Evaluation method for ideal divergence angle of axial expansion combustion chamber

Abstract

The invention relates to the technical field of manufacturing methods of aerospace engines, in particular to a method for evaluating an ideal divergence angle of an axial expansion combustion chamber, which comprises the following steps of: constructing experimental models with different divergence angles; cold flow and ignition tests are carried out under the same working condition, and the heat release rate and the average propagation speed of detonation waves are continuously collected; intercepting a complete period to extract a peak value and a valley value of a heat release rate so as to calculate a heat release increment and a heat release ratio, and calculating a speed attenuation difference value measured by a theory and a test; and establishing a multi-parameter association mapping relationship. Aiming at the problem that the optimal combustion chamber divergence angle capable of maintaining the stable propagation of the detonation wave is difficult to determine in the prior art, the optimal divergence angle under the most stable propagation state of the detonation wave can be scientifically and accurately determined by taking the maximization of the heat release increment and the heat release ratio and the minimization of the speed attenuation difference value as optimization targets; and the design reliability of the axial expansion combustion chamber is improved.

Description

Technical Field

[0001] This invention relates to the field of aerospace engine manufacturing methods, and specifically to a method for evaluating the ideal expansion angle of an axially expanding combustion chamber. Background Technology

[0002] In the development of axially expanding rotary detonation engines, the design of the combustion chamber's geometric parameters is crucial; among them, the combustion chamber's expansion angle α is a core engineering parameter that determines the airflow velocity compensation effect and combustion efficiency.

[0003] However, existing evaluation and testing methods often lack precise quantitative indicators when determining combustion chamber parameters. The specific defects of the related technologies are that, due to the lack of a comprehensive testing and calculation evaluation system for multi-physics fields, it is difficult for designers to accurately determine the optimal combustion chamber expansion angle that can maintain the stable propagation of the knock wave, which makes it difficult for the geometry of the combustion chamber to achieve optimal performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating the ideal expansion angle of an axially expanding combustion chamber, so as to solve the technical problem that it is difficult to accurately determine the optimal combustion chamber expansion angle that can maintain the stable propagation of the knock wave in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] A method for evaluating the ideal expansion angle of an axially expanding combustion chamber includes the following steps:

[0007] An experimental model of an axially expanding combustion chamber with different expansion angles α was constructed, wherein the inner wall of the axially expanding combustion chamber expands outward along the axial direction of the airflow, thereby gradually increasing the cross-sectional area of ​​the inner channel of the axially expanding combustion chamber.

[0008] Under the same operating conditions, cold flow tests and ignition tests were conducted on each of the experimental models.

[0009] During the ignition test, the heat release rate q(t) and the average propagation velocity V of the detonation wave inside the axial expansion combustion chamber were continuously collected. exp ;

[0010] Extract a complete cycle of the heat release rate q(t) curve from a single detonation cycle, and extract the peak heat release rate q within that cycle. peak and the trough of heat release rate q valley ;

[0011] According to the peak heat release rate q peak and the valley value of the heat release rate q valley Calculate the heat release increment ΔQ and the heat release ratio RQ, where ΔQ = q peak -qvalley RQ=q peak / q valley ;

[0012] Calculate the theoretical detonation wave velocity V CJ The average propagation velocity V of the detonation wave measured in the experiment exp The velocity decay difference ΔV, where ΔV = |V CJ -V exp |;

[0013] Establish a mapping relationship to associate and map the heat release increment ΔQ, the heat release ratio RQ, and the velocity decay difference ΔV calculated for different expansion angles α.

[0014] Based on the mapping relationship, with the optimization objectives of maximizing the heat release increment ΔQ and the heat release ratio RQ and minimizing the velocity decay difference ΔV, the ideal expansion angle corresponding to the most stable state of knock wave propagation in the axial expansion combustion chamber is determined.

[0015] Furthermore, the method for acquiring the heat release rate q(t) includes the following steps: acquiring the luminescence signal inside the axially expanding combustion chamber during the ignition test, and using the luminescence signal to characterize the heat release rate q(t).

