1,720,975 research outputs found
Numerical and Experimental Analysis on a Small GDI, Stratified Charge, Motorcycle Engine
No full textIn the field of engines for light motorcycles, two-stroke
cycle survival is submitted to the application of direct fuel
injection and charge stratification, even in the case of low-cost
small engines. However, charge stratification is a difficult
target in two-stroke engines, chiefly because timings of late
injection (necessary for charge stratification) and of early
injection (necessary for homogeneous charge) are much closer
than in four-stroke engines. The compatibility between
stratified and homogeneous charge operations needs a thorough
CFD study of injection and mixing processes, with the support
of techniques of spray visualization. Results strongly depend on
the possibility of optimising the interaction between in-cylinder
gas-dynamic field and spray; experimental activity is necessary
as data source and verification of computational prediction.
This paper shows the latest CFD investigation, experimental
tests and results concerning a 50 cm3 engine for light
motorcycles. The injection is of the liquid type with wall-andair
guided spray produced by a swirl injector. The research has
been focused on the attainment of charge stratification at every
engine speed. Spray actual characteristics have been
investigated, attesting suitable repeatability and proper
variation versus backpressure. Engine satisfactory behaviour
even at light loads in unthrottled condition is proved by good
fuel economy and engine stability in dynamometric bench tests.
Exhaust gas analysis and indicated pressure behaviour confirm
stratification and combustion correctness
Numerical and Experimental Study of Direct Injection for Charge Stratification in a 200 cc Two-Stroke Motorcycle Engine
No full textThis paper shows a numerical and
experimental study concerning liquid highpressure
direct injection with charge stratification
in a 200 cm3 two-stroke motorcycle engine.
Numerical predictions have been performed
using KIVA-3v code with different combustionchamber
shapes and spray characteristics.
Experimental outcomes have substantially
confirmed the predictions of computation and
proved that injector characteristics are of the
utmost importance to achieve satisfactory results
Optimisation of a Stratified Charge Strategy for a Direct Injected Two-Stroke Engine
No full textDirect fuel injection is becoming mandatory in two-stroke S.I. engines, since it prevents one of the major problems of these engines, that is fuel loss from the exhaust port. Another important problem is combustion irregularity at light loads, due to excessive presence of residual gas in the charge, and can be solved by charge stratification.
High-pressure liquid fuel injection is able to control the mixing process inside the cylinder for getting either stratified charge at partial loads or quasi-stoichiometric conditions, as it is required at full load. This paper shows the development of this solution for a small engine for moped and light scooter, using numeric and experimental tools. In order to obtain the best charge characteristics at every load and engine speed, different combustion chambers have been conceived and studied, examining the effects of combustion chamber geometry, together with injector position and injection timing
Studio fluidodinamico della formazione della miscela nel condotto di aspirazione di un motore alimentato con iniettore-pompa pilotato in frequenza
No full textMediante il codice fluidodinamico KIVA3v è stato simulato il comportamento di un motore monocilindrico per usi stazionari alimentato con un sistema d’iniezione indiretta pilotato in frequenza.
Obiettivo dello studio è stato di valutare le discrepanze tra il titolo realizzabile e quello desiderato ed in particolare l’entità delle fluttuazioni di titolo tra un ciclo e l’altro, problemi peculiari di tale sistema d’iniezione e dovuti essenzialmente alla limitazione a poche unità del numero massimo di iniettate per ciclo del motore.
Sono stati indagati l’interazione tra spray e parete del condotto di aspirazione, la formazione del film liquido, l’evaporazione del film e delle gocce, la miscelazione tra l’aria e il vapore per diffusione locale e per trasporto convettivo. Sono state simulate differenti lunghezze del condotto di aspirazione e posizionamenti dell’iniettore ed è stata considerata l’ipotesi di adottare materiali porosi o dispositivi mediante i quali incrementare la superficie bagnata del condotto, al fine di ottenere un vantaggioso “effetto spugna” (o “effetto polmone”)
Direct Injection and Charge Sratification in a 50 cc Two-Stroke Engine: CFD Studies and Test Bench Results
No full textDirect fuel injection has became necessary in two-stroke
S.I. engines, since it prevents one of the major problems of
these engines, that is fuel loss from the exhaust port. Another
important problem is combustion irregularity at light loads, due
to excessive residual gas in the charge, and can be solved by
charge stratification. High-pressure liquid fuel injection is able
to control the mixing process inside the cylinder for getting
either stratified charge at partial loads or quasi-stoichiometric
conditions, as it is required at full load. The feasibility of this
solution for a small engine for light motorcycles has been
studied using CFD tools. An exhaustive investigation carried
out by the KIVA3v code allowed to design a 50 cm3 engine
prototype with a satisfactory behaviour even at light loads in
unthrottled condition, as proved by good fuel economy and
engine stability in dynamometric bench tests. Exhaust gas
analysis and indicated pressure behaviour confirm stratification
and combustion correctness. For the final part of the research
the adoption of the AVL-Fire code has been considered: the
possibility to take into account any combustion chamber and
transfer duct geometric details and the accuracy of spray
breakup and wall film models allow to better understand the
engine behaviour throughout the operating range, obtaining
useful information in order to efficiently shorten the
experimental time required for the EU map-setting
Behaviour of a Small Two-Stroke Engine with Direct Liquid Injection and stratified Charge
No full textHigh-pressure liquid fuel injection is a suitable means to get either stratified charge or homogeneous charge for two-stroke engines. This paper shows the development of this solution for a small 50 cm3 engine for light motorcycles. By means of computational fluid dynamics, a combustion chamber suitable for proper fuel distribution in every engine operating condition has been designed. It has been realized, and experimental results confirm its fairly satisfactory behaviour, with good fuel economy, low exhaust emissions and small cycle-to-cycle variation even at light loads. Recent CFD studies indicate how to improve engine geometry to achieve a better stratification stability at partial loads independently on engine speed
Two Step Concept for Low-Pressure Direct Hydrogen Injection
No full textIn this paper, a low-pressure hydrogen direct-injection
solution is presented that entails low storage residual pressure
(~12 bar). The injection is realised in two steps. First, hydrogen
is simply metered by an electro-injector (a conventional one for
Compressed Natural Gas - CNG application) that feeds a small
intermediate chamber. Next, hydrogen enters the cylinder by
means of a mechanically-actuated valve which allows higher
flow than any electro-injector. Injection must end early enough
to allow good charge homogeneity and, in any case, before incylinder
pressure rise constraints hydrogen admission. Backfire
is avoided by starting injection at intake valve closing. A
prototype has been realised modifying a single-cylinder 650 cc
production engine with three intake valves. The central one has
been modified and properly timed to in-cylinder inject
hydrogen from the intermediate chamber. Hydrogen injection
through different-shape poppet valves in a quiescent, constant
volume has been simulated in order to investigate the effects of
valve and seat-valve geometries in controlling fuel-air mixing
in the cylinder. Additional predictions for the actual engine
configuration indicate that an acceptable fuel distribution can
be obtained in the combustion chamber at the spark timing,
with equivalence ratios in the ignition region that are inside the
flammability range of the mixture for all the operating
conditions (loads and speeds) that have been considered
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
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