Combustion characteristics of oxygenated slurry droplets of nano-Al/EtOH and nano-Al/TPGME blends

Abstract

In this study, two oxygenated slurry fuels were prepared by blending nano-aluminum (Al) particles (5 wt%) with ethanol (EtOH) and tripropylene glycol monomethyl ether (TPGME), respectively. The prepared oxygenated slurries were suspended as droplets on a thermocouple wire, and a laser ignition testing system was used for investigating their combustion characteristics. Snapshots of the combustion process showed that a slurry droplet of nano-Al/EtOH suffered three continuous stages, namely, an ignition delay stage, a droplet combustion stage, and a core combustion stage. In contrast, a slurry droplet of nano-Al/TPGME suffered only the first two stages during its combustion; however, an additional microexplosion phenomenon was also observed. During the droplet combustion stage, nano-Al/EtOH blend displayed higher average burning rate, but lower droplet surface temperature than nano-Al/TPGME blend. Emission spectra indicated the formation of gas-phase intermediate products, namely, Al, AlO, AlO2, and Al2O, via nano-Al oxidation during the combustion of both types of oxygenated slurry fuels. Nano-Al/EtOH and nano-Al/TPGME blends displayed higher emission spectral intensity of AlO and AlO2, respectively. The normalized ignition delay time of nano-Al/EtOH droplets was 41.3% longer than that of nano-Al/TPGME droplets. However, the normalized total combustion time of nano-Al/EtOH droplets was 26.4% shorter than that of nano-Al/TPGME droplets.