bluuebunny/crossref_metadata_2025 huggingface dataset:
Visualization of a Single Boiling Bubble in a DC Electric Field
Authors: Chen Feng , Liu Dong , Song Yaozu
Published: July 2013

The application of electric field has been demonstrated as an effective way to enhance pool boiling heat transfer. In past studies, adiabatic experiments were often conducted to simulate the dynamics of nucleate bubbles in the presence of an electric field, where gas bubbles were injected from an orifice, to avoid complexities involved in the nucleate boiling experiments. While adiabatic studies yield useful information of the bubble dynamics, further studies about bubble dynamics during nucleate boiling heat transfer are still necessary for a full understanding of the effects of applied electric field on the liquid-vapor phase change heat transfer. In this paper, the dynamics of a single boiling bubble in a direct current (DC) electric field was studied experimentally employing R113 as the working fluid. The life cycle of the boiling bubble was visualized using high-speed photography and was compared with that of an injected nitrogen bubble. Under the same electric field, a more appreciable elongation along the field direction was observed for the boiling bubble. A modified relationship between the bubble deformation and the electrical Weber number was proposed for the boiling bubble. As the electric field strength increases, it was found that, although the growth time of the boiling bubble increases, the waiting period decreases. However, it was also found that, the change of the whole life cycle with electric field strength increasing is relevant to the wall temperature. In this work, the wall temperature measured in the vicinity of the nucleation site upon the bubble departure decreases when the electric field is applied.
Numerical Simulation of Multi Species Mass Transfer in a SOFC Electrodes Layer Using Lattice Boltzmann Method
Authors: Xu Han , Dang Zheng , Bai Bo-Feng
Published: July 2013

A two-dimensional multi-component Lattice Boltzmann (LB) model based on kinetic theory for gas mixtures combined with a representative elementary volume (REV) scale LB algorithm based on the Brinkman equation for flows in porous media is developed to simulate the mass transport in the porous anode and cathode of SOFC. The concentration overpotential is calculated and compared with that obtained by the extended Fick’s Model (FM), the Dusty Gas Model (DGM), and the Stefan Maxwell Model (SMM), as well as the experimental results. It is concluded that LB method is a much more accurate method for the simulation of mass transfer within fuel cell electrodes. Moreover, the effects of different electrode geometrical and operating parameters on concentration polarization are also investigated.
Thermal Management of an Air-Cooled PEM Fuel Cell: Cell Level Simulation
Authors: Andisheh Tadbir M. , Shahsavari S. , Bahrami M. , Kjeang E.
Published: July 2013

Air-cooled polymer electrolyte membrane (PEM) fuel cells have recently been the center of attention mainly because of the simplicity they bring into the fuel cell industry. Their main advantage is the elimination of balance-of-plant subsystems such as the liquid coolant loop, heat exchanger, compressor, and air humidifier which greatly reduces the complexity, parasitic power, and cost of the overall system. In air-cooled fuel cells, air is used as a combined oxidant and coolant. However, the net power output is limited by the heat rejection rate and the overall performance and durability are restricted by high temperature gradients during stack operation. An important initial step toward this goal is accurate knowledge of the temperature distribution in the stack in order to optimize heat removal by suitable thermal management strategies.

In the present study, a three dimensional numerical model is developed that can predict the temperature distribution in cell level with an acceptable accuracy. Using this methodology, the maximum temperature in the stack as well as temperature gradients, which are two essential operating parameters for air-cooled fuel cells, can be obtained. The model is validated using experimental data for the 1020ACS fuel cell stack from Ballard Power Systems. A parametric study is performed for bipolar plate thermal conductivity and overall thermal characteristics on the cell level to examine the effects of these parameters on the maximum stack temperature, temperature gradient in the cell, and overall heat rejection rate. Based on these results, recommendations are provided for improved thermal design of air-cooled fuel cells.
Dynamic Simulation of a High Temperature Polymer Electrolyte Membrane Fuel Cell: Stack Performance
Authors: Rabiu Ademola , Nomnqa Myalelo , Ikhuomoregbe Daniel
Published: July 2013

One of the attractions of high temperature polymer electrolyte membrane (PEM) fuel cell is the quality of the heat co-produced with power that could be recovered for use in a combined heat and power system. In this study, a one-dimensional model for a single PEM fuel cell was developed and implemented in Engineering Equations Solver (EES) environment to express the cell voltage as a function of current density among others. The single cell model was employed to investigate the energetic behaviour of a 1 kWe high temperature PEM fuel cell stack system, and the corresponding power and thermal efficiencies at different operating modes. A multiple parametric analyses using the built-in EES uncertainty propagation tool was used to determine the stack performance for the selected parameter range. The influence of the stack operating temperature, hydrogen utilization, the carbon monoxide content in the anode gas feed and the current density, on the efficiency of the fuel cell stack were studied at the required stack electrical output.

