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One dimensional CFD codes are standard tools for engine development, in particular for the optimization of intake and exhaust systems. However, the accurate prediction of both engine brake performance and acoustic outputs is not that trivial. A quite critical issue is the modeling of complex engine components, such as air cleaners, plenums, exhaust junctions, silencers, etc. A trade-off is required in order to balance the accuracy of the acoustic analysis and the computational cost, particularly when DOE techniques have to be applied. In this paper a methodology for an integrated acoustic and performance analysis of a high performance SI engine is described. An engine simulation model has been built by using a commercial software, and it has been validated against experiments, finding a good agreement. It is remarked that the measurements of both acoustic and engine performance parameters are taken by using standard facilities and equipment, no anechoic test bench is required.

The paper reviews the transformation of a 2.8 litre, 4 cylinder, turbocharged Diesel engine, produced by VM Motori (Cento, Italy), into a Compressed Natural Gas (CNG) naturally aspirated power unit. The main goal of the project is to keep an about constant top power value, minimizing engineering costs. The development of the new engine has been supported by experiments and 1D cycle simulations. A first prototype has been built and extensively tested at the dynamometer bench. These data helped the validation of the simulation model, which has been used as an optimisation tool, addressing the next steps of the development process.