Thermal-flow regulation of burning rate and flame centerline temperature by a central opening in ethanol annular pool fires under forced convection

Annular liquid-fuel configurations may occur when a central opening or structural element modifies the geometry of an accumulated fuel layer. Compared with a conventional circular pool, the additional inner boundary changes air entrainment, flame heat feedback, and thermal-plume development, particularly under forced-convection conditions. This study experimentally investigates ethanol annular pool fires with inner-to-outer diameter ratios of 0, 0.316, 0.555, and 0.707 under cross-air-flow velocities of 0–5.0 m/s while maintaining a constant total burning area. The mass burning rate, flame morphology, and temperature distribution along the inclined flame centerline were measured simultaneously. The mass burning rate increased with both cross-air-flow velocity and annular opening ratio, whereas the normalized flame-centerline temperature decreased as the central opening enlarged. Revised correlations for the burning rate and temperature, incorporating the Reynolds number and a dimensionless annular geometry parameter, achieved coefficients of determination R 2 of 0.97 and 0.82, respectively, indicating good agreement with the experimental data. These correlations effectively capture the coupled effects of annular geometry and forced convection on liquid-fuel burning and thermal-plume temperature within the tested geometric and cross-air-flow ranges, providing practical predictive tools and scientific guidance for fire-safety design and risk assessment of annular liquid-fuel fires.