bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Channel-to-Manifold Water Transport in Proton Exchange Membrane Fuel Cells
Authors: Liu X. , Lin J. , McConnaghy K. M. , Trabold T. A. , Gagliardo J. J. , Owejan J. P.
Published: July 2013

Management of liquid water formed by the electrochemical reaction has received considerable attention and is considered a key factor in proton exchange membrane fuel cell (PEMFC) performance and durability. For practical stack applications, an aspect of the water management problem that is often overlooked is the transport of liquid water at the transition between the ends of the bipolar plate channels and the manifolds, where excess reactant flows from all the individual cells are combined and directed to the stack exhaust. In the bipolar plate exit region, gas-phase momentum can be very low, especially on the anode, and thus there is little driving force to remove liquid water. This study seeks to first quantify the characteristics of channel-to-manifold water transport by analysis of in-situ neutron radiography images, and correlation of the volumes of liquid water in the active and non-active regions to the relevant fuel cell operating conditions: temperature, pressure, relative humidity, current density and stoichiometric ratio. This analysis is complimented by new ex-situ experiments that directly control the flow of channel-level water and quantify the attendant increase in two-phase pressure drop in the non-active fuel cell region. The ex-situ apparatus has the additional feature of a simultaneous cross-flow channel at the exit plane of the bipolar plate, which enables simulation of two-phase flow dynamics of a fuel cell positioned anywhere in a stack, from zero cross-flow at the capped end of the stack to maximum cross-flow at the gas connected end of the stack.
Numerical Study on Electric Characteristics and Thermal Stresses of Solid Oxide Fuel Cells
Authors: Fan Pengfei , Zhang Xiongwen , Li Guojun
Published: July 2013

A generalized, three-dimensional (3D) mathematical model of solid oxide fuel cells (SOFCs) for various geometries is constructed in this paper. A finite-volume method is applied to calculate the electric characteristics, which is based on the fundamental conservation law of mass, energy and electrical charge. The electrical potential distribution, the current density distribution, the concentrations distribution of the chemical species and the temperature profile are calculated by solving the governing equations of a single-unit model with double channels of co-flow and counter-flow pattern using the commercial computational fluid dynamic software Fluent. The internal steam reforming and the water shift reactions are taken into account in the mathematical model. The Knudsen diffusion is considered for computation of the gases diffusion in the porous electrodes and the concentration overpotential. The Butler-Volmer equation and the function of the reaction gases composition for the exchange density are used in the model to analyze the activation overpotential. Numerical simulations are performed for a planar geometry solid oxide fuel cell and the detailed features of the temperature, the electrical potential distribution and the gases composition are illustrated. The simulation results agree well with the Benchmark results for planar configuration. With the simulated temperature profile in the planar SOFC, the finite-element method is employed to calculate the thermal stress distribution in the planar solid oxide fuel cell. A 3D finite-element model consists of positive electrode-electrolyte-negative electrode (PEN) and interconnects assembly is constructed by using commercial finite-element code Abaqus. The effects of temperature profile, electrodes and electrolyte thickness, and coefficients of thermal expansion (CTE) mismatch between components are characterized. The calculated results indicate that the maximum stress appears on the electrode and electrolyte interface. The value and distribution of the thermal stress are the functions of the applied materials CTE, applied temperature profiles and the thicknesses of electrode and electrolyte. The calculated results can be applied as the guide for the SOFC materials selection and the SOFC structure design.
The Design and Development of an Evaluation System for Redox Characteristics of Anode Supported SOFCs Using In-Situ Acoustic Emission and Electrochemical Technique
Authors: Hashimoto S. , Watanabe H. , Sakamoto T. , Kawada T. , Yashiro K. , Mizusaki J. , Kumada K. , Changsheng D. , Sato K. , Hashida T.
Published: July 2013

In this study, a redox evaluation system for anode supported SOFCs using in-situ acoustic emission (AE) and electrochemical technique has been developed. The system consists of a gas blending unit, moisture controlling unit, AE cell evaluation probe, gas cooling exhaust, electrochemical cell test system and AE signal measurement system. The anode supported coin cells, which have the same thickness dimension as practical SOFCs have, can be evaluated under temperature and atmosphere controlled conditions. The oxygen partial pressure in the anodic atmospheres can be gradually controlled from air to reducing atmosphere using the gas blending unit which is connected to 6 gas cylinders. Humidity in the anodic atmospheres can be controlled by moisture controlling unit which consists of 2 bubblers form 0.86% (5°C saturation) up to 80% (94°C saturation). Redox process of the anode can be simulated in this system by controlled three oxidation modes, i.e. O2 gas oxidation, steam oxidation and electrochemical oxidation, which correspond to actual troubles, i.e. gas leakage, degradation of downstream and fuel depletion, respectively. An AE transducer can monitor the cell condition via an inner tube for a guide of exhaust from the cathode.

