The variable geometry turbines (VGT) technology has been proved as beneficious for diesel engines turbocharging. Becoming the standard for passenger car turbocharged diesel engines when high boosting pressure and short transient response are both looked for in these engines.

It has not been until recent times that OEMs and turbocharger manufacturers are interested in the advantages of VGTs in petrol engines. The high exhaust gases temperature and the low boost pressure prevented the introduction of petrol VGTs up to now. In modern direct injection petrol engines relevant fuel consumption benefits have been obtained from significant to moderate boosting pressure (downsizing). This benefit joint with the advances in materials and turbocharger cooling technologies have foster exploring the limits of VGT technology in petrols.

Consequently, the 1-D and gas-dynamic modelling of turbocharged petrol engines for matching, benchmarking or analysis purposes has become a significantly more complex task. The reason is the energy loop interaction between turbine, petrol engine and compressor; which makes that all relevant system variables (boosting pressure, back-pressure, VGT inlet gas temperature, residuals, volumetric efficiency, …) are coupled among them. In this case, a proper simulation strategy of the whole system with existing 1-D gas-dynamic codes, i.e.: avoiding excessive use of spurious-non-physical fitting coefficients, has not been enough explored either described in the literature yet.

In addition, proper models of the turbocharger (both compressor and VGT) are more relevant now, since the VGT mechanism is a new variable with a first order influence. It can be destabilizing or tricking the whole system, depending on the engine operative conditions and turbo-model quality.

In this paper a systematic methodology, with physical perspective, for calibrating 1D codes of petrol engines with VGTs is clearly described. The methodology can be easily followed by other engineers or researchers in their modelling activities. In addition, the importance of the turbochager sub-model for achieving successfully previous objectives is depicted. Standard characteristic maps used as look up tables are shown to be a poor source of information when compared with pre-processed adiabatic maps and/or holistic turbocharger models previously calibrated. The focus is mainly kept in transient tip-in accelerations for being the most challenging situation. But also, low-end torque simulation in steady state is discussed as a base line point for the transient simulation.


A Methodology to Calibrate Gas-Dynamic Models of Turbocharged Petrol Engines With Variable Geometry Turbines and With Focus on Dynamics Prediction During Tip-in Load Transient Tests

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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