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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].

In this paper the feasibility of the application of a system conceived by Järvi to a 125 cm3, four strokes motorcycle engine built by Piaggio Company is investigated. This study was carried out using a one-dimensional model built with the well known CFD 1D code Wave and validated in a previous work. An analytical study was performed on the kinematic scheme of the mechanism in order to establish the relationship between control ramp and valve lift. The control ramp shape was then optimized accordingly with the results of the fluid dynamic analysis performed through the above mentioned Wave model.

The potential of direct injection in spark-ignition engines regarding the significant reduction of fuel consumption and pollutant emission as well as advantages in the field of torque characteristic and acceleration behavior induced a remarkable development of GDI engines for automobile applications. The mentioned advantages are of special interest for motorcycle four-stroke engines as well. However, in compact cylinder units, respectively in a wide speed range as for motorcycle engines, the adaptation of direct injection gains on complexity. The paper presents the development results of a GDI four-stroke four-valve single cylinder motorcycle engine with 125 cc. The pressure pulse direct injection system developed for this application is presented from the fluid-dynamic behavior up to the obtained injection spray characteristics.