Spectral Study on Combustion Supporting Effect of Plasma Jet for Methane Combustion in Air

Atmospheric pressure argon plasma jet (APAPJ) is a non-equilibrium plasma producing a large number of electrons, positive ions, excited particles and active groups, which can significantly reduce the activation energy in reactions, and the dynamic effect caused by APAPJ also imposes influence on the transportation process, thereby they both play a very important role in the process of plasma-assisted combustion. In this experiment, By OES, the intermediate radicals (OH, CH and C-2) generated in the non-premixed and premixed combustions are identified. The variation of emission intensity of those radicals is measured with respect to the fuel equivalent ratio and discharge voltage, respectively. It is found that the application of the APPJ causes the overall length of flame to become short 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 at discharge voltage of 22 kV, indicating that the combustion becomes complete and intense. When the voltage reaches 16 kV, the spectral intensity of the free radical OH(A-X) , CH(A-X) and C-2 (d) becomes remarkable, but when the voltage is 22 kV, the spectral intensity decreases, which is because the plasma enhances the gas flow rate in the tube, causing the combustion region to move away from the nozzle so that the less intensity is collected by fiber during the spectrum acquisition process. In addition, the combustion process of premixed gas assisted by plasma jet under different fuel equivalence radio is studied. In the case of Phi = 2, it is found that the spectral intensity of OH (A - X) increases with discharge voltage, while those of CH (A - X) and C-2 (d) decline when the discharge voltage is large enough that the APPJ is merged into flame near the nozzle. It is found that APAPJ plays an importance role in CH4 combustion in open air due to the active radicals generated in APAPJ and the mixing effect caused by ion wind by APAPJ.