自由活塞汽油直线发电机起动过程研究

为获得自由活塞汽油直线发电机起动过程主要工作特点,对自由活塞汽油直线发电机主要起动方式进行了研究。耦合动力学及热力学方程,建立了起动过程数学模型,理论分析了起动过程中能量的传递与转换关系,并结合试验样机对两种典型起动方式进行了试验研究。研究发现:采用恒定加速度起动模式和恒定推力起动模式均可实现自由活塞汽油直线发电机的起动燃烧,其中采用恒定加速模式有利于第一次压缩气缸实现起动燃烧,然而采用恒定推力起动模式更有利于对侧发动机气缸完成起动燃烧;起动过程中摩擦损失所消耗的能量较少,漏气损失所占的比例较大,在起动设计时不应被忽视。     

柴油机起动电机低温起动特性优化匹配

基于柴油机低温起动条件,通过对影响起动电机低温起动的主要特性(起动功率、起动转矩和转速)进行优化分析,实现了起动电机和柴油机合理匹配;利用径向基神经网络(RBFNN)和遗传算法(GA)融合理论,预测出满足低温起动的起动电机合理的结构参数;在环境温度-25℃下,进行了柴油机低温起动试验,对电动机的起动电压、起动电流、起动转矩及起动转速等性能参数进行了测试.结果表明:进行柴油机低温起动时,优化后的起动电机最大起动功率为2.58KW,比原机增加了18.3%;平均拖动转矩为105 N·m,比原机增加了7.1%;拖动柴油机的平均转速为225 r/min,比原机提高了16%;保证了低温工况柴油机快速、可靠地起动.     

柴油机交流变频起动振荡充电的过渡过程分析

用交流同步主发电机作为柴油机的起动电动机实现柴油机起动是一种切实可行的交流起动方案。分析变频起动的振荡充电过程,找出电压及电流的变化规律,指出充电电路中电阻、电容、电感对充电过程及柴油机起动过程的影响。     

用起动液解决柴油机低温起动问题的分析

本文根据用起动液进行柴油机低温起动的试验结果,提出了用起动液起动的特点和注意事项。认为合理使用起动液还应做些深入细致的工作,制定有关使用规范和标准。     

起动发电机负载突变时辅助发电机过压的原因分析

通过对DF8B型机车两起典型的辅助发电机过压现象进行分析，认为起动发电机（QD）负载突变时，造成辅助发电机过压的原因为起动发电机电刷偏离了几何中性线，并提出相应的解决方案。     

起动转速对起动阻力矩的影响规律试验研究

在常温环境下,测试了一台6缸柴油机在80—340r／min下的平均起动阻力矩,采用单因素方差分析法,分析转速对平均起动阻力矩的影响规律,结果表明：平均起动阻力矩随转速升高先快速降低,然后趋于平缓,并存在一个160r／min的拐点转速,当转速在80～160r／min时,平均起动阻力矩快速减小,转速对起动阻力矩有显著影响;当转速在160—340r／min时,平均起动阻力矩有微小波动,转速对平均起动阻力矩影响不显著。     

缸内直喷发动机热机起动模式的研究

在缸内直喷发动机上分别研究传统起动模式、压缩缸起动模式和膨胀缸燃烧辅助起动模式三种起动模式,对比分析了其起动过程中起动转速特性、起动HC排放和起动耗电量。研究结果表明:相比传统起动模式,压缩缸起动模式和膨胀缸燃烧辅助起动模式在起动速度和起动耗电量方面均有较大优势,尤其后者起动耗电量几乎节省一半;在起动HC排放方面,压缩缸起动模式没有太大的增加,而膨胀缸燃烧辅助起动模式因其膨胀缸燃烧不良以致有一定程度的增加;压缩缸起动模式的综合性能更具优势。     

机车柴油机起动辅助储能装置

介绍了电起动、气起动和混合起动三种机车柴油机起动方式,分析了电起动所用三种不同类型蓄电池的优缺点.着重论述了机车用铅酸蓄电池在使用中存在的经济浪费和起动不可靠等问题和采用起动辅助储能装置的意义.以理论分析和试验数据、曲线为依据,说明了起动辅助储能装置可提高起动电流最大值和蓄电池起动最低端压值,从而大大提高起动功率最大值,大大提高起动可靠性;还说明了可延长蓄电池寿命,具有很大的经济价值.     

