Rate-Controlled Constrained-Equilibrium Application in Shock Tube Ignition Delay Time Simulation

Abstract

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium kinetically controlled by relatively a small number of constraints within acceptable accuracies. The full chemical composition at each constrained-equilibrium state is obtained by maximizing (or minimizing) the appropriate thermodynamic quantities, e.g., entropy (or Gibbs functions) subject to the instantaneous values of the constraints. Regardless of the nature of the kinetic constraints, RCCE always guarantees correct final equilibrium state. Ignition delay times measured in shock tube experiments with low initial temperatures are significantly shorter than the values obtained by constant volume models. Low initial temperatures and thus longer shock tube test times cause nonideal heat transfer and fluid flow effects such as boundary layer growth and shock wave attenuation to gradually increase the pressure (and simultaneously increase the temperature) before ignition. To account for these effects, in this paper, the RCCE prescribed enthalpy and pressure (prescribed h/p) model has been further developed and has been applied to methane shock tube ignition delay time simulation using GRI-Mech 3.0. Excellent agreement between RCCE predictions and shock tube experimental data was achieved.