Effects of surrounding gases on direction of ionic wind in Bunsen flame

Bi-directional ionic wind is a key role of flame behaviors under an electric field and modifies a flow field of unburned gas mixture. Generally, ionic wind is known to blow bi-directional due to the movement of positive and negative charges to both the cathode and anode, respectively. The process of positive charges moving to the cathode has been clearly demonstrated, but the process of negative charges moving to the anode is not yet clear. In the present paper, we investigated the transfer process of negative charges toward the anode in premixed bunsen flame with co-flow under a direct current (DC) electric field orthogonal to the direction of jet flow. To vary surrounding gas composition, air and nitrogen were selected and injected into the co-flow section. In the case of air co-flow, bi-directional ionic wind has been observed due to the electron impact attachment which electrons can attach to oxygen molecules on the migration process to the anode. On the other hand, in the case of N2 coflow, ionic wind blew in almost uni-directional from the flame to the cathode, because the amount of negative ions are around 10% of positive ions and most negative charges are electrons. Furthermore, the charge density in the anode side is much smaller than that of cathode side since the electron's movement is much faster than positive ions because of their light mass. In conclusion, in the external environment that contained oxygen, the ionic wind blew bi-directional, and the ionic wind was almost uni-directional in N2 environment.