bluuebunny/crossref_metadata_2025_split huggingface dataset:
Political stability and fiscal consolidation in sub‐Saharan African countries
Authors: Yabré Tobignaré , Semedo Gervasio 
Published: December 2020

AbstractFiscal policy decision‐making in sub‐Saharan African countries has not always been understood, and the existing literature has generally emphasised the role of macroeconomic factors to justify government fiscal performances. This study highlights the essential role of political stability in the fiscal consolidation decision‐making process in sub‐Saharan African countries. We perform a panel logit model for twenty‐seven (27) sub‐Saharan African countries for the period 2000–15. We show that government stability increases the likelihood of fiscal consolidation as measured by the improvement in the cyclically adjusted primary balance (CAPB). This finding shows that governments that face less risk of being overthrown and enjoy institutional support from the political arena are more prone to fiscal consolidation. This result is obtained by examining different aspects of political stability, including government cohesion, popular support, legislative strength, margin of majority and legislative fractionalisation. Moreover, disaggregating fiscal policy into spending and revenue‐based strategies allows us to show that spending‐based consolidation tends to be more significantly associated with government stability than revenue‐based consolidation. Our findings are supported by various robustness checks and contribute to the ongoing efforts in sub‐Saharan countries to enhance sound fiscal policy.
Accurate Registration of Point Clouds of Damaged Aeroengine Blades
Authors: Ghorbani Hamid , Khameneifar Farbod 
Published: December 2020

Abstract
This paper presents a novel method for aligning the scanned point clouds of damaged blades with their nominal computer-aided design (CAD) model. To inspect a damaged blade, the blade surface is scanned and the scan data in the form of a point cloud is compared with the nominal CAD model of the blade. To be able to compare the scanned point cloud and the CAD model, they must be brought to a common coordinate system via a registration algorithm. The geometric nonconformity between the scanned damaged blade and its nominal model stemmed from the damaged regions can affect the registration (alignment) outcome. The alignment errors then cause wrong inspection results. To prevent this from happening, the data points from the damaged regions have to be removed from the alignment calculations. The proposed registration method in this work can accurately and automatically eliminate the unreliable scanned data points of the damaged regions from the registration process. The main feature is a correspondence search technique based on the geometric properties of the local neighborhood of points. By combining the average curvature Hausdorff distance and average Euclidean Hausdorff distance, a metric is defined to locally measure the dissimilarities between the scan data and the nominal model and progressively remove the identified unreliable data points of the damaged regions with each iteration of the fine-tuned alignment algorithm. Implementation results have demonstrated that the proposed method is accurate and robust to noise with superior performance in comparison with the existing methods.
Topology Synthesis of a Three-Kink Contact-Aided Compliant Switch
Authors: Nagendra Reddy B. V. S. , Saxena Anupam 
Published: December 2020

Abstract
A topology synthesis approach to design 2D contact-aided compliant mechanisms (CCMs) to trace output paths with three or more kinks is presented. Synthesis process uses three different types of external, rigid contact surfaces—circular, elliptical, and rectangular—which in combination, offer intricate local curvatures that CCMs can benefit from, to deliver desired, complex output characteristics. A network of line elements is employed to generate topologies. A set of circular subregions is laid over this network, and external contact surfaces are generated within each subregion. Both discrete and continuous design variables are employed–the former set controls the CCM topology, appearance and type of external contact surfaces, whereas the latter set governs shapes and sizes of the CCM constituents and sizes of contact surfaces. All contact types are permitted with contact modeling made significantly easier through identification of outer and inner loops. Line topologies are fleshed out via a user-defined number of quadrilateral elements along lateral and longitudinal directions. Candidate CCM designs are carefully preprocessed before analysis via a commercial software and evolved using a stochastic search. The process is exemplified via a contact-aided, three-kink mechanical switch which is thoroughly analyzed in the presence of friction and wear.
Only as Strong as the Strongest Link: The Relative Contribution of Individual Team Member Proficiency in Configuration Design
Authors: Brownell Ethan , Cagan Jonathan , Kotovsky Kenneth 
Published: December 2020

