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The quest for high efficient internal combustion engines has intensified in the last years due to, among other reasons, increasing fuel costs and the pressure to reduce environmental deterioration. One of the possible alternatives capable of providing the sought efficiency gains is the recovery of the energy wasted in the exhaust gases and turbo-compounding is one obvious option. Compression ignition engines are usually the target of turbo-compounding, however, the rising interest for alternative fuels could result in the use of turbo-compounding for spark ignition engines as well. Due to its different flame propagation mechanism, spark ignition engines may force operation at higher fuel-air ratios, eventually creating a quite distinctive operational behavior.

Health related problems in over populated areas are a major concern and as such, there are specific legislations for noise generated by transport vehicles. In diesel powered commercial vehicles, the source for noise are mainly related to rolling, transmission, aerodynamics and engine. Considering internal combustion engine, three factors can be highlighted as major noise source: combustion, mechanical and tailpipe. The tailpipe noise is considered as the noise radiated from the open terminations of intake and exhaust systems, caused by both pressure pulses propagating to the open ends of the duct systems, and by vortex shedding as the burst leaves the tailpipe (flow generated noise). In order to reduce noise generated by vehicles, it is important to investigate the gas interactions and what can be improved in exhaust line design during the product development phase.