Patent Publication Number: US-9835335-B2

Title: Air directed fuel injection

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2013/073525 filed Nov. 11, 2013, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP12196530 filed Dec. 11, 2012. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The present invention relates to a combustion chamber for a gas turbine which comprises in particular an air blast injector for injecting an air blast into the inner volume. 
     ART BACKGROUND 
     In combustion chambers for gas turbines, it is an aim to reduce the emissions, such as nitrogen oxides NOx and/or carbon monoxide CO. The temperatures inside the combustion chamber cause high CO and NOx emissions. 
     In order to reduce the emissions, so-called dry low emissions (DLE) combustion systems are used which typically have a main and supplementary fuel stream, where the main fuel stream burns in a premixed flame mode. The supplementary fuel stream may generate a so-called pilot flame, which may be of a pure diffusion type or to some extent premixed. This stabilizes a main flame in the combustion chamber. A very lean fuel mixture is burned in the main flame. Under normal circumstances this would cause an unstable flame which is prone to dynamics. Therefore, the DLE systems use the pilot flame. The pilot flame comprises a rich or richer fuel mixture, wherein the rich or richer pilot flame is more stable than the lean main flame and the heat and radicals produced from this hot stable pilot frame stabilizes the main flame. 
     Ignition of liquid system in gas turbines has always proved problematic. There are many factors involved, such as the fuel flow rate, atomization of the fuel, air assistant flow rates, location of fuel injector/ignitor as well as the aerodynamics in the area of ignition. This is particularly true for Dry Low Emissions (DLE) systems as there are pilot/main flow rates to balance as well. 
     The freedom in positioning of an ignitor to achieve reliable ignition of a liquid pilot fuel is very limited. The ignitor and a respective pilot fuel injector are separate items and rely on a local aerodynamics inside the burner volume of the combustor to wash the injected pilot fuel spray over the ignitor. 
     The fluid flow in the burner volume inside the combustion chamber is relied upon to wash the injected pilot fuel over the ignitor. Therefore, if the local fluid flow tends to move away from the ignitor surface, then the fuel could be swept away from the ignitor without being ignited. 
     In particular, the aerodynamics within the combustor is designed to reach an optimum at full load running where fuel wash over any parts of the combustor is undesirable as it can cause build of coke. As a consequence, the aerodynamics at the ignitor is poor in a start and lightning phase of the gas turbine. 
     In order to improve ignition reliability, several methods have been employed such as gas assisted ignition, plasma ignitors and higher power ignitors. Gas assisted ignition requires a further gas supply, e.g. from gas bottles, which can be costly to maintain. Plasma ignitors currently have short lifetimes and there is no running experience of using them in a gas turbine. Higher power ignitors burn out quickly and the service life is short. 
       FIG. 9  shows a conventional pilot burner device, which comprises a conventional pilot body  900 . A conventional pilot surface  901  of the conventional pilot body  900  facing an inner volume (burner volume) of the conventional combustion chamber. A conventional fuel injector  902  and a conventional ignitor unit  903  is installed within the conventional pilot body  900 , such that a conventional fuel spray  904  is injectable into the inner volume. A flow direction  106  of fluids in the inner volume directs the injected conventional fuel spray  904  to the conventional ignitor unit  903 . 
     EP 0 728 989 B1 discloses a gas turbine engine combustor. Fuel is injected by a pilot burner and is directed by lips in the circumference of the pilot burner radially to a centre of an inner volume of the combustion chamber. Columns of air which are injected from a base area of the pilot burner directs the injected fuel away from the pilot burner surface. 
     WO 2009/056425 discloses a combustor for a gas turbine engine which comprises a burner head. Fuel is injected by a pilot fuel nozzle which is positioned off-center with respect to a longitudinal axis of the burner head. A fuel is injected by the nozzle with a predefined cone-shaped spray direction. 
     EP 1 837 597 A2 discloses a burner for a combustion chamber which comprises a pilot body. A spray nozzle is attached to a burner, wherein the spray nozzles spray fuel into an inner volume of the combustion chamber. A plurality of blowing ports injects air for combustion into a mixing portion of the inner volume of the combustion chamber and along a direction away from a burner surface. 
