To study the effects of intake port structure parameters (inlet area and throat area) of a gasoline direct injection engine on mixture formation, a steady-flow test and transient simulation with four kinds of intake ports (named Cases 1–4) were simulated using AVL FIRE; a four-valve, four-cylinder gasoline direct injection engine with Case 1 was also operated under wide-open-throat conditions with a speed of 5500 r/min as the test basis. According to the simulation results, the flow coefficient increased with an increase in throat and decrease in inlet areas; however, a reverse change of them can improve the tumble ratio. In addition, the tumble ratio in a cylinder can be increased by reducing the throat and inlet areas. However, the concentration is not notable at high-speed wide-open-throat conditions. A larger tumble ratio and stronger turbulent kinetic energy intensity of in-cylinder flow are beneficial to form a homogeneous mixture, which ensures a better distribution of air–fuel mixture at ignition time. Moreover, larger inlet area and smaller throat area ensure less NO emissions.
