Dovich Theory Research Articles

Effect of charge diameter on the burning rate of explosives

Zel'dovich's theory of the combustion of gases gives a satisfactory description of the relation between the burning rate of methyl nitrate at 20° and nitroglycol at 40° and tube diameter when transfer of heat through the walls of the tube to the unreacted material can be neglected (the liquid burns in a thin-walled glass tube immersed in water). The ratio of the adiabatic to the critical burning rates (uad/ucr) is close to the value predicted by theory for methyl nitrate (1.50) and significantly smaller for nitroglycol (1.25). A possible explanation is instability associated with the thermal inertia of the heated zone [11].

Nonstationary burning of propellants with variable surface temperature

The author examines nonstationary processes (combustion at varying pressure, quenching, and ignition) for a model propellant whose burning rate u and surface temperature t1 depend on pressure p and initial temperature T0. All the processes in the surface reaction zone and the gas phase are assumed inertialess. It is shown that a theory of nonstationary combustion for such a model can be constructed by analogy with the Zel'dovich theory [1, 2], in which the surface temperature of the powder is assumed fixed. The variation of burning rate with time has been investigated for small sudden pressure changes. It is shown how a sufficiently large and steep pressure drop may cause quenching of the propellant. The process of propellant ignition is subjected to a qualitative analysis.

Combustion stability of explosives

The experimental data on the combustion stability of certain secondary explosives, chiefly at atmospheric pressure, have been examined in the light of the Zel'dovich theory. 1. Of the nitroesters investigated, nitroglycol and methyl nitrate burn stably, while diglycol dinitrate, nitroglycerine, and PETN burn unstably at atmospheric pressure and room temperature, which is in accordance with theory. The behavior of nitrocellulose, tetryl, and RDX is explained by taking into account the part played by heat released in the condensed phase. 2. It has been shown that the critical combustion diameter of nitroglycol increases sharply as the temperature falls from 100 to 5–10°C. Within the limits of scatter of the experimental results, this relation coincides with that obtained theoretically on the assumption that heat is lost by the gas phase, while combustion stability is determined by the temperature gradient at the surface of the condensed phase. 3. It has been established that the ratio of the adiabatic burning rate of nitroglycol at 20–80°C to the limiting rate is much less than the theoretical value for gas mixtures (about 1.2 instead of 1.65). In accordance with theory, it is greater (1.5) for methyl nitrate than for nitroglycol. 4. We have calculated the pressure dependence of the critical combustion diameter for nitroglycol, nitroglycerine, PETN, and methyl nitrate. Certain facts confirming this dependence are presented. It is shown, however, that, for most of the explosives investigated, this dependence is not satisfied over a broad (several hundred atmospheres) pressure interval, probably because of transition of the reaction to the condensed phase and the effect of radiative heat transfer.

Macrokinetics of oxidation of porous substances

A procedure is given for calculating the oxidation kinetics of porous materials obeying a parabolic law of oxidation. The procedure is based cn Zel'dovich's theory. The relations obtained for the reagent concentration, the maximum penetration depth, and the total weight gain as functions of time, temperature, and pore structure, afford a qualitative explanation of all the experimentally observed regularities. The method can be used to calculate the kinetics of diffusion saturation of porous substances by the gas phase, and also of chemical precipitation from solution.