Temperature Calibration of a Single Pulse Shock Tube at Low Pressures Using Unimolecular Decomposition of Cyclohexene

This paper presents the chemical thermometry of a single pulse shock tube with cyclohexene as an external standard to measure the actual temperature behind the reflected shock wave \((T_{5,act} )\) under low-pressure conditions. The temperature behind the reflected shock wave was determined using the initial and final concentration of cyclohexene acquired from the experiments, reaction dwell time and the rate constant expression given in the literature. The shock tube is calibrated in the temperature \((T_{5, act} ) \) range of 970–1136 K, and this calibration is valid to the pressure range of 0.81–3.75 bar. The theoretical temperature behind the reflected shock wave \((T_{5,theo} )\) was computed from the 1-D normal shock relations using the incident shock wave’s end wall Mach number and the initial temperature in the driven section. Finally, the linear correlation has been established between the theoretical and actual temperature behind the reflected shock wave for chemical shock tube (CST-3) present in our lab. These experiments highlight the notable difference in theoretical and actual temperature, which increases with the increase in temperature, underscoring the need for shock tube calibration before ignition delay time measurements and other kinetic studies. The drawback of using cyclohexene’s unimolecular decomposition as a chemical thermometer above a specific temperature has also been discussed.