Investigation and design of an alternative exhaust system for minimum noise, power loss, and pollutant emissions: A theoretical, computational, and experimental approach.

Abstract

The primary function of automotive exhaust systems is the reduction of noise and pollutant levels in the exhaust gases of internal combustion engines. Existing three-way catalysts are effective at converting harmful pollutants to relatively non-toxic gasses when the engine is operated near stoichiometric and sufficient light-off temperatures are achieved within the catalyst. Silencers are utilized to reduce sound pressure levels in the exhaust to acceptable levels, but degrade engine power due to increased back pressure. The study proposes to modify conventional exhaust systems by incorporating the manifold, muffler, and catalyst (MMC) into a single unit. Catalyst light-offtimes and therefore pollutant outputs are improved by reducing exhaust gas heat losses prior to entering the catalyst brick. The expansion volume early in the exhaust stream attenuates sound levels and reduces the need for downstream muffling. The use of less restrictive silencers reduces engine back pressure and therefore improves engine performance. The study first validates the design through analytical means followed by computational simulations and offers further development of the simulation code. Finally, the design is verified through experimental work. Flow bench and impedance tube experiments are used in optimizing the final design. Lastly, experimental procedures are developed for evaluating the alternative designs with fired engine experiments. The investigation finds considerable merit for the design in terms of improved catalyst light-off time, engine performance, and sound attenuation.