bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study and Optimisation of Channel Geometry and Gas Diffusion Layer of a PEM Fuel Cell
Authors: Obayopo Surajudeen O. , Bello-Ochende Tunde , Meyer Josua P.
Published: July 2013

Fuel cell technology offers a promising alternative to conventional fossil fuel energy sources. Proton exchange membrane fuel cells (PEMFC) in particular have become sustainable choice for the automotive industries because of its low pollution, low noise and quick start-up at low temperatures. Researches are on-going to improve its performance and reduce cost of this class of energy systems. In this work, a novel approach to optimise proton exchange membrane (PEM) fuel cell gas channels in the systems bipolar plates with the aim of globally optimising the overall system net power performance at minimised pressure drop and subsequently low pumping power requirement for the reactant species gas was carried out. In addition, the effect of various gas diffusion layer (GDL) properties on the fuel cell performance was examined. Simulations were done ranging from 0.6 to 1.6 mm for channel width, 0.5 to 3.0 mm for channel depth and 0.1 to 0.7 for the GDL porosity. A gradient based optimisation algorithm is implemented which effectively handles an objective function obtained from a computational fluid dynamics simulation to further enhance the obtained optimum values of the examined multiple parameters for the fuel cell system. The results indicate that effective match of reactant gas channel and GDL properties enhance the performance of the fuel cell system. The numerical results computed agree well with experimental data in the literature. Consequently, the results obtained provide useful information for improving the design of fuel cells.
Optimization of Purge Cycle for Dead-Ended Anode Fuel Cell Operation
Authors: Chen Jixin , Siegel Jason B. , Stefanopoulou Anna G.
Published: July 2013

This paper focuses on the optimization of the purge cycle for dead-ended anode (DEA) operation of a proton exchange membrane (PEM) fuel cell. Controling the purge interval at given operating conditions can optimize the fuel cell efficiency and hydrogen loss during the purge. For this optimization, a model capturing the liquid water and nitrogen accumulation in the anode and the purge flow behavior is presented. A target range of purge interval is then defined based on the minimal purge time that removes the plug of liquid and nitrogen in the channel end and the maximum purge interval beyond which hydrogen is wasted since hydrogen molar fraction all along the channel has been restored to one. If the purge is sufficiently long that all of the accumulated water and nitrogen are removed then the power output in the subsequent cycle (galvanostatic operation) would be highest, compared with incomplete purges which do not fully restore hydrogen concentration in the anode. Such purge schedule, however, is associated with certain amount of hydrogen loss. Therefore, there is a trade-off between hydrogen loss and power output, and a corresponding purge interval that produces the largest efficiency. The optimum purge intervals for different cycle durations are identified. The calculated DEA efficiencies are compared with flow-through (FT) operation. The analysis and model-based optimization methodology presented in this paper can be used for optimizing DEA operation of PEMFC with minimum experimentation and development time.
Solar-Powered Reformed Methanol Fuel Cell System
Authors: Hotz Nico
Published: July 2013

The present study investigates the feasibility, efficiency, and system design of a hybrid solar fuel cell system generating electric power for stationary applications such as residential buildings. The system is fed by methanol and combines methanol steam reforming and Proton Exchange Membrane (PEM) fuel cells with solar collectors to generate the required heat for the steam reforming.

The synergies of these technologies lead to a highly efficient system with significantly larger power densities compared to conventional systems and generate tremendous advantages in terms of installation and operation costs. The present investigation describes the entire proposed system and its components and presents first analytical, numerical, and experimental results of a larger project to prove the feasibility of such a system by analyzing first a bench test demonstrator generating around 10 W of electric power and finally a prototype for an entire single-family household. It is shown that the methanol-to-electricity efficiency of the entire system is above 50%.
Hierarchical Modeling and Closure Evaluation for Fin-and-Tube Heat Exchangers Using 3-D Numerical Simulation
Authors: Zhou Feng , Geb David , DeMoulin George , Catton Ivan
Published: July 2013

