bluuebunny/crossref_metadata_2025 huggingface dataset:
English outside the academic sphere: A mobile‐based context‐aware comparison study on collaborative and individual learning
Authors: Lin Chih‐Chung , Barrett Neil E. , Liu Gi‐Zen
Published: December 2020

Context‐aware ubiquitous learning (CAUL) technology provides language learners with interactive learning environments and has been found to increase learning effectiveness and self‐efficacy due to student interaction, discussion and evaluation of the entire learning process. This study used a mobile‐based ubiquitous learning system combined with a collaborative learning approach to develop Fitness‐specific English listening and reading, and fitness knowledge. The researchers recruited two groups of participants, an individual learning group (N = 31) and a collaborative learning group (N = 30), and evaluated their learning performance via pre‐and post‐tests. In addition, a questionnaire explored the perceived usefulness, usability, follow‐up intention of using the system and self‐efficacy regarding fitness‐specific English. The results show that both groups improved fitness‐specific English in terms of listening and reading comprehension. Moreover, collaborative learning was found to facilitate fitness‐specific knowledge, and those in the collaborative learning group improved their self‐efficacy more than those in the individual learning group.
Diagnostic performance of immediate colposcopy among women with high‐risk human papillomavirus (HPV) other than HPV 16/18 and normal cytology
Authors: Aydın Serdar , Öncü Hande Nur , Arıcı Dilek Sema
Published: December 2020

Aim

Persistent infection with 1 of 14 high‐risk genotypes human papillomavirus (HPV) genotypes is the crucial for the development of high‐grade cervical cancer precursors. The reassuring management of women with cytology negative, high‐risk HPV (HrHPV) positive is important especially after the widespread use of HPV testing either as a cotest. The aim of our study was to compare the colposcopic biopsy results of women with HPV 16/18 with other Hr‐HPV genotypes and determine positive predictive values (PPV) for CIN2+ of other HR HPV genotypes.

Methods

We prospectively had included the women with negative cytology and positive Hr‐HPV test other than HPV 16/18. Control group was composed of women with negative cytology positive test results for either HPV 16 or HPV 18. Women with HrHPV positive, cytology negative referred to immediate colposcopy.

Results

The prevalence of CIN1 and CIN2 is significantly higher in HPV 16/18 group than pooled other HrHPV group (34.1% vs 17.5%, P = 0.01 for CIN 1+; 14.8% vs 5.2%, P = 0.03 for CIN 2+). The prevalence of CIN3 was almost three fold in women with HPV 16/18 (9.1% vs 3.1%). PPV for CIN 2+ was 16.4 (9.1–27.3) for HPV 16, 11.7 (2–37.7) for HPV 18, 20 (3.5–55.7) for HPV 31, 11.1 (0.6–49.3) for HPV 51, 12.5 (0.6–53.3) for HPV 58 and 59.

Conclusion

We showed the relative high PPV for CIN2+ in OHrHPV other than HPV 16/18 positive group among cytology negative population. HPV 33, 51, 58, 59 and 18 had similar PPV for CIN2+ in basal cytology negative population.
Family socioeconomic status amplifies unique environmental influences on the dynamics of adolescent daily positive affective process
Authors: Zheng Yao , Hu Yueqin
Published: December 2020

Background and Objective

Affective processes as complex dynamical systems happen in people's daily lives. Affective dynamics characterizing unique features of individual affective systems are linked with long‐term developmental outcomes. This study investigated genetic and environmental contributions, and the moderation by family socioeconomic status (SES), to two affective dynamics characterizing affective system sensitivity to the relative levels and change in affect, respectively.

Methods

Using a sample of 490 17‐year‐old twins (41.1% males, 93.9% White) in a 40‐day‐long daily diary design, dynamical systems modeling estimated individual affective dynamics of positive and negative affect. Twin modeling examined genetic and environmental contributions to affective dynamics as well as the moderation of SES.

Results

For both positive and negative affect, system sensitivity to the relative levels of affect was predominantly under unique environmental influences with negligible genetic influences; system sensitivity to the change in affect was affected by both genetic and unique environmental influences. SES amplifies unique environmental influences on sensitivity to the change in positive affect.

