GB2250215A

GB2250215A - A catalytic converter

Info

Publication number: GB2250215A
Application number: GB9025991A
Authority: GB
Inventors: Geoffrey Keene Wilson
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1990-11-29
Filing date: 1990-11-29
Publication date: 1992-06-03
Also published as: GB9025991D0

Abstract

A catalytic converter includes a matrix (15) comprising a metal substrate formed by rolling corrugated strip (19) interleaved with smooth strip (21) to form a plurality of passages (18). The cross-sectional area of each passage in a central portion of the matrix is less than that of each passage closer to the side walls. <IMAGE>

Description

A CATALYTIC CONVERTER The invention relates to catalytic converters for the exhaust gas of internal combustion engines.

Catalytic converters are required to ensure the complete combustion of carbon monoxide and hydrocarbons and to chemically reduce oxides of nitrogen. A known type of catalytic converter includes a matrix comprising a substrate in the form of a regular solid of uniform cross-section having a plurality of longitudinally extending passages lying parallel to the side walls of the matrix, each passage having a catalytically active coating or layer.

In the known type of catalytic converter the passages are of uniform size and distribution. This creates an uneven flow distribution, with the greater flow concentrated in the passages in a central portion further from the side walls of the matrix. This leads to greater attrition of the catalyst in the passages in the central portion, either due to abrasion or due to temperature effects which lock the catalyst below the surface of the active coating.

The present invention provides a catalytic converter including a matrix comprising a substrate in the form of a regular solid of uniform cross-section and having a plurality of longitudinally extending passages parallel to the side walls of the matrix, each passage having a catalytically active coating or layer, wherein the cross-sectional area of each passage in a central portion of the matrix is less than the cross-sectional area of each passage closer to the side walls.

The catalytic converter according to the invention gives a more even flow distribution and, by better matching of the passage area to the flow requirements, allows the converter to be designed with a lower pressure drop and more economic utilisation of costly catalysts.

Preferably the cross-section of the passages reduces progressively from the side walls towards the centre of the matrix.

The substrate may be formed from an extrusion, eg of a ceramic material. Alternatively, the substrate is formed from corrugated strip, interleaved with a smooth strip.

The strips may be metallic or ceramic and may be formed by rolling the strips to form a volute. The amplitude and/or pitch of the corrugations may progressively increase from the centre of the volute.

The invention will now be described by way of example and with reference to the accompanying drawings, of which: Figure 1 is a longitudinal cross-section through a catalytic converter according to the invention, and Figure 2 is a cross-section on the line Il-Il in Figure 1 on a slightly enlarged scale.

The catalytic converter 11 is of generally conventional construction. A metal casing 12 has inlet and outlet ducts 13 and 14 respectively and houses two matrices 15 and 16 insulated from the casing 12 by fibrous mats 17.

The first matrix 15 is formed from corrugated metal strip 19 interleaved with smooth metal strip 21, the strips being rolled into a volute to form a substrate with a plurality of longitudinally extending passages 18. In Figure 2 parts of the first matrix 15 are shown magnified to illustrate this construction which is generally known, whereas in Figure 1 the passages 18 are shown diagrammatically as cutaway portions of the matrix 15.

The walls of each passage 18 are lined with a catalytically active coating or layer, typically comprising a platinum group metal so that in use hot exhaust gases from an internal combustion engine pass through the passages and the harmful contents are converted to innocuous gases.

In a conventional matrix of the construction outlined, the corrugations are of equal pitch and amplitude to give a density of passages 18 (often referred to as the cell density) in the region of 300 per square inch (46 per square cm) and this is the construction of the second matrix 16. However, in the first matrix 15 the corrugations are of progressively increasing amplitude and pitch the further the passages are from the centre of the volute.

This is illustrated in Figure 2 by the magnified region A near the centre of the matrix 15 and the magnified region B near the side wall 22 of the matrix. These are drawn to the same scale but not to any particular magnification.

In the centre of the first matrix 15 the passages have a cell density of 300 per square inch (46 cells/cm2) but at the outside the cell density is 100 per square inch 2 (15 cells/cm ) , a passage nominal cross-sectional area of 2.15mm2 on the inside and 6.70mm2 on the outside.

However, it is envisaged that the passages in the central region could have a cell density in the range 200 to 500 2 per square inch (31 to 77 cells/cm ) and the passages closer to the side walls a cell density in the range 50 to 200 per square inch (8 to 31 cells/cm2) Instead of being fabricated from metal strip the substrate could be formed from ceramic extrusions. These may take the same form as the substrates of matrices 15 and 16 or, more likely, would be monolith extrusions with square section passages.

The variation in cross-sectional area of the passages 18 in the first matrix 15 gives a more even flow distribution so that the second matrix 16 can be of conventional construction with a uniform cell density. However, it may be beneficial to provide for a variable cell density in the second matrix or to make it identical to the first matrix to benefit from rationalisation of components.

Instead of the corrugations increasing progressively in amplitude and pitch they may increase in pitch only, for example if the corrugations are produced by bending knives. Alternatively, two or more distinct regions may be produced by using two or more corrugating rollers of different pitch and/or amplitude over separate portions of the corrugated strip.

Claims

1. A catalytic converter including a matrix comprising a substrate in the form of a regular solid of uniform cross-section and having a plurality of longitudinally extending passages parallel to the side walls of the matrix, each passage having a catalytically active coating or layer, wherein the cross-sectional area of each passage in a central portion of the matrix is less than the cross-sectional area of each passage closer to the side walls.

2. A catalytic converter according to Claim 1, wherein the cross-section of the passages reduces progressively from the side walls towards the centre of the matrix.

3. A catalytic converter according to Claim 1 or Claim 2, wherein the substrate is formed from an extrusion.

4. A catalytic converter according to Claim 1 or Claim 2, wherein the substrate is formed from corrugated strip interleaved with smooth strip.

5. A catalytic converter according to Claim 4, wherein the substrate is formed by rolling the strips to form a volute.

6. A catalytic converter according to Claim 5 when dependent from Claim 2, wherein the corrugations are of progressively increasing amplitude and/or pitch from the centre of the volute.

7. A catalytic converter according to any preceding claim, wherein the passages in the central portion have a cell density in the range 31 to 77 cells/cm2 and the passages closer to the side walls have a cell 2 density in the range 8 to 31 cells/cm2.

8. A catalytic converter substantially as described herein with reference to the drawings.