Combustion, performance and particulate matter emissions analysis of operating parameters on a GDI engine by traditional experimental investigation and Taguchi method

Despite the thermal efficiency improvement, gasoline direct injection (GDI) engines are facing with the problem of particulate matter (PM) emissions. In this study, the effects of control parameters (spark advance, injection pressure, excess air ratio and EGR) on the combustion, performance and particulate matter emissions of a GDI engine were investigated. Furthermore, Taguchi method was carried out to determine the optimal combination of factors for the specific best engine output by adopting orthogonal array experiment, and ANOVA analysis was applied to examine the influence levels of tested parameters. Experimental results showed that retarding ignition timing, rising injection pressure, adding proper amount of air and EGR diluents will all reduce particulate number (PN) concentration, and the later three methods will improve fuel economy either. Retarding ignition timing and EGR dilution will increase the fraction of nucleation mode particles, while the other two will reduce it. The optimal combination for the lowest PN is 17° spark timing, 7.0 MPa injection pressure, 60°CA ATDC injection timing and 20% cooled EGR at stoichiometric mode, and 17° spark timing, 7.0 MPa injection pressure, 90°CA ATDC injection timing and 20% cooled EGR at lean-burn mode. The most significant factor that affects NOX emissions and BSFC is EGR mode. Injection timing presents the highest contribution level to PN emissions, especially at lean-burn condition.