Validation of a novel numerical model for the electric currents in burner-stabilized methane-air flames

This study presents measurements of electric currents in flat flames, induced by externally applied electric potentials. In addition to these measurements, a theoretical and numerical model for ionized methane-air flames was developed to predict the electric currents based on the charged particle distribution in the flame. Our model comprises Poisson's equation and a multi-component diffusion model in order to incorporate an electric field in the existing CHEM1D combustion software. A comparison of the numerical simulations and experimental data showed a good agreement in the observed current-voltage characteristic for different electrode distances. The model also predicts the dependence of the saturation current on the equivalence ratio well for lean mixtures. Deviations were found in the rich regime, which are largely attributed to shortcomings in the chemical mechanism. For strong applied electric fields the electric current is independent of the applied field strength. This saturation effect is caused by the depletion of electrons from the flame plasma and a domination of the electric forces over Fick diffusion for the cations. According to the simulations, the diodic effect is mostly defined by the distance that the heavier and less mobile ions have to travel to reach the negatively charged electrode.