(625e) The Control and Extinction of Hydrocarbon Flames Via Electric Fields

Hydrocarbon flames contain a variety of charged species ? including electrons, molecular ions, and various carbonaceous particles (i.e., soot) ? created as chemical byproducts of the combustion process. Consequently, flames can be considered not only as the hot, gaseous products of an exothermic oxidation process but also as weakly ionized, nonequilibrium plasmas. Despite the small degree of ionization (typically parts per billion), such flames are highly responsive to strong electric fields. Many of these electrical aspects of flames (e.g., their deflection by a static electric field) have been known for nearly a century; however, our understanding of these phenomena remains largely phenomenological. Furthermore, modern technologies such as high frequency, high voltage power supplies have just recently enabled the exploration of new types of flame-field interactions. Specifically, we have discovered that strong, non-uniform, oscillating electric fields (e.g., E ≈ 1 MV/m, dE/dr ≈ 10^8 V/m^2, and f ≈ 1000 Hz) can have a dramatic influence on hydrocarbon flames, enabling their manipulation and even extinction. The development of numerical methods capable of describing these complex phenomena, coupling mass, energy, and momentum transport, are needed to unravel the mechanism(s) underlying the observed behaviors and to enable assessments of the scale-up feasibility for the suppression/control of larger fires.

Here, we described one such approach based on the extension of an existing algorithm for the simulation of low Mach number reacting flows with complex chemistry on an adaptive hierarchy of grids (see Day, M. S., Bell, J. B. Combust. Theory Model. 2000, 4, 535). The present approach incorporates the generation, recombination, and transport of the various charged species, which couple to the overall gas flows through their collisions with neutral species. The results of the simulations are compared to experiments, and the mechanism underlying the flame's response is discussed.