Experimental and Simulative Investigation on Stratification Potential of Spray-Guided GDI Combustion Systems 2007-01-1407

To meet the requirements for fuel economy new innovative technologies are needed. Such technologies are usually complex and require a detailed analysis to ensure a reliable, well working system. This paper presents some of the experimental and numerical techniques for the investigation on spray-guided combustion systems in gasoline direct injection (GDI) engines. The experiments comprise single cylinder engine tests supported by combustion chamber endoscopy visualizing the in-cylinder injection and combustion processes. Within the simulation activity 3D computational fluid dynamics (CFD) simulation, supported by 1D gas exchange calculation to define boundary conditions, was used to calculate spray penetration and mixture formation. The air fuel (A/F) ratio distribution in the combustion chamber is an important outcome of the simulation work which is not available from the experiment.

Within the investigations the focus was laid on the stratified engine operating mode, due to its challenging characteristics in terms of meeting emission standards and engine performance. The analysis of the stratified combustion is shown on some typical engine operating conditions, where experimental and simulative results are compared.

The fuel consumption reduction potential of the spray-guided combustion system compared to conventional homogeneous concepts was found to be more than 20 percent. The very efficient combustion leads to high nitrogen oxide (NO_x) emissions. Therefore (cooled) exhaust gas recirculation will be necessary to meet the existing and oncoming emission standards.