Technical Paper
Single-cylinder Experiments for Downsizing-Oriented SI Concepts: GDI and VVL Thermodynamic Comparison
2007-09-16
2007-24-0013
In order to compare potential of VVL and GDI concept on a small displacement engine, tests have been made on a single-cylinder engine. Compared to multi-cylinder, single-cylinder offers good flexibility and accessibility for instrumentation but its gas dynamics non-representativeness has to be taken into account, especially for turbocharged engines. Concepts are tested on same engine basis but combustion system - chamber geometry, injection configuration, internal aerodynamics, valve train - is specifically designed for each version. Results confirm that homogeneous stoichiometric GDI is peculiarly adapted to turbo-charged conditions: GDI engine superior knock resistance allows low-end torque improvement and higher compression ratio. In addition to cooling effect, one of the advantages of direct injection is studied: ability to scavenge residual gases without directly transferring mixture to the exhaust. Some synergies between VVL and turbo-charging are also presented in the paper.