Pilot fuel nozzle assembly with ventilated venturi

Abstract

A pilot fuel nozzle assembly includes a fuel nozzle, a swirler and a ventilation pilot venturi. The ventilation pilot venturi has an annular wall with an oxidant flow channel therein. The expansion flow surface portion of the venturi has a larger diameter at the outlet than at the throat of the venturi. A plurality of venturi oxidant outlet ports extend through the expansion flow surface to the oxidant flow channel in the annular wall to provide an oxidant flow through the venturi wall into the mixing chamber of the venturi and the outlet end of the venturi. The oxidant outlet ports are circumferentially spaced around the circumference of the expansion flow surface and can be arranged in multiple rows. The oxidant outlet ports can be inclined relative to the expansion flow surface and can be circumferentially inclined in the same vortex direction as the swirler.

Description

Technical Field

[0001] The present disclosure relates to a venturi tube of a pilot fuel nozzle assembly. Background Art

[0002] Some burners in use are called TAPS (double annular premixing swirler) burners. The TAPS burner includes a premixer / swirler fuel nozzle assembly in which air and fuel are mixed. The TAPS premixer / swirler fuel nozzle assembly includes a pilot swirler and a main premixer. The pilot swirler includes a venturi tube, and the fuel / air mixture is injected into the venturi tube through the pilot fuel nozzle and the surrounding air swirler. The fuel / air mixture leaves the venturi tube and enters the combustion chamber, where it is ignited and burned. At the outlet end of the venturi tube, a heat shield is usually provided to protect the fuel nozzle assembly. The rear surface of the heat shield facing the combustion chamber is subjected to the high temperature from the burning fuel / air mixture leaving the venturi tube. Summary of the invention

[0003] According to one aspect, the present disclosure relates to a pilot fuel nozzle assembly for a combustor of a gas turbine engine. The pilot fuel nozzle assembly includes a pilot fuel nozzle; a pilot oxidant inlet, which is arranged around the pilot fuel nozzle; a pilot oxidant swirler, which is arranged downstream of the pilot oxidant inlet, and the pilot oxidant swirler provides a swirl flow of the oxidant in the pilot swirl direction around the centerline axis of the fuel nozzle; and a ventilation pilot venturi tube, which is arranged radially outside the pilot oxidant swirler and is in fluid communication with the pilot oxidant inlet. The ventilation pilot venturi tube includes an annular wall, which extends circumferentially around the centerline axis of the fuel nozzle and extends from the inlet end of the ventilation pilot venturi tube to the outlet of the ventilation pilot venturi tube in the longitudinal direction along the centerline axis of the fuel nozzle. The annular wall has an oxidant flow channel in the annular wall, and the oxidant flow channel extends from the inlet end of the ventilation pilot venturi tube to the outlet end of the ventilation pilot venturi tube adjacent to the outlet. The oxidant flow channel is in fluid communication with the pilot oxidant inlet.

[0004] In addition, according to this aspect of the present disclosure, the annular wall defines an inner venturi surface that defines an open cavity through the ventilation pilot venturi. The inner venturi surface includes: (a) a throat region disposed between an inlet end of the ventilation pilot venturi and an outlet of the ventilation pilot venturi, the throat region having a smaller diameter than the remaining portion of the inner venturi surface downstream of the throat region; and (b) a diverging flow surface portion disposed in a longitudinal direction from the throat region to the outlet of the ventilation pilot venturi, the diverging flow surface portion having a first diameter at the throat region and a second diameter at the outlet, the second diameter being greater than the first diameter. The annular wall further defines a plurality of venturi oxidant outlet ports that extend from the oxidant flow channel through the diverging flow surface portion, the plurality of venturi oxidant outlet ports being circumferentially spaced about the fuel nozzle centerline axis.

[0005] According to another aspect, the present disclosure relates to a ventilation pilot venturi tube for a pilot fuel nozzle assembly of a gas turbine engine. The ventilation pilot venturi tube includes: an annular wall extending circumferentially around the centerline axis of the venturi tube and extending in a longitudinal direction along the centerline axis of the venturi tube from the inlet end of the ventilation pilot venturi tube to the outlet of the ventilation pilot venturi tube; and an oxidant flow channel within the annular wall, the oxidant flow channel extending from the inlet end of the ventilation pilot venturi tube to the outlet end of the ventilation pilot venturi tube adjacent to the outlet. The oxidant flow channel has a flow channel inlet at the inlet end of the wind pilot venturi tube, and the inner venturi tube surface defines an open cavity passing through the ventilation pilot venturi tube. The inner venturi surface includes: (a) a throat region disposed between an inlet end of the venturi pilot and an outlet of the venturi pilot, the throat region having a smaller diameter than a remainder of the inner venturi surface downstream of the throat region; and (b) a diverging flow surface portion disposed in a longitudinal direction from the throat region to the outlet of the venturi pilot, the diverging flow surface portion having a first diameter at the throat region and a second diameter at the outlet, the second diameter being greater than the first diameter. A plurality of venturi oxidant outlet ports extend from the oxidant flow passage through the diverging flow surface portion, the plurality of venturi oxidant outlet ports being circumferentially spaced about the venturi centerline axis.

[0006] Additional features, advantages and embodiments of the present disclosure are set forth or apparent by considering the following detailed description, drawings and claims. In addition, it should be understood that the foregoing summary and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the present disclosure as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The foregoing and other features and advantages will become apparent from the following more particular description of various exemplary embodiments as illustrated in the accompanying drawings, in which like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements.

[0008] Figure 1 is a schematic partial cross-sectional side view of an exemplary high bypass turbofan jet engine according to aspects of the present disclosure.

[0009] Figure 2 is a partial cross-sectional side view of an exemplary combustion section according to aspects of the present disclosure.

[0010] Figure 3 is a partial cross-sectional side view of an exemplary pilot fuel nozzle assembly according to aspects of the present disclosure.

[0011] Figure 4 According to aspects of the present disclosure Figure 3 Details captured at AA Figure 3 A partial cross-sectional detailed side view of a portion of a fuel nozzle.

[0012] Figure 5 According to another aspect of the present disclosure Figure 3 Details captured at AA Figure 3 A partial cross-sectional detailed side view of a portion of a fuel nozzle.

[0013] Figure 6 According to another aspect of the present disclosure, Figure 3 Details captured at AA Figure 3 A partial cross-sectional detailed side view of a portion of a fuel nozzle.

