GB2054402A

GB2054402A - I.C. engine exhaust gas treatment

Info

Publication number: GB2054402A
Application number: GB8021251A
Authority: GB
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 1979-06-29
Filing date: 1980-06-27
Publication date: 1981-02-18
Also published as: NL8003699A; SE8004632L; IE49846B1; IT1136188B; CA1165247A; IE801344L; DK279280A; DK155541B; FR2460388A1; LU82550A1; DK155541C; DE3024491A1; GB2054402B; IT8012584A0; FR2460388B1

Abstract

An internal combustion engine includes apparatus for reducing pollutants contained in exhaust gases omitted from the engine, the apparatus comprising a casing (1) defining a chamber containing a catalyst (3), the catalyst including a substrate made from filamentary metallic material in knitted, woven or crushed form, a first layer of a refractory metal oxide applied to the substrate and a second layer of a catalytic material applied to the first layer, the chamber having an inlet in communication with the exhaust ports (7, 8, 9, 10) of the engine via which exhaust gas emitted from the engine is lead into the chamber and passed through the catalyst prior to passage through an exhaust system (11) to atmosphere. <IMAGE>

Description

SPECIFICATION Exhaust gas purification This invention relates to the reduction of smoke and other noxious components contained in gases and in particular exhaust gases.

Gases from boilers and internal combustion engines often contain finely divided particles of hydrocarbons and/or carbon or other solid matter which emerge in the form of smoke. The smoke from a diesel engine is composed of solid/liquid particles (i.e., solid particles having a liquid outer covering layer), solid chain aggregates in which spherical particles of between 1 00-800A diameter link up together, liquid sulphates, liquid hydrocarbons and gaseous hydrocarbons. The solid/liquid particles generally comprise carbon particles with adsorbed liquid hydrocarbons and the solid chain aggregates are generally composed of high molecular weight organic compounds and/or inorganis sulphates.

White smoke is produced when the engine first starts up and results from the condensation of water vapour on to particulates contained in the exhaust gas so that a fine mist is formed. Black smokes produced by diesel engines are formed when the engine has warmed up and contains a relatively high proportion of carbon particles. In blue smoke there is some carbon but also a relatively high proportion of gaseous organic compounds such as aldehydes. 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 are less than four microns.

One object of the present invention is at least to reduce the quantity of smoke contained in waste gases by effecting the catalytic oxidation of smoke forming particles in these gases.

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

A further 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.

In this specification the term "pollutants" should be taken to include hydrocarbons, carbon monoxide and oxides of nitrogen formed by the internal combustion engine as well smoke forming particles described above.

According to a first aspect of the present invention internal combustion engine includes apparatus for reducing pollutants contained in exhaust gases emitted from the engine having at least one exhaust port, the apparatus comprising a casing defining a chamber containing a catalyst, the catalyst including a substrate made from filamentary metallic material in knitted, woven or crushed form, a first layer of a refractory metal oxide applied to the substrate and a second layer of a catalytic material applied to the first layer, the chamber having an inlet in communication with the said exhaust port via which exhaust gas emitted from the engine is lead into the chamber and passed through the catalyst prior to passage through an exhaust system to atmosphere.

Usually, the catalytic oxidation of carbon particulates takes place at about 400 C whereas the normal temperatures of combustion of such particulates is 700-800CC. For hydrocarbon particles catalytic oxidation will take place at temperatures about 200 C. 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 where studied. A number of sample catalysts were prepared. The catalysts comprised a substrate fabricated from 310 stainless stell 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: carbond monoxide (44), doubly 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-off temperature 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, when it is desired to effect the catalytic oxidation of any smoke forming particles in the exhaust gas from an internal combustion engine little or no heating is, consequentiy required. This is due to the fact that when a diesel engine is operated at medium to full power the temperature thereof is about 400"C so that no preheating of the exhaust gas issuing from the engine is required before passing the said exhaust gas over a catalyst The filamentary metallic substrate may be in the form of wire and is disposed so as to provide maximum contact of the catalytic metal with the said exhaust gases.Preferably the wire is in a flattened form, usually obtained by rolling down prior to the deposition of washcoat and catalytic metal. In the operation of a diesel or similar engine in which an excess of air or oxygen is present in the combustion chamber such contact ensures that a substantial proportion of the pollutants as above described undergo catalytic oxidation.

