bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral Microscopy Imaging System for High-Resolution and High-Speed Imaging of Fuel Sprays
Authors: Maassen Kenneth F. , Poursadegh Farzad , Genzale Caroline L. 
Published: December 2019

Abstract
Modern high-efficiency engines utilize direct injection for charge preparation at extremely high pressures. At these conditions the scales of atomization become challenging to measure, as primary breakup occurs on the micrometer and nanosecond scales. As such, fuel sprays at these conditions have proven difficult to study via direct imaging. While high-speed cameras now exist that can shutter at tens to hundreds of nanoseconds, and long-range microscopes can be coupled to these cameras to provide high resolution images, the resolving power of these systems is typically limited by pixel size and field of view. The large pixel sizes make the realization of the diffraction-limited optical resolution quite challenging. On the other hand, limited data throughput under high repetition rate operation limits the field of view (FOV) due to reduced sensor area. Therefore, a novel measurement technique is critical to study fuel spray formation at engine-relevant conditions.
In this work, we demonstrate a new high-resolution imaging technique, Spectral Microscopy, which aims to realize diffraction-limited imaging at effective framerates sufficient for capturing primary breakup in engine-relevant sprays. A spectral microscopy system utilizing a consumer-grade DSLR allows for significantly wider FOV with improved resolving power compared to high-speed cameras. Temporal shuttering is accomplished via separate and independently triggered back illumination sources, with wavelengths selected to overlap with the detection bands of the camera sensor’s RGB filter array. The RGB detection channels act as filters to capture independently timed red, green, and blue light pulses, enabling the capture of a three consecutive images at effective framerates exceeding 20 Million fps. To optimize system performance, a backlit illumination system is designed to maximize light throughput, a multi-lens setup is created, and an image processing algorithm is demonstrated that formulates a three-frame image from the camera sensor. The system capabilities are then demonstrated by imaging engine relevant diesel sprays. The spectral microscopy system detailed in this paper allows for micron-scale feature recognition at framerates exceeding 20 Million fps, thus expanding the capability for experimental research on primary breakup in fuel sprays for modern direct-injection engines.
Experimental Study of the Effect of Start of Injection and Blend Ratio on Single Fuel Reformate RCCI
Authors: Hariharan Deivanayagam , Gainey Brian , Yan Ziming , Mamalis Sotirios , Lawler Benjamin 
Published: December 2019

Abstract
A new concept of single-fuel RCCI has been proposed through the catalytic partial oxidation reformation of diesel fuel. The reformed fuel mixture is then used as the low reactivity fuel and diesel itself is used as the high reactivity fuel. In this paper, two selected reformates mixture from the reformation of diesel were selected for further analysis. Each reformate fuel mixture contained a significant fraction of inert gases (89% and 81%). The effects of the difference in the molar concentrations of the reformate mixtures were studied by experimenting with diesel as the direct injected fuel in RCCI over a varying start of injection timings and different blend ratios (i.e., the fraction of low and high reactivities fuels).
The reformate mixture with the lower inert gas concentration had earlier combustion phasing and shorter combustion duration at any given diesel start of injection timing. The higher reactivity separation between reformate mixture and diesel, compared with gasoline and diesel, causes the combustion phasing of reformate-diesel RCCI to be more sensitive to the start of injection timing. The maximum combustion efficiency was found at a CA50 before TDC, whereas the maximum thermal efficiency occurs at a CA50 after TDC. The range of energy-based blend ratios in which reformate-diesel RCCI is possible is between 25% and 45%, limited by ringing intensity (RI) at the low limit of blend ratios, and COV of IMEP and combustion efficiency at the high limit. Intake boosting becomes necessary due to the oxygen deficiency caused by the low energy density of the reformate mixtures as it displaces intake air.
The Challenges of Turbocharger Matching for North American Freight Locomotives
Authors: Lavertu Thomas , Hart Matthew , Homison Christopher , Vaidya Preeti 
Published: December 2019

