Temperature approximations in chemical kinetics studies using single pulse shock tubes

Abstract

Simulations of chemical kinetics processes in single pulse shock tubes are typically modelled by a constant pressure approximation. However, concerns have been raised by the use of such an approximation in the case when the post-reflected-shock-wave pressure profiles in a shock tube do not have perfect square wave profiles. This article discusses the validity of using the constant pressure approximation in such cases for modelling purposes. The constant pressure simulations are compared with changing pressure simulations. They show that the constant pressure simulations can be used as a sufficient modeling approximation for the shock tube chemistry of single reaction processes, complex reaction network models, highly diluted fuel mixtures and highly concentrated mixtures. Any discrepancies between the model predictions from the constant pressure approach and the changing pressure approach are minimal across a wide temperature range. A set of different types of chemical kinetic models and different physical conditions were tested for the comparison of the two approaches. The results justify using species measurements of quenched post rarefaction wave samples and chemical thermometer calibration methods with the constant pressure approximation in reporting reaction product data in single pulse shock tube studies. The study further confirms that the speciation results from the quenched samples obtained from single pulse shock tube experiments that have non-ideal pressure profiles can be well approximated as a constant pressure reaction process even for complex reaction networks and facilitate the reporting of modeling results as pertinent to single pressures, temperatures and times.