[0014] Figure 7 is a rear-to-front view of a pilot fuel nozzle assembly according to aspects of the present disclosure.

[0015] Figure 8 is a partial perspective cross-sectional view of an exemplary pilot fuel nozzle assembly according to yet another aspect of the present disclosure. DETAILED DESCRIPTION

[0016] Various embodiments are discussed in detail below. Although specific embodiments are discussed, this is for illustrative purposes only. Those skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of the present disclosure.

[0017] As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another, and are not intended to indicate the position or importance of each component.

[0018] The terms "upstream" and "downstream" refer to relative directions with respect to the flow of a fluid in a fluid path. For example, "upstream" refers to the direction from which the fluid is flowing, and "downstream" refers to the direction to which the fluid is flowing.

[0019] A known TAPS combustor includes a fuel nozzle assembly having a pilot swirler including a venturi. The pilot swirler injects a fuel / air mixture into the venturi, which then flows into a combustion chamber where it is ignited and burned. At the outlet end of the venturi, a heat shield is typically provided to protect the fuel nozzle assembly. The heat shield typically includes a flange, wherein cooling air is provided to a front surface to cool the flange, and some cooling air is also provided to a rear surface.

[0020] The present disclosure has a fuel nozzle structure that does not have a dedicated heat shield and has a vented venturi feature. More specifically, the present disclosure provides a vented venturi as a part of a pilot fuel nozzle assembly, wherein the arrangement of the vented venturi reduces the high temperature on the surface of the venturi. According to the present disclosure, the vented venturi has an air flow channel in the venturi wall and multiple rows of oxidant outlet ports extending from the air flow channel through the wall of the venturi to the inner surface of the venturi. The oxidant in the air flow channel and through the oxidant outlet port flows to the inner surface of the venturi and provides cooling air to the outer end portion of the venturi. The oxidant outlet ports are circumferentially spaced apart in the circumferential direction around the circumference of the inner surface of the venturi and around the circumference of the outlet end of the venturi.

[0021] Now referring to the accompanying drawings, Figure 1 is a schematic partial cross-sectional side view of an exemplary high bypass turbofan jet engine 10, referred to herein as "engine 10", which may incorporate various embodiments of the present disclosure. Although further described below with reference to a turbofan engine, the present disclosure is also applicable to turbomachinery in general, including turbojets, turbopropellers, and turboshaft gas turbine engines, including marine and industrial turbine engines and auxiliary power units. Figure 1 As shown, engine 10 has a longitudinal or axial centerline axis 12 extending therethrough from an upstream end 98 to a downstream end 99 for reference. Generally, engine 10 may include a fan assembly 14 and a core engine 16 disposed downstream of fan assembly 14.

[0022] The core engine 16 may generally include a substantially tubular outer casing 18 defining an annular inlet 20. The outer casing 18 surrounds or at least partially forms, in series flow relationship, a compressor section having a supercharger or low pressure (LP) compressor 22, a high pressure (HP) compressor 24; a combustion section 26; a turbine section including a high pressure (HP) turbine 28, a low pressure (LP) turbine 30; and an ejection exhaust nozzle section 32. A high pressure (HP) rotor shaft 34 drivingly connects the HP turbine 28 to the HP compressor 24. A low pressure (LP) rotor shaft 36 drivingly connects the LP turbine 30 to the LP compressor 22. The LP rotor shaft 36 may also be connected to a fan shaft 38 of the fan assembly 14. In certain embodiments, as shown in FIG. Figure 1 As shown, LP rotor shaft 36 may be connected to fan shaft 38 via reduction gear 40, such as in an indirect drive or gear drive configuration. In other embodiments, although not shown, engine 10 may also include an intermediate pressure (IP) compressor and a turbine rotatable with the IP shaft.

[0023] like Figure 1 As shown, fan assembly 14 includes a plurality of fan blades 42 coupled to and extending radially outward from fan shaft 38. An annular fan casing or nacelle 44 circumferentially surrounds fan assembly 14 and / or at least a portion of core engine 16. In one embodiment, nacelle 44 may be supported relative to core engine 16 by a plurality of circumferentially spaced outlet guide vanes or struts 46. In addition, at least a portion of nacelle 44 may extend over an outer portion of core engine 16 to define a bypass airflow passage 48 therebetween.

[0024] Figure 2 Yes Figure 1 A partial cross-sectional side view of an exemplary combustion section 26 of the core engine 16 is shown. Figure 2 The combustion section 26 in FIG. 2 is depicted as an exemplary dual annular premixing swirler (TAPS) type combustor section. However, the present disclosure may be implemented in other combustor types, and the TAPS combustion section is merely exemplary. Figure 2As shown, the combustion section 26 may generally include an annular combustor assembly 50 having an annular inner liner 52, an annular outer liner 54, a baffle wall 56, and a dome assembly 58, which together define a combustion chamber 60. The combustion chamber 60 may more specifically define a region defining a primary combustion zone 62, where an initial chemical reaction of a fuel-oxidant mixture and / or recirculation of combustion gases 86 may occur before flowing further downstream, wherein mixing and / or recirculation of combustion products and air may occur before flowing to the HP and LP turbines 28, 30. The combustor assembly 50 also includes a premixer / fuel nozzle assembly, referred to herein as a pilot fuel nozzle assembly 70, having a pilot fuel nozzle portion 73 and a main premixer portion 72. As will be described below, the pilot fuel nozzle portion 73 includes a pilot fuel nozzle and a pilot air swirler, which produce a swirled pilot fuel / air mixture that is injected into a pilot venturi and then into the combustion chamber 60, where it is combusted to produce combustion gases 86. The pilot fuel nozzle section 73 is typically operated under all operating conditions of the engine 10. The main premixer section 72 has main fuel nozzles and a main air swirler that produce a main fuel / air mixture that is injected into the combustion chamber 60 where it is ignited and combusted. The main premixer section 72 is typically operated under higher power operations of the engine 10.

[0025] During operation of the engine 10, as Figure 1 and Figure 2 As shown collectively, a volume of air, schematically indicated by arrows 74, enters engine 10 from upstream end 98 through nacelle 44 and / or associated inlet 76 of fan assembly 14. As air 74 passes through fan blades 42, a portion of the air, schematically indicated by arrows 78, is directed or channeled into bypass airflow passage 48, while another portion of the air, schematically indicated by arrows 80, is directed or channeled into LP compressor 22. Air 80 is progressively compressed as it flows through LP and HP compressors 22, 24 toward combustion section 26. Figure 2 As shown, the now compressed air flows through the compressor exit guide vanes (CEGV) 64 and through the prediffuser 66 into the diffuser cavity 68 of the combustion section 26 as schematically indicated by arrows 82 .

