Investigation On The Characteristics And Chemical Reaction Mechanism Of Small Ethanol Diffusion Flame Under Electric Field

With the increasing demand for micro/small-scale equipments in various fields,Micro Electronic Mechanical Systems have received extensive attention.It is of great significance to develop a high-performance micro-energy system and study the characteristics of micro-burner.Applying the external electric field to improve and control the combustion process has become a promising new combustion technology.With experimental research,numerical simulation and theoretical analysis,this paper studies the combustion characteristics and electrical characteristics of the small ethanol-air diffusion flame under the direct current（DC）and alternating current（AC）electric fields.Combined with related theories of combustion,chemistry,fluid mechanics,and electricity,the mechanism of the effect of the applied electric field on the small flame characteristics is discussed.Firstly,the detailed chemical reaction mechanism of neutral species for ethanol combustion and the mechanism of chemi-ionization reaction for hydrocarbon are presented,and the detailed chemical reaction mechanism of ethanol combustion containing charged species suitable for this study conditions is proposed.Based on the mechanism,a numerical model corresponding to the experimental systems is established,and the simulated results are compared with the experimental results to verify the accuracy and reliability of the numerical model.The improved mechanism model including charged particles proposed in this paper has a better performance than the model that does not contain charged particles in the prediction of the ethanol-air diffusion flame under the electric field.The results show that the concentration of charged particles is extreamly low,but they have an important influence on the flame characteristics,especially under the influence of an applied electric field.In the small ethanol-air diffusion flame,electron is the most important negative charged particle,and H₃O⁺is the most important positive charged particle.H₃O⁺and its reaction H₃O⁺+e^-?OH+H₂ play a leading role in the chemical reactions of charged particles.The combustion characteristics and electrical characteristics of ethanol-air diffusion flames under the appled DC and AC electric fields have changed significantly.For DC electric field and AC electric field,the trends are similar.With the increase of electric field strength,the flame size becomes smaller,the flame temperature increases,the fluid velocity near the flame increases,and each component shrinks inward,and the chemical reaction rate is accelerated.As the frequency of the AC electric field increases,its influence increases.This is mainly due to the electric force caused by the applied electric field to the charged particles in the small flame.In the circuit where the small flame is located,when the applied DC electric field strength increases,the loop current increases firstly and then stays steady until it finally continues to increase,and the equivalent resistance of the small flame decreases firstly and then increases and finally remains unchanged.This is mainly due to the combined effects of an increase in ionic wind effect,an intensified chemi-ionization process,and an increase in the concentration of charged particles in a small flame when an applied electric field is present.On the other hand,the loop current increases approximately linearly with the applied AC electric field strength.The equivalent resistance of the small flame remains almost unchanged.When the frequency of the AC electric field increases,the equivalent resistance of the small flame decreases.This is mainly due to the combined effects of ionic wind,chemi-ionization process,and charged particles.However,when the frequency of the AC electric field is high,the effect of ionic wind is weakened,and the AC electric field enhances the effect of charged particle aggregation.By applying the electric field with appropriate strength and frequency,the characteristics of the small flame are changed,and the cost of electric power is minor but its effects on the flame are major,which makes it a promising combustion technology.