Technical field of the invention

The present invention relates to a fuel injection arrangement for injecting liquid fuel into a cylinder of a piston engine in accordance with the preamble of claim 1 .

Background of the invention

In large internal combustion engines, such as in ship or power plant engines, each cylinder of the engine can be provided with more than one fuel injector. For instance, dual-fuel engines can be provided with one injector for the operation on liquid fuel and with another injector for injecting a small amount of liquid pilot fuel when the engine is operated on a gaseous fuel. Also engines using only liquid fuel can be provided with different injectors for different loads. A problem concerning especially dual-fuel engines is that the amount of fuel in- jected through one of the fuel injectors is very small . Therefore, these engines are usually provided with conventional fuel injection pumps for supplying the fuel at a high pressure to the fuel injectors when the engine is operated on a liquid fuel, and with a common rail system for supplying the liquid fuel to the pilot fuel injectors when the engine is operated on a gaseous fuel. This kind of system enables very small injection amounts and makes it possible to meet even very stringent emission regulations. However, two separate fuel injection systems increase the complexity of the engine.

Summary of the invention The object of the present invention is to provide an improved fuel injection arrangement for injecting liquid fuel into a cylinder of a piston engine. The characterizing features of the arrangement according to the invention are given in the characterizing part of claim 1 .

A fuel injection arrangement according to the invention comprises a first fuel in- jection valve, a second fuel injection valve, a pressure medium source for sup- plying fuel to the first fuel injection valve and to the second fuel injection valve, a selector valve for selectively allowing flow from the pressure medium source to the first fuel injection valve or to the second fuel injection valve, a fuel supply duct for connecting the pressure medium source to the selector valve, a first fuel duct for connecting the first fuel injection valve to the selector valve, and a second fuel duct for connecting the second fuel injection valve to the selector valve. The arrangement further comprises means for regulating pressure in the second fuel duct between the selector valve and the second fuel injection valve. With the arrangement according to the invention, the same source of pressurized fuel can be used for supplying fuel to different fuel injectors that are used for injecting different amounts of fuel at different pressures. The need for separate fuel supply systems for the different fuel injection valves can thus be eliminated, which helps to make the fuel injection system less complicated and ex- pensive.

The pressure medium source can be a high-pressure fuel injection pump. The second fuel injection valve can be, for instance, a pilot fuel valve, which is configured for injecting smaller amounts of fuel than the first fuel injection valve.

According to an embodiment of the invention, the arrangement comprises means for controlling opening and/or closing timing of the second fuel injection valve. The means can be for example a control valve. This enables accurate control of the timing of the second fuel injection valve and of the amount of fuel injected through the second fuel injection valve.

According to an embodiment of the invention, the arrangement comprises an overflow duct branching from the second fuel duct and a throttle that is arranged in the overflow duct for regulating the pressure in the second fuel duct. Instead of a throttle, a pressure reducing valve can be used for regulating the pressure in the second fuel duct.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawing, in which Fig. 1 shows a schematic view of a fuel injection arrangement according to an embodiment of the invention.

Description of embodiments of the invention The fuel injection arrangement according to the invention is suitable particularly for large internal combustion engines, such as main or auxiliary engines of ships, engines of offshore applications or engines that are used at power plants for producing electricity. The invention is beneficial especially in dual- fuel engines, which can be operated both on liquid and gaseous fuel, and in which a small amount of liquid pilot fuel is used when the engine is operated in a gas mode. However, the invention can also be utilized in other engines, in which two or more fuel injectors are used for each cylinder.

Figure 1 shows a schematic view of a fuel injection arrangement according to an embodiment of the invention. The arrangement comprises a first fuel injec- tion valve 1 and a second fuel injection valve 2, which are arranged to inject liquid fuel into a cylinder 1 1 of a piston engine. The second fuel injection valve 2 is configured for injecting smaller amounts of fuel than the first fuel injection valve 1 . In the embodiment of the figure, the second fuel injection valve 2 is a pilot fuel valve, which is used in a dual-fuel engine for injecting a small amount of liquid fuel into the cylinder 1 1 . Burning liquid fuel initiates combustion of the gas-air mixture in the cylinder 1 1 . The second fuel injection valve 2 could also be used in other than dual-fuel engines for injecting fuel at low loads. Each cylinder 1 1 of the engine is provided with a similar fuel injection arrangement. In the embodiment of the figure, the fuel injection valves 1 , 2 are part of a fuel in- jection unit 12, which is used for injecting the fuel directly into the combustion chamber of the cylinder 1 1 . However, the fuel injection valves 1 , 2 do not need to be arranged in a common fuel injection unit, but they can also be separate and one or both of the fuel injection valves 1 , 2 could also be used for injecting fuel into a pre-combustion chamber. Both fuel injection valves 1 , 2 are of a conventional type. Each fuel injection valve 1 , 2 comprises a nozzle 1 a, 2a, which is arranged at the end of the fuel injection valve 1 , 2, and a fuel gallery 1 d, 2d, which is arranged inside the body of the fuel injection valve 1 , 2. The fuel is stored in the fuel gallery 1 d, 2d before being injected into the cylinder 1 1 through the nozzle 1 a, 2a. Each fuel injection valve 1 , 2 is also provided with a valve needle 1 b, 2b for opening and closing flow communication between the fuel gallery 1 d, 2d and the nozzle 1 a, 2a. The valve needle 1 b, 2b is kept in a closed position by a spring 1 c, 2c. Many other constructions of the fuel injection valves 1 , 2 are possible instead of the construction shown in the figure. For instance, the valve needles 1 b, 2b could be coaxial and both fuel injection valves 1 , 2 could utilize a common nozzle part having separate nozzle holes for each of the fuel injection valves 1 , 2.