[0026] The compressed air 82 pressurizes the diffuser cavity 68. A first portion of the compressed air 82, as schematically indicated by arrows 82(a), flows from the diffuser cavity 68 into the pilot fuel nozzle assembly 70 where it is premixed with fuel and ejected from the pilot fuel nozzle assembly 70 and combusted, thereby producing combustion gases within the primary combustion zone 62 of the combustor assembly 50, as schematically indicated by arrows 86. Typically, the LP and HP compressors 22, 24 provide more compressed air to the diffuser cavity 84 than is required for combustion. Thus, a second portion of the compressed air 82, as schematically indicated by arrows 82(b), may be used for various purposes other than combustion.

[0027] Return to common reference Figure 1 and 2 The combustion gases 86 generated in the combustion chamber 60 flow from the combustor assembly 50 into the HP turbine 28, thereby rotating the HP rotor shaft 34 to support the operation of the HP compressor 24. Figure 1 As shown, combustion gases 86 are then channeled through LP turbine 30, thereby causing LP rotor shaft 36 to rotate, thereby supporting operation of LP compressor 22 and / or rotation of fan shaft 38. Combustion gases 86 are then exhausted through jet exhaust nozzle section 32 of core engine 16 to provide propulsive force at downstream end 99.

[0028] Figure 3 is Figure 2 A partial cross-sectional side view of an exemplary pilot fuel nozzle portion 73 taken at Detail 3-3 in FIG. Figure 8 , which depicts Figure 3 A partial perspective cross-sectional view of the pilot fuel nozzle portion 73 is shown in FIG. Figure 2 In the embodiment, the pilot fuel nozzle assembly 70 includes a pilot fuel nozzle portion 73 and a main premixer portion 72 attached thereto. The main premixer portion 72 is not Figure 3 and 7 , and only the pilot fuel nozzle portion 73 is depicted therein. It can be seen that the pilot fuel nozzle portion 73 includes a pilot oxidant inlet 108 and a pilot fuel nozzle 100 aligned along a centerline axis 102. The centerline axis 102 may also be referred to herein as the venturi tube centerline axis 102 (a). Figure 3 In FIG. 1 , the pilot fuel nozzle 100 is shown only as a general representation of a pilot fuel nozzle, and internal components such as fuel lines, etc., which are known to form the pilot fuel nozzle in a TAPS type pilot fuel nozzle are omitted.

[0029] The pilot fuel nozzle 100 is surrounded by a pilot separator 104, which is separated from the pilot fuel nozzle 100 by a pilot inner air passage 110. The inner air passage swirl vanes 106 are located within the pilot inner air passage 110. Surrounding the pilot separator 104 is a ventilation pilot venturi 116, which will be described in more detail below. A pilot outer air passage 112 is formed between the pilot separator 104 and the ventilation pilot venturi 116, and the outer air passage swirl vanes 114 are disposed within the pilot outer air passage 112. In operation, air 82 (a) enters the pilot oxidant inlet 108, and the air 82 (a) flow is separated by the pilot splitter 104 between the pilot inner air passage 110 and the pilot outer air passage 112. The vortex is introduced into the air 82(a) flowing through the pilot inner air passage 110 and the pilot outer air passage 112 by the inner air passage vortex vanes 106 and the outer air passage vortex vanes 114. Therefore, the pilot separator 104, the inner air passage vortex vanes 106 and the outer air passage vortex vanes 114 act as a pilot oxidant swirler 115. The swirled airflow is mixed with the fuel 118 injected from the pilot fuel nozzle 100 in the open cavity portion 120 of the ventilation pilot venturi 116 to produce a swirled fuel / air mixture (not shown). The swirled fuel / air mixture swirls generally circumferentially (C) around the open cavity portion 120 (i.e., swirls in the pilot swirl direction). The swirled fuel / air mixture in the open cavity portion 120 flows to the outlet 122 of the ventilation pilot venturi 116, which is ignited and burned in the combustion chamber 60.

[0030] The ventilation pilot venturi 116 will now be described in more detail. It should first be noted that the ventilation pilot venturi 116 shown in the figures omits some elements that may be included as part of the pilot fuel nozzle assembly 70 and that are not necessary for understanding the pilot venturi 116. In particular, although Figure 3 The cross-section of illustrative embodiment depicts a generally solid area (e.g., area 124) surrounding the outer portion of the venturi, but area 124 may include elements such as a main fuel circuit and a main air flow passage that form part of the main premixer portion 72. Such a main fuel circuit and main air flow passage that form part of a TAPS type premixer are known to those skilled in the art.

[0031] exist Figure 3, it can be seen that the ventilation pilot venturi 116 is formed by a generally annular wall 128 that extends in the longitudinal direction (L) along the centerline axis 102 (102(a)) from an inlet end 126 to an outlet 122. The ventilation pilot venturi 116 also extends circumferentially around the centerline axis 102 (102(a)). The annular wall 128 includes an oxidant flow channel 130 within the annular wall 128. The oxidant flow channel 130 extends from the inlet end 126 of the ventilation pilot venturi 116 to an outlet end 132 of the ventilation pilot venturi 116 adjacent the outlet 122. That is, the oxidant flow channel 130 terminates within the annular wall 128 prior to the outlet 122 near the rounded outlet end portion 134. The oxidant flow channel 130 is in fluid communication with the pilot oxidant inlet 108. That is, the inlet end of the ventilation pilot venturi 116 includes a flow passage inlet 136 in which air 82 ( a ) from the pilot oxidant inlet 108 may enter the oxidant flow passage 130 .

[0032] The annular wall 128 further defines an inner venturi surface 138 extending from the venturi inlet end 126 to the venturi outlet 122, and the inner venturi surface 138 at least partially defines the open cavity portion 120 through the venturi pilot venturi 116. The inner venturi surface 138 extends circumferentially about the centerline axis 102 (102(a)). It can be generally seen that the inner venturi surface 138 (at Figure 3 14 (depicted in bold for emphasis) includes an upstream portion 140 that forms the outer surface of the pilot outer air passage 112, a throat region 142, and a venturi diverging surface 144 downstream of the throat region 142. Thus, the throat region 142 is disposed between the inlet end 126 of the venturi pilot 116 and the outlet 122 of the venturi pilot 116. It can be seen that the throat region 142 has a smaller diameter 117 than the remainder of the venturi diverging surface 144 downstream of the throat region. That is, it can be seen that the venturi diverging surface 144 is a diverging flow surface portion that expands in diameter as the inner venturi surface 138 progresses from the throat region 142 to the outlet 122. Thus, the venturi diverging surface 144 , from the throat region 142 to the outlet 122 of the ventilation pilot venturi 116 , includes a first diameter 117 at the throat region and a second diameter 119 at the outlet 122 , wherein the second diameter 119 at the outlet 122 is greater than the first diameter 117 at the throat region 142 .

