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Nowadays, the electric supercharger for turbocharged downsized automotive engines is mainly used to improve torque at low engine speeds in order to obtain an enhancement of the time to boost. These components are usually designed to fill the gap in terms of torque in transient operation caused by the main turbocharger with reference to the typical turbo lag issues. An advanced solution of the engine boosting system is taken into account, considering the adoption of an electrically assisted compressor (e-compressor) coupled to a waste-gated turbocharger, typically adopted alone, in order to provide a reduced turbo-lag. In order to highlight the behavior of the electric supercharger coupled to the turbocharger, the first experimental investigation regarded the steady flow characterization of the compressor.

Nowadays, turbocharging is a technique widely used to improve fuel consumption and exhaust emissions in automotive engines. Centrifugal compressors are typically adopted, even if an efficient engine integration is often restricted by surge phenomena. The focus of the present work is to describe an experimental analysis developed with the aim at characterizing and identifying compressor behavior in incipient surge conditions. The acoustic and vibrational operative response of two automotive centrifugal compressors has been experimentally analyzed on the test facility operating at the University of Genoa. Each compressor is characterized by a classical architecture and one of them is equipped with a “ported shroud”, which enlarges stable zone. Compressors characteristic curves have been measured under steady flow conditions for different levels of corrected rotational speed from the choking region to the surge line.

Downsizing is widely considered one of the main path to reduce the fuel consumption of spark ignition internal combustion engines. As known, despite the reduced size, the required torque and power targets can be attained thanks to an adequate boost level provided by a turbocharger. However, some drawbacks usually arise when the engine operates at full load and low speeds. In fact, in the above conditions, the boost pressure and the engine performance is limited since the compressor experiences close-to-surge operation. This occurrence is even greater in case of extremely downsized engines with a reduced number of cylinders and a small intake circuit volume, where the compressor works under strongly unsteady flow conditions and its instantaneous operating point most likely overcomes the steady surge margin. In the paper, both experimental and numerical approaches are followed to describe the unsteady behavior of a small in-series turbocharger compressor.

In the last few years, the effect of diabatic test conditions on compressor performance maps has been widely investigated leading some authors to propose different correction models. The accuracy of performance maps constitutes the basis of the turbocharger matching with the engine, for which 1D procedures are more and more adopted. The classical quasi-steady approach generally used is based on the employment of compressor and turbine characteristic maps assuming adiabatic turbocharger conditions. The aim of the paper is to investigate the effect of heat transfer phenomena on the experimental definition of turbocharger maps, focusing on compressor performance. This work was developed within a collaboration between the Polytechnic School of the University of Genoa and CRITT M2A. The compressor steady flow behavior was analyzed through tests performed on different test rigs operating at the University of Genoa and at CRITT M2A, under various heat transfer conditions.

In the paper the results of an experimental campaign regarding the steady characterization of a turbocharger waste-gated turbine (IHI-RHF3) for gasoline engine application are presented. The turbine behavior is analyzed in a specialized test rig operating at the University of Genoa, under different openings of the waste-gate valve. The test facility allows to measure inlet and outlet static pressures, mass flow rate and turbocharger rotational speed. The above data constitute the basis for the tuning and validation of a numerical procedure, recently developed at the University of Naples, following a 1D approach (1D turbine model - 1DTM). The model geometrically schematizes the entire turbine based on few linear and angular dimensions directly measured on the hardware. The 1D steady flow equations are then solved within the stationary and rotating channels constituting the device. All the main flow losses are properly taken into account in the model.

The flow in turbocharger compressors and turbines for automotive engine application is highly unsteady in nature, as it responds to the intake and exhaust manifolds of the internal combustion engine. The optimization of the turbocharger system is therefore a very difficult task, since only steady flow maps are generally provided by turbocharger manufacturer. For several years a specialized components test facility operates at the University of Genoa, particularly suitable to test turbochargers under steady and unsteady flow conditions. The test bench has been continuously upgraded in order to study components under pulsating flow condition by using different layout configurations. A recent set-up makes it possible to study turbocharger compressor under unsteady flow condition by using a rotating valve pulse generator system. Measurements of pressure signals downstream the compressor, instantaneous mass flow rate and turbocharger rotational speed are performed.

Turbocharging technique will play a fundamental role in the near future not only to improve automotive engine performance, but also to reduce fuel consumption and exhaust emissions both in Spark Ignition and diesel automotive applications. To achieve excellent engine performance for road application, it is necessary to overcome some typical turbocharging drawbacks i.e., low end torque level and transient response. Experimental studies, developed on dedicated test facilities, can supply a lot of information to optimize the engine-turbocharger matching, especially if tests can be extended to the typical engine operating conditions (unsteady flow). Different numerical procedures have been developed at the University of Naples to predict automotive turbocharger compressor performance both under steady and unsteady flow conditions. A classical 1D approach, based on the employment of compressor characteristic maps, was firstly followed.

Turbocharging is becoming a key technology for automotive spark ignition engines (fed with both liquid and gaseous fuel) as a support to the downsizing concept in order to reduce fuel consumption and exhaust emissions. A waste-gate valve is usually fitted as turbocharger control system in these applications, due to its ability to work at very high exhaust gas temperatures. However, not much information is generally available on turbine behaviour in the opened waste-gate area. This paper presents the results of an experimental study developed on a waste-gated turbocharger for downsized SI automotive engines, performed on the test rig operating at the University of Genoa (Italy), extended both to steady and unsteady flow operation. Mass flow through the by-pass valve and turbine impeller was measured at different waste-gate settings in steady flow conditions.

Experimental investigations on automotive engine intake and exhaust components are fundamental to achieve a better understanding of their behaviour both in steady and transient operation. To this purpose a dedicated test facility, particularly suited for the evaluation of exhaust turbochargers performance, has been operating at the University of Genoa (ICEG). In the paper a new arrangement of the testing circuit and of the relevant measuring system is presented. At the conclusion of the plant setup a first investigation on a typical automotive turbocharger for spark ignition application was developed. After measuring compressor and turbine steady flow curves in a wide operating range, the attention was focused on unsteady flow phenomena in the exhaust subsystem when using the two pulsating flow generators available on the test rig. The relevant results are presented in the paper referring to measured pressure diagrams.