Effect of Air Flow Velocity in Smoldering Combustion with Opposed Propagation on Cellulosic Material

Abstract

Smoldering combustion is a phenomenon that is quite unique, because it is a flameless combustion. This smoldering phenomenon can be a hazard, because of it's characteristics. The characteristic of smoldering combustion is slow, low-temperature, flameless and sustained combustion. This phenomenon can occur on cellulose material both organic and non-organic. Smoldering combustion in organics material can cause a wildland fires, both in surface and inside the soil. This phenomenon in organics material was studied using tobacco material and found that ignition temperatures of 380-620oC were observed. This reaserch was conducted in small scale, vertically oriented smoldering cylindrical apparatus, with varied air flow and from-up ignition (downward propagation). The oxidizer which contacted with the bottom surface of tobacco, was forced in certain volumetric flow rate. A constant power to igniter is applied until the temperature of tobacco 10mm from the igniter reached 500oC. The main observation of this research is temperature distribution, mass loss rate and optical density from the resulting smoke. The temperature records in this research were measured by six type-K thermocouples. The mass loss rate of the tobacco in this research were masured by digital scale in real time. The optical density from the released smoke in this research were measured by opacity meter, which transmitted intensity value, converted into optical density value. Air flow variations used in this research were 1, 3, 5, 7, and 9 liter per minute (LPM). The result of this research showed that air flow is an important factor in the process of smoldering combustion. The ignition position and direction of air flow affect direction of propagation. In this research the propagation occured in two direction. In the first process, the propagation of smoldering front was in downward direction. Nevertheless, after the smoldering front reached the bottom surface of tobacco, heat released by ember were accumulated. The air flow from the bottom of the tube forced the combustible mixture to move upwards and then followed by the upward propagation of smoldering front.