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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.

It's long time that noise legislations emphasize the need for the development of quieter engines, much has been done for automotive and large industrial engines but now there is a growing interest also in every means of reducing the noise of small Diesel engines widely used in agriculture, gensets and other stationary applications. Furthermore since new engine structure designs require large investements in new plant and production techniques there is a considerable incentive for the engine manufacturer to achieve noise reduction by modification and development of the existing designs. This paper discusses a case in which structural modifications of an existing small Diesel engine caused by design and production constraints have been analyzed also on the noise point of view so that necessary functional changes have given rise also to noise reduction.