bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of mobile technology usage on cognitive, affective, and behavioural learning outcomes in primary and secondary education: A systematic review with meta‐analysis
Authors: Wang Jingxian , Tigelaar Dineke E. H. , Zhou Tian , Admiraal Wilfried
Published: November 2022

Background

The impact of mobile technology usage on student learning in various educational stages has been the subject of ongoing empirical and review research. The most recent meta‐analyses on various types of mobile technology use for potential benefits of learning covered the empirical studies up to about nine years ago. Since then, the use of mobile technology in primary and secondary education has increased tremendously, and numerous empirical studies have been conducted on this topic, but their conclusions were inconsistent.

Objectives

The purpose of this systematic review is to re‐examine this issue by meta‐analyzing the empirical research studies from the last nine years, with a focus on cognitive, affective, and behavioral learning outcomes in primary and secondary education, and to examine the potential moderators that may have contributed to the heterogeneity across findings.

Methods

Based on our inclusion and exclusion criteria, we found 85 studies of 78 peer‐reviewed papers (N = 9157) from electronic databases and major journals in educational technology and mobile learning between 2014 and 2022. We then examined 15 moderators that were expected to affect student learning outcomes.

Results and Conclusions

Compared with traditional technology and non‐technology groups, using mobile technology produced medium positive and statistically significant effects on primary and secondary students' learning, in terms of cognitive (g = 0.498, 95% CI [0.382, 0.614]), affective (g = 0.449, 95% CI [0.301, 0.598]) and behavioural (g = 0.339, 95% CI [0.051, 0.627]) learning outcomes. Further moderator analyses revealed that student factors (i.e., community type, students’ socioeconomic status), learning process (i.e., hardware used, student‐to‐hardware ratio, teaching method) and study quality (i.e., learning topic/content equivalence, degree of technology use in the control group) were among the variables that moderated the summary effect sizes for at least one learning outcome dimension significantly. The findings and their implications for researchers, policymakers and practitioners are discussed.
Systematic review and network meta‐analysis of different types of emollient for the prevention of atopic dermatitis in infants
Authors: Liang Junqin , Hu Fengxia , Tang Hongbo , Jiang Fanhe , Sang Yingbing , Hong Yongzhen , Wang Qian , Nuer Kalibi , Kang Xiaojing
Published: November 2022

Prophylactic application of emollients has been an effective strategy against infant atopic dermatitis (AD); however, the difference of different emollients is unknown. We performed this network meta‐analysis to compare different emollients in preventing infant AD. A systematic search was performed in PubMed, EMBASE and Cochrane library to identify relevant studies from their inception through 28 February, 2022. We evaluated the quality of eligible studies using the Cochrane risk of bias assessment tool. Data analysis was performed using STATA 14.0. Eleven studies were included for data analysis. Direct meta‐analysis suggested that early application of emollients effectively prevented AD development in high‐risk infants (risk ratio [RR], 0.64; 95% confidence interval [CI], 0.47 to 0.88). Network meta‐analysis suggested that emollient emulsion might the better option for preventing infant AD development, with a surface under the cumulative ranking curve (SUCRA) of 82.6% for all populations, 78.0% for high‐risk populations and 79.2% for populations with food sensitization. Moreover, subjects receiving emollients more frequently experienced adverse events. Overall, early application of emollients is an effective strategy for preventing AD development in high‐risk infants and emollient emulsion may be the optimal type. Future study with well‐designed and large scale are warranted to validate our findings.
Mapping access to care and identification of barriers for traumatic brain injury in a South African township
Authors: Owolabi Eyitayo O. , Nyamathe Samukelisiwe , Joseph Conran , Khuabi Lee‐Ann Jacobs‐Nzuzi , English Rene G. , Vlok Adriaan , Erasmus Elaine , Geduld Heike I. , Lategan Hendrick J. , Chu Kathryn M.
Published: November 2022

Rationale

South Africa has a high traumatic injury burden resulting in a significant number of persons suffering from traumatic brain injury (TBI). TBI is a time‐sensitive condition requiring a responsive and organized health system to minimize morbidity and mortality. This study outlined the barriers to accessing TBI care in a South African township.

Methods

This was a multimethod study. A facility survey was carried out on health facilities offering trauma care in Khayelitsha township, Cape Town, South Africa. Perceived barriers to accessing TBI care were explored using qualitative interviews and focus group discussions. The four‐delay framework that describes delays in four phases was used: seeking, reaching, receiving, and remaining in care. We purposively recruited individuals with a history of TBI (n = 6) and 15 healthcare professionals working with persons with TBI (seven individuals representing each of the five facilities, the heads of neurosurgery and emergency medical services and eight additional healthcare providers who participated in the focus group discussions). Quantitative data were analysed descriptively while qualitative data were analysed thematically, following inductive and deductive approaches.

