Multi-fuel injector for an internal combustion engine, method for operating a multi-fuel injector and internal combustion engine

Abstract

In a multi-fuel injector for an internal combustion engine, including a housing with a nozzle needle movably disposed therein between a closed position in which the nozzle needle blocks a discharge of fuel from a collection chamber, to which a first fuel is supplied, above the nozzle needle, a control chamber is arranged to which a high pressure second fuel is supplied which acts on the nozzle needle to bias it into a closed position, and a control valve is provided in a pressure release line extending from the control chamber for a controlled release of the second fuel from the control chamber by opening the control valve so as to relief the closing pressure on the nozzle needle in order to permit lifting of the nozzle needle from the closed position for discharging the fuel from the collection chamber.

Claims

1. A multi-fuel injector (3) for an internal combustion engine for injecting at least a first and a second fuel into a combustion chamber of the internal combustion engine, the multi-fuel injector comprising: a base body (9) with a nozzle needle (11) movably disposed in the base body (9) so as to be movable between a first functional position, in which the nozzle needle (11) is biased toward a nozzle needle seat (13) provided in the base body (9) at one end of the nozzle needle (11) and including at least one injection bore (25) which is blocked by the nozzle needle (11) when the nozzle needle (11) is seated on the nozzle needle seat (13) and a second functional position spaced from the nozzle needle seat (13), a fuel collection chamber (23) formed around the nozzle needle seat (13) whereby a fluid connection between the fuel collection chamber (23) and the at least one injection bore (25) is established when the nozzle needle (11) is in the second functional position, a first inlet opening (19) In communication with the collection chamber (23) for supplying a first, gaseous fuel to the collection chamber (23), a position needle control chamber (27) arranged at an end of the nozzle needle (11) opposite the nozzle needle seat (13) and being in fluid communication with a second inlet (29) for supplying a pressurized second, liquid fuel to the control chamber (27) biasing the nozzle needle (11) into a closed position, and a needle position control chamber discharge line (39) provided with a control valve (37) disposed within the injector in communication with the needle position control chamber (27) and extending within the injector to the collection chamber (23) for a controlled release of the pressurized second, liquid fuel from the control chamber (27) to the collection chamber (23) thereby releasing the pressure in the needle position control chamber (27) to lift the nozzle needle (11) from the nozzle needle seat (13).

2. The multi-fuel injector (3) according to claim 1, wherein the control valve (37) is a leakage-free valve.

3. The multi-fuel injector (3) according to claim 1, wherein the control chamber discharge line (9) extends to the fuel collection chamber (23).

4. A method for operating the multi-fuel injector (3) of claim 1, the method comprising the following steps: conducting the first fuel to the collection chamber (23) ahead of the nozzle needle seat (13) of the nozzle needle (11), releasing the second fuel from the control chamber (27) to the collection chamber (23) via the control valve (37) and the control chamber discharge line (39) andinjecting the first and the second fuel from the collection chamber (23) via the at least one injection bore (25) into a combustion chamber (5) as the nozzle needle (11) is moved off the needle seat (13) by actuation of the control valve (31) for the release therefrom of the pressurized second fuel.

5. The method according to claim 4, wherein a pilot amount of the second fuel is released from the needle position control chamber (27) to the collection chamber (23) by supplying at least one momentary control signal to the control valve (37).

6. The method according to claim 4, wherein the first fuel is gaseous fuel and the second fuel is a self-igniting liquid fuel, in particular Diesel fuel.

7. The method according to claim 4, wherein a pressure of the first, gaseous fuel in the collection chamber (23) is lower than a pressure of the second, liquid fuel in the needle position control chamber (27) when the control valve (37) is closed.

8. The method according to claim 6, wherein the second fuel is disposed in the collection chamber (23) ahead of the first fuel so that, upon opening of the nozzle needle valve the second liquid fuel is first discharged through the injection bore (25) driven by the first gaseous fuel whereby it is atomized in the combustion chamber (5).

9. An internal combustion engine with at least one combustion chamber (5) provided with at least one multi-fuel injector as defined in claim 1.

