Scuola Politecnica,Dipartimento di Ingegneria Meccanica, Energetica, Gestionale e dei Trasporti, Sezione MASET, Via Montallegro 1, I - 16145 Genova, Italia
Since over 25 years the Intake and Exhaust Components Laboratory is operating at the Internal Combustion Engines Group of the University of Genoa.
Many investigations have been developed, most of which using an original experimental facility that allows to study single devices and subassemblies of automotive intake and exhaust circuit, both under steady flow conditions and with a pulsating flow which reproduces the pressure pulses occurring in multi-cylinder engines.
The test rig operating at the Internal Combustion Engines Group is a continuous flow apparatus which allows tests to be performed on individual components and subassemblies of automotive engine intake and exhaust circuits. The test bench, schematically shown in Figure 1, is a hot and cold compressed air apparatus. Three electrical screw compressors can supply a total mass flow rate of 0.6 kg/s at a pressure of 8 bar. An electric heater station allows a temperature of up to 750 °C, depending on the tested component size. The facility is particularly suitable for developing investigations on exhaust turbochargers due to the availability of two independent supply lines. In this case, the turbocharger turbine is fed with compressed air at a controlled temperature level while the compressor, which acts as a dynamometer, can operate at a controlled pressure level by means of an appropriate regulating system. The performance of different turbocharger configurations can be investigated under both steady and unsteady flow conditions by using two different turbine feeding lines.
The first circuit arrangement (Fig. 1a) is designed to perform parametric studies on the effect of the main unsteady flow parameters on turbine performance. Tests on single and two-entry components can be performed, independently controlling thermodynamic parameters at each entry. In both feed branches, pulsating flow is generated by a diametral slot rotating valve. The main pressure pulse parameters (amplitude and mean value) at each turbine entry can be controlled by correctly mixing two flow components (steady and pulsating one) in a Y-junction and adjusting the upstream plenum pressure level. Dedicated flow control valves allow unequal admission conditions to be reproduced in the event of two-entry devices. A variable rotational speed electrical motor allows pulse frequency to be adjusted within the typical range of automotive engines (10 ÷ 200 Hz). In the case of two-entry components, the pulse phase angle can also be changed.
The second configuration (Fig. 1b) of the turbine feeding circuit is designed to more precisely reproduce turbocharger unsteady flow operation when matched to an automotive engine and to extend experimental investigations to a subsystem level. In the case of analysis on turbine side, heated compressed air passes through a flow distributor, designed to replicate the reference engine cylinder block, on top of which a motor-driven cylinder head is connected. The cylinder head can be also fitted with a fully flexible valve actuation system (Multiair system, developed by Fiat Research Centre). In this case, any valve opening profile can be implemented, thus modifying the characteristics of unsteady flow in the exhaust circuit, the geometry of which can be easily changed by installing different manifolds. Engine load transients (referring to mass flow rate) can also be reproduced acting on dedicated throttle valves in the flow distributor.
Alternatively, this layout can be used to perform studies on compressor side, by integrating the turbocharger in a current production automotive engine intake circuit.
The test rig is fitted with a PC-controlled automatic data acquisition system. Mean and instantaneous pressure levels are detected through strain-gauge and piezoresistive transducers characterized by an accuracy of 0.15% of full scale. Platinum resistance thermometers (Pt 100 Ohm) with an accuracy of ± 0.15 °C + 0.2% are adopted to record the mean temperature levels, while the instantaneous ones are calculated assuming an adiabatic process of an ideal gas, using mean pressure and temperature measurements. Instantaneous mass flow rate are estimated by using a hot wire fiber film probe, mounted upstream the turbine or downstream the compressor. Mean level of turbine and compressor mass flow rate are estimated respectively by a laminar flow meter and a thermal mass flow meter. Instantaneous parameters are recorded by means of two synchronized data acquisition cards, using a trigger signal corresponding to a definite position of the rotating valve or of the driving cam shaft.Measurements under steady and unsteady flow conditions are collected by an automatic data acquisition system, using interactive procedures developed in LabVIEW® environment. Moreover, specific tools are available to allow post-processing of instantaneous signals.