Effect of Mixture Distribution on Combustion and Emission Characteristics in a GDI Engine – A CFD Analysis

Paper #:
  • 2017-24-0036

  • 2017-09-04
Mixture distribution in the combustion chamber of gasoline direct injection (GDI) engines significantly affects the combustion, performance and emission characteristics. The mixture distribution in the engine cylinder in turn depends on many parameters viz., fuel injector hole diameter and orientation, fuel injection pressure, start of fuel injection, in-cylinder fluid dynamics etc. In these engines, the mixture distribution is broadly classified as homogeneous and stratified. However, with the currently available engine parameters it is difficult to objectively classify the type of mixture distribution. In this study, an attempt is made to objectively classify the mixture distribution in GDI engines using a parameter called the “stratification index”. The analysis is carried out on a four-stroke wall-guided GDI engine using computational fluid dynamics (CFD). All the CFD sub-models used in this study are validated with the experimental and CFD results available in the literature before carrying out analysis. Three types of mixture distributions viz., ideally homogeneous, ideally stratified and mal-distributed mixtures are defined and their combustion, performance and emission characteristics are analyzed. Further, the effect of fuel injector orientation on mixture distribution in the combustion chamber is analyzed for three different orientations of the injector viz., 30, 50 and 70 degree with the vertical. The mixture distribution for the three fuel injector orientations is compared with the ideal cases using the stratification index., Then the variation in performance and emission characteristics for different mixture distribution patterns is compared with those of the ideal cases to understand the effect of the fuel injector orientation.
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