GB2072038A - Purification of I.C. engine exhaust gases - Google Patents

Abstract

An internal combustion engine includes apparatus for reducing pollutants contained in exhaust gases emitted from the exhaust port(s) of the engine the apparatus comprising a wall 5 defining a chamber, means, e.g. water jacket 7, for cooling the chamber and a catalyst 8, 9 supported within the chamber, the catalyst including a substrate, a layer of refractory metal oxide applied to at least a part of the surface of the substrate and a catalytic material applied to the layer of refractory metal oxide, the chamber also including one or more inlets 10, 11 in communication with the said exhaust port(s) via which exhaust gas emitted from the engine is led into the chamber and passed through the catalyst prior to passage through an exhaust system 13 to atmosphere. The water jacket may be part of a water jacket covering substantially the whole of the engine, e.g. such as used in a mine. <IMAGE>

Description

SPECIFICATION Catalyst reactors This invention relates to the purification of gases and in particular of waste gases. This invention is especially concerned with at least reducing the quantity of pollutants such as carbon monoxide and smoke in gases emitted from internal combustion engines.

Gases from internal combustion engines often contain finely divided particles of hydrocarbons and/or carbon and/or other solid matter which emerge in the form of smoke. The smoke from a diesel engine, for example, is composed of solid/liquid particles, solid chain aggregates in which essentially spherical particles of between 100-800A diameter, link up together liquid sulphates, liquid hydrocarbons and gaseous hydrocarbons. The solid/liquid particles generally comprise carbon particles with adsorbed liquid hydrocarons and the solid chain aggregates are generally composed of high molecular weight organic compounds and/or inorganic sulphates.

Three different types of smoke are commonly observed issuing from diesel engine exhaust pipes. These are "white smoke", "black smoke" and "blue smoke". White smoke is produced when the engine first starts up and results from the condensation of water vapour on to particles contained in the exhaust gas so that a fine mist is formed. Black smoke is produced when the engine has warmed up and contains a relatively high proportion of carbon particles. In blue smoke there is some carbon with a relatively high proportion of gaseous hydrocarbons such as aldehydes.

Throughout the remainder of this specification the particles referred to above will be described as "smoke forming particles". About 90% of these smoke forming particles have maximum dimensions of less than one micron which is within the respirable particle size and the maximum dimension of the remaining 10% of these smoke forming particles is less than four microns.

Other undesirable components present in exhaust gases are noxious gases such as carbon monoxide and hydrocarbons. In this specification the word "pollutants" is to be taken to mean smoke forming particles and noxious gases.

Catalytic oxidation of carbon particles takes place at about 400 C whereas the normal temperature of combustion of these particles is 700-800 C. For hydrocarbon particles catalytic oxidation will take place at temperatures about 2000C. The effect of a catalyst on the temperature at which catalytic oxidation of particulates entrained in the exhaust gas stream of a diesel engine took place were studied. A number of sample catalysts were prepared. The catalysts comprised a substrate fabricated from 310 stainless steel wire of diameter 0.010 inch, rolled down to ribbon 0.004 inch thick, a layer of alumina and a layer of one or more platinum group metal(s) at a loading of 2.46 mg/g of alumina.A portion of coated wire was cut from a catalyst and heated gradually raising the temperature together with particulate matter, collected from the exhaust gas stream of a diesel engine, in the sample pan of a differential scanning colorimeter (a DSC) in an atmosphere of 1% oxygen in argon. Samples of the atmosphere above the sample pan were taken via a heated capillary tube to a mass spectrometer. Four mass numbers were traced: carbon monoxide (44), double charged argon (20), oxygen (32) and water (18) or nitrogen and carbon monoxide (28). The temperature at which the differential plot of the DSC peaked was taken to be the temperature at which combustion of the particulates took place. This temperature can be referred to as the "light-off" temperature.

