A smooth invasive fuel injector and its design method

Abstract

This invention discloses a smooth-intrusion fuel injector and its design method, relating to the field of scramjet engine combustion chamber technology. A fuel injector intruding towards the center of the combustion chamber is disposed on the side wall of the combustion chamber. The fuel injector includes: an arc segment I centered outside the combustion chamber; and arc segments II and III centered inside the combustion chamber and located on either side of arc segment I. Each arc segment is tangent to a straight segment of the combustion chamber at its intersection point, and the injection orifice of the fuel injector is located at the top of arc segment I. There is a smooth transition between the corresponding arc segments and the straight segments of the combustion chamber. Compared to existing wall-mounted injection systems, this invention can increase the fuel momentum to air momentum ratio by more than double, contributing to efficient fuel mixing under high-speed flow conditions.

Description

Technical Field

[0001] This invention relates to the field of scramjet engine combustion chamber technology. More specifically, this invention relates to a smooth-intrusion fuel injector and its design method. Background Technology

[0002] A scramjet engine is a high-speed flight propulsion device. A typical scramjet engine's main components include: an air intake, an isolator, a combustion chamber, and a tailpipe. The function of the combustion chamber is to achieve fuel injection and mixing, reliable ignition, and stable combustion. High-efficiency fuel injection and mixing are necessary conditions for reliable ignition and stable combustion. The pressure, temperature, and velocity of the fuel-air mixture within the combustion chamber must meet certain conditions to achieve efficient mixing. The time required for the fuel to complete physicochemical processes such as atomization, fragmentation, evaporation, and chemical reactions under these conditions is called the ignition time. Under typical operating conditions, the fuel ignition time is approximately 5–10 milliseconds. To achieve reliable ignition, the fuel residence time within the combustion chamber must be greater than the ignition time. Typically, the combustion chamber length is on the order of 1 meter. Under high-speed flow conditions, the airflow velocity within the combustion chamber exceeds 1000 m / s. Therefore, the airflow residence time within the combustion chamber is only about 1 millisecond, which is insufficient to meet the time requirement for sufficient mixing for ignition.

[0003] Currently, researchers both domestically and internationally have proposed various fuel injector design schemes to solve the fuel mixing problem, which can be mainly divided into two categories: (1) Wall injection: The injection holes are arranged on the wall of the combustion chamber. There are no components that penetrate into the flow field inside the combustion chamber. The fuel is injected from the small holes on the wall and relies on its own momentum to achieve shear mixing with the air. The advantage of this scheme is that the injector is not exposed to the high temperature environment generated by combustion and the structural thermal protection pressure is relatively small. The disadvantage is that the fuel penetration depth is limited and the fuel is concentrated near the wall of the combustion chamber. When the size of the combustion chamber is large, it is difficult for the fuel to enter the central area of ​​the combustion chamber. The time and distance required for the fuel to achieve full mixing with the air are long. (2) Intrusive injection: This method uses components such as support plates, support rods, and a central body to "intrude" into the central region of the combustion chamber. Fuel is injected from the intrusive components. The advantage is that the fuel can fully enter the combustion chamber and achieve rapid mixing. The disadvantage is that the inner and outer structures of the above components must withstand extreme aerodynamic and combustion heating, making it difficult to reliably serve under high temperature, high pressure, and high speed conditions for a long time. For example, the ramjet combustion chamber and method based on flow channel center injection and shock wave induced combustion in patent application number 202311208894.9. In addition, intrusive components will also cause additional aerodynamic drag, reducing engine propulsion performance.

[0004] While existing technologies also include S-shaped curved wedge structures on the lower wall of the engine combustion chamber (such as the oblique detonation shock wave aircraft with an S-shaped curved wedge structure as described in patent application number 202311382732.7), these structures are not used as injectors but are primarily used to generate oblique detonation shock waves. Therefore, based on research both domestically and internationally, there is currently a lack of injectors that can effectively enhance fuel mixing while reducing thermal load. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages of the present invention, a smooth-intrusion fuel injector is provided, characterized in that a fuel injector intruding toward the center of the combustion chamber is provided on the side wall of the combustion chamber, the fuel injector comprising: The center of the circle is located in arc segment I outside the combustion chamber; The center of the circle is located inside the combustion chamber, and is situated on either side of arc segment I, arc segment II, and arc segment III; Among them, each arc segment is tangent to the straight segment of the combustion chamber at the intersection point, and the injection hole of the fuel injector is located at the top of arc segment I; There is a smooth transition between the corresponding arc segment and the straight segment of the combustion chamber.

[0007] Preferably, the combustion chamber height is 50-80 mm, the number of injection holes is 30-100, and the diameter of each injection hole is 1 mm.

