60258 - Investigation on the Effects of Field Emission Plasma on the Performance of a Micro-Combustor 

This work focuses on the effects of plasma assisted microcombustion using the FE-DBD configuration devices with a new dual-step modelling approach by considering plasma chemistry and flow dynamics.
Today, micro-devices can be used to compensate for heat losses in combustors. Traditional mems are characterized by batteries with a great impact on the weight of the system as well as batteries charging constitutes a problem that can’t always be solved. Therefore, the production of energy on a smaller scale requires more flexible and robust solutions: the combustion is one because the density of energy delivered by hydrocarbons is about 100 times larger than the batteries. However, supporting the flames on a micro scale is more difficult compared to higher scale combustion devices. Laminar flow makes the fuel mixing with oxygen hard to produce and the high surface-volume ratio involves heat losses with the consequence of lowering the temperature and extinguishing the flames. Plasma combustion applications have reached remarkable results over the last decades at high scales and in the last years technology has also become interesting for micro devices operating at lower voltages. FE-DBD actuator represents the ideal solution because require low power output and low volts with effects on the chemistry and mixture forces. Indeed at atmospheric pressure, and for gaps of few microns, it improves and increases the stability of micro flames by accelerating the chemical kinetics generating radicals. Moreover, oxygen and ozone production are greatly increased. Micro actuators generate body forces and a proper configuration helps fuel air mixing by creating vortexes and increasing the degree and time of mixing. In this work the fluid channel is made of quartz and is located on a silicone plate. Gold is the material chosen for the electrodes because it does not oxidize in the presence of plasma-assisted combustion. Electrodes were arranged in the offset configuration and placed closer to the inlet of the channel. To our modelling purpose, at first, we implemented a microscopic plasma model based on air and methane plasma. Simulations were performed in a nanosecond pulsed plasma and zero-dimensional assumption to evaluate ozone and species densities output using the toolbox ZDPlasKin: this solves plasma reactions by means of Bolsig+ solver.

Frequency has been fixed at 1 Ghz at atmospheric pressure and 300 K temperature in quiescent environment. As a second step, we studied the effect of the plasma radicals and ozone on the combustion mechanism performing 2D-CFD simulations based on the previously predicted species densities at the operating conditions. We estimated the delivered body forces and heat by chemical kinetics results and implemented them as source terms in Navier–Stokes equations using continuum approach to simulate the flow actuation in a laminar, compressible, steady flow. The momentum and energy sources generated are also used to model methane-air combustion using GRIMech 3.0 to which we added ozone reactions.

It was found that field emission based actuators are well suited for microcombustion because they permit to overcome the viscous forces associated with low Reynolds number flows and to initiate and sustain the microcombustion by low power consumption.