Up to now for shock tubes measurements there are no methodologies to take into account the effect of reflected shock wave bifurcation and other wall surface effects on the ignition delay time of reacting gas mixtures. On one hand, the gas in the vicinity of the wall overheats due to friction, the boundary layer vortices and reflected shock wave bifurcation. On the other hand the mixture is cooled by the heat exchange between gas and shock tube wall. A number of theoretical studies suggest the highest gas temperature excess above the gas temperature behind the normal reflected shock wave arise at the center of the vortices formed within the bifurcation structure. Other experimental and computational works point to the existence of such an effect close to the triple point trajectory of the bifurcation structure.
The present work is devoted to the studies of the shock tube roughness effect on the measurements of ignition delay times and the structure of the gas flow behind reflected shock wave. All measurements were performed on cylindrical shock tube at the density of the gas behind the reflected shock wave of 2.8 kg/m3 for the smooth and rough surface of the shock tube. Experimental studies of the reflected shock wave bifurcation structure for a nitrogen-hydrogen mixture, which is a non-reacting referent mixture to the stoichiometric hydrogen-air one, are presented. Values of the oblique shock wave projection at the distance to the endwall of 50, 150 and 250 mm, as well as the local pressure distribution behind reflected shock wave, were determine. Ignition delay time measurements in stoichiometric H2-O2 mixture diluted with Ar were conducted. Induction times were determined using OH emission profiles obtained along the tube axis and in the boundary layer. The influence of the wall roughness on the ignition delay time and the bifurcation structure were analyzed for smooth and rough surface of shock tube.