The study showed that an increase in temperature increased the stack electrical power output whilst the thermal output decreased. The stack electrical power output was seen to increase with increase in the current density and hydrogen stoichiometry. It can be seen that ratio between the electrical power and thermal output increased as the current density increases. This ratio becomes unity at an operating current density of 0.3 A/cm2, representing the optimal operating current density of the stack. An increase in the hydrogen utilization has positive effects on both the cogeneration and thermal efficiency.
Hydrogen Generation Optimization in a Hybrid Photovoltaic-Electrolyzer Using Intelligent Techniques
Authors: Maroufmashat Azadeh , Seyyedyn Farid , Roshandel Ramin , Boroushaki Mehrdad
Published: July 2013

Hydrogen is a flexible energy carrier and storage medium and can be generated by electrolysis of water. In this research, hydrogen generation is maximized by optimizing the optimal sizing and operating condition of an electrolyzer directly connected to a PV module. The method presented here is based on Particle swarm optimization algorithm (PSO). The hydrogen, in this study, was produced using a proton exchange membrane (PEM) electrolyzer. The required power was supplied by a photovoltaic module rated at 80 watt. In order to optimize Hydrogen generation, the cell number of the electrolyser and its activity must be 9 and 3, respectively. As a result, it is possible to closely match the electrolyzer polarization curve to the curve connecting PV system’s maximum power points at different irradiation levels.

PSO is a novel method in optimization inspiring from observation of bird flocking and fish schooling. Comparing to other optimization method, not only PSO is more efficient and require lower functions of evaluations, but it leads to better results, as well.
Condensation Pressure Drop and Heat Transfer in 5-mm-OD Micro-Fin Tubes
Authors: Li Wei , Huang Dan , Wu Zan , Li Hong-Xia , Zhang Zhao-Yan , Hong Rong-Hua , Guo Si-Pu , Li Jing
Published: July 2013

An experimental investigation was performed for convective condensation of R410A inside four micro-fin tubes with the same outside diameter (OD) 5 mm and helix angle 18°. Data are for mass fluxes ranging from about 180 to 650 kg/m2s. The nominal saturation temperature is 320 K, with inlet and outlet qualities of 0.8 and 0.1, respectively. The results suggest that Tube 4 has the best thermal performance for its largest condensation heat transfer coefficient and relatively low pressure drop penalty. Condensation heat transfer coefficient decreases at first and then increases or flattens out gradually as G decreases. This complex mass-flux effect may be explained by the complex interactions between micro-fins and fluid. The heat transfer enhancement mechanism is mainly due to the surface area increase over the plain tube at large mass fluxes, while liquid drainage and interfacial turbulence play important roles in heat transfer enhancement at low mass fluxes. In addition, the experimental data was analyzed using seven existing pressure-drop and four heat-transfer models to verify their respective accuracies.
Laminar Mixed Convection of Large-Prandtl-Number Nanofluids in Horizontal Tube: Experiment, Correlation, and Criterion
Authors: Li Wei , Guo Si-Pu , Feng Zhao-Zan , Zhang Zhao-Yan , Fang Ze-Cong
Published: July 2013

This paper describes an experimental investigation into combined forced and natural convection heat transfer for large-Prandtl-number nanofluids flow in a horizontal tube at low Reynolds number (9 < Re < 450). By the inclusion of nanoparticles, the contribution of natural convection to the overall convective heat transfer can be either deteriorated under the same heat flux or enhanced under a given Grashof number. The huge increasing of the viscosity and Prandtl number were turned out to be the major reason for the observed deterioration and enhancement, respectively. Moreover, the measured heat transfer behavior of nanofluids was illustrated to be in good agreement with the single-phase-based evaluation. However, the experimental data obtained could not be totally reconciled with existing correlations, which relate mainly to specific pure liquids or relatively higher Reynolds number. Therefore, new correlations have been derived by using single-phase fluid approach. These correlations fit our data to within ± 10 percent and also agree with the data in literature quite well. Such results verify that nanofluids can be treated as a homogeneous mixture with effective thermophysical properties. In addition, the new correlations grasp the essence of natural convection and can reduce to both normal forced convection and pure natural convection equations at limiting cases. Whether a flow can be treated as pure forced flow or not (i.e., natural convection effects cannot be neglected) is a crucial problem remains to be determined for the assessment of performance of nanofluids in low-Reynolds-number convection heat transfer application. Generally, the boundary curve function involves the variable parameter of forced main flow (Graetz number) and natural secondary flow (Rayleigh number), constituting a criterion suitable for defining transition of forced flow to mixed flow.
Experimental Investigation and Empirical Analysis of Non-Boiling Gas-Liquid Two Phase Heat Transfer in Vertical Downward Pipe Orientation
Authors: Bhagwat Swanand M. , Mollamahmutoglu Mehmet , Ghajar Afshin J.
Published: July 2013

