Ignition prediction method for a scramjet combustor

Abstract

The present invention discloses a method for predicting the ignition of a scramjet combustion chamber, belonging to the technical field of ignition prediction. The method comprises the following steps: numerically simulating the combustion chamber using a three-dimensional density-based steady-state injection; determining whether convergence conditions have been met; extracting flow field data of the combustion chamber after convergence; and calculating the residence time t of aviation kerosene microclusters in the ignition region based on the flow field data. z ; Calculate the ignition delay time t of the ignition area based on the flow field data c Calculate Da in the ignition area. Predict ignition conditions based on Da. The scramjet engine combustion chamber ignition prediction method of the present invention calculates Da based on injection field data and predicts ignition success based on the relationship between Da and 1. This helps adjust actual ignition conditions and improve ignition success rates. It can meet the ignition prediction needs of combustion chambers of various configurations.

Description

Technical Field

[0001] The present invention relates to the technical field of ignition prediction, and in particular to an ignition prediction method for a scramjet engine combustion chamber. Background Art

[0002] Scramjet engines, due to their ability to self-inhale during operation, require no additional oxidizer, and significantly reduce their mass, offer the advantages of high specific impulse and high speed. They are considered a highly promising power plant, a current hot topic of research in engineering, and are widely used. The performance of a scramjet engine hinges on the efficient operation of its supersonic combustor. During flight, the airflow velocity within the supersonic combustor can reach kilometers per second relative to the combustion chamber, and the fuel's residence time within the chamber is mere milliseconds. Complex hydrocarbon fuels, such as aviation kerosene, undergo fragmentation, atomization, and mixing upon entering the combustion chamber. This results in a long ignition delay, making ignition difficult. To ensure timely adjustments and stable ignition in scramjet engines, it is necessary to develop a criterion for determining ignition success.

[0003] The Damköhler number (Da) is a dimensionless number often used in flow and chemical coupling processes. It is defined as the ratio of the flow characteristic time to the chemical characteristic time in a system. Many scholars at home and abroad have used Da to characterize the stable combustion performance of scramjet engines and have proposed some calculation methods and empirical formulas for Da. For example, Rasmussen et al. fitted the correlation formula for Da under the condition of fuel injection at the trailing edge of the cavity based on experimental data, as shown in the following formula:

[0004]

[0005] where s L0 is the stoichiometric laminar combustion velocity, α0 is the thermal diffusivity, U oo is the incoming flow velocity, H is the cavity height, and m and n are empirical parameters.

[0006] The working process of a scramjet engine can be viewed as first forming a stable high-enthalpy flow field, then injecting fuel to form a stable injection field, and then the igniter works, and finally forming a combustion field. The Da calculated using the injection field data is reasonable. Summary of the Invention

[0007] The present invention aims to provide an ignition prediction method for a scramjet combustion chamber. The method calculates Da based on injection field data and predicts ignition success based on the relationship between Da and 1. This method helps adjust actual ignition conditions and improve the ignition success rate. The method can meet the needs of ignition prediction for combustion chambers of various configurations.

[0008] To achieve the above object, the present invention provides a method for predicting ignition of a scramjet combustion chamber, comprising the following steps:

[0009] S1. Numerical simulation of the combustion chamber using three-dimensional density-based steady-state injection;

[0010] S2, determine whether the convergence condition is met;

[0011] S3, after convergence, extract the flow field data of the combustion chamber;

[0012] S4. Calculate the residence time t of the aviation kerosene micro-clusters in the ignition area based on the flow field data. z ;

[0013] S5. Calculate the ignition delay time t of the ignition area based on the flow field data c ;

[0014] S6. Calculate Da of the ignition area,

[0015] S7. Predict the ignition condition based on Da.

[0016] Preferably, in said S1, the use of three-dimensional density-based steady-state injection to perform numerical simulation on the combustion chamber is specifically: using the SST k-ω turbulence model while considering the component transport model, setting boundary conditions, and performing numerical simulation on the combustion chamber.