Conclusions

These findings highlight different genetic and environmental origins of different adolescent affective dynamics in their daily lives, and suggest that macro contexts could influence micro timescale affective dynamics.
Acute blockade of NR2C/D subunit‐containing N‐methyl‐D‐aspartate receptors modifies sleep and neural oscillations in mice
Authors: Pálfi Emese , Lévay György , Czurkó András , Lendvai Balázs , Kiss Tamás
Published: December 2020

N‐methyl‐d‐aspartate receptors (NMDARs) play an important role in excitatory neurotransmission and have been associated with psychiatric conditions including schizophrenia and major depressive disorder. NMDARs are composed of two NR1 and two NR2 subunits. The type of NR2 subunit determines electrophysiological and pharmacological properties of the receptor. As the precise role of NR2C/D subunit‐containing NMDARs is poorly understood in vivo, we have performed behavioural, quantitative electroencephalographic (qEEG) and polysomnographic analysis following acute pharmacological blockade of these receptor subtypes in adult male CD1 mice. We found that NR2C/D blockade impaired motor coordination and decreased the amount of gross movement. Moreover, EEG power in multiple frequency bands including theta and sigma were found to decrease significantly together with a decrease of theta oscillation frequency. Changes of these qEEG measures were accompanied by a decrease in time spent in slow‐wave and rapid eye movement sleep, but an increase of time spent in quiet wakefulness. Furthermore, there was a significant decrease of sleep spindle oscillation density. These findings highlight the importance of NR2C/D‐containing NMDARs and take a step towards establishing a link between electrophysiological correlates of psychiatric disorders and underlying synaptic dysfunctions.
Growth performance and intestinal microbial changes of Carassius auratus in response to pomegranate (Punica granatum) peel extract‐supplemented diets
Authors: Ahmadniaye Motlagh Hamidreza , Rokhnareh Zahra , Safari Omid , Selahvarzi Yahya
Published: December 2020

This study aimed to investigate the effect of pomegranate (Punica granatum) peel extract (PPE) on growth indices, intestinal bacteria, and total fungi count of Carassius auratus intestine. Ninety C. auratus fries (11.04 ± 0.22 g) were distributed among 15 aquariums (100‐L) in a completely randomized design (triplicated), and were fed diets containing 0.1, 1, 2, and 4% PPE for 60 days at a feeding rate of 2% body weight during the experiment. A spectrophotometry assessment indicated that the total phenol and flavonoid content of PPE was 5.44 ± 0.03 and 49.80 ± 1.00 mg/g, respectively. According to the results, the extract significantly reduced the growth indices (final weight, weight gain, specific growth rate (SGR), and feed conversion ratio (FCR)) at 4% compared to the control (p < .05). PPE did not affect the total aerobic bacteria or total lactic acid bacteria count, but the enteric gram‐negative bacteria count was significantly reduced in the experimental treatments (p < .05). The total fungi count showed a significant increase in all treated fish (p < .05). According to the results, because of the negative effect of the high dose of PPE on growth, there is a recommendation for it to be used at 2% of the diet to reduce intestinal gram‐negative bacteria and increase the total fungi count.
The Role of Education in Mitigating Automation’s Effect on Wage Inequality
Authors: Bentaouet Kattan Raja , Macdonald Kevin , Patrinos Harry Anthony
Published: December 2020

While automation has renewed the debate about labor market policy responses to inequality and job losses, less attention has been given to education policy. We present a general equilibrium model and empirical evidence showing how education mitigates wage inequality resulting from a recent, worst‐case expectation of technology’s ability to automate job tasks. Our model predicts that education could reduce automation’s marginal effect on the wage gap between lower‐ and higher‐skilled labor by up to 3 percentage points. Education policies that promote automation‐complementing skill formation would reduce the need for costly labor market and wealth redistribution interventions later in life.
Political stability and fiscal consolidation in sub‐Saharan African countries
Authors: Yabré Tobignaré , Semedo Gervasio
Published: December 2020

Fiscal 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.
A fix-and-optimize heuristic for the capacitated multi-item stochastic lot-sizing problem
Authors: Gurkan M. Edib , Tunc Huseyin
Published: December 2020

This study addresses the stochastic multi-item capacitated lot-sizing problem. Here, it is assumed that all items are produced on a single production resource and unmet demands are backlogged. The literature shows that the deterministic version of this problem is NP-Hard. We consider the case where period demands are time-varying random variables. The objective is to determine the minimum expected cost production plan so as to meet stochastic period demands over the planning horizon. We extend the mixed integer programming formulation introduced in the literature to capture the problem under consideration. Further, we propose a fix-and-optimize heuristic building on an item-period oriented decomposition scheme. We then conduct a numerical study to evaluate the performance of the proposed heuristic as compared to the heuristic introduced by Tempelmeier and Hilger [16]. The results clearly show that the proposed fix-and-optimize heuristic arises as both cost-efficient and time-efficient solution approach as compared to the benchmark heuristic.
Accurate Registration of Point Clouds of Damaged Aeroengine Blades
Authors: Ghorbani Hamid , Khameneifar Farbod
Published: December 2020

