A dual-band based method for measuring the emissivity of engine nozzle coating

Abstract

The present invention relates to a dual-band based engine tail nozzle coating emissivity measurement method, including obtaining emissivity correction parameters when the tail nozzle coating is in good condition; obtaining fitting parameters of the traditional dual-band method and fitting parameters of the dual-band method including correction coefficients; for the same type of engine in service in the field, collecting the radiation brightness value of the first band and the radiation brightness value of the second band at the regional temperature of the coating; obtaining the radiation brightness ratio in the first band and the second band; obtaining the estimated temperature of the tail nozzle coating area and the corrected coating area temperature; obtaining the coating emissivity of the tail nozzle coating of the same type of engine in service in the field at the corresponding wavelength and regional temperature. The measurement method, based on thermal imager equipment, improves the efficiency of data acquisition and can meet the requirements of rapid measurement. The measurement method improves the accuracy of the temperature of the tail nozzle coating area, thereby improving the measurement accuracy of the emissivity.

Description

Technical Field

[0001] The invention belongs to the technical field of coating emissivity measurement, and in particular relates to a dual-band based engine tail nozzle coating emissivity measurement method. Background Art

[0002] During the flight of a fighter, the engine tail nozzle is in a high temperature state due to the heating effect of the jet, emitting a large amount of infrared radiation into space, which is easily detected by infrared detectors deployed by the enemy. In order to reduce the infrared radiation emitted by the nozzle during operation and reduce the probability of the fighter being detected by enemy detectors, the nozzle surface is generally sprayed with an infrared low-emissivity stealth coating. Emissivity is an important parameter for measuring the infrared stealth performance of the coating. Due to the harsh working environment of the engine tail nozzle, the coating is very easy to be damaged, resulting in an increase in its emissivity, which in turn greatly reduces the stealth performance of the coating. Therefore, measuring and monitoring the emissivity of the engine tail nozzle coating and timely detecting changes in the infrared stealth performance of the tail nozzle coating are important tasks to ensure the battlefield survivability of fighters.

[0003] Common emissivity measurement methods include calorimetry, energy method, reflection method and multi-wavelength method. The calorimetry method requires heating the test object during the test process, introduces additional heating equipment and can only be used to measure the emissivity of conductors; the energy method requires a black body with the same temperature as the test object as a reference, requires the surface temperature of the coating to be tested to be known and the temperature of the black body must be kept consistent with that of the coating. Therefore, both the calorimetry method and the energy method are difficult to meet the measurement requirements of the emissivity of the engine nozzle coating.

[0004] In the 2013 issue 8 of the journal Spectroscopy and Spectral Analysis, Zhang Yufeng's paper "Calibration Method of Infrared Spectral Emissivity Measurement System Based on Integrating Sphere Reflectometer" and the 2022 issue 3 of the journal Laser and Infrared, Li Meng's paper "Research on Calibration of Spectral Emissivity Measurement of Infrared Stealth Coatings" studied the calibration and calibration methods of the integrating sphere reflectometry for measuring emissivity and applied them to the spectral emissivity measurement of aircraft stealth coatings. The method emits infrared radiation to the coating, collects the reflected energy through the integrating sphere, and then obtains the reflectivity of the target. The target emissivity is then calculated through the relationship between reflectivity and emissivity. However, due to the application of the integrating sphere, the measurement range is very small, and the integrating sphere needs to fit closely to the target surface during measurement, so non-contact measurement cannot be achieved. In addition, when the target temperature is high, the proportion of infrared radiation energy emitted by the target itself collected by the integrating sphere increases, and the proportion of reflected signal energy decreases relatively, which reduces the measurement accuracy and is not conducive to the measurement of the emissivity of the engine tail nozzle coating.

