Research On Performance Of Vehicular PEMFC And Its Hybrid Powertrain

In company with automobile tenure amount of substantial increase,energy consumption and environmental pollution problem increasingly extrude. In order to solve the problem, low pollute even pollution-free automobile is studied in many country of the world. Being high efficiency and low pollution, fuel cell both here and abroad is taken as new style power supply for vehicle. Among fuel cells, research is emphasized on PEMFC because of its high power ratio, low working temperature and excellent performance of emission and start-up.This article is incorporation with Ministry of Education academy doctor subject expert term scientific research fund "Fuel cell and accumulator hybrid powertrain automobile simulation analysis and control". Based on the research of former scholars, using the hypothesis of steady state, isothermal and incompressible laminar flow etc, through gridding the modeling region, confirming the solving condition, three-dimensional computational fluid dynamics model is set up in anode and cathode of PEMFC. Anode physical makeup includes hydrogen and vapor, oxygen, vapor and nitrigon in cathode. Simulation is done by using multiple physical coupling analytical software comsol multiphysics in anode and cathode. Analysis of impact of working parameters and structure parameters on reactant gas flow, mass fraction and current density distribution in anode and cathode, results indicate:1) In anode flow field, hydrogen flow velocity submits symmetrical distribution; In both flow field and diffusion layer, distribution of hydrogen is over ingress least,outflow point near catalyze layer department most; In the diffusion layer, current density submits symmetrical distribution. At outflow point of both sides, it reaches its maximum. Anodic performance is discussed through changing temperature and hydrogen pressure. Higher PEMFC temperature results in better anodic performance. The effect of hydrogen pressure on performance is more distinct. Meanwhile, variation amplitude of mass fraction of hydrogen and current density increases.2) Some impaction on anodic performance by different flow field width is certain. More narrow flow field makes distribution of physical quantities more uneven and working stability worse. Wider flow field makes output current density decreasing. Synthesis performance is optimal when the flow field half the width of diffusoin layer.3) Air flow velocity submits symmetrical distribution in cathodic flow field; Distribution of oxygen is most over ingress, lest at outflow near catalyst layer, vice verse the water; Current density distribution bounds up with oxygenous distribution. By advancing air pressure, it is good for water drain and preventing flooding, then for improving performance. But when pressure is enhanced to a certain level, the impact is unsharp. Temperature has an influence on reactant and current density distribution too. Lower temperature leads to a little performance amelioration, but the water distribution becomes worse. This may be to form flooding in cathode, hence be disbennifit to working stability. Decreasing of relative humidity can be benefit to water distribution and avoid flooding. While lower relative humidity results in droping sharply with cathodic performance, air in cathode must be hunidified in reason.4) Variation of cathodic flow field dimension also has an influence on simulation. When flow field becomes narrower, cathodic water distribution gets worse and output current decreases. When becomes wider, performance is improved. Deepening the flow field, reactant gas ingressing more enough, this can be benifit to draining of water, make the amplitude of oxygen and current density be small, cathodic performance get ameliorated. Both wider and deeper flow field can have disadvantage on reaction and mass transfer because of impaction of ridge between flow fields. So the dimension of flow field must be in reason. Structure of the cathodic flow field also has distinct impaction on simulation. When changing the straight flow field into serpentine flow field, amplitude of oxygen distribution increases, reaction becomes more sufficient, output performance is better than straight flow field. But meanwhile, distribution of water becomes worse. Through changing right-angle jointing into arc jointing between flow fields, both physical quantity distribution and output performance are improved.In order to validate the results of CFD model of straight flow field PEMFC, experiment system is set up around homemade 500W PEMFC stack. Experiments are done about PEMFC performance, dynamic response, heavy-load long-time working and start-up performance. It is proven that voltage distribution of unit cell is related with stack connection and output current. The relative error between experiment result and CFD model is within 10%, it indicates that the CFD model of PEMFC was credible. Moreover, efficiency of PEMFC is tested, factors about efficiency are analyzed. Based on characteristic of PEMFC efficiency, approaches of improving energy sources efficiency of vehicular PEMFC are discussed.And then, using some homemade economy car as original car, the car is modeled in software ADVISOR. Fuel economy and driving performance are analyzed. The model is validated by experimental data. Then, the power driving system is virtual refit by PEMFC hybrid powertrain. Configuration and parameters of hybrid powertrain are ascertained. Model of PEMFC hybrid powertrain is set up and performance is calculated. Fuel economy results are compared under different hybrid degree and different driving schedules. The optical scheme of different hybrid degrees is selected. Power-following is confirmed as control mode of PEMFC hybrid powertrain and control strategy is discussed. Aiming at the least fuel consumption, charged power of accumulator, the maximum and minimum working power and final driving ratio are optimized. The production of the research can provide reference in optimization of structural and working parameters of PEMFC and matching its hybrid powertrain.