DYNAMIC PREDICION OF FOREST FUEL LOADS BY GREY VERHULST MODEL

The variation of fuel loads after a fire for three forest types, phododendron -Larix gmetinii forest, herb--Larix gmelinii forest and herb--Betula plalyphlla forest , in the northern forest area of Daxing’anling region was discussed. The dynamic models were developed by gray theory for estimating the fuels loads of arbor- shrub, herbs’ grass, litter, and semi-decomposed litter, inflamma ble fuel and the total fuels in each forest type. After a fire, the inflammabIe fuel loads in phododendron-- Larix gmelinii forest and in the herb- - Betula platyphlla fores was estimated at 10.958 t/hm2and 10.473 t/hm2 respectively’ by 13 years later. and that was 12.297 t/hm 2 in herb--Larix gmeliniiforest by 7 years later.. It was predicated that a big fire may occur after 10 years based on inflammable fuel biomass accumulated.

Fuel load and flight ranges of blackcaps Sylvia atricapilla in northern Iberia during autumn and spring migrations

Fuel accumulation,mainly as fatty acids,is one of the main characteristics of migratory birds.Studying to what extent each population or species manages fuel load and how it varies along routes of migration or between seasons(autumn and spring migrations)is crucial to our understanding of bird migration strategies.Our aim here was to analyse whether migratory blackcaps Sylvia atricapilla passing through northern Iberia differ in their mean fuel loads,rate of fuel accumulation and 'potential' flight ranges between migration seasons.Blackcaps were mist netted for 4 h-periods beginning at dawn from 16 September to 15 November 2003-2005,and from 1 March to 30 April 2004-2006 in a European Atlantic hedgerow at Loza,northern Iberia.Both fuel load and fuel deposition rate(this latter assessed with difference in body mass of within-season recaptured individuals)were higher in autumn than in spring.Possible hypotheses explaining these results could be seasonal-associated variations in food availability(likely lower during spring than during autumn),the fact that a fraction of the migrants captured in spring could breed close to the study area and different selective pressures for breeding and wintering.

Fuel loading pattern optimization of a pressurized water reactor by varying internal weights-based particle swarm optimization

Fuel reload pattern optimization is essential for attaining maximum fuel burnup for minimization of generation cost while minimizing power peaking factor(PPF).The aim of this work is to carry out detailed assessment of particle swarm optimization(PSO) in the context of fuel reload pattern search. With astronomically large number of possible loading patterns, the main constraints are limiting local power peaking factor, fixed number of assemblies,fixed fuel enrichment, and burnable poison rods. In this work, initial loading pattern of fixed batches of fuel assemblies is optimized by using particle swarm optimization technique employing novel feature of varying inertial weights with the objective function to obtain both flat power profile and cycle k_(eff)>1. For neutronics calculation, PSU-LEOPARD-generated assembly depletiondependent group-constant-based ADD files are used. The assembly data description file generated by PSU-LEOPARD is used as input cross-section library to MCRAC code, which computes normalized power profile of all fuel assemblies of PWR nuclear reactor core. The standard PSO with varying inertial weights is then employed to avoid trapping in local minima. A series of experiments havebeen conducted to obtain near-optimal converged fuelloading pattern of 300 MWe PWR Chashma reactor. The optimized loading pattern is found in good agreement with results found in literature. Hybrid scheme of PSO with simulated annealing has also been implemented and resulted in faster convergence.

Fuel characteristics, loads and consumption in Scots pine forests of central Siberia

Forest fuel investigations in central and southern Siberian taiga of Scots pine forest stands dominated by lichen and feather moss ground vegetation cover revealed that total aboveground biomass varied from 13.1 to 21.0 kg/m 2.Stand biomass was higher in plots in the southern taiga,while ground fuel loads were higher in the central taiga.We developed equations for fuel biomass(both aerial and ground)that could be applicable to similar pine forest sites of Central Siberia.Fuel loading variability found among plots is related to the impact and recovery time since the last wildfi re and the mosaic distribution of living vegetation.Fuel consumption due to surface fi res of low to high-intensities ranged from 0.95 to 3.08 kg/m 2,that is,18–74%from prefi re values.The total amount of fuels available to burn in case of fi re was up to 4.5–6.5 kg/m 2.Moisture content of fuels(litter,lichen,feather moss)was related to weather conditions characterized by the Russian Fire Danger Index(PV-1)and FWI code of the Canadian Forest Fire Weather Index System.The data obtained provide a strong foundation for understanding and modeling fi re behavior,emissions,and fi re eff ects on ecosystem processes and carbon stocks and could be used to improve existing global and regional models that incorporate biomass and fuel characteristics.

