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Cooled exhaust gas recirculation is emerging as a promising technology to address the increasing demand for fuel economy without compromising performance in turbocharged spark injection engines. There are a number of different possible architectures, each with its specific characteristics. The objectives of this study are to quantify the increase in knock resistance and to decrease the enrichment at full load in order to target stoichiometric operation over the full operating range, and to define a vehicle compatible cooling system to meet the demanding heat rejection requirements. Based on our knowledge in EGR and air loops, the benefits and risks of various cooled EGR turbocharged systems were evaluated and compared in a preliminary phase. Two architectures, one with high pressure EGR and the other with low pressure EGR, were selected and tested on a 2L turbocharged gasoline engine on a stationary test bench and the performance was compared to the serial production engine.

In order to further reduce NOx emissions in increasing HP EGR cooler performance, several OEMs have decided to use a secondary cooling loop dedicated to bring cold water (around 35°C) to the HP EGR heat exchanger. Nevertheless, strongly cooled EGR gases can condensate in the cooler-producing acidic liquids which can corrode some parts in the loop. It is therefore necessary to define EGR components compatible with such kind of environment and constraints. Testing was performed on a 2.0-liter EU4 diesel engine, using a large panel of current fuels including neat biodiesels from soybean, rapeseed or palm, as well as low and high sulfur petroleum-based diesels. In order to cover all existing cycle conditions, the HP EGR is cooled from 20°C to 90°C independently from the engine coolant circuit.