Exhaust gas recirculation cooler fouling morphology: Characterisation, spatiotemporal nature, and system variable-morphology-property correlation

Fouling is one of the primary causes of failure in exhaust gas recirculation (EGR) coolers. Morphology may provide a powerful perspective for understanding the mechanisms, behaviours, and properties of fouling. However, a systematic review of fouling morphology is currently lacking. Considering the substantial progress made in morphology-related studies within the industry in recent years, this work reviews the findings on EGR cooler fouling morphology from four aspects: characterisation (scale, object, category, and technique), spatiotemporal nature, variable-morphology correlation, and morphology-property correlation. Furthermore, the current challenges and opportunities in this field are discussed. Based on this, we propose a framework for the morphological characterisation of EGR cooler fouling. It is demonstrated that morphology plays a crucial role in revealing the spatiotemporal characteristics of fouling, the formation and removal mechanisms, and the correlations among system variables, morphology, and properties. Morphology still holds significant potential in four areas: multi-scale and quantitative characterisation, nomenclature and taxonomy, and full lifecycle evolution. The findings provide a morphological perspective for fouling research within the industry and contribute to advancing the science of fouling morphology.