Hiroyuki Torikai

Development and control of an aerial extinguisher with an inert gas capsule

Fire extinguishment approaches with inert gases such as carbon dioxide (CO2) and nitrogen (N2) have several advantages compared with ones with water. On the other hand, they have low extinguishment performance and put lives at risk. To enhance the extinguishment performance and to reduce risk to life, the authors have proposed a robotic fire extinguishment approach and a prototype of an aerial extinguisher with an inert gas. The prototype can transport only a small volume of an inert gas, and it can extinguish a very small flame. In this paper, we develop a quadcopter type of aerial extinguisher with a rubber balloon filled with helium. The extinguisher is easily adapted to the volume of helium by changing the length of rods between the motors and the center. It is shown that the extinguisher can be controlled by using a depth sensor. It is also demonstrated that the extinguisher with 5 L of helium achieves flame extinguishment for a diffusion flame of methane with a 10 L/min. flow rate.

Extinguishment of a Laminar Jet Diffusion Flame Using a Soap Bubble Filled with Nitrogen Gas

Inert gases, such as nitrogen, argon and carbon dioxide, are able to extinguish a fire more cleanly than water and dry chemical extinguishing agents. However, to extinguish the fire completely, a large amount of inert gas is needed to be released at the vicinity of the fire or into a confined space containing the fire. If a capsule is filled with an extinguishing inert gas, and ruptures due to contact with the flame zone, the high concentration extinguishing gas can be directly supplied to the fire. By using this capsule, it may be possible to increase the effectiveness and decrease the amount of the extinguishing inert gas needed in firefighting. In the present study, in order to clarify the fundamental characteristics of flame extinguishment by an inert gas capsule, extinguishment experiments of a methane-air laminar jet diffusion flame by a soap bubble capsule filled with nitrogen gas have been performed. Visualization of flow released from the bursting bubble has also been carried out by using laser tomography and schlieren techniques. Results show that, when the soap bubble bursts, two different kinds of nitrogen gas flow are formed. The first flow is generated by the pressure difference between the inside and outside of the soap bubble. The second flow is generated by the soap liquid film dynamics. Combined, these two flows of nitrogen gas extinguish the laminar jet flame. The first flow extinguishes the flame base locally, and the second flow leads to blow out of the whole flame.

Flame extinguishment by cooperation of two aerial extinguishers

Fire extinguishment approaches with inert gas such as carbon dioxide (CO2) or nitrogen (N2) have several advantages compared with ones with water. On the other hand, they have low extinguishment performance and put lives at risk. To enhance the extinguishment performance and to reduce risk to life, the authors have proposed a robotic fire extinguishment approach with massive aerial extinguishers with inert gas. This paper proposes a control algorithm for multiple aerial extinguishers without any markers, while a single extinguisher with an easily extracted marker has been controlled in our previous work. This paper also demonstrates flight control of two extinguishers and flame extinguishment by cooperation with two extinguishers. The cooperative behavior in the flame extinguishment experiment is not explicitly programmed, and the two extinguishers are simply controlled by trajectory tracking using PID controllers.

Examination of Extinguishment Method with Extinguishing Powder Packed in a Spherical Ice Capsule

In the study, the extinguishment method with an extinguishing powder packed in the hollow capsule made of ice has been proposed and investigated experimentally. If a capsule can be used to deliver an extinguishing powder, it will be possible to transport the agent to the fire area over a long distance. The ice capsule is formed by using the double rotational axis casting machine. The amount of water of 1.8 cm3 is used to make the capsule which has 20 mm in outer diameter. ABC extinguishing powder is filled into the ice capsule. To clarify the characteristics of the ice capsule extinguishment, the extinguishing experiments of a methane-air diffusion flame have been performed, and also the extinguishing process has been observed with a high-speed camera. The ice capsule drops in free fall from the height of 1.8 m, and the impact velocity onto the metal plate, in which the burner is embedded, is 5.8 m/s. The extinguishment of the flame with the extinguishing powder of 3 g filled into the ice capsule has been succeeded, and the maximum effective range of the extinguishing method is 120 mm distance from the burner center to the dropping location of the ice capsule.

Effect of Porosity on Flame Spread Along a Thin Combustible Solid with Randomly Distributed Pores

The flame spread route in a residential fire strongly depends on the arrangement of combustible materials like furniture, bedclothes, housewares, etc. In addition, the flame spread rate distinctly varies by individual heat transfer path. There are two situations in residential fires: one is the case in which the flame is extinguished while in progress, and the other is the case in which it burns out. The threshold of burnout or extinguishment may be determined by the quantity of combustible materials and their placement on the floor. Our objectives are to make clear the threshold of flame spread and to estimate the route of flame spread in residential fire. In this paper, we examined nonuniform flame spread along a thin combustible solid with randomly distributed pores. Experimental results show that the flame spread rate increases with increasing the porosity rate and reaches maximum value at around 20–30 % porosity, then decreases. The flame cannot spread and is completely extinguished at 55 % porosity in each pore diameter. In addition, we measured the characteristic length of thermal boundary layer ahead of the flame leading edge, L, using the shadowgraph method, and introduced the scale length ratio of pore diameter with the characteristic length, S ≡ d/L. The modified flame spread probability with the scale length ratio is unified as a function of the porosity rate.

