Numerical analysis of nozzle material thermochemical erosion in hybrid rocket engines

Ablative materials are commonly used to protect the nozzle metallic housing and to provide the internal contour to expand the exhaust gases in both solid rocket motors (SRM) and hybrid rocket engines (HRE). Due to the extremely harsh environment in which these materials operate, they are chemically eroded during motor firing with a resulting nominal performance reduction. The objective of the present work is to study the erosion behavior of graphite nozzles in HRE at different operating conditions and comparing results with those obtained for SRM. A mean distinctive feature of HRE operating conditions is, in fact, a greater concentration of oxygen-containing combustion products than SRM. The adopted approach relies on a validated full Navier-Stokes flow solver coupled with a thermochemical ablation model which takes into account heterogeneous chemical reactions at the nozzle surface, rate of diffusion of the species through the boundary-layer, ablation species injection in the boundary layer, heat conduction inside the nozzle material, and variable multispecies thermophysical properties. The parametric analysis performed in this study allows to assess the impact of various parameters that affect the nozzle erosion rate, taking into account various combinations of fuels and oxidizers operating at different conditions. © 2012 by D. Bianchi and F. Nasuti.