Plasma Jet Flame-Stabilization Mechanism in Supersonic Combustion

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Studies on the mechanism of ignition and flame-holding by upstream injection plasma jets were conducted for H_2 diffusion flames in high speed air streams. The plasma jets were operated with Ar gas involving active species such as O_2, N_2 and H_2, in the range of relatively low power. It was observed that for ignition and flame-holding, the concentration of active species in feedstock is more important than plasma jet power. This fact suggests the effectiveness of active species produced by plasma jets, rather than that of plasma-jet thermal energy, and also the importance of radical concentration supplied to the ignition-point of a fuel jet, compared to the total quantity of radicals produced. It was also found that the effectiveness of additives is in the order, O_2 * N_2 > H_2, and the results of numerical simulation on combustion-reaction promotion by the radicals added agreed qualitatively with the experimental ones. In the case of supersonic air streams, where an oblique shock wave is observed ahead of plasma jet injection, for the establishment of ignition and flame-holding the power of plasma jet must be increased, but the order of effectiveness of plasma jets, differ in the feedstock, are same in the case of subsonic air strems.