Deformation Study of Lean Methane-Air Premixed Spherically Expanding Flames under a Negative Direct Current Electric Field

Abstract

This paper compares numerical simulations with experiments to study the deformation of lean premixed spherically expanding flames under a negative direct current (DC) electric field. The experiments, including the flame deformation and the ionic distribution on the flame surface were investigated in a mesh to mesh electric field. Besides, a numerical model of adding an electric body force to the positive ions on the flame surface was also established to perform a relevant simulation. Results show that the spherical flame will acquire an elliptical shape with a marked flame stretch in the horizontal direction and a slight inhibition in the vertical direction under a negative DC electric field. Meanwhile, a non-uniform ionic distribution on the flame surface was also detected by the Langmuir probe. The simulation results from the numerical model show good agreement with experimental data. According to the velocity field analysis in simulation, it was found the particular motion of positive ions and neutral molecules on the flame surface should be responsible for the special flame deformation. When a negative DC electric field was applied, the majority of positive ions and colliding neutral molecules will form an ionic flow along the flame surface by a superposition of the electric field force and the aerodynamic drag. The ionic flow was not uniform and mainly formed on the upper and lower sides, so it will lead to a non-uniform ionic distribution along the flame surface. What's more, this ionic flow will also induce two vortexes both inside and outside of the flame surface due to viscosity effects. The external vortexes could produce an entraining effect on the premixed gas and take away the heat from the flame surface by forced convection, and then suppress the flame propagation in the vertical direction, while, the inner vortexes would scroll the burned zones and induce an inward flow at the horizontal center, which could be the reason for the pitted structure at the horizontal center when a high voltage was applied.

Influence of DC Electric Field on the Propane-Air Diffusion Flames and NOx Formation

“…The interaction between the electric field and the flame also worked in the premixed flame. Li [26] and Fang [27] investigated the effect of electric field on methane-air mixture premix flame experimentally. The deformation process of the spherically expanding premixed flame was observed, and the application of an electric field commonly promotes flame propagation and increases the heat release rate.…”

Overview of Electric Field Applications in Energy and Process Engineering

“…This mechanism could also contribute to a controlled growth and aggregation of nano-particles in flame synthesis described in Section 2.3. Many fundamental experiments using lab-scale burners have been carried out for studying electric field enhanced combustion using premixed (see, e.g., [22][23][24][25][26][27][28][29][30]) and non-premixed flames [31,32]. Attempts for a technical application at higher thermal load were conducted by Weinberg et al for a meso-scale burner [33], by Sakhrieh et al for a Bunsen flame array [34] and Altendorfner et al [35] for a swirl flame that is usually applied in gas-turbine burners.…”