A plain fin-and-tube heat exchanger was modeled based on Volume Averaging Theory (VAT) and the closure for the model was evaluated using CFD. Modeling a fin-and-tube heat exchanger as porous media based on VAT, specific geometry can be accounted for in such a way that the details of the original structure can be replaced by their averaged counterparts and the VAT based governing equations can be efficiently solved for a wide range of parameters. To complete the VAT based model, proper closure is needed, which is related to a local friction factor and a heat transfer coefficient of a Representative Elementary Volume (REV). The terms in the closure expressions are complex and sometimes relating experimental data to the closure terms is difficult. In this work we use CFD to obtain detailed solutions of flow and heat transfer through an element of a fin-and-tube heat exchanger and use these results to evaluate the closure terms needed for a fast running VAT based code, which can then be used to solve the heat transfer characteristics of a higher level heat exchanger. The objective is to show how heat sinks can be modeled as a porous media based on Volume Averaging Theory and how CFD can be used in place of a detailed, often formidable, experimental effort to obtain closure for a VAT based model.
A Numerical Investigation of Constrained Melting of Nanostructure-Enhanced Phase Change Materials in a Rectangular Cavity Heated From Below
Authors: Fan Li-Wu , Zhang Liang , Yu Zi-Tao , Xu Xu , Hu Ya-Cai , Cen Ke-Fa
Published: July 2013

A numerical study of constrained melting of nanostructure-enhanced phase change materials (NEPCM) consisting of eicosane and various loadings of CNTs in a rectangular cavity heated from below was performed. Assuming that the NEPCM are single-phase PCMs with homogeneous thermophysical properties, the problem was solved using a finite volume method based on the enthalpy-porosity scheme for solid-liquid phase change. The effective thermophysical properties of NEPCM were predicted using the mixture models and empirical equation with respect to the loading of CNTs. Three nominal Grashof numbers corresponding to three sizes of the cavity were considered. Evolutions of the constrained melting processes were presented by means of snapshots of the temperature contour at representative time instants. The melting rates and local heat transfer along the heated bottom were compared quantitatively based on the variations of the instantaneous liquid fraction and average Nusselt number over the bottom during melting, respectively. It was shown that at a given size of the cavity, melting was expedited as more CNTs were introduced. The expediting of melting was mainly attributed to the enhanced thermal conductivity and lowering of latent heat of fusion of NEPCM. The inclusion of CNTs, however, increases considerably the viscosity of melted NEPCM, which in turn leads to less significant natural convection effect during melting. As a result, increase of loading of CNTs was shown to lead to two competing effects. The feasibility of NEPCM in melting is justified when the enhanced heat conduction overweighs the suppressed natural convection.
The Technical Derivation of Heat Transfer Performance of the Airside of a Novel Pin Design Heat Exchanger Using Computational Fluid Dynamics
Authors: Churitter Tosha
Published: July 2013

Pins are a common type of extended surface used in the field of heat transfer; their main application being in the electronics field. Historically, pins used in heat exchangers have diameters that are considered negligible in comparison to their lengths and are therefore termed as tubes.

In this report, the use of pins as an extended surface is investigated for the heat transfer on the airside (cold) of the Compact Advanced Pin Surface Heat Exchanger. The pins are circular in cross section and follow a staggered arrangement. The uniqueness of the pin design is such that they cannot be treated as tubes.

Key Pin Design features are as follows:

• Pins have a maximum Length: Diameter ratio of 3.

• Pin Spacing to Pin Diameter ratio is greater than in traditional arrangements.

• Pins function as a primary as well as secondary surface.

The heat transfer performance of extended surfaces possessing the above features has not been characterized, using commercially available Computational Fluid Dynamics (CFD) software, in any research specifically focused on applications for the aerospace industry.

Based on actual test results, this study specially develops a unique approach that can predict the outlet temperature of the heat exchanger to within 1% accuracy. This ‘developed’ approach is applied over cold-side mass flow rates ranging from 0.05 kg/s to 0.23 kg/s, while keeping the hot side mass flow rate constant at 0.05 kg/s. At worst, the simulation results lie within 5% accuracy and at best the simulation accuracy is 1%, a significant improvement on traditional derivations.

This article specifically discusses the methodology developed to analyse the heat transfer performance of the novel pin design using Fluent 6.2. It highlights the current limitations of existing equations as well as the theoretical knowledge gap that currently exists in the analysis of pins as extended heat transfer surfaces in heat exchangers.
Mathematical Modeling of Heat and Mass Transfer Processes During Pyrolysis and Combustion of a Single Biomass Particle
Authors: Haseli Y. , van Oijen J. A. , de Goey L. P. H.
Published: July 2013

A detailed mathematical model is developed for simulation of heat and mass transfer processes during the pyrolysis and combustion of a single biomass particle. The kinetic scheme of Shafizadeh and Chin is employed to describe the pyrolysis process. The light gases formed during the biomass pyrolysis is assumed to consist of methane, carbon dioxide, carbon monoxide, hydrogen and water vapor with given mass fractions relevant to those found in the experiments of high heating conditions. The combustion model takes into account the reactions of oxygen with methane, hydrogen, carbon monoxide, tar and char as well as gasification of char with water vapor and carbon dioxide. Appropriate correlations taken from past studies are used for computation of the rate of these reactions.

