Ignition of Cellulose Nitrate by High Velocity Particles

Abstract

Ignition of highly flammable surfaces by impinging particles has been studied using cellulose nitrate slabs as the model surface. Spherical particles with various initial temperatures and velocities were assumed to impact and imbed to a depth of one-half a diameter. Kinetic energy of impact is assumed converted to thermal energy absorbed by a shell of cellulose nitrate surrounding the imbedded particle. The heat transfer from the particle to the slab and to the surroundings, as well as the kinetics of chemical decomposition are considered in developing a mathematical model of the ignition process. One decomposition mechanism is considered between 140° and 190 °C, and a second above the latter temperature. The model equations are solved numerically to give temperature/time data from which the time to ignition can be estimated.

The total energy of a particle is important in the ignition process. At velocities below a certain threshold the particle enthalpy (or temperature) determines if ignition will occur. At very high velocities the impact energy is sufficient to bring about ignition. Numerical results are presented for a particular size sphere.