Regional polarity in the laminar premixed flame considering the combined effect of positive and negative charge

Abstract

The study of flame charge is helpful in analyzing the combustion regime, which is significant for optimizing energy conversion in the combustion. In this article, a method to calculate the charge density considering polarity (CDCP) for flame is presented. The charge in the flame local area is obtained by combining the effect of charged particles with positive and negative polarity. The CDCP in different zones of the premixed methane flame with three equivalence ratios of 0.9, 1.0, and 1.3 is measured in the Langmuir probe measurement experiment. The experiment result found that the regional polarity is shown in the premixed flame. Subsequently, the premixed methane flame was simulated using Fluent, and then the simulation distribution of CDCP in the premixed methane flame was obtained. The CDCP and polarity across the reactant, preheat, reaction, and product zones of the premixed flame are analyzed based on the experiment and simulation results. The CDCP of the reaction zone is greater than 0 C/m3 and reaches a peak, showing obvious positive polarity. The CDCP of the reactant zone is less than 0 C/m3, showing negative polarity. The CDCP changes rapidly from less than 0 C/m3 to greater than 0 C/m3 with the approach of the reactant zone to the preheating and reaction zones. The CDCP in the product zone gradually decreases with the increase of the distance from the reaction zone and finally less than and close to 0 C/m3, showing weak negative polarity. Finally, the cause of regional polarity formation is discussed based on the net production rate of charged particles and the velocity distribution of the flow field in the simulation results. The distribution of positive ions and electrons in the premixed flame is different due to the effect of the flow field and the different diffusion properties of charged particles. Thus, the regional polarity is exhibited in the premixed flame.