WO1994023186A1

WO1994023186A1 - Exhaust system for reducing pollutants in the exhaust gases of internal-combustion engines

Info

Publication number: WO1994023186A1
Application number: PCT/EP1994/000970
Authority: WO
Inventors: Placido Zampieri
Original assignee: Denox S.R.L.
Priority date: 1993-03-30
Filing date: 1994-03-28
Publication date: 1994-10-13
Also published as: ITVR930030A1; IL109165A0; AU6536694A; ZA942144B; IT1263498B; ITVR930030A0

Abstract

Exhaust system for reducing pollutants in the exhaust gases of an internal-combustion engine, which comprises: at least one relatively long combustion chamber (2); a burner (3) located at the head of the, or of each, combustion chamber (2) and suitable to produce and maintain a pressurized flame that produces a relatively high temperature along the, or the respective, combustion chamber (2); an expansion and flow reversal chamber (4) located downstream of the, or of the respective, combustion chamber (2) and connected to the exhaust unit (188) of the internal-combustion engine; at least one duct (6) for conveying the exhaust gases to be purified which is arranged so as to exchange heat and extends along and around both the expansion chamber (4) and the combustion chamber (2) starting from a manifold (5) up to at least one first lateral outlet port (7) at the combustion chamber so that the exhaust gases undergo superheating and a reheating process; at least one thermally insulating casing (12) around both the, or each, conveyance duct (6) and around the, or the respective, combustion chamber (2) to delimit, together with said chamber (2), at least one interspace (10) through which the combustion gases from the expansion and reversal chamber (4) flow out in the reverse direction before reaching a second outlet port (11); and at least one cooling unit (12, 13) at the exit of each outlet port (7, 11).

Description

EXHAUST SYSTEM FOR REDUCING POLLUTANTS IN THE EXHAUST GASES OF INTERNAL-COMBUSTION ENGINES

Technical Field

The present invention relates to an exhaust system for reducing pollutants in the exhaust gases of internal- combustion engines.

Background Art

Attempts have been made to solve the severe problem of atmospheric pollution caused by the emissions of the engines of motor vehicles by using so-called catalytic converters, in which chemical reactions are produced for converting the pollutants or contaminants contained in the exhaust gases into harmless compounds. Catalytic converters, however, besides requiring the use of special fuels with a reduced content of lead compounds, are very complicated and expensive to build and require the use of noble metals; their efficiency in eliminating pollutants has furthermore turned out to be generally rather poor.

Disclosure of the Invention The aim of the present invention is to provide an exhaust system that can reduce and destroy all or most of the noxious and polluting compounds contained in the exhaust gases of internal-combustion engines and specifically of Diesel engines. An object of the present invention is to provide an environment-friendly exhaust system that is truly effective in destroying the pollutants present in the exhaust gases of Diesel engines, entails no modifications to the engine or to the fuel used in the engine, and can be competitive, as regards manufacturing costs, with respect to catalytic systems or other conventional systems.

Another object of the present invention is to provide an exhaust system of the above mentioned type that allows easy and rapid maintenance actions during the normal operations for the checkout or periodic maintenance of the engine.

This aim, these objects and others which will become apparent hereinafter are achieved by an exhaust system for reducing pollutants in the exhaust gases of an internal- combustion engine, which comprises: at least one relatively long combustion chamber; a burner located at the head of the, or of each, combustion chamber and suitable to produce and maintain a pressurized flame that produces a relatively high temperature along the, or the respective, combustion chamber; an expansion and flow reversal chamber located downstream of the, or of the respective, combustion chamber; a manifold for the exhaust gases to be purified located adjacent to the, or to the respective, expansion chamber and connected to the exhaust unit of the internal- combustion engine; at least one duct for conveying the exhaust gases to be purified arranged so as to exchange heat and extending along and around both the expansion chamber and the combustion chamber starting from the manifold up to at least one first lateral outlet port at the combustion chamber so that the exhaust gases undergo superheating and a reheating process; at least one thermally insulating casing around both the, or each, conveyance duct and around the, or the respective, combustion chamber to delimit, together with said chamber, at least one interspace through which the combustion gases from the expansion and reversal chamber flow out in the reverse direction before reaching a second outlet port; and at least one cooling unit at the exit of each outlet port. Brief description of the drawings

Further characteristics and advantages of the present invention will become apparent from the following detailed description of two currently preferred embodiments thereof, given merely by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a schematic longitudinal sectional view of an exhaust system according to the invention; figure 2 is an enlarged-scale view of the part related to the burner of the exhaust system of figure 1; figure 3 is an enlarged-scale sectional view, taken along the plane III-III of figure 1; figure 4 is an enlarged-scale sectional view, taken along the plane IV-IV of figure 1; figure 5 is an enlarged-scale view of a detail of figure 1 that relates to the combustion chamber and to the surrounding region; figure 6 is an enlarged-scale view of another detail of figure 1, related to the segment for transition between the combustion chamber and the expansion and flow reversal chamber; figure 7 is an enlarged-scale view of another detail of figure 1 related to the expansion and flow reversal chamber and to the surrounding region; figure 8 is an enlarged-scale view of a detail of figure 1, related to the manifold for the exhaust gases to be purified; figure 9 is an enlarged-scale perspective sectional view, taken along the plane IX-IX of figure 1; figure 10 is an enlarged-scale sectional view taken along the plane X-X of figures 1 and 6; figure 11 is an enlarged-scale perspective view, with some parts shown in cross section, of the back wall of the expansion and flow reversal chamber; figure 12 is a plan view of an annular metal wire screen provided along the exhaust gas conveyance path; figure 13 is a sectional view, taken along the plane

