本文選題：分層燃料　切入點(diǎn)：可燃性　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：針對(duì)樹(shù)冠火發(fā)生和蔓延規(guī)律的研究是森林火災(zāi)預(yù)防和控制技術(shù)中的重要研究課題。生物防火林帶作為林火防控的關(guān)鍵技術(shù),針對(duì)其阻火機(jī)理的研究目前停留在樹(shù)冠葉片可燃性層面,沒(méi)有形成有說(shuō)服力的認(rèn)識(shí)并建立相應(yīng)的技術(shù)理論體系。闊葉樹(shù)葉在樹(shù)冠中呈現(xiàn)顯著分層特性,針對(duì)分層樹(shù)葉燃料可燃性的研究不僅可以加深對(duì)樹(shù)冠火蔓延規(guī)律的認(rèn)識(shí),同時(shí)也增進(jìn)對(duì)生物防火林帶阻火機(jī)理的科學(xué)認(rèn)識(shí),從而推動(dòng)該項(xiàng)技術(shù)的完善與發(fā)展。對(duì)典型闊葉樹(shù)樹(shù)葉的熱解特性及燃燒熱值進(jìn)行測(cè)試和分析,一方面可以直觀呈現(xiàn)闊葉樹(shù)葉形成明火的潛力,另一方面也為后續(xù)工作奠定數(shù)據(jù)基礎(chǔ)。利用綜合熱分析儀開(kāi)展熱解實(shí)驗(yàn),并利用單組分反應(yīng)和多組分平行反應(yīng)模型分別進(jìn)行動(dòng)力學(xué)解析。結(jié)果表明,不同種類(lèi)樹(shù)葉熱解反應(yīng)的表觀活化能范圍為43～80kJmol-1,而莖(枝)的在84～110kJmol-1之間。分析表明,表觀活化能在很大程度上反映葉片中纖維素含量,并不表征特定組分熱解反應(yīng)的能壘信息。實(shí)驗(yàn)測(cè)得失重峰處對(duì)應(yīng)轉(zhuǎn)化率越低,單組分反應(yīng)模型對(duì)植物熱解反應(yīng)過(guò)程描述的貼近程度越高。選取了 27種不同科屬的木本植物葉樣,開(kāi)展元素分析、工業(yè)分析及熱值測(cè)試。結(jié)果表明,植物葉樣的干基高位熱值HHV_d在17.48～24.01 MJkg-1之間變化,平均值為21.30MJkg-1。其中,同種科的植物葉片熱值大小一般較為接近。干基高位熱值受樣品自身灰分含量影響可以忽略。分析表明,葉樣干基高位熱值波動(dòng)與其揮發(fā)分和固定碳的含量分布密切相關(guān)。葉片中揮發(fā)分和固定碳間含量比值隨著樣品中氧碳摩爾比增加而增大,并且固定碳在可燃組分中的相對(duì)含量對(duì)應(yīng)樣品中木質(zhì)素含量。樣品氧碳摩爾比和氫碳摩爾比的增加意味著其木質(zhì)素含量降低,使得其干基高位熱值減小。植物葉片的干基高位熱值可以分別由經(jīng)驗(yàn)式HHV_d=18.93VM_d+36.95FC_d 和 HHV_d=0.4478C_d+1.4072H_d-0.2837O_d來(lái)準(zhǔn)確計(jì)算獲得,據(jù)此還可以迅速確定樣品收到基熱值。利用錐形量熱儀開(kāi)展具有分層特性的樹(shù)葉樣品的著火實(shí)驗(yàn),以模擬野外林火環(huán)境下樹(shù)冠層葉片的輻射引燃過(guò)程。實(shí)驗(yàn)結(jié)果表明,在特定輻射熱流強(qiáng)度下,新鮮樹(shù)葉樣品主要呈現(xiàn)兩種典型著火模式:一種是在點(diǎn)燃初期出現(xiàn)短時(shí)間氣相火焰厚轉(zhuǎn)為陰燃;另一種是在測(cè)試過(guò)程中僅出現(xiàn)陰燃。隨著外部輻射熱流強(qiáng)度提高或揮發(fā)分含量增加,樣品在點(diǎn)燃初期的著火模式會(huì)由純陰燃向有焰燃燒轉(zhuǎn)變。理論分析表明,樣品表層初始揮發(fā)分含量及表層溫升速率是影響樣品產(chǎn)生揮發(fā)分質(zhì)量通量水平的主要因素,進(jìn)而決定樣品在點(diǎn)燃過(guò)程中是否出現(xiàn)明火。根據(jù)樹(shù)葉樣品的分層特性,將樣品分離成具有熱薄特性的表層和熱厚特性的內(nèi)層,由此建立起兩部分的能量守恒和質(zhì)量守恒的積分模型。計(jì)算結(jié)果表明,表層在樣品點(diǎn)燃過(guò)程中接受的輻射能量主要用于表層水分蒸發(fā)和內(nèi)能增加,向內(nèi)層的熱量輸運(yùn)占份額相當(dāng)小。這導(dǎo)致能量分配關(guān)系呈現(xiàn)出典型的表層效應(yīng),進(jìn)而使得內(nèi)層對(duì)點(diǎn)燃現(xiàn)象的影響被嚴(yán)重削弱。水分含量降低會(huì)削弱樣品表層吸收和遮擋熱量的效應(yīng),相應(yīng)導(dǎo)致內(nèi)層傳熱項(xiàng)的量階顯著增加。構(gòu)建考慮熱解反應(yīng)的分層樣品輻射引燃模型,并以臨界揮發(fā)分質(zhì)量通量為點(diǎn)燃判據(jù),可以對(duì)分層燃料出現(xiàn)明火的臨界條件作進(jìn)一步分析。結(jié)果表明,樹(shù)葉樣品產(chǎn)生揮發(fā)分主要來(lái)自于表層,并且表層貢獻(xiàn)比例會(huì)隨著輻射熱流強(qiáng)度提高而增加。樹(shù)葉含水量越低,表層對(duì)樣品揮發(fā)分質(zhì)量通量的貢獻(xiàn)比例相應(yīng)越小,意味著樹(shù)葉樣品分層特性被明顯削弱。分析表明,隨著樹(shù)葉樣品含水量減少,內(nèi)層產(chǎn)生揮發(fā)分質(zhì)量通量會(huì)增加,這導(dǎo)致樣品出現(xiàn)明火的臨界輻射熱流強(qiáng)度降低。作為比對(duì),構(gòu)建出針對(duì)連續(xù)性可燃物的點(diǎn)燃模型,以直觀呈現(xiàn)致密性材料與分層燃料間點(diǎn)燃條件和現(xiàn)象的差異。計(jì)算結(jié)果表明,樣品點(diǎn)燃過(guò)程中實(shí)際吸收凈能量會(huì)因外部輻射熱流強(qiáng)度提高或環(huán)境風(fēng)速減小而相應(yīng)降低,并隨著樣品含水量增加而增加。凈吸收能量與表觀能量比值Eig/Ea主要取決于外部輻射熱流強(qiáng)度和點(diǎn)燃時(shí)刻表面熱損速率,基本與樣品種類(lèi)和含水量無(wú)關(guān)。分析表明,比值Eig/Ea可以表示為表征點(diǎn)燃條件優(yōu)劣程度的參數(shù)γig的函數(shù)。建立的認(rèn)識(shí)不僅可以由表觀能量以及經(jīng)驗(yàn)式來(lái)精確計(jì)算出點(diǎn)燃過(guò)程中固體凈吸收能量,同時(shí)也為構(gòu)建基于"最小所需能量"的著火判據(jù)奠定基礎(chǔ)。
