The thermodynamics of C-J deflagration

Abstract

The mechanisms of detonation instability, detonation quenching, deflagration-to-detonation transition, and thermodynamics of C-J deflagration are fundamental issues of combustion theory. In this paper, these mechanisms are discussed by analyzing the convective flux and heat release flux of one-dimensional numerical simulation. The governing equations are Euler equation with overall one-step chemical reaction kinetics. The mixture is stochiometric H2-air mixture at 1atm and 300K.The activation energy is increased to trigger the instability of C-J detonation. The numerical results show that the detonation instability is induced by the von Neumann spike. The von Neumann spike produces unsteady rarefaction wave, which is determined by the slope of von Neumann spike. The detonation is extinguished to a C-J deflagration abruptly under critical activation energy at one-time step because the strength of rarefaction wave is stronger than heat release under this critical condition. The C-J deflagration propagates with a relative constant velocity about half of C-J detonation velocity. The gas temperature and pressure behind the leading shock wave of C-J deflagration is too low to ignite the mixture. The Taylor wave from the end-wall ceases the mixture behind the leading shock, increases its temperature and decreases its pressure. As a result, combustion takes place at the contact surface with almost constant pressure. Therefore, the C-J deflagration is of constant-pressure combustion and this mechanism makes it propagate downstream with a relatively constant velocity for a long distance.