WO2014173660A1

WO2014173660A1 - Combustion system of a flow engine and method for determining a dimension of a resonator cavity

Info

Publication number: WO2014173660A1
Application number: PCT/EP2014/056803
Authority: WO
Inventors: Charith Jayatunga
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-04-23
Filing date: 2014-04-04
Publication date: 2014-10-30
Also published as: US20160076766A1; GB201516231D0; KR20160003733A; GB2527688A

Abstract

The present invention relates to a combustion system of a flow engine comprising at least one combustion chamber, a shared manifold (18) to feed a flow medium via at least two injectors to the at least one combustion chamber and at least one resonator (20) with at least one resonator cavity (22), wherein the at least one resonator (20) is arranged functionally in/at the manifold (18). To obtain good combustion performance with a homogenous fuel flow rate and high combustion stability, it is provided that the resonator (20) comprises at least one perforated section (24) with at least two orifices (26), wherein the at least two orifices (26) provide access to the at least one resonator cavity (22) of the at least one resonator (20).

Description

COMBUSTION SYSTEM OF A FLOW ENGINE AND METHOD FOR DETERMINING A DIMENSION OF A RESONATOR CAVITY

Field of invention

The present invention relates to a combustion system of a flow engine comprising at least a resonator having a

resonator cavity and a method for determining a dimension of this resonator cavity of the aforementioned resonator.

Art Background

Combustors of a flow engine, like a gas turbine, comprise a combustion chamber provided with a combustion air inlet and with a fuel passage connected to a fuel injector arranged to discharge fuel into the combustion chamber. Combustion air as well as fuel enters the combustion chamber under pressure. The resultant combustion is basically very fast and generates dynamic forces in the form of pressure fluctuations, which may manifest on a casing of the combustor as vibrations.

Moreover, combustion dynamics also occur due to a coupling between pressure oscillations and unsteady heat release. One of the major causes of unsteady heat release is due to fuel flow rate perturbations. These perturbations emerge from an acoustic pressure wave, entering the fuel passage as well as a downstream (direction in reference to entering direction) arranged fuel gallery and/or manifold through the fuel injector. This depends on the impedance at the fuel injector, which in turn is influenced by running conditions of the combustor, namely operation e.g. under full or part load or characteristics of the flame, by properties of the fuel, e.g. Wobbe indices, temperature or gaseous or liquid state of the fuel, by characteristics of the injector, like size or shape of its orifices, or by characteristics of the manifold, e.g. size or shape. Thus, the impedance at the fuel injection point may vary to a great deal. Consequently, it is highly possible that the acoustic wave penetrates the fuel gallery/manifold and establishes itself into a standing or rotating acoustic wave to perturb the fuel flow rate and thus combustion dynamics. When designing a combustion system, it is difficult to predict the frequency, amplitude and wave form of the

vibrations influenced by the fuel flow rate and the

combustion dynamics. As a consequence, it is particularly difficult to design a combustion system which is not

subjected to undesirable vibration for part of its range of operation. Apart from having a mechanical effect on the hardware of the combustion system, the combustion gas

dynamics also influence combustion stability and can cause extinguishing of the combustion flame - so-called "flame-out" - with the result that the engine stops producing power.

From WO 93/10401 it is for example known to provide a fuel supply line of a gas turbine system with a so-called

Helmholtz resonator to suppress combustion-cause vibrations. Such classical Helmholtz type resonators provided damping at a very specific frequency. Problems arise with this resonator types in case of the necessity to attenuate a broad range of frequencies . GB 1 274 529 discloses reheat equipment in an exhaust of a gas turbine engine the equipment comprising a V-section flame stabilizing ring. A fuel ring manifold having injection orifices is supported within the stabilizing ring, fuel being injected from the orifices through aligned orifices. Spaced plates are located within the stabilizing ring, the

downstream plate being formed with orifices so that the assembly of plates forms a vibration damping device for damping combustion instabilities in the wake of the V-section flame stabilizing ring within the exhaust.

US2006/0000220A1 discloses a resonator assembly in the form of a T-shaped pipe and having an inlet end and an outlet end and is connected to fuel flow passage of a fuel nozzle. The resonator assembly is used to produce the effect of wave shifting .

