Silencer and a method of operating a vehicle

A device for silencing a gas flow directed therethrough and being adapted for installation in a flow system, said device comprising:

• a casing,
• at least one acoustic chamber contained in the casing, said chamber being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
• at least one, passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
• said device showing at least two transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• at least one passage selected from said at least one passage being curved,
• wherein the following applies to at least one selected chamber selected from said at least one acoustic chamber:
• the mean cross-sectional area Aj of each of said selected chamber is at least four times the largest of:
• the sum of all cross-sectional areas of passages leading gas to the selected chamber, a1, and
• the sum of all cross-sectional areas of passages leading gas from the selected chamber, a2,
• the mean cross-sectional area, Aj, being defined as the mean value of all cross-sectional areas along a mean trajectory for sound waves travelling from across the selected chamber,
• the volume of the at least one selected chamber, Vj, is at least 8({square root over ((a1+a2)/2)})3, a1 and a2 being defined as stated above,
• the cross-sectional area, Aj, and the volume, Vj, including any elements belonging to sound absorptive material inside the selected chamber and any other parts being in acoustic communication with the selected chamber,
• said at least one passage being curved having an acoustically effective length L which is at least 1.50 times the direct and straight distance in space between passage inlet and passage outlet.

A device for silencing a gas flow directed therethrough and being adapted for installation in a flow system, said device comprising:

• a casing,
• at least two acoustic chambers contained in the casing, said chambers being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least two acoustic chambers,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least two acoustic chambers to another of the at least two acoustic chambers or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least two acoustic chambers,
• said device showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• said inlet pipe being continued by a flow deflecting element causing the gas to flow with a radial component and for causing pressure recovery to the flow upstream of a first one of said at least two acoustic chambers, wherein said passage comprises at least one diffuser for leading the gas flow into a second one of said at least two acoustic chambers, the diffuser of said passage being of an annular diffuser,
• wherein the average sound attenuation {overscore (ΔdB)} conferred by each transition of cross-sectional area, approximated by the following expression:
• Δ ⁢ ⁢ dB _ = 1 n ⁢ k ⁢ ∑ i = 1 n ⁢ log 10 ⁢ A i a i ,
• n being the total number of transitions of cross-sectional area of the device, Ai being the relatively higher cross-sectional area at the i′th transition of cross-sectional area of the gas flow, ai being the relatively lower cross-sectional area at the i′th change of cross-sectional area of the gas flow, k being a constant of the value 6.25 dB,
• is at least
• 6.0 dB when the device comprises no more than two acoustic chambers,
• 5.0 dB when the device comprises three acoustic chambers,
• 4.0 dB when the device comprises 4 or more acoustic chambers.

A method of operating a vehicle comprising a combustion engine and a silencing system, the silencing system comprising a silencer, optionally an exhaust connecting pipe and optionally a tail pipe, said method comprising adapting the silencing system so that its maximum back pressure contributed by the silencing system is at most 1000 mmWG, the silencer being a silencer selected from

• (A) a silencer comprising:
• a casing,
• at least one acoustic chamber and contained in the
• casing, said chamber being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
• said silencer showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• the silencer fulfilling the following criteria:
• the average sound attenuation {overscore (ΔdB)} conferred by each transition of cross-sectional area, approximated by the following expression:
• Δ ⁢ ⁢ dB _ = 1 n ⁢ k ⁢ ∑ i = 1 n ⁢ log 10 ⁢ A i a i ,
• n being the total number of transitions of cross-sectional area of the silencer, Ai being the relatively higher cross-sectional area at the i′th transition of cross-sectional area of the gas flow, ai being the relatively lower cross-sectional area at the i′th change of cross-sectional area of the gas flow, k being a constant of the value 6.25 dB,
• is at least
• 2.9 dB when the device comprises no more than two acoustic chambers,
• 1.8 dB when the device comprises three acoustic chambers,
• 1.1 dB when the device comprises 4 or more acoustic chambers,
• the pressure loss across each acoustic chamber expressed as the dimensionless parameter ζj′, defined as the ratio between the static pressure loss over the chamber and the dynamic pressure at a location in said passage:
• ζ j ′ = Δ ⁢ ⁢ p j 1 2 ⁢ ρ ⁢ ⁢ u 2 ,
• Δpj being the static pressure loss over the j′th chamber, exclusive of the static pressure loss over a monolith optionally comprised in the j′th chamber, ρ being the density of the gas at said location, u being a velocity of the gas at said location, preferably the mean gas velocity,
• is at the most 1.5,
• (B) a silencer comprising
• a casing,
• at least one acoustic chamber contained in the casing, said chamber being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
• said silencer showing at least two transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• at least one passage selected from said at least one passage being curved,
• wherein the following applies to at least one selected chamber selected from said at least one acoustic chamber:
• the mean cross-sectional area Aj of each of said selected chamber is at least four times the largest of:
• the sum of all cross-sectional areas of passages leading gas to the selected chamber, a1, and
• the sum of all cross-sectional areas of passages leading gas from the selected chamber, a2,
• the mean cross-sectional area, Aj, being defined as the mean value of all cross-sectional areas along a mean trajectory for sound waves travelling from across the selected chamber,
• the volume of the at least one selected chamber, Vj, is at least 8({square root over ((a1+a2)/2)})3, a1 and a2 being defined as stated above,
• the cross-sectional area, Aj, and the volume, Vj, including any elements belonging to sound absorptive material inside the selected chamber and any other parts which are in acoustic communication with the selected chamber,
• (C) a silencer comprising
• a casing,
• at least two acoustic chambers contained in the casing, said chambers being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least two acoustic chambers,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least two acoustic chambers to another of the at least two acoustic chambers or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least two acoustic chambers,
• said silencer showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower;
• cross-sectional area ai and a relatively higher cross-sectional area Ai,
• said inlet pipe being continued by a flow deflecting element causing the gas to flow with a radial component and for causing pressure recovery to the flow upstream of a first one of said at least two acoustic chambers, wherein said passage comprises at least one diffuser for leading the gas flow into a second, one of said at least two acoustic chambers, the diffuser of said passage being of a different type than a radial diffuser.

