A numerical investigation of plasma-assisted ignition by a burst of nanosecond repetitively pulsed discharges

Nanosecond repetitive pulse discharges (NRP) are a promising technology to promote the ignition of a lean reactive mixture. The success or failure of ignition results from complex interaction phenomena between the plasma generated by the discharge and the properties of the turbulent flow. This work presents two approaches for modeling plasma-assisted ignition scenarios resulting from NRP discharges. The first consists of a low-order model based on dimensionless analysis, while the second involves a Large Eddy Simulation (LES) of the reactive turbulent flow that requires high-performance computing. Both methods are presented and successfully applied to an experimental setup, which was specifically designed to study the influence of flow operating conditions and electrical discharge properties on plasma-assisted flame ignition. The simple dimensionless analysis can identify coupled and decoupled regimes, which always lead to ignition success or failure, respectively. However, the model is too crude to predict the fine interactions between plasma kinetics, combustion chemistry, and flow dynamics that control the formation of the reactive core in partially coupled regimes. The LES provides a means to capture these complex interaction mechanisms. A quantitative analysis of the reactive kernel growth has been performed by numerically reconstructing the OH-PLIF signal measured by the camera. A very good agreement is observed, validating the numerical strategy for plasma assisted combustion.