EP 2 273 096 A2 discloses an engine having an exhaust gas pipeline for discharging of combustion gas from a cylinder, and a suction pipeline for delivering of fresh air into the cylinder. The cylinder is equipped with a plastic charge air cooler, which is arranged in the suction pipeline. A

resonator is designed as a sound damper and provided

downstream of the cylinder. The resonator is integrated in the charge air cooler. The suction pipeline comprises a charge air hose that is arranged between the cylinder and the charge air cooler. It is a first objective of the present invention to provide a combustion system of a flow engine, which provides damping of a broad range of frequencies, a good combustion performance with a homogenous fuel flow rate and high combustion

stability as well as less combustion noise and vibrations.

It is a further objective of the present invention to provide a method for determining a dimension of a resonator cavity to effectively suppress fuel flow fluctuations and damp

combustion dynamics of the combustion system.

These objectives may be solved by a combustion system and a method according to the subject-matter of the independent claims .

Summary of the Invention

According to a first aspect of the present invention, a combustion system of a flow engine is presented, comprising at least one combustion chamber, a shared manifold to feed a flow medium via at least two injectors to the at least one combustion chamber and at least one resonator with at least one resonator cavity, wherein the at least one resonator is arranged functionally in/at the manifold.

It is proposed, that the resonator comprises at least one perforated section with at least two orifices, wherein the at least two orifices provide access to the at least one

resonator cavity of the at least one resonator.

Due to the inventive matter, fluctuations of a flow medium, like fuel, may be suppressed effectively and successfully. This results advantageously in a suppression of pressure fluctuations in the fuel flow which leads to reduction in combustion dynamics. Compared to a classical Helmholtz type resonator the inventive resonator has a very broad response to frequency, which is a very useful feature to have since the frequency of oscillations varies according to operating conditions and fuel composition. Moreover, equivalence ratio fluctuations in a combustor mixing region may be beneficially reduced leading to a better control of emissions, e.g. NO_x emissions. Furthermore, a damage of pieces of the combustion system, like a combustor can, caused by combustion dynamic pulsations may be prevented. In addition, the life of downstream components such as turbine blades or vanes may be improved compared to state of the art systems through a reduction in heat release fluctuations. Advantageously, the combustion system may be operated over a wide range of Wobbe indices, resulting in flexibility concerning the used fuel. Further, by placing the resonator at the source of the flow fluctuation of the flow medium, namely the manifold,

combustion dynamics may be effectively reduced compared to a state of the art system. Hence, this invention is also concerned with the interaction between the dynamic forces caused by combustion and those caused by the flow of fuel, air and other gases.

In this context a flow engine is intended to mean any engine or machine suitable for a person skilled in the art, e.g. a thermal heating plant, a gas turbine or an internal combustion engine. Further, an injector is intended to mean a nozzle for e.g. fuel, air and/or other gases and especially a fuel nozzle. Moreover, the term "shared manifold" should be understood as "shared by the at least two injectors" or in case of an embodiment with at least two combustion chambers alternatively and/or additionally as "shared by the at least two combustion chamber" and the term "manifold" as a passage for a flow medium and especially as fuel manifold and/or fuel gallery. A flow medium may be any medium feasible for a person skilled in the art, like a fuel (gaseous) , air or other gases.

Furthermore, a resonator is intended to mean a device for modulating and/or damping perturbations, especially of a flow rate of the flow medium e.g. in the manifold and/or that is used to provide damping to an established standing or

rotating wave e.g. in the manifold. A resonator should be understood as a functional unity, thus it may comprise more than one piece or may be a selected arrangement of several pieces. The resonator is especially a so called cavity resonator. The statement the "resonator is arranged

functionally in/at the manifold" should be understood as a functional interaction of the parts and may be independent of a spatial arrangement of the resonator and the manifold.

Moreover, a perforated section is intended to mean a part of the resonator embodied with a perforation, wherein the perforation has at least two orifices. Alternatively, the perforation may have more than two orifices or a plurality of orifices. The wording to "provide access to the at least one resonator cavity of the at least one resonator" should be understood as an access for a wave propagation of a wave that may be established in or travel in the manifold and/or flow medium during operation of the combustion system. A direction of the wave propagation is preferably from the manifold, precisely from its lumen, to the resonator cavity of the resonator. In the following text the phrases "at least one resonator/at least one resonator cavity/at least one perforated section/at least one combustion chamber/the at least two injectors/at least two orifices" are referred to as "the resonator/the resonator cavity/the perforated

section/the combustion chamber/the two injectors/the two orifices".

