Fuel rail assembly

Abstract

A gaseous fuel delivery system 10 for an internal combustion engine (70, Fig.5) comprises a fuel rail 12 and a lubricant supply system 30. The fuel rail includes a supply port 11 for connection to a p

Description

Technical field The present invention generally relates to a fuel rail assembly for gaseous fuel engine. More specifically to a fuel rail assembly with a lubricant supply system which may be easily purged. Background Art For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines since the emissions from a hydrogen engine consist mainly of water. However, the usage of “dry” hydrogen, i.e., without any additional lubricant, may create a wear risk on the components of the engine system. All moving components in the system, e.g., pressure regulators, injectors etc., are prone to wear. Similar problems arise with internal combustion engines that uses other types of gaseous fuel, e.g., natural gas or mixtures of hydrocarbon and hydrogen. Specifically, the service life and operational reliability of fuel injectors used with gaseous fuels may be seriously affected. The lack of lubrication is even more problematic for fuel injectors mounted for direct fuel injection, as they face higher temperatures, resulting in excessive wear, mainly at the pintle / seat interface of the injector nozzle. It has been proposed to provide a lubrication system that releases a liquid lubricant into a fuel-supply system upstream of the fuel injector or into the fuel injector itself. However, such lubricant release faces various challenges. Specifically, it is desirable to precisely control the amount of lubricant and to avoid any over-lubrication of the injector, which could lead to sticking of the movable injector components. In a prior design, a fuel rail assembly for gaseous fuel engine comprises a lubricant supply system with lubricant dozers. Current lubricant supply system with such dozers cannot be easily purged, which may result in air bubbles trapped around various components, thereby negatively affecting the performance of the lubricant supply system. Technical problem It is an object of the present invention to provide a fuel rail assembly with a lubricant supply system which may be easily purged. General Description of the Invention This object is achieved by a fuel delivery system as claimed in claim 1. The invention relates to a fuel delivery system for a gaseous fuel internal combustion engine, comprising a fuel rail and a lubricant supply system, wherein the fuel rail includes a supply port for connection to a pressurized gaseous fuel source and a plurality of outlet ports for coupling with a corresponding plurality of fuel injectors, wherein the lubricant supply system comprises a plurality of lubricant dozers configured to release lubricant in respective gaseous fuel streams at each outlet port of the fuel rail, or downstream thereof, wherein each lubricant dozer includes a pumping chamber communicating with a lubricant outlet port, a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a release process, an inlet port from which lubricant is fed to the pumping chamber, and a control port where lubricant may be applied to actuate the pumping plunger, wherein the lubricant supply system comprises a supply piping, which is connected to the inlet port of each lubricant dozer, and a control piping, which is connected to the control port of each lubricant dozer. According to the invention the lubricant supply system comprises a purging path configured to purge air out of the lubricant dozers. Indeed, whereas the use of lubricant dozers with pumping plunger is considered an viable solution to discharge minute amounts of lubricant into the gaseous fuel stream close to fuel injectors, it has been found that such systems may suffer from from the presence of bubbles that develop and require purging. The invention hence proposes advantageous techniques to allow purging of such fuel delivery system with integrated lubricant supply system. In embodiments, the system further comprises a purging module, the purging module having a first and a second port, wherein the first and second ports are in fluid communication via a purging channel. The purging module is arranged such that the first port is in fluid communication with the supply piping, and the second port is in fluid communication with the control piping, such that the purging path is defined by the purging channel of the purging module. The purging channel may comprise a calibrated orifice. In particular, the calibrated orifice may be at least partially defined by a calibration screw, which is at least partially inserted in the purging channel of the purging module. In embodiments, the lubricant dozer comprises a sealing ring arranged around the pumping plunger to reduce flow between the inlet port and the control port. As will be discussed in more detail below, the use of a purging module is of particular interest where the lubricant dozers are equipped with a piston sealing ring for improved pumping performance. The purging module corresponds to one way of providing a purging path. An alternative way is to provide the purging path by defining a clearance around the pumping plunger. In embodiments, the clearance around the pumping plunger may be comprised between 60 and 110 pm (radial clearance). In embodiments, the supply piping serially connects the inlet ports of a plurality of lubricant dozers and / or the control piping serially connects the control ports of a plurality of lubricant dozers. In embodiments, the lubricant-supply system comprises a pressure source adapted to increase pressure in the supply piping and decrease pressure in the control piping to introduce lubricant through the inlet port of a lubricant dozer into its pumping chamber, and to decrease pressure in the supply piping and increase pressure in the control piping to eject lubricant from the pumping chamber of a lubricant dozer through its outlet port during the release process. Advantageously, the purging path is