WO1994018438A1 - A silencer - Google Patents
A silencer Download PDFInfo
- Publication number
- WO1994018438A1 WO1994018438A1 PCT/DK1994/000049 DK9400049W WO9418438A1 WO 1994018438 A1 WO1994018438 A1 WO 1994018438A1 DK 9400049 W DK9400049 W DK 9400049W WO 9418438 A1 WO9418438 A1 WO 9418438A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- container
- silencer
- pipe
- silencer according
- flow
- Prior art date
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N1/00—Silencing apparatus characterised by method of silencing
- F01N1/08—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling
- F01N1/10—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling in combination with sound-absorbing materials
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N1/00—Silencing apparatus characterised by method of silencing
- F01N1/06—Silencing apparatus characterised by method of silencing by using interference effect
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N1/00—Silencing apparatus characterised by method of silencing
- F01N1/08—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling
- F01N1/085—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling using a central core throttling gas passage
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N1/00—Silencing apparatus characterised by method of silencing
- F01N1/24—Silencing apparatus characterised by method of silencing by using sound-absorbing materials
Definitions
- the present invention concerns silencers to reduce noise in flowing gas media, preferably for incorporation into exhaust pipes from internal combustion engines.
- Silencers for such uses are frequently either of the re ⁇ flection silencer type, absorption silencer type or a com ⁇ bination of these two types. Both are characterized by giving a wideband damping in the acoustic frequency spec ⁇ trum. Such a wideband damping is generally needed, since the unsilenced spectrum from the engine, although it may contain peaks, also contains a considerable share of all frequencies within the audible range.
- Both reflection and absorption silencers are based on si ⁇ lencing mechanisms in connection with one or more cham ⁇ bers, typically in a container having an admission pipe and an exhaust pipe.
- the silencing effect is obtained in the reflection silencer in that sound energy is reflected at cross-sectional transitions between pipes and chambers.
- the effect of the absorption silencer is obtained in that sound energy is transmitted to a sound absorbing material, e.g. mineral wool, in which oscillatory energy is dissi- pated by internal friction in the gas and by interaction between the gas and the fibres of the absorbent.
- the damping range in the frequency spectrum is different for the two silencer types. Since the effect of the ab- sorption silencer requires standing waves in the absor ⁇ bent, this gives a downward limitation in the spectrum. Also the effect of the reflection silencer is limited downwardly in the spectrum, viz. by the filter natural- frequency. This, however, is generally considerably lower. Thus, in many uses for internal combustion engines it is difficult to obtain sufficient low frequency damping with absorption silencer alone. This is of importance, since precisely the most powerful frequency in the unsilenced spectrum, generally the ignition frequency of the engine (attributable to the cyclic process of the engine) is relatively low. A pure reflection silencer, or a combined reflection and absorption silencer is thus generally ne ⁇ cessary.
- the pure reflection silencer has the weakness that inter ⁇ fering passage frequencies occur in its damping spectrum, i.e. declines in the damping spectrum. These declines can be attributed to standing gas oscillations in the cham ⁇ bers. In some cases a decline may be so pronounced that it actually involves negative damping at the characteristic frequency, i.e. this frequency is amplified.
- a known method of counteracting this decline comprises extending the admission pipe to the center of the first chamber.
- Such a geometry is expedient, because the basic natural frequency of a chamber has a pressure node pre ⁇ cisely at the center. This means that oscillatory energy emitted here can excite the basic natural oscillation in the chamber only to a limited degree. Furthermore, this avoids excitation of all higher order natural frequencies which also have a pressure node in the center of the chamber .
- the change in direction, from axial to radial flow, in ⁇ volved by the radial diffuser does not necessarily entail significant irreversibility in the flow. If the geometry of the diffuser is appropriate, flow separation can be avoided.
- a further advantage of using radial diffusers in reflec ⁇ tion silencers according to DK patent No. 128427 is that the transverse plate of the diffuser reflects sound. This provides a sound reducing effect which is added to the initially mentioned reflection effect caused by the cross- sectional transition (from pipe to chamber), and to the above-mentioned effect that can be obtained by pressure node positioning.
