Abstract:
A dual-fuel fuel injector, having: a first nozzle needle for discharge of liquid fuel via a first nozzle arrangement; and a multiplicity of second nozzle needles, arranged around the first nozzle needle and controlled in terms of axial stroke, for discharge of gaseous fuel via a second nozzle arrangement. Each of the second nozzle needles has for controlling the stroke thereof, a respective control chamber in the injector which can be charged with and relieved of pressure by a control fluid. The dual-fuel fuel injector has an annular duct which can be charged with and relieved of pressure by the control fluid. The dual-fuel fuel injector is designed such that, for controlling the stroke of the second nozzle needles, the control chambers for the second nozzle needles are charged with and relieved of pressure by the control fluid proceeding from the annular duct.

Description:
The present application is a 371 of International application PCT/EP2014/003303, filed Dec. 10, 2014, which claims priority of DE 10 2013 022 260.5, filed Dec. 30, 2013, the priority of these applications is hereby claimed and these applications are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns a dual-fuel fuel injector. 
     Publication DE 35 01 236 C1 discloses a cylinder cover for a piston internal combustion engine, wherein the cylinder cover has an injection nozzle in the center and at least two peripheral injection nozzles. 
     Gaseous fuels are gaining importance in the large engine sector, in particular in stationary engines for power generation. Because of its very good availability and more favorable emission potential compared with diesel fuel, natural gas is ideal for economic and environmentally-friendly engine operation. Most gas engines work on the spark-ignition combustion process, i.e. with homogeneous combustion and external ignition, wherein the ignition can be initiated either by a spark plug or by a diesel pilot injector. The spark-ignition combustion process has however the disadvantage that during the charge cycle, due to the external mixture formation, an undesirable methane loop occurs. Methane loops can however only be prevented if a combustion process with internal mixture formation is applied in the engine. For this, a direct high-pressure injection is required. 
     Dual-fuel nozzles, in particular those in which the gas valve and fuel needles are accommodated in the same nozzle body, are very complex to produce. The needles are e.g. arranged nested concentrically in each other in the nozzle body, see for example publication EP 1 274 933 B1, or housed separately in the nozzle body, e.g. the fuel needle is positioned centrally and further gas needles are arranged eccentrically in the nozzle body in order to cover the full combustion chamber range of 360°. 
     Irrespective of the variant concerned, the installation space in the nozzle body is always extremely constricted and hence disadvantageous for production of the nozzle in view of the necessary cost of production. This applies in particular if the gas shut-off elements (gas needles) must sit close to the combustion chamber at the nozzle holes, since otherwise a substantial proportion of gas continues to flow in or out after combustion and can adversely affect the hydrocarbon emissions. 
     SUMMARY OF THE INVENTION 
     On this basis, it is an object of the present invention to propose an improved dual-fuel fuel injector which remedies the problem of construction space while being in particular advantageously simple to produce. 
     According to the invention, a dual-fuel fuel injector is proposed, in particular for use with a first liquid fuel such as diesel fuel, heavy oil, bio-oil, and a second gaseous fuel or combustion gas such as e.g. natural gas, methane, bio-gas. 
     The dual-fuel fuel injector is provided for a fuel injection device of an internal combustion engine, in particular e.g. for a gas common rail system. In general, the fuel injector is preferably used with an internal combustion engine in the form of a gas engine, in particular based on a spark-ignition or diesel engine (with internal mixture formation), furthermore in particular with a large engine and furthermore in particular also for stationary applications, e.g. for engine-based cogeneration systems or industrial applications. 
     By means of the proposed dual-fuel fuel injector, both a purely liquid fuel mode and a combined liquid/gas mode can be implemented with any ratio of gas to liquid, in particular in the pilot injection method (with high-pressure gas injection). 
     The dual-fuel fuel injector proposed according to the invention has a first nozzle needle, the axial stroke of which can be controlled, for the delivery of liquid fuel via a first nozzle arrangement of the dual-fuel fuel injector. The dual-fuel fuel injector is here preferably configured for indirect (hydraulic) control of the first nozzle needle; alternatively however direct control of the first nozzle needle may also be provided. The first nozzle needle is preferably accommodated in a nozzle body of the fuel injector. 