An orifice may have any size or shape, like circular, oval, triangular, rectangular square, etc., feasible for a person skilled in the art. The dimensions of the orifices (like a height, a length or a diameter of an orifice) as also for example a number of orifices (see below) and/or a volume of the resonator cavity define and hence also depend on a target value of a peak resonance which is:

(C=speed of sound, V=resonator volume, S=area of resonator orifices, l=height or length of orifices) . Thus, all the above stated parameters could take different and/or any suitable values. It is further provided, that said orifice is embodied with a circular shape. Thus, the perforation can be easily

manufactured. Preferably, both orifices or all orifices, in case of a plurality of orifices, have a circular shape. In general, it would be also possible to embody the two orifices or all orifices or groups of orifices of one perforated section with different orifice shapes.

Preferably, the resonator has a shape of a linear body, like a pipe or a box, which has an axial extension. A slight bent in a part or the shape of the linear body should not hinder the definition of body as linear and with an axial extension. Advantageously, the perforated section is arranged basically along or basically in parallel to the axial extension of the linear body of the resonator. In the scope of an arrangement of the perforated section as "basically parallel" to an axial extension of the linear body should also lie a divergence of the strictly parallel arrangement of about 30°. Preferably, the perforated section is oriented parallel to the axial extension of the linear body. Furthermore, the perforated section is in radial direction of the resonator spatially arranged between a part, like the lumen or a jacket, of the manifold and a part, e.g. a wall, of the resonator cavity of the resonator. Hence, access to the resonator cavity through the orifices can be easily provided.

The resonator and the manifold may be constructed out of separate pieces or they may share pieces. In a preferred embodiment the perforated section is formed in a part of the manifold. In other words, the perforated section is a part of the manifold or it is formed integrally with the manifold or the perforated section continues the shape of the manifold. Thus, parts, space, costs as well as construction efforts may be saved.

Advantageously, the perforated section has a shape of a hollow cylinder. Consequently, a robust a reliable part that is easy to manufacture can be provided. The cylinder is e.g. a wall of the manifold. According to a further preferred embodiment the perforated section comprises a plurality of orifices, which are distributed along a whole circumference of a jacket of the hollow cylinder. Due to this, the

resonator has a very broad response to frequency, especially compared to a resonator with a hollow space, like a classical Helmholtz type resonator, where the resonator provides damping only at a very specific frequency. The inventive resonator is especially useful, since the frequency of oscillations varies according to operating conditions of the combustion system and the fuel composition. The inventive resonator thus may be called a resonator of a perforated liner type. These perforated liner type resonators provide broadband absorption in the frequency domain therefore would be adequate to provide damping to combustion dynamics of varying frequencies as the Wobbe index of the fuel varies. As stated above the resonator has a shape of a linear body having an axial extension and the perforated section may comprise a plurality of orifices. Beneficially, plurality of orifices is distributed along the whole extension of the linear body. This results in a reliable and good damping of frequencies of the combustion system. The linear body may be a rectangular box or a cylinder or a tubular pipe. Both the resonator cavity and the perforated section may be embodied as a linear body with the same direction of their axial extension or the directions of the axial extensions may diverge from one another (see below) .

To restrict the volume of the resonator the resonator cavity of the resonator is encased by walls. The resonator comprises at least one wall (referred to as the wall in the following text) , which is arranged basically along the axial extension of the linear body of the resonator (for the definition of basically along see the definition of basically in parallel above) . To provide a system that is easily assembled the wall of the resonator cavity and a part of the manifold, which is arranged basically along the axial extension of the linear body (definitions see above) , are arranged like in a so- called - known in the art - pipe in pipe system. In this context the term "pipe in pipe system" should not be applied to strictly tubular arrangements. Also a combination of one or more circular pipe(s) with one or more rectangular pipe(s) or box(es) as well as the combination of two or more

rectangular shapes should be understood as a "pipe in pipe system" .

It is further provided, that the orifices of the plurality of orifices are evenly distributed over the at least one

perforated section. Hence, the damping effect may be

established homogeneously. In general, it would also be feasible to distribute the plurality of orifices in any matter a person skilled in the art sees as practicable, like randomly, in clusters, in lines (arranged axially, diagonally or circumferentially) etc. Furthermore, it has been shown that the feeding of flow medium to the combustion chamber is constructively easy and most reliable, if the manifold has, seen in feeding direction of the combustion chamber, a circular shape or in other words has an overall shape of a closed ring. Thus, in the exemplary and preferred embodiment, where the perforated section is a part of the manifold, the perforated section has a shape of a part cycle. Consequently, in that case, an axial extension of the perforated section is also a circumferential

extension/direction (referred to the circumference of the manifold) .

