Study On Plasma-Assistant Combustion Of Methane With Atmospheric Pressure Argon Plasma Jet

Atmospheric pressure argon plasma jet is a non-equilibrium plasma,which can produce a large number of electrons,positive ions,excited particles and active groups.Since these active particles can greatly reduce the activation energy,they play a very important role in the process of assisted combustion.This experiment is an argon plasma jet generated by applying an AC voltage of 46 kHz in an open atmosphere environment,experimental studies on non-premixed flame and premixed flame plasma jet assisted combustion were carried out in a self-designed cross-type burner.We first studied the effect of the argon flow rate as a carrier gas and the magnitude of the applied alternating voltage to generate a jet on the non-premixed flame,as well as the spectral intensity of the free radical emission at the root of the flame.It is found that the flow field simulated by increasing the flow rate of argon has a significant effect on the change of flame morphology,but the spectral intensity of the radical particles at the root of the flame is not obvious with voltage.It is ascribed to the fact that although increasing the flow rate of argon gas changes the gas flow field,it also dilutes the methane concentration in the mixture.The application of the electric field causes the non-premixed flame to increase the flame jitter and oscillate up and down as the discharge voltage increases,forming a push flame.And the overall length of flame becomes shorter and the flame surface appears wrinkled with the blue area of the flame root continuously enlarged,which accounts for about 1/2 of the total flame area,indicating that the combustion becomes more complete and intense.When the voltage reaches16 kV,the spectral intensity of the free radical increases,but when the voltage is 22 kV,the spectral intensity decreases,this is because when the voltage is 22 kV,the plasma increases the gas flow rate in the tube,causing the combustion region?observation region?to move away from the nozzle,and the collected flame root range is narrowed during the spectrum acquisition process.In the process of premixed flame combustion,we obtained different premixing ratios by changing the oxygen concentration,and then studied the effect of atmospheric pressure argon plasma jet on the premixed flame.By comparing the flame morphology at different discharge voltages and comparing the spectra of the flame roots with or without an electric field,when the fuel equivalent ratio is 8,4,2,the variation of the intensity of the emission of free radicals OH?A-X?,CH?A-X?and C₂?d?with voltage was measured respectively.The gas temperature of the root of the premixed flame was diagnosed by spectra fitting method.It was found that the intensity of free radicals in the root of the flame increased with the increase of voltage.And at the equivalence ratio equal to 4,the rotational temperature of the molecule is measured by the CH?A²??X²??band spectrum emitted in the premixed flame,thereby determining the gas temperature at the root of the flame.It was found that the gas temperature was maintained at a fixed value of 2200±100 K and did not change with an increase in voltage.This shows that the plasma jet has little effect on the change of flame temperature.It is mainly attributed to the fact that the plasma jet not only plays the role of electron collision and dissociation of macromolecules to generate free radicals,but also enhances the thermal convection of rapid heat loss.These two factors counteract with each other,thereby suppressing the rise of the gas temperature in the plasma flame.