Effect of Fuel Injection Pressure on Mixture Stratification in a GDI Engine – a CFD Analysis

Paper #:
  • 2017-01-2317

  • 2017-10-08
The mixture preparation in gasoline direct injection (GDI) engines operating at stratified condition plays an important role in deciding the combustion, performance and emission characteristics of the engine. In a wall-guided GDI engine with a late fuel injection strategy, piston top surface is designed in such a way that the injected fuel is directed towards the spark plug to form a combustible mixture at the time of ignition. In addition, in these engines, fuel injection pressure and timing are also important to create a combustible mixture near the spark plug. Therefore, understanding the mixture formation under the influence of fuel injection pressure is very essential for the optimization of the engine parameters. In this study, an attempt has been made to understand the effect of fuel injection pressure on the mixture preparation in a four-stroke, four valve, and wall-guided GDI engine operating under a stratified condition by using computational fluid dynamics (CFD) analysis. Four fuel injection pressures viz., 90, 120, 150 and 180 bar are considered for the analysis. The CFD analysis is carried out by using the CONVERGE. The mixture preparation is objectively characterized by a new parameter called the “stratification index”, which is calculated based on the equivalence ratio (ER) at different zones inside the combustion chamber. All the CFD simulations will be carried out at an engine speed of 2000 rev/min., and compression ratio of 11.5, at an overall equivalence ratio of about 0.65. The fuel injection and spark timings will be maintained at 605 and 705 CADs respectively. In the full paper, the effect of fuel injection pressure on the extent of mixture stratification in the combustion chamber, and performance and emission characteristic of the engine will be analysed.
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