The model allows calculation of time and space evolution of various parameters including biomass and char densities, gaseous species and temperature. Different experimental data reported in the literature are employed to validate the pyrolysis and combustion models. The reasonable agreement obtained between the predictions and measured data reveals that the presented model is capable of successfully capturing various experiments of wood particle undergoing a pyrolysis or combustion process. In particular, the role of gas phase reactions within and adjacent to particle on the combustion process is examined. The results indicate that for the case of small particles in the order of millimeter size and less, one may neglect any effects of gas phase reactions. However, for larger particles, a combustion model may need to include hydrogen oxidation and even carbon monoxide combustion reactions.
Copper Oxide (CuO) Effect on Heat Transfer Performance in an Oscillating Heat Pipe
Authors: Ji Yulong , Xu Chen , Ma Hongbin
Published: July 2013

An experimental investigation of an oscillating heat pipe (OHP) with an inner surface coated with a copper oxide (CuO) layer was conducted. The OHP has six turns and three sections: evaporator, condenser and adiabatic section with the lengths of 40 mm, 64 mm and 51 mm, respectively. The cleaned copper tubing was chemically treated with a chemical solution and heated in a furnace. A layer of CuO was formed in the inner surface of the OHP. A working fluid (water in this study) at filling ratios ranging from 40% to 70% was studied. The experimental results show that the CuO layer can enhance the heat transfer performance of the OHP. The investigation results in a new way to enhance the heat transfer performance of an OHP.
Thermal Modeling for High Thermal Conductivity Thermal Ground Planes
Authors: Ababneh Mohammed T. , Chamarthy Pramod , Chauhan Shakti , Gerner Frank M. , de Bock Peter , Deng Tao
Published: July 2013

Thermal ground planes (TGPs) are flat, thin (external thickness of 2 mm) heat pipes which utilize two-phase cooling. The goal is to utilize TGPs as thermal spreaders in a variety of microelectronic cooling applications. TGPs are novel high-performance, integrated systems able to operate at a high power density with a reduced weight and temperature gradient. In addition to being able to dissipate large amounts of heat, they have very high effective axial thermal conductivities and (because of nano-porous wicks) can operate in high adverse gravitational fields.

A three-dimensional (3D) finite element model is used to predict the thermal performance of the TGP. The 3D thermal model predicts the temperature field in the TGP, the effective axial thermal conductivity, and the evaporation and the condensation rates. A key feature of this model is that it relies on empirical interfacial heat transfer coefficient data to very accurately model the interfacial energy balance at the vapor-liquid saturated wick interface. Wick samples for a TGP are tested in an experimental setup to measure the interfacial heat transfer coefficient. Then the experimental heat transfer coefficient data are used for the interfacial energy balance. Another key feature of this model is that it demonstrates that for the Jakob numbers of interest, the thermal and flow fields can be decoupled except at the vapor-liquid saturated wick interface. This model can be used to predict the performance of a TGP for different geometries and implementation structures. This paper will describe the model and how it incorporates empirical interfacial heat transfer coefficient data. It will then show theoretical predictions for the thermal performance of TGP’s, and compare with experimental results.
Effects of Heat Transfer on the Spreading and Freezing of Molten Droplets Impinging Onto Textured Surfaces: A Computational Study
Authors: Raessi Mehdi , Sendha Rajkamal
Published: July 2013

We present our recent study on spreading and solidification of micro-droplets of alumina impacting onto patterned surfaces textured by micron-size obstacles. We employed an in-house, three-dimensional computational tool that solves the flow and energy equations and takes into account the solidification. We investigated the spreading dynamics, heat transfer, and solidification of the droplets as a function of the height and spacing of the obstacles as well as the impact velocity. The results show that, independent of the obstacle height, the droplet assumes a disk-shape geometry when the obstacles are either packed tightly or are very distanced. The results at intermediate obstacle spacings exhibit the most significant deformations, where the droplet develops long fingers. A quantitative relationship shows the collapse of the final spread diameter of the droplet normalized by the obstacle spacing when plotted against the spacing for different impact velocity as well as the obstacle height.
Experimental Investigation of Magnetic Field Effect on the Magnetic Nanofluid Oscillating Heat Pipe
Authors: Zhao Nannan , Zhao Dianli , Ma Hongbin
Published: July 2013

