CFD-Based Parametric Optimization of Intake Manifold Geometry for Improved Cyl-inder-to-Cylinder Air Distribution in a Four-Cylinder SI Engine

Abstract

Internal combustion engines require efficient air intake systems to optimize combustion and reduce emissions. The intake manifold plays a critical role in distributing the fresh air or air fuel mixture to each cylinder equally. Any imbalance leads to reduced volumetric efficiency and increased vibration. This study investigates the original intake manifold design of a four cylinder Toyota 4A-FE engine to address flow distribution issues. The primary objective is to evaluate the influence of geometric parameters on the aerodynamic performance of the manifold. To achieve this, a three dimensional model of the manifold was created using SolidWorks software. Numerical simulations were performed using ANSYS Fluent software with the standard k-ω SST turbulence model to capture the flow characteristics accurately. A parametric study was conducted by modifying the angles of the runners relative to the base floor at 36°, 37°, 39°, 41°, 43° and 45°, alongside varying the outlet widths between 40 mm and 50 mm. The computational results provided detailed insights into pressure distribution, velocity profiles, and mass flow rates across the four cylinders. By comparing the original manifold with the modified designs, the study identified the specific configuration that yields the most balanced cylinder to cylinder air distribution. The findings demonstrate that the optimal configuration, featuring a 45° runner angle and a 42.5 mm outlet width, significantly reduces flow imbalances. Specifically, this optimized design decreased the maximum velocity deviation among the cylinders by 62% and narrowed the mass flow rate distribution deviation by 40%, thereby promoting a highly uniform velocity field. This research provides a valuable structural framework for enhancing the performance of naturally aspirated engines through targeted manifold design modifications.