Effects of nitrogen impurity on the atmospheric pressure helium plasma jets exposed to a nitrogen environment

Abstract

In this study, the effects of small nitrogen impurity on the behaviors of helium APPJs propagating into nitrogen surrounding gas are investigated numerically based on a two-dimensional fluid model. The results show that the addition of N2 impurity can change the APPJ length and there exists an optimal N2–helium ratio which enables the plasma jet to reach the maximum length. This is attributed to the variation of helium mole fraction and the ionization rate in the helium flow channel resulting from N2 impurity. Like the APPJ propagating into ambient air, with the addition of nitrogen, the profile of APPJ exposed to a nitrogen environment varies from an annular shape to a nearly uniform structure, though their reaction chemistries inside the jet effluent differ remarkably. Also, under different impurity concentrations, the density distribution and evolution of active species throughout the effluent of APPJ, as well as their dominant reaction pathways, behave differently. The physics mechanisms underlying these behaviors are discussed in detail.