A preferred disposition of the metallic wire substrate within the said chamber is such that turbulence is induced in the exiting gases.

According to a second aspect of the present invention a process for the redution of pollution by exhaust gas from internal combustion engines comprises passing the said exhaust gas from the cylinders of the said engine into a chamber containing a catalyst on a support of design such that turbulence is produced and the pollutants present in the exhaust gas come into contact with the said catalyst and at least part of the said noxious components and particulates undergo catalytic oxidation. Preferably the said engine is a diesel engine.

Features of an internal combustion engine according to the present invention include: i) a chamber having an outerwall with a plurality of entry ports adjacent to the exhaust valves of the said engine and an exit port adjacent to the exhaust pipe; and ii) a supported catalyst so positioned that the exhaust gas flowing into the said chamber from the exhaust ports has to pass through the said catalyst which is so disposed such that the exhaust gas flow is turbulent at least while the said gas is in contact with the said catalyst.

Preferably the catalyst used in the said internal combustion engines comprise: a) a divided substrate which is positioned in the path of the gas flow so as to create turbulence in the exhaust gas stream; 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, alloys thereof and intermetallic compounds containing at least 20% by weight of one or more of the said metals disposed upon the surface or throughout the refractory metal oxide washcoat layer.

The refractory metal oxide washcoat layer preferably contains in the form of their oxides one or more members of 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.

A preferred washcoat material is A1203 and alumina hydrates but stabilising oxides such as BaO and oxides promoting catalytic activity such as TiO2, ZrO2, HfO2, ThO2, Cr203 and NiO may also be present.

One preferred form of catalyst substrate comprises a structure made up from woven or knitted wire and an even more preferred form is woven or knitted wire which has been rolled down before fabrication into woven or knitted form. Suitable alloys which may be used in the manufacture of the wire are corrosion resistant and particularly oxidation resistant base metal alloys.

Examples of such 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 (trace-5) 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.7903817 dated 2nd February 1979 (not GB 2012317A).

Where wire is used as a substrate its thickness is preferably between 0.001 and 0.02 inches thick and more preferably between 0.001 and 0.012 inches thick.

In one embodiment of the present invention the catalyst is contained in a reaction tube which is positioned substantially centrally in the exhaust chamber. The embodiment will be described with reference to Figure 1.

The outer wall, 1, of the exhaust chamber has openings 7,8,9 and 10 which are adjacent to and continuous with the exhaust ports of the cylinders and one exit, 12, adjacent to exhaust pipe, 11. The reaction tube, 2, which is supported in the chamber by struts Sand 6 contains the supported catalyst 3. The reaction tube is so positioned that the exhaust gas on entering the exhaust chamber has to pass through the reaction tube and so come into close and continuous contact with the catalyst before leaving the exhaust chamber and entering the exhaust pipe. The exhaust gas flow through the exhaust chamber is generally indicated by the labelled arrows F1, F2, F3, F4, F5 and F6. Combusted gas flows in from the cylinder ports through the openings 7,8,9 and 10 and flows along the reaction tube, 2, and out into the exhaust pipe, 11. A retaining bar, 4, is placed across the exit of the reaction tube to ensure that the catalyst remains in position.

The catalyst support is preferably of knitted wire mesh. This may be fabricated into a single monolith or it may be made up in annular sections.

The layer of washcoat and the catalytic layer may be applied to each section separately or after the sections have been linked together. Alternatively the support, in sections or linked together, may have the washcoat and catalytic layer applied after it has been placed in the reaction tube.

A further embodiment will be described with reference to Figure 2. The outer wall, 21, of the catalyst chamber has openings 27, 28, 29 and 30, adjacent and continuous with the exhaust ports of the cylinders and one exit, 32, adjacent to the exhaust pipe, 31. The catalyst,23, comprising a support, a washcoat layer and a catalytic metal is so disposed so that the exhaust gas on entering the catalyst chamber is compelled to pass through the interstices of the said catalyst before leaving the chamber and entering the exhaust pipe. The exhaust gas flows through the catalyst chamber as indicated by the labelled arrows, F41, F42, F43, F44 and F4s.