The results are given below: Alumina Loading Catalytic metal(s) Light-off (g/g of wire) temperature ( C) 0.33 5.7% Rh 94.3% Pt 235 0.28 67% Pt 33% Pd 207 0.30 Pd 265 0.28 Pt 220 The light-offtemperature of particulates from the exhaust gas stream of a diesel engine, 207-265"C, is considerably lower than the temperature for combustion to take place when no catalyst is present. Since the presence of a catalyst enables oxidation of the smoke forming particles in a gas to take place at a lower temperature than the normal temperature at which combustion takes place, little or no heating of the exhaust gas from an internal combustion engine should be required when it is desired to effect the catalytic oxidation of any smoke forming particles in the gas.For example, a diesel engine runs at about 4000C when operating at medium to full power so that no preheating of the exhaust gas issuing from the diesel engine would be required before passing the said exhaust gas over a catalyst to remove the smoke forming particles from the gas by catalytic oxidation, provided the catalyst is close to the engine.

Internal combustion engines are often used in areas where there are stringent regulations on their use such as in mines. Diesel engines which are to be used in a NCB mine are modified to comply with regulations controlling the use of diesel machinery in mines. The engine is surrounded by a water jacket so that the temperature of any exterior part of the engine which comes into contact with the atmosphere is less than 120 C. The exhaust gas of the engine is passed through a water conditioner and flame traps before finally being emitted to the atmosphere. The water conditioner may be a container of the water through which the exhaust gas is bubbled or water may be sprayed into the stream of exhaust gas.Any chamber containing a catalyst, for treating the exhaust gas, will have to comply with regulations but still keep the temperature of the exhaust gas up to enable catalytic removal of the pollutants to take place.

An object of the present invention is to at least reduce the quantity of the smoke contained in exhaust gas by effecting catalytic oxidation of smoke forming particles in the gas.

A further object of the present invention is to reduce the quantity of noxious gases and particulates present in the exhaust gas from an internal combustion engine.

Another object of the present invention is to provide a modified diesel or petrol driven internal combustion engine such that a considerably reduced quantity of noxious gases and particulates is produced.

According to a first aspect of the present invention, an internal combustion engine which has a reduced emission of pollutants and which is surrounded by a water jacket includes a chamber which is at least partially surrounded by the waterjacket and in which is disposed a catalyst comprising a substrate which is at least partically covered by a layer of refractory metal oxide onto which is deposited catalytic material, the chamber being continuous with the cylinder exhaust ports so that the exhaust gas expelled through the exhaust ports passes through the chamber and the exhaust pipes to the external atmosphere.

According to a second aspect of the present invention, a process for the reduction of pollution by exhaust gas from an internal combustion engine comprises passing the exhaust gas from the cylinders of the engine into a chamber which is at least partially surrounded by a water jacket and which contains a catalyst such that at least part of the noxious gases and particulates undergo catalytic oxidation.

Preferably the engine is a diesel engine.

According to a further aspect of the present invention, a catalyst for use in diesel exhaust purification comprises; (a) a substrate (b) an adherent refractory metal oxide washcoat layer disposed upon the surface of the substrate, and (c) a catalytic metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, Fe, Co, Ni, V, Cr, Mo, W, Y, Ce and alloys and intermetallic compounds containing at least 20% by weight of one or more of these metals disposed upon the surface of or throughout the refractory metal oxide washcoat layer.

The refractory metal oxide washcoat layer preferably contains in the form of their oxide one or more members of the group consisting of Mg, Ca, Sr, Ba, Sc, Y, the lanthanides, Ti, Zr, Hf, Th, V, Cr, Mn, Co, Ni, B, Al, Si and Sn.

A preferred washcoat material is Awl203 and alumina hydrates but stabilising oxides such as BaO and oxides promoting catalytic activity such as TiO2, ZrO2, HfO2, ThO2, Cur203 and NiO may also be present.