     EP 1 279 897 A2 discloses a pilot nozzle of a gas turbine combustor. The pilot nozzle is arranged near a main nozzle of a combustor which injects fuel. Furthermore, pilot air is injected into the gas turbine combustor which directs the injected fuel away from the pilot burner surface of the pilot burner. 
     SUMMARY OF THE INVENTION 
     It may be an objective of the present invention to improve the ignition performance of injected fuel in a combustion chamber of a gas turbine. 
     This objective may be solved by a combustion chamber for a gas turbine and by a method for operating a combustion chamber according to the independent claims. 
     According to a first aspect of the present invention, a combustion chamber for a gas turbine is presented. The combustion chamber comprises a pilot burner device, a fuel injector, an ignitor unit and an air blast injector. 
     The pilot burner device comprises a pilot body with a pilot surface which is facing an inner volume (i.e. a burner volume) of the combustion chamber. The fuel injector comprises a fuel outlet for injecting a fuel into the inner volume, wherein the fuel outlet is arranged at the pilot surface. The ignitor unit is adapted for igniting the fuel inside the inner volume, wherein the ignitor unit is arranged at the pilot surface such that the fuel which passes the ignitor unit is ignitable. The air blast injector is adapted for injecting an air blast into the inner volume. 
     The air blast injector comprises an air blast outlet at the pilot surface, wherein the air blast outlet is arranged at the pilot surface such that the air blast is injectable in the direction to the fuel outlet and the ignitor unit for directing the fuel to the ignitor unit. 
     According to a further aspect of the present invention, a method for operating a combustion chamber is presented. The fuel is injected into an inner volume (i.e. a burner volume) of the combustion chamber by a fuel injector. The combustion chamber comprises a pilot burner device comprising a pilot body with a pilot surface which is directed to and facing the inner volume of the combustion chamber. The fuel injector comprises a fuel outlet which is arranged at the pilot surface. The fuel inside the inner volume is ignited by an ignitor unit, wherein the ignitor unit is arranged at the pilot surface such that the fuel which passes the ignitor unit is ignitable. An air blast is injected into the inner volume by an air blast injector, which is arranged at the pilot surface, wherein the air blast injector comprises an air blast outlet which is arranged at the pilot surface such that the air blast is injected in the direction to the fuel outlet and the ignitor unit for directing the fuel to the ignitor unit. 
     The combustion chamber may be an annular-type or a can-type combustor for a gas turbine. The combustion chamber may be tubular and may have a cylindrical or an oval cross-section. 
     The combustion chamber may comprise a main combustion section and a pre-combustion section to which a swirler device and the above described pilot burner device is mounted. A pilot flame is generated by the pilot burner device, wherein the pilot flame is used to stabilize a main flame inside inner volume. 
     The pilot burner device comprising the pilot surface may be attached to an end section of the combustion chamber close to a swirler device, for example. The (pilot) fuel injector of the pilot burner device is arranged at the pilot surface for injecting fuel into the inner volume. 
     The pilot surface is facing an inner volume (burner volume) of the combustion chamber. The pilot body may be mounted to an open end (e.g. a hole in the end face) of the combustion chamber. The pilot body is mounted to the end face of the combustion chamber in a detachable manner, for example. The end face of the combustion chamber is located at the most upstream location of the combustion chamber with respect to the flow of gas inside the combustion chamber. The side walls of the combustion chamber are attached to the end face and comprise an angle with respect to the end face. The side walls of the combustion chamber extend (at least with a component) from the end face along a centre axis of the combustion chamber. 
     The fuel injected by the fuel injector at the pilot surface is used for controlling the main flame in which the main fuel which is injected by the swirler device is burned. The injected (pilot) fuel generates a predefined flame shape. The main fuel stream is introduced via the swirler in a generally tangential direction into the combustor with respect to a centre axis of the combustion chamber. The injected main fuel stream and the pilot fuel stream may comprise a liquid fuel or a gaseous fuel. The main fuel and the pilot fuel flow after being injected into the combustion chamber generally along the centre axis away from the pilot surface. The main fuel and the pilot fuel stream may also flow slightly inclined with respect to the centre axis. The pilot fuel is ignited by the ignitor unit to form the pilot flame. The pilot flame ignites the main fuel for forming the main flame. 