[0005] The dual-band emissivity measurement method is a method that can simultaneously measure surface temperature and emissivity in a non-contact manner. In the 6th issue of Volume 24 of the Infrared Technology journal in 2002, Xing Jichuan's paper "Dual-band colorimetric temperature measurement method and its analysis" discussed the sensitivity and applicable range of dual-band infrared colorimetric temperature measurement, but did not study the emissivity measurement. The traditional dual-band emissivity measurement method assumes that the surface of the object being measured is a gray body, that is, the emissivity of the object surface does not change with the band. At the same time, the infrared radiation energy information of the object surface in two adjacent bands is measured. By comparing the infrared radiation energy of the object surface in the two bands, the unknown infrared emissivity is eliminated and the true temperature of the object surface is solved. Finally, the infrared emissivity of the object surface is solved based on the temperature and radiation energy. There are two main sources of error in this method. One is the interference of the environmental background under normal temperature conditions, and the other is that the gray body assumption does not completely conform to the actual situation. Although the engine tail nozzle is at a higher temperature, which can effectively avoid the error caused by environmental background interference in the dual-band temperature measurement process, the gray body assumption on which this method is based is not applicable to the engine nozzle coating, resulting in the temperature measurement accuracy not being able to meet the requirements for accurate calculation of the emissivity, which limits the application of this method in the emissivity measurement of the tail nozzle coating. Summary of the invention

[0006] In order to overcome the shortcomings of low efficiency and low precision in the emissivity measurement of engine tail nozzle coating, the present invention proposes a dual-band based method for measuring the emissivity of engine tail nozzle coating.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A dual-band based engine tail nozzle coating emissivity measurement method comprises the following steps:

[0009] Step 1: Obtain the emissivity correction parameter

[0010] The emissivity correction parameter of an object refers to the negative value of the natural logarithm of the ratio of the average emissivity of the object in two bands. The theoretical calculation formula is:

[0011]

[0012] In formula (1), γ(T) is the emissivity correction parameter, ε(λ1,T) is the average emissivity of the object in the λ1 band at temperature T, and ε(λ2,T) is the average emissivity of the object in the λ2 band at temperature T.

[0013] The emissivity correction parameter γ(T) is related to the performance of the object itself and is a function of the coating temperature T. Its value can be obtained through actual measurement and calculation.

[0014] The coating temperature of the tail nozzle in good condition is T h , Th =150~250℃, at T h Eleven temperature points were selected within the temperature range at intervals of 8 to 12°C. At each temperature point, a thermal imager was used to collect the radiation brightness L(λ1,T h ) and the second band λ2=3.91~4.09μm coating radiation brightness L(λ2,T h ).

[0015] The temperature of the cavity blackbody is T b At the same time, the temperature is set to the same as that of the coating in good condition. At each temperature point, a thermal imager is used to collect the radiation brightness L of the cavity black body in the first band λ1 = 3.22 ~ 3.58μm. b (λ1,T b ) and the second band λ2 = 3.91 ~ 4.09μm cavity black body radiation brightness L b (λ2,T b ).

[0016] The coating is at T h The average emissivity of the first band at temperature is:

[0017]

[0018] In formula (2), T b =T h .

[0019] The coating is at T h The average emissivity of the second band at temperature is:

[0020]

[0021] In formula (3), T b =T h .

[0022] The coating is at temperature T h The emissivity correction factor is calculated according to formula (1).

[0023] Step 2: Obtain fitting parameters

[0024] The fitting parameters include the traditional dual-band method fitting parameters A′, B′, and the dual-band method fitting parameters A, B including the correction coefficient.

[0025] According to the intact coating obtained in step 1, at temperature T h The average emissivity L(λ1,T h ) and the average emissivity L(λ2,T h ), the coating in good condition at temperature Th The radiance ratio R(T h ) is calculated as follows:

[0026]

[0027] The fitting parameters of the tail nozzle coating are obtained by measuring the radiation brightness of the tail nozzle coating and fitting curve of the ratio of temperature to radiation brightness.

[0028] Step 3: Collect the radiation brightness of the first and second bands of the coating to be tested

[0029] For engines serving in the field, after the engine is shut down, when the temperature of the engine tail nozzle drops to the range of 150-250°C, a thermal imager is used to collect the radiation brightness L(λ1) of the engine tail nozzle coating in the first band λ1=3.22-3.58μm and the radiation brightness L(λ2) in the second band λ2=3.91-4.09μm. At this time, the actual surface temperature of the coating area to be measured is unknown.

[0030] The radiation brightness value L(λ1) of the first band and the radiation brightness value L(λ2) of the second band of the coating area to be measured are obtained.

