Fire Dynamics and Surface Oxygen Measurement During Vertical, Buoyancy-Driven Turbulent Fire Spread

Oxygen availability at a pyrolyzing surface during turbulent flame spread remains poorly understood, and the governing fire dynamics are not yet fundamentally resolved. A series of experiments was conducted using a wall-corner configuration to measure surface oxygen concentrations during flame spread at two distinct locations under a 300\,kW hood, using both burner-generated and solid-fuel-generated flame conditions. In burner tests, a propane burner was positioned at the base corner, with mass flow adjusted to achieve steady HRRs. In solid-fuel tests (PMMA, Douglas Fir), ignition was initiated at a 30\,kW propane HRR. Gas sampling tubes were flush-mounted to one of the panels at a vertical height of 100\,cm above the burner and at lateral distances of 10\,cm and 20\,cm from the corner to extract combustion gases. A novel technique was introduced to non-intrusively estimate surface oxygen availability using a correlation between the measured oxygen volume fraction and the normalized image intensities. Radiation intensity measurements were used to quantify fire growth rates, which were, on average, 3.5 times greater in the vertical direction than in the horizontal. Flame sheet growth and acceleration were found to directly influence the measured surface oxygen volume fractions. Time-resolved surface oxygen fields were reconstructed for PMMA, providing new insight into oxygen depletion dynamics across distinct pyrolysis regimes during a turbulent fire spread.