Pre Versus Post Compressor Supply of Cooled EGR for Full Load Fuel Economy in Turbocharged Gasoline Engines

The work was concerned with applying cooled EGR for improved high load fuel economy and reduced pollutant emissions in a turbocharged gasoline engine. While the thermodynamic benefits of EGR were clear, challenges remain to bring the technique to market. A comparison of pre and post compressor EGR supply indicated that post-compressor routing allowed higher compressor efficiencies to be maintained and hence reduced compressor work as the mass flow of EGR was increased. However, with this post-compressor routing, attaining sufficient EGR rate was not possible over the required operating map. Furthermore, at higher engine speeds where the pre-turbine exhaust pressure was greater than the intake plenum pressure, the timing of peak in-cylinder pressure was not as readily advanced towards the optimum. In addition, when using a pre-turbine EGR pick-up, the EGR circuit dead volume had to be closed-off to maintain low-speed torque, insinuating some form of hot-side shut-off valve may be required.