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The problems of Two-Stroke SI engines regarding high fuel consumption and unburned hydrocarbon emissions, both caused by the short circuiting of fresh homogeneous mixture during the scavenge process, are well-known. The progress of Piaggio since 1977 in state-of-art direct fuel injection systems, oriented to development of Hi-Tech solutions for 2T SI engines to overcome the above drawbacks, is analyzed. The analysis includes several streams of research ranging from conventional crankcase scavenged engines with direct solid mechanically controlled fuel injection to solutions with separate scavenging pump with electronically controlled injection units, and from low pressure injectors to air-assisted fuel injection with stratified charge. Each solution is examined with presentation of typical engine parameters and cost data.

The Hi-Tech Two-Stroke SI engine is finding good appreciation in various fields of vehicle application and the final solution appears to include air assisted direct fuel injection and several solutions are now evaluated by the major world engine manufacturers. Those solutions anyway are poorly tailored to be fitted on very small engines such as for moped or light scooter applications both for the complications they require, consequentely the costs, and the difficult tuning of low load and idle caused by the very low quantity of fuel per cycle required. The proposed completely mechanical solution instead does consent with small modifications to the engine, only a new cylinder head is in fact required, to manage very well the engine all over its utilization range. After general considerations of the philosophy of the system and on the main parameters evaluation, a practical application on a 50cc scooter engine is described.

The future urban mobility strategies, especially in cities with high population density, include the individual transportation means as one of the main components to contribute to the solution of the two fundamental problems, namely the traffic concentration and the individual satisfaction. Following the consolidated trend, the 2000's vehicles shall be characterized by extremely reduced environmental impact in terms of pollutant emissions, noise, fuel consumption (low carbon dioxide production). In this sense the two-wheelers appear the most favorable candidate provided that a suitable propulsive unit is available. The present work describes the development of a propulsive unit characterized by a direct injected two-stroke engine with FAST technology, an electronic engine management system and a very efficient CVT transmission.

"In the design of new CI engines, it is of paramount importance to reduce the pollutants and fuel consumption," writes author Marco Nuti. In this, the first book devoted entirely to exhaust emissions from two-stroke engines, Nuti examines the technical design issues that will determine how long the two-stroke engine survives into the twenty-first century. Dr. Nuti, director of Technical Innovation at Piaggio, thoroughly explores pollutant formation and control from unburned hydrocarbon emissions, carbon monoxide emissions, catalytic aftertreatment, and secondary air addition.