XIII-XIII of figure 12; figures 14 and 15 are respectively a lateral elevation view and a plan view of a cage-like wire screen provided in an exhaust gas manifold at the inlet of the exhaust system; figures 16 and 17 are respectively a lateral elevation view and a front view of a tubular wire screen provided in an exhaust gas outlet manifold of the exhaust system; figures 18 to 20 are sectional enlarged-scale views taken respectively along the planes XVIII-XVIII, XIX-XIX and XX-XX of figure l; figure 21 is a view of a detail of figure 20; figure 22 is a sectional enlarged-scale view, taken along the plane XXII-XXII of figure 1; figure 23 is an end view of a cooling-muffler unit; figures 24 and 25 are longitudinal sectional views of a different embodiment of a cooling-muffler unit; figure 26 is a view, similar to figure l, of another embodiment; figure 27 is a longitudinal enlarged-scale sectional view of the burner of the embodiment of figure 26; figure 28 is a longitudinal sectional view of the exhaust system segment shown in figure 26, related to the combustion chamber; figure 29 is a longitudinal sectional exploded view of the exhaust system segment shown in figure 26, between the combustion chamber and the expansion and flow reversal chamber; figure 30 is an enlarged-scale view of a detail of figure 29 in the cold-start operating condition; figure 31 is a view of the same detail as in figure

30, but in the warm operating condition or with the exhaust system in use; figure 32 is a sectional view of the end part of the expansion chamber, where flow reversal occurs, and of the exhaust gas manifold adjacent to it; figure 33 is a front view of the partition that divides the expansion chamber and the exhaust gas manifold; figure 34 is a sectional view, taken along the plane

XXXIV-XXXIV of figure 33; figure 35 is a sectional view, taken along the plane

XXXV-XXXV of figure 33; figure 36 is a front elevation view of a safety valve in case of malfunction; and figure 37 is a side view of the safety valve of figure 36.

Ways of carrying out the invention

In the various figures, identical or similar parts or components have been designated by the same reference numerals.

Initially with reference to the embodiment illustrated in figures 1 to 25, it can be seen that an exhaust system 1 for reducing pollutants in the exhaust gases of an internal-combustion engine is formed by: a combustion chamber 2; a burner 3 arranged at the head of the combustion chamber; an expansion and flow reversal chamber

4 located downstream of the combustion chamber; a manifold

5 for the exhaust gases to be purified which is arranged adjacent to the chamber 4 and connected to the exhaust unit of the internal-combustion engine; a system of ducts 6 for conveying the exhaust gases to be purified which runs from the manifold 5 through the chamber 4 along and around the combustion chamber so as to exchange heat with both until it reaches a lateral evacuation duct 7 at the combustion chamber; a thermally insulating casing formed by one or more layers 8 and 9 and provided both at the duct system 6 and at the combustion chamber to delimit therewith an interspace 10 through which the combustion gases of the burner 3 arriving from the expansion and reversal chamber flow in reverse before reaching a lateral outlet port 11 that passes through the double casing, and two cooling units 12 and 13 located at the outlet of the evacuation duct 7 and of the lateral outlet port 11 respectively.

The burner 3 is of the pressurized type, for example a Diesel fuel burner capable of maintaining a pressure of around 350 mm of water head inside the combustion chamber 2. As more clearly illustrated in figures 1 to 4, the burner 3 is constituted by a front body or nozzle 15 made of insulating material, for example ceramic material or alumina contained in a stainless steel casing that withstands high temperatures and is formed by a cylindrical outer portion 16 and by two internal and coaxial frustum- shaped portions 17 and 18, by an internal atomizer 19 (for example of any suitable commercially available type), by a rear block 20, by a motor-driven compressor 21 for feeding compressed air to the rear block, and by an air intake 22 that opens in an automatically adjustable manner for the compressor 21.

The nozzle 15 has a front annular part 23 that can be fitted on the nozzle, forms an internal shoulder 24 and ends with a portion 25 converging slightly toward the axis x-x of the burner. The shoulder 24 acts as a base for the abutment of a frustum-shaped ring 26 arranged so that its larger flat face rests against the shoulder 24 and is directed toward and along the frustum-shaped portion 18 of the nozzle, with which it forms an annular interspace 27. The ring 26 has the purpose of confining the flame at the outlet of the atomizer 19 and of aiding complete combustion even in the peripheral region of the jet produced by the atomizer, since it is kept incandescent during use. Two holes 28 and 29 are provided at the region comprised between the ring 26 and the tip of the atomizer 19, are orientated in converging directions on opposite sides, and run through the entire thickness of the nozzle

15. An ignition electrode 30 is insertable in the hole 28, and its portion located on the outside of the nozzle 15 can be protected by a tubular sheath 31 of insulating material, such as alumina, which is inserted within a metal container

32, made for example of stainless steel, which is welded or otherwise fixed to the casing 16 and to an annular part 33 for the abutment of the nozzle. The hole 29 is instead closed by a tempered glass part 34 that withstands high temperatures and is retained in position by a snap ring 34a to protect a photocell 35 which, like the electrode 30, is protected by a thermally insulating sheath (alumina) 36 which is inserted within a metal container 37 made of stainless steel which is welded or otherwise fixed to the casing 16 and to the annular part 33. Its photocell 35 acts as flame detector and for greater protection thereof it forms an interspace 38 together with the insulating sheath

36.

