A premixed dual fuel burner with a tapering injection

component for main liquid fuel

The present invention relates to turbomachine components and more particularly to a burner for a dual fuel based

combustion chamber for a turbomachine. In modern day turbomachines , dual fuel i.e. a liquid fuel and a gaseous fuel, are used advantageously as main fuels in many applications for example in Lean Premix combustions, Dry Low ΝΟχ combustions, and so and so forth. In present day

turbomachines that employ dual fuel combustion techniques, a burner assembly in a combustion section includes a burner head connected to a swirl generator or swirler that in turn is connected to a mixer or premixing pathway or section. The burner assembly is connected to or assembled with a

combustion chamber. In combustion section of the

turbomachines that use the dual fuel techniques, the main fuels, distinct from pilot fuel supplies, are mostly both gaseous and liquid.

The basic technique in such dual fuel combustions is to premix the main fuel with air from a compressor of the turbomachine before igniting the combustion mixture, i.e. mixture of the air from the compressor and the main fuel, in the combustion chamber. Usually the air from the compressor is mixed with the main gaseous fuel, either inside the swirler or just before introduction into the swirler, and then swirled by the swirler to create a swirling flow of the air and the main gaseous fuel. This swirling flow of the pressurized air from the compressor and the main gaseous fuel then enters from the swirler into the premixing section. At the premixing section the pressurized air from the compressor and the main gaseous fuel are allowed to mix well before exiting into the combustion chamber or the combustion space where the combustion mixture undergoes combustion. In dual fuel combustors , or combustion sections, the main liquid fuel is discharged by a nozzle positioned at the burner head. The main liquid fuel after exiting the nozzle, preferably in atomized form, enters the swirler and then continues into the premixing section and finally into the combustion chamber where the main liquid fuel participates in the combustion reaction. Also known are burners with a central fuel lance to provide for gaseous and/or liquid fuel. One configuration of a cylindrical central fuel lance is known from the patent publication US 2010/0273117 Al . Further, US 5,791,894 A shows a conical inner body within a premix burner, to generate a swirl about an axis by swirling of a medium around the inner body. The inner body may

comprise optinally also a bore to provide liquid fuel and/or air to a front region of the combustion space.

However, there are some disadvantages in the scheme of presently known dual fuel burners and as described above. Firstly, discharging of the main liquid fuel at the burner head interferes with the swirl generation performed by the swirler by increasing the aerodynamic disturbances inside the swirler. Furthermore, the aerodynamic disturbances also adversely affect an axial flow of the combustion mixture and/or its components, i.e. flow of the combustion mixture and/or its constituents from a burner head side of the burner towards the combustion chamber. Secondly, since the main liquid fuel is discharged before the swirler or just at the beginning of the swirler, in some cases parts of the main liquid fuel get deposited on surfaces of inside walls of the swirler and/or the premixing section. This deposition of the main liquid fuel residues leads to clogging of the interiors of the swirler and especially the interiors of the premixing section. The clogging results in loss of efficiency and in most cases the turbomachine operation is required to be stopped to clean the main liquid fuel residues deposited on surfaces of inside walls of the swirler and/or the premixing section . Furthermore, as a result of the clogging and the aerodynamic disturbances, as mentioned above, a flow of combustion mixture and/or components of the combustion mixture is jeopardized which leads into increased possibility of

formation of recirculation zones within burner interiors such as the premixing section. The formation of the recirculation zones within the burner interiors is undesirable, as it may result into overheating of the burner components for example the premixing section and/or the swirler. A continued problem of overheating over an extended period of time may result into damaging of the parts of the burner components i.e. the premixing section, the swirler, etc. Moreover, as a result of the formation of the undesired recirculation zones within the premixing section, efficiency of the turbomachines in

operation is reduced.

An object of the present technique is to obviate the above mentioned disadvantages and to ensure that recirculation zones for the combustion are formed at a desired spatial position in the combustion chamber or the combustion space. It is undesirable to allow formation of the recirculation zone within the premixing section of the burner. Achieving this object increases the combustion efficiency and thus the efficiency of the overall turbomachine , elongates operational life of the components of the burner and associated

structures that may otherwise get over heated due to

formation or extension of recirculation zones at undesirable spatial positions within the burner interiors, and stabilizes the combustion reaction due to control on the recirculation zone formation and its spatial position in the combustion chamber.

