ARRANGEMENT FOR DAMPENING THE PRESSURE VIBRATION OF A FUEL FEED SYSTEM OF A PISTON ENGINE

The present invention relates to an arrangement for dampening the pressure vibration of the fuel feed system of a piston engine.

In fuel feed systems of internal combustion engines injection pumps are used for introducing pressurized fuel into the cylinders via injector nozzles. The injection pump comprises a cylinder element having a reciprocating piston arranged in a pressure chamber thereof. The movement of the piston causes the increase of the pressure of the fuel. The cylinder element usually includes one or two inlet channels through which fuel is introduced from the low pressure side of the fuel feed system into a pressure plenum as the piston is in its bottom dead center. The piston moving upwards in the pressure plenum covers the fuel inlet channels and pressurized fuel flows from the pressure plenum to the high pressure pipe leading to the injector nozzle. The fuel flow to the injector nozzle stops as a screw-like cut in the piston moves to the inlet channel and uncovers the inlet channel, whereby fuel in high pressure is discharged via the inlet channel to the low pressure side of the fuel feed system. This, in turn, causes a pressure pulse on the low pressure side of the fuel feed system. Usually a number of injection pumps are in flow connection with the main fuel pipe of the low pressure side, whereby the pressure in the pipe will continuously vibrate as the engine is running.

In case the fuel pressure in the low pressure side of the fuel feed system is low, the pressure fluctuation caused by the operation of the injection pumps can cause cavitation in the pipes on the low pressure side. In the worst case cavitation can destroy the low pressure pipes in a short period of time. The cavitation problem is especially serious in engines using crude oil as fuel.

Various dampeners, such as gas dampeners and mechanical dampeners, can be used for dampening the pressure vibration of the fuel feed system. A gas dampener comprises a gas space separated from the fuel feed system by means of a membrane. As the fuel pressure is changed, the membrane moves and the volume of the fuel space is changed, whereby the pressure vibration in the fuel feed system is dampened. The service life of such a dampener is limited, as the membrane can easily be broken, whereby the dampener is unusable.

A mechanical dampener comprises a piston or other intermediate piece arranged inside a space in the dampener. The space is in flow connection with the fuel feed system, whereby the piston moves and thus the volume of the fuel feed system is changed as the pressure fluctuates. The piston is supported by the dampener by means of at least one spring dampening the movement of the piston. The service life of this kind of mechanical dampener is limited by the durability of the springs.

The object of the invention is to produce an improved arrangement for dampening the pressure vibration of the fuel feed system of a piston engine.

The arrangement according to the invention for dampening the pressure vibration of the fuel feed system of a piston engine comprises a vibration dampener having a body part inside which is a space containing a movably arranged intermediate piece. The body part has a first opening arranged to open to the first side of the intermediate piece for connecting the space with the fuel feed system and a second opening arranged to open into the space on the other side of the intermediate piece, the opening being in flow connection with the source of pressurized gas.

More specifically, an arrangement according to the invention is characterized by what is stated in the characterizing part of claim 1.

Considerable advantages are achieved by means of the invention.

In a dampener used in a dampening arrangement according to the invention there is no membrane separating air and fuel from each other and no mechanical spring, whereby the dampener can be produced to be reliable and durable. When needed, the dampening properties of the dampener can easily be adjusted by changing the gas pressure acting on the intermediate piece.

In one embodiment of the invention the intermediate piece comprises a first surface limiting the space in the part on the side of the first opening and a second surface limiting the space in the part on the side of the second opening. Further, the area of the first surface is larger than that of the second surface. Thus, the pressure of the gas applying a force on the intermediate piece can be smaller than the pressure of the fuel for maintaining an equilibrium of the intermediate piece. Due to the low pressure the load on the gas system is low, whereby the design of the system can be simple.

In the following, the invention is described in more detail with reference to the appended schematic drawings.

Figure 1 is an illustration of a part of a fuel feed system of an internal combustion engine, the system being provided with a pressure vibration dampener according to the invention.

Figure 2 illustrates the vibration dampener of figure 1 in a cross-sectional view.

Figure 1 is a schematic view of a part of a fuel feed system 1 of an internal combustion engine. The internal combustion engine is, for example, a large multi- cylinder diesel engine used in ships or power plants. For example, crude oil can be used as fuel. Fuel is fed from the fuel tank 2 with a fuel pump 3 in a relatively low pressure via the low pressure piping 4 to each injection pump 5. The low pressure piping 4 extends from the high pressure side of the fuel pump 3 to each

injection pump 5. The low pressure piping 4 comprises a main line 6 from which a branch line 7 extends to each injection pump 5. Each injection pump 5 is connected to the injector nozzle 9 via high-pressure pipes 10. The injection pump 5 carries out the injection of fuel together with the injector nozzles 9. The injector pump increases the fuel pressure to such a level that a sufficient injection pressure is achieved at injector nozzles 9. The fuel feed system also includes low-pressure return channels 8 returning from each injection pump 5 back to the fuel tank 2. Fuel is directed from the injection pumps 5 back to the fuel tank 2 through return channels 8.