[0017] Preferably, in S2, the convergence condition is: when the difference in mass flow rate between all combustion chamber inlets and combustion chamber outlets is less than 0.3% of the sum of all inlet flow rates, and the difference in mass flow rate between all aviation kerosene inlets and combustion chamber outlets is less than 1% of the sum of all aviation kerosene inlet flow rates.

[0018] Preferably, in said S3, the flow field data includes: the velocity corresponding to each grid unit in the ignition area, the mass-weighted average component distribution percentage in the ignition area, the temperature and pressure values.

[0019] Preferably, in said S4, the residence time t of the ignition area is z The calculation method is as follows: take N streamlines in the ignition area, calculate the residence time corresponding to each streamline, and the average residence time of N streamlines is the residence time t of the ignition area. z .

[0020] Preferably, the residence time corresponding to each streamline is: the integral of the inverse of the velocity component in the tangential direction of the streamline.

[0021] Preferably, in said S5, the ignition delay time t cThe calculation method is: import the mass-weighted average component distribution percentage, temperature and pressure values ​​in the ignition area into Chemkin-Pro software and use a closed homogeneous reactor combined with the chemical reaction mechanism of aviation kerosene to calculate it.

[0022] Preferably, in S7, the relationship between Da and 1 is compared to determine whether the ignition is successful; if Da is greater than or equal to 1, it is predicted that the ignition can be successful; if Da is less than 1, it is predicted that the ignition fails.

[0023] The advantages and positive effects of the scramjet engine combustion chamber ignition prediction method of the present invention are:

[0024] 1. The present invention calculates Da based on the data of the injection field and predicts whether the ignition is successful or not by comparing the size relationship between Da and 1, and the prediction accuracy is good.

[0025] 2. Adjusting the ignition conditions according to the prediction results of the present invention is beneficial to saving experimental costs and improving the ignition success rate.

[0026] 3. The ignition prediction method of the present invention can meet the need for predicting the success or failure of ignition in the combustion chamber of a scramjet engine of any configuration and has wide adaptability.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of the ignition prediction method for a scramjet engine combustion chamber according to the present invention;

[0029] Figure 2 Schematic diagram of the front view of the configuration and ignition area of ​​the scramjet engine model combustion chamber according to an embodiment of the present invention;

[0030] Figure 3 Schematic diagram of the configuration and ignition area of ​​the scramjet engine model combustion chamber according to an embodiment of the present invention;

[0031] Figure 4 This is the numerical simulation result of the three-dimensional density-based steady-state injection according to the embodiment of the present invention;

[0032] Figure 5 This is a schematic front view of a local streamline of an ignition area according to an embodiment of the present invention;

[0033] Figure 6 It is a schematic side view of the local streamline of the ignition area of ​​an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. In the event of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application. In order to accurately describe the technical content in this application and to accurately understand the present invention, the following explanations or definitions are given for the terms used in this specification before describing the specific embodiments:

[0036] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] like Figure 1 A method for predicting ignition of a scramjet combustion chamber comprises the following steps:

[0038] S1. Numerical simulation of the combustion chamber using three-dimensional density-based steady-state injection.

[0039] The combustion chamber was numerically simulated using a three-dimensional density-based steady-state injection system. Specifically, the SST k-ω turbulence model was employed, along with the species transport model. Boundary conditions were set based on the desired operating conditions. The combustion chamber inlet and outlet were pressure-controlled, and the fuel inlet was a mass flow inlet. The specific values ​​were determined based on the specific operating conditions, and the ambient pressure was set to 0 Pa. The combustion chamber was numerically simulated using the finite volume method, second-order upwind differencing, and implicit schemes using the existing Fluent software.

[0040] S2. Determine whether the convergence condition is met.

[0041] The convergence condition is that the difference in mass flow rate between all combustion chamber inlets and combustion chamber outlets is less than 0.3% of the sum of all inlet flows, and the difference in mass flow rate between all aviation kerosene inlets and combustion chamber outlets is less than 1% of the sum of all aviation kerosene inlet flows.

