1,721,017 research outputs found
Correlation Between Spark Ignition Characteristics and Flame Development in a Constant-Volume Combustion Chamber
No full textThe electrical characteristics of transistorized coil ignition (TCI) and capacitor discharge ignition (CDI) systems were investigated in spark-ignited quiescent and flowing propane/air mixtures within an optically-accessible, cylindrical constant-volume combustion chamber. Under quiescent flow conditions, the initial pressure, temperature and equivalence ratio of the mixture as well as the spark gap width and geometry were varied systematically in order to examine the relationship between ignition characteristics and flame initiation and development. The effect of the flow in the spark gap on the electrical characteristics of the ignition system, mixture ignitability and flame development was also examined by varying the pre-ignition mean flow and turbulence as well as the spark plug orientation relative to the mean flow.
Under quiescent flow conditions and despite differences in the electrical characteristics of the two ignition systems examined, TCI and CDI gave rise to similar flame development which implies the absence of a correlation between breakdown/total energy and early flame development; the TCI system, however, with its longer spark duration and higher breakdown energy, allowed extension of the lean ignition limit especially at large spark gaps. For a given ignition system, lower initial mixture pressure, higher initial temperature and wider spark gaps resulted in faster flame propagation.
Under flowing mixture conditions, combustion duration was shortened and the lean limit was extended when the mean flow and turbulence in the spark gap were high provided the orientation of the ground electrode was not in the upwind side of the mean flow direction. As the flow velocities were reduced, the effect of spark plug orientation on ignitability became smaller.The authors would like to acknowledge the financial support provided for this project by the Science and Engineering Reserach Council of the United Kingdom and Jaguar Cars Ltd. They would also like to thank Dr.P.O Witze of the Sandia National Labs. for arranging the loan of the combustion chamber to Imperial College and Dr.R.W.Anderson of the Ford Motor Co. for useful discussion
Flow and Combustion Analysis in a Four-Valve Spark-Ignition Engine
No full textThe in-cylinder flow in the pentroof chamber of a four-valve. single-cylinder, spark-ignition optical engine was quantified by laser Doppler velocimetry(LDV) during compression and correlated with combustion development especially under lean mixture conditions. First, the flow characteristics near the spark plug were quantified under motored conditions at engine speeds of 1000 and 2000rpm and then the cylinder head was modified with sleeves introduced into the two intake ports which generated a stronger tumble motion. The measurements of the flow by LDV confirmed that the modified intake ports with sleeves resulted in 100% higher mean convective velocity (~2Vp, Vp=mean piston speed), and 30% higher turbulence levels (~1Vp) near the spark gap at the time of ignition relative to the unmodified ports. Combustion development was monitored by a pressure transducer and the flame propagation was visualised by a standard and a high framing rate image intensified CCD camera which allowed comparisons to be made of the initial flame images generated by the sleeved and non-sleeved port configurations and their cycle-to-cycle variations under lean burn conditions
Dynamic structure of direct-injection gasoline engine sprays: air flow and density effects
No full textThe characteristics of the hollow-cane fuel spray produced by a centrally- located pressure-swirl atomizer have been investigated in a constant-volume pressure chamber and in a motored single-cylinder direct-injection spark-ignition (DISI) research engine. The aim is to describe the effect of elevated chamber pressure and in-cylinder bulk air motion on the spray development process. In addition to ambient conditions, chamber pressures of 5 and 7 bar absolute, corresponding to air densities of 5.82 and 8.14kg/m3, respectively, at atmospheric temperature (300 ?), were investigated as these conditions are representative of the range of in-cylinder pressure and densities corresponding to "early" through 'late" injection strategies. Spray dynamics in a constant-volume chamber, under near-quiescent flow conditions, are shown to be representative of in-cylinder sprays and therefore provide appropriate means for evaluating the relative effect of the intake air flow and in-cylinder density on the fuel spray development process. A wide range of operating conditions of a four-valve DISI engine with a centrally located pressure-swirl atomizer were examined at engine speeds of 700 and 1500 rpm and for four start-of-injection (SOI) timings of 90', 180', 270', and 300' after top-dead-center (aTDC) of intake. The results revealed that fuel spray impingement on the flat piston occurred only with injection at 300' ATDC, and that larger droplets are produced by pressure-swirl atomizers operating at higher gas pressures which suggests that achieving consistent late injection strategies for low-load operation with spray-guided systems using such injector designs may be an insurmountable problem
Thiesel 2014 (Thermo-and fluid dynamic processes in direct injection engines)
Full text linkThiesel is presented as a valuable platform for exchange of the latest international work and disseminates the results of research to improve engine efficiency and reduce emissions. It provides an ideal opportunity to share theories and methods that provide solutions that respect the environment, and generate great excitement and interest in the automotive industry with the latest discoveries and technologies.Angelberger, C.; Desantes Fernández, JM.; Arcoumanis, C.; Payri González, F.; Margot, XM. (2014). Thiesel 2014 (Thermo-and fluid dynamic processes in direct injection engines). Editorial Universitat Politècnica de València. https://riunet.upv.es/handle/10251/44213Archivo delegad
Effect of piezo-driven and solenoid-driven needle opening of common-rail diesel injectors on internal nozzle flow and spray development
No full textA prototype piezo-driven diesel injector has been developed and characterized in terms of measured flowrate, predicted cavitating nozzle hole flow distribution, and visual spray development. Results are compared with those obtained for a conventional solenoid-driven diesel injector equipped with the same micro-sac multi-hole injection nozzle. The response time and the needle lift trace for both injectors have been predicted for injection pressures up to 1300 bar using a hydraulic simulation model. Mie spray images obtained using a high-speed camera and utilizing diffusion illumination light, have allowed estimation of the spray tip penetration and spray cone angle under a variety of back pressures. The experimental results show that the piezo-driven injector produces longer spray tip penetration and smaller spray cone angle. This has been supported by CFD simulations of the internal nozzle hole cavitating flow obtained using the transient needle profile of the solenoid- and the piezo-driven injectors. Model predictions suggest an increase in the fuel exit momentum of the piezo-driven nozzle during the opening phase of the needle, relative to those of the solenoid-driven one. © IMechE 2006.This research work was supproted by the National Reserach Laboratory (NRL) programme of Korea Ministry of Science and Technology, 2004 and conducted with the cooperation of DPICO, Kore
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
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