Effect of mixing ratio of N2/O2 feedstock on ignition by plasma jet torch

The ignition characteristics of N-2/O-2 plasma jet (PJ) in a high-speed flow were experimentally and analytically investigated. The effect of NOx, which was the major component in the N-2/O-2 PJ, on ignition was investigated by analyzing the ignition delay time. Results indicated that NOx had a strong catalytic effect on combustion reactions of H-2 and low-hydrocarbon fuels such as CH4 and C2H4 at high pressure. Therefore, these results suggested that the N-2/O-2 PJ potentially had higher ignition ability than a pure O-2 or a pure N-2 PJ at high pressure. In the ignition test at atmospheric pressure, however, the PJ whose feedstock was composed of a larger mole fraction of O-2 more greatly enhanced ignition, and the O-2 PJ was most effective. A gas sampling showed that amount of the NOx in the N-2/O-2 PJ was much more than those in pure O-2 and N-2 PJs. These experimental results indicate atmospheric pressure was not high for appearance of the NOx catalytic effect. A local O-2 concentration around the ignition site was very important for successful ignition at low pressure, where the NOx catalytic effect was not strong. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.