Analysis of the Boost System for a High Performance 2-Stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) Engine
A 2-stroke boosted uniflow scavenged direct injection gasoline (BUSDIG) engine was researched and developed at Brunel University London to achieve higher power-to-mass ratio and thermal efficiency. In the BUSDIG engine concept, the intake scavenge ports are integrated to the cylinder liner and controlled by the movement of piston top while exhaust valves are placed in the cylinder head. Systematic studies on scavenging ports, intake plenum, piston design, valve opening profiles and fuel injection strategies have been performed to investigate and optimise the scavenging performance and in-cylinder fuel/air mixing process for optimised combustion process. In order to achieve superior power performance with higher thermal efficiency, the evaluation and optimisation of the boost system for a 1.0 L 2-cylinder 2-stroke BUSDIG engine were performed in this study using one dimensional (1D) engine simulations. The results show that the engine exhaust valve opening (EVO) timing and exhaust duration (ED) are key parameters affecting the engine performance with the single-stage turbocharging (T). By using an earlier EVO timing of 80 0CA and a longer ED of 140 0CA, a maximum brake power of 130.7 kW could be achieved at 3200 rpm and peak torque output of 488 N*m at 1600 rpm. Simulations were also performed to evaluate the engine performance with combined boost systems with a supercharger upstream the turbocharger (S-T) and a turbocharger upstream the supercharger (T-S). The results indicate that the combined boost systems increase both engine power and torque compared to the single-stage turbocharging system. In particular, the peak brake power and torque of the 1.0 L BUSDIG engine could reach 143.7 kW at 4000 rpm and 492 N*m at 800 rpm with the S-T setup.