[0031] Step 4: Calculate the radiation brightness ratio of the coating to be tested

[0032] The calculation formula for the radiant brightness ratio R of the first band and the second band of the coating area to be tested is as follows:

[0033]

[0034] Step 5: Calculate the actual surface temperature of the coating area to be tested

[0035] The estimated temperature T′ of the coating area to be tested in the engine tail nozzle in service in the field and the radiation brightness ratio R have the following relationship:

[0036]

[0037] The estimated temperature T′ of the engine tail nozzle coating area in field service is obtained by formula (8).

[0038] The temperature of the coating area to be measured is corrected by using the emissivity correction parameter γ(T′) at the estimated temperature of the coating area to be measured.

[0039] The actual surface temperature T0 of the coating area to be tested on the tail nozzle of an engine in service in the field and the radiation brightness ratio R have the following relationship:

[0040]

[0041] In formula (9), γ(T') is the emissivity correction parameter at temperature T'.

[0042] The actual surface temperature T0 of the coating area to be tested on the tail nozzle of an engine serving in the field is obtained.

[0043] Step 6: Calculate the average emissivity of the coating to be tested

[0044] The band average emissivity of the coating to be tested on the engine tail nozzle in the field service at the actual surface temperature T0 of the area is calculated by the following formula:

[0045]

[0046] In formula (10), C1 is the first radiation constant, C1 = 3.7415 × 10 8 W·μm 4 / m 2 ; C2 is the second radiation constant, C2=1.4388×10 4 μm·K; λ is the wavelength, and L(λ) is the radiation brightness of the coating to be tested in the λ wavelength band.

[0047] So far, the average emissivity of the coating to be tested on the engine tail nozzle in service in the field at the actual surface temperature T0 in the corresponding band is obtained.

[0048] In the above-mentioned engine tail nozzle coating emissivity measurement method, in step 2, the fitting parameters are obtained according to the fitting curve of the ratio of temperature to radiation brightness. The specific process is as follows:

[0049] The traditional dual-band method fitting parameters A' and B' are obtained by fitting the following formula:

[0050]

[0051] The temperature T measured in step 1 h The radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h ), the fitting parameters A′ and B′ of the traditional dual-band method can be determined by least squares fitting.

[0052] The fitting parameters A and B of the dual-band method including the correction coefficient are obtained by fitting the following formula:

[0053]

[0054] The temperature T measured according to step 1 h , the radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h ) and the emissivity correction factor γ(T h ), the dual-band method fitting parameters A and B including the correction coefficient can be determined by least squares fitting.

[0055] In the above-mentioned engine tail nozzle coating emissivity measurement method, in step 6, the average emissivity is obtained by respectively obtaining the first band and the second band.

[0056] When λ is in the first band, the average emissivity of the coating to be tested in the first band at the true surface temperature T0 of the region is:

[0057]

[0058] In formula (11), λ is the median value of 3.4 μm in the band λ1=3.22-3.58 μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ1 band.

[0059] When λ is in the second band, the average emissivity of the coating to be tested in the second band at the true surface temperature T0 of the region is:

[0060]

[0061] In formula (12), λ is taken as 4.0 μm in the band λ2=3.91-4.09 μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ2 band.

[0062] The beneficial effects of the present invention are:

[0063] A dual-band engine tail nozzle coating emissivity measurement method is proposed. Based on a thermal imager, it can simultaneously collect data on the emissivity of the coating area within the field of view of the thermal imager. Compared with the integrating sphere reflection method, it improves the efficiency of data collection and can meet the requirements of rapid measurement.

[0064] This emissivity measurement method can realize non-contact measurement, avoiding damage to the engine tail nozzle coating caused by direct contact of the measuring equipment, and also avoiding damage to personnel and measuring equipment caused by direct contact with high temperature.