[0016] Furthermore, the step of acquiring the luminous signal includes: arranging an optical fiber sensor inside the axially expanding combustion chamber, wherein the optical fiber sensor acquires the light intensity signal of the CH* channel as the luminous signal.

[0017] Furthermore, the probe of the fiber optic sensor is equipped with a narrowband filter to extract light signals of a specific wavelength, and the fiber optic sensor is connected to a high-speed photomultiplier tube to capture the light signals emitted spontaneously by hydrocarbon fuels during combustion.

[0018] Furthermore, the average propagation speed V of the detonation wave exp The acquisition steps include: arranging at least two [unclear] components with a preset spacing S along the axial direction within the axial expansion combustion chamber. AB A pressure sensor is used to collect pressure signals;

[0019] The time of occurrence of the pressure signal is taken as the time T when the pressure wave arrives at the pressure sensor. The time delay ΔT of the pressure wave arriving at the pressure sensor at different axial positions is calculated, and combined with the axial physical distance S between the pressure sensors. AB The average propagation velocity V of the detonation wave was calculated. exp , where V exp =S AB / |ΔT|.

[0020] Furthermore, at least two pressure sensors are arranged circumferentially at the same axial position, and the pressure signals collected by multiple pressure sensors at the same circumferential position are used to calculate the average value of the time T when the pressure wavefront arrives at that axial position.

[0021] Furthermore, before the calculation step, the light emission signal and pressure signal collected in the ignition test are preprocessed, that is, the background noise signal recorded in the cold flow test of the corresponding channel is subtracted from the collected signal.

[0022] Furthermore, the experimental model includes a base, a valve train assembly, and the axially expanding combustion chamber arranged coaxially along the axial direction.

[0023] The base has a gas intake channel in the center;

[0024] The base has several circular holes that extend axially around its outer perimeter, forming an air intake channel.

[0025] Furthermore, the gas distribution assembly includes a gas distribution plate and an air distribution plate. The gas distribution plate is coaxially fastened to the base and connected to the gas intake channel. The air distribution plate is coaxially fastened to the outside of the gas distribution plate and connected to the air intake channel.

[0026] An annular gap is formed between the air distribution plate and the gas distribution plate, and the annular gap constitutes an air injection channel.

[0027] The gas distribution plate has several radially penetrating gas injection holes distributed along its inner circumference, and the gas intake channel is connected to the air injection channel through the gas injection holes.

[0028] The advantages of this invention compared to the prior art are:

[0029] This invention utilizes experimental models with different expansion angles α, and combines multi-channel light intensity signals and pressure signals to calculate the heat release increment ΔQ, heat release ratio RQ, and velocity decay difference ΔV. This achieves the technical effect of converting multi-physics field signals into quantitative indicators for evaluating the quality of detonation waves. Furthermore, with the goal of maximizing ΔQ and RQ and minimizing ΔV, it provides designers with a scientific and systematic basis for optimal parameter decision-making, effectively improving the accuracy of axial expansion combustion chamber design. Attached Figure Description

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0031] Figure 1 This is a front view of an embodiment of the present invention;

[0032] Figure 2 This is a top view of an embodiment of the present invention;

[0033] Figure 3 for Figure 2 A cross-sectional view along the AA direction;

[0034] The labels in the diagram represent the following:

[0035] 1-Base; 11-Gas intake channel; 12-Air intake channel;

[0036] 2-Gas distribution assembly; 21-Gas distribution panel; 22-Air distribution panel; 23-Air injection channel; 24-Gas injection orifice;

[0037] 3-Axial expansion combustion chamber. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] (First embodiment)

[0040] refer to Figure 1 , Figure 2 and Figure 3 This invention provides an axially expanding rotary detonation engine, the main structure of which includes a base 1, a valve train 2 and an axially expanding combustion chamber 3 arranged coaxially along the axial direction. The base 1 serves as the supporting foundation of the engine, and a gas intake passage 11 is provided in the center of the base 1. Several circular holes are distributed around the base 1, which constitute an air intake passage 12.

