Effect of alternating electric fields on the behaviour of small-scale laminar diffusion flames

• The ionic wind effect on flame in small-scale was discussed.
• Flame temperature and flame height were measured.
• Flame stability was enhanced by external AC electric field.
• Active power of AC was calculated and compared with combustion thermal power.
• A new correlation of the enhancement of upper stability limit was obtained.

The effect of Alternating Current (AC) electric field on flame behaviours of ethanol in small-scale was studied experimentally. A stainless steel tube with inner diameter of 0.9 mm was used as a burner nozzle, and the diffusion flame was established at room temperature and atmospheric pressure. The flame temperatures were measured by a thermocouple and the flame heights were measured by optical visualization method under stable combustion conditions. The ionic wind effect was considered as the dominant mechanism of AC electric field on flame. The charged particles in the flame affected by electric body force have collisions with the neutral particles and transfer the momentum. At a certain flow rate of ethanol, the flame temperature increased with electric field strength and AC frequency, and the dimensionless flame height decreased with the increase of electric field strength. The upper stability limit was enhanced greatly by AC electric field due to the increased Damköhler number (Da). The electric field puts a little effect on the lower stability limits due to thermal quenching and heat loss. The ratios of active power of AC electric field to combustion thermal power were from 0 to 0.202. The selection of AC frequency is very important for the design of small-scale combustion system. A new correlation between the enhancement of upper stability limit and the active power of AC electric field was obtained. The results show that the active power plays an important role in the enhancement of stability of the small-scale flame.