[0065] This emissivity measurement method can realize the accurate measurement of the emissivity of the engine tail nozzle under high temperature state. Compared with the traditional dual-band emissivity measurement method, by introducing the correction parameters related to the dual-band emissivity of the coating into the temperature calculation formula, the accuracy of the temperature of the engine tail nozzle coating area is improved, thereby improving the accuracy of the emissivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0067] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0068] Example

[0069] A dual-band based engine tail nozzle coating emissivity measurement method includes obtaining emissivity correction parameters when the tail nozzle coating is in good condition; collecting the radiation brightness value of the tail nozzle coating to be tested in the first band and the radiation brightness value of the second band for the same type of engine in service in the field; obtaining the radiation brightness ratio between the first band and the second band; obtaining the estimated temperature of the tail nozzle coating area to be tested and the corrected true surface temperature of the coating area; and obtaining the coating emissivity of the tail nozzle coating of the same type of engine in service in the field at the corresponding wavelength and regional temperature. Figure 1 The specific coating emissivity measurement method includes the following steps:

[0070] Step 1: Obtain the emissivity correction parameter

[0071] The emissivity correction parameter of an object refers to the negative value of the natural logarithm of the ratio of the average emissivity of the object in two bands. The theoretical calculation formula is:

[0072]

[0073] In formula (1), γ(T) is the emissivity correction parameter, ε(λ1,T) is the average emissivity of the object in the λ1 band at temperature T, and ε(λ2,T) is the average emissivity of the object in the λ2 band at temperature T.

[0074] The emissivity correction parameter γ(T) is related to the performance of the object itself and is a function of the coating temperature T. Its value can be obtained through actual measurement and calculation.

[0075] For a certain type of engine, the tail nozzle coating status when the engine is delivered is taken as the standard, that is, the coating is in good condition when leaving the factory, and the correction parameters of the tail nozzle coating are measured and calculated.

[0076] The coating temperature of the tail nozzle in good condition is T h , T h =150~250℃, 11 temperature points were selected within the range of 8~12℃. At each temperature point, a thermal imager was used to collect the radiation brightness L(λ1,T h ) and the second band λ2=3.91~4.09μm coating radiation brightness L(λ2,T h ).

[0077] The temperature of the cavity blackbody is T b At the same time, the temperature is set to the same as that of the coating in good condition. At each temperature point, a thermal imager is used to collect the radiation brightness L of the cavity black body in the first band λ1 = 3.22 ~ 3.58μm. b (λ1,T b) and the second band λ2 = 3.91 ~ 4.09μm cavity black body radiation brightness L b (λ2,T b ).

[0078] The coating is at T h The average emissivity of the first band at temperature is:

[0079]

[0080] The coating is at T h The average emissivity of the second band at temperature is:

[0081]

[0082] The coating is at temperature T h The emissivity correction factor is calculated according to formula (1).

[0083] The emissivity correction coefficient corresponding to the temperature of the tail nozzle coating used in this embodiment is shown in the following table:

[0084] <![CDATA[Actual temperature T h > <![CDATA[γ(T h )]]> 153.63 -0.009261 162.80 -0.009603 171.20 -0.003851 182.37 -0.005005 190.33 -0.004524 198.83 -0.003338 209.00 -0.001904 220.33 -0.002667 229.00 -0.010101 238.00 -0.006427 249.00 -0.005028

[0085] Step 2: Obtain fitting parameters

[0086] The fitting parameters include the traditional dual-band method fitting parameters A′, B′, and the dual-band method fitting parameters A, B including the correction coefficient.

[0087] According to the intact coating obtained in step 1, at temperature T h The average emissivity L(λ1,T h ) and the average emissivity L(λ2,T h ), the coating in good condition at temperature T h The radiance ratio R(T h ) is calculated as follows:

[0088]

[0089] The fitting parameters of the tail nozzle coating are obtained by measuring the radiation brightness of the tail nozzle coating and fitting curve of the ratio of temperature to radiation brightness.

[0090] The traditional dual-band method fitting parameters A′ and B′ are obtained by the following fitting formula:

[0091]

[0092] The temperature T measured in step 1 h The radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h), the traditional dual-band method fitting parameters A' and B' can be determined by least square fitting. For the nozzle coating used in this embodiment, A'=207.7590, B'=-0.3265.

[0093] The fitting parameters A and B of the dual-band method including the correction coefficient are obtained by fitting the following formula:

[0094]

[0095] The temperature T measured according to step 1 h , the radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h ) and the emissivity correction factor γ(T h ), the dual-band method fitting parameters A and B including the correction coefficient can be determined by least square fitting. For the nozzle coating used in this embodiment, A=213.4761, B=-0.3057.