Moreover, by an arrangement of the wall of the resonator cavity and the part of the manifold, which is arranged basically along the axial extension of the linear body, as a strictly pipe in pipe system, the axial extensions are both oriented in direction of the circumference of the manifold. Whereas the axial extensions differ slightly by an

arrangement of a circular manifold (e.g. with integrated perforated section) and a linear body of the resonator embodied as a rectangular box or as a cylindrical pipe. Here the axial extension of the manifold is in direction of the circumference of the manifold and the resonator

box/cylindrical pipe has a classical axial extension.

According to a further exemplary embodiment the manifold is embodied as a torus, advantageously, as a ring torus. Thus, the transporting of flow medium in the manifold can be accomplished homogeneously.

Furthermore, the combustion system comprises a selected number of injectors and a selected number of resonators, wherein the number of resonators is equal or less than the number of injectors. Due to this, the damping of the

perturbations is most effective. Moreover, the combustion system may comprise one or more combustion chambers and a selected number of resonators, wherein the number of resonators is equal or less than the number of combustion chambers. Further, measures may be taken for each injector and/or combustion chamber or its feeding region in the manifold, respectively, individually by selectively choose or adjust different resonators depending on their position in reference to the different injectors and/or combustion chambers .

According to a further aspect of the present invention, the resonator has at least one restriction device (referred to as the restriction device in the following text) that is

constructed to prevent a flow of flow medium through the two orifices from the manifold into the resonator cavity. Thus, a leakage of flow medium and therewith a possibility of further unwanted perturbations may advantageously be prevented. The restriction device may be any feature feasible for a person skilled in the art, like a membrane or a pressure.

Beneficially, the restriction device is a pressure in the resonator cavity.

The advantages of the restriction device may be

constructively easy accomplished if a pressure in the

resonator cavity is higher than a pressure in the manifold to prevent a flow of flow medium through the two orifices from the manifold into the resonator cavity. This is not required during resonance condition as pressure in the cavity will always be higher than pressure in the manifold during

resonance. However, a pressure difference across the

perforation may be required, say during shut down, to purge any flow that may be in the cavity out to the manifold.

When the combustion system comprises at least a second resonator (referred to as second resonator in the following text) damping could be increased compared to the use of only one resonator. Moreover, two or multiple resonators in the same fuel line avoid placing a resonator in a pressure node in the case of an established standing wave in the manifold pipe . In an advantageously embodiment of the invention the first resonator and the second resonator differ in at least one characteristic. This results in the possibility to adjust each resonator specifically for its function and/or position. This characteristic may be any function, feature, property, or parameter of the resonator or parts thereof or their arrangement or function together feasible for a person skilled in the art. This may be for example a feature of the perforated section, like an axial (circumferential) length, a diameter, a shape, a size or a pattern of the orifices etc.; or of the linear body, like an axial length, a diameter etc.; or of the resonator cavity of the resonator, like a volume, a shape etc.; or of a special arrangement of a resonator in respect to a specific injector and/or combustion chamber.

Hence, different resonators could have e.g. different orifice sizes, shapes and lengths depending on the frequencies that should be attenuated. For example if multiple frequencies should be damped and they should be attenuated at the same time, then resonators may be designed with different orifice sizes/shapes and resonator lengths such that each resonator deals with a particular frequency. Moreover, since in case of a circular manifold the feeding of fuel to the successively arranged injectors and/or combustion chambers is

consecutively, the conditions differ for each injector and/or combustion chamber. This could be considered by designing each resonator differently and individually. The resonator (s) will be designed to provide optimum damping around the combustion dynamics frequency, using the Helmholtz equation, and specifically in dependency of beforehand determined conditions using the Helmholtz equation. During operation of the combustion system the perturbations establish themselves as a standing or rotating wave e.g. in the manifold. If it is a rotating wave then the position of the resonator (s) may not be of a concern. In turn, if it is a standing wave, the location of the resonator had to be purposefully chosen. Advantageously, the resonator is placed in a location of a pressure anti-node of the standing wave established in the manifold due to perturbations of a flow rate of a flow medium travelling in the manifold. However, multiple resonators in such locations may be required to damping the perturbations to an acceptable level.

In a further advantageous embodiment the resonator cavity has a volume, which is adjustable. By way of this the frequency of damping of the resonator may be controlled. Hence, the combustion system is allowed to operate over a wide range of Wobbe indices i.e. providing a high flexibility in the choice of fuel. It would be either possible to vary the volume beforehand of the operation of the combustion system

according to expected conditions or during the operation of the combustion system depending of in situ measurements.

Preferably, the resonator has an adjustable wall to adjust the volume and the resonator capacity of the resonator. This would be a very easy and effective construction.