     The dual-fuel fuel injector furthermore has a plurality of second nozzle needles, the axial stroke of which can be controlled and which are arranged around the first nozzle needle for the delivery of a gaseous fuel via a second nozzle arrangement of the dual-fuel fuel injector, for example two, three, four, five or more second nozzle needles. In particular, an arrangement is provided with a central first nozzle needle and second nozzle needles arranged eccentrically thereto, preferably concentrically to the first nozzle needle. Like the first nozzle needles, preferably the second nozzle needles are also accommodated in the nozzle body. As part of the second nozzle arrangement, each second nozzle needle is assigned e.g. one or more gas injection nozzle openings (spray holes) on the injector, which can be freely opened via said second nozzle needles. 
     According to the invention, furthermore for each of the second nozzle needles, for controlling their stroke (indirectly), a (separate) control chamber is provided on the dual-fuel fuel injector for pressurization—charging and relief—with a control fluid (pressurized or highly pressurized), preferably in the form of liquid fuel. In particular, it is provided that the control chambers of the second nozzle needles are also formed in the nozzle body. 
     The dual-fuel fuel injector according to the invention furthermore—characteristically—has a ring channel which can be charged and relieved via the control fluid, or pressurized with the control fluid, in particular selectively. Here the dual-fuel fuel injector is configured to charge and relieve—selectively—the control chambers for the second nozzle needles via the control fluid, for controlling the stroke of the second nozzle needles, starting from or via the ring channel (i.e. corresponding to the control fluid pressure level in the ring channel). The control chambers for the second nozzle needles are here in particular each connected communicatively to the ring channel. 
     The proposed dual-fuel fuel injector allows production with structurally significantly reduced complexity for the control of the second nozzle needles, wherein the installation space situation is also more comfortable than with conventional dual-fuel injectors. For example, as well as the gas needles, the pilot valve (without actuator) for the control system may also now be accommodated in the nozzle body. Furthermore, the dual-fuel fuel injector according to the invention allows a control pressure level to be set in the control chambers of the second nozzle needles, in particular indirectly and further preferably uniformly, in an advantageously simple fashion, via the ring channel or its control fluid pressure level (i.e. the ring channel acts as a pre-control chamber for the plurality of control chambers of the second nozzle needles). 
     In order to pressurize the second nozzle needles with an intended control pressure level for their stroke control, the dual-fuel fuel injector is in particular configured to be able to set a predefined control fluid pressure level in the ring channel, i.e. depending on the current operating or injection situation. For this, the ring channel preferably has at least one control fluid inlet and at least one control fluid outlet; furthermore—again, in a manner saving construction space and simple to produce—a small number of flow paths may be sufficient to set the pressure level in the ring channel. 
     Preferred embodiments provide the capacity to selectively relieve the pressure in the ring channel for the pressure level setting, in particular by being able to selectively open the control fluid outlet for this, i.e. to the low-pressure side of the fuel injector. For this, the dual-fuel fuel injector preferably has a pilot valve, in particular a 2/2-way directional control valve or 3/2-way valve. Alternatively or additionally, it may be provided that the control fluid inlet to the ring channel can be opened selectively in a similar manner (starting from a high-pressure side on the injector). A choke device is preferably arranged in each inlet and/or outlet. 
     Further advantages in relation to the improvement of the constricted construction space situation on the nozzle body, and the intended arrangement of the second nozzle needles or gas needles and pilot valve close to the nozzle, arise from refinements of the invention which provide that the dual-fuel fuel injector has a further control chamber for controlling the stroke of the first nozzle needle (liquid-fuel nozzle needle), and the control chambers for the second nozzle needles are formed on the injector closer to the nozzles than the control chamber for the first nozzle needle. 
     In such an arrangement in which the control chamber for the first nozzle needle is arranged in particular in a plane further away from the nozzle, and the control chambers for the second nozzle needles are arranged in a second plane closer to the nozzle, i.e. with an axial offset to the control chamber for the first nozzle needle, a gas unit including second nozzle needles, second control chambers and pilot valve may be provided and mounted close to the nozzle, advantageously utilizing the construction space well, as proposed for example in a ring sleeve housing (which surrounds a guide portion of the nozzle body for the first nozzle needle), in particular as a compact unit (similar to a drum carousel for the second nozzle needles). Also, such a refinement of the dual-fuel fuel injector allows the use of shorter second nozzle needles than in the prior art, with advantageously smaller moving mass. In such a solution, the ring channel may in particular be arranged (viewed in the axial direction) between the control chambers for the second nozzle needles and the control chamber for the first liquid-fuel nozzle needle. 
