PILOTING ARRANGEMENT, NOZZLE DEVICE, GAS TURBINE ARRANGEMENT AND METHOD

A pilot arrangement for a nozzle of a gas turbine, in particular of an aircraft engine, including: a cavity extending along a longitudinal axis for conducting fuel, a narrowest flow cross section of which is larger than a flow cross section of a pilot fuel nozzle, in particular a pilot line. The pilot fuel nozzle, which adjoins the cavity in a downstream direction includes the pilot line and a pilot fuel outlet arranged at the downstream end of the pilot line, the narrowest flow cross section of which is configured to be smaller than that of the cavity. Reliable operation is made possible by virtue of an air opening arranged on the pilot arrangement in flow connection with the cavity so there can be an at least occasional flow of air through at least the cavity and the pilot fuel nozzle during the operation of the gas turbine.

This application claims priority to German Patent Application 102023201244.8 filed Feb. 14, 2023, the entirety of which is incorporated by reference herein.

The invention relates to a pilot arrangement for use in a nozzle device of a gas turbine arrangement, in particular of an aircraft engine, according to the preamble of claim1. The invention furthermore relates to a nozzle device, a gas turbine arrangement and a method for operating a gas turbine arrangement.

Fuel nozzles frequently have a pilot stage (pilot means) so as to carry out combustion processes in a stable manner in an aircraft engine over as wide an operating range as possible. In this case, less fuel is supplied via the pilot means than via a main stage. The combustion process via the pilot stage is operated in a stable range, thus stabilizing the combustion process via the main stage under unstable operating conditions.

A pilot arrangement of the type mentioned at the outset is specified in U.S. Pat. No. 10,072,845 B2. In this document, the dimensions of the nozzle device comprising the pilot arrangement are relatively large.

A further pilot arrangement, in a nozzle device which likewise has relatively large dimensions, is specified in EP 1 445 540 A1.

US 2014/0291418 A1 shows a nozzle device comprising two air channels for operating with two air flows (“two-flow fuel nozzle”), without a pilot means.

With compact pilot arrangements, in particular, there is the risk of coking within fuel-carrying parts containing residual fuel when the pilot arrangement is temporarily not in operation. This can lead to clogging and to restricted operation, and even to failure, of the pilot arrangement.

The object on which the present invention is based is that of providing a pilot arrangement that can be operated in a reliable manner, and a nozzle device having a pilot arrangement, a gas turbine arrangement, and a method for operating a gas turbine arrangement.

The object is achieved with respect to the pilot arrangement by the features of claim1. The object is achieved with regard to the nozzle device by the features of claim11, with regard to the gas turbine arrangement by the features of claim12and with regard to the method by the features of claim13.

In the pilot arrangement, it is envisaged according to the invention that an air opening is arranged on the pilot arrangement in such a way in flow connection with the cavity that there can be an at least occasional flow of air through at least the cavity and the pilot fuel nozzle during the operation of the gas turbine arrangement.

The cavity acts in particular as a settling chamber for pilot fuel supplied from (a) pilot fuel supply line(s).

Any pilot line of the pilot fuel nozzle that may be present can have a constant flow cross section over the axial length.

By means of the air opening, it is advantageously possible to purge fuel-carrying parts of the pilot arrangement, such as the cavity and/or the pilot fuel nozzle, with air in order to remove residual fuel and thus minimize the risk of coking within the pilot arrangement. Thus, the proposed design leads to reliable operation of the pilot arrangement.

For a particularly compact configuration, it is expediently provided that the cavity is arranged in a central body arranged on the longitudinal axis, and that at least one swirling element is arranged in a circumferential manner around the central body, wherein the central body and the at least one swirling element form a swirling arrangement. Thus, the pilot arrangement advantageously has a dual function, wherein the pilot arrangement is simultaneously configured as a swirling arrangement or has the swirling arrangement.

In a particularly preferred configuration variant, it is provided that the at least one swirling element, the central body and the pilot fuel nozzle are configured as a continuous, integral component. The integral component obtained, which serves as a pilot arrangement and as a swirling arrangement, can advantageously have a configuration which is very highly optimized in terms of installation space.

Further contributing to a compact configuration of the pilot arrangement is the provision of at least one pilot fuel supply line for supplying fuel into the cavity, wherein the at least one pilot fuel supply line is guided through the at least one swirling element, for conducting pilot fuel from a circumferential wall of an inner air channel radially inwards into the cavity. Where a plurality of swirling elements is provided, a plurality of pilot fuel supply lines is preferably provided, wherein preferably a plurality and/or each of the swirling elements has at least one pilot fuel supply line.