The magnetic field effect on the oscillating motion and heat transfer in an oscillating heat pipe (OHP) containing magnetic nanofluid was investigated experimentally. The nanofluid consists of distilled water and Dysprosium (III) oxide nanoparticles with sizes less than 100 nm. A magnetic field was applied to the evaporating section of the OHP by using the permanent magnet. The heat pipes charged with magnetic nanofluids at mass ratios of 0.1%, 0.05%, and 0.01%, respectively, were tested. In addition, the effects of orientation and input power ranging from 50 W to 250 W on the heat transport capability of the heat pipe were investigated. The experimental results demonstrate that the magnetic field can affect the oscillating motions and enhance the heat transfer performance of the magnetic nanofluid OHP. The magnetic nanoparticles in a magnetic field can reduce the startup power of oscillating motion and enhance the heat transfer performance in a low input power.
Numerical Analysis of Arc Flash Phenomena in the Air Insulated Cable Box for an Electric Power Machinery
Authors: Lee Sungwon , Lee Joon-Yeob , Yang Jae-Cheol
Published: July 2013

A cable box is a metal enclosure that provides connections to the main electric power machineries such as switchgear or transformer. Cable terminals housed in cable boxes have a high fire risk because very few cable boxes can withstand the pressure generated by a low impedance arc. And the cable boxes usually suffer from significant damage causing breakage of bushings between the cable box and the electric equipment. In case of transformer, oil is then spilled from the damaged bushing and the released oil generates the fire ignition. In this study numerical prediction for the pressure rise and propagation during the arc inside the cable box has been performed considering the effects of the shock waves, the deformation of the tank and the fluid-structure interactions between the pressure wave and the cable box. Based on the Euler-Lagrange coupling method, flow field and structure analysis has been conducted to predict pressure rise value of the cable box and the stresses of the wall. Two arcing positions such as line to line and line to ground has been chosen in order to consider how the initial arc point affects the pressure wave propagation and the shapes of pressure wave pattern due to the interaction with near wall.
CFD Modeling of Skull Formation in a Blast Furnace Hearth
Authors: Fu Dong , Chen Yan , Zhou Chenn Q. , Zhao Yongfu , Lherbier Louis W. , Grindey John G.
Published: July 2013

The formation of the protective layer of solidified metal (skull) is critical to the blast furnace hearth operation. Enhancement of the formation of the skull layer could extend the hearth lining life and blast furnace campaign. In this paper, a CFD model that consists of solidification, flow, heat transfer has been utilized to simulate the skull formation phenomena in a blast furnace hearth. The heat transfer characteristics and temperature distribution of the skull and refractory brick has been investigated. The simulated results are comparable with operating experience of U. S. Steel blast furnaces. Parametric study includes lining property and structure, cooling water temperature and flow rate, hot metal (HM) temperature and the production rate, as well as cast practice.
Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers
Authors: Elapolu Phani Ganesh , Majumdar Pradip , Lottes Steven A. , Kostic Milivoje
Published: July 2013

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier.

The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.
Design and Optimization of Conductive Heat Trees at Micro and Nanoscales for Cooling Electronics
Authors: Daneshi Masoud , Shirani Ebrahim
Published: July 2013

In this research, we consider the generation of conductive heat trees at micro and nano scales for cooling electronics which are considered as heat-generating disc-shaped solids. Due to the development of nano technology and its role in the production of small scale electronics in recent decades, the necessity of designing cooling systems for them will be revealed more than any other time. Therefore, tree-shape conduction paths of highly conductive material including radial patterns, structures with one level of branching, tree-with-loop architectures, and combination of structures with branching and structures with loop are generated for cooling such electronic devices. Furthermore, Constructal method which is used to analytically generate heat trees for cooling a disk-shaped body is modified in the present work, that we call it modified analytical method. Moreover, every feature of the tree-shaped architectures is optimized numerically to make a comparison between numerical and analytical results and to generate novel architectures. When the smallest features of the internal structure are so small, the conventional description of conduction breaks down. Hence, the effective thermal conductivity exhibits the “size effect”, and is governed by the smallest structural dimension which is comparable with the mean free path of the energy carriers. Therefore, we consider a model which was proposed for small-scale bodies in order to evaluate conductivity of heat trees.
Heat Transfer Coefficient in Falling Film Evaporators With Different Tube Arrangements
Authors: Shen Shengqiang , Liang Gangtao , Guo Yali , Mu Xingsen , Liu Rui , Yang Yong
Published: July 2013

