Abstract
In the fuel cooling system of an engine, the heating of aviation kerosene causes it to exhibit complicated, unsteady physicochemical processes and forms undesirable coke deposition. To understand these processes better, we investigated the coupling relationship between turbulent flow, heat transfer, autoxidation, and deposition reactions of fuel in a cooling heat exchanger. The experiments were performed to investigate the whole process within 105 min, separated into five continuous phases of 20, 40, 60, 80, and 105 min, with a heat flux of 38.6 kW/m(2). On the basis of the experimental results, we established a three-dimensional model to study the influence of kerosene's heat-transfer process on oxidation deposition in a long, straight, horizontal pipe under supercritical pressure condition. A modified six-step, pseudo-detailed chemical kinetic and global deposition mechanism has been incorporated into the numerical model with particular attention to temperature variation. The model was validated based on the quantity of deposition and dissolved oxygen consumption rate under different experimental temperatures and heating times. We then analyzed the fluid dynamics profiles and physical parameters of density, specific heat, viscosity, and Reynolds number, species, and deposition rates along the reactor, micrographs, and surface elements of deposition at various temperatures to understand the coupling effect between heat transfer and coke deposition. The results indicated that supercritical characteristics of both the fuel and deposition affect the local heat-transfer characteristics, resulting in some instabilities in the wall temperature distribution. The fuel temperature determines the regime of the chemical reactions in the flow, and the flow conditions and wall temperature determine the deposition rate at the local position of the inner surface.