     Particularly robust embodiments of the dual-fuel fuel injector, which are advantageously simple to produce and save construction space, arise in the invention with embodiments in which the dual-fuel fuel injector has a multi-piece, in particular a three-piece nozzle body housing. Here the ring channel may simply be formed between a first (separately made) and a second (separately made) housing part, e.g. by means of at least one ring groove. Furthermore, the second nozzle needles may be accommodated in a third (separately made) housing part, preferably—as outlined above—in the form of a ring sleeve, and the control chambers thereof for the second nozzle needles may communicate with the ring channel via the second housing part, e.g. a simple-to-produce intermediate plate with bores. 
     The multi-piece nozzle body thus provided may be braced externally and/or internally to create an inseparable unit. 
     Preferably, and again advantageously extremely simply to produce, the dual-fuel fuel injector has a second ring channel (for combustion gas) to which each nozzle chamber of the second nozzle needles is connected communicatively for its supply with gaseous fuel. In particular in a solution which provides a third housing part as a ring sleeve, the second ring channel can easily be worked into the housing of the nozzle body or the third housing part, in particular again as a ring groove, starting from a central opening of the ring sleeve. 
     The invention also proposes a fuel injection device with at least one dual-fuel fuel injector as explained above. 
     Further features and advantages of the invention arise from the description below of exemplary embodiments of the invention, with reference to the drawings which show details essential to the invention, and the claims. The individual features may be implemented individually or as a plurality in any combination in a variant of the invention. 
     Preferred embodiments of the invention are explained in more detail below with reference to the attached drawings. These show: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  as an example and diagrammatically, in particularly greatly simplified, a dual-fuel fuel injector connected to gas and liquid fuel supply devices, according to a possible embodiment of the invention. 
         FIG. 2  as an example and diagrammatically, a section view of the nozzle body (with further components) of a dual-fuel fuel injector according to a preferred embodiment of the invention. 
         FIG. 3  as an example and diagrammatically, a transparent section view of the nozzle body according to  FIG. 2 . 
         FIG. 4  as an example and diagrammatically, a transparent view of the first housing part of the nozzle body according to  FIG. 2  and  FIG. 3 . 
         FIG. 5  as an example and diagrammatically, a transparent top view of the first housing part according to  FIG. 4 . 
         FIG. 6  as an example and diagrammatically, a section view of the second and third housing parts of the nozzle body according to  FIGS. 2 and 3 . 
         FIG. 7  as an example and diagrammatically, a further view of the second and third housing parts according to  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the description which follows and in the drawings, the same reference numerals designate elements with the same or comparable function. 
       FIG. 1  shows as an example a dual-fuel fuel injector (dual-fuel nozzle)  1  according to the invention, for a dual-fuel fuel injection system, in particular a gas common rail system, or for an internal combustion engine (not shown), in particular a gas/diesel engine. The dual-fuel fuel injector  1  is provided for an injection operation both with a first liquid fuel (in particular diesel fuel, bio-oil or heavy oil) and a second gaseous fuel (combustion gas) and has a nozzle body (nozzle element)  3 . 
     The nozzle body  3  houses a first nozzle needle  5 , the axial stroke of which can be controlled, i.e. in an axial bore  7  of the nozzle body  3 . The first nozzle needle  5  is provided for injection processes with liquid fuel. For operation with liquid fuel, the dual-fuel fuel injector  1  furthermore has a high-pressure line  9  which leads from a liquid-fuel inlet  11  on the dual-fuel fuel injector  1  to a liquid-fuel nozzle chamber  13  in the nozzle body  3 . 
     To supply the fuel injector  1  with liquid fuel, as part of a fuel injection device, a high-pressure (HP) supply device  15  may be provided, for example formed by means of a high-pressure pump  17  and a rail  19  and/or individual pressure accumulators, via which high-pressure supply device  15  liquid fuel taken from a tank can be delivered to the liquid-fuel inlet  11 . 