A set of experimental facilities were set up to measure overall heat transfer coefficient of horizontal-tube falling film evaporators with triangular, rotated square and square-pitch bundles. Effect of spray density, saturation temperature, total temperature difference and inlet steam velocity on the overall heat transfer coefficient K is studied respectively. The tubes are made of HAL77-2A aluminium brass with an outer diameter of 25.4 mm. Fluids inside and outside the tubes are steam and fresh water respectively. The results indicate that growth of spray density and saturation temperature helps to increase the K. The K could also be increased by reducing the total temperature difference. However, the impact of the inlet steam velocity on the K is less significant. The K in the evaporator with rotated square-pitch arrangement is supreme. Furthermore, space distribution of local overall heat transfer coefficient K̃ in the evaporators is also discussed. Based on this investigation, basic engineering design information will be provided to establish the governing parameters for horizontal-tube falling film evaporator in the field of seawater desalination.
Numerical Study of Piston Skirt-Liner Lubrication Considering the Effects of Deformation in Internal Combustion Engines
Authors: Ning Lipu , Meng Xianghui , Xie Youbai
Published: July 2013

This paper presents a comprehensive lubrication model for piston skirt-liner system of internal combustion engines. In the model it is included that the effects of the surface roughness, the piston skirt surface geometry, the piston pin offset, the crankshaft offset, and the lubricant viscosity on the piston secondary motion and lubrication performance. Especially, the effects of the thermal and the elastic deformation of the piston skirt and the cylinder liner, and the piston skirt deformations due to the combustion pressure and the piston axial inertia, are considered as the key task in this study. The results show that the combustion force, the working temperature and the piston axial inertia all play important roles in the piston-skirt lubrication. Also, considering the elastic deformation of the piston skirt and the cylinder liner is beneficial to the prediction of piston-skirt lubrication more accurately. The developed program in this study can provide a useful tool for the analysis of the piston-liner system lubrication problem.
The Influence of Thermal Barrier Coating Surface Roughness on Spark-Ignition Engine Performance and Emissions
Authors: Memme Silvio , Wallace James S.
Published: July 2013

The separate effects on heat transfer of 1) piston crown surface finish and 2) the use of a metal based thermal barrier coating (MTBC) on the piston crown of a spark ignition (SI) engine were quantified through experimental analysis in a single cylinder CFR engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal-based thermal barrier coating. Each coating was tested at multiple surface finishes. Tests showed that reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. For both coatings, this resulted in small improvements (∼3%) in power and fuel consumption, while also having a measurable effect on emissions. Oxides of nitrogen emissions increased while total hydrocarbon emissions generally decreased as a result of polishing. The polished coatings were also seen to increase in-cylinder peak pressures and burn rates.

Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the MTBC-coated piston produced slightly higher power output and peak pressures. Hydrocarbon emissions were also seen to be significantly higher for the MTBC-coated piston due to its porosity. The effectiveness of the coating was found to be highly dependent on surface finish.
Integrated Physical and Chemical Measurements of PM Emissions of Dispersing Plume Heavy-Duty Diesel Truck: Wind Tunnel Studies: Part I — Design and Commissioning
Authors: Littera D. , Velardi M. , Cozzolini A. , Yoder G. , Besch M. C. , Carder D. K. , Gautam M.
Published: July 2013

Over the past few decades there has been considerable progress made in understanding the processes leading to formation and evolution of particulate matter (PM) emissions from heavy duty diesel engines (HDDE). This progress has been primarily made under controlled laboratory conditions with the use of constant volume sampling (CVS) systems and to a limited extend through on-road chase studies. West Virginia University (WVU) is attempting to close the present knowledge gap by conducting detailed experiments in a custom designed and constructed environmental wind tunnel. The understanding and knowledge has recently been further extended to new emission reduction technologies, such as the diesel particulate filter (DPF) which has dramatically changed the size distribution and chemical composition of PM. Additionally, the selective catalytic reduction (SCR) technology has shown to further enhance the formation of nucleation mode particles as well as alter their morphology. Even with advances in technology there remains a considerable gap in the current level of understanding of PM formation and evolution, since the combustion generated PM from diesel engines is not discernible from the atmospheric background PM measured beyond 300m from highways. After being emitted from the vehicle exhaust system, the process of dilution in the atmosphere leads to a multitude of PM transformation phenomena, such as volatilization, coagulation, and condensation. The work presented herein has been divided into two parts which are published separately from each another.

The first part describes the design and commissioning process of the wind tunnel focusing on both, aerodynamic and structural constraints, which ultimately led to the definition of the main characteristics of the facility. The resulting design is a subsonic, non-recirculating, suction type tunnel, with a 16ft high and 16ft wide test section capable of housing a full-size heavy-duty tractor cab. A 2,200hp suction fan is employed to provide up to 80 mph wind speeds. The 115ft test cell length guarantees for a 2 second residence time for the exhaust plume evolution (at 35 mph) and complies with turbulence intensity (less than 1%) and quality flow requirement as identified for this type of application. In addition, the West Virginia University (WVU) wind tunnel has been equipped with a custom made sampling system able to move in all three dimensions in order to measure spatially resolved plume characteristics.

