气体扩散层厚度对PEMFC性能的影响

质子交换膜燃料电池(PEMFC)的气体扩散层(GDL)厚度对燃料电池的输出性能有重要影响。文章利用多物理场直接耦合分析软件(COMSOL Multiphysics 5.0),在电池温度为70℃的条件下,对4种不同厚度的GDL进行模拟分析,并在相同的操作条件下,得到了4组极化曲线、阴极氧气浓度、阴极水浓度、阳极氢气浓度以及电流密度的变化趋势图。对比分析4组变化趋势图后发现:GDL的厚度越小,燃料电池的性能越好;GDL的厚度对阳极氢气的浓度分布影响不大;当GDL的厚度增大时,产生的液态水会堵塞GDL的孔隙,降低GDL的孔隙率。     

不同衰退机理对PEMFC怠速工况性能衰退影响的模拟研究

分析质子交换膜燃料电池(PEMFC)怠速工况衰退机理,确定怠速工况不同衰退机理对燃料电池模型参数的影响,采用所建立的PEMFC二维等温多物理场模型,仿真研究燃料电池在怠速工况衰退前后的性能及各种衰退因素对电压衰减量的贡献和内部反应气体分布变化.研究结果表明,阴极活化损失增大是怠速工况下最重要的衰退因素,其次是开路电压衰...     

扩散层孔隙率对PEMFC性能影响的模拟研究

为了研究扩散层孔隙率对质子交换膜燃料电池(PEMFC)性能的影响,采用COMSOL软件,通过数值模拟得出气体扩散层不同孔隙率(0.2,0.4,0.6和0.8)时,单直通道和具有楔形肋片(长1 mm,高1.5 mm,宽2 mm)的PEMFC性能曲线、阴极氧气质量分数分布和水质量分数分布。结果表明:扩散层孔隙率对燃料电池性能具有较大影响,随着扩散层孔隙率从0.2增大到0.8,PEMFC的电流密度逐渐增加,最大可达847 mA/cm~2;相对于单直通道,增加孔隙率比添加楔形肋片更利于提升电池性能;在孔隙率为0.6和0.8时,氧气更易扩散到反应区,排水效果更好。     

PEMFC翅脉流道传质及输出性能分析

为研究流道结构对质子交换膜燃料电池（PEMFC）反应气体质量传输及输出性能的影响,建立翅脉流道、叶脉流道及蛇形流道的三维PEMFC几何模型,并对比3种流道的反应气体浓度分布、压力分布及电流密度分布,最后对翅脉流道结构参数进行优化。结果表明,与蛇形流道、叶脉流道相比,翅脉流道能明显改善流道和扩散层内反应气体浓度分布的均匀性,有利于强化反应气体向催化层的质量传递;翅脉流道能减小气体压力分布梯度,使反应气体扩散更加充分;翅脉流道的平均膜电流密度更大,有利于促进电化学反应稳定进行;翅脉流道能改善PEMFC的输出性能,翅脉流道峰值功率密度比蛇形流道、叶脉流道分别提高7.72%和6.25%;减小翅脉流道的直流道长度或圆弧流道圆心角,可提升翅脉流道输出性能。     

进气加湿与富氧对船用柴油机NOx-Soot排放的影响

通过一台满足TierⅡ排放标准的四冲程增压中冷船用柴油机,模拟研究了富氧燃烧结合进气加湿改善NOx-soot折衷关系的潜力,并探讨了实现TierⅢ排放标准的技术路线.本研究使用AVLFire软件建立仿真模型.结果表明:单独使用富氧燃烧时,缸内温度较高,燃烧持续期较短,soot排放减少,NOx排放恶化,而单独使用进气加湿时呈相反的趋势.当发动机运行在转速为1350 r/min、75%负荷工况下,进气氧体积分数为21%~23%、加湿率为0~100%时,可实现NOx-soot排放同时降低且低于原机.氧体积分数为21%和加湿率为100%匹配,可以实现TierⅢ排放法规.两种措施的优化组合可以获得NOx-soot排放的最佳优化区域.     

