bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Cycle-to-Cycle Hydrocarbon Emissions on Cyclic NO:NO2 Ratio From a HSDI Diesel Engine
Authors: Leach Felix , Shankar Varun , Davy Martin , Peckham Mark 
Published: December 2020

Abstract
Knowledge of the NO:NO2 ratio emitted from a diesel engine is particularly important for ensuring the highest performance of SCR NOx aftertreatment systems. As real driving emissions from vehicles increase in importance, the need to understand the NO:NO2 ratio emitted from a diesel engine during transient operation similarly increases.
Previous work by the authors identified significant differences in NO:NO2 ratio throughout the exhaust period of a single engine cycle, with proportionally more NO2 being emitted during the blowdown period compared to the rest of the exhaust stroke. At the time it was not known what caused this effect.
In this study, crank-angle resolved NO and NO2 measurements using fast response CLD (for NO) and a new fast LIF instrument (for NO2) have been taken from a single cylinder high-speed light duty diesel engine at three different speed and load points including a point with and without EGR. In addition, crank-angle resolved unburned hydrocarbon (UHC) measurements have been taken simultaneously using a fast FID.
The NOx emitted per cycle and the peak cylinder pressure of that cycle have showed high correlation coefficients (R2 &lt; 0.97 at all test points) in this work. In addition, a variation of the NO:NO2 ratio through the engine’s exhaust stroke is also observed indicative of in-cylinder stratification of NO and NO2. A new link between the NO:NO2 ratio and the UHC emissions from an individual engine cycle is observed — the results show that where there are higher levels of UHC emissions in the first part of the exhaust stroke (blowdown), perhaps caused by injector dribble or release from crevices, the proportion of NO2 emitted from that cycle is increased. This effect is observed and analysed across all test points and with and without EGR.
The performance of the new fast LIF analyser has also been evaluated, in comparison with the previous state-of-the-art and standard “slow” emissions measurement apparatus showing a reduction in the noise of the measurement by an order of magnitude.
Simultaneous High-Speed Formaldehyde PLIF and Schlieren Imaging of Multiple Injections From an ECN Spray D Injector
Authors: Maes Noud , Sim Hyung Sub , Weiss Lukas , Pickett Lyle 
Published: December 2020

Abstract
The interaction of multiple injections in a diesel engine facilitates a complex interplay between freshly introduced fuel, previous combustion products, and overall combustion. To improve understanding of the relevant processes, high-speed Planar Laser-Induced Fluorescence (PLIF) with 355-nm excitation of formaldehyde and Polycyclic Aromatic Hydrocarbon (PAH) soot precursors is applied to multiple injections of n-dodecane from Engine Combustion Network Spray D, characterized by a converging 189-μm nozzle. High-speed schlieren imaging is applied simultaneously with 50-kHz PLIF excitation to visualize the spray structures, jet penetration, and ignition processes. For the first injection, formaldehyde (as an indicator of low-temperature chemistry) is first found in the jet periphery, after which it quickly propagates through the center of the jet, towards the jet head prior to high-temperature ignition. At second-stage ignition, downstream formaldehyde is consumed rapidly and upstream formaldehyde develops into a quasi-steady structure for as long as the momentum flux from the injector continues. Since the first injection in this work is relatively short, differences to a single long injection are readily observed, ultimately resulting in high-temperature combustion and PAH structures appearing farther upstream after the end of injection. For the second injection in this work, the first formaldehyde signal is significantly advanced because of the entrained high-temperature combustion products, and an obvious premixed burn event does not occur. The propensity for combustion recession after the end of the first injection changes significantly with ambient temperature, thereby affecting the level of interaction between the first- and second injection.
Dynamic Mode Decomposition for Extracting Cycle-to-Cycle Variation of SIDI Engine In-Cylinder Flow Under Motoring Condition
Authors: Liu Mengqi , Zhao Fengnian , Li Xuesong , Xu Min , Hung David L. S. 
Published: December 2020

Abstract
Cycle-to-cycle variation (CCV) of in-cylinder flow strongly affects the performance and efficiency of spark ignition direct injection (SIDI) engines. In order to achieve a precise flow control inside the engine, the underlying dynamic features of flow field CCV must be thoroughly investigated. In this work, large-eddy simulations (LES) with 50 consecutive cycles are employed for high fidelity numerical realizations of engine flow under motoring condition. To supplement the numerical analysis, time-resolved particle image velocimetry (PIV) measurements are also conducted in several cutting planes. Although the velocity root mean square (RMS) is calculated to quantify the cyclic variation intensity of simulation and experiment results, some important dynamic characteristics cannot be observed directly from velocity data. Therefore, dynamic mode decompositions (DMD), which is a widely used modal decomposition algorithm on fluid study, is used to decompose flow fields into modes with specific frequencies and provide growth rates of corresponding flow structures. This spectral information of in-cylinder flow field is ponderable for uncovering dynamic features of engine CCV. In this study, DMD algorithm is applied on both LES and PIV datasets. The frequency and growth rate differences are employed to elucidate the CCV feature deviations captured by LES and PIV. This research provides a guideline for extracting engine flow field cyclic variability feature using DMD algorithm. Based on the discussion for spectral features and potential sources of flow field variation, the capability of LES to capture CCV features is evaluated. The DMD spectrum differences between PIV and LES can guide the boundary condition perturbations used for simulation fidelity improvements.
A Transported Livengood-Wu Integral Model for Knock Prediction in CFD Simulation
Authors: Yue Zongyu , Xu Chao , Som Sibendu , Sluder C. Scott , Edwards K. Dean , Whitesides Russell , Mcnenly Matthew J. 
Published: December 2020