Abstract
Engine development is centered on developing a solution for best performance while meeting emissions and operational requirements. This will lead to a tradeoff between engine efficiency and emissions across a wide range of load and ambient operating points. Proper airflow to the engine through turbocharger matching is critical to ensure efficient operation and to meet emissions. This study addresses the challenges of turbocharger matching for vehicle advanced emissions control using a North American freight locomotive application as an example. The airflow trends in moving across the various operating points will be shown along with the impact on both the turbocharger and engine performance. First, the airflow trends across the locomotive load set points will be discussed along with the performance and emissions tradeoffs to meet required airflows. Results on the impact on turbocharger performance such as speed will be shown along with the engine efficiency and emissions implications. Next, the ambient operating requirements for a locomotive will be reviewed and the impact on turbocharger matching. Locomotives operate in a wide range of ambient conditions, including altitudes up to 3,050 meters and across ambient air temperatures ranging from −40 °C to well over 38 °C (including higher temperature operation). This thermal swing provides stress on the turbocharger to efficiently deliver the necessary airflow across all conditions. Trends in turbocharger performance will be reviewed and discussed across this range of ambient conditions. In addition, challenges unique to locomotive applications, such as unventilated tunnel operation and vibrational loading, will be reviewed. Finally, potential for advanced technologies such as variable geometry turbines and their applicability to locomotive operation will be discussed.
Experimental Investigations of Marine Diesel Engine Performance Against Dynamic Back Pressure at Varying Sea-States due to Underwater Exhaust Systems
Authors: Sapra Harsh D. , Singh Jaswinder , Dijkstra Chris , De Vos Peter , Visser Klaas 
Published: December 2019

Abstract
Underwater exhaust systems are employed on board ships to allow zero direct emissions to the atmosphere with the possibility of drag reduction via exhaust gas lubrication. However, underwater expulsion of exhaust gases imparts high and dynamic back pressure, which can fluctuate in amplitude and time period as a ship operates in varying sea-states depending on its geographical location and weather conditions. Therefore, this research aims to experimentally investigate the performance of a marine diesel engine against varying amplitudes and time periods of dynamic back pressure at different sea-states due to underwater exhaust systems.
In this study, a turbocharged, marine diesel engine was tested at different loads along the propeller curve against dynamic back pressure waves produced by controlling an electronic butterfly valve placed in the exhaust line after the turbine outlet. Engine performance was investigated against single and multiple back pressure waves of varying amplitudes and wave periods based on real sea-state conditions and wave data.
We found that the adverse effects of dynamic back pressure on engine performance were less severe than those found against static back pressure. Governor control and turbocharger dynamics play an important role in keeping the fuel penalty and thermal loading low against dynamic back pressure. Therefore, a marine engine may be able to handle much higher levels of dynamic back pressures when operating with underwater exhaust systems in higher sea-states.
Operating Limits of Spark-Assisted Compression Ignition Combustion Under Boosted Ultra-EGR Dilute Conditions in a Negative Valve Overlap Engine
Authors: Triantopoulos Vassilis , Martz Jason B. , Sterniak Jeff , Lavoie George , Assanis Dennis N. , Bohac Stanislav V. 
Published: December 2019

Abstract
Spark-assisted compression ignition (SACI) is a low temperature combustion mode that can offer thermal efficiency improvements and lower nitrogen oxide emissions compared to conventional spark-ignited combustion. However, the SACI operating range is often limited due to excessive pressure rise rates driven by rapid heat release rates. Well-controlled experiments were performed to investigate the SACI operating limits under previously unexplored boosted, stoichiometric, EGR dilute conditions, where low temperature combustion engines promise high thermodynamic efficiencies. At higher intake boost, the SACI high load limit shifted towards lower fuel-to-charge equivalence ratio mixtures, creating a larger gap between the conventional spark-ignition EGR dilution limit and the boosted SACI operating limits. Combustion phasing retard was very effective at reducing maximum pressure rise rate levels until the stability limit, primarily due to slower end-gas burn rates. Gross fuel conversion efficiency improvements up to 10% were observed by using intake boost for either load expansion or dilution extension. Changes in engine speed necessitated changes in unburned gas temperature to match autoignition timing, but were shown to have negligible impact on the heat release profile on a crank angle basis. Lower engine speeds were favorable for load expansion, as time-based peak pressure rise rates scaled with engine speed.
Thermal Profiling of a Small Operational Data Center
Authors: Türkmen İsmail , Mercan Cem Ahmet , Erden Hamza Salih 
Published: December 2019