[0041] The gas distribution assembly 2 includes a gas distribution plate 21 and an air distribution plate 22. The gas distribution plate 21 is coaxially mounted on the base 1 by bolts and is connected to the gas intake channel 11. The air distribution plate 22 is coaxially mounted on the outside of the gas distribution plate 21 by bolts and is connected to the air intake channel 12.

[0042] The annular gap formed between the air distribution plate 22 and the gas distribution plate 21 constitutes the air injection channel 23; the inner circumference of the gas distribution plate 21 is provided with several radially penetrating gas injection holes 24, thereby connecting the gas intake channel 11 and the air injection channel 23.

[0043] During engine operation, air (oxidizer) enters through the air intake passage 12 of the base 1, flows through the air injection passage 23 and enters the combustion chamber; gas (fuel) enters through the gas intake passage 11 of the base 1 and is injected into the air injection passage 23 through the gas injection hole 24 on the gas distribution plate 21; the oxidizer and fuel are mixed inside the air injection passage 23 to form a mixture, which is then injected at high speed into the axial expansion combustion chamber 3; subsequently, the mixture is ignited by a hot jet and forms a rotating detonation wave in the axial expansion combustion chamber 3 and is burned.

[0044] To address the issues of deceleration of supersonic airflow due to gas dynamics and reduced flow velocity caused by heat sink effect on the combustion chamber wall in existing constant cross-section combustion chambers, the axial expansion combustion chamber 3 of this invention adopts an internal channel axial expansion design. Internal channel axial expansion means that the inner wall of the combustion chamber of the rotary detonation engine expands outward, that is, the cross-section of the inner channel of the combustion chamber gradually expands along the airflow direction (axial direction) to form an expansion-type flow channel, realizing the integrated layout of the combustion chamber and the tail nozzle; the outer wall of the combustion chamber is usually of constant diameter.

[0045] The axial expansion combustion chamber 3 compensates for the total pressure loss and velocity decay of the airflow during the flow process by changing the cross-sectional dimensions of its inner wall, thereby improving the energy release efficiency in the combustion chamber and enhancing the self-sustaining capability of the engine combustion process.

[0046] (Second Embodiment)

[0047] In order to determine the optimal geometric parameters of the internal channel axial expansion combustion chamber 3, and in particular to determine the ideal expansion angle α of the combustion chamber that can maintain the stable propagation of the knock wave, embodiments of the present invention provide a method for evaluating the ideal expansion angle of the axial expansion combustion chamber.

[0048] This evaluation method establishes an experimental model of an axially expanding combustion chamber with different expansion angles (e.g., discrete values ​​within the range of 0 to 10 degrees), and conducts cold flow tests and ignition tests under the same operating conditions to obtain the ideal expansion angle α of the combustion chamber.

[0049] Specifically, the evaluation method includes the following steps:

[0050] Step 1: Build a data acquisition system:

[0051] Fiber optic sensor probes and pressure sensors are arranged on the wall of the axial expansion combustion chamber 3;

[0052] The fiber optic sensor probe is equipped with a narrowband filter for extracting light signals of a specific wavelength (e.g., CH* signal, wavelength 431±5nm) and is connected to a high-speed photomultiplier tube for collecting the light signals emitted spontaneously by hydrocarbon fuels during combustion.

[0053] At least two need to be arranged with a preset spacing S along the axial direction. AB The pressure sensor is used to acquire pressure fluctuation signals within the combustion chamber, thereby acquiring the time T when the pressure wavefront arrives at that axial position. A and T B .

[0054] At least two pressure sensors are arranged circumferentially at the same axial position. The pressure signals collected by the multiple pressure sensors at the same circumferential position are used to calculate the time T when the pressure wavefront arrives at that axial position. A and T B The average value.