Both the electrode 30 and the photocell 35 are supplied with electric current by a control unit of any suitable kind, generally designated by C in figure 2. The nozzle 15 ends at the rear with an outer flange 39 by means of which it can be detachably fixed, by means of bolts 40, to a front flange 41 of the rear block 20 with the interposition of a disk 42 for supporting the atomizer

19 and of a helical compensation spring 43 between the disk 42 and the adjacent end of the casing 16.

The disk 42, as more clearly shown in figure 3, has spokes 44, for example three angularly spaced spokes separated by an equal number of through openings 45 that ensure connection between the inside of the rear block 20 and the nozzle 15.

The disk 42 has a hub 46 extending axially within the nozzle 15 and having an internal flange at 47 at its distal end in order to keep the sleeve 66 that supports the atomizer 19 centered and perfectly axially aligned, as explained in greater detail hereinafter. Preferably, the disk 42 has an enlarged peripheral edge in which it is possible to provide two radial holes for the passage of a cable and of a supply duct, as described hereinafter. At its rear end, the rear block 20 ends with an outer flange for the detachable coupling, for example by means of bolts 49, of a bottom plate 50 having a relatively large axial opening 51 and a collar 52 which is directed toward the inside of the rear block. A union 54 can be fixed peripherally to the opening 51 by means of bolts 53 and is connected to a duct 55 that is directly connected to the delivery of the compressor 21.

The rear block 20 is constituted by a cylindrical body 56 made of stainless steel which accommodates the rear part of the sleeve 66 that supports the atomizer 19; said rear part is supported by a plurality of radial spacer pins 57 that rest against the collar 52 and can be screwed in the sleeve 66 to allow to arrange said sleeve and said atomizer so that they are centered and perfectly aligned along the axis x-x. A multiple-wire electric cable 58 enters the rear block and is kept secured by a terminal 59; the delivery duct 60 of an electric pump 62 for drawing and feeding

Diesel fuel that arrives along a feed pipe 63 that draws from a Diesel fuel source (not shown) also enters the rear block, and both said cable and said duct enter said rear block for example through the enlarged edge of the disk 42.

The pump 62 is also associated with an electric valve 64 for breaking the connection between the pump 62 and the feed pipe 63 after the burner has switched off and to connect the delivery duct 60 to a duct 65 for return to the Diesel fuel source.

The atomizer 19 is supported at the head of the sleeve

66 or other hollow metal body which internally accommodates, in the following order, a thermostat 67, an electric cartridge resistor 68, a Diesel fuel filter 69 and an atomizing nozzle 70. The thermostat 67 is accommodated in a rearward enlargement 71 of the internal hollow of the sleeve 66, whereas the cartridge resistor 68 is accommodated in an axial cylindrical hollow together with which it forms an annular interspace 72 through which the

Diesel fuel arriving from the duct 60 is forced to flow. During the cold-starting of the burner, the cartridge 68 preheats the Diesel fuel before sending it to the atomizer 19, in order to avoid a period of incomplete combustion with the consequent forming of soot. When the temperature inside the burner has risen to a preset threshold value, the thermostat 67 disconnects the supply of current to the cartridge resistor 68.

The motor-compressor unit 21 receives air from the air intake 22, which can have a head flange 73 for coupling to a union (not shown), for example to the outlet port of an air filter. The air intake 22 can be shut by a butterfly valve 74 which is fixed on a diametrical shaft 75 actuatable by an electric motor 76 that can be driven by an encoder 77 according to a preset program for adjusting the amount of air directed to the compressor 21.

Advantageously, downstream of the valve 74 there is a portion having a narrower diameter so as to increase the speed of the air entering the compressor. The combustion chamber 2 is delimited by a stainless steel pipe 80 which is substantially cylindrical in the portion adjacent to the nozzle 15 of the burner and continues on the other side with a conical portion 81 ending with a tapered outlet 82 (figures 5 and 6). At the inlet end 83, the pipe 80 is supported by an annular part 84 which can be fixed, along its peripheral flange, by means of bolts 85, to an outer metal ring 86 having two levels so as to internally delimit annular shoulders for the resting and fixing of the insulating layer or layers 8 and 9 and to externally delimit an annular recess for the abutment of an annular part or ring 87. Said annular part can be fixed peripherally to the ring 86 by means of bolts

88 and is inserted in the annular part 84, together with which it forms a peripheral annular interspace 89. The internal opening of the annular part 84 has an initial cylindrical portion followed by a slightly convergent portion 91 which is separated from the portion 90 by an annular shoulder 92 against which the annular part 23 provided on the burner nozzle 15 can abut. The annular part or ring 87 has a front recess in which it is possible to accommodate the annular abutment part 33 fitted on the nozzle 15 of the burner. The annular part 87 is crossed in its lower section by a pipe 94 which is connected to the interspace 89 and is meant to collect and drain any unburned Diesel fuel that may be discharged from the atomizer 19 into the combustion chamber 2 when the burner is cold-started or switched off. The pipe 94 is connected to the feed pipe 63 by means of an electric valve

95 and a union tee 96 (figures 1 and 2). The outlet 82 of the combustion chamber 2 is inserted and supported in the axial central hole 97 of an annular part 98 which also has a series of four openings 99 and another series of four outer openings 100 arranged along respective circumferences which are concentric with respect to the axial hole (figures 6 and 10). The annular part 98 has, at its face directed toward the chamber 4, an annular ridge 101 which internally forms a coupling seat for a metal ring 102 and forms, on the outside of the ridge 101, an annular shoulder for supporting the insulating layers 8 and 9. The annular part 98 can be coupled, at its face directed toward the combustion chamber 2, by means of bolts 104, to an annular part 105 having multiple concentric flanges 106 and 107 and circumferential slots 108 that mate with, and have the same dimensions as, a respective opening 100 of the annular part 98.

