bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Pressurized High-Flux Solar Reactor for the Thermochemical Gasification of Charcoal Slurry—Two-Phase Flow and Heat Transfer Analysis
Authors: Müller F. , Steinfeld A. 
Published: December 2019

Abstract
A pressurized solar reactor for effecting the thermochemical gasification of carbonaceous particles driven by concentrated solar energy is modeled by means of a reacting two-phase flow. The governing mass, momentum, and energy conservation equations are formulated and solved numerically by finite volume computational fluid dynamics (CFD) coupled to a Monte Carlo radiation solver for a nongray absorbing, emitting, and scattering participating medium. Implemented are Langmuir–Hinshelwood kinetic rate expressions and size-dependent properties for charcoal particles undergoing shrinkage as gasification progresses. Validation is accomplished by comparing the numerically calculated data with the experimentally measured temperatures in the range 1283–1546 K, chemical conversions in the range 32–94%, and syngas product H2:CO and CO2:CO molar ratios obtained from testing a 3 kW solar reactor prototype with up to 3718 suns concentrated radiation. The simulation model is applied to identify the predominant heat transfer mechanisms and to analyze the effect of the solar rector's geometry and operational parameters (namely: carbon feeding rate, inert gas flowrate, solar concentration ratio, and total pressure) on the solar reactor's performance indicators given by the carbon molar conversion and the solar-to-fuel energy efficiency. Under optimal conditions, these can reach 94% and 40%, respectively.
Cavitation-Vortex-Pressure Fluctuation Interaction in a Centrifugal Pump Using Bubble Rotation Modified Cavitation Model Under Partial Load
Authors: Sun Weihua , Tan Lei 
Published: December 2019

Abstract
Cavitation is a complicated phenomenon in the centrifugal pump. In this work, the improved unsteady calculation model based on bubble-rotation-based Zwart–Gerber–Belamri (BRZGB) cavitation model is used to investigate the cavitation-vortex-pressure fluctuation interaction in a centrifugal pump under partial load with experimental validation. Spatial–temporal evolution of cavitation can be classified into three stages: developing stage, shedding stage, and collapsing stage. The cavitation evolution period is found as 1/4T (T is impeller rotation period), corresponding to the frequency 4fi (fi is impeller rotation frequency). On the analysis of the relative vorticity transport equation, it is revealed that the cavity is stretched by the relative vortex stretching term (RVS) and developed by the relative vortex dilation term (RVD), and they have great influence on the cavity shedding. The peak value of pressure fluctuation intensity occurs near the vapor–liquid interface at cavity rear, and shifts downstream with the cavitation development. The hysteresis between the vapor volume fraction, vorticity, and pressure fluctuation is observed, and the variation of vapor volume fraction is the source of cavitation-vortex-pressure interaction.
Supercritical and Subcritical Hopf Bifurcations in a Delay Differential Equation Model of a Heat-Exchanger Tube Under Cross-Flow
Authors: Vourganti Varun , Kandala Shanti Swaroop , Meesala Vamsi C. , Vyasarayani C. P. 
Published: December 2019

Abstract
Nonlinear vibrations of a heat-exchanger tube modeled as a simply supported Euler–Bernoulli beam under axial load and cross-flow have been studied. The compressive axial loads are a consequence of thermal expansion, and tensile axial loads can be induced by design (prestress). The fluid forces are represented using an added mass, damping, and a time-delayed displacement term. Due to the presence of the time-delayed term, the equation governing the dynamics of the tube becomes a partial delay differential equation (PDDE). Using the modal-expansion procedure, the PDDE is converted into a nonlinear delay differential equation (DDE). The fixed points (zero and buckled equilibria) of the nonlinear DDE are found, and their linear stability is analyzed. It is found that stability can be lost via either supercritical or subcritical Hopf bifurcation. Using Galerkin approximations, the characteristic roots (spectrum) of the DDE are found and reported in the parametric space of fluid velocity and axial load. Furthermore, the stability chart obtained from the Galerkin approximations is compared with the critical curves obtained from analytical calculations. Next, the method of multiple scales (MMS) is used to derive the normal-form equations near the supercritical and subcritical Hopf bifurcation points for both zero and buckled equilibrium configurations. The steady-state amplitude response equation, obtained from the MMS, at Hopf bifurcation points is compared with the numerical solution. The coexistence of multiple limit cycles in the parametric space is found, and has implications in the fatigue life calculations of the heat-exchanger tubes.
Effect of In Situ Post Weld Heat Treatment on Mechanical Behavior and Austenite–Ferrite Phase Balance of Fe-Cr-Ni/Fe-Cr Stainless Steels Upset Resistance Dissimilar Weld
Authors: Ozlati Ashkaan , Movahedi Mojtaba 
Published: December 2019