Redox cell test for the anode supported coin cell has been examined at 770°C using this system. After the reduction of the anode substrate in moist H2, current 0.5Acm−2 loaded to the cell. And then H2 gas concentration had been reduced by stages. The cell voltage was down to below −6V after H2 gas concentration was reduced to pH2 = 2%. This drastic cell voltage drop and AE signal generation occurred at the same time. It is considered that Ni re-oxidation with fracture started at this time. Local delamination between anode and electrolyte, and also cracks at the electrolyte and cathode were observed after redox test. It was confirmed that AE sensing is effective for redox evaluation.
A Fuel Cell Stack Architecture to Make all Cells Have Equal Operational Conditions and Performance
Authors: Liu Hong , Li Peiwen , Hartz Alexandra
Published: July 2013

This paper presents a novel architecture for a proton-exchange membrane (PEM) fuel cell stack, which is based on the concept that every cell in the stack works at the same condition and thus each cell has the same contribution to the overall output voltage and power. To meet this proposed requirement, special flow distributors were used to evenly distribute fuel and airflow to every fuel cell in the stack. Details of the flow distributor and experimental tests of a four-cell fuel cell stack are presented in the paper. The experimental results demonstrated the desired high performance of the fuel cell stack. It is proved that the novel architecture for fuel cell stack is successful and of significance to the development of high performance fuel cell stacks.
Characterization of the Fracture Energy of a PFCB/PVDF Polymer Electrolyte Fuel Cell Membrane Using a Knife Slit Test
Authors: Gordon Ashley R. , Ellis Michael W. , Dillard David A. , Case Scott W. , Moore Robert B. , Li Yongqiang , Lai Yeh-Hung , Gittleman Craig S.
Published: July 2013

Polymer electrolyte membranes (PEM) undergo hygrothermal stress cycling in an operating fuel cell which may lead to pinhole or crack formation and propagation resulting in membrane failure. The fracture energy of a material, measured by fracture tests, is the energy needed for a crack to propagate throughout the material. In this study, the fracture energy of a promising novel fuel cell membrane comprised of a blend of a sulfonated perfluorocyclobutane (PFCB) block copolymer and polyvinylidene fluoride (PVDF) is investigated in various environmental conditions using a knife slit test. Fracture energies determined using the knife slit test have been shown to be several orders of magnitude lower, and therefore closer to the intrinsic fracture energy of a material, than those found by other fracture tests of related membranes. It is believed that the intrinsic fracture energy can give insight into the fracture resistance and durability of the polymer blend membrane. A polymer blend of 70% PFCB and 30% PVDF was tested at dry and nominally 10% relative humidity conditions at 40, 70, and 90°C, as well as at 70°C and nominally 50% relative humidity, to assess the effect of environmental conditions on fracture energy. Results show that the PFCB/PVDF blend had comparable fracture energy to a baseline fuel cell material, Nafion® NRE 211. In addition, the fracture energy of the blend was found to lie between that of the PFCB and PVDF components.
High Temperature Oxidation Behaviour of MnCo2O4 Coating on Crofer 22 APU Manufactured by a Novel Solution Precursor Plasma Spray Process (SPPS)
Authors: Puranen Jouni , Laakso Jarmo , Hyvärinen Leo , Kylmälahti Mikko , Vuoristo Petri
Published: July 2013

MnCo2O4 spinel coatings are designed to be used on metallic interconnectors in SOFC devises to decrease oxidation rate of the metallic interconnect and to prevent the evaporation of harmful CrO3 and Cr2(OH)2 compounds. These Cr-compounds degrade the long-term performance of the SOFC by migrating to the triple phase barrier (TPB) of the cathode and reduce back to Cr2O3. MnCo2O4 spinel coatings, used in this study, were manufactured by using a novel solution precursor plasma spray (SPPS) process and heat treated in oxidizing environment.

Deionized water based solutions of Mn(NO3)2•4H2O and Co(NO3)2•6H2O were used as a feedstock material. Concentration of the metal cations in the solutions was adjusted to 3 M. Ferritic stainless grade Crofer 22 APU with the thickness of 0.5 mm and surface roughness of Ra < 0.5 μm was used as a substrate material. The coatings were manufactured using a Sulzer Metco A3000S plasma spray system with F4-MB plasma gun with modified solution feeding hardware. Coatings with different microstructures were sprayed using different spraying parameters, e.g. the type of plasma gases used. The as-sprayed coatings were aged at 700 °C for 500 h in oxidizing environment, in order to study the stability of the coating, the growth of the Cr-scale and the Cr-transport through the spinel coatings. The microstructural characterization for the as-sprayed and the oxidized coatings were done using a field-emission scanning electron microscopy (FESEM) with SE-mode. The quantitative analyses were executed with energy dispersive spectroscopy (EDS), and in addition X-ray diffraction (XRD) was used for qualitative studies.

