Effect of direct-current electric field on flame propagation characteristics of premixed CH₄/O₂/N₂ flames

In order to investigate the effects of a direct-current (DC) electric field and its polarity on flame propagation characteristics, an experiment investigation on the effects of positive and negative DC electric fields on the spherically expanding premixed CH₄/O₂/N₂ flames was conducted at the stoichiometric fuel/air ratio and room temperature using schlieren photography. The experimental results show that when a DC electric field is applied, the flame front is stretched in the horizontal direction, and the stretched flame propagation speed, unstretched laminar burning velocity and Markstein length increase with an increase in voltage magnitude. The influence of negative electric fields on these characteristics is more effective than that of positive DC electric fields. When the input voltage of -5 kV and 5 kV is applied, the stretched flame propagation speed increases by 10.85% and 5.66%, and unstretched laminar burning velocity rises by 13.13% and 6.98%, respectively, compared with that of 0 kV. It seems that flame propagation and stability can be effectively enhanced by DC electric fields.