TDLAS (tunable diode laser absorption spectroscopy) is an important gas analysis method that can be employed to obtain characteristic parameters non-invasively by the infrared absorption spectra of tracer molecules such as CH₄, H₂O and O₂. In this study, a portable H₂O-based TDLAS system with a dual optical path was developed with the aim of assessing the combustion characteristics of flammable gases. Firstly, a calculation method of gas characteristics including temperature and velocity combining absorption spectra and a HITRAN database was provided. Secondly, to calibrate and validate this TDLAS system precisely, a pressure vessel and a shock tube were introduced innovatively to generate static or steady flow fields with preset constant temperatures, pressures, or velocities. Static tests within environment pressures up to 2 MPa and steady flow field tests with temperatures up to 1600 K and flow velocities up to 950 m/s were performed for verification. It was proved that this system can provide an accurate values for high temperature and velocity gas flows. Finally, an experimental investigation of CH₄/air flames was conducted to test the effectiveness of the system when applied to small diffusion flames. This TDLAS system gave satisfactory flame temperature and velocity data owing to the dual optical path design and high frequency scanning, which compensated for scale effects and pulsation of the flame. This work demonstrates a valuable new approach to thermal hazard analysis in specific environments.

Fire propagation and burning characteristics of upward flame spread over flexible polyurethane (FPU) foam board were investigated under coupling effects of pressure and orientation. As a further comparative research of our previous work, three pressures (70, 85 and 100 kPa) and four fuel surface inclination angles (0°, 30°, 60°, 90°) were applied, respectively, as before, to study the variation of typical parameters including flame spread rate (FSR), burning rate, heat transfer components, flame length, etc. First, a phenomenological interpretation was taken to show the special spreading process with melting flow combustion and flash burning observed. Second, an overall theoretical analysis was proposed to reveal the individual or coupling effects of pressure and inclined burning surface on spreading behavior. A semi-quantitative correlation was developed and formulated to show the tendency of FSR as a function of pressure, inclination and other burning parameters, which was validated by data in paper. Meanwhile, comparison of detailed differences between upward and downward spread was conducted to give a full insight on FPU fire development. At last, comprehensive discussions of coupling effects on variation of spreading characteristics and heat transfer mechanisms were performed based on fire dynamics.