GB2122914A - Process for oxidising particles in diesel exhaust - Google Patents

Abstract

A process for oxidising carbon particles in the exhaust gas from a diesel engine involves passing exhaust gas (F1, F2, F3, F4) when at 200- 400 DEG C, through an interstitial catalyst system (3) wherein the gas is made to execute a sharp change in direction such that carbon particles may be oxidised and removed from the exhaust gas without the need for external heating which can lead to unwanted thermal stresses. <IMAGE>

Description

SPECIFICATION Process for oxidising particles in diesel exhaust This invention relates to a process for oxidising particles in exhaust gas emitted from a diesel engine when the exhaust gas is at a temperature of 200 to 4000 C.

Exhaust gas emitted from a diesel engine contains solid/liquid particles (i.e. solid particles having a liquid outer covering layer). Also present are solid chain aggregates (in which spherical particles of between 100 to 800 A diameter link up together), liquid sulphates, liquid hydrocarbons whereas gaseous hydrocarbons such as aldehydes. 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 inorganic sulphates.

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. Usually, the catalytic oxidation of carbon particles takes place at about 4000C whereas their normal (i.e. uncatalysed) temperature of combustion is 700800 C. For hydrocarbon particles catalytic oxidation will take place at temperatures about 2000C.

An object of the present invention is to reduce the quantity both of noxious gases and particulates especially carbon particles present in exhaust gas emitted from diesel engine when the exhaust gas is at a temperature of from 200 to 4000C.

Accordingly this invention provides a process for oxidising particles in exhaust gas emitted from a diesel engine when the exhaust gas is at a temperature of from 200 to 4000C which comprises passing the exhaust gas through a chamber containing an interstitial catalyst system comprising a catalyst, a layer of refractory metal oxide and a support comprising filamentary metallic material in a knitted or woven form, the catalyst being disposed on or through the layer of refractory metal oxide which in turn is disposed on the surface of the filamentary metallic material wherein the exhaust gas is passed into the chamber in a first direction and caused to pass in a direction transverse to the first direction during a portion of its passage through the chamber thereby increasing turbulence within the interstitial catalyst system.For example the exhaust gas may be passed through the catalyst system in a direction transverse of the first direction. Typically the chamber is defined by a casing having an entry port in communication with an exhaust port in the engine and having an exit port from which exhaust gas can be taken to atmosphere whereby exhaust gas from the engine can be passed through the chamber. The support is mounted within the chamber preferably spaced from the casing so as to define an outer passageway. The support may be shaped so as to define a central passageway within the support.When the support is associated with outer and central passageways, one of the passageways communicates with the entry port or ports and the other communicates with the exit port and the support is positioned so that the exhaust gas discharged from the engine is caused to pass through one passageway then into the interstitial catalyst system and through the other passageway, the outer and central passageways and the support being aligned relative to the entry port or ports such that exhaust gas passing through the chamber is caused to flow in a direction transverse of the entry port or ports during a portion of its passage through the chamber thereby increasing turbulence within the interstitial catalyst system.

Preferably the chamber casing has a plurality of entry ports adjacent to the exhaust valves of the engine. Preferably the exit port in the chamber casing is adjacent to an exhaust pipe.

Preferably the catalyst system contained in the chamber comprises a catalyst selected from the group of catalytic metals 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 metals disposed upon the surface of or throughout the layer refractory metal oxide.

The layer of refractory metal oxide is preferably a washcoat layer containing (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, Bk, Al, Si and Sn. Preferred washcoat materials are Awl203 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.

The filamentary metallic material of the support is preferably made from base metal alloys which are corrosion resistant and preferably oxidation resistant. 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 (trace5) wt %, nickel (trace72) wt % and carbon (trace0.5) wt %. Such supports are described in German DOS 2450664.

Other examples of base metals capable of withstanding the rigorous conditions required are ironaluminium-chromium alloys which may also contain yttrium. The latter alloys may contain 0.5-12 wt % Awl,0.183.0 wt % Y, 0--20 wt % Cr and balance Fe. 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 2 February 1979 (nowGB 2013517A).

Where wire is used as the filamentary metallic material, its thickness is preferably between 0.025 to 0.5 mm (i.e. 0.001 and 0.02 inches) thick and preferably between 0.025 to 0.3 mm (i.e. 0.001 and 0.012 inches) thick. Preferably prior to its fabrication into woven or knitted form the wire is rolled down to a ribbon having two flat opposite surfaces.