The ring 102 has an axial central nosepiece 109 that tapers slightly and converges toward the chamber 4; its slightly tapered inner hollow forms an extension of the hole 97 of the annular part 98. In a peripheral position with respect to the nosepiece 109, the annular part 98 forms, together with the ring 102, a narrow annular chamber 110 in which a double metal wire screen 111 that withstands high temperatures is seated (figures 12 and 13); said wire screen is formed for example by two concentric supporting rings Ilia and 111b to which the wire screen is electrically welded.

The ducts 6 (figures 7 and 11) of the exhaust gas conveyance system, located in the chamber 4, lead into the chamber 110. The ring 102 has, peripherally with respect to the chamber 110, a sequence of circumferential openings 112 that mate with, and have the same dimensions as, an opening

100 in the annular part 98 and respectively a slot 108 in the annular part 105, so as to form passages for passing through the barrier formed by the two annular parts 98 and 105 and by the ring 102.

The expansion and flow reversal chamber 4 is delimited, at the end opposite to the ring 102, by a bottom plate 113 having, starting from its center toward the outside: a substantially frustum-shaped inward-drawn axial portion 113a; an annular enlargement 114, which is affected by a plurality of curved through openings which are arranged along an axial circumference and through which an end of a respective duct 6 is seated; and a peripheral cylindrical ridge 115.

The ducts 6 have a relatively wide but very low internal opening in order to cause the lamination of the exhaust gases to be treated, which are thus forced to flow over a relatively large surface, exchanging heat with the combustion gases arriving from the combustion chamber 2.

The ducts 6 can be distinguished into an upper duct 6a (figure 11), two lateral ducts 6b and 6c, and a lower duct

6d. The ducts 6 can be obtained by pressing in a semicylindrical template or mold (not shown) of a pipe made of relatively thin stainless steel plate.

Preferably, the upper duct 6a can have a greater circumferential extension, for example it can be obtained by pressing a pipe having a diameter of 50 mm; the lateral ducts 6b and 6c can be obtained from a pipe with a diameter of 48 mm, and the duct 6d can be obtained from a pipe with a diameter of 30 mm, whereas the width of the inner hollow of each duct is uniform and measures for example a few millimeters.

Longitudinal slits are thus formed between one duct 6 and the other: the one between the duct 6a and the lateral ducts 6b and 6c is designated by the reference numeral 117, and the one between the lateral ducts and the duct 6d is designated by the reference numeral 118; the combustion gases arriving from the combustion chamber 2 can flow through these slits. Once they have entered the chamber 4, these gases can in fact expand and are mostly directed against the drawn portion 113a, where they undergo a sudden lateral deflection so as to accordingly flow over the inward-facing walls of the ducts 6 and therefore also flow over their outward-facing walls as they begin their backward movement toward the passages formed by the mating of the openings 116 in the ring 102, of the openings 100 in the annular part 98, and of the openings 108 in the annular part 105 (see also the arrows in figure 1). During use, the ducts 6 are heated to a relatively high temperature — approximately 1000 °C — by the combustion gases arriving from the combustion chamber 2, and undergo a considerable thermal expansion that forces them to bend or splay at their intermediate portion, thus widening the slits 117 and 118 and thus facilitating the expansion of the hot gases, whereas once the burner is switched off and after cooling they return, by contraction, into a perfectly parallel condition.

The chamber 4 is delimited at its peripheral region by a tubular wall 120 made of metal (stainless steel) which can be fitted, at its upstream end, over the annular ridge 101 of the annular part 98 and, at its other end, over the cylindrical ridge 115 of the bottom plate 113, so that it can slide on the ridges to compensate the thermal expansions and contractions.

On the outside of the wall 120 there is a good thermal insulation formed, for example, by the insulating layer 8, which is externally separated from the insulating layer 9 by a tubular wall 122 which is supported by a flanged ring 123 at one end and by an annular part 124 at the other end.

This configuration of the insulating layers 8 and 9 is repeated at the various segments of the body of the exhaust system, where each ring 123 can be fixed to a respective annular part 124 by means of bolts 125 with the interposition of the peripheral edges of the annular parts 98 and 105 or of other annular supporting elements.

It can be noted that each annular pat 124 externally surmounts the other components of each joint between one segment and the next of the exhaust system and has accommodation recesses for two consecutive outer walls 126 which, as more clearly shown in figure 9, are individually shaped like a cylindrical half-shell provided with holes

127 along its longitudinal edges to close it by means of fixing screws 129. Advantageously, each annular part 124 has a pair of sealing O-rings 124a, one for each wall 126, to prevent water infiltrations inside the body of the exhaust system. Once they have passed through the openings 112, 100 and 108, the combustion gases enter the annular interspace 10 (figure 6) which is delimited by an inner tubular wall 130 and by an outer tubular wall 131, both made of stainless steel. The outer wall 131 is supported, at one end, by the flange or collar 106 of the annular part 98 and is fitted, at its other end, over a flanged ring 132; the insulating layers 8 and 9 abut against the peripheral flange 133 of said ring 132. The inner wall 130 is instead placed around the frustum-shaped portion 81 of the combustion chamber and is slideably supported by the flange or collar 107 of the annular part 98 on one side and by the collar 134 of a ring 135 at the other side. On the outside of the collar 134, the ring 135 has a series of peripheral passages 136 (figure 9) arranged so that they are angularly equidistant, preferably along a circumference, and are suitable to allow the partially throttled flow of the combustion gases from the interspace 10 to an annular manifold 137 which is connected to the lateral outlet port

11 (figure 5) .