[0096] Step 3: Collect the radiation brightness of the first and second bands of the coating to be tested

[0097] For engines serving in the field, after the engine is shut down, when the temperature of the engine tail nozzle drops to the range of 150-250°C, a thermal imager is used to collect the radiation brightness L(λ1) of the engine tail nozzle coating in the first band λ1=3.22-3.58μm and the radiation brightness L(λ2) in the second band λ2=3.91-4.09μm. At this time, the actual surface temperature of the coating area to be measured is unknown.

[0098] The radiation brightness value L(λ1) of the first band and the radiation brightness value L(λ2) of the second band of the coating area to be measured are obtained.

[0099] Step 4: Calculate the radiation brightness ratio of the coating to be tested

[0100] The calculation formula for the radiant brightness ratio R of the first band and the second band of the coating area to be tested is as follows:

[0101]

[0102] Step 5: Calculate the actual surface temperature of the coating area to be tested

[0103] The estimated temperature T′ of the coating area to be tested in the engine tail nozzle in service in the field and the radiation brightness ratio R have the following relationship:

[0104]

[0105] The estimated temperature T′ of the engine tail nozzle coating area in field service is obtained by formula (8).

[0106] The temperature of the coating area to be measured is corrected by using the emissivity correction parameter γ(T′) at the estimated temperature of the coating area to be measured.

[0107] The actual surface temperature T0 of the coating area to be tested on the tail nozzle of an engine in service in the field and the radiation brightness ratio R have the following relationship:

[0108]

[0109] In formula (9), γ(T') is the emissivity correction parameter at temperature T'.

[0110] The actual surface temperature T0 of the coating area to be tested on the tail nozzle of an engine serving in the field is obtained.

[0111] Step 6: Calculate the average emissivity of the coating to be tested

[0112] The band average emissivity of the coating to be tested on the engine tail nozzle in service in the field at the actual surface temperature T0 of the area is calculated by the following formula:

[0113]

[0114] In formula (10), C1 is the first radiation constant, C1 = 3.7415 × 10 8 W·μm 4 / m 2 ; C2 is the second radiation constant, C2=1.4388×10 4 μm·K; λ is the wavelength, and L(λ) is the radiation brightness of the coating to be tested in the λ wavelength band.

[0115] When λ is in the first band, the average emissivity of the coating to be tested in the first band at the true surface temperature T0 of the region is:

[0116]

[0117] In formula (11), λ is the median value of 3.4 μm in the band λ1=3.22-3.58 μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ1 band.

[0118] When λ is in the second band, the average emissivity of the coating to be tested in the second band at the true surface temperature T0 of the region is:

[0119]

[0120] In formula (12), λ is taken as 4.0 μm in the band λ2=3.91-4.09 μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ2 band.

[0121] So far, the average emissivity ε(λ1,T0) of the first band λ1 and the average emissivity ε(λ2,T0) of the second band λ2 of the engine tail nozzle coating under service in the field at the actual surface temperature T0 are obtained.

