Ignition and flame-holding of H 2 and CH 4 in high temperature airflow by a plasma torch

Abstract

The effect of airflow temperature on ignition characteristics of a plasma torch was experimentally investigated. Various combinations of fuels (CH 4 and H 2) and plasma jets (PJs) (N 2, O 2, and N 2/H 2) were tested for a wide range of airflow temperature from 300K to 700K and the PJ power required for ignition was investigated. Ignition by the PJ occurred more easily in a high temperature airflow than in an atmospheric temperature airflow. The main reason for this was considered to be the increase in the reactivity of the fuel at high temperature rather than the effect of radicals in the PJ, because there was no difference in the spectroscopic measurement of the PJ between T air = 300K and 700K. The addition of H 2 to the N 2 feedstock was also effective for ignition enhancement of both fuels (H 2 and CH 4). In particular, the H 2 30%/N 2 70% PJ was able to ignite both fuels even at atmospheric temperature and the lowest electric power input for the stable operation. One of the reasons for this advantage of the H 2 30%/N 2 70% PJ was the heat release from the diffusion flame of the H 2 included in the feedstock with the airflow after injection. Moreover, the conditions around the local ignition site such as the local fuel concentration or the size of the contact area of the PJ and the fuel jet were found to be important factors for the success of ignition.