The ring 135 has a peripheral edge wall 138 that can be fixed by means of screws 139 to a peripheral annular supporting part 140 that can in turn be bolted, by means of bolts 125, to the flange 133.

On the side directed toward the manifold 137, the ring

135 has a collar 141 having a larger diameter and a collar 142 having a smaller diameter. An end of a cylindrical wall 143 is fitted over the collar 141, and its other end rests on a portion of a flanged ring 144.

The wall 138, together with an outer wall 120 supported by the rings 144 and 135, delimits the manifold

137, whereas on the inner side the wall 143, together with the tubular wall 80 of the combustion chamber and with a coaxial wall 145 supported by the ring 144 and by the annular part 84, delimits a manifold which will be described hereinafter.

Going back to the manifold 5 (figures 1 and 8), it can be seen that it is delimited by the bottom plate 113 on one side, by a cylindrical stainless steel wall 120 laterally, and by a closing disk 146 on the opposite side; said disk has a peripheral flange 147 and a central hole in which it is possible to insert the end 148 of an exhaust pipe 149 of a Diesel engine (not shown). In order to keep at a high level the temperature of the exhaust gases entering the manifold 5, the pipe 149 is advantageously thermally insulated, for example by means of a sheath 150 constituted by alumina held in position by a case 151 made of stainless steel plate. The pipe 149 has a coupling end flange 152 to which the end edge of the case 151 is welded and bolted by means of bolts 153. The flange 152 can be detachably fixed, for example by means of bolts 154, to the peripheral flange

155 of a flanged collar 156 to which the closing disk 146 is in turn bolted by means of bolts 157; said disk 146 is accommodated in said collar and abuts against it. In addition to acting as abutment element for the final portion of the two insulating layers 8 and 9, the collar

156 supports, so that it can slide freely, an end of the lateral wall 120 of the manifold 5, the other end whereof is fitted on the collar 158 of an annular part 159 that can be fixed by means of bolts 160 to the outer edge of the bottom plate 113.

A wire screen 161 is placed inside the manifold 5 and is shaped like a basket which is elastically anchored around the end 148 of the exhaust pipe 149 and substantially reproduces the contour of the internal opening of the manifold 5. During use, the wire screen 161 is meant to become incandescent due to the heat transferred by conduction and convection from the bottom plate 113 which is in turn subjected, on its opposite side, to the jet of the combustion gases arriving from the combustion chamber 2.

The wire screen 161 has a cylindrical shape and has a protrusion 161a so that it partially fits in the inward- drawn portion 113a of the bottom plate, an annular recess 161b which acts as border for the enlargements 114, and an inlet 161c to fit it over the end portion 148 of the pipe 149. The exhaust gases conveyed by the pipe 149 into the manifold 5 increase in speed at the slightly tapered end

148 before striking the wire screen 161 and the overheated bottom plate 113 before being guided along the equally overheated ducts 6 to undergo a lamination process in contact with the inner walls of the ducts 6 and gradually increase their temperature as they advance in countercurrent with respect to the combustion gases of the burner (but without ever making direct contact with them) , in order to complete the combustion of any unburned components contained in them. From the ducts 6, the combustion gases discharge into the annular chamber 110, where they are forced to make contact with the incandescent wire screen 111 before passing through the openings 99 and before passing into the annular compartment 162 delimited internally by the frustum-shaped portion 81 of the combustion chamber and externally by the wall 130, and partially by the collar 107 of the annular part 105 and partially by the ring 135. In the compartment 162, the exhaust gases strike the portion 81, from which they absorb additional heat, reaching a temperature of approximately 900-1000°C to complete the combustion of any solid residue contained in them.

As the carbon monoxide CO contained in the exhaust gases has a strong tendency to combine with oxygen at the relatively high temperature of the compartment 162 (i.e., as mentioned, approximately 900-1000°C), its total conversion into CO₂ is thus facilitated. Around 900-1000°C, carbon dioxide is relatively stable, since CO₂ dissociation starts to be significant only well above 1200-1500°C. However, the temperature in the compartment 162 is not such as to facilitate the forming of nitrogen oxides NO, mainly because nitrogen tends to combine with oxygen only at much higher temperatures, on the order of 1500°C and above, and also because these are burned exhaust gases having therefore an extremely low oxygen content.

The exhaust gases pass from the compartment 162, where as mentioned they undergo a high-temperature reheating process, along an interspace 163 which is delimited between the combustion chamber 2 and the ring 135 and along which they increase in speed and undergo lamination, so that they are forced to flow at a very small distance over the very hot wall of the chamber 2 before entering the manifold 164 delimited between the walls 143 and 145 on one side and 80 on the other side (figure 5). In the manifold 164 there is a metal wire screen 165 (figures 1, 16 and 17) having for example a substantially cylindrical shape with a slightly flared end and supported by the collar 142 of the ring 135 at one of its ends and by the annular part 84 at its other end. The wire screen 165, like the wire screens 111 and 161, is in the incandescent state during use and has the purpose of transferring heat by conduction and radiation to the exhaust gases present in the manifold 164 in order to ensure the most thorough possible reheating before entering the evacuation duct 7. Said duct is configured like the duct 11, and accordingly only one of these ducts is described hereinafter.

