1,721,026 research outputs found
Sulle prestazioni in transitorio del sistema di sovralimentazione di motori automobilistici
No full textIndagine sperimentale in regime non stazionario su una piccola turbina per la sovralimentazione di MCI dotata di valvola waste-gate
No full textSulla valutazione del rendimento non stazionario di una turbina di sovralimentazione dotata di valvola waste-gate
No full textLa tecnica della sovralimentazione risulta allo stato attuale largamente diffusa in ambito veicolistico, specialmente in relazione ai benefici che può portare in termini di riduzione del consumo specifico di combustibile e delle emissioni inquinanti prodotte allo scarico del motore. Può apparire inoltre estremamente vantaggiosa per lo sviluppo di propulsori ad accensione comandata downsized, se ad essa è associato l’impiego di altre tecnologie quali l’iniezione diretta del combustibile ed il controllo flessibile delle valvole. L’ottimizzazione di un motore turbosovralimentato non può però prescindere dalla conoscenza del comportamento del sovralimentatore in condizioni operative non stazionarie. L’instazionarietà dei flussi presenti nei condotti di aspirazione e scarico dei MCI porta infatti a considerare le curve caratteristiche di turbina e compressore, misurate dal costruttore in condizioni di funzionamento stazionario, non indicative delle effettive prestazioni delle turbomacchine. Risulta quindi di fondamentale importanza poter misurare in condizioni di alimentazione correlate a quelle sperimentate su motore, i livelli istantanei delle grandezze d’interesse.
Il banco prova operante presso il laboratorio componenti MCI dell’Università di Genova permette di riprodurre il flusso non stazionario generato dall’apertura periodica delle valvole del motore mediante due sistemi generatori di pulsazioni di differenti caratteristiche. Nella memoria vengono presentate differenti procedure per la valutazione del rendimento di una turbina di sovralimentazione in condizioni di flusso stazionario e non stazionario; vengono quindi analizzati i risultati più salienti di un’estesa campagna di prove condotta su una turbina di sovralimentazione per applicazione automobilistica. L’analisi sarà incentrata sulla valutazione del rendimento in condizioni di flusso non stazionario, includendo l’effetto della valvola waste-gate
Sui fenomeni non stazionari nel circuito di sovralimentazione di piccoli MCI automobilistici
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Experimental investigation into the pulsating flow performance of a turbocharger turbine in the closed and open waste-gate region
No full textNowadays, turbocharging is considered as a key technology for reducing CO2 emissions in downsized automotive engines. However, more information is still required on compressor and turbine behaviour when working under unsteady flow conditions.
The results of an extensive investigation into a small turbocharger turbine fitted with a waste-gate valve are presented in this paper. Measurements were developed at the University of Genoa test facility which allows investigations to be performed under both steady and unsteady flow conditions.
Turbine unsteady performance was evaluated at different operating conditions, starting from the measurement of instantaneous parameters (inlet and outlet static pressure, mass flow rate and turbocharger rotational speed). This paper analyses the effect of flow unsteadiness on turbine performance at different pulse frequencies and waste-gate settings
Unsteady flow behaviour of the turbocharging circuit in downsized SI automotive engines
No full textThe need to reduce CO2 emissions and the increasing cost of fuel will require
the development of high efficiency automotive combustion engines, while complying with
near-zero pollutant emissions. In recent years, the diesel engine was substantially improved,
due to the introduction of electronically controlled fuel injection systems and advanced
turbocharging units. On the other side, the Spark Ignition (SI) engine has to significantly
reduce fuel consumption, especially at part load operation, to accomplish CO2 emission
targets. Downsizing SI engines is a promising way to attain a better fuel economy: a potential
of efficiency increase between 10 and 30 per cent can be achieved if a global approach is
used, by integrating both available and innovative technologies (turbocharging, gasoline
direct injection, variable valve actuation, etc), managed by proper control strategies.
Within this frame, it is apparent that turbocharging is becoming a key technology for both
gasoline and diesel automotive applications. However, a successful application of
turbocharging to SI engines has to face different problems related to the specific operating
environment (exhaust gas temperature level) and to functional aspects (torque curve
configuration, transient response). Research work on this subject is needed, particularly
focusing on the turbocharger behaviour in the typical unsteady flow conditions occurring in
automotive engines. To this purpose, measurements performed on dedicated test facilities can
supply a lot of information to be used both in the development of simulation models and to
assess correlation criteria between steady and unsteady turbocharger performance.
In the paper the results of an extensive experimental investigation, developed on small
turbochargers for downsized gasoline engines by using a flexible test rig operating at the
University of Genoa, are presented. The study was focused on the unsteady flow behaviour of
the turbocharging circuit, referring to different aspects.
As a first item, the effect of exhaust line geometry on flow unsteadiness was deepened by
comparing measured pressure diagrams in different circuit configurations. In the case of a
typical ‘4 into 1’ exhaust manifold, a noticeable increase of turbine inlet pulse amplitude was
achieved by using an appropriate dividing wall in the manifold mixing section.
In the second half of the paper, the influence of the main pulsating flow parameters on the
amount of available energy at the turbine inlet is considered, by evaluating this quantity on
the basis of instantaneous turbine inlet parameters. The available energy confirmed to be
related to the pulse amplitude at the turbine entry, which proved to depend both on the pulse
frequency and the mean pressure level. Finally, turbine overall efficiency values in pulsating
flow conditions are presented and compared with the levels calculated on the basis of mean
measured parameters and with those referred to turbine steady flow operation
One-dimensional simulations and experimental analysis of a wastegated turbine for automotive engines under unsteady flow conditions
No full textIn the paper, the unsteady behaviour of a turbocharger waste-gated turbine (IHI-RHF3) is investigated following both an experimental and numerical approach. First, an experimental campaign is performed in a specialized test rig operating at the University of Genoa, for different openings of the waste-gate valve and under steady and unsteady flow operations. A proper configuration of the turbine outlet circuit fitted with a separating wall is used to carry out instantaneous measurements downstream the turbine wheel and the waste-gate valve.
The above data constitute the basis for the tuning and validation of a 1D turbine model, recently developed at the University of Naples. The procedure geometrically schematizes the entire turbine, starting from few linear and angular dimensions directly measured on the hardware. A preliminary model tuning is carried out on the basis of the characteristic map measured for a completely closed waste-gate valve under steady flow operations.
Then, a refined 1D schematization of the experimental apparatus is implemented within the commercial GT-Power® software, including the turbine, the waste-gate circuit and the upstream and downstream measuring stations. In particular, the classical map-based approach is suitably corrected with a sequence of pipes that schematizes each component of the turbine (inlet/outlet ducts, volute and wheel) to account for the wave propagation and storage phenomena inside the machine. A detailed 1D schematization of the waste-gate circuit is also implemented and independently tuned.
Finally, the turbine model capability under unsteady flow conditions is tested for different waste-gate openings and pulse frequencies, by applying time-dependent boundary conditions. In particular, the upstream and downstream measured pressure and temperature are imposed at the model ends, and the instantaneous mass flow rate and actual power are numerically evaluated. The results are compared with the experimental data, denoting a good accuracy, and showing some improvements with the respect to the standard turbine modelling in the case of the mass flow rate prediction. On the contrary, the computed actual power shows some inaccuracies, especially at higher pulse frequencies
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