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

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

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

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

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

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

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

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

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

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

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.
Assessment of Hydrogen and Natural Gas Mixtures in a Large Bore Gas Engine for Power Generation
Authors: Fercher Bernhard , Wimmer Andreas , Zelenka Jan , Kammel Gernot , Baumann Zita
Published: December 2020

Now more than ever there is a growing global interest to reduce greenhouse gas (GHG) emissions originating from internal combustion engines. One approach consists in the use of hydrogen instead of fossil fuels. Large bore gas engines for power generation are often fueled by gases with high methane content. Relative to natural gas-fueled engines, the power densities of premixed or port-fuel-injected hydrogen engines are limited due to low volumetric efficiencies and moreover by occurring irregular combustion events (knocking, backfire).

The paper presents results from experimental investigations of the impact of different hydrogen substitution rates in natural gas on performance, emissions and operating limits on a single cylinder research engine. The engine is representative for a large bore gas engine for power generation and operates using an open chamber combustion concept with lean mixtures.

Essentially, THC, CO2 and CO emissions decrease with rising hydrogen content of the fuel gas. Even with low concentrations of hydrogen in the fuel gas, significant reductions in THC emissions could be demonstrated. Usually NOX emissions will rise with unchanged operating parameters. However, if excess-air ratio and spark timing are adjusted, a net reduction of NOX emissions can be achieved while the impact on brake thermal efficiency is small.

Furthermore, the paper outlines potential mitigation strategies to expand the operational limits with respect to power density with high hydrogen substitution rates.
Quantification of Losses and Irreversibilities in a Marine Engine for Gas and Diesel Fuelled Operation Using an Exergy Analysis Approach
Authors: Hong Beichuan , Mahendar Senthil Krishnan , Hyvönen Jari , Cronhjort Andreas , Erlandsson Anders Christiansen
Published: December 2020

Large bore marine engines are a major source of fossil fuel consumption in the transport sector. The development of more efficient and cleaner marine engine systems are always required. Exergy analysis is a second-law based approach to indicate the maximum amount of work obtainable from a given system.

In this study, an exergy analysis is used to identify losses and improvement potential of a large bore Wärtsilä 31DF four-stroke marine engine system with two-stage turbocharging. An exergy-based framework is implemented on a calibrated 1D engine model to view the evolution of exergy flow over each engine sub-system while operating on different load points fuelled with natural gas and diesel separately.

The overall distributions of engine energy and exergy are initially compared at a systematic level regarding the impact of fuel mode and operating load. Furthermore, the engine irreversibilities are characterized as three types: combustion, heat dissipation, and gas exchange losses. The first type, combustion irreversibility, is the largest source of engine exergy losses amounting to at least 25% of fuel exergy. A crank resolved analysis showed that premixed gas combustion produces lower exergy losses compared to diesel diffusion combustion. The second type, thermal exergy transferred and destroyed by heat losses, are summarized for the entire engine system. From the exergy view, the charge coolers present an opportunity to recover about 9% of the brake power at full load. The last type, gas exchange losses, are categorized by accounting the flow losses caused by the valve throttling, fluid friction in pipes and the irreversibility of the two-stage turbocharging system. Most of exergy destruction in gas paths occurs at turbocharging system, where the high pressure turbocharger contributes to around 40% of the total flow exergy destruction.
A Multi-Wavelength Extinction Imaging Diagnostic for Quantifying Diesel Spray Mixing at Engine-Relevant Conditions
Authors: Godbold Conner , Poursadegh Farzad , Bibik Oleksandr , Castillo Carlos De La Camara , Genzale Caroline
Published: December 2020