Abstract
This study highlights experimental challenges of setting up a computational fluid dynamics (CFD) model of a 180-m2 small-size high-performance computing (HPC) data center (DC) in a university campus and the validation procedure leading to a reasonably accurate CFD model for the investigation of the thermal environment. Experimental results based on temperature, airflow, pressure, and power measurements help to confirm and identify inefficient design and operational practices as well as problematic areas regarding the thermal management, define the boundary conditions and validate CFD models. Leaky floors, uneven placement of computing equipment and perforated tiles preventing separation of hot and cold air, low-temperature operation, excessive cooling capacity and fan power were identified sources of energy inefficiency in the DC.
CFD model predictions were gradually improved by using experimental measurements in various boundary conditions and detailed geometrical representation of large leakage openings. The performance indicator of the CFD model during the validation process was the temperature prediction error at the rack inlets and exits. After all improvements, the CFD model can make estimations with an error less than 1°C (RMSE &lt; 1.0) at the rack inlet and less than 5°C (RMSE &lt; 5.0) at the rack outlet. The validated CFD model tests the feasibility of various energy efficiency measures. These measures are in the form of operational or design changes in line with the best practices. Impact of leakage between the raised floor and the room, reduced airflow rate, cold-aisle and hot-aisle separation, workload consolidation, and higher temperature operation were among the phenomena tested by using the validated CFD model. The estimated power usage effectiveness (PUE) value reduced from 1.95 to 1.40 with the implemented energy efficiency measures.
Demonstration of a Compliant Micro-Spring Array As a Thermal Interface Material for Pluggable Optoelectronic Transceiver Modules
Authors: Cui Jin , Pan Liang , Weibel Justin A. 
Published: December 2019

Abstract
Pluggable optoelectronic transceiver modules are widely used in the fiber-optic communication infrastructure. It is essential to mitigate thermal contact resistance between the high-power optical module and its riding heat sink in order to maintain the required operation temperature. The pluggable nature of the modules requires dry contact thermal interfaces that permit repeated insertion–disconnect cycles under low compression pressures (∼10–100 kPa). Conventional wet thermal interface materials (TIM), such as greases, or those that require high compression pressures, are not suitable for pluggable operation. Here we demonstrate the use of compliant micro-structured TIM to enhance the thermal contact conductance between an optical module and its riding heat sink under a low compression pressure (20 kPa). The metallized and polymer-coated structures are able to accommodate the surface nonflatness and microscale roughness of the mating surface while maintaining a high effective thermal conductance across the thickness. This dry contact TIM is demonstrated to maintain reliable thermal performance after 100 plug-in and plug-out cycles while under compression.
Thermo-Mechanical Degradation of Thermal Interface Materials: Accelerated Test Development and Reliability Analysis
Authors: Pense Dustin , Carlton Hayden , Huitink David 
Published: December 2019

