Effects of cooled EGR routing on a second-generation DISI turbocharged engine employing an integrated exhaust manifold

The work reports results from tests employing different cooled EGR routes on a 'Sabre' direct-injection spark-ignition (DISI) research engine. As standard, this engine has been configured to provide good fuel consumption from a combination of mild downsizing, a combustion system with close-spaced injection and the adoption of a three-cylinder configuration in concert with an exhaust manifold integrated into the cylinder head. This has already been shown to offer a rated power specific fuel consumption of 272 g/kWh without cooled EGR. Three different EGR configurations are tested, with the best BSFC at nominal rated conditions being found to be 257-258 g/kWh at a cooled EGR rate of 6%. All of the EGR routing configurations tested in this work permit ready operation of the engine at Lambda 1 and MBT conditions, however, the results show little sensitivity in the combustion system to the actual routing employed. With all of the tested configurations there is a trade-off in terms of the effect on the charging system and also combustion stability. This suggests that other technologies, such as a variable geometry turbocharger or a two-stage charging system, may be more beneficial on this engine configuration than cooled EGR when it is considered as an entire system.