According to a further aspect of the present invention, a method for determining a dimension of a resonator cavity of a resonator of a combustion system of a flow engine is

presented.

It is provided, that the method comprises at least the following steps: determining at least one frequency that will be established in the combustion system under defined

conditions and that needs modulation to provide optimum damping around a combustion dynamics frequency of the

combustion system, evaluating the dimension of the resonator cavity of the resonator using the Helmholtz equation in dependency of the at least one determined frequency and adjusting the dimension according to the evaluation.

The method can be extended where two or more cavities are provided either in one resonator or two or more resonators. The method comprises the steps of determining a range of frequencies that will be established in the combustion system under defined conditions and that needs modulation to provide optimum damping around a combustion dynamics frequency of the combustion system, evaluating the dimension of each resonator cavity of the resonator using the Helmholtz equation in dependency of the determined at least one frequency and adjusting the dimension of each resonator cavity according to the evaluation to provide different cavity characteristics and which cover the range of frequencies.

Due to this inventive matter, the resonator will be designed to provide optimum damping around the combustion dynamics frequency. This results advantageously in a suppression of pressure fluctuations in the fuel flow. Thus, a combustion system may be operated even if frequency of oscillations varies according to operating conditions and fuel

composition. Moreover, equivalence ratio fluctuations in a combustor mixing region may be beneficially reduced leading to a better control of emissions, e.g. NO_x emissions.

Furthermore, a damage of pieces of the combustion system, like a combustor can, caused by combustion dynamic pulsations may be prevented. In addition, the life of downstream

components such as turbine blades or vanes may be improved compared to state of the art systems through a reduction in heat release fluctuations. Advantageously, the combustion system may be operated over a wide range of Wobbe indices, resulting in flexibility concerning the used fuel. Further, by placing the resonator at the source of the flow

fluctuation of the flow medium, namely the manifold,

All steps may be executed beforehand of the operation or during the operation of the combustion system. For example, it would be either possible to adjust the dimension of the resonator cavity beforehand of the operation of the

combustion system according to expected conditions or during the operation of the combustion system depending of in situ measurements, in other words, to have a dynamic system.

The above-described characteristics, features and advantages of this invention and the manner in which they are achieved are clear and clearly understood in connection with the following description of exemplary embodiments which are explained in connection with the drawings.

Brief Description of the Drawings

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

FIG 1: shows a schematic view of a flow engine with an

inventive combustion system comprising a manifold with a resonator feeding a flow medium to combustion chambers via injectors, FIG 2: shows a schematic back view of a part of the

combustion system from FIG 1 with six combustion chambers and a shared manifold,

FIG 3: shows a schematic view of the manifold from FIG 2 with two resonators and an established wave, shows a schematic view of a resonator from FIG 3 with a perforated section as a part of the manifold from FIG 3 and shows a perspective view of the part of the manifold and the resonator with the perforated section from FIG 4.

Detailed Description

The illustrations in the drawings are schematically. It is noted that in different figures, similar or identical

elements are provided with the same reference signs.

FIG 1 shows in a schematically view a flow engine 12, e.g. a gas turbine. The flow engine 12 comprises a compressor 48, a combustion system 10 and a turbine 50, which are arranged one after another in a flow direction 52 of a first flow medium, e.g. air (see arrows pointing from left hand side to right hand side of FIG 1) . In the compressor 48 the incoming first flow medium is compressed for application to one or more combustors of the combustion system 10. The combustion system 10 may comprise one combustion chamber e.g. of an annular type or several combustion chambers 14, 16 e.g. of a can type (see also FIG 2) . A second flow medium, like fuel (referred to as fuel in the following text) , is introduced into the combustion chambers 14, 16 from a shared manifold 18 via a separate fuel line 54, 54' and an injector 56 for each combustion chamber 14, 16 separately. After injection the fuel is mixed with a part of the compressed first flow medium leaving the compressor 48. Hot gases created by combustion in the combustion chambers 14, 16 are directed to the turbine 50 having a set of turbine blades 60, being guided in the process by a set of guide vanes 58, and the turbine blades 60 and the shaft forming an axis are turned as a result. The turbine blades 60 in turn rotate the blades of the compressor 48, so that the compressed flow medium is supplied by the flow engine 12 itself once this is in operation.

