A virtual engine laboratory application for use in automotive engineering education is proposed to allow the practical teaching of powertrain calibration. The laboratory software is built as a flexible Matlab tool that can easily be transferred for applications in other disciplines and promotes the link between teaching and research.

The use of turbochargers on both gasoline and diesel engines is started to become a common strategy to comply with stringent limits on CO2. The main action towards lowering fuel consumption of powertrains is achieved by reduction of engine size and number of cylinders, annexed to the lower friction. However, this is directly linked to the worsening of deliverable output power under the natural aspirated configuration. Therefore, turbocharging is often adopted to overcome this problem where useful energy contained in the exhaust gasses is used to increase the air density at the intake. The increase in power from a natural aspirated configuration is a direct consequence of higher fuel quantity to be injected. In order to pursue a systematic evaluation of the powertrain system, engine, turbochargers and auxiliary components are included into 1D models. Several conditions can be simulated without the need of an extensive test plan. In 1D software like Ricardo Wave, turbochargers performance are imposed as input. These are previously measured in appropriate turbocharger gas-stand where hot or cold air is blown through the turbine while load on compressor is controlled by adjusting a back pressure valve. Compressor and turbine maps are generated for constant speed lines which are corrected for total temperature. Pressure ratio, mass flow and isentropic efficiency are also monitored as parameters to characterize performance maps of turbomachinery. In gas-stands, steady flow conditions are imposed at compressor and turbine. However, in turbocharged engines, pulsating flows induced by the engine valvetrain disturb continuously turbocharger conditions during the engine cycle. In fact, the effects that the conditions of the engine air-path could have on the turbocharger operations are excluded from the system modelling. In this study, an appropriate engine gas-stand has been developed in order to improve the accuracy on estimating the turbine extraction power in 1D powertrain simulations. In addition, future analyses on turbocharger transient operations could be investigated. The compressor outlet has been disconnected from the 2.2L Diesel engine intake so that the load on turbocharger and engine can be independently controlled. In order to extend the engine capability in delivering mass flow and pressure at the turbine inlet, an external boost rig has been installed with the capability to control pressure, mass flow and temperature at the engine intake. In a first instance, a 1D model of the system including turbomachinery, Diesel engine and boost rig has been developed using the commercial platform Ricardo Wave. In this way, a preliminary DoE study of the entire system has been performed in order to evaluate the effects of parameters and actuators on the turbocharger operations. Additionally, the control of the rig has been tested by confirming the previous DoE study. Approaches to create turbochargers maps are shown. Last section of the paper focuses on turbine pulsations and the interpretation of efficiency calculated in experiments and simulations.

The paper attempts to correlate simulations and measurements of turbine performance under pulsating flows for automotive turbochargers. Under real automotive powertrain conditions, turbochargers are subjected to pulsating flows, due to the motion of the engine’s valves. Experiments on a purpose-built 2.2 L diesel engine gas-stand have allowed the quantification of unsteady pulsating turbine performance. Temperature, pressure and mass flow measurements are fundamental for the characterisation of turbine performance. An adequate sampling frequency of the instruments and acquisition rates are highly important for the quantification of unsteady turbomachine performance. In the absence of fast, responsive sensors for monitoring mass flow and temperature, however, appropriate considerations would have to be taken into account when making estimates of turbine performance under pulsating flows. A 1D model of the engine gas-stand has been developed and validated against experimental data. A hybrid unsteady/quasi-steady turbine model has been adopted to identify unsteadiness at the turbine inlet and outlet. To evaluate isentropic turbine efficiency and reduce the influence of external heat transfer upon measurements, the turbine inlet temperature has been measured experimentally in the vicinity of the turbine rotor in the inlet section, upstream of the turbine tongue. The hybrid unsteady/quasi-steady turbine model considers the presence of unsteady flows in the turbine inlet and outlet, leaving the rest of the turbine to react quasi-steadily. Virtual sensors and thermocouples have been implemented in a 1D model to correlate experimental time-averaged temperature measurements.

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