Refined design method for heat insulation layer of combustion chamber

Abstract

The invention discloses a fine design method for a heat insulation layer of a combustion chamber, which comprises the following steps of: 1, preliminarily designing an engine scheme, and determining an ablation parameter and an ablation environment type of the combustion chamber of the engine; step 2, calculating an ablation rate estimated value and a heat insulation layer thickness estimated value by taking the basic heat insulation material as a reference in combination with the ablation parameters; the specific model selection of the heat insulation material in the combustion chamber is determined according to the ablation environment type and the ablation rate estimated value; and step 3, according to the refined ablation model, calculating an ablation rate design value of the thermal insulation material corresponding to each design area, and combining the ablation time to obtain a thermal insulation layer thickness design value of the corresponding design area. The problems that according to an existing common heat insulation layer thickness design method, the safety margin of a design result is large, the negative mass is increased, engine performance improvement is not facilitated, and the requirement for refined design is difficult to meet are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of adiabatic layer thickness design, and particularly relates to a refined design method for the adiabatic layer of a combustion chamber.

Background Art

[0002] The adiabatic layer in the engine combustion chamber faces a harsh ablation environment, and the main consumption methods include thermochemical ablation, gas flow erosion, particle erosion, etc. The ablation environments and exposure times of the adiabatic layers at different positions are different, resulting in large differences in ablation rates.

[0003] In addition, there are a wide variety of developed adiabatic material formulations, which can be classified into lightweight adiabatic materials and ablation-resistant adiabatic materials according to their properties. Lightweight adiabatic materials have a low density but poor ablation resistance; ablation-resistant adiabatic materials can withstand a harsh ablation environment but have a high density. There are large differences in the density and ablation resistance of different adiabatic materials.

[0004] The main goal of adiabatic layer design is to determine the thickness, while reducing the negative mass and ensuring the structural safety of the engine. Currently, the commonly used methods for designing the adiabatic layer thickness include referring to existing engine models or calculating the adiabatic layer thickness based on design experience and experimental data. However, these methods have great limitations. The design results often have a large safety margin, increasing the negative mass, which is not conducive to improving the engine performance and is also difficult to meet the refined design requirements.

[0005] Therefore, when conducting refined design of the adiabatic layer, not only factors such as temperature, pressure, and gas velocity need to be considered, but also ablation environment factors such as ablation time, particle erosion state, and ablation change trend need to be considered. In addition, it is necessary to make use of the advantages and avoid the disadvantages of different adiabatic materials to achieve refined design of the adiabatic layer under different ablation / erosion conditions, different ablation times, and different ablation positions.

Summary of the Invention

[0006] The purpose of the present invention is to provide a refined design method for the adiabatic layer of a combustion chamber to solve the problems that the design results of the commonly used existing adiabatic layer thickness design methods have a large safety margin, increase the negative mass, are not conducive to improving the engine performance, and are also difficult to meet the refined design requirements.

[0007] The present invention adopts the following technical solutions: A refined design method for the adiabatic layer of a combustion chamber, including the following:

[0008] Step 1. Initially design the engine scheme and determine the ablation parameters and ablation environment types of the engine combustion chamber;

[0009] Step 2. Combine the ablation parameters, and use the ablation rate and adiabatic layer thickness calculated with the basic adiabatic material as a reference as the ablation rate prediction value and adiabatic layer thickness prediction value;

[0010] Determine the specific type selection of the thermal insulation material in the combustion chamber according to the ablation environment type and the predicted ablation rate value;

[0011] Step 3. Divide the interior of the combustion chamber into different design regions according to different ablation environment types, different ablation parameters, and different types of thermal insulation materials;

[0012] Calculate the designed ablation rate value of the thermal insulation material corresponding to each design region according to the refined ablation model, and then obtain the designed thickness value of the thermal insulation layer for the corresponding design region in combination with the ablation time.

