Effects of doping ceria on flame quenching in a narrow channel with zirconia-based functional coatings

Wall coating modification has been a potential solution to organize the combustion process in space-constrained system. For this purpose, CeO2 doping effects on the flame stability of premixed methane/air mixtures confined within an adjustable-gap narrow channel with coating ZrO2-based ceramics are experimentally investigated. A series of characterization means are utilized to analyze these prepared composite coatings. Results elaborate that the catalytic activities of CeO2-ZrO2 solid solution correlate with the ratio of CeO2 dopant in bulk. Phase structural stabilities can be strengthened through increasing the CeO2 content, which is due to the significant increase in the ratio of tetragonal phase to monoclinic phase of ZrO2. X-ray photoelectron spectroscopy and H2 temperature-programmed reduction analysis outcomes show that the concentration of formed oxygen vacancies increases significantly with richer CeO2 phase doped, which promotes the exaltation of lattice oxygen activity and fluidity. Flame quenching tests demonstrate that the wall surface temperature dependence of the quenching distance is changed substantially by doping CeO2 into the ZrO2 coating wall, eliminating the negative temperature effect observed for a pure ZrO2 case at the medium temperature ranges of 673-773 K. The cases of higherCeO2-content doping provide a lower flame quenching distance, especially at slightly fuel-rich conditions, which arises from the enhancement of the storage and release functions of highly active oxygen ions through Ce4+/Ce3+ redox cycles. Comparing of OH planar laser-induced fluorescence images near the extinction limit indicates that in addition to flow rate and air-fuel ratio, different coating materials also have dramatic effects on the post flame characteristic and flame oscillation. In general, this paper not only provides a good overview of the chemical interaction between the wall and flame, but also makes an implication for the design of high-stability small-scale combustors by reasonably manufacturing this type of CeO2-ZrO2 coating functional materials.