TWA800 fuel tank flammability-an analytical investigation

The mission was to identify the conditions of atmospheric pressure and ambient temperature under which a so-called empty-fuel-tank, containing residual fuel, could contain hazardous air/fuel mixtures. The issues are limited to two applications: explosion safety concerns in gasoline fueled automotive vehicles and explosion safety in jet fueled jet aircraft. In general, we concluded that flammable mixtures, under certain conditions, may exist in an empty fuel tank containing residual fuel, at ambient temperatures ranging from -51°C (-60°F) through 93°C (200°F), at or below atmospheric pressure. However, in the case of a gasoline automotive fuel tank, at normal ambient temperatures above -18°C (0°F), it is absolutely certain that the fuel tank head space contains an over-rich mixture, which cannot explode, unless the automotive fuel tank is completely drained of liquid fuel. Further, in the case of a fixed wing jet aircraft, a combustible mixture also does not exist in a fuel tank containing JetA type fuel at ambient temperatures below 38°C (100°F) which is about the lean limit flash point for commercial jet fuel at sea level. Nevertheless, this study identified six highly unlikely, but rationally possible critical conditions which can occur in a combination which may permit a combustible mixture to exist within a jet aircraft fuel tank and pose a potential hazard. While the scope of this summary paper is limited to fixed wing jet aircraft fuels, details of the automotive vehicle gasoline fueled application are contained in the original paper     

AMTEC electrochemical heat-to electricity conversion defies secondlaw

Sacred among the mechanical engineers is the “second law of thermodynamics,” which defines the maximum possible efficiency of an engine that converts thermal energy into mechanical power. The second law value is the difference between the engine's heat-source temperature and its heat-sink temperature, divided by the absolute value of the engine's heat-source temperature. For example, an engine setting on 0° C ice and running on steam from 100°C boiling water is not allowed to have more than 26.8% efficiency. Power-generating violators of the second law efficiency-limit range from horses to fuel cells. They do not burn fuel to generate mechanical or electrical power. The latest second law violator is the alkali-metal thermal-to-electric converter. Its efficiency approaches 25 percent. AMTEC cells and their variations were the topics of 12 papers at the 35^th Intersociety Energy Conversion Engineering Conference (IECEC) in July 2000     

Fuel cell status, 1994

The high efficiency environmental benefits and other attributes of fuel cells have attracted world-wide attention to the technology. Approximately 250 phosphoric acid fuel cell (PAFC) power units, 35 molten carbonate fuel cell (MCFC) stacks, and 12 solid oxide fuel cell (SOFC) modules have been or are being operated. Total capacity installed or operating is close to 45 MW. Fuel cell development has progressed to where complete power plants have reached nearly 16,000 operating hours and this continues to increase. Developers in the U.S. and Japan have embarked on extensive government and private programs to commercialize the technology in those countries and abroad. By mid-1994, the U.S. sold and shipped to other countries at least 33 PAFC 200 kW plants, 20 675 kW PAFC stacks, two SOFC 25 kW modules, and one MCFC system. Additional units have been produced for the domestic market. There is intense interest in Japan where there are very stringent environmental regulations and fuel prices are high. The fuel cell can respond with its combined attributes of low emissions and relative high efficiency. In Europe, the environmental cleanliness of fuel cell power units holds the promise of preserving the quality of life, motivating support and development of the technology. Canada and Australia have spawned important development programs. Interest continues to increase in other parts of the world. The author reviews the 1994 status and outlines the future development trends in this area     

Performance characteristics of lithium-ion cells for NASA's Mars2001 Lander application

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating over a wide range of temperatures, with high specific energy and energy densities. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars rovers and landers. The Mars 2001 Lander (Mars Surveyor Program MSP 01) will be one of the first missions which will utilize lithium-ion technology. This application will require two lithium-ion batteries, each being 28 V (eight cells), 25 Ah and 8 kg. In addition to the requirement of being able to supply at least 200 cycles and 90 days of operation on the surface of Mars, the battery must be capable of operation (both charge and discharge) at temperatures as low as -20°C. To assess the viability of lithium-ion cells for these applications, a number of performance characterization tests have been performed, including: assessing the room temperature cycle life, low temperature cycle life (-20°C), rate capability as a function of temperature, pulse capability, self-discharge and storage characteristics, as well as mission profile capability. This paper describes the Mars 2001 Lander mission battery requirements and contains results of the cell testing conducted to-date in support of the mission,     