Abstract
Thermal interface materials (TIMs) comprise an important role in the thermal management of a myriad of electronic devices, and their ability to ensure both enhanced thermal conductance and reliable adhesion at thermal interfaces is paramount to the reliability of electronics packaging. Like most aspects of a typical electronics package, on/off cycles undergone during a device’s operation induce thermo-mechanical stresses that can negatively affect the integrity of the package. Due to the inherently low adhesive strength and structural integrity of polymer TIMs, they present a likely point of failure when succumbed to these interfacial stresses. Methods for quantifying TIM degradation during mechanical cycling have been quite infrequent in literature; an accelerated and repeatable method for measuring the thermal reliability of TIMs would prove to be beneficial. Herein, we present a methodology to quantify the thermal reliability of TIMs during mechanical cycling using a custom-built steady-state thermal conductivity tester. Additionally, an optical technique was utilized to observe void formation, pump-out, and dry-out behavior during cycling, in order to correlate the thermal performance with physical behaviors of the TIM under cyclic stress. After an initial long-term static test, cyclic testing was found to degrade the thermal performance of the TIM through increasing its interfacial resistance. Optical qualitative measurements revealed the breakdown of the TIM structure at the interface, which indicated the formation of voids due to TIM degradation. Applying this testing method for future TIM development could help in optimizing TIM structure for particular package applications.
Electrothermal Modeling and Analysis of Gallium Oxide Power Switching Devices
Authors: Kotecha Ramchandra M. , Zakutayev Andriy , Metzger Wyatt K. , Paret Paul , Moreno Gilberto , Kekelia Bidzina , Bennion Kevin , Mather Barry , Narumanchi Sreekant , Kim Samuel , Graham Samuel 
Published: December 2019

Abstract
Gallium oxide is an emerging wide band-gap material that has the potential to penetrate the power electronics market in the near future. In this paper, a finite-element gallium oxide semiconductor model is presented that can predict the electrical and thermal characteristics of the device. The finite element model of the two-dimensional device architecture is developed inside the Sentaurus environment. A vertical FinFET device architecture is employed to assess the device’s behavior and its static and dynamic characteristics. Enhancement-mode device operation is realized with this type of device architecture without the need for any selective area doping. The dynamic thermal behavior of the device is characterized through its short-circuit behavior. Based on the device static and dynamic behavior, it is envisioned that reliable vertical transistors can be fabricated for the power electronics applications.
Degradation Modeling and Reliability Assessment of Capacitors
Authors: Gupta Anunay , Yadav Om Prakash , Roy Arighna , DeVoto Douglas , Major Joshua 
Published: December 2019

Abstract
The degradation of capacitors under accelerated stress conditions occur in a monotonic and non-linear fashion. Several efforts have been made to model the degradation behavior of capacitor considering either physics-of-failure models or statistical models and subsequently estimate its reliability and lifetime parameters. But most of these models fail to reflect the physical properties of the degradation path, which varies according to several intrinsic and extrinsic factors. These factors introduce random and temporal uncertainty among the population of capacitors. The gamma stochastic process can model both type of uncertainties among the population of capacitors. In this paper, we model the capacitor degradation by non-homogeneous gamma stochastic process in which both the model parameters (shape and scale) are dependent on stress variables. The model parameters are estimated using the maximum likelihood estimation approach.
A Numerical Investigation of Additive Manufactured Foam Structures for Single Phase Hotspot Thermal Management
Authors: Broughton Justin , Joshi Yogendra 
Published: December 2019

Abstract
Wide band-gap (WBG) power devices have been investigated for their higher power densities, efficiencies, and operating temperatures. However, implementation of WBG devices may cause increased volumetric heat generation despite efficiency increases due to a significant decrease in volume. To fully take advantage of the benefits offered by these devices, the packaging, including cooling infrastructure, must also be addressed. Additive manufactured (AM) structures, based on unit cells seen in stochastic foams, have been investigated as an improvement in thermal management for electric vehicle power electronics. Metal foams have a high specific surface area, high thermal conductivity, and low relative density, which makes them excellent for heat transfer applications as demonstrated extensively in prior literature. Additionally, additive manufacturing offers the ability to print directly on a substrate which eliminates a thermal interface layer and make complex structures for little to no increase in cost. Designed foams were examined specifically for their ability to locally control relevant parameters to tailor the heat transfer performance. The design of the AM foam samples, as well as discussion of relevant parameters for proper characterization with respect to thermohydraulic performance, were discussed. Two geometries — one with local, spanwise densification with decreased pore size and another with uniform density and pore size throughout — were investigated for thermal management of several discrete heaters. Pore-scale models with decreased computational domains were used to obtain closure terms for volume-averaged (VA) modeling. The VA models were then used for full-scale modeling of five chip heaters cooled with the designed metal foams.
Effects of Test Temperature and Prior Aging on the Cyclic Stress-Strain Behavior of Lead Free Solders
Authors: Haq Mohammad Ashraful , Hoque Mohd Aminul , Suhling Jeffrey C. , Lall Pradeep 
Published: December 2019

