Non-equilibrium plasmas in fuel-air mixtures generated by half of a microwave

The application of a 12ns unipolar pulse-or ‘half of a microwave’-for plasma production is compared in applications to more traditional microwave generated plasma, and evidence of improved pressures and efficiencies will be presented. These include initiation of combustion in fuel-air mixtures wherein the electron energy distribution is fundamentally different, sometimes appearing as streamers with space-charge limited streamer heads. Understanding the dynamics of nanosecond streamer discharges in air and in fuel-air mixtures at multi-atmospheric pressures is needed for applications of the non-equilibrium plasma assisted combustion processes in a variety of engines and with various fuels[1]. Pressure inside internal combustion engines, where transient plasma can be applied to improve combustion efficiency and peak pressure, can be very high. Cathode-directed streamer discharges and streamer propagation characteristics in synthetic air at pressures ranging from 1 to 22 bar are reported, and extension of these methods to fuel-air mixtures, including methane and diesel fuel, will be discussed. The discharges are investigated by optical, electrical and theoretical (phenomenological) methods. Streamer velocity scaling for higher pressures as a function of applied voltage, pressure and reduced electric field, E/P, is measured, and the scaling compared with the result of dimensional analysis. Transient plasma is shown to be useful for improving ignition and combustion in a range of fuels.