Simulation and Analysis of CH₄ Concentration Measurement Based on QCL-TDLAS

Abstract

Tunable diode laser absorption spectroscopy (TDLAS) is a kind of gas concentration measurement technology with high precision widely used in the detection of methane (CH4). Compared with the near-infrared absorption band, CH4 molecule has greater absorption intensity in the range of mid-infrared absorption band. Therefore, the TDLAS performance can be greatly improved when the mid-infrared quantum cascade laser (QCL) is adopted as light source when detecting CH4 concentration. As an important parameter, the effect of modulation factor on the second harmonic signal was analyzed, and the optimal value of modulation factor was obtained to be 2.2 by simulation. In addition, both the TDLAS measurements of CH4 concentration in the range of near-infrared and mid-infrared were simulated and analyzed under normal temperature/pressure and troposphere environment respectively. The results show that the sensitivity of the detection of CH4 gas in the mid-infrared band of 7.6 μm is greatly improved relative to the absorption band of 1.6 μm in the near-infrared.