provided at the last dozer in the series, opposite a pressure source end of the supply and control piping. In embodiments, the dozers, or a sub-set thereof, are serially connected with supply piping and control piping, wherein the dozers each comprise a sealing ring arranged around the pumping plunger to reduce flow between the inlet port and the control port, except the last dozer in the series, opposite a pressure source end of the supply and control piping, where the purging path is defined by a clearance around the pumping plunger. That is, the purging path may be advantageously arranged at last dozer of a section of dozers connected, preferably serially. By last dozer is meant the last dozer in connecting order, opposite to the piping end that is close to the pressurized lubricant source. In some variants, e.g. for 3- or 4-cylinder and up to 6-cylinder engines engines, the common supply and control pipings extend serially through all dozers, and the purging path is provided at the last dozer, opposite the piping end connected to the pressurized lubricant source. In some variants, e.g. in the case of 6 cylinders in line, the dozers can be connected as sub-sections of 3 dozers. The common supply and control pipings extend serially through all dozers, but the connection ports in the supply and control pipings to the pressurized lubricant source is provided in the middle, in between the 3rd and 4th dozer. In such case, a purging path is provided at each end, i.e. on the 1st and 6th dozer. In embodiments, the lubricant dozer comprises a dozer body with a dozer cavity in which the pumping plunger is movable along a plunger axis between a proximal position and a distal position such that a volume of the pumping chamber, which is partially defined by a distal portion of the pumping plunger, is greater in the proximal position than in the distal position, and the outlet port communicates with the pumping chamber through an outlet valve. In embodiments, the dozer cavity comprises a control chamber on a proximal side of the pumping plunger, the control chamber communicating with the control port. The dozer cavity further comprises an intermediate chamber in which an intermediate portion of the pumping plunger is disposed, the intermediate chamber communicating with the inlet port. The pumping plunger moves towards the distal position when pressure in the control chamber exceeds pressure in the intermediate chamber. The pumping plunger moves towards the proximal position when pressure in the intermediate chamber exceeds pressure in the control chamber. In embodiments, the clearance around the pumping plunger is defined by a clearance between the pumping plunger and the dozer cavity, and wherein the clearance enables restricted flow of fluid from the intermediate chamber to the control chamber. In embodiments, a gaseous fuel tank is connected to the inlet of the fuel rail, and a gaseous fuel injector coupled to each outlet of the fuel rail. In embodiments, each lubricant dozer of the lubricant supply system is configured to release lubricant at an inlet of a gaseous fuel injector. In embodiments, the fuel rail outlet ports are defined by injector sockets integrated to the rail, which are configured for direct coupling of the injectors to the fuel rail. In embodiments, the lubricant dozers are mounted to the respective injector sockets to release lubricant in the gaseous fuel stream entering the fuel injector. According to another aspect, the invention relates to a fuel rail assembly as used in the fuel delivery system according to the first aspect. The fuel rail has a supply port for connection to a fuel source and a plurality of sockets for coupling with a corresponding plurality of fuel injectors; wherein a plurality of dozers configured to release lubricant at each socket of the fuel rail. Each lubricant dozer includes a pumping chamber communicating with a lubricant outlet port, a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a release process, an inlet port from which low-pressure lubricant is fed to the pumping chamber, and a control port where high-pressure lubricant may be applied to actuate the pumping plunger. A supply piping is serially connected to the inlet port of each lubricant dozer, and a control piping, is serially connected to the control port of each lubricant dozer. The fuel rail assembly comprises a purging path configured to purge air out of the lubricant dozer. Features and details described herein and pertaining to the fuel rail are likewise applicable to this fuel rail assembly. Brief Description of the Drawings Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig.1 is a perspective view of parts of an inventive fuel rail assembly; Fig.2 is a sectional view of a lubricant dozer and an injector unit of the fuel rail assembly from fig. 1; Fig.3 is a sectional view the lubricant dozer from fig.2 in a first state; Fig.4 is a sectional view the lubricant dozer from fig.2 in a second state; Fig.5 is a schematic view of the fuel rail assembly from fig. 1. and an engine; Fig.6 is a sectional view of another lubricant dozer in a first state; Fig.7 is a sectional view of the lubricant dozer of fig.6 in a second state; Fig.8 is a perspective view of another inventive fuel rail assembly; Fig.9 is a side view of the fuel rail assembly from fig.8; Fig. 10 is a view from the direction X in fig.9; Fig. 11 is a sectional view along the plane XI-XI in fig. 10; Fig. 12 is a sectional view along the plane XII-XII in fig.9; Fig. 13 is a sectional view corresponding to fig. 12 with parts of the lubricant dozer removed; Fig. 14 is a sectional view corresponding to fig. 13 showing another embodiment of an inventive fuel rail assembly; Fig. 15 is a sectional view of a purging module and a lubricant dozer; and Fig. 16 is a perspective view of a purging module and a lubricant dozer. Description of Preferred Embodiments Fig. 1 shows a perspective view of parts of an inventive fuel rail assembly 5 for a gaseous-fuel engine 70, while fig. 5 is a schematic representation