Air valve sealing surface contact thermal resistance online test device and method based on infrared temperature measurement

Abstract

The invention discloses an air valve sealing surface contact thermal resistance online test device and method based on infrared temperature measurement. A constant-temperature heating plate is used for heating an air valve sealing surface, circulating water is used for cooling the top end of a valve rod, high and low temperature constant wall surface temperature boundary conditions are formed at the two ends of an air valve, and an infrared temperature sensor measures the temperature change of the valve rod. Under the test condition, main factors influencing the temperature of the valve rod are convective heat transfer between the air valve and air and contact thermal resistance between the air valve and a heating plate, establishing an unsteady state heat conduction model and an identification function, fitting the temperature of the valve rod by adopting a least square method, and obtaining unsteady state heat conduction parameters of the air valve; and the convection heat exchange amount between the air valve and the air and the contact thermal resistance between the heating plate and the sealing surface are obtained, so that the corresponding relation between the temperature of the valve rod and the contact thermal resistance is constructed. Furthermore, according to the combustion and valve rod temperature of the engine under the actual working condition, the contact thermal resistance of the sealing surface of the air valve is identified, the carbon deposition thickness of the air valve is quantitatively analyzed, and the thermal state parameter of the engine health degree is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of engine evaluation, and particularly relates to an on-line test device and method for contact thermal resistance of a valve sealing surface based on infrared temperature measurement. Background Art

[0002] The thermal state of key parts in the combustion chamber is a core index for evaluating the health of high-power engines. The valve is a key moving seal in the combustion chamber and is subject to gas pressure, thermal load, and mechanical shock. Analyzing the thermal state of the valve is of great significance for ensuring the stability of the engine, improving efficiency, reducing maintenance costs, extending service life, ensuring safe operation, and promoting energy conservation and emission reduction. However, as a high-temperature moving part of the engine, how to measure the valve temperature in real time during operation and how to analyze the contact thermal resistance of the sealing surface through the valve temperature have always been difficult problems in the evaluation of engine health.

[0003] As a non-contact temperature measurement technology, infrared temperature measurement technology has been developed for many years in the measurement field. The infrared temperature measurement method has the characteristics of non-contact, high measurement accuracy, and fast temperature measurement speed, and can observe the temperature of the valve stem in real time without affecting the working state of the valve.

[0004] Traditional steady-state heat balance tests cannot describe the development process of the thermal state of parts online, and the heat flux density (the second type of boundary condition) significantly affects the calculation results of the heat transfer model. Summary of the Invention

[0005] In order to solve the deficiencies of the prior art, achieve the purpose of overcoming the limitations of contact thermal resistance tests, and improving the accuracy of identifying thermal state parameters such as contact thermal resistance, the present invention adopts the following technical solutions:

[0006] An on-line test method for the contact thermal resistance of a valve sealing surface, comprising the following steps:

[0007] Step 1: Construct an unsteady heat conduction test device for the valve, and set constant low-temperature conditions and constant high-temperature conditions at both ends of the valve stem of the valve;

[0008] Step 2: Measure the temperature of the valve stem to obtain the temperature response of the valve stem under the action of heat flux;

[0009] Step 3: Set a thermal resistance unit between the valve stem and the constant high-temperature mechanism to obtain the temperature change process of the valve stem of the valve under different temperature and contact thermal resistance conditions;

[0010] Step 4: Construct an unsteady heat conduction model for the valve according to the heat conduction state of the valve, and based on the unsteady heat conduction model of the valve, identify the temperature of the valve stem through the valve stem temperature identification function;

[0011] Step 5: Perform least squares fitting of a multi-order function on the temperature of the valve stem to identify the heat conduction parameters of the valve and obtain the optimal transient heat flux of the valve.

[0012] Step 6: Calculate the contact thermal resistance of the gas valve based on the change in the valve stem temperature, compare the heat conduction heat fluxes of the gas valves under different contact thermal resistance conditions, and obtain the influence of the contact thermal resistance on the valve stem temperature and heat flux.

[0013] Further, the unsteady heat conduction model of the gas valve in Step 4 is as follows:

[0014]

[0015] where T represents the valve stem temperature, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the gas valve, x ∈ L, q c represents convective heat transfer, and a represents the thermal diffusivity.

[0016] Further, the valve stem temperature identification function in Step 4 is as follows:

[0017]

[0018] where T represents the valve stem temperature, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the gas valve, T w represents the valve stem temperature between the high-temperature boundary condition and the low-temperature boundary condition of the valve stem, a represents the thermal diffusivity, and b represents the time normalization coefficient.