One or more pressure vibration dampener(s) 1 1 is arranged in the fuel feed system. By means of the vibration dampener the fuel pressure fluctuations occurring in the fuel feed system 1 are dampened. Pressure fluctuations are caused, for example, as the high-pressure fuel in the injection pumps 5 is discharged into the low-pressure piping 4 when the injection stops. Because a number of injection pumps 5 are in flow connection with the same main line 6, the pressure in the main line 6 vibrates rapidly. The vibration dampener 11 is arranged in connection with the low-pressure piping 4, for example. In the embodiment of figure 1 there are two dampeners 1 1 and they are arranged in the main line 6, preferably near the openings of the branch lines 7 leading to the injection pumps 5. Alternatively or additionally pressure vibration dampeners 1 1 can be installed in other places of the low pressure piping 4 or other places of the fuel system, such as in connection with the injection pump 5.

Figure 2 illustrates in more detail the vibration dampener 1 1 shown in figure 1. The dampener comprises a body part 12 delimiting a space 13 inside it. The body part 12 includes a first opening 14, by means of which the space 13 is in flow connection with the fuel pipes of the fuel feed system 1 , such as the main line 6. The body part 12 additionally includes a second opening 15 by means of which the space 13 is in flow connection with the gas pipe 20 containing pressurized gas, such as air. The pressure of the gas in gas pipe 20 is higher than the

ambient pressure. The cross-sectional area of the space 13 on the side of the first opening 14 is smaller than on the side of the second opening 15. The space 13 includes an intermediate piece arranged to reciprocate, such as a piston 16. The first opening 14 opens on the first side of the piston 16 and the second opening 15 to the second side of the piston 16. The second side is on the opposite side of the piston 16 in relation to the first side. The piston 16 moves in the space 13 when the pressure difference between the first opening 14 and the second opening 15 changes.

The piston 16 comprises a first surface 17 limiting the space 13 on the side of the first opening 14 and a second surface 18 limiting the space 13 on the side of the second opening 15. The first surface 17 and the second surface 18 limit the space 13 in the direction of the movement of the piston 16. Further, the area of the first surface 17 is smaller than that of the second surface 18.

Annular seals 19, 19' are arranged around the piston 16 for sealing the gap between the piston 16 and the body part 12. The first seal 19 is arranged near the first surface 17 of the piston 16 and the second seal 19' is arranged near the second surface 18 of the piston 16. The body part 12 further includes a drain opening 24 with a drain pipe 25 attached thereto, through which fuel and/or gas leaked past the seals 19, 19' to between the piston 16 and the body part 12 is drained from the space 13. Thus, fuel is not transmitted past the piston 16 from the first side to the second side and gas is not transmitted past the piston 16 from the second side to the first side.

Pressurized gas is introduced into the gas pipe 20 from a gas source 22, such as a tank filled with pressurized gas. The gas pipe 20 is provided with a non-return valve 21 allowing flow therethrough into the space 13 but preventing flow from the space 13. The non-return valve 21 opens when the pressure on its inlet side, i.e. on the side of the gas source 22 is higher than on the outlet side, i.e. on the side of the space 13. The gas pipe 20 includes a pressure regulation valve 23 that

opens and allows flow therethough when the force caused by the pressure on the inlet side, i.e. in the gas pipe 20 is higher than the closing force of the pressure regulation valve 23. The outlet side of the pressure regulation valve 23 is in lower pressure than the inlet side, such as in ambient pressure. The pressure in the gas pipe 20 can be maintained at the desired level by means of the pressure regulation valve 23. In an embodiment according to figure 2 the pressure regulation valve 23 is a spring loaded valve, i.e. the closing force of the valve is formed by means of a spring.

When the pressure of the fuel increases in the fuel pipe of the fuel system, into which pipe the space 13 is in flow connection through the first opening 14, the piston moves in the space 13 towards the second opening 15 and compresses the gas on the second side of the piston 16. As the non-return valve 21 prevents flow of gas therethrough, the pressure of the gas increases as the piston 16 moves and the increased gas pressure counteracts the movement of the piston

16. The volume of the space 13 increases on the first side of the piston 16, thereby dampening the increase of pressure in the fuel pipe. When the pressure in the fuel pipe decreases, the piston 16 moves in the opposite direction. Thus, the volume of the space 13 decreases on the first side of the piston, thereby compensating the decrease of the pressure in the fuel pipe. Because the area of the second surface 18 of the piston 16 is larger than the area of the first surface

17, the gas pressure on the second side of the piston 16 can be lower than the fuel pressure on the first side of the piston 16 for maintaining an equilibrium position of the piston 16. The dampening properties of the dampener 1 1 can be changed by changing the pressure of the gas in the gas pipe 20.