Partially premixed combustion chamber system stabilised by a swirler and a bluff body

Abstract

The invention relates to the combustion chamber system of gas turbine engines used in aerospace propulsion systems. The partially premixed combustion chamber system according to the invention comprises a main jet (1) in the form of a circular cross-sectional tube through which fuel is conveyed, and a secondary jet (2) in the form of a circular cross-sectional tube surrounding the main jet (1), a cylindrical axial swirler (3) placed between the main jet (1) and the secondary jet (2) and containing swirler blades (4) which provide tangential velocity gain by directing the flow, a bluff body (8) in the form of a truncated cone, the upper surface of which is connected to the main jet (1), the lateral surface of which is inside the secondary jet (2), and 16 elliptical, radial injection holes (7) located on the lateral surface of the bluff body (8), placed in the centre of the cone at 22.5° intervals, located alternately one close to the upper surface and one close to the lower surface.

Description

[0001] PARTIALLY PREMIXED COMBUSTION CHAMBER SYSTEM STABILISED BY A SWIRLER AND A BLUFF BODY

[0002] Technical Field

[0003] The invention relates to the combustion chamber system of gas turbine engines used in aerospace propulsion systems.

[0004] Prior Art

[0005] In the combustion chamber design of gas turbine engines, three different systems are generally used as flame types. Non-premixed flame, partially premixed flame and premixed flame. In aerospace propulsion systems, combustion chambers with non-premixed flames are generally used due to their safety advantages. In addition to its safety advantages, this flame type also has a number of disadvantages. The need to mix fuel and oxidizer (usually air) in the combustion chamber causes a reduction in the combustion performance of these systems. In addition, flame instability, formation of unburned products and high harmful emissions have necessitated the development of alternatives to these systems in recent years. In addition, increasing environmental pollution, climate change and global warming disasters in recent years have led to stricter regulations (FAA, EASA) in the aviation industry and have been a driving force in the search for alternative designs and fuels.

[0006] For the reasons mentioned above, partially premixed combustion chamber systems have come to the fore as an important alternative design in recent years. In partially premixed combustion chambers, fuel and combustor are mixed just before the combustion chamber inlet depending on the design features to achieve a more efficient combustion. Partially premixed flames can be as safe and efficient as premixed flames. In addition, thanks to the wide range of application it offers, it provides a new option for the safe use of alternative fuel sources such as hydrogen in aerospace propulsion systems.

[0007] The main parameter in the partially premixed combustion chamber systems is the design features of the partial mixture combustion chambers. The design for the mixing of fuel and oxidizer is vital for the safety and efficiency of these systems. Inadequate fuel mixing creates fuel-rich and fuel-poor regions in the combustion chamber and this heterogeneous mixture causes more harm than benefit for engine efficiency. High efficiency combustion cannot be achieved in fuel rich regions and unburned fuel is discharged from the engine. This increases fuel consumption and environmental pollution. The lack of oxidizer (oxygen) caused by the poor mixture releases gases such as CO (carbon monoxide), which are highly harmful to the environment. In addition, insufficient mixing also affects combustion stability, negatively impacting engine performance and reducing its lifespan.

[0008] In the document numbered JP2008122067 A, which is in the state of the art, mention a premixing device having a surface treatment to facilitate mixing of fuel and oxidizer in a low emission combustion process in a combustion chamber.

[0009] In the document numbered W02002004035187A2, which is in the state of the art, methods of controlling the mixing of a fluid medium, created and formed by mixing two or more fluids are mentioned.

[0010] In the document numbered US2009180939A1, which is in the state of the art, it is mentioned that a thermally diluted exothermic reactor system, a triple fluidised reactor comprising a plurality of holes distributed in a combustor by distributed perforated contactor tubes or channels.

[0011] In the document numbered CN103822231A, which is in the state of the art, the perforations of a combustion chamber of a combustion gas turbine with a low swirl flow are described. In other partially premixed combustion chamber systems found in the literature, the biggest problem is usually the insufficient mixing. Improperly designed fuel injection ports do not allow adequate mixing of the fuel with the combustor. Inadequate mixing can lead to problems such as high emission rates, flame instability and equipment damage.