10. The internal combustion engine according to claim 9, wherein the internal combustion engine is in the form of a combustible gas engine for performing a combustion process with pilot ignition of the combustible gas.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The single FIGURE shows schematically an exemplary embodiment of an internal combustion engine with a multi-fuel injector.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

(2) The FIGURE shows schematically a part of an internal combustion engine 1 with a multi-fuel injector 3 assigned to a combustion chamber 5 for the injection of fuel into the combustion chamber 5. The internal combustion engine is preferably a reciprocating piston engine, wherein the piston 7 is movably disposed in the combustion chamber 5.

(3) The multi-fuel injector 3 includes a base body 9 in which a nozzle needle 11 is movably arranged. The nozzle needle 11 is shown in the FIGURE in a first functional position in which it is biased under pre-tension onto a needle seat 13. The pretension force is generated among others by a spring element 15 which is supported at one end by the base body 9 and at the other end by a support shoulder 17 of the nozzle needle 11.

(4) The multi-fuel injector 3 further has a first inlet opening 19 for a first fuel, in particular combustible gas, which first inlet opening 19 is in fluid communication with a collection chamber 23 via a first channel 21.

(5) The collection chamber 23 is locatedin the flow direction of the first fuel toward the combustion chamber 5upstream of the needle seat 13 and is in the first functional position of the nozzle needle 11 fluidly separated by the nozzle needle 11 from a fuel injection bore 25. Herein the nozzle needle 11 sealingly blocks a fluid communication path from the collection chamber 23 to the injection bore 25.

(6) Above the nozzle needle 11, there is a control chamber 27 which is in fluid communication with a second inlet opening 29 for a second fuel in particular a liquid self-igniting fuel. There is further a second channel 31 which fluidly interconnects the second inlet opening and the control chamber 27.

(7) In this way, the pressure of the fluid in the control chamber acts directly axially on the surface of the nozzle needle at its end opposite the needle seat 13, that is, specifically on a pressure surface 33 arranged at the end of the nozzle needle 11 opposite the needle seat 13. At the same time, the pressure present in the collection chamber 23 acts on a counter pressure surface 35 of the nozzle needle 11 which is provided on the support shoulder 17. The nozzle needle 11 is biased toward the needle seat 11 by the pressure force in the control chamber 27 acting on the pressure surface 33 and also by the force of the tensioned spring element 15, while at the same time the excess pressure force of the pressure in the collection chamber effective on the counter pressure surface 35 acts in opposite direction, that is, tends to lift the nozzle needle 11 off the nozzle seat 13. (The bottom surface of the shoulder is somewhat larger than the top surface).

(8) The pressure in the control chamber 27 can be released via a control valve 37 which is preferably a magnetically controllable valve. The control valve 37 can be activated so that the pressure in the control chamber drops below the pressure threshold at which the pressure effective on the counter pressure surface exceeds the pressure force effective on the pressure surface 33 and the pretensioning force of the pretensioning element 15, whereby the nozzle needle is moved to a second functional position in which it is spaced from the needle valve seat 13. As a result, the fluid connection between the collection chamber 23 and the at least one injection bore 25 is opened so that fuel present in the collection chamber 23 can be injected via the injection bore 25 into the combustion chamber 5.

(9) Herein the control chamber 27 is in fluid communication with the collection chamber 23 via the control valve 37. There is in particular a third channel 39 which fluidly connects the control chamber 27 to the collection chamber 23 and in which the control valve 37 is arranged and either blocks or opens the third channel 39 depending on the control of the control valve 37. A control leakage from the control chamber 27 occurring when pressurized control fluid is released from the control chamber 27 is therefore directed to the collection chamber 23 via the third channel 39.

(10) The nozzle needle 11 is provided as the only nozzle needle and therefore serves as the only valve element for the first and also for the second fuel. There is consequently only one nozzle needle 11 provided in the multi-fuel injector 3. The collection chamber 23 is a common collection chamber for the first and the second fuel.

