Moderate and Intense Low-Oxygen Dilution (MILD) Combustion of Liquid Fuels: A Review

In the past 3 decades or so, the innovative combustion technologies associated with so-called "moderate and intense low-oxygen dilution (MILD) combustion " have been researched and developed to help mitigate greenhouse gases and harmful pollutants from burning fossil fuels. The MILD combustion is characterized by ultra-low emissions of nitric oxides (NOx) and carbon monoxides, uniform temperature and large reaction zone, invisibility and silence, and broadly usable fuels. Currently, it has been successfully used in steel and metallurgy industries worldwide, offering a high thermal efficiency and ultra-low NOx emissions. It also has a high potential to apply in the power generation industries, such as gas turbines, most of which fire liquid fuels. However, this type of combustion for burning liquid fuels has not been well-understood, thus requiring further research and development (R & D). To facilitate the R & D, the present review is undertaken on the past progress made in research into the liquid fuel MILD combustion. Specifically, it summarizes the findings from the previous studies of both open fuel jet flames in hot coflow and enclosed furnace combustion of liquid fuels. Likewise, it analyzes the combustion characteristics of burning liquid fuels and evaluates the challenges in operating with different liquid fuel types. The review is concluded by suggesting some future research directions for the combustion itself, the computational fluid dynamics modeling, and the comprehensive design methods of its applications.