     The centre axis of the combustion chamber may be a symmetry line of the combustion chamber and in particular of the pre-combustion section. The centre axis of the combustion chamber may in another design coincide with the centre line of the gas turbine. 
     The air blast outlet of the air blast injector comprises for example a nozzle, which directs the air blast in a predefined desired direction. According to the present invention, the air blast is injected by the air blast outlet in a direction to the fuel outlet and also to the ignitor unit. For example, the air blast injector, the fuel injector and the ignitor unit are located at the pilot surface one after another, such that the injected air blast streams from the air blast outlet to the fuel injector and further to the ignitor unit. Hence, the air blast directs the injected fuel by the fuel injector to the ignitor unit. 
     The air blast injector injects the air blast in an injecting direction which has a (directional) component that is perpendicular to a normal of the pilot surface. In other words, the air blast is injected by the air blast injector at least partially parallel to the pilot surface and at least partially non-parallel to the normal of the pilot surface or non-parallel to the center axis of the combustion chamber. The air blast may be for example oxygen or air, i.e. compressed air. 
     Hence, by the approach of the present invention, the air blast which is injected by the air blast injector directs an injected fuel spray injected by the fuel injector over an ignitor head of the ignitor unit, which is located at the pilot surface, in particular during the ignition phase. Under normal operation of the gas turbine, the air blast injector and the ignitor unit may be switched off if desired. 
     By the present invention, specifically during the start-up phase of the gas turbine, a reliable amount of injected fuel is directed over the ignitor unit. This is possible by the air blast injected by the air blast injector. No movable parts or additional fluid guiding elements within the combustion chamber are necessary. The injected air blast may be simple controlled by a single on/off valve, for example. 
     According to a further exemplary embodiment, the fuel injector, the ignitor unit and the air blast injector are arranged along a circumferential direction around a centre axis of the pilot burner device. The centre axis of the pilot burner device may be parallel and coaxial with the centre axis of the combustion as described above. By arranging the fuel injector, the ignitor unit and the air blast injector along the circumferential direction means that the fuel injector, the ignitor unit and the air blast injector are spaced from each other but may comprise the same or a similar radius (distance) to the centre axis of the pilot burner device. 
     Generally, the circulation of the combustion fluid (e.g. a fuel/air mixture) in the inner volume of the combustion chamber is directed around the centre axis and hence along a circumferential direction around the centre axis. Hence, if the air blast injector, the fuel injector and the ignitor unit are arranged one after another along the circumferential direction, the air blast is directed at least partially along the circumferential direction of the combustion fluid streaming direction in the combustion chamber. Hence, the directing of the fuel to the ignitor unit may be more efficient because the directing of the fuel to the ignitor unit is assisted by the air blast and additionally by the streaming direction of the combustion fluid inside the combustion chamber. 
     According to a further exemplary embodiment, the fuel injector comprises a fuel nozzle at the fuel outlet such that the fuel is injectable in an atomized manner. 
     According to a further exemplary embodiment of the present invention, the air blast outlet is formed for injecting the air blast with an air blast spray cone. The air blast spray cone may comprise a conical shape for example. Hence, by injecting the air blast within an air blast spray cone, more injected fuel may be captured and directed to the ignitor unit. 
     According to a further exemplary embodiment of the present invention, the pilot body comprises a first passage, which connects the inner volume with an environment of the pilot burner device. The fuel injector (for example a fuel lance) is inserted into the first passage. The pilot body further comprises a second passage which connects the inner volume with the environment of the pilot burner device, wherein the air blast injector is inserted into the second passage. 
     Furthermore, a common passage may be formed into the pilot body according to a further exemplary embodiment of the invention. The common passage connects the inner volume with an environment of the pilot burner device, wherein the fuel injector and the air blast injector are inserted into the common passage and may in this embodiment comprise of a single unit or multiple units. 
     According to a further exemplary embodiment of the present invention, a further air blast injector for injecting a further air blast into the inner volume is provided. The further air blast injector comprises the further air blast outlet which is arranged at the pilot surface such that the further air blast is injectable in the direction to the fuel outlet and the ignitor unit for directing the fuel to the ignitor unit. 
