Manipulation of flames with electric fields.

An electric field is shown to have a strong affect on the blow off limits using both DC and pulsed fields. However, the DC fields only affects stociometric and rich flames whereas pulsed fields also affect lean flames. The modifications using a DC field have been shown to originate from an aerodynamic body force created by the field, known as an ionic wind. The ionic wind has been experimentally measured, using particle image velocimetry (PIV). Its direction has also been modelled by analysing the field produced by the apparatus geometry. There is no standard apparatus used by researchers in this field. It has been shown using electric field modelling techniques that the field will vary significantly between different geometries. It is suggested that a uniform field should be used ensuring that the affects of the field on a flame can be related to the field strength. The most uniform field is produced by parallel plates. However, it is suggested that if one of the electrodes is in the flow path it should be replaced with a mesh as the flow will not be disturbed aerodynamically. It is also proposed that the results be conducted in a Faraday cage to ensure there is no electrical interference. The modelling work was supported by experimental data that showed a greater increase in the blow off limits with field strengths that were amplified by the apparatus geometry. The model also predicted the approximate change to the field when a flame was present. The results showed a close comparison with the ionic wind measured by PIV. The pulsed fields increased the blow off limits more than DC fields. The greatest affect was found with a square wave, however the results showed little difference when the pulse was activated for between 25 and 75% ofthe time period. Up to 5kHz the increase in blow off velocity was greater for higher frequencies. The increase in blow off velocity occurred for all equivalence ratios (although it was stronger for rich flames). The results were shown to be independent of the ionic wind and were therefore caused by chemistry changes within the flame. The mechanism for this is discussed.