Visualization and pod analysis of spray variations in a gasoline direct-injection engine at different fuel injection pressures including split injection and macroscopic spray characteristics

In a gasoline direct-injection engine, the efficiency of the combustion process relies heavily on the quality of the fuel–air mixture, which typically depends on fuel injection parameters and spray characteristics. The core of this work is to study the effect of fuel injection pressure on cycle-to-cy-cle variations (CCV) and macroscopic characteristics of spray at early injection conditions including split injection with homogeneous stoichiometric charge. A single-cylinder gasoline direct-in-jection (GDI) engine was used for fuel spray visualization with optical access and a high-pressure direct-injection 7-hole injector was used with fuel pressures of 5 MPa and 10 MPa. The Mie scat-tering technique was employed to visualize the liquid phase of fuel dispersion with early injection timing of 210 crank angle degree (CAD) before the top dead center (BTDC) of compression. A quantitative analysis of spray variations was performed with the aid of proper orthogonal decomposition and no significant cycle-to-cycle spray variations were detected. However, comparing different injection pressures, the spray variations were relatively higher at an injection pressure of 5 MPa than at 10 MPa. The study of macroscopic characteristics showed that the spray tip pene-tration length and area were higher for 10 MPa when compared to 5 MPa. The injection timings for split (dual) injection were 210 CAD and 120 CAD BTDC of compression for the 1st and 2nd pulse, respectively, and observations revealed that the 2nd pulse of split injection had lower variations when compared to both 1st pulse of split injection and single injection.