Effects of injection timing and CO2 dilution on combustion and emissions behaviors of a stoichiometric GDI engine under medium load conditions

CO2 was introduced to intake, the effect of injection timing (IT) and CO2 dilution on combustion and emissions behaviors of a stoichiometric gasoline direct injection engine at medium load was analyzed and compared in order to assess the role of CO2 dilution under different ITs. Experimental results showed that for obtaining good combustion performance, ITCO2 = 0% > IT (added EGR, CO2 = 15%) > IT (added CO2, CO2 = 15%). Peak cylinder pressure (PCP), peak heat release rate and peak cylinder temperature first increased and then decreased as retarding IT, and their corresponding angle crank had opposite trends. At a constant IT, the order of PCP was as follows: PCP (CO2 = 0%) > PCP (added CO2, CO2 = 15%) > PCP (added EGR, CO2 = 15%). Added EGR or CO2 would keep CA50 and CA05-90 away from top dead center. The COVimep first decreased and then increased with retarding IT. At IT = 240 degrees CA BTDC, the BSCO added EGR, CO2 = 15% and BSCO added CO2, CO2 = 15% emissions were approximately 0.4 and 3 times higher than BSCO (CO2 = 0%) emission, respectively; the BSHC added EGR, CO2 = 15% and BSHC added CO2, CO2 = 15% emissions were approximately 4.8% and 11.9% higher than BSCO (CO2 = 0%) emission, respectively; and the BSNOX (added CO2, CO2 = 15%) and BSNOX (added EGR, CO2 = 15%) emissions were approximately 11.2% and 58.7% lower than BSNOX (CO2 = 0%) emissions, respectively.

Automated summary

This study analyzed and compared the effects of adding CO2 and retarding injection timing on combustion and emissions behaviors of a gasoline direct injection engine. The results showed that adding CO2 reduced peak cylinder pressure and heat release rate, and had an impact on cylinder temperature.