Abstract
This work describes the development of a transported Livengood-Wu (L-W) integral model for computational fluid dynamics (CFD) simulation to predict auto-ignition and engine knock tendency. The currently employed L-W integral model considers both single-stage and two-stage ignition processes, thus can be generally applied to different fuels such as paraffin, olefin, aromatics and alcohol. The model implementation is first validated in simulations of homogeneous charge compression ignition combustion for three different fuels, showing good accuracy in prediction of auto-ignition timing for fuels with either single-stage or two-stage ignition characteristics. Then, the L-W integral model is coupled with G-equation model to indicate end-gas auto-ignition and knock tendency in CFD simulations of a direct-injection spark-ignition engine. This modeling approach is about 10 times more efficient than the ones that based on detailed chemistry calculation and pressure oscillation analysis. Two fuels with same Research Octane Number (RON) but different octane sensitivity are studied, namely Co-Optima Alkylate and Co-Optima E30. Feed-forward neural network model in conjunction with multi-variable minimization technique is used to generate fuel surrogates with targets of matched RON, octane sensitivity and ethanol content. The CFD model is validated against experimental data in terms of pressure traces and heat release rate for both fuels under a wide range of operating conditions. The knock tendency — indicated by the fuel energy contained in the auto-ignited region — of the two fuels at different load conditions correlates well with the experimental results and the fuel octane sensitivity, implying the current knock modeling approach can capture the octane sensitivity effect and can be applied to further investigation on composition of octane sensitivity.
Gasoline Compression Ignition (GCI) on a Light-Duty Multi-Cylinder Engine Using a Wide Range of Fuel Reactivities and Heavy Fuel Stratification
Authors: Dempsey Adam B. , Curran Scott , Wagner Robert , Cannella William , Ickes Andrew 
Published: December 2020

Abstract
Many research studies have focused on utilizing gasoline in modern compression ignition engines to reduce emissions and improve efficiency. Collectively, this combustion mode has become known as gasoline compression ignition (GCI). One of the biggest challenges with GCI operation is maintaining control over the combustion process through the fuel injection strategy, such that the engine can be controlled on a cycle-by-cycle basis. Research studies have investigated a wide variety of GCI injection strategies (i.e., fuel stratification levels) to maintain control over the heat release rate while achieving low temperature combustion (LTC). This work shows that at loads relevant to light-duty engines, partial fuel stratification (PFS) with gasoline provides very little controllability over the timing of combustion. On the contrary, heavy fuel stratification (HFS) provides very linear and pronounced control over the timing of combustion. However, the HFS strategy has challenges achieving LTC operation due to the air handling burdens associated with the high EGR rates that are required to reduce NOx emissions to near zero levels. In this work, a wide variety of gasoline fuel reactivities (octane numbers ranging from &lt; 40 to 87) were investigated to understand the engine performance and emissions of HFS-GCI operation on a multi-cylinder light-duty engine. The results indicate that over an EGR sweep at 4 bar BMEP, the gasoline fuels can achieve LTC operation with ultra-low NOx and soot emissions, while conventional diesel combustion (CDC) is unable to simultaneously achieve low NOx and soot. At 10 bar BMEP, all the gasoline fuels were compared to diesel, but using mixing controlled combustion and not LTC.
Statistical Quantification of Knock With Spark Ignition and Pre-Chamber Jet Ignition in a Light Duty Gasoline Engine
Authors: Yu Xin , Zhang Anqi , Baur Andrew , Voice Alexander , Engineer Nayan 
Published: December 2020