The invention-is further illustrated by the following specific embodiments described with reference to Figures 1 to 4 of the drawings and by the following Examples, results from which are shown as graphs by the figures 5 to 14 of the drawings. In the drawings, Figure 1 shows a section through a chamber suitable for use in combination with a diesel engine according to the invention, Figure 2 shows a section through an alternative chamber, Figure 2a shows on a larger scale a section through a further alternative chamber, Figure 3 shows in perspective an assembly of supporting bars suitable for acting as a central support in the chamber, Figure 4 shows in perspective an alternative central support for the chamber, Figures 5 to 9 show graphs of the composition of pollutants in exhaust discharging from a diesel engine operated on an LA4 cold start cycle versus miles notionally travelled, Figures 10 to 14 shows similar graphs to those of Figures 5 to 9 but obtained from a diesel engine operated on an LA4 hot start cycle.

Figure 1 shows a chamber 1 for use in combination with a diesel engine (not shown). Chamber 1 defined by casing 1 a contains a centrally positioned catalyst system 3 located within a reaction tube 2.

Casing 1 b has entry ports 7, 8, 9 and 10 which are adjacent to and in communication with exhaust ports in the engine (not shown). Casing 1 b also has one exit port 12 adjacent to an exhaust pipe 1 1. A support comprising filamentary metallic material and tube 2 is in turn supported in chamber 1 by struts 5 and 6. Tube 2 is positioned transversely of entry ports 7 to 10 and is spaced from casing 1 so as to define a passageway 2a.The exhaust gas on entering chamber 1 has to pass through tube 2 and so come into close and continuous contact with catalyst system 3 before leaving chamber 1 and entering the exhaust pipe 1 The exhaust gas flow through the chamber 1 is generally indicated by the labelled arrows F1, F2, F3, F4, F5 and F0. Combusted gas flows in from the engine exhaust ports through the openings 7, 8, 9 and 10 and flows along transverse tube 2 and out into exhaust pipe 1 A retaining bar 4 is placed across the exit of tube 2 to ensure that catalyst system 3 remains in position.

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

A layer of refractory metal oxide washcoat and the catalyst may be applied to each section of the support separately or after the sections have been linked together. Alternatively the filamentary metallic material (in sections or linked together) may have the washcoat and catalyst applied after it has been placed in the tube.

Figure 2 shows an alternative chamber 21 defined by a casing 21 a having entry ports 27, 28, 29 and 30, adjacent and in communication with engine exhaust ports (not shown) and one exit port 32 adjacent to the exhaust pipe 31. Interstitial catalysts system 23 (comprising a filamentary metallic support, a refractory metal oxide washcoat layer and a catalyst) is disposed centrally within the chamber 21 and transversely of entry ports 27 to 30 so as to define a transverse passageway 23a. The exhaust gas on entering chamber 21 is compelled to pass through the interstices of the catalyst system before leaving chamber 21 and entering exhaust pipe 31.The exhaust gas flows through chamber 21 as indicated by the labelled arrows, F41, F42, F43, F44 and F45. The gas flows in from the engine exhaust ports (not shown) as indicated by F41, F42, F43 and F44 and then through catalyst system 23 and out into a central passageway 22a defined by perforated tube 22 as indicated by F459 In this embodiment the support in the catalyst system is preferably of knitted wire which may be made up either in sections or in one unit. If the support is in sections, e.g. of doughnut configuration, these are normally linked together before the support is placed in the chamber. One end of tube 22 is closed off by welded disc 26. An annular disc 25 at the other end holds catalyst system 23 in position on tube 22.The catalyst system 23 is located in chamber 21 by attaching the ends covered by the discs 25 and 26 to casing 21 a. Tube 22 also ensures that catalysts system 23 does not collapse inwards.

Tube 22 allows exhaust gas to pass through it into central passageway 22a so that the gas can be taken to atmosphere along exhaust pipe 11. Accordingly tube 22 should be permeable and may be constructed of wire mesh or perforated metal having holes or slots.

Figure 3 shows an alternative central structure in which in place of tube 22 there is provided a series of 5 rigid bars, 100 to 500, running the length of chamber 21 b. Bars 100 to 500 are maintained in fixed spatial relationship to one another by spacing plates 600. Accordingly bars 100 to 500 hold catalyst system 23 rigidly in place within chamber 21. Spacing plates 600 in paris connect three of the five bars and are usually at right angles to each other thus being disposed along a diameter of a central cylindrical exit passageway.Two or more pairs of spacing plates 600 may be used and they are usually positioned at regular intervals in the length of the chamber. AIterniveIy the spacing plates 600 may be adapted to extend the whole length of chamber 21 b as shown in Figure 4 whereupon they may be used instead of bars 100 to 500.

Rods and spacing plates need to be constructed of a material resistant to oxidation up to at least 8000 C.

