The research investigates the effect of insulation fiber spatial orientation and aluminum content in the propellant composition, on particle erosion and thermochemical ablation.
Solid propellants exhibit self-sustained, high-temperature combustion and generate large quantities of gaseous products. Composite propellants have been extensively used in the last 50 years. Metals such as aluminum are added to increase density and total heat of combustion.
In solid rocket motors, charring ablative materials function as heat barriers that protect the motor case through the mechanism of ablation. When exposed to heat, they undergo an endothermic decomposition process. In solid rocket motor applications, case insulations based on Ethylene Propylene Diene Monomer and Kevlar are commonly used.
In the present research, a subscale solid motor was used, with an AP/HTPB/Aluminum based solid propellant. Seven static firing tests (six with low aluminum content and a single test with high content) were conducted successfully. The tested insulations had four different Kevlar reinforcing fibers orientations; circumferential, longitudinal, diagonal and random. Examination and comparison of the test results enabled to reach the conclusion that the longitudinal oriented fiber model had the largest mass loss.
A numerical model of the solid motor with the ablative insulation was incorporated. The measured values of chamber pressure and motor case temperature in the static firing tests served as boundary conditions. The convective and radiative heat flux from the gases transferred to the insulation were evaluated with empirical correlations. The numerical results were compared to the experimental with low Al propellant content and exhibited slight overprediction.
