Development of Optimisation Methodologies for the Internal Combustion Engine Airbox

Abstract

The geometrical design of the airbox for an internal combustion engine has a significant effect on the pressure loss in the entire inlet tract. Due to the location of the airbox, its size and shape is usually limited as a result of the proximity to other under-bonnet features. The shape is also limited by manufacturing, assembly and NVH considerations. The complexity of the unsteady flow through the airbox and the constraints placed upon it by the available volume in the under-bonnet area make this a challenging design task. This work attempts to lay the foundations for a robust optimization strategy for the design of an airbox by coupling a 3D-steady flow Computational Fluid Dynamics (CFD) model to an automatic optimization process. The objective is to formulate a strategy that can be built upon in future to encompass unsteady flow and multi-cylinder engines. The work reviews the current thinking on methods used to optimize CFD problems and how this would apply to the optimization of an airbox for an internal combustion engine. The investigation then continues to detail the findings of the initial validation work on the CFD method for predicting the pressure loss through an airbox. Two simple airboxes are tested on a steady flow rig and the results compared to the CFD predictions. An optimization case study is then presented based on one of the models used for the initial validation. The study compares three different optimization techniques and then validates the results by testing the optimum design found by each method. A second case study is then undertaken to further validate the results using more flexible optimization software.