Applications of TDLAS based multi-species hydrocarbon measurement using a wide scanning range DFG laser

Tunable diode laser absorption spectroscopy (TDLAS) is a widely used hydrocarbon gas sensing method in many fields. However, the short scanning range limits its application where multi-species detection is necessary. In this paper, a laser system based on TDLAS using a difference frequency generation laser was applied for the investigation of the hydrocarbon gases produced in the coal pyrolysis process and engine exhaust. The coal sample was heated up to 623 K and the recorded spectra were analyzed by the comparison with the pure hydrocarbon spectra database. A least-squares fitting was performed to quantitatively determine the concentration of each component of the mixture. Totally nine different hydrocarbons were identified and the R² values close to 1 indicate that the variance between measured and fitted data was small. The spectra of engine exhaust were recorded and analyzed using the same method. Hydrocarbon from C₃–C₈ and a small amount of methane and ethene were identified. The concentration variation with time was observed.