- the present invention is based on the finding that re ⁇ flection silencers having radial diffusers enable almost complete elimination of passage frequencies corresponding to standing gas oscillations axially in the chambers, but not standing gas oscillations transversely thereto. In some uses this is not considered to be a serious drawback, viz. when the mounting conditions make it natural to make the silencer elongated, so that the standing transverse waves correspond to relatively high frequencies that can be reduced relatively efficiently by means of the sound absorbent incorporated in the chambers.
- silencers e.g. where the mounting conditions make it necessary or expedient to select a shorter embodiment with a container diameter which is large with respect to the pipe diameter.
- the use of a radial diffuser involves reflection of sound at the transverse wall in the diffuser and pressure recovery, two of the properties which are advantageous, as described above.
- positioning to the chamber center in an axial direction, while being expe ⁇ trans principle is of less importance because of the disadvantage that exact positioning to the node of the basic natural frequency, which is more serious in this case owing to lower frequency, of standing waves trans- versely in the chamber is not possible.
- Transverse oscillations of passage frequencies are there ⁇ fore of greater importance in short silencers. But this may also be important in those cases where the length of the silencer is somewhat greater than the diameter, viz. in the event that the silencer contains several chambers, one or more of which being shorter than the diameter.
- French patent No. 800850 discloses a silencer of the type stated in the introductory portion of claim 1.
- This silencer is provided with a slot outlet along the shell walls in the silencer, which causes the gas flow to be conveyed into the chamber in the form of a thin veil. Since all rotation-symmetrical transverse os- dilations have their pressure maximum on the inner side of the shell, they will hereby be excited. Of this basi- cally infinite amount of oscillation modes, it is in prac ⁇ tice primarily the lower order modes, and in particular the basic oscillation in the transverse direction which may give rise to interfering passage frequencies.
- the object of the invention is to provide a silencer which exhibits improved properties with respect to damping of transverse oscillations in the chamber. This is achieved by the features defined in the charactering portion of claim 1.
- the exhaust gas discharge opening is thus positioned radially substantially symmetrically about the pressure node of a transverse oscillation in the container, and so that the outer plate or the discharge opening is spaced from the shell, it is possible to construct a silencer which exhibits improved properties with respect to damping of transverse oscillations in the chamber, in particular as regards lower order transverse oscillations.
- the frequency corresponding to the first over ⁇ tone in the transverse direction is particularly predomi ⁇ nant in the unsilenced spectrum before the silencer, and can therefore be given priority in the design of the fre ⁇ quency characteristic of the silencer.
- the subject-matter of claim 4 provides damping of trans ⁇ verse oscillations together with a reasonable damping of axial oscillations in the container.
- the subject-matter defined in claim 5 provides a diffuser effect of the medium flow and thus a lower back-pressure for the silencer.
- claim 7 or claim 8 provides an embodiment of the invention which is particularly easy to manufacture and thus inexpensive.
- fig- 1 shows a schematically axial section in a rotation- symmetrical embodiment of the invention
- fig. 2 shows another embodiment of the invention with a relatively flat design
- fig. 3 shows a distinctly flat embodiment with a reverse flow direction
- fig. 4 shows a fourth embodiment with a deflection of the exhaust gas without sharp bends
- fig. 5 shows an alternative embodiment of the invention
- fig. 5a shows a section at A-A in fig. 5
- fig. 6 shows a multi-chamber embodiment of the invention.
- Fig. 1 shows an axial section of a rotation-symmetrical embodiment of the invention.
- the silencer is here defined by a cylindrical shell 1 and by end bottoms 2 and 3.
- the gas flow is conveyed into the silencer from the inlet pipe 4 and is discharged from the silencer by the discharge pipe 5.