A method of operating a spark-ignited or compression-ignited engine and a silencing system, the silencing system comprising a silencer, optionally an exhaust connecting pipe and optionally a tail pipe, the engine being a stationary engine or an engine placed on a ship, an oil-rig or a barge, said method comprising adapting the silencing system so that its maximum back pressure contributed by the silencing system is at most 400 mmWG, the silencer being a silencer selected from

• (A) a silencer comprising:
• a casing,
• at least one acoustic chamber and contained in the casing, said chamber being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
• said silencer showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• the silencer fulfilling the following criteria:
• the average sound attenuation {overscore (ΔdB)} conferred by each transition of cross-sectional area, approximated by the following expression:
• Δ ⁢ ⁢ dB _ = 1 n ⁢ k ⁢ ∑ i = 1 n ⁢ log 10 ⁢ A i a i ,
• n being the total number of transitions of cross-sectional area of the silencer, Ai being the relatively higher cross-sectional area at the i′th transition of cross-sectional area of the gas flow, ai being the relatively lower cross-sectional area at the i′th change of cross-sectional area of the gas flow, k being a constant of the value 6.25 dB,
• is at least
• 2.9 dB when the device comprises no more than two acoustic chambers,
• 1.8 dB when the device comprises three acoustic chambers,
• 1.1 dB when the device comprises 4 or more acoustic chambers,
• the pressure loss across each acoustic chamber expressed as the dimensionless parameter □j′, defined as the ratio between the static pressure loss over the chamber and the dynamic pressure at a location in said passage:
• ζ j ′ = Δ ⁢ ⁢ p j 1 2 ⁢ ρ ⁢ ⁢ u 2 ,
• Δpj being the static pressure loss over the j′th chamber, exclusive of the static pressure loss over a monolith optionally comprised in the j′th chamber, □ being the density of the gas at said location, u being a velocity of the gas at said location, preferably the mean gas velocity,
• is at the most 1.5,
• (B) a silencer comprising
• a casing,
• at least one acoustic chamber contained in the casing, said chamber being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least one acoustic chamber,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least one acoustic chamber to another of the at least one acoustic chamber or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least one acoustic chamber,
• said silencer showing at least two transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• at least one passage selected from said at least one passage being curved,
• wherein the following applies to at least one selected chamber selected from said at least one acoustic chamber:
• the mean cross-sectional area Aj of each of said selected chamber is at least four times the largest of:
• the sum of all cross-sectional areas of passages leading gas to the selected chamber, a1, and
• the sum of all cross-sectional areas of passages leading gas from the selected chamber, a2,
• the mean cross-sectional area, Aj, being defined as the mean value of all cross-sectional areas along a mean trajectory for sound waves travelling from across the selected chamber,
• the volume of the at least one selected chamber, Vj, is at least 8({square root over ((a1+a2)/2)})3, a1 and a2 being defined as stated above;
• the cross-sectional area, Aj, and the volume, Vj, including any elements belonging to sound absorptive material inside the selected chamber and any other parts which are in acoustic communication with the selected chamber,
• (C) a silencer comprising
• a casing,
• at least two acoustic chambers contained in the casing, said chambers being through-flowed by gas,
• at least one inlet pipe for leading gas into one of said at least two acoustic chambers,
• at least one passage of a length L and of a representative cross-sectional area a for leading gas from each one of the at least two acoustic chambers to another of the at least two acoustic chambers or to an exterior environment or an exterior chamber,
• optionally one or more monolithic bodies comprised in each of one or more of said at least two acoustic chambers,
• said silencer showing at least two through-flowed transitions of cross-sectional area for the flow of the gas between a relatively lower cross-sectional area ai and a relatively higher cross-sectional area Ai,
• said inlet pipe being continued by a flow deflecting element causing the gas to flow with a radial component and for causing pressure recovery to the flow upstream of a first one of said at least two acoustic chambers, wherein said passage comprises at least one diffuser for leading the gas flow into a second one of said at least two acoustic chambers, the diffuser of said passage being of a different type than a radial diffuser.