Design of a Boosted 2-Cylinder SI-Engine with Gasoline Direct Injection to Define the Needs of Future Powertrains

摘要

To meet future CO_2 emissions limits and satisfy the bounds set by exhaust gas legislation reducing the engine displacement while maintaining the power output ("Downsizing") becomes of more and more importance to the SI-engine development process. The total number of cylinders per engine has to be reduced to keep the thermodynamic disadvantages of a small combustion chamber layout as small as possible. Doing so leads to new challenges concerning the mechanical design, the design of the combustion system concept as well as strategies maintaining a satisfying transient torque behavior. To address these challenges a turbocharged 2-cylinder SI engine with gasoline direct injection was designed for research purposes by Weber Motor and Bosch. This paper wants to offer an insight in the design process. The mechanical design as well as the combustion system concept process will be discussed. First of all results of 1d simulations of the engine are presented, which allow the choice of the optimal combustion chamber geometry. Subsequently, the spray targeting of the solenoid multihole high pressure injector as well as the design of the intake runner geometry by means of 3d CFD tools is presented. Further, the design of the optimal intake manifold setup and gas exchange strategy will be described. The incorporation of the results of this process and its impact on the design of the new research engine is shown. Additionally, a special emphasis was set on creating a very modular engine design, e.g., allowing a switch between direct and port fuel injection and the implementation of different boosting systems. DOHC was also implemented as an option for an optimized gas exchange. For analysis purposes the engine is operated at an engine test bed using the standard measurement equipment including high and low pressure indication. Additionally, an optical access to the combustion chamber was realized which allows for high-speed color recording of the working cycle. First measurement results addressing the changes made to the engine and combustion system concept design and their impact on fuel consumption and the transient torque behavior will be shown.