Silvia Marelli

Experimental analysis of unsteady flow performance in an automotive turbocharger turbine fitted with a waste-gate valve

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.

Turbocharger turbine performance under steady and unsteady flow: test bed analysis and correlation criteria

Turbocharging is becoming a key technology for both gasoline and diesel automotive engines. A thorough knowledge of turbine behaviour under steady and unsteady flow conditions is a fundamental requirement for the improvement of engine performance, particularly in transient operation. To this end, a great deal of information can be obtained from investigations developed on dedicated test facilities. This paper presents a new arrangement of the turbocharger test rig operating at the University of Genoa. The results of an extensive experimental programme, focusing on the behaviour of the turbocharger regulating system, on turbine pulsating flow performance and its correlation criteria with steady flow results, are then analysed.

Numerical Comparison of an Electric Turbo Compound Applied to a SI and a CI Engine

In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will 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 ignition (SI) and compression ignition (CI) engines. Following this aspect, the possibility to couple an electric machine to the turbocharger (electric turbo compound, ETC) 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 focused on the comparison of the benefits resulting from the application of an ETC to a small twin-cylinder SI engine (900 cm3) and to a four cylinders CI engine (1600 cm3), both of the same maximum power. Starting from the experimental maps of several turbines and compressors, complete model of both turbocharged engines were created using the AVL BOOST one-dimension code.Concerning the SI engine, first numerical results show that ETC can improve the average overall efficiency at the highest engine speeds and loads. Besides, boost range extension in the lowest engine rotational speed region and a possible reduction of turbo lag represent other benefits related to ETC application.On the other hand, the adoption of an ETC to a CI engine shows larger benefits in term energy recovery at the highest engine speeds, with consequent reduction of fuel consumption, mainly due to the absence of throttling effects in the intake manifold and related pumping losses.Copyright

One-Dimensional Simulations and Experimental Analysis of a Wastegated Turbine for Automotive Engines under Unsteady Flow Conditions

In this paper, the unsteady-state behaviour of a turbocharger wastegated turbine (IHI-RHF3) is investigated using both an experimental approach and a numerical approach. First, an experimental campaign is performed in a specialized test rig operating at the University of Genoa, for different openings of the wastegate valve and under steady flow and unsteady flow operations. An appropriate configuration of the turbine outlet circuit fitted with a separating wall is used to carry out instantaneous measurements downstream of the turbine wheel and the wastegate valve. The above data constitute the basis for the tuning and validation of a one-dimensional turbine model recently developed at the University of Naples. Preliminary model tuning is carried out on the basis of the characteristic map measured for a completely closed wastegate valve under steady flow operations. A refined one-dimensional schematization of the experimental apparatus is implemented within the commercial GT-Power® software, including the turbine, the wastegate 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 (the inlet and outlet ducts, the volute and the wheel) to account for the wave propagation and storage phenomena inside the machine. A detailed one-dimensional schematization of the wastegate circuit is also implemented and independently tuned. The turbine model capability under unsteady flow conditions is tested for different wastegate openings and pulse frequencies, by applying time-dependent boundary conditions. In particular, the pressures and temperatures measured upstream and downstream are imposed at the model ends, and the instantaneous mass flow rate and the actual power are numerically evaluated. The results are compared with the experimental data, demonstrating good accuracy and showing some improvements with 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.