[0055] Step two, signal acquisition and preprocessing:

[0056] The multi-channel synchronous triggering mechanism is activated to synchronously acquire continuous time-series signals from all fiber optic sensor channels and pressure sensors.

[0057] To eliminate the system's inherent noise, the background noise signal recorded in the cold flow test for the corresponding channel needs to be subtracted from the original signal acquired during the ignition test.

[0058] Subsequently, the signal amplitude is normalized to the [0,1] interval based on the maximum value of the corrected signal sequence of each channel.

[0059] Step 3: Convert the collected physical signals into key combustion parameters:

[0060] For the light intensity signal, the chemiluminescence intensity is used to characterize the heat release rate, and the normalized CH* channel light intensity signal is directly used as the instantaneous heat release rate q(t) time series with microsecond-level resolution.

[0061] For pressure signals, the occurrence time of the pressure signal is taken as the time T when the pressure wave arrives at the pressure sensor. The time delay ΔT of the pressure wave arriving at the pressure sensor at different axial positions is calculated, and this is combined with the axial physical distance S between the pressure sensors. AB The average propagation velocity V of the detonation wave, as measured in the experiment, was calculated.exp The calculation formula is as follows:

[0062] ;

[0063] V exp : Average propagation velocity of the detonation wave as measured in the experiment (unit: m / s);

[0064] S AB Physical distance (in meters) between pressure sensor A and pressure sensor B distributed along the combustion chamber axis.

[0065] T A : The time (in seconds) when the pressure front of the detonation wave reaches the same axial position after the average calculation of the pressure sensor A.

[0066] T B : The average time (in seconds) when the pressure front of the detonation wave reaches the same axial position of the pressure sensor B.

[0067] ΔT: The time delay (in seconds) for the pressure wavefront to pass between two axial position sensors.

[0068] Next, three quantitative indicators used to evaluate the quality of the detonation wave were calculated:

[0069] Heat release increment (ΔQ): On the heat release rate q(t) curve of a single detonation cycle, a complete cycle is intercepted based on the zero point of two adjacent crossings of the mean, and the peak q is identified within this complete cycle. peak Valley value q valley Calculate the difference between the two to obtain the heat release increment, i.e., ΔQ = q peak -q valley ;

[0070] Heat release ratio (RQ): The heat release ratio is obtained by calculating the ratio of the peak value to the trough value, i.e., RQ = q. peak / q valley ;

[0071] Velocity attenuation difference (ΔV): Calculated theoretical (CJ) detonation wave velocity V CJ The average propagation velocity V of the detonation wave measured in the experiment exp The difference is used to obtain the velocity decay difference, i.e., ΔV = |V CJ -V exp |

[0072] Step 4: Generate the ideal expansion angle evaluation results for the combustion chamber:

[0073] A statistical database was established to map the heat release increment (ΔQ), heat release ratio (RQ), and velocity decay difference (ΔV) to different combustion chamber expansion angles α.

[0074] Under the same operating conditions, the larger the heat release increment (ΔQ) and heat release ratio (RQ), and the smaller the velocity decay difference (ΔV), the more stable the detonation wave propagation. The expansion angle α corresponding to this state is the ideal expansion angle.

[0075] Designers can query the database as needed and compare experimental results under different α values ​​to determine the optimal expansion angle.

[0076] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered as falling within the scope of protection of the embodiments of the present invention.

