Akihiko Ito

Bio: Akihiko Ito is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Laminar flame speed & Flame spread. The author has an hindex of 1, co-authored 1 publications receiving 23 citations.

Downward flame spread along two vertical, parallel sheets of thin combustible solid

Abstract: This paper is concenred with the steady, two-dimensional vertical downward spread of flame along two parallel sheets of paper placed in air. The purpose of the present study is to correlate experimentally the flame spread rate, the distance separating, the two sheets and the width of the paper, and to model theoretically the flame spread in the presence of interaction of multiple flames. The flame spread rate depends more on the separation distance between the two sheets of paper than on the width of the paper. Within the narrow space region, C≤0.3 cm, the flame spread rate is reduced to about a half of that for burning of a single sheet of paper. On the other hand, in the wider space region, C≥0.5 cm, the flame spread rate increases and becomes greater than that of a single sheet. It reaches the maximum value at a finite separation distance, C=1.5∼2.0 cm. A simple theoretical model was used to explain the experimental results. The theoretical flame spread rates predicted from the model were found to be in good agreement with the experimental data. It is concluded from the experimental and theoretical results that in the narrow space region between the burning sheets of paper the convective heat transfer predominates and controls the flame spread rate, whereas in the wider space region the radiative heat transfer from the opposite flame and ember plays an important role in controlling the flame spread rate.

Heat transfer from flames between vertical parallel walls

Abstract: Measurements of the distribution of total heat flux on a wall exposed to a line burner have been carried out for a number of configurations in which the distance to a parallel wall has been varied. It has been shown that the heat fluxes increase as the separation between the walls is reduced. The burner position and heat output influence not only the levels of heat flux, but also the distribution pattern. Changing the air flow by blocking the ingress of air at the base of the walls is shown to have a dramatic effect. The most extreme case gave almost a four fold increase in the maximum heat flux when the base is closed off. Correlations have been obtained with a line burner symmetrically placed against an instrumented wall for q dot ″ w in terms of x Q l ∗ 2 3 D, y′/D , and a D , with correlation coefficients of at least 0·957. The results and findings have implications for modelling flame spread in confined spaces, and for identifying and assessing the risks associated with the bulk storage of materials.

Experimental and theoretical study on downward flame spread over uninhibited PMMA slabs under different pressure environments

Abstract: This paper presents an experimental and theoretical study of side-edge effects on downward flame spread over two parallel polymethyl methacrylate (PMMA) slabs under different pressure environments. Identical experiments of downward flame spread over thin PMMA slabs with side-edges unrestrained were conducted at different altitudes in Hefei (102 kPa), Geermu (73.2 kPa) and Lhasa (66.3 kPa). Experimental results show that the flame spread rate is controlled by ignition along the side-edge, rather than at the center of the samples, for experiments with both single and two parallel slabs. Based on these results, a thermal model is developed which describes flame spread along the edge and quantitatively agrees with experimental results. In the parallel-slab case, convective heating appears to influence the spread rate only when the separation distance is very small, with radiative heating playing a more important role as separation distance increases. The angle of the pyrolysis front, formed between the faster side-edge spread and slower center-region spread, hardly changes with pressure, but changes significantly with separation distance, due to differing modes of heat transfer between the side-edge and center region. In addition, variations of flame height with pressure and separation distance are reasonably interpreted from diffusion flame theory.

Experimental analysis of diffusion flame spread along thin parallel solid fuel surfaces in a natural convective environment

Abstract: An experimental investigation of diffusion flames spreading along thin solid fuels in concurrent and opposed configurations in a gravity induced flow is presented in this study. Flame spreading over one side as well as on both sides of the fuel is studied. MATLAB is used to post process high definition flame videos to obtain flame spread rate as a function of inclination angle of the fuel surface, number of fuel sheets and separation distance. For one side burning, present results are compared with those from literature. For double side burning, the inclination angle is varied from 90° (upward spread) to −90° (downward spread), measured with respect to the horizontal (0°). The spread rates in double side burning are higher and the maximum spread rate is observed for 90° case, as opposed to 120° in single side burning. The upward flame spread displays a non-uniform temporal variation, especially when the orientation angle is greater than 20°. Fuel cracking was noted to be most severe at 90°. However, the downward flame spread rate is almost steady. The multiple fuel sheets (2 and 3 sheets) are kept parallel to each other with the separation distance between them varied from 0.5 to 3 cm. In upward flame spread, for a small separation distance of 0.5 cm, multiple sheets produce spread rates lower than the single fuel case due to insufficient oxygen supply. At 1.5 cm separation, maximum flame spread rate is observed for multiple sheet cases, due to increased availability of oxygen and enhanced heat transfer from neighboring flames. At 3 cm, the spread rate is almost the same in all cases indicating that the interference effects have become weaker. The variation of flame-spread rate in multiple fuel sheets with respect to inclination angle is almost similar to that of single sheet cases.

An Experimental Study of Upward Flame Spread and Interactions Over Multiple Solid Fuels

Abstract: Upward flame spread and flame interactions over multiple solid fuels are experimentally studied, and the effects of flame interactions on the flame spreading rates are analyzed. Flame spreading cha...

Flame spread and interactions in an array of thin solids in low-speed concurrent flows

Abstract: Flame spread in an array of thin solids in low-speed concurrent flows was investigated and numerical solved. A previous steady, two-dimensional flame-spread model with flame radiation was employed and adapted in this work. The flame structures of spreading flames between parallel solids were demonstrated and some of the features were presented, including flow channelling effect and flame radiation interactions. The channelling effect is caused by flow confinement by the presence of the other solids; the flows through the hot combustion gases are accelerated downstream drastically. Radiation interactions between flames and solids contributed to a less heat-loss system, and radiation re-absorption by flames resulted in a larger flame with higher temperature, which increased the conductive heat fluxes to the solids and flame spread rate. Consequently, the extinction limit for the interacting flames is extended beyond the low-speed quenching limit for a single flame. The influence of the separation distance o...