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When a gas is overvolted at or near atmospheric pressure, it results in a streamer discharge formation. Electrode geometries exert significant impact on the electrical breakdown of gases by altering the spatial profile of the electric field. In many applications the efficient generation of radicals is critical and is determined by the characteristics of the streamer discharge. We examine the effect of electrode geometry on the streamer characteristics and the production of radicals. This is performed for three different electrode geometries: plane–plane, pin–plane, and pin–pin. A two-dimensional rotationally symmetric fluid model is used for the streamer discharge simulation in the hydrogen/air gas mixture. The spatial profile of electron density and the electric field for point electrodes show significant differences when compared to plane electrodes. However, the efficiency of radical generation shows similar trends for the electrode configurations studied. We also present the results of spatial electrical energy density distribution which in turn determines spatial excited species distribution. These results can inform the design of specific applications. 

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the streamer model. The role of the nonthermal plasma in such discharges is to produce radicals, which accelerates the chemical conversion reaction leading to temperature rise and ignition. Therefore, the characterization of the streamer and its energy partitioning is essential to develop a predictive model. We examine the important characteristics of streamers that influence combustion and develop some macroscopic parameters. Our results show that the radicals’ production efficiency at an applied field is nearly independent of time and the radical density generated depends only on the electrical energy density coupled to the plasma. We compare the results of the streamer model to the zero-dimensional uniform field Townsend-like discharge, and our results show a significant difference. The results concerning the influence of energy density and repetition rate on the ignition of a hydrogen/air fuel mixture are presented. 

Many positive laboratory results that have been reported in which non-thermal plasmas, particularly repetitive nano second pulses, showed a reduction of ignition time delay and extension of flammability limits. However, there is a need for predictive models for designing practical systems. We present the results of a self-consistent model and simulation results of plasma assisted combustion of hydrogen air fuel mixture. The electrical discharge phase is modeled as a streamer discharge which is followed by the combustion kinetics phase. Nonequilibrium population of excited states leads to an increase in the reactivity and facilitates ignition and flame propagation. We have quantified some macroscopic properties of streamers such as radical production efficiency which will lead to the development of predictive tools. The concentration of radicals depends on the electrical energy density which is critical in determining ignition. We find that short duration streamers do not deposit enough energy to ignite hydrogen air mixtures. Also, the spatial and temporal electric energy density will influence the ignition delay and flame propagation velocity etc.