AbstractThe application of heavy fuel oil (HFO) in high-speed diesel engines is a practical approach to reducing running costs. However, the physical and chemical properties of HFO may lead to a poor burning rate and increase pollutant emissions. Emulsified HFO has been studied and applied for the purpose of improving combustion and emissions of HFO. However, the stability and water content of emulsified HFO need to be improved. In this study, emulsified HFO with high stability and high water content (up to 30%) was investigated to study the combustion and emission characteristics of the HFO, and a simulation combined with experimental methods was used. The microimages obtained using an electronic microscope highlighted the high stability of emulsified HFO. According to the test results on physical characteristics, compared with low-water-content conditions, HFO has a higher viscosity along with a lower surface tension under high-water-content conditions. To investigate the engine performance with the increasing water content in the HFO, the combustion model was calibrated using engine test experiments. The simulation results showed that with the increasing water content of emulsified HFO, the maximum cylinder pressure, heat release rate, and the crank angle (CA) corresponding to 10% of total heat release (CA10) increased, while the CA corresponding to 50% of total heat release (CA50) decreased. In addition, the experimental results of nitrogen oxide (NOx) and soot emissions maintained a consistent downward tendency with the increase in water content. Compared with fueling HFO, burning emulsified HFO with 30% water content can reduce NOx and soot emissions by 40% and 32%, respectively. The simulation contour maps show the corresponding relationships among the temperature, equivalence ratio, NOx, and soot. The hydrocarbon emissions increased with the water content, and the carbon monoxide emissions similarly maintained the same increasing tendency in addition to fueling the emulsified HFO with 10% water content. Consequently, with a higher water content of the emulsified HFO used in the engine, better combustion was observed with reduced emissions.