Abstract
Effect of the in situ post weld heat treatment (PWHT) was investigated on the flash profile, austenite/ferrite phase balance, and mechanical properties of the upset resistance dissimilar weld between Fe-Cr-Ni and Fe-Cr stainless steels rods. In order to explore the effect of the heat treatment on the joint strength, two as-welded samples with low strength (116 MPa) and high strength (372 MPa) were used. The results showed that in situ PWHT was beneficial for both welded samples, though in different ways. For the weld with low strength, PWHT improved the joint strength (∼130% increase in the optimum condition compared with the as-welded sample) due to the increase in the size of the flash and the related bonded area at the joint interface. However, ferrite percent in the weld zone increased from ∼50% up to ∼70%. For the sample with the high strength, ferrite/austenite phase balance was restored at an optimum condition of PWHT. However, the joint strength decreased slightly (less than 5%) due to the grain growth in the Fe-Cr rod, i.e., the fracture location. Fracture analysis was used for justification of the variations in the joint strength. For both Fe-Cr-Ni side and Fe-Cr side of the welds, in situ PWHT generally reduced the hardness. This observation is discussed in light of the simultaneous effects of the grain growth and formation of little martensite.
Validation Studies of Linear Oscillating Compressor Cascade and Use of Influence Coefficient Method
Authors: Phan H. M. , He L. 
Published: December 2019

Abstract
Advanced predictions of blade flutter have been continually pursued. It is noted however that validation cases of unsteady CFD methods against experimental cases with detailed 3D unsteady pressures are still rather lacking. The main objectives of the present work are two-folds. First, validate and understand the characteristics of blade tip clearance, as well as a bubble-type flow separation for an unsteady CFD solver against a 3D oscillating cascade experiment. And second, examine the applicability of the influence coefficient method (ICM) as widely used in an oscillating linear cascade setup. In the first part, the capability of a widely used commercial solver (CFX) for unsteady flows induced by a 3D oscillating compressor cascade is examined. The present computations have shown consistently a destabilizing effect of increasing blade tip clearance, in agreement with the experiment. More remarkably, the computational analyses reveal a distinctive interplay between the inlet endwall boundary layer and the tip clearance in relation to the aerodynamic damping. Different inlet endwall boundary layer thicknesses are shown to lead to qualitatively different aeroelastic stability characteristics in relation to tip clearance. The aero-damping variation with the tip clearance under the influence of the inlet endwall boundary layer seems to correlate closely to a balancing act between the passage vortex and the tip leakage vortex. The tip clearance aeroelastic behavior seems also in line with a simple quasi-steady analysis. On the other hand, the mid-chord laminar bubble separation on suction surface, though with a clear signature in the local aero-damping, has negligible effects on the overall stability. The second part aims to examine computationally the applicability of the influence coefficient method in a linear cascade setup. The comparison between the cascade-based ICM data and a baseline “tuned cascade” shows that the differences in the sensitivity to the far-field treatment can be significant, depending on inter-blade phase angles. On the other hand, non-linearity effects closely relevant to the basic linear assumption of the ICM are shown to only have a small influence. The present results suggest that extra caution should be exercised when comparing a CFD-based tuned cascade model with a finite cascade-based ICM model, at conditions close to acoustic resonance. The resultant discrepancies may well arise from the inherently different far-field sensitivities between the two models, rather than those typical numerical and physical modeling aspects of interest (e.g., meshing, spatial and temporal discretization errors as well as turbulence modeling).
Modification of Shear Stress Transport Turbulence Model Using Helicity for Predicting Corner Separation Flow in a Linear Compressor Cascade
Authors: Liu Yangwei , Tang Yumeng , Scillitoe Ashley D. , Tucker Paul G. 
Published: December 2019