[0013] Furthermore, in Step 1, the content of the engine scheme includes propellant parameters and the geometric configuration of the engine combustion chamber. Calculate the ablation parameters of the combustion chamber according to the engine scheme. The ablation parameters include the temperature, pressure, gas flow velocity, and particle erosion parameters of the combustion chamber;

[0014] The ablation environment types in the combustion chamber are divided into gas-phase ablation environment, weak erosion ablation environment, and strong erosion ablation environment.

[0015] Furthermore, in Step 2, use the empirical formula to calculate the predicted ablation rate value, and then calculate the predicted thickness value of the thermal insulation layer;

[0016] Before selecting the thermal insulation material type, first determine whether the predicted thickness value of the thermal insulation layer meets the design requirements of the thermal structure in the geometric configuration of the combustion chamber; if not, return to Step 1 to redesign the engine scheme; if it meets, then select the thermal insulation material type.

[0017] Furthermore, the specific method for selecting the thermal insulation material type is as follows:

[0018] If the design region is a gas-phase ablation environment, then use lightweight thermal insulation material in this design region;

[0019] If the design region is a weak erosion ablation section and the predicted ablation rate value < 0.8 mm / s, then use lightweight thermal insulation material in this design region;

[0020] If the design region is a weak erosion ablation section and the predicted ablation rate value > 0.8 mm / s, then use ablation-resistant thermal insulation material in this design region;

[0021] If the design region is a strong erosion ablation section, then use ablation-resistant thermal insulation material in this design region.

[0022] Furthermore, the specific process for calculating the designed thickness value of the thermal insulation layer for each design region in Step 3 is as follows:

[0023] S3.1. Use the refined ablation model considering gas flow erosion to calculate the designed ablation rate value of the corresponding thermal insulation material and the thermal insulation layer temperature response in the design region where the gas-phase ablation environment is located under different ablation parameter conditions;

[0024] S3.2. Calculate the design values of the ablation rates and the temperature responses of the insulation layers of the corresponding insulation materials under different ablation parameter conditions in the design regions where the weak erosion ablation environment and the strong erosion ablation environment are located by using a refined ablation model considering particle erosion.

[0025] S3.3. Determine the corresponding ablation thicknesses according to the design values of the ablation rates and the corresponding ablation times of each design region, and then obtain the corresponding heat insulation thicknesses according to the temperature responses of the insulation layers of each design region.

[0026] Sum up the ablation thicknesses and the heat insulation thicknesses of each design region to obtain the calculated values of the insulation layer thicknesses of each design region.

[0027] Furthermore, perform other performance judgments on the calculated values of the insulation layer thicknesses obtained in step 3. If the other performance is not satisfied, return to step 2 to reselect the insulation material; the other performance includes the bonding performance, tensile performance, and aging performance of the insulation material.

[0028] Furthermore, when the calculated values of the insulation layer thicknesses obtained in step 3 satisfy the other performance, verify them by using a scaled-down engine:

[0029] Calculate the mass of the insulation layer according to the calculated value of the insulation layer thickness, and judge whether the mass of the insulation layer meets the requirements of the overall engine design index; if not, return to step 1 to redesign the engine scheme; if it meets the requirements, the calculated value of the insulation layer thickness is the final insulation layer thickness.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. By comprehensively considering various factors such as the actual working conditions of the engine, the ablation environment, and the performances of different insulation materials, the thickness of the insulation layer can be designed in a refined manner, reducing unnecessary safety margins, thereby reducing the negative mass, lowering the cost, and improving the performance and structural reliability of the engine.

[0032] 2. The design scheme can meet the requirements of different ablation environments, different insulation materials and their combinations, realizing flexible design; and through iterative design and integrated verification, problems can be quickly discovered and the design can be adjusted, improving the design efficiency. The insulation layer design method of the present invention can be applied to solid rockets.