Claims

1. A method for evaluating the ideal expansion angle α of an axially expanding combustion chamber, characterized in that, Includes the following steps: An experimental model of an axially expanding combustion chamber (3) with different expansion angles α was constructed. The inner wall of the axially expanding combustion chamber (3) expands outward along the axial direction of the airflow, so that the cross-sectional area of ​​the inner channel of the axially expanding combustion chamber (3) gradually increases. Under the same operating conditions, cold flow tests and ignition tests were conducted on each of the experimental models. During the ignition test, the heat release rate q(t) and the average propagation velocity V of the detonation wave inside the axial expansion combustion chamber (3) were continuously collected. exp ; Extract a complete cycle of the heat release rate q(t) curve from a single detonation cycle, and extract the peak heat release rate q within that cycle. peak and the trough of heat release rate q valley ; According to the peak heat release rate q peak and the valley value of the heat release rate q valley Calculate the heat release increment ΔQ and the heat release ratio RQ, where ΔQ = q peak -q valley RQ=q peak / q valley ; Calculate the theoretical detonation wave velocity V CJ The average propagation velocity V of the detonation wave measured in the experiment exp The velocity decay difference ΔV, where ΔV = |V CJ -V exp |; Establish a mapping relationship to associate and map the heat release increment ΔQ, the heat release ratio RQ, and the velocity decay difference ΔV calculated for different expansion angles α. Based on the mapping relationship, with the optimization objectives of maximizing the heat release increment ΔQ and the heat release ratio RQ and minimizing the velocity attenuation difference ΔV, the ideal expansion angle α corresponding to the most stable state of detonation wave propagation of the axial expansion combustion chamber (3) is determined.

2. The evaluation method according to claim 1, characterized in that, The method for collecting the heat release rate q(t) includes the following steps: During the ignition test, the luminescence signal inside the axial expansion combustion chamber (3) was collected, and the luminescence signal was used to characterize the heat release rate q(t).

3. The evaluation method according to claim 2, characterized in that, The steps for acquiring the emitted light signal include: An optical fiber sensor is arranged inside the axial expansion combustion chamber (3), and the optical fiber sensor collects the light intensity signal of the CH* channel as the light emission signal.

4. The evaluation method according to claim 3, characterized in that, The fiber optic sensor is equipped with a narrowband filter at its probe to extract light signals of a specific wavelength, and the fiber optic sensor is connected to a high-speed photomultiplier tube to capture the light signals emitted spontaneously by hydrocarbon fuels during combustion.

5. The evaluation method according to claim 1, characterized in that, The average propagation speed of the detonation wave V exp The data collection steps include: At least two combustion chambers with a predetermined spacing S are arranged axially within the axially expanding combustion chamber (3). AB A pressure sensor is used to collect pressure signals; The time of occurrence of the pressure signal is taken as the time T when the pressure wave arrives at the pressure sensor. The time delay ΔT of the pressure wave arriving at the pressure sensor at different axial positions is calculated, and combined with the axial physical distance S between the pressure sensors. AB The average propagation velocity V of the detonation wave was calculated. exp , where V exp =S AB / |ΔT|.

6. The evaluation method according to claim 5, characterized in that, At least two pressure sensors are arranged circumferentially at the same axial position, and the pressure signals collected by multiple pressure sensors at the same circumferential position are used to calculate the average value of the time T when the pressure wavefront arrives at that axial position.

7. The evaluation method according to claim 2 or 5, characterized in that, Before the calculation step, the light emission signal and pressure signal collected in the ignition test are preprocessed, that is, the background noise signal recorded in the cold flow test of the corresponding channel is subtracted from the collected signal.

8. The evaluation method according to claim 1, characterized in that, The experimental model includes a base (1), a gas distribution assembly (2), and an axially expanding combustion chamber (3) arranged coaxially along the axis. A gas inlet channel (11) is provided in the center of the base (1); The base (1) has several circular holes that extend through itself along the axial direction around its outer periphery, and these circular holes constitute an air intake channel (12).

9. The evaluation method according to claim 8, characterized in that, The gas distribution assembly (2) includes a gas distribution plate (21) and an air distribution plate (22). The gas distribution plate (21) is coaxially fastened to the base (1) and connected to the gas intake channel (11). The air distribution plate (22) is coaxially fastened to the outside of the gas distribution plate (21) and connected to the air intake channel (12). An annular gap is formed between the air distribution plate (22) and the gas distribution plate (21), and the annular gap constitutes an air injection channel (23). The gas distribution plate (21) has several radially penetrating gas injection holes (24) distributed along its inner circumference. The gas intake channel (11) is connected to the air injection channel (23) through the gas injection holes (24).

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