     The dual-fuel fuel injector  1  is furthermore configured to deliver high-pressure liquid fuel into the nozzle chamber  13  via a first nozzle arrangement  21  of the dual-fuel fuel injector  1  as a function of the (stroke) setting of the nozzle needle  5 , in particular into a combustion chamber of an internal combustion engine in an injection mode (e.g. purely liquid-fuel mode or pilot injection mode). 
     The dual-fuel fuel injector  1  is—as shown—configured, for injecting the liquid fuel, preferably as an indirectly operated injector  1 , in particular with a pilot valve (control valve)  23  which is preferably controlled by a magnetic actuator (or e.g. a piezo actuator). Alternatively, it may be provided to configure the dual-fuel fuel injector  1 , for the injection of liquid fuel, as a directly actuated injector  1 , wherein the actuator acts in particular directly on the nozzle needle  5 . 
     Via the pilot valve  23 , preferably accommodated with its actuator in an injector housing  25 , a control chamber  27  of the fuel injector  1  for the first nozzle needle  5  may be pressure-relieved depending on the valve position, in particular via a leakage flow path  29  of the fuel system internal to the injector. The leakage flow branch  29  leads from the control chamber  27  to a low-pressure side (LP) leakage outlet  31  of the injector  1 , i.e. via the pilot valve  23  (below choke  33 ), e.g. to a leakage collection container  35  (tank). 
     Furthermore, a high-pressure path  37  of the fuel system internal to the injector (with choke  39 ) opens into the control chamber  27  for the first nozzle needle  5 , via which path the control chamber  27  can be charged with high-pressure liquid fuel starting from the high-pressure line (high-pressure channel)  9 . The control chamber  27  may be defined by means of a needle guide sleeve  41  which is received in the axial bore  7  at its end remote from the nozzle, wherein a closing spring  43  may also be arranged in the axial bore  7  which presses the nozzle needle  5  into the closed position, i.e. against a valve seat or nozzle needle seat next to the nozzle arrangement  21 . 
     In order to deliver liquid fuel via the first nozzle arrangement  21  for liquid-fuel injection mode, i.e. from the nozzle chamber  13 , the (closing) force equilibrium at the nozzle needle  5  may be eliminated by relieving the pressure in the control chamber  27  via the pilot valve  23  (leakage flow path  29  opened), so that the nozzle needle  5  lifts away from the valve seat and can open the flow path to the spray holes of the nozzle arrangement  21 . To close the nozzle valve, the pilot valve  23  is switched to the blocking position (see  FIG. 1 ), whereupon the pressure in the control chamber  27  builds up again via the high-pressure path  9 ,  37  and the nozzle needle  5  returns to the needle seat supported by the closing spring force. 
     Thus evidently liquid fuel serves as the control fluid for charging and relieving the control chamber  27 . 
     As illustrated in  FIG. 1 , the dual-fuel fuel injector  1  furthermore has a plurality of second nozzle needles  45 , the axial stroke of which can be controlled and which are arranged around the first nozzle needle  5 , for the delivery of gaseous fuel via a second nozzle arrangement  47  of the dual-fuel fuel injector  1  (gas (nozzle) needles). The second nozzle needles  45  arranged around the first nozzle needle  5 , e.g. four second nozzle needles  45 , are—like the first nozzle needle  5 —each accommodated in an axial bore  49  of the nozzle body  3 , in particular in a concentric arrangement around the first nozzle needle  5 , so that an advantageously good 360° coverage can be achieved in the combustion chamber in gas injection processes. 
     For operation with gaseous fuel e.g. natural gas, bio-gas etc., the dual-fuel fuel injector  1  furthermore has a high-pressure gas line  51  which leads from a combustion gas inlet  53  on the dual-fuel fuel injector  1  to a respective gas nozzle chamber  55  of the second nozzle needles  45 . A flow path from the respective gas nozzle chamber  55  to at least one gas spray hole of the second gas nozzle arrangement  47  can here be shut off selectively via the respective second nozzle needle  45 . 
