The present invention relates to a gas pipe arrangement for a gas feed system of a piston engine in accordance with the preamble of claim 1 .

Background of the invention

In large piston engines, such as ship or power plant engines, which can be operated using a gaseous fuel, the gaseous fuel is typically conveyed from a gas tank to the cylinders using double-wall pipes. The pipes comprise an inner pipe for conveying the fuel and an outer pipe that is arranged around the inner pipe to form a barrier. The purpose of the outer pipe is to increase safety in case there is a leakage in the inner pipe. Typically an air space is formed between the inner pipe and the outer pipe. Through the air space, leaking fuel can be vented to a safe place. The air space can also be provided with means for de- tecting fuel leakages. From the gas tank, the gaseous fuel is supplied into a gas manifold. The gas manifold is an elongated receiver, from which the fuel is fed to the cylinders of the engine.

Each cylinder of the engine is typically provided with a gas admission valve, which introduces the gaseous fuel into an intake duct if the engine. A double- wall pipe connects each gas admission valve to the gas manifold. A known arrangement for connecting a gas admission valve to a gas manifold is a double- wall pipe, where each end is provided with a flange. One of the flanges can be attached to the gas manifold and the other flange can be attached to a housing of a gas admission valve. At both ends of the pipe, both the inner pipe and the outer pipe are welded to the flange. Because of the manufacturing tolerances, the pipes are provided with corrugated sections to form a bellow structure, which makes the construction flexible and allows tight connection to the gas manifold and to the housing of the gas admission valve.

A drawback of this prior art solution is that the bellow structure requires a small wall thickness, which makes welding of the construction challenging. The construction is also expensive to manufacture. A further drawback is that the structure is closed and the space between the inner pipe and the outer pipe is im- possible to clean properly. Also the inner space of the structure is difficult to clean due to the corrugated pipes.

Summary of the invention The object of the present invention is to provide an improved gas pipe arrangement for a gas feed system of a piston engine. The characterizing features of the arrangement according to the invention are given in the characterizing part of claim 1 .

The gas pipe arrangement according to the present invention is configured to be assembled between a gas manifold and a cylinder of an engine and has a first end and a second end, the gas pipe arrangement comprising an inner pipe for introducing gaseous fuel from a gas manifold to a cylinder, an outer pipe for forming a barrier around the inner pipe, and a first flange that is arranged at the first end of the gas pipe arrangement and extends radially outwards from the inner pipe. The gas pipe arrangement further comprises a second flange that is arranged at the first end of the gas pipe arrangement and extends radially outwards from the outer pipe for attaching the outer pipe to the inner pipe.

Because of the two separate flanges, the manufacturing process of the gas pipe arrangement is simplified. The arrangement can also be easily disassem- bled for cleaning.

According to an embodiment of the invention, the first flange is welded to the inner pipe and/or the second flange is welded to the outer pipe.

According to an embodiment of the invention, the first flange is provided with one or more openings for allowing fluid flow from a space formed between the inner pipe and the outer pipe. Fuel leaking from the inner pipe into the space between the pipes can be vented via the openings.

According to an embodiment of the invention, the second flange comprises bolt holes for detachably attaching the outer pipe to the inner pipe.

According to an embodiment of the invention, the second flange is provided with an opening for a gas leak indicator. According to an embodiment of the invention, the gas pipe arrangement comprises a connecting piece comprising a flange and a cylindrical section that protrudes axially outwards from the flange and is configured to be inserted into a space formed between the inner pipe and the outer pipe at the second end of the gas pipe arrangement. Because of the connecting piece protruding into the space between the inner pipe and the outer pipe, the length of the gas pipe arrangement can be adjusted. The inner pipe and the outer pipe can thus be made as rigid pipes. That makes the construction of the gas pipe arrangement simple and also facilitates cleaning of the pipes. According to an embodiment of the invention, a sealing ring is arranged between the inner pipe and the connecting piece for sealing the joint between the inner pipe and the connecting piece. The inner pipe or the connecting piece can comprise a groove for accommodating the sealing ring. The other part of the joint can be provided with an even sealing surface allowing the inner pipe to be moved relative to the connecting piece in the longitudinal direction of the inner pipe. The groove keeps the sealing ring in a desired position and the even sealing surface of the other part allows adjustment of the length of the gas pipe arrangement.