The catalyst substrate may be a ceramic or metallic monolith, a unitary body with channels running through it or the substrate may be of such a design that the exhaust gas flow is turbulent. A structure of knitted or woven wire may be used as a substrate so the exhaust gas flow through the catalyst is turbulent.

Metals or alloys used in the fabrication of a substrate are preferably oxidation resistant and should be thermally stable up to at least 600 C.

Suitable base metal alloys are nickel and chromium alloys having an aggregate Ni plus Cr content greater than 20% by weight and alloys of iron including at least one of the elements chromium (3-40) wt %, aluminium (1-10) wt %, cobalt (traced) wt %, nickel (trace-72) wt % and carbon (trace-0.5) wt %. Such substrates are described in German DOS 2450664.

Other examples of base metal alloys capable of withstanding the rigorous conditions required are iron-aluminium-chromium alloys which may also contain yttrium. The latter alloys may contain 0.5-12 wt % Al, 0.1-3.0 wt % Y, 0-20 wt % Cr and balance Fe. These are described in United States Patent No. 3298826.

Another range of Fe-Cr-AI-Y alloys contain 0.5-4 wt % Al, 0.5-3.0 wt % Y, 20.0-95 wt % Cr and balance Fe and these are described in United States Patent No. 3027252.

Alternatively the base metal alloys may have less corrosion resistance, e.g., mild steel, but with a protective coating composition covering the surface of the substrate as described in our co-pending British Patent Application No. GB 2,013 517A dated 2nd February 1979.

Where wire is used as substrate its thickness is preferably between 0.0254 and 0.508 mm diameter and more preferably between 0.0254 and 0.305 mm diameter.

A first embodiment of the present invention will be described with reference to Figure 1. The outer wall, 7, of a catalyst chamber has openings, 10 and 11, which are adjacent to and continuous with the exhaust ports of the cylinders of the engine and one exit, 12, adjacent to the exhaust pipe, 13. Catalysts, 1,2,8 and 9 are positioned as shown. The catalyst chamber has an inner wall, and two outer walls, 6 and 7, with an air gap between the walls 5 and 6 and the gaps between 6 and 7 filled with circulating water. The water is provided from the water jacket surrounding the engine. The exhaust gas flow is generally indicated by the labelled arrows F1, F2, F3, F4, F5 and F6. Exhaust gas flows from the cylinders, through the exhaust ports and through into the openings, 10 and 11, into the chamber and makes contact with catalysts 1 or 2 and then catalyst 8 and possibly catalyst 9 before passing through the opening, 12, to the exhaust pipe.

The substrate may be a monolith or a structure of wire. If a wire substrate is used one unit for each catalyst may be used or a number of small units linked together.

A second embodiment will be described with reference to Figure 2. The catalyst chamber has openings, 10 and 11, adjacent to and continuous with the exhaust ports of the cylinders and one exit, 12, adjacent to the exhaust pipe, 13. Between the inner wall, 25, and outer wall, 27, of the catalyst chamber, water from the cooling water jacket of the engine circulates. An inner chamber, 24, containing two catalysts, 1 and 2, is arranged in the catalyst chamber as shown in Figure 2 such that the exhaust gas on entering the catalyst chamber has to pass through an inner chamber, 24, and makes contact with the catalysts before leaving the chamber and entering the exhaust pipe. Part of the inner chamber, 29, is perforated with holes or slots to allow the exhaust gas therein to pass from the inner chamber to the catalyst chamber and thence to the exhaust pipe.Exhaust gas entering the catalyst chamber at opening, 10, flows through the chamber as indicated by the labelled arrows F21, F23, F25, F27, F28 and F31 while gas entering at the other opening, 11, flows through as indicated by the labelled arrows F22, F24, F26, F29, F30 and F31.

The support may be a monolith or fabricated from metallic wire. The two catalysts are positioned in the catalyst chamber as shown in Figure 2 so that approximately the same amount of exhaust gas passes through each catalyst, the exhaust gas from one cylinder passing through one catalyst.

