Spectroscopic studies of longitudinal discharges in a supersonic air flow during the injection of propane, ethylene, and oxygen into the discharge zone

The paper presents the results of studies of longitudinal electric discharges in a supersonic air flow with a Mach number $\rm M = 2$ in the range of static pressures $(2.94$–$4.9) \times 10^4$ Pa $(\sim220$–$367$ Torr$)$ and discharge currents of $\sim1.5$–$1.8$ A during the injection of propane, ethylene, and hydrogen, along with oxygen, into the discharge zone through the two types of upstream electrodes (anodes). The design of the electric discharge modules was such that the discharge was carried downstream by the supersonic flow and closed, mainly to the cathode located downstream. Emission spectroscopy was used to obtain data on the composition of the emitting products that arose in the processes of converting a fuel-air mixture in a discharge and their spatial distribution. In particular, data on the distribution of the radiation intensity of $\rm CN$, $\rm C_2$ molecules and $\rm OH$ radical, as well as atomic hydrogen and oxygen in a number of sections of the discharge channel, are presented. The used methodology allowed us to determine the change in the transverse dimensions of the discharge channels along the length and the value of the rotational temperature of molecule $\rm C_2$ for discharges with the injection of propane and ethylene into the discharge zone. The relationship between its value and the conditions for the formation of the discharge and the coefficient of excess oxygen injected into the discharge is established.