of the fuel rail assembly 5 and the engine 70. The fuel rail assembly 5 comprises a fuel-supply system 10, which is adapted to supply a gaseous fuel, in this case hydrogen fuel, to the engine 70, which is only shown schematically in Fig.5. It comprises a plurality of cylinders (not shown), each of which can receive fuel from fuel injectors 20 of the fuel-supply system. In other words, there is one fuel injector 20 for each cylinder, in this case a total of four. Each fuel injector 20 is connected to a fuel rail 12 via an injector socket 14, which is fixedly connected to the fuel rail 12. Specifically, each fuel injector 20 is connected to an injector interface 17, which may be regarded as part of the injector socket 14. The fuel injector 20 and the injector socket 14 together form an injector unit 13. During operation of the engine 70, pressurized fuel (having a fuel pressure of, e.g., 40 bar) is supplied through a connecting pipe 11 to the fuel rail 12 and from there to each injector unit 13. The exact working principle of the fuel injector 20 is here not relevant and will not be described in detail. As shown in fig.2, the fuel injector 20 comprises an injector body 21 which defines a fuel passage 22 that extends from an inlet opening 23 to an outlet opening (not shown). The outlet opening can be closed by a pintle that cooperates with a valve seat. The pintle may be moved by an armature that is movable by an electric field generated by a magnetic coil. The inlet opening 23 communicates with a socket channel 15 of the socket 14. A socket-lubricant channel 16, which will be explained later, branches off the socket channel 15. The fuel rail 12 may be of conventional design. It typically comprises a tubular body 12.1 that defines a plenum chamber 12.2 in which fuel gas accumulates before flowing to the individual injectors. The fuel rail 12 has one gas supply port 12.3 through which gaseous fuel enters the plenum chamber 12.2. In the shown embodiment, the supply port 12.3 is centrally located, whereby the tubular body 12.1 is closed at both axial ends, in particular at one end by a plug 13 with integrated pressure sensor 9. Further, the fuel rail assembly 5 comprises a lubricant-supply system 30, which is adapted to provide a liquid lubricant L to the fuel injectors 20. It comprises in this case a total of four lubricant dozers 31, each of which is mounted to an injector socket 14. Each lubricant dozer 31 can also be referred to as a volumetric dozer or pumping dozer. It comprises a dozer body 32 that defines a dozer cavity 33. At least a part of the dozer body 32 may be non-detachably and sealably connected to the injector socket 14, e.g., by brazing. Within the dozer cavity 33, a pumping plunger 34 is movable along a plunger axis A. On a distal side of the pumping plunger 34, there is a pumping chamber 35 which is part of the dozer cavity 33. The pumping chamber 35 may communicate with an inlet port 36 through an optional inlet valve 37, and with an outlet port 38 through an outlet valve 39. The outlet port 38, in turn, communicates with the socket-lubricant channel 15. Accordingly, lubricant L that is released from the outlet port 37 can traverse the socket-lubricant channel 16 and the socket channel 15 and enter the injector 20. The fuel rail 12, the injector sockets 14, and the lubricant dozers 31 are parts of a fuel-rail assembly 5. The operation of the lubricant dozer 31 will now be explained with reference to figs. 3-5. The pumping plunger 34 is movable along the plunger axis A between a proximal position that is shown inf fig.3 and a distal position that is shown in fig. 4. A volume of the pumping chamber 35, which is partially defined by a distal portion 33.1 of the pumping plunger 33, is greater in the proximal position than in the distal position. The movement of the pumping plunger 33 to the distal position corresponds to a release process in which lubricant L is released through the outlet port 38, as indicated in fig.4. The lubricant L in the pumping chamber 35 is compressed, and the increased pressure opens the outlet valve 39, which is a check valve. On the other hand, the inlet valve 37, which is also a check valve, is closed at this time, due to an overpressure in the pumping chamber 35 relative to the inlet port 36. This overpressure is partially due to a reduction in pressure at the inlet port 36. As can be seen in fig.5, the inlet ports 36 of all lubricant dozers 31 are connected to a supply piping 45. The supply piping 45 is connected to a valve device 47 (in this case a multi-port valve), which connects the supply piping 45 to a high-pressure pipe 49 in a first state and to a low-pressure pipe 51 in a second state (which is shown in fig.5), while the lower-pressure pipe 51 is directly connected to a lubricant reservoir 48, the higher-pressure pipe 49 is connected to the lubricant reservoir 48 via a pressure pump 50 that increases the lubricant pressure from 1 bar at the reservoir 48 to, e.g., between 2 and 5 bar. The high-pressure pipe 49 and the low-pressure pipe 51 are connected via a relief valve 52 that bypasses the pressure pump 50. A control unit 75 controls the switching state of the valve device 47. For the release process, the supply piping 45 is connected to the low-pressure pipe 51. A control piping 46, on the other hand, is connected to the high-pressure pipe 49. The control piping 46 is connected to a control port 42 of each lubricant dozer 31. As can be seen in figs. 3 and 4, the control port 42 communicates with a control chamber 41, which is disposed on a proximal side of the pumping plunger 34 and is partially delimited by a proximal portion 34.3 of the pumping plunger 34. As the control piping 46 is connected to the high-pressure pipe 49, an elevated pressure acts on the proximal portion 34.3. At the same time, the considerably lower pressure of the low-pressure pipe 51 acts on an intermediate portion 34.2 of the pumping plunger 34 which is disposed in an intermediate chamber 40 of the dozer cavity 33. This is