Guido Saccone, Pasquale Natale, Luigi Cutrone, Marco Marini
Abstract: In the field of air-breathing hypersonic scramjet vehicles design and development, the Italian Aerospace Research Centre – CIRA contributed to an international project, called Stratospheric Flying Opportunities for High-Speed Propulsion Concepts – STRATOFLY, in collaboration with several European organizations, coordinated by Politecnico di Torino under the EC Horizon 2020 programme financial support. The aim of this project was the improvement of enabling technologies for the realization of a commercial hypersonic aircraft, able to fly at Mach 8, at 30÷35 km of altitude, for at least 4 hours with a minimum environmental impact and especially low NOx emissions. Understanding the complex, supersonic, turbulent, combustion processes occurring during scramjet operations is of fundamental importance. For this purpose, a thorough 0D kinetic assessment was carried out by means of the open-source Cantera software for the identification of the most suitable kinetic mechanisms, able to predict with satisfactory accuracy both the ignition delay times and the NOx emissions at the relevant scramjet operating conditions. Several kinetic schemes were investigated and the computed results were compared with the literature available shock tubes experimental data. In the entire investigated operative box, the best agreement, in terms of induction times, was achieved using the kinetic mechanism developed by Zettervall and Fureby with the exception of the ignition tests carried out in presence of argon as diluent bath gas, where the kinetic schemes by Kéromnès and CRECK together with the Aramco-II full mechanism provide the best matching. Moreover, for considering the generation of NOx, the three fundamental thermal route reactions by Zel’dovič, were added. Furthermore, full 3D CFD simulations were carried out by means of Ansys® Fluent in order to compare experimental data and evaluate the predictivity and accuracy of the chemical/kinetic sub-model conceived in this way when coupled with mixing, turbulence and fluid dynamic interactions arising from the simulations of the whole propulsive system. For the sake of comparison, the experiments carried out on the small-scale scramjet vehicle of LAPCAT-II by the HEG (DLR) were rebuilt.
Keywords: scramjet, hypersonic flight, hydrogen combustion, kinetic analysis, CFD.
Date Published: October 23, 2022 DOI: 10.11159/jffhmt.2022.017
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