The non-boiling gas-liquid two phase flow is pertinent to industrial applications like the reduction of paraffin wax depositions in petroleum transport lines, air lift systems and the chemical processes such as ethanol-water fractionation seeking enhanced heat and mass transfer. The non-boiling two phase heat transfer mechanism in horizontal and vertical orientations has been investigated by many researchers. However, till date very little experimental work and investigation has been performed for vertical downward flow. In order to contribute more to this research and have a better understanding of the non-boiling two phase heat transfer phenomenon for this pipe orientation, experimental investigation is undertaken for a vertical downward oriented 0.01252 m I.D. schedule 10 S stainless steel pipe using air-water as fluid combination. The influence of different flow patterns on the two phase convective heat transfer coefficient is studied using experimental measurements of 165 data points for bubbly, slug, froth, falling film and annular flow patterns spanned over the entire range of the void fraction. In general the two phase heat transfer coefficients are found to be consistently higher than that of the single phase flow. This tendency is observed to increase with increase in the gas flow rate as the flow regime migrates from bubbly to the annular flow. The concept of Reynolds analogy as implemented by Tang and Ghajar [1] for horizontal and vertical upward flow is analyzed against the vertical downward flow data collected in the present study. Due to lack of correlations available for predicting the two phase heat transfer coefficient in vertical downward orientation it was decided to perform the quantitative analysis of the seventeen two phase heat transfer correlations available for vertical upward flow. This analysis is concluded by the recommendation of the top performing correlations in the literature for each flow pattern. Based on the pressure drop data and using Reynolds analogy, a simple equation is proposed to correlate the two phase heat transfer coefficient with the single phase heat transfer coefficient.
Enhancement of Nucleate Boiling Heat Transfer With Nanofiber Mat
Authors: Yang L. , Patel V. , Seyed-Yagoobi J. , Jun S. , Sinha-Ray S. , Zhang Y. , Yarin A.
Published: July 2013

Nucleate pool boiling heat transfer has been experimentally studied at ambient temperature, on a surface with a novel nanofiber mat coating. The nano-textured surface was made of alumina ceramic substrate covered by an electrospun polymer nanofiber mat with a thickness of about 30 μm and immersed in saturated HCFC-123. The surfaces of the individual polymer nanofibers in the mat were copper-plated. Significant enhancements in nucleate boiling heat transfer as well as reduction of surface temperature have been achieved for the copper nanofiber-coated surface compared to a bare surface.
Active Hot Spot Cooling Controlled by Single-Sided Electrowetting-on-Dielectric (SEWOD)
Authors: Park Sung-Yong , Cheng Jiangtao , Chen Chung-Lung (C.-L. )
Published: July 2013

Electrowetting-on-dielectric (EWOD) has attracted as one of the effective on-chip cooling technologies. It enables rapid transport of coolant droplets and heat transfer from target heat sources, while consuming extremely low power for fluid transport. However, a sandwiched configuration in conventional EWOD devices only allows sensible heat transfer, which very limits heat transfer capability of the device. In this paper, we report a novel single-sided EWOD (SEWOD) technology that enables two-phase cooling on a single-sided plate. As a result, heat transfer capability of the SEWOD device can be significantly enhanced. A complete set of droplet manipulation functions necessary for active hot spot cooling has been achieved on SEWOD. Hot spot surface modification to hydrophilic makes a droplet stick on a hot spot and maximize its contact area, greatly improving thermal rejection capability of the device. We have demonstrated two-phase cooling on SEWOD. With successive transportation of four droplets with a volume of 30 μL, the hot spot temperature that was initially heated up to 172°C was able to be stably maintained below 100 °C for 475s. This novel SEWOD-driven cooling technique promises to potentially function as a wickless vapor chamber with enhanced thermal managing capabilities.
The M-1 Radiation Model: Evaluation for Predicting Thermal Radiation From Fires
Authors: Brown Alexander L. , Pierce Flint
Published: July 2013

The M-1 radiation model is a thermal radiation transport model that is derived from a maximum entropy approximation to the radiative transport equation. It involves the solution of four hyperbolic equations for conservation of radiative energy. The M-1 model has similarities to the classical diffusion approximations (like P-1), but is able to better predict directed flux. Consequently, shadowing and long-range transport can be well resolved for a fraction of the cost of methods with exponentially increasing accuracy costs like the method of discrete ordinates and Monte Carlo ray-tracing. The M-1 method is mostly used historically in astronomical radiation transport, but has recently been shown to work for combustion applications of smaller scale. Past work has shown it to give good comparisons to fire problems with length scales of interest. Because of the potential for the model to predict radiation transport more cost-effectively, it is being examined for implementation as an option in our fire codes. We present the theory behind the model. The Eddington factor is used to partition directed and diffuse radiation. It is normally modeled since it is derived from a transcendental functional relationship. We analyze Eddington factor models presented in previous work, and present a new model that we show to be superior in most ways to all the previously presented models. Some 1-dimensional calculations are also shown that illustrate the potential accuracy and challenges with implementing the M-1 model. Such challenges include the specification of boundary conditions and the development of robust solver methods.
A Numerical Study of the Effect of Thermal Mass on the Transient Thermal Performance of a Simple Three Storied Atrium Building
Authors: Hussain Shafqat , Oosthuizen Patrick H.
Published: July 2013

