Oxidative and pyrolytic coking characteristics of supercritical-pressure n-decane and its influence mechanism on heat transfer

Coking of endothermic hydrocarbon fuels can affect heat transfer performance and block the cooling channels, threatening the safe operation of regenerative cooling system for hypersonic aircraft. In this study, an experimental investigation of the influence of coking of supercritical-pressure n-decane on heat transfer was presented. The mechanism by which coking affects heat transfer was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and other characterization methods. The influence of coke on heat transfer can be divided into three regions. In oxidative coking region, coke is generated primarily through catalytic reactions, and coking leads to a slight heat transfer deterioration. In the lower conversion region, filamentous coke is generated, which improves porosity and surface roughness, and leads to heat transfer enhancement. In the higher conversion region, the increase of coking rate leads to an increase in the thickness of the coke and uniformity of coke distribution. The thermal resistance effect exceeds that of rough surfaces, leading to heat transfer deterioration. From the heat transfer and coke characterization results, an indicator related with temperature and coking precursor content was proposed for evaluating the impact of pyrolytic coking on heat transfer. This study can help design the regenerative cooling system more accurately.