Ignition prediction method for combustion chamber of scramjet engine

Abstract

The invention discloses an ignition prediction method for a scramjet engine combustion chamber, and belongs to the technical field of ignition prediction. The ignition prediction method for the combustion chamber of the scramjet engine comprises the following steps that numerical simulation is conducted on the combustion chamber through three-dimensional density-based steady-state injection; judging whether a convergence condition is met; extracting flow field data of the combustion chamber after convergence; the residence time tz of the aviation kerosene micelles in the ignition area is calculated according to the flow field data; the ignition delay time tc of the ignition area is calculated according to the flow field data; and calculating the Da of the ignition area. And predicting the ignition condition according to the Da. According to the ignition prediction method for the combustion chamber of the scramjet engine, Da is calculated according to injection field data, whether ignition succeeds or not is predicted according to the size relation between Da and 1, the actual ignition working condition can be adjusted, and the ignition success rate is increased; and ignition prediction requirements of combustion chambers of various configurations can be met.

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] Since scramjet engines can inhale air by themselves during operation, do not require additional oxidizers, and can greatly reduce their own mass, they have the advantages of high specific impulse and high speed. They are considered to be a power device with great development prospects. They are currently a hot topic in the field of engineering research and are widely used. The performance of scramjet engines depends on whether the supersonic combustion chamber can operate efficiently. During flight, the air flow velocity in the supersonic combustion chamber can reach kilometers per second relative to the combustion chamber, and the residence time of the fuel in the combustion chamber is only in the millisecond range. Complex hydrocarbon fuels represented by aviation kerosene need to undergo processes such as fragmentation, atomization, and mixing after entering the combustion chamber. The ignition delay time is long, which makes it difficult to ignite the combustion chamber. In order to be able to make timely adjustments and achieve stable ignition of scramjet engines, it is necessary to propose a criterion for judging whether the ignition is successful or not.

[0003] The Damköhler number (Da) is a dimensionless number often used in the flow and chemical coupling process, which is defined as the ratio of the flow characteristic time to the chemical characteristic time in the system. Many scholars at home and abroad use 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 of Da under the condition of fuel injection at the trailing edge of the cavity through experimental research data, as shown in the following formula,

[0004]

[0005] where s L0 is the stoichiometric laminar combustion velocity, α0 is the thermal diffusion coefficient, 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 to form a combustion field. The Da calculated using the injection field data is reasonable. Summary of the invention

[0007] The purpose of the present invention is to provide an ignition prediction method for a scramjet combustion chamber, which calculates Da based on injection field data and predicts whether the ignition is successful or not based on the relationship between Da and 1, which helps to adjust the actual ignition conditions and improve the ignition success rate; and can meet the needs of ignition prediction for combustion chambers of various configurations.

[0008] To achieve the above object, the present invention provides an ignition prediction method for 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, extracting the flow field data of the combustion chamber after convergence;

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

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

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

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

[0016] Preferably, in S1, the three-dimensional density-based steady-state injection is used to perform numerical simulation on the combustion chamber, 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 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 the 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 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 the Chemkin-Pro software and use a closed homogeneous reactor combined with the aviation kerosene chemical reaction mechanism 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 ignition prediction method for the scramjet combustion chamber 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 a scramjet combustion chamber 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 It is a flow chart of the ignition prediction method of the scramjet engine combustion chamber of the present invention;

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

[0030] Figure 3 A schematic top view of the configuration and ignition area of ​​a scramjet engine model combustion chamber according to an embodiment of the present invention;

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

[0032] Figure 5 It 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 streamlines 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", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly 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 it can be an indirect connection through an intermediate medium, or it can be a connection between the 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 those commonly understood by technicians in the technical field of this application. 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 the present application and are not intended to limit the present 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 to the terms used in this specification before describing the specific embodiments:

[0036] The embodiments of the present invention are described in detail below in conjunction with 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 three-dimensional density-based steady-state injection is used to numerically simulate the combustion chamber. Specifically, the SST k-ω turbulence model is used while considering the species transport model (Species Transport), and the boundary conditions are set according to the required working conditions. The boundary conditions include: the combustion chamber inlet is a pressure inlet, the outlet is a pressure outlet, and the fuel inlet is a mass flow inlet. The specific values ​​are determined according to the specific working conditions, and the ambient pressure is set to 0Pa. The combustion chamber is numerically simulated. The existing Fluent software is used for finite volume method, second-order upwind difference, and implicit format simulation.

