Comparison between 2 and 4-stroke engines for a 30 kW range extender

The paper compares two different design concepts for a range extender engine rated at 30 kW at 4500 rpm. The first project is a conventional 4-Stroke SI engine, 2-cylinder, 2-valve, equipped with port fuel injection. The second is a new type of 2-Stroke loop scavenged SI engine, featuring a direct gasoline injection and a patented rotary valve for enhancing the induction and scavenging processes. Both power units have been virtually designed with the help of CFD simulation. Moreover, for the 2-Stroke engine, a prototype has been also built and tested at the dynamometer bench, allowing the authors to make a reliable theoretical comparison with the well assessed 4-Stroke unit. Even if the optimized design of each one of the two engines is similar to that of existing prototypes, the paper is not intended to be a benchmarking, but a general study, aimed to define the fundamental project guidelines and compare different solutions under the same conditions, including the unavoidable arbitrary hypotheses. The main results of the comparison may be summarized as follows: the 2-Stroke engine is more compact and light (â?38% of frontal area, 35 vs. 50 kg); its fuel efficiency is slightly better, and further improvements are possible running on stratified charge; the reduction of NOx in the 2-S catalyst may not be complete, due to the unavoidable air short-circuit.