The mixing of fuel and air in the combustion chamber of an IC engine is crucial to emissions formation. Therefore, developing effective diagnostic techniques for measuring mixing is critical for progressing IC engines. Existing methodologies for the optical measurement of air-fuel mixing, including Rayleigh scattering and Laser Induced Fluorescence (LIF), have demonstrated various diagnostic-implementation challenges, high uncertainties under engine-relevant environments, and strong interferences from the liquid spray which prevents their use in near-spray measurements. This work presents the use of an alternative approach based on a laser-absorption/scattering technique called Ultraviolet-Visible Diffuse Back-Illumination (UV-Vis DBI) to quantify local equivalence ratio in a vaporizing diesel spray. Ultraviolet and visible light are generated using a ND:YAG pumped frequency-doubled tunable dye laser operating at 9.9 kHz. The simultaneous UV-Visible illumination is used to back-illuminate a vaporizing diesel spray, and the resulting extinction of each signal is recorded by a pair of high-speed cameras. Using an aromatic tracer (naphthalene, BP = 218 °C) in a base fuel of dodecane (BP = 215–217 °C), the UV illumination (280 nm) is absorbed along the illumination path through the spray, yielding a projected image of line-of-sight optical depth that is proportional to the path-average fuel vapor concentration in the vapor region of the spray. The visible illumination is chosen at a non-absorbing wavelength (560 nm), such that the light extinction is only due to liquid scattering, yielding a projected image of the liquid spray. A key advantage of the method is that the absorption coefficient of the selected tracer is relatively independent of temperature and pressure for 280-nm illumination, reducing measurement uncertainties at engine-relevant conditions. Measurements are also achievable in near-spray vapor regions since there is no mie-scattering interference from the liquid spray. The diagnostic is applied to measure the fuel-air mixing field of a diesel spray produced by a Bosch CRI3-20 ks1.5 single-orifice injector (90 μm diameter) similar to ECN Spray A. Measurements are conducted in a non-reacting high-pressure and temperature nitrogen environment using a constant-flow, optically-accessible spray chamber operating at 60 bar and 900 K. The results are evaluated against existing ECN mixing measurements based on Rayleigh scattering. The diagnostic yields centerline and radial mixture fraction measurements that match the ECN Rayleigh measurements within uncertainty bounds.
Controlled End Gas Auto Ignition With Exhaust Gas Recirculation on a Stoichiometric, Spark Ignited, Natural Gas Engine
Authors: Bayliff Scott , Windom Bret , Marchese Anthony , Hampson Greg , Carlson Jeffrey , Chiera Domenico , Olsen Daniel
Published: December 2020

The goal of this study is to address fundamental limitations to achieving diesel-like efficiencies in heavy duty on-highway natural gas (NG) engines. Engine knock and misfire are barriers to pathways leading to higher efficiency engines. This study explores enabling technologies for development of high efficiency stoichiometric, spark ignited, natural gas engines. These include design strategies for fast and stable combustion and higher dilution tolerance. Additionally, advanced control methodologies are implemented to maintain stable operation between knock and misfire limits. To implement controlled end-gas autoignition (C-EGAI) strategies a Combustion Intensity Metric (CIM) is used for ignition control with the use of a Woodward large engine control module (LECM).

Tests were conducted using a single cylinder, variable compression ratio, cooperative fuel research (CFR) engine with baseline conditions of 900 RPM, engine load of 800 kPa indicated mean effective pressure (IMEP), and stoichiometric air/fuel ratio. Exhaust gas recirculation (EGR) tests were performed using a custom EGR system that simulates a high pressure EGR loop and can provide a range of EGR rates from 0 to 40%. The experimental measurements included the variance of EGR rate, compression ratio, engine speed, IMEP, and CIM. These five variables were optimized through a Modified BoxBenken design Surface Response Method (RSM), with brake efficiency as the merit function.

A positive linear correlation between CIM and f-EGAI was identified. Consequently, CIM was used as the feedback control parameter for C-EGAI. As such, implementation of C-EGAI effectively allowed for the utilization of high EGR rates and CRs, controlling combustion between a narrower gap between knock and lean limits. The change from fixed to parametric ignition timing with CIM targeted select values of f-EGAI with an average coefficient of variance (COV) of peak pressure of 5.4. The RSM efficiency optimization concluded with operational conditions of 1080 RPM, 1150 kPa IMEP, 10.55:1 compression ratio, and 17.8% EGR rate with a brake efficiency of 21.3%. At this optimized point of peak performance, a f-EGAI for C-EGAI was observed at 34.1% heat release due to auto ignition, a knock onset crank angle value of 10.3° aTDC and ignition timing of −24.7° aTDC. This work has demonstrated that combustion at a fixed f-EGAI can be maintained through advanced ignition control of CIM without experiencing heavy knocking events.
An Investigation Into OME3 on a High Compression Ratio Engine
Authors: LeBlanc Simon , Sandhu Navjot , Yu Xiao , Han Xiaoye , Wang Meiping , Tjong Jimi , Zheng Ming
Published: December 2020

