The Influence of the Operating Duty Cycles on the Composition of Exhaust Gas Recirculation Cooler Deposits of Industrial Diesel Engines

Exhaust Gas Recirculation (EGR) coolers are commonly used in on-road and off-road diesel engines to reduce the recirculated gas temperature in order to reduce NOx emissions. One of the common performance behaviors for EGR coolers in use on diesel engines is a reduction of the heat exchanger effectiveness, mainly due to particulate matter (PM) deposition and condensation of hydrocarbons (HC) from the diesel exhaust on the inside walls of the EGR cooler. According to previous studies, typically, the effectiveness decreases rapidly initially, then asymptotically stabilizes over time. Prior work has postulated a deposit removal mechanism to explain this stabilization phenomenon. In the present study, five field aged EGR cooler samples that were used on construction machines for over 10,000 hours were analyzed in order to understand the deposit structure as well as the deposit composition after long duration use. Three of them were disassembled from 15.2L off-road diesel engines, the rest of two were taken from 23.1L off-road diesel engines, then torn down to analyze the deposits. The duty cycle of each vehicle was calculated from the average fuel consumption during total operating hours. In the analysis, the deposit surface was examined by a scanning electron microscope (SEM), thickness measurement was performed by an optical microscope, and the volatile content of the deposit was characterized by a thermogravimetric analyzer (TGA). The results of this study showed that most deposits on the gas outlet side (low temperature side) had greater mass and higher density, and included slightly more volatile content than on the gas inlet side (high temperature side). Furthermore, their densities were much higher than reported in previous studies. These data indicate that there is possibly a correlation between the duty cycle and growth of deposit density.