Cold-state experimental simulation device and method for combustion stability boundary

Abstract

The invention relates to a cold state experiment simulation device and method for a combustion stability boundary, belongs to the technical field of liquid rocket engine combustion chamber experiment simulation, and solves the technical problem that a coaxial double centrifugal nozzle combustion stability boundary cold state experiment cannot be simulated, and the device comprises nozzles, a damping grid, a simulation combustion chamber, a flat plate and a pulsating pressure sensor. The simulation combustion chamber is located on the horizontally-arranged flat plate, the damping grid is located in the simulation combustion chamber on the downstream of the nozzle, the nozzle is fixed to the flat plate, and the pulsating pressure sensor is installed on the side wall of the simulation combustion chamber. The method comprises the steps of calculating nitrogen mass flow, and determining the optimal position of a rectifier grid; and fixing the optimal position of the rectification grid, and determining the stability boundary. The device is used for determining the cold state experiment of the combustion instability boundary of the liquid rocket engine combustion chamber.

Description

Technical Field

[0001] This invention belongs to the field of experimental simulation technology for liquid rocket engine combustion chambers, specifically relating to a cold-state experimental simulation device and method for combustion stability boundary. Background Technology

[0002] Combustion instability is a key concern in the development of liquid rocket engines. To mitigate development risks, most engine development programs involve a series of scaled-down experiments. Based on the operating characteristics of different nozzle types, simplified physical models characterizing combustion instability are established. Simulation experiments are then conducted to obtain the nozzle's combustion stability margin at a lower cost, clarify the impact of structural and operating parameters on nozzle stability, and evaluate the effectiveness of stability control measures. This is crucial for achieving efficient and stable operation of the engine combustion chamber.

[0003] When the combustion chamber pressure exceeds the propellant's critical pressure, the mixing process of components within the nozzle becomes the primary factor determining combustion characteristics. Therefore, under low-pressure conditions, gas / gas combustion can be used to replace gas / liquid or liquid / liquid combustion in a real combustion chamber to study the nozzle's combustion kinetics. For example, Zhang Mengzheng, Lee, and Song conducted single-nozzle low-pressure combustion experiments using oxygen / kerosene vapor or methane-propane mixtures, obtaining the influence of nozzle structure and operating parameters on combustion stability margin. To further reduce the cost of combustion stability simulation experiments, this invention proposes a cold-state experimental simulation method suitable for the combustion stability boundary of coaxial dual centrifugal nozzles.

[0004] According to the Rayleigh criterion, combustion instability arises from the coupling of acoustic modes and unsteady heat release rate oscillations. For combustion systems where the mixing process is rate-controlled, the coupling of acoustic mode oscillations and unsteady heat release rate oscillations is generally achieved through flow as an intermediate process, which can be described as follows: pressure oscillations (sound field) affect the mixing process, generating large-scale vortex structures. These vortex structures alter the flame area and combustion rate, producing heat release rate oscillations. These oscillations transfer energy to the sound field, forming an acoustic-vortex-combustion coupled closed loop. (See...) Figure 1 The lower middle section is a dashed line. Even without combustion, the flow itself can create acoustic-vortex coupling. This can be described as follows: pressure oscillations (sound field) affect the flow (such as shear layers), causing the flow to generate large-scale vortex structures. These vortex structures impact the downstream wall, transferring energy to the sound field, forming an acoustic-vortex coupling closed loop. See [link to relevant documentation]. Figure 1 Solid line in the upper middle part.

[0005] Both cold-state acoustic-vortex coupling and acoustic-vortex-combustion coupling can generate self-excited oscillations, and their stability boundaries are related. Therefore, cold-state acoustic-vortex coupling can be used to simulate acoustic-vortex-combustion coupling. Shibanov found that the stability boundaries of a coaxial DC nozzle are very close under both cold and combustion conditions. However, for a coaxial dual centrifugal nozzle, experiments showed that no obvious stability boundary appeared under cold conditions, so the stability boundary under combustion conditions cannot be simulated.

