GB2158878A

GB2158878A - Exhaust silencer

Info

Publication number: GB2158878A
Application number: GB08511127A
Authority: GB
Inventors: David James Dixon
Original assignee: DIXON RACING Ltd
Current assignee: DIXON RACING Ltd
Priority date: 1984-05-03
Filing date: 1985-05-02
Publication date: 1985-11-20
Also published as: GB8411431D0; GB8511127D0

Abstract

An engine exhaust gas silencer in which a conical baffle 2 is mounted within the silencer casing 3 with its apex directed towards the gas input end of the silencer and its base is spaced by a small amount from the walls of the casing, leaving an annular space 4 through which the exhaust gas expands into the silencer output chamber 5 and thence passes through a perforated output pipe 6. A second cone 8 (Fig. 2) having perforations (10) may be provided downstream of the conical baffle 2. Further baffles, perforated or imperforate, may be located in chambers 1 and 5. <IMAGE>

Description

SPECIFICATION Exhaust silencer This invention relates to a silencer for use in an exhaust system for prime movers, engines, whatever, of any type be such combustion, chemical or gaseous in the method of achieving output.

Exhaust systems for power engines are used to achieve both silencing of the noise generated by the exhaust gases and provide exhaust assistance to improve power output from the engine. The maximum noise level permitted by the exhaust is subject to government legislation and silencing systems need to keep within these bounds.

Exhaust assistance to improve engine power output is conventionally achieved by tuning the pipe lengths to engine exhaust characteristics. This entails matching pipe lengths toexhaust output wavelengths and, accordingly, the overall length of a simple silencer system is affected and to a certain extent governed by the engine characteristics if the exhaust is to be used to improve engine power output.

The purpose of the present invention is to provide a silencer of minimal length which will meet the government noise level requirements and provide exhaust assistance.

According to the present invention there is provided an engine exhaust gas silencer comprising an outer casing enclosing a primary exhaust gas expansion chamber, an imperforate conical wedge shaped baffle mounted within the primary chamber, the base of baffle being spaced from the outer walls of the chamber and the apex being directed towards the input to said chamber, a secondary exhaust gas expansion chamber, the inlet to which being through an annular space between the base of the wedge shaped baffle and the outer casing, and a perforated length of outlet pipe within the secondary chamber and extending through the casing so forming an outlet passage.

Figure 1 is a section through one embodiment of the silencer according to the invention.

Figure 2 is a section through a second embodiment of the silencer according to the invention.

The invention will now be further described by way of example, with reference to the accompanying drawing in which Fig. 1 is a section through one embodiment of a silencer according to the invention.

The silencer comprises a primary expansion chamber 1 having an inlet flange 7 which is adapted to fit over the end of an exhaust pipe (not shown) and clamped to such by a known means. Within the primary expansion chamber 1 there is fixed a cone 2. The pinocle of the cone 2 is situated within the primary expansion chamber and is upstream of the base of such, the base effectively forming the downstream curtailment of expansion chamber 1. The base diameter is marginally smaller than the outer case 3 of the exhaust so forming an annulus 4 through which exhaust gases pass into secondary expansion chamber 5. The cross sectional area of this annulus 4 should be greater than or equal to the cross sectional area of the exhaust pipe over which the flange 7 fits.Within secondary chamber 5 and concentric with the silencer centre line is fixed a perforated pipe 6 through which the exhaust gases pass to the atmosphere.

The base of the cone 2 maybe omitted or alternatively perforated to allow exhaust resonance within the cone void.

In the second embodiment shown in Fig. 2, a second frusto-conical baffle 8 is mounted at the rear of the silencer with its larger diameter end sealed and secured to the inner surface of the case 3. The smaller diameter end 9 of the second cone 8 projects into the open base of the cone 2. The surface of the second cone 8 is perforated with a number of apertures 10.

The sum of the cross sectional areas of all the apertures 10 is preferably approximately 45% of the surface area of the cone 8. The perforated outlet pipe 6 is connected to the smaller diameter open end of the second cone 8.

The volume of the two expansion chambers 1 and 5, the inclusive angle of the cones 2 and 3, the base design details of cone 2, (Fig.

1), and the overall length of perforated pipe 6, will depend for optimum performance and minimal power loss on, among other things, the unsilenced exhaust gas volume flow rate and the length of exhaust piping from the engine outlet to the primary chamber of the silencer. The actual dimensions of the silencer and the arrangements and design of its constituent parts are therefore dependent on the engine characteristics and the exhaust pipe attached to such and so the design of the silencer according to the invention must be found by experiment for any particular engine.

The extremely rapid expansion of the exhaust gas that occurs as it passes beyond the annulus 4, causes severe turbulence. This attenuates the low and medium frequency noise which is fundamental to a reciprocating internal combustion engine. Substantially lower sound pressure levels have been measured than those occuring in silencers of known design having the same expansion ratios.

In the embodiment shown in Fig. 2, the narrow passage provided for the exiting gas by the annular passage between the inner face of the first cone 2 and the outer face of the second cone 8, attenuates the medium and higher frequencies of the exhaust noise.

The individual components may be varied in materials, length, diameter and cross sectional shape, and by the inclusion of baffles, perforated or otherwise, within any of the chambers so described, in order to accousti cally match the exhaust system to the performance characteristics of any engine.

Claims

1. An engine exhaust gas silencer comprising an outer casing enclosing a primary exhaust gas expansion chamber, an imperforate conical wedge shaped baffle mounted within the primary chamber, the base of baffle being spaced from the outer walls of the chamber and the apex being directed towards the input to said chamber, a secondary exhaust gas expansion chamber, the inlet to which being through an annular space between the base of the wedge shaped baffle and the outer casing, and a perforated length of outlet pipe within the secondary chamber and extending through the casing so forming an outlet passage.

2. A silencer as claimed in claim 1 wherein the cross section area of the input to the primary chamber is equal to or less than the cross section area of the annular space.

3. A silencer as claimed in claim 1 wherein a perforated second, frusto conical baffle is mounted within the secondary chamber, the base of the second baffle being sealed to the outer casing, the tip of the second baffle projecting into the open base of the first baffle, the inward end of said pipe being connected to the open tip of said second baffle.

4. An engine exhaust gas silencer subtantially as described herein with reference to the accompanying drawings.