Section B Fire and Explosion - Effect of Gravity on Flame Spread Along a Thin Combustible Solid for Different Sample Orientations in Opposed Flow

In order to secure fire safety over the entire period of a manned space mission, gaining a systematic understanding of the effects of gravity on flame spread is important. In this study, opposed-flow flame spread along a thermally thin combustible solid for different sample orientations (−20° downward, horizontal, and +20° upward) was experimentally investigated by changing the ambient oxygen concentration and gravity level. The flame spread rate decreases with decreasing oxygen concentration under normal gravity, and its rate at 18 % oxygen concentration is equivalent to that at 21 % oxygen concentration under microgravity. The downward flame spread rate decreases with an increase in gravity. In contrast, the horizontal and the +20° upward flame spread rates clearly increase as the gravity level increases. The flame spread rate varies remarkably with sample orientation in a supergravity environment. To clarify the effect of gravity on flame spread, the relation between the non-dimensional flame spread rate and the Rayleigh number was examined. The Ra number both for horizontal and upward flame spread increases with increasing gravity, while the Ra number for downward flame spread decreases slightly with a decrease in gravity. The non-dimensional flame spread rate is almost constant under normal and supergravity conditions for Ra numbers less than 103 and is equivalent to that under microgravity. When the Ra number is greater than 103, the non-dimensional flame spread rate increases with increasing Ra number and is proportional to Ra1/3.

Section B Fire and Explosion - Extinguishment Characteristics of a Jet Diffusion Flame with Inert-Gas Vortex Ring

For firefighting, we propose a Jet Diffusion Flame…?>the vortex-ring transport method using a gaseous fire-extinguishing agent. The vortex ring formed with a gaseous extinguishing agent has a possibility to transport the extinguishing gas more effectively and over longer distance than jet flows which issue from conventional extinguishers. To clarify the extinguishing characteristics of the inert-gas vortex ring, blowout experiments using a methane-air jet diffusion flame have been performed. Nitrogen, carbon dioxide, argon, and air are used for forming a vortex ring with a round orifice. The extinguishing velocity limit has been measured. The extinguishing velocity limit is defined as the lowest displacement velocity of the vortex ring which can blow the jet diffusion flame off perfectly. From the experimental results, it is found that all inert-gas vortex rings indicate the lower extinguishing velocity limit than the air vortex ring. This means that the inert-gas vortex ring can travel in air while keeping its extinguishing ability. All inert-gas vortex rings retain extinguishing effectiveness over a distance longer than seven times that of the orifice diameter. Significantly, after a distance larger than four times the orifice diameter, the extinguishing velocity limits of all inert gases show constant values independent of the traveling distance of the vortex ring. Furthermore, the order of the extinguishing effectiveness of the inert-gas vortex ring is CO2 > Ar > N2. This result is different from the extinguishing effectiveness ranking determined by a cup-burner method, and it is considered that the extinguishing effectiveness ranking is influenced by the transport process of the inert gas to the flame. When the extinguishing velocity limit is scaled by the Peclet number which is defined as the ratio between displacement velocity of vortex ring at extinguishment limit and mass diffusion rate of inert gas, the data of the Peclet number can be expressed as a single curve as a function of the normalized traveled distance of the vortex ring.

対向流CH4-N2/O2-N2非予混合火炎の消炎に対する巨視的な火炎構造の変化と流体変動の影響

Extinction limits of counterflow CH4-N2/O2-N2 non-premixed flames were investigated experimentally by manipulating the global flame structure, that is flame location in counterflow, by varying stoichiometric mixture fraction : Zst, and under fixed stoichiometric adiabatic flame temperature by keeping molar stoichiometry : Mst constant. Furthermore, the effects of two fluid dynamical fluctuations that were oscillated flow at frequency : 20 Hz and perforated plate turbulent flow on the extinction characteristics of the counterflow flames were also examined. As a result, the extinction limits of the laminar flame increase with increase in Zst. Amount of oxygen in oxidizer flow increases with Zst and oxygen promotes chain-branching reaction : O2+H→OH+O. Therefore the laminar flames stability becomes higher with increase in Zst under the constant adiabatic flame temperature. For the oscillatory flow, the extinction character indicates the similar tendency to the laminar flame, that is, the oscillated flame shows quasi-steady extinction phenomena and the extinction limits always depend on the flow condition of oxidizer even if the flame is located in the fuel side. On the other hands, the perforated plate turbulent flame stability always depends on both the flame location and the streamside with turbulence. The extinction limits of the counterflow turbulent flame are more influenced by the turbulent fluctuation of the flow in which the flame is located than that of the flow without the flame. It is thought to be that the difference for the extinction character between the oscillatory flame and the turbulent flame is due to unsteadiness of the fluctuation in the flow.