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Two-stroke spark-ignition engines with fuel injection constitute a good alternative to four-stroke engines in meeting the demand for ever lighter-weight and higher-performance vehicle engines; they are also suitable for industrial applications if their inherent advantages of design simplicity, low cost and high specific power are maintained. In both cases, for these machines to constitute a successful alternative, emission levels must be equal to or lower than those of comparable four-stroke engines. Several studies are currently dealing with the so-called ‘new generation two-stroke engines’. In nearly all these, charge control by means of fuel injection has been proposed to overcome the well-known problems of fuel and lube-oil consumption, and the probably unacceptable level of pollutant emissions. Direct injection, in particular, seems to guarantee the best results as it allows to avoid the short-circuiting of the fuel to the exhaust.

Recently, emission regulations formerly concentrated on the acknowledged major polluters, such as motor vehicle engine, have been extended to the smaller engines. This forced the two-stroke engines manufacturers to search for environmentally cleaner solutions. In this respect the most promising technology seems to be the adoption of direct-injection and the challenge is not to complicate excessively a power system which has in simplicity and low cost its best advantages. The paper reports on a two-stroke gasoline direct-injection engine prototype which even if equipped with a low-pressure fuel pump, provides high injection pressure values thanks to a Water-Hammer effect. The engine is a two-cylinders-water-cooled type and its design follows previous experiences on single-cylinder engines prototype. Once described the basic working principles of the proposed concept the engine realization phases and its running results on a test bed are presented.