Improvement of the specific fuel consumption at partial load in SI engines by design strategies based on high compression ratio

In the last years, the engineering in the automotive industry is revolutionized by the continuous research of solutions for the reduction of consumptions and pollutant emissions. On this topic maximum attention is paid by both the legislative bodies and the costumers. The more and more severe limitations in pollutant and CO2 emissions imposed by international standards and the increasing price of the fuel force the automotive research to more efficient and ecological engines. Commonly the standard approach for the definition of the engine parameters at the beginning of the design process is based on the wide-open throttle condition although, both in homologation cycles and in the daily usage of the scooters, the engines work mainly at partial load where the efficiency dramatically decreases. This aspect has recently become strongly relevant also for two wheeled vehicles especially for urban purpose. Within this context the authors developed an integrated numerical model, in MatLab Simulink ambient, in order to couple the engine simulation, performed by means of a 1D computer-aided engineering code, with the dynamic behaviour of the whole vehicle. The model allows to estimate, along an imposed time-velocity profile, the operating conditions, the performance and the consumption of the engine simulating its real functioning in the vehicle. This approach was used by the authors for improving the efficiency of a scooter engine in its real functioning conditions. In detail, the effects of a high compression ratio were evaluated and a dedicated spark advance strategy was carried out in order to take under control the maximum in-cylinder pressure and as a consequence the occurrence of knocking phenomena. The results, supported also by a dedicated experimental activity, show the benefits of this approach in the engine design.