[Abstract]:Study on regularity and spread of crown fire is an important research topic in the prevention and control technology in forest fires. Biological fire belt is the key technology of prevention and control of forest fire, the research on the mechanism of fire resistance of the stay in the leaf canopy combustible level, there is no convincing understanding and establish the corresponding theoretical system technology. The leaf showed significant stratification characteristics in the canopy, based on hierarchical leaves fuel flammability can not only deepen our understanding of the spread regularity of crown fire, but also to promote bio Fuelbreak fire resistance mechanism of scientific understanding, so as to promote the perfection and development of the technology. The pyrolysis characteristics of typical broad-leaved tree leaves and combustion the calorific value of test and analysis, one can visualize the leaf form fire potential, on the other hand also lay the foundation for the follow-up work data. By using the comprehensive Carry out the pyrolysis and kinetics of thermal analyzer, respectively analysis by using single component reaction and multicomponent parallel reaction model. The results show that different kinds of leaves of pyrolysis reaction apparent activation energy range is 43 ~ 80kJmol-1, and the stem (Branch) between 84 ~ 110kJmol-1. The analysis shows that the apparent activation energy of cellulose the content of leaves in a large extent, does not characterize the specific components of the pyrolysis reaction energy barrier information. The experimental peaks corresponding to the conversion rate and the lower the higher the single component reaction model to describe plant pyrolytic reaction degree. Selected 27 different genera of woody plant leaf samples, carry out elemental analysis, industrial analysis and calorific value test. The results showed that the plant leaf samples of dry basis perch calorific value HHV_d varies between 17.48 ~ 24.01 MJkg-1, the average value of 21.30MJkg-1. the same section of the plant leaves are generally small high calorific value Close. Dry basis perch calorific value is affected by the sample itself can be ignored. The ash content analysis showed that the leaf like stem base with high calorific value fluctuation of volatile matter and fixed carbon content is closely related to the distribution. In the leaves of volatile matter and fixed carbon content ratio increases with the mole ratio of oxygen and carbon in the sample, and the relative content in combustible in the corresponding fixed carbon in the sample. The content of lignin samples and the molar ratio of hydrogen to carbon ratio of carbon and oxygen increase means that reduce the lignin content, the dry high calorific value decreased. Leaf dry high calorific value can be measured by the experience of HHV_d=18.93VM_d+36.95FC_d and HHV_d=0.4478C_d+1.4072H_d-0.2837O_d to obtain accurate calculation, it also can quickly determine samples basic calorific value. Fire experiments carried out with hierarchical properties of leaf samples using a cone calorimeter, to simulate the field of fire The tree canopy radiation environment of ignition process. The experimental results show that the specific heat radiation intensity, fresh leaf samples showed two typical fire models: one is in the early short time light gas flame thickness to smolder; the other is a smoldering appears only in the testing