- the double-deflecting element is composed of an outer plate 6, which forms an abrupt bend at the contour K to form the cover plate 7, and of the curved inner plate 8 and of a plurality of radial ribs 9, which are welded to both the cover plate 7 and the inner plate 8 to retain the latter.
- Sound absorbents 10 and 11, respectively, pro ⁇ tected by perforated plates 12 and 13, are arranged around the inlet pipe 4 and behind the inner plate 8.
- Pressure oscillation modes of basic natural frequencies in the longitudinal direction as well as in the transverse direction are plotted in the figure. The positioning of the gas flow to the pressure node will appear from this.
- the node occurs approximately at two thirds of the radius, calculated from the center axis toward the inner contour of the shell. More precisely, the position can be calculated to 0.63 times radius. This re- suit occurs by the solution of the partial differential equation called wave equation, which describes the rota ⁇ tion-symmetrical, three-dimensional gas oscillation field in the chamber.
- the flow will be turbulent in most cases, i.e. the smooth flow along flow lines will be superimposed by random particle movements in all direc ⁇ tions.
- the average travel of such movements characterizes the degree of turbulence in the flow.
- This degree of tur ⁇ bulence is somewhat greater in the double-deflecting ele ⁇ ment than in a straight pipe flow, which involves a some- what greater friction loss.
- this loss is useful in the sense that it contributes to the resistive acoustic resistance of the element, i.e. is associated with a silencing effect.
- the double-deflecting element has a controlled turbulence degree.
- Fig. 2 shows another, distinctly flat embodiment of the invention.
- the outer plate is omitted here, the inlet end bottom 2 serving the dual function of forming part of the silencer boundary toward the surroundings and of forming the flow directing outer plate.
- the discharge pipe 5 is shown to be laterally directed with respect to the longi- tudinal axis of the otherwise rotation-symmetrical si ⁇ lencer.
- An embodiment according to fig. 2 may e.g. be expedient in case of a silencer which is positioned below the engine of a truck with a downwardly directed admission pipe from the engine, the extension of the exhaust pipe being horizontal along the undercarriage.
- the embodiment may e.g. be combined with an elongate silencer of a known type.
- Fig. 3 shows a third, likewise distincly flat embodiment of the invention.
- the inner plate co ⁇ incides with the other end bottom 3 in such a manner that the double directional change of the gas flow results in a veil-like inflow to the chamber directly against the flow direction in the admission pipe.
- Directional changes will here involve a particularly efficient sound reflection in the double-deflecting flow element.
- the embodiment according to fig. 3 is almost rotation-symmetrical; the only deviation from rotation-symmetry is that the dis- charge pipe 5 is secured to the end bottom 2 on a certain radius.
- the embodiment according to fig. 3 may e.g. be expedient in the positioning of a silencer below a truck engine like in fig. 2, but where the extension of the exhaust system is upward e.g. to a mouth at the level of the roof of the driver's cab.
- an elongate silencer of a known type may be incorporated in the upwardly directed discharge pipe.
- Fig. 4 shows a fourth embodiment of the invention. This embodiment differs from those described above in that the cover plate forms an extension of the outer plate 6 with ⁇ out sharp bends, so that the contour K is omitted. This reduces the sound-reflecting effect of the double-deflect ⁇ ing pipe element to some degree. But e.g. in case of gas flows having a great content of soot, this embodiment may be appropriate in order to prevent accumulation of soot in the corner which is included in the double-deflecting flow element embodied with the contour K.
- Figs. 5 and 5a show an embodiment of the invention in which the double-deflecting flow element is fork-shaped, enabling a split tangential flow veil into a silencer chamber.
- the veil flow is axial.
- An embodiment with a tangential veil may be expedient in those cases where the mounting conditions make it advisable to mount the admission pipe transversely to the shell 1, and not via the end bottom 2.
- the tangential veil flow in the embodiment according to fig. 5 involves a slightly reduced possibility of posi ⁇ tioning at the pressure node of transverse oscillations in the chamber in comparison with embodiments having an axial veil.
