Appraisal of Secondary Air Injection for Emission Reduction in Small 2T SI Engines 2000-01-0899

The emission standards compliance is really becoming effective generally for all the class of engines and particularly for two-stroke SI. While for larger capacity and more valuable applications, such as scooters, snowmobiles, marine engines, the state of the art appears consolidated with the use of direct fuel injection systems, the engines dedicated to very light and simple applications need a different approach in terms of simplicity and cost. Aiming in this direction a system including a self - sustained air injection system in the exhaust and oxidation catalysts was prepared. The influence of the main design parameters governing the system performances and their mathematical relationships were experimentally studied with the aid of a DOE (Design of Experiment) technique methodology.

The combination of the different geometrical and mechanical characteristics does not seems critical in order to define a robust solution but it appears instead very difficult with such system to get a good matching all over the engine utilization range. In this sense the solution can be optimized only for well-defined running conditions. According to the DOE results, the application of the system to a light moped is presented and analyzed with particular reference to the emission reduction capability.

Even if the solution appears able to cope with the required future most stringent standards for this class, still maintaining unchanged its intrinsic simplicity, low cost, easy servicing, the results are not generally transferable to any kind of applications especially characterized by high output engines operating over a broad range.