A Multi-Cycle Large-Eddy Simulation Study of Combustion Cyclic Variation in a SI-engine

Övrigt konferensbidrag, 2019

This study investigates the influence of ow and thermal eect on the early-burn combustion variability in a single cylinder spark-ignited engine fueled with a homogeneous lean (phi=0.8) isooctane-air mixture by the means of Large-Eddy Simulation. Emphasis is put on the early stage combustion, which is considered to be of key importance for cycle-to-cycle variation (CCV). The flame propagation is modeled by the Extended Coherent Flame Model for LES (ECFM-LES), which is based on a transport equation for the filtered flame surface density (FSD). The ignition process is modeled by the Imposed Stretch Spark Ignition model (ISSIMLES). Reactive simulations were concurrently performed on the ten consecutive cold ow LES cycles followed by two initialization cycles using a real engine geometry, and observed results were compared with an experimental data. Firstly, validation of the simulation was done by comparison to measured pressure traces. Secondly, a probability analysis of the flame development, using 10% fuel burnt mass fraction was done, which revealed an asymmetric flame kernel development persisted through the whole initial-to-turbulent transition period. Finally, an evaluation of the flow and thermal field is made at global and local level. Overall good agreement was found between the measurement and the simulation data. The results reveal, that the velocity magnitude and fluctuation around the spark vicinity affect the growth of the early flame kernel and cause combustion cyclic variability.