Partially Stratified Charge Natural Gas Combustion: The Impact of Uncertainties on LES Modeling

The aim of this work is to carry out statistical analyses on simulated results obtained from large eddy simulations (LES) to characterize spark-ignited combustion process in a partially premixed natural gas mixture in a constant volume combustion chamber (CVCC). Inhomogeneity in fuel concentration was introduced through a fuel jet comprising up to 0.6 per cent of the total fuel mass, in the vicinity of the spark ignition gap. The numerical data were validated against experimental measurements, in particular, in terms of jet penetration and spread, flame front propagation and overall pressure trace. Perturbations in key flow parameters, namely inlet velocity, initial velocity field, and turbulent kinetic energy, were also introduced to evaluate their influence on the combustion event. A total of 12 simulations were conducted. The results show how the perturbations affect flame front propagation, although the ensemble average shows that the position of the flame front can still be reasonably predicted with a single simulation. It has been also highlighted the role of turbulence in the evolution of the combustion process. This demonstrates the accuracy of LES in simulating such combustion process, a key step towards its application on more complex problems such as direct injection engines.