The effect of thermal mass is becoming increasingly important under the scope of low energy use building construction and energy conservation. In this paper the dynamic behaviour of the effect of the thermal mass of external walls on the development of solar-assisted buoyancy-driven ventilation flow rates, air flow patterns and temperature distributions in a simple three-storied atrium building was investigated using unsteady Reynolds Averaged Navier-Stokes equations (RANS) modelling approach. The SST-k-omega turbulence model and the Discrete Transfer Radiation Model (DTRM) were used in the CFD simulations. The unsteady-state governing equations were solved using a commercial CFD solver FLUENT©. The numerical results were obtained for indoor transient thermal conditions by assuming the external concrete walls of the building under three situations: (i) walls with internal insulation covering (ii) walls with external insulation covering, and (iii) walls without insulation covering. The buoyancy-driven ventilation volume flow rates and internal temperature variations from 8:00 to 15:00hrs on July 15, 2011 were calculated using CFD simulations. Numerical results obtained indicate that the transient CFD simulations provide important information about the effect of the thermal mass on the thermal behaviour of the building. It was found that the thermal mass of external walls with external insulation covering was a better option which helped to control the diurnal temperature swings making the conditions within the building more comfortable. Heat stored in the walls can be useful for the night-time buoyancy-driven ventilation when there is no solar radiation.
Temperature Sensing of Joule Heating Inside an Optical Whispering-Gallery Mode Micro-Annulus
Authors: Frenkel Matthew , Avellan Marlon , Guo Zhixiong
Published: July 2013

It has been previously demonstrated that the optical whispering-gallery modes inside a micro-sphere resonators can be used for extremely sensitive temperature sensing. This work attempts to utilize the high-resolution measurements of an optical micro-annulus in order to detect the temperature change in a current carrying wire. A wire is coated with a thin layer of dielectric material as an annular sensor and positioned next to an optical taper. Current is then run through the wire to create joule heating and the temperature change is correlated with the frequency shift in the whispering-gallery mode resonance inside the micro-annulus. The experimental results will be analyzed and presented.
Characterization of Thermal Interface Materials Using a Steady State Experimental Method
Authors: Sponagle Benjamin , Groulx Dominic
Published: July 2013

One method for characterizing the contact conductance of Thermal Interface Materials (TIMs) is the steady state one dimensional heat flow method typified by ASTM D5470. A test apparatus and procedure were developed which use the basic theory of steady state testing TIMs and improves upon the accuracy and repeatability of the standard test. This procedure and apparatus were used to test the contact conductance of the interface four commercial available TIMs. These materials include: Laird Tflex 720, Laird Tmate 2905c, Chomerics Cho-Therm T500, and Chomerics Cho-Therm 1671. It was found that the Laird products underperformed the available manufacturer published values and the Chomerics products only met performance expectations at relatively high clamping pressures (400 psi).
Analytical and Numerical Modeling of Conductive and Convective Heat Transfer Through Open-Cell Metal Foams
Authors: Taheri Mehrdad , Chandra Sanjeev , Mostaghimi Javad
Published: July 2013

In this paper, a comprehensive analytical and numerical study of conductive and convective heat transfer through high porosity metal foams is presented. In the first part a novel theoretical model for determination of effective thermal conductivity of metal foams is introduced. This general analysis can be applied to any complex array of interconnected foam cells. Assuming dodecahedron unit cell for modeling the structure of metal foams, an approximate equation for evaluation of effective thermal conductivity of foam with a known porosity is obtained. In this approximation method, unlike the previous two-dimensional (2D) models, porosity is the only geometric input parameter used for evaluation of effective thermal conductivity, while its predictions of effective thermal conductivity are in excellent agreement with the previous models. In the second part a 3D numerical model for conduction in metal foam is constructed. The foam has a square cross section and is exposed to constant temperature at both ends and constant heat flux from the sides. We assume local thermal equilibrium (LTE), i.e., the solid and fluid temperatures are to be locally equal. Comparison of the 3D numerical results to the experiments shows very good agreement. The last part of the study is concerned with the 3D numerical modeling of convective heat transfer through metal foams. Experimentally determined values of permeability and Forchheimer coefficient for 10 pores per inch (PPI) nickel foam are applied to the Brinkman-Forchheimer equation to calculate fluid flow through the foam. Local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) methods were both employed for heat transfer simulations. While LTE method resulted in faster calculations and also did not need surface area to volume ratio (αsf) and internal convective coefficient (hsf) as its input, it was not accurate for high temperatures. LTNE should be used to obtain distinct local solid and fluid temperatures.
Numerical Simulation of the Effect of the Size of Nanoparticles on the Solidification Process of Nanoparticle-Enhanced Phase Change Materials
Authors: El Hasadi Yousef M. F. , Khodadadi J. M.
Published: July 2013