An advantageous air supply for purging the pilot arrangement can be achieved if the air opening is arranged on a side of the pilot arrangement which (after installation) faces upstream in relation to an air inflow direction (during operation), in direct flow contact with the (i.e. at the) cavity, in particular centrally on the longitudinal axis. During operation, the air inflow is provided by the air flowing through the inner air channel. In this case, the air opening is preferably routed to the cavity from the outside through the central body. In this case, any hollow chamber which is present is penetrated by the air opening, with fluid-tight sealing being provided by means of the wall around the air opening, for example. Alternatively or in addition, the air opening is arranged on the at least one swirling element in direct flow contact with the (i.e. at the) at least one pilot fuel supply line, preferably as far as possible radially outwards on the swirling element within the inner air channel. This ensures that, when there is a throughflow of air, the at least one pilot fuel supply line is purged in addition to the cavity and the pilot fuel nozzle. If there is a plurality of swirling elements present, the air opening is preferably arranged on each swirling element that carries fuel, i.e. has a pilot fuel supply line.

The air opening is preferably configured to generate a pressure loss during operation such that, when there is a fuel flow through the pilot arrangement, there is no flow of air through the air opening and, after the fuel has been switched off, there is an at least occasional flow of air through it. The configuration is furthermore preferably such that air flows from upstream to downstream through the air opening (with respect to the routing of air in the nozzle arrangement), but not in the opposite direction (and especially not with fuel). As a particular preference, the air opening is configured as a throttle element, which sets the desired air flow on the basis of fluid-dynamic self-regulation, without additional open-loop and/or closed-loop control. The fuel flow itself also preferably contributes to generating the required pressure loss, e.g. by forming standing vortices within the fuel flow at or within the air opening and/or by influencing the flow cross section on the basis of adhesion or capillarity of the fuel, e.g. at walls and/or downstream of orifice openings.

In particular, the above functionality can be achieved if the air opening has at least one orifice opening and/or a porous structure, e.g. a porous structure formed by sintering loose material such as balls, particles or chips. In the configuration with an orifice opening, it is possible, in particular, to arrange and form a plurality of orifice openings and/or spaces of widened cross section in a suitable manner, e.g. in series, in order to bring about the required pressure drop and/or pressure profile (pressure difference) across the air opening, in particular the throttle element. The precise configuration of the precise design and/or arrangement is preferably carried out experimentally and/or with computer support by means of flow simulation.

In a preferred configuration variant, the air opening can be configured as a throttle element produced integrally with the pilot arrangement or produced separately and installed afterwards, in particular welded or brazed in.

For thermal shielding of the cavity and/or the pilot line, a hollow chamber is arranged as a heat shield, preferably in a circumferential manner around the pilot fuel nozzle, in particular around the pilot line, and/or the cavity. The hollow chamber is preferably fluidically connected, i.e. a single continuous hollow chamber is provided. The hollow chamber is configured around the pilot line, for example as a gap-like chamber which is, at least in portions, fully circumferential. Around the cavity, the hollow chamber is preferably configured so as to be complementary to the shape of the cavity, wherein a wall provided between the cavity and the hollow chamber can, for example, have an at least substantially constant thickness. Air and/or fuel-carrying fluid ducts (for example the air opening, pilot fuel supply line(s) and/or the pilot line) passing through the hollow chamber into or out of the cavity are configured to be fluid-tight relative to the hollow chamber.

In this case, it can advantageously be provided that the hollow chamber is sealed in a flow-tight manner relative to the environment (an air atmosphere surrounding the pilot arrangement). In this way, no exchange of substances, in particular no gas exchange, can occur between the hollow chamber and the environment.

Particularly effective thermal shielding is achieved if the hollow chamber is filled with an inert gas (for example argon or xenon) or evacuated (i.e. subjected to a vacuum). The inert gas takes the form in particular of a gas with a lower thermal conductivity than air (which has a thermal conductivity of 0.0262 W/mK).

The pilot means can be advantageously relocated into the region of the outlet of the inner air channel if, at the downstream end of the central body, a lance is provided which extends on the longitudinal axis and in which the pilot line extends at least for the most part, wherein the lance comprising the pilot line has an axial length such that the fuel outlet is positioned at least in a downstream third or quarter, preferably at least substantially at an outlet, of an inner air channel of the nozzle device.

