Burning droplets of heavy oil residual blended with diesel light oil: Distinction of burning phases

Abstract

This work succeeds a previous report in Combustion Science and Technology (Vol. 174, pp. 115-145, 2002), and aims at distinguishing between the liquid and solid phases of burning heavy fuel oil (HFO) droplets in terms of burning times. The durations of the two burning phases were determined from the previously measured component times for burning steps that prevailed inburning droplets of blend oils between a heavy oil residual (HOR) and adiesel light oil (LO). A hot-air chamber was employed to acquire the high-temperature conditions of droplets occurring in actual burners. The result showed that the duration of the solid phase is generally larger than, and in some particular cases it is comparable to, that of the liquid phase. As for the examined blend oils, the pure HOR exhibited comparable phase durations, while the other blend oils had longer durations for the solid phase than for the liquid phase. Under the tested conditions, the durations of both phases tended to decrease with increasing LO fraction and ambience temperature and decreasing the initial droplet diameter. For typical HFOs, such as those equivalent to the blend oils with LO fractions greater than 26 wt. %, the relative ratio of durations between the solid phase and the liquid phase appeared weakly dependent on oil composition, temperature, and droplet size. This resulted in an average ratio of about 1.3 and a corresponding fluctuation from 1.0 to 1.6. The pure HOR slightly deviated from such values, however, manifesting an average of 1.0 and a fluctuation of 0.8 to 1.3. Furthermore, the HOR amount in the oil droplets determined the duration of the solid phase, whereas the initial droplet diameter was linearly correlated with the duration of the liquid phase. This work finally compared the ember times for burning out soot and coke particles, which further verified the dominance of coke burning over the solid phase.