Abstract
Prior research has demonstrated how the average characteristics of a team impact team performance. The relative contribution of team members has been largely ignored, especially in the context of engineering design. In this work, a behavioral study was conducted with 78 participants to uncover whether the most or least proficient member of a configuration design team had a larger impact on overall performance. Proficiency is an individual's ability to deal with a specific range of problem. It was found that a configuration design team is most dependent on the proficiency of its most proficient member. The most proficient member had a significant positive effect on how quickly the team reached performance thresholds and the other members of the team were not found to have the same positive impact throughout the design study. Behavioral heuristics were found using hidden Markov modeling to capture the differences in behavior and design strategy between different proficiency members. Results show that high proficiency and low proficiency team members exhibit different behavior, with the most proficient member's behavior leading to topologically simpler designs and other members adopting their designs, leading to the most proficient member driving the team design and thus the team performance. These results underscore the value of the relative contribution model in constructing engineering teams by demonstrating that different team members had unequal effects on team performance. It is shown that enhancing the most proficient member of a team is more likely to contribute to increased team performance than enhancing the least proficient member.
A Design Methodology for Hybrid Electric Vehicle Powertrain Configurations With Planetary Gear Sets
Authors: Jiang Xingyue , Hu Jianjun , Peng Hang , Chen Zhipeng 
Published: December 2020

Abstract
Increasingly strict emission and fuel economy standards stimulate the researches on hybrid electric vehicle techniques in the automobile industry and one of the most important techniques is the design of powertrain configurations. In this paper, a theoretical design methodology for hybrid electric vehicle powertrain configurations is proposed to find the configurations with excellent performance in a large pool of configurations. There are two main parts in a powertrain configuration, power/coupling devices (engine, electric machine, wheel, and planetary gear set) and mechanical connections between these devices. Different connections will lead to configurations having different performances. This paper divides all connections in configurations into three categories and a novel matrix representation method is developed to express these kinds of connections to reflect system dynamics and physical structure of configurations. With the support of the matrix representation method, configuration selections from large pools can automatically be completed by computer and manual calculation and comparison can be avoided, which saves much energy and time. Finally, the proposed method is vigorously verified by simulations.
Experimental and Numerical Analysis on the Influence of Direct Fuel Injection Into O2-Depleted Environment of a GDI-HCCI Engine
Authors: Sok Ratnak , Kusaka Jin 
Published: December 2020

Abstract
Injected gasoline into the O2-depleted environment in the recompression stroke can be converted into light hydrocarbons due to thermal cracking, partial oxidation, and water-gas shift reaction. These reformate species influence the combustion phenomena of gasoline direct injection homogeneous charge compression ignition (GDI-HCCI) engines. In this work, a production-based single-cylinder research engine was boosted to reach IMEPn = 0.55 MPa in which its indicated efficiency peaks at 40–41%. Experimentally, the main combustion phases are advanced under single-pulse direct fuel injection into the negative valve overlap (NVO) compared with that of the intake stroke. NVO peak in-cylinder pressures are lower than that of motoring, which emphasizes that endothermic reaction occurs during the interval. Low O2 concentration could play a role in this evaporative charge cooling effect. This phenomenon limits the oxidation reaction, and the thermal effect is not pronounced. For understanding the recompression reaction phenomena, 0D simulation with three different chemical reaction mechanisms is studied to clarify that influences of direct injection timing in NVO on combustion advancements are kinetically limited by reforming. The 0D results show the same increasing tendencies of classical reformed species of rich-mixture such as C3H6, C2H4, CH4, CO, and H2 as functions of injection timings. By combining these reformed species into the main fuel-air mixture, predicted ignition delays are shortened.
The effects of the reformed species on the main combustion are confirmed by 3D-CFD calculation, and the results show that OH radical generation is advanced under NVO fuel injection compared with that of intake stroke conditions thus earlier heat release and cylinder pressure are noticeable. Also, parametric studies on injection pressure and double-pulse injections on engine combustion are performed experimentally.
Infrared Experimental Investigations on the Effects of Direct Water Injection in an Optical Engine
Authors: Farhat Amer , Kim Taewon , Lai Ming-Chia , Jansons Marcis , Yu Xin 
Published: December 2020

Abstract
The effects of water injection on combustion characteristics were investigated in an optically-accessible light-duty engine retrofitted with a side-mounted water injector. The main objective was to study the effect of water injection on autoignition and subsequent combustion process in compression ignition engines. Numerical zero-dimensional simulations were first performed to separate the thermal from the kinetic effects of water on the ignition delay and maximum temperature reached by a reacting mixture. Then, experimental investigations were performed at different intake temperatures and levels of thermal stratification achieved via direct water injection. Combustion analysis was performed on cylinder pressure data to study the effect of water injection on the overall combustion process. Infrared imaging was performed to provide insight to how water injection and the resulting water distributions affect thermal stratification, autoignition, and combustion characteristics. A new method in quantifying the water distributions is suggested. The results show that the overall level of stratification is sensitive to water injection timing and pressure, where increased water injection pressures and advanced injection timings result in more homogenous distributions. Moreover, water injection was found to affect the location of ignition kernels and the local presence of water suppressed ignition. The level of water stratification was also observed to affect the combustion process, where more homogenous distributions lost their ability to influence ignition locations. Finally, the infrared images showed high levels of residual water left over from prior water-injected cycles, suggesting that hardware configurations and injection strategies must be optimized to avoid wall wetting for stable engine operation.
Accelerating Computational Fluid Dynamics Simulations of Engine Knock Using a Concurrent Cycles Approach
Authors: Probst Daniel , Wijeyakulasuriya Sameera , Pal Pinaki , Kolodziej Christopher , Pomraning Eric 
Published: December 2020

