1,720,958 research outputs found
The influence of contaminants and their interactions of diesel engine oil tribology using electrostatic condition monitoring
No full textIn modern automotive engines, especially in diesel engines, consumer demand for ever
increasing service intervals for vehicles has led to longer oil drain periods.
Consequently this has increased contamination levels in lubricating oils that will in turn
reduce engine efficiency and increase the possibility of system failure due to increases
in viscosity and the potential of oil starvation leading to scuffing and catastrophic
failure of the engine. Therefore it is necessary to investigate the effects of diesel engine
oil contaminants on the tribological performance of tribocontacts and also the possible
interaction between the contaminants. The thesis aims to investigate the influence of
contaminants and their interactions on diesel engine oil using Electro sensing (ES)
monitoring.
ES monitoring suggest sensitivity to tribocharging, triboemission, surface charging, and
wear debris generated in the tribocontact. However, ES monitoring is still in its initial
stages of development but the relationships between the ES charge signal and
corresponding wear mechanisms are established.
Initial experiments showed the sensitivities between charge and wear to changes in
additive chemistry, as well as contamination (specifically a soot stimulant). The results
indicated some interesting findings which were difficult to elucidate but paved the way
for a parametric study.
The parametric matrix examined the effect of contaminants and it was observed that
wear rate was mainly influenced by acid and soot additions. The best correlation of
steady state charge with the other measured tribological parameters of wear rate, friction
and temperature is seen for the series of oxidised oils. The multi-contaminated oil
(L4×4) shows remarkably little degradation in tribological performance with a reduced
friction level compared with the uncontaminated oil and only a modest increase in wear
rate, slight increase in charge levels. This clearly showed that there were interactions
between the contaminants.
The factorial matrix studied interactions between the diesel engine oil contaminants on
various tribo-couple materials, including silicon nitride, using ES monitoring. For
charge, pin material – sulphuric acid and oxidation –sulphuric acid, interactions were
statistically identified as having significant influence on performance. For friction, both
pin and disc materials were identified as main influences along with pin material –
sulphuric acid interactions. For wear, the presence of soot and the influence of pin
material were identified statistically as the main effects.
To conclude, the ES monitoring was sensitive to the presence and levels of
contaminants in diesel lubricating oil, particularly diesel soot. The change in charge
levels indicated the concentration of soot level present in the contact, which was directly
related to wear. ES monitoring also detected interactions between the contaminants
through statistical analysis. ES monitoring has shown that monitoring lubricant
performance and the effects of contamination are feasible under laboratory conditions
Factorial study of diesel engine oil contamination effects on steel and ceramic sliding contacts
No full textThe present work investigates the effects of diesel contaminants and their interaction on tribological properties for bearing steel (En31) and ceramic (Si3N4) sliding contacts using a factorial study. The contaminants are soot, sulphuric acid, moisture and oxidation, and each contaminant has three different level of concentration (low, medium and high) in the test matrix. The factorial test matrix consisted of 20 tests, constructed from a quarter fractional factorial test matrix with four points at the medium values for the contaminants. Results from this matrix required six further tests to elucidate aliased pairs of interactions using Bayesian model selection. A pin-on-disc tribometer was used to carry out all the experiments. All tests were carried out under ambient conditions at 5 m/s sliding speed and contact stress of 1.5–2.05 GPa to simulate a valve-train in a diesel engine with fully formulated heavy-duty diesel engine oil used as lubricant. Four different tribological properties were studied. The factorial study showed that charge was influenced by tribocouple material; the silicon nitride discs produced higher charge than steel discs. However, it was opposite for friction; the silicon nitride disc gave lower friction and the pins showed higher friction than their steel counterparts. For wear scar and temperature, soot contaminant was found to be important. The two important interactions were found for the charge response, with the interaction between sulphuric acid and pin material being more important than sulphuric acid–oxidation interaction. Similarly to charge, an interaction between sulphuric acid and pin material interaction was found for friction
Effect of Micro Texture on Tribological Performance of Piston Ring-Cylinder Liner System under Different Lubrication Regimes
No full textTribological Effects of Multiwall Carbon Nanotube (MWCNT) on Cu Based Hybrid Composite Brake Friction Material for Medium Duty Automotive Applications
No full text
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
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
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