The gas flows in from the exhaust ports as shown by F41, F42, F43 and F44 and then through the catalyst and out into the exit tube 22 as shown by F45.

In this embodiment the support for the catalyst is preferably of knitted wire which may be made up into sections or as one unit but if it is in sections, e.g., of doughnut configuration, these are normally linked together before the support is placed in the chamber. One end of the support is closed off by joining, e.g., by welding, a disc, 26, to it and an annular disc, 25, at the other end holds the support in position. The supported catalyst is disposed in the catalyst chamber as shown in Figure 2 by attaching the ends covered by the discs, 25 and 26, to the outer walls of the chamber. To ensure that the support does not collapse inwards a cylindrical and perforated exit tube, 22, positioned in the catalyst chamber allows gas to pass through it and continue to the exhaust pipe, 31.The tube, 22, may be constructed of wire mesh or it may be a perforated metal tube having hoies or slots.

Figure 3 depicts an alternative embodiment in which in place of a perforated exit tube in the catalyst clamber 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 4. Rods and spacing plates need to be constructed of a material resistant to oxidation up to at least 8000C.

A further embodiment will be described with reference to Figure 2A in which, for convenience, only two exhaust ports are shown. The outer wall 100 of the catalyst chamber has openings, 101 and 102 adjacent to and continuous with the exhaust ports of the cylinders and one exit, 103, adjacent to the exhaust pipe. The catalyst, 104, comprising a support, a washcoat layer and a catalytic metal is so disposed that the exhaust gas has to pass through the catalyst before leaving the chamber. The catalyst is disposed in the chamber using spacing plates, 105, as described above.One end of the spacing plates, 109, is fixed to the chamber wall, 100, and a disc or metal plate, 108, 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, 101 and 102, and down through sleeves, 106 and 107, into the inner space 110 provided by the spacing plates, 105. The exhaust gas then flows through the catalyst outwards and then through the exit, 103. The flow of the exhaust gas is indicated by the labelled arrows F90- Flus.

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.

Example 1 The (2000 cc capacity) muiticylinder engine of a commercially available diesel engine-powered automobile was modified to demonstrate the resuls obtained in operation of the present invention.

A catalyst chamber as outlined in the first embodiment (Figure 1) of the invention, as described above, was fitted to the engine. A knitted mesh catalyst support was made from wire having the following composition: %wt Cr 15 Al 4 Y 0.3 Fe Balance Deposited on this support was a washcoat consisting of gamma alumina stabilized with 5% by weight BaO and a catalytic metal layer composed of platinum and palladium. The Pt/Pd loading was 2.5 g total (Pt: Pd ratio 1:1) on a total catalyst volume of 84 cubic inches. The results were obtained by driving the automobile through the LA4 diesel cycle. The hydrocarbons, carbon monoxide, nitrogen oxides and particulates present in the exhaust gas emissions were measured in g/mile. Base line measurements were first taken without a catalyst in the chamber but with back pressure adjusted to the same value as with the catalyst present.

Results are given in Table 1: TABLE 1 Particulates HC g/mile CO g/mile NOxg/mile g/mile Baseline figures 1.54 .i.93 1.53 0.85 Modified engine 0.214 1.892 0.979 0.44 The back pressure was found to be high.

Example 1A Further experiments were carried out using the same catalyst as in Example 1 above. Baseline particulates emissions using the same vehicle were determined in four tests as g/mile figures. These were expanded to include thermogravimetric determinations of the percentage carbon and volatiles contained within the particulates and the g/mile sulphate contained within the particulates. The results obtained are shown as follows: Baseline figures Test No. Particulates %Carbon % Volatiles Sulphates g/mile g/mile 1 0.582 62.5 37.5 0.015 2 0.512 58.0 42.0 0.011 3 0.509 59.6 40.4 0.012 4 0.482 61.8 38.2 0.012 NOTE: All above measurements completed on a hot LA4 driving cycle.

