An apparatus and method are provided for a drone elimination muffler to attenuate drone exhibited by engine exhaust systems. The drone elimination muffler comprises a hollow canister having a length and a diameter, and a tuned port comprising a first end connected to the canister and a second end connected to the exhaust system. The canister operates in concert with the tuned port as a dampener configured to substantially attenuate exhaust drone, or resonance, at one or more frequencies of engine operation. A valve is configured to switch the drone elimination muffler between a closed state in which the exhaust system operates without acoustic influence due to the drone elimination muffler, and an open state in which the drone elimination muffler directly influences the acoustic properties of the exhaust system.

A vehicle exhaust system includes an exhaust component having an outer surface and an inner surface that defines an internal exhaust component cavity. At least one hole is formed in the exhaust component to extend through a wall of the exhaust component from the outer surface to the inner surface. A member is formed from a resistive material and is configured to overlap the at least one hole. At least one spacer is configured to space the member away from the inner or outer surface of the exhaust component to create an open cavity between the member and the exhaust component. In one example, an actuator is configured to cover and uncover the member dependent upon an operating characteristic to vary damping.

An apparatus and method are provided for a drone elimination muffler to attenuate drone exhibited by engine exhaust systems. The drone elimination muffler comprises a hollow canister having a length and a diameter, and a tuned port comprising a first end connected to the canister and a second end connected to the exhaust system. The canister operates in concert with the tuned port as a dampener configured to substantially attenuate exhaust drone, or resonance, at one or more frequencies of engine operation. A valve is configured to switch the drone elimination muffler between a closed state in which the exhaust system operates without acoustic influence due to the drone elimination muffler, and an open state in which the drone elimination muffler directly influences the acoustic properties of the exhaust system.

A silencer for noise reduction at an internal combustion engine is disclosed. The silencer comprises an input opening, an output opening, at least one chamber, and at least one partition configured to be inserted into and removed from the at least one chamber to convert the silencer to a collector.

A work vehicle having an engine that generates exhaust gases flowing through an exhaust flow path to an exhaust vent includes a nitrogen-oxide (NOx) reduction device, a particulate filter, a temperature sensor sensing a temperature associated with the exhaust gases, and a plurality of flow control devices in the exhaust flow path between the engine and the exhaust vent. The plurality of flow control devices are operable to define a first flow path when the sensed temperature is less than a predetermined temperature threshold and a second flow path otherwise. The NOx reduction device is upstream of the particulate filter relative to the exhaust flow path in the first flow path and the particulate filter is upstream of the NOx reduction device relative to the exhaust flow path in the second flow path.

An exhaust duct assembly for conveying exhaust gases emanating from a combustion zone to atmosphere is disclosed. The assembly includes: an exhaust gas outlet for exhausting exhaust gas into the atmosphere; and an acoustic duct portion located upstream of the exhaust gas outlet, the acoustic duct portion having a peripheral wall defining a through-passage arranged and constructed to promote propagation of sound there-through. The acoustic duct portion has a length in a flow direction that is at least 50% of an average hydraulic diameter of the through-passage.

A sound damper for a fuel-cell system includes a tubular sound-damper casing made of plastic material. The casing is elongate in the direction of a sound-damper longitudinal axis. A first sound-damper end piece made of plastic material is fixed to the sound-damper casing at a first axial end of the sound-damper casing. A second sound-damper end piece made of plastic material is fixed to the sound-damper casing at a second axial end of the sound-damper casing. On at least one sound-damper end piece, at least one fastening element is provided for fastening the sound damper to a support structure.

A silencer for noise reduction at an internal combustion engine is disclosed. The silencer comprises an input opening, an output opening, at least one chamber, and at least one partition configured to be inserted into and removed from the at least one chamber to convert the silencer to a collector.