A New GDI 2-Stroke Engine to Meet Future Emission Limits: The Design and Prototype Architecture

As more stringent emission limits and low consumption requirements also involve s.i. 2-stroke engines, one of the most important design modifications that can cope with these constraints is to perform the scavenging process using pure air, which means not only fuel-free air but also oil-free air. A new single-cylinder prototype engine, equipped with a gasoline direct injection (GDI) apparatus has therefore been designed and built. In order to reduce manufacturing costs, this prototype was obtained by modifying a mass-produced 4-stroke 4-cylinder automotive engine. Apart from the replacement of the original indirect fuel feeding system with GDI, two more remarkable features should be pointed out: the use of a force-fed lubrication system, like those used in current 4-stroke engines and, as a consequence, the use of an external scavenging pump.

Before using an electronically controlled direct injection system on the new prototype engine, the whole apparatus was tested on a mass-produced crankcase scavenged 2-stroke engine (Husqvarna WR 250) in order to evaluate the magnitude of the improvements. A comparison of a carburettor fuel feeding system with a direct fuel injection system was carried out, under cubic power requirements, to check whether the GDI strategies were advantageous. As satisfying results were obtained, the direct injection apparatus was mounted onto the prototype engine for the first experimental tests.