Li, MSF; (2014) Investigating the effects of applying a high voltage DC electric field in a flame using a point to plane electrode arrangement. Doctoral thesis , UCL (University College London).

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Abstract

A high voltage DC electric field was applied to methane and hydrogen flames using electrodes in a point to plane configuration. In a methane flame the Townsend mechanisms were observed along with the streamer, glow and spark corona discharge and were characterised using electrical, visual, audio and mass spectrometry data. A Pt point electrode was used to explore the region where the Townsend mechanisms took place by taking full mass spectrums from 10 – 50 amu for various voltages, varying oxygen concentration and using different inert gases. Large decreases in H2O and CO2 was observed in the ratio of 2:1 while an increase of N2 and O2 was also seen. These changes were attributed to transport effects moving the H2O and CO2 molecules away from the sample inlet. As the H2O and CO2 molecules were displaced, air was drawn in which caused the appearance of an increase in N2 and O2. One possible explanation for the transport effect is the electric field ionized O2 while the positive electrode repelled the ions. It is this movement that then pushes the H2O and CO2 molecules away from the sample inlet. The effect of a spark corona discharge on SO2 and CO2 in a hydrogen flame was also explored. Both were observed to decrease upon the creation of the discharge. Again transport effects could be used to explain these findings. The thesis also documents the design and creation of an automated experimental system used to obtain the results. This included hardware design, controlling software and scripts to analyse the large volume of data. The platform enabled an experimenter to control the gas flow, electrode placement, voltage and current applied automatically, while taking synchronised voltage, current, audio, visual and mass spectrometry data.

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