[0033] Still reference Figure 3, the annular wall 128 further defines a plurality of oxidant outlet ports 146. The oxidant outlet ports 146 extend from the oxidant flow channel 130 through the venturi diverging surface 144. Thus, the oxidant outlet ports 146 are holes that allow air 82(a) flowing through the oxidant flow channel 130 in the annular wall to flow through the holes and into the open cavity portion 120. The oxidant outlet ports 146 will be described in more detail below, but it can be readily seen that the plurality of oxidant outlet ports 146 are circumferentially spaced apart in the circumferential direction (C) about the centerline axis 102 (120(a)).

[0034] Figures 4 to 6 is Figure 3 A magnified view of the detail seen in AA. Figure 4 , it can be seen that the venturi expansion surface 144 has a generally curved contour shape extending from the throat region 142 to the outlet 122. Alternatively, the venturi expansion surface 144 can be a generally conical portion (i.e., a conical surface) extending from the throat region 142 to the outlet 122. The half angle 148 of a single conical venturi expansion surface 144 can have a range from fifteen degrees to forty degrees. Of course, the present invention is not limited to the above range, and other half angles can also be implemented alternatively.

[0035] Figure 5 An exemplary venturi expansion surface 144 is depicted, which is a double-inclined surface. That is, the first conical surface 150 of the venturi expansion surface 144 can be a generally conical surface extending from the throat area 142 to the breakpoint 158 ​​along the first conical surface 150. The first conical surface 150 can have a first conical half-angle 154. The second conical surface 152 of the venturi expansion surface 144 can also be a generally conical surface extending from the breakpoint 158 ​​to the outlet 122. The second conical surface 152 can have a second conical half-angle 156. In one aspect, the first conical half-angle can range from fifteen to thirty degrees, while the second conical half-angle can range from thirty to forty degrees. In another aspect, the first conical half-angle can range from thirty to forty degrees, while the second conical half-angle can range from fifteen to thirty degrees. Of course, the present disclosure is not limited to the above ranges, and other half-angles can also be implemented alternatively. In addition, the expansion surfaces of the present disclosure are not limited to only two conical surfaces, and other arrangements can also be implemented alternatively. For example, the first tapered surface 150 may be implemented to the breakpoint 158, and the curved surface may be implemented downstream of the breakpoint. Alternatively, a curved surface may be implemented in place of the first tapered surface 150 to the breakpoint 158, and then the second tapered surface 152 may be included from the breakpoint 158 ​​to the outlet 122. Furthermore, the present disclosure is not limited to dividing the venturi expansion surface 144 into two parts, but more than two parts may be implemented. For example, three tapered surface parts may be implemented, wherein two separate breakpoints will exist between the tapered surfaces.

[0036] Figure 6 is Figure 3 The enlarged view taken at AA in the detail of Figure 3 The arrangement of the venturi oxidant outlet port 146 is seen in FIG. Figure 6 It is about Figure 5 144. Thus, the arrangement of the oxidant outlet port 146 relative to the dual-inclined expansion surface will be described. It can be seen that the first conical surface 150 includes the oxidant outlet ports 162 and 182 (corresponding to Figure 3 146 in the oxidant outlet port). Each of the oxidant outlet ports 162 and 182 extends from the oxidant flow channel 130 through the first tapered surface 150. In the venturi tube of the present disclosure, a plurality of oxidant outlet ports 162 are arranged around the circumference of the first tapered surface 150, and a plurality of oxidant outlet ports 182 are arranged around the circumference of the first tapered surface 150. (See, e.g. Figure 7 and 8 ). The plurality of oxidant outlet ports 162 arranged around the circumference of the first tapered surface 150 may be referred to as a first row of oxidant outlet ports, and the plurality of oxidant outlet ports 182 arranged around the circumference of the first tapered surface 150 may be referred to as a second row of oxidant outlet ports. Collectively, the first and second rows of oxidant outlet ports 162, 182 may be referred to as a first group of oxidant outlet ports. Figure 6 In the first row, you can see 194 (see Figure 7 ) oxidant outlet ports 162 are arranged at a radial distance 178 from the centerline axis 102 (102(a)), and the second row 196 (see Figure 7 ) The oxidant outlet port 182 is arranged at a radial distance 180 that is different from the radial distance 178.

[0037] It can be seen that the oxidant outlet port 162 is aligned at an angle 184 relative to the first tapered surface 150 in the longitudinal direction (L). It can be seen that the oxidant outlet port 182 is aligned at an angle 166 relative to the first tapered surface 150 in the longitudinal direction (L). Angles 184 and 166 can be the same, or they can be different from each other. In some aspects of the present disclosure, angles 184 and 166 can have a range from twelve degrees to thirty degrees. Of course, the present disclosure is not limited to the above ranges, and angles 184 and 166 can also be arranged at other angles instead.

[0038] It can be seen that the second tapered surface 152 includes oxidant outlet ports 164 and 172 (again, corresponding to Figure 3Each of the oxidant outlet ports 164 and 172 extends from the oxidant flow channel 130 through the second tapered surface 152. In the ventilating venturi of the present disclosure, a plurality of oxidant outlet ports 164 are arranged around the circumference of the second tapered surface, and a plurality of oxidant outlet ports 172 are arranged around the circumference of the second tapered surface 152. (See, e.g. Figure 7 and Figure 8 ). The plurality of oxidant outlet ports 164 arranged around the circumference of the second tapered surface 152 may be referred to as a third row of oxidant outlet ports, and the plurality of oxidant outlet ports 172 arranged around the circumference of the second tapered surface 152 may be referred to as a fourth row of oxidant outlet ports. Collectively, the third and fourth rows of oxidant outlet ports 164, 172 may be referred to as a second group of oxidant outlet ports. Figure 6 , the third row of oxidant outlet ports 164 can be seen arranged at a radial distance 176 from the centerline axis 102 ( 102 ( a )), while the fourth row of oxidant outlet ports 172 can be seen arranged at a radial distance 174 that is different from the radial distance 176 .

