Combustion, Explosion, and Shock Waves, Vol. 39, No. 1, pp. 1–10, 2003 Turbulent Diffusion Combustion under Conditions of Limited Ventilation: Flame Projection Through an Opening UDC 536.46:614.841.41 A. Yu. Snegirev, 1 G. M. Makhviladze, 1 V. A. Talalov, 2 and A. V. Shamshin 1 Translated from Fizika Goreniya i Vzryva, Vol. 39, No. 1, pp. 3–14, January–February, 2003. Original article submitted March 19, 2002. Development of turbulent diffuse flame in a compartment with a vertical opening is studied experimentally and numerically. Flame projection through the opening ob- served under conditions of limited natural-convective ventilation is considered. The measurements are performed in a laboratory box designed for compartment-fire sim- ulation. The critical (minimum) flow rate of the fuel sufficient for flame projection is determined, as well as the delay between fuel ignition and flame projection with sub- sequent establishment of external combustion. Dimensionless variables for processing experimental data are proposed. A generic empirical dependence of the dimension- less time of flame projection on the dimensionless flow rate of the fuel is obtained for various opening sizes, burner positions, and box sizes. The dimensionless critical flow rate of the fuel obtained is in agreement with the previously published measure- ments performed for gaseous and condensed fuels. Unsteady stages of flame evolution before the projection and scenarios of flame projection through the opening are iden- tified and analyzed. A three-dimensional numerical model is developed for calculating turbulent diffusion combustion in a compartment with an opening. The model takes into account the conjugate radiative-convective heat transfer on solid surfaces and the thermal conductivity of the wall and floor materials. The experimentally observed stages of flame development, flame projection through the opening, and stabilization of external combustion are reproduced in numerical calculations. The numerical val- ues of flame-projection time are in good agreement with the measurement results and proposed empirical relation. Key word: turbulent diffusion combustion, fire simulation. INTRODUCTION Turbulent diffusion combustion in a bounded vol- ume includes critical phenomena, in particular, self- induced oscillations of the flame and its projection through an opening. Emergence of external flame rapidly increases the propagation rate of compartment fire [1, 2], and the products of incomplete combustion in 1 Center for Research in Fire and Explosion Studies, University of Central Lancashire, Preston, PR1 2HE, UK; asnegirev1@uclan.ac.uk. 2 St. Petersburg State Technical University, St. Petersburg 195251. this regime contain large amounts of toxic components. Unsteady combustion accompanied by flame projection is caused by oxidizer deficit in the flame zone, which, in turn, is determined by the regime of natural-convective gas transfer through the opening. The intensity of tur- bulent mixing of the reagents and the complicated heat transfer in the flame zone are also important. The possibility of flame projection and establish- ment of external combustion is determined by the rate of fuel addition to the combustion region. Under con- ditions of natural fire, the fuel-addition rate is the rate of gasification of the condensed (solid or liquid) fuel, 0010-5082/03/3901-0001 $25.00 c  2003 Plenum Publishing Corporation 1