The coatings with various microstructures were sprayed. The densest microstructure was sprayed using Ar-He plasma gas. Also the crystallographic equivalence for MnCo2O4 was achieved when Ar-He plasma was used with 40 mm spraying distance. Ageing caused the increase in structural porosity. On the interface between the coating and the interconnect, a dense spinel layer was formed which effectively prevented the Cr-transport forming approximately 500 nm thick Cr-rich sub-scale.
Pore Space Characterization of Compressed PEMFC GDLs Using 3D Micro-Computed Tomography
Authors: Challa Pradyumna R. , Bazylak A.
Published: July 2013

In this work, micro-computed tomography was employed to characterize the effect of rib and channel compression on the through-plane porosity distributions of polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). Two GDLs with micro-porous layers (MPLs): a paper based GDL (GDL A), and a felt GDL (GDL B) were compressed at 1.2 MPa in an ex situ flow field apparatus with 1mm × 1mm channels. Porosity distributions of compressed GDLs were compared with those of uncompressed GDLs, and the microstructural differences caused during the manufacturing of paper, felt, and cloth GDLs are discussed. The results of this study will aid modellers in generating realistic stochastic GDL pore structures for multiphase flow simulations.
The Use of the Anode Water Removal Method to Understand Cathode Gas Diffusion Layer Flooding
Authors: Anderson Ryan , Blanco Mauricio , Wilkinson David P. , Bi Xiaotao
Published: July 2013

Anode water removal (AWR) is studied as a diagnostic tool in proton exchange membrane (PEM) fuel cell flooding. In this method, the stoichiometry of a dry hydrogen stream (no humidification) is increased stepwise at constant current, which establishes a water concentration gradient between the cathode and anode. As the anode stoichiometry is increased (in the range of 1.5–15), the anode removes more water, and the corresponding gain in voltage is measured along with the anode and cathode pressure drops. This method can be used to determine what the maximum voltage of a fuel cell is in the absence of cathode GDL and catalyst layer mass transport limitations due to liquid water. This study focused on GDLs with differing wetting properties, the inclusion/exclusion of a microporous layer (MPL), and thickness. GDLs without an MPL are more prone to flooding and show a large voltage gain (70 mV) through AWR. The effect of current density and cathode stoichiometry are also studied. Lower current densities do not produce as much water electrochemically and thus do not saturate the cathode GDL as much, leading to less gain in voltage during the AWR process. The AWR voltage gain diminishes with increasing cathode stoichiometry (1.5, 2, 4), since more water can be removed convectively from the cathode at higher air flows. Exacerbated cathode GDL flooding conditions are also studied to determine the extent to which AWR can mitigate flooding. This was accomplished via multiple GDLs on the cathode side and external water injection into the cathode flow field. In each case, the GDL saturation increases, which lowers the initial voltage. The AWR process is able to substantially increase the voltage in both cases. Thus, AWR is a useful and efficient method to observe how different fuel cell components, particularly various GDL structures, influence the cell performance due to water related mass transport losses.
Performance Investigation of YSZ-SDC Solid Oxide Fuel Cells
Authors: Wang Kang , Zeng Pingying , Ahn Jeongmin
Published: July 2013

This work presents the performance of YSZ-SDC multilayered anode-supported solid oxide fuel cell (AS-SOFC). The anode-supported SOFC showed an extraordinary fuel cell performance of ∼1.57 W/cm2 by wet spraying a SDC layer onto YSZ layer. It was found that the fuel cell performance varied with the sintering temperature of fuel cell. At the high sintering temperatures, the reactions between YSZ and SDC have a significant effect on the fuel cell performance.
Exergy and Economic Analysis of Catalytic Coal Gasifiers Coupled With Solid Oxide Fuel Cells
Authors: Siefert Nicholas , Litster Shawn
Published: July 2013

The National Energy Technology Laboratory (NETL) as well as Li et al. [1] have shown that integrating a catalytic coal gasifier with a solid oxide fuel cell (SOFC) can achieve high system efficiencies (∼60%) while capturing and sequestering >90% of the carbon dioxide. Integration of a catalytic gasifier with a SOFC is aided by the minimal exergy destruction inside a catalytic, steam-coal gasifier producing a high-methane content syngas, and the decreased exergy destruction in the SOFC due to the ability to operate at lower air stoichiometric flow ratios compared with a SOFC operating only on hydrogen. For a given temperature difference across the inlet and outlet of the fuel cell and for a given current density, a SOFC can be operated at a lower air stoichiometric ratio if there is a significant amount of methane in syngas and if the pressure of the fuel cell is above atmospheric pressure. Here, we present both an exergy analysis of one possible way of integrating a SOFC with a catalytic gasifier. The gasifier is a fluidized bed gasifier that uses ∼20%wt potassium carbonate along with the coal. Before entering the SOFC, carbon dioxide in the syngas is captured using lime, and then the anode tail gas from the SOFC is recycled back to the gasifier, similar to the configuration modeled by Li et al. [2]. We will present the exergy efficiency as a function of the pressure of the SOFC, and compare the exergy efficiency to other coal-based powerplants on the scale of 100–500 MWe.

In addition, we use capital and other cost estimates from NETL [3] and others [4] to estimate the internal rate of return on investment (IRR) of various coal based fuel cell power plants, and compare the IRR of these plants with other fossil fuel based base load power plants. We also present the IRR of the catalytic gasification-SOFC power plant as a function of the pressure of the SOFC. Assuming recent fuel & electricity prices, a natural gas combined cycle (NGCC) power plant yields the highest value of rate of return on investment. However, our results suggest that, in the case of a CO2 tax near $30/t CO2, then three different configurations are equally viable economically: NGCC, advanced IGCC-CCS-EOR, and advanced IGFC-CCS-EOR that integrates a catalytic coal gasifier with a pressurized SOFC.
Effects of Surface Coating of Nanoparticles on Thermal Performance of Open Loop Pulsating Heat Pipes
Authors: Taslimifar Mehdi , Mohammadi Maziar , Adibnia Ali , Afshin Hossein , Saidi Mohammad Hassan , Shafii Mohammad Behshad , Kazemzadeh Hannani Siamak
Published: July 2013

