Visualization of Obstacle-Induced Shock-Compression Ignition

Abstract

Experimental and numerical investigations of shock-compression ignition induced by a disturbance have been carried out. Experiments were performed in a square cross-section shock tube behind reflected shock waves at temperature between 1401 and 1681 K and the total densities were kept constant at around 30 mol/m3. The mixture used was a stoichiometric methane/oxygen/argon with 89.5 percent argon dilution. A thin plate or a fine wire was installed apart from the tube-end of the shock tube to generate density disturbance. The shape of shock-compression ignition flame under different disturbance was observed by direct and schlieren high-speed photography. The disturbance in the shape of a vortex appeared after the reflected shock wave passes through the obstacles. Ignition appears in the vicinity downstream of the obstacle in the tube-end side. The ignition flame is the same shape of the density disturbance. These disturbances made with obstacles promote ignition delay and fixes the position of ignition. The temperature in the disturbed region was evaluated using the temperature-dependent molar extinction coefficients of CO2 at 220 nm. An infrared absorption method with an infrared He-Ne laser (3.39 μm) was used for measuring the density in the disturbed region. The second order explicit MacCormack-TVD scheme is used to solve two-dimension Navier-Stokes equations. The density of the downstream side of the obstacle is lower than that of the upstream side. Temperature in the disturbed region was higher than others; this high temperature was caused by reflected shock wave acceleration in a rarefaction wave region at the rear of the obstacle.