Cenosphere formation of heavy fuel oil/water emulsion combustion in a swirling flame

Heavy fuel oil (HFO) is a good alternative and economical fuel for power generation and marine transport industry because of its low price and high energy density. However, HFO's incomplete and complex combustion results in high levels of emissions. One way to improve HFO combustion and reduce its high-level pollutant emissions is by emulsifying HFO with water to form water-in-oil emulsion fuel by virtue of its characteristic of the micro-explosion phenomenon of emulsion fuel. In this work, we tested HFO samples with water contents of 0% (normal HFO), 5%, 10%, 20%, and 30% in mass. A lab-scale burner with an air-blast nozzle and swirling airflow was applied to simulate the industrial boiler's typical features. The properties of various water contents emulsion fuel, including composition, water droplet size distribution, heating value, density, viscosity, and TGA were analyzed. The influence of water-HFO emulsion on the swirling flame combustion performance and the primary pollutant emissions, listed as CO, CO2, NOx, SOx, particulate matter (PM), and its composition, was studied. The results show that, in general, multiple various beneficial processes come into effect when water-in-HFO emulsion augments the combustion. HFO emulsion technology offers tremendous potential to enhance combustion processes' efficiency with reduced SOx, NOx, and particulate matter emissions. The emulsion fuel has a considerable effect on the formation process of cenospheres. This effect varies with different water levels in HFO due to the different intensities of secondary atomization of emulsion fuel combustion.