Evolution of EGR cooler deposits under hydrocarbon condensation: Analysis of local thickness, roughness, and fouling layer density

Abstract

Stringent new automobile emission standards have prompted extended the use of exhaust gas recirculation (EGR) systems in additional areas of engine maps, resulting in the operation of engines with exhaust gas flows having higher concentrations of particulate matter and hydrocarbons. These new operating conditions promote the formation of fouling layers inside the EGR cooler, owing to the accumulation of soot agglomerates and their interactions with hydrocarbon condensates. Hence, this study analyses the effects of hydrocarbons on the formation and evolution of deposits that grow on a ribbed surface. Using an experimental layout, an exhaust flow with soot agglomerates and a representative species of hydrocarbon vapour typically encountered in EGR flows are generated. The particulate matter of the exhaust stream is categorised using transmission electron microscopy images, while the deposits generated are analysed at different instants of the fouling process through tests of different durations. The effects of a high HC content on the fouling are assessed through the measurement of the local fouling layer thickness and the local roughness of the deposit. The outlet gas temperature and thermal efficiency are monitored during the fouling process; additionally, the density of the fouling layer is evaluated. The results reveal that, considering higher hydrocarbon concentrations, the thickness of the fouling layer decreased in regions near the outlet section of the deposit during the early stages of the deposit formation. When the large agglomerates generated under a high HC content hit the fouling layer on the windward side of the ribs, they modify the surface texture of the deposit, resulting in higher roughness values. Moreover, the analysis of the deposit density reveals that when hydrocarbon condensation occurs during the early phases of the fouling process, the density of the deposit can be 1.9 times higher than those of deposits generated in longer-duration tests.