Study On The Complex Response Processes Of Explosive In Thermal Environment Based On CE/SE Method

The detonation performance and security of explosive is an important index in the evaluation of weapon system safety. Factors affect the security of explosive include impact, thermal stimulation, static electricity and light stimulation, etc. Series of complex responses may occur when the explosive is simulated, such as thermal decomposition, ignition, burning and deflagration to detonation transition, among which the most serious effect is detonation. Therefore it is meaningful to study the complex response processes of explosive in thermal environment in the evaluation of explosive thermal security. In this thesis we carry out simulation study of processes of explosive in thermal environment including thermal decomposition, ignition, burning and deflagration to detonation transition. Major research work is as follows:1) Analysis of the one-dimensional deflagration to detonation transition process of explosive in thermal environment.The process of explosive from ignition to detonation formation is simulated using a one-dimensional CE/SE code. Characteristics of physical quantities in stages of slow burning, violent burning, detonation growing up and stable detonation are analyzed. A criterion of steady detonation is identified through a detailed analysis of the characteristics of the reaction process:steady detonation occurs at locations where different physical quantities, such as pressure, density, temperature, and velocity, reach peak values simultaneously.2) Physical describing of the response processes of explosive in thermal environment.Device containing explosive is simplified to two-dimensional plane or axial symmetry geometry. The coupled thermal, mechanical and chemical response processes of explosive in thermal environment are described as two stages, before ignition and after ignition. Before ignition, Arrhenius reaction rate and two-dimensional thermal conduct equations under certain boundary conditions are used to describe the thermal decomposition process. Then the state of explosive at the time of ignition is evaluated. After ignition, two phase flow model of solid explosive and gas reaction product is utilized to describe the process.3) CE/SE method of the reactive two phase flow.The space-time Conservation Element and Solution Element (CE/SE) method is used to solve the two phase flow equations. Calculation frameworks for two-dimensional plan and axial symmetry are constructed and algorithm of space derivatives is given. The reactive dynamics source term is treated by two steps. In the first step, equations without source terms are solved by CE/SE method. In the second step, a smaller time step is used to solve the first order initial value problem of normal differential equation.4) Two-dimensional simulation of the response processes of explosive in thermal environment.Two-dimensional simulation of the response processes of explosive in thermal environment is carried out, including thermal decomposition, ignition, burning and deflagration to detonation transition. Simulation results of time and location of ignition, pressure of convective burning and chemical reaction propagation accord with the experimental data of thermal ignition experiment, flash experiment and high temperature DDT tube experiment. The relation between ignition time and initial temperature is that the logarithm of ignition is of linearity with the reciprocal of initial temperature.5) Study of factors affecting the deflagration to detonation transition process of explosive in thermal environment.Factors affecting the deflagration to detonation transition process of explosive in thermal environment are studied, including ignition temperature, temperature gradient, porosity, grain size, column diameter and confinement condition. With higher ignition temperature, the energy state of the system is higher and detonation is easier to form. The effect of temperature gradient is smaller with lower porosity and greater with higher porosity. Detonation is harder to form with greater temperature gradient. In thermal environment the effect of porosity on detonation formation is not monotonous, so detonation is hard to form with either too high or too low porosity. With the same porosity, reactive is more violent and detonation is easier to form with smaller grain size. Under solid wall confinement condition, distance to detonation decreases with the increasing of column diameter and time to detonation changes obviously, but not increasing monotonously. When the confinement condition is weakened, the spread speed of chemical reaction is slower and detonation is harder to form.