Limitations of the Reflected Shock Technique for Studying Fast Chemical Reactions and Its Application to the Observation of Relaxation in Nitrogen and Oxygen

Abstract

Strip film and multiple spark schlieren pictures of reflected shocks were taken in the gases He, A, N2, O2, H2, NO, CO2, N2O, CH4, and C3H8. Interaction of the reflected shock with the boundary layer behind the incident shock was observed in all gases except He and A. The bifurcation and acceleration associated with the interaction limits the use of the reflected shock region for high-temperature kinetic and equilibrium studies. It was possible to minimize the effects of this interaction by using gases with high γ and confining measurements to a region near the back wall. Reflected shock observations agreed with Mark's theory of the development of bifurcation but disagreed with his predicted deceleration of the reflected shock. From comparison of incident and reflected shock velocities, measured at the backwall, with ideal one-dimensional theory, it was concluded that calculations of the temperature behind the reflected shock from incident shock velocities would yield high results. Decelerations of the reflected shock in N2 and O2 have been observed in the strip films and were related to the vibrational relaxation behind the reflected shock. Measurements of relaxation times from the film yielded values which are in good agreement with Blackman's data. These experiments indicate that changes in reflected shock velocity can be used to observe the overall reaction rates of fast chemical reactions.