Effect of different long-chain oxygenated fuels on the nanostructure and physico-chemical properties of soot in n-heptane flames: An experimental comparative study

As a potential e-fuel, polyoxymethylene dimethyl ether (PODEn) not only has the potential to reduce carbon dioxide, but its properties, similar to diesel, also determine its broad application prospects as a fuel additive. So as to study the effects of the unique long-chain structure and high oxygen content of PODEn on soot formation, n -heptane was employed as a diesel alternative fuel in this research. Methyl butyrate (MB), which is chosen as the comparative oxygenated fuel, has the same carbon chain length as PODE3. With the aim of comparing the effects of different oxygenated functional groups in long-chain oxygenated fuels and analyzing the advantages and disadvantages of PODE3 as a fuel additive, two lines of thought were taken. The blending ratio of long-chain oxygenated fuels and total oxygen content in the fuel mixture were fixed. In this work, the high-resolution transmission electron microscope was used to observe the nanostructure of soot. The impact of blending different long-chain oxygenated fuels on soot was analyzed. Compared with pure n- heptane flame, the mean particle diameters of flames from n -heptane blended with 15 vol% PODE3 and 15 vol% MB decreased by 4.07 and 3.55 nm, respectively. As the MB blending ratio increased, the mean soot particle diameter decreased by 6.82 nm compared with pure n- heptane flame. Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to analyze the physico-chemical properties of soot samples. It was found that both PODE3 and MB effectively inhibited the soot formation and reduced the soot graphitization degree in flames. The effect of PODE3 on soot inhibition was more obvious at the same blending ratio. However, when the oxygen content in the fuel mixture was the same, the advantage of PODE3 was no longer maintained.