FIG 2 shows a schematic back view of the combustion system 10 in direction of the arrows II in FIG 1. The combustion system 10 has in this exemplary embodiment six combustion chambers 14, 16 (only two combustion chambers are equipped with reference signs) , which are arranged one after another evenly spaced in a circumferential direction 62 around the turbine shaft. The manifold 18 is arranged, in respect to the

combustion chambers 14, 16, with a greater radial distance from the shaft than the combustion chambers 14, 16. Moreover, it has the shape of a closed ring and/or is a circular pipe and, as could be seen in FIG 1, is embodied as a torus. The manifold 18 is a shared manifold 18. Thus, all combustion chambers 14, 16 are fed via the same manifold 18 with fuel from the same source.

During operation of the combustion system 10 e.g. self- excited combustion oscillations may manifest in the

combustion chambers 14, 16. These oscillations or vibrations travel through the fuel lines 54, 54' and into the manifold 18. Inside the manifold 18, either a travelling (rotating) or standing acoustic wave 46 is formed. The wave 46 may

fluctuate the fuel being fed to the fuel manifold 18.

Consequently, the flame in the combustion chamber 14, 16 is fed with an unsteady (fluctuating) fuel supply which causes even more combustion dynamics. This situation is

schematically shown in FIG 3 that depicts a snap-shot of an established wave 46 in the manifold 18 due to perturbations of the flow rate of the fuel travelling in the manifold 18.

To reduce or preferably suppress the fuel flow fluctuations and thus to obtain a reduction in combustion dynamics the combustion system 10 comprises in this exemplary embodiment two resonators 20, 20' (In the following text also specified as the first resonator 20 and the second resonator 20' to distinguish when needed between the two resonators 20, 20')_/ wherein each resonator 20, 20' has a resonator cavity 22 (for details see FIG 4 and 5) . The resonators 20, 20' are arranged functionally in the manifold 18. Hence, by placing the resonators 20, 20' in the manifold 18 they are placed

directly at the source of fuel flow fluctuations.

The combustion system 10 comprises a selected number of injectors 56 as well as combustion chambers 14, 16,

specifically in this exemplary embodiment in each case six, and a selected number of resonators 20, 20', namely in this exemplary embodiment two, thus the number of resonators 20, 20' is less than the number of injectors 56 and combustion chambers 14, 16. If the established wave 46 is a standing wave 46 at least one of the resonators 20 is placed in a location of a pressure anti-node 44 of the standing wave 46. By placing at least two resonators 20, 20' non-periodically it could be easily avoided to have a resonator 20, 20' accidently in a location of a pressure node (not shown) . FIG 4 and 5 show exemplarily the first resonator 20 from

FIG 3 in more detail and in a linear configuration for better presentability. Generally all the features described for resonator 20 could also be applied to resonator 20' . The resonator 20 has a shape of a linear, rectangular, box-like body 34 having an axial extension 36. The linear body 34 is only shown partially in FIG 1 (without reference sign) and in phantom in FIG 1 and FIG 5 for better presentability of the perforated section 24 (see below) . In general, it would also be possible to construct the linear body 34 with a slight bent to follow the shape or the circumference of the manifold 18 or as a cylindrical linear or bended pipe.

Moreover, to provide a broad response to frequency the resonator 20 comprises a perforated section 24 with at least two or a plurality of orifices 26. The orifices 26 provide access for a wave propagation of the wave 46 from a lumen 64 of the manifold 18 to the resonator cavity 22 of the

resonator 20. All orifices 26 are embodied with a circular , _n

shape. Further, the perforated section 24 has a shape of a hollow cylinder 28 (see FIG 5) . Hence, it is a perforated liner . The orifices 26 of the plurality of orifices 26 are evenly distributed over the perforated section 24 and along a whole circumference 30 of a jacket 32 of the hollow cylinder 28 (see FIG 5) . Furthermore, they are distributed along the whole axial extension 36 of the linear body 34. The

perforated section 24 is formed in a part of the manifold 18 or is a part of the manifold 18.

To prevent that fuel enters through the orifices 26 the resonator cavity 22 of the resonator 20, the resonator 20 is embodied with a restriction device. The restriction device is a pressure P in the resonator cavity 22, wherein the pressure P in the resonator cavity 22 is higher than a pressure p in the manifold 18. A pressure difference of 0.5 bar would for example be sufficient.

The resonator cavity 22 of the resonator 20 is encased by six walls, wherein two of these walls are walls 38 that are arranged along or in parallel to the axial extension 36 of the linear body 34 of the resonator 20. These walls 38 and a part 40 of the manifold 18, which is also arranged along or in parallel to the axial extension 36 of the linear body 34, are arranged like in a so-called pipe in pipe system 42. The part 40 of the manifold 18 is at least a region of the perforated section 24. Thus, the axial extension 36, the walls 38 and the part 40 - the region of perforated section 24, are arranged in parallel to one another.

