Effect of Fuel Injection Mode on Performance and Emission Characteristics of a Spark-Ignition Engine—A Computational Fluid Dynamics Analysis 2021-01-5065

Gasoline direct injection (GDI) engines are well known for their ability to operate at the stratified fuel-air mixture, and thereby they are highly efficient than port fuel injection (PFI) engines. However, the stratification of the in-cylinder mixture leads to higher nitrogen oxides (NO_x) and soot emissions with lower hydrocarbon (HC) emissions. The PFI works under a homogeneous mixture, which leads to lower NO_x and soot emissions with compensation of HC emissions. By combining the advantages of GDI and PFI modes, it is possible to achieve higher fuel efficiency with lower emissions. Therefore, in the present study, four different injection strategies, namely, pure GDI, gasoline-direct multiple-injection (GDMI), combined GDI with PFI (GDI-PFI), and pure PFI are investigated under various load conditions using computational fluid dynamics (CFD) analysis. The effect of these strategies on mixture formation, indicated mean effective pressure (IMEP), and emissions are evaluated. For the analysis, the equivalence ratio (ER) is varied from 0.5 to 0.9 under naturally aspirated conditions. From the results, it is found that in the GDI-PFI mode, at the split fraction of 0.6 and ER of 0.9, the NO_x and soot emissions are at the minimum levels because of good partial stratification. The IMEP improved by about 10.6% and the HC emissions reduced by about 82.8% than that of the corresponding GDMI mode. However, the NO_x and soot emissions increased by about 39.4% and 9.24%, respectively compared to that of the corresponding GDMI modes. Also, the average flame speed for the GDMI mode with the split fraction of 0.6 and ER of 0.9 is higher by about 3% than that of the GDI-PFI mode.