For decades, alternative fuels have been studied to further engine efficiency and lower combustion emissions. Of these fuels, biodiesel, alcohols, and ethers have shown advantageous benefits of improved mixing capability or reduced combustion emissions. Ether fuels consist of a range of C-O-C chain lengths that offer various noteworthy fuel properties such as fuel oxygen content and cetane number. In this work, oxymethylene dimethyl ether (OME3) and diesel are used as neat and blended fuels on a single-cylinder high compression ratio engine. Four test fuels are investigated in this work; baseline diesel, two diesel/OME3 blends, and neat OME3 fuel. Engine tests are conducted at an engine load of 6 bar and the intake oxygen concentration is modulated via EGR to realize the resulting engine performance, stability, and exhaust emissions among the test fuels. The results show that blending OME3 fuels with diesel is an effective technique to reduce soot emissions with minimal effect on NOx emissions. Moreover, neat OME3 was capable of emitting low NOx and soot emissions with a lower EGR amount than that of diesel-blends, mitigating negative combustion implication of EGR at high levels.
Comparison Between a Center-Mounted and a Side-Mounted Injector for Gasoline Applications: A Computational Study
Authors: Nocivelli Lorenzo , Zhang Anqi , Sforzo Brandon A. , Tekawade Aniket , Voice Alexander K. , Tang Meng , Powell Christopher F. , Som Sibendu , Pei Yuanjiang , Levy Robert S.
Published: December 2020

The differences between a center-mounted and a side-mounted injector for gasoline direct injection (GDI) applications are analyzed through computational fluid dynamics (CFD). The Engine Combustion Network’s (ECN) axisymmetric 8-hole Spray G injector is compared to a 6-hole injector designed to be side-mounted in an engine. Nozzle-flow simulations are carried out with the commercial CFD software CONVERGE, injecting Euro 5 certification gasoline into a constant volume chamber. Low-load operating conditions are targeted, setting the injection pressure at 50 bar and the ambient pressure to be representative of very early pilot injections. The phase change is handled with the Homogeneous Relaxation Model (HRM), which is assessed and adapted to gasoline flash-boiling conditions. The simulation domains are generated leveraging real injector internal geometries obtained by micron-resolution X-ray tomographic measurements, which introduce manufacturing tolerances and surface roughness in the computational study. Steady needle lift conditions are analyzed. The near-field fuel density distributions and plume morphologies are evaluated, validated and compared to X-ray radiography measurements. A computational best practice is defined and single plume characteristics and variability trends are highlighted as functions of the geometry of the orifices. The plume-plume interaction dynamics are identified and assessed, underlining differences from center- to side-mounted injectors at strong flashing conditions. The obtained numerical framework allows the identification of near-nozzle injection characteristics such as single plume direction, cone angle, spray initial velocity and spatial fuel density distribution. The presented results represent a unique dataset for the initialization of more-affordable Lagrangian spray models, which differentiate the behavior of side-mounted and center-mounted injectors.
Homogeneous Ignition Delay, Flame Propagation Rate and End-Gas Autoignition Fraction Measurements of Natural Gas and Exhaust Gas Recirculation Blends in a Rapid Compression Machine
Authors: Mohr Jeffrey , Windom Bret , Olsen Daniel B. , Marchese Anthony J.
Published: December 2020

To evaluate the effect of exhaust gas recirculation (EGR) and variable fuel reactivity on knock and misfire in spark ignited national gas engines, experiments were conducted in a rapid compression machine to measure homogeneous ignition delay, flame propagation rate, and end-gas autoignition fraction for stoichiometric natural gas/oxidizer/EGR blends. Natural gas with a range of chemical reactivity was simulated using mixtures of CH4, C2H6, and C3H8. Reactive exhaust gas recirculation (R-EGR) gases were simulated with mixtures of Ar, CO2, CO, and NO and non-reactive exhaust gas recirculation gases (NR-EGR) were simulated with mixtures of AR and CO2. Homogeneous ignition delay period, flame propagation rate and end-gas autoignition fraction were measured at compressed pressures and temperatures of 30.2 to 34.0 bar and 667 to 980 K, respectively. Flame propagation rate decreased with both R-EGR and NR-EGR substitution. The substitution of R-EGR increased the end-gas autoignition fraction, whereas NR-EGR substitution decreased the end-gas autoignition fraction. The results indicate that the presence of the reactive species NO in the R-EGR has a strong impact on end-gas autoignition fraction. An 82-species reduced chemical kinetic mechanism was also developed that reproduces measured homogeneous ignition delay period with a total average relative error of 11.0%.