Effects of direct-current (DC) electric fields on flame propagation and combustion characteristics of lean premixed CH₄/O₂/N ₂ flames

Lean combustion is an efficient technology for low pollutant emissions and high efficiency engines. However, the relatively low flame propagation speed makes it difficult to achieve stable combustion in lean burn regime. Electric field assisted combustion is considered as a very promising and attractive approach for improving the lean combustion and enhancing flame propagation. In this work, effects of direct-current (DC) electric fields on the flame propagation and combustion characteristics of lean premixed CH ₄/O₂/N₂ mixtures were experimentally investigated at excess air ratios of 1.2, 1.4, 1.6, and 1.8, room temperature and atmospheric pressure. Results show that the existence of the DC electric fields significantly affects the flame propagation and combustion properties. Specifically, the flame shape becomes a prolate spheroid, with the major axis in the electric field direction as a result of the movement of positive ions by the electric body force, and a further increase in the applied voltage distorts the flame front more significantly. Additionally, the flame propagation speed in the electric field direction (S_n) and corresponding normalized mean flame propagation speed () are increased as the electric field becomes more intense, and this behavior is more pronounced for the leaner mixtures. Finally, the initial and main combustion durations defined by the pressure evolution profiles are shortened. The peak pressure and peak rate of pressure rise are increased with the increase of the electric field intensity. The observation of the flame propagation speed and the pressure evolution behavior substantiates the potential of the electric field in enhancing lean combustion.