Future perspectives of the two-stroke spark ignition engine

As more stringent emission limits and low consumption requirements necessary for all current vehicle propulsion systems also apply to s.i. 2-stroke engines, one of the most important design modifications that can cope with these constraints involves performing the scavenging process using pure air, which means not only fuel-free air but also oil-free air. Current two stroke s.i. engines are therefore equipped with a gasoline direct injection systems (GDI) and are the lubrication apparatus has also been modified in order to reduce both pollutant emissions and oil consumption. After a short introduction on the two stroke s.i. engine, some examples of this kind of engine that apply these new technical solutions are presented and analyzed. The second part of the paper instead presents the research activities conducted at the Energy Department Politecnico di Torino on two stroke s.i. engine over the last two decades. After presenting the first experience gained a two stroke prototype engine, the first experimental results obtained on two mass-produced crankcase scavenged 2-stroke engines, the Benelli FB-1226 and the Husqvarna WR 250, provided with gasoline direct injection, are presented. These experimental results refer to a comparison between a carburettor or gasoline indirect injection fuel feeding system with a direct fuel injection system, as far as fuel consumption and pollutant emissions are concerned. As satisfactory results were obtained, the direct injection apparatus was mounted onto a new prototype engine and the first experimental tests once more showed encouraging results, as far as fuel consumption and pollutant emissions are concerned.