Simulation of Laser-Induced Detonation in Particulate Systems with Applications to Pulse Detonation Engines

Abstract

Reacting two-phase flows attract particular interest because of their applicability to pulse detonation engines. Use of laser pulse allows to create desired temporal and spatial distributions of ignition centres and to perform a homogeneous ignition within the sub-microsecond interval. The injection of metal particles with low evaporation temperature and ionization potential or liquid droplets causes optical breakdown on individual particle or droplet, and leads to drop of detonation minimum pulse energy of the mixture. The physical and mathematical models and up-to-date numerical methodology for computer modelling are developed and validated. Laser-induced detonation in particulate systems is studied, and possibilities of the new methodology are demonstrated. Introduction A pulse detonation engine is an unsteady propulsive device in which the combustion chamber is periodically filled with a reactive gas mixture, a detonation is initiated , the detonation propagates through the chamber, and the product gases are exhausted. The high pressures and resultant momentum flux out of the chamber generate thrust. Use of laser pulse allows to create desired temporal and spatial distributions of ignition centres and to perform a homogeneous ignition within the sub-microsecond interval. The reactive metal particles are used to enhance blast performance. Although the total energy released by the metal combustion is significant and comparable to the total energy released by the explosive itself, the timescale of this energy release (timescale of particle reaction) for typical particle sizes (from 1 to 100 µm), is too long to contribute directly to the detonation front itself. The metal particles react with gas or detonation products behind the blast wave. It has been shown that the metal particle reaction significantly increases the strength of the blast and the total impulse delivered to nearby objects or structures [1]. Processes that control transport and combustion of particles and droplets remain unresolved, and introduce significant uncertainties into modeling and simulation. One of the most important parameters for practical applications is the minimum pulse energy (MPE) required to induce ignition and detonation of the mixture. When a power laser pulse (I * ∼ 10 11 W/cm 2) interacts with a gas, the gas breaks down and becomes highly ionized [2, 3]. This process is always accompanied by a light flash and generation of sound. The development of electron cascade requires the existence of initial free electrons in a gas. Particles or droplets, trapped by a laser beam, considerably influence results of the process [4]. It is well