Divided exhaust period for a highly turbocharged SI engine – Timing Optimization

Poor cylinder scavenging, negative PMEP and knock sensitivity are the three main obstacles which prevent downsized SI engines from further improving BSFC while maintaining the same performance compared to the naturally aspirated counterpart. In order to simultaneously address these issues, it is necessary to reduce the exhaust pressure. However, backpressure is also the driving force for the turbocharger which recovers some energy from the exhaust to achieve the target torque performance. Thus, finding some means to isolate the backpressure between the exhaust port and the turbine inlet is worth giving more attention to in the near future.
In this paper, the Divided Exhaust Period (DEP) concept will be investigated based on a validated extremely turbocharged SI engine model. The objective of this project is to further improve its BSFC and BMEP performance using simulation tool - GT-power. Several degrees of freedom with focus on the timing of valves were optimized. The BSFC & BMEP performance of the engine were found to improve by up to 5% for some speed and load range. In addition, the compression ratio could also be increased to further improve its thermodynamic efficiency.