     Specifically, the further air blast injector is spaced from the above-described air blast injector. Hence, a plurality of spaced apart air blast injectors may inject different air blast streams with different directions with respect to one and the same fuel injector outlet. Hence, a proper control and a more exact streaming direction of the fuel may be provided. 
     According to further exemplary embodiment of the present invention, the pilot burner device further comprises a centre axis and the pilot body comprises a recess. The fuel outlet is arranged within the recess. The recess is located and formed off-centred from the centre axis. 
     The centre axis of the pilot burner device may be parallel and coaxial with the centre axis of the combustion as described above. 
     Hence, the “off-centred” location of the recess at the pilot surface defines a location of the recess which is spaced apart to the centre axis of the pilot burner device. In particular, the centre axis of the pilot body does not run through the “off-centred” recess. 
     Hence, the fuel outlet is recessed with respect to a section of the pilot surface surrounding the recess. In particular, in an exemplary embodiment, the fuel injector is recessed into the pilot body with respect to the ignitor unit, which may be placed at a section of the pilot surface surrounding the recess. 
     Hence, the fuel injector injects the fuel into the off-centred recess. A flow of fluid inside the inner volume 
     (burner volume) of the combustion chamber flows along a circumferential direction within the combustion chamber around the centre axis of the pilot burner device. The flow of fluid (air/fuel mixture) passes the off-centred recess and directs the injected and atomized fuel by the fuel injector to the ignitor. By installing the fuel injector outlet within the recess a proper injection of the fuel with respect to ignitor unit is achieved without compromising the fuel atomization or the running of the fuel once the flame has lit. 
     Hence, a proper ignition performance is achieved. 
     Generally, the circulation of the combustion fluid (e.g. a fuel/air mixture) in the inner volume of the combustion chamber is directed around the centre axis and hence along a circumferential direction around the centre axis. Hence, because the recess is located off-centred with respect to the centre axis and at a circumference around the centre axis, the flow of the combustion fluid blows the injected fluid effectively in the direction to the ignitor. Furthermore, because the recess is located off-centred and does not extend all the way through the centre of the pilot surface, smaller recesses into which the fuel injector is installed may be formed, so that also negative aerodynamical effects cause by large recesses in the burner surface may be reduced. 
     In particular, if the fuel injector is recessed into the pilot body, the fuel which is injected into the recess has more space and time to be atomized before it reaches the combustion fluid flow in the combustion chamber. Hence, the ignition performance is increased because the injected fluid had time to atomize in the recess before being directed to the ignitor unit. 
     Specifically, according to a further exemplary embodiment, the recess comprises a base area and a lateral surface. The base area is arranged recessed into the pilot body and spaced apart from a section of the pilot surface surrounding the recess. The lateral surface connects the section of the pilot surface surrounding the recess and the base area. Between the lateral surface and the base area an angle exists. The angle may be in a range between approximately 10° and approximately 80°, in particular approximately 30° to approximately 60°, more particularly approximately 45°. 
     In an exemplary embodiment, the fuel outlet is arranged at the base area. The base area may be formed by the fuel outlet, for example. Moreover, the base area may comprise a hole into which the fuel outlet may be installed, for example. Hence, the size of the base are may be similar to the fuel outlet, such that the size of the recess may be reduced. 
     According to further exemplary embodiments, the fuel outlet is arranged at the lateral surface. 
     If the fuel outlet is arranged at the lateral surface, the fuel is injected along an injecting direction which may be approximately parallel to a normal of the lateral surface. 
     Hence, the injecting direction may be adapted such that the fuel is directed to the ignitor unit. 
     According to a further exemplary embodiment, the lateral surface comprises a curved shape, in particular a concave or a convex shape. Hence, corners may be prevented by the smooth curvature of the lateral surfaces such that the aerodynamic losses by the recess are reduced and turbulences may be reduced. 
     Furthermore, according to a further exemplary embodiment, the base area comprises a circular, elliptical or rectangular profile. 
     Furthermore, according to a further exemplary embodiment, a plurality of further off-centred recesses may be formed and located off-centre with respect to the centre axis of the pilot burner device. The plurality of recesses may be arranged along the circumferential direction around the centre axis. A respective further fuel injector may be installed into a respective further off-centred recess. To each fuel injector, a respective ignitor unit may be located. Further optionally, respective further air blast injectors may be located close to respective fuel injectors. 
