The Effect of Exhaust Emission Conditions and Coolant Temperature on the Composition of Exhaust Gas Recirculation Cooler Deposits 2023-01-0438

Exhaust Gas Recirculation (EGR) coolers are widely used on diesel engines to reduce in-cylinder NOx formation. A common problem is the accumulation of a fouling layer inside the heat exchanger, mainly due to thermophoresis that leads to deposition of particulate matter (PM), and condensation of hydrocarbons (HC) from the diesel exhaust. From a recent investigation of deposits from field samples of EGR coolers, it was confirmed that the densities of their deposits were much higher than reported in previous studies. In this study, the experiments were conducted in order to verify hypotheses about deposit growth, especially densification. An experimental set up which included a custom-made shell and tube type heat exchanger with six surrogate tubes was designed to control flow rate independently, and was installed on a 1.9 L L-4 common rail turbo diesel engine. The test cycle and conditions were higher PM/ lower HC with 75°C coolant temperature for 1.5h, then lower PM/ higher HC with 75°C or 35°C coolant temperature for 0.5h, which was repeated 3 times. Deposits from a tube were collected every cycle for a total of 6h. In the analysis, the deposit surface was observed with a scanning electron microscope, thickness was measured by an optical microscope, and the volatile content was analyzed by a thermogravimetric analyzer (TGA). The results of this study showed that including the cold coolant condition cycle could keep higher heat exchanger effectiveness compared to the hot coolant condition, even though total deposit weight was almost the same. In addition, growth of the deposit thickness was not seen with the cold coolant condition, which was confirmed via the measurements of deposit densification. These data indicate that there is possibly a correlation between repeated hydration of the deposit by condensed water and drying.