小型プール火災の非定常燃焼時の燃焼速度 Unsteady Burning Rates of Small Pool Fires
In this paper, burning rates measured during unsteady combustion of small pool fires using three different fuels are discussed. Unsteady combustion is obtained by a batch test in which the fuel level in the tank decreases after ignition. We measured the burning rates, the fuel temperature, and the tank temperature of three different fuels. Experimental results allow the following conclusions: <br>1. Three major processes, so called preheating, transition and boiling process, were found from the fuel temperature change curves of small pool fires during unsteady combustion. <br>2. Burning rates of heptane and kerosene increase when fuel temperatures and tank temperatures go up. The burning rates in the boiling process are about 1.64 for heptane and about 1.3 for kerosene times as much as those during the preheating process. <br>3. Preheating, transition and boiling processes were easily found from the fuel temperature change curves of the methanol pool fire. Nevertheless methanol does not show a distinct increase of burning rate. <br>4. The reason for various burning rate changes of small pool fires are clearly explained by the calculation of fuel evaporation using measured burning rates and fuel temperatures. Heptane and kerosene fires change their burning rates because both evaporation heats and preheating heat are not large. The evaporation heat of methanol is the largest and it is about three or five times bigger than that of heptane and kerosene. This is one of the reasons for the constant burning rate of methanol. <br>5. From the above discussion, the concept of maximum burning rate ratio (MBRR) is introduced to explain the burning rate change of various fuels. MBRR becomes larger as the number of carbon atoms in fuel increases. <br>Finally, the above mentioned phenomena will happen when heat supply by convection and conduction are not so small compared with by radiation. In medium and large size pool fires, sufficient heat will be supplied from the flame, mainly by radiation, so that the above mentioned preheating and transition processes may not easily be found. In small pool fires, burning rates are strongly affected by circumferential conditions such as fuel and tank temperatures. This may be one reason for various burning rates obtained by experiments using the same tank size and fuel.
日本火災学会論文集 45(1), 19-25, 1996-07-30