1,720,967 research outputs found
Effect of fuel chemistry and physical influences on low temperature heat release
Get PDFMost passenger vehicles are powered by internal combustion engines (ICE), which emit CO2 and contribute to global warming. Despite this, ICEs are forecasted to be used for decades to come, hence their CO2 impact must be reduced urgently. Three viable options for achieving this are extending the knocking limit, using advanced combustion strategies and using low carbon fuels.
Low Temperature Heat Release (LTHR) is the phenomenon in which some of the fuel-air mixture undergoes a slower, exothermic reaction at relatively lower temperatures, producing intermediate species prior to the main combustion event. LTHR can be seen in fuels that exhibit two-stage autoignition, due to their negative temperature coefficient characteristics. It has mostly be studied in homogeneous charge compression ignition (HCCI) engines, but recently it has been observed in spark ignition (SI) engines where it is termed pre-spark heat release (PSHR). Understanding and controlling LTHR has the potential to contribute to extending the knocking limit and enabling advanced combustion strategies though this would be highly dependant on fuel choice and its individual LTHR behaviour.
This thesis presents a methodology to isolate LTHR in SI engines, paving the way for new studies of many parameters that previously were not accessible. The effect of pressure, temperature and engine speed on isolated LTHR were investigated. For LTHR to occur, cylinder pressures must be high enough, cylinder temperatures must fall within the LTHR region and engine speed must be low enough to provide enough time for LTHR to occur. The effect of equivalence ratio on LTHR is also investigated. Heat released from LTHR in a direct injection engine is found to increase linearly with equivalence ratio, up until the point where charge cooling reduced cylinder temperatures below the LTHR threshold.
The LTHR behaviour of binary blends of n-heptane, iso-octane and ethanol is explored. Ethanol is shown to strongly inhibit LTHR by increasing competition for hydroxyl radicals which would otherwise initiate the low temperature oxidation of n-heptane or iso-octane. Combustion residuals, specifically nitric oxide is shown to strongly inhibit LTHR in iso-octane. It is also found that popular chemical kinetic mechanisms were unable to model the behaviour of nitric oxide and iso-octane at temperature relevant to LTHR.
Finally, an optically accessible SI engine is used to show formaldehyde planar laser-induced fluorescence (PLIF) signal intensity under motored conditions is well correlated to cumulative isolated LTHR intensity. An alternative ignition method using four side-mounted spark plugs is implemented to generate end gas close to the cylinder axis. This enabled measurement of LTHR within the end gas during the deflagration process of a SI engine, demonstrating the utility of formaldehyde PLIF to optically measure LTHR under conditions where pressure-based diagnostics cannot isolate the contribution of LTHR
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Effect of ambient pressure on ammonia sprays using a single hole injector
Get PDFAmmonia has received attention as an alternative hydrogen carrier and a potential fuel for thermal propulsion systems with a lower carbon footprint. One strategy for high power density in ammonia applications will be direct injection of liquid ammonia. Understanding the evaporation and mixing processes associated with this is important for model development. Additionally, as a prior step for developing new injectors, it is of interest to understand how a conventional gasoline direct injection (GDI) injector would behave when used for liquid ammonia without any modifications. Pure anhydrous ammonia, in its liquid form, was injected from a single hole GDI injector at a fuel pressure of 150 bar into an optically accessible constant volume chamber filled with nitrogen for ammonia spray measurements. The chamber conditions spanned a wide range of pressures from 3 - 15 bar at an increment of 1 or 2 bar between the test points. These conditions lead to sprays which are both flash boiling and non-flash boiling as well as a transition region. Spray morphology studies were performed based on high-speed backlit images recorded at 10 kHz. Droplet size distributions for the bulk spray were simultaneously measured using a laser diffraction technique at the same sampling rate. The results show that at a higher ambient pressure, shorter spray penetration lengths and smaller spray spread widths are observed compared to those at lower pressures. While these macroscopic spray geometrical parameters change gradually at different ambient pressures, the droplet size distribution undergoes a slightly more abrupt transition across the saturation vapor pressure at chamber temperature. These results provide a fundamental dataset for liquid ammonia injection and could be used to validate against simulation data or to build surrogate models
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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