A Comparative Study on the Combustion Chemistry of Two Bio-hybrid Fuels: 1,3-Dioxane and 1,3-Dioxolane

Bio-hybrid fuels are a promising solution to accomplish
a carbon-neutral
and low-emission future for the transportation sector. Two potential
candidates are the heterocyclic acetals 1,3-dioxane (C4H8O2) and 1,3-dioxolane (C3H6O2), which can be produced from the combination
of biobased feedstocks, carbon dioxide, and renewable electricity.
In this work, comprehensive experimental and numerical investigations
of 1,3-dioxane and 1,3-dioxolane were performed to support their application
in internal combustion engines. Ignition delay times and laminar flame
speeds were measured to reveal the combustion chemistry on the macroscale,
while speciation measurements in a jet-stirred reactor and ethylene-based
counterflow diffusion flames provided insights into combustion chemistry
and pollutant formation on the microscale. Comparing the experimental
and numerical data using either available or proposed kinetic models
revealed that the combustion chemistry and pollutant formation differ
substantially between 1,3-dioxane and 1,3-dioxolane, although their
molecular structures are similar. For example, 1,3-dioxane showed
higher reactivity in the low-temperature regime (500–800 K),
while 1,3-dioxolane addition to ethylene increased polycyclic aromatic
hydrocarbons and soot formation in high-temperature (>800 K)
counterflow diffusion flames. Reaction pathway analyses were performed
to examine and explain the differences between these two bio-hybrid
fuels, which originate from the chemical bond dissociation energies
in their molecular structures.