Effect of KOH concentration on LEO cycle life of IPVnickel-hydrogen flight cell-update II

For update I see Energy and Environment: A Continuing Partnership, vol.3, American Nuclear Society (1991). An update of validation test results confirming the breakthrough in the low-Earth-orbit (LEO) cycle life of nickel-hydrogen cells containing 26% KOH electrolyte is presented. The results are part of an investigation of the effect of KOH concentration on life cycle. The cycle life of boiler plate cells was about 40000 LEO cycles compared to 3500 cycles for cells containing 31% KOH. The cycle regime was a stressful accelerated LEO, which consisted of a 27.5 min charge followed by a 17.5 min discharge (2×normal rate). The depth-of-discharge (DOD) was 80%. The cell temperature was maintained at 23°C. Results for six 48-Ah recirculation design IPV nickel-hydrogen flight battery cells currently being evaluated to validate the above findings are reported. Three of the cells contain 26% KOH (test cells), and three contain 31% KOH (control cells). They are undergoing real-time LEO cycle life testing. The 31% KOH cells failed at cycles 3729, 4165, and 11355. One of the 26% KOH cells failed at cycle 15314. The other two 26% KOH cells have been cycled for over 16600 cycles without failure     

Performance, life-cycle cost, and emissions of fuel cells

In this tutorial we evaluate the present status and future direction of fuel cell development. The three most promising types of fuel cells being evaluated for electric vehicle propulsion are: (1) direct hydrogen-consuming fuel cells; (2) methanol-consuming fuel cells; and (3) zinc-air fuel cells. The author evaluates the advantages and disadvantages of each type.     

Latest progress in fuel cell technology

A brief review of advances in fuel cell technology is given. The major types of cells being developed and their characteristics are tabulated. Also in table form is a summary of worldwide fuel cell application and developmental interests, particularly in Europe, Japan, and the US. Performance improvements for phosphoric acid fuel cells (PAFC) over the years 1969-92 are discussed. Potential fuel cell markets are indicated     

新世纪小型发电装置的开发研究

分布式发电计划涉及到新世纪小型发电机组 (一般低于 30MW)的开发研究。该计划的最终目标是在 2 0 15年提供效率高达 80 %、接近零污染物排放和廉价的发电装置。通过对该计划相关资料的分析 ,介绍了这一计划的主要内容和执行情况 ,燃料电池和高性能燃机研究开发最新动向 ,高性能陶瓷基复合材料 ,燃料处理器等关键技术。     

航空用燃料电池及混合电推进系统发展综述

随着世界范围内碳减排需求的日益增长及长航时飞机的发展需要,高效率的燃料电池航空电推进系统逐渐受到重视,氢能航空的理念被人们所熟知。可使用碳氢燃料的高温燃料电池还可与燃气涡轮组成混合动力系统,发电效率进一步提高至70%。本文首先回顾了燃料电池及燃料电池涡轮混合系统在航空能源、动力系统方向应用概况;接着,概述了几种突破现有涡轮发动机技术瓶颈的新概念混合电推进系统,如发电与推进一体化燃料电池涡轮混合动力系统和无涡轮燃料电池混合推进系统;基于此,本文分析了限制燃料电池混合系统实际应用的关键技术难题,主要体现在混合动力系统功重比较低、大分子碳氢燃料重整技术未突破两方面。     

High energy density regenerative fuel cell systems for terrestrialapplications

Regenerative Fuel Cell System (RFCS) technology for energy storage has been a NASA power system concept for many years. Compared to battery-based energy storage systems, RFCS has received relatively little attention or resources for development because the energy density and electrical efficiency were not sufficiently attractive relative to advanced battery systems. Even today, RFCS remains at a very low technology readiness level (TRL of about 2 indicating feasibility has been demonstrated). Commercial development of the Proton Exchange Membrane (PEM) fuel cells for automobiles and other terrestrial applications and improvements in lightweight pressure vessel design to reduce weight and improve performance make possible a high energy density RFCS energy storage system. The results from this study of a lightweight RFCS energy storage system for a remotely piloted, solar-powered, high altitude aircraft indicate an energy density up to 790 wh/kg with electrical efficiency of 53.4% is attainable. Such an energy storage system would allow a solar-powered aircraft to carry hundreds of kilograms of payload and remain in flight indefinitely for use in atmospheric research, Earth observation, resource mapping, and telecommunications. Future developments in the areas of hydrogen and oxygen storage, pressure vessel design, higher temperature and higher pressure fuel cell operation, unitized regenerative fuel cells, and commercial development of fuel cell technology will improve both the energy density and electrical efficiency of the RFCS     