进气畸变对回流燃烧室性能的影响研究

针对燃气轮机实际运行过程中不同火焰筒之间的空气流量畸变问题,以回流燃烧室为研究对象,开展三维数值模拟,分析进气流量改变对燃烧室多物理场分布特征和燃烧室性能的影响。结果表明：进气流量偏离理想设计对燃烧室回流区结构、温度场、总压恢复系数和燃烧效率等参数产生不利影响,而对燃烧室空气流量分配比例、主燃孔和掺混孔射流深度等参数的影响不明显;随着进气流量的减小,燃烧火焰拉长,燃烧室出口温度均匀性变差,燃烧效率急剧降低。     

出口形式对防浪级阻力性能影响的研究

燃气轮机进气系统的结构和气动性能是燃气轮机装舰技术研究的重要组成部分。针对这方面的要求，进行了燃气轮机进气防浪级的设计及数值模拟计算，为设计制造高性能的船用燃气轮机进气系统提供可靠的依据。对进气防浪级作的数值计算和实验研究，其结果是相当令人满意的，研究方法对燃气轮机进气系统的研究有一定的参考价值和指导意义。     

进气参数及燃烧室结构对LNG发动机排放性能的影响

以L23/30A发动机为研究对象,研究了不同进气参数及不同燃烧室几何形状对缸内燃烧特性对柴油机性能及排放的影响。研究结果表明:随着进气压力的增大和燃烧室过渡圆深度的加深,缸内挤流作用加强,油气混合均匀,缸内燃烧充分,降低了soot及NO_x的生成;减小燃烧室的缩口直径及提高进气温度,缸内湍流分层严重,滞缓了缸内涡团的破碎与聚合,局部油气分布过浓燃烧不完全,导致局部温度、压力过高,诱发燃烧过程中soot及NO_x的生成。因此,在加深燃烧室过渡圆深度的前提下,通过提高低温燃烧的进气压力,可以改善发动机的燃烧特性。     

进气加湿耦合涡流比对船用柴油机燃烧和排放的影响

针对某一款四冲程船用柴油机,利用商业模拟软件AVL-Fire建立柴油机三维数值模型,研究进气加湿耦合涡流比对燃烧的影响以及改善NOx和碳烟折中关系的潜力,给出优化方案,得到满足TierⅢ排放法规的技术路线并保证指示燃油消耗率增长在2%以下.结果表明,加湿率增大,缸内温度和压力的峰值均降低,且最大降幅都约为2%;滞燃期延长,燃烧重心后移,对燃烧热效率不利.缸内温度和进气氧浓度的下降有效降低了NOx排放,最大降低幅度约为56.7%.一定的涡流比可以促进油气混合,而太大的涡流比会降低油束贯穿距,使喷雾前端偏转角度增大,影响油气混合.涡流比的增大对NOx和碳烟的排放形成先增后降的影响,在涡流比为0.5时碳烟排放最低.此外,对各种进气加湿率和初始涡流比获得的结果进行优化,其中有9种算例同时降低了NOx和碳烟排放,并且在初始涡流比为0.50时,加湿率100%和80%的两种方案满足TierⅢ的排放标准.     

Effects of the membrane thickness and ionomer volume fraction on the performance of PEMFC with U-shaped serpentine channel

A three-dimensional, multi-component, single-phase model is applied for analyzing the electrochemical performance of the proton exchange membrane fuel cell (PEMFC) with U-shaped channel using COMSOL Multiphysics software. To validate the numerical model, the results are compared with the experimental data available in the literature. This work numerically investigates the effects of convection and diffusion under the rib, membrane thickness, ionomer content, and current density distribution at an interface between the gas diffusion layer and the catalyst layer. These effects were not studied for a U-shaped single serpentine channel despite having several benefits such as uniform reactant distribution through convection and diffusion under the rib and the resulting uniform current generation. A total of three membranes with 2, 3.5, and 5 mil thicknesses are analyzed, and an improvement of 17% in PEMFC performance with 2 mil thickness is observed owing to a decrease in internal resistance compared to 3.5 and 5 mil. Furthermore, an ionomer volume fraction in the catalyst layer is varied from 0.3 to 0.6, and the performance enhancement of 7% is reported at 0.5 volume fraction.     

