Shock-Tube Studies in Exothermic Systems

Abstract

Three types of behavior are possible: (1) planar incident shocks, with reaction, may be produced and studied; (2) detonation may be initiated by longitudinal nonsteady processes; or (3) distinct transverse instabilities may appear. Case (2) occurs when the incident shock velocity is adjusted to be less than the Chapman-Jouguet velocity. Here, if a reaction occurs, it leads to nonsteady processes which may initiate detonation. Examples are presented to discuss the inherent limitations of this case, and to show that reaction kinetic processes may be studied even though nonsteady flow processes are occurring. Cases (1) and (3) occur when the shock is adjusted to be above the Chapman-Jouguet velocity, usually in diluted mixtures. Case (3) instabilities (which negate the quantitative study of reaction kinetics) are always observed when the reaction zone length becomes of the order of, or less than, the tube diameter. Case (1) behavior is observed for longer reaction zone length, even though there are also recorded cases of unstable flow under these circumstances. An acoustic theory of transverse waves is used to discuss the possible occurrence of case (1) and case (3) flows.