Selection of EGR system is very complex for a particular engine application. The performance of the EGR system depends highly on the Cooler Heat Transfer Efficiency. Cooler effectiveness drops over a period of operation due to soot deposition, HC condensation, and fuel quality. This phenomenon is called as Cooler Fouling. Fouling cannot be avoided completely but the level of performance drop over time has to be studied and minimized. The minimum pressure drop and the highest efficiency in fouled condition is the target for selection of a cooler.
In this study, various parameter combinations like tube shape and profile, tube length, number of tubes, tube diameter, and pitch of corrugations, which influence the cooler performance were tested. A better understanding of each of its effect on cooler effectiveness and fouling behavior was obtained. The tube shape was changed from rectangular to circular, also from smooth surface to corrugate. Fouling behavior also changed with change in cooler tube specifications. A common cooler fouling cycle was derived and different cooler specifications were tested so that fouling could be understood in a common platform.
By optimizing the number of tubes and pitch, a 20% increase in heat transfer rate was achieved with a 15% reduction in fouling behavior and a net NOx emission reduction of 15% was possible on a 2.2L diesel engine.