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Abstract:
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Experimental measurements and model predictions of ignition delay times for single component and two-component liquid fuels are presented. The methodology used is the suspended-droplet/moving-furnace technique, in which a droplet of fuel is suspended from the tip of a thin quartz fibre. A preheated electric furnace moves towards and encompasses the droplet locality, producing a sudden rise in ambient temperature, and thus initiating the ignition process. The entire apparatus is enclosed in a pressure vessel and is remotely operated. Data were collected for pressures up to 18 atm absolute and in a temperature range of 773 K to 973 K. Fuels tested comprised n-paraffins (decane, dodecane, and hexadecane), aromatics (mesitylene, o-xylene, and isobutylbenzene) and a cycloparaffin (decalin), as well as selected binary combinations: n-decane/n-dodecane, n-dodecane/n-hexadecane, n-decane/decalin, n-decane/isobutylbenzene, n-decane/mesitylene, and n-decane/o-xylene. Paraffin measurements at low pressures and high temperature revealed a monotonic decrease in ignition times with increasing pressure. However, higher pressure ignitions at lower temperatures showed more complex behaviour by the measurement of two or "twinned" ignition times for the same pressure and temperature condition, indicating a change in reaction mechanism, possibly from one-stage to two-stage ignition. Aromatic fuels did not show "twinned" ignition time behaviour and responded with a slight increase in ignition times with increasing pressure, owing to a weaker reaction rate dependence on pressure. The cycloparaffin behaved analogously to the n-paraffin family. The behaviour of mixtures was largely controlled by the more volatile component. (Abstract shortened by UMI.) |