Characteristics of Dynamic Load Response of a Fuel Cell with a Dead-ended Anode

The dynamic load characteristics of a proton exchange membrane fuel cell（PEMFC） with a dead-ended anode were studied. In a 70 h experiment, the effects of anode pressure, operating temperature, and relative humidity of the cathode on the performances of the fuel cell were investigated. The obtained results show that, with different relative humidity of the cathode at 65 ℃, dynamic loading has little effect on the performances of fuel cell and the electrochemically active surface area（ECSA）. However, the fuel cell operating under dynamic load is unstable when the relative humidity is 50%, and at 50 ℃ with 100% relative humidity, applying a dynamic load has a significant influence on the fuel cell performances. Scanning electron microscopy（SEM） showed that both the upstream and middle catalyst layers of the cell were unchanged, whereas the downstream cathode catalyst layer thinned as a response to dynamic load.

风电接入远海油气平台的规划方法

海上风电直供远海油气平台可降低发电成本和碳排放,但传统规划方法不适用于远海油气平台的负荷特性。在考虑海上油田电力系统燃气透平机组与负荷特性的基础上,建立计及风-燃-荷功率动态匹配特性的扩展概率潮流模型,提出适用于远海油气平台的风机规划方法。采用所提潮流计算方法,在满足远海油田电力系统的电压、线路载流量等约束条件下,以年发电成本与年碳排放量的综合成本最低为目标建立规划模型,并采用粒子群优化算法对模型进行求解。以我国某远海油田电力系统为例,提出针对远海油田电力系统特点的风电接入方案,算例结果表明,所提规划方法具有可行性。

农用拖拉机发动机负荷和燃料消耗特性研究

农用拖拉机负荷是影响其发动机工作性能的主要参数指标,直接影响拖拉机的田间工作效率及性能。相关研究表明:拖拉机发动机功率至少使用80%,且发动机转速较低时可以实现拖拉机高效运行。为此,对麦赛福格森-MF 8480的发动机在田间作物收获时的发动机负载参数进行了控制测试,构建相关数学模型反映发动机功率、发动机转速和燃料消耗特性之间的关系,并给出拖拉机运行期间不同发动机转速下的工作时间和油耗分布图,揭示了拖拉机田间运行效率及发动机各个参数运行关系。研究结果可为研究农用拖拉机发动机运行参数关系及提高田间运行效率提供理论依据及参考。

计及热负荷柔性的户用氢能系统运行优化研究

针对风电/光伏出力的随机性和间歇性给户用氢能系统热电联供可靠性带来的挑战,提出基于热负荷柔性松弛运行约束的户用氢能系统热电联供优化策略。首先,搭建包含不同模块的户用氢能系统基础架构,并详细说明该系统的运行原理;其次,建立系统中关键环节的数学模型,确定电解槽平均氢/热比和燃料电池在不同温度下电/热比的范围;然后,为了兼顾用户的舒适度和热负荷的灵活性,根据热感觉平均标度预测指标对户用氢能系统的热负荷需求进行调整;最后,综合考虑储氢罐的容量限制、氢能设备的电/热功率和用户侧柔性热能需求等约束条件,以总投资成本最少和新能源弃电率最低为目标,建立户用氢能系统优化运行模型。仿真结果表明:引入柔性热负荷进行运行调节时,不仅增强了可再生能源的消纳能力,还显著降低了系统的运行成本。

超临界660 MW机组直流锅炉动态特性仿真研究

为提升煤电机组灵活性,锅炉需具备良好的可控性和适应负荷快速变化的能力。锅炉灵活性与控制系统性能密切相关,而后者是基于动态特性设计的。为研究锅炉的动态特性,在Dymola平台中建立了某超临界660 MW机组直流锅炉的动态模型。结果表明:当锅炉入口参数发生扰动时,蒸汽温度的响应时间比蒸汽流量更长;当给水温度、给水量与燃料量分别阶跃增加5%时,主蒸汽温度分别变化10.2℃、-28.5℃和35.7℃;在锅炉的水煤配比调节过程中,给水量和燃料量变化时间不同会对主蒸汽温度产生不同的影响;当给水量比燃料量延迟约100 s作用时,主蒸汽温度在瞬态过程中的最大偏差相对于二者同时变化的情况减少了27.4℃;当变负荷幅度相同时,变负荷速率越大,主蒸汽参数的波动越剧烈,趋于稳定所需的时间越长。

进气相对湿度对变载工况下PEMFC电堆性能的影响

为了探究进气相对湿度对质子交换膜燃料电池电堆变载工况性能的影响,设计了一个动态循环工况,包括电流密度从0.10到0.35 A/cm^(2)、从0.10到1.00 A/cm^(2)的2种阶跃工况和电流密度分别为0.10、0.35、1.00 A/cm^(2)的稳定工况,进行了相对湿度分别为20%、30%、50%、70%、80%的5组试验.结果表明:恒流状态时,电堆在不同电流密度下对相对湿度的敏感性不同,在大电流密度下相对湿度对电堆性能影响较大;变载过程中,电堆电压出现下冲和过冲现象,加载过程的电压下冲量与变载幅度和相对湿度有关,电堆单电池电压一致性变差,电压一致性与进气相对湿度有关.