柴油机冬季起动问题

柴油机冬季起动困难的主要原因是: (1)柴油在低温下粘度增大,雾化性能变差,不易形成理想的混合气体。 (2)由于冬季里蓄电池端电压及容量下降,加之曲轴箱内机油粘稠,机件运动阻力增大,导致柴油机起动转速下降;起动转速下降后,活塞在气缸中的运动速度变慢,燃烧室中散热损失和漏气损失加大,压缩终了时的压力和温度变低,不足以引起柴油自燃;起动转速降低后,气缸中空气旋流速度     

基于目标起动转速变化规律的起动过程瞬态喷油量控制策略研究

提出了一种基于目标起动转速变化规律的起动过程瞬态喷油量的控制策略以改善柴油机起动性能,详细介绍了这种控制策略的起动过程瞬态喷油量的确定方法,并在2.8T型4缸直喷高压共轨柴油机上与恒定油量控制方法和标定转矩MAP控制方法进行了台架对比试验。结果表明:标定转矩MAP控制方式虽然NO_x排放量最低,但燃烧效率普遍较低,HC与CO排放水平较高;而基于目标转速变化规律的控制策略可根据起动过程中目标转速的变化所对应的需求转矩精确地控制起动过程各循环的瞬态喷油量,实现对起动过程喷油量的循环控制,使各循环燃烧效率均保持在高水平,有效地降低了CO_2排放,且在保持HC和CO排放水平较低的前提下明显降低了NO_x排放量,同时很好地改善了起动到怠速的过渡过程转速的波动现象。     

Experimental investigation of parameters influencing the freeze start ability of a fuel cell system

To improve the freeze start ability of a fuel cell system some significant influencing parameters are defined and investigated. Experiments with a fuel cell test system are carried out in a climate chamber at various conditions. The time interval until fuel cell stack power equals 50% of its maximum power is defined as an indicator for a successful freeze start as well as a value for comparison and evaluation of the results. The target of this work is the minimization of this freeze start time by avoiding the freezing of process water on the catalyst layer of the Membrane Electrode Assembly (MEA), since this leads to temporary performance losses.The shut down strategy of the fuel cell system is identified to be one of the main parameters influencing the freeze start. It is found that a higher degree of dryness in the stack leads to a significant improvement in the freeze start performance, since the water absorbing capacity of the membrane increases and therefore also the time until its saturation. If this saturation takes place after the temperature of the MEA reached 0 °C, no significant ice-formation occurs. It is shown that by improving the shut down strategy of the fuel cell system at T_Start = −6 °C a start without performance loss can be realized. At temperatures lower than that temporary performance losses occur.Even if a lower voltage leads to a higher current and therefore to a higher water production rate, its effect on the freeze start due to the increased heat of reaction is positive. Further investigated parameters, for example the volume of the coolant loop, also affect the freeze start ability, but it can be concluded that the shut down strategy is of main importance.     

基于联络矩阵法的黑启动分区与机组启动顺序选择方案

针对黑启动过程中合理分区的重要性,考虑黑启动过程中线路恢复成功率与机组启动成功率,提出了机组恢复期望功率这一黑启动恢复指标。首先利用所提指标结合线路恢复时间建立节点分区判定目标函数,初步确定各待恢复节点所属分区;然后利用分区子系统期望恢复功率与分区网架结构形成时间建立新的分区目标函数,利用改进的模拟退火法求解该目标函数以实现黑启动分区的全局优化;最后得出了待恢复机组所属分区以及各分区内机组恢复顺序,并找到了所有待恢复机组的最优黑启动路径。     

Maximum power cold start mode of proton exchange membrane fuel cell

Successful and fast cold start is important for proton exchange membrane (PEM) fuel cell in vehicular applications in addition to the desired maximum power in any case. In this study, the maximum power cold start mode is investigated in details and compared with other cold start modes based on a multiphase stack model. It is found that for the maximum power cold start mode, the current density is generally kept at high levels, and the performance improvement caused by the membrane hydration and temperature increment may not be observable. Therefore, before the melting point, the performance drops continuously. The maximum power cold start mode could better balance the heat generation and ice formation, leading to improved cold start survivability than that in the constant voltage and constant current modes, with a fast start-up generally guaranteed. Once the survivability can be ensured, the initial water content needs to be higher for fast cold start, suggesting that over purging should be avoided. The maximum power mode is suggested to be optimal for PEM fuel cell cold start based on the modeling results.     

