Dynamic changes in global diffusion flame characteristics in response to transient variations in a DC electric field were observed in the NASA Glenn 2.2 Second Drop Tower. Methane or ethylene was injected from a fuel tube (2.1 mm i.d.) into quiescent air toward a circular mesh electrode placed perpendicular to the axis and 5 cm downstream of the fuel tube exit. An electric potential of up to ±10 kV, relative to the grounded fuel tube, was applied to the mesh electrode and varied at a controlled ramping rate. The flame was observed by digital and analog video cameras; and the ion current, thermal radiation, flame height, and flame-base standoff height were measured at various high-voltage ramping rates. Although the ion current and flame dimensions responded quickly to the electric field strength variations, it required a few hundred-millisecond settling time to gain a new steady state because of slower diffusion processes. This microgravity research was carried out in preparation for an experiment that will be conducted on the International Space Station.
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