     It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this application. 
    
    
     
       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 top view of a pilot burner device according to an exemplary embodiment of the present invention; 
         FIG. 2  shows a perspective view of a pilot burner device according to  FIG. 1 ; 
         FIG. 3  shows a schematical view of a pilot burner device comprising three passages according to an exemplary embodiment of the present invention; 
         FIG. 4  shows a schematical view of a pilot burner device comprising a common passage according to an exemplary embodiment of the present invention; 
         FIG. 5  shows a schematical view of a pilot burner device comprising a recess into which a fuel injector is installed according to an exemplary embodiment of the present invention; 
         FIG. 6  shows a schematical view of a pilot burner device comprising a recess into which a fuel injector and an ignitor unit is installed, according to an exemplary embodiment of the present invention; 
         FIG. 7  shows a perspective view of a pilot burner device comprising a recess with curved lateral surfaces according to an exemplary embodiment of the present invention; 
         FIG. 8  shows a perspective view of a pilot burner device comprising a recess with a groove-like shape, according to an exemplary embodiment of the present invention; and 
         FIG. 9  shows a conventional pilot burner device. 
     
    
    
     DETAILED DESCRIPTION 
     The illustrations in the drawings are schematic. It is noted that in different figures similar or identical elements are provided with the same reference signs. 
       FIG. 1  shows a combustion chamber  120  for a gas turbine. In particular,  FIG. 1  shows an end face of the combustion chamber  120 . The combustion chamber  120  comprises a pilot burner device, a fuel injector  102 , an ignitor unit  103  and an air blast injector  104 . 
     The pilot burner device comprises a pilot body  100  with a pilot surface  101  which is facing an inner volume (burner volume) of the combustion chamber  120 . The pilot body  100  may be mounted to an open end (e.g. a hole in the end face) of the combustion chamber  120 . 
     The fuel injector  102  comprises a fuel outlet for injecting a fuel into the inner volume. The fuel outlet is arranged at the pilot surface  101 . The ignitor unit  103  is adapted for igniting the fuel inside the inner volume, wherein the ignitor unit  103  is arranged at the pilot surface  101  such that the fuel which passes the ignitor unit  103  is ignitable. 
     The air blast injector  104  is adapted for injecting an air blast into the inner volume. The air blast injector  104  comprises an air blast outlet which is arranged at the pilot surface  101  such that the air blast is injectable in the direction to the fuel outlet and the ignitor unit  103  for directing the fuel to the ignitor unit  103 . 
     A combustion fluid comprises fuel and air streams inside the inner volume along a circumferential direction around a centre axis  105  of the pilot burner device and hence of the combustion chamber  120 , for example. Along the flow direction  106  (i.e. the circumferential direction), the air blast injector  104 , the fuel injector  102  and the ignitor unit  103  are arranged one after another at the pilot surface  101 . 
     Hence, the air blast of the air blast injector  104  is directed to the fuel injector  102  and further to the ignitor unit  103 . Hence, the air blast guides the injected fuel at the fuel injector outlet to the ignitor unit  103  such that more fuel is guided to the ignitor unit  103 . 
     Specifically, the air blast injector  104  injects an air blast along an air blast injecting direction  107 , wherein the air blast injecting direction  107  streams generally along the pilot surface  101 . In particular, the air blast injecting direction  107  is directed at least with a (directional) component perpendicular to a normal of the pilot surface  101  and streams at least partially parallel to the pilot surface  101 . Furthermore, the air blast injector  104  may inject the air blast in such a way that an air blast spray cone  108  is formed. Hence, the air blast stream comprises a larger width at the region of the fuel injector  102  and the ignitor unit  103 , such that more injected fuel may be captured and directed to the ignitor unit  103 . 
     Additionally, as shown in  FIG. 1 , further air blast injectors  104 ′ may be arranged to the pilot surface  101  for injecting further air blast streams in the direction to the fuel injector  102  and the ignitor unit  103 . The further air blast streams may slightly differ in its direction to the air blast injecting direction  107  so that a large air blast streaming field may be generated. 
     Furthermore, a recess  501  with similar features as shown in  FIG. 5  may be formed into the pilot body  100  shown in  FIG. 1 , wherein the fuel injector  102  may be installed into the recess  501 . 
