One-dimensional modelling of pulse separation strategy, waste-gated turbines and electric turbocharger systems for downsized turbocharged gasoline engines

Abstract

The demand for CO2 emission reduction for modern road vehicles has seen engine downsizing become a key trend in internal combustion engine design: a smaller engine has reduced pumping, frictional and heat losses, and therefore better fuel economy. Turbocharger technology is one of the enabling technologies, offering lower specific fuel consumption and producing more power for a given engine capacity. The turbocharger matching process, which specifies an appropriate turbocharger design for a particular engine, is crucial in obtaining optimum engine performance. In order to achieve a high level of accuracy in the system-level prediction, high fidelity turbocharger models are required; but such models have not yet reached fruition. The present study has assessed the effect of preserving the exhaust pulse energy from an engine right through to the turbine on the steady and transient engine performance. A combination of appropriate turbine sizing and pulse-divided exhaust manifold was applied, and as a consequence, lower back pressure and improved engine scavenging reduced residual content by 28%, while the brake specific fuel consumption (BSFC) improves by approx. 1.2% on average over speed range. Furthermore, the implementation of electric turbo assist (ETA) system on the engine results in better fuel economy by 2.4%. The present work has also assessed the overall engine performance using a commercial 1-D gas dynamics simulation tool by modelling the waste-gated turbines in a novel manner. This approach has been validated experimentally. The study also examined the benefits of electric turbocharger systems for a highly-downsized engine, a modified version of the baseline engine. Some potential multi-boosting systems were applied, and the overall benefits in terms of engine performance were assessed. An integration of an electric turbocharger and a low-pressure turbine with electric turbo compounding gives the best advantages particularly in pumping loss, residual and transient performance while improving fuel economy in comparison with other systems.