Figure 2a shows a further alternative chamber 100 defined by a casing 1 00a having entry ports 101 and 102 comprising sleeves 106 and 107 adjacent to and in communication with engine exhaust ports (not shown) and having an exit port 103 adjacent to an exhaust pipe (not shown). An interstitial catalyst system 104 (comprising a support, a refractory metal oxide washcoat and a catalyst disposed centrally within chamber 100 and transversely of entry ports 101 and 102 so as to define a passageway 104a. Exhaust gas emitted from the engine has to press through catalyst system 104 before leaving chamber 100. Catalyst system 104 is located in chamber 100 using spacing plates, 105,-as shown in Figure 4.One end 109 of spacing plates 105 is fixed to casing 100 and a disc 108 is attached to the other end of spacing plates 105 to ensure that no exhaust gas can leave chamber 100 without passing through catalyst 104. The exhaust gas flows into chamber 100 through the entry ports 101 and 102, through interstitial catalyst system 104 and into the inner passageway 110 defined by spacing plates 105. The exhaust gas then flows out of chamber 100 through exit port 103. The flow of the exhaust gas is indicated by the labelled arrows Fgo to F,o. For simplicity, Figure 2a shows only two entry ports 101 and 102.

The support for the catalyst system in 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 effect of a catalyst system on the temperature at which catalytic oxidation of particles entrained in the exhaust gas stream of a diesel engine took place were studied. A number of sample catalyst systems were prepared. The catalyst systems comprised a support fabricated from 310 stainless steel wire of diameter 0.010 inch (0.25 mm) rolled down to ribbon 0.0004 inch (0.01 mm) thick, a layer of alumina and a layer of one or more platinum group metal catalysts at a loading of 2.46 mg/g of alumina. A portion of coated wire was cut from a catalyst system. The portion was heated together with particulate matter, collected from the exhaust gas stream of a diesel engine. Heating was performed in the simple pan of a differential scanning colorimeter (a DSC) in an atmosphere of 1% oxygen in argon.As the temperature was gradually raised, 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 dioxide (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 particles took place. This temperature can be referred to as the "light-off" temperature.The results were given below: Alumina loading Light-off (g/g of wire) Catalytic metal(s) 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 temperatures observed for particulates from the exhaust gas stream of a diesel engine, 207-2650C, is considerably lower than the temperature required for combustion to take place when no catalyst is present.

Since the presence of a catalyst enables oxidation of the particles in the exhaust gas to take place at a lower temperature than the normal temperature at which combustion takes place it is possible to oxidise the particles in the exhaust gas emitted from a diesel engine with little or no extra heating. This is due to the fact that the operating temperature of a diesel engine at medium to full power is about 4000C so that no preheating of the emitted exhaust gas is required before passing the exhaust gas into the catalyst system.

Example 2 The (2000 cc capacity) multicylinder engine of a commercially available diesel engine-powered automobile was modified to demonstrate the results obtained in operation of the present invention.

A chamber and catalyst system as outlined in the first embodiment of the invention as described with reference to Figure 1 was fitted to the engine. The support in the catalyst system comprised knitted mesh 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 stabilised 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 ration 1 :1) on a total catalyst volume of 84 cubic inches (1377 cm3). The results were obtained by driving the automobile-through the LA4 diesel cycle (as hereinafter defined). The hydrocarbons, carbon monoxide (CO), nitrogen oxides (NOx) and particles present in the exhaust gas emissions were measured in g/mile.Base line measurements were first taken without a catalyst system in the chamber but with back pressure adjusted to the same value as with the catalyst system present.

Results are given in Table 1: Table 1 Hydrocarbons CO/g NOx Particles smile mile gimile glmile Baseline figures 1.54 1.93 1.53 0.85 Modified engine 0.214 1.892 0.979 0.44 The back pressure was found to be high.

Example 3 Further experiments were carried out using the same catalyst as in Example 2 above. Baseline particle 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 with the particles and the g/mile sulphate contained within the particles. The results are shown as follows: Baseline figures Test Particles % % Sulphates No. glmile Carbon Volatiles g/mile 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. Hydrocarbons CO glmile NOx glmile 1 0.350 1.564 1.775 2 0.339 1.529 1.803 3 0.354 1.561 1.786 The apparatus 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 Particles % % Sulphate No. glmile Carbons Volatiles smile 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 simulated city driving conditions using the LA4 cycle.