       FIG. 2  shows the same features as  FIG. 1 , wherein in  FIG. 2  a perspective view of the pilot burner device as shown in  FIG. 1  is shown. 
       FIG. 3  shows a further exemplary embodiment of a pilot burner device according to the invention, wherein the pilot body  100  comprises a first passage  301  which connects the inner volume with an environment of the pilot burner device, wherein the fuel injector  102  is inserted into the first passage  301 . The fuel injector  102  may be for example a fuel lance which is detachably inserted into the first passage  301  such that the fuel outlet is positioned at the pilot surface  101 . Spaced apart to the first passage  301 , the pilot body  100  further comprises a second passage  302  which connects the inner volume with the environment of the pilot burner device, wherein the air blast injector  104  is inserted (e.g. detachably) into the second passage  302 . The injectors  102  and  104  and the ignitor unit  103  may for example be tube-like in shape and extend through the pilot body. 
     As can be taken from  FIG. 3 , the fuel injector  102  injects the fuel in an atomized manner, i.e. with a fuel spray  304 . The air blast injector  104  injects the air blast in an air blast injecting direction  107 . As can be taken from  FIG. 3 , the air blast injecting direction  107  comprises a component which is almost parallel to the pilot surface  101  and comprises an angle perpendicular to a normal of the pilot surface  101 . 
     The fuel injector  102  and hence the second passage  302  are arranged within the pilot body  100  in such a way that the air blast directs with the air blast injecting direction  107  the fuel spray  304  to the direction to a third passage  303  into which the ignitor unit  103  is arranged close to the pilot surface  101 . 
     Furthermore, the first passage  301 , the second passage  302  and the third passage  303  are arranged to the pilot body  100  in such a way, that the flow direction  106  of the combustion fluid supports the air blast injector  104 . Specifically, along a flow direction  106  of the fluid inside the inner volume, first, the air blast injector  104  is located, next, the fuel injector  102  is located further downstream and finally further downstream the ignitor unit  103  is located. 
       FIG. 4  shows an exemplary embodiment of the pilot body  100  into which a common passage  401  is formed which connects the inner volume with an environment of the pilot burner device. The fuel injector  102  and the air blast injector are inserted together into the common passage  401 . Hence, as more simple design of the pilot body  100  may be provided because for example only a common passage  401  and a third passage  303  for the ignitor unit  103  is necessary. In a further exemplary embodiment can the air blast injector  104  be arranged around the fuel injector  102  as eccentric tube directing the air blast to a desired sector of the circumference of the fuel injector  102 . 
       FIG. 5  shows a further exemplary embodiment of the pilot burner device of the combustion chamber  120 . The pilot burner device comprises a pilot body  100  with a pilot surface  101  which is directed to an inner volume of the combustion chamber  120 . Furthermore, a recess  501  is formed into the pilot body  100 . The fuel outlet of a fuel injector  102  for injecting a fuel into the inner volume is arranged within the recess  501 . The recess  501  is located and formed off-centred from the centre axis  105 . 
     Hence, the “off-centred” location of the recess  501  at the pilot surface  101  defines a location of the recess  501  which is spaced apart from the centre axis  105  of the pilot burner device. In particular, the centre axis  105  of the pilot body does not run through the “off-centred” recess  501 . 
     For example, the fuel may be injected by the fuel injector  102  almost parallel to a normal of a section of the pilot surface  101  surrounding the recess  501  and/or parallel to a center axis  105  of the pilot burner device. In the recess  501 , the injected fuel is not directly blown away from the recess  501  by a combustion fluid inside the inner volume which streams generally along a flow direction  106 . In the recess  501 , the fuel has time to spread and diffuse before the combustion fluid in the inner volume streaming along the flow direction  106  takes the injected fuel away to the ignitor unit  103 . If the diffused and atomized fuel passes the ignitor unit  103 , ignition occurs. In particular, the ignitor unit  103  is located at the pilot surface  101  further downstream with respect to the flow direction  106  in comparison to the further upstream located recess  501  and hence the fuel injector  102 . 