Findings

Five healthcare facilities (three community health centres, one district hospital and one tertiary hospital) were surveyed. We conducted 13 individual interviews (six with persons with TBI history, seven with healthcare providers from each of the five facilities, neurosurgery department and emergency medical service heads and two focus group discussions involving eight additional healthcare providers. Participants mentioned that alcohol abuse and high neighbourhood crime could lead to delays in seeking and reaching care. The most significant barriers reported were related to receiving definitive care, mostly due to a lack of diagnostic imaging at community health centres and the district hospital, delays in interfacility transfers due to ambulance delays and human and infrastructural limitations. A barrier to remaining in care was the lack of clear communication between persons with TBI and health facilities regarding follow‐up care.

Conclusion

Our study revealed that various individual‐level, community and health system factors impacted TBI care. Efforts to improve TBI care and reduce injury‐related morbidity and mortality must put in place more community‐level security measures, institute alcohol regulatory policies, improve access to diagnostics and invest in hospital infrastructures.
Oligodendrocyte lineage cells: Advances in development, disease, and heterogeneity
Authors: Wang Jia‐Qi , Gao Meng‐Yuan , Gao Rui , Zhao Ke‐Han , Zhang Yuan , Li Xing
Published: November 2022

Oligodendrocyte progenitor cells (OPCs) originate in the ventricular zone (VZ) of the brain and spinal cord, and their primary function is to differentiate into oligodendrocytes (OLs). Studies have shown that OPCs and OLs are pathologically and physiologically heterogeneous. Previous transcriptome analyses used Bulk RNA‐seq, which compares average gene expression in cells and does not allow for heterogeneity. In recent years, the development of single‐cell sequencing (scRNA‐seq) and single‐cell nuclear sequencing (snRNA‐seq) has allowed us to study an individual cell. In this review, sc/snRNA‐seq was used to study the different subpopulations of OL lineage cells, their developmental trajectories, and their applications in related diseases. These techniques can distinguish different subpopulations of cells, and identify differentially expressed genes in particular cell types under certain conditions, such as treatment or disease. It is of great significance to the study of the occurrence, prevention, and treatment of various diseases.

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Milk fatty acids as covariates in multiple regression analysis is a robust approach to model the decrease in milk fat concentration and yield in small ruminants
Authors: Padilha Charline G. , Ribeiro Claudio V. D. M. , Oliveira Dimas E.
Published: November 2022

Milk fat depression (MFD) syndrome has been associated with the antilipogenic effects of trans‐10 fatty acids (FA), such as t10, c12‐CLA (CLA) and t10‐18:1 (T10). However, these FA alone cannot completely explain the changes in milk fat in small ruminants. Thus, the aim of this study was to use multiple regression analysis to evaluate other FA that may be related to shifts in milk fat, as well as to improve model accuracy when different milk FA are used as covariates in the models. Previously published data were used in multiple regression analysis for goats (n = 106) and ewes (n = 68). Body weight (BW), vaccenic acid (t11‐18:1), both trans‐10 FA and the major milk FA were tested as covariates to model four response variables associated with MFD: fat concentration (FC), percentage change in milk fat concentration (CFC; %), fat yield (FY; g/d) and percentage change in milk fat yield (CFY; %). All four multiple regression models were significant for both species. When compared with simple regression models, all multiple regression models improved accuracy when estimating MFD. The improvements in model accuracy (lower RMSE) for FC, CFC, FY and CFY were 60.6%, 43.3%, 35.6% and 44.4% for ewes, and 52.1%, 60.1%, 33.6% and 14.9% for goats respectively. Linolenic acid and t11‐18:1 were covariates in all models for goats, and palmitic acid and CLA were covariates in all ewe models. These FA should be investigated regarding their direct effect on gene expression associated with milk fat metabolism in the mammary gland of small ruminants. Multiple regression analysis is the most robust approach to account for the variation of milk fat and yield in goats and ewes.
Probing dual harm and non‐violent misconduct among imprisoned adult men in Northern Ireland
Authors: Butler Michelle , Kelly Dominic , McNamee Catherine B.
Published: November 2022

Purpose

This study examines the prevalence of dual harm (i.e. self‐harm and violence) among imprisoned adult men in Northern Ireland, the relationship between dual harm and non‐violent misconduct, while controlling for other known risk factors for misconduct, as well as how those who engage in dual harm may differ from other groups.

Methods

Using the administrative records of 892 adult men, descriptive statistics assessed the prevalence of dual harm. A negative binominal regression followed by predicted margins examined the relationship between dual harm and non‐violent misconduct accounting for controls. Additionally, a multinomial logistic regression was utilised to identify if those engaged in dual harm differed from others in terms of their characteristics and in‐prison experiences.

Results

The findings indicate that 1‐in‐5 adult men were engaged in dual harm, with these men accounting for 72% of all non‐violent misconduct incidents examined. Dual harm was significantly related to an increased involvement in non‐violent misconduct compared to other harm histories (self‐harm only, violence only, or no harm) even when other known risk factors were considered. Those engaged in dual harm were also discovered to possess a number of characteristics that differ significantly from other groups.

