On Cooler and Mixing Condensation Phenomena in the Long-Route Exhaust Gas Recirculation Line

The abatement of nitrogen oxides emissions is a topic of major concern for automotive manufacturers. In addition to aftertreatment solutions such as LNT or SCR devices, the use of exhaust gas recirculation (EGR) is necessary in most of the applications to meet emissions regulations. Due to the high specific humidity of the exhaust gases, a high condensate flow may be generated if EGR gases are significantly cooled down. In the case of long-route EGR (LR-EGR) usage, this condensate flow would reach the compressor wheel. This paper explores the variables governing the condensation process and the potential effects of the liquid droplets and streams on the compressor wheel durability combining experimental and theoretical approach. For this purpose, visualization of both the condensate flow and the compressor wheel are performed. Tests are conducted in a flow test rig in which LR-EGR water content is reproduced by water injection on the hot air mass flow. Two different sources of condensate flow are considered: LR-EGR cooling and fresh air and LR-EGR mixing. The potential of both of these sources to generate condensates is explored by means of a lumped psychrometric model solving LR-EGR cooling and mixing with intake flow. While LR-EGR cooling is a source of condensate flow at low coolant temperature (during engine warm-up) and limits LR-EGR rate at low load, condensation in the mixing process is very dependent on the ambient temperature. This source becomes important as ambient temperature comes down combined with low LR-EGR rate and high LR-EGR outlet specific humidity, imposing additional constraints to LR-EGR usage.