Coke Inhibition For Thermal Cracking Of Supercritical Hydrocarbon Over Treated Surface Of Cooling Channel

For future hypersonic aircrafts, hydrocarbon fuels not only serve as a conventional role of the propellant but also an ideal coolant to resolve the problem of thermal management by removing the waste heat from aircrafts. However, a byproduct of carbonaceous deposits is inevitably generated accompanied with the cracking of jet fuel, which is taken as one of uncertain issues in utilizing hydrocarbon fuels as the heat sink for advanced cooling.In this work, the stainless steel tube ((?)3mmxo.5mm) was pretreated by means of pre-oxidation and MOCVD coating. We characterized the pretreated tubes, and studied the thermal cracking/coking of supercritical RP-3over pretreated tubes.The amount of carbon deposition was decreased as pre-oxidation temperature increased. However, the surfaces of tubes pre-oxidated at600～800℃were very rough, even though the coking amounts gradually decreased but still exceeding the amouts in bare tube. Only when the tube surface pre-oxidated at900℃formed a compact film, the cokes were inhibited. Increasing pre-oxidation temperature, Cr was migrated to the surface and Fe, Ni was migrated inner to the bulk, resulting in dramatically decrease of filamentous carbon.Alumina coatings with various thicknesses (318-1280nm) were prepared in SS321tubes via metal organic chemical vapor deposition (MOCVD) using aluminium tri-sec-butoxide. X-ray diffraction characterization showed the prepared MOCVD alumina coatings were essentially amorphous. The anti-coking performance increased from37to69%with the thickness of alumina coatings increased from318to1280nm. The further characterizations on the cokes with temperature-programmed oxidation and scanning electron microscopy indicated that the MOCVD alumina coatings were favorable for depressing metal catalysis cokes over tube surface as well as aromatic condensation cokes from bulk cracked fuel.Compared with the Al2O3, TiO2, and ZrO2coatings about1μm, we found that the anti-coking performance was64%,60%, and23%, respectively. The anti-coking performance of ZrO2coating was much poor, owing to its weak thermal shock resistance.