Method for inhibiting combustion asymmetry of scramjet engine

Abstract

The invention relates to the field of scramjet engines, in particular to a method for inhibiting combustion asymmetry of a scramjet engine, which comprises the following steps of: releasing high-temperature airflow at the upstream of shock wave string head shock wave in an isolation section of the engine, or releasing and igniting auxiliary fuel in the isolation section of the engine, therefore, high-temperature airflow is formed at the upstream of shock waves of the shock wave string head. According to the embodiment of the invention, the flow field in the isolation section is reconstructed through combustion of high-temperature airflow or auxiliary fuel, so that the quality of the flow field at the inlet of the combustion chamber is improved, and the purpose of inhibiting combustion asymmetry of the combustion chamber is finally achieved.

Description

Technical Field

[0001] The present invention relates to the field of scramjet engines, and particularly to a method for suppressing combustion asymmetry in scramjet engines. Background Art

[0002] A scramjet engine is an air-breathing engine designed for flight at extremely high speeds (usually above Mach 5). Different from ordinary ramjet engines, the airflow in its combustion chamber 2 remains supersonic during combustion.

[0003] Reference Figure 1 , the cross-section of the internal structure of a scramjet engine is a circular cross-section, a rectangular cross-section or other equivalent structures, and successively includes along the flow direction: an isolator 1, a combustion chamber 2 and a nozzle 3. The isolator 1 is a component downstream of the engine inlet and upstream of the combustion chamber 2. The interior of the combustion chamber 2 is equipped with a flame holder 21 (taking a cavity flame holder as an example in the figure).

[0004] The combustion chamber 2 is equipped with a main injection module 22, and the main injection module 22 is used to inject main fuel (such as aviation kerosene) into the interior of the combustion chamber 2, and the injection direction is perpendicular to the wall surface of the combustion chamber 2.

[0005] Optionally, an igniter (not shown in the figure) is provided inside the flame holder 21, and the igniter is used to ignite the main fuel (such as aviation kerosene) that cannot be self-ignited.

[0006] Reference Figure 2 , when the scramjet engine operates under the oncoming flow condition of Ma>5, the internal flow field in the combustion chamber 2 exhibits strong unsteady characteristics, and the reasons include shock-wave boundary layer interference and fuel-oncoming flow mixing, resulting in asymmetric combustion in the combustion chamber 2.

[0007] Shock-wave boundary layer interference: The upstream shock wave impacts the boundary layer of the isolator 1, causing the boundary layer to thicken and separate in an undetermined direction, forming complex recirculation zones and vortex structures.

[0008] Fuel-oncoming flow mixing: Uneven fuel mixing leads to too high (rich oil) or too low (lean oil) fuel concentration in local areas.

[0009] Asymmetric combustion: The phenomenon that the flame spatial distribution (in the height direction and spanwise direction) is uneven when the main working fuel (such as aviation kerosene, hydrogen, etc.) of the engine burns.

[0010] On the one hand, the upstream shock wave train is coupled with asymmetric combustion. Uneven combustion causes the pressure on one side to be higher than that on the other side, pushing the core flow towards the side with lower pressure. The skewing of the core flow will change the diffusion trajectory of the fuel in the airflow after injection, making the fuel unevenly distributed in each area of the combustion chamber 2, increasing the amount of unburned fuel and reducing the overall combustion efficiency.

[0011] On the other hand, during the combustion process, the heat release rate, pressure, etc. fluctuate violently with time, and the strong pressure waves generated will repeatedly push and pull the upstream shock wave train, causing it to oscillate greatly back and forth, thereby leading to unstable combustion. Summary of the Invention

[0012] The object of the present invention is to provide a method for suppressing combustion asymmetry in a scramjet engine, which aims to suppress combustion asymmetry in the combustion chamber when the scramjet engine operates under high Mach number incoming flow conditions.

[0013] To solve the above technical problems, the present invention specifically provides the following technical solutions:

[0014] The present invention provides a method for suppressing asymmetric combustion in a scramjet engine, including the following steps: releasing high-temperature air flow upstream of the head shock of the shock wave train inside the isolation section of the engine, and using the high-temperature air flow and the heat it carries to change the thickness and separation starting point of the downstream boundary layer, and improving the flow field quality at the combustion chamber inlet.

[0015] Furthermore, the high-temperature air flow contains active free radical groups, and the active free radical groups enter the combustion chamber along with the high-temperature air flow to form a chain reaction synergistic effect with the main fuel, shortening the ignition delay time of the main fuel.

[0016] Furthermore, the temperature of the high-temperature air flow is greater than 30% of the total temperature of the incoming flight flow.

