A method of active cooling applied to an engine

Abstract

The present application relates to a kind of active cooling method applied to engine, comprising: one, establish the active thermal protection theory analysis model suitable for oblique knock engine;Two, preliminary determination active thermal protection theory analysis model parameter;Three, load heat flow condition, active thermal protection theory analysis model is carried out active cooling simulation analysis, obtains coolant temperature distribution;Four, confirm whether coolant temperature distribution satisfies the upper limit requirement of coolant temperature and the use requirement of solid wall material temperature, if satisfy, enter step six, if not satisfy, enter step five;Five, change active thermal protection theory analysis model parameter, repeat step three-four;Six, the rectangular cooling channel of local high heat flow area is modified to cooling channel configuration with different bending structure, until meet the demand;Seven, according to the active thermal protection theory analysis model and parameter of final processing active thermal protection structure.The present application solves the heat protection problem of oblique knock engine structure.

Description

Technical Field

[0001] This invention belongs to the field of detonation force and relates to an active cooling method for engines. Background Technology

[0002] The oblique detonation engine is a highly promising power type that is expected to extend air-breathing power to higher Mach numbers. It features high operating speed, high specific impulse, and small size, and is a potential power type for future horizontal take-off and landing aerospace vehicles. It is an important development direction for cutting-edge power technology.

[0003] Currently, research on oblique detonation engine technology is in its early stages. Related studies mainly focus on stable combustion and detonation stabilization under ultra-high-speed flow, and systematic research has not yet been carried out on thermal protection for macromolecular hydrocarbon fuel engines during long-term operation.

[0004] Compared to the external thermal protection issues that primarily rely on passive thermal protection in flight, internal thermal protection for engines faces the challenge of preventing structural ablation and damage in aerobic environments with high total temperature and high heat flux. Regenerative cooling using engine fuel as a coolant is currently a widely adopted cooling method for high Mach number air-breathing engines. However, current active cooling systems for air-breathing engines are mainly applied at Mach 6 and have not yet been extended to Mach 8 and above.

[0005] Compared to traditional ramjet engines, oblique detonation engines operate at higher Mach numbers and have higher combustion efficiency. The combined effects of aerodynamic heating and combustion heat release significantly increase the difficulty of thermal protection, especially given the oblique detonation engine's detonation wedge structure. This structure features high heat flux within a small space, resulting in extremely high local heat flux peaks and uneven heat flux distribution, further complicating thermal protection. Oblique detonation engines operate at speeds above Mach 8, requiring approximately 4.0 MJ / kg for heat sink. While large-molecule hydrocarbon fuels are currently the most commonly used fuels in engines, their heat sink capacity is only about 2.9–3.6 MJ / kg. This presents challenges for thermal protection, including insufficient available kerosene heat sinks and structural temperatures exceeding permissible limits. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose an active cooling method for engines.

[0007] The solution of the present invention is:

[0008] An active cooling method for an engine, the method comprising the following steps:

[0009] Step 1: Establish an active thermal protection theoretical analysis model suitable for oblique detonation engines. The active thermal protection theoretical analysis model includes a cooling plate and a wall plate with cooling channels. The cooling plate covers the thick wall plate, with the upper surface of the cooling plate being a hot wall and the lower surface being a cold wall. The cooling channels are multiple rectangular cooling channels evenly distributed along the flow direction.

[0010] Step 2: Preliminarily determine the parameters of the active thermal protection theoretical analysis model, including the materials of the cooling plate and wall panel, and design the dimensions of the rectangular cooling channel and the thickness of the cooling plate;

[0011] Step 3: Apply heat flux conditions as the thermal boundary input to the active thermal protection theoretical analysis model, and perform active cooling simulation analysis on the active thermal protection theoretical analysis model to obtain the coolant temperature distribution;

[0012] Step 4: Confirm whether the coolant temperature distribution and fuel temperature distribution meet the upper limit requirements of coolant temperature and the temperature requirements of solid wall material. If they meet the requirements, proceed to Step 6; otherwise, proceed to Step 5.

[0013] Step 5: Based on the active cooling simulation analysis results, modify the parameters of the active thermal protection theoretical analysis model and repeat steps 3-4.

[0014] Step 6: Modify the rectangular cooling channel in the local high heat flux area into a cooling channel configuration with different bending structures, and perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux area. If it does, proceed to Step 7; if it does not, continue to modify the cooling channel configuration in the local high heat flux area until the requirements are met.

