Numerical Study of the Effect of Piston Shapes and Fuel Injection Strategies on In-Cylinder Conditions in a PFI/GDI Gasoline Engine

Abstract

INTRODUCTIONControlled Auto-ignition (CAI) combustion has been shown to effectively reduce the NOx emissions and increase fuel efficiency [1] and it has been subject to extensive studies in the past few decades. However, the lack of direct control on the auto-ignition process and relatively narrow operation range inhibit the practical application of this low temperature high efficient combustion mode [2]. In order to enhance the control of auto-ignition and extend the operation range of CAI combustion, spark ignition (SI) was used to assist CAI combustion. In this case, the early flame propagation induced by spark discharge could effectively control the later autoignition [3,4]. In addition, this hybrid combustion mode could be used to bridge pure SI mode and CAI mode during mode transition when applying to the full load operations in the practical engine [2,5,6,7,8]. However, the recent study on the SI-CAI hybrid combustion indicated the existence of significant cycle-to-cycle variation (CCV) during mode transition [8, 9, 10, 11].In the SI-CAI hybrid combustion, the flame propagation is mainly controlled by the transport of heat and active species in the flame front and distorted by the in-cylinder turbulence [12]. The variation of the early flame propagation would in turn affect the later auto-ignition process [13]. The premise of controlling and stabling SI-CAI hybrid combustion is to effectively manage the early flame propagation process. The local fuel/air equivalence ratio around the spark plug significantly affects the spark kernel formation and flame propagation process in spark ignition engine. Persson et al. [14] used high speed fuel Planar Laser-Induced Fluorescence (PLIF) to study the effect of fuel stratification on spark assisted compression ignition (SACI) with ethanol as fuel. They found the lower fuel concentration in the vicinity of the spark plug decreased the flame expansion speed with the overall lean mixture (lambda 1.4). Middleton et al. [15] investigated the propagation of premixed laminar reaction fronts with different fuel/air equivalence ratios using transient one-dimensional flame simulations and indicated the increased flame burning velocity with the isooctane/air equivalence ratio increasing from 0.1 to 1.0. The experimental Numerical Study of the Effect of Piston Shapes and Fuel Injection Strategies on In-Cylinder Conditions in a PFI/GDI Gasoline EngineXinyan Wang and Hua Zhao Tianjin Univ., Brunel Univ.Hui Xie and Bang-Quan He Tianjin Univ.ABSTRACT SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In order to stabilize the hybrid combustion process, the port fuel injection (PFI) combined with gasoline direct injection (GDI) strategy is proposed in this study to form the in-cylinder fuel stratification to enhance the early flame propagation process and control the auto-...

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

“…Three piston bowl designs, as shown in Fig. 3, were designed from the origin Flat Piston (FP) in order to achieve the stratified mixture [37]. Compared to Piston A (PA), Piston B (PB) has a larger bowl diameter.…”

“…In addition to the piston shapes, both the start of injection timing [20,[34][35][36] and the direct injection ratio [20,26,31] play important roles on controlling in-cylinder fuel stratification patterns and combustion process. Our previous study revealed the effect of piston shapes, start of injection (SOI) timings and direct injection ratios on the in-cylinder conditions, including in-cylinder flow conditions, fuel stratification patterns and thermal conditions [37].…”

Numerical Simulation of the Gasoline Spray with an Outward-Opening Piezoelectric Injector: A Comparative Study of Different Breakup Models

“…Dam and Rutland [16] predicted the gasoline sprays from a multi-hole injector at various background temperatures (400-900 K) and densities (3-9 kg/m3) with the standard KHRT breakup model and found that it was necessary to adjust breakup model parameters, including the break-up length, as functions of the density ratio in order to accurately simulate the large-scale vapor mixing. Wang et al [17][18][19] and Bonatesta et al [20] calibrated the RD model to predict the gasoline spray and combustion process in wall-guided DI gasoline engines with the multi-hole injector. Sim et al [21] modeled the gasoline spray from an outward-opening piezoelectric injector with the modified KHRT breakup model, and the initial Sauter mean diameter (SMD) values were varied in order to validate against the measurements under different background conditions.…”

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

“…In order to achieve optimal combustion during the spark ignition operation in the BUSDIG engine, the fuel injection and local fuel-air equivalence ratio (ER) around the spark plug should be controlled to near stoichiometry for stable ignition and faster flame propagation. [10][11][12][13] It has been shown that the fuel stratification can be achieved by a suitable bowl piston shape 14,15 and organized in-cylinder flow motions 16,17 in combination with an appropriate DI strategy. Both the start of injection (SOI) timing [18][19][20][21] and the split DI ratio 10,19,22 play important roles on controlling in-cylinder fuel stratification patterns and the subsequent combustion process.…”