1,720,952 research outputs found
Modelling and simulation of combustion of dilute syngas fuels in a CFR engine
Full text link2019 Fall.Includes bibliographical references.With increasing interest towards discovery of alternative fuels to act as sources of energy, many conventional internal combustion engines are being modified to operate on these new fuels. Optimization of engine specifications including compression ratio, intake/piston geometry, valve timing, and combustion phasing, can greatly improve performance when an engine is modified to operate on alternative fuels such as syngas and producer gas. However, the inability to predict the combustion characteristics of the alternative fuel, such as burn rates and auto-ignition conditions, is a significant challenge when simulation-based design of an engine is intended. The following thesis describes the development of a predictive model to simulate the combustion of a dilute syngas fuel in a Cooperative Fuel Research (CFR) spark ignited engine. The laminar flame speeds of the unique fuel mixtures calculated using CHEMKIN were coupled with the geometric features of the CFR engine to create a combustion model of the CFR engine in GT-POWER. Using two-zone modelling and detailed chemical kinetics, the model is also able to determine the performance of the engine along with any associated knocking tendency of the fuel and its corresponding operating conditions. Validation and tuning of the combustion parameters were performed through comparison to experimental pressure data taken from the CFR engine. The completed engine model can support the design and selection of operating conditions to maximize efficiency of other spark ignited internal combustion engines when powered by the dilute syngas fuel
Experimental investigation of automotive refueling system flow and emissions dynamics to support CFD development
Full text link2019 Summer.Includes bibliographical references.Government regulations restrict the evaporative emissions during refueling to 0.20 grams per gallon of dispensed fuel. This requires virtually all of the vapors generated and displaced while refueling to be stored onboard the vehicle. The refueling phenomenon of spit-back and early click-off are also important considerations in designing refueling systems. Spit-back is fuel bursting past the nozzle and into the environment and early click-off is the pump shutoff mechanism being triggered before the tank is full. Both are detrimental to customer satisfaction, and spit-back leads to failing government regulations. Development of a new refueling system design is required for each vehicle as packaging requirements change. Each new design (or redesign) must be prototyped and tested to ensure government regulations and customer satisfaction criteria are satisfied. Often designs need multiple iterations, costing money and time in prototype-based validation procedures. To conserve resources, it is desired to create a Computational Fluid Dynamics (CFD) tool to assist in design validation. To aid in creating such a model, controlled experiments were performed to inform and validate simulations. The simulations and experiments were performed on the same in-production refueling system. Test data provided characterization of non-trivial boundary conditions. Refueling experiments gave points of comparison for CFD results, especially the tank pressure. Finally, collection of emissions data during refueling experiments provided insight into the travel of gasoline vapor in the refueling system. All the information gathered provides greater understanding of the refueling process and will aid the continued development of CFD models for refueling
High pressure vapor-liquid equilibrium measurements of methane and water mixtures using nuclear magnetic resonance spectroscopy
Full text link2021 Spring.Includes bibliographical references.Gas composition, which can vary from location to location in natural gas pipelines, constrains the allowable operating conditions and compressor package design. Compressor systems are designed such that they provide the optimal balance between efficiency and gas throughput with safety margins to maintain component lifetime. The presence of liquid in the compressor can lead to excessive wear of intake and discharge valves and impact performance. To prevent ingestion of liquid slugs, operating conditions and separation equipment must be selected appropriately using mixture dew point calculations from commercially available mixture property prediction software such as NIST-REFPROP. NIST-REFPROP is highly reliant on mixture Vapor liquid Equilibrium (VLE) data to predict phases. Thus, there is a need for low uncertainty VLE data for gas mixtures at pressures (1 - 10 MPa) and temperatures (<0 – 100 °C) experienced within natural gas infrastructure, especially for mixtures containing H2O, which would lead to more accurate dew point calculations and allow designers to maximize system performance without compromising component wear and tear. For a mixture comprised completely of hydrocarbon species, VLE calculations at high pressures are accurate as the interaction parameters between the constituents are close to unity and there is typically a wealth of low-uncertainty data available. However, when H2O is present in natural gas significant intermolecular interactions cause the mixture VLE to deviate from ideality. In order to accurately model the VLE of these mixtures, the energy associated with these interactions must be known and accounted for in the calculations. As such, high quality experimental VLE data are needed to improve and validate the thermodynamic models. Nuclear magnetic resonance (NMR) spectroscopy allows for high-quality data collection for water containing samples. This thesis provides the groundwork for using NMR spectroscopy to conduct low-uncertainty VLE measurements of water-hydrocarbon mixtures. Two NMR spectrometers were investigated, and methods were developed to accurately characterize the temperature, pressure, vapor phase and liquid phase molar composition of methane-water systems at equilibrium, the five conditions required for VLE measurement. Preliminary results for low pressure (0-2.06MPa) samples of methane and water showed that the liquid phase methane compositional data taken utilizing NMR spectroscopy significantly deviated from the NISTREFPROP model, revealing the lack of low uncertainty VLE data required to determine the needed interaction parameters for methane and water systems. Future work should target the collection of the high-fidelity methane-water VLE data, and NMR spectroscopy has the potential to perform this task
Effect of endothermic reactions on the global extinction strain rate of large hydrocarbon fuels
Full text link2018 Fall.Includes bibliographical references.When a hydrocarbon fuel is used as a coolant, the extreme environment can have a significant impact on the fuel composition. Heat exchange occurs through phase change, sensible heat extraction, and endothermic reactions experienced by the liquid fuel. From previous studies it has been demonstrated that the fuel composition changes significantly as well as the fuel properties as a result of the endothermic reactions. To investigate the effect of endothermic reactions on the fundamental flame behavior we have developed a counterflow flame burner that can measure the flame extinction strain rate of a thermally stressed fuel. The counterflow flame burner is coupled with a high-pressure reactor, capable of exposing the fuel to extreme conditions of 170 atm and 650 °C. Flame robustness is quantified by measuring the flame extinction strain rate. n-heptane is studied as a first attempt to understand the role of the endothermic reactions on the combustion and flame behavior of a liquid rocket propellant fuel. Modeling of the reactor and the counterflow flame is carried out using CHEMKIN. The flame extinction strain rate of the reacted n-heptane is compared with the unreacted n-heptane flame, thus allowing us to determine and extrapolate the role of endothermic reactions on the combustion behavior of jet and rocket fuels
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
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