The nozzle device according to the invention comprises a pilot arrangement according to any one of the configuration variants specified above and an inner air channel, which is arranged on a central longitudinal axis of the nozzle device and within which the pilot arrangement is arranged coaxially with the inner air channel, wherein, in particular, the longitudinal axis lies on the central longitudinal axis. The air opening is arranged within the inner air channel.

To achieve relatively low pressure loss and a relatively large available installation space, the central body and the swirling element(s) are preferably arranged upstream of the narrowest flow cross section of the inner air channel.

Optionally, the inner air channel, comprising a (for example cylindrical) wall enclosing the inner air channel, can form, at least in part, a portion of the integral component which comprises and/or forms the pilot arrangement.

The pilot fuel nozzle is arranged in the central body and/or at least in part within the lance. Where the lance is provided, the lance is preferably manufactured together with the integral component and is thus an integral part thereof.

In the method for operating a gas turbine arrangement, it is provided that, in a pilot arrangement of a nozzle device, there is an at least occasional flow of air through at least a (fuel-carrying) cavity and a pilot fuel nozzle during operation, wherein, during operation of the pilot arrangement, with fuel flow through the same, there is no flow of a medium, in particular air and/or fuel, through an air opening in flow contact with the cavity and the pilot fuel nozzle, and, when the pilot arrangement is deactivated (without fuel flow through the latter), there is an at least occasional throughflow of air in the direction of the pilot fuel nozzle.

Advantageous embodiment variants of the method are set out in connection with the configuration variants of the pilot arrangement.

FIG.1Ashows a longitudinal sectional view of a nozzle device100comprising three air channels5,7(“3-flow fuel nozzle”), as known from the prior art. Nozzle devices100of this type are used in gas turbine arrangements, in particular in aircraft engines.FIG.1Bshows a longitudinal sectional view of the inner air channel7of the nozzle device100, with an integrated central body8.FIG.1Cshows a partial sectional view of the inner air channel7along the line A of intersection.

The nozzle device100shown inFIGS.1A to1Cis configured in particular for operating with a liquid fuel (kerosene-based or kerosene-related).

The nozzle device100has a fuel feed1which is connected in terms of flow for providing fuel during operation to an annular fuel reservoir2of the nozzle device100. Arranged downstream of the annular fuel reservoir2is an annular fuel line3, which provides fuel to a fuel injector4of the nozzle device100during operation. The fuel is injected into a combustion chamber (not shown in this case) by means of the fuel injector4.

The fuel injector4is radially surrounded by two circumferential air channels5, a radially outer air channel and a radially central air channel. Swirling elements6are arranged within each of the air channels5.

In a central position on a central longitudinal axis M, the nozzle device100comprises the inner air channel7which is enclosed by a wall70, in particular a cylindrical wall. The inner air channel7, at the downstream end thereof, has an outlet71for adjoining the combustion chamber. An internal diameter D in a downstream portion and/or at the outlet71can be 7 mm to 15 mm for example.

Provided between the inner air channel7and the annular fuel line3and/or the fuel injector4is an air chamber10for thermally shielding (i.e. acting as a heat shield) these fuel-carrying lines.

Arranged within the inner air channel7is a swirling arrangement9, which has a central body8in a central position on the central longitudinal axis M. Swirling elements90of the swirling arrangement9are arranged around the central body8for generating a swirl flow within the inner air channel7during operation and extend from the central body8in a radial-tangential direction to the wall70. An example thickness d of the swirling elements90is 0.8 mm to 1.5 mm. The swirling elements90and the central body8are manufactured as separate components which are joined to one another prior to installation, for example during assembly of the nozzle device100.

Stability problems can arise during operation using the nozzle device100according toFIGS.1A to1C, wherein for example, a lean blowout can occur. A pilot means can be used for stabilisation purposes, but this is difficult to implement, however, in particular in small nozzle devices100due to a lack of installation space.

FIG.2Ashows the inner air channel7in a longitudinal section, andFIG.2Bshows a pilot arrangement23in a partial section along section line B, as indicated in DE 10 2022 208 337.7, filed at the German Patent and Trademark Office on 10 Aug. 2022, as prior art which was not a prior publication on the application date. By virtue of the possibility of its compact construction, the pilot arrangement23can be inserted easily into nozzle devices100, even those of relatively small dimensions, as shown, for example, inFIG.1A.