- the reason is that on an average the veil flow, which has a length of the order of some times the veil width, follows a cylinder face having a somewhat varying radius, seen in relation to a cylinder face concentric with the shell.
- the shell diameter is not too small, this deterioration of the positioning is not of great im ⁇ portance however. It may moreover be reduced if the veil ⁇ like tangential flow to the chamber is withdrawn slightly (as shown in fig.
- Fig. 6 shows an example of a two-chamber embodiment.
- the last one of the chambers here utilizes a flow element of the same type as in fig. 3, while a variant of a flow ele ⁇ ment according to the invention is additionally provided in the first chamber.
- a ring channel 15 is inter ⁇ posed between the admission pipe 4 and the discharge open ⁇ ing 14.
- This variant enables an axial veil flow to the first chamber, even though the axial direction of the ad ⁇ mission pipe is transverse to the axis of the container (like in fig. 5).
- Peripheral flow takes place in the ring channel, so that the exhaust gas, without a major loss of total pressure, can be distributed evenly along the peri ⁇ phery before flowing axially into the slot at the dis ⁇ charge opening.
- the examples of embodiments of the invention shown above are built with a circular cylindrical shell and with a considerable degree of rotation symmetry.
- the basic ideas of the invention are not bound to the circular cylinder shape.
- the shell may e.g. be conical or elliptic. This may e.g. be of interest in uses where the mounting conditions make it advisable for the silencer to have a flat shape.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP94906136A EP0683849B1 (en) | 1993-02-01 | 1994-01-31 | A silencer |
AU59985/94A AU5998594A (en) | 1993-02-01 | 1994-01-31 | A silencer |
DE69401264T DE69401264T2 (en) | 1993-02-01 | 1994-01-31 | SILENCER |
DK94906136.0T DK0683849T3 (en) | 1993-02-01 | 1994-01-31 |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DK0112/93 | 1993-02-01 | ||
DK011293A DK169823B1 (en) | 1993-02-01 | 1993-02-01 | Muffler |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1994018438A1 true WO1994018438A1 (en) | 1994-08-18 |
Family
ID=8089886
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/DK1994/000049 WO1994018438A1 (en) | 1993-02-01 | 1994-01-31 | A silencer |
Country Status (7)
Country | Link |
---|---|
EP (1) | EP0683849B1 (en) |
AT (1) | ATE146850T1 (en) |
AU (1) | AU5998594A (en) |
DE (1) | DE69401264T2 (en) |
DK (2) | DK169823B1 (en) |
ES (1) | ES2095745T3 (en) |
WO (1) | WO1994018438A1 (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1996036796A1 (en) * | 1995-05-19 | 1996-11-21 | Silentor A/S | A silencer with incorporated catalyst |
EP0960650A1 (en) * | 1998-05-11 | 1999-12-01 | Haldor Topsoe A/S | Mixing device |
AU730401B2 (en) * | 1996-09-30 | 2001-03-08 | Silentor Notox A/S | Gas flow silencer |
US6257754B1 (en) * | 1997-11-13 | 2001-07-10 | Haldor Topsoe A/S | Mixing device and flue gas channel provided therewith |
WO2002036944A1 (en) * | 2000-11-02 | 2002-05-10 | Rouse Gregory C | Turbogenerator exhaust silencer |
US6520286B1 (en) | 1996-09-30 | 2003-02-18 | Silentor Holding A/S | Silencer and a method of operating a vehicle |
FR2854427A1 (en) * | 2003-04-29 | 2004-11-05 | Mig Production | Silencer for vehicle e.g. motorcycle, has elongated central body with upstream end having convex surface such that central body has guiding part for guiding exhaust gas and distributing pressure on soundproof sides |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DK57996A (en) | 1996-05-15 | 1997-11-16 | Silentor As | Muffler |