天然气燃料在油田压裂增产中的应用

天然气燃料在油田压裂增产领域的应用越来越多,天然气涡轮机、天然气发动机等以天然气燃料作为能源的压裂设备技术不断发展,而双燃料发动机同时使用燃油和天然气两种燃料,降本增效的同时能最大限度适应压裂作业工况。通过分析对比采用天然气燃料为压裂提供动力的几种方案,从总的燃料利用率来看,双燃料发动机或天然气发动机对天然气的利用率最高,且技术方案相对简单。天然气发动机天然气利用率最高,燃烧效率也相对较高,结构和控制相对简单,但天然气燃烧的负载瞬态响应性比较差,对压裂工况的负载突变情况适应性差,需增加辅助的动力系统。国内目前还没有双燃料技术应用在压裂领域的案例,为此研究制定基于多点喷射技术的双燃料压裂系统方案,在压裂用发动机基础上增加双燃料系统,每个缸采用单独的喷射阀控制进气喷射,电子控制单元(ECU)对燃气喷射量进行精准控制,并根据发动机运行状态对双燃料模式进行自动切换。该方案在提升天然气燃料利用率的同时也保证了设备运行安全。今后在双燃料技术方面,需要持续推动双燃料核心部件喷射器、ECU以及燃料供给系统等关键技术的研究;在纯天然气燃料技术方面,要研究提高天然气燃烧瞬态响应的方法 ,并研究新的喷射技术。

宽度和载荷对沟槽地表火蔓延特性的影响

为探究燃料床的宽度和燃料载荷对沟槽地表火蔓延燃烧特性的影响,设计了宽度分别为10、15、20 cm的燃料槽,分析了不同宽度和载荷条件下地表火蔓延速度、火焰高度和夹角、质量损失、滞留时间等燃烧特性的变化规律。结果表明,载荷越高,燃料的质量损失速率越大;相同载荷下,沟槽宽度越小,燃料消耗率越高。燃料槽侧壁使卷吸受限,火线成线性。火蔓延速率随宽度增加而增大,火焰高度随宽度和载荷增大而增大。在高载荷的情况下,火蔓延过程中产生大量可燃烟气,火焰形成向火蔓延方向的火焰夹角。

不同粒度级配的硼基粉末燃料装填特性和流动性

为了阐明粒度级配对粉末燃料装填特性和流动性的影响规律,提高粉末冲压发动机工作性能,以硼基粉末燃料为对象,研究了颗粒物性和级配方式等对粉末燃料装填特性和流动性的影响,并利用粉末供给系统验证了级配粉末的流化输运性能。结果表明,大粒径颗粒间隙中填充小粒径颗粒能够提升装填密度,但却会降低其流动性;多级级配粉末中的小粒径颗粒流动性较差时,预混装填方式的级配颗粒装填密度高于分批装填方式,反之则分批装填方式更好;团聚造粒制备的硼基粉末燃料粒度分布均有分形分布特征,分形级配的方式也可以提高颗粒装填密度,提升幅度约15.7%,分形级配后分形维数为2.33,装填密度为0.957g/cm^(3),装填率为53.8%,并保持较好的流化性能。

车用质子交换膜燃料电池低铂化展望及应用

质子交换膜燃料电池作为氢能产业应用的核心产品,具有能量转换效率高、零排放、无污染等特点,是车用领域的重要动力来源之一。然而,高昂的成本限制了车用质子交换膜燃料电池的大规模应用及推广。低铂化膜电极技术的开发是提高其价格竞争力的重要手段,但低铂化过程中面临的严重传质和寿命问题急需解决。总结了低铂化膜电极技术的研究进展及现有技术的不足,并展望了未来的发展趋势,可为车用质子交换膜燃料电池的低铂化膜电极技术开发提供参考。

不同喷油嘴的PEMS试验排放特性研究

针对自卸车喷油嘴选型问题,采用便携式车载排放测试系统(PEMS),对两款喷油嘴A、B开展实际道路行驶排放试验,选取恶劣的工况(低载荷、试验持续时间长),对比分析2次PEMS试验的整体试验结果、瞬时排放结果、比排放以及排放因子结果(冷启动、市区、市郊、高速各阶段),最终确认喷油嘴B在实际道路的排放效果优于喷油嘴A。

