(364d) Poly(oxymethylene) Ethers: Potential Diesel Fuels with Low Sooting Tendencies

Soot has been identified as the second largest source of climate change after CO₂ and it contributes to ambient fine particulates that cause millions of deaths worldwide each year. Diesel engines are a major contributor to total soot emissions because diesel fuels have high sooting tendencies. Poly(oxymethylene) ethers (POMEs) are biomass-derived sustainable diesel fuels reported to have low soot emissions from engines. The structures of the POMEs in these earlier studies are alternating oxygen and carbon atoms terminated with methyl groups on both ends. Unfortunately, methyl-POMEs suffer from high water solubility and low energy density. Replacing the methyl groups with larger alkyl groups can overcome these disadvantages. However, larger alkyl groups will lead to higher sooting tendencies. To optimize this trade-off, the sooting tendencies of methyl-POMEs and alkyl-POMEs need to be quantified. In this work, a series of methyl-POMEs and alkyl-POMEs were synthesized and their sooting tendencies were quantified.

The sooting tendencies were characterized by the Yield Sooting Index (YSI). This parameter is based on the maximum soot concentration measured in coflow diffusion flames whose fuel is CH₄ doped with 1000 ppm of each test compound. The YSIs of the methyl-POMEs and alkyl-POMEs are at least one order of magnitude lower than a certification diesel fuel. The ratio of YSI to lower heating value (LHV) was calculated to evaluate the energy penalty of the oxygen atoms. The calculated YSI/LHV of the POMEs are lower than conventional diesel fuels and their components. These results demonstrate that all POMEs have soot emission benefits, and ongoing work is examining the trade-off between different POMEs.