Experimental study of positive and negative DC electric fields in lean premixed spherically expanding flames

- Positive and negative DC electric fields show a great effect on lean combustion.
- Positive voltage is more efficient than the negative one in enhancing the combustion.
- Stability of the spherical flames at high voltage becomes poor.
- The negative applied voltage is more likely to cause the flame instability.

This paper investigates the effects associated with applying both positive and negative DC electric fields to premixed CH4/N2/O2 spherically expanding flames with excess air ratio λ = 1.2/1.4/1.6 in a constant volume combustion chamber. The results show that, both positive and negative DC electric fields enhance the combustion rates. Firstly, the mean flame propagation speed increases in the electric field direction and decreases in a direction perpendicular to the electric field with the increase of applied voltages. This effect is most significant at lambda = 1.6, and decreases with the excess air. Secondly, the combustion peak pressure under both positive and negative electric fields increases with the applied voltage, while the peak time decreases. At the same voltage value, the pressure increase and the burning time shortening are more pronounced under a positive voltage. applied voltage. Third, under a lower voltage and a smaller excess air, the flame is basically stable. However, when the applied voltage and the excess air increase to a high value (10 kV, λ = 1.6), the stability of the flame front will rapidly becomes worse.