Two-Line Absorption Thermometry Characterization of a Miniature Shock Tube

High repetition rate shock tubes (HRRSTs) are used for chemical kinetics and other studies. These shock tubes have advantages in high repeatability for some low signal-to-noise level (S/N) measurements but suffer from large increases in the temperature and pressure in the conditions behind the reflected shock compared to a conventional shock tube. This pressure and temperature rise is because of the combination of the small diameter of the shock tube and the use of a fast-acting valve. The correct assignment of temperature throughout the shock tube test time is important. In this study two-line laser absorption thermometry targeting R(9) and R(17) transitions of CO is applied to measure the gas temperature behind the reflected shock in test gases containing Ar, He, and CO. Many different laser modulation frequencies are possible, and wavelength scanning at 20kHz is reported here. Results indicate that this diagnostic approach can successfully capture the evolving temperature profile in the HRRST. The measured temperature profile is similar yet distinct from the profile estimated from the isentropic equations and the measured reflected shock pressure profile. This work focuses upon comparison against models and chemical thermometry approaches for temperature assignment.