Combustion of frozen nanoaluminum and water mixtures

Steady-state strand burner and laboratory-scale static fire motor experiments were used to determine the relative performance and viability of an environmentally friendly solid propellant composed of only nanoaluminum and frozen water. The nominal size of the nanoaluminum particles was 80 nm. The particles were homogeneously mixed with water to form pastes or colloids and then frozen. The measured parameters include burning rates, slag accumulation, thrust, and pressure. A system scaling study was performed to examine the effect of the size of the smallscale motors. The equivalence ratio was fixed at 0.71 for the strand burner and the laboratory-scale motor experiments. The effect of pressure on the linear burning rate was also examined. For an equivalence ratio of 0.71, the mixture exhibited a linear burning rate of 4.8 cm/s at a pressure of 10.7 MPa and a pressure exponent of 0.79. Three motors of internal diameters in the range of 1.91-7.62 cm were studied. Grain configuration, nozzle throat diameter, and igniter strength were varied. The propellants were successfully ignited and combusted in each laboratory-scale motor, generating thrust levels above 992 N in the 7.62-cm-diam motor with a center-perforated grain configuration (7.62 cm length) and an expansion ratio of 10. For the 7.62 cm motor, combustion efficiency was 69%, whereas the specific impulse efficiency was 64%. Increased combustion efficiency and improved ease of ignition were observed at higher chamber pressures (greater than 8 MPa).