Performance evaluation and correction of Al ₂O ₃ and YSZ-doped In ₂O ₃/In ₂O ₃ multilayer heterogeneous thin-film thermocouples up to 1850 °C

The combustion chamber temperature of the new generation aircraft engines can reach an ultra-high temperature of 1800 °C, making temperature monitoring of key components crucial. Thin-film thermocouples (TFTCs) are highly sensitive and have rapid response time; however, their upper temperature limit remains below 1800 °C. This study proposes an ultra-high temperature film thermocouple, enhanced by yttria-stabilized zirconia (YSZ) for positive film, indium oxide (In₂O₃) for negative film, aluminium oxide (Al₂O₃) for protect film. The thermocouple is designed based on temperature measurement principles, First-principles, and simulations, and it is manufactured via screen-printing. The results indicate that the maximum working temperature is 1850 ℃. In experiments with different doping ratios at 1800 ℃, the thermocouple achieves a maximum temperature electromotive force (TEMF) of 258.5 mV and a maximum Seebeck coefficient of 180.9 μV/°C, with an In₂O₃:YSZ92(ZrO₂:Y₂O₃= 92:8 wt%) ratio of 9:1 wt%. Using the lumped heat capacity method, the response time is measured at 2.8 ms, demonstrating good dynamic response characteristics. The film thermocouple is successfully utilized to measure the gas temperature of 1090 °C at the outlet of air turbine rocket engine, confirming its high-temperature operational capability. To improve the repeatability of the TFTCs without affecting their thermoelectric outputs, a CNN-LSTM-attention neural network is implemented to mitigate repeatability errors, achieving a high repeatability of 99.53%. Additionally, the compensated temperature data are compared with those obtained from a standard B-type thermocouple, showing a full-scale error of ±0.73% FS. This study provides a feasible solution for ultra-high temperature measurements.