[0012] Rich and poor mixing zones caused by the insufficient mixing lead to high soot formation and increase engine life and maintenance costs. Furthermore, unburned gases in these fuel-rich regions are expelled from the exhaust and reduce engine efficiency.

[0013] Flame stability is another design parameter in partially-premixed combustion chambers found in the literature. Low flame stability can cause flame rupture, extinction, chaotic flame lengthening and shortening. In addition, low flame stability also reduces the safety coefficient of the product.

[0014] There has arisen a need to develop a better partially premixed combustion chamber system that eliminates all these disadvantages and offers an alternative design for today's partially premixed combustor systems.

[0015] Objects of the Invention

[0016] The object of this invention is to implement a partially premixed combustion chamber system that ensures sufficient mixing.

[0017] Another object of this invention is to implement a partially premixed combustion chamber system where lean mixture regions do not form, thereby reducing soot formation and extending engine lifespan.

[0018] Another object of the present invention is to implement a partially premixed combustion chamber system that ensures high flame stability, thereby increasing the safety margin. Detailed Description of the Invention

[0019] The partially premixed combustion chamber system realised to achieve the object of the present invention is shown in the accompanying figures.

[0020] These figures are;

[0021] Figure 1: Side cross section view of the inventive partially premixed combustion chamber system.

[0022] Figure 2: Perspective view of the inventive partially premixed combustion chamber system.

[0023] Figure 3: Rear view of the inventive partially premixed combustion chamber system.

[0024] Figure 4: Detail view of the injection holes in the inventive partially premixed combustion chamber system.

[0025] Figure 5: Detail view of the bluff body and injection holes in the inventive partially premixed combustion chamber system.

[0026] The parts in the figure are individually numbered and the corresponding numbers are given below.

[0027] 1. Main jet

[0028] 2. Secondary jet

[0029] 3. Swirler

[0030] 4. Swirler blades

[0031] 5. Secondary jet wall

[0032] 6. Main jet wall

[0033] 7. Injection holes

[0034] 8. Bluff body The partially premixed combustion chamber system according to the invention comprises a tubular main jet (1) of circular cross-section through which fuel is transported, a tubular secondary jet (2) of circular cross-section surrounding the main jet (1), axial swirler (3) in the form of a cylinder placed between the main jet (1) and the secondary jet (2) and containing swirler blades (4) which direct the flow and provide tangential velocity gain, a bluff body (8) of truncated conical shape, the upper surface of which is connected to the main jet (1), the lateral surface of which is inside the secondary jet (2)

[0035] 16 elliptical radial injection holes (7) located on the lateral surface of the bluff body (8), placed in the centre of the cone at 22.5° intervals, located alternately one close to the upper surface and one close to the lower surface.

[0036] In other partially premixed combustion chamber designs found in the literature, the fuel injection holes are generally circular or rectangular in cross-section. The fuel injection holes (7) designed with our invention have an elliptical shape. The injection holes (7) are located longitudinally in the flow direction above the main jet (1) and it is aimed to provide injection in the radial direction. Here, the aspect that distinguishes our invention from other similar ones is that it has elliptical injection holes (7) and thanks to this design, the surface area where the fuel flow is exposed to the incoming oxidizer flow is increased. This increased surface area allows better mixing of the fuel with the oxidizer. In addition, 16 injection ports are arranged circularly at 22.5° intervals. Injection ports are also positioned with a zig-zag distribution in the axial direction. Thanks to this positioning, fuel-air mixing efficiency is increased.

[0037] In combustion chambers found in the literature, secondary instruments such as swirler (3) and bluff body (8) are also used. The main objective of these instruments is to improve flame stability and mixture efficiency.

[0038] In our design, one axial swirler (3) is used in the secondary jet (2) of the combustor and swirler blades (4) are used in the swirler (3). In this way, it is ensured that the fluid transported through the secondary jet (2) gains momentum in the tangential direction. The axial swirler (3) is positioned in contact with the secondary jet wall (5) and the main jet wall (6). Our design can also fulfil all its functions by using radial swirler. The resulting swirled air is better mixed with the fuel, resulting in improved mixing efficiency.

