Fig. 1. Schematic of time division multiplexing

Fig. 2. Coal pyrolysis gas detection system

Fig. 3. Amplitude of second harmonic signal versus volume fraction. (a) CH₄; (b) C₂H₄

Fig. 4. Device response time

Fig. 5. Results of 1000 s continuous measurement and Allan variance analysis results. (a) 1000 s continuous measurement result for CH₄; (b) Allan variance analysis result for CH₄; (c) 1000 s continuous measurement result for C₂H₄; (d) Allan variance analysis result for C₂H₄

Fig. 6. Volume fractions of CH₄ and C₂H₄ versus temperature under different heating rates

Fig. 7. Volume fraction of CH₄ and C₂H₄ versus temperature under different particle sizes

Fig. 8. Volume fractions of CH₄ and C₂H₄ versus temperature under different oxygen volume fractions