Conclusion

These findings strengthen emerging research indicating those who engage in dual harm are a distinct group that can be challenging to manage due to their increased involvement in misconduct and their multiple needs, which existing services and supports may be ill suited to address.
Research progress of odontogenic extracellular vesicles in regeneration of dental pulp
Authors: Li Yanan , Liu Chaoran , Han Guanghong
Published: November 2022

It is well understood that maintaining viable pulp is critical for tooth retention. This review focused on cell‐free therapy based on extracellular vesicles (EVs), a novel minimally invasive treatment strategy for endodontic restoration. This study was conducted by searching mainstream electronic databases such as Web of Science and PubMed for relevant studies on the therapeutic role of odontogenic EVs in pulp healing published in the last five years. We selected 89 relevant articles and discovered that dental stem cells (DSCs) derived EVs (DSC‐EVs) have become a research hotspot in oral regenerative medicine, with significant advantages over cell transplantation in terms of low immunogenicity, ease of isolation, preservation, and management. Here, we introduce in detail the therapeutic effects of DSC‐EVs for pulp restoration from three perspectives: excellent odontogenic properties, clinical applications, and possible molecular mechanisms. This article contributes a new viewpoint to the field of regenerative endodontics.
Developmental trajectories at a high risk for childhood overweight/obesity
Authors: Yoshinaga Masao , Takahashi Hideto , Ito Yoshiya , Aoki Machiko , Miyazaki Ayumi , Kubo Toshihide , Shinomiya Masaki , Horigome Hitoshi , Tokuda Masakuni , Lin Lisheng , Ogata Hiromitsu , Nagashima Masami
Published: November 2022

Background

The associations between developmental patterns (trajectories) in children and maternal factors have been widely investigated, but paternal effects on these trajectories are unclear. This study aimed to determine child and parental factors involved in developmental trajectories at high risk for causing adverse cardiovascular (CV) profiles in children.

Methods

We analyzed longitudinal anthropometric data from birth to the present and CV profiles of 1,832 healthy volunteers (51% girls) aged 3–15 years who participated in a nationwide study between July 2012 and January 2014. Six trajectory latent class growth models were developed using body mass index z‐ scores. Predictors for being in developmental trajectories at high risk for causing adverse CV profiles were determined by multivariate regression analysis.

Results

The mean±standard deviation number of anthropometric data points was 12±3 for both boys and girls. Among the six trajectories, the infantile onset and continual increase groups had significantly worse levels of many CV profiles than those in the remaining groups. Paternal overweight/obesity was an independent predictor for boys being in the infantile onset group and for girls being in the continual increase group. Additionally, maternal pre‐pregnancy overweight/obesity in boys and maternal excessive gestational weight gain in girls were independent predictors for being in the infantile onset group. Having no sibling in boys and an older maternal age were independent predictors for being in the continual increase group.

Conclusions

Interventions to prevent childhood obesity should include strategies that focus on fathers and mothers as well as those that focus on children with certain types of familial background.
Internal but not external locus of control predicts acute stress response
Authors: Zhan Lei , Lin Li , Wang Xiaoyu , Zhang Jingyu , Zhang Liang
Published: November 2022

Fluctuation patterns of physiological response after acute stress might indicate one's coping potential with stress, yet this relationship has not been widely examined. The present study investigated how Locus of Control (LOC) can influence cortisol and HR responses in an uncontrollable stressful situation. Seventy‐three participants were exposed to acute stress through the Trier Social Stress Test (TSST) after finishing the LOC measures. Multilevel regression results suggested that a curvilinear function best captured the shape of the cortisol trajectories which was further moderated by the level of internal LOC. Moreover, higher internality was associated with greater cortisol reactivity and faster recovery. Our study reveals the link between internal control and endocrine stress response. Finally, cortisol upregulation was discussed, as well as the internality‐related accelerated recovery of cortisol, which may be involved in the effect of motivation arousal for better adaptation.
Multinational production and intra‐firm trade
Authors: Alviarez Vanessa , Saad Ayhab F.
Published: November 2022

Intra‐firm trade, from parents to affiliates, has been combined with standard models of multinational production (MP) to deliver gravity‐style predictions for foreign affiliates sales. Nonetheless, the evidence shows that intra‐firm trade is concentrated among a small set of large multinational firms. Using firm level data from 35 countries, we document that only firms belonging to multinational corporations (MNCs) in the upper tail of the firm's size distribution are significantly affected by the distance to their parents. We present a simple framework featuring MNCs selection into intra‐firm trade and derive the analytical gravity equations that are consistent with the empirical findings.
Bayesian Spatio-Temporal Modeling for the Inpatient Hospital Costs of Alcohol-Related Disorders
Authors: Yu Zhen , Yu Keming , Härdle Wolfgang K. , Zhang Xueliang , Wang Kai , Tian Maozai
Published: November 2022