[0033] 3. The present invention comprehensively considers the requirements of the insulation layer for the ablation thickness and the heat insulation thickness; and also considers the effects of the insulation layer on the propellant charging space, the combustion chamber configuration, the engine performance index, the bonding performance, and the tensile performance, etc., and can be iterated during the design process to meet various indexes and requirements.

Description of the Drawings

[0034] Figure 1This is the flowchart of the method of the present invention.

Specific Embodiments

[0035] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0036] The present invention provides a refined design method for the insulation layer of a combustion chamber. As Figure 1 shown, in the refined design of the insulation layer of the present invention, first, the operating conditions of the engine need to be determined, and then the ablation environment is estimated. According to different ablation environments and ablation rate estimates, the appropriate type of insulation material is selected, and the required thickness of the insulation layer is calculated. Then, the bonding performance of the insulation layer and the performance indicators of the engine are evaluated. Finally, the reliability of the design is ensured through integrated verification. The entire process is iterative and can be adjusted repeatedly to meet the design requirements.

[0037] Specifically, it includes the following contents:

[0038] Step 1. Initially design the engine scheme and determine the ablation parameters and ablation environment types of the engine combustion chamber;

[0039] Step 2. Combine the ablation parameters, and use the ablation rate and insulation layer thickness calculated with the basic insulation material as a reference as the ablation rate estimate and insulation layer thickness estimate;

[0040] Determine the specific selection of the insulation material in the combustion chamber according to the ablation environment type and the ablation rate estimate;

[0041] Step 3. Divide the interior of the combustion chamber into different design regions according to different ablation environment types, different ablation parameters, and different types of insulation materials;

[0042] Calculate the designed ablation rate of the insulation material corresponding to each design region according to the refined ablation model, and then obtain the designed thickness of the insulation layer of the corresponding design region in combination with the ablation time. The refined ablation model can calculate thermochemical ablation, pyrolysis gas flow and deposition, insulation layer expansion, and internal pressure failure. According to different ablation environments, it can be divided into a refined ablation model considering gas flow erosion and a refined ablation model considering particle erosion.

[0043] In some embodiments, in step 1, the content of the engine scheme includes propellant parameters and the geometric configuration of the engine combustion chamber. The propellant parameters include combustion temperature, burning rate, specific heat ratio, specific heat, molecular weight, aluminum content, and gas thermal conductivity; the engine geometric configuration refers to the engine size and shape, such as the propellant charge space and the combustion chamber configuration. The ablation parameters of the combustion chamber are calculated according to the engine scheme, and the ablation parameters include the temperature, pressure, gas flow velocity, and particle erosion parameters of the combustion chamber. Based on the research of ablation mechanism, the ablation environment types in the combustion chamber are divided into gas-phase ablation environment, weak erosion ablation environment, and strong erosion ablation environment.

[0044] Among them, gas-phase ablation is a pure gas-phase environment or a particle erosion environment with a very low concentration. At this time, the ablation of the thermal insulation material is mainly caused by thermal chemical reaction and gas flow erosion; weak erosion ablation refers to the situation where the particle incident velocity is relatively low and the ablation rate does not increase significantly; strong erosion ablation refers to the situation where the particle incident velocity is relatively high and the ablation rate suddenly increases. The wall particle concentration < 10 kg / m 3 can be considered as gas-phase ablation; if the wall particle concentration > 10 kg / m 3 , and the wall particle incident velocity > 26 m / s is considered as strong erosion ablation, otherwise it is considered as weak erosion ablation.

[0045] In some embodiments, in step 2, the basic thermal insulation material is a thermal insulation material with a density and ablation resistance performance between those of the lightweight thermal insulation material and the ablation-resistant thermal insulation material; the basic thermal insulation material is a widely used and performance-balanced thermal insulation material at present, and is often used as a benchmark to judge the effectiveness of other formulations, with a density and ablation resistance performance between those of the lightweight thermal insulation material and the ablation-resistant thermal insulation material. Generally speaking, the basic thermal insulation material is the EPDM conventional formulation, and the fillers added include aramid fiber, phenolic resin, fumed silica, zinc borate, etc., with a density of about 1 g / cm3. The lightweight thermal insulation material is foamed by adding expandable microspheres on the basis of the conventional formulation, with a density of 0.6 - 0.8 g / cm3. The ablation-resistant thermal insulation material is added with carbon-based reinforcing fillers such as carbon nanotubes and carbon fibers on the basis of the EPDM conventional formulation, with a density of 1.2 - 1.5 g / cm3.