     To supply the fuel injector  1  with gaseous fuel (at the nozzle chambers  55 )—again, as part of a fuel injection device—a high-pressure gas supply device  57  may be provided, for example formed by means of a combustion gas store (tank) and a compressor or a liquid gas supply with high-pressure pump and evaporator, furthermore e.g. a rail etc., via which high-pressure supply device  57  the gaseous fuel e.g. natural gas can be supplied to the combustion gas inlet  53 . 
     For gas mode, the dual-fuel fuel injector  1  is configured similarly to the active principle outlined above for the first nozzle needle  5  or liquid-fuel mode, for indirect control of the second nozzle needles  45 . Highly pressurized combustion gas delivered to the gas nozzle chamber  55  can be emitted, depending on the (stroke) setting of the second nozzle needle  45 , via the second nozzle arrangement  47  of the dual-fuel fuel injector  1 , in particular injected into the combustion chamber of an internal combustion engine for an injection operation (e.g. pilot injection mode). With regard to the nozzle arrangement  47 , one or more spray holes which can be selectively opened may be assigned to each second nozzle needle  45 . 
     As part of the present invention, as also illustrated in  FIG. 1 , for each of the second nozzle needles  45 , for their stroke control, a separate control chamber  59  is provided on the injector  1  for pressurization with a control fluid. As before, liquid fuel supplied via the liquid fuel inlet  11  to the dual-fuel fuel injector  1  serves as a control fluid for the indirect control of the second nozzle needles  45 . A respective control chamber  59  for a second nozzle needle  45  may be defined preferably, like the control chamber  27  for the first nozzle needle  5 , by means of a needle guide sleeve  61  which is accommodated in the axial bore  49  at its end remote from the nozzle, wherein furthermore a closing spring  63  may be arranged in the axial bore  49  which presses the second nozzle needle  45  into the closed position, i.e. against a valve seat or nozzle needle seat at the nozzle arrangement  47 . 
     According to the invention, the dual-fuel fuel injector  1  furthermore has a ring channel  65  which can be charged and relieved via the control fluid (liquid fuel). 
     For charging, the ring channel  65  is connected to the high-pressure liquid-fuel line  9  via a control fluid inlet  67 , wherein in particular an inlet choke device  69  is also arranged in the inlet branch  67 . For pressure relief, the ring channel  65  can be connected via a control fluid outlet  71  selectively to the low pressure side (LP) of the fuel injector  1 , i.e. towards the leakage side. The outlet branch  71  is here conducted in particular via an outlet choke device  73 . 
     According to the invention, the dual-fuel fuel injector  1  is furthermore configured to charge and relieve or pressurize the control chambers  59  for the second nozzle needles  45 , for controlling the stroke of the second nozzle needles  45 , with the control fluid (via the control fluid) via or starting from the ring channel  65 . For this, as shown in  FIG. 1 , the control chambers  59 —in particular all control chambers  59 —for the second nozzle needles  45  are each connected communicatively to the ring channel  65 . The communicative connection of a respective control chamber  59  for a second nozzle needle  45  to the ring channel  65  advantageously requires with the invention only one (single) branch channel  75  to be provided in each case. The communication connection is here conducted in particular via a choke device  77 . 
     During the pressurization of the ring channel  65  with control fluid, wherein in particular a predefined control fluid pressure level is set in the ring channel  65 , also the communicatively connected control chambers  59  (of the second nozzle needles  45 ) are pressurized with control fluid, and thus necessarily a control pressure level is set in each of these, i.e. indirectly via the ring channel  65 . To this extent, the ring channel  65  constitutes or forms a (common) pre-control chamber for the control chambers  59  of the second nozzle needles  45 . 
     As part of the present invention, the dual-fuel fuel injector  1  is here preferably configured in particular to control the strokes of the second nozzle needles  45  via the ring channel  65  and the connected control chambers  59  largely simultaneously and with the same stroke profile over time. This is firstly achieved by using as far as possible the same parts on the gas injector unit formed with the second nozzle needles  45 , but is made more difficult by the ever-present tolerances. Because of the tolerances (of the choke devices, the needle sleeve play (leakage through ring gap), the nozzle needle spring tension, the line or control chamber dead volume etc.), the equilibrium pressure (at which each second nozzle needle  45  begins to open) may be different over the second control chambers  59 , so that the second nozzle needles  42  open with a time offset. 