Abstract
Three-dimensional corner separation significantly affects compressor performance, but turbulence models struggle to predict it accurately. This paper assesses the capability of the original shear stress transport (SST) turbulence model to predict the corner separation in a linear highly loaded prescribed velocity distribution (PVD) compressor cascade. Modifications for streamline curvature, Menter’s production limiter, and the Kato-Launder production term are examined. Comparisons with experimental data show that the original SST model and the SST model with different modifications can predict the corner flow well at an incidence angle of −7 deg, where the corner separation is small. However, all the models overpredict the extent of the flow separation when the corner separation is larger, at an incidence angle of 0 deg. The SST model is then modified using the helicity to take account of the energy backscatter, which previous studies have shown to be important in the corner separation regions of compressors. A Reynolds stress model (RSM) is also used for comparison. By comparing the numerical results with experiments and RSM results, it can be concluded that sensitizing the SST model to helicity can greatly improve the predictive accuracy for simulating the corner separation flow. The accuracy is quite competitive with the RSM, whereas in terms of computational cost and robustness it is superior to the RSM.
Reduced Chemical Kinetic Models of C1 - C4 Alcohols Using the Alternate Species Elimination Approach
Authors: Zhou Apeng , Jouzdani Shirin , Akih-Kumgeh Ben 
Published: December 2019

Abstract
This study presents four separate reduced chemical kinetic models of methanol/ethanol, propanol isomers, n- and iso-butanol, and n- and s-butanol isomers, derived from a comprehensive chemical kinetic model of C1-C5 alcohols using the Alternate Species Elimination approach. It is motivated by complexity of the detailed model (comprising 600 species and 4100 elementary reactions) and the need for simpler kinetic models for analysis of combustion of smaller alcohols. The reduced models are obtained on the basis of ignition delay time simulations with imposed thresholds on the resulting normalized changes in ignition delay times. The following reduced models are obtained: methanol/ethanol: 38 species and 197 reactions; propanol isomers: 68 species and 419 reactions; n- and iso-butanol: 140 species and 745 reactions; and n- and s-butanol: 134 species and 739 reactions. Predictions of ignition delay times by the reduced models are found to be in good with the detailed models. The reduced models are further tested against other relevant combustion properties. These properties include burning velocities of laminar premixed flames, global pyrolysis time scales, and heat release timing in Homogeneous Charge Compression Ignition engines. This verification shows that reduced models can replace the comprehensive model in combustion analysis without loss of predictive performance. The reduced models can also serve as starting models for developing combined chemical kinetic models of gasoline/diesel and alcohol blends.
Development of an Artificial Neural Network Model for the Performance Prediction of a Variable Compression Ratio Gasoline Spark Ignition Engine
Authors: Tripathy Srinibas , Sahoo Sridhar , Srivastava Dhananjay Kumar 
Published: December 2019

Abstract
The purpose of this study is to develop an artificial neural network (ANN) model for performance prediction of a variable compression ratio gasoline port fuel injection spark ignition engine. For ANN modeling, a large experimental data set was generated in which at random 85% was assigned for training the network, and 15% that are not included during the training process was used for testing the network. A multilayer perception feed forward neural network was used to predict the correlation between input and output layer. The input layer consists of engine speed, throttle position, spark timing, and compression ratio. Whereas, the output layer consists of torque, brake power and indicated mean effective pressure (IMEP). Neurons in the hidden layer were varied and optimized based on a specified goal error. A standard supervised back propagation learning algorithm was used in which the error between the target and network output was calculated and minimized. In the hidden and output layers, a non-linear tan-sigmoid and a linear transfer function were used, respectively, for input-output mapping. The performance of the network was evaluated by statistical parameters like correlation coefficient (R), mean relative error (MRE) and root mean square error (RMSE). It was found from the test data that the R and MRE values are lies in between 0.99853 to 0.99875 and 0.42% to 0.58%, respectively. Whereas, RMSE value for all performance parameters was found to be very low. Hence, this study reveals that the application of ANN modeling has the ability to predict the performance of a variable compression ratio gasoline engine and is the best alternative tool over all classical modeling techniques.
Implementing Natural Gas in a Compression Ignition Cycle Using Noble Gas Addition
Authors: Shahsavan Martia , Morovatiyan Mohammadrasool , Baghirzade Mammadbaghir , Mack J. Hunter 
Published: December 2019

