Multi-Mode Combustion Strategies with CAI for a GDI Engine 2007-01-0214
The controlled auto-ignition1 (CAI) improves dramatically the efficiency of a gasoline engine and brings it in close competition to the diesel engine without penalties in emissions. With CAI run in part-load, the gasoline engine reaches a standard driving cycle advantage of 12% in fuel economy compared to current commercial engines operating solely in homogeneous gasoline direct injection (GDI) with a stoichiometric charge. CAI is run lean in fuel and thus limited in load similar to the second generation spray guided stratified GDI strategy that promises at least the same fuel efficiency but is plagued with high NOx emissions requiring complex after-treatment systems. Although CAI produces negligible NOx, and a simple three-way catalyst suffices, it depends strongly on judiciously operating the engine within the dynamic operating cycle. Direct injection, valve actuation flexibility and advanced controls based on combustion state sensing are indispensable for this. Benefits, limitations, technological requirements, and suggested engine control strategies using CAI in part-load are examined in a dynamic standard test cycle, and compared with the most promising gasoline competing technologies at test cycle relevant operating points. For the analysis of CAI, test bench investigation on a single-cylinder and a 4-cylinder research engines were undertaken. Additionally, thermodynamic and chemical kinetics simulations are provided to shed more light on the application of this multi-mode combustion concept.