Laboratoire d'Acoustique, URA 1101 CNRS, Ave. Olivier Messiaen, BP 535, 72017 Le Mans Cedex, France
Excitation of eigenmodes in intake and exhaust manifolds of multi-cylinder internal combustion engine is investigated. It is shown that some of the eigenmodes do not depend very much on the intake, and exhaust systems are jointing behind the manifold. The sound increase (particularly for an asymmetrical excitation) caused by these modes depends on the degree of the asymmetry of the manifold and on sound energy dissipation in the manifold. Under some conditions this increase is the reason for resonance sound radiation. The tendency for resonance excitation at the branch of intake (exhaust) pipes with mufflers is considered to be one of the criteria in assessing the quality of manifold construction. Special attention is paid to the asymmetrical exhaust and intake manifolds of trucks. It is shown that the influence of the manifolds design of their engines allows a decrease truck intake and exhaust noise in a wide range of crankshaft RPM.