The above objects are achieved by a premixed dual fuel burner according to claim 1 of the present technique. Advantageous embodiments of the present technique are provided in

dependent claims. Features of claim 1 may be combined with features of dependent claims, and features of dependent claims can be combined together.

According to the present technique, a premixed dual fuel burner for a combustion chamber of a turbomachine is

presented. The premixed dual fuel burner, hereinafter referred to as the burner, includes a burner head, a burner interior, a swirler, a premixing section and an injection component. The swirler is arranged in series between the burner head and the premixing section. The burner head includes a burner head end. The burner interior is elongated along a main axis of the burner and is formed of an upstream side and a downstream side. The upstream side is disposed between the burner head and the downstream side. The upstream side is fluidly connected to the downstream side, i.e. the upstream side and the downstream side are continuous and together form the burner interior. A part of the burner interior enclosed by the swirler is the upstream side of the burner interior and the other part of the burner interior enclosed by the premixing section is the downstream side of the burner interior. The swirler includes an inlet section. The inlet section is configured to introduce air and a main gas fuel into the burner interior. The premixing section has a burner outlet through which the premixing side is

configured to be arranged or fixed or assembled with the combustion chamber such that the downstream side is fluidly connected to the combustion chamber.

The injection component has a tapering structure positioned along the main axis. The tapering structure of the injection component extends from the burner head into the burner interior. The injection component has a burner head side and an injection side. The injection component tapers from the burner head side to the injection side along the main axis. The injection component includes at least one liquid fuel outlet at the injection side. The injection component is configured to introduce a main liquid fuel into the burner interior through the at least one liquid fuel outlet. The main liquid fuel introduced in the burner interior by the injection component via the liquid fuel outlet is directed towards the combustion chamber. The injection side of the injection component is disposed in the burner interior.

Besides, at least one of the at least one liquid fuel outlet is at a side - i.e. a side face of the tapering - of the injection side of the injection component. Thus, the liquid fuel outlet is angled in respect of an axial direction of the burner .

The injection component is particularly a fuel lance.

The tapering structure of the injection component minimizes aerodynamic disturbances in the burner interior, and thus ensuring efficient functioning of the swirler in generating swirl which in turn aids in achieving a desired spatial position of a central recirculation zone, preferably the central recirculation zone or the main recirculation zone is formed and limited completely within the combustion chamber, and thus minimizing possibilities of a flashback into the burner interior. Furthermore, the tapering structure of the injection component facilitates an axial velocity, i.e. along the main axis, of the combustion mixture i.e. the main fuel gas and the air mixture exiting from the swirler into the premixing section and continuing further into the combustion chamber. The facilitation of the axial velocity results from directed flow of the combustion mixture and/or its

constituents along the tapering structure. The tapering form of the injection component acts as a guide to the flow of main gas fuel and air facilitating the axial flow direction. This also helps in achieving the desired spatial position of the recirculation zone, which is preferably positioned in the combustion chamber and outside the premixing section. The positioning of the recirculation zone outside the premixing zone and within the combustion chamber minimizes possibilities of a flashback into the burner interior for example into the premixing section interior.

Furthermore, by introducing the main liquid fuel via the liquid fuel outlet on the injection component extending into the burner interior and by directing the main liquid fuel towards the combustion chamber, it is ensured that deposition of residues of the main liquid fuel is minimized in inner walls of the swirler and/or the premixing section, and thus clogging of the burner cavity enclosed by the swirler and/or the premixing section is at least partially prevented which in turn leads to proper swirl action by the swirler and/or proper fuel premixing action by the premixing section and which subsequently also helps in formation of the

recirculation zone at the desired spatial position and in increasing efficiency of the turbomachine .

In an embodiment of the burner, the tapering structure of the injection component is a conical structure. The conical structure has preferably a regular geometrical shape i.e. the conical structure is symmetrical about a longitudinal axis of the conical structure. The tapering of the structure is smooth and gradual . The regular conical structure helps in further reduction of the aerodynamic disturbances in the burner interior. Moreover, the conical shape being a regular shape is easy to manufacture and assemble.

