Study On The Preparation Of Inert Oxide Films On Stainless Steel Surface And Anti-Coking Performance

Using endotherrmic fuel to cool high temperature parts of aircraft engine is the effective way to improve engine performance. Endothermic hydrocarbon fuel has two roles. On one hand, it can provide power for the aircraft, on the other hand, it changes heat for high temperature parts as coolant. The rising of fule temperature is good for burning in the combustion chamber. Coking phenomenon appeares because of the contact pipes road surface with high temperature fuel for a long time. Coking is harmful for the produce of engine heat and fuel system. Therefore, studying how to effectively restrain the metal surface fuel coked has important meaning.Aviation fuel coked reaction has two kinds. One is oxygen coking caused by dissolved oxygen. The other is pyrolysis coking mainly caused by the metal. In the present work, the raw material was kerosene. Firstly, the content of dissolved oxygen was determined using chemical analysis method. In this paper, on the basis of iodine volume method a novel chemical analysis method was proposed for the determination on of dissolved oxygen in kerosene. The content of dissolved oxygen in kerosene was 68.84 mg/kg using this analysisi method.SiO2 thin films were prepared on the surface of SS304 stainless steel substrate by Sol-gel method. TEOS was precursor body. Silane coupling agent was used for modification. The pH value, additives, dosage of solvent and quantity of the water were inspected to study the stability sol and coating. Using scanning electron microscopy (SEM) and energy spectrum (EDS) SiO2 coatings were analyzed after heat-treatment at 500℃. The results showed that single-layer SiO2 coating was prepared on stainless steel substrate surface by Sol-gel method. And the coating was smooth and combined closely with the substrate. Obvious cracks appered on the surface of multilayer SiO2 coating.SiO2-Al2O3 films were prepared on the surface of SS304 stainless steel substrate by Sol-gel method. Aluminum isopropanol and aluminum nitrate were as aluminum source. TEOS was silicon source. The hydrolysis temperature, water and rubber solvents were inspected to study the effect in the process of AI2O3 sol by aluminum isopropanol. The analysis results of SEM and EDS showed that SiO2-Al2O3 composite coating by aluminum isopropanol and TEOS was smooth and small fine lines. SiO2-Al2O3 composite coating whose SiO2 and Al2O3 mole ratio was 2:1 was composed by different sizes of the island and the coating surface was discontinuous.Stainless steel without any coating is proceeded anti-coking test with each coating in kerosene cracking unit, examining the influence pyrolysis temperature, reaction time and kerosene velocity to the coking quantity of kerosene pyrolysis. The experimental data of anti-coking test explain that each coating plays the inhibition to aviation kerosene crack coking in high temperature. When aviation kerosene velocity was 0.15 ml/min, and cracking temperature was 600℃, the coating coked quantity reduced by 28.5%. The characterization results of SEM and EDS on the surface coking show that the oxidized coating of stainless steel surface plays barrier layer in coked reaction, and multilayer SiCO2 coating passive metal surface with Sol-gel has optimum effect.