Nonuniform laser ignition in energetic materials

Abstract

Laser ignition of energetic materials is typically described in terms of a one-dimensional homogeneous ignition model. However, the Gaussian energy distribution from a laser can induce multidimensional effects on ignition. A two-dimensional numerical model that simulates radiant heating and subsequent ignition of energetic materials was developed. A laser with a Gaussian energy distribution was used as the external energy source applied to the flat surface of a cylindrical pellet. The nonuniform behavior of thermal ignition leads to radially dependent ignition times, temperatures, and energy associated with the front surface of the pellet. Existing experimental ignition data was compared to the numerical results. The model shows the importance of a two-dimensional analysis for ignition because the nonuniform external heat source can result in the formation of localized heating that will develop into nonplanar flame propagation. The model is compared to experimental results that further validate the importance of a two-dimensional ignition model and show that ignition occurs first in the center of the pellet where the Gaussian beam intensity is greatest.