In a similar way, a sealing ring can be arranged between the outer pipe and the connecting piece for sealing the joint between the outer pipe and the connecting piece, and the outer pipe or the connecting piece can comprise a groove for accommodating the sealing ring. The other part of the joint can be provided with an even sealing surface allowing the outer pipe to be moved relative to the connecting piece in the longitudinal direction of the outer pipe. According to an embodiment of the invention, the connecting piece is provided with one or more openings for allowing fluid flow into the space between the inner pipe and the outer pipe.

According to the invention, a gas feed system for a multi-cylinder piston engine comprises a gas admission valve for each cylinder of the engine for controlling supply of a gaseous fuel into the cylinder and a gas manifold for supplying gaseous fuel to the gas admission valves. A gas pipe arrangement defined above is arranged between a valve housing of each gas admission valve and the gas manifold. Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

Fig. 1 shows an inner pipe of a gas pipe arrangement according to an embod- iment of the invention,

Fig. 2 shows an outer pipe of a gas pipe arrangement according to an embodiment of the invention,

Fig. 3 shows a connecting piece for the gas pipe arrangement,

Fig. 4 shows an assembled gas pipe arrangement according to an embodi- ment of the invention,

Fig. 5 shows a cross-sectional view of a gas pipe arrangement according to an embodiment of the invention,

Fig. 6 shows a cross-sectional view of a gas pipe arrangement with a connecting piece, Fig. 7 shows a gas pipe arrangement arranged between a gas manifold and a gas admission valve, and

Fig. 8 shows a cross-sectional view of an upper end of a gas pipe arrangement according to an embodiment of the invention.

Description of embodiments of the invention

Figures 1 to 3 show different parts of a gas pipe arrangement according to an embodiment of the invention. Figures 4 to 7 show an assembled gas pipe arrangement and figure 8 a detail of a gas pipe arrangement according to an embodiment of the invention. The gas pipe arrangement can be used in a gas feed system of an internal combustion engine. The gas pipe arrangement is suitable in particular for a gas feed system of a large piston engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity. The expression "large piston engine" refers here to engines having a cylinder bore of at least 150 mm. The gas feed system sup- plies gaseous fuel, such as natural gas, into the cylinders of the engine. The engine can be a gas engine, which is operated on a gaseous fuel that can be ignited, for instance, by means of spark plugs or by using liquid pilot fuel. The engine could also be a dual-fuel or multi-fuel engine, which can be operated using either a gaseous fuel or a liquid fuel.

Figure 7 shows a gas pipe arrangement according to an embodiment of the invention in connection with a gas feed system of a piston engine. The gas pipe arrangement is used for connecting a valve housing 1 1 of a gas admission valve 10 to a gas manifold 5. The gas manifold 5 supplies gaseous fuel from a fuel source to the cylinders of the engine. All the cylinders of the engine can be connected to the same gas manifold 5, or alternatively the gas feed system can be provided with two or more gas manifolds. For instance, in a V-engine each cylinder bank can be provided with an own gas manifold. The gas pipe arrangement has a first end and a second end. In the embodiment of figure 7, the first end is attached to the gas manifold 5 by means of bolts 33 and the second end is attached to the housing 1 1 of the gas admission valve 10 by means of bolts 29.

