CAREER: Control of Additively Manufactured Solid Rocket Fuel Grain Geometries and Combustion Analysis

Energetic materials such as explosives, fuels, pyrotechnic compositions, or propellants have a relatively large amount of stored chemical energy. The energy conversion processes that energetic propellants undergo, coupled with gas expulsion, lead to a highly efficient method for vehicle propulsion. This is typically achieved by igniting the propellant, which is constructed in segments called grains, causing it to burn and expel gasses, such as those expelled from a rocket during powered flight.

Presently, there is limited understanding of energetic material additive manufacturing, or 3D printing, when a three-dimensional part is constructed from multiple layers of material deposited as a slurry or paste. The current grain manufacturing processes are limited by the thick nature and resistance to pouring of the energetic materials during grain formation.

The research supported by this Faculty Early Career Development (CAREER) award aims at building fundamental knowledge about the effects of the additive manufacturing process, material parameters, and part geometry on printability and combustion efficiency. The work encompasses several disciplines including combustion, fluid dynamics, computational sciences, material science, controls, and propulsion.

The outcomes from this research directly relate to the aerospace, aeronautic, and defense industries with additional benefits for similar materials and processes used in the automotive, chemical, energy, and healthcare sectors. The project also incorporates an engineering education component involving outreach to middle school students and integration of research outcomes into undergraduate coursework.

Additive manufacturing provides a means to create complex grain geometries not possible with current conventional manufacturing methods, which typically involve a casting process. Producing propellants through additive manufacturing offers several advantages including the ability to create helical ports, center perforations with internal size and shape variations, different materials, and embedded components.

With these advantages come performance improvements such as increased combustion efficiency, improved regression rates, and better controllability. The limiting factors for additive manufacturing of these energetic materials are knowledge gaps in governing parameters for optimal performance and manufacture such as viscous parameters for slurry or binder transfer, interlayer bonding, layer/surface roughness, sedimentation during material transfer, layer composition, resolution, and void defects.

This award supports the development of mathematical models for the manufacturing process, grain performance simulations, the experimental apparatus to manufacture grains, and the testing of manufactured grains. This work will test the hypothesis that a formulation of parameters – viscosity for slurry or binder transfer, layer/surface roughness, resolution, and sedimentation – can be achieved to obtain optimized propellant efficiency of motors constructed using additive manufacturing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.