Gelled Propellant Rheology

Gelled MMH (left), Gelled RFNA (right)
(Click to enlarge).

This effort, funded by the Army Research Office (ARO) MURI grant, seeks to understand the rheological properties of non-Newtonian gelled hypergolic propellants. Monomethylhydrazine (MMH), red fuming nitric acid (RFNA) and representative inert simulants have been the primary focus of this effort. Characterization is performed with a commercial rotational rheometer and a custom propellant grade capillary rheometer.

Schematic of propellant grade capillary rheometer (Click to enlarge).

• Characterization of gelled propellants from low shear storage to high shear injection conditions.
• Propellant-Grade Capillary Rheometer:
  • Designed system to reduce risks to personnel and equipment when testing with toxic materials.
  • Capable of typical rocket injector shear rates up to 1,000,000 1/s with variable capillary geometry.
• Commercial Rotational Rheometer:
  • Operation in a laboratory fume hood for toxic propellant handling.
  • Low shear viscometry, yield stress and frequency dependent measurements.
• Refrigerated Centrifuge:
  • Evaluation of gel stability over a range of temperatures (-9°C to 40°C).
  • Accelerated settling studies for energetic additives in propellants.

High shear viscosity results for MMH and simulant gels (Click for details).

• Identification of key rheological properties for a viable gelled hypergolic propellant.
• Measurement of gel viscosity at shear rates typical of rocket injectors.
  • Standard assumption is that high shear gel viscosity is equal to the base fluid.
  • Results indicate that even at 6% loading the fumed silica properties dominate the gel viscosity.
  • Gel viscosity ~14 times higher than base fluid at high shear rates.
• Demonstrated that less toxic gel simulants can match the rheological properties of MMH gels allowing for experimentation with reduced risk.