Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were...Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were performed in laboratory experiments,with a focus on the source of ignition and wind speed.Variability in fuel moisture content at time of ignition and during fire spread was observed for different fuels.Matches were more efficient to result in ignition and spread fire with high values of fuel moisture content compared to the use of cigarette butts.Some fuels did not ignite at 15%moisture content,whereas others ignited at 40%moisture content and fire spread at 38%moisture content in the case of matches,or ignited at 27%moisture content and spread fire at 25%moisture content using cigarette butts.A two-way ANOVA showed that both the source of ignition and the wind speed affected ignition and fire spread threshold significantly,but there was no interaction between these factors.The relationship between ignition and fire spread was strong,with R2=98%for cigarette butts,and 92%for matches.Further information is needed,especially on the density of fuels,fuel proportion(case of mixed fuels),fuel age,and fuel combustibility.展开更多
Spot fire increase the difficulty of fire-fighting and threaten public safety,and therefore it is important to study ignition probabilities of fuel bed by different firebrands,in order to understand ignition mechanism...Spot fire increase the difficulty of fire-fighting and threaten public safety,and therefore it is important to study ignition probabilities of fuel bed by different firebrands,in order to understand ignition mechanisms and analyze the formation of spot fires.This will provide an important basis for further study to improve the fire-fighting efficiency and reduce casualties.In this study,the ignition probabilities of larch(Larix gmelinii)fuel beds with different moisture levels and packing ratios by diffreent firebrands,including cones and twigs of different sizes,was investigated.Ignition experiments were conducted at different wind speeds generated by fans.The results show that,regardless of moisture content and packing ratio,ignition probability is zero when there is no wind.Both moisture content and wind speed significantly infuence ignition probability,while packing ratio has almost no effect.The maximum moisture content at which firebrand ignition occurred was 50%,and ignition probability increased with wind speed and decreased with moisture content.Cones have the highest ignition probability,followed by large twigs and by small twigs.Ignition probability is also affected by firebrand shapes and sizes that determine their potential heat and contact area to the fuel bed.Two empirical models were established to link ignition probability with fuel properties and wind speed.This study will help clarify the mechanism of spot ignition and reduce corresponding losses.展开更多
针对基于电压源换流器的高压直流输电(voltage source converter based high voltage direct current,VSC-HVDC),提出了基于永磁同步风力发电机、不控整流和Boost电路的变速直流风力发电系统结构。首先给出先并后串的新型风电场结构;然...针对基于电压源换流器的高压直流输电(voltage source converter based high voltage direct current,VSC-HVDC),提出了基于永磁同步风力发电机、不控整流和Boost电路的变速直流风力发电系统结构。首先给出先并后串的新型风电场结构;然后建立最小串联系统的简化模型,用一种基于直流电压电流乘积控制的最大风能跟踪控制算法解析出输出电压和输出功率的关系。仿真结果表明:最小串联系统中的2个机组可以互不影响地独立运行,输出电压按照输出功率的变化而变化,同时2个机组均具有较好的最大风能跟踪精度和速度。展开更多
基金funded by the National Key Research and Development Program of China(2018YFE0207800)the Fundamental Research Funds for the Central Universities(2572019CP10)+1 种基金the National Innovation Alliance of Wildland Fire Prevention and Control Technology of Chinathe Northern Forest Fire Management Key Laboratory of the State Forestry and Grassland Bureau。
文摘Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were performed in laboratory experiments,with a focus on the source of ignition and wind speed.Variability in fuel moisture content at time of ignition and during fire spread was observed for different fuels.Matches were more efficient to result in ignition and spread fire with high values of fuel moisture content compared to the use of cigarette butts.Some fuels did not ignite at 15%moisture content,whereas others ignited at 40%moisture content and fire spread at 38%moisture content in the case of matches,or ignited at 27%moisture content and spread fire at 25%moisture content using cigarette butts.A two-way ANOVA showed that both the source of ignition and the wind speed affected ignition and fire spread threshold significantly,but there was no interaction between these factors.The relationship between ignition and fire spread was strong,with R2=98%for cigarette butts,and 92%for matches.Further information is needed,especially on the density of fuels,fuel proportion(case of mixed fuels),fuel age,and fuel combustibility.
基金funded by the Sub topic of 13th Five-Year-Plan National Key Research and Development Project(2017YFD0600106-2)National Natural Science Foundation Project(31,400,551,31,870,644)。
文摘Spot fire increase the difficulty of fire-fighting and threaten public safety,and therefore it is important to study ignition probabilities of fuel bed by different firebrands,in order to understand ignition mechanisms and analyze the formation of spot fires.This will provide an important basis for further study to improve the fire-fighting efficiency and reduce casualties.In this study,the ignition probabilities of larch(Larix gmelinii)fuel beds with different moisture levels and packing ratios by diffreent firebrands,including cones and twigs of different sizes,was investigated.Ignition experiments were conducted at different wind speeds generated by fans.The results show that,regardless of moisture content and packing ratio,ignition probability is zero when there is no wind.Both moisture content and wind speed significantly infuence ignition probability,while packing ratio has almost no effect.The maximum moisture content at which firebrand ignition occurred was 50%,and ignition probability increased with wind speed and decreased with moisture content.Cones have the highest ignition probability,followed by large twigs and by small twigs.Ignition probability is also affected by firebrand shapes and sizes that determine their potential heat and contact area to the fuel bed.Two empirical models were established to link ignition probability with fuel properties and wind speed.This study will help clarify the mechanism of spot ignition and reduce corresponding losses.
文摘针对基于电压源换流器的高压直流输电(voltage source converter based high voltage direct current,VSC-HVDC),提出了基于永磁同步风力发电机、不控整流和Boost电路的变速直流风力发电系统结构。首先给出先并后串的新型风电场结构;然后建立最小串联系统的简化模型,用一种基于直流电压电流乘积控制的最大风能跟踪控制算法解析出输出电压和输出功率的关系。仿真结果表明:最小串联系统中的2个机组可以互不影响地独立运行,输出电压按照输出功率的变化而变化,同时2个机组均具有较好的最大风能跟踪精度和速度。
