Analysis of mixture formation process in a two-stroke boosted uniflow scavenged direct injection gasoline engine

Abstract

The two-stroke engine has the great potential for aggressive engine downsizing and downspeeding because of its double firing frequency. For a given torque, it is characterized with a lower mean effective pressure and lower peak in-cylinder pressure than a four-stroke counterpart. In order to explore the potential of two-stroke cycle while avoiding the drawbacks of conventional ported two-stroke engines, a novel two-stroke boosted uniflow scavenged direct injection gasoline engine was proposed and designed. In order to achieve the stable lean-burn combustion in the boosted uniflow scavenged direct injection gasoline engine, the mixture preparation, especially the fuel stratification around the spark plug, should be accurately controlled. As the angled intake scavenge ports produce strong swirl flow motion and complex transfer between the swirl and tumble flows in the two-stroke boosted uniflow scavenged direct injection gasoline engine, the interaction between the in-cylinder flow motions and the direct injection and its impact on the charge preparation in the boosted uniflow scavenged direct injection gasoline engine are investigated in this study by three-dimensional computational fluid dynamics simulations. Both the single injection and split injections are applied and their impact on the mixture formation process is investigated. The start of injection timing and split injection ratio are adjusted accordingly to optimize the charge preparation for each injection strategy. The results show that the strong interaction between the fuel injection and in-cylinder flow motions dominates the mixture preparation in the boosted uniflow scavenged direct injection gasoline engine. Compared to the single injection, the split injection shows less impact on the large-scale flow motions. Good fuel stratification around the spark plug was obtained by the late start of injection timings at 300 °CA/320 °CA with an equal amount in each injection. However, when a higher tumble flow motion is produced by the eight scavenge ports’ design, a better fuel charge stratification can be achieved with the later single injection at start of injection of 320 °CA.

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

“…Our previous research on the mixture preparation in a two-stroke boosted uniflow scavenged direct injection gasoline (BUSDIG) engine showed that the application of narrowly spaced split injection in conjunction with a bowl piston produced stable rich mixture around the spark plug before the spark ignition. 36…”

Simulation and experimental investigation of swirl-loop scavenging in two-stroke diesel engine with two poppet valves

“…5 Scavenging process is one of the determinants of two-stroke engine performance, 6 because it not only affects the quality of gas exchange but also influences the fuel spray mixing in the subsequent combustion phase, which is related to the fuel economy and emission of the engine. 7,8 In two-stroke engine, the short time of exchanging gas brings the challenge of scavenging performance, which has become a concerned topic. 9,10 For the PV2S engines, it is necessary to establish a relatively high positive pressure drop between the intake and exhaust ports to ensure the efficient scavenging and sufficient intake flow rate.…”

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.…”