Computational study of the influence of in-cylinder flow on spark ignition–controlled auto-ignition hybrid combustion in a gasoline engine

Energy Conversion and Management

Xie

2015

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a b s t r a c tIn this research, the stratified flame ignition (SFI) hybrid combustion process was proposed to enhance the control of SI-CAI hybrid combustion and moderate the maximum pressure rise rate (PRR max ) by the combination of port fuel injection (PFI) and direct injection (DI). The effect of the stratified flame formed by different piston shapes, start of direct injection (SOI) timings and direct injection ratios (r DI ) on the stoichiometric SFI hybrid combustion and heat release process was studied using the three-dimensional computational fluid dynamics (3-D CFD) simulations. The spark ignited flame propagation near the spark plug and the auto-ignition heat release process of the diluted mixture were modelled in the framework of 3-Zones Extended Coherent Flame Model (ECFM3Z) by the extended coherent flame model and tabulated auto-ignition chemistry of a 4-component gasoline surrogate, respectively. The operating load of indicated mean effective pressure (IMEP) 3.6 bar was selected to represent a typical part-load operation. The sweep of the spark timing (ST) was performed for different pistons, SOI timings and direct injection ratios. The SFI hybrid combustion process with the same combustion phasing was investigated in details. The optimal stratified mixture pattern, characterized with the central rich mixture around spark plug and stratified lean mixture at the peripheral region, formed by the newly designed Piston A and B effectively lowers the PRR max with a slight deterioration of IMEP. The later SOI timing advances the crank angle of 50% total heat release (CA50) and significantly reduces the PRR max with a little deterioration of IMEP. As the direct injection ratio is increased, both the PRR max and IMEP decrease. During the SFI hybrid heat release process, spark timing is effective to control CA50, IMEP and PRR max regardless the piston shapes, SOI timings and direct injection ratios. However, the sensitivity of SFI hybrid combustion to the stratified mixture varies with the spark timing. The reduction of the PRR max caused by the stratified flame enables the advance of spark timing to achieve maximum IMEP.

Section: Introductionmentioning

confidence: 99%

Effect of piston shapes and fuel injection strategies on stoichiometric stratified flame ignition (SFI) hybrid combustion in a PFI/DI gasoline engine by numerical simulations

Energy Conversion and Management

Xie

2015

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“…In order to quantify the overall flow motions, the swirl ratio (SR) is defined by the following equation 31…”

Section: Resultsmentioning

confidence: 99%

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

International Journal of Engine Research

2017

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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.

“…The tumble/cross tumble axis is parallel to y/x axis and crosses the central point between maximum and minimum z value of the cylinder [11]. The direction of each flow motion has been marked in Figure 1.…”

Section: Effect Of the Ratio Of Inlet Area To The Total Scavenge Portmentioning

confidence: 99%

Analysis of the Effect of Intake Plenum Design on the Scavenging Process in a 2-Stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) Engine

SAE Technical Paper Series

2017

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In this study, the effect of the intake plenum design on the scavenging process in a newly proposed 2-stroke Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) engine was studied in detail by three dimensional (3D) computational fluid dynamics (CFD) simulations. In the BUSDIG engine, the intake scavenge ports are integrated into the cylinder liner and their opening and closure are controlled by the movement of piston top while exhaust valves are placed in the cylinder head. In order to accommodate the optimized scavenge ports in the real engine application, the intake plenum with an inlet pipe and a scavenge chamber was designed and connected to the 12 evenly distributed scavenge ports in a single cylinder BUSDIG engine. In order to achieve optimal scavenge performances and sufficient in-cylinder flow motions to enhance the fuel/air mixing, five design parameters of the intake plenum were investigated, including the ratio of the inlet area relative to the scavenge port area (r I/S ), the radius of the round connecting the inlet pipe and the scavenge chamber (r R ), the ratio of the scavenge chamber volume to the cylinder displacement volume (r S/C ), the angle between the inlet pipe and exhaust pipe (α I/E ) and the ratio of bore to the scavenge port length (r B/PL ). It is found that the best scavenging performance is achieved at low engine speed when the intake plenum design shows less impact on the scavenging performances. As the engine speed increases, the impact on the scavenging performance by the intake plenum design becomes more significant. There is a trade-off between the tumble ratio (TR) and cross tumble ratio (CTR) for each intake plenum design. Based on the systematic study carried out, the intake plenum design parameters were optimized for high scavenging performance and strong large scale flow motions in the BUSDIG engine.