Induction Time Measurements in Shock Tube of Different Roughness

Abstract

The article 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 80% 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. It is found that the small surface roughness strongly affects the reflected shock wave bifurcation in hydrogen-nitrogen mixture but it does not affect the ignition delay time measurements significantly in stoichiometric H₂-O₂ mixture diluted with Ar.