Investigation of oxygen dissociation and vibrational relaxation at temperatures 4000–10 800 K

Abstract

The oxygen absorbance was studied at wavelengths 200–270 nm in Schumann-Runge system behind the front of a strong shock wave. Using these data, the vibrational temperature Tv behind the front of shock waves was measured at temperatures 4000–10 800 K in undiluted oxygen. Determination of Tv was based on the measurements of time histories of absorbance for two wavelengths behind the shock front and on the results of detail calculations of oxygen absorption spectrum. Solving the system of standard quasi-one-dimensional gas dynamics equations and using the measured vibrational temperature, the time evolution of oxygen concentration and other gas parameters in each experiment were calculated. Based on these data, the oxygen dissociation rate constants were obtained for thermal equilibrium and thermal non-equilibrium conditions. Furthermore, the oxygen vibrational relaxation time was also determined at high temperatures. Using the experimental data, various theoretical and empirical models of high-temperature dissociation were tested, including the empirical model proposed in the present work.

Measurements of Oxygen Dissociation Using Laser Absorption

“…Figure 3 shows the results of these measurements on an Arrhenius plot. Our measurements are compared to the models from Camac and Vaughan [7] and Baulch et al [6] as well as the previous measurements by Shexnayder and Evans [8], Camac and Vaughan [7], Breshears et al [9], Wray [10], and the more recent work by Ibraguimova et al [11].…”

“…There are three effects in play that affect the pressure in the test gas: 1) negative dP∕dt because of cooling by dissociation, 2) positive dP∕dt due to shock tube boundary layer and attenuation effects, and 3) positive dP∕dt effects by the fact that the shock tube is not a constant-volume reactor, and it will try to achieve a uniform pressure behind the reflected shock (somewhere between the pressure caused by the drop from the dissociation and the pressure immediately behind the reflected shock wave as it moves away from the end wall). The pressure rise for the measurements was always less than 15%, and so Bauch et al [6] Camac and Vaughn [7] Schexnayder and Evans [8] Camac and Vaughan (1961) 7 Breshears et al [9] Wray [10] Ibraguimova et al [11] This work − dP/dt > 5% This work − dP/dt < 5% Best−fit to current measurements at least although a pressure change is within this deviation, the results are still valid as long as the pressure rise is included in the model. This eliminates the necessity to use driver inserts to maintain a constant pressure during dissociation, which require numerous repeated shocks to design the proper insert for the each specific test condition.…”

“…Experiments were performed on mixtures of 2% oxygen in argon behind reflected shock waves with initial equilibrium temperatures from 4400 to 7900 K and pressure from 0.2 to 1 atm. Previous models have been developed that include rates for this reaction that differ by a factor of ∼2 over this temperature range [6,7] as well as previous experiments [7][8][9][10][11] with results scattered near the rates predicted by the models.…”

Vibrational relaxation and dissociation in O2-O mixtures

“…The vibrational relaxation time in O 2 -O 2 collisions was measured experimentally in multiple works [31,[38][39][40][41]. In the present work, recommendations on τ v given in [30] are implemented.…”

“…(13) and (15) is the following: dx = u dt. Since the original experimental data in [38] was reported for the laboratory system of coordinates, one needs to convert the time in this system of coordinates into the distance behind the shock wave: x = V sh dt L , where V sh is the shock speed, t L is the time in the laboratory coordinates system.…”