Comprehensive Review of the Impact of 2,5-Dimethylfuran and 2-Methylfuran on Soot Emissions: Experiments in Diesel Engines and at Laboratory-Scale

2,5-Dimethylfuran (2,5-DMF) and 2-methylfuran (2-MF) are furan derivatives that are shown to be able to reduce soot emissions from diesel engines. However, their capacity to form soot is high due to their cyclic structures. Therefore, the question arises that if the tendency to form soot of these oxygenated compounds is high, how do they have the ability to reduce soot emissions when added to diesel fuel. The operating conditions, as well as their physicochemical and combustion characteristics, can contribute significantly in such reduction. Moreover, the reactivity and physicochemical properties of the soot originated in the combustion chamber can also be important. However, this factor is hardly taking into account when an explanation is given for the reduction of soot emissions when furan derivatives are used. With the aim of analyzing the main factors that control the reduction of soot emissions from diesel engines when diesel/furan derivatives blends are used, the present review paper compiles and analyzes the studies that address: (1) the reduction of soot emissions when diesel/2,5-DMF and diesel/2-MF blends are used in diesel engines; (2) the formation of soot precursors and soot from the conversion of 2,5-DMF and 2-MF at laboratory-scale; and (3) the reactivity and characteristics of soot formed from the conversion of blends of a base fuel with 2,5-DMF or 2-MF and in the conversion of pure 2,5-DMF and 2-MF. This compilation will help focus future research works that may help understand the phenomena through which soot emissions are reduced when diesel fuel is blended with 2,5-DMF or 2-MF.