S. A. Losev

Modeling of diatomic molecules dissociation under quasistationary conditions

The description of high-temperature chemically reacting gas flow requires the model representations of chemical reactions rate constants. At present there is a rich variety of two-temperature models of dissociation rate constants. At the same time it is known that behind the front of a shock wave, the process of dissociation proceeds mainly in quasistationa ry state (QSS) , when the vibrational excitation of a molecule is compensated by the loss of vibrational energy during the dissociation. In this paper a brief revue of some models is given and it is shown that in QSS conditions these models have practically coinsident numerical values,that removes a question on their choice. Statament of the problem

Avogadro program: Environmental problems of heat engineering

Results of some studies of formation and transformation of harmful substances during combustion of organic fuels are presented. The studies were conducted within the framework of the program “Environmental Problems of Heat Engineering” of the AVOGADRO system.

Two-Temperature Chemical Kinetics. Dissociation of Diatomic Molecules Behind a Strong Shock Wave

Experimental data about the vibrational temperature during the process of dissociation of diatomic molecules are discussed. The experiments allowed to substantiate the two- temperature model of the dissociation rate constant K d (T,T v ). Constancy of the vibrational temperature T v , revealed in experiments during the quasistationary stage of the dissociation permits to present the rate constant as a function of T (translational temperature) only, with T v =const, and to recommend an expression for K d to the range of high and extremely high temperatures, where the experimental data are absent.

Some techniques for physical experiments in a shock tube with a nozzle

The authors describe a technique for experiments in a shock tube with a nozzle: operation of the high-pressure chamber, the pumping system, measurements of velocity and pressure, and absorption measurements in the nozzles.

Study of vibrational deactivation of molecules of carbon dioxide gas during cooling of stream in a supersonic nozzle

The vibrational temperature of the antisymmetrical type of vibrations (v3) of the CO2 molecule at the exit of a supersonic nozzle is measured in the present work using the method of recording the infrared emission. Freezing in of thev3-type vibrations was observed during the flow of undiluted carbon dioxide in a nozzle. In this case the vibrational temperature T3 considerably exceeded the translational temperature. On the basis of a comparison of the experimental results with calculation it can be concluded that vibrational deactivation of CO2 molecules occurs three to five times faster than the excitation of the vibrations during heating in a shock wave. All the experiments were conducted under the following conditions: maximum expansion of gas in nozzle A/A* = 115, temperature range 1900–2400 °K, pressure range 1–17.5 atm.

Relaxation equation for the vibrational energy of the molecules in the gas behind an intense shock front

Here e is the v ibra t ional energy per unit volume of the gas, e ~ is the equi l ibr ium value of e, T is the re laxat ion t ime, E* is the average v ib ra t iona l energy lost dur ing each molecular d issocia t ion, and n is the number density of molecu les . In a descr ip t ion of the re laxa t ion p rocesses in intense shock waves in a gas, the anharmonic i ty and thus mul t iquantum t rans i t ions and d i ssoc ia t ion become impor tant . To de te rmine whether Eq. (1) can be used in this case, we mus t examine the sys tem of kinetic equations for the number of molecules x i at each v ibra t ional level under the assumpt ion that t r ans i t i ons i ~ j a re poss ib le between any two levels , and that t r ans i t ions i * d a re possible f rom any level to the d issocia t ion cont inuum: