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Spray combustion tests of gaseous oxygen atomized sprays of RP-1 gel propellants with ultra-fine aluminum particles were performed in a rocket engine. The addition of aluminum particles to RP-1 gel propellants has the potential to significantly increase the heat of reaction over neat RP-1 due to the high volumetric energy release of the aluminum. Alex® powders, which have an average particle size of 100 nanometers, are formed by exploding aluminum wires. The use of these nano-sized particles can, theoretically, lead to more complete combustion, and thus, lead to performance increases such as higher flame temperature, increased specific impulse, and greater c* combustion efficiency. The engine operating conditions were as follows: chamber pressures ranging from 1-2.8 MPa (150-400 psia); gel propellant mass flow rates ranging from 8-40 g/s; gaseous oxygen mass flow rates ranging from 14-60 g/s; and oxygen-tofuel (O/F) ratios ranging from 0.5-5.0. The percentage of Alex® particles in the RP-1 gel propellants ranged from 0-55% by weight. The c* combustion efficiency was found to range from 60-99%. Results show that among the formulations, the RP-1 gel propellant with 5% of Alex® powders by weight appears to be the best in terms of range of c* efficiencies and the least amount of data scatter.