ABSTRACT
In a launch vehicle momentum for the rocket is gained through conversion of chemical energy to mechanical energy. In a typical propulsion system, fuel and oxidizer undergo combustion thereby generating low molecular weight gases at high temperatures (3500 K) and pressure (200 bar). When this hot high pressure gas is expanded through nozzle, thrust is created and the rocket experiences forward motion. For most of inner wall portions of the nozzle temperature would be in the range 700-1200 K. All known structural materials cannot survive under such severe erosive and thermal shock conditions. Thus the metals form nozzle needs protection from very high speed extremely hot gas streams. Traditionally, highly dense silica/ phenolic and carbon/phenolic composites (1.8 g/cc) are employed as nozzle liners. Ablation lining thickness is about 8-12 mm. It is envisaged that the fully dense liner is replaced with a porous, low dense and light weight material with a thick anti erosion coating, a huge reduction in weight of the nozzle with improved performance as the porous material would have a much lower thermal conductivity than the fully dense counterparts. In view of the above, carbon felt impregnated phenolic composites are investigated for their role as light weight ablative liners. Carbon felt-based ablators have several advantages over classical fully dense ablative liner materials. Most importantly, they reduce the limited strain response of large rigid substrates. Carbon felt materials are known for their benign insulating property, uniform bulk density and better shape retention properties with macro and micro communication channels among the cells allowing efficient resin infiltration. Enabling manufacturing in larger sizes, felt based substrates reduce the number of independent parts mitigating the need of gap fillers. They also offer improved robustness in absorbing loads and deflections, and
ing a uniform and low thermal conductivity in the system. In this study, the evaluation of mechanical as well as thermal performance of the composites are carried out as the preliminary screening exercise before such low density composites are considered for the intended applications. Because of the highly porous nature, it enhances efficient infiltration of the resin and accounts for its uniform properties.
