Surface deposition within treated and untreated stainless steel tubes resulting from thermal-oxidative and pyrolytic degradation of jet fuel

Flow experiments using heated Jet-A fuel and additives were performed to study the effects of treated surfaces on surface deposition. The experimental apparatus was designed to view deposition due to both thermal oxidative and pyrolytic degradation of the fuel. Carbon burnoff and scanning electron microscopy were used to examine the deposits. To understand the effect of fuel temperature on surface deposition, computational fluid dynamics was used to calculate the two-dimensional temperature profile within the tube. Three kinds of experiments were performed. In the first kind, the dissolved O-2 Consumption of heated fuel is measured on different surface types over a range of temperatures. It is found that use of treated tubes significantly delays oxidation of the fuel. In the second kind, the treated length of tubing is progressively increased which varies the characteristics of the thermal-oxidative deposits formed. In the third type of experiment, pyrolytic surface deposition in either fully treated or untreated tubes is studied. It is found that the treated surface significantly reduced the formation of surface deposits for both thermal oxidative and pyrolytic degradation mechanisms. Moreover, it was found that the chemical reactions resulting in pyrolytic deposition on the untreated surface are more sensitive to pressure level than those causing pyrolytic deposition on the treated surface.