[0039] It can be seen that the oxidant outlet port 164 is aligned at an angle 168 relative to the second tapered surface 152 in the longitudinal direction (L). It can be seen that the oxidant outlet port 172 is aligned at an angle 186 relative to the second tapered surface 152 in the longitudinal direction (L). Angles 168 and 186 can be the same, or they can be different from each other. In some aspects of the present disclosure, angles 168 and 186 can have a range from twelve degrees to thirty degrees. Of course, the present disclosure is not limited to the above ranges, and other angles can also be implemented alternatively.

[0040] Although the foregoing description is made with reference to two rows of oxidant outlet ports 162, 182 around the circumference of the first tapered surface 150 of the annular wall, and two rows of oxidant outlet ports 164, 172 around the circumference of the second tapered surface 152 of the annular wall, for a total of four rows, the present disclosure is not limited to four rows of oxidant outlet ports. More specifically, the number of rows of oxidant outlet ports may range from three rows to eight rows of oxidant outlet ports. Figure 6 , the cross-sectional view depicted therein includes a total of seven rows of oxidant outlet ports on the first tapered surface 150 and the second tapered surface 152. However, the number of rows is not limited to the foregoing, and the number of rows may be selected based on the desired cooling effect to be achieved.

[0041] exist Figure 6, it can be seen that the rounded outlet end portion 134 includes a terminal oxidant outlet port 160. The terminal oxidant outlet port 160 extends from the oxidant flow channel 130 through the rounded outlet end portion 134. It can be seen that the terminal oxidant outlet port 160 is aligned at an angle 190 relative to the centerline axis 102 (102(a)), wherein the angle 190 extends radially outward and rearward. Similar to the oxidant outlet ports 164, 172, the angle 190 of the terminal oxidant outlet port can be in the range of twelve to thirty degrees. Of course, the present disclosure is not limited to a single terminal oxidant outlet port 160 at the rounded outlet end portion 134, and as Figure 6 As shown, a second terminal oxidant outlet port 170 may be included. Depending on the cooling effect to be achieved, additional terminal oxidant outlet ports may also be included. Of course, the present disclosure is not limited to the above range, and the angle 190 may also be arranged at other angles instead.

[0042] refer to Figure 7 , the end oxidant outlet ports 160 are circumferentially spaced around the circumference of the rounded outlet end portion 134. The circumferential spacing 188 of the end oxidant outlet ports 160 can be based on the size of the end oxidant outlet ports 160. For example, the circumferential spacing 188 can be from two times the diameter of the end oxidant outlet ports 160 to six times the diameter of the end oxidant outlet ports 160. Here, the diameter of the end oxidant outlet ports 160 can be from 0.02 inches to 0.038 inches (or approximately 0.50 mm to 0.965 mm). The aforementioned spacing and outlet port diameter sizes can also apply to the oxidant outlet ports 162, 164, 172, 182 that pass through the first tapered surface 150 and the second tapered surface 152. For example, as Figure 7 As shown, the second row 196 of outlet ports may have a spacing 198 ranging from two times the diameter of the outlet port to six times the diameter of the outlet port. Of course, the spacing and size of the outlet ports are not limited to the above, and other spacing or port sizes may be implemented alternatively depending on the cooling effect to be achieved.

[0043] The leading oxidant outlet ports (e.g., oxidant outlet ports 162, 164, 172, 182, etc.) may also be arranged at an angle relative to the circumferential direction (C) to provide a swirl of the air within the venturi. For example, the leading oxidant outlet ports may be arranged at a co-swirl circumferential angle 192 to provide an air flow in a co-swirl direction relative to the leading swirl direction. In one aspect, the co-swirl circumferential angle 192 may be in a range from zero to sixty degrees. Of course, the co-swirl circumferential angle 192 is not limited to the above range, but other angles may be implemented alternatively based on the desired swirl effect. In addition, although Figure 7A single co-swirl circumferential angle 92 is depicted for the row of oxidant outlet ports closest to the centerline axis 102, but rows of oxidant outlet ports arranged outboard of the innermost row may also be tilted in the co-swirl direction.

[0044] The vented venturi described above provides additional cooling of the outlet end of the venturi as well as further mixing of the oxidant gas with the fuel / air mixture within the venturi.

[0045] Although the foregoing description generally relates to gas turbine engines, it can be readily appreciated that gas turbine engines can be implemented in a variety of environments. For example, the engine can be implemented in an aircraft, but can also be implemented in non-aircraft applications, such as power plants, marine applications, or oil and gas production applications. Therefore, the present disclosure is not limited to use in aircraft.

[0046] Other aspects of the disclosure are provided by the subject matter of the following clauses.

[0047] A pilot fuel nozzle assembly for a combustor of a gas turbine engine, the pilot fuel nozzle assembly comprising: a pilot fuel nozzle; a pilot oxidant inlet, the pilot oxidant inlet being arranged around the pilot fuel nozzle; a pilot oxidant swirler, the pilot oxidant swirler being arranged downstream of the pilot oxidant inlet, the pilot oxidant swirler providing a swirling flow of oxidant in a pilot swirl direction around a centerline axis of the fuel nozzle; and a ventilation pilot venturi tube, the ventilation pilot venturi tube being arranged radially outside the pilot oxidant swirler and being fluidly connected to the pilot oxidant inlet, wherein the ventilation pilot venturi tube comprises an annular wall, the annular wall extending circumferentially around the centerline axis of the fuel nozzle and extending in a longitudinal direction along the centerline axis of the fuel nozzle from an inlet end of the ventilation pilot venturi tube to an outlet of the ventilation pilot venturi tube, wherein the annular wall comprises an oxidant flow channel within the annular wall, the oxidant flow channel extending from the inlet end of the ventilation pilot venturi tube to an outlet of the ventilation pilot venturi tube adjacent to the outlet end, and the oxidant flow passage is connected to the pilot oxidant inlet fluid, wherein the annular wall defines an inner venturi surface, the inner venturi surface defines an open cavity through the ventilation pilot venturi, the inner venturi surface includes: (a) a throat region, the throat region is arranged between the inlet end of the ventilation pilot venturi and the outlet of the ventilation pilot venturi, the throat region has a smaller diameter than the remaining portion of the inner venturi surface downstream of the throat region; and (b) a diverging flow surface portion, the diverging flow surface portion is arranged in a longitudinal direction from the throat region to the outlet of the ventilation pilot venturi, the diverging flow surface portion has a first diameter at the throat region and a second diameter at the outlet, the second diameter being larger than the first diameter, wherein the annular wall further defines a plurality of venturi oxidant outlet ports, the plurality of venturi oxidant outlet ports extend from the oxidant flow passage through the diverging flow surface portion, the plurality of venturi oxidant outlet ports are circumferentially spaced around the centerline axis of the fuel nozzle.