Homogenous dispersing of nanoparticles in a base fluid is an excellent way to increase the thermal performance of heat transfer devices especially Heat Pipes (HPs). As a wickless, cheap and efficient heat pipe, Pulsating Heat Pipes (PHPs) are important candidates for thermal application considerations. In the present research an Open Loop Pulsating Heat Pipe (OLPHP) is fabricated and tested experimentally. The effects of working fluid namely, water, Silica Coated ferrofluid (SC ferrofluid), and ferrofluid without surface coating of nanoparticles (ferrofluid), charging ratio, heat input, and application of magnetic field on the overall thermal performance of the OLPHPs are investigated. Experimental results show that ferrofluid has better heat transport capability relative to SC ferrofluid. Furthermore, application of magnetic field improves the heat transfer performance of OLPHPs charged with both ferrofluids.
Numerical Investigation of Thermal Performance of a Tube Fitted With Regularly Spaced Twisted Tape Elements
Authors: Gunes Sibel , Erdemir Dogan , Ozceyhan Veysel , Altuntop Necdet
Published: July 2013

This work presents a numerical investigation on thermal performance of a tube fitted with regularly spaced twisted tape elements in turbulent flow regime. Two different twisted tape widths of 46 mm and 44 mm which are lower than the tube inside diameter of 50 mm are used, in order to reduce excessive pressure drops associated with full width twisted tape elements. The numerical analyses were performed with various free space ratios (S = 0.0, 1.0, and 2.0) at a constant twist ratio (TR) of 5. Uniform heat flux was applied to the external surface of the tube and Reynolds numbers varied from 5918 to 46875 in the numerical calculations. The numerical results obtained from a plain tube were compared with those from the studies in literature for validation of numerical technique. The use of twisted tape elements leads to a considerable increase in heat transfer and pressure drop over the plain tube. Consequently, the numerical results reveal that the best operating regime of all twisted tape elements was found at low Reynolds number, leading to more compact heat exchanger.
A Technoeconomic Analysis of the Potential for Portable Pyrolysis in Northern New Mexico Forests
Authors: Brown Alexander L. , Brady Patrick D.
Published: July 2013

Biomass pyrolysis systems can be designed to yield significant quantities of liquid. The liquids have approximately half the heating value of transportation fuels, depending strongly on the water content in the liquids. They are acidic, and tend to change with time, becoming more viscous and higher in molecular weight. However the process required to generate them is simple, and they hold promise to be a renewable source of liquid fuel if they can be produced in a way that is cost-effective. Northern New Mexico forests are mostly characterized by small diameter (less than or equal to 10 cm) conifer trees. For mitigation of fire risk, land owners are required to periodically thin their lands. This generates significant waste product with little or no commercial value. The most widely used current practice is to accumulate and burn the cut wood, or to leave it to rot. Seeking a more effective and ecologically friendly use of the waste, a scaled experimental pyrolysis system was developed using design principles focused on the portable model. The data from this test unit and historical data are used to evaluate the break-even costs of performing pyrolysis. The char co-product is found to have a slight beneficial effect on the economics of the analysis. Labor is a significant fraction of the cost. Economies of scale are important, so the largest system that can be transported will make the most economic sense. On a price per unit energy, this model may be competitive with liquid transportation fuels and fuel oil. However pyrolysis oils will have difficulty competing with natural gas at current regional prices. Other regions may show a more positive comparison, especially in parts of the world where labor is much less expensive.
Compact Cooling Devices Based on Giant Electrocaloric Effect Dielectrics
Authors: Gu Haiming , Li Xinyu , Lu S. G. , Lin Minren , Qian Xiaoshi , Cheng J. P. , Zhang Q. M. , Cheng Ailan , Craven Brent
Published: July 2013

The electrocaloric effect (ECE) refers to the change in temperature and/or entropy of a dielectric material due to the electric field induced change of dipolar states. Giant ECE is discovered in P(VDF-TrFE) ferroelectric copolymers near ferroelectric-paraelectric (F-P) transition temperature which is normally much higher than room temperature. This paper presents the two defect-inducing methods to lower and broaden working temperature range of P(VDF-TrFE) based copolymers for ECE, and thus make it preferable for practical cooling device. Giant ECE is experimentally demonstrated in large temperature range (0–55°C). In addition, an electrocaloric oscillatory refrigerator (ECOR) was proposed and simulated by finite volume method and its high performance was theoretically demonstrated. Temperature gradient larger than 30 °C can be maintained across the two sides of a 1 cm device. For ΔT = 20 °C cooling condition, a high cooling power (5.4 W/cm2) and significantly higher coefficient of performance (COP) can be achieved (50% of Carnot efficiency).
Enhanced Laminar Flow Convection Heat Transfer in Longitudinally Twisted Rectangular Ducts
Authors: Manglik Raj M. , Patel Prashant , Jog Milind A.
Published: July 2013