Understanding how health care costs vary across different demographics and health conditions is essential to developing policies for health care cost reduction. It may not be optimal to apply the conventional mean regression due to its sensitivity to the high level of skewness and spatio-temporal heterogeneity presented in the cost data. To find an alternative method for spatio-temporal analysis with robustness and high estimation efficiency, we combine information across multiple quantiles and propose a Bayesian spatio-temporal weighted composite quantile regression (ST-WCQR) model. An easy-to-implement Gibbs sampling algorithm is provided based on the asymmetric Laplace mixture representation of the error term. Extensive simulation studies show that ST-WCQR outperforms existing methods for skewed error distributions. We apply ST-WCQR to investigate how patients’ characteristics affected the inpatient hospital costs for alcohol-related disorders and identify areas that could be targeted for cost reduction in New York State from 2015 to 2017.
Physical, chemical and microbiological soil attributes influence soil greenhouse gases fluxes in Atlantic Forest and pine (Pinus taeda) plantations in Brazil
Authors: Tulio Rafael Hennel , Rachwal Marcos Fernando Glück , Zanatta Josiléia Acordi , da Silva Krisle , Kaschuk Glaciela
Published: November 2022

Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro‐organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m2 in native forests of the Atlantic Forest biome and in loblolly pine (Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO2, N2O and CH4. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water‐filled pore space (WFPS), microbial biomass carbon (MB‐C), basal respiration (BR), microbial (qMic) and metabolic (qCO2) quotient and activities of soil urease and β‐glucosidase enzymes. The seasons influenced the CO2 and N2O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH4 than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB‐C, 67% higher urease activity and 30% higher β‐glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH4 consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH4 consumption, and to reduce GHGs emissions in forest ecosystems.
Identity Cards, Semiotic Instability, and Signs of State Recognition for Indonesian Warias
Authors: HEGARTY BENJAMIN
Published: November 2022

Following the authoritarian New Order in Indonesia (1965–1998) the state‐issued identity card was transformed into a symbol available for reproduction by ordinary citizens. One Indonesian transgender population known as warias used the card to engage with the terms of recognition offered by the state. In 2014, warias in Yogyakarta made organizational membership cards that closely mimicked but did not copy the visual form of the original. Warias efforts to expand the state's bureaucratic form through the manipulation of the symbolic and material qualities of cards raised the possibility that the state did not hold a monopoly over powers of recognition.
Comparing attitudes toward Caribbean, British, and American accents in Trinidad and Tobago, the United Kingdom, and the United States
Authors: Hänsel Eva Canan , Meer Philipp
Published: November 2022

This article compares the attitudes of respondents from Trinidad and Tobago, the United Kingdom, and the United States toward speakers from these countries and from Grenada. Analyses of mean values on the attitude dimensions of status and solidarity reveal striking similarities between the rankings of the stimuli by the three respondent groups, especially regarding the British and American stimuli and a Creole‐influenced Grenadian stimulus. Only the rankings by the Trinbagonian respondents differ slightly regarding the Caribbean stimuli. The results suggest that similar stereotypes might have influenced the evaluations of the British, American, and Creole‐influenced Grenadian speakers across all respondent groups, while the rankings by the Trinbagonian respondents might reflect the social connotations of the fine‐grained nuances of Caribbean (standardized) accents.
Seroprevalence and genetic characterization of Toxoplasma gondii in domestic pigs intended for human consumption in Cuba
Authors: Castillo‐Cuenca Julio César , Almería Sonia , Calero‐Bernal Rafael , Fernández‐Escobar Mercedes , Fraga Jorge , Entrena‐García Angel , Arias Pedro Casanova , Martínez‐Moreno Álvaro , García‐Bocanegra Ignacio
Published: November 2022

Domestic pigs are considered as one of the main intermediate hosts in the zoonotic transmission of Toxoplasma gondii in many countries. Serological and molecular studies are warranted to better understand the epidemiology and transmission patterns of this parasite worldwide. To date, seroepidemiological information on T. gondii in domestic pigs in Cuba is very scarce and there are no reports of T. gondii genotypes circulating in this country. Here, we aimed to estimate the seroprevalence of T. gondii and provide genetic characterization of the strains circulating in slaughtered pigs intended for human consumption in Central Cuba. Seroprevalence was determined in 450 serum samples from slaughtered pigs in Villa Clara province using ELISA. Anti‐Toxoplasma gondii IgG antibodies were detected in 100 animals (22.2%, 95% CI: 18.5–26.2). Conventional PCR of the 529‐bp marker of T. gondii was performed in hearts and diaphragm tissues of all ELISA‐seropositive pigs. Toxoplasma gondii DNA was detected in four animals. Further genetic characterization of the positive DNA samples was performed by multilocus PCR‐RFLP and PCR‐sequencing typing tools. Molecular analysis revealed four different genetic profiles that were combinations of type I, II, III and u‐1 alleles, suggesting the circulation of non‐clonal genotypes of T. gondii in domestic pigs in Cuba. Our results indicate that T. gondii is widely distributed in slaughtered pigs in this country, which might have important implications for public health. To the best of our knowledge, this is the first report on genetic characterization of T. gondii in Cuba. Although preliminary, the results suggest a high genetic diversity of T. gondii in the study region. Further studies based on parasite isolation are needed to definitively identify the genotypes circulating and characterize the virulence of strains detected in pigs in Cuba, and to assess the risk of zoonotic transmission from pork products in this country.
Spatial and Temporal Mapping of Articular Cartilage Poro-Viscoelastic Material Properties Using Indentation
Authors: Valluru Pranay Kumar Reddy , Su Alison , Mehta Shikhar , Bajpayee Ambika , Shefelbine Sandra
Published: November 2022