[0017] The present invention also provides a method for suppressing asymmetric combustion in a scramjet engine, including the following steps: releasing and igniting auxiliary fuel inside the isolation section of the engine, thereby forming a high-temperature air flow with a temperature greater than 3000K upstream of the head shock of the shock wave train, and using the high-temperature air flow and the heat it carries to change the thickness and separation starting point of the downstream boundary layer, and improving the flow field quality at the combustion chamber inlet.

[0018] Furthermore, the auxiliary fuel generates active free radical groups during combustion, and the active free radical groups enter the combustion chamber along with the high-temperature air flow to form a chain reaction synergistic effect with the main fuel, shortening the ignition delay time of the main fuel.

[0019] Furthermore, the equivalence ratio of the auxiliary fuel is 0.05 - 0.15.

[0020] Furthermore, an auxiliary injection module is provided in the isolation section of the engine, and the auxiliary injection module is used to inject high-temperature air flow or auxiliary fuel into the inside of the isolation section, and the injection direction is perpendicular to the wall surface of the isolation section.

[0021] Furthermore, the auxiliary injection module includes a group of circumferentially symmetric injection units, and each injection unit can independently inject the high-temperature air flow.

[0022] Furthermore, a plurality of groups of the auxiliary injection modules are arranged along the flow direction in the isolation section, and a plurality of pressure sensors are arranged on the wall surface along the engine. The controller controls the opening and closing and the opening degree of each injection unit according to the pressure signals sent by the pressure sensors.

[0023] Furthermore, the auxiliary injection module further includes an igniter for igniting the auxiliary fuel.

[0024] The present application has the following beneficial effects compared with the prior art:

[0025] The embodiments of the present invention utilize the combustion of high-temperature air flow or auxiliary fuel to reconstruct the internal flow field in the isolation section, thereby improving the quality of the flow field at the inlet of the combustion chamber. Description of the Drawings

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained according to the provided drawings.

[0027] Figure 1 is the internal structure diagram of an existing scramjet engine;

[0028] Figure 2 is a schematic diagram of asymmetric combustion in the combustion chamber of an existing scramjet engine;

[0029] Figure 3 is a schematic diagram of symmetric combustion in the combustion chamber of the embodiment of the present invention;

[0030] Figure 4 is the different combustion conditions before and after releasing high-temperature air flow or releasing and igniting auxiliary fuel in the isolation section of the combustion chamber of the embodiment of the present invention;

[0031] The reference numerals in the drawings are respectively represented as follows:

[0032] 1 - isolation section; 11 - auxiliary injection module; 2 - combustion chamber; 21 - flame stabilizer; 22 - main injection module; 3 - tail nozzle. Detailed Embodiments

[0033] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] In order to suppress combustion asymmetry in the combustion chamber of a scramjet engine, the present application provides a method for suppressing combustion asymmetry in a scramjet engine, hereinafter referred to as the combustion asymmetry suppression method.

[0035] (First Embodiment, refer to Figure 3 )

[0036] The combustion asymmetry suppression method includes: releasing a certain flow rate of high-temperature gas at a predetermined position inside the isolator 1 of the engine, and using the gas flow and the heat carried by it to change the thickness and separation starting point of the downstream boundary layer.

[0037] The specific implementation form is as follows:

[0038] 1. The high-temperature gas flow inside the isolator 1 thickens the thickness of the boundary layer after its release position, thereby changing the separation characteristics of the boundary layer and achieving the purpose of actively controlling the shape of the shock train inside the isolator 1.

[0039] 2. The high-temperature gas flow inside the isolator 1 suppresses the asymmetric distortion of the shock train inside the isolator 1 under the condition of high Mach number incoming flow, weakens the asymmetric deflection of the core flow of the shock train at the end of the isolator 1, and finally achieves the purpose of improving the quality of the inlet flow field of the combustion chamber 2.

[0040] Preferably, the distance between the release position of the high-temperature gas flow and the inlet of the combustion chamber 2 is within the range of 30% to 80% of the length of the isolator 1. The specific distance can exceed this preferred range, but it should not cause the engine to fail to start.

[0041] The structure that can be used to release the high-temperature gas flow is: an auxiliary injection module 11 is provided in the isolator 1 of the engine, and the auxiliary injection module 11 is used to inject high-temperature gas flow into the inside of the isolator 1.

[0042] Preferably, in order to actively control the injection position of the high-temperature gas flow, the auxiliary injection module 11 includes a set of circumferentially symmetric injection units, and each injection unit can independently inject high-temperature gas flow, and the injection direction is perpendicular to the wall surface of the isolator 1.

[0043] Since the installation position of the injection unit is basically the same as the release position of the high-temperature air flow, preferably, the distance between the injection unit and the inlet of the combustion chamber 2 is within the range of 30% to 80% of the length of the isolation section 1. The specific distance can exceed this preferred range, but it should not cause the engine to fail to start.