[0039] A bluff body (8) is also used in our design. The bluff body (8) is located at the position where the secondary jet (2) opens into the combustion chamber. It has a conical shape. Fuel injection holes (7) are also located on the bluff body (8). Thanks to the bluff body (8), a recirculation zone is created in the combustion chamber. The recirculation zone helps the additional mixing of the fuel and has a positive effect on the flame stability. In addition, since the fuel injection holes (7) are positioned on the bluff body (8), the fuel is injected from a higher position and thus better mixing with the combustor from the secondary jet (2) is ensured.

[0040] In the literature, there is no partially premixed combustor design with radial injectors and stabilised with a bluff body (8) and a swirler (3). This fact distinguishes our design from its peers. All the design features mentioned in the previous sections interact harmoniously with each other, mainly aiming to provide mixture efficiency and high flame stability. The technical parts in our design can be listed under 3 main headings as follows:

[0041] 1- Axial swirler (3)

[0042] 2- Canonical bluff body (8)

[0043] 3- Radial injection holes (7) with elliptical shape

[0044] The axial swirler (3) is located in the secondary jet (2) opening into the combustion chamber. In this way, the incoming fluid (oxidizer), which has only axial velocity, also gains a tangential velocity. The gained tangential velocity creates a centrifugal effect on the flow. This causes the fluid to move close to the pipe wall. In other words, there is a fluid with higher momentum at the pipe wall, while the momentum of the fluid towards the centre of the pipe is lower. In order to inject the fuel into the region with higher momentum, the second product of our design, the conical bluff body (8), was used. The swirler (3) used in our invention is not of our own design, but an axial swirler frequently used in the literature is incorporated. At the same time, our invention can also fulfil its ultimate purpose by using a radial swirler. The bluff body (8) is positioned at the exit point of the secondary jet (2). It is one of the most important elements of our design. The bluff body (8) acts as a ramp due to its structure. The cone angle is determined as 80° in the preliminary design, but it is envisaged that this angle can be designed as 60°- 100° considering different flow rates and the use of different swirlers. Injection holes (7) are placed on this bluff body (8) and the fuel is injected from there. In this way, the fuel is injected directly into the flow region with higher momentum. In addition, the bluff body (8) forms a recirculation zone in its downstream by means of its structure. Since the downstream of the bluff body (8) is the inlet of the combustion chamber, the lowest mixture is observed in this region in other combustion chamber designs in the literature. In the present invention, thanks to the bluff body (8), the mixing efficiency can be increased in this region.

[0045] The fuel injection holes (7) are also designed to be in harmony with the other parts of this system. It is critical for the design. In order for the fuel to better penetrate into the swirling flow, the injection holes (7) are elliptically designed and positioned with the long side in the direction of the flow. The 16 holes are also positioned axially in a zig-zag pattern. In this context, the fluid with tangential velocity generated by the swirler (3) penetrates the fuel flow better due to the shape and position of the injection system. Placing the injection holes (7) on the bluff body (8) helps to distribute the fuel more homogeneously. At the same time, the shape and positioning of the injection holes (7) increase the surface area penetrated by air with incoming tangential velocity. In this way, the mixing time of fuel and air is reduced.

Claims

CLAIMS1. A partially premixed combustion chamber system comprising a tubular main jet (1) of circular cross-section through which fuel is transported, a tubular secondary jet (2) of circular cross-section surrounding the main jet (1), axial swirler (3) in the form of a cylinder placed between the main jet (1) and the secondary jet (2) and containing swirler blades (4) which direct the flow and provide tangential velocity gain, characterised by further comprising a bluff body (8) of truncated conical shape, the upper surface of which is connected to the main jet (1), the lateral surface of which is inside the secondary jet (2) and radial injection holes (7) located on the lateral surface of the bluff body (8), located alternately one close to the upper surface and one close to the lower surface.

2. A partially premixed combustion chamber system according to claim 1 characterised by comprising 16 injection holes (7) placed at 22.5° intervals in the centre of the cone.

3. A partially premixed combustion chamber system according to claim 1 or 2 characterised by comprising a bluff body (8) with a cone angle between 60°-100°.

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