[0046] The estimated ablation rate of the basic thermal insulation material is calculated using an empirical formula, and then the estimated thickness of the insulation layer is calculated. The empirical formula refers to the relational expression of the ablation rate with respect to the gas temperature, gas pressure, gas flow velocity, and particle erosion parameters obtained by fitting the engine experimental data.

[0047] Before selecting the thermal insulation material, first judge whether the estimated thickness of the insulation layer meets the design requirements of the thermal structure in the combustion chamber geometry; if not, return to step 1 to redesign the engine scheme, that is, re-determine the engine ablation parameters and ablation environment; if it meets, then select the thermal insulation material.

[0048] In some embodiments, the method for selecting the thermal insulation material is specifically as follows:

[0049] If the design area is a gas-phase ablation environment, lightweight thermal insulation material is used in this design area;

[0050] If the design area is a weak erosion ablation section and the predicted ablation rate < 0.8 mm / s, lightweight thermal insulation material is used in this design area;

[0051] If the design area is a weak erosion ablation section and the predicted ablation rate > 0.8 mm / s, ablation-resistant thermal insulation material is used in this design area;

[0052] If the design area is a strong erosion ablation section, ablation-resistant thermal insulation material is used in this design area.

[0053] Among them, the lightweight thermal insulation material has a low density and poor erosion resistance, and is suitable for gas-phase ablation and weak erosion ablation; among them, the ablation-resistant thermal insulation material has a slightly higher density and excellent erosion resistance, and can resist particle erosion in a strong erosion state. Generally speaking, the lightweight thermal insulation material is a conventional EPDM formula, and the fillers added are aramid fiber, phenolic resin, fumed silica, zinc borate, etc., and the density is 0.9 - 1 g / cm 3 . The ablation-resistant thermal insulation material is based on the conventional EPDM formula and also adds carbon-based reinforcing fillers such as carbon nanotubes and carbon fibers, and the density is 1.2 - 1.5 g / cm 3 .

[0054] In some embodiments, the specific process of calculating the design value of the thermal insulation layer thickness in each design area in step 3 is as follows:

[0055] S3.1. Use a refined ablation model considering gas flow erosion to calculate the ablation rate design value and the thermal insulation layer temperature response of the corresponding thermal insulation material in the design area where the gas-phase ablation environment is located under different ablation parameter conditions; the refined ablation model considering gas flow erosion can calculate gas-phase ablation;

[0056] S3.2. Use a refined ablation model considering particle erosion to calculate the ablation rate design value and the thermal insulation layer temperature response of the corresponding thermal insulation material in the design areas where the weak erosion ablation environment and the strong erosion ablation environment are located under different ablation parameter conditions; the refined ablation model considering particle erosion can calculate weak erosion ablation and strong erosion ablation;

[0057] S3.3. Determine the corresponding ablation thickness according to the ablation rate design value and the corresponding ablation time of each design area, and then obtain the corresponding heat insulation thickness according to the thermal insulation layer temperature response of each design area;

[0058] Sum up the ablation thickness and the heat insulation thickness of each design area, and the calculated value of the thermal insulation layer thickness of each design area can be obtained.

[0059] In some embodiments, the calculated values of the thicknesses of the respective thermal insulation layers obtained in step 3 are judged for other properties. If the other properties are not satisfied, return to step 2 to reselect the thermal insulation material; the other properties are the bonding property, tensile property, and aging property of the thermal insulation material.

