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The first part of the paper gives an overview of the environmental conditions with which a future two stroke powered vehicle must comply and explains the reasons for which a direct gasoline injection into the combustion chamber offers a potential solution. The paper continues with a description of the fuel/air mixture injection used in the F.A.S.T. concept and gives a detailed overview of the layout of the 125 cc engine to which it is applied. The structure of its electronic engine management system, mandatory for the necessary control precision, is presented. Hereafter is made a short introduction to the visualization and numerical computation tools used for the engine design optimization. The paper concludes with a detailed presentation and discussion of the experimental results obtained with the engine operated, either in steady state and transient conditions on an engine test rig, and mounted in a classic small dimension two-wheel vehicle submitted to road tests.

One of the characteristic features of two-stroke cycle engines is to have the cylinder filling phase with fresh charge over-lapped to the exhaust phase. This situation leads to an inevitable loss of fresh mixture through the exhaust port. The first part of this work deals with the possible methods of evaluating the percentage of fresh charge so wasted. The validity of the simplifying hypothe sis is verified by analysis both of gas composition inside the cylinder as a function of crankangle, carried out by electrovalve sampling, and hydrocarbon composition in the exhaust gases carried out by gaschromatogra-Phy. A calculation method for evaluating the short-circuiting loss in S.I. two-stroke engines fed with air only, with subsequent gasoline injection, is then described. In fact, this system seems to be a valid solution for the future development of this type of engine.