Experimental study on prediction models of diffusion flame geometry in moving fires

Abstract

Flame geometry is a fundamental problem in assessing the thermal hazard during the transport process of hazardous chemicals, while the existing literature mainly focuses on stationary fires, with little understanding of flame behavior in moving fires. The objective of this study is to address the air entrainment mechanism of moving fires and derive the characterization models of relevant flame parameters. Dimensional analysis was used to determine the main factors influencing flame geometry in moving fires. A 1:10 scale burning car was then designed, and a series of moving model experiments were conducted to investigate the flame geometry. The results show that the flame height decreases monotonically with the increasing moving velocity, while the flame tilt angle gradually increases to a constant value. The variation of the flame width and the flame length includes three regimes: the decreasing regime, the transition regime, and the increasing regime. The evolution mechanism of the flame geometry can be attributed to the competition between the buoyancy and the inertia forces, which forms the bilateral, unilateral, and enhanced unilateral entrainment modes. Dimensionless correlations are provided to describe the flame geometries. Comparison between previous wind-blown flame models and the experimental data suggests that considerable error exists when studying moving fires by using wind tunnel experiments, despite their applicability to relevant aerodynamics studies.