     As part of the invention, it has however been found that the tolerances become negligible if secondly—as proposed—the sum of the cross-sections of the individual choke devices  77  is selected very much smaller than the cross-sections of the outlet choke device  73  and inlet choke device  69 . Because of the small choke cross-sections  77 , a very slow opening of the second nozzle needles  45  occurs, which however has a positive effect on the deflaming of the combustion gas jet in the upstream pilot injection flame (like in a blowlamp which is switched first preferably to a low level and only later turned up). 
     Insofar as the injection dynamic of the liquid fuel mode is furthermore not necessary for gas mode (since in gas mode, only the relatively long main injection is used), then—as evident from the overall view—the slightly temporally offset opening times are advantageously not necessary (furthermore, in addition the system only switches to gas mode above a specific part load level, so that even a minimal quantity capacity need not be taken into account). 
     In order to be able to close the second nozzle needles  45  more quickly (than the duration of the opening process) at the end of injection, in particular simultaneously, preferably the arrangement of at least one trigger plate may be provided in a respective control chamber  59  for a second nozzle needle  45 , e.g. according to publication DE 10 2012 010 614 A1. 
     As in liquid fuel mode, preferably a further pilot valve (control valve)  79 , in particular a single pilot valve  79 , is provided on the injector  1  to relieve the pressure in the ring channel  65 . The pilot valve  79  (and its actuator) is also accommodated in the injector housing  25 , wherein the pilot valve  79 —due to the improved combustion space situation with the invention—can advantageously also be provided in the nozzle body  3  (without actuator). The resulting advantage is that short second nozzle needles  45  with small moving masses may be used, giving an improved response behavior with less complexity. Depending on the valve setting of the pilot valve  79 , the pressure in the ring channel  65  may be relieved via the control fluid outlet  71  conducted via the pilot valve  79 , i.e. to the low-pressure side (LP) leakage outlet, e.g. to a leakage collection container (tank)  35 . The pilot valve  79  is preferably a 2/2-way directional control valve or e.g. a 3/2-way valve. 
     In order to be able to deliver combustion gas for combustion gas injection mode via the second nozzle arrangement  47 , i.e. from the gas nozzle chambers  55 , the (closing) force equilibrium at a respective second nozzle needle  45  may be eliminated by relieving the pressure in the ring channel  65  and hence in the control chamber  59 , communicatively connected thereto, for the second nozzle needle  45  via the pilot valve  79  (outlet  71  opened), so that the respective second nozzle needle  45  lifts away from a valve seat and can open the flow path to the nozzle needle arrangement  47 . To close the nozzle valve, the pilot valve  79  is switched to the blocking position (see  FIG. 1 ), whereupon the pressure in the ring channel  65  and hence in the communicatively connected control chamber  59  for the second nozzle needle  45  builds up again via the high-pressure path  9 ,  67 , and the respective second nozzle needle  45  returns to the needle seat supported by the closing spring force. 
     As  FIG. 1  shows, the dual-fuel fuel injector  1  is furthermore preferably advantageously designed structurally simply in that the gas nozzle chambers  55  are also connected communicatively to a (further) ring channel  81  in the dual-fuel fuel injector  1 , wherein the gas nozzle chambers  55  are supplied with all the combustion gas to be delivered from the combustion gas supply line  51  via the further ring channel  81 . 
     With reference to  FIGS. 2 to 7 , a preferred embodiment of the dual-fuel fuel injector is now explained in more detail. 
       FIG. 2  shows the nozzle body  3  of the dual-fuel fuel injector  1  (with components accommodated therein, e.g. an actuator  79   a  of the second pilot valve  79 ) in a section view. The nozzle body  3  has a multi-piece housing  83 , wherein a first  83   a  of three housing parts receives the liquid-fuel nozzle needle  5  and its needle guide sleeve  41  and its nozzle spring  43 . At the end of the first housing part  83   a  close to the nozzle, the first nozzle arrangement  21  is formed for delivering liquid fuel, i.e. by several spray holes. At the end of the first housing part  83   a  remote from the nozzle, the control chamber  27  for the first nozzle needle  5  can be provided by the needle guide sleeve  41 , i.e. in a first plane remote from the nozzle, see also  FIG. 1  (plane  1 ). 
