On the use of ion current measurements to detect ignition in the cone calorimeter

Measurements of the ion current between two electrodes have been conducted in a premixed propane flame and in a cone calorimeter in order to assess whether the ion current can be used for combustion diagnostics in general and for detection of ignition in a cone calorimeter in particular. It was seen that the ion current responds distinctly to where it is positioned in a propane flame and also to the fuel/air ratio of the flame. In the cone calorimeter the measured ion current shows clearly when ignition occurs. The ignition detected by the ion current measurement agreed with visual inspection. It was also seen that soot deposits on the electrodes do not affect the ion current in such a way the ignition detection could be jeopardized. However, short circuiting could occur if the electrodes were kept in a sooty flame long enough for the soot to completely bridge the gap between the electrodes. The latter scenario is not a problem from an ignition detection point of view since soot growth occurs after ignition has taken place. The general conclusion from the study is that no unforeseen obstacles with the use of ion current measurements in combustion diagnostics were observed