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World-wide attention to environmental issues in recent years has resulted in a greater demand for cleaner engines, especially with regards to the two-stroke. Considering the techniques for reduction of exhaust emissions the direct injection of fuel into the combustion chamber adapted for a loop scavenged cylinder seems to be an advantageous method. This paper describes the application of advanced experimental and computational techniques to evaluate mixture formation produced on a commercial engine by means of a direct fuel injection strategy, namely a ram-tuned injection system. The injection system data are experimental while air flow and fuel air mix for the direct injection engine are calculated using a turbulent model of the three dimensional code FLUENT. Extension of a first work in this field is presented. In particular two possible strategies to simulate direct injection are tested. The influence of different boundary conditions on the scavenging process was examined too.

A very stringent problem in most of European cities is the individual mobility. This problem is mainly caused by traffic jam and arising from this are two particularly interesting environmental issues: pollution and noise [1]. Use of two wheeler vehicles does not represent the final solution to these problems, nevertheless they can supply a useful aid to ease them. Recently, two stroke engines are being replaced with four stroke engines. For small capacity engines this means a true reduction in exhaust emissions, especially unburned hydrocarbons (HC), but, on the other hand it involves a performance reduction, particularly for sudden accelerations, which constitute an essential requirement for these vehicles [2, 3, 4, 5]. Hybridisation can help to fill the gap between two stroke engines and cleaner, but less performing four stroke engines [6]. At the same time, it can help to lower fuel consumption, by means of a reduction in the revolution speed [2, 5].