(11) It is further noted that the control chamber 27 releases pressurized fluid exclusively into the collection chamber 23. There is no other fluid discharge passage for releasing pressurized fluid from the control chamber 27.

(12) Since the multi-fuel injector 3 includes only a single nozzle needle 11 for both fuels, its design is quite simple and, as a result, it is robust compact and relatively inexpensive. And since the control leakage from the control chamber 27 is released into the collection chamber, any mixing of the fuels upstream of the multi-fuel injector 3 is excluded.

(13) The control valve 37 is preferably a permanently leakage-free valve in particular a permanent leakage-free pilot valve so that it does not provide for pressure relief to a fuel reservoir either. In this way, a mixing of the fuels upstream of the multi-fuel injector 3 is prevented in a particular efficient manner.

(14) In particular, the multi-fuel injector has no pressure release bore from the control chamber 27 to a fuel reservoir for the second fuel.

(15) The multi-fuel injector 3 is operated by conducting, the first fuel into the collection chamber 23 ahead of the needle seat 13. There may be a permanent fluid connection between a reservoir for the first fuel and the collection chamber 23 via the first inlet opening 19. An amount of the second fuel is released from the control chamber 27 via the control valve 37 and the third channel 39 into the collecting chamber 23. This can be done in particular by applying short control signals to the control valve 37 causing in particular a so-called blank-shot-activation or an activation without effects. By multiple repetitions of the application of such short signals, the amount of second fuel released into the collection chamber 23 can be controlled. With the application of such short signals, the nozzle needle 11 is not displaced but remains in its first functional position as shown in the FIGURE.

(16) The preferably liquid second fuel displaces the preferably gaseous first fuel from the area directly around the needle seat so that the second fuel is disposed ahead of the first fuel which serves as pilot fuel.

(17) By applying a control signal to the control valve 37, the first and the second fuel are injected from the collection chamber 23 via the injection bore 25 into the combustion chamber 5 as the nozzle needle 11 is lifted off the needle seat 13 by a depressurization of the control chamber.

(18) It is possible herein that both fuels are injected in a single injection one after the other that is during a single lift-off event of the needle from the needle seat. Alternatively, it is also possible that, first during a short injection event, the second fuel is injected into the combustion chamber 5 as a pilot fuel, whereupon, subsequently, in a second injection event that is during a second nozzle needle lift-off, an amount of the first fuel is injected into the combustion chamber. It is also possible that, before the first injection event, a larger amount of the second fuel is supplied to the collection chamber and, in connection with the second injection event, alsothough a small unavoidable control leakage amount of the second fuel is injected into the combustion chamber 5 together with the first fuel. This unavoidable control leakage amount is determined by the flow cross-section of the control valve 37 and the third channel 39 as well as the pressure conditions in the control chamber 27 and in the collection chamber 23.

(19) Preferably, with the control valve 37 closed, the pressure of the first fuel in the collection chamber 23 is lower than a pressure of the second fuel in the control chamber 27. For gaseous first fuels, the pressure is preferably 100 bar to at most 300 bar. For liquid first fuels, the pressure is between 1000 bar and at most 3000 bar. The value of the pressure difference between fuels is selected together with the surface areas generating the hydraulic forces and the pressure losses from the control chamber 27 to the collection chamber 23 preferably in such a way that the desired opening behavior of the nozzle needle 11 as well as the desired flow volume of the second fuel is obtained.

(20) The combustion process in the combustion chamber 5 is preferably so controlled that the first fuel serves as main fuel which generates a major amount of the energy which is provided to the combustion chamber 5 during a working cycle whereas the second fuel serves as pilot fuel which essentially provides for the ignition of the first fuel but which contributes little to the energy supplied to the combustion chamber 5.

(21) Upon injection of the second fuel into the combustion chamber via the injection bore 25, the second fuel is driven by the first fuel and atomized by the first fuel. In this way, a quasi Air Blast is obtained wherein, in spite of the comparably small pressure level in the collection chamber 23, an efficient atomization of the liquid second fuel is made possible so that this fuel burns while producing only little soot.