Influence of the low-pressure exhaust gas recirculation injection point on engine performance

The use of low-pressure exhaust gas recirculation (EGR) has been extended in spark-ignited engines in recent years due to advantages from efficiency perspective. However, the potential condensation of the water contained in the exhaust gases and eventual compressor erosion can limit the usage of such systems during engine warm-up and/or cold ambient conditions. One possibility to avoid condensation at cold ambient is to place the EGR injection close to the compressor wheel, avoiding a complete mixture of both streams, but it alters the flow distribution upstream of the compressor, potentially affecting its performance. In order to assess the impact of this phenomenon in engine operation, a detailed experimental campaign in a state-of-the-art spark-ignition engine was performed comparing this close-coupled configuration with another one where the injection point was far upstream the compressor, ensuring a perfect mixing. A previously developed and validated one-dimensional model of the variable geometry turbocharger was used to analyze in further detail the compressor and turbine operation. The results show a general deterioration of the engine pumping mean effective pressure (up to 0.02 bar) and the specific fuel consumption (up to 4 g/kWh) when applying the close configuration, higher as the EGR rate increases, which is partially due to the change in turbine operation induced by the new compressor working point.