Biphasic poro-viscoelastic constitutive material model (BPVE) captures both the fluid flow dependent and independent behavior of cartilage under stress relaxation type indentation. A finite element model based on BPVE formulation was developed to explore the sensitivity of the model to Young's modulus, Poisson's ratio, permeability, and viscoelastic constitutive parameters expressed in terms of Prony series coefficients. Then we fit the numerical model to experimental force versus time curves from stress relaxation indents on bovine tibial plateaus to extract the material properties. Measurements were made over the period of two days to capture the material property changes that resulted from trypsin-induced degradation. We measured spatial and temporal changes in mechanical properties in the cartilage. The areas of degradation were characterized by an increase in both permeability and summation of Prony series shear relaxation amplitude constants. These findings suggest that cartilage degradation reduces the intrinsic viscoelastic properties of the solid phase of the tissue in addition to impairing its capacity to offer frictional drag to the interstitial fluid flow (permeability). The changes in material properties are measurable well before structural degradation occurs.
Direct Injection Strategy to Extend the Lean Limit of a Passive Pre-Chamber
Authors: Almatrafi Fahad , Uddeen Kalim , Ben Houidi Moez , Cenker Emre , Turner James
Published: November 2022

Lean operation increases the efficiency of the Otto-cycle internal combustion engine and decreases its emissions. However, increasing the air-fuel ratio beyond stoichiometry requires higher ignition energy to maintain the stable operation of the engine. The pre-chamber emerges as one of the promising enablers of lean operation, providing much larger energy into the main combustion chamber than simple a spark plug at multiple sites to increase combustion stability. Pre-chambers are classified into two categories based on their fuel input; active pre-chambers, with a dedicated fuel injection system, and passive pre-chambers, which are solely charged with the main chamber air-fuel mixture through nozzle holes. Therefore, the passive pre-chamber type is favorable for existing engines because of its compact design and limited modification requirements. Nevertheless, passive pre-chambers have issues with igniting very lean mixtures. In this study, a single-cylinder light-duty engine is used to study the possibility of extending the lean limit of the passive pre-chamber using a split direct injection (DI) strategy and indirect enrichment of the pre-chamber mixture. The results of the split injection method were then compared to port fuel injection (PFI) measurements. Also, another set of experiments was performed with a standard spark plug using PFI and split DI for comparison. The results showed an increase in the lean limit of passive pre-chamber operation when using the split DI strategy compared to PFI, from λ = 1.5 to 1.7. However, increased soot production was observed when using the split injection strategy.
A Design Approach of a Dedicated EGR-System for a Naturally Aspirated Gas Engine - From 1D Engine Process Simulation and Design of Experiments Up to the Experimental Validation
Authors: Beltaifa Youssef , Kettner Maurice , Eilts Peter , Ruchel Bosse
Published: November 2022

This work presents a systematic approach proceeding from the engine process simulation (1D-CFD) and design of experiments (DoE) up to the experimental validation to build a dedicated exhaust-gas recirculation (EGR) system for a stationary four-cylinder naturally aspirated gas engine. This system should ensure an equal distribution of the recirculated exhaust gas, coming entirely from the rich-operated dedicated cylinder. The rich combustion enables an in-cylinder production of highly reactive species (mainly H2 and CO), resulting in increased EGR reactivity, which improves the dilution tolerance, leading to reduced wall heat losses and lower knock tendency in the EGR receiving cylinders.

However, the EGR system design represents a challenge due to the pulsating exhaust gas flow from the dedicated cylinder, which leads to a considerable EGR maldistribution in the receiving cylinders. A numerical analysis of this effect demonstrated, that the EGR distribution uniformity depends on the design and dimensions of the EGR path. Considering the numerous design parameters and taking into account that the optimum design of the EGR path is not necessarily the sum of optima from the one-factor-at-a-time variations, efficient DoE methodologies were applied. They enabled identifying the optimum set of the EGR path design-parameters, with an EGR rate maldistribution of about 1%-points.

To evaluate the quality of the numerical results, the dedicated EGR path with the optimum parameters set was built on the engine test bench. The experimental results confirm the simulative prediction accuracy, demonstrating the reliability of the pursued approach.
Study of Injector Geometry and Parcel Injection Location on Spray Simulation of the ECN Spray G Injector
Authors: Kumar Aman , Van Dam Noah
Published: November 2022

