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The aim of this paper is to propose a design approach for a two-stroke free-piston diesel engine. A simulation tool is provided in order to study the behavior and the design of the engine coupled with a linear alternator. A thermodynamic and dynamical analysis, which makes use of both classic thermodynamic equations and empirical formulas typically used for internal combustion engines, is presented together with theoretical results of the operational characteristics.

Recent research on internal combustion spark ignited engines has focused more and more on charge control by means of direct injection. Nevertheless most of the systems proposed so far do not seem to be suitable for small engines as they are high-cost. A new direct injection system, based on the hydraulic phenomenon commonly known as “water hammer” has been recently proposed by the authors to be used for small two-stroke engines. It constitutes a reliable means of achieving high injection pressures while maintaining the simple manufacturing and low-cost characteristics of this kind of engines. It is equipped with a low-pressure fuel pump and 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 automatic valve.

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. The direct-injection systems proposed in recent times do not seem to be widely applicable especially to small two-stroke engines as they introduce considerably complicated and consequently high-cost systems. A new direct injection system, based on the hydraulic phenomenon commonly known as “water hammer”, has been proposed by the authors as a reliable means of achieving high injection pressures while maintaining the simple manufacturing and low-cost characteristics of two-stroke engines.

Several researches are on line dealing with the so called ‘new generation two-stroke engine’. In almost all of these the charge control by means of fuel injection has been proposed to overcome the well known fuel and lube oil consumption and the likely unacceptable pollutant emissions. Direct injection in particular seems the method which guarantee the best results in avoiding the short circuiting of the fuel to the exhaust. This paper summarises the experimental research carried on in the Ancona University both on high pressure mechanical and low pressure electronic direct injection systems and overlights their relative benefits and problems. Furthermore a new system using the “water hammer” phenomenon is proposed as a mean of achieving rather high injection pressures maintaining the simple manufacturing and low cost proper characteristics of two-stroke engines.