because the intermediate chamber 40 communicates with the inlet port 36 through a bypass channel 43 that bypasses the inlet valve 37. A force resulting from this pressure acting on the intermediate portion 34.2 is much smaller than the force acting on the proximal portion 34.3. Also, although the pressure in the pumping chamber 35 is as high or even higher than the pressure in the control chamber 41, the resulting force is much smaller, since the proximal portion 34.3 has a considerably greater cross-section perpendicular to the plunger axis A than the distal portion 34.1. Thus results the movement of the pumping plunger 34 to the distal position and the release process (i.e. delivery of lubricant), which is performed by all lubricant dozers 31 simultaneously. The pumping chamber 35 and the pumping plunger 34 are designed so that a pumping volume, which is displaced by the pumping plunger between the proximal position and the distal position, is less than 20 mm3, preferably less than 10 mm3, more preferably less than 5 mm3. This pumping volume is at least approximately identical to a defined release volume that is released from each lubricant dozer 34. For an intake process, the control unit 75 connects the supply piping 45 to the high-pressure pipe 49 and the control piping 46 to the low-pressure pipe 51. This results in a pressure increase at the inlet port 36 and in the intermediate chamber, while the pressure at the control port is decreased. Accordingly, the pumping plunger 34 moves to the proximal position. Also, the inlet valve 46 opens so that lubricant L flows into the pumping chamber 35, which is now ready for another release process. As regards inlet valve 37 and outlet valve 39, they may be designed as check valves, as previously indicated. Typically, they include a ball-shaped valve member 37.1, 39.1 that cooperates with a valve seat. The ball-shaped valve member is biased in closed position by a coil spring 37.2, 39.2. As for the inlet valve, the coil is arranged around a stop pin 37.3. The stop pin 37.3 extends from a base member that is screwed in the body and thereby allows adjusting the spacing between the pin end and the valve member in closed position. As previously mentioned, the inlet valve 37 of the dozer is optional. As regards the outlet valve 39, it is arranged in an outlet channel of the body 32. The ball 39.1 is arranged in a recess of a support member 39.3. This support member comprises an annular shoulder against which one end of the coil spring 39.2 abuts. The other end of coil spring rests on an annular shoulder of a fixing piece that is screwed in the outlet channel. The ball 39.2 is thus moveable inside outlet channel. The ball may be made of resilient plastic material, e.g. an elastomer, or may be a metal ball coated with plastic / elastomeric material. The ball 39.1 protrudes partly out of its support member 39.3, the rim of the recess being surrounded by an annular stop surface 39.4 that limits the compression of the ball 39. Figs. 6 and 7 show another embodiment of a lubricant dozer 31, which may be used instead of the embodiment shown in figs. 2-4. This second embodiment will only be described insofar as it differs from the first embodiment. In this case, the dozer body 32 comprises two outer parts, namely a cup-like housing shell 53 and a housing lid 54, which together form a dozer housing. The dozer housing contains an inner assembly 55, which comprises inner parts of the dozer body 32, which are connected, e.g., by press-fitting. A plunger part 56 defines the pumping chamber 35 and a major portion of the dozer cavity 33. A seat part 57, which is connected to a distal end of the plunger part 56, forms a seat of the outlet valve 39. The inner assembly 55 also comprises the pumping plunger 34. The inner assembly 55 may be pre-assembled before it is placed into the housing shell 53. Afterwards, the housing lid 54 may be assembled to the housing shell 53 and connected thereto by screwing. Thus, the inner assembly 55 is enclosed between the housing shell 53 and the housing lid 54. The housing lid 54 comprises a plurality of protruding ribs 54.1 which engage the plunger part 56 while leaving space in between them for the control chamber 41. Before the inner assembly 55 is placed inside the housing shell 53, the housing shell can be non-detachably connected to the injector socket 14 by brazing. An elastomeric O-ring 44 is disposed circumferentially around the pumping plunger 34. It provides a reliable seal between the control chamber 41 and the intermediate chamber 40 while the length of the pumping plunger 34, as well as its stroke length (i.e., the distance between the proximal position and the distal position) can be kept small. This helps to limit the total size of the lubricant dozer 31. In contrast to the first embodiment, the lubricant dozer 31 does not comprise an inlet valve. Instead, the inlet port 36 communicates with the pumping chamber 35 through an inflow opening 59, which may be formed as a micro bore. It is disposed adjacent to the pumping chamber 35. When the pumping plunger 34 is in the proximal position, as shown in fig.6, the inflow opening 59 is uncovered by the pumping plunger 34, wherefore lubricant L may flow into the pumping chamber 35, as indicated by the arrow. As pressure in the control chamber 41 is increased, the pumping plunger 34 moves towards the distal position and blocks the inflow opening 59, thereby preventing lubricant L from escaping towards the inlet port 36. Instead, the lubricant L is expelled through the outlet valve 39 and the outlet port 38. In order to promote lubricant distribution, a porous outlet cap 58 is disposed at the outlet port 38. It comprises a plurality of through-openings through which the lubricant L is released. The through-openings are too small to be shown in the figures. In this embodiment, the outlet cap 58 is a single metal body with a plurality of through-holes. As the pressure at the control port 42 is decreased and the pressure at the inlet port 36 is decreased