[0015] Step 7: Fabricate the active thermal protection structure based on the final active thermal protection theoretical analysis model and parameters.

[0016] Preferably, the cooling sheet and the wall panel are connected by brazing or diffusion welding.

[0017] Preferably, the heat flow conditions in step three include three types of thermal boundary conditions in the local high heat flow peak region and three types of thermal boundary conditions in the engine internal flow channel;

[0018] The three types of thermal boundary conditions refer to the given wall heat flow conditions, the given wall temperature conditions, and the given total temperature and heat transfer coefficient of the fluid near the wall conditions.

[0019] Preferably, active cooling simulation analysis refers to performing gas-solid-liquid coupling calculations based on thermal boundary inputs, given the incoming flow and engine operating mode.

[0020] Preferably, the method for obtaining the coolant temperature distribution by performing active cooling simulation analysis on the active thermal protection theoretical analysis model in step three is as follows:

[0021] Establish the momentum and energy equations for coolant flow;

[0022] Solve for the heat flux loaded on the hot wall surface corresponding to each cooling channel;

[0023] Solve for the convective heat transfer generated by the flow within each cooling channel;

[0024] Calculate the total heat absorbed by the coolant;

[0025] The distribution of hot wall temperature, cold wall temperature, and coolant temperature along the path was obtained from the active thermal protection theoretical analysis model.

[0026] Preferably, the heat flow Q applied to the hot wall surface of each cooling channel within time t is... w1 satisfy:

[0027]

[0028] q w The heat flux density distribution on the hot wall surface is given by W, the total width of the cooling structure is given by L, and the total length of the cooling structure is given by T. w1 T is the hot wall temperature. w2 K represents the cold wall temperature. w Let dx be the thermal conductivity of the cooling plate, and dx be the length of each micro-element. Each cooling channel is divided into several micro-elements; the cooling structure is the theoretical analysis model of active thermal protection.

[0029] Preferably, heat flow is applied to all four sides of each cooling channel, and the convective heat transfer of the coolant flowing within each dx is Qw. cool satisfy

[0030] Qw cool =N*dx*(h2+s / 2)*η f h f (Tw2-T f )+N*dx*h1*(Tw2-T f )

[0031] N is the total number of cooling channels, h1 is the cross-sectional width of the cooling channel, h2 is the cross-sectional height of the cooling channel, s is the distance between the adjacent walls of two adjacent cooling channels, and h f T is the convective heat transfer coefficient. f η is the coolant temperature. f This is a correction factor.

[0032] Preferred,

[0033]

[0034] th() is the hyperbolic tangent function, and H is the equivalent length of the solid wall portion between adjacent cooling channels.

[0035] Preferably, the total heat absorbed by the coolant, Q w2 satisfy

[0036]

[0037] This is the chemical endothermic reaction of kerosene cracking.

[0038] Preferably, the coolant is kerosene.

[0039] The advantages of this invention compared to the prior art are:

[0040] (1) This invention matches the different structural characteristics of the internal flow channel and local structure of the engine, and optimizes the channel size parameters by combining gas-solid-liquid coupling simulation analysis. It establishes a new cooling structure optimization design method, which effectively enhances the convective heat transfer effect in the high heat flow zone and reduces the structural temperature.

[0041] (2) This invention designs a feasible regenerative cooling scheme and a universal design process for kerosene-fueled oblique detonation engines with Ma8 and above, initially solving the problem of heat protection of oblique detonation engine structure, and at the same time providing a technical basis for expanding its application to other high Mach number air-breathing engines. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of an active thermal protection theoretical analysis model;

[0043] Figure 2 A schematic diagram of the equivalent "ribs" of the cooling structure;

[0044] Figure 3 The diagram shows the distribution of cooling structure and coolant temperature, coolant convective heat transfer coefficient, pressure and flow velocity along the flow path, where (a) is the temperature distribution, (b) is the convective heat transfer coefficient distribution, (c) is the pressure distribution, and (d) is the flow velocity distribution.

[0045] Figure 4 The following are the cooling channel design and heat transfer analysis results in the embodiments, where (a) is the cooling channel design for a local high heat flux region such as a wedge structure, and (b) is the heat transfer analysis result for a local high heat flux region such as a wedge structure. Detailed Implementation

[0046] The invention will now be further described with reference to the accompanying drawings.

