An EGR Cooler Fouling Model: Experimental Correlation and Model Uses

Thermal effectiveness of Exhaust Gas Recirculation (EGR) coolers used in diesel engines can progressively decrease and stabilize over time due to inner fouling layer of the cooler tubes. Thermophoretic force has been identified as the major cause of diesel exhaust soot fouling, and models are proposed in the literature but improvements in simulation are needed especially for the long-term trend of soot deposition. To describe the fouling stabilization behavior, a removal mechanism is required to account for stabilization of the soot layer. Observations from previous experiments on surrogate circular tubes suggest there are three primary factors to determine removal mechanisms: surface temperature, thickness, and shear velocity. Based on this hypothesis, we developed a 1D CFD fouling model for predicting the thermal effectiveness reduction of real EGR coolers. The model includes the two competing mechanisms mentioned that results in fouling balance. The deposition rate is calculated on a theoretical basis, while the removal rate calculation is based on empirical correlations derived from surrogate tubes. In combination with real world EGR cooler fouling data, the 1D fouling model is used to predict the long-term fouling behavior of production representative EGR coolers on a medium duty diesel engine for steady state conditions. Applicability of this model for various size and geometries of cooler tubes is discussed. Reduction of EGR cooler effectiveness is explored by running this model with regulatory driving cycle conditions and steady state conditions over the engine speed-load map.