In this example, the duct 7 is formed by a series of supporting rings 166, 167 and 168. The ring 166 rests and is welded externally with respect to the edge of a hole formed in the metal wall 145, whereas it is internally provided with two diameters so as to have an abutment for a pipe 169 insertable therein. The pipe 169 also fits in the ring 167 and in the ring 168, to which it can be fixed, for example by providing a flanged edge 170 n the ring 168 and a ring 171 which is welded externally to the pipe 169, so that the edge 170 and the ring 171 can be mutually coupled by means of bolts 172.

The pipe 169 enters a cooling unit 12 or 13 (figure 1) that performs several functions, i.e. cooling, sound deadening, and filtration of the burned gases discharged into it. The cooling units 12 and 13 are advantageously identical, and therefore only one is described in detail.

As more clearly shown in figures 1 and 18 to 23, each cooling unit 12 and 13 comprises an outer shell made of stainless steel which is formed by a plurality of flanged segments which can be fixed to each other by means of bolts 173 and, in the following order, an inlet segment 174, in which the exhaust pipe 169 enters laterally, a segment 175 for accommodating a burned gas/air heat exchanger 176, a segment 177 for accommodating filters for the burned gases, and a final sound-deadening segment 178 which also contains filters for the burned gas/air mixture.

The inlet segment 174 supports, at its head, a blower unit 179 which is formed by an axial fan 180 and by an electric motor 181 for driving the fan, both of which are supported within a flanged ring 182 for ducting the fan that can be fixed to the segment 174 by means of bolts 173.

The fan 180 is suitable to blow air into the shell so as to strike and flow over the exchanger 176, which forms an interspace 183 together with the shell. The air then passes in an interspace 184 which is formed between the segment

177 and an inner wall 185 for containing filters 186 and 187 before passing through the opening of the final segment

178, where it mixes with the burned gases arriving from the exchanger 176 and is then released into the atmosphere through an L-shaped pipe 188.

The burned gases that are released from the exhaust pipe 169 (and arrive from the manifold 162 for the unit 12 and from the manifold 137 for the unit 13) are sent, by means of an L-shaped pipe 189, into the respective exchanger 176, which forms a relatively narrow internal opening so as to force the gases to flow over the wall of the exchanger, which is externally in contact with the air injected by the fan 180 for an effective and rapid cooling of the burned gases. When they leave the heat exchanger 176, the cooled gases are forced to pass through a filter 190, for example of the activated-charcoal type, which is mainly meant to absorb any traces of CO remaining in the burned gases. The gases then pass into the compartment 191 (delimited by the wall 185) for the containment of the filters 186 and 187. The filters 186 and 187 are made for example of foamed material, such as foam rubber, supported by treated cardboard, for example plastic-laminated cardboard, to retain the condensate, which can if required be discharged outside by means of a cock 192.

When they leave the compartment 191, the burned gases mix partially with the air arriving along the interspace

184, pass through a dust filter 193 and are finally conveyed onto a filter 194 for dust and for eliminating any ammonia traces before being discharged into the pipe 188, fully purified and at low temperature. If required, the filter 193 can have an external interspace for easier flow of the air and gases through it.

The heat exchanger 176, as more clearly shown in figures 19 to 22, can be constituted by two flanged halves

195 and 196 made of stainless steel plate and held together by a plurality of bolts 197 with the interposition of an internal stiffening frame 198; the entire assembly is supported within a containment case 175. The final segment 178 (figure 22) is instead soundproofed externally by a double layer 199 which is constituted for example by alumina wool or by a mixture of alumina and foamed plastic material.

For the safe and fully automated operation of the burner 3, in the compartment 162 there is advantageously a probe 200 insertable in a set of rings 201, for example such as the one of the ducts 7 and 11, and constituted for example by a thermocouple that detects the temperature within the chamber in order to switch on the burner 3, during use (by means of appropriate electrical connections which are not illustrated) , as soon as the temperature drops below a preset threshold value.

For safety, a second safety thermocouple 202 can be

1 provided in the expansion chamber 4; this thermocouple may operate together with, or alternatively to, the probe 200 for the same purpose.

Advantageously, adjacent to the annular part 84

(figures 1, 5, 24 and 25) it is possible to provide an insulating layer 203 of alumina contained within an annular wire screen 204 that helps to better dissipate heat without dangerously heating the rings 86 and 93, which can therefore be touched at any time by an operator without the risk of burns, for example for inspection and/or maintenance. Naturally, the above described exhaust system can also operate in combination with other similar exhaust systems, for example in the case of high-power Diesel engines, or it can be provided with a plurality of pairs of cooling units 12 and 13, for example distributed around the combustion chamber.

The embodiment illustrated in figures 26 to 37 illustrates some constructive variations that simplify both assembly and maintenance of the exhaust system.

As more clearly shown in figures 26 and 27, the front annular part 23 can be fixed to the abutment plate or annular part 33 by means of screws 230, and there is no ring 26 inside it; the task of confining the flame at the outlet of the atomizer 19 is accomplished by the annular part 23 itself. The ignition electrode 30 accommodated in the hole 28, and the flame detector constituted by a bar 231 placed in the hole 29, have their proximal end engaged at the head of an electrically conducting rod 232 which is supported in a respective block 233 made of insulating material, for example ceramic, and is electrically in contact, at its other end, with an electric cable 234, 235 from the control unit C. Each block 232 can in turn be fixed in position, for example by means of screws 236, in a respective seat formed on the casing 16. Preferably, the bars 232 and their connection to the respective cables 234 and 235 are sheathed in a respective shielding sheath 237.