as described above, the pumping plunger 34 moves towards the proximal position, finally uncovering the inflow opening 59 again so that the pumping chamber 35 is again fluidly connected to the inlet port 36. As in the previous embodiment, a bypass channel 43 is arranged so that movement of the pumping plunger 34 into the proximal position can be promoted by lubricant pressure in the intermediate chamber 40 while the inflow opening 59 is blocked by the pumping plunger 34. Figs.8-13 show a second embodiment of an inventive fuel rail assembly 5. Like the first embodiment, it comprises a fuel rail 12 and a total of four injector sockets 14 with injector interfaces 17. A lubricant dozer 31 is mounted to each injector socket 14. The design of the lubricant dozer 31, which can be seen in the sectional view of fig. 12, is largely identical to the embodiment shown in figs. 6 and 7 and will insofar not be explained again. The housing shell 53 is connected to the injector socket 14 by brazing. In this embodiment, there is no inlet valve, but the inlet port communicates with the pumping chamber through an inflow opening 59, like in the embodiment of figs. 6 and 7. The inlet port 36 also communicates with the intermediate chamber 40 through a bypass channel 43 that bypasses the inflow opening 59, similar to the first embodiment. Another difference is that the inlet port 36 and the control port 42 do not traverse the housing shell 53 radially with respect to the plunger axis A, but tangentially. The inlet port 36 and a supply-forwarding port 60 are formed by a single through-bore that traverses the housing shell 53, while the control port 42 and a control-forwarding port 61 are formed by another through-bore, which also traverses the housing shell 53. The position and diameter of the through-bores are selected so that they intersect with the dozer cavity 33, which can be seen in the sectional view of fig. 11. One end of a pipe segment 62-65 (or simply pipe) is inserted into the through-bore from either side. A portion of the through-bore in which the end of the respective pipe 62-65 is disposed may have a somewhat greater diameter, as indicated in fig. 11, to define a stop surface. However, the end of the pipe segment at the time of assembly is preferably not in contact with the stop surface to allow for thermal expansion (in particular during brazing). Specifically, an end of a supply-connection pipe 62 is connected to the inlet port 36 of a first lubricant dozer 31 (the one to far left in figs. 8 and 9), while an end of a control-connection pipe 64 is connected to the control port 42 of this first lubricant dozer 31. A supply-forwarding pipe 63 is connected to the supply-forwarding port 60 of the first lubricant dozer 31, and a control-forwarding pipe 65 is connected to the control-forwarding port 61 of the first lubricant dozer 31. The supply-forwarding pipe 63 is also connected to the inlet port 36 of a second lubricant dozer 31, and the control-forwarding pipe 65 is also connected to the control port 42 of the second lubricant dozer 31. In a similar way, connections are established to a third and fourth lubricant dozer 31. The fourth lubricant dozer 31 does not comprise a supply-forwarding port 60 or a controlforwarding port 61, though. Each of the pipes 62-65 is connected to the housing shell 53 of the respective lubricant dozer 31 by brazing. These brazing connections may be applied together with the connection between the housing shell 53 and the injector socket 14. The brazed connections are generally carried out to form a continuous metallurgical bond, to also provide a gas-tight connection. In yet another embodiment, which is shown in fig. 14, the housing shell 53 and the injector socket 14 are made from a single piece of metal. Thus, the assembly and brazing process for the fuel-rail assembly 5 is simplified. As can be seen in figs. 8 and 9, all pipes 62-65 are straight and aligned with each other. They connect the various lubricant dozer 31 in a row, one after another. It can thus be said that the lubricant dozers 31 are serially connected. Pipes segments 62-65 are fixedly mounted to the fuel rail 12. Hence, pipes 62, 63 form an integrated supply piping whereas pipes 64, 65 form an integrated control piping. On Fig. 12 one will note the tubular body 12.1 of the fuel rail 12 with its plenum chamber 12.2 in communication with the socket channel 15 of the socket 14 (through radial orifice in body 12.1). The lubricant dozer 31 is mounted to the socket 14 to inject lubricant directly into the socket channel 15. Reference sign 66 indicates continuous annular brazed joints that unite the dozer shell 53 and injector interface 17 do the injector socket 14. The injector interface 17 is useful for direct coupling with the injector. Accordingly, it defines a coupling channel 17.1 that communicates with the socket channel 15 and which is adapted to receive the injector inlet portion (with its inlet opening). In other embodiments, not shown, the injector socket 14 may comprise an outlet fitting at the end of the socket channel 14, by which the injector may be connected via a pipe to the injector socket. Still to be noticed in Fig. 12, the inlet port 36 opens in an inlet chamber 36.1 upstream of the pumping chamber that is outwardly delimited by the shell 53. Likewise, the control port 42 communicates with the control chamber 41. This is actually common to all embodiments, where the subdivision inside shell 53 is realized by a cylindrical portion of the inner assembly 55 - herein portion 56.1 of plunger part 56 - that tightly fits inside shell 53. Preferably, cylindrical portion 56.1 comprises a peripheral groove 56.2 with an annular seal 56.3. In this third embodiment however, one can note that the supply-forwarding port 60 also communicates with the inlet chamber 36.1. Likewise, the control-forwarding port 61 also communicates with the control chamber 41. This is due to the tangential boring of these ports within the shell wall thickness such that they communicate with the inner