process with external radiation. The content of volatile heat flux intensity increase or increase in sample mode by pure smoldering to flaming combustion transformation ignited early. Theoretical analysis shows that the sample surface initial volatile content and the surface temperature rise rate is essential factors mainly cause the sample mass flux level, and then decide whether the sample in the ignition process in fire. According to the layered characteristics of leaf samples, the samples were separated into the inner surface and the thermal characteristics with thermal characteristics of thin thickness, thereby establishing the mass and energy conservation of the two part The integral model. The calculation results show that the sample surface in the ignition process of the radiant energy received mainly for surface water evaporation and can increase, to the inner layer of the heat transport accounted for a relatively small share. This leads to energy distribution showing a typical surface effect, which makes the effect of inner layer on kindling phenomenon has been seriously weakened moisture. The content of reducing will weaken the effect of sample surface absorption and heat shielding, resulting in heat transfer of the inner order amount increased significantly. The layered sample pyrolysis reaction and radiation ignition model, based on the critical quality of volatile flux for ignition criterion, the critical condition for further analysis of layered fuel flame appears. The results showed that the leaves the sample volatiles mainly from the surface, and the surface contribution ratio will increase with the increased heat radiation intensity. The water content is low, the surface of the sample The volatile products of mass flux ratio with corresponding smaller mean leaf samples was attenuated by the hierarchical characteristics. The results show that, with the leaf moisture content of the samples decreased, the inner produced volatile mass flux will increase, which leads to the decrease of the critical heat flux of radiation samples. As the flames appear for comparison, construct the continuous flammable kindling model the difference to show the density of material and Fuel Stratified between igniting conditions and phenomena. The calculation results show that the samples of the ignition process of the actual absorption of net energy due to external heat radiation intensity increase or decreases while the wind speed decreased, and increased with the increase of the moisture content of the sample. The net energy absorption and apparent energy ratio Eig/Ea mainly depends on the external heat radiation intensity and light time of surface heat loss rate, and sample type and content. Analysis shows that the ratio of Eig/Ea Can express the function parameter Ig lit conditions. The degree for the characterization of knowledge can not only establish energy and experience to accurately calculate the ignition process of the solid net energy absorbed by the apparent, is also based on the "minimum energy required for ignition criterion" lay the foundation.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：S762.1

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