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Distributions in reactant species concentration in a PEMFC due to local consumption of fuel and local transport of water through the membrane cause distributions in current density, temperature, and water concentration in three dimensions in a PEMFC. These distributions can lead to flooding or drying of the membrane that may shorten the life of an MEA. Changing the cell's flow-field pattern to distribute the gas more evenly is one method of minimizing these stresses. This paper investigates how 200 cm 2 serpentine flow-fields with different number of gas paths, and thus different gas path...
To reduce diesel engine emissions, a split injection strategy with PHCCI combustion in a diesel engine was investigated with simulation. A multidimensional CFD application, Star-CD coupled with a modified 2-D flamelet was used to simulate multiple injection combustion. Several mass ratios of the first injection and second injection conditions compared to the conventional pilot and main injection strategy were evaluated. The injection angle and the injection timing of the first injection were fixed to 150° and 55° BTDC, respectively. Because of the early injection, the in-cylinder pressure and...
Computational fluid dynamics (CFD) simulations were performed for four 10cm2 serpentine flow-fields with single channel, double channel, cyclic-single channel, and symmetric-single channel patterns to investigate the effect of flow-field design. High and low inlet humidity operating conditions were studied by calculating the distributions of overpotentials, current density distribution, and membrane water content at different cell voltages. At high inlet humidity, the double channel flow-field was predicted to have better polarization performance and uniform current density distribution,...
Many mechanisms of colloid retention in porous media under unfavorable conditions have been identified from experiments or theory, such as attachment at surface heterogeneities, wedging at grain to grain contacts, retention via secondary energy minimum association in zones of low flow drag, and straining in pore throats too small to pass.However, no previously published model is capable of representing all of these mechanisms of colloid retention. In this work, we demonstrate that incorporation of surface heterogeneity into our hemispheres-in-cell model yields all experimentally observed non-...
Viscous flow around the self-propelled hull is investigated at model scale with RANSE (Reynolds Averaged Navier stokes Equations) solver using realizable k-e turbulence model by coupling the flow around the model hull with the flow generated by the rotating propeller in time domain. The challenges involved in coupling of flow past ship hull with the propeller flow, have been brought out and addressed. The technique used is based on a sliding model method where the numerical tank is divided into two regions which are modeled separately.They are the propeller domain and the tank domain...
New measurements have been done in order to obtain information concerning the effect of EGR and a paraffinic hydrotreated fuel for the smoke and NOx emissions of a heavy-duty diesel engine. Measured smoke number and NOx emissions are explained using detailed chemical kinetic calculations and CFD simulations. The local conditions in the research engine are analyzed by creating equivalence ratio -temperature (Phi-T) maps and analyzing the CFD results within these maps. The study uses different amount of EGR and two different diesel fuels; standard EN590 diesel fuel anda paraffinic hydrotreated...
Much research has been devoted to reducing NOx and soot emissions simultaneously in diesel engines. The low temperature combustion (LTC) concept has the potential to reduce these emissions at the same time, but it has limitations to its commercialization. In-cylinder EGR stratification is another combustion concept meant to reduce both types of emissions simultaneously using non-uniform in-cylinder EGR gas distribution. The EGR stratification concept uses a locally high EGR region of the in-cylinder so that the emissions can be reduced without increasing the overall EGR rate. In this study,...
Particle image velocimetry was used in a low-speed wind tunnel to investigate the vortex structures of a slender reverse delta wing at various angles of attack and roll. This work investigates the characteristics of the vortices generated downstream in planes perpendicular to the freestream direction and their dependence on angles of attack and roll at a chord-based Reynolds number of Rec 3:82 105. The peak tangential velocities at>5 show a trend similar to a delta wing. A six-component balance was used to obtain the aerodynamic coefficients for a reverse delta wing as well as a delta wing...

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