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Effects of Solid Concentration and Oleic Acid Dispersant on Stability and Combustion Characteristics of Aluminum/Bioethanol Nanofluid Fuel

In this work, four samples of nanofluid fuel were prepared by blending bioethanol with 1 wt% aluminum (Al), 5 wt% Al, 10 wt% Al, and 5 wt% Al + 1 wt% oleic acid (OA), respectively, according to the two-step method. Stability of the samples was investigated by comparing the settling time and microstructure of sediments, while combustion characteristics of them were revealed based on the combustion images, normalized durations of different combustion stages, combustion rate constants, and surface temperature curves. Experimental results indicate the addition of OA has significant benefit on the stability of sample by preventing the formation and growth of Al agglomerates. Moreover, the sample containing OA shows the shortest normalized ignition delay time (0.015 s/mm2), largest combustion rate constant (28.79), and highest maximum surface temperature (932.60 °C) during combustion, which demonstrates OA as a superior additive for Al/bioethanol nanofluid fuels. The increase of solid concentration is also helpful to improve the stability, ignition, and energy release of the samples within the experimental range. However, the excessive solid concentration enlarges the size of Al core (residual partially oxidized agglomerates of Al after exhausting of most bioethanol) during combustion, and will further decrease the overall combustion efficiency.