High-Precision Temperature Measurement Using Frequency-Division Multiplexing Laser Dispersion Spectroscopy for Dynamic Combustion Monitoring

This paper proposes a frequency-division multiplexing laser dispersion spectroscopy method to implement high-precision water vapor temperature measurement in a dynamic combustion environment. Two laser beams at 7185.6 cm ^-1 and 7444.4 cm ^-1 pass through the flame simultaneously along a common path through the intensity-modulated frequency-division multiplexing approach. A pair of lock-in amplifiers are used to demodulate the dispersion phase signals of the two laser beams. Then, the two-line thermometry is used to obtain the water vapor temperature in the flame. Static and dynamic experiments were carried out on a McKenna burner and a kerosene-fueled multi-swirl staged combustor, respectively. The in-situ and time-resolved measurement results show that the method is more immune to laser power fluctuation than Direct laser absorption spectroscopy and the measurement results obtained by using the proposed method are more precise than those by using the time division multiplexing method. Therefore, the proposed method is more suitable for dynamic combustion monitoring.