CA2373774A1 (en) | 1998-03-30 | 1999-10-07 | Silentor Holding A/S | A silencer and a method of operating a vehicle |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1226438A (en) * | 1958-10-09 | 1960-07-11 | Silencer for the flow of fluids | |
US2990906A (en) * | 1958-10-08 | 1961-07-04 | Koppers Co Inc | Acoustic absorber |
EP0020823A1 (en) * | 1979-04-10 | 1981-01-07 | Lionel Fothergill | Engine exhaust silencer |
-
1993
- 1993-02-01 DK DK011293A patent/DK169823B1/en not_active IP Right Cessation
-
1994
- 1994-01-31 AU AU59985/94A patent/AU5998594A/en not_active Abandoned
- 1994-01-31 EP EP94906136A patent/EP0683849B1/en not_active Expired - Lifetime
- 1994-01-31 AT AT94906136T patent/ATE146850T1/en not_active IP Right Cessation
- 1994-01-31 ES ES94906136T patent/ES2095745T3/en not_active Expired - Lifetime
- 1994-01-31 DK DK94906136.0T patent/DK0683849T3/da active
- 1994-01-31 DE DE69401264T patent/DE69401264T2/en not_active Expired - Fee Related
- 1994-01-31 WO PCT/DK1994/000049 patent/WO1994018438A1/en active IP Right Grant
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2990906A (en) * | 1958-10-08 | 1961-07-04 | Koppers Co Inc | Acoustic absorber |
FR1226438A (en) * | 1958-10-09 | 1960-07-11 | Silencer for the flow of fluids | |
EP0020823A1 (en) * | 1979-04-10 | 1981-01-07 | Lionel Fothergill | Engine exhaust silencer |
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6220021B1 (en) | 1995-05-19 | 2001-04-24 | Silentor Notox A/S | Silencer with incorporated catalyst |
EP0744536A2 (en) * | 1995-05-19 | 1996-11-27 | Silentor A/S | Silencer |
EP0744536A3 (en) * | 1995-05-19 | 1997-11-05 | Silentor A/S | Silencer |
US5758497A (en) * | 1995-05-19 | 1998-06-02 | Silentor A/S | Silencer |
WO1996036796A1 (en) * | 1995-05-19 | 1996-11-21 | Silentor A/S | A silencer with incorporated catalyst |
AU730401B2 (en) * | 1996-09-30 | 2001-03-08 | Silentor Notox A/S | Gas flow silencer |
US6332510B1 (en) | 1996-09-30 | 2001-12-25 | Silentor Holding A/S | Gas flow silencer |
US6520286B1 (en) | 1996-09-30 | 2003-02-18 | Silentor Holding A/S | Silencer and a method of operating a vehicle |
EP2182186A3 (en) * | 1996-09-30 | 2010-12-22 | Silentor Holding A/S | Gas flow silencer |
US6257754B1 (en) * | 1997-11-13 | 2001-07-10 | Haldor Topsoe A/S | Mixing device and flue gas channel provided therewith |
EP0960650A1 (en) * | 1998-05-11 | 1999-12-01 | Haldor Topsoe A/S | Mixing device |
WO2002036944A1 (en) * | 2000-11-02 | 2002-05-10 | Rouse Gregory C | Turbogenerator exhaust silencer |
FR2854427A1 (en) * | 2003-04-29 | 2004-11-05 | Mig Production | Silencer for vehicle e.g. motorcycle, has elongated central body with upstream end having convex surface such that central body has guiding part for guiding exhaust gas and distributing pressure on soundproof sides |
Also Published As
Publication number | Publication date |
---|---|
DK11293A (en) | 1994-08-02 |
DK0683849T3 (en) | 1997-03-10 |
EP0683849B1 (en) | 1996-12-27 |
ES2095745T3 (en) | 1997-02-16 |
DK11293D0 (en) | 1993-02-01 |
DK169823B1 (en) | 1995-03-06 |
DE69401264T2 (en) | 1997-05-15 |
EP0683849A1 (en) | 1995-11-29 |
ATE146850T1 (en) | 1997-01-15 |
AU5998594A (en) | 1994-08-29 |
DE69401264D1 (en) | 1997-02-06 |
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