Masaaki Kawamata

Flame Spread Over Fuel Soaked Sand In An Opposed Air Stream

Flame spread over kerosene soaked sand in a quiescent, atmosphere and an opposed air stream has been examined, and the effects of the air stream on the fl arne spread mechanisms are discussed. The aspects of spreading flames, the flame spread rate, and t.he temperature d i.s t.r i buti.ons near leading flame edges were examined for various initial temperatures T. of kerosene soaked sand and free stream velocities U of the opposed i. air stream. As U increases, the flame near Lt.s leading edge approaches the sand surface. The flame spread r a t.e Vf at U=O increases considerably with T.. As U increases, V f decreases rapidly and then gradually decreas1?s until U becomes 275 cmls in the Li.mi ts of present e xpe r i.men ts . When U exceeds 275 cm y s , the flame spread becomes unstable and V f decreases rapidly. In the case of U=O, the heat transfer from the flame zone t.o the unburned region ahead of the leading flame edge seems t.o depend largely on the flame radiation. On the other hand in the case of U 0, the heat transfer t.o the unburned region seems to depend largely on t.he heat conduction through the sand layer. The stabil izat ion of the leading flame edge associated with the aerodynamic atru c tur e of the reverse flow region is found t.o be necessary for the stable flame spread.

Behavior Of The Reverse Flow In Front Of The Leading Flame Edge Spreading Over Fuel-soaked Sand In An Air Stream

The behavior of the reverse flow in f r o nt. of t.h e leading flame edge spreading over kerosene-soaked sand in an a i r s t.r e a:n has been examined using a few flow visualization techniques, and r.h e role of t.h e reverse flow in the flame spread is discussed. In a wide range of the free stream velocities U from 30 t.o 210 cm/s, a stable reverse flow region in f r o nt. of the leading flame edge was observed clearly, and its horizontal dimension was found to be almost independent of U. As U increases, the velocity of the reverse flow increases. The reverse flow takes an important role in the stable flame spread in an opposed air stream, although it has no apprec iable e f f e ct. on the f lame spread rate. The reverse f low provides a slow gas stream region, through which gasified fuel as well as heat from the reacteion zone would be transferred in the upstream direction.

Simultaneous measurements of gas flow and flame front movement in a turbulent premixed flame zone

Instantaneous local flame front movement and the flow velicity of unburned mixture or burned gas near the flame front in a turbulent flame zone have been measured simultaneously by using a micro-electrostatic probe with three sensors and a dual beam LDV system. The mean gas flow was also measured to explore the flow field of the turbulent premixed burner flame. It was found that there are evident differences in the velicity and direction between the mean gas flow and the most probable flame front movement at the side of the turbulent flame zone. The flow velocity of the burned gas near the flame front was found to be generally larger than that of the unburned mixture when the flame front moves toward the burned gas side, although no appreciable difference in their flow velocities is seen when it moves toward the unburned mixture side. Based on the relation between the flame front velocity and the flow velocity of the unburned mixture near the flame front, it was estimated that the local flame velocity is equal to the vector sum of the laminar burning velocity and the flow velocity of unburned mixture near the flame front. The relation between the overall flame front movement and the instantaneous local flame front movements was discussed using a simple model of a flame front movement.

Numerical Analysis on the Structures and Characteristics of Diffusion Flames in Laminar Boundary Layers.

Numerical analysis of a diffusion flame established in a laminar boundary layer over a flat surface with fuel injection has been carried out for typical three cases. The conservation equations of continuity, momentum, energy and chemical species are solved using a finite-difference method for two-dimensional flow field with single step raction of methane with air. The flame shape, flow field, diffusion of component gas, heat transfer, and the structure of leading flame edge are examined in detail. A separation region is found to be formed in front of the leading flame edge, which brings a slow gas steam region near the flame edge. Caused by the concentration of oxygen diffusion in the slow gas stream region, a sharp peak of the reaction rate appears at the leading flame edge. Such an aerodynamic structure is inferred to take an important role in the flame stabilization. The reaction rate at the center of the flame zone is found to depend strongly on the free stream velocity, however, to be almost independent of the fuel injection velocity.

Polyurethane Foam Smoldering Supported By External Heating

The temperature fluctuations during the smoldering spread in a rigid polyurethane foam were measured in order to explore the spread mechanisms and thermal structures of the smoldering combustion supported by external heating. The experiments were conducted under natural and forced draft conditions, and the effects of the heat source intensity H and the air supply content Q on smoldering were examined. It was found that smoldering spreads faster in the upward direction than the downward direction under natural draft conditions but that the spread rates become almost the same as Q increases under forced draft conditions. The smoldering spread rate Vs increases linearly as H or Q increases. The Vs is proportional to the temperature gradient (dT/dx)s at the charring front, i.e., the heat flux transferred to the unburned solid. When the representative smoldering temperature Tg in the smoldering zone is larger than 300 C, the smoldering spread is maintained, and Vs increases linearly as Tg increases.