In another embodiment of the burner, the tapering structure of the injection component is arranged coaxially to the main axis. The longitudinal axis of the conical structure overlaps with the main axis. This adds symmetry to the burner interior and this facilitates the further reduction of the aerodynamic disturbances in the burner interior. In another embodiment of the burner, a first distance is between 20% and 80% of a second distance. The first distance is a distance measured along the main axis between the at least one liquid fuel outlet and the burner head end. The second distance is a distance measured along the main axis between the burner outlet of the premixing section and the burner head end, in other words a length of the burner interior along the main axis. Thus, the main liquid fuel is transported, confined within the injection component, at least partially through parts of the burner interior that are enclosed by the swirler and/or the premixing section and is delivered into the burner interior at a desired position within the burner interior depending on a ratio of the first and the second distances. By maintaining a proper ratio of the first and the second distances, the main liquid fuel is ejected or injected out into the burner interior at a

desirable position in the burner interior thus at least partially decreasing the risk of spraying the liquid fuel on surfaces of the inner walls of the swirler and/or the

premixing section.

In another embodiment of the burner, the injection component is configured to be longitudinally adjustable along the main axis such that a position of the at least one liquid fuel outlet of the injection component is changeable from a first location along the main axis to a second location along the main axis. Thus a desirable position in the burner interior to eject or inject out the main liquid fuel can be adjusted during an operation of the turbomachine and/or may be set as desired between two operations of the turbomachine.

In another embodiment of the burner, the at least one liquid fuel outlet is positioned in the upstream side of the burner interior. This provides an embodiment in which, if so desired for a particular mode of operation of the turbomachine, the main liquid fuel can be injected out of the liquid fuel outlet before the premixing section. In another embodiment of the burner, the at least one liquid fuel outlet is positioned in the downstream side of the burner interior. This provides an embodiment in which, if so desired for a particular mode of operation of the turbomachine , the main liquid fuel can be injected out of the liquid fuel outlet into the burner interior enclosed by the premixing section. Furthermore, this embodiment ensures that spraying of the liquid fuel on surfaces of the inner wall of the swirler and at least a part of the surfaces of the inner wall of the premixing section are minimized.

In another embodiment of the burner, one of the at least one liquid fuel outlet is at an end of the injection side of the injection component, particularly at a tip of the injection component. The end is the most axial position of the

injection component. This ensures that a spray or a fluid stream of the main liquid fuel is directed along the main axis towards the combustion chamber. According to the

invention a further one - also called "first additional outlet" - of the at least one liquid fuel outlet is at a side of the injection side of the injection component. The first additional outlet is configured to introduce the main liquid fuel into the burner interior. The first additional outlet is at a side of the injection side of the injection component. This provides an additional direction in which an additional spray or an additional fluid stream of the main liquid fuel is directed towards the combustion chamber. This additional direction is at an acute angle to the main axis and is directed towards the combustion chamber.

According to the invention, the at least one liquid fuel outlet is at a side of the injection side of the injection component. This ensures that a spray or a fluid stream of the main liquid fuel is directed towards the combustion chamber along an angle to the main axis. This direction is at an acute angle to the main axis and is directed towards the combustion chamber. In a related embodiment, the injection component includes a second additional outlet configured to introduce the main liquid fuel into the burner interior. The second additional outlet is at an end of the injection side of the injection component. This provides an additional direction, i.e. along the main axis, in which an additional spray or an additional fluid stream of the main liquid fuel is directed towards the combustion chamber.

In another embodiment of the burner, the inlet section of the swirler includes at least one air inlet and at least one main fuel gas inlet. Thus the main gas fuel and the air from a compressor of the turbomachine may be introduced into the burner interior separately at the swirler. In an alternate embodiment, the main gas fuel and the air from the compressor may be introduced via a common inlet.

In another embodiment of the burner, the at least one air inlet and/or the at least one main fuel gas inlet is arranged tangentially along the swirler with respect to the main axis. This provides a commonly used embodiment of the swirler and thus the burner of the present technique may be realized, operated and manufactured with ease.