The pilot arrangement23has a cavity12which is arranged centrally on a longitudinal axis L and extends along the longitudinal axis L. In particular, the longitudinal axis L is arranged on the central longitudinal axis M of the nozzle device100. Furthermore, the pilot arrangement23has a pilot fuel nozzle13comprising a pilot line130, which extends in an axial manner centrally on the longitudinal axis L, and a fuel outlet131, which is arranged at the downstream end of the pilot line130. The pilot fuel nozzle13is arranged directly downstream of and is connected in terms of flow to the cavity12and is fed with fuel from the cavity12during operation.

The narrowest flow cross section of the cavity12is configured to be larger than the flow cross section of the pilot fuel nozzle13, in particular the pilot line130. For example, a maximum height H of the cavity (for example a diameter) corresponds to ¼ to ¾ of the smallest diameter D of the inner air channel7. The cavity12acts in particular as a settling chamber for the fuel flow.

The pilot arrangement23is integrated into the swirling arrangement9for a particularly compact construction. In this case, the cavity12is arranged in the central body8of the swirling arrangement9, in particular symmetrically relative to the longitudinal axis L. The swirling elements90are arranged radially in a circumferential manner around the central body8comprising the cavity12. The pilot fuel nozzle13can also be arranged in the central body8and/or at least partially in a lance16which is arranged at the downstream end of the central body8and extends centrally on the longitudinal axis L (cf. for exampleFIGS.4and5).

For a compact, fluid-tight configuration, the pilot arrangement23is configured with the swirling elements90and the central body8comprising the cavity12, preferably as a continuous, integral component.

The pilot arrangement23moreover comprises, by way of example, a plurality of pilot fuel supply lines11for supplying fuel into the cavity12. For a particularly compact design, the pilot fuel supply lines11are guided through the swirling elements90from the radially exterior region, i.e. from the wall70of the inner air channel7, inwards to the cavity12. For this purpose, a corresponding distribution line for providing the pilot fuel supply lines11with fuel (not shown in this case) is preferably arranged in the wall70.

For thermal shielding of the cavity12and/or the pilot line130, a hollow chamber14, for example, is arranged as a heat shield within the central body8in a circumferential, preferably at least substantially fully circumferential, manner around the pilot line130and/or the cavity12. Preferably, precisely one (continuous in terms of flow) hollow chamber14is provided. On its upstream side, the hollow chamber14is sealed by means of a weld15. The pilot fuel supply lines11are configured to be fluid-tight relative to the hollow chamber14.

For effective heat shielding, the hollow chamber14is sealed in a flow-tight manner relative to an environment22, i.e. an air atmosphere surrounding the pilot arrangement23, and is particularly advantageously filled with an inert gas or evacuated. The inert gas can take the form in particular of a gas with a lower thermal conductivity than air, for example argon (thermal conductivity 0.0179 W/mK) or xenon (thermal conductivity: 0.0055 W/mK). An optimized heat shield effect is achieved by the inert gas or vacuum, thereby effectively minimizing heat input from the inner air channel7(with air temperatures of approximately 600° C.) to the fuel (approximately 50° C.) within the cavity12and/or the pilot line130, even when the dimensions involved are small.

FIG.3shows the pilot arrangement23illustrated inFIG.2Awith the addition of a refinement according to the invention. In this case, an air opening18is arranged on the pilot arrangement23in such a way in flow connection with the cavity12that there can be an at least occasional flow of air through the cavity12and the pilot fuel nozzle13during the operation of the gas turbine arrangement. During operation, at least at certain operating points, the air inflow is provided by the air flowing through the inner air channel7, of which a proportion flows through the pilot arrangement23. By means of the air opening18, it is thus possible for fuel-carrying parts of the pilot arrangement23, such as the cavity12and the pilot fuel nozzle13, to be purged with air in order to remove residual fuel. In this way, coking within the pilot line130and/or the cavity12, which may lead to clogging of fuel-carrying parts, associated with restricted operation of the pilot arrangement23and even failure thereof, is prevented.

The air opening18is configured to generate a pressure loss during operation such that there is no flow of air through the air opening when fuel is flowing through the pilot arrangement23. After the fuel is switched off, there is an at least occasional flow of air through the pilot arrangement23from the direction of the inner air channel7into the pilot arrangement23, in the exemplary embodiment shown into the cavity12. The throughflow is from the same side as the inner air channel7but not in the opposite direction (and especially not with fuel).