Low Reynolds number fully developed swirl flows through rectangular ducts that are helically twisted along their axis are considered. The twist ratio (180 degree twist pitch-to-hydraulic diameter) and flow cross-section aspect ratio (height-to-width) characterize the channel’s geometrical attributes. Based on computational modeling and simulation results, parametric influences of flow rate (10 ≤ Re ≤ 1000) and duct geometry on swirl-flow generation and the consequent heat transfer and friction losses are discussed. The helically twisted duct-surface curvature is found to induce lateral fluid circulation, which results in the formation of axially helical swirl in the core of the duct. With increasing severity of duct twist and flow Reynolds number, or decreasing cross-section aspect ratio, the swirl structure breaks up into multiple peripheral vortices but with increased magnitude of the primary core secondary-flow cell. Consequently, in fixed pressure-gradient driven flows, the heat transfer is enhanced significantly, which is evaluated relative to the friction loss penalty and the concomitant performance in straight ducts of the same cross section.
Normalization for Ultrafast Radiative Transfer Analysis With Collimated Irradiation
Authors: Hunter Brian , Guo Zhixiong
Published: July 2013

Normalization of the scattering phase function is applied to the transient discrete ordinates method for ultrafast radiative transfer analysis in a turbid medium subject to a normal collimated incidence. Previously, the authors have developed a normalization technique which accurately conserves both scattered energy and phase function asymmetry factor after directional discretization for the Henyey-Greenstein phase function approximation in steady-state diffuse radiative transfer analysis. When collimated irradiation is considered, additional normalization must be applied to ensure that the collimated phase function also satisfies both scattered energy and asymmetry factor conservation. The authors’ technique is applied to both the diffuse and collimated components of scattering using the general Legendre polynomial phase function approximation for accurate and efficient ultrafast radiative transfer analysis. The impact of phase function normalization on both predicted heat fluxes and overall energy deposition in a model tissue cylinder is investigated for various phase functions and optical properties. A comparison is shown between the discrete ordinates method and the finite volume method. It is discovered that a lack of conservation of asymmetry factor for the collimated component of scattering causes over-predictions in both energy deposition and heat flux for highly anisotropic media.
Thermal Storage Device for High-Power-Density Systems
Authors: Homitz Joseph , Tucker Brian P. , Messmer Janelle M.
Published: July 2013

High power levels and high power densities associated with directed energy weapon (DEW) systems, electronic warfare systems, and high thrust-to-weight propulsion systems require the development of effective and efficient thermal management solutions. Among many critical thermal management issues, high peak waste heat generation and limited cooling capacity onboard mobile weapon platforms necessitate the development of advanced thermal storage devices. In addition to storing large amounts of energy in a compact, lightweight package, the devices must be able to store energy rapidly at high power levels.

This paper presents the design of an advanced phase-change thermal storage device developed to meet the requirements of high-power-density systems. Results of experimental performance evaluations are also presented. Based on these evaluations, it is predicted that the device will be able to store an average heat load of up to 2.9 kW/kg over a 20-second period. This thermal storage device is applicable to many different thermal management architectures, is easily adapted to meet the requirements of a wide range of high-power systems, and has potential to significantly reduce thermal management size, weight, and power requirements.
Thermal Performance of Poly Alpha Olefin Nanofluid With Spherical and Non-Spherical Nanoparticles
Authors: Park Chan Hyun , Alvarado Jorge L.
Published: July 2013

In this study, several heat transfer fluids consisting of Poly-Alpha-Olefin (PAO) as base fluid and non-spherical alumina (Al2O3) nanoparticles such as nanorods and nanoplatelets have been used to formulate thermally enhanced nanofluids. Thermal properties such as thermal conductivity and viscosity have been measured, and the corresponding thermal conductivity enhancement has been calculated. The heat transfer coefficient under laminar flow under constant heat flux conditions has been measured experimentally. Results indicate that nanofluids containing spherical and non-spherical nanoparticles depict a Newtonian behavior at low concentrations. Nanofluids containing non-spherical alumina nanoparticles exhibit the greatest thermal conductivity enhancement when compared to pure PAO. Moreover, heat transfer enhancement was also observed when non-spherical nanoparticles were used. Likewise, the percentage enhancement in convective heat transfer coefficient was shown to increase non-linearly with axial distance (x/Di) in a circular heat transfer section. Nanofluids containing non-spherical nanoparticles exhibits a lower Re*Ra (Reynolds number*Rayleigh number) than pure PAO under laminar flow constant heat flux conditions indicating that nanoparticle morphology and composition are the two main factors responsible for convective heat transfer enhancement at low Reynolds number. Convection and axial conduction can explain the increase in Nusselt number when x/Di is greater than 400. The expected radial movement of nanoparticles within the fluid at relatively low Reynolds number could explain the enhanced convection when factoring in changes in viscosity and the effect of buoyancy.
A Transient Modified Fourier-Based Approach for Thermal Transport Modelling in Sub-Continuum Regime
Authors: Mishra Vivek , Nabovati Aydin , Sellan Daniel P. , Amon Cristina H.
Published: July 2013

