1,721,101 research outputs found
Relating Knocking Combustions Effects to Measurable Data
No full textKnocking combustions heavily influence the efficiency of Spark Ignition
engines, limiting the compression ratio and sometimes preventing
the use of Maximum Brake Torque (MBT) Spark Advance (SA). A detailed
analysis of knocking events can help in improving the engine performance
and diagnostic strategies. An effective way is to use advanced 3D
Computational Fluid Dynamics (CFD) simulation for the analysis and
prediction of the combustion process. The standard 3D CFD approach
based on RANS (Reynolds Averaged Navier Stokes) equations allows
the analysis of the average engine cycle. However, the knocking phenomenon
is heavily affected by the Cycle to Cycle Variation (CCV): the effects
of CCV on knocking combustions are then taken into account, maintaining
a RANS CFD approach, while representing a complex running condition,
where knock intensity changes from cycle to cycle. The focus of the
numerical methodology is the statistical evaluation of the local
air-to-fuel and turbulence distribution at the spark plugs and their
correlation with the variability of the initial stages of combustion.
CFD simulations have been used to reproduce knock effect on the in-cylinder
pressure trace. For this purpose, the CFD model has been validated,
proving its ability to predict the combustion evolution with respect
to SA variations, from non-knocking up to heavy knocking conditions.
The CFD model allowed relating measurable data (i.e., the simulated
cylinder pressure signal) to other factors, representative of the
phenomena actually taking place during knocking combustions: for
each cell used in the CFD simulation, information such as pressure,
heat release, etc. are available and can be traced over the angular
domain. Furthermore, the analysis refers to hundredths of engine
cycles, leading to a comprehensive correlation between standard cylinder
pressure-based knock indexes and other indexes (only available in
a simulation environment), more representative of the actual knock
intensity. Copyright © 2015 SAE International
Evaluation of the Effects of a Twin Spark Ignition System on Combustion Stability of a High Performance PFI Engine
No full textAbstractThe continuous demand for high performances and low emissions engines leads the engine manufactures to set the operating range of combustion devices near to their stability limit. Combustion stability is closely related to the formation of the first ignition kernel: an effective way of lowering Cycle-by-Cycle Variation (CCV) is to enhance the start of combustion by means of multiple sparks. A Ducati engine was equipped with a Twin Spark ignition system and a consistent improvement in combustion stability arised for both part load and full load conditions.At part load a sensible reduction of cycle-by-cycle variability of indicated mean effective pressure was found, while at full load condition the twin spark configuration showed an increase of power, but with higher knocking tendency. The aim of this work is to better understand the root causes of the increased level of knock and to make a critical evaluation of most used knock indexes, by means of an accurate analysis of the experimental and simulated pressure signals.The numerical methodology based on a perturbation of the initial kernel by a statistical evaluation of mixture condition at ignition location. A lagrangian ignition model developed at University of Bologna was used, here modified to take into account the statistical distribution of mixture around the spark plugs. The RANS simulations proved to be accurate in representing all the main information related to combustion efficiency and knocking events
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Automatic Combustion Control for Calibration Purposes in a GDI Turbocharged Engine
No full textCombustion phasing is crucial to achieve high performance and efficiency: for gasoline engines control variables such as Spark Advance (SA), Air-to-Fuel Ratio (AFR), Variable Valve Timing (VVT), Exhaust Gas Recirculation (EGR), Tumble Flaps (TF) can influence the way heat is released. The optimal control setting can be chosen taking into account performance indicators, such as Indicated Mean Effective Pressure (IMEP), Brake Specific Fuel Consumption (BSFC), pollutant emissions, or other indexes inherent to reliability issues, such as exhaust gas temperature, or knock intensity. Given the high number of actuations, the calibration of control parameters is becoming challenging. Many different approaches can be used to reach the best calibration settings: Design Of Experiment (DOE) is a common option when many parameters influence the results, but other methodologies are in use: some of them are based on the knowledge of the controlled system behavior, by means of models that are identified during the calibration process. The paper shows how the calibration can be managed using a different concept, based on the Extremum Seeking (ES) approach. The main idea consists in changing the values of each control parameter at the same time, identifying its effect on a cost or merit function (target function), allowing to shift automatically the control setting towards the optimum solution throughout the calibration procedure. The function is evaluated cycle by cycle, based on combustion analysis. Due to the control parameters continuous variations the target function values change: the ES objective is to drive the variations towards the setting minimizing the cost function. The methodology has been applied to data referring to a GDI turbocharged engine, trying to maximize IMEP or minimize BSFC, while limiting the knock intensity and exhaust gas temperature, using SA, AFR and VVT as control variables. Experimental data referring to the considered engine have been used to feed a combustion model, allowing to test the calibration approach: results show that the ES-based calibration is able to automatically change SA, lambda and VVT values, taking into account all the constraints, and finally reaching the optimal control setting, independently of the starting setting. Copyright © 2014 SAE International
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