Characteristic studies of diffusion flame tilt angle and length in a branched tunnel fire under the effect of airflow

The reduced scale experiments were conducted to investigate the LPG flame geometry in branched tunnel fire under different airflow velocities to better comprehend the diffusion flame characteristics in narrow - long space with multiple entrance. Five different heat release rates varied from 1.72 kW to 5.18 kW were considered. The flame tilt angle and flame length were measured and correlated. Results show that the flame tilts downward to multiple entrance direction (ramp and mainline) under natural ventilation, which is mainly related to the asymmetry tunnel cross-section dimensions between fire source two sides. The experiments presented three different flame tilting conditions under different heat release rates and airflow velocities due to the dominance of buoyancy force or inertial force. The flame tilt angle is correlated using the nondimensional heat release rate and Froude number, and the predictions by proposed correlation agree reasonably well with the experimental data. The flame length increases with the heat release rate and elongated by airflow. The empirical model for dimensionless flame length are developed both under natural and longitudinal ventilation.