     The first housing part  83   a  of the nozzle body  3  has a portion of tapering cross-section (constant outer cross-section), forming a step (surface)  85 , which extends from a longitudinal center region of the first housing part  83   a  to the nozzle arrangement  21 . A ring groove  87  is worked in the step surface  85  as an advantageously simple means of providing the ring channel  65 . 
       FIG. 3 , which corresponds to the view of  FIG. 2  in transparent depiction, illustrates the ring groove  87  at the step surface  85  with the control fluid inlet  67  branching into it and the control fluid outlet  71  branching off it, wherein the inlet  67  and outlet  71  are each formed by means of a choke bore  69  and  73 . Also with reference to the production of the flow connections  69 ,  73  to the ring channel  65 , the design with step surface  85  evidently allows advantageously good access from this. 
       FIG. 4  and  FIG. 5  illustrate the first housing part  83   a  with in particular the flow paths formed therein, each in a transparent view in more detail. 
     With reference now again to  FIG. 2  and  FIG. 3 , the nozzle body housing  83  has a second housing part  83   b . The second housing part  83   b  is provided as an intermediate plate and surrounds the tapered portion as a ring, resting against the step surface  85 . The second housing part  83   b  furthermore has passages (bores)  91  which serve for the communicative connection of the control chambers  59  of the second nozzle needles  45  to the ring channel  65 . The passages  91  may each form a choke device  77 ; alternatively or additionally, the ring channel  65  may provide the choke device  77 . 
     In the multi-piece nozzle body housing  83  illustrated, a third housing part  83   c  is pressed against the second housing part  83   b  and receives the second nozzle needles  45  and their needle guide sleeves  61  and their nozzle springs  63  (not shown). 
       FIG. 6  and  FIG. 7  illustrate this arrangement—like  FIG. 2  and  FIG. 3 —in more detail, in particular also the passages (communication connections)  91  of the control chambers  59  for the second nozzle needles  45  with the ring channel  65  at the second housing part  83   b.    
     As  FIG. 6  and  FIG. 7  furthermore show, also at the end face  89  of the second housing part  83   b  resting against the step surface  85 , a ring groove  93  complementary to the ring groove  87  on the step surface  85  may be worked into the intermediate plate  83   b , and the ring channel  65  may be formed by this groove and the ring groove  87  of the step surface  85 . Alternatively, only a single ring groove  87  may be provided for forming the ring channel  65 , i.e. in the housing part  83   a  or  83   b . Preferably, the ring channel  65  is generally formed—as shown—between two housing parts ( 83   a ,  83   b ). 
     The third housing part  83   c  is provided as a ring sleeve (like a drum magazine accommodating the second nozzle needles  45 ) and is arranged on the nozzle body  3 , also around the tapered portion of the first housing part  83   a , here resting with an end face remote from the nozzle against the second housing part  83   b.    
     Resting against the second housing part  83   b , the passages  91  in the second housing part  83   b  allow the communication of the control chambers  59  with the ring channel  65 , wherein the control chambers  59 —formed by means of the needle guide sleeves  61  and the second housing part  83   b —of the second nozzle needles  45  are located correspondingly at the end of the third housing part  83   c  remote from the nozzle, i.e. in a second plane closer to the nozzle than the first plane, see also  FIG. 1  (plane  2 ). At the end of the third housing part  83   c  close to the nozzle, the second nozzle arrangement  47  is formed for the delivery of the combustion gas i.e. by means of several spray holes. 
     In this embodiment of the dual-fuel fuel injector  1 , the ring channel  65  is thus provided between the first plane (of the first control chamber  27 ) and the second plane (of the second control chambers  59 ). 
     The dual-fuel fuel injector  1 , see for example  FIG. 2  or  FIG. 6 , also has a second ring channel  81 , to which nozzle chambers  55  (ring chambers at the gas nozzle needle tips) of the second nozzle needles  45  are each connected communicatively for their supply with gaseous fuel. Structurally advantageously simply, the second ring channel  81  is worked into the housing  83  of the nozzle body  3  or the third housing part  83   c , starting from the central opening of the third housing part (ring sleeve)  83   c , in a simple manner, in particular again as a ring groove. The connection to the high-pressure line  51  can advantageously take place via a single branch channel.