Viscosity and regression rate of liquefying hybrid rocket fuels

The combustion behavior of paraffin-based hybrid rocket fuels with gaseous oxygen as an oxidizer has been analyzed in detail. Regression rate tests have been done in a two-dimensional radial microburner at the DLR, German Aerospace Center and at the Space Propulsion Laboratory. Fuel samples have been characterized by viscosity measurements, tensile tests, and a differential scanning calorimeter. Tensile tests showed significant improvement in maximum stress and elongation when polymers in low concentration were added to the paraffin samples. The values of the liquid fuel viscosities differed significantly between the selected fuels. This affected the droplet entrainment process during combustion and the regression rates of the fuels. The entrainment and regression rate increased for the decreasing fuel liquid layer viscosity. An exponential relation has been found between the liquid fuel layer viscosity and the regression rate, which can be used to predict the regression rate of new liquefying fuels by measuring their viscosity.