LES Modelling of Spark-Ignition Cycle-to-Cycle Variability on a Highly Downsized DISI Engine

Abstract

The paper reports an activity aiming at characterizing cycle-to-cycle variability (CCV) of the spark-ignition (SI) process in a high performance engine. The numerical simulation of spark-ignition and of early flame kernel evolution are major challenges, mainly due to the time scales of the spark discharge process and to the reduced spatial scales of flame kernel. Typical mesh resolutions are insufficient to resolve the process and a dedicated treatment has to be provided at a subgrid level if the ignition process is to be properly modelled. The focus of this work is on the recent ISSIM-LES (Imposed Stretch Spark-Ignition Model) ignition model, which is based on an extension of the flame surface density (FSD) transport equation for a dedicated flame kernel treatment at subgrid scales. The FSD equation is solved immediately after spark discharge. The interaction of the flame kernel with the flow field is fully accounted for since spark formation and a transition is provided from ignition to propagation phase. The comparison is carried out with the AKTIM-Euler ignition model in terms of flame interaction with the flow field (e.g. arc convection, flame blow-off, flame holder effect). A multiple cycle LES activity provided a set of cycle-resolved conditions for spark-ignition comparisons, and the flame kernel development is carefully analyzed for the two ignition models on a wide range of thermo-physical conditions. Spark-ignition cyclic\ud variability and combustion traces are compared with experiments. Results confirm that the simulated cycle-to-cycle variability increases through the adoption of the ISSIM-LES ignition model

Examining the role of flame topologies and in-cylinder flow fields on cyclic variability in spark-ignited engines using large-eddy simulation

“…Looking at the equivalence ratio distributions for the two cases (on the right side of Figure 11), we note a non-insignificant level of stratification for both cases, given that this is a PFI engine. 16,43 There also seems to be a pattern where the right side of the plane in both cycles has a richer mixture, compared to the left. In this work, we see equivalence ratios ranging from 0.8 to 1.2.…”

The potential of statistical RANS to predict knock tendency: Comparison with LES and experiments on a spark-ignition engine

“…This is needed in order to accurately simulate flame size as small as the typical cell size. The adopted model constitutes a remarkable simulation improvement over traditional SI models based on the deposition of a resolved profile of fully-burnt gases [61] and it was demonstrated to explain the governing reasons for CCV origin in different SI engines in [62].…”

Simulation studies of combustion in spark ignition engine using OpenFOAM

“…In addition to the aforementioned techniques, sophisticated approaches such as the G-equations [5], flame surface density [6,7], artificial flame thickening [8,9,10] or conditional moment closure [11,12] are presently been employed to accurately predict flame propagation under the influence of turbulence. In spite of the attendant issues associated with in-cylinder flow and combustion, the Large Eddy Simulation (LES) of internal combustion engine is also being used to analyze a variety of complex issues like NOx formation [13], cycle-to-cycle variations [14,15] and flame-acoustics interactions [16,17]. As long as the demands for low emissions, higher efficiency and improved fuel economy of the internal combustion engine continues, research efforts into the mathematical and numerical techniques for modeling turbulent combustion and associated complex physical phenomena will continue to be of vital interest to engine manufacturers and the engine research community.…”