Research PaperThermal oxidation coking of aviation kerosene RP-3 at supercritical pressure in helical tubes

•Thermal oxidation coking amount distribution is more uniform in helical tubes.•Smaller helical diameter makes the coking peak closer to the flow downstream.•The total coking amount sharply decreased with the increase of helical coil numbers.•Three coking morphologies and various elements distributions are detected.

The mechanism of thermal oxidation coking of aviation kerosene RP-3 at a supercritical pressure of 5 MPa in helical tubes was analyzed. The bulk temperature of the fuel was varied from 400 K to 723 K, and the mass flux was varied from 393 kg/m2 s to 1178 kg/m2 s. Four types of helical tubes with different helical diameters were bent and tested for a maximum duration of 5 h. The total coking amount and distribution were analyzed using weighing method, and the standard error was less than 0.07 mg. The results indicate that coking distribution is more uniform than in the case of a straight tube, and that there is no prominent coking peak because of the effect of centrifugal force. The maximum total coking amount among all the experiments decreased by approximately 69.5% compared with that in a straight tube. Through measurements performed using a scanning electron microscope, three main types of coking morphologies were observed: thin coking layer, dense clumps, and crystalline particles. Moreover, various types of coking elements were detected under different working conditions.