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
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
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DOI：
10.1016/j.enconman.2015.03.063
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发表时间：
2015-07-01
影响因子：
10.4
通讯作者：
Xie, Hui
中科院分区：
文献类型：
--
作者：
Wang, Xinyan;Zhao, Hua;Xie, Hui
在这项研究中，分层火焰点火（SF！）提出了一种通过进气道燃油喷射（PFI）和缸内直喷（DI）相结合的混合燃烧过程，以加强SI-CAI混合燃烧的控制，降低最大压力上升率（PRRmax）。采用三维计算流体动力学（3-D CFD）模拟方法，研究了不同活塞形状、直接喷射开始时刻（SOI）和直喷比（rot）形成的分层火焰对化学计量比SFI混合燃烧和放热过程的影响。在三区扩展相干火焰模型（ECFM 3 Z）的框架下，分别采用扩展相干火焰模型和四组分汽油表列自燃化学模型，模拟了火花塞附近火花点火火焰的传播过程和稀释混合气自燃放热过程。选择指示平均有效压力（IMEP）3.6巴的操作负荷来代表典型的部分负荷操作。针对不同的活塞、SOI正时和直喷比进行了火花正时（ST）的扫描。对相同燃烧相位下的SFI混合燃烧过程进行了详细研究。新设计的A、B活塞形成了以火花塞为中心的浓混合气和以火花塞为中心的稀混合气分层的最佳分层混合气模式，有效地降低了PRRmax，但IMEP略有恶化。较晚的SOI正时提前了50%总放热（CA 50）的曲轴转角，并显著降低了PRRmax，同时IMEP略有恶化。随着直接喷射比的增加，PRRmax和IMEP都减小。在SFI混合动力放热过程中，无论活塞形状、SOI正时和直喷比如何，点火正时都能有效地控制CA 50、IMEP和PRRmax。然而，SFI混合燃烧对分层混合气的敏感性随点火正时而变化。PRRmax的降低。由分层火焰引起的燃烧使点火正时提前，以实现最大IMEP。(C)2015爱思唯尔有限公司版权所有。
In this research, the stratified flame ignition (SF!) hybrid combustion process was proposed to enhance the control of SI-CAI hybrid combustion and moderate the maximum pressure rise rate (PRRmax) 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 (rot) 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 PRRmax with a slight deterioration of IMEP. The later SOI timing advances the crank angle of 50% total heat release (CA50) and significantly reduces the PRRmax with a little deterioration of IMEP. As the direct injection ratio is increased, both the PRRmax, and IMEP decrease. During the SFI hybrid heat release process, spark timing is effective to control CA50, IMEP and PRRmax, 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 PRRmax. caused by the stratified flame enables the advance of spark timing to achieve maximum IMEP. (C) 2015 Elsevier Ltd. All rights reserved.