To solve the problems of high computational cost and the long time required by the simulation and calculation of aeroengines’ exhaust systems, a method of predicting the characteristics of infrared radiation based on the hybrid kernel extreme learning machine (HKELM) optimized by the improved dung beetle optimizer (IDBO) was proposed. Firstly, the Levy flight strategy and variable spiral strategy were introduced to improve the optimization performance of the dung beetle optimizer (DBO) algorithm. Secondly, the superiority of IDBO algorithm was verified by using 23 benchmark functions. In addition, the Wilcoxon signed-rank test was applied to evaluate the experimental results, which proved the superiority of the IDBO algorithm over other current prominent metaheuristic algorithms. Finally, the hyperparameters of HKELM were optimized by the IDBO algorithm, and the IDBO-HKELM model was applied to the prediction of characteristics of infrared radiation of a typical axisymmetric nozzle. The results showed that the RMSE and MAE of the IDBO-HKELM model were 20.64 and 8.83, respectively, which verified the high accuracy and feasibility of the proposed method for predictions of aeroengines’ infrared radiation characteristics.

To achieve rapid and precise non-contact measurements of coating emissivity at room temperature, a measurement method based on infrared thermal imager was proposed. By applying two irradiations with different energies to the target and reference surfaces, the influences of atmospheric transmittance, radiation of the target itself, environmental radiation, and atmospheric path radiation were eliminated, thereby enabling accurate emissivity measurement. Experiments were designed for validation with a mid-wave infrared thermal imager and a surface blackbody as the radiation source. Several combinations of irradiation energy were set to investigate the effects of average energy and energy difference between the two irradiations on the measured results. The normal emissivity of the coated sample plate in the mid-wave band was measured to generate the image of coating surface emissivity. Then, the emissivity measurement results of the proposed method were compared with those of the energy method and the point emissivity measuring instrument under the same conditions, and the comparison indicated that the proposed method can effectively measure the emissivity of coating. Some factors causing measurement errors were analyzed. Finally, an experiment was designed to compare the measurement speed between the proposed method and the currently used methods, and the experimental results were analyzed.

In this paper, a measurement correction method is proposed to correct the error of the irradiation reflection method when measuring the emissivity of curved surface targets. First, by introducing an angle parameter related to the target surface shape, the formulas of emissivity measurements for curved surface targets under various types of radiation sources were obtained. Then, the variation law of these emissivity measurement formulas was analyzed, the concept of the measurement correction factor was proposed, and then a unified correction measurement formula was obtained. Finally, a scene of measuring the emissivity of a curved surface target based on the irradiation reflection method was simulated. Different target emissivities and different distances between the radiation source and target were set, and the errors between the measured and corrected emissivities were compared. The results revealed that the proposed method could effectively correct the error caused by the curvature of the target surface when measuring its emissivity by the irradiation reflection method. This is of great significance to expanding the application scope of the irradiation reflection method and improving the measurement accuracy.

This study explores a novel method for removing Al metal coatings by using nanosecond pulsed lasers to clean Al metal layers from ceramic substrate surfaces. The impact of laser power and pulse width on the effectiveness of the removal of the Al metal layer from the ceramic substrate was examined. The findings revealed that a laser with a power of 120 W, a pulse width of 200 ns, a frequency of 240 kHz, and a speed of 6000 mm/s could effectively remove the Al metal layer (50 μm) in a single laser cleaning cycle without causing damage to the ceramic substrate. The mechanism behind the removal of the Al metal layer from the ceramic substrate surface was also investigated. It was discovered that local high temperatures caused by laser irradiation and the difference in thermal expansion coefficients between the metal layer and the ceramic substrate both contribute to the removal of the Al metal layer during the laser cleaning process. This research provides an effective process for removing the Al metal layer.

Low Infrared emissivity coating (LIREC) is prone to generating some problems such as bulges, degumming, and abrasion. In order to study whether the performance of LIREC under different damages can meet the work needs, it is essential to timely measure and evaluate the performance state of LIREC in the application process. The existing methods for measuring the damage of LIREC have some disadvantages such as expensive equipment, complex operation, and inaccurate measurement results. In this paper, a measurement method of LIREC damage capability based on thermal imager is proposed. The radiation temperature is measured by thermal imager, the real temperature and ambient temperature of coating surface are measured by thermocouple, and the emittance of coating surface is calculated. Non-contact and continuous large-area emissivity measurements are carried out on the damaged parts of the coating and verified by experiments. The measurement results show that the different damage types and damage degrees directly affect the measurement results of LIREC. Wear damage increases the emissivity of the coating while debonding damage basically does not change the coating emissivity. Shedding damage of small diameter forms voids, which causes the increase of the damage parts of emittance. In addition, bulge damage impedes temperature transfer and reduces emissivity. This method can timely and accurately measure and evaluate the performance state of LIREC and can provide a new idea for the accurate measurement of damage emissivity of LIREC.