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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 (C 4 H 8 O 2 ) and 1,3-dioxolane (C 3 H 6 O 2 ), 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.

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Spontaneous Raman scattering is a conventional in-situ laser-diagnostic method that has been widely used for measurements of temperature and major species. However, utilization of Raman scattering in sooting flames suffers from strong interference including laser-induced fluorescence, laser-induced incandescence, and flame luminosity, which has been a challenge for a long time. This work introduces an easy-to-implement and calibration-free Raman scattering thermometry in sooting flames based on a 355-nm nanosecond-pulsed laser beam. Several strategies were utilized to increase the signal-to-noise ratio and suppress the interference: (1) nanosecond intensified CCD gate width; (2) optimized intensified CCD gate delay; (3) specially designed focused laser beam; (4) ultraviolet polarizer filter. The temperature was obtained by fitting the spectral profile of Stokes-Raman scattering of N2 molecules without any calibrations. Based on the measured temperature, the mole fraction of major species can be evaluated. This method was applied to measure the temperature and major species profiles in a steady ethylene–air counterflow diffusion flame with a spatial resolution of 1.2 mm × 10.8 mm × 0.13 mm. The experimental results agree well with the simulation results in both sooting and non-sooting regions, demonstrating the feasibility of this method for quantitative diagnostics of temperature and major species in multiphase reacting flows.