Fully Resolved Auto-Igniting Transient Jet Flame Simulation

This work investigates an auto-igniting impulsively started jet flame issuing into hot and vitiated co-flow by large eddy simulation (LES) with direct chemistry. The experiment from German Aerospace Center is reproduced. The direct chemistry model uses an augmented reduced mechanism that consists of 19 transported species. The targets are first to quantify the growth of the initial ignition kernel using fully resolved flow-fields and species concentrations, then to establish a reliable benchmark case for further studies. The grid study has shown that employed resolution is sufficient to describe the ignition chemistry since the ignition kernel appears at low velocities and fuel-lean conditions. Initial comparisons showed a perfect agreement between the simulations and the experiments for the statistically steady jet. For the transient part of this work, two injection cycles with higher-resolution and six injection cycles with lower-resolution LES have been performed. The estimated delay times and the location of the auto-ignition matched experimental observations. Most importantly, both the low and high-resolution LES show quite similar results, which implies that the resolved flow-fields are statistically converged, independent from the grid resolution. Only after rigorous validation, this simulation is planned to be an ideal benchmark case for such studies of pulsed jets.