Experimental Comparison of Different Diesel-Biodiesel Blends in a CFR Engine

A wide experimental investigation was performed on a CFR engine with a view to comparing different renewable fuels in terms of Cetane Number, engine brake thermal efficiency and exhaust emissions.The CFR engine available at the Internal Combustion Engines Group of the University of Genoa was properly modified and fully instrumented in order to control operating conditions and to measure the average engine parameters and in-cylinder pressure diagrams.Aiming at the comparison of fuels obtained from various feedstock, an experimental procedure was then defined, including the standard Cetane Number evaluation and the definition of engine operating quantities in 16 different working points, considering four levels of rotational speed and load, for fixed levels of compression ratio and injection advance.Methyl-esters of rapeseed oil and of vegetable oils mix were investigated, while rapeseed, palm and coconut oil were also available. Several blends, obtained by mixing different biodiesel fractions with conventional diesel oil, assumed as reference fuel, were tested applying the defined experimental procedure.In the paper the experimental setup is firstly presented describing changes and instrumentation of CFR engine. The investigation program is then summarized in order to introduce results discussion, mainly focused on the analysis of the influence of the biodiesel content on brake thermal efficiency, NOx and soot emissions, taking into account fuel properties.Copyright

An experimental apparatus for testing biodiesels based on a CFR engine - setup and validation with different methyl ester blends.

ABSTRACT A cooperative fuel research (CFR) engine was modified and instrumented in order to control operating conditions and to measure engine parameters and in-cylinder pressure diagrams. Aiming at the comparison of different alternative fuels, an experimental procedure was defined, including cetane number (CN) evaluation and the definition of engine operating quantities in different working points, for fixed levels of compression ratio (CR) and injection advance. An investigation was made considering several blends of methyl-esters of rapeseed oil (RME) and of a mix of vegetable oils (VOME) with conventional diesel oil. The defined experimental procedure was applied to assess CN, engine brake thermal efficiency (bte) and exhaust emissions. Results show that the biodiesel content has a positive influence on soot emissions, with strong reduction, while thermal efficiency and NOX emissions are negatively affected, which can be justified taking into account fuel properties and changes in combustion process. As observed outcomes are generally in line with those presented in literature, the facility proved to be a suitable tool for basic investigations on alternative fuels to be used in specific applications.

Characterization of Driving Patterns and Operations of Heavy Duty Vehicles in a Port Area and Their Influence on Exhaust Emissions and Fuel Consumption Evaluation Through Different Emission Models

An experimental and theoretical investigation is being performed with a view to evaluate the contribution of Heavy duty vehicles (HDVs) to exhaust emissions and fuel consumption in urban areas involved by commercial shipping activities.Reference is made to the city of Genoa, whose urban road network is influenced both by shipping activities and highway connections, as more than twenty accesses to port area and seven motorway exits are available within the urban area.Different aspects were deepened in this study. Firstly, the HDV flows crossing highway exits, urban zones and port areas were assessed, as well as the relevant vehicle classes. Secondly, the typical urban trips linking highway exits to port gates and the HDV mission profiles within the port area were identified. Measurements of HDV instantaneous speed related to the urban trips were then planned aiming at the definition of the most representative speed patterns through a proper statistical data processing, enabling the application of Passenger Car and Heavy Duty Emission Model (PHEM) for the estimation of emission and fuel consumption factors for selected HDV classes.The main results of the different investigation steps are presented and discussed in the paper, outlining the peculiar mission of HDVs in port area and the related emissive behavior.Copyright

A detailed one-dimensional model to predict the unsteady behavior of turbocharger turbines for internal combustion engine applications

This article describes an investigation of the unsteady behavior of turbocharger turbines by one-dimensional modeling and experimental analysis. A one-dimensional model has been developed to predict the performance of a vaneless radial-inflow turbine submitted to unsteady flow conditions. Different from other approaches proposed in the literature, the turbine has been simulated by separating the effects of casing and rotor on the unsteady flow and by modeling the multiple rotor entries from the volute. This is a simple and effective way to represent the turbine volute by a network of one-dimensional pipes, in order to capture the mass storage effect due to the system volume, as well as the circumferential variation of fluid dynamic conditions along the volute, responsible for variable admittance of mass into the rotor through blade passages. The method developed is described, and the accuracy of the one-dimensional model is shown by comparing predicted results with measured data, achieved on a test rig dedicated to the investigation of automotive turbochargers. The validation of the code is presented and an analysis of the flow unsteadiness, based on a variety of parameters, is proposed.