Performance Improvement of Two-Stroke SI Engines for Motor-Gliders and Ultra-Light Aircraft by Means of a GDI System *

Experimental tests have been carried out on a single-cylinder crankcase-scavenged two-stroke engine, with both indirect and direct gasoline injection, in order to compare the results obtained with these two different fuel-feeding systems. Engine operating conditions were chosen like those of a typical aeronautical application. They were determined using a theoretical method, that is by computing the power of an aircraft, that is necessary for a steady-state flight at different aircraft velocities. This power curve turned out to be in good agreement with the “propeller load” that was experimentally found through preliminary bench tests, that is, the cubic characteristic, of power versus engine revolution speed, matching the maximum power of the engine. Brake specific fuel consumption (bsfc) and exhaust emission measurements were then carried out using bench tests along the “propeller load”. When the indirect injection setting was used, a specific electromagnetic injector was placed in the intake manifold of the engine; instead, when the direct injection setting was used, a different electromagnetic injector was mounted in the cylinder head, each injector having its own electronic control unit. A comparison between the engine performance obtained with gasoline indirect injection (GII) and gasoline direct injection (GDI) has highlighted a remarkable reduction of both unburned hydrocarbons and specific fuel consumption.