InAsP cells for solar thermophotovoltaic applications

High temperature wide band gap InAsP cells have been specifically designed and fabricated for operating temperatures up 250°C to match with selective emitters operating near 1 μm in a TPV system. An important assumption is that the emitters can be heated up to the range of 1400 K to 2000 K by either solar concentrators or some other heat source. The efficiency of a selective emitter, which can be selected depending on the emitter operating temperatures, will be significantly higher than either a blackbody or a graybody emitter. The key for the TPV success is that the match between the band gap and selective emission must occur at the cell operating temperature. An appropriate cell band gap needs to be carefully selected; so when the band gap shrinks at the operating temperature, the desired match can be achieved. In this paper, two types of InAsP cells were investigated for this concept. The performance of these cells at elevated temperature and energy conversion efficiency are reported in this paper     

基于彩色编码的副油箱风洞模型位姿测量方法

高速飞行器副油箱分离位姿参数是飞行器以及副油箱设计的重要基础数据。位姿参数测量工作多在高度模拟飞行器飞行状态的风洞环境下进行,对缩比模型实施高速非接触测量。受风洞试验段观察视窗限制以及副油箱模型形状影响,副油箱模型位姿测量十分困难。首先针对风洞观察视窗以及风洞复杂环境对图像采集效果的影响,提出了基于自发光单元的副油箱运动序列图像采集方法,采用双目视觉系统高速采集获得目标物的清晰序列图像;其次,提出基于环绕式彩色编码的自发光标记点匹配方法,实现风洞复杂环境内标记点的高精度匹配;最后,根据副油箱表面合作标记点的三维坐标获取副油箱模型的位姿信息。试验结果表明:所提出的位姿测量方法满足测量要求,其最大位移误差不超过0.102mm、最大角度误差不超过0.201°。     

基于自适应神经模糊推理算法的无人机电推进燃料电池供气系统性能优化

本文针对某无人机基于聚合物交换膜燃料电池和锂离子电池的混合动力电推进系统的应用,研究开发了一种基于自适应神经模糊推理系统的电源管理系统控制技术,以控制混合动力电力推进系统,同时优化燃料电池供气系统的性能。本文以所建立的某无人机混合电推进系统数学模型为研究对象,研究了燃料电池电流与燃料电池供气系统压缩机功率之间的关系,建立了燃料电池电流与最佳压缩机功率关系的参考模型。在参考模型的基础上,引入自适应控制器来优化燃料电池供气系统的性能。基于自适应神经模糊推理系统的控制器将压缩机的实际运行功率动态调整到参考模型中定义的最佳值。自适应控制器的在线学习和训练能力用来辨识燃料电池电流的非线性变化,并产生压缩机电机电压的控制信号,以优化燃料电池供气系统的性能。在Matlab 仿真环境中开发了质子交换膜燃料电池和锂离子混合动力电推进系统模型并对所设计的控制器进行了仿真分析,结果表明基于自适应神经模糊推理系统的控制器为燃料电池供气系统压缩机性能优化提供了一种新颖而全面的途径,使燃料电池供气系统获得最大净功率输出。将燃料电池系统的净功率输出与最佳压缩机功率和恒定压缩机功率进行了比较,结果表明优化的压缩机功率配置比恒定的压缩机功率配置节能2.62%。同时,燃料电池自适应神经模糊推理系统控制器优化了燃料电池供气系统的能量利用。     

水下燃料电池推进技术研究进展

水下燃料电池推进系统具有能量转换效率和比能量高、振动噪声低、无尾气排放等诸多优势,可大幅提高无人潜航器的航程、航深和隐蔽性等关键性能,是水下推进领域极具发展潜力的技术方向。本文介绍了水下燃料电池推进系统组成和工作原理,归纳了国内外在无人潜航器、氢氧燃料电池和高能氢氧源方面的研究进展,探讨了燃料电池推进技术未来的发展重点。在氢氧燃料电池方面,应重点解决纯氧供应和闭式循环带来的排水、腐蚀等问题。在高能氢氧源方面,能量密度较高的是铝水反应制氢、柴油重整制氢和高氯酸锂制氧,应予以重点关注。     