Nanoparticle-enhanced phase change materials (NEPCM) were proposed recently as alternatives to conventional phase change materials due to their enhanced thermophysical properties. In this study, the effect of the size of the nanoparticles on the morphology of the solid-liquid interface and evolving concentration field, during solidification had been reported. The numerical method that was used is based on the one-fluid-mixture model. The model takes into account the thermal as well as the solutal convection effects. A square cavity model was used in the simulation. The NEPCM that was composed of a suspension of copper nanoparticles in water was solidified from the bottom. The nanoparticles size used were 5 nm and 2 nm. The temperature difference between the hot and cold sides was 5 degrees centigrade and the loading of the nanoparticles that have been used in the simulation was 10% by mass. The results obtained from the model were compared with those existing in the literature, and the comparison was satisfactory. The solid-liquid interface for the case of NEPCM with 5 nm particle size was almost planar throughout the solidification process. However, for the case of the NEPCM with particle size of 2 nm, the solid-liquid interface evolved from a planar stable shape to an unstable dendritic shape, as the solidification process proceeded with time. This was attributed to the constitutional supercooling effect. It has been observed that the constitutional supercooling effect is more pronounced as the particle size decreases. Furthermore, the freezing time increases as the particle size decreases.
Numerical Investigation of Slip Flow and Heat Transfer in Rotating Rectangular Microchannels
Authors: Roy Pratanu , Anand N. K. , Banerjee Debjyoti
Published: July 2013

Investigation of fluid flow and heat transfer in rotating microchannels is important for centrifugal microfluidics, which has emerged as an advanced technique in biomedical applications and chemical separations. The pseudo forces namely the centrifugal force and the Coriolis force arising as a consequence of the rotating reference frame change the flow pattern significantly from the parabolic profile in a non-rotating channel. The convective heat transfer process is also influenced by the secondary flow introduced by the rotational effect. Moreover, if the microchannel wall is hydrophobic, slip flow can occur inside the channel when the conventional no slip boundary condition is no longer valid. In this work, we have numerically investigated the flow and heat transfer inside a straight rotating rectangular microchannel in the slip flow regime. A pressure based finite volume technique in a staggered grid was applied to solve the steady incompressible Navier-Stokes and energy equations. It has been observed that, depending on the rotational velocity, different slip velocities are induced at the channel walls. The average fluid temperature increases with the increase of rotation as convective heat transfer mechanism is increased due to the secondary flow. However, the slip boundary condition has a negligible effect on the temperature profiles.
Evaluation of Selective Catalytic Reduction Technology Retrofit for NOx Reduction in Diesel Mining Vehicles
Authors: Rubeli Brent , Gangal Mahe , Hardcastle Stephen , Caravaggio Gianni
Published: July 2013

Two heavy-duty diesel vehicles operating in an underground salt mine were retrofitted with emission control systems based on selective catalytic reduction technology. The vehicles were then released for production in the mine and the emissions were measured periodically over 18 months.

The systems were very effective in reducing oxides of nitrogen (NOx) emissions from the diesel vehicle engines. The systems were able to provide NOx reductions of 60% to 65% over typical vehicle duty cycles.

This paper will describe the SCR systems, emissions reductions, operability issues and secondary emissions for both vehicles.
Miller Cycle-Regulatable Two Stage Turbocharging System Design of Marine Diesel Engines
Authors: Cui Yi , Hu Zhilong , Deng Kangyao , Wang Qifu
Published: July 2013

Satisfying the coming International Marine Organization (IMO) NOx emissions requirements and regulations is the main focus of attention in marine engine design. Miller cycle, which reduces in-cylinder combustion temperature by reducing effective compression ratio, is the main measure to reduce NOx specific emissions on the cost of volumetric efficiency and engine power. Therefore, it is essential to combine Miller cycle with highly boosted turbocharging system, for example, two stage turbocharing, to recover the power. In this paper, different two stage turbocharging system scenarios are introduced and compared. The system design and matching process is presented. A multi-zone combustion model based one dimensional cycle simulation model is established. The intake valve closure timing and the intake exhaust valves overlap duration are optimized according to the IMO NOx emission limits by the simulation model. The high and low stage turbochargers are selected by an iterative matching method. Then the control strategies of the boost air and the high stage turbine bypass valves are also studied. As an example, a Miller cycle-regulatable two stage turbocharging system is designed for a type of highly boosted high speed marine diesel engine. The results show that the NOx emissions can be reduced 30% and break specific fuel consumption can also be improved by means of moderate Miller cycle combined with regulatable two stage turbocharing.
Application of a Cartesian-Grid Immersed Boundary Method to 3D In-Cylinder Flow
Authors: Günther Claudia , Meinke Matthias , Schröder Wolfgang
Published: July 2013

In this work, a Cartesian-grid immersed boundary method using a cut-cell approach is applied to three-dimensional in-cylinder flow. A hierarchically coupled level-set solver is used to capture the boundary motion by a signed distance function. Topological changes in the geometry due to the opening and closing events of the valves are modeled consistently using multiple signed distance functions for the different components of the engine and taking advantage of a level-set reinitialization method. A continuous discretization of the flow equations in time near the moving interfaces is used to prevent nonphysical oscillations. To ensure an efficient implementation, independent grid adaptation for the flow and the level-set grid is applied. A narrow band approach and an efficient joining/splitting algorithm for the level-set functions minimize the computational overhead to track multiple interfaces. The ability of the current method to handle complex 3D setups is demonstrated for the interface capturing and the flow solution in a three-dimensional piston engine geometry.
A Hydrogen-Fueled, Direct-Injected, Two-Stroke, Small-Displacement Engine for Recreational Marine Applications With High Efficiency and Low Emissions
Authors: Oh David , Plante Jean-Sébastien
Published: July 2013