As could be seen in FIG 3 the first resonator 20 and the second resonator 20' differ in a characteristic,

specifically, as an exemplary embodiment, in their axial length L. Thus, both resonators 20, 20' are designed

specifically for their location and function in reference to the locations and properties of the injectors 56 and the combustion chambers 14, 16. In general, the resonators 20, 20' may differ in more than one characteristic and/or in another characteristic (see listing above) . The resonators 20, 20' will be designed to provide optimum damping around the combustion dynamics frequency, using the Helmholtz equation, and specifically in dependency of

beforehand determined conditions using the Helmholtz

equation, which is:

C=speed of sound, V=resonator volume, S=area of resonator orifices, l=height or length of orifices. Thus, the

determines conditions and the peak resonance frequency that will need damping define the dimensions of the orifices 26 (like a height, a length or a diameter) , a number of orifices 26 and/or a volume V of the resonator cavity 22.

Hence, to determine a dimension (volume) of the resonator cavity 22 of exemplarily the resonator 20 at least one frequency and preferably a broad range of frequencies that will be established in the combustion system 10 under defined conditions and that need(s) modulation to provide optimum damping around the combustion dynamics frequency of the combustion system 10 is determined. Subsequently, the

dimension of the resonator cavity 22 of the resonator 20 using the Helmholtz equation in dependency of the at least one determined frequency or the determined range of

frequencies is evaluated and finally the dimension according to the evaluation is adjusted (not shown in detail) .

Alternatively and/or additionally the resonator cavity 22 has a volume V, which is adjustable. Therefore, a moveable wall 66 is provided. That may be any of the walls encasing the resonator volume 22. As an exemplary embodiment the moveable wall 66 is one of the walls 38, arranged in parallel to the axial extension 36 of the linear body 34. This is shown in FIG 4 as a dashed line with a bidirectional arrow. It should be appreciated that there is no overall or nett fuel flow through the present resonator arrangement (20, 20')_/ in other words, there is no inlet or outlet. The present resonator acts as an accumulator for a fluid such as the fuel. The resonator is an accumulator of a set volume and pressure balances as it acts as an expansion volume to damp the fuel flow perturbations and pressure variances or waves .

Where two or more resonators (20, 20') are provided on the manifold 18 each resonator may define different volumes from one another. Each volume may be determined to attenuate different frequencies. The different volumes of each

resonator can be set by virtue of setting a ^>height' or

^>length' in a direction away from the orifices 26; in the case of Figure 4, the length of the resonator is a (radial) distance from the orifices 26 to the wall 38. The distance can be a radial distance with respect to the central axis of the manifold 18. Thus an even broader range of frequencies can be attenuated.

In another embodiment, the area of the orifices can be different between the at least two resonators, such that a first resonator has a first total area of orifices and a second resonator has a second total area of orifices. The first area of orifices is greater than the second area of orifices. A greater total area of orifices can be achieved by virtue of a greater number of orifices or a greater area of each or some of the orifices in a plurality of orifices associated to each volume.

As can be seen in Figures 4 and 5 the perforated section 24 is a wall of the manifold 18 and therefore defines the flow path of the fuel. The resonator 20, 20' is shown as

completely surrounding an axial extension or length 36 of the manifold 18. With respect to the central axis of the

manifold 18, the resonator's 20, 20' volume 22 is defined by radially outer walls and radially inwardly by the wall of the manifold 18. Thus the fuel flow in the manifold has direct access to the volume 22 from the manifold 18 via the

perforated section 24.

Although Figures 4 and 5 show a resonator 20, 20' having a single cavity or volume 22, it is possible that the volume 22 is circumferentially segmented. Each circumferential sub- volume may comprise a different volume than the other (s) sub- volume (s) . For example there may be two, three or more sub- volumes. In this example, the perforated section 24 may have a constant perforation size and density and thus the same area of resonator orifices. Alternatively, the perforated section associated with each sub-volume may have a different area of resonator orifices. This may be achieved by

different density of orifices and/or a different size of orifices .

