Numerical simulation of the deflagration-to-detonation transition of iso-octane vapor in an obstacle-filled tube

Abstract

Flame acceleration and deflagration-to-detonation transition of an iso-octane vapor–air mixture in an obstacle-filled detonation tube were simulated by solving Navier–Stokes equations with a single-step reaction mechanism. A variable specific heat ratio was used in these simulations. Detonation cell size was successfully simulated for the iso-octane vapor–air mixture. Two methods for initiating detonation waves were revealed in a detonation tube with obstacles. Pressure and flame parameters, such as the temporal variation of total energy release rate, flame front location, propagation velocity of the flame front, and flame front area, were investigated during the flame acceleration and deflagration-to-detonation transition process. According to the variation of these parameters, flame acceleration and deflagration-to-detonation transition processes could be divided into four stages, i.e. the early stage of flame acceleration, the middle stage of flame acceleration, the end stage of flame acceleration, and the detonation transition stage. The effects of activation energy and pre-exponential factor on deflagration-to-detonation transition processes were examined. The results indicate that the pre-exponential factor and activation energy influence the flame parameters, but not the development law of flame acceleration or deflagration-to-detonation transition processes. For lower reactants activity, detonation wave is easy to fail in couple while bypassing obstacles in the obstacle-filled detonation tube, which causes a large fluctuation in flame propagation velocity and total energy release rate. The length of detonation tube filled by obstacles should not be more than deflagration-to-detonation transition distance. These investigations are conducive to understanding the flame acceleration and deflagration-to-detonation transition and developing detonation combustion chamber of pulse detonation engine.