In another embodiment of the burner, the swirler has a conical frustum shape having a top side and a bottom side. A cross-section of the conical frustum increases from the top side towards the bottom side. The top side is connected to the burner head and the bottom side is connected to the pre- mixing section. This provides another commonly used

embodiment of the swirler and thus the burner of the present technique may be realized, operated and manufactured with ease .

In an embodiment, the premixed dual fuel burner may have a radial width - taken in a radial direction in respect of an axis of the burner - of the injection component that reduces over an axial distance D by only or less than D/10,

preferably less than D/15. In other embodidment the radial width may reduce by less than D/20.

In another embodiment of the burner, the premixing section has a part of the premixing section which surrounds the burner outlet of the premixing section. The part of the premixing section includes an external pilot. The external pilot is configured to introduce a pilot fuel into the combustion chamber. This aids in formation an external recirculation zone in the combustion chamber and thus aiding in lean combustion. Furthermore the present technique may be implemented in turbomachines that use Dry Low N0 _X

combustions .

The present technique is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawing, in which:

FIG 1 schematically illustrates a cross-sectional view of an exemplary embodiment of a premixed dual fuel burner including an injection component,

FIG 2 schematically illustrates a cross-sectional view of the injection component of the embodiment depicted in FIG 1,

FIG 3 schematically illustrates a cross-sectional view of another exemplary embodiment of the premixed dual fuel burner including the injection component, FIG 4 schematically illustrates a cross-sectional view of the injection component of the embodiment depicted in FIG 3,

FIG 5 schematically illustrates a cross-sectional view of an exemplary embodiment of the premixed dual fuel burner depicting the injection component at a first position,

FIG 6 schematically illustrates a cross-sectional view of an exemplary embodiment of the premixed dual fuel burner depicting the injection component at a second position as compared to the first position depicted in FIG 5, and FIG 7 schematically illustrates a cross-sectional view of an exemplary embodiment of the premixed dual fuel burner depicting the injection component at another second position as compared to the first position depicted in FIG 5 and the second position depicted in FIG 6, in accordance with the present technique.

Hereinafter, above-mentioned and other features of the present technique are described in details. Various

embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details.

It may be noted that in the present disclosure, the terms "first", "second", "another second" etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated.

Referring to FIG 1, a cross-sectional view of an exemplary embodiment of a premixed dual fuel burner 1, hereinafter referred to as the burner 1 has been schematically

represented. The burner 1 essentially uses at least two main fuels - a main gas fuel and a main liquid fuel - in addition to and besides a pilot fuel and associated pilot fuel supply lines and techniques.

The burner 1 includes a burner head 10, a burner interior 20, a swirler 30, a premixing section 40 and an injection

component 50. The burner 1 is assembled in association with a combustion chamber 99 in a turbomachine (not shown) which work with dual fuel combustion reaction. The main fuel is combusted in the combustion chamber 99 in form of a

combustion mixture after being mixed with an air from a compressor section (now shown) of the turbomachine . The main gas fuel mixed with air and the main liquid fuel may be combusted in the combustion chamber 99 separately or

simultaneously.

The burner head 10 includes a burner head end 12. The swirler 30 is arranged in series between the burner head 10 and the premixing section 40. The burner 1 has a main axis 9. The burner head 10, the swirler 30 and the premixing section 40 are arranged along the main axis 9. The swirler 30 is an elongated 3 -dimensional body. When visualized as not

integrated as a part of the burner 1, the swirler 30 is open at both ends and has a side wall enclosing a volume or limiting a volume within the side wall and the open ends. Similarly, the premixing section 40 is an elongated 3- dimensional body. When visualized as not integrated as a part of the burner 1, the premixing section 40 is open at both ends and has a side wall enclosing a volume or limiting a volume within the side wall and the open ends.