The presence of sub-continuum effects in nano-scale systems, including size and boundary effects, causes the continuum-level relations (e.g., Fourier heat equation) to break down at such scales. The thermal sub-continuum effects are manifested as a temperature jump at the system boundaries and a reduced heat flux across the system. In this work, we reproduce transient and steady-state results of Gray lattice Boltzmann simulations by developing a one-dimensional, transient, modified Fourier-based approach. The proposed methodology introduces the following two modifications into the Fourier heat equation: (i) an increase in the sample length by a fixed length at the two ends, in order to capture the steady-state temperature jumps at the system boundaries, and (ii) a size-dependent effective thermal diffusivity, to recover the transient temperature profiles and heat flux values. The predicted temperature and heat flux values from the proposed modified Fourier approach are in good agreement with those predicted by the Gray lattice Boltzmann simulations.
Numerical Simulation of Convective Heat Transfer in Structured Packed Beds of Particles With Different Particle Contact Treatment Methods
Authors: Bu S. S. , Yang J. , Li S. Y. , Wang Q. W.
Published: July 2013

The treatment of sphere contact is a crucial issue on the numerical analysis of the flow and heat transfer in packed beds of particles. In this work, the effects of three different methods including introducing a gap, area contacting and cylindrically bridging on the flow and heat transfer performances of structured packed beds of particles are investigated with CFD methods. The simulation results have shown that the influence of different treatment methods on the contact point on flow and heat transfer gets greater as the porosity decreases and the Reynolds number increases. There are no large differences among these three methods on the pressure drop and heat transfer under laminar flow regime. Compared with the experimental results, cylindrically bridging method is proved to be reasonable to simplify the sphere–sphere contact points. Therefore, cylindrically bridging treatment method is encouraged to be used instead of point contact method between particles with CFD analysis in structured packed beds of particles.
A Conformal Decomposition Finite Element Method for Material Death
Authors: Noble David R.
Published: July 2013

A Conformal Decomposition Finite Element Method (CDFEM) is developed for modeling material death. Material death is used to model the continuous removal of material that exceeds a prescribed temperature. CDFEM allows for the moving front to move through the material without having to conform to the finite element geometry. The method is tested using 2-dimensional simulations of a 1-dimensional problem with an analytical solution. CDFEM is shown to be optimal for the chosen discretization with first order convergence in time and second order convergence in space. In comparison, a traditional element death algorithm does not converge at all on unstructured meshes. A correction is proposed for remedying this problem, resulting in first order convergence for traditional element death in space and time.
Numerical and Experimental Investigations of an Orifice Type Cryogenic Pulse Tube Refrigerator
Authors: Antao Dion Savio , Farouk Bakhtier
Published: July 2013

A helium filled orifice type pulse tube refrigerator (OPTR) was designed, built and operated to provide cryogenic cooling. The OTPR is a travelling wave thermoacoustic refrigerator that operates on a modified reverse Stirling cycle. The experimental studies are carried out at various values of the mean pressure of helium (0.35 MPa – 2.2 MPa), amplitudes of pressure oscillations, frequencies of operation and sizes of orifice opening. The experimental results are compared with the predictions from a detailed time-dependent numerical model. In the CFD model, the compressible forms of the continuity, momentum and energy equations are solved for both the refrigerant gas (helium) and the porous media regions (the regenerator and the three heat-exchangers) in the OPTR. An improved representation of heat transfer in the porous media is achieved by employing a thermal non-equilibrium model to couple the gas and solid (porous media) energy equations. The model predictions show better comparisons with the experimental results when the effects of wall thicknesses of the various components of the OPTR are included in the model.
Effects of Intake Air Humidity on the NOX Emissions and Performance of a Light-Duty Diesel Engine
Authors: Asad Usman , Kelly Christopher , Wang Meiping , Tjong Jimi
Published: July 2013

The effects of intake air humidity on the performance of a turbo-charged 4-cylinder diesel engine have been investigated. The relative humidity of the intake charge was varied from 31 to 80% at a fixed ambient air temperature of 26°C. The intake humidity was controlled to within ±1% of the desired value by using a steam generator-equipped intake-air conditioning system. The tests were conducted at 3 load points (4.1, 9.1 and 15 bar BMEP) at engine speeds of 1500, 2500 and 3500 RPM without exhaust gas recirculation. The results indicate that increasing the intake air moisture leads to a reduction of 3∼14% in the NOX emissions for the tested conditions. The smoke was found to increase with speed but no significant increase in the smoke values was observed with the increased humidity. The CO and HC emissions were found to be largely insensitive to the humidity levels and were otherwise extremely low. The emissions have been analyzed on both the volumetric (ppm) and brake-specific basis to provide an insight into the effect of humidity on the quantitative results.
Experimental Investigations on Combustion, Performance and Emission Characteristics of Neat Jatropha Biodiesel and its Methanol Blend in a Diesel Engine
Authors: Thangaraja J. , Anand K. , Mehta Pramod S.
Published: July 2013

