In the past few years the gasoline direct injection (GDI) downsizing approach was the dominating gasoline engine technology used to reduce CO2 emission and to guarantee excellent transient performance. Forecasts for the next several years indicate that the worldwide market share of GDI engines will grow further. By 2022 it is expected that the gasoline DI engine will be the most popular combustion engine for passenger car application. However in the future the gasoline engine will have to comply with more stringent emission and CO2 standards. The European legislation demands a fleet average CO2 emission of 95g/km latest by 2021. Therefore, CO2 emission improvement, without compromising driveability, is the major goal of powertrain development.
The perspective of more stringent CO2 and emission legislation in highly loaded drive cycle necessitates major development efforts. In this study Millerization in combination with an increase of the geometric compression ratio as a concept to improve the CO2 emissions of spark ignition engines is evaluated. It is shown that the concept has an adverse impact on transient performance i.e. the driveability of the engine. Therefore, Millerization has a strong influence on the charging system. To compensate for these adverse impacts is one goal for the turbocharger development.
The development of an engine concept which offers both improved CO2 emissions and improved driveability is presented. A joint approach of 1-D engine simulation, dedicated turbocharger thermodynamic development and engine measurements was applied. The full load behavior of the combustion system is derived from engine measurements, which provide the required boundary conditions for the 1-D engine and turbocharger simulations. The resulting engine concept was subsequently realized in hardware and tested on a dynamic engine dyno. The CO2 emission improvement and the transient behavior of this new engine concept are presented in this paper.