Coking during the endothermic hydrocarbon fuel pyrolysis is a key issue that needs to be solved in the development of regenerative cooling technology for high-speed aircrafts. The compounds containing hydroxyl groups are developed to inhibit coking by regulating coking pathway during the thermal cracking of hydrocarbon fuels. Pyrolytic deposition experiments of n -decane with additives were performed using the method of electrical heating. The anti-coking performance of the additives was characterized by means of gas chromatograph–mass spectrometer (GC–MS), scanning electron microscopy (SEM), temperature programmed oxidation (TPO) and Raman spectroscopy. The results showed that the degree of cracking is reduced at low fuel temperature due to the dilution of the additives, and the additives do not affect the fuel cracking as the fuel temperature increased. With the function of additives, the masses of filamentous and amorphous coke were decreased. A possible mechanism for the additives inhibiting coking has been proposed. The additives containing hydroxyl groups can block the initial coking reaction path to inhibit coking at the source. In general, the hydroxyl radicals released by the additives oxidize the coking precursors to prevent its further growth, and react with the substrate to form particulate matters serving as passivation coating, inhibiting the bulk phase coking and metal catalytic coking simultaneously. This work provides significant ideas for inhibiting coking by regulating coking reaction pathways.
Qiao Wang,Wanchen Sun,Liang Guo,Shaodian Lin,Peng Cheng,Hao Zhang,Yuying Yan
The laminar burning speed, Markstein length and cellular instability of three oxygenated fuels, polyoxymethylene dimethyl ether 3 (PODE 3 ), dimethyl carbonate (DMC) and n-butanol (NB), were experimentally studied using spherical flame propagation method. Both of the three fuels are potential alternatives for petrochemical gasoline and diesel. Laminar burning speeds and Markstein lengths were measured at ambient pressure and elevated temperature (363 K-423 K) with three extrapolation models including linear and non-linear employed to extract the unstretched flame speed. Onset of flame cellular instability of the three fuels was determined at high pressure (0.5–0.75 MPa) which was favored to the occurrence of cellular instability. Three well-validated mechanisms for PODE 3 , DMC and NB respectively were used to numerically analyze the flame structure and then understand the underlying effect of the molecular structure of oxygenated fuels on laminar flame propagation. Results show that PODE 3 has the highest laminar burning speed among the three, supporting by both thermal effect and kinetic effect. While the laminar burning speed of NB is higher than that of DMC, which is due to the combined effect of thermal factor and kinetic factor. The molecular structure of oxygenated fuels exerts an influence on the laminar flame propagation through the fuel-specific cracking pathway and resulting formed intermediates with different reactivity. The absence of C–C bond within PODE 3 and DMC leads to the formation of substantial oxy-intermediates (CH 2 O) with high reactivity during fuel decomposition. PODE 3 has the most stable flame among the three because of the strong stretching of PODE 3 flame. The flame stability of DMC and NB is approximately similar especially at high initial pressure.
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