Test results obtained for the HC, CO and NOx emissions were as follows: Test Hydrocarbons CO NOx No. g/mile smile smile 1 0.224 0.979 1.892 2 0.238 1.073 1.874 3 0.215 0.981 2.014 Example 4 .A chamber and catalyst system as described with reference to Figure 2 was fitted onto the diesel engine of Example 2. The support comprised a mesh made of the same wire as used in Example 1 and was again provided with a washcoat of gamma alumina. The catalyst comprised rhodium 771 wt % and platinum 921 wt %. The total volume of the catalyst system was 110 cubic inches (1803cm3). The weight of support and alumina washcoat were approximately 1.6 kga 5 g respectively. 2.9 g of the catalytic metals Rh and Pt in the above ratio were applied to the support.Baseline measurements were taken with no catalyst system present. The results are given below in Table 2 with the car being driven through the LA4 cycle with a hot start.

Table 2 Hydrocarbons CO NOx Particles g/mile smile smile smile 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 system present was 2.4 inches of mercury (0.08 bar) but was 3.5 inches of mercury (0.12 bar) when the catalyst system was present in the chamber. The C/H atomic ratio of the particles present in the exhaust gas before and after passage through the chamber was measured and is given below in Table 3.

Table 3 C/H ratio of particles present 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 after the catalyst was measured and found to be unchanged.

Further results obtained are given below in Table 4, this time following a cold start for the engine.

Table 4 Hydrocarbons CO NOx Particles g/mile smile smile smile 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 particles present in the exhaust gas is given below in Table 5 again following a cold start for the engine.

Adsorbed Sulphates Carbon hydrocarbons g/mile smile smile 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 enginepowered automobile. The automobile had first completed 500 miles round a test circuit and had then been driven through the taxi cycle (hereinafter defined) with a maximum speed of 25 mph.

Example 5 Further tests were conducted using a commercially available diesel engine-powered automobile.

A chamber and catalyst as described with reference to Figure 2 was fitted onto the engine. A support was made of 310 stainless steel wire of diameter 0.01 inch (0.25 mm) which was flattened to 0.004 inch (0.01 mm) across before being knitted. The knitted support was coated with a washcoat of gamma alumina. The catalyst comprised rhodium 5.7% and platinum 94.3% with a loading of 25 g/ft3 (883 g/m3). The weight of wire used was 217 cubic inches (3557 cm3).

The weight of particles 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 particles enables a value for the particles in g/hr to be calculated. The particles present in the exhaust gas 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 particles was measured by wet chemical analysis of the particles. Another sample was placed in a thermogravimetric balance where the sample was heated in an inert atmosphere to a temperature of 7800C 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 apparatus. Measurements were taken up with the automobile driven through the LA4 cold start diesel cycle are given in Table 6 below, LA4 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 59, LA4 cycle cold start, and in Figures 10-14 for LA4 cycle hot start. (Baseline figures dotted line and modified engine continuous line).

The reduction in particle concentration (measured in g/mile) by a process according to the present invention is shown in column 3. Reductions in adsorbed hydrocarbons and carbon present in the particles 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 engine 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

Total Adsorbed particle Parcentage Sulphate Percentage hydrocarbons Percentage Carbon Percentage Miles g/mile difference g/mile difference g/mile difference g/mile difference 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 0.0176 +95.6 0.0537 -77.6 0.2117 -45.5 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 550 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 0.306 -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 (Cold start LA4)

Total Adsorbed particles percentage Sulphate Percentage hydrocarbons Percentage Carbon Percentage Miles g/mile difference g/mile difference g/mile difference g/mile difference 0 Baseline 0.572 0.00802 0.230 0.334 0 Modified 0.264 -53.8 0.0068 -17.7 0.043 -81.3 0.214 -35.9 engine 600 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 -51.0 3000 0.311 -45.6 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 0.227 -58.6 0.0191 -1.0 0.0304 -84.5 0.1776 -16.7 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 engine Table 8 (Highway driving test)

