Benefits of a Dual HP and LP EGR Circuit on a Turbocharged Direct Injection Gasoline Engine 2022-01-0429

Internal combustion engines (ICE) will be a part of personal transportation for the foreseeable future. One recent trend for engines has been downsizing which enables the engine to be run more efficiently over regulatory drive cycles. Due to downsizing, engine power density has increased which leads to problems with engine knock. Therefore, there is an increasing need to find a means to reduce the knock propensity of downsized engines. One of the ways of reducing knock propensity is by introducing Exhaust Gas Recirculation (EGR) into the combustion chamber, however, volumetric efficiency also reduces with EGR which places challenges on the boosting system. The individual benefits of high-pressure (HP-EGR) and low-pressure (LP-EGR) loop EGR system to assist the boosting system of a 2.0 L Gasoline Direct Injection (GDI) production engine are explored in this paper. Further, the benefits of the individual systems are coupled in a ‘Blended-EGR’ concept to generate BSFC maps for each EGR strategy which shows benefits of improving fuel economy over regulatory US and EU drive-cycles.

The engine was configured with individual HP-EGR and LP-EGR circuits while the engine was operated at minimal test points representative of regulatory drive cycles. Results are then compared to a baseline, no-EGR case. The two EGR systems are combined in a blended concept to be tested out on a 2.0 L turbocharged downsized engine. The results of engine testing were passed to vehicle modeling using GT-Drive software and a sedan class vehicle. The LP-EGR concept led to fuel economy improvements over all the drive cycles compared to the no-EGR case. The use of HP-EGR yielded further improvement as this configuration due to lower pumping losses compared to LP-EGR. The downside of HP-EGR is that it could not be operated at all engine speed-load conditions. Blended EGR operation combined the benefits of the individual EGR system and improved the fuel economy by 9.9%, 7.6%, 10.5% and 3% during the FTP, HWFET, NEDC and WLTP respectively. As a final task for the project, both the EGR systems are evaluated and compared at full-load conditions at both constant Charge Air Cooler (CAC) temperature and constant CAC effectiveness temperatures.