Parcel-based simulations are the most common method to simulate fuel sprays, especially for reacting conditions, due to their lower computational cost compared to more highly resolved simulations. It is important, however, to understand how spray boundary conditions used to initialize the parcels that represent the atomizing fluid affect downstream conditions and overall simulation performance. Traditionally, when parcel simulations are used, the injector tip geometry is either significantly simplified or removed altogether due to resolution limits. Recent advances in computational power and numerical methods, however, have made it possible to resolve flow through these features. Previous work has shown some potential effects of even simple injector tip geometries, and this study investigates the effect of very detailed nozzle geometries on parcel-based simulations that have typically ignored these details. Four different parameters were investigated: whether a simulation includes a detailed injector tip geometry, or a flat surface; whether parcels are initialized at the counterbore exit, which is more common, or at the nozzle exit; the use of an experimentally-derived rate of injection or one-way coupling with a separate internal nozzle VOF simulation; the use of nominal or measured injector geometry. Simulations were compared using both global penetration as well as local data near the injector. Spray penetration and other global measures showed limited sensitivity to boundary conditions/initialization procedure, but local data such as the local liquid volume fraction showed greater variation between the conditions, which may have an impact on mixing and combustion predictions in engine applications.
Aerosol Separation and Pressure Control of a Smart Crankcase Ventilation System
Authors: Nowak Niclas , Sirtl Christian , Rymann Othmar , Flynn Paul , Stieler Christian , Heller Marc-Tran
Published: November 2022

Crankcase ventilation systems are coming into new focus due to safety concerns associated with alternative fuels such as ammonia and hydrogen. In addition, innovation is being driven by increasingly stringent legislation that plays an important role in limiting crankcase emissions. This study characterizes aerosol separation and pressure control of a modern crankcase ventilation system, which is referred to as “smart” due to enabling monitoring, diagnostics, and predictive maintenance. Experiments were conducted on custom-built and commercial test rigs that mimic the physical conditions to which crankcase ventilation systems are subjected. The main findings were that the pressure drop of the filter media followed the profile described by the “jump-and-channel model”, also indicating the presence of an oil film. However, such an oil film was not detected on the full-size element, which had a positive effect on the pressure drop. Excellent separation efficiencies around 99.9% were achieved for all flow rates and filter conditions. In addition, re-entrainment of oil was not detected. The electronic pressure regulator (EPR) was found to accurately (± 1 mbar) adjust the crankcase pressure to the required level. Moreover, the fully open EPR featured a low differential pressure of about 1 mbar, which effectively reduces crankcase peak pressure during engine startup. These features exceed those of conventional pressure control valves. In addition, only the electronic regulator enables “smart” features.
A CFD Study on Mixture Preparation and Combustion in a Heavy-Duty Locomotive Diesel Engine at High Load Condition
Authors: Addepalli Srinivasa Krishna , Magnotti Gina M. , Som Sibendu , Sheth Pushkar , Jayakar Vijayaselvan , Klingbeil Adam , Lavertu Thomas
Published: November 2022

Diesel engines are one of the most commonly used combustion systems for heavy-duty applications like locomotives. Although computational fluid dynamics (CFD) modeling of diesel engines is a mature research topic, CFD modeling of large-bore engines like those used in locomotives has not been as extensively studied as their smaller bore on-road and stationary counterparts. The present paper aims at identifying and outlining best practices for performing 3D CFD simulations of locomotive diesel engines and comparing them with the established best practices for heavy-duty diesel engines in the literature. The locomotive diesel engine considered in this study has a bore of 168mm and operates at speeds of up to 1800 rpm. Open cycle engine CFD simulations were carried out for both motored and fired cases. Two turbulence models viz., Re-Normalization group (RNG) k-ε model and Reynolds stress model (RSM) were used in this study to assess their performance. The fuel spray break up was modelled using Kelvin Helmholtz and Rayleigh Taylor (KH-RT) model. A grid and statistical convergence study was performed to assess the effect of mesh size on the predicted results. It was found that a minimum cell size of 0.25 mm near the fuel spray and 1 mm in the rest of the cylinder was sufficient to achieve grid convergence in terms of spray and combustion characteristics. The boundary wall temperatures are shown to affect the in-cylinder pressure predictions. Higher wall temperatures were found to reduce the trapped mass and increase the peak motored pressure. The CFD model was validated by comparing the simulation results with the experimental measurements at full rated power. It was found that the RSM was able to capture the combustion characteristics more accurately compared to RNG k-ε model. Overall, the CFD model was able to predict the engine combustion and performance characteristics at three injection timings.
Effect of Ethanol Addition on the Laminar Burning Velocity of Gasoline Surrogates With Toluene
Authors: Shankar Varun , Fang XiaoHang , Hinton Nathan , Davy Martin , Leach Felix
Published: November 2022

