1,721,015 research outputs found
METODO PER CONTROLLARE LO SQUILIBRIO NEL RAPPORTO ARIA-COMBUSTIBILE DEI CILINDRI DI UN MOTORE A COMBUSTIONE INTERNA
No full textMetodo per controllare lo squilibrio nel rapporto aria-combustibile dei cilindri (3) di un motore (1) a combustione interna provvisto di una pluralità di cilindri (3) e di almeno un sensore (17) atto a misurare il rapporto aria/combustibile dei gas di scarico prodotti dai cilindri (3); il metodo prevede di determinare la portata (ṁi) teorica di combustibile da iniettare in ciascun cilindro (3) nel caso in cui il rapporto aria-combustibile dei cilindri (3) sia bilanciato; in funzione del segnale proveniente dal sensore (17), determinare sia il rapporto aria/combustibile medio dei gas di scarico, sia un indicatore (ISi) dello squilibrio nel rapporto aria-combustibile dei cilindri (3); e determinare la portata (ṁreal) effettiva di combustibile da iniettare in ciascun cilindro (3) in funzione della portata (ṁi) teorica di combustibile, del rapporto aria/combustibile medio dei gas di scarico e dell’indicatore (ISi) dello squilibrio nel rapporto aria-combustibile dei cilindri (3)
METODO PER RILEVARE LO SQUILIBRIO NEL RAPPORTO ARIA-COMBUSTIBILE DEI CILINDRI DI UN MOTORE A COMBUSTIONE INTERNA
No full textMetodo per determinare la presenza di uno squilibrio nel rapporto aria-combustibile dei cilindri (3) di un motore (1) a combustione interna comprendente un sensore (17) atto a misurare il rapporto aria/combustibile dei gas di scarico prodotti dai cilindri (3); il metodo prevede di selezionare una finestra (DW) angolare di osservazione all’interno del segnale rilevato dal sensore (17) pari ad un ciclo completo di combustione; calcolare un indicatore (ISi) dello squilibrio nel rapporto aria-combustibile dei cilindri (3) attraverso la differenza fra il valore (λMAX_i) massimo ed il valore (λMIN_i) minimo del segnale rilevato dal sensore (17) nella finestra (DW) angolare di osservazione; confrontare il detto indicatore (ISi) con un valore (TV) di soglia; e riconoscere la presenza di uno squilibrio nel rapporto aria-combustibile dei cilindri (3) nel caso in cui l’indicatore (ISi) dello squilibrio nel rapporto aria-combustibile dei cilindri (3) sia superiore al valore (TV) di soglia
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
Innovative Techniques for On-Board Exhaust Gas Dynamic Properties Measurement
No full textThe purpose of this paper is to present some innovative techniques developed for an unconventional utilization of currently standard exhaust sensors, such as HEGO, UEGO, and NOx probes. In order to comply with always more stringent legislation about pollutant emissions, intake-exhaust systems are becoming even more complex and sophisticated, especially for CI engines, often including one or two UEGO sensors and a NOx sensor, and potentially equipped with both short-route and long-route EGR. Within this context, the effort to carry out novel methods for measuring the main exhaust gas dynamic properties exploiting sensors installed for different purposes, could be useful both for control applications, such as EGR rates estimation, or cost reduction, minimizing the on-board devices number.
In this work, a gray-box model for measuring the gas mass flow rate, based on standard NOx sensor operating parameters of its heating circuit, is analyzed. Its accuracy is then compared to the one of a similar model applied to the UEGO probe, presented in a previous paper, to on-board standard MAF and speed-density measurements, and to a simple pressure loss-flow characteristic model, whose robustness derives from the particular NOx probe location in the exhaust pipe. The comparison is performed for steady-state tests. The sensitivity to model input variables is also considered, that is gas temperature and pressure, leading to the introduction of a complementary physical model and besides describing an adaptive method for estimating exhaust gas static pressure, which is based on the pressure-current dependence of UEGO and NOx sensors
Experimental Validation of a Model-Based Water Injection Combustion Control System for On-Board Application
No full textWater Injection (WI) has become a key technology for increasing combustion efficiency in modern GDI turbocharged engines. In fact, the addition of water mitigates significantly the occurrence of knock, reduces exhaust gas temperatures, and opens the possibility to reach optimum heat release phasing even at high load.
This work presents the latest development of a model-based WI controller, and its experimental validation on a GDI TC engine. The controller is based on a novel approach that involves an analytic combustion model to define the spark advance (SA) required to reach a combustion phase target, considering injected water mass effects. The calibration and experimental validation of the proposed controller is shown in detail in the paper. At first, the focus is on the open-loop branch, to evaluate the performance of the combustion model and its ability to manage Spark Advance (SA) taking in account the phasing implications of WI, maintaining a pre-defined combustion phase target. Then the closed-loop (CL) chain is introduced, defining a structure that allows reaching the target while keeping knock intensity (KI) levels under an established threshold using two different control levers (SA and WI). At the same time, the controller has been designed to minimize water consumption. The proposed controller has then been implemented in a Rapid Control Prototyping environment, to validate the strategy on a real engine. As shown in the paper, this approach allows to manage both combustion phasing and knock level in an engine equipped with WI.
The closed-loop controller was initially based on in-cylinder pressure signals both for knock intensity and combustion phasing measurements. To allow the proposed controller to be ready for an on-board implementation, there is the need to replace the pressure signal used from the in-cylinder pressure sensor, not available on commercial vehicles. For this, a specific signal processing algorithm has been developed to extract the angular combustion phase from the accelerometric signals available on-board, and it has been validated with experimental data
Real-Time Estimation of Intake O2 Concentration in Turbocharged Common-Rail Diesel Engines
No full textAutomotive engines and control systems are more and more sophisticated due to increasingly restrictive environmental
regulations. Particularly in both Diesel and SI lean-burn engines NOx emissions are the key pollutants to deal with and
sophisticated Engine Management System (EMS) strategies and after-treatment devices have to be applied. In this context,
the in-cylinder oxygen mass fraction plays a key-role due its direct influence on the NOx formation mechanism. Real-time
estimation of the intake O2 charge enhances the NOx prediction during engine transients, suitable for both dynamic
adjustments of EMS strategies and management of after-treatment devices.
The paper focuses on the development and experimental validation of a real-time estimator of O2 concentration in the
intake manifold of an automotive common-rail Diesel engine, equipped with turbocharger and EGR system. The paper
analyzes the air intake process and the influence of the exhaust gas recirculation system based on a mean value modeling
approach. All variables required are available at EMS level, thus allowing an on-board implementation without extra costs
for additional sensors.
The accuracy of the developed estimator is assessed by comparing simulated and experimental trajectories of O2
concentration, measured by a Universal Exhaust Gas Oxygen (UEGO) sensor located in the intake manifold. The
experimental tests were carried out at the test bench, imposing severe engine transients. The results evidence that the O2
estimator presents a good accuracy vs. experiments and offers significant opportunities for improving engine control and
after-treatment devices management during transient operation
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