Mixed-Source EGR for Enabling High Efficiency Clean Combustion Modes in a Light-Duty Diesel Engine 2008-01-0645

The source of exhaust gas recirculation (EGR), and consequently composition and temperature, has a significant effect on advanced combustion modes including stability, efficiency, and emissions. The effects of high-pressure loop EGR (HPL EGR) and low-pressure loop EGR (LPL EGR) on achieving high efficiency clean combustion (HECC) modes in a light-duty diesel engine were characterized in this study. High dilution operation is complicated in real-world situations due to inadequate control of mixture temperature and the slow response of LPL EGR systems. Mixed-source EGR (combination of HPL EGR and LPL EGR) was investigated as a reasonable approach for controlling mixture temperature. The potential of mixed-source EGR has been explored using LPL EGR as a ‘base’ for dilution rather than as a sole source. HPL EGR provides the ‘trim’ for controlling mixture temperature and has the potential for enabling precise control of dilution targets. This approach also has a benefit where LPL EGR does not provide sufficient dilution for achieving conditions appropriate for HECC operation. The balance of the required dilution could be achieved with HPL EGR mitigating the need for throttling or a LPL EGR pump. The results of this investigation revealed significant differences in engine-out emissions and performance for various EGR sources.