Experimental investigation of the effects of paraffin/aluminum blended fuels on aluminum particle size

The combustion behavior of paraffin/aluminum blended fuels was investigated to determine the effects on the size of nano- and micro-sized aluminum particles and assess their respective combustion performance in hybrid rocket applications. The base paraffin fuel considered in this study was Sasol 0907 microcrystalline wax. Two additional blended fuels, each with particles with average sizes of 8 μm and 100 nm were used. The thermal and rheological behavior of the paraffin/aluminum blended fuels were evaluated, and their homogeneity was verified by scanning electron microscopy. Results confirmed that the nano-sized and micro-sized particles were well distributed in space without agglomeration. The average regression rate of the paraffin added with micro-sized particles was higher than that of the case with nano-sized particles mainly because of the strong viscosity of the nanofuel. This result was justified by the augmented average chamber pressure of the micro-sized paraffin fuel. Generally, the characteristic velocity of the microfuel was greater than that of the nanofuel for the overall range of the oxidizer-to-fuel ratio considered in this study. This difference became pronounced as the oxidizer mass flux increased. The characteristic velocity efficiency of the two blended fuels (microfuel and nanofuel) merely showed a notable difference in the oxidizer-to-fuel ratio range, except for the particle-free base fuel, which showed a wide scatter of combustion efficiency probably because of its low melt layer viscosity, which leads to an undesirable high entrainment of non-combusted pure paraffin fuel.