[0006] The applicant's research revealed that self-excited oscillations occur in coaxial dual centrifugal nozzles under cold conditions. These self-excited oscillations correspond to instability in the swirling vortex core flow within the nozzle vortex. Previous studies have shown that swirling vortex core flow instability is a global (or absolute) instability, meaning that the flow itself generates self-excited oscillations and is not very sensitive to external acoustic disturbances. Furthermore, the large amplitude of the oscillation in the swirling vortex core suppresses other types of flow instability, such as shear layer flow instability. However, under combustion conditions, swirling vortex core flow instability is suppressed, and shear layer flow instability plays a dominant role in the acoustic-vortex-combustion coupling. Shear layer flow instability is a convective instability, sensitive to acoustic disturbances; low-amplitude acoustic disturbances produce an approximately linear flow stability response. Specifically, under external acoustic disturbances, vortex shedding merges during downstream convection, matching the external disturbance frequency and forming the maximum flow response. Summary of the Invention

[0007] To overcome the problem that cold-state experiments on the combustion stability boundary of coaxial dual centrifugal nozzles cannot be simulated, this invention proposes a cold-state experimental simulation device and method for the combustion stability boundary.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A cold-state experimental simulation device for combustion stability boundary includes a nozzle, a rectifier grid, a simulated combustion chamber, a plate, and a pulsating pressure sensor;

[0010] The simulated combustion chamber is cylindrical and located on a horizontally placed flat plate, with the front end of the simulated combustion chamber connected to the flat plate.

[0011] The rectifier grid is located inside the simulated combustion chamber, downstream of the nozzle. The center of the front end of the rectifier grid is located on the center line of the nozzle outlet, at a distance of h from the nozzle outlet, where h is a set value.

[0012] The nozzle is fixed on a flat plate, with its outlet flush with the front end of the simulated combustion chamber. The nozzle has an oxidizer inlet and a fuel inlet for the oxidizer and fuel, respectively. The nozzle consists of an inner nozzle and an outer nozzle connected to each other. The center of the front end of the rectifier grid is located on the center line of the inner nozzle outlet, at a distance h from the inner nozzle outlet.

[0013] The pulsating pressure sensor is installed on the side wall of the simulated combustion chamber and is used to measure the pulsating pressure inside the simulated combustion chamber.

[0014] In the aforementioned cold-state experimental simulation device, the nozzle is a coaxial DC nozzle or a coaxial DC centrifugal nozzle.

[0015] The aforementioned cold-state experimental simulation device includes a coaxial dual centrifugal nozzle and a cylindrical rod. The cylindrical rod is located inside the inner nozzle, on the center line of the inner nozzle, with a length equal to the length of the inner nozzle and a diameter smaller than the diameter of the air vortex within the inner nozzle.

[0016] In the aforementioned cold-state experimental simulation apparatus, the oxidant inlet is supplied with oxidant, and the fuel inlet is supplied with fuel. Both the oxidant and the fuel are nitrogen, or one of the oxidant and the fuel is mixed with helium.

[0017] In the aforementioned cold-state experimental simulation device, the first-order tangential and second-order longitudinal composite acoustic mode frequencies and the second-order longitudinal acoustic mode frequencies of the simulated combustion chamber are the same as the first-order tangential and first-order longitudinal acoustic mode frequencies of the hot-state combustion chamber, respectively.

[0018] The aforementioned cold-state experimental simulation device includes a rectifier grid comprising several stainless steel tubes. Each stainless steel tube is parallel, and the centerline of each tube is parallel to the centerline of the nozzle outlet.

[0019] In the aforementioned cold-state experimental simulation device, each stainless steel tube has a length of 10mm to 20mm, an outer diameter of 2mm to 4mm, a wall thickness of 0.2mm to 0.4mm, and the diameter of the rectifier grid cross-section is 8 to 10 times the inner diameter of the outer nozzle.

[0020] A cold-state experimental simulation method for combustion stability boundary includes the following steps:

[0021] Step 1, Determine the position of the downstream rectifier grid of the nozzle.

[0022] The first step is to calculate the nitrogen mass flow rate.

[0023] Assuming the nozzle exit velocity is the same under both combustion and cold conditions, the nitrogen mass flow rate is calculated based on the rated operating conditions under the nozzle combustion conditions in the cold experimental simulation.

[0024] The second step is to determine the optimal position of the rectifier grid.