[0042] After the convergence condition is reached, the flow field data is extracted. If the convergence condition is not reached, the numerical simulation is continued until the convergence condition is reached.

[0043] S3. After convergence, the flow field data of the combustion chamber is extracted.

[0044] The flow field data include: the velocity corresponding to each grid cell in the ignition area, the mass-weighted average component distribution percentage in the ignition area, the temperature and pressure values.

[0045] First, the combustion chamber is divided into ignition zones based on the selected ignition method and location. The velocity corresponding to each grid cell within the ignition zone is then determined. The mass-weighted average component distribution percentages, temperature, and pressure values ​​within the ignition zone are then obtained. In the post-processing software Tecplot, value blanking is used to hide the portion of the ignition zone removed. The mass-weighted average function in Perform Integration is then used to obtain the mass-weighted average component distribution percentages, temperature, and pressure values ​​for the corresponding region.

[0046] S4. Calculate the residence time t of the aviation kerosene micro-clusters in the ignition area based on the flow field data. z .

[0047] Dwell time t in the ignition area z The calculation method is as follows: take N streamlines in the ignition area, calculate the residence time corresponding to each streamline, and the average residence time of N streamlines is the residence time t of the ignition area. z .

[0048] The residence time corresponding to each streamline is: the integral of the inverse of the velocity component in the tangential direction of the streamline.

[0049] S5. Calculate the ignition delay time t of the ignition area based on the flow field data c .

[0050] Ignition delay time t cThe calculation method is to import the mass-weighted average component distribution percentage, temperature, and pressure values ​​within the ignition region into Chemkin-Pro software and calculate using a closed homogeneous batch reactor combined with the chemical reaction mechanism of aviation kerosene. The chemical reaction mechanism of aviation kerosene describes the components present during the kerosene reaction process, their corresponding reactions, and thermodynamic properties. In this example, the 44-component, 78-step reaction mechanism of kerosene is used.

[0051] S6. Calculate Da of the ignition area. Dwell time t z Divide by the ignition delay time t c Get the Da of the ignition area,

[0052] S7. Predict the ignition condition based on Da.

[0053] Compare Da with 1 to determine whether the ignition is successful. If Da is greater than or equal to 1, it is predicted that the ignition will be successful; if Da is less than 1, it is predicted that the ignition will fail.

[0054] Example

[0055] This embodiment takes the model combustion chamber under Ma6 working condition as an example to specifically describe the ignition prediction method for the scramjet engine combustion chamber.

[0056] Figure 2 Schematic diagram of the configuration and ignition area of ​​the scramjet engine model combustion chamber according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the configuration of the scramjet engine model combustion chamber and the ignition area from above. As shown in the figure, the coordinates of the ignition area are -5mm. <X<5mm,470mm<Y<480mm,Z<10mm。

[0057] Figure 4 This is the numerical simulation result of the three-dimensional density-based steady-state injection of the embodiment of the present invention. Figure 4 As shown in the figure, the temperature, pressure, velocity and aviation kerosene component distribution percentage of each grid cell in the ignition area can be obtained from the three-dimensional density-based steady-state injection numerical simulation results. The temperature in the ignition area is 802.4257K, the pressure is 37895.14Pa, and the average composition in the area is 33.9% C 12 H 23 , 15.2% O2 and 50.9% N2.

[0058] Figure 5 This is a schematic front view of the local streamlines of the ignition area according to an embodiment of the present invention. Figure 6This is a schematic side view of local streamlines in the ignition region according to an embodiment of the present invention. As shown in the figure, five streamlines within the ignition region were selected. The residence time of the jet fuel pellets on each streamline was calculated by integrating the inverse of the tangential component of the velocity along each streamline. The residence time for each of the five streamlines was then averaged to obtain the final residence time.

