Research On Matching Characteristics Of Plasma Assisted CH₄ Combustion

In recent years,natural gas,as a clean primary energy source,has received extensive attention.As the main component of natural gas,methane,because of its stable molecular structure and high C-H bond energy,makes the combustion reaction conditions harsh.The addition of plasma helps to overcome these shortcomings.In addition,methane,as the simplest hydrocarbon fuel,is often used to study the mechanism of plasma assisted combustion.However,the current research on plasma assisted methane combustion fails to fully explore the influence of various factors on combustion support,and there are great differences in experimental conditions and combustion characteristics in the existing research.In this paper,aiming at the above problems,through the perspective of material matching,space matching and energy matching,the research work o f plasma assisted methane combustion is as follows:Firstly,the experimental platform of plasma assisted methane premixed combustion is designed and built,which can realize multi factor change and characteristic parameter observation.Then the method and principle of plasma and combustion diagnosis are introduced,and the imaging diagnosis method based on spectral analysis is developed.The characteristic parameters of plasma assisted combustion are also discussed and analyzed.Secondly,the material matching characteristics of plasma assisted methane combustion are studied.The plasma chemical model of methane air mixed discharge is established.The characteristics of ignition delay time and flame propagation rate of methane air premixed combustion with O,H,CH3 and O3 as initial reactants are studied by means of combustion reaction dynamics simulation.It is found that O,O 3 have more significant influence on combustion characteristics than H and CH 3.The influence of chemical equivalence ratio on auxiliary combustion characteristics is studied.It is found that the increase of methane content in premixed gas will weaken discharge intensity,increase gas temperature Tg of the discharge area.With the effect of plasma discharge,there are great differences in the flame temperature distribution under different equivalence ratioThirdly,the space matching characteristics of plasma assisted methane combustion are studied.The experimental research on the distance between plasma discharge and combustion flame(i.e.discharge position)and the flow velocity of premixed gas is carried out.The reduction of the distance between the discharge area and the combustion area is conducive to the combustion reaction,and the discharge intensity,combustion reaction temperature and flame propagation speed increase accordingly.If the distance between the discharge area and the combustion area is too close,the original discharge mode may be changed,and the purpose of enhancing combustion cannot be achieved.Therefore,there is an optimal distance between the discharge and combustion to optimize the plasma assisted methane combustion,and make the plasma discharge and combustion achieve a better match in space.In this study,when the experimental flow rate changes in the range of 0.141m/s-0.915m/s,the characteristics of the discharge region hardly change with the flow rate,but the methane combustion reaction is enhanced more obviously in the low flow rate state with the plasma discharge.Finally,the energy matching characteristics of plasma assisted methane combustion are studied.The experiments are carried out by using high-frequency AC power supply,nanosecond pulse power supply and microwave power supply.Compared with the increase of excitation frequency(38k Hz-50 k Hz),the increase of excitation voltage(17k V-24 k V)in high-frequency AC power supply can enhance the discharge intensity and promote the combustion reaction Under the excitation,the increase of peak voltage(13k V-21 k V)and repetition frequency(500Hz-3000Hz)can promote the intensity of plasma discharge,and then promote the combustion reaction of methane.In addition,a coaxial microwave resonator is designed for the research of microwave power supply as the excitation source,and the increase of output power of microwave power supply can promote the combustion reaction of methane.By comparing the experimental results of three kinds of plasma excitation sources,it is found that the influence of the change of plasma excitation sources on the combustion characteristics is quite different.The research work of this paper comprehensively studies the change rule of plasma assisted methane combustion when various factors change from the perspectives of material matching,space matching and energy matching,whic h is conducive to promoting the understanding of plasma assisted methane combustion kinetic and finding the appropriate mode of assisted methane combustion.In addition,the idea and method of imaging diagnosis based on spectral analysis can also be used in other research work of plasma assisted combustion.