Analysis of Cyclic Fluctuations of Charge Motion and Mixture Formation in a DISI Engine in Stratified Operation

Abstract

The processes of an internal combustion engine are subject to cyclic fluctuations, which have direct consequence on the operational and emission behavior of the engine. Direct injection gasoline engines have fluctuations that are induced and superimposed by the flow and the injection. In stratified operation they can cause serious operating problems, such as misfiring. Currently, the state of knowledge on the formation and causes of cyclic fluctuations is rather limited, which can be attributed to the complex nature of flow instabilities. Recent analyzes of a direct injection gasoline engine's cyclic fluctuations of the in-cylinder charge motion and the mixture formation utilizes laser-optical diagnostics and numerical 3D-calculations. Individual cycles are measured using optical measurement techniques and pressure indicators for determining flow, mixture formation, and the combustion processes. Large-scale turbulence and cyclic fluctuations are modeled using 3D-calculations that are performed with a Large Eddy Simulation (LES). The results of the calculations are used to analyze the formation of cyclic fluctuations and their effect on injection and mixture formation. The intensity of the cyclic fluctuations rises dramatically during the injection phase, because of the relationship between the cyclic fluctuating in-cylinder flow and the injection. These results are confirmed by calculations, which when combined with reproducible injection predict strongly differing mixture states at the ignition point with significant asymmetries. These asymmetries with their broad scatter range of mixture formation can explain the stochastic misfires that occur in the engine.

Hybrid presumed pdf and flame surface density approaches for Large-Eddy Simulation of premixed turbulent combustion

“…In the past few years, the development of massively parallel computers led to increasingly fast computations, making possible Large-Eddy Simulation (LES) of real combustion systems, such as gas turbines [1][2][3][4] or piston engines [5][6][7][8][9]. LES that was previously limited to laboratory-flame oversimplified geometries, nowadays appears as a useful tool for the design of new combustion chambers, specifically in the field of premixed turbulent combustion, where it has already been used for understanding flame and flow unsteadiness [10,11,3,9].…”

Investigation of the temporal evolution and spatial variation of in-cylinder engine fuel spray characteristics

“…The instantaneous spray fields at 4 different conditions at 3°a SOI from 3 individual injection cycles are decomposed into four parts and presented in Figs. [6][7][8][9]. Each spray field is reconstructed by using the modes listed in Table 2.…”

“…In addition, the advanced numerical simulation tools can also help the researchers to understand the in-cylinder phenomena [5][6][7][8][9][10][11]. Extensive research studies have been performed to study in-cylinder turbulent flow field CCV [12][13][14][15][16][17][18][19][20].…”

Large-Eddy Simulations of Spray Variability Effects on Flow Variability in a Direct-Injection Spark-Ignition Engine Under Non-Combusting Operating Conditions

“…For direct-injection engines, the fuel spray plays a significant role in in-cylinder mixing and is a potential source of significant CCVs. Previous research has included work looking at both the isolated spray in a constant volume chamber [26][27][28] and in engines [29][30][31][32][33][34]. However few of these studies focused on the effects of spray variability, and there remains work to increase our understanding of the relative impacts of spray variability on the overall flow and mixing variability in a direct-injection engine.…”