'Doing More with Less' - The Fuel Economy Benefits of Cooled EGR on a Direct-Injected Spark-Ignited Boosted Engine

摘要

Due to the rising costs of fuel and increasingly stringent regulations, auto makers are in need of technology to enable more fuel-efficient powertrain technologies to be introduced to the marketplace. Such powertrains must not sacrifice performance, safety or driver comfort. Today's engine and powertrain manufacturers must, therefore, do more with less by achieving acceptable vehicle performance while reducing fuel consumption. One effective method to achieve this is the extreme downsizing of current direct injection spark-ignited (DISI) engines through the use of high levels of boosting and cooled exhaust gas recirculation (EGR). Key challenges to highly downsized gasoline engines are retarded combustion to prevent engine knocking and the necessity to operate at air/fuel ratios that are significantly richer than the stoichiometric ratio. As a result of changes to the combustion process, cooled EGR offers the potential benefit of engine knock reduction and the elimination of overfuelling. This allows higher compression ratios and the production of more torque at low engine speeds, which in turn enables downsized fuel-efficient engines to become more accepted in the market place. Low pressure EGR was chosen for this research project due to the advantages of being able to drive EGR over a large area of the engine speed and load map, due to the differential pressure between the turbine and compressor. In this paper the fuel economy savings on SI engines as a direct result of adding low pressure cooled EGR to the combustion process are considered. Laboratory tests were run in order to compare engine efficiency and performance with and without cooled EGR. A 3.2-liter V6 spark-ignited engine was used for the testing; both E0 (gasoline) and E85 fuels were studied. The testing was conducted across the entire range of engine speeds and loads. The laboratory tests have shown that cooled EGR is a key technology for enabling downsized engines and provide a means to meet the market requirement of "doing more with less."