Abstract
Natural gas is known as a relatively clean fossil fuel due to its low carbon to hydrogen ratio compared to other transportation fuels, which yields a reduction of carbon monoxide, carbon dioxide, and unburned hydrocarbons emissions. However, it has a low cetane number, which makes it a difficult fuel for use in compression ignition engines. A potential solution for this issue can be adding small amounts of argon, as a noble gas with a low specific heat to modify the intake conditions. In this numerical study, a commercial compression ignition engine has been modeled to evaluate the auto-ignition of natural gas with the modified intake conditions. Different amounts of argon added to the intake air are examined in order to attain the optimal operating conditions. A detailed chemistry solver is implemented on a 53-species chemical kinetics mechanism to calculate the rate constants. The results show that compression ignition of natural gas can be achieved by adding small amounts of argon to the intake air. It drastically increases the in-cylinder temperature and pressure near TDC, which enables the auto-ignition of the injected natural gas. Moreover, it leads to the reduction in ignition delay and heat release rate, and expands the combustion duration. Emissions analysis indicates that NOx and CO2 can be significantly diminished by increasing the amount of argon in the intake composition. This study introduces an efficient and clean compression ignition engine fueled with natural gas running in optimal operating conditions using argon addition to the intake.
A Study on the Distribution of Oil Film Thickness in the Circumferential Direction of Oil Ring in a Gasoline Engine
Authors: Ito Akemi , Hakkaku Tadatsugu , Mochiduki Kazuya , Tomotsune Keita , Inui Masatsugu , Akamatsu Hirotaka 
Published: December 2019

Abstract
Oil traveling upward through the sliding surface of a piston ring causes oil consumption of an engine. Piston rings are designed considering conformability to deformed cylinder bore. However, cylinder deformation sometimes affects strongly oil consumption. It suggests that a piston ring cannot conform dynamically to the cylinder bore. In this study, distribution of oil film thickness of an oil ring was measured for investigating the dynamic conformability. An optical fiber has embedded in the sliding surface of the lower rail of the oil ring, and oil film thickness was measured by laser induced fluorescence method. The measuring point was rotated in the circumferential direction, so the distribution in both the circumferential and the axial direction could be measured. Thick oil films partially were found and it was found that the oil ring did not conformed to the deformed cylinder bore dynamically. Furthermore, such oil film showed thicker value than those expected theoretically. It was showed that dynamic conformability must be considered for piston ring design for reducing oil consumption.
Investigation of the Effect of Plume Number on Spray Collapse
Authors: Sphicas Panos 
Published: December 2019

Abstract
The plumes of a gasoline spray collapse into a single entity under the influence of ambient pressure, ambient temperature and injection duration. Previous work by the author studied experimentally [1] and numerically [2] the phenomenon of spray collapse. It was observed that the entrained air from every single plume, accumulatively creates a recirculation zone in the middle of the spray. The recirculation zone of high velocity, creates a low pressure region, which causes the collapse of the spray. In this paper, the influence of the number of plumes in the spray, is investigated numerically. The plume angle and ambient conditions matched Spray G, but the number of plumes was varied from two to eight. The effect of the plume number on the spray collapse was investigated numerically. It was evident that increased number of plumes in the spray promotes spray collapse.
Optimization of the Mechanical and Thermodynamic Efficiency Loss Dynamic in a Lean Single Cylinder Natural Gas-Fueled Jet Ignition Engine
Authors: Peters Nathan , Subramanyam Sai Krishna Pothuraju , Bunce Michael , Blaxill Hugh 
Published: December 2019

