Field-emission plasma enhancement of H₂–O₂ micro-combustion

Abstract

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.

Combustion Characteristics of Hydrogen/Air Mixtures in a Plasma-Assisted Micro Combustor

“…An upward suction effect can be observed upstream of the actuators. The flow encounters the surface of the plasma actuators near the exposed electrode edge and then moves downstream along the dielectric surface, in accordance with [43,55]. Plasma actuation was able to sustain a stable flame under all tested conditions thanks to the heat and initial chemical radicals.…”

“…An upward suction effect can be observed upstream of the actuators. The flow encounters the surface of the plasma actuators near the exposed electrode edge and then moves downstream along the dielectric surface, in accordance with [43,55]. The flame behavior under the plasma effect has been compared to the case without actuation (clean case, W/O PAC): temperature and species distributions were studied for mean mixture velocities at the inlet of the combustion chamber of 1 m/s, 2 m/s, and 6 m/s, using two different equivalence ratios.…”

“…The results showed that the efficiency of the system is significantly less impacted by the power of the plasma discharge than by the power of the combustion. Each actuator consumes 2.97 × 10 2 W m −2 , resulting in a total power of approximately 0.25 W for the entire chamber, approximately one order of magnitude less than the fuel power output, in accordance with [28,43]. The lowest heating value of hydrogen is around 1.19 × 10 8 J/kg.…”

“…The dielectric is made of silicon nitride and has a thickness of 4 µm. The voltage input is sinusoidal, with a peak-to-peak voltage of 325 V and a DC bias of 162.5 V. Mackay et al [43] studied various designs for actuator positions and body force directions in a Y-shaped combustor geometry. Based on that work, the pump configuration is used to stabilize the flame because it increases the fluid velocity to compensate for potential viscous losses in the channel, with a longitudinal component of the plasma momentum contribution.…”

“…The electrode system, which consists of nine pairs at the entrance of the combustion chamber in the mixing zone, is designed such that the coordinate x = 0 is at the inlet of the combustion chamber, just downstream of the Y-shaped inlet ducts. Mackay et al [43] studied various designs for actuator positions and body force directions in a Y-shaped combustor geometry. Based on that work, the pump configuration is used to stabilize the flame because it increases the fluid velocity to compensate for potential viscous losses in the channel, with a longitudinal component of the plasma momentum contribution.…”