The one-dimensional gas dynamic modelling of unsteady flows in both the exhaust manifold and the silencing pipe system of a six-cylinder turbo-charged diesel engine has been carried out, calculating the wave motion induced in the muffling section downstream of a twin-entry turbine. Different silencers have been modelled via quasi-steady boundary conditions, whereas the wave action in the ducts has been calculated solving the hyperbolic system of conservation equations by three numerical techniques: the mesh-method of characteristics, the two-step Lax-Wendroff method and the MacCormack method. The pressure pulses and the s.p.l. spectrum have been evaluated downstream of the turbine, and the gas dynamic noise spectrum radiated from the tailpipe outlet has been predicted for each configuration. (A)
Abstract