[0044] Furthermore, in order to release a predetermined flow rate of high-temperature air flow to a predetermined position in the isolation section 1 in a timely and controllable manner, thereby reducing the possibility of the engine failing to start, multiple groups of auxiliary injection modules 11 are arranged along the flow direction in the isolation section 1, and several pressure sensors (not shown in the figure) are arranged on the wall surface along the engine. The controller controls the opening and closing and the opening degree of each injection unit according to the pressure signal sent by the pressure sensors, thereby controlling the release position and the release flow rate of the high-temperature air flow.

[0045] The specific steps include:

[0046] Step 1: The pressure sensors continuously monitor the wall pressures of the isolation section 1 and the combustion chamber 2. When the controller determines that the deviation between the wall pressures of the isolation section 1 and the combustion chamber 2 at the same flow direction position (such as the upper and lower wall pressure measurement points at the same flow direction position) is greater than a preset first threshold, it indicates that combustion asymmetry occurs in the combustion chamber 2. Among them, the position with an excessive pressure deviation inside the isolation section 1 is called the upstream deviation position, and the position with an excessive pressure deviation inside the combustion chamber 2 is called the downstream deviation position.

[0047] Step 2: Upstream of the upstream deviation position, all injection units at the same flow direction position inside the isolation section 1 are opened, or the opening degree of all injection units is increased, thereby thickening the thickness of the boundary layer after the injection units and suppressing the asymmetric distortion of the shock wave train inside the isolation section 1, and finally suppressing the combustion asymmetry in the combustion chamber 2.

[0048] Step 3: When the controller determines that the deviation between the wall pressures of the upstream deviation position and the downstream deviation position is less than a preset second threshold, it indicates that the combustion asymmetry in the combustion chamber 2 is successfully suppressed, and then step 2 is executed in reverse, closing the opened injection units or reducing the opening degree of the injection units.

[0049] In addition, in order to further suppress the asymmetric combustion in the combustion chamber 2, the method that can be adopted is: using methods such as pyrolysis, corona discharge, and plasma jet to form active free radical groups in the high-temperature air flow, and the active free radical groups enter the combustion chamber 2 along with the high-temperature air flow.

[0050] The specific manifestation is: the active free radical groups generated during the combustion of the auxiliary fuel form a chain reaction synergy with the subsequent main fuel (such as aviation kerosene), shortening the ignition delay time of the main fuel, thereby suppressing the generation of local rich fuel areas and lean fuel areas, and finally suppressing the asymmetric combustion in the combustion chamber 2.

[0051] (Second Embodiment, refer to Figure 3 )

[0052] The method for suppressing combustion asymmetry includes: releasing a certain flow rate of auxiliary fuel at a predetermined position inside the isolator 1 of the engine, and igniting the auxiliary fuel to form a high-temperature gas flow, and using the gas flow and the heat carried by it to change the thickness of the downstream boundary layer and the starting point of separation.

[0053] The specific implementation form is:

[0054] 1. The heat generated by the combustion of the auxiliary fuel in the isolator 1 thickens the thickness of the boundary layer after its release position, thereby changing the separation characteristics of the boundary layer and achieving the purpose of actively controlling the shape of the shock train in the isolator 1.

[0055] 2. The gas generated by the combustion of the auxiliary fuel in the isolator 1 suppresses the asymmetric distortion of the shock train in the isolator 1 under the condition of high Mach number incoming flow, weakens the asymmetric deflection of the core flow of the shock train at the end of the isolator 1, and finally achieves the purpose of improving the quality of the inlet flow field of the combustor 2.

[0056] Preferably, the distance between the release position of the auxiliary fuel and the inlet of the combustor 2 is within the range of 30% to 80% of the length of the isolator 1. The specific distance can exceed this preferred range, but it should not cause the engine to fail to start.

[0057] Preferably, the equivalence ratio of the auxiliary fuel is 0.05 to 0.15. The specific equivalence ratio can exceed this preferred range, but it should not cause the engine to fail to start.

[0058] In order to further suppress the asymmetric combustion in the combustor 2, the method that can be adopted is: releasing an auxiliary fuel that generates active free radical groups during combustion at a predetermined position inside the isolator 1 of the engine, and igniting the auxiliary fuel to form a high-temperature gas flow and active free radical groups.

[0059] The specific implementation form is: the active free radical groups enter the combustor 2 along with the high-temperature gas flow, and the active free radical groups form a chain reaction synergistic effect with the subsequent main fuel (such as aviation kerosene), shortening the ignition delay time of the main fuel, thereby suppressing the generation of local rich fuel areas and lean fuel areas, and finally achieving the suppression of asymmetric combustion in the combustor 2.

[0060] The auxiliary fuel can be selected as the same fuel as the main fuel for the operation of the engine.