新建大型火电厂“黑启动”的技术探讨

国内新建大型火电厂均需要采用辅助蒸汽(厂外引进或启动锅炉)进行机组启动和调试。从机组启动蒸汽的作用入手,进行启动蒸汽替代方案的研究,并结合具体工程讨论具备"黑启动"功能机组的配套系统和启动过程,为后续工程的"黑启动"方案设计提供参考。     

Investigation on sub-zero start-up of polymer electrolyte membrane fuel cell using un-assisted cold start strategy

The technical barriers for commercialization of polymer electrolyte membrane fuel cell (PEMFC) are the startup ability and survivability at sub-zero temperatures. Ice formation causes cold start fail and volume change damages the cell components leading to performance decay. Many strategies are used to assist successful cold start and to reduce the performance decay. But, unassisted cold start is very crucial and needs attention. Here, an experimental protocol is reported for successful unassisted cold start using low temperature gas purging at various temperatures (-5,-8,-10,-15, and -20 °C) as well as to recover temporary performance decay. The stability of the membrane electrode assembly is also studied in freeze/thaw and sequential cold start cycles. At temperature −10 °C, there is small performance decay after the 6th freeze/thaw cycle. However, the subsequent cold start cycle shows significant performance decay after the 6th cycle. Changes in microstructures and loss of hydrophobicity in the gas diffusion layer are attributed to the performance decay in both freeze/thaw and sequential cold start cycles. The effect of cold start temperature on the performance of a PEMFC in subsequent freeze/thaw cycles is also studied. It shows that depending upon the start-up temperature, the preferential ice formation can affect the performance decay characteristics.     

燃气轮机发电机组黑启动方案探讨

不同电厂的黑启动方案由于机型和系统接线的差异而千差万别,但黑启动过程设计中的关键因素如黑启动负荷加载顺序、黑启动柴油发电机组选型、死母线合闸、孤岛运行控制等却有着原理一致性和可归纳性。基于9E机组的黑启动成功案例,阐述燃气轮机电厂黑启动必须考虑的重要负荷顺序以及黑启动柴油机的选型计算过程。对死母线合闸、孤岛运行控制等黑启动方案中关键步骤进行原理描述和经验总结,并介绍了优化方法和现场经验及需要注意的特殊环节,为今后黑启动方案设计提供参考和借鉴。     

50 MW水煤浆机组电网黑启动实践和改进

＂黑启动＂是电网机组启动的一种特殊而重要的方式.介绍了50 MW水煤浆机组首次电网黑启动实践,对水煤浆机组通过黑启动演习暴露出来的问题提出解决对策,相关问题的妥当解决可以使水煤浆机组成为真正意义的实现黑启动机组.     

Internal behavior of segmented fuel cell during cold start

In order to improve cold start capability and survivability of proton exchange membrane fuel cell (PEMFC), a fundamental understanding of its internal behavior is required. In this study, the cold start processes of a PEMFC with different operating conditions have been investigated, and the characteristics of current density and temperature distributions are studied through in-situ experiments with a printed circuit board (PCB). It is found that the start ability of PEMFC is strong at −3 and −5 °C, but weak at −7 and −10 °C. Also the self-start ability can be enhanced by decreasing the initial current load. Polarization curves show almost no degradation after successful cold start at −3 and −5 °C, while the PEMFC degrades a lot after failed cold start at low temperature like −10 °C. Also electrochemical impedance spectroscopy (EIS) shows a big degradation after galvanostatic mode cold starts. Local current density of segmented cell results shows that the highest current density is initially near the inlet region and then quickly moves downstream, reaching to the region near the middle eventually during the successful cold start process. However, during the failed cold start process, the highest current density is initially near the inlet region of the flow channels and quickly moves down stream, reaching the upper left corner region (A1) before shut down eventually. For both successful and failed cold starts, the highest temperature can be observed near the middle of the cell after the reaching of the highest current density.     

Reversible performance loss induced by sequential failed cold start of PEM fuel cells

This study correlates the post start cell performance and impedance with the cold start process in the subzero environment. The sequential failed cold starts are deliberately conducted as well as the start at small current density. Here the failed cold start means the cell voltage drops to or below zero within very short time during the start process. It is found that there are reversible performance losses for the sequential failed cold starts, while not obvious degradation and no recovery happen for the start at small current density. Using the thin film and agglomerate model, it is confirmed that this is due to the water blocking effect. Comparing the results from different start processes, a model with respect to the shifting of reactive region within the catalyst layer is applied to explain that the reversible performance loss is associated with the amount of the generated water or ice and the water location or distribution during cold start. The relationship of the cold start performance at high current density and the pore volume in the catalyst layer is also discussed.