Effect of operational parameters on the performance of PEMFC assembled with Au-coated Ni-foam

An innovative proton exchange membrane fuel cell was assembled using Au-coated nickel foam instead of the conventional flow field (carbon plate). The effect of operational parameters on the performance of this cell was investigated by DC polarization and electrochemical impedance spectroscopy techniques. Parameters such as cell operating temperature, cathode humidification temperature, and cathode-gas stoichiometry were of concern.     

CFD investigating the effects of different operating conditions on the performance and the characteristics of a high-temperature PEMFC

The effects of different operating conditions on the performance and the characteristics of a high-temperature proton exchange membrane fuel cell (PEMFC) are investigated using a three-dimensional (3-D) computational fluid dynamics (CFD) fuel-cell model. This model consists of the thermal-hydraulic equations and the electrochemical equations. Different operating conditions studied in this paper include the inlet gas temperature, system pressure, and inlet gas flow rate, respectively. Corresponding experiments are also carried out to assess the accuracy of this CFD model. Under the different operating conditions, the PEMFC performance curves predicted by the model correspond well with the experimentally measured ones. The performance of PEMFC is improved as the increase in the inlet temperature, system pressure or flow rate, which is precisely captured by the CFD fuel cell model. In addition, the concentration polarization caused by the insufficient supply of fuel gas can be also simulated as the high-temperature PEMFC is operated at the higher current density. Based on the calculation results, the localized thermal-hydraulic characteristics within a PEMFC can be reasonably captured. These characteristics include the fuel gas distribution, temperature variation, liquid water saturation distribution, and membrane conductivity, etc.     

蛇形流场结构质子交换膜燃料电池的性能研究

建立包括催化层、扩散层、质子膜在内的三维质子交换膜燃料电池模型,通过Fluent软件模拟4种不同结构的蛇形流场,通过对速度、膜中水含量以及功率密度等分析得出蛇形流场的最优结构,并对最优结构进行参数优化。研究表明,4种不同蛇形流场结构中,Multi-serpentine II为最优,随着温度、压强的增加,这种流场结构的燃料电池呈现出良好的性能,从而为质子交换膜燃料电池双极板的设计提供依据。     

Numerical study on the compression effect of gas diffusion layer on PEMFC performance

A numerical method is developed to study the effect of the compression deformation of the gas diffusion layer (GDL) on the performance of the proton exchange membrane fuel cell (PEMFC). The GDL compression deformation, caused by the clamping force, plays an important role in controlling the performance of PEMFC since the compression deformation affects the contact resistance, the GDL porosity distribution, and the cross-section area of the gas channel. In the present paper, finite element method (FEM) is used to first analyze the ohmic contact resistance between the bipolar plate and the GDL, the GDL deformation, and the GDL porosity distribution. Then, finite volume method is used to analyze the transport of the reactants and products. We investigate the effects of the GDL compression deformation, the ohmic contact resistivity, the air relative humidity, and the thickness of the catalyst layer (CL) on the performance of the PEMFC. The numerical results show that the fuel cell performance decreases with increasing compression deformation if the contact resistance is negligible, but an optimal compression deformation exists if the contact resistance is considerable.     

Effects of PEMFC operating parameters on the performance of an integrated ethanol processor

In this paper the performance of a complete fuel cell system processing ethanol fuel has been analyzed as a function of the main fuel cell operating parameters. The fuel processor is based on the steam reforming process, followed by high- and low-temperature shift reactors, and carbon monoxide preferential oxidation reactor, which are coupled to a polymeric fuel cell (PEMFC). The goal was to analyze and improve the fuel cell system performance by simulation techniques. PEMFC operation has been analyzed using an available parametric model, which was implemented within HYSYS environment software. Pinch Analysis concepts were used to investigate the process energy integration and determine the maximum efficiency minimizing ethanol consumption. The system performance was analyzed for the SR-12 Modular PEM Generator, the Ballard Mark V fuel cell and the BCS 500 W stack. The net system efficiency is dependent on the required power demand. Efficiency values higher than 50% at low loads and less than 30% at high power demands are computed. In addition, the effect of fuel cell temperature, pressure and hydrogen utilization was analyzed. The trade-off between the reformer yield and the fuel cell performance defines the optimal operation pressure. The cell temperature determines operating zones where the water, involved in the reforming reactions, can be produced or demanded.     

