Downsizing and turbocharging is today an effective way of enhancing fuel economy in automotive engines. However, more information on compressor and turbine behaviour when working under unsteady flow conditions typically occurring in automotive turbocharged engines is still required to improve simulation models.The results of an experimental investigation into a small turbocharger turbine fitted with a waste-gate valve are presented in this paper. Turbine performance was measured under both steady and unsteady flow operation. Particular attention was given to pulsating flow performance, evaluated starting from the measurement of instantaneous parameters (inlet and outlet static pressure, mass flowrate, and turbocharger rotational speed). The effect of flow unsteadiness on turbine behaviour is analysed, referring to different pulse frequencies and waste-gate settings.The paper highlights that steady and unsteady turbine performance when the waste-gate valve is partially or totally open should be known in order to improve engine-turbocharger matching calculations.
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. A different and more refined procedure has been recently proposed. The new approach is based on the solution of the 1D unsteady flow within the stationary and rotating channels constituting the compressor device, starting from a reduced set of geometrical data. The refined methodology can be utilized to directly compute the stationary map of the compressor but also to reproduce the unsteady flow behavior of the device. A specialized components test rig (particularly suited to study automotive turbochargers) has been operating since several years at the University of Genoa. The test facility also allows to develop studies under unsteady flow conditions both on single components and subassemblies of engine intake and exhaust circuit. In the paper the results of a preliminary experimental study developed on a turbocharger compressor for gasoline engine application under unsteady flow conditions are presented. Instantaneous inlet and outlet static pressure and mass flow rate are compared with the corresponding numerical data supplied by simulation codes. The numerical results showed a good agreement with experimental data. In addition, the comparison between the classical and the refined procedure results highlighted the potential of the performed unsteady 1D calculation, especially in specific compressor operating conditions. The integration of the experimental activity with the numerical analysis represents a methodology that can be helpfully employed during the design process of internal combustion engine intake systems
In a medium term scenario hybrid powertrain and Internal Combustion Engine (ICE) downsizing represent the actual trend in vehicle technology to reduce fuel consumption and CO2 emission. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory both for spark ignited (SI) and compression ignited (CI) engines. Following this aspect, the possibility to couple an electric drive to the turbocharger (electric turbo compound) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world and by the current application in the F1 Championship. The present paper shows the first numerical results of a research program in collaboration between the Universities of Pisa and Genoa. This first study is focused on the evaluation of the benefits resulting from the application of an ETC (Electric Turbo Compound) to a small twin-cylinder SI engine (900 cm3). Starting from the experimental maps of two turbines and one compressor, the complete model of a turbocharged engine was created using the AVL BOOST one-dimension code. The numerical activity then moves to the whole vehicle/powertrain modelling, considering three driving cycles and two different vehicle configurations, in order to verify the effectiveness of the proposed ETC solution. Results show that the adoption of ETC is not advantageous if used for a conventional turbocharger turbine, if the target is to optimize the overall efficiency in one specific operating point of the ICE, like in the case of range-extended electric vehicles. Besides, ETC can slightly improve the average overall efficiency when the ICE must provide variable power output, as in the case of conventional or hybrid vehicles. However, the major benefits coming from ETC are the boost range extension in the lowest engine rotational speed region and a possible reduction of turbo lag, which are key points in parallel-hybrid and especially in conventional vehicles. Concerning the whole vehicle/powertrain simulation, first results show that the ETC does not improve fuel economy of the smaller vehicle, especially when employed in urban cycles. The ETC is much more advantageous in the case of the larger vehicle, particularly when extra-urban roads or motorways are considered
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