Validation of a Species-Based Extended Coherent Flamelet Model (SB-ECFM) in a Spark Ignition Engine 2019-01-0222
The recently developed Species-Based Extended Coherent Flamelet Model (SB-ECFM) is coupled with the Imposed Stretch Spark Ignition Model (ISSIM) to simulate a spark-ignition engine, the transparent combustion chamber (TCC) engine.
While the previous version ECFM is limited to lower order upwinding schemes to minimize the numerical discrepancy between species and tracers which can lead to inaccurate estimation of the progress variable and consequently to negative conditional mass fractions in the burned gases after ignition, the new version SB-ECFM removes the species tracers from the definition of the progress variable to allow higher order schemes, which can give more accurate predictions.
Since higher order schemes can be used in the SB-ECFM, to examine the spatial discretization effect and demonstrate the improvement from using higher order schemes, Reynolds-Averaged-Navier-Stokes (RANS) simulations are performed with first-order upwinding scheme and second-order central differencing scheme, respectively. The simulation results are then compared with experimental data. Two major observations are found in this study. First, with same model parameters, the second-order scheme provides better predictions than the first-order scheme compared with measurements. Second, the comparison shows that the second-order scheme is able to capture the cycle-to-cycle variation of in-cylinder pressure, however, results from the first-order scheme do not show variation after the first few cycles.