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.A new injection system, based on the hydraulic phenomenon commonly known as “water hammer”, is proposed as a reliable means of achieving high injection pressures while maintaining the simple manufacturing and low-cost characteristics of two-stroke engines.The system, equipped with a low-pressure fuel pump, provides high injection pressure values thanks to the conversion of the kinetic energy of the fluid into a local pressure rise which takes place when the fuel flow is suddenly halted by an electronically-controlled solenoid valve. To raise as much as possible the injection pressure, the valve is forced to work at frequencies close to the system's resonant frequency.The results from a preliminary test-bed evaluation of the injection system are shown and the influence of various parameters on system performance is discussed.Though ideal for small two-stroke engines this concept appears suitable also for every other kind of spark-ignited engine.