Edge flame propagation via parallel electric fields in nonpremixed coflow jets

Abstract

Recent investigations suggested that the primary influence of an electric field on a flame is flow modification caused by ionic wind, and that negative ions produced by the electron impact attachment should play a key role in the bi-directional ionic wind. In order to prove this hypothesis in electric fields parallel to the propagating flames, we designed a coflow experiment with laminar lifted flames in vertical electric fields produced by a nozzle and ground electrode installed over the flame.We found that applying DC and AC increased the flame displacement speed, and decreased the unburned velocity even to negative velocity. Velocity measurements revealed the influence of the electric body force on the flow volume, indicating the importance of the electron impact attachment when the nozzle was charged with positive voltage. The flame propagation speeds were estimated by subtracting the unburned velocity from the displacement speed, and were well correlated with those of stationary lifted flames without an applied electric field as a function of flame curvature. This supported our hypothesis that the effect of the electric field is reflected in the flow modification, and that the flame is affected by the modified flow. It also suggested that the propagation direction of premixed or nonpremixed edge flames can be manipulated by coupling the appropriate electric fields.

Study on the electrical response of small ethanol‐air diffusion flame under the uniform electric field

“…Through the action on the charged species in the flame, the external electric field will have a significant impact on the flow field in the combustion process, thus changing the combustion and electrical characteristics of the small flame. The flow near the flame will change when the electric field is applied 6 . The corresponding flow velocity, u , is defined as the ratio of flow velocity under external electric field to that without external electric field, u = u E / u E =0 , and u E =0 = 0.09 m/s.…”

“…The flow near the flame will change when the electric field is applied. 6 The corresponding flow velocity, u, is defined as the ratio of flow velocity under external electric field to that without external electric field, u = u E /u E=0 , and u E=0 = 0.09 m/s. The dashed line with squares in Figure 12 shows the corresponding flow velocity with various electric field strengths.…”

“…In recent years, the promising technologies such as electric field and plasma assisting combustion have attracted the attention of researchers. [1][2][3] And those technologies are studied to improve the combustion process, especially to enhance flame stability, 4,5 change flame propagation 6 and apply ion-current method. 7 Nowadays, the demand for miniaturization of equipment is increasing.…”

Dynamic responses of counterflow nonpremixed flames to AC electric field

“…For example, ionic wind-driven flow-field modification was speculated to cause reduction in soot formation under a direct current (DC) electric field [1]; ionic wind-driven hydrodynamic instability and/or a modification of the transport property was hypothesized to lead to the faster burning character of outwardly propagating premixed flames under an alternating current (AC) electric field [6]; ionic wind improved flame stability in a numerical study of nonpremixed laminar jet flames under a DC field [11]; and, recently, bidirectional ionic wind blowing from a flame to both electrodes was observed in nonpremixed counterflow flames [16] followed by generalized visualization in premixed and nonpremixed jet flames with DC and AC fields [24], suggesting new understanding of the nature of ionic wind and its interaction with flames' structures. As a result of the insight of the bidirectional ionic wind, we proved that a propagation speed of a nonpremixed edge flame could be augmented [25], [26] or retarded [27] depending on a relative direction of electric field with respect to that of flame propagation. This implies that we should be able to actively control a propagating character of a flame using electric field.…”

A Comprehensive Review of the Influence of Electric Field on Flame Characteristics

“…This change makes the flame cells appear, which increases the flame surface area, promotes the mixing of fuel and oxidant, and increases fuel consumption and heat release per unit area. Yoon et al and Altendorfner et al applied an AC electric field in the original DC electric field research and used PIV and PLIF techniques to observe [11][12]. Experimental studies have shown that the addition of DC and AC reduces the speed of the flame upstream, resulting in an increase in the flame displacement speed.…”