A third hole 28a can also be provided in the nozzle 15; a temperature sensing electrode can be installed in said hole and be connected to a digital display located in the control unit C to have real-time confirmation of the actual presence of the flame.

It can be seen that the electric cable 58, the cable

238 for a temperature detector 239, and the delivery pipe 60 of the pump 62 all pass through the bottom plate 50, in order to simplify construction and provide faster burner maintenance when required. The pipe 60 is also partially wound in a coil at 60a to compensate for the inevitable thermal expansions and contractions of the pipe.

The bottom plate 113 of the expansion and flow reversal chamber 4 (figures 32 to 35) has, on the side of the chamber 4, a central frustum-shaped drawn portion 113a, four ducts 240, 241, 242 and 243 angularly spaced around the drawn portion 113a, and a collar 115, and has, on the side of the manifold 5, a coupling 114a for a cylindrical wire screen 161. The ducts 240, 241, 242 and 243 are through ducts, in that they allow direct connection between the chamber 5 and an annular duct 244 within which a series of wire screen rings 111 is arranged. The other end of the duct 244 abuts against the ring 102 at the chambers 110. Four openings 245 are formed between the ducts 240,

241, 242 and 243; the combustion gases arriving from the combustion chamber 2 and deflected by the bottom plate 113, and particularly by the drawn portion 113a, can pass through said openings to start their backward flow along the chamber 4.

The chambers 4 and 5 and the interspace 10 are delimited by a respective portion of metal tubular wall 120 which ends, at its tips (see particularly figures 30 and

31), with a chamfered edge 120a which is meant to abut against a corresponding groove 120b in the respective supporting and abutment element. The dimensions are such that when cold (figure 30) there is a certain preset slack between the edge 120a and the groove 120b, so as to compensate thermal expansion when hot, i.e. when the burner 3 is running, as shown in figure 31.

As shown in figures 28 and 29, it is also possible to provide three layers of insulation on the outside of the wall 120, but it is also possible to provide a single layer of insulating material. Advantageously, the thermocouples 202 can be completely embedded in the insulating layer or layers 8 and 9 and can be connected to the control unit C by means of a wire that runs within the outer insulation and exits from the end flange 152, so as to eliminate heat losses due to conduction through said thermocouples.

The cooling units 12 and 13 illustrated in figure 26 are structurally much simpler than those of the example of figure 1. First of all, the inlet segment 174 does not accommodate any fan, but simply acts as an air intake. The segment 175 is thermally insulated on the outside by means of a layer 175a, and accommodates filters 186 and 187 in its end portion.

The L-shaped pipe 189 within the segment 175 ends with a tapered nosepiece 189a which is arranged in a frustum- shaped inner portion 175b so as to make use of the Venturi effect.

A safety valve 250 (figures 36 and 37) can advantageously be installed on the exhaust pipe 149 that leaves an internal-combustion engine; said valve can be constituted by a port 251 connected to the inside of the pipe 149 and is closed by a cap-like door 252 which is hinged by means of two vertical articulation flaps 253 and a pair of horizontal flaps 254 about a rotation pivot 255 supported by the flaps 254. Said flaps 254 also support a terminal 266 for a sheathed control wire 267 which is anchored to the distal end of the flaps 253. The door 252 is elastically loaded, for example by a pair of helical traction springs 268, so that it is kept normally closed.

In case of malfunction of the exhaust system, and in any case if overpressure forms within the pipe 149, or even by control, by actuating the wire 267, the door 252 can be opened to vent the exhaust gases of the engine. The malfunction of the exhaust system, for example due to the failed ignition of the burner or to other reasons, can be indicated on the dashboard so that the driver is warned that the exhaust system is out of order.

Claims

1. Exhaust system for reducing pollutants in the exhaust gases of an internal-combustion engine, which comprises: at least one relatively long combustion chamber; a burner located at the head of the, or of each, combustion chamber and suitable to produce and maintain a pressurized flame that produces a relatively high temperature along the, or the respective, combustion chamber; an expansion and flow reversal chamber located downstream of the, or of the respective, combustion chamber and connected to the exhaust unit of the internal-combustion engine; at least one duct for conveying the exhaust gases to be purified which is arranged so as to exchange heat and extends along and around both the expansion chamber and the combustion chamber starting from the manifold up to at least one first lateral outlet port at the combustion chamber so that the exhaust gases undergo superheating and a reheating process; at least one thermally insulating casing around both the, or each, conveyance duct and around the, or the respective, combustion chamber to delimit, together with said chamber, at least one interspace through which the combustion gases from the expansion and reversal chamber flow out in the reverse direction before reaching a second outlet port; and at least one cooling unit at the exit of each outlet port. 2. Exhaust system according to claim 1, characterized in that said combustion chamber has an initial portion with a constant inner passage section, followed by a portion that tapers toward an outlet for discharging in said expansion and flow reversal chamber to release the 6 combustion gases at a higher speed.

