Model validation and parametric study of fluid flows and heat transfer of aviation kerosene with endothermic pyrolysis at supercritical pressure

The regenerative cooling technology is a promising approach for effective thermal protection of propulsion and power-generation systems.A mathematical model has been used to examine fluid flows and heat transfer of the aviation kerosene RP-3 with endothermic fuel pyrolysis at a supercritical pressure of 5 MPa.A pyrolytic reaction mechanism,which consists of 18 species and 24 elementary reactions,is incorporated to account for fuel pyrolysis.Detailed model validations are conducted against a series of experimental data,including fluid temperature,fuel conversion rate,various product yields,and chemical heat sink,fully verifying the accuracy and reliability of the model.Effects of fuel pyrolysis and inlet flow velocity on flow dynamics and heat transfer characteristics of RP-3 are investigated.Results reveal that the endothermic fuel pyrolysis significantly improves the heat transfer process in the high fluid temperature region.During the supercritical-pressure heat transfer process,the flow velocity significantly increases,caused by the drastic variations of thermophysical properties.Under all the tested conditions,the Nusselt number initially increases,consistent with the increased flow velocity,and then slightly decreases in the high fluid temperature region,mainly owing to the decreased heat absorption rate from the endothermic pyrolytic chemical reactions.

Thermal stability enhancement and prediction by ANN model

Supersonic aircraft requires thermal endurance of aviation fuel in the process of cooling engine and aircraft. As the composition of petroleum-based jet fuel (RP-3) is confined by crude oil and refining process, sustainable alternative jet fuel with green house gas reduction become to undertake the composition optimization for improving thermal stability. For designing aviation fuel with robust thermal stability and the detail understanding of thermal stability mechanism, RP-3, Fischer–Tropsch fuel, and additives with cyclic structure for absorbing free radical, were investigated thermal stability by modifying different blend ratios under different conditions. Thermal endurance degree was assessed by chroma and deposition tendency. FT blend with cyclic hydrocarbon can improve thermal endurance degree. In compliance with individual optimized blend ratio, the contribution follows methyl cyclopentane > decalin > methyl cyclohexane > tetralin > n-propyl-benzene > 1,2,4 trimethyl-benzene. The appropriate blend ratio could undertake hydrogen donors for terminating the propagation of oxygen-carrying radical, but hydrocarbons with cyclic structure could enhance deposition tendency. Methyl cyclopentane and its oxidation derivatives take the roles of solvent by anti-polymerization and hydrogen donor by opening cyclic structure in the thermal endurance process, and thus lead to a wide range of blend ratio for improving significantly thermal stability. β-scission leading to C–C bond cleavage is the major reaction at the early decomposition stage, which resulted in most abundant derivatives plus C2. The effects of additives on thermal stability are complex and nonlinear on the tendency of thermal deposits and thermal endurance degree, and thus the appropriate ANN-thermal stability model has been trained based on the experiment data and can achieve above 0.995 correlation coefficient. ANN - thermal stability model can predict not only the content of derivatives including ester, olefin, alcohol, ketone, cyclic oxide, aromatics but also the degree of thermal endurance.