Another embodiment is depicted in Figure 3, in which one or more catalysts with optional spools are utilised. The catalyst chamber has openings, 50 and 51, adjacent to and continuous with the exhaust ports of the cylinders and one exit, 52, adjacent to the exhaust pipe, 53. The catalysts, 41,42 and 43, comprising a support, a washcoat layer and a catalyst metal, are disposed so that the exhaust gas on entering the catalyst chamber is compelled to pass through the interstices of at least one catalyst before leaving the chamber and entering the exhaust pipe. The exhaust gas flows through the chamber as indicated by the labelled arrows, F41, F42, F43, For F45, F46, F47, F48, F49, F50, F51, F52, F53, F54, F55 and F56.The exhaust gas enters the catalyst chamber through a sleeve arrangement, 45, which is set into the chamber, and is deflected by a spool, 47, before passing through the catalyst.

In this embodiment the substrate for the catalyst is preferably of knitted wire which may be unitary or in sections. Sections, for example, of doughnut configuration, are normally linked together before being placed in the chamber. Annular discs, 48, may be used to secure the catalyst to the walls of the chamber. In the centre of catalysts, there is a spacer unit, 45, which supports the catalysts and spools and forms an exit tube through which the exhaust gas passes to enter the exhaust pipe. The spools are not essential and one long catalyst may be used.

Figure 4 depicts one form of a spacer unit in which a series of 5 rigid bars 100-500 running the length of the chamber are used. These are maintained in fixed spatial relationship to one another, thus holding the supported catalyst rigidly in place within the chamber, by the use of spacing plates 600. The spacing plates in pairs connect three of the five bars and are usually at right angles to each other thus being disposed along a diameter of the central cylindrical exit tube. Two or more pairs of spacing plates may be used and they are usually positioned at regular intervals in the length of the chamber. Alternatively the spacing plates may be used instead of rods where they would be continuous throughout the length of the chamber as shown in Figure 5. Rods and spacing plates need to be constructed of a material resistant to oxidation up to 800 C.

A further embodiment will be described with reference to Figure 3A. The catalyst chamber has openings 82 and 83 adjacent to and continuous with the exhaust ports of the cylinders and one exit 84 adjacent to the exhaust pipe. Water from the cooling water jacket of the engine circulates between the inner wall 81 and the outer wall 80 of the catalyst chamber. The catalyst 85 comprising a support, a washcoat layer and a catalytic metal is so disposed that the exhaust gas has to flow through the catalyst before leaving the chamber. The catalyst is disposed in the chamber using spacing plates 86 as described above. One end of the spacing plates 89 is fixed to the chamber wall 81 and a disc or metal plate 90 is attached to the other end of the spacing plates to ensure that no exhaust gas can leave the chamber without passing through the catalyst.

The exhaust gas flows into the chamber through the openings 82 and 83 down through sleeves 87 and 88 and through intermediate chambers 92 and 93 into the inner space 91 provided by the spacing plates 86. The exhaust gas then flows through the catalyst outwards and then through the exit 84. The flow of the exhaust gas is indicated by the labelled arrows F50-F79. The intermediate chambers 92 and 93 comprise a hollow cylinder with integral end flanges having substantially centrally positioned holes to allow the spacing plates 86 to pass through and a sleeve, either 87 or 88, is fitted radially into the cylinder wall such that the joint is gas tight.

The support for the catalyst is preferably of knitted wire which may be made up into four sections or three units. If the support is in sections, e.g. of doughnut configuration, these are normally linked together before the support is placed in the chamber.

A Perkins 4.236 diesel engine, a low emissions diesel engine, modified for mine use was used to demonstrate the results obtained in the operation of the present invention.