shell volume. <lnvention> To enable of purging air out of lubricant dozers 31, the invention provides a fuel rail assembly with a lubricant supply system 30 with a purging path 100. In a first embodiment of the invention, the purging path 100 is provided by a purging module 104, as shown on figs. 8, 9, 15 and 16. More specifically, a purging module 104 is arranged on / near a lubricant dozer 31. The purging module 104 is designed as a metal body that comprises a first port 104a which is fluidly coupled with the inlet port 36 of the lubricant dozer 31, and a second port 104b which is fluidly coupled to the control port 38 of the lubricant dozer 31. In this embodiment, this communication occurs via the control-forwarding port 61 and supply-forwarding port 63, since the purging module is on the side opposite to the connection with the previous dozer. A purging channel 104c enables flow of air and oil from the first port 104a to the second port 104b. The purging channel 104c defines a calibrated orifice, which enables restricted / controlled flow of air and oil, such that purging is enabled without excessively reducing the pumping efficiency of the lubricant dozers 31. In the shown embodiment, the calibrated orifice is partially defined by a calibration screw 106 which extends into the purging channel 104c. The calibration screw 106 may be rotated to increase or decrease the size of the orifice, or to completely obstruct it, thereby closing the purging path. The purging module 104 may be attached to the lubricant dozer 31 by brazing. Advantageously, as shown on figure 9, the supply piping 45 serially connects the inlet ports of all lubricant dozers 31 and the control piping 46 serially connects the control ports 42 of all lubricant dozers 31. The purging module 104 is connected to the last socket of the lubrication line, i.e. to the lubricant dozer 31 at the end of the series of lubricant dozers 31, opposite to the pressure source. A single purging module 104 is thus able to provide a purging path 100 for all lubricant dozers 31, simplifying assembly and reducing costs. In practice, the purging module 104 is operated every time a purging of the lubrication system may be desired. This is typically the case at engine installation (first start) and possibly when the car is back for routine maintenance. So, one operating mode of the purging module 104 is that it is normally closed: screw 106 fully screwed sealingly obstructs flow through passage 104c. When a purging operation is desired, screw 106 is manually unscrewed during a short time period (dozens of seconds) to allow fluid circulation between the supply and control pipings via open passage 104c. And it is finally screwed back into sealing position (closed passage 104c). Alternatively, the passage 104c could be left open during engine normal operation, the screw 106 being set in a given position to define a predetermine orifice I flow cross-section. It may further be noted that when such purging module 104 is used, all dozers / housing can have the same design, as the purging module 104 closes the control-forwarding port 61 and supply-forwarding pipe 63 of the last dozer. In a second embodiment of the invention, the purging path is provided by a clearance 102 between the pumping plunger 34 and the inner wall of the dozer cavity 33, as shown on figs. 3 and 4. This clearance 102 should effectively allow restricted flow of air and oil from the intermediate chamber 40 to the control chamber 41. Purged air / oil then flows out of the control port 38, through the control piping 46 towards the low-pressure pipe 51 and the lubricant reservoir 48. In this embodiment, the pumping plunger 34 should not include an elastomeric Oring 44, which would isolate the inlet port 36 from the control port 38. The clearance 102 should be large enough to allow enough oil flow to be able to purge the lubricant supply system 30, but also small enough to limit reduction of pumping efficiency. For example, lubricant pipes in the range of 2-3mm would work with a clearance 102 in the range of 60-110 pm between the pumping plunger 34 and the inner wall of the dozer cavity 33. A higher flow from the lubricant pressure source may be used to compensate for the reduced pumping efficiency. When no purging module is provided, all lubricant dozers 31 have a clearance 102 as described above to define the purging path. However, in embodiments, only a portion of the lubricant dozers have such a clearance 102, e.g. only 16%, 25%, 33%, 50%, 66%, 75% or 83% of the lubricant dozers, or only 1,2, 3, 4 or 5 lubricant dozers have a clearance 102 as defined above. The remaining lubricant dozers may have an elastomeric O-ring 44. In other words, only a portion of the lubricant dozers may have a purging path and, when a purge is triggered, air / oil in lubricant dozers which do not have a purging path flows through the purging paths of lubricants which do have a purging path. In a particular embodiment, all the dozers have their piston provided with an O-ring 44, except the last dozer (opposite pressure source) which does not have an O-ring but has a controlled clearance 102 to provide a purging path. The embodiments described above are compatible, i.e. a lubricant supply system 30 may comprise both a purging module 104 and lubricant dozers with a clearance 102 between the pumping plunger 34 and the inner wall of the dozer cavity 33 which is large enough to define a purging path. However, the use of a purging module 104 has been found to be particularly effective with lubricant dozers 31 with an elastomeric O-ring 44 arranged around the pumping plunger 34, as shown on figures 6 and 7. These elastomeric O-ring 44 have been found to increase the pumping efficiency of the lubricant dozers 31 more than the purging module 104 reduces it, resulting in a net increase in pumping efficiency and a net decrease in flow required from the lubricant supply source. The elastomeric O-rings 44 may be fixed to the pumping plunger 34 or to the inner wall of the dozer cavity 33.

