Effect of Engine Parameters on Mixture Stratification in a Wall-Guided GDI Engine – A Quantitative CFD Analysis

Paper #:
  • 2017-01-0570

Published:
  • 2017-03-28
Abstract:
Today, gasoline direct injection (GDI) engines are becoming popular because of their better fuel economy and reduced emissions. The gain in fuel economy in GDI engines is realized when the engine runs on stratified mode of operation. In wall-guided GDI engines, the mixture stratification in the engine cylinder is realized by properly shaping the combustion chamber. However, the level of mixture stratification varies significantly with the engine operating conditions viz., compression ratio, engine speed, conditions of the air at the inlet, in-cylinder flow structure etc. In this study, an attempt has been made to understand the effect of engine operating parameters viz., compression ratio, engine speed and intake air pressure on the level of mixture stratification in a four-stroke wall-guided GDI engine using computational fluid dynamics (CFD). Three compression ratios viz, 9.5, 10.6 and 11.5, three engine speeds viz., 2000, 3000 and 4000 rev/min., and three intake air pressures viz., 1, 1.2 and 1.4 bar are considered for simulations. The CONVERGE software is used to perform the numerical analysis. Cu-cell Cartesian grid is used for mesh generation. PISO algorithm along with Rhie-chow scheme is used to solve pressure velocity coupling. Flow turbulence is analyzed using RNG k-ε model and fuel spray break up and atomization is analyzed by using the kh-rt model. Simulation results are presented for one full cycle. The CFD models used, in this study, are validated with the experimental results available in the literature to the extent possible. Mixture stratification is quantitatively estimated by a new method developed by the authors based on the mixture distribution at all regions in the engine cylinder. The effect of certain engine parameters on mixture formation and in-cylinder distribution are thoroughly investigated.
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