Uma proposta para a modelagem de descargas elétricas em gases

Abstract

This work aims at presenting a methodology for the analysis of electric discharges in gases, in conditions mimicking a commercial spark ignition. Effects of heat transfer and mass transport, besides a discrete submodel that contemplates chemical reactions and energy transfer between electrons and diverse species, are considered. Two approaches are here proposed. In the first one, the domain of study was divided into two regions, with and without electric discharge. In the region where the electric discharge occurs, effects of the electron, chemical and heat transfer and mass collisions were considered. For the spatial pos-discharge region, the effect of electronic collisions are not included. The composition of the gas present in the simulation is based on dry atmospheric air, but the addition of several components is used. In the second approach, the entire region of analysis is on the effects of the electric discharge since this region is comprised between the terminals of a vehicular spark-plug. For this approach, the effects of the electron, chemical, and heat and mass transfer collisions were considered. The spatial resolution of the proposed model is obtained through the finite volume method. A mathematical operator separation strategy is used to facilitate model resolution. Once this separation occurs, the discrete submodel has its resolution obtained through the ZDPlasKin plasma analysis tool. Some settings were used for the working regime for electric discharge. Results were analyzed concerning the temperature profile in the domain at different instants of time, besides analyzing the temporal variation in several species contained in the mixtures, in certain points of the domain. Due to the high cost of solving the equations, a Master-Slave parallelization strategy was used by the MPI (Message Passing Interface). For the first approach, the transport of energy and mass mainly from the internal to the external region was observed due to convection and diffusion. Due to the difference in pressure between the regions, energy and species generated exclusively in the discharge region are transported out of the discharge region generating heating. Within the second approach a potential difference is applied at the edges of the spark-plug, and consequently, an electric field is applied to the medium. The application of the electric field in the gas mixture causes several effects to be observed, such as the appearance of species due to collision with electrons, transport of species that have a non-zero load and subsequent heating of the region. Both approaches shown in this work allow the analysis of the temporal evolution of the temperature and the species composing the mixture including those generated due to interaction with electrons. The magnitudes such as reduced electric field, electronic temperature and the role of humidity in the experiments are also discussed.