While engines fueled with neat or blended biodiesel have favorable combustion-emission profile in terms of carbon monoxide, particulate matter and unburned hydrocarbons emissions, they are reported to have higher NOx emissions as compared to petro-diesel. On the other hand, use of alcohols especially methanol, though limited in diesel engines, is found to decrease engine exhaust emissions including smoke and NOx emissions. The present experimental investigation evaluates the use of biodiesel-methanol blend in mitigating higher NOx emissions in biodiesel fuelled engines along with its effect on other engine performance conditions. The experimental results obtained for a blend of 90% Jatropha methyl ester and 10% methanol (J90M10) and neat Jatropha methyl ester (J100) by varying engine output load at maximum torque speed of 1400 rpm are analyzed and discussed in this paper. The experimental results at full load operation for J90M10 blend compared with neat J100 indicate a reduction in exhaust nitric oxide and smoke concentrations by 28% and 50% respectively along with a reduction of 2% in peak pressure and 0.5% in brake thermal efficiency. Also, a marginal retard in injection timing and a higher ignition delay period is observed with Jatropha methyl ester -methanol blend operation.
Performance Measurement and Analysis of Vertical Shaft V-Twin Engines, and Comparison With Horizontal Engines of the Same Model Class
Authors: Lemieux Patrick , Moore C. Dennis , Nahab Andrew
Published: July 2013

Over the past two years, we have conducted two experimental test series aimed at examining typical performance of gasoline V-twin engines in the 25 hp class, and the suitability of assumed mechanical efficiency in correcting observed measurements. We used engines manufactured by Honda, Kawasaki, Kohler, and Subaru (Robin). The tests were conducted at the Engines Laboratory of the California Polytechnic State University, San Luis Obispo (Cal Poly). The Kohler engines are fuel injected while the others three are carbureted. We tested twenty-eight engines in total. The first series of tests included four horizontal shaft engines from each of the manufacturers (sixteen in total), and followed the general guidelines of SAE standard J1349-199506.

This paper reports primarily on the subsequent series of twelve engine tests, which included vertical shaft engines of an equivalent family (and displacement class), from three of the original manufacturers: Honda, Kawasaki and Kohler. All three engines have roughly the same engine speed range (2000–4000), and all three reportedly reach peak power at 3600rpm. This is typical of small engines, which may be used to drive small generators in addition to being installed on other equipment.

Vertical shaft engines are typically tested on a vertical shaft dynamometer, or one that converts from a horizontal to vertical position. However, these dynamometers are typically either of the water brake or eddy current type. They cannot motor the engine, and thus cannot measure friction mean effective pressure (FMEP) directly, which is the preferred method to quantify friction and mechanical efficiency for engine testing. However, testing vertical shaft engines on a horizontal shaft motoring dynamometer requires an angled gear drive to mate the engine to the dynamometer, and thus adds a loss that complicates the accurate measurement of FMEP and brake output. We present here results using a simple method with which our measurements can be corrected for this loss, in tests of this sort.

The study thus expands on our previous results, and shows the extent by which engine to engine variations are affected by shaft configurations, within a given model family, and within similar offerings by different manufacturers. We also analyzed our results to contrast the methodology of SAE J1349-199506 with that of the updated J1349-201109, specifically with respect to using an assumed value of mechanical efficiency to characterize FMEP and correct dynamometer data on small, general utility engines.
Technology and Contribution of SUMEBore Cylinder Liner Surface Coatings on Lubricant Oil Consumption Reduction on an EMD710 Diesel Engine
Authors: Ernst Peter , Garcia Villarreal Jaime de Jesus , Froelund Kent
Published: July 2013

Rising fuel prices and more stringent requirements in the field of emissions such as nitrogen oxides, particulate matter and carbon dioxide are increasing the pressure on the engine manufacturers to utilize technologies that contribute to a reduction in these emissions. As a result, interest in cylinder surface coatings has risen considerably in the last three to four years, and particularly in the SUMEBore® coating solution from Sulzer Metco. Such coatings are applied by a powder-based atmospheric plasma spray process (APS). The APS method is very flexible and can also process materials to which wire-based methods do not have access, particularly high chromium containing steels, metal matrix composites (MMCs) and pure ceramics. The compositions can be tailored to the specific challenges in an engine, e.g. excessive abrasive wear, scuffing or corrosion caused by adulterated fuels and/or high exhaust gas recirculation rates (EGR). Over the past four to five years cylinder liner surfaces from trucks, diesel locomotives, marine and gas engines, for power generation and gas compression have been coated with such materials. These engines have been tested successfully. Most of the tested engines achieved significant reductions of lubrication oil consumption (LOC), sometimes in excess of 75%, reduced fuel consumption, very low wear rates and corrosion resistance on the liner surfaces. As an example the paper will highlight the coating of cylinder surfaces in a 4,000 hp EMD 16-710G3 locomotive diesel engine. Details of the application of a corrosion resistant MMC will be shown, together with results obtained with the Da Vinci DALOC measurement technique in an engine test where the lubricant oil consumption was accurately quantified at 4 steady-state operating conditions typical of North American freight locomotive and which clearly showed the significant contribution of the liner ID coating to reduction of lubricant oil consumption (LOC).
Phenomenological Simulation of Non-Premixed Gas Jet Flames Including Soot Formation and Oxidation
Authors: Faghani Ehsan , Rogak Steven N.
Published: July 2013

