Effect of charge diameter on the burning rate of explosives

Conclusions

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 (u_ad/u_cr) 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].

Owing to heat transfer through the walls, the burning rate of methyl nitrate and nitroglycol in narrow glass tubes in air may be much higher than the adiabatic burning rate. The value 0.045 g/cm²·sec, usually taken as the burning rate of nitroglycol at atmospheric pressure and room temperature [8, 9] is 20–30% higher than u_ad.

In the case of melting powdered explosives (RDX, octogen, and tetryl) the charge diameter was not observed to have a significant influence on burning rate. It is suggested that the principal reason for this is combustion turbulence due to intense motion of the molten film over the surface of the powder as a result of surface tension forces.