NUMERICAL STUDY OF THE EFFECTS OF VITIATION SPECIES ON FLOW FIELD PARAMETERS AND BASIC COMBUSTION CHARACTERISTICS

In view of the problem of test gas vitiation by combustion heating associated with ground test facility, considering the main vitiation species H₂O and CO₂, the effects of these two vitiation species on the thermos-physical properties of the gas was systematically explored under the vitiation condition of 0 ~ 20% mole fraction. Based on the direct-connected experiment conditions of shock tunnel corresponding to flight Ma 8, the influence of single vitiation specie on shock tunnel flow field parameters is also systematically analyzed. In addition, the effects of single vitiation specie on the zero-dimensional ignition process and laminar flame characteristics of H₂ were studied at the initial temperatures of 1100 K and 298 K, respectively. The results show that both H₂O and CO₂ can increase the specific heat capacity of vitiated air at constant pressure, and H₂O can also increase the sound velocity, viscosity and diffusion coefficient of vitiated air, but CO₂ can make the thermos-physical properties of vitiated air show opposite changes. In addition, the vitiation species not only affect the intensity of the incident shock wave, but also affect the state of the gas behind shock wave, which can lead to the angle of oblique shock and the temperature behind normal shock wave decrease, but the influence of the vitiation species on the pressure behind shock wave is very small. On the other hand, under the same total temperature, total pressure and Mach number of nozzle outlet, both H₂O and CO₂ make the temperature of nozzle outlet flow increase and the pressure decrease, and the corresponding total enthalpy and stagnation heat flux decrease, thus interfering with the incoming flow parameters and quality of engine ground test. In terms of basic combustion characteristics, both H₂O and CO₂ make the ignition delay time of H₂ increase, the laminar flame velocity and the adiabatic flame of temperature H₂ decrease. Under the condition of 20% vitiation, H₂O and CO₂ can increase the ignition delay time of H₂ by 44% and 6.6% respectively, and decrease the adiabatic flame temperature of H₂ by 83 K and 159 K respectively. The former is embodied in chemical kinetics and thermodynamics, while the latter is mainly embodied in thermodynamics.