A phenomenological model (called here “Slice Model”) has been developed to simulate non-premixed gas jet flames including soot formation in the domain. The Slice Model is based on the self-similarity solution of gas jets and forced to satisfy momentum, mass and energy balances in every cross section. The Slice Model can predict the velocity, mass fraction and temperature field of non-reacting and reacting jets over a wide range of changes in the jet parameters. A sub-model for soot formation based on Hiroyasu’ model is applied to predict soot formation in non-premixed flames. Cantera, an open-source chemical kinetics software, is integrated with the Slice Model to predict the temperature distribution (based on equilibrium composition) of reacting jets. The soot formation prediction of the Slice Model is compared with experimental data in the literature. For velocity, soot mass fraction and temperature, agreement with experiment is about as good as it is for the much more computationally intensive RANS CFD simulations. On this basis, the Slice Model is promising as the core of a non-premixed natural gas engine simulation package under development.
Statically Indeterminate Main Bearing Load Calculation in Frequency Domain for Usage in Early Concept Phase
Authors: Parikyan Tigran , Resch Thomas
Published: July 2013

The paper discusses the importance of a numerical method for fast and accurate prediction of main bearing loads of inner combustion engine and its place in the concept phase of engine development process.

An approach based on linear dynamic analysis of 3D engine model in frequency domain is presented. Implemented within a separate module of AVL software package EXCITE Designer, it delivers a combination of accuracy and performance suitable for this task.

An application example illustrates the method.
Experimental Exhaust Gas Recirculation (EGR) on EMD SD59MX 2.238 Megawatt Diesel-Electric Freight Locomotives
Authors: Iden Michael , Goetzke Michael , Bandyopadhyay Deep
Published: July 2013

In July 2008, Union Pacific Railroad (UP) and Electro-Motive Diesel, Inc. (EMD) began discussions to jointly investigate the potential for exhaust gas recirculation (EGR) on a small group of re-powered UP locomotives, to assess the potential for EGR as a technology to meet the oxides of nitrogen (NOx) requirement in US Environmental Protection Agency (EPA) Tier 4 locomotive emissions regulations on newly-manufactured future diesel locomotives effective January 1, 2015 [1].

After several years of research, engineering and experimental testing, EMD began delivering to UP in late-2011 nine SD59MX experimental locomotives equipped with prototype EGR technology as a first step to achieving Tier 4 NOx reductions, plus a tenth SD59MX unit equipped with both the EGR technology and an experimental whole-engine aftertreatment package to migrate toward Tier 4 particulate matter (PM) levels on future new Tier 4 locomotives. Compared to today’s Tier 2 emission limits, the EGR equipped SD59MX produces 42 percent less NOx, a significant step toward the development of new Tier 4 locomotives.
Modeling of Film Boiling and Film Vaporization on Engine Piston Tops
Authors: Lee Timothy H. , Kyritsis Dimitrios C. , Lee Chia-fon F.
Published: July 2013

Engine-out HC emissions resulting from liquid fuel, which escapes from the combustion process, provides the motivation to better understand the film vaporization in a combustion chamber. Previous work theorized that the removal of liquid fuel from the combustion cycle was a result of the increase in film vaporization time due to the Leidenfrost phenomenon. Currently, KIVA 3V predicts a continuous decrease in vaporization time for piston top films. The objective of this work is to improve the KIVA 3V film vaporization model through the inclusion of established boiling correlations, and thus, the Leidenfrost phenomenon.

Experimental results have been reviewed from which expressions encompassing high acceleration effects for the nucleate boiling regime and the film boiling regime were investigated, implemented, and validated. Validation was conducted using published experimental data sets for boiling heat flux. As a result of the implementation, a noticeable increase in heat flux occurred due to high accelerations for films in saturated film boiling in both nucleate and film boiling.

Computational simulations were conducted using a semi-infinite plate and a direct-injection spark-ignition engine. The semi-infinite plate provided a controlled environment which could separate the effects of pressure and acceleration on film boiling heat flux, film vaporization rates, and film vaporization times. The effect of decreased film vaporization rates, during the Leidenfrost phenomenon, was observed to decrease with increasing acceleration. Finally, the engine computations were used to provide the first film boiling and film vaporization rates for engine fuel films at temperatures above saturation temperature. As a result of this work, a film vaporization model capable of improved prediction of vaporization rates of piston top films in saturated boiling conditions has been created.
Estimation of the Occurrence of Micro-Explosion for the Diesel-Biofuel Multi-Components Droplets
Authors: Shen Cai , Lee Chia-fon F. , Cheng Way L.
Published: July 2013

A numerical study of micro-explosion in multi-component bio-fuel droplets is presented. The onset of micro-explosion is characterized by the normalized onset radius (NOR). Bubble expansion is described by a modified Rayleigh equation. The final breakup is modeled from a surface energy approach by determining the minimal surface energy (MSE). After the breakup, the Sauter mean radius (SMR) for initially small size droplets can be estimated from a look-up table generated from the current breakup model. There exists an optimal droplet size for the onset of micro-explosion. The MSE approach reaches the same conclusion as previous model determining atomization by aerodynamic disturbances. The SMR of secondary droplets can be estimated by the possible void fraction, ε, at breakup and the corresponding surface Weber number, Wes, at the minimal surface energy ratio (MSER). Biodiesel can enhance micro-explosion in the fuel blends of ethanol and diesel (which is represented by a single composition tetradecane). The simulation results show that the secondary atomization of bio-fuel and diesel blends can be achieved by micro-explosion under typical diesel engine operation conditions.