Abstract
Knock is a major design challenge for spark-ignited engines. Knock constrains high load operation and limits efficiency gains that can be achieved by implementing higher compression ratios. The propensity to knock depends on the interaction among fuel properties, engine geometry, and operating conditions. Moreover, cycle-to-cycle variability (CCV) in knock intensity is commonly encountered under abnormal combustion conditions. In this situation, knock needs to be assessed with multiple engine cycles. Therefore, when using computational fluid dynamics (CFD) to predict knock behavior, multi-cycle simulations must be performed. The wall clock time for simulating multiple consecutive engine cycles is prohibitive, especially for a statistically valid sample size (i.e. 30–100 cycles).
In this work, 3-d CFD simulations were used to model knocking phenomena in the cooperative fuel research (CFR) engine. Unsteady Reynolds-Averaged Navier Stokes (uRANS) simulations were performed with a hybrid combustion modeling approach using the G-equation method to track the turbulent flame front and finite-rate chemistry model to predict end-gas autoignition. To circumvent the high cost of running simulations with a large number of consecutive engine cycles, a concurrent perturbation method (CPM) was evaluated to predict knock CCV. The CPM was based on previous work by the authors, in which concurrent engine cycles were used to predict engine CCV in a non-knocking gasoline direct injection (GDI) engine. Concurrent cycles were initialized by perturbing a saved flow field with a random isotropic velocity field. By initializing each cycle with a perturbation sufficiently early in the cycle, each case yields a distinct and valid prediction of combustion due to the chaotic nature of the system.
Three operating points were simulated, with different spark timings corresponding to heavy knock, light knock, and no knock. For all the operating points, other conditions were based on the standard research octane number (RON) test specification for iso-octane. The spark timing of the heavy knock case was the same as that of the RON test. The in-cylinder pressure fluctuations were isolated using a frequency filtering method. A bandpass filter was applied to eliminate high and low frequencies. The knocking pressures were calculated consistently between the experimental and simulation data, including the sampling frequency of the data. The simulation data was sampled to match the sampling rate of the experimental data.
The knock intensities were compared for the concurrently obtained cycles, the consecutively obtained cycles, and experimental cycles. Knock predictions from the concurrent and consecutive simulations compared well to each other and with experiments, thereby demonstrating the validity of the CPM approach.
Development of the Additive Content Turbocharger (ACT)
Authors: Felton Adam , Bailey Kevin 
Published: December 2020

Abstract
As part of an initiative to explore additive manufacturing technologies and their application to internal combustion engines, Wabtec Corporation invested in the development of a new turbocharger for high speed engines. This program had a primary goal of utilizing additive manufacturing methods to enable improvements in product performance, cost and development time. This paper will provide an overview of the Additive Content Turbocharger design and additive processes used for production of functional prototypes.
Use of a Thermodynamic Cycle Simulation to Identify Fundamental Thermodynamic Factors of NOx Formation in a Natural Gas Engine
Authors: Wallace Kevin L. , Caton Jerald A. , Jacobs Timothy J. 
Published: December 2020

Abstract
Natural gas pipelines form a vital part of the energy infrastructure of the United States. In order to overcome head losses in moving the natural gas from one area of the country to another, large compressors are needed to pressurize the gas. For decades, the most efficient and cost-effective method of compressing the gas has been through the use of integral compressor engines. Pipeline companies have great financial incentive to continue using these engines, but increasingly stringent emissions regulations threaten their continued operation.
In this study, the above problem was addressed by developing a zero-dimensional thermodynamic cycle simulation to predict NOx emissions for a large bore, single cylinder, naturally aspirated, 2-stroke, natural gas engine. Excellent agreement was obtained between experimental measurements and simulated predictions of the average exhaust NOx concentration.
Once the simulation was validated by experimental data, a sensitivity analysis was conducted to determine the response of NOx emissions to changes in three factors: trapped equivalence ratio (TER), burned gas fraction (xb), and stuffing box temperature (SBT). This study sought to identify the fundamental thermodynamic reasons that NOx varied with each factor, and to quantify their respective effects.
It was found that changes in each factor effected linear changes in the combustion temperatures, which effected linear changes in the rate constant of the first reaction in the extended Zeldovich mechanism, which effected exponential changes in the NOx emissions. TER and SBT were shown to be directly related to NOx, while xb was shown to be inversely related to NOx.
Simulations of Multi-Mode Combustion Regimes Realizable in a Gasoline Direct Injection Engine
Authors: Kim Sayop , Scarcelli Riccardo , Wu Yunchao , Rohwer Johannes , Shah Ashish , Rockstroh Toby , Lu Tianfeng 
Published: December 2020