[0060] In some embodiments, when the calculated values of the thicknesses of the respective thermal insulation layers obtained in step 3 satisfy the other properties, a scaled-down engine is used to verify it:

[0061] Calculate the mass of the thermal insulation layer according to the calculated value of the thermal insulation layer thickness, and judge whether the mass of the thermal insulation layer meets the requirements of the overall engine design index; if not, return to step 1 to redesign the engine scheme; if it meets, the calculated value of the thermal insulation layer thickness is the final thermal insulation layer thickness.

[0062] The following takes a simulated ablation engine as an example, and the specific steps include:

[0063] S1. Determine the ablation parameters of the engine: The simulated ablation engine mainly consists of a combustion chamber, a convergent section, a high-speed section, and a nozzle. It uses NEPE propellant, the gas temperature is 3720K, the designed pressure is 7MPa, and the engine operating time is 9.7s. The cross-section of the combustion chamber is a circle with a diameter of 200mm, the cross-section of the high-speed section is a square of 40mm×40mm, the gas flow velocity in the combustion chamber is 5.5m / s, and the gas flow velocity in the high-speed section is 65.5m / s. It can achieve the ablation assessment of two erosion speeds in a real engine environment. There is no high-concentration particle aggregation in this ablation environment, so the ablation environment is considered to be gas-phase ablation.

[0064] S2. Estimate the ablation rate: Taking the basic thermal insulation material as a reference, the ablation rate is estimated using the following empirical formula (1). Substituting the engine ablation parameters, the pre-estimated values of the ablation rates of the combustion chamber and the high-speed section are 0.18mm / s and 0.48mm / s respectively. At this time, the pre-estimated values of the thermal insulation layer thicknesses are 1.746mm and 4.656mm respectively. It meets the thermal structure design requirements such as the propellant charging space and the combustion chamber configuration.

[0065]

[0066] In the formula, r is the ablation rate, u is the gas flow velocity, T is the gas temperature, and P is the engine operating pressure.

[0067] Since the pre-estimated value of the thermal insulation layer thickness meets the thermal structure design requirements in the combustion chamber geometry, and this ablation environment is gas-phase ablation, a lightweight thermal insulation material is used in this design area. Specifically, a typical EPDM thermal insulation material is selected, and the fillers mainly include aramid fiber, phenolic resin, fumed silica, and zinc borate, etc.

[0068] S3. Calculate the thickness of the insulation layer: The ablation environment is gas-phase ablation. Therefore, the designed ablation rates of the combustion chamber and the high-speed section obtained by using the gas flow erosion model are 0.16 mm / s and 0.5 mm / s respectively. The insulation thickness of the insulation layer is calculated by the following empirical formula (2), and the insulation thickness is obtained as 1.98 mm. Therefore, the designed thicknesses of the insulation layers of the combustion chamber and the high-speed section are finally determined to be 3.532 mm and 6.83 mm respectively.

[0069] d = 0.503t 0.604 (2),

[0070] where d is the insulation thickness and t is the engine operating time.

[0071] S4. Examine other properties of the insulation layer: In this simulated ablation engine experiment, the insulation material is fixed by a T-shaped slot. It is only used for ablation verification and does not involve other properties of the insulation layer. Therefore, this step is skipped.

[0072] S5. Integrated verification: An engine ablation experiment is carried out. The measured ablation rates of the combustion chamber and the high-speed section are 0.16 mm / s and 0.47 mm / s respectively, and the ablation thicknesses are 1.552 mm and 4.559 mm respectively, both of which are less than the designed thickness of the insulation layer, meeting the engine design requirements. This simulated ablation engine experiment is only a ground-based ablation assessment experiment and does not involve the overall design index requirements of the engine.

