Experimental Study On The Transformation Of Forest Humus From Smoldering To Flaming

Forest is an important natural resource of human beings and plays a unique role in the long history of human existence and development.However,in recent years,with the global warming and frequent drought,forest fires occur more and more frequently,causing great damage and serious losses to forests.Especially the fire caused by forest underground fire,because of its great concealment,is not easy to be found,the potential harm is very great.There are a lot of forest humus in the forest,which is prone to smoldering.When the climate,temperature,wind speed and wind direction change,the forest humus may become flaming and form fire.Therefore,it is of great significance to study the factors influencing the conversion of forest humus smoldering to flaming.Before smoldering,forest humus will enter pyrolysis stage,and the combustible gas produced during pyrolysis is beneficial to the propagation of smoldering.Therefore,it is very important to study the reaction mechanism of pyrolysis.In this paper,the pyrolysis characteristics in nitrogen and air atmosphere are analyzed.It is found that the reaction is complete and the flaming is produced in the air atmosphere,and the temperature ranges from 400 ? to 560 ?.The Coats-Redfern equation shows that the mechanism function is(1-?)-1-1 in air atmosphere and a+(1-?)ln(1-?)in nitrogen atmosphere.In the self designed horizontal experimental device,the forest humus was subjected to a smoldering experiment.The wind speed,oxygen content,the direction of the smoldering transmission,the heat exchange condition,the effect of the humus plasmid diameter and moisture content on the transformation of the smoldering to the flaming were studied.The results show that the smoldering process of humus can be divided into three stages:endothermic heating,self-sustaining propagation and cooling quenching.The humus has long ignition time,high peak temperature and long self-sustaining time.The speed of propagation is slow and so on.When the above conditions are changed,the results show that there is a linear relationship between the wind speed and the propagation velocity of smoldering.The higher the wind speed,the greater the propagation speed of smoldering,the shorter the time to flaming,and the more critical wind speed is 4 m/s.Under the condition of oxygen enrichment,the smoldering temperature rises rapidly,the propagation speed increases,and the smoldering tends to change to flaming.Compared with positive smoldering,reverse smoldering is stable and not easy to change to flaming.When the external temperature is high,smoldering is easy to change to open fire,and the highest temperature is higher.The particle size of humus has little effect on the transition from smoldering to flaming;When the moisture content of humus is less than 20%,the smoldering energy changes to flaming.With the increase of moisture content,the average maximum temperature decreases,and the transition time is shorter.When the moisture content is larger than 20%,the smoldering can not change to the flaming,and with the increase of moisture content,the smoldering cannot self-maintain propagation,and gradually extinguishes.