However, when integrated as parts of the burner 1, and when arranged in series such that the swirler 30 is positioned between the burner head 10 and the premixing section 40, as depicted in FIG 1, the volume enclosed by swirler 30 and the volume enclosed by the premixing section 40 together form a volume referred to as the burner interior 20. The swirler 30 may be connected to the burner head 10 by direct physical contact, as depicted in FIG 1, or may be connected to the burner head 10 through an intermediate piece (not shown) or a connecting region (not shown) . Similarly, in the burner 1, the swirler 30 may be connected to the premixing section 40 by direct physical contact with the premixing section 40 or may be connected to the premixing section 40 through an intermediate connecting piece (not shown) . The burner

interior 20 represents a total volume enclosed by the swirler 30 and the premixing section 40 with burner head 10 at one end of the total volume and the combustion chamber 99 at the other end of the total volume, either with or without one or more such intermediate connecting pieces. The burner interior 20 is a volume or a hollow that is elongated along the main axis 9. The burner interior 20 is formed of an upstream side 22 and a downstream side 24. The upstream side 22 is disposed between the burner head 10 and the downstream side 24. As depicted in FIG 1, the upstream side 22 and the downstream side 24 may be understood as a continuous volume, or in other words, the upstream side 22 is fluidly connected to the downstream side 24, i.e. the

upstream side 22 and the downstream side 24 are continuous and together form the burner interior 20 in FIG 1. A part of the burner interior 20 enclosed by the swirler 30 is the upstream side 22 of the burner interior 20 and the other part of the burner interior 20 enclosed by the premixing section 40 is the downstream side 24 of the burner interior 20. As depicted in FIG 1, in an exemplary embodiment of the burner 1, the swirler 30 is directly connected to or affixed to or assembled with the burner head end 12 of the burner head 10, and the swirler 30 is also directly connected to or affixed to or assembled with the premixing section 40. As shown in FIG 1, the swirler 30 may be conically designed for example having a conical frustum shape. The conical frustum shape of the swirler 30 has a top side 36 and a bottom side 38. A cross-sectional area of the bottom side 38 is greater than a cross-sectional area of the top side 36, or in other words, a cross-section of the conical frustum increases from the top side 36 towards the bottom side 38 along the main axis 9. The top side 36 is connected to the burner head end 12 of the burner head 10 and the bottom side 38 is connected to the pre-mixing section 40.

The swirler 30 includes an inlet section 32. The inlet section 32 is fluidly connected to the compressor (not shown) of the turbomachine (not shown) . The inlet section 32 receives compressed air from the compressor and introduces the compressed air into the burner interior 20, more

precisely into the upstream side 22 of the burner interior 20. Similarly, the inlet section 32 is fluidly connected to a fuel supply (not shown) of the turbomachine . The inlet section 32 receives main gas fuel from the fuel supply and introduces the main gas fuel into the burner interior 20, more precisely into the upstream side 22 of the burner interior 20.

In an exemplary embodiment of the burner 1 as depicted in FIG 1, the inlet section 32 of the swirler 30 includes at least one air inlet 33 and at least one main fuel gas inlet 34. The compressed air is introduced into the burner interior 20 via the air inlet 33 and the main gas fuel is introduced into the burner interior 20 via the main fuel gas inlet 34. The air inlet 33 may be tangentially arranged along the swirler 30 with respect to the main axis 9. Similarly, the main fuel gas inlet 34 may be tangentially arranged along the swirler 30 with respect to the main axis 9. For example, when the swirler 30 is conical frustum shaped, the air inlet 33 and/or the main fuel gas inlet 34 may be formed as longitudinally extending slots through a body wall (now shown) of the conical frustum. In an exemplary embodiment of the burner 1, the inlet section 32 includes a plurality of the air inlets 33 and a plurality of the main fuel gas inlets 34 arranged around the swirler 30 in a distributed way such that when the main gas fuel and the compressed air enter the burner

interior 20 though the air inlets 33 and the main fuel gas inlets 34, a swirl is generated in the compressed air and the main gas fuel . Principle of swirl generation through

longitudinal slots i.e. the air inlets 33 and the main fuel gas inlets 34, on such a conical shaped swirler 30 is known in the art of turbomachines and thus not explained in details herein for sake of brevity.

