Enhancement of hydrogen microcombustion via field-emission dielectric barrier discharge

A particle-in-cell (PIC) model is constructed for a similar to 100 mu m field-emission dielectric barrier discharge (FE-DBD) actuator in atmospheric pressure mixtures of oxygen, hydrogen, and water vapor. The discharge is characterized, including the effects of gas temperature and gas composition. Quantities relevant to plasma-coupled combustion, such as Joule heating, Lorenz body force, and radical generation are estimated for gas temperatures and compositions relevant for combustion energy conversion. Due to its low ionization energy, O-2 increases the magnitude of Joule heating and body forces in the discharge. However, water vapor weakens these effects because of its high ionization energy and many excitational degrees of freedom that remove energy from electrons through inelastic collisions. At higher gas temperatures the discharge becomes more diffuse on account of lower gas densities. At room temperature, and operated at an easily achieved 300 V at 10MHz, the FE-DBD produces both intense local body forces (10(7) N/m(3)) and Joule heating (10(9)W/m(3)) at the corner of the exposed electrode. A boundary layer model provides an estimate that the FE-DBD can induce flow velocities of around 10-20m/s and temperature increases of around 5-20 K in room temperature H-2/O-2/H2O mixtures. Sources based on the PIC model are applied in continuum simulations of non-premixed hydrogen combustion in a microchannel. Without the FE-DBD, the inflow of fuel and oxygen is hindered by viscous losses, thermal conduction to wall boundaries, and thermal expansion of gasses, leading to flame extinction. The FE-DBD actuators pre-heat and dissociate the fuel and produce body forces that counter viscous resistance, sustaining combustion. In another example, FE-DBD plasma coupling reduces the autoignition time of a stoichiometric, 950 K H-2-O-2 mixture from 117 mu s to 49 mu s.