Experimental study on burning characteristic of liquid fuel immersed in porous media bed: Effect of particle gradation

Abstract

A series of burning test was conducted to investigate the effect mechanism of particle gradation on burning characteristic of liquid fuel immersed in porous media. High-purity quartz equipped with two-component discontinuous gradation and ethanol liquid were employed as porous bed and liquid fuel. The characteristic parameters, e.g., burning rate, temperature distribution, flame feature and burning duration, etc., were recorded and identified. Results show that the burning characteristic of liquid fuel immersed in porous media with gradation configuration is conjunctively influenced by capillary effect and thermal conductivity of porous media. For the porous media bed with fine particles, capillary effect plays a dominant role in the variation trend of burning rate. While for the porous media bed with good gradation, under the effect of better contact condition and more coordination numbers, thermal conduction enhanced by particle gradation dominates the burning characteristic. Meanwhile, the burning rate of porous bed immersed by liquid fuel demonstrates stage-variation feature: a rapid growth stage dominated by direct flame thermal feedback and an attenuation-stable stage dominated by thermal conduction. Due to the “back effect”, the burning rate has a quasi-stable phase in middle-and-late stage, which is positively correlated with the one-half power of media porosity. Moreover, due to the enhancement of thermal conductivity, the downward heat transfer rate of porous media with good gradation is relatively faster. In addition, there is still a positive tendency between flame height and burning rate. This work is expected to provide some references for understanding the burning characteristics of liquid fuel immersed in porous media and burning-decontamination operation.