[0025] The flow rate of the internal nozzle is set to several times the rated flow rate. The distance h between the rectifier and the nozzle is changed. When the pressure oscillation reaches a peak, the distance between the rectifier and the nozzle is hp. At this time, the position of the rectifier is the optimal position of the rectifier.

[0026] Step 2, Stability Experiment

[0027] The first step is to fix the optimal position of the rectifier grid.

[0028] Fix the rectifier grid in the optimal position.

[0029] The second step is to determine the stability boundary.

[0030] The external nozzle is selected from 5 to 10 operating conditions within the range of 1 / 2 to 3 times its rated flow. Under each operating condition, the internal nozzle is gradually increased within the range of 1 / 2 to 3 times its rated flow. When the pressure oscillation amplitude suddenly increases and the increase exceeds the set multiple of the original amplitude, the point is determined as the stability boundary point under that operating condition.

[0031] Connecting the stability boundary points under each operating condition yields the stability boundary of the nozzle.

[0032] In the above-mentioned cold-state experimental simulation method, in the second step of step 1, the flow rate of the inner nozzle is 2 to 3 times the rated flow rate, and the distance h between the rectifier grid and the nozzle gradually increases in the range of 1 mm to 20 mm, with a step size of 1 mm to 1.5 mm.

[0033] In the above-mentioned cold-state experimental simulation method, in the second step of step 2, the pressure oscillation amplitude suddenly increases, and the increase exceeds the original amplitude by a set multiple of 2.

[0034] The beneficial effects of this invention are:

[0035] A cold-state experimental simulation device for combustion stability boundary is proposed. A cylindrical rod structure is added to the inner nozzle to suppress the instability of the vortex core flow under cold conditions and promote the instability of the shear layer flow to play a dominant role. This enables cold-state experimental simulation of the acoustic-vortex-combustion coupling process under combustion conditions and obtains the combustion stability boundary of the coaxial dual centrifugal nozzle.

[0036] A cold-state experimental simulation method for combustion stability boundary is proposed. The size and structure of the cylindrical rod are clearly defined. It has little impact on the original nozzle flow field but a significant impact on flow stability, thus improving the accuracy of the cold-state simulation method. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the existing acoustic-vortex-combustion coupling relationship;

[0038] Figure 2 This is a schematic diagram of the cold-state experimental simulation device for the combustion stability boundary according to Embodiment 1 of the present invention;

[0039] Figure 3 This is a schematic diagram of the existing coaxial dual centrifugal nozzle structure;

[0040] Figure 4 This is a schematic diagram of a coaxial dual centrifugal nozzle structure according to an embodiment of the present invention;

[0041] Figure 5 This is a graph showing the change in pressure oscillation amplitude with the position of the rectifier grid according to Embodiment 1 of the present invention;

[0042] Figure 6 This is a graph showing the change in pressure oscillation amplitude with the flow rate of the internal nozzle in Embodiment 1 of the present invention.

[0043] Figure label:

[0044] 1. Nozzle; 2. Rectifier grid; 3. Simulated combustion chamber; 4. Flat plate; 5. Pulsating pressure sensor; 6. Oxidizer inlet; 7. Fuel inlet; 11. Inner nozzle; 12. Outer nozzle; 13. Cylindrical rod. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] A cold-state experimental simulation device for combustion stability boundary, such as Figure 2 As shown, the system includes a nozzle 1, a rectifier grid 2, a simulated combustion chamber 3, a flat plate 4, a pulsed pressure sensor 5, an oxidizer inlet 6, and a fuel inlet 7. The simulated combustion chamber 3 is a cylindrical structure with openings at both ends, placed on a horizontal flat plate 4. The nozzle 1 is mounted on the flat plate 4, with its outlet flush with the plate 4. The rectifier grid 2 is located at a downstream position h from the nozzle 1. The pulsed pressure sensor 5 is mounted on the side wall of the simulated combustion chamber 3, near the end of the flat plate 4. Both the oxidizer and fuel are nitrogen; to simulate the density ratio of the oxidizer and fuel, helium can be mixed into one of the inlets.

[0048] Nozzle 1 can be a coaxial DC (shear) nozzle, a coaxial DC centrifugal nozzle, or a coaxial dual centrifugal nozzle. This application describes the coaxial dual centrifugal nozzle. The original nozzle of the coaxial dual centrifugal nozzle is as follows: Figure 3 As shown, after adding the cylindrical rod 13 structure to the inner nozzle 11, as Figure 4 As shown. The downstream end of the cylindrical rod is flush with the outlet of the inner nozzle 11, and its diameter is smaller than the diameter of the air vortex of the inner nozzle 11.