It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

Although the invention is illustrated and described in detail by the preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

Claims

1. Combustion system (10) of a flow engine (12) comprising at least one combustion chamber (14, 16), a shared manifold

(18) to feed a flow medium via at least two injectors (56) to the at least one combustion chamber (14, 16), and at least one resonator (20, 20') with at least one resonator cavity (22), wherein the at least one resonator (20, 20') is

arranged functionally in/at the manifold (18), characterised in that the resonator (20, 20') comprises at least one perforated section (24) with at least two orifices (26), wherein the at least two orifices (26) provide access for the flow medium in the manifold directly to the at least one resonator cavity (22) of the at least one resonator (20, 20') to modulate and/or damp perturbations in the flow medium in the manifold.

2. Combustion system according to claim 1,

wherein at least two resonators (20, 20') are provided and each resonator has a different resonator cavity (22) volume.

3. Combustion system according to claim 1 or claim 2,

wherein at least one of the resonators (20, 20') has at least two resonator cavities (22) and each resonator cavity (22) has a different resonator cavity (22) volume.

4. Combustion system according to any one of claims 1-3, wherein the at least one perforated section (24) is formed in a part of the manifold (18) .

5. Combustion system according to any one of claims 1-4, wherein the at least one perforated section (24) is formed in a wall of the manifold (18) and defines part of the flow path of the fuel through the manifold, the at least one resonator cavity (22) is partly defined by the at least one perforated section (24 ) .

6. Combustion system according to any preceding claim, wherein the at least one perforated section (24) has a shape of a hollow cylinder (28) .

7. Combustion system according to claim 6,

wherein the at least one perforated section (24) comprises a plurality of orifices (26), which are distributed along a whole circumference (30) of a jacket (32) of the hollow cylinder (28) .

8. Combustion system according to any preceding claim, wherein the at least one resonator (20, 20') has a shape of a linear body (34) having an axial extension (36) and wherein the at least one perforated section (24) comprises a

plurality of orifices (26), which is distributed along the whole axial extension (36) of the linear body (34) .

9. Combustion system according to claim 8,

wherein the at least one resonator cavity (22) of the at least one resonator (20, 20') comprises at least one wall (38) arranged basically along the axial extension (36) of the linear body (34) of the at least one resonator (20, 20') and wherein the at least one wall (38) of the at least one resonator cavity (22) and a part (40) of the manifold (18), which is arranged basically along the axial extension (36) of the linear body (34), are arranged like in a pipe in pipe system ( 42 ) .

10. Combustion system according to any preceding claim, wherein the at least one perforated section (24) comprises a plurality of orifices (26), which are evenly distributed over the at least one perforated section (24) .

11. Combustion system according to any preceding claim, wherein the combustion system (10) comprises a selected number of injectors (56) and a selected number of resonators (20, 20')_/ wherein the number of resonators (20, 20') is equal or less than the number of injectors (56) .

12. Combustion system according to any preceding claim, wherein a pressure (P) in the at least one resonator cavity (22) is higher than a pressure (p) in the manifold (18) to prevent a flow of flow medium through the at least two orifices (26) from the manifold (18) into the at least one resonator cavity (22).

13. Combustion system according to any preceding claim, comprising at least a second resonator (20, 20')_/ wherein the first resonator (20) and the at least second resonator (20') differ in at least one characteristic.

14. Combustion system according to any preceding claim, wherein the at least one resonator (14, 16) is placed in a location of a pressure anti-node (44) of a standing wave (46) established in the manifold (18) due to perturbations of a flow rate of a flow medium travelling in the manifold (18) .

15. Combustion system according to any preceding claim, wherein the at least one resonator cavity (22) has a volume, which is adjustable.

16. Method for determining a dimension of a resonator cavity (22) of a resonator (20, 20') of a combustion system (10) of a flow engine (12) according to at least one of claims 1 to 15,

comprising at least the following steps:

-determining at least one frequency that will be established in the combustion system (10) under defined conditions and that needs modulation to provide optimum damping around a combustion dynamics frequency of the combustion system (10), -evaluating the dimension of the resonator cavity (22) of the resonator (20, 20') using the Helmholtz equation in

dependency of the determined at least one frequency and

-adjusting the dimension according to the evaluation.

17. Method for determining a dimension of a resonator cavity (22) of a resonator (20, 20') of a combustion system (10) of a flow engine (12) according to claim 16, wherein two or more cavities are provided,

comprising at least the following steps:

-determining a range of frequencies that will be established in the combustion system (10) under defined conditions and that needs modulation to provide optimum damping around a combustion dynamics frequency of the combustion system (10), -evaluating the dimension of each resonator cavity (22) of the resonator (20, 20') using the Helmholtz equation in dependency of the determined at least one frequency and

-adjusting the dimension of each resonator cavity (22) according to the evaluation to provide different cavity characteristics and which cover the range of frequencies.