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The isentropic efficiency estimation of small radial turbines is an important aspect of turbocharger performance evaluation. Because of inaccuracies in measuring the outlet temperature due to the non-homogeneous flow field distribution, it is common practice to refer to the thermomechanical efficiency, defined as the product of mechanical and turbine isentropic efficiencies. This paper proposes a method for the indirect evaluation of turbine isentropic efficiency through specific experimental tests. In particular, the evaluation of friction losses in the bearings can be assessed thanks to experimental investigations in quasi-adiabatic condition. By maintaining the turbine inlet temperature and the average temperature of lubricating oil and water-cooling circuit equal to the compressor outlet temperature, a negligible heat transfer between turbine and compressor can be achieved.

Fun to drive and drivability are important issues in modern vehicles, and the propulsion system plays a key role in achieving these goals. Today most engines are characterized by the presence of a turbocharging system to achieve a high level of specific power and efficiency. Unfortunately, turbocharged engines are characterized by a delay in the delivery of toque, especially at low load and low speed, a phenomenon commonly called turbo-lag. In this paper an innovative turbocharging system is studied with the aim of providing a solution to this annoying behavior; a hybrid boosting system consisting of a traditional turbocharger and an electrically assisted compressor is analyzed. This architecture, especially thanks to the good dynamic behavior of the e-compressor, achieves the goal of an important reduction in terms of time-to-boost, providing an important improvement in engine readiness.

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.

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 turbocharger performance map constitute the basis for the tuning and validation of a numerical method, usually adopted for the prediction of engine-turbocharger matching. Actually, it is common practice in automotive applications to use simulation codes, which can either require measured compression ratio and efficiency maps as input values or calculate them “on the fly” throughout specific sub-models integrated in the numerical procedures. Therefore, the ability to correct the measured performance maps taking into account internal heat transfer would allow the implementation of commercial simulation codes used for engine-turbocharger matching calculations.

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.

In this work the 3Dcell method, a quasi3D approach developed by the Internal Combustion Engine Group at Politecnico di Milano, has been extended and applied to the fluid dynamic simulation of turbocharging devices for internal combustion engines, focusing on the compressor side. The 3Dcell is based on a pseudo-staggered leapfrog method applied to the governing equation of a 1D problem arbitrarily oriented in space. The system of equations is solved referring to the relative system in the rotating zone, whereas the absolute reference system has been used elsewhere. The vaneless diffuser has been modelled resorting to the conservation of the angular momentum of the flow stream in the tangential direction, combined with the solution of the momentum equation in the radial direction.

Downsizing and boosting is currently the principal solution to reduce fuel consumption in automotive engines without penalizing the power output. A key challenge for controlling the boost pressure during highly transient operations lies in avoiding to operate the turbocharger compressor in its instability region, also known as surge. While this phenomenon is well known by control engineers, it is still difficult to accurately predict during transient operations. For this reason, the scientific community has directed considerable efforts to understand the phenomena leading to the onset of unstable behavior, principally through experimental investigations or high-fidelity CFD simulations. On the other hand, less emphasis has been placed on creating control-oriented models that adopt a physics-based (rather than data-driven) approach to predict the onset of instability phenomena.

Downsizing and turbocharging are today considered an effective way to reduce CO2 emissions in automotive gasoline engines, especially for the European and US markets. In the broad field of research and development for engine boosting systems, the instability phenomenon of surge has gathered considerable interest in recent years, as the main limiting factor to high performance boosting and boost pressure control. To this extent, developing an in-depth knowledge of the surge dynamics and on the phenomena governing the transition from stable to unstable operation can provide very valuable information for the design of the intake system and boost pressure control algorithms, allowing optimal boost pressure without compromising the transient response.

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 aim of the paper is to investigate the effect of heat transfer phenomena on the experimental definition of turbocharger maps, focusing on turbine performance. An experimental investigation on a small turbocharger for automotive application has been carried out and presented. The study focused onto the effects of internal heat transfer on turbine thermomechanical efficiency. The experimental campaign was developed considering the effect of different heat transfer state by varying turbine inlet temperature, oil and coolant temperature and compressor inlet pressure. An original model previously developed by the Authors is adopted for the correction of compressor steady flow maps.

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.

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.