[0048] A pilot fuel nozzle assembly as claimed in any preceding clause, wherein the diverging flow surface portion comprises a curved surface extending circumferentially about the fuel nozzle centreline axis.

[0049] A pilot fuel nozzle assembly as claimed in any preceding clause, wherein the diverging flow surface portion comprises a tapered surface extending circumferentially about the fuel nozzle centreline axis.

[0050] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the diverging flow surface portion comprises a first tapered portion extending in a longitudinal direction from a throat region to a breakpoint between the throat region and the outlet, and a second tapered portion extending from the breakpoint to the outlet.

[0051] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the first conical portion has a first conical half-angle relative to the fuel nozzle centerline axis, the first conical half-angle being in the range of from fifteen to thirty degrees, and the second conical portion has a second conical half-angle relative to the fuel nozzle centerline axis, the second conical half-angle being in the range of from thirty to forty degrees.

[0052] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the first conical portion has a first conical half-angle relative to the fuel nozzle centerline axis, the first conical half-angle being in the range of thirty to forty degrees, and the second conical portion has a second conical half-angle relative to the fuel nozzle centerline axis, the second conical half-angle being in the range of fifteen to thirty degrees.

[0053] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the outlet includes a rounded outlet end portion, and wherein the ventilation pilot venturi defines a plurality of end oxidant outlet ports around a circumference of the rounded outlet end portion, and wherein the plurality of end oxidant outlet ports extend from an outlet end of the oxidant flow passage through the rounded outlet end portion.

[0054] A pilot fuel nozzle assembly as in any preceding clause, wherein each of the plurality of terminal oxidant outlet ports is arranged at an angle extending radially outwardly relative to a centerline axis of the fuel nozzle.

[0055] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the plurality of venturi oxidant outlet ports are arranged in a plurality of rows around the circumference of the diverging flow surface portion, each of the plurality of rows being disposed at a different radial distance from the fuel nozzle centreline axis.

[0056] A pilot fuel nozzle assembly according to any preceding clause, wherein the number of rows comprising a plurality of rows ranges from three rows to eight rows.

[0057] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein the plurality of venturi oxidant outlet ports comprises a first set of venturi oxidant outlet ports disposed through the first tapered portion and a second set of venturi oxidant outlet ports disposed through the second tapered portion.

[0058] A pilot fuel nozzle assembly according to any of the preceding items, wherein a first group of venturi tube oxidizer outlet ports are arranged in a plurality of rows around the circumference of a first conical portion, each of the plurality of rows of the first group of venturi tube oxidizer outlet ports being disposed at a different radial distance from a centerline axis of the fuel nozzle, and wherein a second group of venturi tube oxidizer outlet ports are arranged in a plurality of rows around the circumference of a second conical portion, each of the plurality of rows of the second group of venturi tube oxidizer outlet ports being disposed at a different radial distance from a centerline axis of the fuel nozzle.

[0059] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein each venturi oxidant outlet port in a first group of venturi oxidant outlet ports is arranged at a first angle relative to a first tapered portion in a longitudinal direction, and wherein each venturi oxidant outlet port in a second group of venturi oxidant outlet ports is arranged at a second angle relative to a second tapered portion in a longitudinal direction.

[0060] A pilot fuel nozzle assembly as in any preceding clause, wherein the first angle has a range from twelve to thirty degrees and the second angle has a range from twelve to thirty degrees.

[0061] A pilot fuel nozzle assembly according to any of the preceding clauses, wherein a plurality of venturi oxidant outlet ports are arranged in a row circumferentially around a diverging flow surface portion, and wherein the circumferential spacing between each venturi oxidant outlet port in the row ranges from twice the diameter of the venturi oxidant outlet port to six times the diameter of the venturi oxidant outlet port.

[0062] A pilot fuel nozzle assembly according to any of the preceding items, wherein a plurality of venturi oxidant outlet ports are arranged at a co-directional vortex circumferential angle relative to a circumferential direction around a centerline axis of the fuel nozzle, the co-directional vortex circumferential angle being in a range from zero to sixty degrees, and the co-directional vortex circumferential angle being in the same direction as a pilot vortex direction of the pilot oxidant swirler.

[0063] Further aspects of the disclosure are provided by the subject matter of the following further clauses.

[0064] A ventilation pilot venturi tube for a pilot fuel nozzle assembly of a gas turbine engine, the ventilation pilot venturi tube comprising: an annular wall extending circumferentially around a venturi tube centerline axis and extending in a longitudinal direction along the venturi tube centerline axis from an inlet end of the ventilation pilot venturi tube to an outlet of the ventilation pilot venturi tube; an oxidant flow channel within the annular wall, the oxidant flow channel extending from the inlet end of the ventilation pilot venturi tube to an outlet end of the ventilation pilot venturi tube adjacent to the outlet, the oxidant flow channel having a flow channel inlet at the inlet end of the ventilation pilot venturi tube; an inner venturi tube surface defining an open cavity through the ventilation pilot venturi tube, the inner venturi tube surface comprising: (a) a throat region disposed between an inlet end of the venturi pilot tube and an outlet of the venturi pilot tube, the throat region having a smaller diameter than a remaining portion of the inner venturi tube surface downstream of the throat region; and (b) a diverging flow surface portion disposed in a longitudinal direction from the throat region to the outlet of the venturi pilot tube, the diverging flow surface portion having a first diameter at the throat region and a second diameter at the outlet, the second diameter being greater than the first diameter; and a plurality of venturi oxidant outlet ports extending from the oxidant flow channel through the diverging flow surface portion, the plurality of venturi oxidant outlet ports being circumferentially spaced about a centerline axis of the venturi tube.

[0065] A ventilating pilot venturi as claimed in any preceding clause wherein the diverging flow surface portion comprises a curved surface extending circumferentially about the venturi centreline axis.

[0066] A ventilating pilot venturi as claimed in any preceding clause wherein the diverging flow surface portion comprises a tapered surface extending circumferentially about the venturi centreline axis.