[0049] The first-order tangential and second-order longitudinal composite acoustic mode frequencies and the second-order longitudinal acoustic mode frequency of the simulated combustion chamber 3 should be the same as the first-order tangential and first-order longitudinal acoustic mode frequencies of the hot combustion chamber, thereby determining the diameter and height of the simulated combustion chamber. The rectifier grid 2 is assembled from stainless steel thin tubes with a length of 10mm to 20mm, an outer diameter of 2mm to 4mm, and a wall thickness of 0.2mm to 0.4mm. The cross-sectional diameter of the rectifier grid 2 is 8 to 10 times the inner diameter of the outlet of the outer nozzle 12.

[0050] A cold-state experimental simulation method for combustion stability boundary includes the following steps:

[0051] Step 1, Determine the position of the downstream rectifier grid of the nozzle.

[0052] Based on the rated operating conditions under the combustion conditions of nozzle 1, calculate the nitrogen mass flow rate under the corresponding rated operating conditions in the cold test to ensure that the nozzle outlet velocity is the same under both combustion and cold conditions. With the nitrogen flow rate of the outer nozzle 12 fixed at the rated operating conditions, the flow rate of the inner nozzle 11 is determined to be 2 to 3 times the rated flow rate. The distance h of the rectifier grid 2 is gradually increased within the range of 1 mm to 20 mm, with a change step size of 1 mm to 1.5 mm. The value of h at which the pressure oscillation reaches its peak is determined as the optimal position hp of the rectifier grid.

[0053] For example: outer nozzle 0.11g / s, inner nozzle 0.3g / s, move the rectifier grid position at intervals of 1.2mm. Figure 5 The data shows the change in pressure oscillation amplitude with the position of the rectifier grid. As the rectifier grid moves downstream, the pressure oscillation amplitude exhibits a periodic trend with a period of 6 mm. The position of the rectifier grid is determined to be the second peak value, i.e., h. p =7.2mm.

[0054] Step 2, Stability Experiment

[0055] The rectifier grid position hp is fixed. Five to ten operating conditions are selected for the outer nozzle 12 within a range of 1 / 2 to 3 times its rated flow. For each fixed outer nozzle flow condition, the inner nozzle 11 is gradually increased within a range of 1 / 2 to 3 times its rated flow. The condition where the pressure oscillation amplitude suddenly increases significantly (the increased amplitude is greater than twice the original amplitude) is identified as the stability boundary point. Finally, the stability boundaries corresponding to the 5 to 10 operating conditions of the outer nozzle 12 are obtained, forming the stability boundary of nozzle 1.

[0056] For example: fixing the rectifier grid position h p With the outer nozzle flow rate fixed at 0.19 g / s and the inner nozzle flow rate gradually increased while keeping the outer nozzle diameter constant at 7.2 mm, the change in pressure oscillation amplitude with the inner nozzle flow rate was observed. Figure 6 As shown, when the flow rate of the internal nozzle reaches 0.30 g / s, the pressure oscillation amplitude suddenly increases, and this point is determined to be the stability boundary point.

Claims

1. A cold-state experimental simulation apparatus for combustion stability boundary, characterized in that, Includes nozzle (1), rectifier grid (2), simulated combustion chamber (3), plate (4), and pulsating pressure sensor (5); The simulated combustion chamber (3) is cylindrical and located on a horizontally placed plate (4). The front end of the simulated combustion chamber (3) is connected to the plate (4). The rectifier grid (2) is located inside the simulated combustion chamber (3), downstream of the nozzle (1); the center of the front end of the rectifier grid (2) is located on the center line of the nozzle (1) outlet, and the distance between it and the nozzle (1) outlet is h, where h is a set value; The nozzle (1) is fixed on the plate (4), and the outlet of the nozzle (1) is flush with the front end of the simulated combustion chamber (3); the nozzle (1) is provided with an oxidant inlet (6) and a fuel inlet (7) for the inlet of oxidant and fuel, respectively; the nozzle (1) includes an inner nozzle (11) and an outer nozzle (12) connected to each other, and the front end center of the rectifier grid (2) is located on the center line of the outlet of the inner nozzle (1), and the distance between the inner nozzle (1) outlet and the inner nozzle (1) outlet is h; The pulsating pressure sensor (5) is installed on the side wall of the simulated combustion chamber (3) and is used to measure the pulsating pressure inside the simulated combustion chamber (3).

