Experimental Investigation and Modeling of Early Flame Propagation Stages in Operating Conditions Representative of Modern High Efficiency Spark Ignition Engines

The present social context imposes effective reductions of transport greenhouse gases and pollutant emissions. To answer to this demand, car manufacturers adopted technologies such as downsizing, turbocharging, intense in-cylinder aerodynamics and diluted combustion process. In this context, to master mixture ignition is crucial to ensure an efficient heat release. To get to a clearer knowledge about the physics holding early stages of premixed mixture combustion, the PRISME institute in the framework of the French government research project ANR MACDOC generated a consistent experimental database to study ignition and spherical flame propagation processes in a constant volume vessel in laminar and turbulent environment. This allows to have a detailed description of the flame dynamics of an air / isooctane mixture depending on thermochemical properties of the mixture and nature of the diluent (O₂, H₂O, CO₂ and synthetic stoichiometric exhaust gas recirculation), as well as on turbulence intensity and ignition energy. A system simulation model based on the coherent flame model approach was then setup at IFP Energies nouvelles accounting for the influence of the flame stretch, through the integration of a non-linear formulation of the mixture Markstein number, and the flame wrinkling due to turbulence. The model allowed to have a deeper insight in the interpretation of experiments and to dissociate the interacting phenomena holding the combustion process. This modeling improving seems to be a necessary step to model next generation spark ignition engines operating under steady and transient conditions.