The premixing section 40 is an elongated tubular body. The premixing section 40 has a burner outlet 42 through which the premixing section 40 is arranged or fixed or assembled with the combustion chamber 99. As seen in FIG 1, in the burner 1 the burner outlet 42 of the premixing section 40 is an opening through which the burner interior 20, more precisely the downstream side 24 of the burner interior 20 fluidly connects to the combustion chamber 99. Thus the burner interior 20 is continuous with the combustion chamber 99 through the burner outlet 42. The combustion mixture and/or its constituents flow from the swirler 30 into the premixing section 40 and then into the combustion chamber 99 though the burner outlet 42. The premixing section 40, also referred to as mixer 40, performs or allows the mixing of the compressed air and the main gas fuel . The injection component 50 has a tapering structure

positioned along the main axis 9. The tapering structure of the injection component 50 extends from the burner head 12 into the burner interior 20. The injection component has a burner head side 52 and an injection side 54. The injection component 50 tapers from the burner head side 52 to the injection side 54 along the main axis 9. The tapering means a cross-sectional area perpendicular to the main axis 9 of the injection component 50 decreases when moving from the head side 52 to the injection side 54 along the main axis 9. In one embodiment the decrease in the cross-sectional area is gradual for example when the injection body 50 is designed like in form of a regular conical structure, as also depicted in FIG 2. The injection component 50 may be hollow for guiding fuel. Particularly, as the injection component 50 is tapered, the inner hollow space may also be tapered accordingly. So the fuel passage within the injection component 50 reduces in width along an axial direction of the tapered section of the injection component 50.

As seen in FIG 1 in combination with FIG 2, the injection component 50 includes at least one liquid fuel outlet 55 at the injection side 54. A main liquid fuel is introduced into the burner interior 20 through the at least one liquid fuel outlet 55. The main liquid fuel may be fed to the liquid fuel outlet 55 via fuel lines (not shown) formed inside the injection body 50. The fuel lines within the injection component 50 may in turn be connected to a liquid fuel supply (now shown) of the turbomachine . As depicted in FIG 1, the injection side 54 of the injection component 50 is disposed in the burner interior 20 as a free standing manner i.e.

without any physical supports at the injection side 54. As seen in FIG 1, the injection body 50, in an exemplary

embodiment of the burner 1, is coaxially positioned with the main axis 9. As shown in FIGs 1 and 2, the at least one liquid fuel outlet 55 is at a side 58 of the injection side 54 of the injection component 50. In an exemplary embodiment of the burner 1, there are more than one liquid fuel outlets 55 located on the injection side 54 of the injection component 50, for example FIG 1 shows two liquid fuel outlets 55, from each of the liquid fuel outlets 55 the main liquid fuel is discharged in form of a fluid stream or in atomized form with a direction towards the combustion chamber 99, for example as depicted by arrows 71. Furthermore, as depicted in FIG 2, the injection component 50 may include a second additional outlet 62 which may have different shape or size as compared to the liquid fuel outlet 55. The second additional outlet 62 is also used to introduce the main liquid fuel into the burner interior 20, albeit the second additional outlet 62 is at a different position on the injection side 54 for example an end 56 of the injection side 54 of the injection component 50.

Referring now to FIGs 3 and 4 that schematically illustrate a cross-sectional view of another exemplary embodiment of the burner 1. As shown in FIGs 3 and 4, the at least one liquid fuel outlet 55 is at an end 56 of the injection side 54 of the injection component 50. In an exemplary embodiment of the burner 1, there may be more than one liquid fuel outlets 55 located on the end 56 of the injection side 54 of the

injection component 50. FIG 3 shows one liquid fuel outlet 55 from which the main liquid fuel is discharged in form of a fluid stream or in atomized form with a direction towards the combustion chamber 99, for example as depicted by arrow 71. Furthermore, as depicted in FIG 4, the injection component 50 may include a first additional outlet 61 which may have different shape or size as compared to the liquid fuel outlet 55. Fig 4 depicts two such first additional outlets 61. The additional outlet 61 is also used to introduce the main liquid fuel into the burner interior 20, albeit the first additional outlet 61 is at a different position on the injection side 54 for example a side 58 of the injection side 54 of the injection component 50.

