  Alternative synthetic fuels can be produced by renewable energy sources and
represent a potential route for solving long-term energy storage. Among them,
oxygenated fuels have the advantage of significantly reducing pollutant
emissions and can therefore be used as carbon-neutral substitute fuels for
transportation. In this work, the sooting propensity of different oxymethylene
ethers (OMEn) is investigated using a combined experimental and numerical study
on a series of burner-stabilized premixed flames under mild to severe sooting
conditions. Herein, mixtures of ethylene in combination with the three
individual OMEn for n=2-4 are compared in terms of soot formation behavior with
pure ethylene flames. The kinetic mechanism from Sun et al. (Proc. Combust.
Inst. 36, 1269-1278, 2017) for oxymethylene ether OMEn combustion with n=1-3 is
extended to include OME4 decomposition and combustion kinetics. In the
numerical simulations, the kinetic mechanism is combined with a detailed
quadvariate soot model which uses the Conditional Quadrature Method of Moments
and validated with Laser-Induced Fluorescence (LIF) and Laser-Induced
Incandescence (LII) measurements. It is observed, that the three investigated
OMEn with n=2-4 show similar sooting behavior, mainly reducing larger
aggregates while not significantly affecting the formation of smaller
particles. Furthermore, the extent of soot reduction is comparable among the
three OMEn. The trends and overall reduction are very well captured by the
model. The modeling results are analyzed through reaction path analyses and
sensitivity studies which show the important role of OMEn decomposition and the
formation of CH2O under these rich conditions to reduce species relevant for
soot formation. This is at the base of the negligible observed differences in
terms of soot formation for the different OMEn fuels.
