Diesel EGR Cooler Fouling with Ni-Fe-Cr-Al DPF at Freeway Cruise

This study investigates the effect of diesel particulate filters (DPF) on the performance of exhaust gas recirculation (EGR) coolers. EGR coolers were tested with and without the use of a DPF and their measured performances were compared. The exhaust gas was filtered using a Ni-Fe-Cr-Al metallic foam wall flow diesel particulate filter. The DPFs used in this investigation had very low Space Velocity (SV) characteristics in order to minimize the effect of filtration on the pressure drop. Two different measurement methods were employed to determine particulate matter (PM) emission levels at locations before and after the DPF. The first method involved the collection of PM on quartz filters followed by thermal analysis of the filters to monitor the removal of soot, semi-volatile organics, and sulfate across the DPF. The second method measured the time resolved PM mass in the exhaust with a Dekati Mass Monitor. A smoke meter was used to measure smoke levels in units of Filter Smoke Number (FSN) throughout the duration of the test. Mass soot flows were then derived using the FSN readings and the relationship between soot mass concentration and the EGR cooler effectiveness was established over EGR runtime. Without a DPF, the EGR cooler effectiveness degraded significantly with time while a periodic cooler recovery and degradation was noticed after the half hour shut down period at the end of every 5 hour testing cycle. In contrast, with the use of a DPF, the EGR cooler effectiveness showed less degradation developing at a slower rate, and in addition, there were almost no or minor recovery actions throughout the test.