Claims

1. A fuel delivery system for a gaseous fuel internal combustion engine, comprising a fuel rail and a lubricant supply system,wherein the fuel rail includes a supply port for connection to a pressurized gaseous fuel source and a plurality of outlet ports for coupling with a corresponding plurality of fuel injectors,wherein the lubricant supply system comprises a plurality of lubricant dozers configured to release lubricant into respective gaseous fuel streams at each outlet port of the fuel rail, or downstream thereof,wherein each lubricant dozer includes a pumping chamber communicating with a lubricant outlet port, a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a release process, an inlet port from which lubricant is fed to the pumping chamber, and a control port where lubricant may be applied to actuate the pumping plunger,wherein the lubricant supply system (30) comprises a supply piping (45), which is connected to the inlet port (36) of each lubricant dozer (31), and a control piping (46), which is connected to the control port (42) of each lubricant dozer (31),characterized in that the lubricant supply system comprises a purging path configured to purge air out of the lubricant dozers.

2. Fuel delivery system according to claim 1, further comprising a purging module, the purging module having a first and a second port, wherein the first and second ports are in fluid communication via a purging channel, andwherein the purging module is arranged such that the first port is in fluid communication with the supply piping, and the second port is in fluid communication with the control piping, such that the purging path is defined by the purging channel of the purging module.

3. Fuel delivery system according to the previous claim, wherein the purging channel comprises a calibrated orifice.

4. Fuel delivery system according to the previous claim, wherein the calibrated orifice is at least partially defined by a calibration screw, which is at least partially inserted in the purging channel of the purging module.

5. Fuel delivery system according to any of the preceding claims, wherein the lubricant dozer (31) comprises a sealing ring (44) arranged around the pumping plunger (34) to reduce flow between the inlet port and the control port.

