Assessment of Cooled Low Pressure EGR in a Turbocharged Direct Injection Gasoline Engine

The use of Low Pressure - Exhaust Gas Recirculation (EGR) is intended to allow displacement reduction in turbocharged gasoline engines and improve fuel economy. Low Pressure EGR designs have an advantage over High Pressure configurations since they interfere less with turbocharger efficiency and improve the uniformity of air-EGR mixing in the engine. In this research, Low Pressure (LP) cooled EGR is evaluated on a turbocharged direct injection gasoline engine with variable valve timing using both simulation and experimental results. First, a model-based calibration study is conducted using simulation tools to identify fuel efficiency gains of LP EGR over the base calibration. The main sources of the efficiency improvement are then quantified individually, focusing on part-load de-throttling of the engine, heat loss reduction, knock mitigation as well as decreased high-load fuel enrichment through exhaust temperature reduction. Synergies between EGR and features of the modern multi-actuated engines are investigated to provide a deeper understanding of this technology. Several limitations of this approach are also addressed. The EGR dilution effect on combustion variability for different operating conditions is characterized using experimental results. In addition, water condensates passing through the compressor as well as the cooling capacity of the EGR cooler and intercooler could also be limiting factors for this technology.