The full baseline emissions determined for HC, CO and NOx were also determined, the results being as follows: Test No. HC g/mile CO g/mile NOx gimile 1 0.350 1.564 1.775 2 0.339 1.529 1.803 3 0.354 1.561 1.786 A catalyst chamber was designed within the constraints available in the vehicle without any modification being made to the engine compartment layout. This resulted in a catalyst volume of 0.9 litres which was anticipated to be inadequate but upon which full tests were completed. The results of these are as follows: Test No. Particulates %Carbons % Volatiles Sulphate gimile gimile 1 0.494 79.4 20.6 0.036 2 0.441 76.4 23.6 0.037 3 0.444 75.3 24.7 0.035 4 0.515 67.3 32.7 0.055 5 0.466 63.4 36.6 0.064 6 0.492 76.1 23.9 0.051 NOTE: The vehicle had completed 500 road miles prior to the first test and the entire period of testing was completed under simultated city driving conditions using the LA4 cycle.

Test results obtained for the HC, CO and NOx emissions were as follows: Test No. HC gimile CO g/mile %Carbons 1 0.224 0.979 1.892 2 0.238 1.073 1.874 3 0.215 0.981 2.014 Example 2 A second catalyst chamber as described in the second embodiment (Figure 2) was fitted onto the engine. A knitted mesh support made of the same wire as used in Example 1 again with a washcoat of gamma alumina. The catalytic metal layer comprises rhodium 7B wt % and platinum 922 wt %. The total catalyst volume was 110 cubic inches. The weight of support used was approximately 1.6 kg, 5 g of washcoat, alumina, and 2.99 of the catalytic metals Rh and Pt in the above ratio were applied to the support. Baseline measurements were taken with no catalyst present in the chamber attached to the engine.The results are given below in Table 2 with the car being driven through the LA4 cycle with a hot start.

TABLE 2 Particulates HC g/mile CO g/mile NOx g/mile g/mile Baseline figures 0.35 1.55 1.8 0.57 Modified engine 0.2 0.5 2.1 0.31 The back pressure without a catalyst present in the chamber was 2.4 inches of mercury and 3.5 inches of mercury with catalyst present in the chamber. the C/H atomic ratio of the particulates present in the exhaust gas before and after passage through the catalyst chamber was measured and is given below in Table 3 with a hot start for the engine.

TABLE 3 C/H ratio ofparticulatespresent in the exhaust gas Before catalyst After catalyst C 63 80 H 37 20 This is a measure of the reduction in the organic compound content of the exhaust gases. The concentration of sulphate present in the exhaust gases before and afterthe catalyst was measured and found to be unchanged.

Further results obtained are given below in Table 4 with a cold start for the engine.

TABLE 4 Particulates HC g/mile CO g/mile NOx g/mile g/mile Baseline figures 0.41 1.3 1.9 0.62 Modified engine 0.242 0.274 1.86 0.42 Modified engine 0.218 0.252 1.86 0.4 The composition of the particulates present in the exhaust gas is given below in Table 5 with a cold start for the engine.

Adsorbed HC's Suiphates g/mile Carbon g/mile g/mile Baseline figures 0.11 0.34 0.165 Modified engine 0.11 0.28 0.025 The results in tables 2,3,4 and 5 were obtained using a commercially available diesel engine-powered automobile. The engine had been modified with a catalyst chamber in place as previously described. The automobile had completed 500 miles round a test circuit before being driven through the taxi cycle with a maximum speed of 25 mph.

Further tests were conducted using a commercially available diesel engine powered automobile. A catalyst chamber as described in the second embodiment, as shown in Figure 2, was fitted onto the engine.

A support was made of 310 stainless stell wire of diameter 0.01 inch which was flattened to 0.004 inch across before being knitted. The support was coated with a washcoat of gamma alumina. The catalytic metal layer comprises rhodium 5.7% and platinum 94.3% with a loading of 25 g/ft3. The weight of wire used was 3,200 g with 1,200 9 of washcoat. The total volume of catalyst used was 217 cubic inches.

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 fiiter pad. The weight of particulates enables a value for the particulates in g/hrto 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.