6. Fuel delivery system according to claim 1, wherein the purging path is defined by a clearance (102) around the pumping plunger (34).

7. Fuel delivery system according to the previous claim, wherein the clearance (102) around the pumping plunger (34) is comprised between 60 and 110 pm.

8. Fuel delivery system according to any of the preceding claims, wherein the supply piping (45) serially connects the inlet ports (36) of a plurality of lubricant dozers (31) and / or the control piping (46) serially connects the control ports (42) of a plurality of lubricant dozers (31).

9. Fuel delivery system according to any of the preceding claims, wherein the lubricant-supply system (30) comprises a pressure source adapted to increase pressure in the supply piping and decrease pressure in the control piping to introduce lubricant through the inlet port (36) of a lubricant dozer into its pumping chamber (35), and to decrease pressure in the supply piping and increase pressure in the control piping to eject lubricant from the pumping chamber (35) of a lubricant dozer through its outlet port (38) during the release process.

10. Fuel delivery system according to claim 6 or 7 depending on claim 8 and 9, wherein the purging path is provided at the last dozer in the series, opposite a pressure source end of the supply and control piping.

11. Fuel delivery system according to claim 6 or 7 depending on claim 8 and 9, wherein the dozers, or a sub-set thereof, are serially connected with supplypiping and control piping, wherein the dozers (31) each comprise a sealing ring (44) arranged around the pumping plunger (34) to reduce flow between the inlet port and the control port, except the last dozer in the series, opposite a pressure source end of the supply and control piping, where the purging path is defined by a clearance (102) around the pumping plunger (34).

12. Fuel delivery system according to any of the preceding claims, wherein the lubricant dozer (31) comprises a dozer body (32) with a dozer cavity (33) in which the pumping plunger (34) is movable along a plunger axis (A) between a proximal position and a distal position such that a volume of the pumping chamber (35), which is partially defined by a distal portion (34.1) of the pumping plunger (34), is greater in the proximal position than in the distal position, and the outlet port (38) communicates with the pumping chamber (35) through an outlet valve (39).

13. Fuel delivery system according to the previous claim, wherein the dozer cavity (33) comprises a control chamber (41) on a proximal side of the pumping plunger (34), the control chamber (41) communicating with the control port (42), wherein the dozer cavity (33) further comprises an intermediate chamber (40) in which an intermediate portion (34.2) of the pumping plunger (34) is disposed, the intermediate chamber communicating with the inlet port (36); andwherein the pumping plunger (34) moves towards the distal position when pressure in the control chamber (41) exceeds pressure in the intermediate chamber (40), and wherein the pumping plunger (34) moves towards the proximal position when pressure in the intermediate chamber (40) exceeds pressure in the control chamber (41).

14. Fuel delivery system according to the previous claim when depending on claim 6, wherein the clearance (102) around the pumping plunger (34) is defined by a clearance (102) between the pumping plunger (34) and the dozer cavity (33), and wherein the clearance (102) enables restricted flow of fluid from the intermediate chamber (40) to the control chamber (41).

15. Fuel delivery system according to any of the preceding claims, wherein a gaseous fuel tank connected to the inlet of the fuel rail, and a gaseous fuel injector coupled to each outlet of the fuel rail.

16. Fuel delivery system according to the previous claim, wherein each lubricant dozer of the lubricant supply system is configured to release lubricant at an inlet of a gaseous fuel injector.

17. Fuel delivery system according to the previous claim, wherein the fuel rail outlet ports are defined by injector sockets integrated to the rail, which are configured for direct coupling of the injectors to the fuel rail.

18. Fuel delivery system according to the previous claim, wherein the lubricant dozers are mounted to the respective injector sockets to release lubricant in the gaseous fuel stream entering the fuel injector.

19. A fuel rail assembly for a fuel delivery system of a gaseous fuel internal combustion engine, wherein the fuel rail has a supply port for connection to a fuel source and a plurality of sockets for coupling with a corresponding plurality of fuel injectors; wherein a plurality of dozers configured to release lubricant at each socket of the fuel rail;wherein each lubricant dozer includes a pumping chamber communicating with a lubricant outlet port, a pumping plunger that is adapted to displace lubricant from the pumping chamber in order to release a defined volume of lubricant during a release process, an inlet port from which low-pressure lubricant is fed to the pumping chamber, and a control port where high-pressure lubricant may be applied to actuate the pumping plunger,wherein a supply piping (45) is serially connected to the inlet port (36) of each lubricant dozer (31), and a control piping (46), is serially connected to the control port (42) of each lubricant dozer (31),characterized by a purging path configured to purge air out of the lubricant dozers.

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