[0067] A ventilation pilot venturi according to any of the preceding clauses, wherein the diverging flow surface portion comprises a first tapered portion extending in a longitudinal direction from a throat region to a breakpoint between the throat region and the outlet, and a second tapered portion extending from the breakpoint to the outlet.

[0068] A ventilation pilot venturi tube according to any of the preceding clauses, wherein the first tapered portion has a first tapered half angle relative to the centerline axis of the venturi tube, the first tapered half angle being in the range of from fifteen to thirty degrees, and the second tapered portion has a second tapered half angle relative to the centerline axis of the venturi tube, the second tapered half angle being in the range of from thirty to forty degrees.

[0069] A ventilation pilot venturi according to any of the preceding clauses, wherein the first tapered portion has a first tapered half angle relative to the venturi centerline axis, the first tapered half angle being in the range of thirty to forty degrees, and the second tapered portion has a second tapered half angle relative to the venturi centerline axis, the second tapered half angle being in the range of fifteen to thirty degrees.

[0070] A ventilated pilot venturi according to any of the preceding clauses, wherein the outlet comprises a rounded outlet end portion, and wherein the ventilated pilot venturi defines a plurality of end oxidant outlet ports around a circumference of the rounded outlet end portion, and wherein the plurality of end oxidant outlet ports extend from an outlet end of the oxidant flow channel through the rounded outlet end portion.

[0071] A ventilated pilot venturi as in any preceding clause, wherein each of the plurality of terminal oxidant outlet ports is arranged at an angle extending radially outwardly relative to a fuel nozzle centreline axis.

[0072] A ventilated pilot venturi according to any of the preceding clauses, wherein a plurality of venturi oxidant outlet ports are arranged in a plurality of rows around the circumference of the diverging flow surface portion, each of the plurality of rows being disposed at a different radial distance from the venturi centreline axis.

[0073] A ventilation pilot venturi according to any preceding clause, wherein the number of rows comprising a plurality of rows ranges from three rows to eight rows.

[0074] A ventilated pilot venturi according to any of the preceding clauses, wherein the plurality of venturi oxidant outlet ports comprises a first set of venturi oxidant outlet ports disposed through the first tapered portion and a second set of venturi oxidant outlet ports disposed through the second tapered portion.

[0075] A ventilated pilot venturi tube according to any of the preceding items, wherein a first group of venturi tube oxidant outlet ports are arranged in a plurality of rows around the circumference of a first conical portion, each of the plurality of rows of the first group of venturi tube oxidant outlet ports being disposed at a different radial distance from a centerline axis of the venturi tube, and wherein a second group of venturi tube oxidant outlet ports are arranged in a plurality of rows around the circumference of a second conical portion, each of the plurality of rows of the second group of venturi tube oxidant outlet ports being disposed at a different radial distance from a centerline axis of the venturi tube.

[0076] A ventilated pilot venturi according to any of the preceding clauses, wherein each venturi oxidant outlet port in a first group of venturi oxidant outlet ports is arranged at a first angle relative to a first tapered portion in a longitudinal direction, and wherein each venturi oxidant outlet port in a second group of venturi oxidant outlet ports is arranged at a second angle relative to a second tapered portion in a longitudinal direction.

[0077] A ventilation pilot venturi as claimed in any preceding clause, wherein the first angle has a range from twelve to thirty degrees and the second angle has a range from twelve to thirty degrees.

[0078] A ventilated pilot venturi according to any of the preceding clauses, wherein a plurality of venturi oxidant outlet ports are arranged in a row circumferentially around a diverging flow surface portion, and wherein the circumferential spacing between each venturi oxidant outlet port in the row ranges from twice the diameter of the venturi oxidant outlet port to six times the diameter of the venturi oxidant outlet port.

[0079] A ventilated pilot venturi according to any of the preceding clauses, wherein a plurality of venturi oxidant outlet ports are arranged at a co-directional swirl circumferential angle relative to a circumferential direction about a centerline axis of the venturi, the co-directional swirl circumferential angle being in a range from zero to sixty degrees.

[0080] Although the foregoing description is directed to some exemplary embodiments of the present disclosure, it should be noted that other changes and modifications will be apparent to those skilled in the art and may be made without departing from the spirit or scope of the present disclosure. In addition, features described in conjunction with one embodiment of the present disclosure may be used in conjunction with other embodiments, even if not explicitly stated above.

Claims

1. A pilot fuel nozzle assembly for a combustor of a gas turbine engine, characterized in that: The pilot fuel nozzle assembly comprises: a pilot fuel nozzle defined about a fuel nozzle centerline axis; a pilot oxidant inlet disposed around the pilot fuel nozzle; a pilot separator disposed radially outwardly of the pilot fuel nozzle, a pilot inner air passage defined between the pilot fuel nozzle and the pilot separator and in fluid communication with the pilot oxidant inlet; and A ventilation pilot venturi tube, the ventilation pilot venturi tube is arranged radially outside the pilot separator and is in fluid communication with the pilot oxidant inlet, a pilot outer air passage is defined between the pilot separator and the ventilation pilot venturi tube, wherein the ventilation pilot venturi tube includes an annular wall, the annular wall extends circumferentially around the fuel nozzle centerline axis and extends in a longitudinal direction along the fuel nozzle centerline axis from the inlet end of the ventilation pilot venturi tube to the outlet of the ventilation pilot venturi tube, wherein the annular wall includes an oxidant flow channel within the annular wall, the oxidant flow channel extends from the inlet end of the ventilation pilot venturi tube to the outlet end of the ventilation pilot venturi tube adjacent to the outlet, and the oxidant flow channel is in fluid communication with the pilot oxidant inlet, wherein the annular wall defines an inner venturi tube surface, the inner venturi tube surface defines an open cavity through the ventilation pilot venturi tube, the inner venturi tube surface includes: (a) a throat region disposed between the inlet end of the ventilation pilot venturi and the outlet of the ventilation pilot venturi, the throat region having a smaller diameter than the remainder of the inner venturi surface downstream of the throat region; and (b) a diverging flow surface portion disposed in the longitudinal direction from the throat region to the outlet of the ventilation pilot venturi, the diverging flow surface portion having a first diameter at the throat region and a second diameter at the outlet, the second diameter being greater than the first diameter, wherein the annular wall further defines a plurality of venturi oxidant outlet ports extending from the oxidant flow passage through the diverging flow surface portion, the plurality of venturi oxidant outlet ports being circumferentially spaced about the fuel nozzle centerline axis, and wherein the diverging flow surface portion includes a first tapered portion and a second tapered portion, the first tapered portion extending in the longitudinal direction from the throat region to a breakpoint arranged between the throat region and the outlet, the second tapered portion extending from the breakpoint to the outlet, the first tapered portion being arranged at a first tapered half-angle relative to the fuel nozzle centerline axis, and the second tapered portion being arranged at a second tapered half-angle relative to the fuel nozzle centerline axis, the second tapered half-angle being greater than the first tapered half-angle, and wherein the outlet includes a rounded outlet end portion extending from a downstream end of the second conical portion and in fluid communication with the downstream end of the second conical portion, wherein the ventilating pilot venturi defines a plurality of terminal oxidant outlet ports around a circumference of the rounded outlet end portion, and wherein the plurality of terminal oxidant outlet ports extend from the outlet end of the oxidant flow channel through the rounded outlet end portion.

2. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, Each of the plurality of terminal oxidant outlet ports is arranged at an angle extending radially outwardly relative to the fuel nozzle centerline axis.

3. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, The plurality of venturi oxidant outlet ports are arranged in a row circumferentially around the diverging flow surface portion, and Wherein, the circumferential spacing between each of the venturi oxidant outlet ports in the row ranges from twice the diameter of the venturi oxidant outlet port to six times the diameter of the venturi oxidant outlet port.

4. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, The plurality of venturi oxidant outlet ports are arranged at a co-swirl circumferential angle relative to a circumferential direction about a centerline axis of the fuel nozzle, the co-swirl circumferential angle being within a range from zero to sixty degrees.

5. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, The plurality of venturi oxidant outlet ports are arranged in a plurality of rows about a circumference of the diverging flow surface portion, with each of the plurality of rows being disposed at a different radial distance from a centerline axis of the fuel nozzle.

6. The pilot fuel nozzle assembly according to claim 5, characterized in that: in, The number of rows comprising the plurality of rows ranges from three rows to eight rows.

7. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, The first tapered portion has the first tapered half angle in a range from fifteen to thirty degrees, and the second tapered portion has the second tapered half angle in a range from thirty to forty degrees.

8. The pilot fuel nozzle assembly according to claim 1, characterized in that: in, The plurality of venturi oxidant outlet ports include a first set of venturi oxidant outlet ports disposed through the first tapered portion and a second set of venturi oxidant outlet ports disposed through the second tapered portion.

9. The pilot fuel nozzle assembly according to claim 8, characterized in that: in, the first set of venturi oxidant outlet ports being arranged in a plurality of rows around a circumference of the first conical portion, each of the plurality of rows of the first set of venturi oxidant outlet ports being disposed at a different radial distance from a centerline axis of the fuel nozzle, Wherein, the second group of venturi tube oxidant outlet ports are arranged in multiple rows around the circumference of the second conical portion, and each of the multiple rows of the second group of venturi tube oxidant outlet ports is set at a different radial distance from the centerline axis of the fuel nozzle.

10. The pilot fuel nozzle assembly according to claim 8, characterized in that in, Each venturi oxidant outlet port in the first group of venturi oxidant outlet ports is arranged at a first angle relative to the first tapered portion in the longitudinal direction, and wherein each venturi oxidant outlet port in the second group of venturi oxidant outlet ports is arranged at a second angle relative to the second tapered portion in the longitudinal direction.

11. The pilot fuel nozzle assembly according to claim 10, characterized in that: in, The first angle has a range from twelve to thirty degrees, and the second angle has a range from twelve to thirty degrees.

12. A ventilation pilot venturi tube for a pilot fuel nozzle assembly of a gas turbine engine, characterized in that: The ventilation pilot venturi tube comprises: an annular wall extending circumferentially about the venturi centerline axis and extending in a longitudinal direction along the venturi centerline axis from an inlet end of the ventilation pilot venturi to an outlet of the ventilation pilot venturi; an oxidant flow passage within the annular wall, the oxidant flow passage extending from the inlet end of the venting pilot venturi to an outlet end of the venting pilot venturi adjacent the outlet, the oxidant flow passage having a flow passage inlet at the inlet end of the venting pilot venturi; an inner venturi surface defining an open cavity through the venting pilot venturi, the inner venturi surface comprising: (a) a throat region disposed between the inlet end of the ventilation pilot venturi and the outlet of the ventilation pilot venturi, the throat region having a smaller diameter than the remainder of the inner venturi surface downstream of the throat region; and (b) a diverging flow surface portion disposed in the longitudinal direction from the throat region to the outlet of the ventilation pilot venturi, the diverging flow surface portion having a first diameter at the throat region and a second diameter at the outlet, the second diameter being larger than the first diameter; and a plurality of venturi oxidant outlet ports extending from the oxidant flow passage through the diverging flow surface portion, the plurality of venturi oxidant outlet ports being circumferentially spaced about the venturi centerline axis, wherein the divergent flow surface portion comprises a first conical portion and a second conical portion, the first conical portion extending in the longitudinal direction from the throat region to a breakpoint arranged between the throat region and the outlet, the second conical portion extending from the breakpoint to the outlet, the first conical portion being arranged at a first conical half-angle relative to the venturi centerline axis, and the second conical portion being arranged at a second conical half-angle relative to the venturi centerline axis, the second conical half-angle being greater than the first conical half-angle, and wherein the outlet includes a rounded outlet end portion extending from a downstream end of the second conical portion and in fluid communication with the downstream end of the second conical portion, wherein the ventilating pilot venturi defines a plurality of terminal oxidant outlet ports around a circumference of the rounded outlet end portion, and wherein the plurality of terminal oxidant outlet ports extend from the outlet end of the oxidant flow channel through the rounded outlet end portion.

13. The ventilation pilot venturi tube according to claim 12, characterized in that: in, The plurality of venturi oxidant outlet ports are arranged in a plurality of rows around a circumference of the diverging flow surface portion, with each of the plurality of rows being disposed at a different radial distance from a centerline axis of the venturi.

14. The ventilation pilot venturi tube according to claim 12, characterized in that: in, The first tapered portion has the first tapered half angle in a range from fifteen to forty degrees, and the second tapered portion has the second tapered half angle in a range from fifteen to thirty to forty degrees.

15. The ventilation pilot venturi tube according to claim 12, characterized in that: in, The plurality of venturi oxidant outlet ports include a first set of venturi oxidant outlet ports disposed through the first tapered portion and a second set of venturi oxidant outlet ports disposed through the second tapered portion.

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