     Further upstream with respect to the flow direction  106 , an air blast injector  104  for injecting an air blast into the inner volume is for example arranged to the pilot body  100 . The air blast injector  104  comprises an air blast outlet which is arranged upstream with respect to the flow direction  106  in comparison to the fuel injector  102  and the ignitor unit  103 . The air blast is injectable in the direction to the fuel outlet and the ignitor unit  103  for directing the fuel to the ignitor unit  103 . The air blast injector  104  may be arranged at a surface section of the pilot surface  101  surrounding the recess  501  (see  FIG. 6 ) or, as can be taken from  FIG. 5 , arranged within the recess  501 . 
     Specifically, the recess  501  may comprise a base area  502  which is spaced from the section of the pilot surface  101  surrounding the recess  501 . Furthermore, the recess  501  comprises a lateral surface  503 , wherein the lateral surface  503  connects the section of the pilot surface  101  surrounding the recess  501  and the base area  502 . 
     As can be taken in the exemplary embodiment of  FIG. 5 , the air blast injector  104  may be installed at the lateral surface  503 . 
     The pilot body  100  may comprise a first passage  301  into which the fuel injector  102 , such as a fuel lance, is detachably insertable. Furthermore, in particular further upstream of the first passage  301  with respect to the flow direction  106 , a second passage  302  may be formed into the pilot body  100 , wherein to the second passage  302  the air blast injector  104  is detachably insertable. 
       FIG. 6  shows a further exemplary embodiment of the present invention, wherein the recess  501  in the pilot body  100  comprises the base area  502  and the lateral surface  503 . 
     The fuel injector  102  is arranged at the lateral surface  503 . Furthermore, further downstream of the fuel injector  102  with respect to the flow direction  106 , the ignitor unit  103  is arranged to the base area  502  or, as shown in  FIG. 6 , to the lateral surface  503 . The fuel injector  102  injects the fuel into the recess  501  in an atomized manner, wherein the fuel injector  102  directs the fuel directly to the ignitor unit  103  which is located inside the recess  501 . Hence, the atomized fuel is ignited when passing the ignitor unit  103 . Next, the fluid in the inner volume flowing along the flow direction  106  takes the ignited fuel away from the recess  501  and guides the ignited fuel further into the inner volume. 
     In order to improve the ignition efficiency, the air blast injector  104  is attached to the pilot body  100  further upstream of the fuel injector  102  and the ignitor unit  103 . For example, the air blast injector  104  is located upstream of the fuel injector  102  and the ignitor unit  103  at the surface section of the pilot surface  101  surrounding the recess  501 . Alternatively, the air blast injector  104  may also be located at the lateral surface  503  at a location which is located further upstream to the fuel injector  102  and the ignitor unit  103  (see e.g. in  FIG. 5 ). 
     The term “upstream” and “downstream” relates to the flow direction  106  of the fluid inside the inner volume around the centre axis  105 . 
       FIG. 7  shows an exemplary embodiment of the combustion chamber  120  and the pilot burner device as shown in  FIG. 5 . As can be taken from  FIG. 7 , the lateral surface  503  may comprise a curved shape, in particular in a convex shape. As can be taken from  FIG. 7 , the flow direction  106  of the fluid inside the inner volume flows along a circumferential direction around the centre axis  105 . At the base area  502 , the fuel injector  102  is installed. The air blast injector  104  is installed at the lateral face  503  such that an air blast is injected along the circumferential direction (flow direction  106 ) to the fuel injector  102  and further to the ignitor unit  103 . The ignitor unit  103  is located onto the pilot surface  101  of the combustion chamber  120 . 
     As can be taken from  FIG. 7 , the base area  502  may be a hole through which the fuel injector  102  is attachable, such that the fuel outlet is arranged within the base area  502 . Furthermore, a further recess  501 ′ into which a further fuel injector may be installed may be formed into the pilot body  101 . In particular, along the circumferential direction around the centre axis  105 , a plurality of recesses  501 ,  501 ′ may be formed into the pilot body  101 . 
       FIG. 8  shows a pilot burner body  100  with the same features as shown in  FIG. 7 , whereas the recess  501  is formed with a groove-like profile which has an open area in the side surface of the pilot burner body  100 . The groove shaped recess  501  as shown in  FIG. 8  may be easier to manufacture with respect to the tubular and donut-like shaped recess  501  as shown in  FIG. 7 . 
     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.