The Influence of Post-combustion Chemistry and Presence of Condensed Species in Solid Rocket Plumes

Kurzfassung

Plumes from solid rocket motors (SRM) are strongly influenced by complex hydrogen/carbon/oxygen/chlorine after-burning chemistry as well as the presence of solid/condensed phases. These after burning reactions within the plume but also the temperature lag of the solid phase have a significant impact onto the temperature distribution within the plume which in turn may influence infrared (IR) irradiance signatures.

The combustion chamber conditions with oxidizer-fuel ratios considerably less than stoichiometric lead to the increased occurrence of combustion intermediate products at the chamber exit. Combined with partial freezing within the nozzle this allows for a significant amount of post-combustion within oxygen-rich the shear layer of the exhaust plume. Additionally the presence of a condensed (or possibly liquid) phase within the chamber influences the temperature distribution within the nozzle and subsequent plume, increasing the gas temperature and enhancing reaction speeds.

Within this study we provide an overview on the currently available combustion mechanism for current motor fuel (e.g AP/HTPB/Al or other relevant formulations) combinations and evaluate their applicability to SRM plume post-combustion modelling. In a first step, the performance of the possible mechanisms is evaluated using a constant volume reactor, extending on a previous study by Ecker et al. (2019) and then subsequently applied to a 2D CFD test case for a sounding rocket in flight at different atmosphere conditions. Further we extend on the options of modelling the condensed phase (e.g. Euler/Lagrangian pseudo-gas phase or modified molecular mass) within standard CFD applications, comparing their influence on the selection of boundary conditions parameters as well as on the temperature distribution of the plume. In this context, reviews of recent experimental efforts aimed at establishing end-to-end boundary conditions for multiphase CFD simulations are presented, with particular focus on recent particles collection in the plume (Carlotti and Maggi, 2021) and on the comparison between the aforementioned CFD modelling approach and empirical correlations validated through experimental campaigns. The results of this study offer a relevant evaluation of the performance of CFD models for solid rocket powered vehicles