[0019] Further, the least squares fitting of the multi-order function in Step 5 is as follows:

[0020]

[0021] where T represents the valve stem temperature, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the gas valve, x ∈ L, T w represents the valve stem temperature between the high-temperature boundary condition and the low-temperature boundary condition of the valve stem, n represents the order, a n and b n are intermediate variables, ρ represents the density of the gas valve, C P represents the specific heat capacity of the gas valve, and λ represents the thermal conductivity;

[0022] By increasing the fitting order, the fitting error is reduced, and thus the transient heat conduction heat flux of the gas valve is obtained:

[0023]

[0024] Further, since the fitting error does not decrease linearly and a higher order will not result in higher fitting accuracy, in order to ensure the identification accuracy and reduce the calculation amount, the order is set to 3.

[0025] Online test method for contact thermal resistance of gas valve sealing surface based on infrared temperature measurement. The temperature of the valve stem is measured by an infrared temperature sensor, and the laser center line of the infrared temperature sensor is perpendicular to the axis of the valve stem. By using the online test method for contact thermal resistance of gas valve sealing surface, the influence of contact thermal resistance on the temperature and heat flow of the valve stem is obtained.

[0026] Online test device for contact thermal resistance of gas valve sealing surface based on infrared temperature measurement, including a gas valve, an infrared temperature sensor, a constant high-temperature mechanism, a constant low-temperature mechanism and a thermal resistance unit. A constant low-temperature mechanism and a constant high-temperature mechanism are respectively arranged at both ends of the valve stem of the gas valve, a thermal resistance unit is arranged between the valve stem and the constant high-temperature mechanism, the temperature of the valve stem is measured by the infrared temperature sensor, and by using the online test method for contact thermal resistance of gas valve sealing surface based on infrared temperature measurement, the influence of contact thermal resistance on the temperature and heat flow of the valve stem is obtained.

[0027] Further, the constant low-temperature mechanism includes a water pipe and a cooling water cavity. The cooling water cavity is connected to one end of the valve stem, and the water pipes are arranged on both sides of the cooling water cavity to form a cooling water circulation; the constant high-temperature mechanism is a heating plate.

[0028] Further, the thermal resistance unit is a multi-layer aluminum foil.

[0029] Online test device for contact thermal resistance of gas valve sealing surface based on infrared temperature measurement, applied to an engine. The infrared temperature sensor is used to measure the temperature change process of the valve stem to obtain the contact thermal resistance of the gas valve sealing surface, which is used to analyze the carbon deposition thickness of the gas valve.

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

[0031] The present invention uses the infrared temperature measurement method to online measure the temperature of the valve stem during the actual operation of the engine, establishes a non-steady heat conduction model and identification function of the gas valve, obtains the heat conduction parameters of the gas valve by using the least square fitting method, obtains the heat conduction heat flow of the gas valve from the temperature change of the valve stem, and establishes the corresponding relationship between the temperature change of the valve stem and the contact thermal resistance of the sealing surface, so as to accurately analyze the contact thermal resistance of the gas valve sealing surface through the temperature of the valve stem. The contact thermal resistance of the gas valve sealing surface during the operation of the engine can reflect the carbon deposition state of the gas valve, providing key thermal state parameters for the online identification of the engine health. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of the device in the embodiment of the present invention.

[0033] Figure 2 It is a flow chart of the method in the embodiment of the present invention.

[0034] Figure 3a Identification diagram of the non-steady heat conduction model of the gas valve temperature response in the embodiment of the present invention.

[0035] Figure 3bComparison diagram of identification parameters of the unsteady heat conduction model in the embodiments of the present invention.

[0036] Figure 4a Variation diagram of the temperature and heat flux density of the air valve caused by the simulated contact thermal resistance of the aluminum foil in the embodiments of the present invention.

[0037] Figure 4b Contact thermal resistance diagram for identifying the unsteady heat conduction model in the embodiments of the present invention. Specific embodiments

[0038] The following will describe the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustration and explanation of the present invention, and are not intended to limit the present invention.

[0039] As Figure 1 shown, an on-line test device for the contact thermal resistance of the air valve sealing surface based on infrared temperature measurement, including a heating plate 1, an infrared temperature sensor 2, a water pipe 3, a cooling water chamber 4, an air valve 5, and an aluminum foil 6. The air valve 5 is placed at a fixed position on the heating plate 1, the infrared temperature sensor 2 is focused on the center position of the valve stem of the air valve 5, the cooling water chamber 4 is fixed at the top of the valve stem of the air valve 5, and the water pipe 3 is connected to both sides of the cooling water chamber 4.