Example 1 A catalyst chamber as outlined in the first embodiment, Figure 1, was fitted to the engine. The substrate was a monolith of cell density 400 cell/sq. in. made from an alloy of the following composition: %wt Cr 15 Al 4 Y 0.3 Fe balance A washcoat of alumina stabilised with ceria at a loading of 1.5 g/cu ft was applied. The catalytic metal layer comprising Pt and Pd in the ratio of 3:1 was applied at a loading of 80 g/cu ft. The variation of the amount of hydrocarbons, carbon monoxide, nitrogen oxides and particulates, present in the exhaust gas, with the load of the diesel engine as brake mean effective pressure was measured at 1,000 rpm and 2200 rpm. The results of these measurements are given in graphical form in the attached figures 5-21. Table 1 below gives the details of the measurements taken and the figures giving the results.

TABLE 1 Speed of Pollutant in exhaust gas measured engine in Figure rpm Carbon monoxide, CO, in ppm 1,000 6 Carbon monoxide, CO, in ppm 1,400 7 Carbon monoxide, CO, in ppm 1,800 8 Carbon monoxide, CO, in ppm 2,200 9 Hydrocarbons, HC, in ppm 1,000 10 Hydrocarbons, HC, in ppm 1,400 11 Hydrocarbons, HC, in ppm 1,800 12 Hydrocarbons, HC, in ppm 2,200 13 Nitrogen oxides, NOx, in ppm 1,000 14 Nitrogen oxides, NOx, in ppm 1,400 15 Nitrogen oxides, NOx, in ppm 1,800 16 Nitrogen oxides, NOx, in ppm 2,200 17 Particulates in glhr 1,000 18 Particulates in glhr 1,400 19 Particulates in glhr 1,800 20 Particulates in gthr 2,200 21 The two lines show the difference between the pollutants present in the exhaust gas when no catalyst chamber is used, ('baseline'), represented in the figures by

and after the exhaust gas has passed through a catalyst chamber, represented in the figures by fuel with 0.7% sulphur was the fuel for the engine.

A high sulphur containing A further set of results were obtained using the catalyst fitted to the engine as described above. The results were obtained with the engine running at 1,400 rpm for Figures 36, 37, 38, 39 and 40 and at 2,200 rpm for Figures 41,42,43,44 and 45.

Example 2 Further experiments were carried out using a catalyst chamber as described in the third embodiment, Figure 3. A knitted mesh substrate was fabricated from wire of diameter 10 thou". Two catalysts were prepared. The substrate for catalyst A was fabricated from wire of an alloy of the following composition.

%wt Cr 15 Al 4 Y 0.3 Fe balance The washcoat of alumina stablished with ceria was present at a loading of 0.13 g/g of wire substrate. The catalytic metal layer comprising 71/2% Hr, 921/2% Pt was applied at a loading of 80 g/cu ft. Catalyst B had a washcoat of alumina at a loading of 0.2 g/g of wire onto which was applied the catalytic metal layer of 51/2% Rh, 94.5% Pt with a loading of 7 g of catalytic metal over the three catalyst units. The substrate was fabricated from 310 stainless steel which was treated with a protective coating composition as described in our co-pending British PatentApplication No. GB 2,013 517A dated 2nd February 1979.

The variation of the amount of hydrocarbons, carbon monoxide, nitrogen oxides and particulates, present in the exhaust gas, with the load of the diesel enging as brake mean effective pressure was measured at 1400 rpm and 2200 rpm for catalyst A. The fuel used in the engine was a high sulphur fuel containing 0.7% sulphur. The variation of the particulates present in the exhaust gas with the power of the engine was measured using a low sulphur fuel containing 0.07% sulphur in the engine with catalyst A in the catalyst chamber.

Using catalyst B the variation of the particulates with the power of the engine was measured with the engine running on high and lowsulphurfuels.

The results are given in graphical form in the attached Figures 22-35. Table 2 below gives the details of the measurements taken.