[0059] The five streamlines are calculated to have residence times of 1.3196e-5s, 1.3251e-5s, 9.0868e-6s, 1.2927e-5s and 1.4124e-5 respectively. The average residence time t z is 1.2517e-5s.

[0060] Initial fuel C 12 H 23 The mass fraction is 73% of n-dodecane, 14.7% of 1,3,5-trimethylcyclohexane, and 12.3% of n-propylbenzene. The temperature in the ignition area is 802.4257K, the pressure is 37895.14Pa, and the average composition in the area is 33.9%. 12 H 23 , 15.2% O2 and 50.9% N2 were imported into Chemkin-Pro to obtain the ignition delay time t c It is 0.685s.

[0061] The calculation yields Da = 1.2517e-5 / 0.685 = 1.8273e-5.

[0062] If the calculated value of Da is less than 1, the ignition prediction fails. Adjust the ignition conditions, repeat the above steps, and perform the ignition prediction again.

[0063] Therefore, the scramjet engine combustion chamber ignition prediction method of the present invention calculates Da based on injection field data, and predicts ignition success based on the relationship between Da and 1. This helps to adjust the actual ignition conditions and improve the ignition success rate. It can meet the needs of ignition prediction for combustion chambers of various configurations.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for predicting ignition of a scramjet combustion chamber, characterized in that: The following steps are involved: S1. Numerical simulation of the combustion chamber using three-dimensional density-based steady-state injection; S2, determine whether the convergence condition is met; S3, after convergence, extract the flow field data of the combustion chamber; S4. Calculate the residence time t of the aviation kerosene micro-clusters in the ignition area based on the flow field data. z ; S5. Calculate the ignition delay time t of the ignition area based on the flow field data c ; S6. Calculate Da of the ignition area, S7. Predict the ignition condition based on Da.

2. The method for predicting ignition of a scramjet combustion chamber according to claim 1, characterized in that: In S1, the three-dimensional density-based steady-state injection is used to perform numerical simulation of the combustion chamber. Specifically, the SST k-ω turbulence model is used while considering the component transport model, boundary conditions are set, and the combustion chamber is numerically simulated.

3. The method for predicting ignition of a scramjet combustion chamber according to claim 2, wherein: In S2, the convergence condition is: when the difference in mass flow rate between all combustion chamber inlets and combustion chamber outlets is less than 0.3% of the sum of all inlet flow rates, and the difference in mass flow rate between all aviation kerosene inlets and combustion chamber outlets is less than 1% of the sum of all aviation kerosene inlet flow rates.

4. The method for predicting ignition of a scramjet combustion chamber according to claim 3, wherein: In S3, the flow field data includes: the velocity corresponding to each grid cell in the ignition area, the mass-weighted average component distribution percentage in the ignition area, the temperature and pressure values.

5. The method for predicting ignition of a scramjet combustion chamber according to claim 4, characterized in that: In the above S4, the residence time t of the ignition area z The calculation method is as follows: take N streamlines in the ignition area, calculate the residence time corresponding to each streamline, and the average residence time of N streamlines is the residence time t of the ignition area. z .

6. The method for predicting ignition of a scramjet combustion chamber according to claim 5, characterized in that: The residence time corresponding to each streamline is: the integral of the inverse of the velocity component in the tangential direction of the streamline.

7. The method for predicting ignition of a scramjet combustion chamber according to claim 6, characterized in that: In the above S5, the ignition delay time t c The calculation method is: import the mass-weighted average component distribution percentage, temperature and pressure values ​​in the ignition area into Chemkin-Pro software and use a closed homogeneous reactor combined with the chemical reaction mechanism of aviation kerosene to calculate it.

8. The method for predicting ignition of a scramjet combustion chamber according to claim 7, characterized in that: In S7, the relationship between Da and 1 is compared to determine whether the ignition is successful; if Da is greater than or equal to 1, it is predicted that the ignition can be successful; if Da is less than 1, it is predicted that the ignition fails.

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