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The concept of D-EGR (Dedicated EGR) used high EGR rate and fuel reformation to improve thermal efficiency, entire exhaust gas which supplied from a single cylinder is recirculated to the intake system and then entered into all cylinders to improve combustion. In this study, the D-EGR system is performed on a 1.5 L port fuel injection 4-cylinder gasoline engine, in comparison to the basic engine, the reduction of fuel consumption is about 20~30 g/kWh in most of the D-EGR engine operating range, a maximum 104.1 g/kWh BSFC reduction is found at 14.0bar@1800rpm, the lowest fuel consumption is decreased from 253.7 to 224.3 g/kWh by D-EGR, and the corresponding maximum brake thermal efficiency is improved from 32.6 to 36.9%. D-lambda (the lambda of dedicated cylinder) is considered as the most significant factor to influence the fuel economy and combustion stability, the suitable range of D-lambda is around 0.69~0.82 to gain better engine performance under the whole operating points.

Downsizing is regarded as a promising strategy to reduce the fuel consumption of gasoline engines. But downsized turbocharged engines need to take knocking into account to avoid engine damage. Low Pressure (LP) cooled exhaust gas recirculation (EGR) is an effective suppressant of knocking at boosted high load and EGR could reduce pumping loss at low loads. Both of them are helpful to improve fuel economy. In the research, a LP cooled EGR system is added to a 1.5L turbocharged PFI production gasoline engine and the compression ratio is changed from 9.3 to 11.5. The results show that the fuel reduction is 4.5% at 2000rpm 5bar (20% EGR ratio) and 9.7 % at 3000rpm 10bar (20% EGR ratio) compared with no EGR case. But at boosted high loads the fuel consumption is almost same to the production engine due to high compression ratio which results in severe knocking. In order to further reduce fuel consumption, the engine is operated in lean burn conditions.