A hydrogen-fueled two-stroke prototype demonstrator based on a 9.9 horsepower (7.4 kW) production gasoline marine outboard is presented, which, while matching the original engine’s rated power output on hydrogen, achieves a best-point gross indicated thermal efficiency (ITE) of 42.4% at the ICOMIA Mode 4 operating point corresponding to 80% and 71.6% of rated engine speed and torque, respectively. Brake thermal efficiency (BTE) at rated power is 32.3%. Preliminary exhaust gas measurements suggest that the engine could also meet the most stringent CARB 5-Star marine spark-ignition emission standards limiting HC+NOx emissions to 2.5 g/kWh without any after-treatment. Later fuel injection is found to improve thermal efficiency at the expense of increased NOx emissions and, at the extreme, increased cyclic variation. The mechanism for these observations is reasoned to be increasing charge stratification with the later timings.

All these are realized in a cost-effective concept around a proven two-stroke base engine and a low-pressure, direct-injected gaseous hydrogen (LPDI GH2) system, which employs no additional fuel pump and is adapted uniquely from volume production components. This work outlines the pathway — including investigations of several fuel delivery strategies with limited success — leading to the current status including design; modeling with GT-POWER; delivery of lube oil; lubrication issues using hydrogen; and calibration sweeps. Experimental results comprising steady-state dynamometer performance, cylinder pressure traces, NOx emission measurements, as well as heat release analyses, support the reported numbers and the key finding that late fuel injection timing and charge stratification drive the high efficiencies and the NOx trade-off; this is discussed and forms the basis for future work.
An Investigation of Various Chemical Kinetic Models for the Prediction of Autoignition in HCCI Engine
Authors: Khan A. F. , Burluka A. A.
Published: July 2013

Diverse kinetic models for iso-octane, n-heptane, toluene and ethanol i.e. main gasoline surrogates, have been investigated. The models have different levels of complexity and strong and weak points. Firstly, ignition delay times for various fuel blends have been calculated and compared with published shock tube measurements. Kinetic models which are capable of distinguishing between Primary and Toluene Reference Fuels have been used further on in a zero-dimensional Homogeneous Charge Compression Ignition engine model to predict auto-ignition. The modelling results have been compared to the experimental results obtained in a single cylinder research engine. A discussion has been made on the ability of these models to predict autoignition.
Design of a Stepped Tube Exhaust Primary for High Performance Applications Using Unsteady Computational Fluid Dynamics
Authors: Callies Justin D. , Anderson David E. , Prucka Robert G.
Published: July 2013

High performance naturally-aspirated internal combustion engines require effective use of exhaust pressure waves during the gas exchange process to maximize volumetric efficiency and torque. Under certain conditions sudden increases, or steps, in exhaust runner diameter are used to control pressure wave reflections to provide appropriately timed low pressure waves to the cylinder that reduce pumping work and improve air scavenging. This research evaluates gas exchange performance for an exhaust port and an attached stepped-tube primary using unsteady conditions with 1-D and 3-D CFD. The objectives of this research are to (1) discuss the importance of using unsteady flow simulations in the design of high performance exhaust systems, (2) describe the use of stepped-runners to provide performance gains, and (3) discuss the influence of runner step geometry and the number of steps on gas exchange. Simulations are correlated with experimental data to ensure accuracy of the results. A correlation is found between the step size and the magnitude as well as phase of tuning effects. The number of steps is also found to have a direct impact on tuning. The pumping work of the cycle was significantly affected by the stepped primary design, while the scavenging efficiency was not.
High-Pressure Gaseous Injection: A Comprehensive Analysis of Gas Dynamics and Mixing Effects
Authors: Scarcelli Riccardo , Kastengren Alan L. , Powell Christopher F. , Wallner Thomas , Matthias Nicholas S.
Published: July 2013

While the transportation field is mostly characterized by the use of liquid fuels, gaseous fuels like hydrogen and natural gas have shown high thermal efficiency and low exhaust emissions when used in internal combustion engines (ICEs). In particular, high-pressure direct injection of a gaseous fuel within the cylinder overcomes the loss of volumetric efficiency and allows stratifying the mixture around the spark plug at the ignition time. Direct injection and mixture stratification can extend the lean flammability limit and improve efficiency and emissions of ICEs.

Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model. Nevertheless, the numerical simulation of a high-pressure gas jet is not a simple task. At high injection pressure, immediately downstream of the nozzle exit the flow is supersonic, the gas is under-expanded, and a large series of shocks occurs due to the effect of compressibility. To simulate and capture these phenomena, grid resolution, computational time-step, discretization scheme, and turbulence model need to be properly set.