[0047] This invention provides an active cooling method for enhanced heat transfer in local high heat flux regions, achieving the thermal protection requirements of the oblique detonation engine structure and providing a technical basis for supporting the long-term operation of the oblique detonation engine.

[0048] The steps of this invention are as follows:

[0049] Step one: Establish an active thermal protection theoretical analysis model suitable for oblique detonation engines. This model includes a thin cooling plate and a wall plate with machined cooling channels. The thin cooling plate covers the thick wall plate; the upper surface of the thin cooling plate, the side in contact with the high-temperature combustion gas, is the hot wall, and the lower surface is the cold wall. The cooling channels are multiple rectangular cooling channels evenly distributed along the flow direction. Figure 1 As shown. The active thermal protection theoretical analysis model will be referred to as the cooling structure below.

[0050] Step 2: Initially determine the parameters of the active thermal protection theoretical analysis model, including the materials of the cooling plate and wall panel, and design the dimensions of the rectangular cooling channel and the thickness of the cooling plate.

[0051] Step 3: Apply heat flow conditions as the thermal boundary input to the active thermal protection theoretical analysis model, and perform active cooling simulation analysis on the active thermal protection theoretical analysis model to obtain the coolant temperature distribution.

[0052] For the flow of coolant in each cooling channel, a steady-state one-dimensional mass, momentum and energy conservation equation is established. Based on the heat transfer process, the coolant velocity, temperature and density distributed along the flow direction are obtained by differentially solving the physical parameters at discrete points along the flow direction.

[0053] (1) The momentum equation is as follows:

[0054]

[0055] in, For coolant flow rate, A f Let ρ be the cross-sectional area of ​​the channel, and dx be the length of each micro-element, set to 0.0001m; each cooling channel is divided into several micro-elements. f u f These represent coolant density and velocity, respectively; p f τ is the pressure of kerosene. w The shear stress on the cold wall surface can be determined using the friction formula; G is the perimeter of the cooling channel cross section, i.e., G = 2(h1 + h2).

[0056] (2) The energy equation is as follows:

[0057]

[0058] Where h is the enthalpy of the coolant, u is the flow rate of the coolant, and the subscript f indicates the coolant. This refers to the convective heat transfer generated by the coolant flowing within the channel and interacting with the wall.

[0059] In addition, the coefficient of friction C f With τw The relation is: The friction coefficient can be calculated using the classical Prandtl formula or determined based on a relationship fitted from kerosene experimental data.

[0060] The Prandtl formula is: C f =0.046Re -0.2 (3)

[0061] The fitting relationship is: C f =0.046Re -0.2 (μ f / μ w ) -0.25 (4)

[0062] (3) Heat flow is first conducted through the cooling plate, and then absorbed by the coolant in the cooling channel. The heat flow rate loaded on the hot wall surface of each micro-element can be solved by the one-dimensional heat conduction equation:

[0063]

[0064] Among them, Q w1 Let W be the heat flux loaded onto the hot wall surface within each micro-element, W be the total width of the cooling structure, L be the total length of the cooling structure, and T be the total heat flux loaded onto the hot wall surface within each micro-element. w1 T is the hot wall temperature. w2 K represents the cold wall temperature. w Let dx be the thermal conductivity of the cooling plate, and dx be the length of each micro-element. Each cooling channel is divided into several micro-elements.

[0065] (4) The mechanism by which fuel absorbs structural heat in the cooling channel consists of two parts:

[0066] (i) Convective heat transfer generated by flow, especially turbulence, within the cooling channel.

[0067] at this time:

[0068]

[0069] Where h f T is the convective heat transfer coefficient. f This refers to the temperature of the kerosene.

[0070] The convective heat transfer coefficient can be calculated using the classic Sider-Tate formula, as shown below:

[0071] Nu = 0.027Re 0.8 Pr 1 / 3 (μ f / μ w ) 0.14 (7)

[0072] Where Nu is the dimensionless heat transfer coefficient—the Nusselt number. d is the hydraulic diameter of the cooling channel, λ is the thermal conductivity of the coolant; Re is the Reynolds number, Pr is the Prandtl number, μ f μ w These are the viscosity coefficients of the coolant, determined based on the coolant temperature and the cold wall surface temperature, respectively.