As can be seen in FIGs 1 and 3, in both embodiments of the burner 1, due to the tapering structure of the injection component 50 which aids in the axial flow of the air from the compressor and/or combustion mixture along the main axis 9 and due to injection of the main liquid fuel via the liquid fuel outlet 55 in a suitable position within the downstream side 24 of the burner interior 20, formation of a central recirculation zone 4 in the combustion chamber 99 is

achieved, and undesired formation of any recirculation zone extending into the burner interior 20 is obviated.

Furthermore, as seen in FIGs 1 and 3, in the burner 1, the premixing section 40 has a part 44 of the premixing section 40 that surrounds the burner outlet 42 of the premixing section 40. The part 44 includes an external pilot 45, as depicted in FIG 1. From the external pilot 45, a pilot fuel is introduced into the combustion chamber 99. FIGs 1 and 3 show introduction of the pilot fuel through the part 44 into the combustion chamber 99. A direction of injection of the pilot fuel is depicted by arrow 72 in FIGs 1 and 3. It may be noted that though FIG 1 shows just one external pilot 45, it is well within the scope of the present technique that a plurality of the external pilots 45 are present distributed circumferentially around a body (not shown) of the premixing section 40 around the burner outlet 42.

As depicted in FIGs 1 and 3, in both embodiments of the burner 1, due to the external pilot 45 and the ejection of the pilot fuel from the external pilot 45 in the direction 72, formation of an external recirculation zone 5 in the combustion chamber 99 is achieved. In exemplary embodiment of the burner 1, the external recirculation zone 5 surrounds the central recirculation zone 4 annularly and helps to further stabilize the central recirculation zone 4.

Now referring to FIGs 5, 6 and 7, different positions of the injection component 50 along the main axis 9 are depicted. As seen in FIG 5, in an embodiment of the burner 1, the liquid fuel outlet 55 is positioned in the downstream side 24 of the burner interior 20. Similarly, as seen in FIG 6, in another embodiment of the burner 1, the liquid fuel outlet 55 is positioned in the downstream side 24 of the burner interior 20 albeit in a different position with respect to the

position of the liquid fuel outlet 55 of FIG 5.

Alternatively, as seen in FIG 7, in an alternate embodiment of the burner 1, the liquid fuel outlet 55 is positioned in the upstream side 22 of the burner interior 20.

As depicted in FIGs 1, 3 and 5, a first distance 91 is a distance along the main axis 9 between the at least one liquid fuel outlet 55 and the burner head end 12, and a second distance 92 is a distance along the main axis 9 between the burner outlet 42 of the premixing section 40 and the burner head end 12. In embodiments of the burner 1, where there are more than one liquid fuel outlets 55, the first length 91 is calculated as a mathematical average of all the distances of each individual liquid fuel outlets 55 from the burner head end 12. In other embodiments of the burner 1, as depicted in way of exemplary embodiments of FIGs 5, 6 and 7 mainly, a ratio of the first distance 91 and the second distance 92 may vary, for example the first distance 91 may be between 20% and 80% of the second distance 92 along the main axis 9.

Furthermore, in one embodiment of the burner 1, the injection component 50 is longitudinally adjustable or moveable along the central axis 9, such that a position of the at least one liquid fuel outlet 55 of the injection component 50 gets changed from a first location 93, as depicted in FIG 5 along the main axis 9 to a second location 94 along the main axis 9, as depicted in FIG 6. Thus the injection component 50 is retractable into the burner interior 20 from the combustor chamber outlet 42 towards the burner head 10 and/or is extendable into the burner interior 20 from burner head 10 towards the combustor chamber outlet 42.

Furthermore, as depicted from a combination of FIGs 5, 6 and 7, it can been seen that the injection component 50 has progressively retracted into the burner interior 20 from the combustor chamber outlet 42 towards the burner head 10 gradually from FIGs 5 to 7. FIG 7 shows another second location 94 depicted in FIG 7 as compared to the second location 94 of FIG 6 and as compared to the first location 93 of FIG 5. The shape of a fuel lance - i.e. the injection component 50 - is tapered in a way, that the fuel lance is an elongated component. Preferably it may reduce its width taken in radial direction along an axial distance D only by or less than D/10, preferably less than D/20.

While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.