Abstract
In temperature changing environments, solder joints often experience fatigue failure due to cyclic mechanical stresses and strains induced by mismatches in the coefficients of thermal expansion. These stresses and strains lead to damage accumulation and contribute to the crack initiation, crack propagation, and eventually to failure. In this study, we have investigated the cyclic stress-strain behavior of SAC305 and SAC_Q reflowed lead free solders that occur at various testing temperatures and with various prior aging conditions. Lead free solder uniaxial test specimens with circular cross-section have been prepared using vacuum suction method and then were aged for 0 to 20 days at 125 °C. The samples were then subjected to cyclic stress-strain loading using a Micro-mechanical tester at different testing temperatures from T = 25 C to T = 100 C. The evolution of hysteresis loops with duration of prior aging was characterized by measuring the strain energy density dissipated per cycle (loop area), peak stress, and plastic strain range. It was observed that aging degrades the mechanical fatigue properties due to microstructural coarsening. At elevated temperatures, a drop in the loop area and peak stress and an increase in the plastic strain range for both lead free reflowed solder materials were obtained. In addition, SAC_Q samples had a higher loop area and peak stress compared to SAC305.
Investigation of the Effects of High Temperature Aging on Mechanical Behavior and Microstructural Changes in Lead Free Solders
Authors: Wu Jing , Alam Mohammad S. , Suhling Jeffrey C. , Lall Pradeep 
Published: December 2019

Abstract
Aging effects are common in lead free solder joints within electronic assemblies that are exposed to isothermal environments for extended periods. Such exposures lead to evolution of the solder microstructure, which results in changes in the mechanical properties and creep behavior of the solder joints. In our recent investigations, we have been utilizing Scanning Electron Microscopy (SEM) to better understand aging induced degradations. The microstructural evolutions were observed in SAC305 and SAC_Q (SAC+Bi) alloys exposed to isothermal conditions at T = 125 °C for several different regions from several different joints. The microstructures in several fixed regions of interest were recorded after predetermined time intervals of aging, which were 1 hour (up to 24 hours) and 10 hours (up to 150 hours) for the short term aging samples; and 250 hours (up to 2500 hours) for the long term aging samples. Using the recorded images and imaging processing software, the area and diameter of each IMC particle was tracked during the aging process.
As expected, the quantitative analysis of the evolving SAC_Q microstructure showed that the particles coalesced during aging leading to a decrease in the number of particles. This caused an increase in the average diameter of the particles of slightly more than 100% for long term aging of 2500 hours. For SAC305, the average particle diameter was found to increase at three times the rate (increase of 200% after 2500 hours of aging). Thus, coarsening of IMC particles was greatly mitigated in the SAC_Q alloy relative to that observed in SAC305. Immediately after reflow solidification, Bismuth rich phases were present in the SAC_Q joints. During aging at T = 125 °C, the bismuth was observed to quickly go into solution both within the beta-Sn dendrites and in the intermetallic rich regions between dendrites. This resulted in solid solution strengthening of the lead free solder. It was also found that the aging-induced presence of bismuth in solution within the beta-Sn matrix provided an increased resistance to the Ostwald ripening diffusion process that coarsens the Ag3Sn IMC particles. The combination of these two effects in the SAC+Bi alloy lead to greatly improved resistance to aging induced effects relative to the SAC305 solder alloy. Finally, we have compared the time dependent evolution of microstructure with the degradation in strength during aging for of the two solder alloys, and good correlations were observed.