The gas pipe arrangement comprises an inner pipe 1 and an outer pipe 2, of which only the outer pipe 2 can be seen in figure 7. The construction of the gas pipe arrangement can be seen in more detail in particular in figures 5 and 6. The inner pipe 1 is configured to convey gaseous fuel and the outer pipe 2 forms a barrier around the inner pipe 1 . The inner diameter of the outer pipe 2 is greater than the outer diameter of the inner pipe 1 for forming an air space 9 between the pipes 1 , 2. There is thus a gap between the inner pipe 1 and the outer pipe 2. The width of the space 9 can be, for instance, in the range of 2 to 10 mm. However, at the second end of the gas pipe arrangement the gap can be greater for facilitating attachment of the inner pipe 1 and the outer pipe 2 to an adjacent part of the gas feed system. Fuel leaking from the inner pipe 1 enters the space 9 between the inner pipe 1 and the outer pipe 2. The space 9 can be vented outside an engine room for reducing the risk of fires. The space 9 could also be constantly flushed with air for effectively venting the space 9. The gas pipe arrangement has a first end, which is the upper end in figures 5 and 6, and a second end. The first end of the inner pipe 1 is provided with a first flange 3. The first flange 3 extends radially outwards from the outer sur- face of the inner pipe 1 . In the embodiment of the figures, the first flange 3 is square-shaped. The first flange 3 can be used for attaching the gas pipe ar- rangement to another part of the gas feed system, such as a gas manifold 5. The first flange 3 is provided with bolt holes 32 for allowing the first pipe 1 to be detachably attached to an adjacent part of the gas feed system. The first flange 3 is also used for attaching the outer pipe 2 to the inner pipe 1 . The out- er pipe 2 is provided with a second flange 4, which extends radially outwards from the outer surface of the second pipe 2. In the embodiment of the figures, also the second flange 4 is square-shaped. The second flange 4 is used for attaching the outer pipe 2 to the inner pipe 1 . The second flange 4 is provided with a plurality of holes 12, which allow outflow from the space 9 between the inner pipe 1 and the outer pipe 2. The second flange 4 is provided with bolt holes 19 for detachably attaching the outer pipe 2 to the inner pipe 1 . Because of the flanges 3, 4, the gas pipe arrangement can be easily assembled from two separate pieces. The gas pipe arrangement is also easy to disassemble for cleaning. The second flange 4 is provided with a groove 24 that is arranged on the surface facing the first flange 3. The groove 24 can accommodate a sealing ring sealing the joint between the first flange 3 and the second flange 4. Alternatively, the groove 24 could be arranged in the first flange 3. The first flange 3 is provided with a first groove 25 and with a second groove 26. The grooves 25, 26 are arranged on the surface facing an adjacent part of the gas feed system. The grooves 25, 26 are thus arranged on a surface facing away from the second flange 4. Each of the grooves 25, 26 can accommodate a sealing ring. The first groove 25 is an outer groove and the second groove 26 is an inner groove. Sealing rings arranged in the grooves 25, 26 can seal the inner pipe 1 against an adjacent part of the gas feed system for preventing leakages from the inner pipe 1 and from the space 9 between the inner pipe 1 and the outer pipe 2.

At the second end of the gas pipe arrangement, the outer perimeter of the inner pipe 1 is provided with a groove 13. Also the inner perimeter of the outer pipe 2 is provided with a groove 14. Each of the grooves 13, 14 is provided with a sealing ring 17, 18 (shown in Fig. 6). The purpose of the sealing rings 17, 18 is to make the joint between the pipes 1 , 2 and the adjacent part of the gas feed system gas tight.

The gas pipe arrangement further comprises a connecting piece 6, which is shown in figure 3. Figures 4, 6 and 7 show the connecting piece 6 as attached to the pipes 1 , 2. The connecting piece 6 comprises a flange 7 and a cylindrical section 8, which protrudes axially outwards from the flange 7. The flange 7 can be attached to another part of a gas feed system, such as the housing 1 1 of a gas admission valve 10. The flange 7 is provided with holes 23 for attachment bolts 29. The cylindrical section 8 is configured to be inserted into the space 9 between the inner pipe 1 and the outer pipe 2. The connecting piece 6 can thus form the second end of the gas pipe arrangement. As can be seen in the figures, the inner pipe 1 can be tapered at the second end so that the space 9 between the inner pipe 1 and the outer pipe 2 can better accommodate the cylindrical section 8 of the connecting piece 6.

