A linear temperature extraction method from Voigt lineshape profile in laser absorption spectroscopy

Monitoring of combustion parameters, especially temperature and gas concentration in the flames is essential to improve the combustion efficiency and reduce pollutant exhausts. A linear temperature extraction method was proposed in this work from the laser absorption profile. It was derived from the solution of a variable coefficient differential equation. The equation holds in case of gas species distributed homogeneously in the laser path and serves as an indicator for average temperature even it is heterogeneously distributed along the path. Only one absorption spectrum was required in the proposed method to extract the value of temperature along the path, and this simplified the applications of the laser absorption spectroscopy techniques, where two different absorption spectra are required as usually to carry out the typical dual line method. Noisy data were used to verify the feasibility of the proposed method and the error of linear temperature extraction was below 20K for temperature from 300K to 1200K, if the signal-to-noise ratio (SNR) was above 60dB. Also, the nonlinear fitting method was carried out and compared with the proposed method. It showed that the proposed method yielded temperature values with slightly larger deviations in case of noisy data but took much shorter calculation time. The proposed linear temperature extraction method is more feasible in hardware implementation for real-time temperature readings.