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

[0041] 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.

[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 unit in the ignition area, the mass-weighted average component distribution percentage in the ignition area, the temperature and pressure values.

[0045] First, the ignition area is divided in the combustion chamber according to the selected ignition method and position, and the corresponding velocity of each grid unit in the ignition area is obtained. At the same time, the mass-weighted average component distribution percentage, temperature and pressure values ​​in the ignition area are obtained. In the post-processing software Tecplot, value blanking is used to hide the part without the ignition area, and then the Mass-weighted average in Perform Integration can be used to obtain the mass-weighted average component distribution percentage, temperature and pressure values ​​of the corresponding area.

[0046] S4. Calculate the residence time t of the aviation kerosene micro-groups 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 the 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 reciprocal of the velocity component in the tangential direction of the streamline.

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

[0050] Ignition delay time t cThe calculation method is: the mass weighted average component distribution percentage, temperature and pressure values ​​in the ignition area are imported into Chemkin-Pro software and calculated using a closed homogeneous batch reactor combined with the chemical reaction mechanism of aviation kerosene. The chemical reaction mechanism of aviation kerosene reflects the components that appear in the kerosene reaction process and their corresponding reactions and thermodynamic properties. In this embodiment, 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 situation based on Da.

[0053] Compare the relationship between Da and 1 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.

[0054] Example

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

[0056] Figure 2 FIG. 1 is a front view schematic diagram of the configuration and ignition area of ​​a scramjet engine model combustion chamber according to an embodiment of the present invention. Figure 3 The configuration of the scramjet engine model combustion chamber and the schematic top view of the ignition area of ​​the embodiment of the present invention. As shown in the figure, the coordinates of the ignition area are -5mm <X<5mm,470mm<Y<480mm,Z<10mm。

[0057] Figure 4 3D density-based steady-state injection numerical simulation results of the embodiment of the present invention. Figure 4 As shown in the figure, the temperature, pressure, velocity and distribution percentage of aviation kerosene components corresponding to each grid unit 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 a local streamline of the ignition area of ​​an embodiment of the present invention. Figure 6The schematic diagram of the side view of the local streamlines in the ignition area of ​​the embodiment of the present invention is shown in the figure. As shown in the figure, 5 streamlines in the ignition area are selected, and the residence time of the aviation kerosene micro-group in the ignition area on this streamline is obtained by integrating the reciprocal of the velocity in the tangential direction of each streamline. Then the residence time of the 5 streamlines is averaged to obtain the final residence time.

[0059] According to calculation, the residence time of the five streamlines in the area is 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% C 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] Calculation yields Da = 1.2517e-5 / 0.685 = 1.8273e-5.

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

[0063] Therefore, by adopting the ignition prediction method for the scramjet engine combustion chamber of the present invention, Da is calculated according to the injection field data, and the ignition success is predicted according to the size relationship between Da and 1, which is helpful to adjust the actual ignition conditions and improve the ignition success rate; and can meet the needs of ignition prediction of combustion chambers of various configurations.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution 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, extracting the flow field data of the combustion chamber after convergence; S4. Calculate the residence time t of the aviation kerosene micro-groups in the ignition area based on the flow field data z ; S5. Calculate the ignition delay time t of the ignition area according to the flow field data c ; S6. Calculate Da of the ignition area, S7. Predict the ignition situation 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 on 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, characterized in that: 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, characterized in that: In 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.

5. The method for predicting ignition of a scramjet combustion chamber according to claim 4, characterized in that: In 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 the 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 reciprocal 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 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 the Chemkin-Pro software and use a closed homogeneous reactor combined with the aviation kerosene chemical reaction mechanism 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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