Numerical investigation on critical ignition in shock tube with controlled expansion rate

Abstract

To evaluate the potential of studying the competition between chemical heat release and expansion-induced cooling in shock tube facilities, one-dimensional numerical simulations using Stanshock were performed with focus on two approaches to obtain controlled expansion rate in the post-reflected shock region. A first approach is through the utilization of driver insert, and a second approach relies on the utilization of the reflected expansion head. Auto-ignition in hydrogen-oxygen-argon mixtures in the driven section was studied. Numerical simulations for the first approach were performed for various expansion rates induced by the driver insert, for two Ar dilutions of 99 % and 95 %, and for various target temperatures in two shock tubes with different lengths. For the second approach, numerical simulations were performed for various target temperatures, and for two Ar dilutions of 95 % and 90 %. Depending on the expansion rate, either ignition or chemical quenching could be effectively observed, which is consistent with the critical decay rate concept. To further investigate the mechanisms responsible for ignition and quenching, quantitative thermo-chemical analyses were performed for quenching and successful ignition conditions. Because of the lower expansion rates generated by using driver inserts, the first strategy is limited to the low-temperature regime, with dominant pathways at critical conditions related to the chemical dynamics of HO2. For the second strategy, the much higher expansion rate enables to access the high-temperature regime, for which successful ignition is driven by chain-branching chemistry.