[0040] The air valve 5 is vertically placed at a fixed position on the heating plate 1 at room temperature. The center line of the infrared laser temperature sensor 2 is perpendicular to the axis of the valve stem of the air valve 5. The top end of the air valve 5 passes through the center position at the bottom of the cooling water chamber 4, so that the top end of the air valve 5 is immersed in the cooling water. The water pipe 3 is connected to the center positions on both sides of the cooling water chamber 4 to form a cooling water circulation. A multi-layer aluminum foil 6 is provided between the bottom surface of the air valve 5 and the heating plate 1 as a simulated contact thermal resistance.

[0041] As Figure 2 shown, an on-line test method for the contact thermal resistance of the air valve sealing surface based on infrared temperature measurement. Starting from the unsteady response test method under the constant temperature boundary condition, an unsteady heat conduction model and a fitting function of the air valve are constructed to fit the process of the temperature rise of the valve stem, so as to accurately obtain the thermal state parameters such as the contact thermal resistance of the air valve. The specific steps are as follows:

[0042] Step 1: Construct an unsteady heat conduction test device for the air valve, and set a constant low temperature condition and a constant high temperature condition at both ends of the air valve 5 respectively;

[0043] In the present invention, an electric heating plate 1 is adopted to form a constant wall surface high temperature condition, and a cooling water cavity is designed at the top end of the valve stem of the air valve to form a constant wall surface low temperature condition; specifically, the heating plate 1 is powered on to keep the heating plate at a stable temperature, and the bottom of the air valve 5 is heated at a constant temperature to form a high temperature boundary condition at the bottom surface of the valve stem; the cooling water forms a cooling water cycle through the water pipe 3 in the cooling water cavity 4 at the top of the air valve 5 to simulate the cooling of the valve guide and form a low temperature boundary condition at the top of the valve stem; the high temperature boundary condition at the bottom surface of the valve stem and the low temperature boundary condition at the top of the valve stem constitute the constant boundary temperature condition for the unsteady heat conduction of the air valve.

[0044] The air valve 5 is stably placed on the constant temperature electric heating plate 1 at room temperature, and an unsteady heat conduction heat flux q(τ) that changes with time is formed in the air valve. An aluminum foil is added between the bottom surface of the air valve and the electric heating plate to form a contact thermal resistance.

[0045] Step 2: Measure the temperature of the valve stem to obtain the temperature response of the valve stem 5 under the action of the heat flux;

[0046] Use an infrared temperature sensor to measure the temperature change process of the valve stem. The infrared temperature sensor 2 is focused on the axis position of the valve stem of the air valve 5 to measure the temperature response T(τ) of the valve stem of the air valve 5 under the action of the heat flux q(τ);

[0047] Step 3: Set a thermal resistance unit between the valve stem 5 and the constant high temperature mechanism to obtain the temperature change process of the valve stem of the air valve 5 under different temperature and contact thermal resistance conditions;

[0048] Specifically, set different electric heating plate temperatures, and set different numbers of layers of aluminum foil 6 between the heating plate 1 and the air valve 5 to form different contact thermal resistance states at the bottom surface of the air valve. Repeat steps 1 and 2 to obtain the temperature change process T(τ) of the valve stem of the air valve 5 under different temperature and contact thermal resistance conditions.

[0049] Step 4: According to the heat conduction state of the air valve, construct an unsteady heat conduction model of the air valve as shown in Equation (1):

[0050]

[0051] Among them, T represents the temperature of the valve stem, in °C, τ represents time, in s, L represents the distance between the temperature measurement point and the bottom surface of the air valve, in m, x ∈ L, q c represents convective heat transfer, in W / m 2 , and a represents the thermal diffusivity, in m2 / s.

[0052] Based on the general solution of the heat conduction equation of the unsteady heat conduction model of the air valve, a valve stem temperature identification function is proposed for valve stem temperature identification, as shown in Equation (2):

[0053]

[0054] Among them, the initial condition T| x＝0 = T w1 , T| x＝L = T w2 , T w1 , T w2 respectively represent the high-temperature and low-temperature boundary conditions, T w represents the stem temperature between the high-temperature boundary condition and the low-temperature boundary condition of the stem, and b represents the time normalization coefficient with the unit of s.