Both fuel injection valves 1 , 2 are connected to a pressure medium source 3, which is in the embodiment of the figure a high-pressure fuel injection pump. The fuel does not need to be supplied to the fuel injection valves 1 , 2 directly from the fuel injection pump 3, but it can be pressurized by the pump 3 and stored in a chamber before being supplied to the fuel injection valves 1 , 2. The pump 3 is a conventional fuel injection pump, which can be adjusted for choosing appropriate fuel injection timing and quantity at different loads. The fuel in- jection arrangement is provided with a fuel supply duct 5 for delivering the fuel from the fuel injection pump 3 to the fuel injection valves 1 , 2. Only one of the fuel injection valves 1 , 2 is used at a time, and therefore the arrangement is provided with a selector valve 4 for allowing flow from the fuel injection pump 3 either to the first fuel injection valve 1 or to the second fuel injection valve 2. The selector valve 4 is a three-way valve, which is provided with one inlet port 4a and with a first outlet port 4b and a second outlet port 4c. A first fuel duct 6 connects the first outlet port 4b of the selector valve 4 to the first fuel injection valve 1 , and a second fuel duct 7 connects the second outlet port 4c to the second fuel injection valve 2. The inlet port 4a of the selector valve 4 is connect- ed to the fuel supply duct 5. In the embodiment of the figure, the selector valve 4 is a solenoid valve.

When the engine is operated on liquid fuel, the selector valve 4 is in a position allowing flow from the fuel injection pump 3 to the first fuel injection valve 1 and preventing flow to the second fuel injection valve 2. The timing of the fuel injection and the quantity of the injected fuel is adjusted by the fuel injection pump 3 in a conventional manner. When the pressure in the fuel gallery 1 d of the first fuel injection valve 1 is high enough, the valve needle 1 b is pushed against the spring 1 c, and the first fuel injection valve 1 is opened. Fuel is thus injected through the nozzle 1 a of the first fuel injection valve 1 into the com- bustion chamber of the cylinder 1 1 . The spring 1 c pushes the valve needle 1 b of the first fuel injection valve 1 into a closed position when the pressure in the fuel gallery 1 d drops enough and the fuel injection is consequently terminated.

When the engine is operated in a gas mode, the selector valve 4 is switched into a position, in which flow from the fuel injection pump 3 to the second fuel injection valve 2 is allowed and flow from the fuel injection pump 3 to the first fuel injection valve 1 is prevented. In the gas mode, only a small amount of liquid fuel is used. The whole amount supplied by the fuel injection pump 3 is thus not needed. Therefore, the arrangement is provided with means 9 for controlling the opening of the second fuel injection valve 2. In the embodiment of the figure, the arrangement is provided with a control valve 9, which is used for actuating the second fuel injection valve 2. With the control valve 9, opening of the second fuel injection valve 2 can be prevented even in the case the pressure in the fuel gallery 2d would be high enough for moving the valve needle 2b against the spring 2c. The opening and closing moments of the second fuel injection valve 2 are thus determined by the control valve 9, which enables accurate timing. The control valve 9 is electrically operated. Also other kinds of actuators could be used for controlling the opening and/or closing timing of the second fuel injection valve 2. The arrangement is further provided with an overflow duct 10, through which the excess fuel can be returned into a tank 12. The overflow duct 10 is connected to the second fuel duct 7, i.e. between the selector valve 4 and the second fuel injection valve 2. The injection pressure needed in the second fuel injection valve 2 is lower than the maximum pressure of the fuel injection pump 3. Therefore, the overflow duct 10 is provided with means 8 for regulating the pressure in the second fuel duct 7. In the em- bodiment of the figure, the means are an adjustable throttle 8. Instead of a throttle 8, the overflow duct 10 could be provided with a pressure reducing valve. With the pressure regulating means, the injection pressure of the second fuel injection valve 2 can be adjusted to an appropriate level irrespective of the pressure of the fuel injection pump 3. With an arrangement according to the invention, separate fuel injection system is not needed for injecting the pilot fuel in dual-fuel engines, which make the fuel injection system less complicated and expensive.

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, it is possible that all the cylinders of the engine are not provided with an own fuel injection pump, but one pump supplies fuel to several cylinders of the engine.