The second part will describe the actual test procedures and the experimental results and will be published in a separate paper.
Modeling of Ignition and Combustion for Glow Plug Assisted Direct Injection Natural Gas Engines
Authors: Cheng Stewart Xu , Wallace James S.
Published: July 2013

Direct injection natural gas (DING) engines offer the advantages of high thermal efficiency and high power output compared to spark ignition natural gas engines. Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist.

Simple experiments show that the thickness of the heat penetration layer of a glow plug is very small (≈10−5 m) within the time scale of the ignition preparation period (1–2 ms). Meanwhile, the theoretical analyses reveal that only a very thin layer of the surrounding gases (in micrometer scale) can be heated to high temperature to achieve spontaneous ignition. A discretized glow plug model and virtual gas sub-layer model have been developed for CFD modeling of glow plug ignition and combustion for DING diesel engines.

In this paper, CFD modeling results are presented. The results were obtained using a KIVA3 code modified to include the above mentioned new developed models. Natural gas ignition over a bare glow plug was simulated. The results were validated against experiments. Simulation of natural gas ignition over a shielded glow plug was also carried out and the results illustrate the necessity of using a shield.

This paper shows the success of the discretized glow plug model working together with the virtual gas sub-layer model for modeling glow plug assisted natural gas direct injection engines. The modeling can aid in the design of injection and ignition systems for glow plug assisted DING engines.
Microscale Study of Ash Accumulation Process in DPF Walls Using the Diesel Exhaust Filtration Analysis (DEFA) System
Authors: Viswanathan S. , Rakovec N. , Foster D. E.
Published: July 2013

The Diesel Exhaust Filtration Analysis (DEFA) system, developed at the University of Wisconsin – Madison Engine Research Center (ERC), was used to study diesel particulate filters at the micro scale level. Previous measurements using the system have shown that there is a considerable effect of ash accumulation on the filter permeability evolution. Also the pressure drop and loading history are dependent on the number of times a filter had been filled and regenerated. The current investigation of the ash accumulation process has been done to understand its impact on the filter wall permeability over multiple loadings. Three different PM loading conditions were tested over four consecutive loading/regeneration cycles. The pressure history and particle breakthrough for each subsequent loading and regeneration has been recorded. The measurements examine the ash penetration and accumulation for the different operating conditions and for the different number of loadings and regenerations. The results show that the PM deposition mechanism has a significant impact on the ash accumulation process especially within the filter walls. The ash deposition process appears to have a distinct wall loading stage followed by ash membrane formation.
An Enabling Study of Low Temperature Combustion With Ethanol in a Diesel Engine
Authors: Gao Tongyang , Divekar Prasad , Asad Usman , Han Xiaoye , Reader Graham T. , Wang Meiping , Zheng Ming , Tjong Jimi
Published: July 2013

Previous research indicates that the low temperature combustion (LTC) is capable of producing ultra-low nitrogen oxides (NOx) and soot emissions. The LTC in diesel engines can be enabled by the heavy use of exhaust gas recirculation (EGR) at moderate engine loads. However, when operating at higher engine loads, elevated demands of both intake boost and EGR levels to ensure ultra-low emissions make engine controllability a challenging task. In this work, a multi-fuel combustion strategy is implemented to improve the emission performance and engine controllability at higher engine loads. The port fueling of ethanol is ignited by the direct injection of diesel fuel. The ethanol impacts on the engine emissions, ignition delay, heat-release shaping and cylinder-charge cooling have been empirically analyzed with the sweeps of different ethanol-to-diesel ratios. Zero-dimensional phenomenological engine cycle simulations have been conducted to supplement the empirical work. The multi-fuel combustion of ethanol and diesel produces lower emissions of NOx and soot while maintaining the engine efficiency. The experimental set-up and study cases are described and the potential for the application of ethanol-to-diesel multi-fuel system at higher loads has been proposed and discussed.
Comparison of Piston Temperature Measurement Methods: Templugs Versus Wireless Telemetry With Thermocouples
Authors: Madison Daniel P. , Miers Scott A. , Barna Glen L. , Richerson Jay L.
Published: July 2013