As a particular preference, the air opening18is configured as a throttle element17, which sets the desired air flow on the basis of fluid-dynamic self-regulation, without additional open-loop and/or closed-loop control. When fuel is flowing, the fuel flow itself also preferably contributes to generating the required pressure loss, e.g. by forming standing vortices within the fuel flow at or within the air opening18and/or by influencing the flow cross section on the basis of adhesion or capillarity of the fuel, e.g. at walls and/or downstream of orifice openings180.

To produce these modes of operation, the throttle element17is configured inFIG.3, by way of example, as comprising an orifice opening180, upstream and downstream of which there are respective spaces19of widened cross section (cf. alsoFIG.6C). The space19arranged upstream (on the same side as the inner air channel7) has a conical portion as a transition to the orifice opening180, whereas the orifice opening180makes a transition to the downstream space19(on the same side as the cavity) by means of a step change in the cross section.

The side of the air opening18which faces in the upstream direction is arranged in the direction of the upstream-facing side of the inner air channel7, i.e. on that side of the pilot arrangement23which faces upstream with respect to the air inflow direction. This ensures that, during operation, it is the air flowing through the inner air channel7that flows into the air opening18. In the exemplary embodiment shown inFIG.3, the air opening18is arranged in direct flow contact with the cavity12and lies centrally on the longitudinal axis L. In this case, the air opening18is arranged on the cavity12by means of the wall of the central body8and, at the same time, in a manner sealed off fluid-tightly with respect to the hollow chamber14.

FIG.4shows an exemplary embodiment of the pilot arrangement23according to the invention, in which the pilot fuel outlet131is arranged in the downstream third of the inner air channel7in the vicinity of the outlet71. For this purpose, the lance16, which extends coaxially with the inner air channel7on the longitudinal axis L, is arranged at the downstream end of the central body8. At least the majority of the pilot line130extends within the lance16. A portion of the hollow chamber14, which surrounds the pilot line130at least for the most part, is also configured within the lance16. The lance16enables the heat release zone to be located further downstream during the pilot combustion process.

The lance16is preferably also manufactured integrally with the central body8and the swirling elements90, i.e. the integral component comprising the pilot arrangement also comprises the lance16.

Just as in the exemplary embodiment shown inFIG.3, the air opening18is arranged centrally on the longitudinal axis L in direct flow contact with the cavity12.

The flow cross sections of the pilot line130and/or the pilot fuel supply lines11are preferably configured to be round and/or rhombic.

FIG.5shows an exemplary embodiment of the pilot arrangement23according to the invention, wherein the air opening18is arranged in direct flow contact with, here by way of example, one of the pilot fuel supply lines11on one of the swirling elements19. The upstream side of the air opening18likewise faces in the direction of the upstream side of the inner air channel7. The air opening18is likewise aligned coaxially with the longitudinal axis L. The arrangement of a respective air opening18on each pilot fuel supply line11would also be advantageous. By means of this arrangement it is possible not only to purge the cavity12and the pilot fuel nozzle13but also some portion or portions of the pilot fuel supply line/s11with air.

FIGS.6A to6Dshow air openings18, each configured as throttle elements17, as possible exemplary embodiments for generating the self-regulating modes of operation. The configuration of the precise shapes, arrangement, cross section and/or length ratios is preferably carried out experimentally and/or with computer support by means of flow simulation.

The air opening18in the configuration as a throttle element17can, for example, be produced integrally with the pilot arrangement23and, if appropriate, with the nozzle device100itself, in particular printed in an additive manufacturing method. Separate manufacture of the throttle element17, e.g. from several parts, conventionally as an individual part or by means of additive manufacturing (3D printing) is also possible. The preferred manufacturing method also depends, in particular, on the precise configuration of the throttle element17.

FIG.6Ashows the throttle element17with, by way of example, three orifice openings180arranged one behind the other, upstream and downstream of which a respective space19of widened cross section is arranged. On the downstream side in each case, the orifice openings180and the spaces19are connected to one another by means of step changes in cross section, while, as regards the upstream sides, they merge continuously, by means of conical portions, into the orifice openings180.

FIG.6Bshows the throttle element17by way of example, comprising an open porous structure20, in this case with sintered spherical elements. Other sintered loose materials, e.g. particles, pellets or chips, are also possible. The porous structure20can consist of metal, glass and/or ceramic, or can contain at least one of these materials.

FIG.6Cshows the throttle element17by way of example with a single orifice opening180, the flow diameter of which is configured so as to be smaller than the orifice openings shown inFIG.6A.