The connecting piece 6 is provided with a plurality of holes 22, which extend through the connecting piece 6 in the longitudinal direction of the connecting piece 6 and open into the space 9 between the inner pipe 1 and the outer pipe 2 when the connecting piece 6 is connected to the pipes 1 , 2. Through the holes 22 of the connecting piece 6, flow into the space 9 between the inner pipe 1 and the outer pipe 2 is allowed. Leaking fuel from a housing 1 1 of a gas admission valve 10 and/or flushing air can thus be introduced into the space 9 between the inner pipe 1 and the outer pipe 2 through the holes 22.

The connecting piece 6 comprises a first sealing surface 15, which is arranged on the inner perimeter of the cylindrical section 8. The connecting piece 6 further comprises a second sealing surface 16, which is arranged on the outer circumference of the cylindrical section 8. The first sealing surface 15 and the second sealing surface 16 are configured to cooperate with the sealing rings 17, 18 for sealing the joints between the connecting piece 6 and the inner pipe 1 and between the connecting piece 6 and the outer pipe 2. The end surface of the flange 7 of the connecting piece is provided with grooves 27, 28 for accommodating sealing rings. The sealing rings seal the joint between the connecting piece 6 and an adjacent part of the gas feed system.

The connecting piece 6 can also be configured to accommodate a filter 30 that protects a gas admission valve 10. By arranging a filter 30 inside the connecting piece 6 in such a way that it does not protrude into the housing 1 1 of the gas admission valve 10, the gas pipe arrangement can be easily removed for cleaning or other service purposes without a need to remove the gas admission valve 10. Figure 6 shows as a cross-sectional view the connecting piece 6 as being attached to the inner pipe 1 and the outer pipe 2. Since the connecting piece 6 is provided with even sealing surfaces 15, 16, the mutual position of the pipes 1 , 2 and the connecting piece 6 is not strictly defined, but the connecting piece 6 can be moved in the longitudinal direction of the pipes 1 , 2 without compromising the gas tightness of the joints. This allows the pipes 1 , 2 to be formed as rigid pipes without bellow-type or other resilient sections. This simplifies the manufacturing of the pipes 1 , 2. Compared to corrugated pipes, also the cleaning of the gas pipe arrangement is facilitated. Instead of providing the inner pipe 1 and the outer pipe 2 with grooves 13, 14 for sealing rings 17, 18 and the connecting piece 6 with even sealing surfaces 15, 16, the connecting piece 6 could be provided with grooves for the sealing rings 17, 18 and the inner pipe 1 and the outer pipe 2 could have even sealing surfaces.

The inner pipe 1 can be assembled from a pipe section and the flange 3. The flange 3 can be attached to the pipe section by welding. Due to the new construction of the gas pipe arrangement, the inner pipe 1 and the outer pipe 2 can be made of a thicker material. This makes welding of the pipes 1 , 2 easier. For example laser welding can be used for attaching the first flange 3 to the pipe section. The outer pipe 2 can be manufactured in a similar way by provid- ing a pipe section and the second flange 4 and attaching the second flange 4 to the pipe section by welding. The flanges 3, 4 can be cut from a plate by water cutting. Water cutting can also be used for cutting a blank for manufacturing the connecting piece 6. The inner pipe 1 , the outer pipe 2 and the connecting piece 6 can be made of steel. Figure 8 shows a cross-sectional view of the first end of the pipe arrangement. An opening 21 for a leakage indicator can be seen in figure 8. A plug 31 for a leakage indicator is arranged in the opening 21 . A leakage indicator can be arranged to monitor the space 9 between the inner pipe 1 and the outer pipe 2 for detecting any fuel leakage. It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, the flanges of the inner pipe and the outer pipe could be used for attaching the pipes to the housing of a gas admission valve, and the connecting piece could be attached to the gas manifold.