TABLE 2 Speed of Pollutant in exhaust gas measured Catalyst engine in Fuel Figure rpm Hydrocarbons HC in ppm A 1,400 High S 22 Carbon monoxide CO in ppm A 1,400 High S 23 Particulates in g/hr A 1,400 High S 24 Nitrogen oxides in ppm A 1,400 High S 25 Hydrocarbons HC in ppm A 2,200 High S 26 Carbon monoxide CO in ppm A 2,200 High S 27 Particulates in g/hr A 2,200 High S 28 Nitrogen oxides in ppm A 2,200 High S 29 Particulates in g/hr A 1,400 Low S 30 Particulates in g/hr A 2,200 Low S 31 Particulates in g/hr B 1,400 Low and high S 32 Particulates in g/hr B 2,200 Low and high S 33 Particulates in g/hr B 1,400 High S 34 Particulates in g/hr B 2,200 High S 35 The two lines in Figures 22-31 show the difference between the pollutants present in the exhaust gas when no catalyst chamber is used, 'baseline', and after the exhaust gas has passed through a catalyst chamber.

denotes baseline measurements denotes measurements after exhaust gas lows passed through the catalyst chamber In Figures 32 and 33

denotes high sulphur fuel baseline measurement denotes high sulphur fuel after catalyst denotes low sulphur fuel baseline measurement denotes low sulphur fuel after catalyst In Figures 34 and 35

denotes baseline measurement denotes preliminary test after catalyst denotes after catalyst after 7 hours denotes after catalyst after 50 hours Figures 34 and 35 show the effect of time on the properties of the catalyst.

The maximum temperature on the flange of the catalyst chamber when the engine is running at a speed of 2,200 rpm and 107 brake mean effect pressure Ib/in2 was 1 030C and on the outer wall of the chamber was 75 C. The back pressure was negligible.

The weight of particulates present in the exhaust gas was measured by passing a known volume of exhaust through a dilution tunnel where it was diluted with a set volume of air to prevent the solids settling before passing the gases through a filter pad. The weight of particulates enables a value for the particulates in glhrto be calculated. The particulates present in the exhaust gas were analysed further to give thermogravimetric weight, and the weight of volatile components, hydrocarbons, carbon and sulphate.

Using the above method a number of filter pads were obtained for analysis. The weight of sulphate in the particulates was measured by wet chemical analysis of the particulates. Another sample was placed in a thermogravimetric balance where the sample was heated in an inert atmosphere to a temperature of 780"C until the weight was constant. The weight loss between the initial weight and the new gives the weight of volatile components present. Air was introduced and heating continued until the weight was again constant.

The difference in this weight and the value for the previous constant weight gives the weight of carbon components present. The remainder was ash and non-combustible materials such as iron.

The results of the analysis of the particulates present in the exhaust gas for an engine using high and low sulphur fuels are given in Figures 46-49 Figures 46 and 47 are with catalyst A in the catalyst chamber and Figures 48 and 49 are with catalyst B in the catalyst chamber.

Table 3 gives sulphate levels in g/hr in the particulates using a high and low sulphur fuel in the engine.

Table 4 below gives sulphate levels in g/hr in the exhaust gas using a high sulphur fuel in the engine with catalyst B in the catalyst chamber. Measurements were taken after 7 and 50 hours.

TABLE 3 1400 rev/min Base line Catalyst 'A' Catalyst 'B' Base line Catalyst 'A' Catalyst 'B' gas oil gas oil gas oil conoco conoco conoco High S Fuel High S Fuel High S Fuel Low S Fuel Low S Fuel Low S Fuel %load 2 1.58 1.48 3.60 5.04 2.09 Nil %load 50 1.13 4.05 2.64 0.07 Nil Nil %load 100 1.15 82.39 37.68 0.02 1.15 1.73 2200 rev/min %load 100 1.82 68.57 53.28 4.89 7.44 10.1 %load 50 1.20 21.53 18.0 1.08 2.64 5.0 %load 2 2.40 7.99 5.76 1.73 Nil 1.44 TABLE 4 1400 Rev/Min initial level g/h After 7 hours After 50 hours Stablising g/h Stabllising g/h %load 2 3.50 0.67 0.6 %load 50 2.64 1.32 0.9 %load 100 37.68 22.80 9.6 2200 Rev/Min %load 100 52.28 36.20 55.7 %load 50 18.00 21.10 15.10 %load 2 5.78 6.40 2.3

