Experimental study of droplet vaporization and combustion of diesel, biodiesel and their blends in a turbulent environment at elevated pressure and temperature conditions
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Date
2014-02-14
Authors
Toth, Stephen L.
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Abstract
Droplet vaporization and combustion of biodiesel, diesel and their blends was examined experimentally in a turbulent flow at elevated ambient temperature and pressure conditions. A high pressure vessel capable of generating high levels of turbulence was employed in this study. The linear relationship between turbulence intensity and fans rotational speed, which was developed at room temperature, was found to be unaffected by the gas ambient temperature.
Droplet vaporization experiments were performed by varying turbulence intensity (i.e., the fans rotational speed) from 0 up to 3.1 m/s, ambient temperature and pressure up to 473 K and 16 bar, respectively. The results revealed that diesel droplet vaporization did not follow the d2-law under the aforementioned test conditions. However, biodiesel droplet vaporization obeyed the d2-law. Droplet vaporization of the blends, i.e. B20 and B50, displayed a mixed behaviour of both parent fuels with the biodiesel behaviour predominating where biodiesel content slows down the droplet vaporization of the blends. Turbulence was found to reduce the droplet lifetime of all fuels (i.e., increases droplet vaporization rate), and its effect becomes more effective with increasing ambient pressure.
Droplet combustion experiments were performed by varying turbulence intensity from 0 up to 1.20 m/s, and ambient temperature up to 423K at ambient pressure of 1 atm. Diesel droplet combustion rate showed negligible change with turbulence intensity up to 0.40 m/s beyond which the burning rate decreased slightly with turbulence intensity. Similarly, biodiesel droplet combustion rate did not show an increase with the presence of a turbulent flow around the droplet. However, in contrast to diesel, biodiesel burning rate remained nearly constant until the flame extinction limit. The combustion rate of B20 and B50 displayed a mixed behaviour of both parent fuels. Nevertheless, both blends showed that diesel had predominance over the burning rate. Finally, the droplet flame extinction of all fuel droplets occurred at turbulent velocity slightly greater than the laminar flame speed.
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Keywords
diesel, biodiesel, turbulent, temperature, pressure, vaporization, combustion, blends