层流预混 CH₄/O₂/N₂火焰温度的 TR-CARS 光谱研究

Objective The study aims to apply femtosecond time-resolved coherent anti-Stokes Raman scattering (TR-CARS) technology for non-invasive, high-precision temperature measurements in laminar premixed CH₄/O₂/N₂ flames under ambient conditions. This work seeks to address the limitations of traditional contact-based thermometry and conventional CARS methods, ultimately providing a novel approach to evaluate combustion efficiency, optimize fuel ratios, and reduce harmful emissions in practical combustion systems. Methods The experimental setup utilized a commercial femtosecond laser system (800 nm central wavelength, 40 fs pulse duration) to generate pump, Stokes, and probe beams. A BOXCARS phase-matching configuration ensured precise spatial and temporal overlap of the beams, while a high-precision piezoelectric stage enabled controlled delay adjustments of the probe pulse. Nitrogen (N₂) was selected as the probe molecule due to its strong coherent Raman vibrational response in the v=0 to v=1 transition (2358 cm^-1). TR-CARS signals were collected from different flame regions by varying the probe delay time (t>0), and the temporal decay of the N₂ vibrational coherence was analyzed. Experimental data were processed using a theoretical model based on resonance polarization decay kinetics, with temperature values extracted via least-squares fitting to validate the correlation between signal decay rates and thermal equilibrium conditions. Results and Discussions This work represents the first successful application of femtosecond TR-CARS for spatially resolved temperature measurements in laminar premixed CH₄/O₂/N₂ flames in China. The technique demonstrated exceptional noninterference capabilities, enabling high-sensitivity temperature detection without perturbing the flame’s flow field or chemical composition. A direct relationship between TR-CARS signal decay rates and flame temperatures was established, with signal attenuation accelerating significantly in higher-temperature regions (Fig. 6, 30 mm flame height) compared to cooler zones (Fig. 6, 21 mm height). Experimental results aligned closely with theoretical predictions, achieving random errors from -15 K to +15 K. This precision highlights the method’s reliability for transient combustion diagnostics and its potential to replace invasive probes in industrial settings. Additionally, the study confirmed that resonance-dominated TR-CARS signals could suppress non-resonant background noise, enhancing signal-to-noise ratios and measurement fidelity. Conclusions By selecting N₂ as the probe molecule and adjusting the sequence of light pulses detected by CARS spectra (t>0), we successfully detected the femtosecond TR-CARS spectral signals at different positions of laminar premixed CH₄/O₂/N₂ flame. By analyzing the decay rate of TR-CARS signal, the instantaneous temperature distribution at each position in the flame can be determined. In summary, it is feasible to measure the temperature information of laminar premixed CH₄/O₂/N₂ flame by femtosecond TR-CARS technique with high sensitivity and accuracy. The experimental results show that the decay rate of TR-CARS signal can uniquely and directly reflect the temperature under the condition of constant component concentration. The results of this study help to optimize the design and operation of combustion equipment, improve the thermal efficiency of combustion systems, and reduce harmful emissions, thus promoting the development of sustainable combustion technology. The work not only enriches the theoretical basis of laminar premixed flame research, but also opens up a new direction for the exploration of combustion science in the future.