ISSN Online: 2379-1748
9th Thermal and Fluids Engineering Conference (TFEC)
Transient Supercritical-Pressure Heat Transfer of Kerosene with Thermal Oxidation Coking Accumulation
Аннотация
A modern aircraft engine, in pursuit of higher thrust and higher operation efficiency, is faced with higher- temperature environment and requires advanced thermal management, in order to run stably and reliably. Regenerative cooling [1], a method that uses onboard fuel as the coolant to directly or indirectly cool high- temperature components of the engine, is a preferred technology, because it is possible to fully utilize the fuel's heat sink.
Regenerative cooling technology often involves supercritical-pressure heat transfer of the engine fuel, and in the process, thermal chemical reactions and surface coking become an important issue. There exist extensive experimental and numerical studies [2-5] on supercritical-pressure heat transfer of the hydrocarbon fuel in heat exchange channels. Many RANS turbulence models have been tested for their accuracy and reliability in supercritical-pressure heat transfer simulations [6].
Thermal chemical reactions and surface coking of the engine fuel include the thermal pyrolytic reactions and coking (occur at >750K) and the thermal oxidative reactions and coking (occur at >420K). Although fuel pyrolysis would lead to extra chemical heat sink, its fast coking process could block the flow channel in a short period of time [7]. Therefore, fuel pyrolysis should be avoided, by limiting the maximum fuel temperature, in long-term regenerative cooling operations. Thermal oxidative coking is, in general, unavoidable because of its low initiating temperature, but it has relatively low surface coking rate [8].
Studies on thermal oxidative reaction and coking mechanism have been conducted. Pei. et. al. [9] discovered that the axial temperature gradient could cause direct fuel coking. Liu. et al. [10] revealed the different roles played by hindered phenols and non-hindered phenols in fuel oxidative coking, based on their experimental results. They added three additional reaction and coking pathways to a mechanism proposed by Sander et al. [11]. The effect of thermal oxidative coking on flow and heat transfer have also been studied. In the experiments of Fu et al. [12] and Liu et al. [13], the largest wall temperature rise (ΔT) caused by surface coking accumulation could reach 89 K and 160 K, respectively. Meanwhile, the coke density (~1100 kg/m3) and thermal conductivity were also measured [13].
In this work, transient supercritical-pressure heat transfer of an engine fuel, kerosene, has been numerically investigated, and the accumulation of thermal oxidative coking is treated using dynamic grids. The effects of different surface heat fluxes, thermal conductivities of the coking layer and concentrations of the dissolved oxygen on flow, heat transfer and surface coking in a long-term operation process are examined.
Regenerative cooling technology often involves supercritical-pressure heat transfer of the engine fuel, and in the process, thermal chemical reactions and surface coking become an important issue. There exist extensive experimental and numerical studies [2-5] on supercritical-pressure heat transfer of the hydrocarbon fuel in heat exchange channels. Many RANS turbulence models have been tested for their accuracy and reliability in supercritical-pressure heat transfer simulations [6].
Thermal chemical reactions and surface coking of the engine fuel include the thermal pyrolytic reactions and coking (occur at >750K) and the thermal oxidative reactions and coking (occur at >420K). Although fuel pyrolysis would lead to extra chemical heat sink, its fast coking process could block the flow channel in a short period of time [7]. Therefore, fuel pyrolysis should be avoided, by limiting the maximum fuel temperature, in long-term regenerative cooling operations. Thermal oxidative coking is, in general, unavoidable because of its low initiating temperature, but it has relatively low surface coking rate [8].
Studies on thermal oxidative reaction and coking mechanism have been conducted. Pei. et. al. [9] discovered that the axial temperature gradient could cause direct fuel coking. Liu. et al. [10] revealed the different roles played by hindered phenols and non-hindered phenols in fuel oxidative coking, based on their experimental results. They added three additional reaction and coking pathways to a mechanism proposed by Sander et al. [11]. The effect of thermal oxidative coking on flow and heat transfer have also been studied. In the experiments of Fu et al. [12] and Liu et al. [13], the largest wall temperature rise (ΔT) caused by surface coking accumulation could reach 89 K and 160 K, respectively. Meanwhile, the coke density (~1100 kg/m3) and thermal conductivity were also measured [13].
In this work, transient supercritical-pressure heat transfer of an engine fuel, kerosene, has been numerically investigated, and the accumulation of thermal oxidative coking is treated using dynamic grids. The effects of different surface heat fluxes, thermal conductivities of the coking layer and concentrations of the dissolved oxygen on flow, heat transfer and surface coking in a long-term operation process are examined.