Theory of nonstationary combustion of homogeneous propellants

Conclusions

A comparison of the results of the theory outlined above and the experimental data shows that theory and experiment are in qualitative agreement. Thus, taking into account the variability of the surface temperature eliminates the principal difficulty of the theory with constant temperature—instability of the steady—state regimes of propellant combustion under ordinary practical conditions (k>1)—and, hence, leads to the possibility of investigating nonstationary phenomena associated with the combustion of actual systems. It is also possible to explain experimental facts such as combustion stability in a chamber and the existence of a natural frequency of the burning rate oscillations. The order of the frequency and its pressure dependence are in agreement with experiment. The theory is also in qualitative agreement with experimental data on quenching and on the nonstationary burning rate at variable pressure. A number of problems remain to be investigated from the standpoint of the theory described; for example, the dynamic erosive burning regime, or a propellant burning in the presence of a variable-velocity gas flow at its surface.

Further development of the theory and its quantitative comparison with experiment must be based on the steady-state dependences of burning rate and surface temperature on initial temperature and pressure. To obtain these relations is the primary task of experimenters and theorists in the area of steady-state combustion.

In conclusion, the directions to be followed are now plain: it is necessary to account for the inertia of the reaction layer in the condensed phase and to improve the theory by accounting for the variability in the thermal diffusivity of the propellant, which increases with temperature. As calculations show [46, 47], this effect increases the regions of stable combustion at constant pressure and possible oscillatory combustion modes.