Combined effects of excess air ratio and EGR rate on combustion and emissions behaviors of a GDI engine with CO2 as simulated EGR (CO2) at low load

Exhaust gas recirculation (EGR) is one of the most measure to decrease NOX emissions in the cylinder. CO2 was introduced to intake charge as a simulated EGR (CO2), the combined effects of excess air ratio and EGR rate on combustion and emissions behaviors of a gasoline direct injection (GDI) engine with simulated EGR (CO2) at low load were analyzed and compared to assess the difference between actual EGR and simulated EGR (CO2). The results show that EGR slows combustion, and simulated EGR (CO2) deterioration combustion is weaker than actual EGR. The peak cylinder pressure, heat release rate and cylinder temperature of simulated EGR (CO2) all increase and their phases all advance compare to actual EGR under the same EGR rate and excess air ratio. Combustion center and combustion duration for simulated EGR (CO2) delay slowly with EGR rate at any excess air ratios. Simulated EGR (CO2) can significantly improve the COVimep of the engine. For actual EGR rate > 10% and excess air ratio of 1.2, the COVimep sharply increases. Simulated EGR (CO2) has a little effect on CO emission at lean-burn condition, and on HC emission at stoichiometric condition. The NOX and soot emissions decrease significantly with EGR rate under different forms of EGR and excess air ratios. At a fixed EGR rate, the soot emissions of simulated EGR (CO2) is higher than that of actual under any excess air ratios. Added 10-15% CO2 to intake charge, CO2 as simulated EGR (CO2) can be well applied in GDI engine.