Additive manufactured thermoplastic-nanocomposite aluminum hybrid rocket fuel grain and method of manufacturing same

Abstract

A hybrid rocket solid fuel grain having a cylindrical shape and defining a center port is additive manufactured from a compound of thermoplastic fuel and passivated nanocomposite aluminum additive. The fuel grain comprises a stack of fused layers, each layer formed as a plurality of fused abutting concentric circular beaded structures arrayed to define a center port. During operation, an oxidizer is introduced along the center port, with combustion occurring along the exposed port wall. Each circular beaded structure defines geometry that increases the surface area available for combustion. As each layer ablates the next abutting layer, exhibiting a similar geometry, is revealed, undergoes a gas phase change, and ablates. This process repeats and persists until oxidizer flow is terminated or the fuel grain material is exhausted. To safely achieve this construction, a fused deposition additive manufacturing apparatus, modified to shield the nanocomposite material from the atmosphere, is used.

What is claimed is: 
     
       1. A method of making a fuel grain for use in a hybrid rocket engine, the method comprising:
 compounding a first material suitable as a hybrid rocket fuel and a second energetic and pyrophoric nanoscale metallic material according to a predetermined mixture ratio to form a third material; 
 the third material serving as feedstock material for use in an additive manufacturing apparatus; 
 operating the additive manufacturing apparatus using the feedstock material to fabricate a fuel grain comprising a plurality of fused stacked layers of solidified fuel grain material; 
 each layer of the plurality of fused stacked layers further comprising a plurality of abutting and fused ring-shaped beads concentrically configured to form a central opening in each layer; 
 the central opening extending through the plurality of fused stacked layers to define a combustion port bounded by a boundary wall; and 
 an inner circumferential surface of each ring-shaped bead defining projections therein, such that as a ring-shaped bead forming the boundary wall ablates due to combustion in the combustion port, an inner circumferential wall of an adjacent ring-shaped bead defining projections therein presents to form the boundary wall of the combustion port. 
 
     
     
       2. The method of  claim 1  the projections in the inner circumference of each ring-shaped bead configured to form a progressive axial twist through the combustion port to induce a swirling gaseous flow within the combustion port. 
     
     
       3. The method of  claim 2  wherein the progressive twist comprises a helical grooved rifling pattern of projections. 
     
     
       4. The method of  claim 1  the projections in the inner circumference of each ring-shaped bead configured to increase a surface area of the combustion port or to induce an oxidizer vortex flow within the combustion port. 
     
     
       5. The method of  claim 1  wherein the additive manufacturing apparatus comprises a fused deposition additive manufacturing apparatus. 
     
     
       6. The method of  claim 1  further comprising drying the feedstock material and then elevating a temperature of the feedstock material to attain a predetermined viscosity for the feedstock material. 
     
     
       7. The method of  claim 6  wherein the step of elevating the temperature further comprises processing the feedstock material to increase internal friction and thereby elevate the temperature of the feedstock material to achieve the predetermined viscosity for deposition during the step of operating. 
     
     
       8. The method of  claim 1  the step of operating comprising urging the feedstock material through an extrusion die of a predetermined diameter to fabricate the plurality of fused stack of layers of solidified fuel grain material. 
     
     
       9. The method of  claim 1  wherein the first material comprises Acrylonitrile Butadiene Styrene (ABS) thermoplastic having a predetermined monomer composition. 
     
     
       10. The method of  claim 1  wherein the second material comprises a plurality of nanoscale elemental aluminum core particles capped with an oligomer polymer or the second material comprises polymer-capped nanocomposite aluminum powder. 
     
     
       11. The method of  claim 1  wherein the first material comprises ABS thermoplastic and the second material comprises polymer-capped nanocomposite aluminum powder, the third material comprising ABS thermoplastic by mass of about 75% to 95% and polymer-capped nanocomposite aluminum powder by corresponding mass of about 25% to 5%. 
     
     
       12. The method of  claim 1  wherein a heavier-than-air inert or non-nanocomposite aluminum reactive gas covers a print bed and an extruder of the additive manufacturing apparatus during a step of operating. 
     
     
       13. The method of  claim 12  wherein the heavier-than-air inert gas comprises argon, carbon dioxide, nitrogen, or nitrogen dioxide. 
     
     
       14. The method of  claim 12  wherein a temperature of the heavier-than-air inert gas is maintained at a value below a temperature of the additive manufacturing apparatus during a step of operating. 
     
     
       15. The method of  claim 1  further comprising storing the second material in an inert atmosphere for transporting, handling, and compounding with the first material, and storing the third material in an inert atmosphere prior to using the third material as the feedstock material during the step of operating. 
     
     
       16. The method of  claim 1  further comprising during the step of operating, maintaining a temperature of the second material below a gas transition temperature, melting temperature, and ignition temperature of the second material. 
     
     
       17. The method of  claim 1  further comprising encasing the fuel grain within an insulating material. 
     
     
       18. The method of  claim 1  the projections comprising one or more of a plurality of ribs, a plurality of undulations, a plurality of protrusions and recessions, and a plurality of depressions. 
     