Total Adsorbed particles percentage Sulphate Percentage hydrocarbons Percentage Carbon Percentage Miles g/mile difference g/mile difference g/mile difference g/mile difference 0 Baseline 0.352 0.0169 0.206 0.309 1800 Modified 0.355 -33.3 0.0557 +229.6 0.0782 -62.0 0.221 -28.5 engine 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 0.285 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 (or bar) Hot start Baseline After catalyst chamber Miles covered Max.Average Max, Average 3.12 (0.11) 0.63 (0.02) 2.88 (0.10) 0.75 (0.03) 1800 3.42 (0.12) 1.0 (0.03) 4200 3.8 (0.13) 0.98 (0.03) 4900 3.67 (0.12) 0.91(0.03) 5500 5.35 (0.18) 1.9 (0.06) 6100 2.42 (0.08) 0.65 (0.02) 4.58 (0.16) 1.43 (0.23) 8500 3.31 (0.11) 0.96 (0.03) 12500 2.38 (0.08) 0.85 (0.03) Cold start Baseline After catalyst chamber Miles covered Max. Average Max.Average 0 2.64 (0.09) 0.48 (0.02) 3.54 (0.12) 0.86 (0.03) 1800 3.15(0.11) 1.15(0.04) 4200 4.6 (0.16) 0.96 (0.03) 4900 4.5 (0.15) 0.95 (0.03) 5500 4.86 (0.16) 1.65 (0.06) 6100 *4.84(0.16) 0.61 (0.02) 4.62(0.15) 1.38(0.05) 8500 3.28 (0.11) 0.95 (0.03) 12500 2.5 (0.08) 0.83 (0.03) *High figure probably due to build up of carbon deposits Table 10 Back pressure in inches of mercury (or bar) Hot start Baseline After catalyst chamber Miles covered Max. Average Max, Average 1800 3.34 (0.11) 1.98 (0.07) 6100 2.0 (0.07) 1.1(0.04) 4.05(0.14) 2.9 (0.10) 8500 3.12(0.11) 2.0 (0.07) Table 11 Back pressure in inches of mercury (or bar) Baseline After catalyst chamber Miles covered Max. Average Max. Average O 2.88 (0.10) 0.56 (0.02) 3.20 (0.11) 0.80 (0.03) 8500 4.48(0.06) 0.61(0.02) 4.62(0.16) 1.38(0.05) 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) of 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 mph and includes periods when the car is stationary and the engine is idling.

Claims (7)

Claims

1. A process for oxidising particles in exhaust gas emitted from a diesel engine when the exhaust gas is at a temperature of from 200 to 4000C which comprises passing the exhaust gas through a chamber containing an interstitial catalyst system comprising a catalyst, a layer of refractory metal oxide and a support comprising filamentary metallic material in a knitted or woven form, the catalyst being disposed on or throughout the layer of refractory metal oxide which in turn is disposed on the surface of the filamentary metallic material wherein the exhaust gas is passed into the chamber in a first direction and caused to pass in a direction transverse to the first direction during a portion of its passage through the chamber thereby increasing turbulence within the interstitial catalyst system.

2. A process according to claim 1 wherein the chamber casing has a plurality of entry ports disposed adjacent a plurality of exhaust ports in the engine.

3. A process according to claim 1 or claim 2 wherein the filamentary metallic material is in the form of wire having a thickness of from 0.025 to 0.5 mm (i.e. 0.001 to 0.02 inches).

4. A process according to claim 3 wherein prior to its fabrication into woven or knitted form, the wire is rolled down to a ribbon having two flat opposite surfaces.

5. A process according to any one of the preceding claims wherein the catalyst comprises a metal chosen from platinum, rhodium, or palladium or their alloys.

6. A process for oxidising particles in exhaust gas emitted from a diesel engine substantially as herein described and illustrated in the examples.

7. A process for oxidising particles in exhaust gas emitted from a diesel engine substantially as herein described and illustrated in the drawings.

7. A process for oxidising particles in exhaust gas emitted from a diesel engine substantially as herein described and illustrated in the drawings.

New claims or amendments to claims filed on 4 August 1983.

Superseded claims: All.

1. A process for enabling the oxidation of particles in exhaust gas emitted from a diesel engine to be initiated at temperature of from 200 to 4000C which comprises passing the exhaust gas through a chamber containing an interstitial catalyst system comprising a catalyst, a layer of refractory metal oxide and a support comprising filamentary metallic material in a knitted or woven form, the catalyst being disposed on or throughout the layer of refractory metal oxide which in turn is disposed on the surface of the filamentary metallic material wherein the exhaust gas is passed into the chamber in a first direction and caused to pass in a direction transverse to the first direction during a portion of its passage through the chamber thereby increasing turbulence within the interstitial catalyst system.

2. A process according to claim 1 wherein the chamber casing has a plurality of entry ports in communication with a plurality of exhaust ports in the engine.

3. A process according to claim 1 or claim 2 wherein the filamentary metallic material is in the form of wire having a thickness of from 0.025 to 0.5 mm (i.e. 0.001 to 0.02 inches).

4. A process according to claim 3 wherein prior to its fabrication into woven or knitted form, the wire is rolled down to a ribbon having two flat opposite surfaces.

5. A process according to any one of the preceding claims wherein the catalyst comprises a metal chosen from platinum, rhodium, or palladium or their alloys.

6. A process for oxidising particles in exhaust gas emitted from a diesel engine substantially as herein described and illustrated in Examples 2 to 5.