Abstract
In an effort to reduce fuel consumption and lower emissions output, there is a growing need for high efficiency engines in power generation. Ultra-lean (λ &gt; ∼1.6) combustion via air dilution is an enabling technology for achieving high efficiencies while simultaneously reducing emissions of nitrogen oxides (NOx). Jet ignition is a pre-chamber-based combustion system that enables ultra-lean operation beyond what is achievable with traditional spark ignition engines. In this paper, results and analyses related to the downspeeding of a 390cc, high efficiency low-output single cylinder jet ignition engine operating ultra-lean are presented. The engine was developed as part of the US Department of Energy’s Advanced Research Projects Agency–Energy (DOE ARPA-E) GENSETS program1. The purpose of the program is to develop technologies for use in high efficiency combined heat and power generator sets.
Due to the intended application of power generation, optimization of the engine for a specific operating condition is critical. An efficiency loss breakdown based on the Thermodynamic First Law is used to analyze the interdependent trends of engine speed, brake power, and normalized air-fuel ratio, lambda, with the aim of optimizing these parameters for brake thermal efficiency. The general trends of efficiency loss pathways with enleanment are found to be relatively insensitive to speed and load although the magnitude of the loss pathways changes. As the relative importance of the efficiency loss pathways changes with operating condition, so too does the lambda at which peak brake thermal efficiency occurs. The “peak efficiency lambda” was found to be at its leanest at low speed and high power where the influence of heat transfer is greatest and mechanical losses are minimized.
Engine Combustion System Optimization Using CFD and Machine Learning: A Methodological Approach
Authors: Badra Jihad , Khaled Fethi , Tang Meng , Pei Yuanjiang , Kodavasal Janardhan , Pal Pinaki , Owoyele Opeoluwa , Fuetterer Carsten , Brenner Mattia , Farooq Aamir 
Published: December 2019

Abstract
Gasoline compression ignition (GCI) engines are considered an attractive alternative to traditional spark-ignition and diesel engines. In this work, a Machine Learning-Grid Gradient Algorithm (ML-GGA) approach was developed to optimize the performance of internal combustion engines. Machine learning (ML) offers a pathway to transform complex physical processes that occur in a combustion engine into compact informational processes. The developed ML-GGA model was compared with a recently developed Machine learning Genetic Algorithm (ML-GA). Detailed investigations of optimization solver parameters and variables limits extension were performed in the present ML-GGA model to improve the accuracy and robustness of the optimization process. Detailed descriptions of the different procedures, optimization tools and criteria that must be followed for a successful output are provided here. The developed ML-GGA approach was used to optimize the operating conditions (case 1) and the piston bowl design (case 2) of a heavy-duty diesel engine running on a gasoline fuel with a Research Octane Number (RON) of 80. The ML-GGA approach yielded &gt; 2% improvements in the merit function, compared to the optimum obtained from a thorough computational fluid dynamics (CFD) guided system optimization. The predictions from the ML-GGA approach were validated with engine CFD simulations. This study demonstrates the potential of ML-GGA to significantly reduce the time needed for optimization problems, without loss in accuracy compared to traditional approaches.
An Experimental Study on the Effects of Intake Charge and Pilot Injection on Premixed Burn Fraction and NOx Emission Characteristics of a CRDI Turbocharged Diesel Engine
Authors: Chacko Nivin , Jeyaseelan Thangaraja , Premnath Vijay Anirudh 
Published: December 2019

Abstract
The engine-out NOx emission from the combustion process depends on the fraction of premixed fuel burned. Hence, the study of the premixed combustion phase provides the flexibility to understand the NOx and other emissions. Here we performed an experimental study by modifying the intake charge along with pilot fueling on a twin-cylinder turbocharged CRDi diesel engine. The operating parameters, exhaust gas recirculation (EGR) and pilot injection were controlled to study about the premixed combustion phase, which gives minimum NOx emission without compromising other emissions particularly smoke. The results indicate that the premixed burn fraction decreased with an increase in pilot fuel quantity, dwell period and increased with higher EGR percentage. The optimum pilot sequences yielded a 41% reduction in NOx and 60% with smoke emissions. Also, the combination of pilot injection and EGR resulted in a drastic reduction of HC and CO emissions ∼54%.