[0055] Step 5: Perform a least squares fitting of a multi-order function on the stem temperature to identify the gas valve heat conduction parameter and obtain the optimal transient heat flux of the gas valve;

[0056] Perform a least squares fitting of a multi-order function on the stem temperature T(L,τ) using the function shown in Equation (2) to obtain the numerical solution of the unsteady heat conduction model as shown in Equation (3):

[0057]

[0058] Among them, ρ represents the gas valve density with the unit of kg / m 3 , C P represents the specific heat capacity of the gas valve with the unit of J / (kg*K), and λ represents the thermal conductivity with the unit of W / (m*K).

[0059] Increase the fitting order (from 1st order to 5th order), and the fitting error gradually decreases, thereby obtaining the transient heat flux q(L,τ) of the gas valve as shown in Equation (4):

[0060]

[0061] There is an obvious correlation between the fitting order of the function shown in Equation (2) and the fitting error. The test results of the stem temperature and the function identification results are as Figure 3a shown. The curves in the figure correspond to the following formulas:

[0062]

[0063] The error of the identification results using the 2nd to 5th order functions is less than the measurement error of the temperature sensor, which proves the effectiveness of the identification function.

[0064] The number of iterative calculations of the function identification and the identification results of the heat flux q are as Figure 3b shown. However, the fitting error does not decrease linearly, and a higher order does not result in a higher fitting accuracy. When using the 4th and 5th order functions for fitting, the fitting error remains stable. Therefore, in order to ensure the identification accuracy and reduce the calculation amount, the present invention uses a 3rd order function to identify the test results of the unsteady heat conduction temperature of the gas valve.

[0065] Step 6: Contact thermal resistance analysis: According to the change in the valve stem temperature, calculate the contact thermal resistance of the gas valve 5, and compare the heat conduction heat fluxes of the gas valves under different contact thermal resistance conditions to obtain the influence of the contact thermal resistance on the valve stem temperature and heat flux.

[0066] Set different numbers of aluminum foil layers between the gas valve and the electric heating plate to simulate the change in the contact thermal resistance of the gas valve sealing surface. As the contact thermal resistance increases, the heat flux q of the valve stem decreases, and the temperature difference between the bottom surface of the gas valve and the electric heating plate increases. As Figure 4a shown, from the heat flux and temperature difference on the bottom surface of the gas valve, calculate the contact thermal resistance of the bottom surface of the gas valve, as Figure 4b shown.

[0067] Compare the heat conduction heat fluxes of the gas valves under different contact thermal resistance conditions to obtain the influence of the contact thermal resistance of the bottom surface of the gas valve on the valve stem temperature and heat flux.

[0068] Under the actual working conditions of the engine, use the infrared temperature sensor 2 to measure the change process of the valve stem temperature of the gas valve 5, and the contact thermal resistance of the sealing surface of the gas valve 5 can be obtained, so as to analyze the carbon deposition thickness of the gas valve 5.

[0069] In an embodiment of the present invention, the calculation of the contact thermal resistance of the bottom surface of the gas valve includes the following steps:

[0070] 1) Start the electric heating plate 1 to reach a constant high temperature condition;

[0071] 2) Place the gas valve 5 at room temperature on the electric heating plate 1 to form unsteady heat conduction in the gas valve;

[0072] 3) The infrared temperature sensor 2 is focused on the valve stem axis of the gas valve 5 to measure the change in the valve stem temperature;

[0073] 4) The cooling water forms a circulating water cooling through the water pipe 3 in the cooling water cavity 4 at the top of the gas valve 5 to form a constant low temperature condition;

[0074] 5) Add aluminum foil between the bottom surface of the gas valve 5 and the electric heating plate 1 to form different contact thermal resistance conditions. Repeat steps 1) to 4) to obtain the change process of the valve stem temperature of the gas valve 5 under different contact thermal resistance conditions;

[0075] 6) Establish an unsteady heat conduction model (such as Equation (1)) and an identification function (such as Equation (2)), and perform parameter identification (such as Equation (3)) on the valve stem temperature obtained from the experiment to obtain the heat flux of the gas valve (such as Equation (4));