Baseline measurements were taken with a manifold connected to the engine in place of the chamber containing the catalyst. Measurements were taken with the automobile driven through the LA4 cold start diesel cycle are given in Table 6 below, iA4 hot start diesel cycle results are given in Table 7 below, and the Highway driving test results are given in Table 8 below. The Highway test used was the standard test cycle used in the US for fuel consumption trials.

The results given in Tables 6 and 7 are shown in graphical form in Figures 5-9, LA4 cycle cold start, and in Figures 10-14forthe LA4 cycle hot start. (Baseline figures dotted line and modified engine continuous line.) The reduction in particulate concentration (measured in g/mile) in an I C engine according to the present invention is shown in column 3. Reduction in adsorbed hydrocarbons and carbond present in the particulates are shown in columns 7 and 9 respectively. Sulphate figures show an increase in some cases but the absolute level of the emission remains low.

Back pressure measurements were made. This is the difference in the pressure of the gases on leaving the exhaust ports and on leaving the chamber. The results are given in Table 9 for the automobile being driven through the LA4 cycle and in Table 10 for the Highway driving test.

TABLE 6 (Cold Start LA4)

0 0.636 0.009 0.2402 0.388 0 Modified 0.286 -55.0 0.0094 +44 0.043 -82.1 0.234 -39.7 Engine 600 0.283 -55.5 0.0178 +95.6 0.0537 -77.6 0.2117 -45.4 1200 0.340 -46.5 0.0121 +34.5 0.0722 -69.9 0.2557 -34.1 1800 0.221 -65.3 0.00994 +10.4 0.0316 -86.6 0.1795 -53.7 3000 0.314 -50.6 0.0233 +158.9 0.0653 -72.8 0.2255 -41.9 3600 0.418 -34.3 0.066 +633.3 0.1323 -44.9 0.2199 -43.3 4200 0.364 -42.8 0.0199 +121.1 0.0380 -84.2 0.3061 -21.1 4900 0.279 -56.1 0.01 +11.1 0.0522 -78.3 0.2168 -44.1 5100 Baseline 0.692 0.0259 0.2038 0.4623 5500 Modified 0.264 -61.9 0.0139 -46.3 0.0487 -76.1 0.2014 -56.4 Engine 6100 0.316 -54.3 0.0375 +44.8 0.0677 -66.8 0.2108 -54.4 8500 0.308 -55.8 0.0152 -41.3 0.0439 -78.5 0.247 -46.6 12500 Baseline 0.649 0.0231 0.201 0.424 12500 Modified 0.309 -52.4 0.0192 -16.9 0.0491 -75.6 0.241 -43.2 Engine

TABLE 7 (Hot Start LA4) 0 Baseline 0.572 0.00802 0.230 0.334 0 Modified 0.264 -53.8 0.0066 -17.7 0.043 -81.3 0.214 -35.9 Engine 800 0.215 -62.4 0.0075 -6.5 0.0362 -84.3 0.1714 -48.7 1200 0.238 -58.4 0.00729 -9.1 0.0365 -84.1 0.1942 -41.9 1800 0.205 -64.2 0.00944 +17.7 0.0328 -85.7 0.1628 -51 3000 0.311 -45.8 0.035 +336.4 0.0608 -73.6 0.2152 -35.6 3600 0.304 -46.9 0.041 +411.2 0.0705 -69.3 0.1927 -42.3 4200 0.283 -50.5 0.0229 +185.5 0.0272 -88.2 0.233 -30.2 4900 0.263 -54.0 0.0146 +82.0 0.0304 -86.8 0.218 -34.7 5100 Baseline 0.548 0.0193 0.1955 0.3332 5500 Modified 0.277 -58.6 0.0191 -1.0 0.0304 -84.5 0.1775 -46.7 Engine 6100 0.266 -51.5 0.037 +91.7 0.026 -86.7 0.203 -39.0 8500 0.278 -49.3 0.0182 -5.7 0.0299 -84.7 0.23 -30.9 12500 Baseline 0.521 0.0165 0.209 0.296 12500 Modified 0.286 -45.1 0.013 -21.2 0.0349 -83.3 0.238 -19.6

