High Impulse Nanoparticulate-Based Gel Propellants

NASA Phase I Contract No. NNG05CA49C

The objective of this SBIR Phase I was to develop high specific impulse propellant gels. The gels developed were contained nanomaterials, including nanoparticle metals and nanostructured carbon. Phase I consisted of:

  1. Identification of gel components, including nanoparticulate additives and formulation of gels.
  2. Measurement of gel properties, including mass and volumetric energy density, viscosity and rheological properties, settling rate, spray properties, vapor pressure, and stability.
  3. Identification of particularly influential gel and experimental variables.
  4. Initial (coarse) optimization of gels.
  5. Initial burn tests, including temperature and pressure rise and burn rate measurements.

The following were key accomplishments and results of Phase I:

  1. Using chemical equilibrium routines, calculated energy densities and specific impulses of a number of potential candidate fuels and fuel gels. Selected out a number of potential candidates.
  2. Tested potential gel components for compatibility and potential utility in gels. Identified several novel fuel gel agents and formulations.
  3. Using results of calculations and compatibility tests, formulated a number of gels.
  4. Evaluated energy density, viscosity, settling rate, and vapor pressure of gel candidates. The highest energy density was obtained with carbon loaded kerosene (11.7 kcal/mole). Additionally, a kerosene “soap” was identified which possessed gravimetric energy density about 4% above that of the baseline fuel (11.4 versus 10.9 kJ/mole). Nanostructured carbon exhibited surprising strong gel properties: 8wt% in kerosene gave rise to a friable solid fuel, which could be sprayed.
  5. Down-selected candidates to kerosene, MMH, and DMAZ-based gels.
  6. Measured energy density, viscosity, vapor pressure, and settling rate of selected gels containing metal particles ranging from 18 nm to 4.5 µm. Gravimetric and volumetric energy density of kerosene loaded with 50 nm aluminum was found to be 12 and 17% higher, respectively, than the corresponding figures for a gel constituted with the same loading of microparticle aluminum. Viscosity increased with decreasing particle size. These observations held for gels based on the other fuels as well. Vapor pressure of gels was found to be lower in nanoparticle- than in microparticle-containing gels.
  7. Nanoparticle-containing gels displayed superior spray properties compared with microparticle-based gels. Specifically, gels based on nanoparticles sprayed more uniformly, with finer droplets.
  8. Particle coating (i.e., organic versus metal oxide protective film) was observed to exert a profound influence on gel viscosity. Viscosities were, in some fuels, reduced by more than an order of magnitude using the organic protected particles.
  9. On the basis of experimental designs, identified experimental variables (other than particle size, fuel type, and particle type) exerting significant influence on viscosity. Particle coating, gel agent type, and gel agent loading were found to exert significant loading on viscosity.
  10. On the basis of variables identified, prepared coarse optimized gels. Measured viscosities of gels.
  11. Performed spot combustion tests on optimized and selected other gels based on DMAZ, kerosene, and MMH.

It was found that gels containing nanoparticles generally gave higher gas temperatures upon combustion than the baseline fuels as well as gels based on microparticles, possibly suggesting higher specific impulse. Nanoparticles also gave enhanced burn rates relative to neat fuels and microparticle gels.