position raised from said valve seat (28) to allow 1 gas discharge from the nozzle tip;wherein the pintle head (32) has a seat-facing side (42) with an annular sealing surface (44) comprised between an inner annular surface (46) and outer annular surface (48), said annular sealing surface (44) defining, in a 20 closed position of said pintle (30), a sealing diameter Ds with the valve seat surface (28);wherein said annular sealing surface (44) of said pintle head (32) has a predetermined curvature radius Rs;wherein said valve seat surface (28) and said seat-facing side (42) of said 25 pintle head (32) are configured such as to form, in closed position, an annular gap (50) that tapers from said edge junction (40) towards said sealing diameter Ds;wherein said annular gap (50) is such that a distance, referred to as gap opening (g), corresponding to the axial length between the edge junction (40) 30 and its axial projection on the seat-facing side (42) of said pintle (30) is at least 5 pm.

2. The nozzle portion (24) according to claim 1, wherein the difference between said sealing diameter Ds and said diameter Di at said edge junction (40) is greater than 0.20, preferably greater than 0.32 times the sine of Av / 2, and smaller than 1.67, preferably smaller than 1.44, more preferably smaller than5 0.84, still more preferably smaller than 0.72 times the sine of Av / 2.

3. The nozzle portion (24) according to claim 1 or 2, wherein the curvature radius Rs of said annular sealing surface (44) of said seat facing side (42) of said pintle (30) is comprised between 1 and 2 mm, preferably between 1 and 1.8 mm.10 4. The nozzle portion (24) according to claim 1, 2 or 3, wherein the annularsealing surface (44) of said seat facing side (42) of said pintle (30) extends beyond the axial projection of the edge junction (40) on said seat-facing side (42) of said pintle (30).co(XJ 5. The nozzle portion (24) according to any of the preceding claims, wherein the15 annular sealing surface (44) of said seat facing side (42) of said pintle (30) i— has a cone aperture Ai greater than 132° at its junction with the inner annularsurface (46), preferably of at least 140°.

6. The nozzle portion (24) according to any of the preceding claims, wherein the annular sealing surface (44) of said seat facing side (42) of said pintle (30)20 has a cone aperture Ao smaller than 108° at its junction with the outer annular surface (48), preferably not more than 100°.

7. The nozzle portion (24) according to any of the preceding claims, wherein said valve seat (28) is configured such that the conical annular valve seat surface (28) faces towards the distal end and said pintle head (32) presses 25 proximally onto said annular valve seat surface (28) in closed position.

8. The nozzle portion (24) according to any one of the preceding claims, wherein the sealing diameter Ds lies between 3.88 mm and 5.97 mm.

9. The nozzle portion (24) according to any of the preceding claims, wherein the distance between said sealing diameter Ds and said edge junction (40) along 30 the valve seat surface (28) is greater than 0.104 mm, preferably greater than 0.162 mm, and smaller than 0.831 mm, preferably smaller than 0.716 mm,29 11 23more preferably smaller than 0.416 mm, still more preferably smaller than 0.358 mm.

10. The nozzle portion (24) according to any of the preceding claims, wherein said diameter Di at said edge junction (40) is greater than 3.6 mm and smaller 5 than 5.35 mm.

11. The nozzle portion (24) according to any one of the preceding claims, wherein the difference between said sealing diameter Ds and said diameter Di at said edge junction (40) is greater than 0.18 mm, preferably greater than 0.28 mm, and is smaller than 1.44 mm, preferably smaller than 1.24 mm, more10 preferably smaller than 0.72 mm, still more preferably smaller than 0.62 mm.

12. The nozzle portion (24) according to any one of the preceding claims, the central passage (14) comprises at its distal end a cylindrical end section that connects with said valve seat (28) at said edge junction (40).

13. The nozzle portion (24) according to any one of the preceding claims, wherein 15 the gap opening (g) is at least 8 pm, preferably over 10 pm.

14. The nozzle portion (24) according to any one of the preceding claims, wherein the conical annular valve seat (28) may have a cone angle Av between 5 and 175°, preferably between 90 and 150°, more preferably between 110 and 130°.20 15. An injector (10) for gaseous fuel comprising a nozzle portion (24) accordingto any one of the preceding claims and a solenoid actuator (22) configured to selectively actuate said pintle (30).

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