1 3. Exhaust system according to claims 1 or 2,

2 characterized in that said burner comprises: a nozzle made

3 of thermally insulating material that delimits a convergent

4 portion and a diverging portion; an atomizer which is

5 located in the convergent portion and is connected to a

6 source of fluid fuel; a motor-driven compressor for feeding

7 pressurized air axially along and around the atomizer; an

8 ignition electrode and a flame detector which are

9 accommodated in transverse seats that run on opposite sides

10 from the outside to a region that is directly adjacent to

11 the tip of the atomizer; and a ring which is located at the

12 inlet of the combustion chamber and is meant, during use,

13. to become incandescent to facilitate the complete

14 combustion of the fuel in the peripheral part of the flame.

1 4. Exhaust system according to claim 3, characterized

2 in that it comprises a supporting annular part or ring that

3 converges downstream of said ring and is meant to confine the flame supported by the atomizer and to keep the

5 diverging ring separated from an interspace of the

6 diverging portion of the nozzle.

1 5. Exhaust system according to claims 3 or 4,

2 characterized in that it comprises a pumping unit having a

3 supply duct connected to said fuel source and a delivery

4 for supplying said atomizer, and valve means for switching

5 the delivery to produce a suction effect on the atomizer

6 when the burner is switched off. 6. Exhaust system according to claim 5, characterized

2 in that a lower duct is provided between said nozzle and

3 said combustion chamber to collect and discharge any unburned liquid fuel, said lower duct being connected to said collection duct, said ducts being meant to operate according to a program prior to each ignition of the burner simultaneously with said switching means. 7. Exhaust system according to any one of the preceding claims, characterized in that said expansion and flow reversal chamber comprises: a head ring, through which the outlet port of the combustion chamber discharges; a jet-breaking bottom plate, arranged opposite the discharge outlet on the opposite side with respect to the head ring; ducts for conveying the exhaust gases to be purified, which are arranged around the jet-breaking bottom plate and run along the entire length of the chamber so as to be struck by the combustion gases which are expanding and are forced to change advancement direction and to pass between one duct and the other toward the wall or walls of the chamber; a plurality of peripheral passages through said head ring for the backward flow of the combustion gases; an annular interspace for collecting the combustion gases arriving from said peripheral passages and for guiding them toward said second exhaust. 8. Exhaust system according to claim 7, characterized in that said expansion and flow reversal chamber comprises at least one thermocouple probe to detect the temperature inside the chamber. 9. Exhaust system according to claims 7 and 8, characterized in that said head ring delimits, between said discharge outlet and said peripheral passages, an annular chamber in which the ducts for conveying the exhaust gases to be purified end, said first exhaust being connected to said annular chamber. 10. Exhaust system according to claim 9, characterized in that it comprises a metal wire screen, or rings of wire screen, said screen or rings covering the entire passage section of said annular chamber and is meant to become incandescent during use to facilitate the combustion of any unburned substances present in the exhaust gases to be purified. 11. Exhaust system according to any one of the preceding claims 7 to 10, characterized in that it comprises an annular space which is connected to said first exhaust, which is delimited internally by the combustion chamber and externally by said annular interspace for collecting the combustion gases, with which it exchanges heat. 12. Exhaust system according to claim 11, characterized in that said annular chamber comprises a thermocouple probe to detect the temperature inside said chamber. 13. Exhaust system according to any one of the preceding claims, characterized in that said exhaust gas manifold accommodates a metal wire screen which is meant, during use, to become incandescent because it exchanges heat with the bottom plate of the expansion and flow reversal chamber, in order to trigger a process for the reheating of the exhaust gases to be purified. 14. Exhaust system according to any one of the preceding claims, characterized in that said thermally insulating casing comprises a plurality of adjacent tubular segments which are kept together by connecting rings, each 5 of which is contained within at least one metal sheath.

1 15. Exhaust system according to claim 14,

2 characterized in that one of said rings, between one

3 segment and the next, is of the overlap type and comprises

4 at least one sealing gasket for the sheath of each segment,

5 so as to prevent water infiltrations.

1 16. Exhaust system according to claim 14 or 15,

2 characterized in that each segment is formed by a plurality

3 of annular concentric layers which are in mutual contact.

1 17. Exhaust system according to claim 16,

2 characterized in that the outer layer and the respective

3 sheath are made of two halves that can be fixed together

4 longitudinally.

1.

18. Exhaust system according to any one of the

2 preceding claims, characterized in that each cooling unit

3 comprises an external accommodation duct which is connected

4 to the atmosphere at its head and receives a respective

5 exhaust that conveys into it the purified exhaust gases or

6 the combustion gases to mix them with the incoming air and

7 thus cool them, said duct accommodating, in its end part, a

8 filtration and condensate retention unit.

1 19. Exhaust system according to claim 18,

2 characterized in that each cooling unit comprises, at the

3 head of its outer accommodation duct, a blower unit, a heat

4 exchanger arranged downstream of the blower unit, which is

5 connected to a respective exhaust and is meant to receive

6 the purified gases or the combustion gases to cool them,

7 and a terminal sound-deadening and filtration unit in which

8 the cooled gases mix with the air injected by the blower n unit.

20. Exhaust system according to claim 18 or 19, characterized in that said filtration and condensate retention unit comprises at least one filter for any traces of carbon monoxide, at least one condensate retention filter, and a valve for the external discharge of the condensate.

21. Exhaust system according to any one of the preceding claims 18 to 20, characterized in that said end unit comprises soundproofed walls, a dust filter and a filter for any ammonia traces.

22. Exhaust system according to any one of the preceding claims, characterized in that it comprises a safety valve on the duct for the conveyance of the exhaust gases, said valve being meant to vent the exhaust gases externally in case of malfunction.

23. Exhaust system according to claim 22, characterized in that said safety valve is a lever-like spring-loaded valve.