Bika, A., Warey, A., Szymkowicz, P., Balestrino, S. et al., "An Investigation of Diesel EGR Cooler Fouling and Effectiveness Recovery," SAE Technical Paper 2013-01-0533, 2013, doi:10.4271/2013-01-0533.
Diesel engine developers are continually striving to reduce harmful NOx emissions through various calibration and hardware strategies. One strategy being implemented in production Diesel engines involves utilizing cooled exhaust gas recirculation (EGR). Although there is a significant NOx reduction potential by utilizing cooled EGR, there are also several issues associated with it, such as EGR cooler fouling and a reduction in cooler effectiveness that can occur over time. The exact cause of these issues and many others related to cooler fouling are not clearly understood. One such unanswered issue or phenomenon that has been observed in both field tested and lab tested EGR coolers is that of a recovery in EGR cooler effectiveness after a shutdown or after cycling between various conditions. The purpose of the current work was to show that an effectiveness restoration or effectiveness recovery can occur in an EGR cooler that has been exposed to soot-laden exhaust gases, through changes in operating conditions, with specific emphasis on exposure to high condensation conditions. The work was conducted on a multi-cylinder diesel engine using a shell and tube EGR cooler, with independent control over temperature, flow rate, and EGR soot/HC concentrations. The effectiveness recovery demonstrated in this work was likely caused by morphological changes of the soot layer, rather than actual cleaning or removal of the soot layer.