GB2027489A - Gas flow silencer - Google Patents

Abstract

A reactive silencer comprises a hollow cylindrical chamber subdivided by baffle plates (P1 and P2) into an intake compartment (A), traversed by a pipe (I) entering from the exterior and extending into an intermediate compartment (B) and an outlet compartment (C) having an outlet pipe (O), a skew pipe (S) extending between the intermediate and outlet compartments (B and C), the axis of said skew pipe (S) lying in the axially extending diametric plane of the chamber but being inclined from the intermediate compartment (B) to the outlet compartment (C). <IMAGE>

Description

SPECIFICATION Industrial silencers This invention relates to active mufflers or silencers for use in the exhaust of industrial engines burning either gas oii or gasoline.

Industriai engines burning either gas oil or gasoline may have four-stroke or two-stroke cycles and may be naturally aspirated or supercharged or turbocharged, and, in designing reactive mufflers or silencers for such engines, it is essential to take the following factors into consideration:: (a) Is the engine of the compression-ignition or spark-ignition type? (b) Is the engine naturally aspirated or is it supercharged or turbocharged? (c) How many cylinders does the engine have, how many exhaust silencers are to be provided, and how many cylinders feed into each silencer? (d) What is the acceptable level of back pressure on the engine at the exhaust valve so that it will function correctly? (e) What is the desired exhaust noise level for the application and environment for and in which the engine is to be used? (f) What is the overall exhaust mass flow rate entering each silencer.

Apart from the unique nature of the wave analytical procedures from which the performance of a reactive muffler or silencer can be accurately predicted, the muffler or silencer itself has a design concept which stems from these procedures and an understanding of the results obtained therefrom.

An object of the present invention is to provide a basic silencer design which can readily be adapted to meet the requirements contingent upon its contemplated use.

According to the present invention we provide a reactive muffler or silencer comprising a hollow cylindrical chamber subdivided by baffle plates parallel to the end walls of the casing into three compartments, namely an intake compartment co-axial with the chamber, traversed by a pipe entering from the exterior and extending into the intermediate compartment, and having holes in the wall region thereof within the intake compartment, an intermediate compartment and an outlet compartment from which an outlet pipe, also co-axial with the chamber, extends to the exterior, and a skew pipe extending between the intermediate and outlet compartments, the axis of said skew pipe being in the same vertical plane as the axis of the chamber but being inclined downwardly from the intermediate compartment to the outlet compartment.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing showing a vertical mid-longitudinal section through a reactive muffler or silencer in accordance with the invention.

Referring now to the drawing, the silencer is a hollow cylindrical chamber of length 108 units and diameter 58 units which is subdivided into three compartments A, B and C by baffle plates P1 and P2 parallel to the end walls E, and E2 of the chamber and spaced from the latter such that the intermediate compartment B is of length LB equivalent to 45 units, the compartment A at the intake end of the silencer is of length LA equivalent to 28 units, and the compartment C at the discharge end of the silencer is of length Lc equivalent to 34 units.

At the intake end of the silencer is an intake pipe I of diameter D1 equivalent to 11 units, which is co-axial with the silencer chamber and traverses the compartment A to project through baffle plate P, and over a length XAB equivalent to 6 units into the compartment B.

The pipe I has an external peripheral connecting flange F1 at its outer end, and over its length bridging the compartment A has in its wall a number of holes N of diameter DN equivalent to 3.5 units.

At the discharge end of the silencer is an outlet pipe 0 of diameter D3 also equivalent to 11 units and which is also co-axial with the silencer chamber. The outlet pipe 0 projects through the end wall E2 and over a length Xc3 equivalent to 10 units into the chamber, and has an external peripheral connecting flange F2 at its outer end.

The baffle plate P2 is penetrated by a skew pipe S the axis of which is in the same vertical plane as the axis of the intake and outlet pipes I and 0, i.e. to the axis of the chamber, but is at an angle of 45 to the latter axis with the inclination downwardly from the intermediate compartment B to the compartment C at the outlet end of the silencer. The pipe S is of length equivalent to 38 units and diameter equivalent to 10 units, and is substantially bisected by the plane of baffle plate P2 with, however, the shorter and horizontal axis of the resulting oval in the baffle plate P2 spaced the equivalent of two units below the horizontal axial plane of the chamber.

In use of the silencer just described, exhaust gases enter the intake pipe i and, when they pass over the holes N, the fundamental forcing frequency of the exhaust gas pulses which are coming from the engine at its rated speed, is attenuated in a very marked manner.

This provides a considerable attenuation of the fundamental exhaust noise before the gases enter compartments B and C which provide broad-band attenuation of noise in a range from about 400 H2 to 2800 H2, depending on the engine type, etc.

The nett effect of the three-compartment layout is to provide very strong attenuation of the fundamental pulse and its frequency in compartment A and then a broad-band attenu ation of the residual pressure wave situation in compartments B and C. By appropriate adjustment of the dimensions in the embodiment shown and described, it is possible to achieve the correct level of exhaust noise attenuation for a particular engine by knowing its design configuration of type, cycle type and number of cylinders so as to satisfy the requisite environmental and ecological criteria.

This enables the optimum use of materials and of the packaging of the complete silencer to produce in an economical manner the design which will effect the correct level of exhaust noise attenuation.

The diameters D1, D2, D3 and D4 along with the lengths of the compartments A, B and C are vital in ensuring that the nett mass flow can be handled and that the resultant back pressure on the engine exhaust valve is at the correct value.

The number of holes N and their diameter DN may be varied in association with the length and diameter of compartment A and in conjunction with diameter D1 may be varied, so that there is a strong attenuation of the fundamental pulse and its associated frequency arriving at the point for any combination of engine type, number of cylinders, cycle type, etc.

Claims (2)

1. A reactive muffler or silencer comprising a hollow cylindrical chamber subdivided by baffle plates parallel to the end walls of the casing into three compartments, namely an intake compartment co-axial with the chamber, traversed by a pipe entering from the exterior and extending into the intermediate compartment, and having holes in the wall region thereof within the intake compartment an intermediate compartment and an outlet compartment from which an outlet pipe, also co-axial with the chamber, extends to the exerior, and a skew pipe extending between the intermediate and outlet compartments, the axis of said skew pipe being in the same vertical plane as the axis of the chamber but being inclined downwardly from the intermediate compartment to the outlet compartment.

2. A reactive muffler or silencer substantially as hereinbefore described with reference to the accompanying drawing.