1,721,130 research outputs found
Experimental Activity on a Hydrogen Fuelled S.I. Engine with Two-Step D.I
No full textAn innovative hydrogen DI system was conceived, realized and tested that requires only 12 bar rail pressure, typical value of
PFI systems, and does not need special injectors. The purpose is to combine the well known benefits of DI with the ones of
PFI. The injection is accomplished in two steps: at first hydrogen, metered by an electroinjector (a conventional one for CNG
application), enters a small intermediate chamber; then it is injected into the cylinder by means of a mechanically-actuated
valve that allows very high flow rate (compared with the one of electroinjectors). In-cylinder injection starts at intake valve
closing (an earlier injection start could lead to backfire) and stops early enough to allow proper charge homogeneity and, in
any case, before cylinder pressure rise constrains hydrogen admission.
The prototype engine was realised modifying a production single-cylinder 650 cm3 engine with three intake valves. The central
one was modified and properly timed to inject hydrogen into the cylinder from the intermediate chamber.
The experimental results satisfied the expectations. The prototype engine ran properly at full load, without pre-ignition,
knocking or roughness even with stoichiometric or slightly rich mixtures, providing higher maximum power than with
gasoline. Also at part load the engine proved to work correctly even with very lean mixtures (till λ~4), reaching its maximum
brake thermal efficiency with λ ~ 2.4
Sistema di iniezione diretta di idrogeno per motori ad A.C
No full textIl presente trovato realizza un sistema di iniezione diretta di idrogeno in fase gassosa per motori ad accensione comandata, il quale permette di non incorre negli inconvenienti sopra detti di sfruttamento solo parziale dell’idrogeno stoccato a bordo del veicolo e della necessità di iniettori di caratteristiche eccezionali. Infatti, grazie al fatto che l’iniezione dell’idrogeno nel cilindro motore avviene attraverso una valvola a fungo attuata meccanicamente, che permette un’ampia sezione di passaggio, è possibile iniettare considerevoli quantità di idrogeno in tempi ridotti utilizzando basse pressioni di iniezione (ad esempio 6 bar). A monte della valvola di iniezione è collocato un piccolo serbatoio all’interno del quale viene iniettata la voluta quantità di idrogeno attraverso un normale elettro-iniettore utilizzato su motori alimentati a gas naturale. La pressione di iniezione verso il piccolo serbatoio è tale da garantire sempre le condizioni di efflusso sonico attraverso l’elettro-iniettore, in modo da avere dipendenza lineare tra durata di iniezione e quantità d’idrogeno iniettata
Further Insight into the Possibility to Fuel a SI Engine with Ammonia plus Hydrogen
No full textStoring hydrogen is one of the major issues concerning its utilization on board vehicles. A promising solution is storing hydrogen in the form of ammonia that contains almost 18% hydrogen by mass and is liquid at roughly 9 bar at environmental temperature. As a matter of fact, liquid ammonia contains 1.7 times as much hydrogen as liquid hydrogen itself, thus involving relatively small volumes and light and low-cost tanks.
It is well known that ammonia can be burned directly in I.C. engines, however a combustion promoter is necessary to support and speed up combustion especially in the case of high-speed S.I. engines.
The best promoter is hydrogen, due to its opposed and complementary characteristics to those of ammonia, Hydrogen has high combustion velocity, low ignition energy and wide flammability range, whereas ammonia has low flame speed, narrow flammability range, high ignition energy and high self-ignition temperature. Another important point is the possibility to obtain hydrogen on board from ammonia, by means of a catalytic reactor.
In a previous research the possibility to run a small 4-stroke twin-cylinder SI engine of 505 cm3 with ammonia plus a small amount of hydrogen was demonstrated. Apart, the suitability of a custom-designed catalytic reactor to produce hydrogen from ammonia with the required flow rate was verified as well.
This paper shows experimental results obtained coupling the catalytic reactor to the engine and using the heat of the exhaust gases as energy source to keep the reactor at its operative temperature. The device necessary to control the ammonia reactor is described too
Numerical Investigation of an Innovative low pressure Direct-Injection System for hydrogen Engine
No full textThe paper shows CFD activity concerning an innovative hydrogen direct-injection system,
characterized by low fuel rail pressure.
The system allows combining the benefits of hydrogen direct injection, mainly consisting in
high specific power and in backfire prevention, with the typical ones of indirect injection,
mainly consisting in the almost complete utilization of the on-board stored hydrogen, as well
as in low cost and reliability.
The injection is split in two steps: first an electroinjector meters hydrogen and feeds a small
intermediate chamber, then the hydrogen stored in the chamber is injected into the cylinder
with proper timing by a mechanically-actuated valve.
A prototype was derived from a production single-cylinder motorcycle engine on the basis of
previous CFD predictions and, despite important limitations in design freedom, proved to run
correctly, without the typical drawbacks of hydrogen engines. Maximum power was higher
than with gasoline.
Present CFD activity is aimed at designing a new engine originally intended for hydrogen.
Axisymmetric analyses have been carried out for several valve and seat-valve profiles,
proving that proper geometrical details allow quite satisfactory fuel distribution at the ignition
time for every engine speed and load
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
- …
