The evolution of the temperature field during cavity collapse in liquid nitromethane. Part II: Reactive case

TL;DR

This study investigates how cavity collapse in nitromethane influences hot spot formation and ignition, using advanced 2D and 3D reactive simulations to understand sensitivity and reaction growth.

Contribution

It introduces a multi-phase reactive model for cavity collapse, enabling accurate temperature and reaction rate predictions in explosive media, validated against experimental data.

Findings

Cavity collapse significantly reduces ignition time in nitromethane.

3D simulations reveal different hot spot topology and reactive strength compared to 2D.

Reactive effects alter hot spot temperature growth and topology over time.

Abstract

We study effect of cavity collapse in non-ideal explosives as a means of controlling their sensitivity. The main aim is to understand the origin of localised temperature peaks (hot spots) that play a leading order role at early ignition stages. Thus, we perform 2D and 3D numerical simulations of shock induced single gas-cavity collapse in nitromethane. Ignition is the result of a complex interplay between fluid dynamics and exothermic chemical reaction. In part I of this work we focused on the hydrodynamic effects in the collapse process by switching off the reaction terms in the mathematical model. Here, we reinstate the reactive terms and study the collapse of the cavity in the presence of chemical reactions. We use a multi-phase formulation which overcomes current challenges of cavity collapse modelling in reactive media to obtain oscillation-free temperature fields across material interfaces to allow the use of a temperature-based reaction rate law. The mathematical and physical models are validated against experimental and analytic data. We identify which of the previously-determined (in part I of this work) high-temperature regions lead to ignition and comment on their reactive strength and reaction growth rate. We quantify the sensitisation of nitromethane by the collapse of the cavity by comparing ignition times of neat and single-cavity material; the ignition occurs in less than half the ignition time of the neat material. We compare 2D and 3D simulations to examine the change in topology, temperature and reactive strength of the hot spots by the third dimension. It is apparent that belated ignition times can be avoided by the use of 3D simulations. The effect of the chemical reactions on the topology and strength of the hot spots in the timescales considered is studied by comparing inert and reactive simulations and examine maximum temperature fields and their growth rates.