The Volkswagen GCI Combustion System for Gasoline Engines - Potentials and Limits in CO_2 Emissions

摘要

The Golf with a 1.6 l GCI engine presented at the end of 2006 was the first drivable car in the world with a gasoline compression ignition engine. The implemented Volkswagen GCI combustion system presented in the car is a part-load combustion system based on homogeneous gasoline autoignition. In a limited region of the characteristic engine map GCI allows reduction of fuel consumption in combination with minimum raw emissions of nitrous oxide compared to the conventional spark ignited stoichiometric combustion. This paper describes the procedure employed designing the GCI combustion system. It is characterized by the extensive use of innovative computational methods like the three-dimensional simulation of the mixture formation and linking the CFD flow simulation with chemical reaction kinetics to predict the autoignition process. Furthermore, this paper describes the necessary adaptations of the engine control unit in order to transfer the GCI combustion system from the engine test bench to a drivable car. A fundamental and overall systemic approach to study the possibilities and limits of partload combustion systems in order to reduce the fuel consumption at driving operation conditions lead to the following result: Although these combustion systems can improve fuel consumption, they cannot match the consumption benefits of downsizing concepts based on TSI technology regarding the boundary conditions relevant for Volkswagen. This can mainly be explained by the fact that the engine is only rarely operated in the limited partload range enabling corresponding fuel consumption benefits. If the same engine is operated outside of this part-load range instead, the relevant specific fuel consumption is higher throughout the characteristic engine map compared to a respective downsized engine with reduced displacement.