Methane and carbon dioxide mixed gas detection based on sphere–tube coupled photoacoustic cell

Methane (CH4) and carbon dioxide (CO2) are the main components of greenhouse gases and coal mine gases, which quantitative detection is beneficial to environmental governance and disaster warning. To realize the online detection, a sphere–tube coupled photoacoustic cell was employed as the core unit, a photoacoustic detection setup for mixed gas based on time division multiplexing was designed. Distributed feedback lasers (DFB) with central wavelengths of 1653 nm and 2004 nm were employed as the excitation light source. The experimental results show that there was no mutual interference between the photoacoustic signals of the mixed gas. The minimum detection limits for CH4 and CO2 within 5 s were 509 ppb and 23 ppm, and the normalized noise equivalent absorption coefficients were 2.1 × 10−9 cm−1 WHz−1/2 and 8.98 × 10−9 cm−1 WHz−1/2 respectively.