Exhaust System Optimization via 1D Simulation of a High-Performance SI Engine

Nowadays, the limits of acoustic vehicle emissions imposed by the regulations are progressively reducing. One of the most important noise sources is the engine, mainly from the side of the exhaust system, therefore it has to be kept under control. However, supercars need to make the engine “roar” as much as possible because the sound emitted from the tailpipe is one of their distinguishing features. In this scenario, the present thesis work has been developed, aiming at fulfilling both the requirements. The project has been conducted in POWERTECH Engineering S.r.l., a consultancy company providing CAE simulation services to the powertrain and vehicle industries, in collaboration with Automobili Lamborghini S.p.A., the iconic super-sports car manufacturer. GT-SUITE, a 1D-CFD software developed by Gamma Technologies, has been used for the simulations. In the first part of the project, the provided model has been transformed to be suitable for acoustic investigations, and steady-state analysis of the exhaust system has been conducted, both on the original line and on a modified version. Subsequently, a sensitivity analysis has been carried out, leading to the development of an optimized configuration, with benefits on both backpressure and acoustic emissions. In the second part of the work, transient simulations have been executed in order to replicate the actual manoeuvres performed by the vehicle during acoustic approval tests. After analysing the data, it has been possible to determine the correct engine speed to be used as the opening threshold of the exhaust bypass valve.