Simultaneous measurement of temperature and C2H4 concentration in hydrocarbon flames using interference-immune differential absorption spectroscopy at 3.3 μm.

• Simultaneous and interference-free measurements of T and C 2 H 4 are performed using differential absorption spectroscopy. An Interband Cascade Laser near 3.3 μm is employed to improve the detection sensitivity of this system. The interference from non-target absorption lines and background radiation is suppressed. The effects of particle or droplet extinction and scattering in the flame are also reduced. In diagnostic applications based on tunable diode laser absorption spectroscopy, the measurement of target substances can be influenced by factors such as background thermal radiation in the combustion environment, extinction caused by solid or liquid particles, and other interfering absorptions. In this work, we developed a differential absorption diagnostic technique based on wavelength pairs, utilizing an interband cascade laser near 3.3 μm to simultaneously measure temperature and C 2 H 4 concentration in hydrocarbon flames. Based on a detailed study of the C 2 H 4 spectrum in this region and considering the optimal standard for spectral lines, two wavelength pairs were selected. The temperature is determined by the ratio of the absorption cross-sections of two wavelength pairs, and the C 2 H 4 concentration is inferred based on the wavelength pair with higher differential absorption. In the initial stage, the system's accuracy was verified in high-temperature static conditions (T = 300–800 K, P = 1 atm), and continuous time series measurements demonstrated the system's stability. The limit of detection achieved by Allan-Werle variance analysis is 2.5 ppm at the optimal average time of 100 s. Subsequently, measurements were taken in a hydrocarbon flame. The obtained results indicate an average deviation of 1.021 % between the measured temperature in the flame and the reference value, with a standard deviation of 1.381 % for concentration measurement. All the measurements show that the system can be potentially applied to combustion diagnosis. [ABSTRACT FROM AUTHOR]