某超大型双燃料动力集装箱船LNG燃料舱布置方案分析

以某新巴拿马型15000~16000 TEU级别液化天然气(Liquefied Natural Gas,LNG)动力集装箱船建造项目为背景,对超大型双燃料动力集装箱船LNG燃料舱布置方案进行研究。通过对比不同LNG燃料舱的结构尺寸和布置位置,并从燃料舱的晃荡载荷、船舶的装载能力和稳性等方面进行分析论证,得到一种成熟可靠的超大型双燃料集装箱船LNG燃料舱布置方案。在该方案中,LNG燃料舱的宽度不超过船宽的56%,且其整体或前半段位于上层建筑下方。与市场上常见的燃料舱布置方案相比,该方案不仅能提升船舶的空间利用率,而且能在保障船舶续航能力的同时,提升LNG燃料舱的抗液货晃荡能力,增加船舶的集装箱装载量。

小型丁烷气燃料发电机低温环境的试验研究

本文是针对小型丁烷气燃料发电机在低温环境下的试验研究,主要进行低温环境下的起动试验和加载试验的研究。由于丁烷沸点高、易液化的特性,决定了以丁烷为燃料的发动机很难在10℃以下的环境温度下正常使用。改进措施为,对丁烷的输送管道和汽化器进行加热。通过多组试验对比得出,小型丁烷气燃料发电机在输送管道加热、输送管道加热+汽化器加热、输送管道加热+汽化器加热+汽化器预加热三种状态下的最低起动环境温度和最低满载加载环境温度。

两种不同大小喷孔直径喷油器对柴油机组经济性的影响

柴油机喷油器喷孔直径影响喷油器的雾化特性,而喷油器的雾化特性对柴油机热效率、燃油消耗率、有害物排放、机械故障等有着重要的影响。以某电控单体泵柴油机组为例,分别使用喷孔直径为0.28 mm和0.30 mm的2种喷油器进行负荷试验,对比2种喷油器柴油机组的燃油缸内爆发压力、燃油喷射压力、涡前排温及燃油消耗率。结果表明:使用喷孔直径为0.28 mm喷油器的柴油机组,其经济性优于使用喷孔直径为0.30 mm喷油器的柴油机组。

In-core fuel management strategy for the basket-fuel-assembly molten salt reactor

Molten salt reactor, with good economics and inherent reliability, is one of the six types of Generation IV candidate reactors. The Basket-Fuel-Assembly Molten Salt Reactor(BFAMSR) is a new concept design based on fuel assemblies composed of fuel pebbles made of TRISOcoated particles. Four refueling patterns, similar to the fuel management strategy for water reactors, are designed and analyzed for BFAMSR in terms of economy and security.The MCNPX is employed to calculate the parameters, such as the total duration time, cycle length, discharge burnup,total discharge quantity of ^(235)U, total discharge quantity of ^(239)Pu, neutron flux distribution and power distribution. The in–out loading pattern has the highest burnup and duration time, the worst neutron flux and power distribution and the lowest neutron leakage. The out–in pattern possesses the most uniform neutron flux distribution, the lowest burnup and total duration time, and the highest neutron leakage.The out–in partition alternate pattern has slightly higher burnup, longer total duration time and smaller neutron leakage than that of the out–in loading pattern at the cost of sacrificing some neutron flux distribution and power distribution. However, its alternative distribution of fuelelements cut down the refueling time. The low-leakage pattern is the second highest in burnup, and total duration time, and its neutron flux and power distributions are the second most uniform.

Effect of electrode Pt-loading and cathode flow-field plate type on the degradation of PEMFC

The electrode Pt-loading has an effect on the number of active sites and the thickness of catalyst layer,which has huge influence on the mass transfer and water management during dynamic process in PEMFCs. In this study, membrane electrode assemblies with different Pt-loadings were prepared, and PEMFCs were assembled using those membrane electrode assemblies with traditional solid plate and water transport plate as cathode flow-field plates, respectively. The performance and electrochemical surface area of cells were characterized to evaluate the membrane electrode assemblies degradation after rapid currentvariation cycles. Scanning electron microscope and transmission electron microscope were used to investigate the decay of catalyst layers and Pt/C catalyst. With the increase of Pt-loading, the performance degradation of membrane electrode assemblies will be mitigated. But higher Pt-loading means thicker catalyst layer, which leads to a longer pathway of mass transfer, and it may result in carbon material corrosion in membrane electrode assemblies. The decay of Pt/C catalyst in cathode is mainly caused by the corrosion of carbon support, and the degradation of anode Pt/C catalyst is a consequence of migration and aggregation of Pt particles. And using water transport plate is beneficial to alleviating the age of cathode Pt/C catalyst.