A RANS CFD 3D Methodology for the Evaluation of the Effects of Cycle By Cycle Variation on Knock Tendency of a High Performance Spark Ignition Engine

Modelling of early flame kernel growth towards a better understanding of cyclic combustion variability in SI engines

“…The study presented in [13] also showed that the variations in turbulence intensity have a dominant impact on the combustion instability. In [15] it was found that CCV of combustion is also influenced by the cyclic fluctuations of the stratification of mixture around the spark plug, while the results of the study presented in [16] show that the direction of fluid motion and turbulence intensity around the spark plug fluctuate from cycle to cycle, and that these oscillations induce CCV during the initial combustion phase.…”

“…The distribution of the intake turbulence production constant S 10 is defined by a relative standard deviation r rel,S10 which represents the ratio between the standard deviation (r S10 ) and the mean value of the turbulence production parameter (S 10 ). The research results of in-cylinder flow and combustion published in [14,15,31] showed that the statistical results of flow velocity (at the specific position) in the cylinder and combustion progress (at the specific time) can be approximated by the normal (Gaussian) distribution. Therefore, the distribution of the intake turbulence production constant S 10 in this study is in accordance with the findings presented in the published literature.…”

“…In the real operating conditions of SI engine it is expected that the air equivalence ratio profile is nonlinear curve, but to satisfy the previously mentioned closure condition in the applied mixture stratification sub-model it has to be simplified and considered as fully linear profile over the combustion process. The standard deviation of DU init norm is defined as input parameter and for all simulations that were performed in the presented analysis it was set to r U = 0.08, according to the 3D-CFD results presented in [15]. In cycles whose initial difference DU init norm of normalized air equivalence ratio is negative, the air equivalence ratio of the flame U flame is below the stoichiometric value until 50% of the in-cylinder mass is burned defining the flame propagation across the lean mixture in the cylinder.…”

“…For studying CCV in SI engines numerically the most promising technique is based on LES (large eddy simulation) [14,[18][19][20] or even DNS (direct numerical simulation) [21], but those techniques require extremely high spatial and temporal resolutions that significantly increase computational time of each calculated cycle. By the specific use of RANS (Reynolds Averaged Navier-Stokes) approach it is possible to model and to analyze the cyclic combustion variability [15,22,23], but it would take several weeks to calculate the results required by this study. Therefore a reduced model is required.…”

A Fast CFD-Based Methodology for Determining the Cyclic Variability and Its Effects on Performance and Emissions of Spark-Ignition Engines

“…The numerical tools that can provide valuable information of the flame propagation at the local level are the ones based on computational fluid dynamics (CFD) [18,19]. Recently, CFD codes based on large-eddy simulation (LES) for investigating cyclic variability in engines have been reported [20], mostly due to the increase of computers power and the advancement of parallel processing.…”