Effect of Particle Agglomeration on Propulsive Performance of Frozen Aluminum–Water Propellants

The propulsive performance of frozen nanoaluminum–water (ALICE) propellants is studied by conducting computer simulations of rocket motor firing. The chamber pressure, thrust, characteristic velocity ([Formula: see text]), and specific impulse ([Formula: see text]) are computed. The computed ideal propulsive performance metrics are far greater than the actual values. The primary reasons for the performance losses in the experiments are identified to be combustion inefficiency, particle retention in the motor, and particle agglomeration. The combustion inefficiency contributed to a 6–11% loss in [Formula: see text], while particle retention resulted in an [Formula: see text] loss of 13–21%. Particle agglomeration increased two-phase flow losses and caused an additional 10–16% [Formula: see text] reduction. It is found that particle agglomeration increases the choked mass flow rate, leading to a reduction in [Formula: see text]. The agglomerate diameters are estimated to be in the range of 2–4 μm. Strand burner combustion simulations assuming nanoparticle combustion overpredicted pressure exponents significantly, but the predicted burning rates agreed reasonably with experimental data when agglomeration was considered. The present study reveals that it is micron-sized agglomerates that burn in the flame zone and flow through the nozzle, resulting in higher two-phase flow losses and lower specific impulse efficiencies of ALICE rocket motors.