On the Use of Laser-Induced Ionization to Detect Soot Inception in Premixed Flames
Samuel Manzello, E J. Lee, George Mulholland
Experimental measurements of laser-induced ionization were performed for ethene/air premixed flames operated near the soot inception point. Soot was ionized using a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the post-flame region. Ionization signals were collected using both a single electrode and dual electrode configuration. Prior laser-induced ionization studies have focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced ionization diagnostic to these geometries, a dual electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced ionization diagnostic to detect soot inception in the post-flame region of a premixed flame using a dual electrode configuration was investigated. For the different dual electrode configurations tested, the dual electrode geometry oriented parallel to the laser beam, was observed to be most sensitive to detect the soot inception point in a premixed flame.