The objective of this investigation was to compare the results of metallurgical temperature sensors and thermocouples when used to measure piston temperatures in a running engine. Type J thermocouples and a microwave wireless telemetry system were used to gather real time temperature data on the piston in the vicinity of each metallurgical sensor. Eight pairs of metallurgical temperature sensors were installed in the piston with a thermocouple junction in-between. The engine was ramped up to steady state quickly and then held for approximately four hours at 1800 RPM and 1980 N-m before being quickly ramped back down in accordance with the metallurgical sensors’ recommended test cycle. During the test, continuous temperature data at each of the sensor locations was monitored and recorded using the telemetry system. After the test was complete, the metallurgical temperature sensors were removed and independently analyzed. The results indicate that readings from the metallurgical temperature sensors were similar to those of the embedded thermocouples for locations without large thermal gradients. However, when thermal gradients were present, the metallurgical sensor’s reading was influenced measurably.
Accurate Gas Exchange and Combustion Analysis Directly at the Test Bed
Authors: Fairbrother Robert , Leifert Thomas , Gande Rudolf , Salentinig Georg
Published: July 2013

Accurate combustion analysis at the test bed is an important tool for the development engineer. It can help engine design, efficiency improvements or emissions reduction by providing instantaneous feedback on the combustion process. It can also provide detailed combustion information to help speed-up the engine calibration process. By implementing shared memory communication, multiple core capability and streamlined calculation techniques, the calculation time of AVL gas exchange and combustion analysis software GCA (Gas Exchange and Combustion Analysis) has been dramatically reduced without significantly decreasing calculation results accuracy. This allows AVL IndiCOM (in combination with AVL GCA) to perform accurate gas exchange and combustion analysis calculations directly and promptly at the test bed. This opens the door to a number of promising new applications by erasing the bridge between measurement data acquisition and post-processing analysis. Increase of measurement data consistency and the reduction of development time are two of the most important benefits of being able to perform “on-line” plausibility checks of measurement data. The strong links connecting AVL GCA calculation results to the measurement data and the redundancy between calculation and measurement for the assessment of some highly relevant engine parameters (e.g. IMEP, air mass flow) can greatly extend the “on-line” plausibility checks functions already available in AVL IndiCom or AVL test bed automation software PUMA. Some passenger car application examples, where valve train flexibility is used to enhance fuel economy or reduce exhaust emissions of internal combustion engines, show that the immediate availability at the test bed of gas exchange related parameters (e.g. internal EGR rate, scavenged mass, mass flows through the valves) supports an intuitive optimization of the valve train parameters.
Performance Analysis of Worn Misaligned 4-Lobe Multirecess Hybrid Journal Bearing System Compensated With Orifice Restrictor
Authors: Phalle Vikas M. , Sharma Satish C.
Published: July 2013

Owing to the fast technological developments, the operating conditions of the machines are becoming very stringent, exact and more demanding. Various journal bearing designs have been developed to prevent the undesired effect of bearing whirl. An example of a successful design is the four-lobe multirecess journal bearing. The bearing which having four curved segments that referred to as four lobes is the four-lobe multirecess journal bearing. Further, as the 4-lobe journal bearing is expected to run over a number of cycles during its lifetime, it is subjected to several start/stop operations. These transient periods causes the bearing bush to wear out between the recesses and significantly affects the bearing performance. The modified Reynolds equation governing the flow of lubricant in the clearance space of bearing have been solved including the combined effects of three aspects, the worn effect, the misalignment angle and offset factors, using an iterative scheme based on FEM and Newton-Raphson method. The simulated results have been presented for a wide range of offset factor δ, wear depth parameter, journal misalignment factors (φ, Ψ) and external load. The simulated results suggests that it is an imperative to account for the effect of wear along with misalignment of journal in order to predict the performance of the bearing accurately. Further, it has been observed that in general as the value of offset factor increases the static and dynamic performance of the 4-lobe four pocket worn misaligned hybrid journal bearing compensated with orifice restrictor is clearly affected as compared to similar four pocket unworn aligned hybrid circular journal bearing. Further the bearing having offset factor δ = 1.2 improves the stability due to increase in the bearing stiffness and reduced magnitude of the cross-stiffness components.
Influence of Surface Texture on Micro EHL in Boundary Regime Sliding
Authors: Erck Robert , Ajayi Oyelayo O. , Lorenzo-Martin Cinta , Fenske George R.
Published: July 2013

A hard steel ball was slid against textured coated and uncoated steel disks that had strongly directionally ground surfaces. The friction coefficient during ball-on-disk rotating low-speed lubricated sliding was continuously measured. The coefficient of friction rose from ≈ 0.12, which is typical for boundary lubrication regime, to as high as 0.45 whenever the ball was sliding parallel to the grinding ridges on the disc surface. The persistence of this “spike” in the friction was observed to be correlated with the hardness of the disc surface and the nature of the coating. We propose that the frictional spike is due to loss of micro-elastohydrodynamic lubrication, combined with side leakage, leading to intimate asperity-asperity contact. As a result, the coefficient of friction is close to that which is obtained there is no or minimal lubrication. This conclusion is supported by enhanced and persistent frictional spikes in tests conducted with discs coated with a very hard nitride thin film, and constant friction for a disk coated with hydrogenated amorphous carbon, which has low coefficient of friction when there is no/minimal lubrication.
Direct Observation of Surface Transition During Scuffing in Dry Condition
Authors: Yagi Kazuyuki , Ikeda Naoya , Sugimura Joichi , Kajita Seiji , Ohmori Toshihide , Shinyoshi Takatoshi , Suzuki Atsushi
Published: July 2013