[0073] When the coolant is kerosene, the empirical formula for fitting the heat transfer experimental data of kerosene is used, as shown in equation (8):

[0074] Nu = 0.0126Re 0.87 Pr 0.4 (μ f / μ w ) 0.1 (8)

[0075] Considering the heat transfer on all four circumferential surfaces of the rectangular channel in actual cooling structures and the unilateral loading effect of heat flow in practical problems, this paper is based on the fin efficiency η f The concept of (correction factor) is relevant to... Make corrections.

[0076] This invention equates multi-channel convective heat transfer to convective heat transfer through a group of fins. First, it introduces the method for calculating the efficiency of a single fin. For example... Figure 2 As shown, the solid wall portion between the channels is equivalent to a "rib" of width s, as indicated by the yellow dashed line in the figure. The intersection of the "rib" with the cooling plate between the hot and cold walls in the cooling structure, i.e., the rib root, has the temperature T at the cold wall temperature. w2 For a single rib, η f The calculation formula is

[0077]

[0078] in, It is a constant, and P is the perimeter of the cross section in which the infinitesimal element participates in heat transfer:

[0079] P = 2(1 + s), A c The cross-sectional area A of the infinitesimal element c = 1·s. Considering the heat dissipation at the tip of the fin, the equivalent fin length H = h² + s / 2. Assuming the cooling channels are uniformly distributed, then with N cooling channels, there are N "fins". Therefore, the convective heat transfer Qw of the coolant flowing within each infinitesimal element length dx of the cooling channel. cool Equivalent to the rib surface area A f The root surface area A between the two ribs r Convective heat transfer on the surface, i.e.

[0080]

[0081] Qw cool =A f η f h f (Tw2-T f )+A r h f (Tw2-T f )=N*dx*(h2+s / 2)*η f h f (Tw2-T f )+N*dx*h1*(Tw2-T f (11)

[0082] (ii) An endothermic process in which the coolant undergoes a chemical endothermic reaction or a phase transition.

[0083] When kerosene absorbs heat and heats up to the pyrolysis initiation temperature, a pyrolysis reaction occurs. This pyrolysis reaction, being endothermic, generates additional chemical heat sinks, further absorbing heat from the cooling channel walls. From this, the total heat absorbed by the coolant, Q, can be obtained. w2

[0084]

[0085] The kerosene pyrolysis endothermic reaction is determined by the degree of kerosene cracking and the kerosene pyrolysis endothermic reaction per unit mass, and is also related to the residence time in the cooling channel. The kerosene cracking process utilizes a thermal / catalytic cracking overall reaction model, and experimental data are used to determine the kerosene pyrolysis endothermic reaction per unit mass and the degree of cracking at different temperatures.

[0086] By solving equations (1), (2), (5), and (12) in a coupled manner, the hot wall temperature T of the cooling structure when kerosene is used as the coolant can be obtained. w1 Cold wall temperature T w2 and coolant temperature T f Distribution along the route.

[0087] Step 4: Confirm whether the coolant temperature distribution and fuel temperature distribution meet the upper limit requirements of coolant temperature and the temperature requirements of solid wall material. If they meet the requirements, proceed to Step 6; otherwise, proceed to Step 5.

[0088] Step 5: Based on the results of the active cooling simulation analysis, change the parameters of the active thermal protection theoretical analysis model and repeat steps 3-4.

[0089] Step Six: Modify the rectangular cooling channel in the local high heat flux region into a cooling channel configuration with different bending structures. Perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux region. If it does, proceed to Step Seven; if it does not, continue to modify the cooling channel configuration in the local high heat flux region until the requirements are met.

[0090] Step 7: Fabricate the active thermal protection structure based on the final active thermal protection theoretical analysis model and parameters.

[0091] Example:

[0092] First, given the wall heat flow conditions on the wedge, based on the active thermal protection theoretical analysis model established in step one, a pipe scheme with a channel diameter of 2mm is formed through steps two and three, such as... Figure 3 The diagram shows the cooling structure and the distribution of coolant temperature, convective heat transfer coefficient, pressure, and flow velocity along the pipe. (a) represents the temperature distribution, (b) the convective heat transfer coefficient distribution, (c) the pressure distribution, and (d) the flow velocity distribution. Analysis of the wall temperature and the highest outlet temperature of the cooling structure shows that the material temperature and kerosene temperature requirements are met, leading to a preliminary active cooling structure scheme. Further three-dimensional structural design is carried out for the wedge-shaped structure. Considering the enhanced heat transfer effect of eddies, the pipes are designed in a spiral bend-like distribution pattern, such as... Figure 4 As shown in (a), through fluid-structure interaction simulation analysis of the three-dimensional structure, the following results were obtained. Figure 4 The distribution in (b) further verifies that the active cooling structure meets the thermal protection requirements, forming the final closed-loop design scheme.

