4D temperature measurements using tomographic two-color pyrometry

Comparison of a two-wavelength pyrometer system and spectral pyrometry for high-temperature measurements

A pyrometer system is an optically passive, non-intrusive method that uses thermal radiation law to determine temperature. It combines electronic and optical instruments to detect low-level signals of radiation measurements. Surface high-temperature measurements are successfully obtained using a two-wavelength pyrometer system. This study used a pyrometer system to achieve high stability, minimize errors due to changing emissivity, and remove background noise from the radiation measurement for surface high-temperature measurements. Temperature measurements were also obtained from Planck's model, and the results were compared with logarithmic assumption. The precision of these measurements is improved through variable optimization of the instruments, validation of the data, and calibration of the pyrometer system. The 16 temperature measurements were obtained (800-1600°C temperature measurement range) with a correlation coefficient above 97%. The response time between temperature readings is within 785 µs. Furthermore, the high-temperature measurements were obtained with higher stability (±2.99∘ C at 1600°C) and less error (less than 2.29% for Si sensor). In addition, the error of the temperature measurement was reduced from 5.33% to 0.86% at 850°C by using Planck's model compared with using logarithmic assumption. A cooling system temperature is also optimized to reduce the error temperature reading. It was found to be at 10°C that the uncertainty was reduced from 2.29% at ambient temperature to 1.53% at 1600°C. The spectral pyrometry system was also used in comparison with the two-wavelength pyrometer system to confirm that the calibration curves of the spectral pyrometry can be used to determine temperature measurements.

Theoretical and experimental verification of wide-spectrum thermometry based on Taylor series de-integration method

In response to the challenges encountered in solving the integral equations and the disadvantages of requiring additional calibration parameters in the existing three-channel wide-spectrum temperature measurement, a wavelength-based Taylor series de-integration method is proposed. By combining the coefficient of determination, which characterizes the approximation effect, the selection criterion of characteristic wavelength (optimal expansion wavelength, OEW) is constructed. In the influence analysis of spectral emissivity on the de-integration method, the insensitivity of OEW to spectral emissivity is revealed. The feasibility of using blackbody OEW for de-integration processing is proved when the spectral emissivity is unknown, which provides necessary theoretical support for the selection of characteristic wavelengths in practical application. Based on this integration method, algebraic temperature measurement equations in the forms of graybody, three-channel fusion, and two-color are derived, and the theoretical errors of each form are discussed from both horizontal and longitudinal perspectives. Furthermore, thermometry experiments with multiple acquisition parameters and diverse samples were conducted corresponding to three solution forms, the universality of acquisition parameters and sample applicability are proven.

Correction procedure for a tomographic optical setup employing imaging fiber bundles and intensified cameras

For reliable tomographic measurements the underlying 2D images from different viewing angles must be matched in terms of signal detection characteristics. Non-linearity effects introduced by intensified cameras and spatial intensity variations induced from inhomogeneous transmission of the optical setup can lead, if not corrected, to a biased tomographic reconstruction result. This paper presents a complete correction procedure consisting of a combination of a non-linearity and flatfield correction for a tomographic optical setup employing imaging fiber bundles and four intensified cameras. Influencing parameters on the camera non-linearity are investigated and discussed. The correction procedure is applied to 3D temperature measurements by two-color pyrometry and compared to results without correction. The present paper may serve as a guideline for an appropriate correction procedure for any type of measurement involving optical tomography and intensified cameras.

Spectroscopic measurement of the two-dimensional flame temperature based on a perovskite single photodetector

Existing non-contact flame temperature measuring methods depend on complex, bulky and expensive optical instruments, which make it difficult for portable applications and high-density distributed networking monitoring. Here, we demonstrate a flame temperature imaging method based on a perovskite single photodetector. High-quality perovskite film epitaxy grows on the SiO₂/Si substrate to fabricate the photodetector. Duo to the Si/MAPbBr₃ heterojunction, the light detection wavelength is extended from 400 nm to 900 nm. Then, a perovskite single photodetector spectrometer has been developed using the deep-learning method for spectroscopic measurement of flame temperature. In the temperature test experiment, the spectral line of doping element K⁺ has been selected to measure the flame temperature. The photoresponsivity function of the wavelength was learned based on a commercial standard blackbody source. The spectral line of element K⁺ has been reconstructed using the photocurrents matrix by the regression solving photoresponsivity function. As a validation experiment, the "NUC" pattern is realized by scanning the perovskite single-pixel photodetector. Finally, the flame temperature of adulterated element K⁺ has been imaged with the error of 5%. It provides a way to develop high precision, portable, low-cost flame temperature imaging technology.

Development and validation of a hybrid constraint spectral thermometry for laminar sooting flames

A hybrid constraint spectral thermometry (HCST) method based on combined light extinction and spectral soot emission was developed for temperature measurements in sooting flames. Light extinction measurements were performed in the 635-1064 nm spectral range to constrain the fitting of the soot optical property E(m) as a function of the wavelength for separately measured spectral emission data. This hybrid constraint methodology helps to avoid complete reliance on either measurement, which significantly increases the immunity of the temperature determination to measurement noises. After numerically validating the performance of HCST, measurements were performed for a series of representative sooting premixed flames. Additional measurements were conducted with the proven tunable diode laser absorption technique to provide a reference temperature, and satisfactory agreements demonstrate the accuracy and robustness of the proposed HCST method.