Abstract
Knock is a major challenge for high load operation of spark ignited gasoline engines with higher compression ratios, since the end-gas undergoes higher temperature and pressure trajectories during combustion. Pre-chamber combustion creates long-reach ignition jets that have the potential to mitigate knock due to their rapid consumption of end-gas. However, conventional pressure oscillation-based knock metrics may not accurately capture the end-gas autoignition severity in pre-chamber systems due to differences in ignition and combustion behavior. This work investigates the knock behavior of both traditional spark ignition and pre-chamber combustion (including different nozzle designs) in a high compression ratio engine fueled with regular octane certification gasoline. The data was analyzed using statistical methods to show the random nature of knock events. Detailed analysis was used to explain the pressure oscillations of both knocking and non-knocking cycles of pre-chamber jet combustion and show that conventional pressure oscillation-based knock metrics may not adequately quantify end-gas autoignition severity. A novel knock metric is introduced to avoid consideration of the non-knock related pressure oscillation and better quantify the end-gas autoignition severity. The new metric was used to explain the knock mitigation mechanism for pre-chamber jet combustion and demonstrate an additional pre-chamber jet ignition benefit of reduced combustion variability during engine operation with cooled exhaust gas circulation within its dilution limit.
The Sensitivity Study of a Mechanical Loss Model in Turbocharger System
Authors: Wang Haizhu , Burke Richard , Copeland Colin 
Published: December 2020

Abstract
3D modelling can be a very useful tool for optimising the design of turbocharger turbines. However, it is difficult to achieve high levels of correlation with experimental data which can undermine confidence in the 3D model results. A key difference between modelling and experiments is the way turbine efficiency is estimated: in CFD this is estimated directly from the shaft torque created by the turbine, however in experiments this is usually estimated based on the enthalpy rise measured at the compressor. This means that there is an inherent offset between the two which is the mechanical losses of the bearing system used to support the connecting shaft. The accuracy of the mechanical loss estimate can therefore play a critical role in the correlation of 3D modelling with experiments.
A 3D CFD model of a turbocharger turbine of a 1.5L gasoline engine has been coupled with a 0D mechanical losses model. The model comprises of seven parameters that characterise the bearing losses such as oil film thickness, bearing surface finish and clearances. A sensitivity study is conducted on these parameters to understand which are the critical aspects that should be parameterised and what relationship these parameters may have with the operating state of the turbocharger (shaft speed, shaft torque etc.). Experimental measurements were conducted for the same turbocharger to provide a baseline for assessing the impact of the mechanical losses model. These provide the boundary conditions to the CFD by ignoring the effects of heat transfer, and the results were compared to the 3D simulation results.
Design, Actuation, Experimental Setup and Testing of a 4-Cylinder Gasoline Spark Ignited Variable Compression Ratio Engine
Authors: Miller Tyler , Duncan Joel , Hensley William , Beard John , Worm Jeremy , Naber Jeffrey 
Published: December 2020

Abstract
The thermal efficiency of an Otto cycle engine is directly related to the compression ratio (CR). However, in a spark-ignited engine, the CR is often restricted by full load knock, thus limiting part load efficiency. A proof of concept design and experimental study has been conducted on a 4-cylinder naturally aspirated spark-ignited (SI) engine whereby a four-bar linkage mechanism has been implemented to vary the CR. The base engine selected was a production 2.0L GM-LNF SI 4-cylinder engine with a stock CR of 9.2:1 and with a bore and stroke of 86mm and 86mm, respectively. The engine was modified to allow the centerline axis of rotation of the crankshaft to translate in an arc about a fixed point. With the use of the four-bar mechanism, and larger dome volume pistons, a range of 8:1 to 11.5:1 CR was achieved.
The prototype VCR engine was tested and analyzed at three different CR’s at a fixed load of 600 kPa net indicated mean effective pressure gross (IMEPGROSS) at an engine speed of 1000 revolutions per minute (RPM). At this condition, a sweep of combustion phasing was conducted. with a stoichiometric air to fuel mixture for each case. The CR’s selected for engine testing were 8.7:1, 10.2:1, and 11.1:1. The processed data includes averaged cycle analysis of each of the test conditions including combustion phasing, combustion duration, and cycle variation. The combustion data was also analyzed to determine overall heat release, indicated gross, net, pumping mean effective pressures, and indicated fuel conversion efficiency for each of the CR’s. The studies show an indicated fuel conversion efficiency of 31.2% for the 8.7:1 CR. As the CR was increased to 10.2:1 and 11.1:1 the relative increase in efficiency was 7.1% and 9.7% respectively at MBT combustion phasing.
Modeling Nanosecond-Pulsed Spark Discharge and Flame Kernel Evolution
Authors: Kim Joohan , Gururajan Vyaas , Scarcelli Riccardo , Biswas Sayan , Ekoto Isaac 
Published: December 2020