[0076] 7) Calculate the bottom surface temperature and heat flux of the gas valve according to the unsteady heat conduction model of the gas valve, and calculate the contact thermal resistance of the bottom surface of the gas valve from the temperature difference and heat flux between the bottom surface of the gas valve and the electric heating plate.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Online test method for contact thermal resistance of valve sealing surface, characterized in that It includes the following steps: Step 1: Construct an unsteady heat conduction test device for the air valve (5), and set constant low-temperature conditions and constant high-temperature conditions at both ends of the valve stem of the air valve (5); Step 2: Measure the valve stem temperature to obtain the temperature response of the valve stem under the action of heat flux; Step 3: Set a thermal resistance unit between the valve stem and the constant high-temperature mechanism to obtain the temperature change process of the valve stem of the air valve (5) under different temperature and contact thermal resistance conditions; Step 4: Construct an unsteady heat conduction model for the air valve according to the heat conduction state of the air valve, and based on the unsteady heat conduction model of the air valve, identify the valve stem temperature through the valve stem temperature identification function; Step 5: Fit the valve stem temperature by the least squares method of multi-order functions to identify the heat conduction parameters of the air valve and obtain the optimal transient heat flux of the air valve; Step 6: Calculate the contact thermal resistance of the air valve (5) according to the change of the valve stem temperature, compare the heat fluxes of the air valve with different contact thermal resistance conditions, and obtain the influence of the contact thermal resistance on the valve stem temperature and heat flux.

2. The online test method for the contact thermal resistance of the gas valve sealing surface according to claim 1, characterized in that: The unsteady heat conduction model of the air valve in Step 4 has the following formula: Among them, T represents the temperature of the valve stem, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the air valve, x ∈ L, q c represents convective heat transfer, and a represents the thermal diffusivity.

3. The online test method for the contact thermal resistance of the valve sealing surface according to claim 1, characterized in that: The valve stem temperature identification function in Step 4 has the following formula: Among them, T represents the valve stem temperature, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the air valve, T w represents the valve stem temperature between the high-temperature boundary condition and the low-temperature boundary condition of the valve stem, a represents the thermal diffusivity, and b represents the time normalization coefficient.

4. The on-line test method for the contact thermal resistance of the valve sealing surface according to claim 1, wherein: The least squares method of multi-order functions fitting in Step 5 has the following formula: Among them, T represents the temperature of the valve stem, τ represents time, L represents the distance between the temperature measurement point and the bottom surface of the air valve, x ∈ L, and T w represents the temperature of the valve stem between the high-temperature boundary condition and the low-temperature boundary condition of the valve stem, n represents the order, a n and b n are intermediate variables, ρ represents the density of the air valve, C P represents the specific heat capacity of the air valve, and λ represents the thermal conductivity; By increasing the fitting order to reduce the fitting error, thereby obtaining the transient heat flux of the air valve:

5. The on-line test method for the contact thermal resistance of the valve sealing surface according to claim 4, characterized in that: Set the order to 3.

6. An on-line test method for contact thermal resistance of gas valve sealing surface based on infrared temperature measurement, characterized in that: Measure the valve stem temperature by the infrared temperature sensor (2), the laser center line of the infrared temperature sensor (2) is perpendicular to the axis of the valve stem, and adopt the on-line test method for the contact thermal resistance of the air valve sealing surface described in any one of claims 1 to 5 to obtain the influence of the contact thermal resistance on the valve stem temperature and heat flux.

7. An on-line test device for contact thermal resistance of the valve sealing surface based on infrared temperature measurement, comprising a valve (5), an infrared temperature sensor (2), a constant high-temperature mechanism, a constant low-temperature mechanism and a thermal resistance unit, characterized in that: Set a constant low-temperature mechanism and a constant high-temperature mechanism at both ends of the valve stem of the air valve (5), set a thermal resistance unit between the valve stem and the constant high-temperature mechanism, measure the valve stem temperature by the infrared temperature sensor (2), and adopt the on-line test method for the contact thermal resistance of the air valve sealing surface based on infrared temperature measurement described in claim 6 to obtain the influence of the contact thermal resistance on the valve stem temperature and heat flux.

8. The on-line test device for the contact thermal resistance of the gas valve sealing surface based on infrared temperature measurement according to claim 7, characterized in that: The constant low-temperature mechanism includes a water pipe (3) and a cooling water cavity (4), the cooling water cavity (4) is connected to one end of the valve stem, and the water pipe (3) is arranged on both sides of the cooling water cavity (4) to form a cooling water circulation; the constant high-temperature mechanism is a heating plate (1).

9. The on-line test device for contact thermal resistance of the gas valve sealing surface based on infrared temperature measurement according to claim 7, characterized in that: The thermal resistance unit is a multi-layer aluminum foil (6).

10. The on-line test device for contact thermal resistance of the gas valve sealing surface based on infrared temperature measurement according to claim 7, which is applied to an engine, is characterized in that: Adopt the infrared temperature sensor (2) to measure the temperature change process of the valve stem to obtain the contact thermal resistance of the sealing surface of the air valve (5) for analyzing the carbon deposition thickness of the air valve (5).

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