[0061] Preferably, the auxiliary fuel is hydrogen. Hydrogen has a short ignition delay. When hydrogen is ejected from the isolator 1, it immediately undergoes a pre-combustion reaction with the oxygen in the incoming flow, and active free radical groups are generated during the combustion of hydrogen.

[0062] Preferably, the auxiliary fuel is ethylene, which has a long ignition delay. When ethylene is ejected from the isolator 1, it does not burn immediately, but burns at the leading shock wave of the shock wave train in the isolator.

[0063] The structure for releasing the auxiliary fuel can be: an auxiliary injection module 11 is provided in the isolator 1 of the engine, and the auxiliary injection module 11 is used to inject the auxiliary fuel into the interior of the isolator 1.

[0064] Preferably, in order to actively control the injection position of the high-temperature airflow, the auxiliary injection module 11 includes at least one set of circumferentially symmetric injection units, and each injection unit can independently inject the auxiliary fuel, and the injection direction is perpendicular to the wall surface of the isolator 1.

[0065] Optionally, the auxiliary injection module 11 further includes an igniter, which is used to actively ignite the auxiliary fuel released inside the isolator 1 when the auxiliary fuel injected by the auxiliary injection module 11 cannot achieve self-ignition.

[0066] Furthermore, in order to release the auxiliary fuel with a predetermined flow rate and a predetermined equivalence ratio to a predetermined position in the isolator 1 in a timely and controllable manner, thereby reducing the possibility of engine non-start, multiple sets of auxiliary injection modules 11 are arranged along the flow direction in the isolator 1, and several pressure sensors are arranged on the wall surface along the engine. The controller controls the opening and closing and the opening degree of each injection unit according to the pressure signal sent by the pressure sensor, so as to control the release position, release flow rate and equivalence ratio of the auxiliary fuel.

[0067] The specific steps are the same as those of the first embodiment and will not be repeated here.

[0068] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the embodiments of the present invention.

Claims

1. A method for suppressing asymmetric combustion in a scramjet engine, characterized in that: It includes the following steps: releasing high-temperature airflow upstream of the head shock of the shock train inside the isolator (1) of the engine, and using the high-temperature airflow to change the thickness and separation starting point of the downstream boundary layer, and improving the inlet flow field quality of the combustion chamber (2).

2. The method for suppressing asymmetric combustion in a scramjet engine according to claim 1, characterized in that: The high-temperature airflow contains active free radical groups, and the active free radical groups enter the combustion chamber (2) with the high-temperature airflow to form a chain reaction synergistic effect with the main fuel, shortening the ignition delay time of the main fuel.

3. The method for suppressing asymmetric combustion in a scramjet engine according to claim 1, characterized in that: The temperature of the high-temperature airflow is greater than 30% of the total flight incoming flow temperature.

4. A method for suppressing asymmetric combustion in a scramjet engine, characterized in that: It includes the following steps: releasing and igniting auxiliary fuel inside the isolator (1) of the engine, thereby forming high-temperature airflow upstream of the head shock of the shock train, and using the high-temperature airflow and the heat carried by it to change the thickness and separation starting point of the downstream boundary layer, and improving the inlet flow field quality of the combustion chamber (2).

5. The method for suppressing asymmetric combustion in a scramjet engine according to claim 4, characterized in that: The auxiliary fuel generates active free radical groups during combustion, and the active free radical groups enter the combustion chamber (2) with the high-temperature airflow to form a chain reaction synergistic effect with the main fuel, shortening the ignition delay time of the main fuel.

6. The method for suppressing asymmetric combustion in a scramjet engine according to claim 4, characterized in that: The equivalence ratio of the auxiliary fuel is 0.05 - 0.

15.

7. The method for suppressing asymmetric combustion in a scramjet engine according to any one of claims 1 - 6, characterized in that: An auxiliary injection module (11) is provided in the isolator (1) of the engine, and the auxiliary injection module (11) is used to inject high-temperature airflow or auxiliary fuel into the interior of the isolator (1), and the injection direction is perpendicular to the wall surface of the isolator (1).

8. The method for suppressing asymmetric combustion in a scramjet engine according to claim 7, characterized in that: The auxiliary injection module (11) includes a group of circumferentially symmetric injection units, and each injection unit can independently inject the high-temperature airflow or the auxiliary fuel.

9. The method for suppressing asymmetric combustion in a scramjet engine according to claim 8, characterized in that: A plurality of groups of the auxiliary injection modules (11) are arranged along the flow direction in the isolator (1), and a plurality of pressure sensors are arranged on the wall surface along the engine. The controller controls the opening and closing and the opening degree of each injection unit according to the pressure signals sent by the pressure sensors.

10. The method for suppressing asymmetric combustion in a scramjet engine according to claim 7, characterized in that: The auxiliary injection module (11) further includes an igniter, and the igniter is used to ignite the auxiliary fuel.

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