High-Precision WMS-TDLAS Hydrogen Detection System with a Long Optical Path Length Multipass Matrix Cell.

The weak absorption features of hydrogen and the coexistence of various interfering gases make it considerably challenging to achieve high-precision hydrogen detection in complex environments via tunable diode laser absorption spectroscopy (TDLAS). To address these challenges, this study employed a spectral line overlap decoupling algorithm as well as a low-pressure detection strategy and designed a TDLAS hydrogen detection system based on wavelength modulation spectroscopy and a novel long optical path length (OPL) Pickett Bradley White cell (PBWC)-PBWC multipass matrix cell (MMC), aiming to realize hydrogen sensing in biomass gasification environments. To resolve interference from coexisting methane and carbon dioxide, a reduced pressure of 200 Torr was employed to mitigate spectral line overlaps and pressure broadening effects. Additionally, a least-squares algorithm was implemented to decouple the mixed absorption spectra, enabling the high-precision retrieval of hydrogen concentration. In response to the limitation of the insufficient absorption of hydrogen, an MMC featuring a multiloop reflective architecture was designed, achieving an effective OPL of up to 314 m while possessing a high ratio of OPL to volume. The experimental results indicate that the system has good measurement linearity and accuracy, achieves a detection limit of 38.5 ppm, and can accurately measure hydrogen concentration even when interfering gases fluctuate over a wide range. This work highlights the application potential of TDLAS in hydrogen detection and fills the research gap in this field.