The research group on hydrogen ICEs at Argonne National Laboratory has been extensively working on validating numerical results on gaseous direct injection and mixture formation against PIV and PLIF data from an optically accessible engine. While a good general agreement was observed, simulations still could not perfectly predict the mixing of fuel with the surrounding air, which sometimes led to significant under-prediction of fuel dispersion. The challenge is to correctly describe the gas dynamic phenomena of under-expanded gas jets. To this aim, x-ray radiography was performed at the Advanced Photon Source (APS) at Argonne to provide high-detail data of the mass distribution within a high-pressure gas jet, with the main focus on the under-expanded region.

In this paper, the numerical simulation of high-pressure (100 bar) injection of argon in a cylindrical chamber is performed using the computational fluid dynamic (CFD) solver Fluent. Numerical results of jet penetration and mass distribution are compared with x-ray data. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm directed along the injector axis, is chosen as a canonical case for modeling validation. A sector (90°) mesh, with high resolution in the under-expanded region, is used and the assumption of symmetry is made. Results show good agreement between CFD and x-ray data. Gas dynamics and mass distribution within the jet are well predicted by numerical simulations.
Method for Determining Instantaneous Temperature at the Surface of Combustion Chamber Deposits in an HCCI Engine
Authors: Güralp Orgun , Najt Paul , Filipi Zoran S.
Published: July 2013

Homogeneous charge compression ignition (HCCI) combustion is widely regarded an attractive option for future high efficiency gasoline engines. HCCI combustion permits operation with a highly dilute, well mixed charge, resulting in high thermal efficiency and extremely low NOx and soot emissions, two qualities essential for future propulsion system solutions.

Because HCCI is a thermo-kinetically dominated process, full understanding of how combustion chamber boundary thermal conditions affect the combustion process are crucial. This includes the dynamics of the effective chamber wall surface temperature, as dictated by the formation of combustion chamber deposits (CCD). It has been demonstrated that, due to the combination of CCD thermal properties and the sensitivity of HCCI to wall temperature, the phasing of auto-ignition can vary significantly as CCD coverage in the chamber increases.

In order to better characterize and quantify the influence of CCDs, a numerical methodology has been developed which permits calculation of the crank-angle resolved local temperature profile at the surface of a layer of combustion chamber deposits. This unique predictor-corrector methodology relies on experimental measurement of instantaneous temperature underneath the layer, i.e. at the metal-CCD interface, and known deposit layer thickness. A numerical method for validation of these calculations has also been devised. The resultant crank-angle resolved CCD surface temperature and heat flux profiles both on top and under the CCD layer provide valuable insight into the near wall phenomena, and shed light on the interplay between the dynamics of the heat transfer process and HCCI burn rates.
A Novel Automation System for Microplasma Surface Patterning and Biologics Printing
Authors: Wang Chengyang , Hamid Qudus , Snyder Jessica , Ayan Halim , Sun Wei
Published: July 2013

In the field of tissue engineering, regenerative medicine, and life sciences, the topological biochemical cues regulate cell attachment and alignment within the construct. In a native biological system, these cues are inherent. However, most of the biological materials utilized in the fabrication of tissue construct do not possess the appropriate cues required to develop an architecture to support the cell attachment and growth of a functional tissue Therefore the ability to manipulate structural and biochemical cues plays an important role in biofabrication process, and it is a key element to evaluate a engineered cellular model. Plasma surface functionalization and biologics printing have been investigated and validated as two effective techniques to guide cell functions by creating microenvironments. The objective of this work is to develop a novel dual functional platform for freeform microplasma surface patterning and biologics printing process as well as to study the underlying process science and the process induced cellular functions. The microplasma jet system was assembled by two parts. The upper part is a plastic NPT connector surrounding an extending high voltage copper electrode. The lower part is a dielectric Pasteur pipette connected with a capillary micro-scale nozzle tip. The lower part is interchangeable and the diameter of the tip ranges from 50 μm to 1 mm. With up to 20 kV output capability, a high-voltage power supply was connected to the copper electrode through the NPT connector which also served as gas inlet. A high-voltage probe linked to an oscilloscope is used to monitor the real time voltage. The whole microplasma jet system was set up on automation platform, which allows X-Y-Z motion control and switch control. This integrated system operates at atmospheric pressured environment. All tissue constructs could be fabricated at room temperature without the use of a mask. Clear polystyrene microplates were used as plasma treatment substrates. After O2-He mixed microplasma treatment, 7F2 mouse osteoblastic cells were cultured in the microplates for cell biology studies. We demonstrated the capability of our dual functional platform by applying microplasma in the polystyrene wells and control group (without any treatment) in other wells of the same microplate substrate. The results show that the microplasma treatment changed the surface properties and improved cell attachment. This dual functional freeform system allows for surface patterning and printing of cells, proteins, growth factors, etc. to fabricate three-dimensional tissue constructs.
Structural Optimization Using Adaptive Level Set Method
Authors: Zhou Mingdong , Wang Michael Yu , Li Li
Published: July 2013