     
       19. The method of  claim 1  wherein the combustion port defines a substantially circular cross-section. 
     
     
       20. The method of  claim 1  wherein a shape of the combustion port comprises an oval shape, a polygonal shape, a quatrefoil shape, a star shape, or an irregular shape. 
     
     
       21. The method of  claim 1  wherein the fuel grain defines an outer diameter of about 19.0 inches and the center combustion port has an initial diameter of about 4 inches prior to consumption of the fuel grain material during a combustion process. 
     
     
       22. Forming a fuel grain segment having a plurality of stacked fuel grains according to the method of  claim 1 , further comprising disposing viscous ABS material between a surface of a first fuel grain segment and an abutting surface of a second fuel grain segment to create a fusion bond between the first and second fuel grain segments. 
     
     
       23. The method of  claim 1  wherein each one of the plurality of fused stacked layers is substantially uniform in material composition. 
     
     
       24. The method of  claim 1  further comprising insulating the fuel grain from an ambient atmosphere prior to removing the fuel grain from a print bed of the additive manufacturing apparatus. 
     
     
       25. A method for constructing a rocket motor comprising:
 compounding a first material suitable as a hybrid rocket fuel and a second energetic and pyrophoric nanoscale metallic material according to a predetermined mixture ratio to form a third material; 
 the third material serving as feedstock material for use in an additive manufacturing apparatus; 
 operating the additive manufacturing apparatus using the feedstock material to fabricate a fuel grain comprising a plurality of fused stacked layers of solidified fuel grain material; 
 each layer comprising a plurality of abutting and fused ring-shaped beads concentrically configured to form a central opening in each layer 
 the central opening extending through the plurality of fused stacked layers to form a combustion port; 
 as an inner circumference of a ring-shaped bead forming a boundary of the combustion port ablates due to combustion in the combustion port, an inner circumference of an adjacent ring-shaped bead presents to form the boundary of the combustion port; 
 the inner circumference of each ring-shaped bead presenting irregular surface features; 
 the irregular surface features presenting a larger surface area for combustion and therefore an increased regression rate of the fuel grain relative to an inner surface presenting a smooth surface; and 
 connecting the fuel grain to a rocket nozzle. 
 
     
     
       26. The method of  claim 25  wherein the irregular surface comprises projections, the projections forming a progressive twist through the combustion port to induce a swirling gaseous flow within the combustion port. 
     
     
       27. A method of making a fuel grain for use in a hybrid rocket engine, the method comprising:
 compounding a first material suitable as a hybrid rocket fuel and a second energetic and pyrophoric nanoscale metallic material according to a predetermined mixture ratio to form a third material; 
 the third material serving as feedstock material for use in an additive manufacturing apparatus; 
 operating the additive manufacturing apparatus using the feedstock material to fabricate a fuel grain comprising a plurality of fused stacked layers of solidified fuel grain material; 
 each layer comprising a plurality of abutting and fused ring-shaped beads concentrically configured to form a central opening in each layer; 
 the central opening extending through the plurality of fused stacked layers to form a combustion port; 
 an inner circumference of each ring-shaped bead in a layer defining a sustaining material pattern such that as a first ring-shaped bead forming a boundary of the combustion port ablates a second ring-shaped bead presents to form the boundary of the combustion port, the second ring-shaped bead and each subsequent ring-shaped bead presenting a sustaining material pattern in its inner circumference, wherein the sustaining material pattern in the inner circumference of each of the ring-shaped beads comprises an irregular surface thereby presenting a greater surface area than an inner circumference having a smooth surface, or the inner circumference of each of the ring-shaped beads generating a vortex flow for an oxidizer flowing through the combustion port. 
 
     
     
       28. The method of  claim 27  wherein the irregular surface comprises one or more of a plurality of ribs, a plurality of undulations, a plurality of protrusions and recessions, a plurality of depressions, and a plurality of projections. 
     
     
       29. The method of  claim 27  wherein a same sustaining material pattern is presented in each ring-shaped bead. 
     
     
       30. The method of  claim 27  wherein the material pattern exhibits a progressive twist through the combustion port to induce a swirling gaseous flow within the combustion port. 
     
     
       31. A method of making a fuel grain for use in a hybrid rocket engine, the method comprising:
 compounding a first material suitable as a hybrid rocket fuel and a second energetic and pyrophoric nanoscale metallic material according to a predetermined mixture ratio to form a third material;   the third material serving as feedstock material for use in an additive manufacturing apparatus;   operating the additive manufacturing apparatus using the feedstock material to fabricate a fuel grain comprising a plurality of fused layers of solidified fuel grain material;   each layer of the plurality of fused layers further comprising a plurality of beads configured to form a central opening in each layer;   the central opening extending through the plurality of fused layers to define a combustion port bounded by a boundary wall; and   an inner circumferential surface of each bead defining projections therein, such that as a bead forming the boundary wall ablates due to combustion in the combustion port, an inner circumferential wall of an adjacent bead defining projections therein presents to form the boundary wall of the combustion port.