Abstract
Lean and dilute gasoline compression ignition (GCI) operation in spark ignition (SI) engines are an attractive strategy to attain high fuel efficiency and low NOx levels. However, this combustion mode is often limited to low-load engine conditions due to the challenges associated with autoignition controllability. In order to overcome this constrain, multi-mode (MM) operating strategies, consisting of advanced compression ignition (ACI) at low load and conventional SI at high load, have been proposed. In this 3-D CFD study the concept of multi-mode combustion using two RON98 gasoline fuel blends (Co-Optima Alkylate and E30) in a gasoline direct injection (GDI) engine were explored. To this end, a new reduced mechanism for simulating the kinetics of E30 fuel blend is introduced in this study. To cover the varying engine load demands for multi-mode engines, primary combustion dynamics observed in ACI and SI combustion modes was characterized and validated against experimental measurements. In order to implement part-load conditions, a strategy of mode-transition between SI and ACI combustion (i.e., mixed-mode combustion) was then explored numerically by creating a virtual test condition. The results obtained from the mixed-mode simulations highlight an important feature that deflagrative flame propagation regime coexists with ignition-assisted end-gas autoignition. This study also identifies a role of turbulent flow property adjacent to premixed flame front in characterizing the mixed-mode combustion. The employed hybrid combustion model was verified to perform simulations aiming at suitable range of multi-mode engine operations.
Development of an Efficient Conjugate Heat Transfer Modeling Framework to Optimize Mixing-Limited Combustion of Ethanol in a Diesel Engine
Authors: Magnotti Gina M. , Mohapatra Chinmoy K. , Mashayekh Alireza , Wijeyakulasuriya Sameera , Schanz Robert , Blumreiter Julie , Johnson Bernard H. , El-Hannouny Essam M. , Longman Douglas E. , Som Sibendu 
Published: December 2020

Abstract
Long-term petroleum prices and increasingly-stringent emissions regulations are driving manufacturers and users alike to consider alternatives to diesel-fueled engines. Mixing controlled combustion of alcohol fuels, such as ethanol, has been identified as a promising technology based the low propensity for particulate and NOx production, but the higher heats of vaporization and auto-ignition temperatures of these fuels make their direct use in diesel engine architectures a challenge. However, because alcohol fuels do not form appreciable levels of soot even in mixing-controlled (MCCI) mode, and because stoichiometric air/fuel ratios (AFR) can be used to simplify NOx aftertreatment, engine design optimization efforts can be targeted to maximize thermal efficiency. Therefore, to realize the potential of alcohol-fueled combustion, engineering insight is required to understand how design parameters, such as increased engine insulation, piston bowl geometry, or spray targeting, should be optimally utilized.
In this work, a computational fluid dynamics (CFD) modeling framework is developed and validated in order to identify pathways to improve the performance of an ethanol-fueled engine operating in an MCCI mode at a stoichiometric AFR. To evaluate the use of TBCs as an engine insulation method, a simplified 1-D conjugate heat transfer (CHT) modeling framework is employed. The CFD model is first validated against baseline engine data over selected inlet air heating temperatures for two piston bowl-injector configurations that define the extrema of the design space. The addition of the 1-D CHT model only increases the computational expense by 15% relative to traditional approaches, yet offers more accurate heat transfer predictions over constant temperature boundary conditions. The model is then used to explore the efficacy of injector orientations and piston bowl geometries in improving the indicated thermal efficiency of alcohol fueled compression ignition engines. Using a design of experiments approach, several candidate designs were identified that improved fuel-air mixing, shortened the combustion duration, and increased thermal efficiency. The most promising design was then fabricated and tested in a Caterpillar 1Y3700 Single Cylinder Oil Test Engine (SCOTE). The engine testing confirmed the findings from the CFD simulations, and found that the co-optimized injector and piston bowl design yielded over 2-percentage point increase in thermal efficiency at the same equivalence ratio (0.96) and over 6-percentage point increase at the same engine load (10.1 bar indicated mean effective pressure), while satisfying design constraints for peak pressure and maximum pressure rise rate.