The Effects of Temperature, Shear Stress, and Deposit Thickness on EGR Cooler Fouling Removal Mechanism - Part 2 2016-01-0186
Exhaust gas recirculation (EGR) coolers are used on diesel engines to reduce peak in-cylinder flame temperatures, leading to less NOx formation during the combustion process. There is an ongoing concern with soot and hydrocarbon fouling inside the cold surface of the cooler. The fouling layer reduces the heat transfer efficiency and causes pressure drop to increase across the cooler. A number of experimental studies have demonstrated that the fouling layer tends to asymptotically approach a critical height, after which the layer growth ceases. One potential explanation for this behavior is the removal mechanism derived by the shear force applied on the soot and hydrocarbon deposit surface. As the deposit layer thickens, shear force applied on the fouling surface increases due to the flow velocity growth. When a critical shear force is applied, deposit particles start to get removed. In this study, a 1-D model is developed to predict effectiveness drop and fouling layer distribution across the cooler. To model the removal mechanism, experiments described in Part 1 of this paper were conducted. Removal of particles was measured by blowing compressed air in various conditions through the fouled tube from the shell-in-tube type EGR cooler rig. A deposit removal regression equation was developed using the blow out experiment data, which was incorporated into the model. The resulting model showed good correspondence with the experimental data, indicating that removal mechanism improves the prediction of modeling. For the first time, the new model with the empirically derived removal function is able to predict the trend of thermal effectiveness stabilization observed in experiments.