[0008] Preferably, the fuel injector is located in the inlet section of the combustion chamber.

[0009] A design method for a smooth intrusion fuel injector, which is applied to the design of a smooth intrusion fuel injector, includes: a fuel injector based on the intrusion flow field of the combustion chamber, generating a set of oblique shock waves inside the combustion chamber, and based on the front-to-back relationship of the oblique shock waves, the front is denoted as region I and region II; Under the known airflow parameters of region I, and based on the mixing requirements of the combustion chamber fuel injection, the center position and radius of each arc segment are optimized to adjust the airflow parameters after the oblique shock wave, so as to obtain a fuel injector shape that is conducive to fuel mixing conditions.

[0010] The present invention has at least the following beneficial effects: The present invention utilizes the design of a fuel injector that matches the combustion chamber profile. That is, through the segmented design of the fuel injector surface and the continuous tangent point, it enables the fuel to fully enter the combustion chamber for rapid mixing, compared with the existing technology that uses components such as support plates, support rods, and central bodies to "intrude" into the central area of ​​the combustion chamber. In addition, it can also eliminate the need to consider the feasibility of reliable operation of components under extreme aerodynamic and combustion heating conditions at high temperature, high pressure, and high speed (i.e., no need to consider thermal load). Compared with the existing wall injection, it can increase the ratio of fuel momentum to air momentum by more than 100%, which helps to achieve efficient fuel mixing under high-speed flow conditions.

[0011] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of a smooth invasive fuel injector in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the calculation of the wavefront and waveback parameters of the oblique shock wave in an embodiment of the present invention; Figure 3 In the verification example of the present invention, the hydrogen concentration distribution diagram of the smooth invasive fuel injector of the present invention was not used; Figure 4 The hydrogen concentration distribution diagram after using the smooth invasive fuel injector of the present invention is shown in the verification example of the present invention. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0014] This invention proposes a smooth-intrusion fuel injector with an undulating geometry. The top of the injector intrudes into the central region of the combustion chamber, while the bottom smoothly transitions to the combustion chamber wall. The undulating geometry generates an adjustable-intensity shock wave. Fuel injection holes are designed at the top of the structure, allowing fuel to be ejected downstream of the shock wave and injected into the combustion chamber, while avoiding the extreme thermal loads experienced by other intrusion injectors. By slowing down and heating the airflow in the combustion chamber through the shock wave, the fuel residence time and penetration depth are increased, achieving efficient fuel-air mixing. In practical applications, the fuel injector is located at the inlet section of the combustion chamber.

[0015] Example 1 A smooth-intrusion fuel injector with a rectangular combustion chamber inlet, the two-dimensional cross-section of which is shown below. Figure 1As shown, the upper wall of the combustion chamber inlet is A, and the lower wall of the inlet is B, meaning the combustion chamber inlet height is AB. The upper wall of the combustion chamber outlet is H, and the lower wall of the outlet is G, meaning the outlet height is HG. The smooth intrusion injector is CDEF, which can be divided into three segments: CD, DE, and EF. CD is an arc centered at point O1, DE is an arc centered at point O2, and EF is an arc centered at point O3. Arc CD is tangent to line BC at point C, arc DE is tangent to CD and EF at points D and E respectively, and arc EF is tangent to line FG at point F. In practical applications, the geometric dimensions of each section of the smooth intrusion fuel injector can be set as needed. A typical set of dimensions can be set as follows: AB=HG=70mm, AH=BG=500mm, radius of circle O1 20mm, radius of circle O2 15mm, radius of circle O3 20mm, and the vertical distance from the center point O2 of circle O2 to the combustion chamber inlet AB is 100mm.

[0016] Example 2 When designing the structure of a fuel injector, the flow length and vertical height of the injector can be adjusted by changing the centers and radii of the three circular arcs. Fuel is injected into the combustion chamber from the top of the smooth, intrusive injector. Because the injector intrudes into the combustion chamber flow field, it generates a set of oblique shock waves, such as... Figure 2 As shown by the dashed line, the area before and after the oblique shock wave can be denoted as Region I and Region II, respectively. The airflow parameters in Region I include: velocity V1, pressure P1, temperature T1, and density. ρ 1. The airflow parameters in region II include: velocity V2, pressure P2, temperature T2, and density. ρ 2. Therefore, under the design condition that the airflow parameters of Region I are known, the center position and radius of each circle of the smooth invasive injector can be optimized according to the fuel injection and mixing requirements of the combustion chamber. This can adjust the airflow parameters after the oblique shock wave, increase the airflow pressure and temperature, reduce the airflow velocity, and create conditions conducive to fuel mixing.