TABLE 8 (Highway Driving Test) 0 Baseline 0.532 0.0169 0.206 0.309 1800 Modified 0.355 -33.3 0.0557 +229.6 0.0782 -62.0 0.221 -28.5 6100 Baseline 0.493 0.0176 0.1693 0.306 6100 Modified 0.898 +82.1 0.129 +633.0 0.0227 -86.6 0.746 +143.8 Engine 8500 Baseline 0.616 0.0285 0.2234 0.3641 8500 Modified 0.554 -10.1 0.0351 +23.2 0.0995 -55.5 0.419 +15.1 Engine 12500 Baseline 0.625 0.031 0.2301 0.3639 12500 Modified 0.373 -40.3 0.042 +35.5 0.0981 -57.4 0.232 -36.3 Engine TABLE 9 Back pressure in inches of mercury Baseline After catalyst chamber Miles covered Max. Average Max.Average Hot Start 0 3.12 0.63 2.88 0.75 1,800 3.42 1.0 4,200 3.8 0.98 4,900 3.67 0.91 5,500 5.35 1.9 6,100 2.42 0.65 4.58 1.43 8,500 3.31 0.96 12,500 2.38 0.85 Cold Start 0 2.64 0.48 3.54 0.86 1,800 3.15 1.15 4,200 4.6 0.96 4,900 4.5 0.95 5,500 4.86 1.65 6,100 4.84* 0.61 4.62 1.38 8,500 3.28 0.96 12,500 2.5 0.83 * High figure probably due to build up of soot deposits TABLE 10 Back pressure in inches of mercury Baseline After catalyst chamber Miles covered Max. Average Max. Average 1,800 3.34 1.98 6,100 2.0 1.1 4.05 2.9 8,500 3.12 2.0 TABLE 11 Back pressure in inches of mercury Baseline After catalyst chamber Miles covered Max. Average Max. Average 0 2.88 0.56 3.20 0.80 8,500 4.48 0.61 4.62 1.38 In the foregoing description the following abbreviations have been used and their meanings are indicated.

CVS - constant volume sampling.

LA4- Los Angeles Cycle as laid down by the Environmental Protection Agency (EPA) and the United States and is a standard test cycle devised to simulate a drive to work in Los Angeles traffic conditions. It is furthermore a test to which all new vehicles are subjected.

Taxi Cycle - A test cycle of about 50 miles long approved by EPA and carried out at low speeds up to 25 m.p.h. and includes periods when the car is stationary and the engine is idling.

Claims

1. An internal comubustion engine including apparatus for reducing pollutants contained in exhaust gases emitted from the engine having at least one exhaust port, the apparatus comprising a casing defining a chamber containing a catalyst, the catalyst including a substrate made from filamentary metallic material in knitted, woven or crushed form, a first layer of a refractory metal oxide applied to the substrate and a second layer of a catalytic material applied to the first layer, the chamber having an inlet in communication with the said exhaust port via which exhaust gas emitted from the engine is lead 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 casing 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 said apparatus is disposed adjacent the exhaust ports of the engine.

4. An engine according to anyone of claims 1, 2 or 3, wherein the metallic substrate is disposed to establish maximum contact between the catalytic material and the exhaust gas.

5. An engine according to anyone of claims 1 to 4, wherein 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 1, wherein the metallic substrate is in the form of ribbon with at least two substantially flat opposite surfaces.

7. An engine according to claim 1, wherein the filamentary metallic material is in the from of wire.

8. An engine according to any preceding claim, wherein the metallic substrate induces turbulence in exhaust gases leaving the 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 Awl203, alumina hydrates, BaO, TiO2, ZrO2, HfO2, ThO2 or Cr203.

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 of the elements:- chromium (w to 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 yittrium in an amount of 0.1 to3.Owt%.

15. An engine according to claim 1, wherein the substrate is made from a metallic material having a thickness falling within the range 0.001 and 0.02 inch.

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. A process for the reduction of pollution by exhaust gas from internal combustion engines comprises passing the said exhaust gas from the cylinders of the said engine into a chamber containing a catalyst on a support of design such that turbulence is produced and the pollutants present in the exhaust gas come into contact with the said catalyst and at least part of the said noxious components and particulates undergo catalytic oxidation.