Abstract
Dilute combustion, either using exhaust gas recirculation or with excess-air, is considered a promising strategy to improve the thermal efficiency of internal combustion engines. However, the dilute air-fuel mixture, especially under intensified turbulence and high-pressure conditions, poses significant challenges for ignitability and combustion stability, which may limit the attainable efficiency benefits. In-depth knowledge of the flame kernel evolution to stabilize ignition and combustion in a challenging environment is crucial for effective engine development and optimization. To date, comprehensive understanding of ignition processes that result in the development of fully predictive ignition models usable by the automotive industry does not yet exist. Spark-ignition consists of a wide range of physics that includes electrical discharge, plasma evolution, joule-heating of gas, and flame kernel initiation and growth into a self-sustainable flame. In this study, an advanced approach is proposed to model spark-ignition energy deposition and flame kernel growth. To decouple the flame kernel growth from the electrical discharge, a nanosecond pulsed high-voltage discharge is used to trigger spark-ignition in an optically accessible small ignition test vessel with a quiescent mixture of air and methane. Initial conditions for the flame kernel, including its thermodynamic state and species composition, are derived from a plasma-chemical equilibrium calculation. The geometric shape and dimension of the kernel are characterized using a multi-dimensional thermal plasma solver. The proposed modeling approach is evaluated using a high-fidelity computational fluid dynamics procedure to compare the simulated flame kernel evolution against flame boundaries from companion schlieren images.
Assessing the quality of primary healthcare for diabetes in China: multivariate analysis using the China Health and Retirement Longitudinal Study (CHARLS) Database
Authors: Sun Meiping , Rasooly Alon , Fan Xiaoqi , Jian Weiyan 
Published: December 2020

ObjectiveTo assess the quality of primary healthcare (PHC) for patients with diabetes in China from 2011 to 2015.SettingThis study analysed data on 1006, 1472 and 1771 participants with diabetes who were surveyed in 2011, 2013 and 2015, respectively, in the China Health and Retirement Longitudinal Study, a nationally representative survey conducted in 29 provinces of China.Outcome measuresThe study measured the proportions of patients with diabetes who received diabetes-related health education, examinations and treatments, as well as the hospital admission rate due to diabetes of these patients. Multilevel logistic regression was used to adjust sociodemographic variables.ResultsAccording to the multivariate analysis, the proportion of patients who received diabetes-related health education decreased significantly (OR=0.74, 95% CI 0.61 to 0.90), and the proportion of those receiving examinations and treatments remained unchanged from 2011 to 2015. Diabetes-related hospitalisation increased from 4.01% in 2011 to 6.08% in 2013 (OR=1.47, 95% CI 0.97 to 2.22), and recurrent hospitalisations increased from 18.87% in 2011 to 28.45% in 2015 (OR=1.78, 95% CI 1.44 to 2.20). The proportions of patients with diabetes-related and recurrent hospitalisations in western China were higher than those in the east (OR=1.80, 95% CI 1.13 to 2.87; OR=1.92, 95% CI 1.50 to 2.45).ConclusionsNationally, the analysis of patient-reported process and outcome indicators cannot confirm that the quality of PHC has improved in China during 2011–2015. Regional disparities in primary diabetes care require urgent resource allocation to western China. Establishing a national quality registry for PHC, which transparently reports outcomes by region and social-economic position, is essential for countries sharing the challenge of improving both quality and equity of PHC.
Comparing the prevalence of multimorbidity using different operational definitions in primary care in Singapore based on a cross-sectional study using retrospective, large administrative data
Authors: Lee Yi An Janis , Xie Ying , Lee Poay Sian Sabrina , Lee Eng Sing 
Published: December 2020

ObjectivesMultimorbidity is a norm in primary care. A consensus on its operational definition remains lacking especially in the list of chronic conditions considered. This study aimed to compare six different operational definitions of multimorbidity previously reported in the literature for the context of primary care in Singapore.Design, setting and participantsThis is a retrospective study using anonymised primary care data from a study population of 787 446 patients. We defined multimorbidity as having three or more chronic conditions in an individual. The prevalence of single conditions and multimorbidity with each operational definition was tabulated and standardised prevalence rates (SPRs) were obtained by adjusting for age, sex and ethnicity. We compared the operational definitions based on (1) number of chronic diseases, (2) presence of chronic diseases of high burden and (3) relevance in primary care in Singapore. IBM SPSS V.23 and Microsoft Office Excel 2019 were used for all statistical calculations and analyses.ResultsThe SPRs of multimorbidity in primary care in Singapore varied from 5.7% to 17.2%. The lists by Fortinet al, Geet al, Lowet aland Quahet alincluded at least 12 chronic conditions, the recommended minimal number of conditions. Quahet alconsidered the highest proportion of chronic diseases (92.3%) of high burden in primary care in Singapore, with SPRs of at least 1.0%. Piccoet aland Subramaniamet alconsidered the fewest number of conditions of high relevance in primary care in Singapore.ConclusionsFortinet al’s list of conditions is most suitable for describing multimorbidity in the Singapore primary care setting. Prediabetes and ‘physical disability’ should be added to Fortinet al’s list to augment its comprehensiveness. We propose a similar study methodology be performed in other countries to identify the most suitable operational definition in their own context.