[0017] The airflow parameters after the shock wave can be calculated using the parameters before the shock wave and the shock wave angle. Taking pressure as an example, the pressure calculation formula before and after the oblique shock wave is shown in equation (1): (1) In the above formula, P1 is the pressure in region I, P2 is the pressure in region II, ε represents the shock wave angle, M1 is the Mach number in region I, and γ is the gas constant in region I. The fuel injection effect can be compared by the momentum ratio of fuel to air. The higher the momentum ratio, the easier it is for the fuel to enter the combustion chamber, which is more conducive to mixing. The momentum ratio calculation formula is shown in equation (2): (2) in,q The momentum ratio of fuel to air. For fuel density, For fuel speed, air density, This refers to air speed.

[0018] Verification example: A typical implementation example: Based on the Computational Fluid Dynamics (CFD) method, a typical fuel injection condition was implemented and verified.

[0019] Given conditions: Combustion chamber inlet height AB = 70 mm, airflow parameters for combustion chamber region I are V1 = 952 m / s, density... The fuel is hydrogen, the injection orifice diameter is 1 mm, the number of injection orifices is 30-100, the hydrogen injection pressure is 3 MPa, then the hydrogen injection velocity is 1272 m / s, and the density is 1.466 kg / m3. Without implementing this invention, the fuel needs to be injected from region I. According to formula (2), the air momentum of region I is 71392 Pa, the hydrogen momentum is 1187000 Pa, and the momentum ratio of fuel to air is 16.63, as shown in Table 1. The hydrogen distribution at this time is as follows: Figure 3 As shown, hydrogen gas has difficulty penetrating into the mainstream of the combustion chamber, and a large amount of high-concentration hydrogen gas still exists near the lower wall of the combustion chamber.

[0020] Table 1: Fuel to Air Momentum Ratio Without Implementing the Invention After adopting the smooth invasive injector proposed in this invention, the fuel injection conditions remain unchanged. However, the air velocity decreases after being compressed by the shock wave generated by the injector, and the air density also decreases significantly under the action of the expansion wave downstream of the shock wave. The air momentum decreases to 36258 Pa, and the momentum ratio of fuel to air increases to 32.74, which is about 1 time, significantly improving the fuel penetration capability, as shown in Table 2. The hydrogen distribution at this time is as follows... Figure 4 As shown, hydrogen has rapidly entered the combustion chamber, and the high-concentration hydrogen area at the combustion chamber outlet has significantly decreased, indicating that the fuel has been well mixed with air.

[0021] Table 2: Fuel to Air Momentum Ratio After Implementing the Invention As can be seen from Tables 1 and 2, the present invention can increase the fuel-to-air momentum ratio by more than 100%, which is more conducive to achieving efficient fuel mixing under high-speed flow conditions.

[0022] The above solution is merely an illustration of a preferred example and is not limited thereto. When implementing this invention, appropriate substitutions and / or modifications can be made according to the user's needs.

[0023] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A smooth invasive fuel injector, characterized in that, A fuel injector is provided on the side wall of the combustion chamber, extending towards the center of the combustion chamber. The fuel injector includes: The center of the circle is located in arc segment I outside the combustion chamber; The center of the circle is located inside the combustion chamber, and is situated on either side of arc segment I, arc segment II, and arc segment III; Among them, each arc segment is tangent to the straight segment of the combustion chamber at the intersection point, and the injection hole of the fuel injector is located at the top of arc segment I; The transition between the corresponding arc segment and the straight segment of the combustion chamber is smooth; Specifically, when the inlet and outlet heights of the combustion chamber are both 70mm, and the distance between the inlet and outlet of the combustion chamber is 500mm, the radius of arc segment II is 20mm, the radius of arc segment I is 15mm, the radius of arc segment III is 20mm, and the vertical distance from the center point of arc segment I to the inlet of the combustion chamber is 100mm.

2. The smooth invasive fuel injector as described in claim 1, characterized in that, The number of injection holes is 30 to 100, and the diameter of each injection hole is 1 mm.

3. The smooth invasive fuel injector as described in claim 1, characterized in that, The fuel injector is located in the inlet section of the combustion chamber.

4. A design method for a smooth invasive fuel injector, applied in the design of a smooth invasive fuel injector as described in any one of claims 1-3, characterized in that, Based on the fuel injector that intrudes into the combustion chamber flow field, a set of oblique shock waves are generated inside the combustion chamber. Based on the relationship between the front and back of the oblique shock waves, the front is denoted as Region I and Region II. Under the known airflow parameters of region I, and based on the mixing requirements of fuel injection in the combustion chamber, the center position and radius of each arc segment are optimized to adjust the airflow parameters after the oblique shock wave, so as to obtain a fuel injector shape that is conducive to fuel mixing conditions.

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