Numerical studies on the combustion and liquid fuel films characteristics with the dependence on injection and spark timing of GDI engine

GDI(Gasoline direct injection) engine can be one of the solutionsto increase the fuel efficiency and reduceNOx(nitrogen oxide) emissions. TheLFF (liquid fuel film) formation within the engine cylinder due to direct injection is an impediment to both fuel efficiency and environment problems. To achieve the proper operating conditions, liquid fuel film formation and combustion characteristics in the cylinder of GDI engine must be investigated. The numerical simulations for the characteristics of GDI engine including the effect of both fuel injection and spark timing have been carried out to optimize the liquid fuel film phenomenon and combustion characteristics. In this study, 3D unsteady Eularian-Langrangian two-phase model was used to obtain an optimal operating condition of a GDI engine by using S/W STAR-CD (CD-adapco). The k-ε/RNG model was used as a turbulence model. Simulation results indicate the flow field and mixture distribution inside the cylinder to obtain subsequent combustion and emission characteristics. Moreover, conditions minimizing the amount of LFF withincylinderhave been suggested. The results show that the evaporation rate is improved in early injection timing. Fuel uniformity tends to be higher as the start of injection, in short SOI, advances due to improvement in mixing duration with the intake air and evaporation rate. Total film mass has been remarkably reduced when SOI is BTDC_comp120 CA. When SOI is BTDC_comp140CA, maximum peak pressure appears approximately 38.97 bar having the highest among cases. For the effect of spark timing, no difference of the flow field was observed inside the cylinder. Peak pressure, peak temperature, NO formation has increased when the spark timing advances. Peak pressure is more sensitive to the effect of spark timing than peak temperature.