Measurement of combustion temperature field is essential for combustion diagnosis. As intrusive devices for temperature measurement interfere the flow field of flame, non-intrusive thermometry techniques are highly desired. Electrical tomography, which is a non-contact technique and can reconstruct the complex admittivity distribution in the flame, is promising for combustion diagnosis. However, the admittivity distribution need to be mapped to temperature field in practical applications. In this paper, an ion current probe and a thermocouple measured the electrical admittivity and temperature in the flame, served as calibration devices for establishing the mapping model from the reconstructed admittivity to temperature. Polynomial, exponential and eXtreme Gradient Boosting (XGBoost) regression modeling methods were used to fit the mapping model. Accuracies of training and test data sets of the XGBoost mapping model were the highest, and their mean relative error were only 0.69% and 16.69% respectively. An alcohol lamp flame was monitored by using the dual-modality electrical tomography. Reconstructed images of conductivity and permittivity were mapped to temperature distributions with the established mapping model. The estimated highest temperature was ring-shaped distributed, and it was verified by the longitudinal image of temperature reconstructed from a flame photo of 432 nm radiation. The proposed method was also used to monitor the temperature variations during the ignition and blowout processes of the alcohol lamp flame. Experimental results showed that the proposed method was effective to capture the evolution of temperature distributions in highly dynamic combustion field.

Wavelength modulation spectroscopy (WMS) is recognized as a good noise immunity method in tunable diode laser absorption spectroscopy (TDLAS). It can obtain high signal-to-noise ratio harmonic intensity signals for precise gas parameter measurement, like temperature and concentration. However, the TDLAS-based velocity is sensitive to the Doppler shift in the laser frequency caused by the high-speed flow, which usually requires complex wavelength calibration and precise signal alignment. This work proposed a novel method for the precise velocity measurement directly by extracting the time interval of the even-symmetric 2f/1f harmonics signal with a self-convolution algorithm. The even-symmetric 2f/1f harmonics signal is obtained from the up-and-down laser optical frequency scanning WMS with lock-in amplification technology. A portable measurement system has been developed to achieve simultaneous velocity and temperature measurement of the gas in turbojet engine exhaust with different operation states. The maximum standard deviation of the velocity derived by the proposed method is 15.6 m/s, while that by traditional DAS and WMS are 69.2 m/s and 26.4 m/s, respectively. Experiment results have verified the improvement of velocity precision by the proposed method. It can provide reliable experimental data for improving the design of combustors and optimizing numerical combustion simulations.

Increasing aviation activities have heightened concerns about particulate emissions from aircraft engines. Current ICAO standards mainly focus on large civil turbofan engines, leaving a gap in the research on PN emissions from small aircraft engines. This study examined the PN emission characteristics of micro-turbojet engines, including the morphology, PN, and size distribution under different load conditions, compared with a micro-piston engine. The results showed that the nvPM from micro-turbojet engines was larger and more complex than typical aviation soot, likely due to reduced combustion efficiency and incomplete fuel combustion. Micro-turbojet engines exhibited fewer fluctuations in their emission index number (EIn) and emission index mass (EIm) at lower speeds. The geometric mean diameter (GMD) of particles was inversely correlated with thrust, while the geometric standard deviation (GSD) slightly increased with thrust. Quantitative comparisons indicated that PN emissions from micro-turbojet engines were higher, with EIn values ranging from 2.0 to 3.3 × 10¹⁶/kg fuel compared with 1.2 to 1.5 × 10¹⁶/kg fuel for micro-piston engines. EIm values for micro-turbojet engines ranged from 8 to 40 mg/kg fuel, while micro-piston engines had slightly higher values due to better carbonization. These findings validated the measurement methodology used to accurately assess PN emissions under low-thrust conditions in micro-turbojet engines. These results provide crucial insights and support for the future monitoring and regulation of PN emissions across all thrust conditions in small aircraft engines.

In this article, an annular electrical capacitance tomography (ECT) sensor was designed, and a revised Calderon image reconstruction method was proposed for monitoring the flashback flame of a bluff-body burner. The central support of the bluff-body was used as the internal electrode of the sensor, and the external electrode array was fixed on the outer surface of the burner. The capacitance values of all pairs of electrodes, including the internal and external, composed a boundary capacitance matrix of the annular sensing field. The revised Calderon method was compared with the commonly used sensitivity matrix-based methods including the linear back projection (LBP) and Landweber methods for imaging the cross-sectional distribution of permittivity which is continuous in value. Simulation results show that the revised Calderon method is of higher image reconstruction quality than the LBP and Landweber methods. In the experiment, the designed annular ECT sensor and revised Calderon method were used to monitor the flame flashback phenomenon of the bluff-body burner. The experiment results not only monitored the occurrence of flame flashback, revealed the variations of flame flashback intensity and time with the fuel:air equivalent ratio, but also determined the boundary condition of flame flashback of the bluff-body burner. The proposed method provides a new approach for experimental study on the influencing factors of flame flashback, and thus can be applied to research on combustion stability and high-performance burner design.

Aviation soot constitutes a significant threat to human well-being, underscoring the critical importance of accurate measurements. The condensation particle counter (CPC) is the primary instrument for quantifying aviation soot, with detection efficiency being a crucial parameter. The properties of small particles and the symmetry of their growth pathways are closely related to the detection efficiency of the CPC. In laboratory environments, sodium chloride is conventionally utilized to calibrate the CPC’s detection efficiency. However, aviation soot exhibits distinctive morphological characteristics compared to the calibration particles, leading to detection efficiencies obtained from calibration particles that may not be applicable to aviation soot. To address this issue, a quantitative study was performed to explore the detection efficiency deviations between aviation soot and calibration particles. The experiment initially utilized a differential mobility analyzer to size select the two types of polydisperse particles into monodisperse particles. Subsequently, measurements of the separated particles were performed using the TSI Corporation’s aerosol electrometer and a rigorously validated CPC (BH-CPC). These allowed for determining the detection efficiency deviation in the BH-CPC for the two types of particles at different particle sizes. Furthermore, the influence of the operating temperature of the BH-CPC on this detection efficiency deviation was investigated. The experimental results indicate a significant detection efficiency deviation between aviation soot and sodium chloride. In the range of 10–40 nm, the absolute detection efficiency deviation can reach a maximum of 0.15, and the relative deviation can reach a maximum of 0.75. And this detection efficiency deviation can be reduced by establishing a relevant relationship between the detection efficiency of the operating temperature and the calibration temperature. Compared to the saturated segment calibration temperature of 50 °C, the aviation soot detection efficiency is closer to the sodium chloride detection efficiency at the calibration temperature of 50 °C when the saturated segment operates at a temperature of 45 °C. These studies provide crucial theoretical guidance for enhancing the precision of aviation soot emission detection and establish a foundation for future research in monitoring and controlling soot emissions within the aviation sector.