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ABSTRACT
The characteristics of burning jets of magnesium/polytetrafluoroethylene (MT) pyrotechnic base bleed igniter in the atmosphere are studied by a high-speed camera (HSC) combined with the infrared thermal imager (ITI) for MT igniters with different mass ratios. A 3D steady combustion model is established based on the simplified three-step chemical kinetic mechanism. Finite volume method (FVM) is applied to the numerical simulation of the time-averaged combustion field using a RANS two-equation eddy viscosity model coupled with the eddy dissipation concept (EDC) model. The results indicate that the highest temperature region in the combustion field is located above the potential core of each single jet, corresponding to the most intense chemical reaction region, whereas the maximum velocity region is located on the perimeter side of the potential core. In the converging region, the momentum, heat, and components Mg, MgF2, and C2 transfer and diffuse rapidly from each burning jet to the centerline of the combustion field, except that the component C2F4 is consumed completely in and around the potential core. However, in the combined region, the temperature, velocity, and concentration of each component all reach the maximum on the central axis of the combustion field. Simultaneously, the similarity of cross sections is shown. An increase in the concentration of Mg in the range of 0.45–0.61 occurs, and the reaction rate and reaction heat decrease, so that the temperature and velocity of the combustion flow decay and the gradient are also reduced. In addition, the mass fractions of C2F4, MgF2, and C2 decrease.
Nomenclature
| A | = | preexponential factor |
| b | = | half width |
| B | = | temperature index |
| cp | = | specific heat capacity |
| d | = | nozzle diameter |
| Di,m | = | turbulent diffusion coefficient of the species |
| E | = | activation energy |
| Gk | = | generation term of turbulent kinetic energy |
| i | = | gas-phase species |
| Ji | = | diffusion flux of species |
| k | = | turbulent kinetic energy |
| K | = | reaction rate constant |
| Mi | = | molar mass of species |
| N | = | total number of gas-phase chemical species |
| p | = | pressure |
| r | = | reaction rate |
| R | = | universal gas constant |
| Ri | = | net production rate |
| S | = | longitudinal displacement |
| ST | = | energy source term |
| Sct | = | turbulent Schmidt number |
| t | = | time |
| T | = | temperature |
| ui, uj | = | velocity tensors |
| V0 | = | initial injection velocity |
| Vm | = | maximum velocity |
| V | = | velocity vector |
| Yi | = | mass fraction of species i |
| Greek symbols | = | |
| α, β | = | burning jet expansion angles |
| ρ | = | density |
| ε | = | dissipation rate |
| εMg | = | mass fraction of Mg |
| λ | = | heat transfer coefficient |
| μ | = | dynamic viscosity |
| μt | = | turbulent viscosity |
| σk, σT, σε | = | Prandtl numbers |
Nomenclature
| A | = | preexponential factor |
| b | = | half width |
| B | = | temperature index |
| cp | = | specific heat capacity |
| d | = | nozzle diameter |
| Di,m | = | turbulent diffusion coefficient of the species |
| E | = | activation energy |
| Gk | = | generation term of turbulent kinetic energy |
| i | = | gas-phase species |
| Ji | = | diffusion flux of species |
| k | = | turbulent kinetic energy |
| K | = | reaction rate constant |
| Mi | = | molar mass of species |
| N | = | total number of gas-phase chemical species |
| p | = | pressure |
| r | = | reaction rate |
| R | = | universal gas constant |
| Ri | = | net production rate |
| S | = | longitudinal displacement |
| ST | = | energy source term |
| Sct | = | turbulent Schmidt number |
| t | = | time |
| T | = | temperature |
| ui, uj | = | velocity tensors |
| V0 | = | initial injection velocity |
| Vm | = | maximum velocity |
| V | = | velocity vector |
| Yi | = | mass fraction of species i |
| Greek symbols | = | |
| α, β | = | burning jet expansion angles |
| ρ | = | density |
| ε | = | dissipation rate |
| εMg | = | mass fraction of Mg |
| λ | = | heat transfer coefficient |
| μ | = | dynamic viscosity |
| μt | = | turbulent viscosity |
| σk, σT, σε | = | Prandtl numbers |