Operation Characteristics of a Plasma Torch for Supersonic Combustion Applications with Simulated Cracked JP-7 Feedstock
Research conducted at Virginia Tech has examined plasma torch operational characteristics using a feedstock gas of mixed hydrocarbons representing a cracked JP-7 surrogate. The tests were part of a program to examine the torch as an igniter and flame-holder for hydrocarbon-fueled scramjet engines. Previous research has shown that the plasma torch has promise as a robust igniter and flame-holder using gaseous fuels such as methane, ethylene and propylene when combined with an aeroramp to assist with the combustion process. The present investigation tested the plasma torch with a feedstock mixture of gaseous hydrocarbons that simulates thermally cracked JP-7 jet fuel. This simulation of a cracked hydrocarbon fuel was studied to lay the foundation for work with liquid hydrocarbon fuel, which is of interest for today's aerospace vehicles. The cracked JP-7 surrogate consists of a 15/25/60 mixture of methane/ethane/ethylene. The research results include torch operational characteristics such as downstream plume temperatures and emission spectroscopy within the combustion plume, as well as the power supplied to the torch over a range of mass flow rates. Filtered photographs of the emissions plume were studied to aid torch plume diagnostics. Other observations made were erosion and alignment of the electrodes, which will help determine the potential lifespan of the torch using cracked JP-7 fuel. The results show successful operation over a range of powers with simulated cracked JP-7 feedstock flows. Measured spectra, current, and voltage are compared with similar results for other hydrocarbon feedstock gases. The torch operating on the JP-7 surrogate feedstock appears to be a satisfactory device for ignition, flame-holding, and combustion enhancement of cracked hydrocarbons in supersonic combustion.