Comparison of Fuel Economy Improvement by High and Low Pressure EGR System on a Downsized Boosted Gasoline Engine

In this paper comparisons were made between the fuel economy improvement between a High Pressure loop (HP) water-cooled Exhaust Gas Recirculation (EGR) system and a Low Pressure loop (LP) water-cooled EGR system. Experiments were implemented on a 1.3-Litre turbocharged PFI gasoline engine in two pars. One was EGR rate as single operating point to compare the different effect of HP- and LP-EGR. The other was mini map from 1500rpm to 3000rpm and BMEP from 2bar to 14bar because of the relative narrow available range of HP-EGR system. In consideration of practical application of EGR system, the coolant used in this experiment was kept almost the same temperature as in real vehicles (88±3°C) instead of underground water temperature, besides a model was built to calculate constant volume ratio (CVR). The results indicated that the effect of HP-EGR was weaker than that of LP-EGR under the same EGR rate, which could be seen from change of combustion parameters. In mini map HP-EGR usually got higher best EGR rates for fuel economy at low-load region, and a better improvement (up to 2.96%) of fuel economy was expected. In contrast at moderate-to-high loads, especially at low speed high load region, HP-EGR rates were severely constrained by the application of turbo. So the application range of HP-EGR and LP-EGR was also compared in this paper. Thus at these regions worse fuel economy improvements compared with LP-EGR were observed. And cylinder-to-cylinder variations of combustion parameters of HP-EGR, for example IMEP, were wider than those of LP-EGR mainly for the non-uniform mixture of fresh working fluid and exhaust gas.