The single pulse shock tube: its Odyssey in chemical kinetics

Abstract

In their early days, shock tubes were not taken seriously by the chemical kinetics community. They were not accepted as a legitimate tool for chemical kinetics studies at high temperatures. The main objection was the uncertainty in the temperature behind the shock wave. Whereas most physical processes depend on \( \sqrt T \), the temperature dependence of reaction rates is exponential, exp(−E/RT), which imposes a much higher sensitivity to the temperature, particularly for high E/T. As temperatures are not measured directly but are rather calculated from ideal gas dynamics, significant errors in the temperature may occur when deviations from ideal conditions exist. The skepticism towards accepting chemical kinetics data obtained by the single pulse shock tube was even greater since the chemical reactions were studied behind reflected shocks. The build up of the boundary layer behind the incident shock and its subsequent interaction with the reflected shock could lead to deviations from ideal conditions. However, as more and more data were accumulated, and a very good agreement between low temperature flow and static systems, and high temperature single pulse shock tube experiments was obtained, it became clear that the shock tube is not just a “legitimate tool” for chemical kinetics studies but it is the main source of the data for high temperature chemical kinetics. Moreover, the use of “chemical thermometers” (will be discussed later) for determining temperatures behind reflected shock waves that was introduced in the early sixties by Tsang [1], improved considerably the accuracy of the temperature determination.