The impact of air contaminants on PEMFC performance and durability

The impact of air contaminants such as sulfur compounds (SO₂, H₂S) and nitrogen compounds (NO_x and NH₃) was investigated using subscale fuel cells. The severity of the effect of these impurities varies depending on the contaminants. Among air contaminants, sulfur compounds cause the most severe performance loss due to decrease of available Pt sites for oxygen reduction reaction (ORR). We found that sulfur compounds adsorbed on Pt surface tend to be oxidized to sulfate at 0.9 V and higher potentials. The cell performance can be recovered partially by excursions to high potentials due to increase of available Pt sites. Furthermore, flushing the cathode with high humidity gases results in almost complete recovery of the cell performance. We conclude that these recovery effects are due to oxidation/removal of the contaminants from the Pt surface.     

A numerical study on the performance of PEMFC with wedge-shaped fins in the cathode channel

The gas flow field design has a significant influence on the overall performance of a proton exchange membrane fuel cell (PEMFC). A single-channel PEMFC with wedge-shaped fins in the cathode channel was proposed, and the effects of fin parameters such as volume (0.5 mm³, 1.0 mm³, and 1.5 mm³), number (3, 5, and 9), and porosity of the gas diffusion layer (GDL) (0.2, 0.4, 0.6, and 0.8) on the performance of PEMFC were numerically examined based on the growth rate of power density (GRPD) and polarization curve. It was shown that wedge-shaped fins could effectively improve the PEMFC performance. With an increase in fin volume, the distributions of oxygen mass fraction in the outlet area of the cathode channel were lower, the drainage effect of the PEMFC improved, and GRPD also increased accordingly. Similar results were obtained as the number of fins increased. The GDL porosity had a greater effect than the wedge-shaped fins on the improvement in PEMFC performance, but the influence of GDL porosity weakened and the GRPD of porosity decreased as the porosity increased. This study provides an effective guideline for the optimization of the cathode channel in a PEMFC.     

Experimental analysis of cathode flow stoichiometry on the electrical performance of a PEMFC stack

The paper describes an experimental analysis on the effect of cathode flow stoichiometry on the electrical performance of a PEMFC stack. The electrical power output of a PEMFC stack is influenced by several independent variables (factors). In order to analyse their reciprocal influence, an experimental design methodology was adopted in a previous experimental session, to determine which factors deserve particular attention. In this work, a further experimental analysis has been carried out on a very significant factor: cathode stoichiometry. Its effects on the electrical power of the PEMFC stack have been investigated. The tests were performed on a 3.5 kW_el ZSW stack using the GreenLight GEN VI FC Test Station. The stack characteristics have been obtained running a predefined loading pattern. Some parameters were kept constant during the tests: anode and cathode inlet temperature, anode and cathode inlet relative humidity, anode stoichiometry and inlet temperature of the cooling water. The experimental analysis has shown that an increase in air stoichiometry causes a significant positive effect (increment) on electric power, especially at high-current density, and up to the value of 2 stoichs. These results have been connected to the cathode water flooding, and a discussion was performed concerning the influence of air stoichiometry on electrode flooding at different levels of current density operation.     

Study of the impact of reactants utilization on the performance of PEMFC commercial stacks by impedance spectroscopy

Reactants utilization is a key stake for a PEMFC system: a too low utilization leads to a waste of reactant but a too high utilization may result in a detrimental starvation. To study these impacts, two commercial stacks were characterised by impedance spectroscopy under different hydrogen and oxygen utilizations (from nominal conditions to quasi-starvation). One was fresh while the other was operated on-field during 10,000 h. This study shows that the two capacitive loops in the lowest frequency range (1 Hz and below) correspond respectively to oxygen and hydrogen mass transfer limitations: the limiting reactant can be clearly identified from the impacted frequencies. The size of these loops was increased by up to 30% when the cell operated at high reactant utilizations. These results could therefore pave the way to the development of algorithms able to estimate the degree of starvation of some cells.