Analysis of scavenge port designs and exhaust valve profiles on the in-cylinder flow and scavenging performance in a two-stroke boosted uniflow scavenged direct injection gasoline engine

Abstract

In this study, effects of intake scavenge port designs and exhaust valve opening profiles were studied on the scavenging process in a newly proposed two-stroke boosted uniflow scavenged direct injection gasoline engine by detailed threedimensional engine simulations. As the most important geometric parameters, the axis inclination angle and swirl orientation angle of scavenge ports, as shown in Figure 1, were investigated and optimized for best scavenging performances at first. With the optimal axis inclination angle of 90°and swirl orientation angle of 20°, various combinations of scavenge port opening timing, exhaust valve opening duration and exhaust valve opening timing were then analysed. Four distinct scavenging periods, that is, early backflow period, backflow scavenging period, main scavenging period and post backflow period, were identified and their impacts on the in-cylinder flow motions and scavenging performances were investigated. The results show that the optimal scavenging performance can be achieved with a higher delivery ratio, charging efficiency and scavenging efficiency when the post backflow is just avoided by tuning the difference between the closing timings of scavenge ports and exhaust valves (D close ) and the overlap between the opening profiles of scavenge ports and exhaust valves (D overlap ) for a specific exhaust valve opening duration. A longer exhaust valve opening duration can be used to further improve the scavenging performances. In addition, the difference between the opening timings of scavenge ports and exhaust valves (D open ) can be increased to improve scavenging efficiency. The D close also shows strong positive correlation with in-cylinder swirl ratio and negative correlation with tumble ratio. The results presented in this study provide the fundamental knowledge of the scavenging process in the uniflow scavenged two-stroke engine and assist the design of scavenge ports and valve strategies to optimize in-cylinder flow motion and scavenge performances in the two-stroke boosted uniflow scavenged direct injection gasoline engine with a variable valve actuation system for exhaust valves.

Effect of piston shape design on the scavenging performance and mixture preparation in a two-stroke boosted uniflow scavenged direct injection gasoline engine

“…Figure 6 compares the mass flow rate through the intake scavenging ports into the cylinder with different piston shapes at engine speed of 2000 r/min. As detailed in a previous work, 41 a typical scavenging process starts with an early backflow (EB) to the scavenge ports due to higher in-cylinder pressure at SPO. After the EB stage, the backflow mixture will start to enter cylinder and scavenge the cylinder in the backflow scavenging (BS) stage after which the pure fresh charge in the scavenge ports starts to scavenge the cylinder in the main scavenge (MS) stage.…”

“…The centrally mounted DI injector and spark plug on the cylinder head were positioned to place the spray recirculation region around the spark plug. The key engine design parameters, including engine bore/stroke ratio, 39 scavenge port angles, 40–42 opening profiles of scavenge ports and exhaust valves 43 and intake plenum, 44 have been analysed and evaluated for optimal scavenging performance and in-cylinder flow motions. A full review of the BUSDIG engine concept can be found in a recently published article.…”

Effect of Valve Timing and Excess Air Ratio on Torque in Hydrogen-Fueled Internal Combustion Engine for UAV

“…When the opening timing of the exhaust valve was retarded under the condition of a constant intake valve opening time, and when the amount of the exhaust remaining after opening the intake valve was increased due to the decreased blowdown duration and a hindered scavenging process, the intake airflow rate and torque decreased. However, the thermal efficiency increased, since the scavenging air/fuel mixture decreases during the valve overlap [29]. On the other way, when the opening time of the exhaust valve advanced excessively, the effective work resulting from the blowdown and scavenging effect decreased due to the exhaust gas leaving the cylinder.…”

Analysis of the Boost System for a High Performance 2-Stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) Engine

“…In light of the advantages of the 2-stroke operation, a novel 2-stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) engine has been designed and extensively researched at Brunel since 2015 [7]. Key designs of the proposed BUSDIG engine, including engine bore/stroke ratio [8], scavenge ports [9][10][11], opening profiles of scavenge ports and exhaust valves [12], intake plenum [13], injection strategies [14,15] and piston shape [16] have been systematically studied to optimise the scavenging performance and charge preparation of the BUSDIG engine.…”