A system for protocol processing in a computer network has a TCPIP Offload Network Interface Device associated with a host computer. A shutter assembly is located at the container opening, having at least one shutter opening formed therein. The said chambers respectively communicate with the intake pipe and with the outlet pipe, or vice versa, in such a way that, during use, the flow of the engine exhaust gases that traverses the shell passing from the intake pipe to the outlet pipe is forced to traverse the aforesaid filtering elements, thus assuming a component of radial velocity with respect to the longitudinal axis of the shell.