Spectroscopic investigations of longitudinal discharge in supersonic flow of air with injection of propane into the discharge zone

Results are given of investigations of a longitudinal contracted electric discharge in a supersonic flow of air at Mach number $M = 2$, static pressure of $3.47 \times 10^4$ Pa ($260$ torr), and discharge current of $1$ A with injection of propane into the discharge zone via electrode located upstream. The special feature of the discharge is that only one, anode, branch is realized in this case. Emission spectroscopy is used to obtain data on the composition of radiating products arising in the process of conversion of fuel-and-air mixture in the discharge and on their space distribution. In particular, data are given on the distribution of intensity of radiation of $\mathrm{C}_2$, $\mathrm{OH}$, $\mathrm{CN}$, $\mathrm{CH}$ radicals, as well as of atomic hydrogen, oxygen, carbon, and nitrogen, in a number of discharge channel sections. It is found that the main reaction zone in such a channel is preceded by the induction zone, where the development of reactions is hampered in spite of the electron flow in this zone. The employed procedure makes it possible to determine the variation of the transverse dimensions along the discharge channel and the details of flow such as a gradual shift of the gasdynamic lines of current due to the pattern of flow past the electrodes. Analysis of distribution of radiation intensity in the spectrum of atomic oxygen in a discharge without injection of propane gives estimates of the electron temperature which turns out to be approximately 1.1—1.2 eV.