Laminar burning velocity (LBV) is a crucial parameter in many practical combustion simulations, and the acquisition of LBVs is a critical step for evaluating potential alternative fuels and/or suitable surrogates. Ethanol is regarded as one of the most promising alternative fuels, particularly for spark ignition engines, as it may be produced from renewable biomass. While there exists data showing the pressure dependence on ethanol’s LBV compared to iso-octane and n-heptane (primary reference fuels (PRFs)), the relative magnitude of the pressure dependence of LBV between ethanol and toluene has not been established. The inclusion of toluene is important because commercial gasoline has significant levels of aromatics. In this work, common gasoline surrogate components of iso-octane, n-heptane, toluene, and ethanol were studied as pure compounds and in equal volume binary, ternary, and quaternary mixtures. Experiments are conducted in a spherical combustion bomb at elevated temperatures (380 K and 450 K) and pressures (1 to 4 bar). Under these conditions, ethanol and n-heptane present faster LBVs than iso-octane and toluene, particularly at 450 K. Ethanol and iso-octane present strong pressure dependence, with this effect accentuated at higher temperature conditions. As equal volume mixtures were studied, the effect of these distinct behaviours was examined in comparison to chemical kinetic predictions and widely used mixing rules.
A Computational Assessment of Combustion Submodels for Predictive Simulations of Pre-Chamber Combustion Engines
Authors: Silva Mickael , Liu Xinlei , Hlaing Ponnya , Cenker Emre , Turner James , Im Hong G.
Published: November 2022

Pre-chamber combustion (PCC) modeling has been progressing in recent years, while there are lingering questions on fundamental modeling aspects, whether a flame-based or an ignition-based model predicts the combustion with higher fidelity. This mode of ignition concept is known to enable a stable engine operation at ultralean conditions with a short combustion duration, thus enhancing engine efficiency. The current work utilizes computational fluid dynamics to assess well-known combustion models: multi-zone well-stirred reactor (MZ-WSR) and G-Equation. The former models combustion as an ignition-based phenomenon while the latter as a flame propagation type of combustion. A pre-chamber containing twelve nozzles divided into two layers on a narrow throat was chosen. The jets from the two layers of nozzles and the local thermodynamic conditions differ substantially, which makes it a suitable configuration for assessing the predictive capabilities of distinct combustion models. The fuel utilized was methane and the global air-fuel ratio (λ) was varied, ranging from global-λ of 1.6, 1.8, and 2.0, and the total fuel injected through the pre-chamber was varied for one of the cases (3%, 7%, and 13%). The results suggest that both combustion models can potentially match experimental engine performance data upon appropriate calibration; however, fundamental differences in jet topology arise since the G-Equation formulation accounts for turbulence-chemistry interaction, while MZ-WSR does not.
Experimental Investigation of Gasoline Direct Injection (GDI) Sprays Using Diffused Back Illumination (DBI) and Structured Laser Illumination Planar Imaging (SLIPI) Techniques
Authors: Gaur Anurag , Ailaboina Akhil , Saha Kaushik
Published: November 2022

A large share of passenger vehicles are currently running on gasoline, which is considered the major contributor to carbon emissions from the transportation sector. In gasoline direct injection (GDI), the fuel is introduced directly into the combustion chamber in a spark ignition (SI) engine. GDI has the advantage of operating at a higher compression ratio due to the charge cooling effect, resulting in better fuel utilization and lower pollutant emissions. The spray formed from fuel injection under different engine running conditions governs the charge (air-fuel) characteristics. The present work focuses on experiments using a GDI system with a multi-hole injector for gasoline fuel sprays in a constant volume chamber. The saturation pressure of the fuel present within the nozzle increases with rising temperature (80 to 90°C) from heat transfer due to the placement of the injector directly into the combustion chamber. At part-load running conditions, when the heated fuel injected into an environment has a pressure sufficiently lower (achieved in early injection) than its saturation pressure, it attains the state of superheating and undergoes flash boiling. The abrupt vaporization of injected fuel results from flash boiling and affects spray characteristics. The ratio of chamber pressure to saturation pressure (Pch/Psat) indicates the propensity of flashing for a given super-heated operating condition. Macroscopic analysis of GDI sprays is reported in this study under flashing and non-flashing conditions through different experimental techniques to provide a comprehensive understanding. Experimental studies reported in this kind of literature typically adopt a specific technique to elucidate the details of spray evolution.

A Diffused Back Illumination (DBI) imaging technique with a low-speed Nd: YAG laser has been carried out to analyse the liquid phase of the spray, such as penetration, cone angle, and width. Additionally, a novel Structured Laser Illumination Planar Imaging (SLIPI) technique has been adopted to identify the relatively dense spray regions by addressing the difficulty due to multiple scattering of light illuminating from surrounding scatterer media (droplets). SLIPI is used to suppress the effect of the surrounding light artefacts, helping explore the structure in a new dimension. A multi-plume spray is expected to have voids, dense, and dilute portions at different locations, affecting the fuel mixture, and interestingly, it appears after subduing the effects of multi-scattering from a modulated laser sheet using SLIPI. An LED-based spray illumination was also used to compare the DBI and SLIPI results to better understand the utility and effectiveness of different imaging techniques in a densely populated and highly transient spray phenomenon.
Investigations Into the Performance and Emissions Characteristics of FT Synthetic Aviation Fuel, Isoparaffinic Kerosene (IPK), in a Single-Cylinder Indirect Injection (IDI) Engine
Authors: Soloiu Valentin , Weaver Amanda , Parker Lily , Smith Richard , Brant Austin , Brock Dillan , Ilie Marcel
Published: November 2022

In this study, iso-paraffinic kerosene (IPK) was analyzed for ignition delay, combustion delay, pressure trace, pressure rise rate and, apparent heat release rate in an experimental single cylinder indirect injection (IDI) compression ignition engine as well as in a constant volume combustion chamber (CVCC). Neat IPK, neat ULSD, and a by-mass blend of 50%IPK50%ULSD were analyzed in a CVCC and an IDI engine to determine the effect of Derived Cetane Number (DCN), Ignition Delay (ID), and Low Temperature Heat Release (LTHR) on combustion timing and engine knock.

