A Single-Laser TDLAS Sensor with Dual-Gas Modulation and BiLSTM-Based Spectral Decoupling for CH₄/C₂H₆ Detection.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Environmental Science

Background:

• Tunable Diode Laser Absorption Spectroscopy (TDLAS) offers high sensitivity for trace gas detection.
• Multigas analysis using TDLAS faces challenges like spectral cross-interference and harmonic imbalance, especially for coexisting gases like methane (CH4) and ethane (C2H6).
• Overlapping absorption features of CH4 and C2H6 near 1680 nm complicate simultaneous detection.

Purpose of the Study:

• To develop a single-laser TDLAS system for accurate simultaneous detection of CH4 and C2H6.
• To address spectral cross-interference and harmonic imbalance in dual-gas sensing.
• To enhance the precision and reliability of concentration estimation for coexisting gases.

Main Methods:

• Integration of a dual-gas modulation strategy with a Bidirectional Long Short-Term Memory (BiLSTM) based spectral decoupling approach.
• Dynamic alternation of harmonic responses to match the full width at half-maximum (FWHM) of CH4 and C2H6.
• Application of BiLSTM model to compensate for spectral overlap and enhance concentration estimation accuracy.

Main Results:

• The proposed TDLAS-BiLSTM system effectively eliminated harmonic mismatch and compensated for spectral cross-interference.
• Stability tests showed low standard deviations: 3.66 ppm for CH4 and 0.56 ppm for C2H6.
• High correlation coefficients (R² > 0.99) were achieved for predicted versus reference concentrations of both gases.

Conclusions:

• The combined TDLAS-BiLSTM system significantly improves measurement precision and reliability in dual-gas sensing.
• This approach offers a practical and robust solution for accurate concentration retrieval in the presence of spectral cross-sensitivity.
• The study presents an effective strategy for multicomponent gas analysis, particularly for CH4 and C2H6 detection.