It has been shown that an automotive, stratified charge, direct injected (DI) 2-stroke engine is capable of meeting the proposed Stage 3 European emissions standards and the Ultra Low Emissions Vehicle standards of California at low mileage. In order to meet these stringent standards and develop a high in-field mileage capability for this lean burn engine, new engine control strategies and catalyst formulations have been developed.
Engine out emissions and catalyst temperatures over both the proposed Stage 3 New European Drive Cycle (NEDC) and Federal Test Procedure (FTP) are described. Also with catalyst light-off time being an important factor in determining the overall cycle emissions, engine calibration based Fast Light Off and light load exhaust temperature strategies have been developed, in conjunction with optimised catalyst system configurations.
The extreme lean operation of this stratified charge, D.I. 2-stroke engine, and the inherently low Oxides of Nitrogen emission levels, mean that Rhodium-free precious metal oxidation only catalyst formulations are used. Catalyst screening techniques and results of different Platinum and Palladium precious metal mixes are presented.
In order to assess the performance of the catalyst systems under high mileage conditions, in-vehicle ageing cycles that simulate temperature regimes and oil deposition mechanisms of 2-stroke engines have been developed.
Finally exhaust and catalyst system configurations developed to meet future high mileage emissions durability requirements of extreme lean burning engines are also described.