Claims

1. A dual-band engine nozzle coating emissivity measurement method, characterized in that: The steps include: Step 1, obtain the emissivity correction parameters: The emissivity correction parameter of an object refers to the negative value of the natural logarithm of the ratio of the average emissivity of the object in two bands. The theoretical calculation formula is: In formula (1), γ(T) is the emissivity correction parameter, ε(λ1,T) is the average emissivity of the object in the λ1 band at temperature T, and ε(λ2,T) is the average emissivity of the object in the λ2 band at temperature T; The emissivity correction parameter γ(T) is related to the performance of the object itself and is a function of the coating temperature T. Its value can be obtained through actual measurement and calculation; The coating temperature of the tail nozzle in good condition is T h , T h =150~250℃, at T h Eleven temperature points were selected at intervals of 8 to 12 °C within the temperature range. At each temperature point, a thermal imager was used to collect the radiation brightness L(λ1,T h ) and the second band λ2=3.91~4.09μm coating radiation brightness L(λ2,T h ); The temperature of the cavity blackbody is T b At the same time, the temperature is set to the same as that of the coating in good condition; at each temperature point, a thermal imager is used to collect the radiation brightness L of the cavity black body in the first band λ1 = 3.22 ~ 3.58μm b (λ1,T b ) and the second band λ2 = 3.91 ~ 4.09μm cavity black body radiation brightness L b (λ2,T b ); The coating is at T h The average emissivity of the first band at temperature is: In formula (2), T b =T h ; The coating is at T h The average emissivity of the second band at temperature is: In formula (3), T b =T h ; The coating is at temperature T h The emissivity correction factor is calculated according to formula (1); Step 2, obtain the fitting parameters: The fitting parameters include the traditional dual-band method fitting parameters A′, B′, and the dual-band method fitting parameters A, B including the correction coefficient; According to the intact coating obtained in step 1, at temperature T h The average emissivity L(λ1,T h ) and the average emissivity L(λ2,T h ), the coating in good condition at temperature T h The radiance ratio R(T h ) is calculated as follows: The fitting parameters of the nozzle coating are obtained by measuring the radiation brightness of the nozzle coating and fitting the curve of the ratio of temperature to radiation brightness. Step 3, collect the radiation brightness of the first band and the second band of the coating to be tested: For engines in service in the field, after the engine is shut down, when the temperature of the engine tail nozzle drops to the range of 150-250°C, a thermal imager is used to collect the radiation brightness L(λ1) of the engine tail nozzle coating in the first band λ1=3.22-3.58μm and the radiation brightness L(λ2) in the second band λ2=3.91-4.09μm; Obtaining the radiation brightness value L(λ1) of the first band and the radiation brightness value L(λ2) of the second band of the coating area to be measured; Step 4, calculate the radiation brightness ratio of the coating to be tested: The calculation formula for the radiant brightness ratio R of the first band and the second band of the coating area to be tested is as follows: Step 5, calculate the actual surface temperature of the coating area to be tested: The estimated temperature T′ of the coating area to be tested in the engine tail nozzle in service in the field and the radiation brightness ratio R have the following relationship: The estimated temperature T′ of the engine tail nozzle coating area in field service is obtained by formula (8); The emissivity correction parameter γ(T′) at the estimated temperature of the coating area to be tested is used to correct the temperature of the coating area to be tested; then the actual surface temperature T0 of the coating area to be tested on the engine tail nozzle in service in the field and the radiation brightness ratio R have the following relationship: In formula (9), γ(T') is the emissivity correction parameter at temperature T'; Get the actual surface temperature T0 of the coating area to be tested on the tail nozzle of the engine in service in the field; Step 6, calculate the average emissivity of the coating to be tested: The band average emissivity of the coating to be tested on the engine tail nozzle in the field service at the actual surface temperature T0 is calculated by the following formula: In formula (10), C1 is the first radiation constant, C1 = 3.7415 × 10 8 W·μm 4 / m 2 ; C2 is the second radiation constant, C2=1.4388×10 4 μm·K; λ is the wavelength, and L(λ) is the radiation brightness of the coating to be tested in the λ wavelength band; So far, the average emissivity of the coating to be tested on the engine tail nozzle in service in the field at the actual surface temperature T0 in the corresponding band is obtained.

2. The dual-band engine nozzle coating emissivity measurement method according to claim 1, characterized in that: In step 2, the fitting parameters are obtained according to the fitting curve of the ratio of temperature to radiant brightness; the specific process is as follows: The traditional dual-band method fitting parameters A' and B' are obtained by fitting the following formula: The temperature T measured in step 1 h The radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h ), the fitting parameters A′ and B′ of the traditional dual-band method can be determined by least square fitting; The fitting parameters A and B of the dual-band method including the correction coefficient are obtained by fitting the following formula: The temperature T measured in step 1 h , the radiance ratio of the first band and the second band of the intact coating at the corresponding temperature R(T h ) and the emissivity correction factor γ(T h ), the dual-band method fitting parameters A and B including the correction coefficient can be determined by least squares fitting.

3. The dual-band engine nozzle coating emissivity measurement method according to claim 1, characterized in that: In step 6, the average emissivity is obtained according to the first band and the second band respectively; When λ is in the first band, the average emissivity of the coating to be tested in the first band at the true surface temperature T0 of the region is: In formula (11), λ is the median value of 3.4μm in the band λ1=3.22-3.58μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ1 band; When λ is in the second band, the average emissivity of the coating to be tested in the second band at the true surface temperature T0 of the region is: In formula (12), λ is the median value of 4.0 μm in the band λ2=3.91-4.09 μm, and L(λ1) is the radiation brightness of the coating to be tested in the λ2 band.

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