Abstract
Heavy fuel oils consist of a blend of middle distillates, mainly diesel fuel, and heavy oil residuals. Varying the fraction of the mixture changes the weight percentage of the asphaltene in the heavy fuel oil (HFO) sample. Asphaltene is a very high molecular weight complex component in the fuel that increases the fuel viscosity, surface tension, and chemical reaction rate. Here, we investigate the influence of high asphaltene concentration on the combustion of a single HFO droplet. In this experimental work, we used the thermogravimetric analysis (TGA) and the suspended droplet techniques. We tested HFO samples containing asphaltene at 8, 16, 24 wt % (HFO8, HFO16, and HFO24). The TGA result shows a residual amount of approximately 2.4 wt % of HFO24 compared to no residuals for HFO8 at the end of the process. The suspended droplet technique results reveal the following seven consecutive burning stages for the entire burning process of the liquid and solid phases: (1) preheating, (2) flame startup, (3) inner evaporation, (4) thermal decomposition, (5) solidification, (6) coke preignition, and (7) smoldering. The temperature range of the various burning stages is seen to be independent of both the concentration of the asphaltene and the initial size of the droplet. On the other hand, both the total burning time and ignition delay time become longer by 40 and 26%, respectively, as the content of the asphaltene increases from 8 to 24 wt % in the HFO sample. The evolution of the droplet's size in time shows that the maximum size of the droplet becomes larger by a factor of 2 for the HFO24 compared to the HFO8 sample.