[0093] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. An active cooling method for an engine, characterized in that... The steps of this method include: Step 1: Establish an active thermal protection theoretical analysis model suitable for oblique detonation engines. The active thermal protection theoretical analysis model includes a cooling plate and a wall plate with cooling channels. The cooling plate covers the thick wall plate, with the upper surface of the cooling plate being a hot wall and the lower surface being a cold wall. The cooling channels are multiple rectangular cooling channels evenly distributed along the flow direction. Step 2: Preliminarily determine the parameters of the active thermal protection theoretical analysis model, including the materials of the cooling plate and wall panel, and design the dimensions of the rectangular cooling channel and the thickness of the cooling plate; Step 3: Apply heat flow conditions as the thermal boundary input to the active thermal protection theoretical analysis model, and perform active cooling simulation analysis on the active thermal protection theoretical analysis model to obtain the coolant temperature distribution; Step 4: Confirm whether the coolant temperature distribution and fuel temperature distribution meet the upper limit requirements of coolant temperature and the temperature requirements of solid wall material. If they meet the requirements, proceed to Step 6; otherwise, proceed to Step 5. Step 5: Based on the active cooling simulation analysis results, modify the parameters of the active thermal protection theoretical analysis model and repeat steps 3-4. Step 6: Modify the rectangular cooling channel in the local high heat flux area into a cooling channel configuration with different bending structures, and perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux area. If it does, proceed to Step 7; if it does not, continue to modify the cooling channel configuration in the local high heat flux area until the requirements are met. Step 7: Fabricate the active thermal protection structure based on the final active thermal protection theoretical analysis model and parameters; The method for obtaining the coolant temperature distribution by performing active cooling simulation analysis on the active thermal protection theoretical analysis model in step three is as follows: Establish the momentum and energy equations for coolant flow; Solve for the heat flux loaded on the hot wall surface corresponding to each cooling channel; Solve for the convective heat transfer generated by the flow within each cooling channel; Calculate the total heat absorbed by the coolant; The distribution of hot wall temperature, cold wall temperature, and coolant temperature along the path was obtained from the active thermal protection theoretical analysis model.

2. The active cooling method for an engine according to claim 1, characterized in that: The cooling sheet and wall panel are joined by brazing or diffusion welding.

3. The active cooling method for an engine according to claim 1, characterized in that: The heat flow conditions in step three include three types of thermal boundary conditions in the local high heat flow peak region and three types of thermal boundary conditions in the engine internal flow channel. The three types of thermal boundary conditions refer to the given wall heat flow conditions, the given wall temperature conditions, and the given total temperature and heat transfer coefficient of the fluid near the wall conditions.

4. The active cooling method for an engine according to claim 1, characterized in that: Active cooling simulation analysis refers to performing gas-solid-liquid coupling calculations based on thermal boundary inputs, given the incoming flow and engine operating mode.

5. The active cooling method for an engine according to claim 1, characterized in that: The heat flow rate loaded on the hot wall surface of each cooling channel within time t. satisfy: For the heat flux density distribution on the hot wall surface, The total width of the cooling structure, It is the total length of the cooling structure. This refers to the hot wall temperature. This refers to the cold wall temperature. For cooling the thin plate, the thermal conductivity is... Each cooling channel is divided into several micro-elements based on its length; the cooling structure is the theoretical analysis model for active thermal protection.

6. The active cooling method for an engine according to claim 5, characterized in that: Each cooling channel is loaded with heat flow on all four sides of its circumference, and the convective heat transfer of the coolant flowing within each dx is... satisfy N is the total number of cooling channels. The width of the cooling channel cross section. The height of the cooling channel cross section. This is the distance between the adjacent walls of two adjacent cooling channels. The convective heat transfer coefficient, This refers to the coolant temperature. This is a correction factor.

7. The active cooling method for an engine according to claim 6, characterized in that: It is a hyperbolic tangent function, and H is the equivalent length of the solid wall portion between adjacent cooling channels.

8. The active cooling method for an engine according to claim 6, characterized in that: Total heat absorbed by the coolant satisfy This is the chemical endothermic reaction of kerosene cracking.

9. The active cooling method for an engine according to claim 1, characterized in that: The coolant is kerosene.

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