In the CVCC, IPK was found to have a significantly lower DCN than ULSD at 26 and 47, respectively. The blend was found to have a DCN between the two neat fuels at 37.5. Additionally, the ignition delay increased in the CVCC from 3.56 ms for ULSD to 5.3 ms for IPK with the blend falling between the two at 4.38 ms.

For engine research, the single-cylinder experimental IDI engine was run at 2400 rpm at 5, 6, and 7 Indicated Mean Effective Pressure (IMEP) using each of the three researched fuels. It was found that when running neat IPK, there was a profound level of engine knock at all loads characterized by the 60% increase in the Peak Pressure Rise Rate (PPRR) when compared to ULSD. The pressure trace for IPK at all loads showed a significant delay in combustion due to IPK’s resistance to autoignition. This was observed in the increasing ignition delay in the engine from 0.88 ms for ULSD to 1.1 ms at 7 bar IMEP for IPK. Despite the delay in ignition for IPK, all three researched fuels reached peak Apparent Heat Release Rate (AHRR) at approximately 370° leading to a much more rapid increase in AHRR for IPK when compared to ULSD. This steep slope in the AHRR, also seen in the increased PPRR, and longer ID caused the high levels of engine knock, observed as oscillations in the pressure trace which decreased in magnitude as IMEP increased.
Development of a Liquid-Phase LPG Delivery System for Direct Injection, Spark-Ignited Engines
Authors: Kar Tanmay , Fosudo Toluwalase , Windom Bret , Olsen Daniel , Hoke Jensen , Rogers Jeff
Published: November 2022

Liquefied petroleum gas (LPG) is a promising diesel fuel alternative for heavy-duty vehicle applications due to its CO2 reduction potential, high knock resistance, easy liquefication capability, and lower fuel cost. Direct injection (DI) of liquid-phase LPG has emerged as a promising technology in spark-ignited (SI) engines due to the benefits from the in-cylinder charge cooling effect in comparison to external mixture formation systems. But this DI LPG technology requires a fuel delivery system that can supply the desired amount of LPG fuel in the liquid state at high pressure.

This work first describes the design and component integration of an LPG fuel system that delivers fuel from the tank to the injector in the liquid state at around 172 bar, mainly focusing on thermal management aspects to avoid multi-phase behavior within the system. A detailed description of the injector developmental work, from reverse engineering of stock injectors to manufacturing a prototype LPG direct injector, is also presented, including nozzle modifications to accommodate a high LPG flow rate for heavy-duty applications. A one-dimensional (1D) flow model of the fuel delivery system is developed using the MATLAB/Simulink software platform to guide the selection and sizing of components and characterize the prototype injector. Bench testing of the fuel delivery system is performed with the unmodified stock and prototype LPG injectors using a Viscor calibration fluid and LPG to study the effect of fuel pressure and current profiles on the injected fuel quantity. The simulation models are shown to be capable of predicting the experimental results. Durability tests are also performed to understand the failure modes of different components in the fuel delivery system.
Understanding Ammonia/Hydrogen Fuel Combustion Modeling in a Quiescent Environment
Authors: Shaalan Amr , Nasim Md Nayer , Mack J. Hunter , Van Dam Noah , Assanis Dimitris
Published: November 2022

Ammonia and Hydrogen are attractive alternative fuels for a zero-carbon combustion solution that can rapidly decarbonize the transportation industry. Understanding the chemical behavior and combustion characteristics of these fuels individually, as well as blended together, is pivotal to ensuring their widespread adoption and utilization. Furthermore, in the era of computer-aided engineering, it is critical to evaluate our ability to computationally model the chemical reactivity of these two fuels and validate predictions of experimentally observed phenomena using multi-dimensional simulations. In this study, ammonia/hydrogen chemical kinetics mechanisms available from the research literature are investigated through 0-D, 1-D, and 3-D simulations. The 0-D and 1-D simulations were carried out to understand the ignition delay and laminar flame speeds, respectively, at different operating pressures and temperatures. 3-D simulations were also performed to test the fuels’ behavior in a closed volume combustion chamber. The multi-dimensional computational results were compared against optically measured experimental data available in recent publications. Specifically, a comparison of unstretched flame speeds determined from stretched flame speeds of post-processed computational results is made. Lean and rich combustion limits have been computationally evaluated as well. Lastly, observed physical buoyancy effects were reproducible in a quiescent computational environment leading to increased confidence in using the evaluated chemical kinetics mechanisms for high-fidelity reciprocating piston engine computational research and development.