The hybrid vehicle engines modified for high exhaust gas recirculation (EGR) is a good choice for high efficiency and low NOx emissions. However, high EGR will dilute the engine charge and may cause serious performance problems, such as incomplete combustion, torque fluctuation, and engine misfire. An efficient way to overcome these drawbacks is to intensify tumble leading to increased turbulent intensity at the time of ignition. The enhancement of turbulent intensity will increase flame velocity and improve combustion quality, therefore increasing engine tolerance to higher EGR.
To achieve the goal of increasing tolerance to EGR, this work reports a CFD investigation of high tumble intake port design using STAR-CD. The validations had been performed through the comparison with PIV experimental tests. An assessment of the standard κ-ε (SKE), renormalization group (RNG) κ-ε, and Reynolds stress model (RSM) turbulence models was performed for a series of intake valve lift and intake pressure combinations. The results indicate that SKE is the best suited over RNG and RSM models because it is most accurate, within the parameters of the current test conditions. The investigation of parameter sensitivity study is also presented. After validation, a transient study was performed on a straight-shape intake port model by adding an upper vane. The resulting tumble ratio in the modified intake port has a much larger peak value: about twice the original peak. This indicates that airflow is well organized and the momentum provided by the intake port is also well preserved in modified design. In the modified design, the well-preserved tumble breaks up through the end of compression, which will transfer the energy stored as tumble into kinetic turbulence energy. It is found that the turbulent kinetic energy in the modified case is twice that of the original version when tumble breaks up, which will greatly improve the combustion quality and increase tolerance to EGR.