不同气体喷嘴的燃气轮机燃烧室性能对比

将原型使用-10#柴油的燃气轮机燃烧室改为使用天然气燃料的燃烧室,遵循对原型机改动量最少的原则,只对燃油喷嘴做改动设计,其余部分不做改动。为了解改型机的喷嘴与燃烧室的匹配特性,设计了三种不同孔径的天然气喷嘴（气体喷嘴开孔大小决定了燃料的喷射速度、燃料的浓度分布,进而影响燃烧室的燃烧性能）,并在改型机上进行燃烧性能试验研究。试验结果表明:改烧天然气后,设计状态燃烧效率增加,但出口温度分布有所变差,而对壁面温度分布影响不大;通过对燃烧性能进行对比分析,天然气3＃喷嘴的综合燃烧性能最优。      

数值研究低热值燃料环管燃烧室燃烧流场

在任意曲线坐标系下对采用两种不同组分(天然气掺混氮气、一氧化碳)的低热值燃料环管燃烧室燃烧流场进行计算,结果表明低热值燃料的化学反应速率与其组分直接有关,燃料一氧化碳的燃烧效率高于天然气与氮气掺混物燃料,燃料组分变化对燃烧室燃烧效率与出口温度影响很大,因此选用合适的燃料十分重要.计算所得的燃烧室的燃烧效率和出口温度分布与试验数据符合较好,表明所用的数学模型与计算方法合理,计算程序可靠,可为低热值气体燃料燃烧室研制和优化设计提供有用的数据.      

无人机用燃料电池阴极供气系统建模与控制

燃料电池因其高效、无污染、噪声小等特点,被认为是未来最具有潜力的无人机（UAV）用动力源,燃料电池阴极供气系统的控制技术是决定燃料电池系统性能和可靠性的关键。针对无人机用质子交换膜燃料电池（PEMFC）阴极供气系统,首先,考虑外界温度、压力、空气密度以及雷诺数等随高度变化的参数,建立了跨高度离心空压机模型并分析了其在不同高度下的工作特性,基于无刷直流电机反电势特征构建了高速空压机驱动电机模型。其次,通过计算燃料电池阴极氧气和氮气的动态分压获取了PEMFC电堆输出电压。设计了基于分数阶PI^λD^μ的过氧比和阴极气压控制方法,驱动电机采用有限集模型预测控制（MPC）实现快速的转矩响应,仿真结果表明设计的控制器可在无人机跨高度运行条件下实现过氧比的快速调节,同时维持阴极气压稳定,满足燃料电池阴极供气需求。     

适用无人机的小型燃料电池控制方法

燃料电池动力系统作为一种长航时电动无人机的动力方案,其燃料电池的控制技术是决定动力系统可靠性和高效性的关键技术。针对用于无人机的小型空冷型开放阴极的质子交换膜燃料电池,考虑面向工程应用的燃料电池整体控制过程,兼顾电堆温度控制和水管理,提出了一种前馈型模糊PID的电堆温度控制方法,同时设计了一种基于安时积分门限法的膜水含量调节策略,以实现对整个燃料电池系统的高效控制。通过搭建燃料电池温度控制与水管理试验平台,对所提出的控制技术进行了试验验证,并与现有温控和水管理方法进行了对比分析。试验结果表明：所提前馈型模糊PID方法在较长时间的燃料电池启动过程中能够较快地达到目标温度,相比于PID方法减少了7%的调节时间,与传统模糊PID方法相当;燃料电池电流持续减小时,所提前馈型模糊PID方法对超调量的抑制效果具有明显优势,其超调量仅为PID方法的34%,为传统模糊PID方法的43%;所提安时积分门限排水控制方法既能防止水淹故障,又可提高燃料经济性,在所给工况中相比现有方法节约了15%的氢气。     

Galileo probe Li-SO2 battery cell life testing

Several hundred D-sized, Li-SO₂ battery cells have been in a carefully controlled quiescent storage test for up to 14 years, starting at Honeywell but completing at the NASA Ames Research Center, in support of the Atmospheric Probe portion of the Galileo Mission to the planet Jupiter. This population of cells includes similar samples from 8 different manufacturing lots; the earliest from October 1981, the latest from October 1988. The baseline samples have been divided among several storage chambers, each having its own constant temperature, respectively, set between 0°C to 40°C. Non-invasive measurements have been made repeatedly of open circuit voltage and internal resistance (at 1000 Hz). At intervals, a small portion of the cells has been removed from storage and fully discharged under repetitive conditions, thus assessing any storage related loss of discharge capacity. The results show that for storage up to 20°C the cells have excellent stability. Above 20°C noticeable degradation occurs