This study investigates surface changes during scuffing in a dry condition. In the test a ball-on-disc apparatus was used, in which a rotating sapphire disc was loaded to a stationary steel ball. The contact area was directly observed and recorded by a digital camera attached to a microscope during the test. The variations in frictional force were synchronously measured with the capturing of images of the camera. After the test, the hardness of the scuffed steel ball were measured at different points in the contact area. The direct observation of the contact area shows that areas of macro plastic flow appeared from the trailing side of the contact area with a dramatic increase in frictional force. The macro plastic flow areas were changed, resulting in a dramatic expansion of the contact area. During the dramatic expansion, the friction coefficient kept a high constant value of about 0.4. The hardness distributions of the scuffed steel ball showed that the hardness was smaller at the tailing side of the contact area, in which macro plastic flows started, than that at the leading side. On the other hand the temperature rise calculated by a simple temperature estimation model was insufficient to cause the hardness reduction.
Lubrication Film Thickness Behavior Under Transient Speed and Load Conditions
Authors: Zimmerman Martin , Krupka Ivan , Hartl Martin , Houska Pavel
Published: July 2013

In engineering practice no machine parts are working under ideal steady-state conditions. The transient conditions involved in particular cases of real machine assemblies like cam follower contacts, ball bearings etc. represent a really complex sequence of movements. In these applications high sliding conditions are often replaced by zero entrainment speed connected with squeezing action and followed by opposite sliding. In general the variation in speed of contact surfaces strongly affects the film thickness and it can result in a lubricant film breakdown and in consequence also damage of contact surfaces. Experimental study will also consider the effect of surface topography and dynamic change of load.

A new concept of experimental apparatus was used for experimental study of cam and tappet contact under simplified operational conditions. To simplify the problem the concept of cam and tappet contact was replaced by EHD contact of the flat surface of chromium coated glass disk and a steel ball. Also only transient speed and load were taken into account. The method used to measure film thickness was thin film colorimetric interferometry. A high-speed digital camera was used in combination with a high power xenon lamp to capture rapid changes of film thickness in the contact area. Servomotors and piezo-actuator were used to control the speed of contact surfaces and also the load of the contact during the experiment.

The experimental results show that the change of speed has a great impact on film behavior during sequences where opposite sliding or zero entrainment speed is involved. It was found that shallow grooves can behave as a reservoir of lubricant which can supply the contact area and increase the film thickness during the above described transient phenomena.
Anisotropy: Benefits for UOE Line Pipe
Authors: Hilgert Oliver , Zimmermann Steffen , Kalwa Christoph
Published: July 2013

Plastic anisotropic material behavior of UOE line pipe is investigated in view of its structural response. Common load cases are considered and their resultant strain capacity concerning Strain Based Design demands are discussed. Hill’s yield function is used to analyze steel line pipe under internal pressure and bending moment. Here, a three-dimensional anisotropic plastic strain evolution is considered. It was shown, that underlying anisotropic material behavior can be beneficial for the structural response of line pipe, although it depends on the load case and the directional anisotropy. That is in some way contrary to the demands in specifications, where isotropic material behavior is desired.
Research on Fiber Perimeter Security Technique of Station
Authors: Song Ning , Zhou Yan , Tan Dongjie , Ma Yunbin , Qiu Honghui , Li Baisong
Published: July 2013

The oil or gas station is an important producing unit, building a perimeter security system is an available method for protecting the stations and improving the capacity of dealing with the emergency incident. However, building high walls or fence and patrolling the stations are the main protecting methods, it is difficult to detect invasion immediately. So, it is necessary to construct a stable and reliable perimeter security system to protect the station. Traditional fiber perimeter security technology protects the station by sensing fiber on the fence or wall, but the wind will produce many false alarms. In this paper, a multi-mode sensing cable buried in the ground, systems can not only effectively detect intrusions, but more importantly, avoid false alarms by wind disturbance. Intrusions will produce non-stationary random signals, through the signal processing and recognizing technique, we can identify the invasion and improve the accuracy and stability of the system.