2. The cold-state experimental simulation device according to claim 1, characterized in that, The nozzle (1) is a coaxial DC nozzle or a coaxial DC centrifugal nozzle.

3. The cold-state experimental simulation device according to claim 1, characterized in that, The nozzle (1) is a coaxial double centrifugal nozzle and also includes a cylindrical rod (13); the cylindrical rod (13) is a cylinder located inside the inner nozzle (11), on the center line of the inner nozzle (11), with the same length as the inner nozzle (11) and a diameter smaller than the vortex diameter of the inner nozzle (11).

4. The cold-state experimental simulation device according to claim 1, characterized in that, The oxidant inlet (6) is supplied with oxidant, and the fuel inlet (7) is supplied with fuel; both the oxidant and the fuel are nitrogen, or one of the oxidant and the fuel is mixed with helium.

5. The cold-state experimental simulation device according to claim 1, characterized in that, The first-order tangential and second-order longitudinal composite acoustic mode frequencies and the second-order longitudinal acoustic mode frequencies of the simulated combustion chamber (3) are the same as the first-order tangential and first-order longitudinal acoustic mode frequencies of the hot combustion chamber, respectively.

6. The cold-state experimental simulation device according to claim 1, characterized in that, The rectifier grid (2) includes several stainless steel tubes; each stainless steel tube is parallel, and the center line of each stainless steel tube is parallel to the center line of the nozzle (1) outlet.

7. The cold-state experimental simulation device according to claim 6, characterized in that, The length of each stainless steel tube of the rectifier grid is 10mm to 20mm, the outer diameter is 2mm to 4mm, and the wall thickness is 0.2mm to 0.4mm. The cross-sectional diameter of the rectifier grid is 8 to 10 times the inner diameter of the outer nozzle (12).

8. A cold-state experimental simulation method for combustion stability boundary, using the cold-state experimental simulation apparatus according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1, determine the position of the downstream rectifier grid (2) of the nozzle (1): The first step is to calculate the nitrogen mass flow rate: Assuming that the outlet velocity of the nozzle (1) is the same under both combustion and cold conditions, the nitrogen mass flow rate under the corresponding rated conditions in the cold experimental simulation is calculated based on the rated operating conditions under the nozzle combustion conditions. The second step is to determine the optimal position of the rectifier grid (2): The flow rate of the inner nozzle (11) is determined to be several times the rated flow rate. The distance h between the rectifier grid (2) and the nozzle (1) is changed. When the pressure oscillation reaches a peak, the distance between the rectifier grid (2) and the nozzle (1) is hp. At this time, the position of the rectifier grid (2) is the optimal position of the rectifier grid. Step 2, Stability Experiment: The first step is to fix the optimal position of the rectifier grid: Fix the rectifier grid (2) in the optimal position of the rectifier grid; The second step is to determine the stability boundary: The external nozzle (12) selects 5 to 10 working conditions within the range of 1 / 2 to 3 times its rated flow. Under each working condition, the internal nozzle (11) gradually increases within the range of 1 / 2 to 3 times its rated flow. When the pressure oscillation amplitude suddenly increases and the increase exceeds the set multiple of the original amplitude, the point is determined as the stability boundary point under the working condition. The stability boundary points under each working condition are connected to obtain the stability boundary of the nozzle.

9. The cold-state experimental simulation method according to claim 8, characterized in that, In the second step of step 1, the flow rate of the inner nozzle is 2 to 3 times the rated flow rate, and the distance h between the rectifier grid (2) and the nozzle (1) gradually increases in the range of 1 mm to 20 mm, with a step size of 1 mm to 1.5 mm.

10. The cold-state experimental simulation method according to claim 8, characterized in that, In the second step of step 2, The pressure oscillation amplitude suddenly increases, and the increase exceeds the original amplitude by a set multiple of 2.

Images