Claims

1. A refined design method for a combustion chamber insulation layer, characterized in that: Includes the following: Step 1. Preliminary design of the engine scheme and determination of the ablation parameters and ablation environment type of the engine combustion chamber; Step 2. In combination with the ablation parameters, the ablation rate and the insulation layer thickness calculated with reference to the basic insulation material are used as the ablation rate estimate and the insulation layer thickness estimate; Determine the specific selection of the thermal insulation material in the combustion chamber according to the ablation environment type and the ablation rate estimate; Step 3. Divide the interior of the combustion chamber into different design areas according to different ablation environment types, different ablation parameters and different types of thermal insulation materials; The ablation rate design value of the insulation material corresponding to each design area is calculated according to the refined ablation model, and then combined with the ablation time to obtain the insulation layer thickness design value of the corresponding design area.

2. A refined design method for a combustion chamber insulation layer according to claim 1, characterized in that: In step 1, the contents of the engine scheme include propellant parameters and the geometric configuration of the engine combustion chamber, and the ablation parameters of the combustion chamber are calculated according to the engine scheme, wherein the ablation parameters include the temperature, pressure, airflow velocity and particle scouring parameters of the combustion chamber; The ablation environment types in the combustion chamber are divided into gas phase ablation environment, weak erosion ablation environment and strong erosion ablation environment.

3. A refined design method for a combustion chamber insulation layer as claimed in claim 2, characterized in that: In the step 2, the estimated value of the ablation rate is calculated using an empirical formula, and then the estimated value of the thickness of the thermal insulation layer is calculated; Before selecting the insulation material, first determine whether the estimated thickness of the insulation layer meets the design requirements of the thermal structure in the geometric configuration of the combustion chamber; if not, return to step 1 to redesign the engine solution; if so, select the insulation material.

4. A refined design method for a combustion chamber insulation layer as claimed in claim 3, characterized in that: The method for selecting the thermal insulation material is specifically as follows: If the design area is a gas phase ablation environment, lightweight insulation materials are used in the design area; The design area is a weak erosion and ablation section, and the estimated ablation rate is <0.8 mm / s, so lightweight insulation materials are used in the design area; The design area is a weak erosion and ablation section, and the estimated ablation rate is greater than 0.8 mm / s, then the design area adopts ablation-resistant insulation material; If the designed area is a strong erosion and ablation section, then ablation-resistant insulation material is used in the designed area.

5. A refined design method for a combustion chamber insulation layer as claimed in claim 4, characterized in that: The specific process of calculating the design value of the insulation thickness of each design area in step 3 is: S3.

1. Calculate the design area where the gas phase ablation environment is located by using a refined ablation model that takes into account airflow erosion, and the corresponding ablation rate design value of the insulation material and the temperature response of the insulation layer under different ablation parameter conditions; S3.

2. Calculate the design value of the ablation rate of the corresponding insulation material and the temperature response of the insulation layer under different ablation parameter conditions in the design area where the weak scour ablation environment and the strong scour ablation environment are located using a refined ablation model that takes into account particle erosion; S3.3, determining the corresponding ablation thickness according to the ablation rate design value and the corresponding ablation time of each design area, and then obtaining the corresponding insulation thickness according to the insulation layer temperature response of each design area; The ablation thickness and the insulation thickness of each design area are summed to obtain the calculated value of the insulation layer thickness of each design area.

6. A refined design method for a combustion chamber insulation layer as claimed in claim 5, characterized in that: The calculated values ​​of the thickness of each insulation layer obtained in step 3 are judged for other properties. If the other properties are not satisfied, return to step 2 to reselect the insulation material; the other properties are the adhesion, tensile and aging properties of the insulation material.

7. A refined design method for a combustion chamber insulation layer as claimed in claim 6, characterized in that: When the calculated values ​​of the thickness of each insulation layer obtained in step 3 meet the other performance requirements, a scaled engine is used to verify the calculated values: The mass of the insulation layer is calculated according to the calculated value of the insulation layer thickness to determine whether the mass of the insulation layer meets the overall design index requirements of the engine; if not, return to step 1 and redesign the engine solution; if so, the calculated value of the insulation layer thickness is the final insulation layer thickness.

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