Claims (20)

1. An internal combustion engine including apparatus for reducing pollutants contained in exhaust gases emitted from the engine having at least one exhaust port, the apparatus comprising a chamber, means for cooling the chamber and a catalyst supported within the chamber, the catalyst including a substrate, a layer of refractory metal oxide applied to at least a part of the surface of the substrate and a catalytic material applied to the layer of refractory metal oxide, the chamber also including an inlet in communication with the said exhaust port via which exhaust gas emitted from the engine is led into the chamber and passed through the catalyst prior to passage through an exhaust system to atmosphere.

2. An engine according to Claim 1 wherein the chamber includes a number of inlets corresponding to the number of exhaust ports of the engine.

3. An engine according to Claim 1 or Claim 2 wherein the apparatus is disposed adjacent the exhaust ports of the engine.

4. An engine according to any preceding claim wherein the substrate is made from a material selected from the group consisting of ceramic material and metallic materials.

5. An engine according to Claim 4wherein the catalytic material is a metal or a metallic alloy or a composition containing two or more metals and/or the oxides thereof.

6. An engine according to Claim 4 wherein the metallic substrate is in the form of knitted or woven material.

7. An engine according to Claim 6 wherein the metallic substrate material is in the form of wire.

8. An engine according to any preceding claim wherein the metallic substrate induces turbulence in exhaust gases leaving the said chamber.

9. An engine according to any one of Claims 1 to 8, wherein the refractory metal oxide layer is selected from the group consisting of:- Mg, Ca, Sr, Ba, Sc, Y, the lanthanides, Ti, Zr, Hf, Th, Ta, V, Cr, Mn, Co, Ni, B, Al, Si and Sn.

10. An engine according to Claim 9, wherein the first layer is made from Al2O3, alumina hydrates, BaO, TiO2, ZrO2, HfO2, ThO2 or Cur203.

11. An engine according to Claim 1, wherein the substrate is made from a corrosion-resistant alloy containing a base metal.

12. An engine according to Claim 11, wherein the substrate is made from an alloy containing nickel and chromium, having an aggregate nickel plus chromium content greater than 20 weight percent.

13. An engine according to Claim 12, wherein the substrate is made from an alloy of iron including at least one ofthe elements:- chromium (wto 40) wt%, aluminium (1 to 10) wt %, cobalt (trace to 5) wt %, nickel (trace to 72) wt % and carbon (trace to 0.5) wt %.

14. An engine according to Claim 13, wherein the base metal alloy includes yttrium in an amount of 0.1 to 3.Owt%.

15. An engine according to Claim 1, wherein the substrate is made from a metallic material having a thickness falling within the range 0.0254 and 0.508 mm.

16. An engine according to any preceding Claim, wherein the catalyst material is a metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, Fe, Co, Ni, V, Cr, Mo, W, Y, Ce, alloys containing at least one of said metals and intermetallic compounds containing at least 20 wt % of one or more of the said metals.

17. An internal combustion engine according to any preceding claim operable on the diesel combustion cycle.

18. An engine according to any preceding claim wherein the means for cooling the chamber comprises a water jacket.

19. An engine according to any preceding claim wherein the said water jacket is part of a water jacket covering substantially the whole of the engine.

20. A process for the reduction of pollution by exhaust gas from an internal combustion engine comprising passing the exhaust gas from the cylinders of the engine into a chamber which is at least partially surrounded by a water jacket and which contains a catalyst such that at least part of the noxious gases and particulates undergo catalytic oxidation.