Studies of Chemi-Ionization and Chemiluminescence in Supersonice Flows of Combustion Products

Abstract

A stable ethylene/oxygen/argon flame is sustained and nearly complete combustion is achieved in the combustion chamber of an M = 3 supersonic nozzle, at a stagnation pressure of P 0 =1 atm. Ultraviolet and visible emission is detected both from the combustion chamber and from the M = 3 flow of combustion products. Temperature in the combustor, inferred from the visible emission spectra, is To = 2000 ± 200 K. Electron density in M = 3 flow of combustion products has been measured using Thomson discharge n, = 1.4 ± 0.2·10 8 cm -3 , at an ionization fraction of n e /N = (0.65 ± 0.15) · 10 -9 . This corresponds to an electron density of n e0 = 2.2 ·10 9 cm -3 in the combustor. The chemi-ionization current measured in the M = 3 flow is found to be proportional to the equivalence ratio in the combustor. The time-resolved chemi-ionization current is in very good correlation with the visible emission from ethylene-air and propane-oxygen-argon flames in the combustor at unstable combustion conditions. The results show that nearly all electrons can be removed from the supersonic flow of combustion products by applying a moderate transverse electric field. No effect of electron removal on visible emission has been detected. A similar result was obtained for nitric oxide β bands and cyanogen violet band emission, when nitric oxide was injected into the combustion product flow.