Analysis of parameters influencing acoustics and performance in a high specific power engine

This master thesis, developed in Powertech Engineering Srl, is a parametric study concerning the engine-related parameters, to identify their influence on performance and acoustics. Powertech, born as a spin-off of Politecnico di Torino, is a consulting company which works in the field of 1D powertrain simulation and 3D computational fluid-dynamics. The work has been developed for Ferrari SpA, with the aim of giving them a support to find the best engine setup from both performance and sound viewpoints. GT-POWER was the software used during the whole thesis. It is included in GT-SUITE, of which Powertech is the technical representative for Italy. Being a 1D code, its potentials in the trade-off between simulation accuracy and computational time make it a suitable tool to perform such kind of numerical analyses and provide to the client, step by step, the results of the simulations. This allows the car manufacturer to have at disposal, during the design phase of a project, a precious set of data that is at the base of the following experimental testing and validation phase. The work was structured in this way: first a preliminary study on a mono-cylinder spark-ignition (SI) engine was carried out, with the intent of initially simplifying the analysis by separating as much as possible any effect of any parameter.?? The results of this first step turned out to be an important background for the subsequent study on an in-line 4-cylinder SI engine, which is the bulk of the thesis work. It can be stated that the first study was an “idealized” one, carried out by a pure analytic approach (so by isolating the cause of the observed effects, whenever possible), thanks to the simplicity of the model. On the other hand, the second study was a more “physical” one, meaning that it was carried out on an engine capable to give more realistic results in terms of acoustics (for example the interaction among the exhaust flows of the cylinders that influence the wave propagation phenomena could not be accounted for with a single cylinder). It must be said that these models are generic, since the aim of the activity is to provide a technical advice about the impact that engine parameters have on the performance and acoustic characteristics of the engine itself. The simulations were run in steady-state conditions and at full load of the engine. The results selected during the post-processing phase were the main performance ones (brake torque, power, volumetric efficiency, pressure and temperature at inlet/outlet of turbo components and so on), together with acoustics-related results. These latter include basically the instantaneous pressure signals at some significative points of the engine exhaust system, the instantaneous velocity at tailpipe exit, the Fast Fourier Transform (FFT) of these signals and the acoustic results in the strict sense; these are the total pulsation Sound Pressure Level (SPL) measured at a certain point from the exhaust tailpipe and its constituting harmonics. For each engine parameter that was varied, a comparison was performed with the baseline engine model (which is the model “as-received”, with some modifications if needed), and conclusions were drawn on the impact of the parameter itself on performance and acoustics, with a clear goal: trying to optimize the engine sound without jeopardizing its performance.