A particle-in-cell (PIC) model is constructed for a ∼100 μm 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 10 MHz, 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 10-20 m/s and temperature increases of around 5-20 K in room temperature H 2 /O 2 /H 2 O 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 μs to 49 μs.

A combined molecular dynamics (MD) and Monte Carlo approach was used to bridge time scales, enabling calculations of surface recombination rates for hydrogen on silica. MD was used for temperatures between 10 and 600 K at a high pressure of 10 atm, yielding recombination coefficients between 0.1 and 1. For the lower pressures more common in applications, low recombination rates make the corresponding calculations intractably expensive. A Monte Carlo technique, informed by the MD simulations, was designed to bridge the essential time scales. Distinct weak and strong surface binding sites for atomic hydrogen with densities of approximately 10 nm −2 were found using grand canonical Monte Carlo (GCMC) simulations, which, in turn, were used to obtain Eley−Rideal rate constants based on semiequilibrium theory. Monte Carlo variational transition state theory (MCVTST) was used to calculate Langmuir−Hinshelwood and thermal desorption rate constants for hydrogen atoms in strong and weak adsorption sites. Calculated reaction rates were used in a Langmuir kinetics model to estimate the recombination coefficient γ for T = 10−2000 K at gasphase radical densities between 10 12 and 10 16 cm −3 , yielding values of γ = 10 −4 −0.9.

A detailed three-dimensional computational model is developed to assess the potential of micronscale field emission dielectric barrier discharge (FE-DBD) plasma actuators in non-premixed microburners with channel heights in the range of L z =0.25-0.75 mm. Results for H 2 -O 2 combustion with Reynolds number Re=100 are studied for different configurations of plasma actuator arrays. Without plasma actuation, results agree with corresponding experiments, although in this case the burner typically suffers from incomplete combustion due to thermal quenching, radical quenching, and slow diffusive mixing. For the range of conditions simulated, plasma actuation increases combustion completeness from 25%-70% to 40%-80% by enhancing mixing, generating radicals, and Joule heating. Ionic wind resulting from the FE-DBD plasma disrupts the otherwise simple laminar flow in the burner, accelerating the growth of a mixing layer and enhancing heat transfer to channel walls. The larger, lower temperature flames reduce thermal gradients (and thereby thermal stresses) in the walls. Radical generation due to electron-impact dissociation extends the reaction zone in the diffusion flame and increases combustion completeness. In all cases, the additional heat release with plasma actuation (100-190 W) is significantly larger than the power needed to sustain the plasma (0.1 W), suggesting that plasma actuation may provide a significant advantage in energy generation using realistic portable micro-combustion devices.

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