Effect of Engine Parameters on Mixture Stratification in a Wall-Guided GDI Engine - A Quantitative CFD Analysis 2017-01-0570

Today, GDI engines are becoming very popular because of better fuel economy and low exhaust emissions. The gain in fuel economy in these engines is realized only in the stratified mode of operation. In wall-guided GDI engines, the mixture stratification is realized by properly shaping the combustion chamber. However, the level of mixture stratification varies significantly with engine operating conditions. In this study, an attempt has been made to understand the effect of engine operating parameters viz., compression ratio, engine speed and inlet air pressure on the level of mixture stratification in a four-stroke wall-guided GDI engine using CFD analysis. Three compression ratios of 10.5, 11.5 and 12.5, three engine speeds of 2000, 3000 and 4000 rev/min., and three inlet air pressures of 1, 1.2 and 1.4 bar are considered for the analysis. The CONVERGE software is used to perform the CFD analysis. Simulation is done for one full cycle of the engine. The CFD models used are validated with the available experimental results in the literature to the extent possible. The mixture stratification is quantitatively estimated by a new method developed by the authors. From the results, it is found that, the mixture stratification is better at low engine speeds and low inlet air pressure. Also, it is found that higher stratification index (SI) resulted in low heat release rate.