Ignition Delay Time Study of HTPB with Additives Using a Shock-Tube Endwall Injector System

Hydroxyl-terminated polybutadiene (HTPB) has been an important fuel for aerospace applications due to its long use in rocket propellants and in emerging propulsion technologies such as solid fuel ramjets. HTPB acts as a binder, and it can be mixed with solid oxidizer particles and also with various additives to boost the performance of the propellant. However, there has been an absence of chemical kinetics data for HTPB combustion due to the inability to vaporize HTPB directly in shock tubes. To avoid this obstruction, an endwall injector system employed at Texas A&M University was utilized. The injector system uses the incident wave to heat up and atomize the HTPB, thereby vaporizing it and subjecting it to the post-reflected shock conditions. This study investigated the effect of including a nano-sized titania (TiO2) additive with the HTPB. The titania-HTPB mixture was created at the University of Central Florida using an in-situ synthesis process to allow for uniform dispersion of the nanoadditive. The tests were conducted for temperatures of 1250 to 1375K at pressures of 4.25 atm. When compared to the base HTPB mixture, it was determined that adding titania negligibly changes the reactivity of the mixture. The primary utility of this work was the demonstration, for the first time, of the endwall injection method to explore the ignition and combustion of HTPB mixed with advanced additives behind reflected shock waves.