The effect of divided exhaust period for improved performance in a highly downsized turbocharged gasoline engine

Cylinder scavenging, negative PMEP and knock sensitivity at high engine speeds are some of the main challenges facing downsized turbocharged SI engines, while torque deficiency is more of a problem related to engines under low speed conditions. Traditional downsized engine can currently only address the above problems within a very small window inevitably leaving the other situation compromised which would either affect fuel efficiency or engine power. In order to simultaneously enhance the already competitive advantages while mitigating inherent deficiencies of turbocharged engines, some novel techniques need to be investigated. Divided Exhaust Period (DEP) is such a gas exchange concept where two exhaust ports from each cylinder are separated into different manifolds. The blow-down pulse is directed through one valve that leads to the turbocharger in order to boost the intake charge, while the other valve path (termed scavenge valve) bypasses the turbine to scavenge the remainder of the exhaust. By combining the characteristics of the downsized turbocharged engine and the scavenging process of a more-normal naturally aspirated engine, both the torque performance and the gas exchange process could be enhanced. In this paper, the DEP concept will be investigated in simulation using a validated highly downsized 2.0 Litre SI engine model. The final results showed that the BMEP & transient performance, BSFC and the stability of the engine were all improved due to the fact that the DEP concept features better gas exchange process and improved combustion efficiency.