FIG.6Dshows the throttle element17by way of example with an inlet-side orifice opening180, wherein an elongate space19with a widened cross section is arranged downstream of the orifice opening180.

FIG.7shows a diagram24, which is used to explain an illustrative mode of operation of the air opening18. In this case, an absolute pressure P is plotted logarithmically on an ordinate25, as is an absolute pressure difference dP, against an abscissa26with a logarithmically plotted fuel mass flow m via the nozzle device100under different illustrative operating conditions. More specifically, the operating conditions are an ignition condition A, a low load condition B, and a high load condition C of the illustrative engine.

The diagram24shows qualitatively the characteristic of an absolute air pressure P0of the air upstream of the pilot arrangement23within the inner air channel7. Furthermore, the diagram24shows the characteristic of an absolute pressure difference dP1of the air via the nozzle device100(dP1=P0−P(pressure downstream of the nozzle device100)). Furthermore, the diagram24shows the characteristic of an absolute pressure difference dP2of the air via the air opening18in relation to the fuel located in the cavity12(dP2=P0−P(fuel in the cavity12)). Furthermore, the diagram24shows the characteristic of an absolute pressure difference dP3of the air via the pilot arrangement23, i.e. via the air opening18, the cavity12and the pilot fuel nozzle13.

Under the ignition conditions A, the pilot arrangement23is in operation, i.e. there is a flow of pilot fuel through it (fuel throughflow27). Within the cavity12, the fuel pressure (not shown directly in the diagram24) is close to or slightly above the air pressure P0upstream of the pilot arrangement23. Within the pilot fuel nozzle13with the pilot line130, the fuel pressure at the pilot fuel outlet131is significantly lower than the air pressure P0. The fuel thus flows downstream out of the cavity12into the pilot line130, since it is in this direction that the greatest pressure gradient is present, and not via the air opening18. No air flows via the air opening18into the cavity12since there is no pressure gradient across the air opening18(cf. pressure difference dP2under pressure condition A inFIG.7) or the pressure gradient is too small (cf. pressure difference dP2under ignition condition B with fuel throughflow27inFIG.7) to generate an air flow, wherein the configuration as a throttle element17counteracts the formation of an air flow, especially in conjunction with the fuel flow. The throttle element17is, for example, designed in such a way that slight pressure fluctuations of, for example, up to 2% are possible without generating an air flow via the air opening18.

Under the low load conditions B, the pilot arrangement23is deactivated, wherein the transition from fuel throughflow27(illustrated by means of dP2) to air throughflow28(illustrated by means of dP3) of the pilot arrangement23takes place via the air opening18, without pilot operation.

Before the pilot fuel is switched off, with fuel throughflow27, the pressure prevailing in the cavity12is somewhat lower than the air pressure P0, but higher than the pressure downstream of the nozzle device100, within a combustion chamber arranged downstream of the nozzle device100(i.e. dP2is lower than dP1under low load conditions B). No air flows via the air opening18since, by virtue of its configuration as a throttle element17, especially in conjunction with the fuel flow, as indicated above, an inflow of the air is hindered or prevented.

If the pilot fuel flow is switched off (change over to air throughflow28), the pressure in the cavity12falls since it is no longer maintained by a fuel pump (in particular, the fuel pump is switched off or decoupled by a valve). Effects of the fuel that hinder an air flow, such as standing vortices, disappear. The result is a larger pressure gradient from the inner air channel7to the cavity12. As a result, there is an air flow via the air opening18into the pilot arrangement23, and this gradually displaces the fuel from the cavity12and the pilot fuel nozzle13in the direction of the outlet71of the nozzle device100into the combustion chamber. In the process, the pressure difference dP3is established across the air opening18, the cavity12and the pilot line130, such that it (almost) corresponds to the pressure difference dP1across the remainder of the nozzle device100(cf. pressure difference dP1and pressure difference dP3in region28). Thus, it is air rather than fuel which now flows through the deactivated pilot arrangement23.

Under the high load conditions C, the pilot arrangement23is deactivated, i.e. it is air flowing in via the air opening18which flows through it. This state is qualitatively equivalent to the state under low load conditions B after fuel shut-off, with air throughflow28.

In summary, the proposed configuration with the air opening18contributes to the at least occasional purging of the pilot arrangement23with air, and to reliable operation of the pilot arrangement23, wherein it is possible, by means of the purging of fuel-carrying parts within the pilot arrangement23, to effectively minimize or prevent coking of said parts.

LIST OF REFERENCE SIGNS