Combustion of a dilute carbon black/ethanol nanofuel droplet in elevated pressure conditions

Combustion of carbon black/ethanol nanofuel droplet at elevated temperature and pressure was carried out in this study. Ethanol was designated as a base fuel, and (0.5 and 1.0) wt.% of carbon black was added to produce nanofuel. One vol.% of Triton X-100 was used as a surfactant, and the mixture was ultrasonically homogenized. The stability of nanofuel and carbon black size distribution was evaluated before the experiments. The droplet diameter of (750 ? 50) ?m was suspended at the tip of a fine K-type thermocouple to measure the temporal variation of droplet temperature. Droplet image was obtained by using high-speed cameras, and the change of droplet diameter, ignition delay, and burning rate were determined by post-processing of the droplet images. The ambient temperature was set to 750 ?C, while the ambient pressure was changed to (5, 10, and 15) bar. The combustion process of carbon black nanofuel droplets was divided into 3 stages of droplet heating, classical combustion, and carbon black combustion. During the classical combustion stage, stable combustion was observed. On the other hand, in the carbon black combustion stage, combustion of carbon black particle with mild puffing was shown. As the ambient pressure increased, ignition was delayed, and the burning rate rose, due to the change of droplet behavior. Rise of carbon black concentration did not significantly affect the ignition delay, but the burning rate increased, due to the effect of thermal radiation. This effect was emphasized in the higher pressure condition.

Automated summary

In this study, combustion of carbon black/ethanol nanofuel droplet was conducted at elevated temperature and pressure. Different stages of droplet combustion process were observed, including droplet heating, classical combustion, and carbon black combustion. Increase in ambient pressure led to delayed ignition and higher burning rate. Rise of carbon black concentration did not significantly affect ignition delay, but increased burning rate, especially under high pressure conditions.