Dynamics of shock induced ignition in Fickett's model with chain-branching kinetics: influence of $\chi$

TL;DR

This paper investigates shock-induced ignition dynamics using Fickett's model with chain-branching kinetics, deriving analytical solutions and analyzing how parameters influence ignition and acceleration of the reaction zone.

Contribution

It provides a simplified analytical framework for understanding shock ignition mechanisms with chain-branching kinetics, linking key parameters to ignition behavior.

Findings

Acceleration proportional to activation energy and heat release

Both subsonic and supersonic regimes observed

Analytical solutions match numerical simulations

Abstract

The problem of shock induced ignition by a piston is addressed in the framework of Fickett's model for reactive compressible flows, i.e., the reactive form of Burgers' equation. An induction-reaction two-step chain-branching model is used to study the coupling between the energy release and the compressible hydrodynamics occurring during the shock ignition transient leading to a detonation. Owing to the model's simplicity, the ignition and acceleration mechanism is explained using the two families of characteristics admitted by the model. The energy release along the particle paths provides the amplification of forward-travelling pressure waves. These waves pre-compress the medium in the induction layer ahead of the reaction zone, therefore changing the induction delays of successive particles. The variation of the induction delay provides the modulation of the amplification of the forward travelling pressure waves by controlling the residence time of the pressure waves in the reaction zone. A closed form analytical solution is obtained by the method of characteristics and high activation energy asymptotics. The acceleration of the reaction zone was found to be proportional to the product of the activation energy, the ratio of the induction to reaction time and the heat release. This finding provides a theoretical justification for the previous use of this non-dimensional number to characterize the ignition regimes observed experimentally in detonations and shock induced ignition phenomena. Numerical simulations are presented and analysed. Both subsonic and supersonic internal flame propagation regimes are observed, consistent with experiment and previous reactive Euler models.