A novel structural optimization method that utilizes both explicit and implicit geometric representations is presented. In this method, an octree grid is adopted to accommodate the free structural interface of an implicit level set model and a corresponding 2-manifold triangle mesh model. Within each iteration of optimization, the interface is evolved implicitly by using a semi-Lagrange level set method, during which the signed distance field is evaluated directly and accurately from the current surface model other than interpolation. After that, another mesh model is extracted from the updated field and serves as the input of subsequent design process. This hybrid and adaptive representation scheme not only achieves “narrow band computation”, but also facilitates the structural analysis by using a geometry-aware mesh-free approach. Moreover, a feature preserving and topological errorless mesh simplification algorithm can also be leveraged to enhance the computational efficiency. A three dimensional benchmark example is provided to demonstrate the capability and potential of this method.
Direct and Indirect Adaptive Process Control of Sheet Metal Forming
Authors: Lim Yongseob , Venugopal Ravinder , Ulsoy A. Galip
Published: July 2013

This paper compares the design, implementation and performance of direct and indirect adaptive control (AC) to improve part quality in the stamping process in the presence of disturbances. First, previous work on the design and performance of a direct AC approach (i.e., model reference adaptive control or MRAC) is summarized. The direct AC filter uses nominal process parameters, and so requires some knowledge of the process. Consequently, an indirect AC approach, which estimates process parameters on-line, was also considered. However, due to the simple proportional plus integral (PI) control structure selected, the computation of the controller gains from the estimated parameters requires an optimization procedure, which is not amenable to real-time implementation. Consequently, the indirect AC is implemented using a look-up table, with controller gains that are pre-computed off-line via optimization. The indirect AC with the look-up table is compared to the direct AC via simulations and experiments in terms of tracking performance as well as part quality, in the presence of plant variations. The indirect AC, with a sufficiently high level of discretization in the look-up table, performs well in simulations. However, due to extensive memory requirements, a smaller look-up table is used in the experiments, where it is outperformed by the direct AC.
Design Tension Controller of Unwinding System Based on LMI-Based H∞ Robust Control
Authors: Liu Shanhui , Mei Xuesong , Kong Fanfeng , Li Jian , Liu Zhihui
Published: July 2013

The unwinding system is the most important section for tension generating of the gravure printing machine, and how to maintain the stability of the tension in unwinding system is a key problem to ensure the printing quality. In this paper, an H∞ controller based on Linear Matrix Inequality (LMI) method is presented to strengthen the stability of the tension in unwinding section, and the controller is analyzed and verified by the simulation. Firstly, a nonlinear mathematical model is established according to unwinding system’s working principle, and a linear mathematical model is constructed by analyzing the uncertain and time-varying parameters. Secondly, based on the mathematical model and LMI framework, a H∞ robust controller is designed. Finally, the performance of the H∞ controller is verified by the simulation, and the results show that the proposed tension controller has better robustness and disturbance rejection than traditional PID controller in tension control of the unwinding system.
Monitoring System for the Micro EDM Process
Authors: Narasimhan Jayakumar , Rajurkar Kamlakar P.
Published: July 2013

Now-a-days, many sophisticated systems are available to monitor the process in real time that drastically reduce the cost and lead time to manufacture a part because it takes away the offline sampling. For Electrical Discharge Machining (EDM), current signal monitors are very useful to predict the material removal rate and determine the arcing that can damage the surface. This paper discusses the design and development of an online monitoring for micro-EDM using correlation developed via experimentation. Surface roughness is predicted based on online monitoring.
Force Prediction in Milling of Titanium Alloy
Authors: Matsumura Takashi , Tamura Shouichi
Published: July 2013

Titanium alloy plate formed in rolling has anisotropic properties. The effect of anisotropy on cutting force should be considered in determination of the cutting parameters. A force model of anisotropic materials is presented to predict the cutting forces in milling. In the force model, three-dimensional chip flow is made by piling up the orthogonal cuttings in the planes containing the cutting velocities and the chip flow velocities, where the chip flow direction is determined to minimize the cutting energy. In the anisotropic material model, the shear stress on the shear plane is defined as a function of the orientation angle of the cutting edge in milling. Therefore, the cutting force depends on the feed direction of the end mill. The force model for milling of Ti-6Al-4V is verified in comparison between the simulated and the measurement.
A Study on Facility Layout Using Evolution Strategies in Case of Different Shapes and Areas of Facilities
Authors: Hirabayashi Naoki , Morizawa Kazuko
Published: July 2013

Evolution Strategies have more excellent property than the other existing metaheuristics in a sense of easiness of coding and its manageability of self-adaptive strategy, Hirabayashi et al. proposed a facility layout method using Evolution Strategies for obtaining near optimum solutions efficiently. The shapes of all facilities were, however, assumed to be square. This paper proposes a facility layout method using Evolution Strategies for the case of different shapes and areas of facilities. Some numerical experiments made it clear that the proposed method provides solutions whose average relative error to the optimum or near-optimum solutions obtained by CPLEX are less than 2%, reducing computation time drastically.